Introduction

Custom assistive devices, also known as Custom Assistive Products (CAP) have been shown to positively impact functioning and quality of life in different settings around the world while being a low-cost, easy to tune alternative to commercially available assistive products. This high adaptability should make it an especially useful tool to meet the needs of disabled students1,2,3. Research in this general area has rarely been initiated and often focuses on detailed descriptions of specific products or showcases of the cost effectiveness of the general technique rather than establishing general guidelines or protocols4,5. The aim of this paper is to analyze the impact of custom assistive devices on the quality of life (QOL) and functioning of disabled students in a systematic way as exploratory research.

The International Classification of Functioning, Disability and Health (ICF), created by the World Health Organization (WHO) in 2001 established the basis for a paradigm change that affected all health-related areas of expertise and established a thorough way of integrating all components that could define the health and functioning of a person ranging from its bodily structures and functions to the environmental factors whose interaction partially defines the activities in which the person takes part and how he or she participates6,7. While its core ideas were widely used in Occupational Therapy (OT) practice well before its inception, such a broad and impactful change opened the door for OTs to broaden their officially recognized areas of work to many different areas including the design of support products, also known as assistive tech or assistive products.

According to the European standardization standard UNE-EN ISO 9999:2023 assistive products can be described as any product that optimizes a person’s functioning and reduces disability8. This includes devices, instruments, equipment and software and places a special emphasis on the fact that this broad variety of devices and equipment includes specially produced or generally available items. Within the specially produced category the aim of this text is to explore the effectiveness of custom, individually designed devices tailored to a specific person tied to a specific activity.

CAP is already the standard practice in some areas such as seating, positioning and electrical wheelchair control, where only a custom solution is considered suitable in most cases or the creation of orthosis where the effectiveness of the product is directly tied to how well it can contour to the person’s limbs9,10. Following these conclusions, broadening this design paradigm that includes the person in the design process to ensure a fit and suitable design while empowering him or her to decide and express preferences into other areas of design and other specific types of assistive products may show benefits yet to be explored. Investigation into the use of these technics in other areas may bring to light useful comparisons between already proven commercially available designs and new customized assistive products11,12.

Another benefit of CAP is its ability to be created via low-cost materials and design processes, which are usually defined as low-cost assistive products (LCAP). LCAP has been found to produce effective and useful assistive tech while using only 8.23% the cost of its commercially available alternatives and has been widely used in developing areas such as Brazil and India1,2. CAP and LCAP can be considered two sides of the same coin in which the resources available to any specific individual are used to produce custom devices. CAP refers to any assistive product personalized to better suit the user’s needs (like the previously mentioned orthosis that are usually designed with high-cost thermoplastic materials) while LCAP specifically refers to the use of low-cost solutions such as the use of recycled materials of 3D printing to generate these same products. While CAP may seem to be the obvious choice when resources are available, LCAP may allow a more thorough, fine and iterative design process achieving a much higher level of customization with lower costs with the aid of high-tech techniques such as 3D printing.

3D printing can be defined as an additive manufacturing technique in which layers of melted plastic are rearranged following a computer-designed path to create a 3D body with custom shape, materials and characteristics13. In its current form, 3D printing is, in some ways, the most effective LCAP tool, as it can quickly produce low-cost durable devices while also being a great companion for the design process being able to produce mockups and prototypes with an even lower cost14.

LCAP is especially useful in children and teenagers as their needs change as they grow and develop swift biopsychosocial changes that alter their physical characteristics, needs and abilities as defined by the IFC classification for infants and adolescents ICF-IA in 200715. This rapid change may render assistive tech obsolete rather quickly which may be problematic for commercially available assistive tech while providing an excellent opportunity to reassess and redesign CAP to fully cover all needs and adapt.

This constant redesign process, in addition, requires constant education and reeducation of any person directly related to the use of the specific assistive tech16,17. Not being successful in the process of educating professionals directly related to the use of these devices may result in heightened or unrealistic expectations about their function, sometimes resulting in a progressive loss of use that may render otherwise useful products into forgotten ones18,19.

While CAP design may appear unique owing to how changing and living it is following the changes in its person’s needs and abilities it is comparable to any other design process and thus, needs to follow basic product design guidelines. Assistive technology needs to be designed with human interaction as its main goal and needs to be first and foremost functional, reliable and usable to be able to achieve the task for which it is designed. However, it can only be truly human-centered and considered a final and successful design once it is convenient, pleasurable to use and meaningful to the user according to Anderson’s hierarchy of needs20.

