Chuyuan Li

Chloé Braud
email: chloe.braud@irit.fr

Maxime Amblard

Multi-Task Learning for Depression Detection in Dialogs

Depression is a serious mental illness that impacts the way people communicate, especially through their emotions, and, allegedly, the way they interact with others. This work examines depression signals in dialogs, a less studied setting that suffers from data sparsity. We hypothesize that depression and emotion can inform each other, and we propose to explore the influence of dialog structure through topic and dialog act prediction. We investigate a Multi-Task Learning (MTL) approach, where all tasks mentioned above are learned jointly with dialog-tailored hierarchical modeling. We experiment on the DAIC and DailyDialog corpora -both contain dialogs in English -and show important improvements over state-ofthe-art on depression detection (at best 70.6% F 1 ), which demonstrates the correlation of depression with emotion and dialog organization and the power of MTL to leverage information from different sources.

Introduction

Depression is a serious mental disorder that affects around 5% of adults worldwide. 1 It comes with multiple causes and symptoms, leading to major disability, but is often hard to diagnose, with about half the cases not detected by primary care physicians [START_REF] Cepoiu | Recognition of depression by non-psychiatric physicians-a systematic literature review and metaanalysis[END_REF]. Automated detection of depression, sometimes associated to other mental health disorders, has been the topic of several studies recently, with a particular focus on social media data and online forums [START_REF] Coppersmith | Clpsych 2015 shared task: Depression and ptsd on twitter[END_REF][START_REF] Benton | Multitask learning for mental health conditions with limited social media data[END_REF][START_REF] Sharath | Detecting depression and mental illness on social media: an integrative review[END_REF][START_REF] Yates | Depression and self-harm risk assessment in online forums[END_REF][START_REF] Song | Feature attention network: Interpretable depression detection from social media[END_REF][START_REF] Akhtar | All-inone: Emotion, sentiment and intensity prediction using a multi-task ensemble framework[END_REF][START_REF] Ríssola | A survey of computational methods for online mental state assessment on social media[END_REF]. The ultimate goal of such system would be to complement expert assessments, but such empirical studies are also valuable to better understand how communication is affected by health disorders. In this paper, we propose to investigate depression detection within dialogs, a scenario less studied but more similar to the interviews with clinicians, which allegedly involves dialog features and allows to also examine how interaction is affected.

However, depression detection suffers from data sparsity. In fact, using social media data was a way to tackle this issue, including considering data generated by self diagnosed users, a method that leads to potentially noisy data and comes with ethical issues [START_REF] Chancellor | A taxonomy of ethical tensions in inferring mental health states from social media[END_REF]. We rather examine a dataset of 189 clinical interviews, the DAIC-WOZ [START_REF] Gratch | The distress analysis interview corpus of human and computer interviews[END_REF], collected by experts to support the diagnosis of distress conditions. Participants are identified as depressive or not, and if so they receive a severity score. A line of work proposed to overcome data scarcity by leveraging varied modalities, e.g. using audio as in Al [START_REF] Tuka | Detecting depression with audio/text sequence modeling of interviews[END_REF]. Previous approaches solely based on textual information relied on hierarchical contextual attention networks on word and sentence-level representations [START_REF] Mallol-Ragolta | A hierarchical attention network-based approach for depression detection from transcribed clinical interviews[END_REF], or multi-task learning (MTL) but limited to combing identification and severity prediction [START_REF] Syed | Multitask representation learning for multimodal estimation of depression level[END_REF][START_REF] Dinkel | Textbased depression detection on sparse data[END_REF], possibly with emotion [START_REF] Syed | Improving depression level estimation by concurrently learning emotion intensity[END_REF].

Inspired by the latter approaches, we also propose to rely on MTL framework to help our model leveraging information from different sources. We exploit three auxiliary tasks: emotion -naturally tied to mental health states -, but also dialog act and topic classification, hoping this shallow information about the dialog structure could further enhance the performance. Our architecture is classic, based on hard-parameter sharing [START_REF] Ruder | An overview of multi-task learning in deep neural networks[END_REF], simpler than the shared-private architecture in [START_REF] Syed | Improving depression level estimation by concurrently learning emotion intensity[END_REF] but shown effective. In order to take into account dialog organization, we advocate for a dialog-tailored hierarchical architecture with some tasks performed at the speech turn level and others at the document level.

Our contributions are: (i) An empirical study on depression detection in dialogs, leveraging the power of multi-task learning to deal with data sparsity; (ii) An extension of previous work in examining the effects of depression on dialog structure via shallow markers, i.e., dialog acts and topics, as a first step; (iii) State-of-the-art results on depression detection in DAIC test set with 70.6% in F 1 at best.

Related work

Within multi-task learning (MTL), a model has to learn shared representations to generalize the target task better. It improves the performance over single-task learning (STL) by leveraging commonalities or correlations between tasks. Recent years have witnessed a series of successful applications in various NLP tasks, as in [START_REF] Collobert | A unified architecture for natural language processing: Deep neural networks with multitask learning[END_REF]; [START_REF] Søgaard | Deep multitask learning with low level tasks supervised at lower layers[END_REF]; Ruder (2017); [START_REF] Ruder | Latent multi-task architecture learning[END_REF], which demonstrates the effectiveness of MTL in learning information from different but related sources. It also tackles the data sparsity issue and reduces the risk of overfitting [START_REF] Mishra | Learning cognitive features from gaze data for sentiment and sarcasm classification using convolutional neural network[END_REF][START_REF] Benton | Multitask learning for mental health conditions with limited social media data[END_REF][START_REF] Bingel | Identifying beneficial task relations for multi-task learning in deep neural networks[END_REF]. [START_REF] Joshi | Does multi-task learning always help?: An evaluation on health informatics[END_REF] demonstrated the benefit of MTL for specific pairs of close health prediction tasks on tweets. [START_REF] Benton | Multitask learning for mental health conditions with limited social media data[END_REF] used MTL on social media data and achieved important improvements in predicting several mental health signals, including suicide risks, depression, and anxiety, together with gender prediction. With a focus on depression detection, the shared task AVEC in 2016 [START_REF] Valstar | Avec 2016: Depression, mood, and emotion recognition workshop and challenge[END_REF] has brought out a series of multi-modal studies using vocal and visual features on the DAIC-WOZ dataset [START_REF] Gratch | The distress analysis interview corpus of human and computer interviews[END_REF] dings. Qureshi et al. (2019dings. Qureshi et al. ( , 2020) ) proposed MTL approaches in adding emotion intensity and depression severity (i.e., a regression problem) prediction to the main classification task. They, however, found that the emotion-unaware model obtained the best result. They used a monologue corpus for the emotion task, a domain bias that possibly harms the performance. On the contrary, we hypothesize that emotional information would benefit depression detection. Mallol-Ragolta et al. ( 2019) used a hierarchical contextual attention network with static word embeddings within a single-task setting and then combined representations at the word and sentence levels. They reported at best 63% in F 1 . Recently, Xezonaki et al. ( 2020) presented even better results, 70% in F 1 , by augmenting the attention network with a conditioning mechanism based on effective external lexicons and incorporating the summary associated with each interview. We instead rely on MTL in this work, where incorporating external sources is more direct.

None of the previous studies investigated potential links between depression and dialog structure. We note that [START_REF] Cerisara | Multi-task dialog act and sentiment recognition on mastodon[END_REF] explored MTL with sentiment2 and dialog act prediction on Mastodon (a Twitter-like dataset), where both annotations are available, and found a positive correlation. To the best of our knowledge, we are the first to tackle depression detection in dialog transcriptions with the MTL approach and explore joint learning techniques with tasks related to the dialog structure.

Model Architecture

One condition generally assumed for success within MTL, at least in NLP, is that the primary and auxiliary tasks should be related [START_REF] Ruder | An overview of multi-task learning in deep neural networks[END_REF]. The emotion-related task is thus a natural choice since it is linked to mental states. We hypothesize that depressive disorder can also affect how people interact with others during conversations. We thus take a first step toward linking dialog structure and depression by examining shallow signals: dialog acts and topics. In addition, since the information comes at different levels, we propose hierarchical modeling, from speech turns to documents.

Baseline Model: Our basic model is a two-level recurrent network, similar to the one in [START_REF] Cerisara | Multi-task dialog act and sentiment recognition on mastodon[END_REF]. The input words are mapped to vectors using word embeddings from scratch. The first level (turn-level) takes the embeddings into a bi- LSTM network to obtain one vector for each turn. The second level (dialog-level) takes a sequence of turns into an RNN network, and the output is finally passed into a linear layer for depression prediction.

MTL Model:

The MTL architecture is composed of shared hidden layers and task-specific output layers (see Fig. 1) and corresponds to the hard parameter sharing approach [START_REF] Caruana | Multitask learning: A knowledgebased source of inductive bias[END_REF][START_REF] Caruana | Multitask learning[END_REF][START_REF] Ruder | An overview of multi-task learning in deep neural networks[END_REF]. Since some auxiliary tasks are at the speech-turn level (i.e., emotion, dialog act) while others are annotated at the document level (i.e., depression, topic), our architecture is hierarchical and arranges task-specific output layers (MLP) at two levels. Speech-turn level emotion and dialog act information can be learned in the turn-level LSTM network and transferred upwards to help depression and topic prediction. On the other hand, higher-level information can be backpropagated to update the network at the lower level. The loss is simply the sum of the losses for each task. When it comes to the MTL setting, we set equal weight for each task as the standard choice.

4 Datasets DAIC-WOZ: This dataset is a subset of the DAIC corpus [START_REF] Gratch | The distress analysis interview corpus of human and computer interviews[END_REF]. 3 It contains 189 sessions (one session is one dialog with avg. 250 speech turns) of two-party interviews between participants and Ellie -an animated virtual interviewer controlled by two humans. (2020). We do not compare to [START_REF] James R Williamson | Detecting depression using vocal, facial and semantic communication cues[END_REF][START_REF] Haque | Measuring depression symptom severity from spoken language and 3d facial expressions[END_REF][START_REF] Tuka | Detecting depression with audio/text sequence modeling of interviews[END_REF][START_REF] Dinkel | Textbased depression detection on sparse data[END_REF][START_REF] Syed | Improving depression level estimation by concurrently learning emotion intensity[END_REF] who only report on the development set.

