Karine Lan
email: karine.lan@utt.fr

Hing Ting

Guillaume Dessinger
email: gdessinger@fondationcos.org

Dimitri Voilmy
email: dimitri.voilmy@utt.fr

Examining usage to ensure utility: Co-design of a tool for fall prevention

Keywords: Balance quality tester, Fall prevention, Interdisciplinarity, Co-design, Needs analysis, Utility, Domestication I

Ambient Assisted Living (AAL) technologies can play an important role in helping elderly people achieve healthy ageing and maintain their autonomy. The balance quality tester (BQT) is a device for remote assessment of balance quality for older people at risk of falling. It has been validated both from a technical and a clinical perspective. However, for the BQT to be considered as a useful tool for long-term home monitoring of people with balance impairments, two issues are at stake: ease-of-use on a regular basis and trust in the validity of the data acquisition. To ensure this utility, a usage study has been made to understand the needs and values of different stakeholders: elders at risk of falling and their entourage, as well as health professionals. One main insight was the need to redesign the BQT, so as to fit the needs concerning ease-ofuse and trust in validity of data acquisition. Using a Human-centred and Participatory Design approach, the redesigning work relates to hardware design, interaction design, interface design, and most of all to standardizing the protocol of stepping-on the BQT. This paper describes the main results, i.e. the design recommendations, and discusses the collaborative and iterative design process, which allowed the successful redesign of the BQT.

INTRODUCTION

According to the UN estimation, by 2050, one out of every five people will be over 60 years old. The ageing population therefore represents a demographic challenge, questioning new and innovative models to help elderly people achieve healthy ageing and maintain their autonomy. People live longer, but with an increased risk of diseases or of developing disability, due to a decrease in physical functioning. Linked to physical decline, one of the major healthcare problems associated with ageing is that of falls. The number of fallers each year has been estimated at 30% for people aged over 65 years, rising to 50% for those aged over 80 years [START_REF] Todd | What are the main risk factors for falls among older people and what are the most effective interventions to prevent these falls?[END_REF], [START_REF]Global health and ageing[END_REF]. Falls constitute a major cause of death among older people. In addition to the medical aspect of falls, there is also a considerable societal impact due to the increased vulnerability of the faller and the difficulties for their entourage [START_REF] Guberman | Families" values and attitudes regarding responsibility for the frail elderly[END_REF].

Part of the solution to this large-scale problem is prevention. The key issue is the possibility of detecting those at most risk of falling in order to be able to perform a targeted intervention [START_REF] Hewson | Validation of balance-quality assessment using a modified bathroom scale[END_REF]. Innovative technologies can play an important role in remote monitoring and early identification of elderly people who suffer from functional decline [START_REF] Vermeulen | Construct validity of a modified bathroom scale that can measure balance in elderly people[END_REF]. Thus, an adapted prevention or rehabilitation program could be put in place, with progress followed over time [START_REF] Duchêne | Apport des technologies au suivi des personnes âgées fragiles[END_REF]. A screening tool that could detect elderlies with risk factors for falls could therefore be useful. Indeed, the early detection of gait impairment for estimating falls risk is the first step to reduce falling rates among older populations. This detection leads to the implementation of proper interventions that can engage behavioral changes, environmental modifications, and better health management.

Currently, detection and falls risk estimation is made through measurements of balance quality, routinely made as part of clinical evaluation of balance. The Berg Balance Scale [START_REF] Berg | Measuring balance in the elderly: validation of an instrument[END_REF], the Timed up and go test [START_REF] Podsiadlo | The timed "Up & Go": a test of basic functional mobility for frail elderly persons[END_REF], the Tinetti test [START_REF] Tinetti | Performance-oriented assessment of mobility problems in elderly patients[END_REF], are the three most currently used tests in the rehabilitation centre, partner of this research study. Laboratory-based measures of balance, e.g. with the Satel force plate, are made complementarily to the clinical evaluation. Physiotherapists explain that coupling these two types of evaluation is useful to confirm their diagnosis, completing their visual analysis with objective measures.

However, the major drawback of these measurements of balance is that of cost. Therefore, these evaluations prove inadequate to be implemented as part of a long-term evaluation program or a large-scale prevention protocol. Any evaluation tool needs to be easy to use (non-professional users), socially acceptable (community dwelling elderly) and relevant with respect to well-established clinical tests [START_REF] Duchêne | Apport des technologies au suivi des personnes âgées fragiles[END_REF].

A. Balance Quality Tester

Based on the observation of the organizational restrictions linked to the existing evaluations described above, the Balance Quality Tester (BQT) appears as a promising solution for early detection of falls risks. First, the cost would make it accessible: the BQT was developed as a low-cost balance assessment tool based on a commercial bathroom scale (estimated cost of around €50 per device) [10]. It looks like a bathroom scale, which measures weight, and is therefore an ordinary practical device, but it also measures balance like a force plate. The BQT calculates four parameters of balance, that are then scored (over 16) and weighted, thus creating an overall indicator of balance quality. A BQT empirical score of less than seven can detect fall risk in a community dwelling population. In terms of data collection and processing, after the weighing process is completed, the data are transferred from the BQT device to a local receiver (mobile phone, tablet or PC), which in turn sends the data to a remote server for storage. A prototype application initially targeting healthcare professionalsenables to visualize the score.

1) Previous work

Previous research from our colleagues have examined: i) the relationship between frailty indicators and balance assessment [START_REF] Chkeir | In-home physical frailty monitoring: relevance with respect to clinical tests[END_REF], ii) the technical validity of the BQT (see [10] for details), iii) the accuracy of calculation of balance from a clinical perspective (see [START_REF] Duchêne | Modified bathroom scale and balance assessment: a comparison with clinical tests[END_REF] for details), iv) the usability and acceptability of the BQT during a longitudinal pilot study [START_REF] Duchêne | Using a modified bathroom scale for long-term balance quality assessment: relevance, usability and acceptability[END_REF].

B. Utility: Perceived and Actual

The insights that needed to be examined at that stage were: what moreother than technical and clinical validityis needed for the BQT to succeed in being a useful tool for largescale prevention of falls? Like for other AAL products, in order for older adults to voluntarily adopt a technology, the benefits of use of a product/service must be made clear [START_REF] Alaoui | The urge for empirically-informed design of social oriented AAL applications -The example of 2 AAL projects[END_REF]. This perception of a device as being useful will ensure that it is adopted and actually used. It is only at this condition, i.e. that older adults at risk of falling use the BQT on a regular basis for long-term home-monitoring, that the BQT will play an important role as part of an adapted prevention or rehabilitation program. Therefore, the first level of Utilityof the device as perceived by usersimpacts the second level of Utilityto be considered at a global level of falls prevention for autonomy. Thus, where to start this virtuous circle?

1) Research questions

For this utility to be clearly perceived by the end-users, two issues empirically emerged from the needs analysis as being important for stakeholders: ease-of-use on a regular basis and trust in the validity of the data acquisition.

Thus, the main research questions which guided this study: 1) To what extent usability of the device and application can support the everyday ease-of-use? 2) How to ensure trust in the validity of the data acquisition?

II. MATERIAL AND METHODS

Based on these research questions, a usage study has been made, where usability and ease-of-use guided the co-design from a practical perspective, with trust in validity of data acquisition being the final objective to attain. Before presenting in detail the insights gained in the "Results" section, first, the related work, the approach and the first step of the design process, are presented.

A. Usability and ease-of-use: Related work

Recent research shows that improving the usability of falls assessment technologies will have a positive impact on healthcare, helping users identify subtle changes in gait and balance, improving the reliability of parameters and measures, as well as empowering the users [START_REF] Genaro | HCI Challenges in Human Movement Analysis: Quantitative Assessment of Gait and Balance[END_REF]. Based also on insights of self-care monitoring studies, where data visualization is a determining aspect, the research hypothesis to be examined was that usability of the BQT application for balance score visualization could play an important part in this perceived utility of achieving a proper balance follow-up.

B. Approach used: Living Lab approach

The approach to research and design that has been used is the Living Lab approach, which combines these 3 characteristics: Human-centered, Participatory and Iterative.

1) Human-centred design

For Bannon [START_REF] Bannon | Reimagining HCI: Toward a More Human-Centered Perspective[END_REF], Human-centred interaction design would be HCI "centered on the exploration of new forms of living in and through technologies that give primacy to human actors, their values and their activities". It takes as a starting point human (elderly) capabilities, with a focus on how to support, develop and extend people"s capabilities through the latest technological developments [START_REF] Bannon | Re-framing HCI: From human-computer interaction to human-centred interaction design[END_REF]. A radically reworked agenda is therefore proposed, for example, on the theme of Ambient Assisted Living. Instead of a technology-first or even medicalfirst approach, Bannon recommends to consider first the fundamental needs and concerns of the ones at the centre of the investigationsthe elderly peopleso that these AAL technologies could be, of course life-saving, but also actually add to elderly people"s dignity or empowerment.