This seemingly small difference between being useable and meaningful is fundamental in the design process of assistive tech as it relates slightly differently to the user than any other object interacts as it is integrated into his or her user’s function, not being ontologically separated owing to the way it answers his or her needs21,22,23. The only way of achieving this is with the use of a truly human-centered design process that bridges the gap between industrial and interactional design and posts itself as a service rather than as a series of individual products according to Buchannan’s four orders of design that categorize all design in 4 incrementally complicated areas: graphic design (That generates signs or symbols), industrial design (That generates products), interactional design (That creates services) and the design of systems (That makes organizations)24.

The present study focuses on the creation of 11 CAP to the students of three specific special educational needs and disability schools or inclusive schools in Valencia, Spain, following an iterative design process spanning 8 months from November 2023 to June 2024 with an interventional window spanning March to June 2024.

The aim of this study is to measure the impact of CAP on the quality of life and functioning of disabled students while measuring student aid crew (Described as personal assistants or specific professionals working for the school to take care of and improve function and independence of students) or teacher satisfaction with the process and specific products implemented.

Methods

The stated protocol was revised and accepted by the Catholic University of Valencia San Vicente Martyr’s ethics committee and was approved with the code UCV/2023–2024/010 one the 31st of October 2023. All the experimental data was collected in accordance with the relevant regulations and rules stated by the committee. Informed consent (Which included testing and publication of data obtained) was obtained from all participants or, in this specific case, their legal guardians.

The study design is an exploratory clinical trial, structured with an adaptive design and evaluated pre- and post-test in the case of QOL evaluations and one-shot in the case of functioning evaluation. The study can be divided into 3 main phases. The first one, that could be considered as recruitment and initial evaluations, is contained in a period spanning March to April 2024 and focuses on pinpointing the final sample as well as their needs with the help of inclusion and exclusion criteria as well as indirect interviews to the staff (Tables 1 and 2). The second phase focused on designing, implementing and reevaluating each device to be as custom, user friendly and useful as possible, being able to be redesigned as many times as possible spanning April to May 2024. The third and final phase is the final evaluation and data management phase (Using Jamovi as statistical analysis software) that was limited to June 2024. The adjusted timeline of the study can be found in Table 3, after it was adjusted to take place in 6 months.

The participants were selected from two special education schools and one inclusive school in Valencia, Spain, in the form of interest sampling following the initial eligibility check with inclusion and exclusion criteria as well as the initial analysis of needs and wants from the students and the teaching and student’s aid crew.

Table 1 Inclusion criteria.
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Table 2 Exclusion criteria.
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These inclusion and exclusion criteria focus the study on children aged according to our evaluation tools, who must be actively present in their evaluation setting and whose needs may be efficiently met without an unreasonable use of an annual budget that may limit the final sample size. Any student in need of an assistive device or with needs that may be helped with its implementation and who fit these criteria was considered eligible to be part of the study. Students whose needs could be easily and affordably addressed with commercially available devices were removed from the final sample and given commercially available devices as therapeutic effort was better spent in designing non-existent products or alternatives to products already existing that didn’t completely answer any given student’s full needs. This specific criterion shows how both technics may coexist and how beneficial the combined use of both can be. These criteria limited the sample size to 11. These 11 students, after all the legal and necessary documents were signed by their parents or legal guardians, then received computer generated and 3D printed devices created customized in each specific case.

Three specific evaluation tools were used to measure each of the three variables. These are the KIDSLIFE QOL Questionnaire, the Psychosocial Impact of Assistive Devices Scale (PIADS) and the quality-of-service evaluation (ServQual).

The KIDSLIFE QOL Questionnaire is an evaluation tool created around the 8 QOL dimensions established by Schalock, Verdugo and Braddock in 2002. It is composed of 8 subscales, these being: social inclusion, self-determination, emotional wellbeing, physical wellbeing, material wellbeing, rights, personal growth and social relationships. The Spanish version of this questionnaire was validated by the University of Oviedo and the University Institute of Integration into the Community (INICO) in 2016.