Evaluation Metrics: For depression classification we follow [START_REF] Dinkel | Textbased depression detection on sparse data[END_REF] and report accuracy, macro-F 1 , precision, and recall. For emotion analysis, we follow Cerisara et al. ( 2018) and report macro-F 1 .

Implementation Details: We implement our model with AllenNLP library [START_REF] Gardner | AllenNLP: A deep semantic natural language processing platform[END_REF]. We use the original separation of train, validation, and test sets for both corpora. The model is trained for a maximum of 100 epochs with early stopping. For STL as well as for MTL scenario, we optimize on macro-F 1 metric for depression classification. We use cross-entropy loss. The batch size is 4 for DailyDialog and 1 for DAIC (within the limit of GPU VRAM). We use the tokenizer from spaCy Library [START_REF] Honnibal | spacy: Industrialstrength natural language processing in python[END_REF] and construct the word embeddings by default with a dimension of 128. The turn level has one hidden layer and 128 output neurons. We tune document RNN layers in {1, 2, 3} and hidden size in {128, 256, 512}. Model parameters are optimized using Adam (Kingma and Ba, 2014) with 1e -3 learning rate. Dropout rate is set to 0.1 for both turn and document encoders. The source code is available at https: //github.com/chuyuanli/MTL4Depr. Using the multi-task architecture, we get improvements when adding each task separately. We see more than a +11.5% increase in F 1 when adding emotion ('+Emo') or topic ('+Top') classification task and, at best, +16.9% with dialog acts ('+Diag'). This demonstrates the relevance of each task to the primary problem of depression detection, especially the interest of dialog acts. When adding topics, we observe a small drop in accuracy compared to STL while the F 1 is better, meaning that the prediction for minority class (non-depressive) improves. Interestingly, in terms of accuracy, the tasks at different levels (depression '+Emo' and depression '+Diag') seem to help more. We deduce that they help build a better local representation (speech turns) before the global representation.

Results and Discussion

When jointly learning all four tasks -combining depression detection with three auxiliary tasks ('+Emo+Diag+Top') -, all metrics improve. We obtain our best system with an improvement of +26.7% in F 1 compared to STL baseline, outperforming the state-of-the-art with a +7.6% increase compared to the best system in Mallol-Ragolta et al. ( 2019) and about +0.5% compared to [START_REF] Danai Xezonaki | Affective conditioning on hierarchical attention networks applied to depression detection from transcribed clinical interviews[END_REF]. Depressed people tend to express specific emotions; it is thus natural to think that emotion is beneficial for the main task. These results indicate that both emotion and dialog structure help as they provide complementary information, paving the way for new research directions with more fine-grained modeling of dialog structure for tasks in conversational scenarios.

Analysis

Performance on Auxiliary Tasks: To better understand our model, we look at the performance of emotion, dialog act, and topic auxiliary tasks. Directly comparing the results of our MTL approach ('+Emo+Diag+Top') with a STL architecture for each task, however, seems unfair. The optimized objective and structural complexity are different: the former is optimized on the depression detection task on two levels, while the latter is tuned on the target auxiliary task with either speech turn (emotion and dialog act) or full dialog (topic). Unsurprisingly, the results show that the MTL system underperforms the basic STL structure for dialog acts and topics, with at best 67.8 in F1 (MTL) vs. 68.8 (STL) for dialog acts, and 52.0 (MTL) vs. 52.4 (STL) for topic classification.

For emotion, on the other hand, our best MTL system obtains 40.0 in F 1 compared to 38.3 for the STL baseline, showing the mutual benefit of both tasks. Even though the score is lower than the SOTA for emotion classification (51.0 F 1 in Qin et al. ( 2021))8 , we believe that refining our model for this task could lead to further improvements in depression detection. In addition, we observe that our MTL approach is particularly beneficial for negative and rare emotion classes, with anger, disgust and sadness gaining resp. 5%, 6% and 1% in F 1 . Finally, we conduct a manual inspection of the types of utterances (mostly questions) from Ellie, and classify them into high-level dialog acts: Backchannel, Comment, Opening, Other, Question.9 We find that around 13% of the utterances are emotion-related, for instance "things which make you mad / you feel guilty about, last time feel really happy", etc., and that mentions of topics related to happiness or regret appear in almost all the interviews. Dialog act distribution is shown in Table 3. We release our annotation to the community for future studies.

Effectiveness of Hierarchical

Conclusion

In this paper, we demonstrate the correlation between depression and emotion and show the relevance of features related to dialog structures via shallow markers: dialog acts and topics. In the near future, we intend to investigate more refined modeling of dialog structures, possibly relying on discourse parsing [START_REF] Shi | A deep sequential model for discourse parsing on multi-party dialogues[END_REF]. We would also like to explore depression severity classification as an extension to binary classification, possibly through a cascading structure: first detect depression and then classify the severity. We intend to refine our work and report on cross-validation splits of the data to test the stability of the model, an issue even more crucial when dealing with sparse data with possibly representativeness problem. A further step will be to investigate the generalization of our model to other mental health disorders.

tings could prove detrimental or even dangerous. Another issue is the representativeness of the data. Currently, it is very complex to access patients in order to have more examples. The institutional complexity leads researchers to systematically use the same data set, creating a bias between the representation of the pathology, in particular for mental ones whose expression can take very varied forms. This also implies defining a variation in relation to a normative use of language that comes with a strong risk in this type of approach.

Moreover, we carefully select the dialog corpora used in this paper to control for potential biases and personal information leakage. We only work with interview transcription, with no audio or visual information. For the text part, all the participant's name have been marked out with pseudo-ID.

A Auxiliary Tasks Class Distribution in DailyDialog

Figure 1 :

 1 Figure 1: Multi-task fully shared hierarchical structure. Light blue is for DAIC dataset and depression task; orange is for DailyDialog and three auxiliary tasks.

  with a score related to the Patient Health Questionnaire (PHQ-9): a patient is considered depressive if PHQ-9 ≥ 10 ([START_REF] Kroenke | The phq-9: a new depression diagnostic and severity measure[END_REF].DailyDialog: This dataset[START_REF] Li | DailyDialog: A manually labelled multi-turn dialogue dataset[END_REF] contains 13, 118 two-party dialogs (with averaged 7.9 speech turns per dialog) for English learners, 4 covering various topics from ordinary life to finance. Three expert-annotated information are provided: 7 emotions[START_REF] Ekman | Basic emotions[END_REF], 4 coarse-grain dialog acts, and 10 topics. We select this corpus due to its large size, two-level annotations and high quality. The train set contains > 87k turns for emotions and dialog acts and > 11k dialogs for topics. Detailed statistics are given in Appendix A.5 Experimental setupBaselines: We compare our MTL results with: (1) Majority class where the model predicts all positive; (2) Baseline single-task model (see Sec. 3); (3) State-of-the-art results on test set reported by Mallol-Ragolta et al. (2019) and Xezonaki et al.

6. 1

 1 Depression Detection Results on DAIC Results using our MTL hierarchical structure are shown in Table 2, which are compared to SOTA models (at the top). Our baseline model is a singletask naive hierarchical model which obtains similar results (F 1 44) as the baseline model (NHN) in Mallol-Ragolta et al. (2019) (F 1 45).

Table 1 :

 1 Table 1 gives the partition of train (107), development (35), and test (47) sets. Originally, patients are associated 3 https://dcapswoz.ict.usc.edu Number of sessions (dialogs) in DAIC-WOZ.

		Train Dev Test
	Depressed	77	23	33
	Non Depressed 30	12	14
	Total	107	35	47

  Prec. Rec. Acc.

	BSL Majority vote	41.3 35.1	50.0 70.2
	State-of-the-art
	NHN 5 (Mallol-Ragolta et al., 2019)	45	-	50	-
	HCAN 6 (Mallol-Ragolta et al., 2019)	63	-	66	-
	HAN+L 7 (Xezonaki et al., 2020)	70	-	70	-
	Ours
	STL Depression	43.9 44.5	47.5 63.8
	MTL +Emo	55.5 56.2	61.6 70.2
	MTL +Top	55.6 55.9	56.8 59.6
	MTL +Diag	60.8 60.6	61.4 66.0
	MTL +Emo+Diag+Top	70.6 * 70.1 71.5 * 74.5
	Table 2: Depression detection results on DAIC. STL:
	single-task using DAIC only; MTL: multi-task using
	DAIC and adding classification for Emotion (+Emo),
	Topic (+Top), Dialog Act (+Diag) from DailyDialog.
	*Significantly better than SOTA performance with p-
	value < 0.05.

F 1

Table 3 :

 3 High-level dialog act distribution of Ellie in DAIC-WOZ. # and % represent the number and percentage of Ellie's utterances, respectively.

	High-level DA	#	%	Sub-cat.	#	%
	Question	7, 907 53%	Emo 1, 054 13% Non-emo 6, 853 87%
	Backchannel	3, 231 22%	-	-	-
	Comment	3, 074 20%	-	-	-
	Opening	611	4%	-	-	-
	Other	171	1%	-	-	-

Table 4 :

 4 Ablation study on hierarchical structure.

	Structure: To ex-
	amine the effectiveness of hierarchical structure,
	we conduct ablation studies on the full multi-
	learning setting ('+Emo+Diag+Top'). For dialog
	RNN level, we use topic information; for turn
	level, we test either emotion or dialog act. The
	results are shown in Table 4. Unsurprisingly, both
	ablated models ('+Emo+Top' and '+Diag+Top')
	underperform the full model, with F 1 scores de-
	creasing ≈ 6% each. Without dialog act, all met-
	rics drop, showing the importance of this informa-
	tion for dialog structure. Without emotion, recall
	drops dramatically while accuracy and precision
	increase, indicating that the model '+Diag+Top'
	predicts more positive classes but fails in negative
	ones, which could result in too many false positives
	in real-life scenarios. On the other hand, when
	comparing hierarchical models ('+Emo+Top',
	'+Diag+Top', '+Emo+Diag+Top') with single-level
	models ('+Emo', '+Top', '+Diag'), we see consid-
	erable improvements in all metrics, and this holds
	for all auxiliary tasks. We can thus confirm the
	advantage of hierarchical structure for model per-
	formance.