In order to consider elderlies" needs, Ethnography has been used, both at elderlies" homes and in a rehab hospital, combining interviews (mainly informal) and participant observations. Indeed, Ethnography offers the opportunity to reveal needs or practices of users, which they may not themselves attend to, because they take them so much for granted that they do not think about them, or are too busy [START_REF] Randall | Fieldwork for Design: Theory and Practice April[END_REF]. This inability to articulate "needs" is even more true of dependent elderlies.

2) Participatory design

Participatory design (PD) is a cooperative design process, with a focus on enabling different stakeholders with different perspectives and competencies to cooperate. It comprises active user involvement and participation in the design of IT artefacts and systems in professional settings, where it is largely and increasingly used. Designers invite future users to participate in all phases of the design process [START_REF] Bratteteig | Unpacking the Notion of participation in Participatory Design[END_REF]. PD is generally united by an ethos of empowerment and "meaningful" involvement for stakeholders in the design of the systems they will use.

Participatory design has traditionally been useful in the design of technology applications or the co-realisation of a more holistic socio-technical bricolage of new and existing technologies and practices. Moving away from the traditional computer and "user" notion, e.g. with Ambient Assisted Living technologies [START_REF] Bannon | Reimagining HCI: Toward a More Human-Centered Perspective[END_REF], like connected objects or social robots [START_REF] Hing Ting | Designing Human-Robot Interaction for Dependent Elderlies: a Living Lab Approach[END_REF], there is indeed the need for participatory design.

3) Participationto what extent ?

Following the participatory approach adopted to design this specific new technology, the very role and participation of stakeholders in this research requires reflexive questioning. Indeed, the three professionals of the rehabilitation centre, involved in this research, would be considered in more traditional Ethnography-based needs analysis as informants. Adopting this PD approachwhose principle guided the fieldwork, but without any a priori planning about how this participation would actually be achievedthe three professionals are considered as participants, i.e actors who have a greater implication in our research than simply "informing" it. What actually emerged during the fieldwork and were achieved in a naturally-organized way [START_REF] Lynch | From naturally occurring data to naturally organized ordinary activities: comment on Speer[END_REF], are codesign sessions as part of the observations being done. Therefore, this in situ co-designing implies a degree of participation and a role in the design process in which the participants become / achieve being co-designers. It is therefore, in a voluntary attempt to reflexively examine what is at stake in "participation-in-action" that this research pushes PD a step further. The authors argue that it is necessary to find a way to consider the effective participation of the co-designers in collaboratively producing the design ideas, which are the "results" of this design-oriented research. This recognition of contribution in the participatory design process, as a further degree in participation and greater agency to the participants, takes the form, in this research, of co-authoring. One of the participant/co-designer is also a co-author of this paper and others that have been published from this research [START_REF] Hing Ting | Examining usage to ensure utility : Co-design of a tool for fall prevention[END_REF], [START_REF] Hing Ting | L"utilisabilité pour l"utilité : nouveau design d"un pèse personne connecté[END_REF]. The two other participants/co-designers are cited and receive special thanks in the Acknowledgment section. This reflexive discussion about participation, role and categorization being done, in order to pragmatically ensure clarity in the rest of paper, they will simply be referred to as the "professionals".

4) Living Lab approach to achieve "adequate design"

Therefore, combining the best practices of Human-centred, participatory and iterative design, the Living Lab approach, the authors argue, allows to achieve "adequate design". The most important principle is to adopt the participants" perspective and use the empirical insights gained through the different methods mobilized as part of the approach, to relevantly inform design.

C. Empirical insights constantly guiding the design process

The main insight that emerged from the analysis of practices and understanding of needs was the necessity to completely redesign the BQT. This redesign appeared as essential, in order for the BQT to fit the requirements concerning ease-of-use and validity of data acquisition. Informed by these empirical insights, the redesigning work that has been done relates to: hardware design, interface design, interaction design, and most of all to protocol design, in terms of standardizing the protocol. of stepping-on the BQT. (cf. presentation of the design recommendations in the "Results" section infra.) So as to guarantee the appropriateness of the design ideas, these have been evaluated, and iteratively improved with senior users" participation. In fact, as shown in Fig 1, throughout the design process -from the needs analysis to the validation of the new design proposals -the participants, part of the community Amis du Living Lab, whether seniors or health professionals, have been actively involved in the different tasks. Starting with the needs analysis, observations and in-depth interviews were made with: elderlies and their informal caregivers, as well as with health professionals (GPs, geriatricians, pharmacists, physiotherapists), including the ones from the rehab hospital.

III. RESULTS

As part of the first step of analysis of practices, ethnographic observations of clinical tests and force-plate assessments were made at the rehabilitation centre. The objective was to understand current professional practices [START_REF] Kuutti | The turn to practice in HCI: towards a research agenda[END_REF] and the use of existing tools: parameters of the force-plate, patient data that are required, how these data allow to recontextualize the assessment made, especially for follow-up (e.g. patient wearing orthopedic shoes). This understanding of practices, as well as the insights about how diagnostic explanation is efficiently achieved between health professional and patient, have inspired the important values that needed to be implemented in the interface design of the BQT application.

Important design ideas have emerged, focusing on 4 aspects: The position of the feetglued knees, "duck" feetis not very pleasant. However, looking at a fixed point in front in front of oneself, indeed, helps to remain more stable. The (till then) absence of any markings on the physical device of the BQT emerged from the collaborative sessions with the three professionals as being a failing, that required improvement. Also, left free to step on the BQT (without any instructions), all of the three professionals started by looking at the display, like a traditional bathroom scale, then straightened up to look up right in front of them, i.e. a position in which one has the best balance. When asked about that, which they did naturally without realizing it, one of them answered "(Laughing) we know the techniques". This "technique" is the best balance position according to the rules of proprioception.

2) Design idea: Standardizing position with stickers

Following the understanding of this "technique", that can be found in the force plate protocol also, this good practice has been implemented in the design of the BQT (Fig 2 ,right). The design needed to find this compromise between, on the one hand, the ease-of-use of the BQT (ordinary bathroom scale) and, on the other hand, the need to standardize both the feet position and the standing position, in order to guarantee the rigor of the measures for an efficient follow-up. To ensure this necessary standardization, the use of simple stickers have been proposed by the co-designers: the first time, the stickers are positioned with a health professional, considering patients" height and size as well as comfort perception. During everyday use at home by the elder person, the stickers guarantee the standardization of the feet position.

B. Interaction design 1) Method: observation of sense-making in interaction

Like for stepping on the BQT, the health professionals were voluntarily left to make sense of the results by themselves, as if they were any user, without information about the indicators and how they are measured or about the designers/developers" intentions and previous research.

In trying to make sense of how the BQT worked and how the indicators figured in generating a score, the professionals tried it several times and compared the different scores that were generated. One of the main questionings was about the "time" indicator. Seeing that each one of them had different scores, they were wondering: Is time calculated when the "0.0" display appears (see Fig. 2, right), which would then be a relevant signal for the user, or can the user step on anytime? These difficulties in understanding how the data were measured, and all the sense-making discussions, led to this need identification: the necessity to have an audible sound to indicate the start signal. However, they explain thatin their professional practicethe indicator "time" does not appear to be relevant, except for certain pathologies, e.g. Parkinson, but in that case, a "classical" visual analysis would probably be more effective. However, the professionals" opinion was that, for a domestic use, a start signal could be useful. Indeed, this utility was confirmed by the user tests" results.

2) Design idea: Adding sound signal

Therefore, the interaction design included an audible signal (volume that can be customized) to indicate the time for stepping on and stepping down, each with a distinctive highpitched "beep", as well as an accompanying sound (rather neutral watch sound) for the duration of the test, as shown below.

The sound modality was successfully evaluated by seniors during the user tests: 3 out of 5 users rated the sound utility on 5/5; 1 user: 4/5; 1 user: 2/5). Rather than a neutral accompanying sound, during the second iteration, this issue was discussed with the professionals, and the proposal was that the BQT could play a different music for each weighing session. The objective is that the music"s role, of course, is to "accompany" the test (like the watch sound, which had been positively evaluated during the user tests) but also to both distract and disturb the user. Indeed, on the one hand, the objective of "distraction" is that the patient has a better balance than if she were focused on thinking about her balance. On the other hand, older patients sometimes have difficulty speaking and walking at the same time, while in a real situation of functional activities, they often move around doing other things. The objective is to bring the test as close as possible to an ordinary everyday situation, in which falls occur.

1) Method: observation of sense-making in interaction

Another main insight is that the interface with the 4 indicators (Figure 4, left) was very difficult to understand and did not make any sense to the professionals: "It doesn't speak to me" or "the way it's represented, it doesn't remind me of anything." This representation of information made even less sense to senior users. One important information, the professionals explained, regardless of the user, is the centre of gravity: "What would be significant from the current square is for the persons to know where their centre of gravity is. Imagine, you have the surface there, and he knows where his center of gravity is. For any user, us, patients, even a doctor. This is your square, you have your lifting polygon indicated, and you see that your center of gravity moves further to the top right, further forward, further back. You already know that there is a position in relation to this centre of gravity that can be disturbed. And that's super significant for everyone, I think."