Table 3 Study timeline.
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The Psychosocial Impact of Assistive Devices Scale (PIADS) is the default tool used to measure the psychosocial impact of assistive technology by measuring the competence, adaptability and self-esteem of people while each specific tool is used. It has been widely used to measure products such as brain-computer interfaces, eye-trackers and low-cost custom low tech27,28,29.

The quality-of-service evaluation (ServQual) measures the perceptions of users related to a service as well as how it measures their expectations, focusing on which areas need to be improved, such as empathy in service, sensibility or physical elements related to the service, which, in this case, refer to the specific CAP used30.

Data collection was conducted one shot at the end of the intervention for the PIADS and ServQual evaluations, as they do not allow pretest evaluation, and pre- and post-test in the case of the KIDSLIFE questionnaire. Additionally, owing to the adaptive design used, a weekly evaluation was put in place to assess the need for adjustments or changes to the CAP implemented to achieve the best level of customization possible before the final evaluation phase. This evaluation was conducted as a non-structured interview with the student’s main teacher or main aid, as the students themselves were unable to answer interviews or evaluation tools, trying to establish any possible changes or adjustments that may produce a better product or an improved experience. All feedback was considered, and the designs were adjusted, tested next week and subjectively compared by these professionals mentioned. This workflow not only guaranteed that the professionals understood and liked the implemented device (As it was essentially born from their ideas) but gave the possibility to form a robust iterative design process where any device could be improved, rolled back to a previous version or completely changed. All final products were developed using commercially available computer aided design (CAD) programs such as Fusion and a commercially available 3D printer (Creality Ender-3) and printed using standard PLA filament with a 40–70% infill and no further adjustments.

The statistical analysis integrated both analytical and descriptive approaches. The Wilcoxon signed-rank test, a non-parametric alternative to the paired t-test, was applied to the KidsLife questionnaire to compare pre- and post-intervention scores without assuming normality of the data due to the rather small sample size; this test evaluates whether the median differences between paired observations are positive or negative. The PIADS and SERVQUAL questionnaires, being one-time evaluations and only being taken after implementing the products, were summarized using descriptive statistics (mean, median, standard deviation, minimum, and maximum). To explore relationships among PIADS subscales, as a clear trend between two of the three dimensions was observed, Spearman’s Rho correlations were calculated to measure the strength and direction of associations. Given the strong correlation shown between competence and adaptability, a linear regression analysis was then performed to model the predictive relationship between these variables. A linear regression allowed quantifying how much one variable predicted change in the other, and in this case showed that 60.3% of the variance in adaptability could be explained by competence. All analyses were conducted using Jamovi statistical software version 2.3.28.0, which allowed both non-parametric testing and regression modeling within the same platform.

Results

Eleven participants aged 4 to 16 years were included and reported full consent. The most common diagnosis is cerebral palsy (5) followed by spinal muscular atrophy (2). Available sociodemographic data as well as a brief explanation of all devices developed can be found in Table 4. All participants gave consent to take part in the study and any further publications made with the data collected. A total of 32 assistive custom devices were designed and implemented in the iterative design process, ending with a final sample of 11 finalized and implemented designs. The most common areas designed for (according to AOTA’s occupational therapy practice framework) are toileting and toilet hygiene (6), communication management (5) and formal education participation (10). In the case of toilet hygiene users couldn’t reach the faucet or sink. Figure 1 shows some of the products implemented. Users in need of products regarding communication management were unable to properly use their communication devices (Tablets) as poor hand eye coordination and hand control resulted in many different non useful cells being pressed while trying to press a specific one. Students in need of products regarding the area of formal education participation were unable to comfortably hold and use pencils, pens or any other writing and painting tool the amount of time needed to fully take part in activities in the classroom.

Fig. 1
figure 1

Vertical pen holder that keeps all pens and pencils vertical on the desk allowing the user to look at all pens at once and choose which one to use without rummaging in a pencil case and pen support that allows the pen to be held horizontally while writing with the hand in a complete pronation.

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Table 4 Sociodemographic data and devices developed. Legend: male (M), female (F),
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QOL was analyzed by comparing the pretest and posttest scores of the KIDSLIFE questionnaire with the use of Wilcoxon T paired tests (Table 5). Using this method, the subscale scores most impacted are those of social inclusion (p 0.013), rights (p 0.021), emotional wellbeing (p 0.042) and self-determination (p 0.050). These areas that were statistically significantly impacted are the ones most closely tied to the clinical benefits of the intervention with the students being able to participate in activities previously impossible to take part in and thus being more included in their classrooms. Material well-being (p. 0.053), physical well-being (p 0.109), personal development (p 0.262) and interpersonal relationships (p 0.235) were not statistically positively impacted.