Table 5 ,

 5 Table 6, and Table 7 show the number and percentage of emotion, dialog act, topic for each subset, resp.

	Emotion	Train		Dev		Test
		#	%	#	%	#	%
	0-no emotion 72, 143	82.8 7, 108	88.1 6, 321	81.7
	1-anger	827	0.9	77	1.0	118	1.5
	2-disgust	303	0.3	3	0.04	47	0.6
	3-fear	146	0.2	11	0.1	17	0.2
	4-happiness	11, 182	12.8	684	8.5	1019	13.2
	5-sadness	969	1.1	79	1.0	102	1.3
	6-surprise	1, 600	1.8	107	1.3	116	1.5
	Utt. Total	87, 170 100.0 8, 069 100.0 7, 740 100.0

Table 5 :

 5 Emotion distribution in train, dev. and test sets.

	Dialog Act	Train		Dev		Test
		#	%	#	%	#	%
	1-inform	39, 873	45.7 3, 125	38.7 3, 534	45.7
	2-question	24, 974	28.6 2, 244	27.8 2, 210	28.6
	3-directive	12, 242	16.3 1, 775	22.0 1, 278	16.5
	4-commissive	8, 081	9.23	925	11.5	718	9.3
	Utt. Total	87, 170 100.0 8, 069 100.0 7, 740 100.0

Table 6 :

 6 Dialog act distribution in train, dev. and test sets.

	Topic	Train		Dev		Test
		#	%	#	%	#	%
	1-ordinary life	2, 975	26.8	418	41.8	252	25.2
	2-school life	453	4.1	0	0	34	3.4
	3-culture & education	50	0	0	0.0	5	0.5
	4-attitude & emotion	616	5.5	1	0.0	50	0.5
	5-relationship	3, 879	34.9	129	12.9	384	38.4
	6-tourism	860	7.7	124	12.4	79	7.9
	7-health	205	1.8	41	4.1	21	2.1
	8-work	1, 574	14.2	215	21.5	135	1.4
	9-politics	105	0.9	13	1.3	13	1.3
	10-finance	399	3.6	59	5.9	27	2.7
	Total	11, 118 100.0 1, 000 100.0 1, 000 100.0

Table 7 :

 7 Topic distribution in train, dev. and test sets.

https://www.who.int/news-room/ fact-sheets/detail/depression

Sentiment and emotion are closely related with different function and/or granularity, cf.[START_REF] Munezero | Are they different? affect, feeling, emotion, sentiment, and opinion detection in text[END_REF].[START_REF] Cerisara | Multi-task dialog act and sentiment recognition on mastodon[END_REF] use three labels for sentiment: positive, negative, neutral. In this paper, we use seven emotional labels: anger, disgust, fear, happiness, sadness, surprise, neutral.

http://yanran.li/dailydialog

Naive hierarchical network (baseline).

Hierarchical contextual attention network.

Hierarchical attention network with LIWC lexicon.

Precision: in[START_REF] Qin | Co-gat: A co-interactive graph attention network for joint dialog act recognition and sentiment classification[END_REF] authors report results on sentiment classification. It is yet unclear how they convert emotion annotation (7 labels) to sentiment (3 labels).

Backchannel refers to phatic expressions such as yeah, hum mm. Here we use different dialog acts from those in DailyDialog.

Acknowledgement

The authors thank the anonymous reviewers for their insightful comments and suggestions. This work was supported by the PIA project "Lorraine Université d'Excellence", ANR-15-IDEX-04-LUE, as well as the CPER LCHN (Contrat de Plan État-Région -Langues, Connaissances et Humanités Numériques). It was also partially supported by the ANR (ANR-19-PI3A-0004) through the AI Interdisciplinary Institute, ANITI, as a part of France's "Investing for the Future -PIA3" program, and through the project AnDiAMO (ANR-21-CE23-0020). Experiments presented were carried out in secured clusters on the Grid'5000 testbed. We would like to thank the Grid'5000 community (https://www.grid5000.fr).

Ethical Considerations

The goal of such systems is not to replace human healthcare providers. All these systems may be used only in support to human decision. The principle of leaving the decision to the machine would imply major risks for decision making in the health field, a mistake that in high-stakes healthcare set-


Stéphane Gorsse

Bernard Chevalier
email: chevalie@icmcb-bordeaux.cnrs.fr

Selcan Tuncel

Rainer Pöttgen

Metamagnetic transition in the 75 K antiferromagnet Gd4Co2Mg3

Keywords: Gadolinium based compound, Magnetically ordered material, Metamagnet, Magnetocaloric effect

come   L'archive ouverte pluridisciplinaire

Introduction

The rare earth (RE)-transition metal (T)-magnesium systems have intensively been studied in the last ten years. Although more than 200 ternary compounds have been structurally characterized [1-6, and ref. therein] only little is known on their physical properties. Highly interesting compounds are the intermediatevalent systems Ce 2 Ni 2 Mg and CeNi 4 Mg [7], the metamagnet Pr 2 Pd 2 Mg [8] presenting a low critical magnetic field, and the 43 K ferromagnet Nd 2 Cu 2 Mg [9]. This last intermetallic exhibits a pronounced square loop behavior in its magnetization at 4.5 K.

Much higher magnetic ordering temperatures have been observed for the gadolinium based materials. Such compounds are of special interest with respect to their application potentials owing to a large magnetocaloric effect and giant magnetoresistance. For instance, Gd 2 Ni 2 Mg shows antiferromagnetic ordering at 49 K [10], while stable ferromagnetic ground states have been observed for GdTMg (T = Pd, Ag, Pt) [11] with Curie temperatures of 95.7 K (GdPdMg), 39.3 K (GdAgMg), and 97.6 K (GdPtMg). Again, GdAuMg [12] orders antiferromagnetically at 81.1 K with a spin reorientation near 19 K. Several GdTMg intermetallics reveal slightly enhanced magnetic moments in the paramagnetic range, indicating a contribution of the gadolinium 5d electrons induced via 4f-5d exchange interactions.

During our systematic studies of the RE-T-Mg systems, we have started to investigate the gadolinium based compounds in more detail. Herein we report on the electrical, magnetic and thermal properties of the gadolinium-rich phase Gd 4 Co 2 Mg 3 with crystallizes in the monoclinic Nd 4 Co 2 Mg 3 type structure [13,14].

Experimental details

Starting materials for the synthesis of Gd 4 Co 2 Mg 3 were a gadolinium ingot (smart elements), cobalt powder (Sigma-Aldrich, 100 mesh, >99.9 %), and a magnesium rod (Johnson Matthey,  16 mm, >99.95 %). The elements (4:2:3 atomic ratio) were arc-welded [15] in a small tantalum tube under an argon pressure of ca. 600 mbar. The argon was purified before over molecular sieves, silica gel and titanium sponge (900 K). The tantalum tube was placed in a watercooled quartz sample chamber [16] of a high-frequency furnace (Hüttinger Elektronik, Freiburg, Typ TIG 1.5/300), first heated for 2 min at ca. 1300 K and subsequently annealed for 2 h at ca. 920 K, followed by quenching. The temperature was controlled through a Sensor Therm Metis MS09 pyrometer with an accuracy of ±30 K. The brittle reaction product is stable in air over months.

The Gd 4 Co 2 Mg 3 sample was checked by X-ray powder diffraction (Guinier technique) using Cu Kα 1 radiation and α-quartz as an internal standard. The experimental pattern matched a calculated one [17] indicating pure Gd 4 Co 2 Mg 3 on the level of X-ray powder diffraction.

Magnetization measurements were performed using a superconducting quantum interference device (SQUID) magnetometer in the temperature range 4.2-300 K and applied fields up to 4.6 T. The measurement of the electrical resistivity was carried out above 4.2 K on a bar of 1.5 x 1.5 x 5 mm 3 using a standard dc four probe method with silver paint contacts and an intensity current of 10 mA. Heat capacity measurement was realized by a relaxation method with a Quantum Design PPMS system and using a two tau model analysis.

Results and discussion

Gd 4 Co 2 Mg 3 [14] crystallizes with the monoclinic Nd 4 Co 2 Mg 3 type structure [13]. Since the crystal chemistry and the chemical bonding peculiarities were discussed in detail in previous work, we give only a brief account on Gd 4 Co 2 Mg 3 here. The coordination polyhedra of the two crystallographically independent Gd atoms (both with site symmetry m) are presented in Fig. 1. The Gd1 and Gd2 atoms have coordination numbers 16 and 14, respectively. Both Gd sites have closest Co neighbors with Gd-Co distances ranging from 272 to 294 pm, near to the sum of the covalent radii of 277 pm [START_REF] Emsley | The Elements[END_REF]. This is in line with recent electronic structure calculations [14] which revealed strong RE-Co interactions. Similar Gd-Co distances occur for the Gd 6 trigonal prismatic units in the other ternary compound rich in gadolinium Gd 4 CoMg (281-282 pm) [START_REF] Tuncel | [END_REF]. Both Gd sites have six nearest Gd neighbours 349-401 pm, similar to Gd 4 CoMg (351-370 pm) [START_REF] Tuncel | [END_REF].

These distances are comparable to hcp gadolinium (6  357 and 6  363 pm) [START_REF] Donohue | The Structures of the Elements[END_REF]. (where n = 4 is the concentration of Gd 3+ ions per mol) is found to be around 8.20(5) µ B , which is slightly higher than the free-ion moment of the Gd 3+ ion (7.94 µ B ). This suggests a contribution to the magnetic properties of Gd 4 Co 2 Mg 3 from (i) the cobalt atoms or/and (ii) the conduction electrons as observed previously for the intermetallics GdAgMg and GdPtMg [11]. Also, the positive value of  p = 83(1) K indicates the predominance of the ferromagnetic interactions in this ternary compound.