Indeed, the ethnographic observations of the tests conducted by the professionals with two of the rehab centre"s patients, clearly show that patients easily understand the diagnostic when explanations are combined to the visualization of the forceplate data. The main understanding of needs is the necessity for clarity and understandability of data visualization.

It appeared that representing the "centre of gravity" data with the BQT would allow rehab clinicians to know precisely on which type of rehabilitation exercise to work on.

2) Design idea: Clear and understandable visualization

The interface was considerably improved to cater for the clarity of the visual representation of information that need to be shared with patients, so as to explain the assessment to them (cf. Fig 4, Middle and right picture). The first criteria to be catered for, linked to the research questions and objective of usability for utility, is the factor of accessibility, also called Universal Design or Design for All factor [START_REF] Iwarsson | Accessibility, usability and universal design positioning and definition of concepts describing person-environment relationships[END_REF]. Universal Accessibility is a HCI concept whose main objective is to produce systems that can be used by everyone, regardless of their physical or cognitive abilities [START_REF] Abascal | Moving towards inclusive design guidelines for socially and ethically aware hci[END_REF]. Accessible software is, therefore, a software that all people (people with disabilities, elderly people, people in special environments, etc.) can perceive, understand, navigate and interact with. The distinct concepts of software accessibility and usability are therefore related [START_REF] Petrie | The relationship between accessibility and usability of websites[END_REF] and, according to the principles of Universal Design, it is more effective to address them together during the inclusive design process.

Accessibility emerged as a relevant factor to be addressed linked to the Usability research question because two distinct categories of end-users emerged out of this study: professional users and elder users. Elder users at risk of falling are those users whose age also implies reading, hearing and sometimes cognitive impairments. The idea was to make the two main informationweight and gait scoreeasily accessible to them, in terms of understandability and readability. Presented in a minimalistic way, the weight is simply indicated in terms of kilograms, and the gait score in terms of "balance". These information are visible at a glance at strategic placescentre top and downin a size big enough and sufficient contrast (black on white background, bold). It was also suggested that in some cases, to encourage patients" efforts, like undergoing rehabilitation in order to gain back some functional capacities or following a diet to lose or gain weight, it could be interesting to include the progression, in the form of arrows (Fig. 4, right). However, in the case of an ordinary everyday follow-up, this function would be avoided, in order to avoid discouragement effect.

Then, coherent with this objective of understandability for patients and sufficient detail for professional use, the 4 important design ideas are:

1.

The area is indicated by a pelota -that would allow the patient to see how far he or she is "pitching" 2.

The colour code -green, yellow, red -depending on the alert level: Green -score of 10-16 ; Yellow -score of 7-9 ; Red -score of 1-7

3.

The size of the footindicates on which side and the degree to which the body is leaning 4.

The details of the analysis with the precise data for each of the 4 indicators will be immediately accessible on the BQT application.

On the current version of the application, the detailed information, as regards the 4 indicators, is found in a separate folder, not immediately accessible to the user. Till then, the use case scenario was a domestic-only use. This research revealed that a professional use was considered usefulby health professionals themselves (a geriatrician, a general practitioner, physiotherapists from 2 centres who participated in the needs analysis)as long as the detailed information would be available. Coherent with this new professional use scenario, the need to have more detailed data took the form of a general level for patients and a more detailed level for clinicians, with a flowchart organization to access to details, only if needed.

D. Protocol design 1) Issue at stake : validity of data acquisition

Linked to usability and ease-of-use of the BQT on a daily basis, the issue of validity in acquiring the data appeared as a sine qua non aspect, both for health professionals and senior users. The previous stepping-on protocol, as described in [START_REF] Duchêne | Using a modified bathroom scale for long-term balance quality assessment: relevance, usability and acceptability[END_REF], is presented left. The new iteratively and collaboratively designed protocolco-designed with the health professionals, evaluated by elder users, and validated by the health professionalsis presented right.

Previous protocol

New protocol (home scenario)

(1) Stand in front of the scale, thus triggering the infrared detector;

(2) Wait for the scale to display "0.0";

(3) Step onto the scale;

(4) Wait for the scale to display the body weight;

(5) Step off the scale.

2) Method: Achieving previous stepping-on protocol

Although no specific position of the feet was required in the former protocol, the relatively small size of the scale (320 x 295 mm) did not allow for much variation in position. Likewise, no precise position was specified for the head, after preliminary trials had shown that everybody looked down at the display, waiting for the weight value to be displayed [START_REF] Duchêne | Using a modified bathroom scale for long-term balance quality assessment: relevance, usability and acceptability[END_REF]. Like for the other design requirements that emerged, the professionals were left to step on freely on the BQT, so that their in situ sense-making and questions that emerged, could inform the values that they attach to such a procedure. As described already, they all looked up, after stepping on, explaining the "technique" for optimal balance, which appeared naturally to them. Also, before looking up, they had all looked at the BQT, to check the display, and mind the height, cautious not to fall. The new designed protocol was inspired by their action and its underlying principles of proprioception.

3) Co-designing the new protocol

Therefore, based on sense-making and "best practices" in balance assessment (force-plate practices as well as the rules of proprioception), it appeared that a more rigorous standardization would ensure: technical validity of measurements, and linked to that, trust in the validity of the data being acquired. First, an efficient follow-up (no false alerts) depends on that condition. Second, in order for the BQT to be a useful tool as part of an adapted prevention or rehabilitation program, it is required that older adults at risk of falling actually use the BQT on a regular basis. Thus, the first issue is the research question and design objective of usability: that the deviceas well as the protocol, and the interfaceis easy to use on a daily basis. Linked to it, the second issue is whether elder users perceive the BQT as an efficient tool, which is capturing exact measures. As discussed supra (the stickers contribute to fixing the feet position), standardization is key to this trust.

So, based on this understanding of what is considered as important aspects to be measured from a physiotherapy perspectiveboth assessment and the rehab that followsa new protocol was designed with two variants: one for the home environment, and one for the professional context (new use scenario that emerged from this study). The Fig. 4 above presents the home scenario. The test is performed once, one looking in front of him, at a fixed point at eye level, which allows the best balance position. This newly co-designed protocol has been evaluated very positively during user tests: senior participants find the protocol easy to follow and nonconstraining.

For the professional context, all the professionals explained that, for a first screening, a balance score with the BQT would be useful. However, it would be insufficient to gather the same data as with tests traditionally used, like the Tinetti tests or evaluations with the force plate where, gait is also evaluated with the closed eyes position. Therefore, as a compromise, it was suggested that the professional use protocol would include the tests being done twice, once eyes open and a second time with the eyes closed. Unlike the home scenario, where the risk of falling (while, most probably being alone in one"s bathroom) would override the benefit of data acquisition, in the professional context, the patient would do the test with a professional, secured with a walker or fixed support.

IV. DISCUSSION

Coherent with the participatory and iterative approach, the "results" presented in the section above, that is, the design ideas that emerged from this design-oriented research, have been tested and validated with the relevant stakeholders. This final section discusses the insights and the professional participants" feedback about the approach.

1) User tests

At middle stage of the design process, senior participants (5 in all -following Nielsen"s recommendations [START_REF] Nielsen | Usability engineering[END_REF]) have evaluated the design ideas during the user tests of the intermediary design. The user tests comprised predefined tasks and a questionnaire-based interview. The different design aspects have been evaluated: hardware, interface, interaction, stepping-on protocol. Also, feedback has been sought concerning the two use scenarios: home and professional. In order to gather objectified data, a Lickert scale allowed users to give a formal score of 1 to 5. This score was complemented with open feedback, comments and suggestions that users were invited to give. The insights from the tests, in terms of user satisfaction, are generally very positive.

Due to space limitations, only the results linked to main research questions are succinctly presented here. All 5 participants find the new test protocol simple: 4 users give a rating of 5/5; 1 rates 4/5. They also find that the follow-up of their balance quality would be useful: 3 users rate 5/5; 1 user rates 4/5; 1 user rates 2/5. All the users" feedback (both positive and critical) allowed to improve the design during a second iteration.

2) Validation of design ideas

After these iterative improvements, the new design proposals were submitted to the three professionals for validation of the design ideas that they had proposed during the needs analysis phase.

First, the Home scenario protocol was collectively discussed, including the latency time (rate of ascent) which was considered relevant. In this respect, the start and end beeps were considered as good indicators. Also, the idea of music was seen as relevant, and the idea of changing music with each weighing session emerged collectively.

When the interviewer explained mock-up of the pelota and the colour code, their reactions were "Oh yes, this is great", "this is evident right now", "like this, it speaks very very well". Then, the size of the feet was immediately understood: "there, you have more support on the right, is that it? That's great!", "like this, it is very understandable". Concerning the display of the percentage of tilting, the need to have two levelsone general for the patients and one detailed for the professionals -was confirmed. Also, the new graph to access to the details, so that the information are relevantly available for patients" follow-up, the professionals confirm its usefulness to them.