Rights contains items such as “72. Take part in activities with the same opportunities as other people” (Mean improvement from 2.55 to 2.91). Social inclusion on the other hand contains items such as “9. Receives support and interventions in natural contexts” (Improved from 3.18 to 3.45) to or “10. Specific measures are taken to enhance their participation in the community” (Improved from 2.82 to 3.18).

Emotional wellbeing, as a positively impacted area, could also have been impacted by participation in more activities as it contains items such as “26. Receives praise and compliments when doing something well” (Improved from 3.82 to 4). The presence of items such as this one in this area could point to participation being done in a more complete and active way thus prompting more praise from peers and teachers.

This more complete and active way to independently take part in activities could also have a positive impact on self-determination, which includes items such as “13. Specific measures are taken to enable choice making” (Improved from 3.09 to 3.27) or “22. At the center, support is provided that takes into account needs, desires and preferences” (Improved from 3.10 to 3.36). All these specific items not only make clinical sense but could also be considered as key to the improvement of the results as they are amongst the most impacted items.

Table 5 T paired test for KIDSLIFE initial and final data collected.
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Table 6 Descriptive results of the PIADS evaluation.
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Table 7 PIADS matrix correlation.
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Table 8 Linear regression of the PIADS results and model coefficients.
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Quality of service, analyzed with the help of the SERVQUAL questionnaire (Table 9), showed positive scores across all the evaluation tools, with more positive scores tied to responsibility (6.47/7), empathy (6.25) and functional quality (6.20). The scores less positively impacted were security and efficiency (6.09), perceived value (6.00), reliability (5.67) and tangibles (5.62).

Specifically, when the physical and functional qualities were analyzed, all the devices implemented were in continued use during the entire intervention except for those scheduled to be redesigned or in the process of being remade because they were broken or lost. The only broken devices were those designed with an infill of less than 45% during the first phases of the design process and quickly developed stronger.

Table 9 Descriptive results of the SERVQUAL evaluation.
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Discussion

We could understand the results obtained following the 3 main areas evaluated. Regarding QOL, we can observe a general positive impact with some subscales being impacted in a more statistically significant way. Functioning seems to have improved in a similar manner with significant improvement in two of three subscales and a modest but smaller improvement in the self-esteem subscale. Lastly, satisfaction seems to have been positively rated across the board, pointing to the responsibility of the intervention and the product’s functional quality as their biggest advantage.

QOL was positively impacted and showed greater impact in three specific subscales (social inclusion (p 0.013), rights (p 0.021), emotional wellbeing (p 0.042) and self-determination (p 0.050)) that follow the observed clinical effect of increased interaction and participation. The results obtained from the KIDSLIFE questionnaire are broad and measure many different and unrelated aspects that may impact quality of life. As such, these many different areas have been impacted in a very specific way that is directly related to which areas could be more related to the implementation of assistive devices. We divided the results obtained into highly impacted areas, positively impacted areas and nonimpacted areas.

The highly impacted areas correspond to rights and social inclusion. This could be attributed to the fact that the assistive devices implemented directly allowed the students to independently take part in activities that previously were not available to them (such as students who were unable to hold a pencil being able to take part in coloring activities or students unable to reach the faucet being able to wash their hands independently), directly improving their relationships with their peers by allowing them more areas and situations to interact with them. As such, the devices supported their right to play and took advantage of the activities provided to them to their fullest extent. The conclusions drawn are well supported by the items contained in these areas. The Items previously mentioned in the area Rights such as “72. Take part in activities with the same opportunities as other people”. Social inclusion on the other hand contains items such as “9. Receives support and interventions in natural contexts” or “10. Specific measures are taken to enhance their participation in the community” show relevant improvements that impacted the improvements in this area.

As such, Emotional wellbeing could also have been impacted by participation in more activities as it contains items as the one mentioned “26. Receives praise and compliments when doing something well”. The presence of items such as this one in this area could point to participation being done in a more complete and active way thus prompting more praise from peers and teachers.