For an applied magnetic field of H = 0.025 T, the curve M/H versus T (M = magnetization) exhibits a sharp maximum at about T N = 75(1) K suggesting an antiferromagnetic ordering (Fig. 3(a)). This Néel temperature T N agrees with that where the electrical resistivity presents a sudden decrease (Fig. 2). For higher fields H, the maximum observed from the curves M/H versus T is both enlarged and shifted towards lower temperatures; for instance, for H = 0.1 and 0.2 T, the maximum appears at 72(1) and 63(1) K, respectively (Fig. 3(a)). This behaviour characterizes a metamagnetic transition occurring at very low critical magnetic fields as observed for the ternary stannide UCo 1.45 Sn 2 [START_REF] Mirambet | [END_REF]. This transition antiferromagnetic  ferro(ferri)magnetic is confirmed by magnetization measurements at high magnetic fields. For H = 0.85 and 1 T (Fig. 3 saturates at H = 4.6 T with 25.2 µ B /mol or 6.3(1) µ B as saturation magnetic moment per Gd-atom, a value significantly smaller than the theoretically one calculated free Gd 3+ -ion (7 µ B ). This result suggests: (i) either a small antiferromagnetic contribution of the cobalt atoms induced by the strong Gd-Co bonding [14] or (ii) that the metamagnetic transition evidenced for this ternary compound leads to a ferrimagnetic arrangement for the gadolinium substructure formed by two crystallographically independent Gd atoms.

Combining the results determined from the measurements M/H versus T and M versus H, we can draw a tentative magnetic phase diagram for Gd 4 Co 2 Mg 3 (Fig. 5). Three magnetic phases are distinguished: (i) the paramagnetic (P) phase; (ii) the antiferromagnetic (AF) phase observed at low magnetic fields and (ii) the ferro(ferri)magnetic (F) arrangement appearing after the metamagnetic transition.

The borderline between the (AF) and (F) phases is deduced from the peak (in magnetic field) observed in the M/H versus H derivative curves whereas that between (F) and (P) is determined from the maximum (in temperature) observed in the (M/H)/T versus T derivative curves. We note that the critical magnetic field H cr inducing the metamagnetic transition, varies practically linearly with the temperature; at 6 K, H cr takes a small value of 0.93(2) T whereas at 1 T (Fig. 3 The magnetic entropy change associated to the magnetic ordering of Gd 4 Co 2 Mg 3 , S M , is calculated for both observed transitions from the isothermal magnetization M versus H curves using the well-known Maxwell relationship [START_REF] Morrish | The Physical Principles of Magnetism[END_REF]:

  dH T M S H H M      0 . ( 1
)
The sign of S M is positive for the (F) to (AF) metamagnetic transition and negative for the (P) to (F) ordering transition (Fig. 7). The ternary compound Gd 4 Co 2 Mg 3 exhibits both a magnetocaloric effect (MCE) at 77 K giving rise to a temperature increase when applying a magnetic field adiabatically and an inverse MCE at 6 K that cools the sample.

The inverse MCE gives rise to a moderate entropy increase of 0.56(2) Jkg -1 K -1 at 6 K under the application of field of 1 T. In The adiabatic temperature change, T ad , linked to the MCE can be evaluated using the relationship [24,25]:

T ad T;0  H    TS M C P,0 (T)
where C P , 0 (T) represents the specific heat measured without applied magnetic field. T ad reaches 1.3(1) and 3.4(1) K for H = 2 and 4.6 T, respectively. well with these high-MCE intermetallic compounds bearing lanthanide metals.

Conclusion

Gd 4 Co 2 Mg 3 orders antiferromagnetically below T N = 75 K and shows a fieldinduced transition at approximately 0.93 T at 6 K. This metamagnetic transition is closely associated with the fact that the paramagnetic Curie temperature is positive ( p = 83 K). This means that the overall interaction between the Gd moments in this ternary compound is ferro(ferri)magnetic and that the antiferromagnetic ground state is rather unstable. We found a maximum value of the magnetic entropy change S M of about -10.3 Jkg -1 K -1 at 77 K and a field change of 4.6 T, due to the field-induced magnetic phase transition. This value is comparable to that observed for the metamagnet Gd 3 Co (S M = -11 Jkg -1 K -1 near 140 K and H = 5 T) [START_REF] Tripathy | [END_REF] and suggests that Gd 4 Co 2 Mg 3 could be useful for magnetic refrigeration around 77 K.

Figure Captions

  The temperature dependence of the reduced electrical resistivity (T)/(270 K) of Gd 4 Co 2 Mg 3 is shown in Fig.2. (Owing to the presence of microcracks in the sample, absolute values of (T) could not be determined accurately; for this reason, we report the reduced resistivity). In the temperature range 280-77 K, the resistivity exhibits metallic behaviour, decreasing almost linearly with the lowering of temperature. A sudden change of slope is detected at 77(1) K on the curve (T)/(270 K) versus T, suggesting the occurrence of a transition which can be linked to the existence of an antiferromagnetic ordering as detected by magnetization measurement (see below). Finally, at low temperatures, below 23 K, (T)/(270 K) data can be represented by a T 2 function (inset of Fig. 2) in reasonable agreement with the quadratic temperature dependence expected for a magnetic material. The temperature dependence of the reciprocal magnetic susceptibility  m -1 of Gd 4 Co 2 Mg 3 in a magnetic field of H = 3 T is shown in Fig. 3(a) (inset). Above 120 K, the curve  m -1 versus T is fitted with a Curie-Weiss expression  m -1 = (T - p )/C m where C m is the molar Curie constant and  p the paramagnetic Curie temperature. The estimated effective moment µ eff = (8C m /n) 1/2

  (b)), the curves M/H versus T exhibit: (i) a sharp increase in the magnetization at the Curie temperature T C = 81(1) K (this T C -temperature was defined by the maximum appearing in the (M/H)/T versus T derivative curves) and (ii) a small decrease of M below 12(1) K for H = 0.85 T but this behaviour is not observed for H = 1 T where M presents a saturation at low temperatures. These results indicate that the magnetic ordering of Gd 4 Co 2 Mg 3 is strongly dependent of the H-field.The curves M versus H presented in Fig.4for various temperatures below T N , confirm that Gd 4 Co 2 Mg 3 is a metamagnet. Clearly at T = 6 K, the magnetization, as H increases, varies linearly for H < 0.2 T (Fig.4(a)) and then increases rapidly towards saturation (Fig.4(b)). The metamagnetic transition occurs at lower magnetic fields as the temperature is increased; for instance at the Néel temperature (T N = 75(1) K), this transition is not detected. Moreover, isothermal magnetization performed at low temperatures, for instance at 6 K (Fig.4(b)),

  (b)) the (AF) phase is not detected. This result indicates that the metamagnetic behaviour of the ternary compound Gd 4 Co 2 Mg 3 is easily observable in agreement with the positive value of the paramagnetic Curie temperature  p = 83(1) K. Specific heat C P , 0 measured without applied magnetic field for Gd 4 Co 2 Mg 3 is shown in Fig.6as a function of temperature. The most important feature is the well defined -type anomaly signalling the antiferromagnetic transition. The ordering temperature is associated with the maximum at 75(1) K, in excellent agreement with that determined from magnetization and electrical resistivity measurements. The tails above T N suggest the existence of short range magnetic correlations.

  Gd 4 Co 2 Mg 3 , inverse MCE resulting of the (F) to (AF) transition can be attributed to the presence of two different crystalographic sites for Gd atoms and different Gd-Gd interatomic distances.The peak entropy change at 77 K in a magnetic field of 2 and 4.6 T reaches -5.8(2) and -10.3(2) Jkg -1 K -1 , respectively. These values are comparable to that observed for the metamagnet Gd 3 Co (S M = -11 Jkg -1 K -1 near 140 K and H = 5 T)[START_REF] Tripathy | [END_REF] suggest that Gd 4 Co 2 Mg 3 could be useful for magnetic refrigeration around 77 K. The resulting refrigeration capacity, RCP = S M ,P F PEAK . T FWHM , is 500(10) Jkg - 1 for H = 4.6 T (T FWHM is the full width at half length of S M ). Fig.8shows the 10 normalized RCP/H plotted against the magnetic ordering temperature T t for several compounds of references and high MCE Gd-based materials from the literature together with the Gd 4 Co 2 Mg 3 from this work. It can be seen that Gd 4 Co 2 Mg 3 exhibit the highest refrigeration capacity for working temperature in the range of 60-100 K.

Fig. 9

 9 Fig. 9 compares the normalized adiabatic temperature change,T ad /H, for Gd 4 Co 2 Mg 3 and other materials having the largest MCE between 10 and 80 K. In this temperature range, the application of magnetocaloric cooling is gas liquefaction. The Gd 4 Co 2 Mg 3 ternary compound from the present work competes

Fig. 1 .Fig. 2 .

 12 Fig. 1. Coordination polyhedra of the two crystallographically independent Gd sites in Gd 4 Co 2 Mg 3 . Gd, Co and Mg atoms are drawn as medium gray, black

Fig. 3 .

 3 Fig. 3. Temperature dependence at various fields of the magnetization of Gd 4 Co 2 Mg 3 divided by magnetic field: (a) for H = 0.025, 0.1 and 0.2 T and (b) for H = 0.85 and 1 T. The inset of Fig. 3(a) presents the reciprocal magnetic susceptibility (measured at H = 3 T) versus temperature and the Curie-Weiss law (dashed line).

Fig. 4 .Fig. 5 .

 45 Fig. 4. Field dependence at various temperatures of the magnetization of Gd 4 Co 2 Mg 3 : (a) for H < 0.5 T and (b) for H < 4.6 T. Fig. 5. Field-temperature phase diagram of Gd 4 Co 2 Mg 3 deduced from the magnetization measurements.

Fig. 6 .Fig. 7 .

 67 Fig. 6. Temperature dependence without applied magnetic field of the specific heat C p, 0 of Gd 4 Co 2 Mg 3 . Fig. 7. Temperature and field dependences of the magnetic entropy change for Gd 4 Co 2 Mg 3 deduced from the magnetization measurements. S M ,F AF PEAK

Fig. 8 .Fig. 9 .