Most importantly, regarding standardizationwhich was absent from the initial protocol and which had raised many questions on their partthey were delighted to discover the stickers, whose idea they had put forward. Regarding the integration of the criteria "eyes open, eyes closed" in the professional use scenario, the professionals agree that the presence of a professional will cater for two important aspects: first secure the test, second explain the protocol to the patient clearly, without the need for a specific display on the BQT itself. Therefore the same tool with the same interface, with a simple variant in the protocol (making the test a second time with eyes closed) can prove useful in two complementary use scenarios.

The discussion also confirmed the BQT's interest in the motivational aspects of the elderly personin a more motivating and fun way that simply "weighing oneself" -and the efficiency of follow-up by the doctor, who would make visits at the patients" home (as is often the case for elderly people). In case the data are not tele-transmitted to the doctor and remain on a tablet or smartphone, it would be interesting for the doctor to have a look during the visit. Also, in the event that these balance data remain transparent to the elderly user himself (no tablet or smartphone), it would be interesting for professional or family caregivers to receive alerts, for example by email.

In conclusion to this participatory validation session of the design ideas, the very process of participatory and collaborative design was discussed. The professionals appreciate the general new design: "it's better", "it's good, it becomes intuitive, more relevant", "more standardized"; as well as the participatory approach in which they have been actively involved, saying: "I'm proud".

V. CONCLUSION AND PERSPECTIVES

This paper has presented the collaborative redesign of the BQT, so as to address two essential issues. In order that the BQT can actually be a useful prevention tool: first, usability and ease-of-use on a regular basis and second, trust in the validity of the data acquisition. Several avenues for future work are emerging from the knowledge generated in this study and of the next step in the development of the BQT application. This future work will focus, on the one hand, as a follow-up to this study, on prospective uses, and on the other hand, on research aimed at improving the algorithm for calculating the measurement, in order to guarantee optimal performance of the BQT. Most of all, apart from the observation of insufficient identification and management of frailty among the elderly population, this research revealed the lack of common ground for inter-professional collaboration in the follow-up of frail patients, especially regarding physical frailty. E.g., when a general practitioner prescribes physiotherapy sessions for a geriatric patient, his prescription is a (vague) comment addressed to the primary care physiotherapist. All professionals involved in this study agree with the hypothesis that a formal score generated by the BQT, could become a shared norm among health professionals and thus, has the potential to ensure a much more efficient coordination between health professionals.

Figure 1 :

 1 Figure 1: Iterative design process

  1. Hardware design 2. Interaction design 3. Interface design 4. Protocol design A. Hardware design 1) Method: Analysis of practices The observation from the analysis of practices is that, contrary to the initial design and protocol of the BQT (see Fig 4, left), the force-plate strongly constrains the body position. The feet are positioned by the wedges inserted in the forceplate (Fig 2, picture left), and the patient is asked to look at the red line projected by the video projector in front at eye level.

Figure 2 .

 2 Figure 2. Left: highly standardized position of force-plate Right: standardization at home with BQT

Figure 3 :

 3 Figure 3: Sound modality as start and end signals

Figure 4 .

 4 Figure 4. Previous interface (left), new interface (middle, right)

1 . 4 .

 14 The user stands in front of the BQT, well in front of the foot marks 2. The BQT instructs the user to step on, simultaneously by both display "0.0" and beep tone 3. The user climbs onto the BQT looking where he puts his feet, positions his feet on the marks, then fixes the label in front of him at eye level. The BQT measures weight and balance, indicating -visually and acoustically -that the measurement is in progress 5. The BQT indicates -by a distinctive audible signal (or ideally, the weight announcement), and the weight display (numbers) -to the user that he can step down 6. The user descends from the BQT 7. The weight display is replaced by the balance score display Figure 4: Previous protocol (left); Newly co-designed protocol (right)

ACKNOWLEDGMENT

The authors warmly thank the members of the Les Amis du Living Lab community who participated in the needs analysis and user tests of the BQT, whose enthusiasm in participating in the Living Lab"s research is a constant source of inspiration. The authors also thank their colleagues from Troyes University of Technology, and most of all, their colleagues from CRRF COS Pasteur: Anaïs Corneloup and Adeline Delancret, who were actively involved as participants and co-designers in this research, as well as Dr Quitterie De Roll and Mr Philippe Voisin for their constant support.


Bianca C Maniglia
email: biancamaniglia@usp.br

Dâmaris C Lima

Manoel Da

Matta Júnior

Anthony Oge

Patricia Le-Bail

Pedro E D Augusto

Alain Le-Bail
email: alain.lebail@oniris-nantes.fr

Dâmaris C Lima D , Manoel Da Matta Júnior

Dry heating treatment: A potential tool to improve the wheat starch properties for 3D food printing application

Keywords: modified starch, 3D food printing, additive manufacturing, personalized food, food texture

de niveau recherche, publiés ou non, émanant des établissements d'enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.

1.

Introduction

The three-dimensional (3D) printing is an emerging technology to create personalized objects from digital models through the successive layer-by-layer deposition of materials such as plastic, metal, ceramics, or even living cells [START_REF] Bhatia | 3D printing and bio-based materials in global health[END_REF]. Currently, 3D printing technology has been used for food printing, defining new borders for food processing and being able to deliver a product that suits special consumer's criteria of taste, texture, cost, convenience and nutrition. For instance, 3D food printing can create unique novel textured foods, healthy foods, and smooth and easy-to-swallow foods for elderly people [START_REF] Dankar | 3D printing technology: The new era for food customization and elaboration[END_REF].

Extrusion is the most common 3D printing method for food applications, being relatively easy to develop and presenting different alternatives of "inks" [START_REF] Guvendiren | Designing biomaterials for 3D printing[END_REF][START_REF] Tan | Extrusion-based 3D food printing -Materials and machines[END_REF]. This process depends heavily on the physical properties of the material to be processed, which is one of the most important research topics about 3D printing [START_REF] Liu | Properties of 3D printed dough and optimization of printing parameters[END_REF]. Therefore, it is important to study physicochemical and rheological aspects of possible "inks" used to printin other words, their printability, i.e. their ability to make a 3D-object by layer-by-layer deposition, to obtain a defined shape and to support its structure once printed [START_REF] Godoi | 3d printing technologies applied for food design: Status and prospects[END_REF].

In this context, it is important to study the ability of starch sources to be used as "inks". As one of the most important carbohydrates in human diets and one of the most available in nature, starch is widely used as thickening and gelling agents in many food formulations [START_REF] Bemiller | Pasting, paste, and gel properties of starch-hydrocolloid combinations[END_REF]. The gelatinized starch paste shows a shear-thinning behavior and instant responses to the applied shear strains, being easily extruded from the fine nozzle [START_REF] Evans | Rheology of gelatinised starch suspensions[END_REF][START_REF] Tohic | Effect of 3D printing on the structure and textural properties of processed cheese[END_REF]. Finally, the starch hydrogel can present good printability, depending on the sources and modification processes.

In fact, some studies have already explored starchy products as "inks" for 3D printing, like potato starch [START_REF] Yang | Investigation on lemon juice gel as food material for 3D printing and optimization of printing parameters[END_REF], mashed potatoes [START_REF] Liu | Creation of internal structure of mashed potato construct by 3D printing and its textural properties[END_REF], potato puree [START_REF] Dankar | 3D printing technology: The new era for food customization and elaboration[END_REF], wheat flour (Liu, Liang, Saeed, Lan, & Qin, 2019a), rice flour [START_REF] Anukiruthika | 3D printing of egg yolk and white with rice flour blends[END_REF]. Moreover, our group has evaluated some alternatives to modify starches and improve the 3D printability, such as the ozone and dry heating treatment of cassava starch [START_REF] Maniglia | Hydrogels based on ozonated cassava starch: Effect of ozone processing and gelatinization conditions on enhancing 3D-printing applications[END_REF] and Maniglia et al. (2020)). However, the approach of starch modification for 3D printing application is still under-explored in the literature, considering different sources and modification technologies.

Wheat starch is the third most-produced starch in the world, being a coproduct in the vital gluten industry [START_REF] Shevkani | Wheat starch production, structure, functionality and applications-a review[END_REF]. It has an important role in many food products [START_REF] Agama-Acevedo | Cereal Starch Production for Food Applications[END_REF][START_REF] Ubeyitogullari | Formation of nanoporous aerogels from wheat starch[END_REF], being frequently used in gluten-free baked products [START_REF] Houben | Possibilities to increase the quality in gluten-free bread production: an overview[END_REF]. However, native wheat starch produces weak-bodied, cohesive, rubbery pastes when heated and undesirable gels when the pastes are cooled [START_REF] Punia | Dynamic, shear and pasting behaviour of native and octenyl succinic anhydride (OSA) modified wheat starch and their utilization in preparation of edible films[END_REF].

In this way, modification processes can be used to improve wheat starch properties and applicability. Among different possibilities, dry heat treatment (DHT) is a simple physical method, considered a "green" technology (chemical-free, simple, safe and pollution-free) to alter starch structure and functionality [START_REF] Chandanasree | Effect of hydrocolloids and dry heat modification on physicochemical, thermal, pasting and morphological characteristics of cassava (Manihot esculenta) starch[END_REF][START_REF] Gou | Effects of repeated and continuous dry heat treatments on properties of sweet potato starch[END_REF][START_REF] Liu | Effects of dry heat treatment on the structure and physicochemical properties of waxy potato starch[END_REF][START_REF] Maniglia | Starch modification through environmentally friendly alternatives: a review[END_REF][START_REF] Oh | Effect of dry heat treatment on physical property and in vitro starch digestibility of high amylose rice starch[END_REF]. Moreover, Maniglia et al. (2020) described that cassava starch DHT resulted in stronger gels with better 3D printability than the native starch. It is worth mention each starch source reacts differently to each modification technology, justifying the present work.

Wheat starch modification by DHT has scarcely been reported in the literature, although some studies are available with wheat flour [START_REF] Nakamura | Increased volume of Kasutera cake (Japanese sponge cake) by dry heating of wheat flour[END_REF][START_REF] Ozawa | Investigation of Dry-Heated Hard and Soft Wheat Flour[END_REF][START_REF] Seguchi | Oil binding ability of chlorinated and heated wheat starch granules and their use in breadmaking and pancake baking[END_REF] -where the observed changes are mainly associated to the proteins.

Based on this context, this study aimed to use the DHT as a tool to improve the 3D printability of "inks" based on wheat starch hydrogels. To achieve it, firstly the effect of DHT was studied in relation to the wheat starch structure and properties. Then, the potential for 3D printing application was evaluated. The innovation of this study involves developing functional ingredients to be used as gelling and thickening agents to bring better printability for food products, also expanding the application and potential of wheat starch.

Material and methods

Material and dry heating treatment (DHT)

Native wheat starch (moisture content: 10.1 g/100 g) was purchased from Merck KGaA (Germany). All the chemicals were of analytical grade.

The dry heating treatment (DHT) was based on the work of [START_REF] Chandanasree | Effect of hydrocolloids and dry heat modification on physicochemical, thermal, pasting and morphological characteristics of cassava (Manihot esculenta) starch[END_REF]. Wheat starch (50 g) was distributed evenly in a thin layer (~ 1 mm) and packaged on aluminum foil, as an envelope (30 x 20 cm), which was closed with a high-temperature tape to avoid moisture loss. The envelope was then placed in a hot-air convective oven (XU032, Frances Etuves, Chelles, France) with air at 130 °C and 1 ± 0.1 m. s -1 for 2 and 4 h (named DHT_2h and DHT_4h, respectively).

The temperature was recorded using a datalogger with six K-type thermocouples (AOIP Datalog, Ris-Orangis, France) of 0.5 mm diameter for measuring the temperature in different locations within the sample (Supplementary Fig. S1A). The treatment time was counted from the moment where all parts of the envelope reached the processing temperature (130 °C) -the heat-up time was 20 min (Supplementary Fig. S1B). After processing, the starch was cooled, sieved (250 μm), and stored in glass containers for further analysis.

Granule characterization: morphology and size distribution

The starch granules morphology (control and modified) was observed using a light microscope (model L1000, Bioval, Curitiba, Brazil; with a 20 W halogen lamp, the magnification of 40 x) and a digital camera of 5.1 megapixels (MT9P001, Aptina, Colorado, USA). The starch granules were dispersed in distilled water (1:1, v/v). Then, they were placed on a glass slide, covered by a glass coverslip, and directly evaluated. A polarized light filter coupled to the system was used to observe the Maltese crosses.

The granule size distribution was determined using the dynamic light scattering (DLS)

of Malvern Master Size (3000, Malvern Instruments Ltd, Worcestershire, UK). The samples were dispersed in the air. The analyse was carried out 4 times for each sample. From the obtained data, the volume-based mean (D[4,3]) and the area-based mean (D[3,2]) diameters were calculated. The diameters d(0.1), d(0.5), and d(0.9) were also obtained, describing the dimension that 10 %, 50 %, and 90 % of the granules were smaller, respectively.

Molecular characterization: pH, functional groups, molecular size distribution

pH values were measured in the starch suspension of 10.7% (w/w) in distilled water, under constant stirring at room temperature (25 °C), using a potentiometer (model TEC-5 mode, Tecnal, Piracicaba, Brazil).

The carboxyl and carbonyl contents were determined by the method of [START_REF] Smith | Production and use of hypochlorite oxidized starches[END_REF] and [START_REF] Chattopadhyay | Optimisation of conditions of synthesis of oxidised starch from corn and amaranth for use in film-forming applications[END_REF], respectively, with some modifications, as described by Maniglia et al. (2020). Their content was expressed as the number of carboxyl (COOH / 100 GU) or carbonyl (CO/100 GU) groups in relation to 100 units of glucose. The analyses were done in triplicate.

The changes in the functional groups were also evaluated using the infrared spectroscopy technique. Fourier transform infrared (FTIR) spectroscopy was conducted using a Spectrum 100™ FTIR instrument (Perkin-Elmer, Shelton, USA) equipped with an attenuated total reflection (ATR) accessory. All the spectra were the average of 16 scans from 4000 cm -1 to 650 cm -1 and were acquired at a resolution of 4 cm -1 .

The molecular size distribution profile (control, DHT_2h, and DHT_4h) was determined using a gel permeation chromatography (GPC) system, according to [START_REF] Song | Characterization of barley starches of waxy, normal, and high amylose varieties[END_REF], with some modifications described by [START_REF] Maniglia | Hydrogels based on ozonated cassava starch: Effect of ozone processing and gelatinization conditions on enhancing 3D-printing applications[END_REF].

Thermal and crystalline properties of starch

The thermal properties during starch gelatinization were determined using a Multi-Cell Differential Scanning Calorimeter (MC-DSC) -(TA Instruments, Lindon, USA). The starch samples were weighed and hydrated directly into the ampoules (10 g dry starch / 100 g suspension). An ampoule with deionized water was used as a reference and three runs for each sample were analysed. The MC-DSC heating program consisted of going from 20 to 120 °C at a rate of 2 °C/min. The onset temperature (To), the peak temperature (Tp), the conclusion temperature (Tc), and the enthalpy (ΔH) associated with the starch gelatinization interval were calculated with the aid of the Universal Analyzer software (TA Instruments, New Castle, USA).

The crystallinity of starch samples was determined by X-ray diffraction (XRD).

Before the XRD analysis, the starch samples were maintained in a desiccator containing a saturated BaCl2 solution (25 °C, aw = 0.900) for 7 days to ensure constant water activity. The sample was examined by X-ray diffraction equipment Inel X-ray equipment (Inel, Centre-Val de Loire, France) operated at 40 kV and 30 mA. The CuKα radiation (0.15405 nm) was selected using a quartz monochromator. Diffracted intensities were monitored (2θ) by a sensitive detector (CPS 120, Inel, Centre-Val de Loire, France). The resulting diffraction diagrams were normalized between 3 and 30 ° (2θ). The curves obtained were smoothed using the Origin software, version 2018 (Microcal Inc., Northampton, USA). The relative crystallinity was calculated as the ratio of upper diffraction peak area to the total diffraction area, following the method described by [START_REF] Nara | Studies on the Relationship Between Water-satured State and Crystallinity by the Diffraction Method for Moistened Potato Starch[END_REF] and considering 2θ ranging from 3 to 30 °.

Starch pasting behaviour and hydrogel properties (rheology and firmness)

Starch pasting properties were determined using a Rapid Visco Analyzer (RVA4, Newport Scientific Pvt. Ltd., Warriewood, Australia) with Thermocline for Windows software, version 3.0. The RVA analysis consisted of heating, retention, and cooling cycle under constant shear (160 rpm). Following the standard conditions for starch characterization, starch suspensions of 10.7 g starch / 100 g (correct to 14 % moisture basis) were prepared for the RVA analyses. The procedure used was: keep at 50 o C for 1 min, then heat up to 95 o C ( 6o C.min -1 and maintained 5 min), followed by cooling to 50 o C (6 o C.min -1 ), and finally, maintained at 50 o C for 2 min.

Different parameters are obtained to describe the pasting behaviour: peak apparent viscosity -PAV (the maximum paste apparent viscosity achieved in the heating stage), through apparent viscosity -TAV (minimum paste apparent viscosity achieved after holding at the maximum temperature), final apparent viscosity -FAV (the apparent viscosity at end of run), breakdown -BD (difference between PAV and TAV), setback -SB (the difference between FAV and PAV), and pasting temperature -PT (the temperature at which starch granules begin to swell and gelatinize due to water uptake). For a better interpretation of these parameters, the relative breakdown (RBD) and relative setback (RSB) were also calculated, following the study of [START_REF] Castanha | Potato starch modification using the ozone technology[END_REF]. The RBD (calculated as the ratio between the BD and PAV values) can be associated with the facility of starch granules to disrupt, while the RSB (calculated as the ratio between the SB and TAV values) can be associated to the retrogradation tendency.