 89 Fig. 8. Normalized relative cooling power, RCP/∆H, plotted against the magnetic ordering temperature Tt for the Gd 4 Co 2 Mg 3 ternary compound (present work) and

Fig. 1 .Fig. 2 .

 12 Fig. 1. Coordination polyhedra of the two crystallographically independent Gd sites in Gd 4 Co 2 Mg 3 . Gd, Co and Mg atoms are drawn as medium gray, black filled, and open circles, respectively. Atom designation and site symmetries are indicated.

Fig. 3 .

 3 Fig. 3. Temperature dependence at various fields of the magnetization of Gd 4 Co 2 Mg 3 divided by magnetic field: (a) for H = 0.025, 0.1 and 0.2 T and (b) for H = 0.85 and 1 T. The inset of Fig. 3(a) presents the reciprocal magnetic susceptibility (measured at H = 3 T) versus temperature and the Curie-Weiss law (dashed line).

Fig. 4 . 20 Fig. 5 . 21 Fig. 6 . 22 Fig. 7 .

 4205216227 Fig. 4. Field dependence at various temperatures of the magnetization of Gd 4 Co 2 Mg 3 : (a) for H < 0.5 T and (b) for H < 4.6 T.

Fig. 8 .

 8 Fig. 8. Normalized relative cooling power, RCP/∆H, plotted against the magnetic ordering temperature Tt for the Gd 4 Co 2 Mg 3 ternary compound (present work) and the largest MCE materials [26-30].

Fig. 9 .

 9 Fig. 9. Normalized adiabatic temperature change, RCP/∆H, plotted against the magnetic ordering temperature T t , for the best magnetic refrigerant materials in the range of 10-80 K [31-38].

Acknowledgments

This work was financially supported by the Deutsche Forschungsgemeinschaft. B.C. and R.P. are indebted to EGIDE and DAAD for research grants within the PROCOPE programs (11457RD and D/0502176).


Ambre Scarmoncin
email: ambre.scarmoncin@aphp.fr

Clothilde Portelli
email: clothilde@humaniteam-design.com

Ferney Osorio
email: ferney.osorio@univ-lorraine.fr

Guillaume Eckerlein
email: guillaume.eckerlein@aphp.fr

Unfolding innovation lab services in public hospitals: a hospital FabLab case study

Keywords: hospital, health institution, innovation, design thinking, FabLab

Along with the first pandemic wave of COVID-19, many makers' initiatives shed light on the innovative potential of developing computer assisted machinery services for the health sector. Even since before that, collaborative innovation structures such as FabLabs have been arising in public health institutions, which indicates the increasing demand for technological tools as well as innovation assistance in the public health sector. However, how FabLabs facilitate innovation processes contingent on hospital context is a question that needs to be further explored. In this article, a single case study on the Hephaïstos FabLab at the Bicêtre Hospital in France is developed in order to understand the role that a FabLab service can play in fostering innovation in a hospital ecosystem. The results show how innovation is stimulated by the FabLab proximity, the methodological approach developed by the FabLab team and the participants' profiles. These insights are pertinent for hospital managers to help identify strategies and ensure continuity of a FabLab service.

I. INTRODUCTION

Initiated by the Massachusetts Institute of Technology (MIT) in the 90s, the FabLab (from Fabrication Laboratories) concept rapidly spread around the world. Organized in a worldwide network coordinated by the FabFoundation, one must follow the Fab Charter [START_REF]The Fab Charter[END_REF] to be part of the movement. In the last 20 years, the FabLab community grew over 2000 members in more than 120 countries [2] and more than 10% of these labs are located in France [START_REF] Garnier | Les FabLabs, un réseau mondial et en croissance d'organisations collaboratives : une analyse des modes de coordination intra et inter-organisationnels[END_REF]. FabLabs-and innovation laboratories (or innovation labs) in a broader sense-are part of a larger phenomenon known as the Maker Movement in which every individual is considered a potential solution maker if given access to adequate tools [START_REF] Dougherty | The Maker Movement[END_REF], such as digital solutions and computer assisted machines. Understanding and encouraging the creation of such spaces can favor new working practices that rely on collaboration, co-design, co-production and co-creation approaches, with a high innovative potential [START_REF] Rayna | Open social innovation dynamics and impact: exploratory study of a fab lab network[END_REF]. Hence the growing interest in private companies [START_REF] Lô | Unsilencing power dynamics within third spaces. The case of Renault's Fab Lab[END_REF], public institutions [START_REF] Ferchaud | Fabriques numériques, action publique et territoire : en quête des living labs, fablabs et hackerspaces (France, Belgique)[END_REF] and academics [START_REF] Lhoste | FabLabs. L'institutionnalisation de Tiers-Lieux du "soft hacking[END_REF], [START_REF] Suire | La performance des lieux de cocréation de connaissances[END_REF] where innovation has become a leitmotiv in strategic plans and short-term objectives. Top-down decisions to stimulate innovation might lead to the creation of innovation labs which provide space and technological resources but are often disconnected from the users' experience [START_REF] Fecher | Innovation labs from a participants' perspective[END_REF]. Furthermore, to succeed in the long term, these organizational forms should also provide a methodological expertise in user-driven design to ensure the facilitation of today's increasingly more open and collaborative innovation processes [START_REF] Morel | Espace d'innovation : de nouveaux lieux pour l'intelligence collective ?[END_REF], [START_REF] Dupont | Collaborative innovation projects engaging open communities: A case study on emerging challenges[END_REF].

In this paper, we focus on FabLabs-as innovation labs-in the public health sector for which the recent health crisis exacerbated the need for organizational transformations. In early 2020, when the COVID-19 pandemic had become a globally dominating health concern, bringing the healthcare systems in many countries to their absolute limits, the reaction of the maker movement was instantaneous. Maker communities around the globe have been very active during the first wave of the COVID-19 crisis by responding to the shortage of PPE and other medical and healthcare-related products [START_REF] Kieslinger | COVID-19 Response from Global Makers: The Careables Cases of Global Design and Local Production[END_REF]. Consequently, FabLab settings have become a catalyst for makers and healthcare communities to amplify their work by accelerating the development of frugal innovations [START_REF] Corsini | Frugal innovation in a crisis: the digital fabrication maker response to COVID-19[END_REF] (i.e., doing more, for less, for people) and fostering more networked and collaborative healthcare ecosystems [START_REF] Abbassi | Maker movement contribution to fighting COVID-19 pandemic: insights from Tunisian FabLabs[END_REF].

Although public hospitals are not usually fast-pace innovative environments given their organizational and regulatory complexity [START_REF] Williams | Organizational readiness for innovation in health care: Some lessons from the recent literature[END_REF], they have been witnessing the emergence of the lab phenomenon as collaborative tools in action to overcome innovation barriers [START_REF] Osorio | Constellation of Innovation Laboratories: A Scientific Outlook[END_REF], [START_REF] Svensson | Policies to promote user innovation: Makerspaces and clinician innovation in Swedish hospitals[END_REF]. However, despite the positive impact that collaborative innovation environments such as FabLabs might have to a hospital's innovation capacity and culture [START_REF] Torvinen | Public health care innovation lab tackling the barriers of public sector innovation[END_REF], establishing methodological and practical guidelines on how FabLabs orchestrate innovation projects contingent on the hospital context needs to be further explored. How are user-driven design projects carried out in a hospital FabLab? To what extent does a FabLab setting act as a facilitating interface for hospital innovation processes? These are some of the questions that motivate this study and Pre-print version, please cite as: Scarmoncin, A., Portelli, C., Osorio, F., Eckerlein, G. (2022). Unfolding innovation lab services in public hospitals: a hospital FabLab case study. 2022 IEEE 28th International Conference on Engineering, Technology and Innovation (ICE/ITMC) and 31st International Association For Management of Technology (IAMOT).

that we consider to be of high relevance, since they raise the operational and methodological issues that lab managers, researchers and users often have to deal with [START_REF] Roux-Marchand | Connecting the strategic intent of innovation labs and projects: the case of the Green Fablab[END_REF].

In order to better understand the role that FabLabs can play in fostering innovation in hospital ecosystems, this work develops a single case study on the experience of the Hephaïstos FabLab, created in 2019 at Bicêtre Hospital in France. By filling the gap let by discontinued global supply chains in March 2020, the Hephaïstos FabLab proved to be an agile mechanism for adapting production to users, coordinating actors on a local scale, sharing practical ideas and teaching design methodologies to ensure an emergency procurement [START_REF] Fauchille | Le fablab, service d'innovation. L'exemple d'Héphaïstos au Kremlin-Bicêtre[END_REF]. This episode contributed to the popularity of the FabLab setting, but beyond its role in supporting the healthcare crisis, Hephaïstos grew into a cradle of innovation for the whole public hospital ecosystem; as of March 2022, more than 160 projects are being led on seven hospitals, some of them leading to intellectual property protection.

Accordingly, the main goal of this paper is thus to provide insights from empirical work on how innovative solutions are developed within a hospital FabLab. This way, we can identify how a FabLab service is used under different configurations in a hospital context. We reflect on the evolution of the services provided by our case and the methodological considerations implemented during this process. To this end, we frame our analysis in three main aspects: participants' profiles, applied services methodology and outcomes. Then, a cross-case analysis is structured to reflect on 10 projects which were completed between the creation of the FabLab three years ago and today. The results allow us to observe that innovation triggered by the FabLab service takes several forms and this approach could allow hospital managers to identify strategies, competences and methodologies that could lead to innovation opportunities.

The remainder of this document is structured as follows. First, an overview on hospital innovation and innovation labs in public health institutions is explored. Then, the research methodology is presented including a hospital FabLab's presentation and our framework design. Finally, results are presented through the description of a single project and a cross-case analysis before concluding with some perspectives for further research.