Hydrogels were prepared by dispersing starch in distilled water (10.7 g dry starch/ 100 g, being the starch mass corrected to 14 % moisture basis), and then heating it at 85 ± 2 °C in glass containers in a water bath for 20 min. Then, the pastes were placed in plastic cups (40 mm diameter × 20 mm height) and stored for 24 h in the refrigerator (5 ± 2 °C) to gelling.

The cups were kept in a desiccator with water at the bottom to ensure uniform moisture. The obtained hydrogels were evaluated in relation to their viscoelasticity and firmness behaviours.

The viscoelastic properties were analysed by oscillatory stress sweep using a HAAKE MARS rheometer (Vane FL40, ThermoFisher, Karlsruhe, Germany). The hydrogels were loaded between the stainless steel parallel plates geometry (with a diameter of 25 mm and a gap of 1 mm), trimmed, and their edge was covered with silicon oil to prevent water vaporization. The stress sweep measurements were carried out at 22 o C with a logarithmically increasing shear stress at a frequency of 0.1 Hz (initial stress 0.001 Pa). This analysis was conducted in triplicate.

The hydrogel firmness was determined by a puncture assay using a texture analyzer TA TX Plus (Stable Micro Systems Ltd., Surrey, UK) with a load cell of 50 kgf (490.3 N).

The samples were removed from the refrigerator and analysed immediately to ensure a constant temperature. The samples were penetrated until a distance of 4 mm using a cylindrical probe (P/0.5R, 0.5 in of diameter) at 1 mm•s -1 . The equipment measured the force as a function of penetration depth. Gel firmness was evaluated by the energy required to penetrate the material (calculated by the area below the curve force versus distance of penetration). This analysis was conducted in triplicate.

Syneresis measurement

Syneresis was determined according to the method of [START_REF] Yeh | Some Characteristics of Hydroxypropylated and Crosslinked Rice Starches[END_REF]. Briefly, starch suspensions (5 % w/w) were gelatinized at 85 °C for 20 min in a temperaturecontrolled water bath followed by cooling to room temperature. The pastes were then stored for 24 h at 4 °C. Syneresis was measured gravimetrically as the amount of water (g water/ 100

g gel) released after centrifugation at 1500 g for 15 min. Triplicate of the results were read and the mean reported.

3D printing process

The "inks" (starch hydrogels) were prepared identically as described on the last section. After heating, the hydrogels were transferred for the printer syringes (60 mL), cooled to room temperature to form a weak gel-like structure, and stored in the refrigerator (5 ± 2 °C)

for 24 h before the printing.

The printing process was carried out in a 3D printer (Stampante 3DRAG V1.2, Futura Elettronica, Gallarate, Italy) presented in Fig. 1. The syringes with the hydrogels were removed from the refrigerator and immediately positioned in the 3D printer. A nozzle with diameter of 0.8 mm and height of 18 mm was coupled in the syringes. The 3D printing conditions were: nozzle movement of 5 mm/s and an extrusion rate of 4.5 mg/s at 20 o C.

Three physical models (heart, star, and cylinder shapes) were created using the Repetier Host V2.0.1 and Slic3r software (Hot-World GmbH & Co. KG, Willich, Germany).

The dimensions of the cylinder shape were 2 cm x 4 cm (diameter × height), for the star shape were 2.5 cm × 2.5 cm × 2 mm (Length × Width × Height), and for the heart shape were 5 cm × 6 cm × 2 mm (Length × Width × Height). 5 samples were printed for each hydrogel and shape. All the printing experiments were carried out at room temperature. After printing, the samples were photographed.

The reproducibility of the 3D printed samples was evaluated considering the weigh and the dimensions of the sample printed. Each printed cylinder was weighed in analytical balance (AZ214, Sartorius, Göttingen, Germany) and their dimensions (height and diameter)

were measured in five different positions using a digital paquimeter (CD-6 CSX-B model, Mitutoyo, Roissy-en-France, France).

Printed samples in cylinder shape were conditioned in a refrigerator (at 5 ± 2 °C) for 24 h, inside of a desiccator with water to avoid dehydration. Then, these printed samples were used for texture analysis.

Texture profile of the printed hydrogels

A texture analyser TA-XT+ (Stable Microsystems, Surrey, UK) was used to assess the printed cylinders. These analyses were conducted immediately in the samples removed from the refrigerator in triplicates for each sample.

The texture profile analysis (TPA) measurement consisted of two compressiondecompression cycles separated by a time interval of 10 s, at a rate of 1 mm/s, using a cylindric probe (25 mm diameter, Code P/25, Stable Micro System Ltd., Surrey, UK). The probe compressed the sample to 25 % (6.25 mm) of the initial height (25 mm) before decompression using a 50 kgf (490.3 N) load cell.

All the textural parameters were measured and calculated by the instrument software from the resulting force-deformation curves, including hardness, adhesiveness, cohesiveness, springiness, gumminess, and chewiness.

Experimental design and Statistical analysis

A completely randomized design was conducted. All processes and analyses were carried out at least in triplicate. To evaluate differences, analysis of variance (ANOVA) and Tukey's test at a 5 % significance level were accomplished by using the software Statistic 13 (StatSoft, USA).

Results and Discussion

Starch granule: size distribution and morphology

Fig. 2 shows the granule size distribution (A) and specific diameters (B) for the control and modified wheat starch. The samples displayed a unimodal size distribution and DHT resulted in larger granules sizes (Fig. 2A), being this effect consistent with the duration of the dry heating process: the D[4,3] varied from 21.7 μm for the control starch to 22.6 and 24.1 μm for DHT_2h and DHT_4h, respectively (Fig. 2B). The same was observed for the D[3,2], varied from 13.3 μm for the control starch to 13.7 and 14.1 μm for DHT_2h and DHT_4h, respectively (Fig. 2B). Since the parameter D[4,3] is more sensitive to larger granules, while D[3,2] is more sensitive to the fraction of smaller granules [START_REF] Lopez-Sanchez | Effect of mechanical and thermal treatments on the microstructure and rheological properties of carrot, broccoli and tomato dispersions[END_REF], it is noted that the greatest effect of the DHT occurred for the larger granules. This behavior is similar to that observed for cassava starch treated with DHT (Maniglia et al., 2020). It can be associated with a possible expansion in the starch granule due to water vaporization, such as during flash vaporization. In fact, part of the water content in the samples was vaporized during DHT, as reflected by the moisture of modified wheat starches (control: 10.1 g/100 g; DHT_2h: 4.7 g/100 g and DHT_4h: 4.5 g/100 g). The dry heating process also increased the number of granules with bigger sizes considering the d0.1, d0.5, and d0.9 values.

Fig. 3 shows the optical microscopy of the control and treated wheat starches using both nonpolarized and polarized light. The microscopies show wheat starch granules with lenticular morphology with a large variety of granules size, which is consistent with previous observation [START_REF] Hruska | Impedance characterization of wheat starch at various water contents[END_REF].While the birefringence effect (Maltese cross is visible) can be seen in all the images, the processed samples showed a shine reduction. [START_REF] Chung | Effect of single and dual hydrothermal treatments on the crystalline structure, thermal properties, and nutritional fractions of pea, lentil, and navy bean starches[END_REF] attributed this behavior to the temperature elevation at the center of the starch granule, which supposedly damage the amylopectin double helices structure. The same behavior was observed by Liu et al. (2019) in the case of dry heating treatment for waxy potato starch. Once the Maltese crosses still can be seen, it indicates the thermal energy provided was not sufficient to destroy amylopectin double helices structure.

These results indicated that DHT did not alter the shape nor altered the granules surface; however, it slightly affected the internal microstructure of wheat starch granules and promoted an expansion of the granule size -which can affect starch properties.

Starch molecular properties

DHT processing did not change the pH of the wheat starches suspensions (control:

5.90 ± 0.10, DHT_2h: 6.06 ± 0.15, and DHT_4h: 5.98 ± 0.18), and no carbonyl and carboxyl formation was found. It indicates that DHT did not promote starch oxidation. It is interesting to observe that cassava starch, at the same processing conditions, presented carbonyl groups formation (Maniglia et al., 2020), highlighting each starch source are differently affect by processing.