II. PREVIOUS WORKS A. Hospital innovation

With rising costs and an aging population, innovation has become a critical factor in the development and survival of organizations within the healthcare system [START_REF] Thune | Hospitals as innovators in the health-care system: A literature review and research agenda[END_REF]. One of the measures taken by the Regional Health Agency (ARS) a year after the first pandemic wave is to reinforce its action in public healthcare innovations [START_REF] Santé | L'innovation en santé : l'engagement des agences régionales de santé[END_REF]. Although medical (and technological) innovation has dominated the research on the transformation of the public healthcare sector [START_REF] Williams | Organizational readiness for innovation in health care: Some lessons from the recent literature[END_REF], as a consequence of the production function that hospitals took over time and technologies development, Djellal and Boullaj [START_REF] Djellal | Innovation in hospitals: a survey of the literature[END_REF] argue that medical innovation in not synonymous with hospital innovation and that the field of exploration should be broadened to other areas to improve hospital performance. Hospitals are in fact complex service organizations composed of a network of healthcare units and support functions that provide an extensive range of services supporting the quality of care [START_REF] Djellal | Innovation in hospitals: a survey of the literature[END_REF].

Accordingly, hospitals as public institutions are not exempt from organizational barriers to innovation. In fact, there is a call from recent studies for addressing issues hindering innovation in the hospital context such as complexity, risk aversion, organizational flexibility, lack of competence (for innovation), bureaucracy and external cooperation [START_REF] Torvinen | Public health care innovation lab tackling the barriers of public sector innovation[END_REF], [START_REF] Svensson | Policies to promote user innovation: Makerspaces and clinician innovation in Swedish hospitals[END_REF], [START_REF] Dias | The open nature of innovation in the hospital sector: The role of external collaboration networks[END_REF]. In this sense, Dias and Escoval [START_REF] Dias | Improvement of Hospital Performance Through Innovation[END_REF] explain that "the organizational innovations that promote communication and interaction across departments and other organizations are key factors to accelerate innovation in the hospital sector". Lee and Kong [START_REF] Lee | Factors Affecting Hospital Employees' Knowledge Sharing Intention and Behavior, and Innovation Behavior[END_REF] also highlight that in order to achieve knowledge sharing and innovation behavior, hospital workers should be encouraged to share their expertise and innovation with their counterparts through diversity, autonomy and open communication.

B. Innovation labs in public health institutions

Torvinen and Jansson [START_REF] Torvinen | Public health care innovation lab tackling the barriers of public sector innovation[END_REF] present innovation labs as an opportunity to tackle the barriers of public sector innovation by adding interaction in complex organizations, enhancing mutual learning across hospital units but also with potential external partners and allowing a smoother journey when bureaucracy can slow down promising projects. Such labs have the ability to make innovation prospects more tangible, which motivates frontline organizations to take an active role in the innovation process.

As organizational structures, innovation labs take several forms such as FabLabs, makerspaces, living labs, open labs among others, each one of them being the manifestation of the innovation intent of an organization (or group of organizations) operationalized through specific resources, methods, techniques and competences ( [START_REF] Osorio | Constellation of Innovation Laboratories: A Scientific Outlook[END_REF]). Amid the diversity of lab concepts we mainly observe two approaches that have spread significantly among practitioners and researchers: Living Labs and FabLabs. In a general context, a Living Lab is defined as a space dedicated to collective experiment and assimilation around a community of thinkers while a FabLab revolves around a community of makers who conduct experiments and share practices on digital technologies [START_REF] Scaillerez | Coworking, fab labs et living labs[END_REF]. Although there is often interest in establishing clear distinctions and differences between such approaches, there are also scholars who encourage how they are complementary and closely related. As an example, researchers from the ERPI research institute (Nancy, France) unified both concepts by creating their Fab Living Lab [START_REF] Dupont | Le Lorraine Fab Living Lab : la 4ème dimension de l'innovation[END_REF] in which users can develop, codesign, prototype, evaluate and diffuse their ideas with the assistance of the lab team [START_REF] Ten | Designing interactive museum visitors' experience using a Fab Living Lab platform: The Museum-Aquarium of Nancy case[END_REF] (Fig. 1). Relatively to those definitions, our hospital FabLab case is closer to the Fab Living Lab approach as it relies on both a technology platform and an innovation methodology. In public hospitals, multiple innovation lab-related initiatives have been developed and oriented toward clinician innovation but Svensson and Hartman [START_REF] Svensson | Policies to promote user innovation: Makerspaces and clinician innovation in Swedish hospitals[END_REF] deplore that, although this setting proves to be very efficient to develop innovations of high value, in terms of usage it mostly benefits directly to the innovation makers and less to the overall hospital functioning, especially regarding the patients experience, and the potential of diffusion which is limited. In a modern healthcare context, patients are playing a role in the co-design of services they need [START_REF] Reay | Designing the future of healthcare together: prototyping a hospital co-design space[END_REF] and some lab structures in public health institutions are putting them as central actors of their healthcare journey [START_REF] Berthou | De l'intention d'innovation à son institutionnalisation[END_REF], generating for instance innovations in the technical aid field like at the Rehab Lab (Lorient, France) [START_REF] Allegre | REHAB-LAB, aides techniques et impression 3D : de ≪patient ≫ à ≪créateur ≫[END_REF].

This literature confirms that an innovation lab with a making culture is relevant to a public health institution as it has already been developed with successful results in clinicianand patient-centered settings. However, there remains fields of exploration in hospital innovation that are yet to be covered by such collaborative spaces. Thus, in the next session we present the case of the Hephaïstos FabLab as an innovation lab in a public hospital which has been conceived as a complex multiconnected service provider where a user at any stage of the hospital network has a potential to innovate.

III. RESEARCH APPROACH

This study seeks to shed light on how an embedded FabLab service can enhance hospital innovation processes. We aim to reflect on the evolution of the services provided by a FabLab initiative through time while identifying key practices, routines and competences that shape its operation. To this end, a case study is proposed on the Hephaïstos FabLab to examine the operational and methodological considerations that have allowed to consolidate the FabLab service in a hospital context.

In this section we describe the main characteristics of our case followed by the definition of the analysis framework.

A. Case description

The Hephaïstos FabLab is an innovation lab providing digital fabrication tools (3D printers, laser cutting machine, 3D scanner, injection molder...) to the seven hospitals of the APHP Paris-Saclay University Hospital Group. Founded in 2019 after a successful first project with the Humaniteam design team as service provider, Hephaïstos is located at the heart of the Bicêtre Hospital, the largest hospital of the group. The Hospital FabLab is defined as a distinct hospital support unit with a cross-disciplinary connection to healthcare units but also support functions (analysis laboratories, pharmacy, biomedical, transport, general procurement, maintenance etc.) and is dedicated to the creation of solutions to make hospital users' life easier whether they are patients, healthcare workers or any hospital staff. More than a physical space, the FabLab is also a team composed of a Fab-manager (permanent position) and digital makers (fixed-term positions such as internships or civic services) which are mobile and available to animate brainstorming sessions, to guide hospital staff on the machines utilization, to update an open source database (called the Wiki) documenting all projects and to give a methodology support.

The format of the Hephaïstos FabLab service allows any hospital staff to submit his project or to participate in a brainstorming session as a collective approach to a problem. The composition of the FabLab team offers an abundance of skills, from a machines technical support, to a design methodology assistance but always with an educational approach and a proximity in the hospital space. The Fablab space itself have been thought to be an open hospital unit, located in the main building of the biggest hospital of the group, close to healthcare units and at the same floor than most support functions units, the service is very accessible. As for further hospital units, the FabLab team can come directly on site with the light machinery. The technology chosen at the FabLab is accessible and easily taught to any user. The FabLab team is giving guidance and support on modeling and prototyping for all users, and adapts to all profiles. The FabLab's approach is inspired by the agile methodology, lean management and design thinking to stimulate usagedriven innovation. Iterations between the FabLab team, the users and the experts allow to explore the problem space with a concrete ground approach, to converge toward a specific problem, to explore several ideas to generate prototypes that can be tested in real-time conditions then perfected with experience. This process is illustrated as a double diamond (Fig. 2) and shows that design thinking helps to keep in touch with the problem relevant environment and can use this information for refining and revising the chosen solution path(s) [START_REF] Plattner | Design Thinking: Understand -Improve -Apply[END_REF].

The double diamond design process comes in parallel to the 2D-3D-4D approach in which users are integrated in the FabLab environment from different interfaces of a project : idea generation (2D), concept creation (3D) and evaluation of usage scenarios (4D) [START_REF] Ten | Designing interactive museum visitors' experience using a Fab Living Lab platform: The Museum-Aquarium of Nancy case[END_REF]. After 3 years of service, the Hephaïstos FabLab has been involved in more than 160 projects (Fig. 3) on seven hospitals with different duration, participant profiles and entry points. A project is considered completed when an object have been designed and prototyped. Some projects may be paused as a consequence of material procurement delivery time or the users' lack of time to invest in the project. Very few projects have been rejected until now, the main reason is that either the solution is already available on the market, or the user is mistaken on the FabLab's purpose, i.e., regarding the FabLab as an external service provider with which an order is placed with no intention of taking part in the design or production process. The Hephaïstos FabLab was not created in one step, it was shaped by the users' needs and is still evolving.

B. Analysis framework

From the literature we have reckon the importance for innovation lab and FabLab initiatives in hospital settings to consider not only infrastructural or technological aspects but rather to (1) prioritize a user-driven approach, (2) to be aware of the methodological tools and activities that could facilitate the hospital community engagement and (3) to be sensible that hospital innovation outcomes may go beyond medical and clinician solutions to instead tackle organizational issues. Subsequently, to build our framework of analysis, we isolated three dimensions in a FabLab project: the participants' profiles (how a project is started, who leads it), the project methodology (how it is developed) and the outcomes (what resulted from it) to then identify comparison points in a crosscase analysis.

We chose to represent 10 projects out of the dozens that have been completed at the FabLab in a chronological order to illustrate the evolution of the service methodology of our case and understand how it was built over time. Tab. 1 summarizes the main project insights. The first project is special as it started when the FabLab was not existing yet. Hephaïstos was funded as one of the outcomes of this project, the initial intent also evolved as we will see later in this article. Projects 2, 3 and 4 are intended to show the plurality of actors and profiles that are enrolling in FabLab projects as it is one of the differentiating features among the literature. Projects 5 to 10 highlight the chronological evolution of the FabLab users and how projects are more and more linked through the participants. This way, we can perceive how this innovation lab has been built.