Fig. 4(A) shows the vibrational spectra of the control and modified starches. All samples showed the same characteristic bands at 3323 cm -1 , 2934 cm -1 , 1648 cm -1 , 1339 cm -1 , 1150 cm -1 , 1020 cm -1 , and 996 cm -1 . The bands at 3500 and 2900 cm -1 are associated with OH bonds and CH2 deformation, respectively [START_REF] Kačuráková | FTIR and laser-Raman spectra of oligosaccharides in water: characterization of the glycosidic bond[END_REF]. Bands at 1650 cm -1 are associated with water molecules absorbed in the amorphous region [START_REF] Kizil | Characterization of irradiated starches by using FT-Raman and FTIR spectroscopy[END_REF] and the stretching vibration of the CO band (amide I). The peak at 1339 cm -1 can be associated to OH bending due to the primary or secondary alcohols [START_REF] Muscat | Comparative study of film forming behaviour of low and high amylose starches using glycerol and xylitol as plasticizers[END_REF]. The fingerprint region of starch is the bands at 1200-900 cm -1 (showed in Fig. 4(B)) and this region provided information about changes in the polymeric structure and conformation of starch [START_REF] Dankar | 3D printing technology: The new era for food customization and elaboration[END_REF]. The intense IR band at 996 cm -1 can be mainly attributed to skeletal mode vibrations of α 1 → 4 skeletal glycoside bonds [START_REF] Jao | 1, 1-Diphenyl-2-picrylhydrazyl (DPPH) radical scavenging by protein hydrolyzates from tuna cooking juice[END_REF]. In addition, the middle strong peaks at 1150 cm -1 and 1060 cm -1 are mainly attributed to the stretching vibration of CO and bending vibration of C-O-H [START_REF] Hou | Integrated recognition and quantitative detection of starch in surimi by infrared spectroscopy and spectroscopic imaging[END_REF]. The band at 1060 cm -1 has been linked to amorphous structures [START_REF] Xiong | Interactions between wheat starch and cellulose derivatives in short-term retrogradation: Rheology and FTIR study[END_REF]. On the other hand, the band at 996 cm -1 can be associated with the single helix crystalline related to hydrogen bonds of anhydroglucose unit [START_REF] Xiong | Interactions between wheat starch and cellulose derivatives in short-term retrogradation: Rheology and FTIR study[END_REF].

It was not observed a significant difference between the presence and intensity of the bands in control and modified starches. These results indicate and confirm that the dry heating treatment did not modify the functional groups.

Fig. 5 shows the molecular size distribution of the control and treated wheat starches.

The first peak consists of molecules of larger size and more ramifications, which can be associated with amylopectins, while the second peak represents molecules of smaller size and a linear structure, which can be associated with amyloses. DHT reduced the molecular size (Fig. 5): the first peak was slightly reduced, the fraction of molecules with intermediary size was also reduced, and the second peak was increased; moreover, the first and second peaks 2020) also observed this behaviour for cassava starch, although with a much more accentuated effect. These results are also consistent with the study of [START_REF] Lei | Effect of dry heating treatment on multi-levels of structure and physicochemical properties of maize starch: A thermodynamic study[END_REF] involving maize starch. The authors observed the temperature increasing of DHT reduced drastically the long-amylose chains, while more short-amylose chains were formed.

The molecular results reinforce each starch source are differently affect by processing.

Consequently, further structure and properties evaluations are needed.

Thermal and crystalline properties of starch

The differential scanning calorimetry (DSC) thermograms (A) and the X-ray diffractograms (B) of the control and modified wheat starches are shown in Fig. 6. The gelatinization properties were obtained (Table 1) from Fig. 6 crystals and decreased the order of starch crystalline structure -as also observed by [START_REF] Lei | Effect of dry heating treatment on multi-levels of structure and physicochemical properties of maize starch: A thermodynamic study[END_REF].

The thermal and crystalline results are consistent with the behavior observed by optical microscopy about the reduction of Maltese crosses brightness in modified starches. All these results pointed out that the DHT reduced the crystalline zones of wheat starch. Even so, the starch properties must be evaluated.

Starch pasting properties

Fig. 7 (A) shows the RVA curves for control and wheat starch treated by DHT. Table 2 shows the pasting parameters obtained from RVA and the parameters.

The dry heating treatment significantly (p < 0.05) decreased the peak apparent viscosity (PAV), and there was a greater effect on this parameter as treatment time increased.

This effect can be associated with cleavage of glycosidic linkages which resulted in weakening of starch granules resulting in minor capacity to maintain the granule integrity [START_REF] Chung | Effect of minor addition of xanthan on cross-linking of rice starches by dry heating with phosphate salts[END_REF].

The pasting temperature (PT) is the temperature at which starch granules begin to swell due to water uptake [START_REF] Gałkowska | Effects of amino acids on gelatinization, pasting and rheological properties of modified potato starches[END_REF]. DHT applied for 4 h slightly increased PT, which can be related with the presence of a greater fraction of small-sized molecules, that require more energy to gelatinize than large-size molecules similar to that observed by [START_REF] Lima | Ozone Processing of Cassava Starch[END_REF].

Moreover, as the dry heating treatment period increased, a significant reduction (p < 0.05) of the through apparent viscosity (TAV) and final apparent viscosity (FAV) occurred. It can be associated with the thermal degradation of crystalline structures (observed in DSC and XRD analysis) and depolymerization (cleavage of glycosidic linkages) promoted by DHT [START_REF] Zou | Impact of continuous and repeated dry heating treatments on the physicochemical and structural properties of waxy corn starch[END_REF].

The increase of the DHT period also increased the RBD and reduced the RSB parameters, when compared to control starch (data shown in Table 2), indicating that the granules are more fragile, more susceptible to rupture, and less prone to re-associate.

According to [START_REF] Castanha | Potato starch modification using the ozone technology[END_REF], this behavior can be attributed to the change in the molecular size distribution.

Therefore, pasting properties confirm the structural modifications due to DHT processing, as well as they indicate hydrogels can present unique properties.

Hydrogel properties: rheology, firmness, and syneresis

Fig. 7 shows the results of (B) oscillatory stress sweep analysis, (C) gel firmness, and (D) the energy required in a puncture assay, considering the control and the wheat starch modified by DHT (2 and 4 h). Table 2 shows the parameters obtained from oscillatory stress sweep analysis. in this plateau region is a measure of the elasticity of material at very small deformation and it can be taken as a measure of the structural strength of mechanical rigidity of material at rest [START_REF] Lille | Applicability of protein and fiber-rich food materials in extrusion-based 3D printing[END_REF][START_REF] Mezger | The rheology handbook: for users of rotational and oscillatory rheometers[END_REF]. Moreover, for both control and modified starches, G' > G'' which indicates that all samples show a solid/elasticity dominating gel-like structure. G' increased with the DHT period, as well as the ration G'/G'', which indicates this treatment promoted the formation of a gel with greater rigidity and capacity to recover the shape after suffering stress. Therefore, this hydrogel probably shows good properties to be printed, because it can recover better the shape when it is deposited on the surface -being this evaluated in the next section.

The yield stress (σ0,G') is the stress where G' starts to decrease after the plateau region (Table 2), which indicates the stress at which the network/structure of the material starts to break down. The σ0,G' can be related to the ability of the material to keep its shape under gravity and the stresses generated by material layers deposited on top of it [START_REF] Lille | Applicability of protein and fiber-rich food materials in extrusion-based 3D printing[END_REF].

The σ0,G' value was greater as the DHT period increases. According to [START_REF] Lille | Applicability of protein and fiber-rich food materials in extrusion-based 3D printing[END_REF], a material with high structural strength at rest (G′) and a certain degree of resistance to external stresses (σ0,G') is required to ensure good printability of a material. In this way, we can observe that the DHT improved these rheological parameters of the wheat starch hydrogel, indicating that it can be a better material to be used in 3D printing.

Fig. 7(C) and 7(D) show the gels produced with modified starches showed higher firmness than the control, and this behavior was more accentuated as the treatment period increased. The molecular depolymerization promoted by DHT (Fig. 5) probably resulted in size distribution that better re-associate and packing, forming a stronger three-dimensional network structure. In this way, DHT promoted the formation of stronger gels, expanding the industrial applications of wheat starch.

During starch gels cooling, molecular retrogradation and amylose tendency to crystallize releases water from the gels -which is called synereis. The syneresis prejudices the printability of the hydrogels, as well as the consumer perception. DHT reduced syneresis, which is an interesting result: control: 7.38 ± 0.71 g water/ 100 g gel, DHT_2h: 5.19 ± 0.19 g water/ 100 g gel, DHT_4h: 3.62 ± 0.13 g water/ 100 g gel). As a result, these "inks" appeared well adapted to 3D printing use -in fact, this behavior can be seen in Fig. 8. Pictures of the syneresis in the hydrogels are shown in the Supplementary Fig. S2.

3D printing performance and characterization

Fig. 8 shows the star, heart, and cylinder shaped structures, printed using the hydrogels based on control and modified starches as "inks". Overall, the printed samples in our work were very similar to the pre-designed virtual model, indicating that the 3D printing could achieve precise printing with a personalized design using wheat hydrogels. All hydrogels could be smoothly extruded from the nozzle. However, the hydrogel based on control starch showed a scattering on the surface and a syneresis effect (visible in the star shape, which is consistent with the results presented in Section 3.4). The modified starches showed higher gel consistency, without spreading on the surface. The hydrogel based on DHT_4h starch showed the best resolution with the lines having higher cohesiveness and being more continuous. The behavior of the hydrogels after 3D printing can be associated with the rheological parameters:

the hydrogels with higher G´ and σ0,G' showed the best printability.