IV. RESULTS

A. Single project analysis

We detail Project 1 to understand the results of table 1 in a vertical reading as an example.

The first project, entitled "The Hanger tools", took place in late 2018 and funded the Hephaïstos FabLab. Starting as a top-down decision, the hospital logistics director wanted to conduct an immersive project directly with the internal patient transport team at Bicêtre Hospital to find a solution to frequent lateness.

A dozen of volunteer stretcher-bearers, including patients transportation regulators, were involved in the project: some have more than twenty years of experience, they have a great knowledge of practices and organization in patients transportation. Some are recent graduate, they have a basic knowledge in modeling and 3D printing recently provided in the secondary school curriculum. Others have an intermediate profile, they are motivated by the use of their cross-disciplinary skills. The experiment is based on the internal transport of hospitalized patients in the Cardiology department whose Health executive and nursing team took part in the project. The Cardiology unit is responsible for preparing the patient for transport. The Health executive is also in charge of ordering equipment and brings its experience to overcome compatibility problems. At As for the first project's methodology, there was not yet a specific frame. The logistics director, a fervent supporter of agile methods and lean management, made the decision to surround himself with designers of the Humaniteam studio whose goal is to drive innovation in hospital environment through design thinking and user experience. The entry point of the project was an immersive experience where the designers team explored the daily life of stretcher-bearers and the Cardiology department in order to discover together the causes of patient transport delays.

After 3 days of observation and cross-talks between the different participants, the statement is that lateness in patients transportation is random and unpredictable. Stretcher-bearers are being slowed down by the research time of the equipment necessary to patient transportation. The project team brings together the definition of the causes for the extended equipment search: the different brands of equipment are the cause of a fitting problem between transportation equipment (beds, stretchers, wheelchairs) and IV poles, along with a degradation of the fitting parts (blocked receptacles, broken poles). This precise definition of the causes by the users themselves allows the problem formulation from which the form of the solution will derive: How to allow stretcher-bearers to solve broken equipment and fitting problems without searching around the whole place ?

The development of the solution was based on the most frequent pain points: to replace a broken bag holder on an IV pole, to set a new IV pole receptacle on a wheelchair, to adapt a large hole to a thin IV pole on beds or stretchers, to turn a bed gallows into an IV bag holder, to roll around the equipment's cables during transportation or to set a urinal. The project format consisted of 3 co-design sessions. The first began with a period of inspiration through similar projects, projecting the problem in other contexts, defining user paths, sketching solutions and confronting them. Several ideas emerged, the selected one was to design objects that fit on each type of transport equipment to create a new support for IV's pole.

During the second the stretcher-bearers materialized their ideas in 3D using hardening modeling clay in order to define the shape of these objects. Finally, during the third workshop, the stretcher-bearers discovered how to quickly develop a prototype with 3D modeling and 3D printing machines to prepare for user tests. At this point, the idea of a FabLab structure emerged: by centralizing and sharing the modeling files, the objects designed by hospital staff could remain configurable according to the evolution of the hospital's equipment fleet, but also serve as inspiration for future prospects.

"The Hanger tools" project's outcome is the delivery of a collection of 3D printed animal-objects with adjustable parameters (Fig. 4). They solve in-between situations when transportation equipment is not in good enough conditions to be used but not degraded enough to be purchased new. The diffusion of this collection by Creative Commons license may be of interest to any healthcare facility.

The first intent of the Hephaïstos FabLab was born, based on a problem-solving approach through experience and users consultation. Many projects came after this one and the Hephaïstos FabLab setup and methodology evolved in parallel to adjust to the hospital's needs.

B. Cross-case analysis

The profile of the participants of the Hephaïstos FabLab projects are very diverse: healthcare workers, healthcare executives, technicians, engineers... of every hospital field and different hierarchical levels. In some other projects that are not depicted in the tab, medical, pharmacy, hygiene, information system and logistics staff are also represented.

Hospital staff with technical functions (engineer, technicians) are more likely to be tech-savvy so they don't hesitate to start a project on their own (projects 4, 6, 7, 9), whether they have a background in design methods and computer assisted machines or not. Healthcare workers tend to participate in groups to encourage collective thinking and cross-disciplinary synergy among the unit's team (projects 5, 8, 10) but also with patients (project 3) and with support functions (project 1).

Apart from project 1 which originally founded the Hephaïstos FabLab, projects are either motivated by the Fa-bLab communication efforts (as in projects 3, 5 and 6 : usually the team introduces the role the FabLab and previous projects during staff meetings and emphasize on the collaborative and user-driven aspect), or word-of-mouth from colleagues of a different unit (projects 4 and 8) which previously participated in a FabLab project, or a spontaneous project idea of staff who previously participated in FabLab projects (projects 2, 7, 9 and 10).

Based on the the multiple starting configurations of the projects illustrated in our framework, having no background on design and computer-assisted machinery or no previous history with the FabLab is not an obstacle to complete a project, whether in group or alone. However, once a project is completed, the empowerment feeling it provides is an additional reason to come back for another project. Some users come back with the intention to deepen an aspect of a previous Pre-print version, please cite as: Scarmoncin, A., Portelli, C., Osorio, F., Eckerlein, G. (2022). Unfolding innovation lab services in public hospitals: a hospital FabLab case study. 2022 IEEE 28th International Conference on Engineering, Technology and Innovation (ICE/ITMC) and 31st International Association For Management of Technology (IAMOT).

project: project 9 extends problems encountered in project 7 to a surrounding element, project 10 is the improved version of project with a few months feedback. Others, who grasp the FabLab concept and manage to visualize a new way to make the most of it, come back with new ideas: project 7 came right after project 6 in time as it raised multiple ideas of the same main pain point (storage efficiency for lab tools), project 2 have been submitted by users involved in project 1 for the same reasons (equipment dysfunction) but on a whole different field (IV poles enhancement VS windows' repair).

For the project methodology, group projects tend to start from a 4D approach with an immersion on site and a brainstorming session animated by the Hephaïstos team to codesign an idea that will be prototyped at the FabLab or in live if machines have been brought to the session. Such interventions in a hospital unit are called a popup session to insist on the punctual and efficient rhythm of participation because long project implication can be a deterrent for hospital staff who already have an operational full-time function. For project participants who need to come in the FabLab space to develop ideas, flash workshop can be organized and are more tool-oriented.

For projects with one participant, the entry point is generally a 2D approach as the problem definition is more objectcentered. The FabLab team ensures a methodological support on such projects to question usage and explore existing solutions. By suggesting a 4D approach, the team makes the most of the user's experience to link design features to operational usage and take into account potential side users.

Once a problem haven been explored and precisely defined, an idea is developed, leading to the prototyping of one or several objects. During this development phase, design is adapted to the exact need of users and it can sometimes lead to ideas of elaborated project titles. In project 1 for instance, the need was made explicit : "I need something to hang the IV bag, the equipment cables, the pee pot...", so the collection of "Hanger tools" was designed.

In every completed project, development leads to the design and delivery of at least one prototype. In our sample, 2 projects out of 10 lead to more, mainly because of the profusion of ideas during co-design sessions with large users' teams (project 1 and 3). Far form being high-tech objects, the FabLab production can be quite simple: a gutter, a rack, a strap, a box... In project 3, the created objects themselves are not particularly new ideas (movie tickets, brainstorming tools...) but imagining a new event to improve patients' sense of reality and linking the objects to this event is a very innovative approach. As of March 2022, the project have been submitted to the Hospital Innovation Award of the year. Some projects even have a low-tech approach, such as project 2 in which spare parts were produced from recycled plastic to extend windows' lifespan or project 4 in which an extension was created to avoid a machine's degradation. After such outcomes on several similar projects, a larger project have been launched in February 2022 with technical and biomedical units to work on several ideas to extend equipment's lifespan.

Saving the projects' design files was first intended to allow reproduction of the prototypes with different parameters to adapt to any isolated case in other units. The Wiki was created as an open-source platform to share those files and document the design process to allow a community to get inspiration and a modeling basis to design similar prototypes, as opposed to an industrial production. This is particularly important because producing these products in an industrial environment, which is ruled by many norms, would have much higher costs and less flexibility to fit a specific need. Hence the creation of Creative Commons Licenses to share the modeling files while protecting it from any commercial use.

For some projects, the diffusion potential is nonetheless interesting to take into account. This indicator is still being elaborated at this time so we classified the 10 projects of our sample into three categories to simplify comparisons: 1) Very local interest, 2) Public hospitals interest and 3) Interest beyond public institution.

We notice than even though most users design solutions for their specific needs, the potential of diffusion is 2 or 3 on our scale because the problem they encounter can be common in public institutions or health structures. Many problems with equipment is linked to regulations of public procurement, in which a new contract is made every 3 to 5 years for an entire hospital or a group of hospitals. In consequence, equipment's features are very heterogeneous and not always adapted to users' needs.

Among the projects' deliveries, several could have an industrial interest and a larger diffusion than what the FabLab is entitled to produce. For such outcomes, the FabLab engaged in 2021 in industrial development projects (projects 4, 5 and 8) supported by the hospital innovation department. Two other projects have a potential for an industrial development prospect. However, the format of these partnerships are still work in progress as public regulations are fuzzy around this new topic.

As for the intangible outcomes, the activity of the Hephaïstos FabLab has brought cross-disciplinary visions to daily problems, thus acknowledging every workers' expertise on usage, reinforcing self-appropriation, bringing cohesion inside a unit and collaboration between different departments. Also, completing a project from a problem observation to a tangible solution's delivery is fulfilling for hospital staff who are used to tortuous validation processes and never-ending projects.