Texture is an important sensory attribute of food acceptability [START_REF] Yu | Effects of native starch and modified starches on the textural, rheological and microstructural characteristics of soybean protein gel[END_REF]. In this way, the printed cylinders were evaluated in relation to its textural parameters (Table 3). Results showed there was no significant difference in the cohesiveness, springiness, and chewiness values of printed samples. On the other hand, the increase of the heating period caused a significant (p<0.05) increase on hardness. According to Yang, Zhang, Finally, comparing this study with the previous of our group (Maniglia et al., 2020), we can observe that the same physical modification, DHT, showed different effects for each starch source, affecting the final printability characteristic. The modified cassava starch was more depolymerized, suffered oxidation, and showed gel firmness much higher than the native one, when compared with the changes here reported for wheat starch. Modified wheat starch showed a reduction in syneresis, which is important for 3D printing application. In this way, our results provide information on the benefits DHT modification can bring to each source, mainly focusing on the application of 3D printing.

Conclusion

This work investigated the use of dry heating treatment (DHT) as a tool to improve the printability of hydrogels ("inks") based on wheat starch. DHT caused a slightly expansion of granule size; however, it did not alter the shape of the starch granules nor their surface. DHT did not change the functional groups of the starch, indicating a negligible oxidation. However, slight depolymerization of starch was observed, in special in the middle size molecules, as well as a reduction of the crystalline zones in starch granule. The hydrogels based on the modified starches showed lower apparent viscosity during pasting and greater structural strength at rest. The longer duration of DHT processing, higher was the firmness of the hydrogels, and more reduced was the syneresis. The changes promoted by DHT in wheat starch, in special in 4 h treatment, resulted in hydrogels with better printability and reproducibility in 3D printing.

In this study, we demonstrated that the DHT is a simple alternative to improve the properties of wheat starch, as well as extend the texture possibilities of printed samples based on wheat starch hydrogels. Finally, this study shows the possibilities to expand the potential application of this starchy source.

  scrolled to the right. It indicates the DHT promoted the formation of molecules with lower size (which are retained longer in the chromatographic column) due to depolymerization promoted by cleavage of glycosidic linkages. The depolymerization affected mainly the intermediate size molecules. Maniglia et al. (

  (A). There was no difference in the onset (To) and the final (Tf) temperatures among treatments. The peak temperature (Tp) increased significantly (p ˂ 0.05) as the treatment period increased, and the gelatinization enthalpy (ΔH) was reduced (p ˂ 0.05) only for the DHT_4h starch. Lei et al. (2020) also observed a reduction of the gelatinization enthalpy (△H) for maize starch treated by DHT. The enthalpy of gelatinization is an indirect measure of the amount of starch crystalline region (or double helices structure) which are broken during heating (Liu, Yu, Xie, & Chen, 2006). Therefore, ΔH reduction can indicates the formation of weaker structures, which were less crystalline. In fact, Fig. 6(B) show the typical A-type diffraction pattern of wheat starch, with two singlet peaks (2θ) at 15° and 22.8°, a doublet peak (2θ) at 16.8° and 17.8°, and two weak peaks (2θ) at 5.6° and 20°. In addition, Fig. 6(B) shows the relative crystallinity of DHT_4h was lower than control and DHT_2h starches. Therefore, the XRD results are consistent with the DSC results, indicating that DHT reduced the double-helical

Fig. 7 (

 7 Fig. 7(B) shows the representative storage (G') and loss (G'') modulus curves: the G'

  Prakash, & Liu (2018b), higher G′ indicates stronger mechanical strength often accompanied by greater hardness, behavior also observed in our results. The modified starches resulted in printed samples with less adhesiveness. According to Anukiruthika, Moses, & Anandharamakrishnan (2020), less adhesive "inks" flow more easily through the nozzle, contributing to the 3D printing process. In this way, DHT extended the possibility of textures of printed samples based on wheat starch hydrogels. About reproducibility, the hydrogels based on modified starches showed lower weight and higher height than hydrogel based on control starch. The diameter did not show a significant difference among the treatments. Moreover, by comparing the standard deviation, we observed lower values for DHT_4h, indicating this treatment formed hydrogel were more reproducible 3D printing.

Fig. 1 .

 1 Fig. 1. The picture of 3D printer with the main parts: the extruder motor, syringe (cartridge) with the nozzle (movement in z direction), heating control, and mobile platform (movement in x and y directions).

Fig. 2 .

 2 Fig. 2. (A) Granule size distribution (B) Specific diameters (D[4,3], D[3,2], d0.1, d0.5, d0.9 -vertical red bars are the standard deviation) of the control and modified starches by dry heating (DHT_2h and DHT_4h):

Fig. 3 .Fig. 4 .

 34 Fig. 3. Photographs from light microscopy (40×) using (A) nonpolarized and (B) polarized light of the control and modified starches by dry heating (DHT_2h and DHT_4h).

Fig. 5 .Fig. 6 .

 56 Fig. 5. Molecular size distribution of the control and modified starches by dry heating (DHT_2h and DHT_4h).

Fig. 7 .

 7 Fig. 7. (A) RVA curves, (B) oscillatory stress sweep analysis (G´: storage modulus and G´´: loss modulus), (C) Gel firmness, and (D) the energy required in a puncture assay of the control and the wheat starch treated by dry heating (DHT_2 and DHT_4 h).

Fig. 8 .

 8 Fig. 8. The 3D printed hydrogels (star, heart, and cylindrical shapes) based on control wheat starch and modified wheat starch by dry heating treatment (DHT_2h and DHT_4h).

Table 1 .

 1 Gelatinization properties of the control and modified starches by dry heating (DHT_2h and DHT_4h) (average ± standard deviation). , b, c: different letters in the same column indicates significant difference among samples, as revealed by Tukey's test, p < 0.05 To = onset temperature, Tp = peak temperature, Tf = final temperature and ΔH = enthalpy. DHT_2h: wheat starch dry heating treated for 2 h. DHT_4h: wheat starch dry heating treated for 4 h.

	Samples	To ( o C)	Tp ( o C)	Tf ( o C)	ΔH (J/g)
	Control	47.99 ± 0.28 a	58.05 ± 0.10 c	74.32 ± 0.56 a	9.85 ± 0.12 a
	DHT_2 h	47.43 ± 0.37 a	58.30 ± 0.06 b	74.65 ± 0.62 a	9.89 ± 0.28 a
	DHT_4 h	47.23 ± 0.43 a	59.85 ± 0.10 a	74.42 ± 0.35 a	7.57 ± 0.10 b

a

Table 2 .

 2 Pasting parameters from RVA and parameters from oscillatory stress sweep analysis of the

control and modified starches by dry heating (DHT_2h and DHT_4h

  ) (average ± standard deviation) Peak Apparent Viscosity (PAV), Through Apparent Viscosity (TAV), Relative Breakdown (RBD), Final Apparent Viscosity (FAV), Relative Setback (RSB) and Pasting Temperature (PT), Storage modulus (G'), Loss modulus (G''), Yield stress (σ0,G') a -c: different letters in the same column indicates significant difference among samples, as revealed by Tukey's test, p < 0.05. DHT_2h: wheat starch dry heating treated for 2 h. DHT_4h: wheat starch dry heating treated for 4 h.

	Samples	PAV (mPa.s)	TAV (mPa.s)	RBD (%)	FAV (mPa.s)	RSB (%)	PT (ºC)	G´ (Pa)	G´´ (Pa)	σ0,G' (Pa)
	Control	2250.40±40.92 a 1378.43±18.30 a 37.36±1.09 c 2757.50±14.95 a	40.71±0.72 a	73.53±0.32 b	175±25 c	33.4±2.2 c 12.74±0.05 c
	DHT_2 h 2017.00±30.15 b 1172.80±22.30 b 40.45±0.82 b 2257.00±70.21 b	31.91±0.49 b	73.68±0.38 b	257±32 b	40.1±1.6 b 26.37±0.20 b
	DHT_4 h 1820.72±22.17 c 1034.02±10.12 c 43.93±0.65 a 1927.50±82.73 c	18.73±0.42 c	74.53±0.25 a	430±14 a	88.9±4.5 a 54.56±0.08 a

Table 3 .

 3 Texture parameters and reproducibility of the starch hydrogels printed in cylinder shape. The hydrogels are based on control and modified starches by dry heating (DHT_2h and DHT_4h) (average ± standard deviation) -c: different letters in the same column indicates significant difference among samples, as revealed by Tukey's test, p < 0.05 DHT_2h: wheat starch dry heating treated for 2 h. DHT_4h: wheat starch dry heating treated for 4 h.

	Starch	Texture
	hydrogels

a

Acknowledgments

The authors are grateful to:

-the Région Pays de la Loire (France) / RFI "FOOD 4 TOMORROW" for funding the Postdoctoral fellowship "STARCH-3D" of BC Maniglia;

-the São Paulo Research Foundation (FAPESP, Brazil) for funding project n° 2019/05043-6; -the National Council for Scientific and Technological Development (CNPq, Brazil) for funding the productivity grant of PED Augusto (306557/2017-7);

Declaration of Conflict of Interest

The authors declare no conflict of interest.