V. DISCUSSION

This article described a sample of projects developed at a hospital FabLab which illustrates the evolution of service methodology of our case and its integration in the hospital ecosystem. This in an ongoing research with the main aim to understand how an embedded FabLab can enhance innovation prospects for a public hospital and which format for this new service is best fitted to reach this purpose. One of the first elements to highlight is the return rate. Once a project is completed, participants are likely to come back for another project, or at least to spread the word to colleagues, thus motivating personal initiatives, group dynamics and propagating innovative behaviours. Over time, the FabLab team needs less and less self promotion interventions in staff meetings because word-of-mouth spreads faster with the number of completed projects. The main limitation of our study lies in the lack of quantitative and standardized qualitative data collected for each project. We could gather those data for the sample of projects in this article and give interpretation with the feedback given through a punctual impact study led by external auditors, but further work must be done with the FabLab team to register data more systematically during operational functioning.

Interestingly, a genuine challenge for the FabLab team is to attract female staff to the innovation lab. Women represent more than 70% of all hospital staff [START_REF]Chiffres-clés de l'égalité professionnelle entre les femmes et les hommes dans la fonction publique -éd[END_REF], [START_REF] Holcman | Les composantes du personnel hospitalier[END_REF], but we observed that technical staff (who happen to be males) seem at first more at ease with the tools and technologies, they initiate more personal projects and tend to be more autonomous. Although more quantitative data must be exploited, out of 10 projects, only half have female participants and none is led by a female user alone so there is yet a potential to be revealed. Our case does not intend to become an extension of technical units as it would be missing innovation opportunities for the hospital as a whole [START_REF] Djellal | Innovation in hospitals: a survey of the literature[END_REF]. In the general context, FabLabs and makerspaces tend to attract far more men than women [START_REF] Maric | The gender-based digital divide in maker culture: features, challenges and possible solutions[END_REF] and exhibit a primarily "male" culture, reflected in the interior design of places, or by the language and attitudes of their members [START_REF] Eckhardt | Gender in the making: An empirical approach to understand gender relations in the maker movement[END_REF]. Far from being reluctant to evolve, makers community can benefit from the Hephaistos FabLab's experience which developed in a female-dominated environment. Further research can be explored on that topic.

Innovation also lies in the new approach that the Hephaïstos FabLab is promoting, through immersion, user-driven projects, collaboration and openness to hospital users as a whole. This dynamic brings additional trust and mutual assistance between hospital units. This users community is particularly important and must not be neglected of the strategic development of a FabLab initiative. Interaction must be facilitated and focused on sharing practices, designs and users' experiences. The Hephaïstos FabLab is not necessarily shaping a specific innovation process, but the multiple innovation intents of its users are shaping the FabLab service.

Figure 5 consolidates the methodological approach that has been progressively developed from our case experience and which constitutes a FabLab service methodology adapted to the hospital context. This proposition illustrates how the open communication surrounding the FabLab service, whether from the FabLab team or from users, is a driving force to start new projects.

The plurality of entry points and guidance formats provided by the FabLab team is crucial to make users feel at ease with the design thinking process. The figure shows that whatever the starting point (a problem, an idea or an existing object), the users can be guided toward the double diamond process.

Relatively to the project development phase and the users' needs, the FabLab team organizes digital tools awareness presentations, brainstorming sessions at different stage of the double diamond process or teaching sessions through popup sessions in hospital units or flash workshops directly in the Fa-bLab space. Every prototype design process and modeling files are saved on the Wiki for future prospects. The development of the Wiki platform is still in progress and needs additional study to categorize data relevantly for different authorization levels.

These FabLab interventions help users to go past 2D-3D-4D interfaces and reach a 3D production. The double diamond process is not linear in terms of project development as it is generally punctuated by usage feedback to eventually deliver adapted prototypes. This process itself is integrated in a larger 2D-3D-4D cycle in which the created object is always being questioned for possible enhancements [START_REF] Ten | Designing interactive museum visitors' experience using a Fab Living Lab platform: The Museum-Aquarium of Nancy case[END_REF], [START_REF] Dupont | Exploring the appropriateness of different immersive environments in the context of an innovation process for smart-cities[END_REF].

In terms of outcomes, innovation resulting from the FabLab service takes several forms. First, the large majority of projects result in a tangible object that is prototyped and does not exist on the market to fit exactly to users' need (as it is a project's rejection criteria), reinforcing self-appropriation. Then, even if the designed object itself is not new, the usage that is done behind and the customized feature to fit with the user's environment is innovative. The design and production processes can also be low-tech innovations, putting the FabLab in a frontline position to develop more frugal and sustainable practices in public hospitals which are important energy and materials consumers [START_REF] Corsini | Frugal innovation in a crisis: the digital fabrication maker response to COVID-19[END_REF]. This branch of development is quite central to our case strategy and could be the object of future research.

The Hephaïstos FabLab methodology is also part of a management paradigm shift in the hospital ecosystem. Hospitals are very pyramidal structures where top-down decisions are governing daily practices. The hospital FabLab encourages bottom-up initiatives. It also restores bonding between professionals which are gathered in a users community around fabrication protocols elaboration, skills development, crossdisciplinary confrontations and project communication. All of these outcomes are shaping what we could define as a hospital innovation culture. The positive feedback on the open communication surrounding a FabLab service is a key-element to make innovation projects thrive at the hospital [START_REF] Torvinen | Public health care innovation lab tackling the barriers of public sector innovation[END_REF].

Finally, it is interesting to recognize the innovation potential of a hospital FabLab service in the implementation of commercial partnerships with industries from income sources perspective. Some projects developed at the FabLab have been judged worthy, by the institution's Innovation Department, to be invested for an industrial production.The Hopistal FabLab outcomes could be deepened in terms of knowledge management, stakeholder trust and communication, which turn out to be key factors to improve external collaborations [START_REF] Dias | Improvement of Hospital Performance Through Innovation[END_REF]. However, embedded FabLab services in public hospitals is a relatively new strand of research that has yet to be developed, so further study should consider intellectual property and partnership formats between public hospitals and industries

VI. CONCLUSIONS

Innovation labs providing computer assisted technology offer an opportunity for public health institutions to stimulate innovative behaviour, especially for hospitals where non medical innovation still has space to be explored and has potential to improve the hospital system performance as a whole. Therefore, the objective of this article is to describe the development of a FabLab service in a public hospital using a framework conceived from empirical observations on several projects brought by hospital staff and completed at the Hephaïstos FabLab. The aim was to explore through a single case study how the evolution of a FabLab setting shapes a hospital innovation process.

One main conclusion of the case study is that fabrication tools and collaborative maker environments in a hospital should be brought to the staff with an open communication and a user-centered and usage-driven methodological guidance. User-centered because the pedagogical approach is adapted to any user's profile and allows many entry points to start a project. Usage-driven because the design methodology relies on the users' experience, immersive exploration and recurring feedback through practical sessions.

Beyond the production of tangible prototypes, a FabLab service strengthens an innovation culture in the hospital by encouraging cross-disciplinary dynamics, empowering staff to create solutions adapted to their needs and uniting users into a community to share practices. Thus, a hospital FabLab service fosters a culture in which innovative spirit spreads and ensures a virtuous feedback on future innovation prospects.

As the implementation of a hospital FabLab is emerging, qualitative and quantitative data on projects must be strengthened to evaluate the FabLab's impact. This article opens up many perspectives for further researches: future prospects of building public-industry partnerships through the hospital FabLab as an experimental space leading to commercial innovations can be developed, qualitative data of the FabLab's managerial impact can be studied or even gender-related issues can be deepen on the topic of developing a FabLab in a femaledominated environment.

  Pre-print version, please cite as: Scarmoncin, A., Portelli, C., Osorio, F., Eckerlein, G. (2022). Unfolding innovation lab services in public hospitals: a hospital FabLab case study. 2022 IEEE 28th International Conference on Engineering, Technology and Innovation (ICE/ITMC) and 31st International Association For Management of Technology (IAMOT).

Figure 1 .

 1 Figure1. Fab Living Lab approach[START_REF] Dupont | Exploring the appropriateness of different immersive environments in the context of an innovation process for smart-cities[END_REF]

  Pre-print version, please cite as: Scarmoncin, A., Portelli, C., Osorio, F., Eckerlein, G. (2022). Unfolding innovation lab services in public hospitals: a hospital FabLab case study. 2022 IEEE 28th International Conference on Engineering, Technology and Innovation (ICE/ITMC) and 31st International Association For Management of Technology (IAMOT).

Figure 2 .

 2 Figure2. Double diamond design process[START_REF]Double diamond design process[END_REF]

Figure 3 .

 3 Figure 3. FabLab's projects overview on March 1 st , 2022

  Pre-print version, please cite as: Scarmoncin, A., Portelli, C., Osorio, F., Eckerlein, G. (2022). Unfolding innovation lab services in public hospitals: a hospital FabLab case study. 2022 IEEE 28th International Conference on Engineering, Technology and Innovation (ICE/ITMC) and 31st International Association For Management of Technology (IAMOT).

Tab 1 .

 1 Projects sample at Bicêtre Hospital FabLab Project

Figure 4 .

 4 Figure 4. The "Hanger tools" collection

  Pre-print version, please cite as: Scarmoncin, A., Portelli, C., Osorio, F., Eckerlein, G. (2022). Unfolding innovation lab services in public hospitals: a hospital FabLab case study. 2022 IEEE 28th International Conference on Engineering, Technology and Innovation (ICE/ITMC) and 31st International Association For Management of Technology (IAMOT).

  Pre-print version, please cite as: Scarmoncin, A., Portelli, C., Osorio, F., Eckerlein, G. (2022). Unfolding innovation lab services in public hospitals: a hospital FabLab case study. 2022 IEEE 28th International Conference on Engineering, Technology and Innovation (ICE/ITMC) and 31st International Association For Management of Technology (IAMOT).

Figure 5 .

 5 Figure 5. Proposition of a hospital FabLab methodology

Pre-print version, please cite as: Scarmoncin, A., Portelli, C., Osorio, F., Eckerlein, G. (2022). Unfolding innovation lab services in public hospitals: a hospital FabLab case study. 2022 IEEE 28th International Conference on Engineering, Technology and Innovation (ICE/ITMC) and 31st International Association For Management of Technology (IAMOT).