This more complete and active way to independently take part in activities could also have a positive impact on self-determination, which includes items such as the mentioned items “13. Specific measures are taken to enable choice making” or “22. At the center, support is provided that takes into account needs, desires and preferences”. All these specific items not only make clinical sense but could also be considered as key to the improvement of the results as they are amongst the most impacted items.

Material well-being with physical well-being, personal development and interpersonal relationships as not impacted areas contain items broadly related to clothing and toys, eating and hygiene, activities of daily living (ADLs) at home and friendship and social networks. These areas, while they could be positively impacted by assistive tech under other conditions, are hardly related to the implemented products that have stayed in school and are related mainly to writing and toileting. Studies that measure quality of life after the implementation of custom assistive devices show also a small but positive impact with improvements in tools like the Health-related Quality-of-Life (HRQOL) improving from 58 to 61 total points in one case and improving from mean 0.672 pre-test to mean 0.75 posttest31,32. These scores, that show small but promising results utilizing much broader and less specific tools, cannot possibly be compared to the results obtained with the help of the KIDSLIFE questionnaire and its 8 different QOL dimensions. Further studies may need to be conducted utilizing this specific QOL framework to establish comparisons.

The PIADS tool showed great improvements in competence (1.89) and adaptability (1.92) with a milder improvement in self-esteem (1.60). These results hinted at the fact that competence and adaptability may be related in a stronger way than self-esteem. When plotting the data in a matrix correlation, competence and adaptability were shown to have a much stronger correlation that self-esteem had with the other dimensions. The use of linear regression helped explain this correlation and showed how the change in adaptability was due in 60.3% to the changes in competence. Studies that focus on the implementation of CAP and measure results with the help of the PIADS show similar results with scores of 1.94, 1.83 and 1.62 respectively which show the mentioned higher impact on competence and adaptability than self-esteem33. Other studies that implement 3D printed custom products not individually customized in each case, show lower scores with 0.95, 0.88 and 0.73 respectively showing worse results but the same pattern34. This data seems to point to the fact that customizability may be of great importance to be able to achieve significant results and may point to the fact that these products may have a hard time being as impactful to self-esteem as they are to competence and adaptability.

Finally, satisfaction was positively impacted as well, being the subscales responsibility (6.47/7), empathy (6.25/7) and functional quality (6.20/7) being the most highly rated. This high satisfaction is in the line of previously mentioned studies that show satisfaction being highly rated with mean ratings of 7.32 out of 10 and other studies that show satisfaction being a positively impacted area when analyzed with tools such as the QUEST or QUEST 2.0 (Quebec User Satisfaction Test) having mean results of 4.5 out of 5 and 4.76 out of 5 with the use of this tools5,35,36.

Regarding the general application of 3D printed assistive devices to children in the school environment, studies have shown that this technology is a useful tool to meet the needs of students with such different tools such as customized one-handed recorders, guitar playing tools or eating aids being successful in helping children take part in activities previously impossible and showing benefits tied to functioning and satisfaction34,37.

This exploratory clinical trial presents several limitations that should be acknowledged. First, the small sample size (n = 11) restricts the generalizability of the results and reduces statistical power. Second, the non-randomized design and lack of a control group limit the ability to definitely establish relationships between the implementation of custom assistive products and improvements in the areas evaluated. Third, two evaluation tools (PIADS and SERVQUAL) can only be administered post-intervention, which hinders the analysis of changes over time. Additionally, reliance on interviews obtaining data from teachers and support staff rather than direct student self-reports, as the final sample was unable to answer direct interviews or evaluation, could introduce response bias. Finally, the short duration of follow-up does not allow conclusions on long-term device use, maintenance, or sustainability.

Future research should address these limitations by including larger samples, applying randomized designs, and incorporating longer follow-up periods to evaluate durability and continued use of devices. It will also be valuable to obtain information directly from the students changing the sample to include more non-intellectually disabled students and exploring child-centered assessment strategies that may also open the doors to broaden investigation related to the co-creation process. Furthermore, comparative studies could examine the effectiveness of 3D printed CAP in classroom settings against commercially available products, to better define when custom low-cost solutions are most beneficial. Finally, future work should consider cost-effectiveness analyses to better analyze the benefits of 3D printing as a low-cost alternative to commercially available products.

Conclusions

In conclusion, custom assistive products may be developed to support students with disabilities to achieve their full potential in the classroom, and to meet the ever-changing needs of the pediatric population. We could divide conclusions into three specific areas regarding the 3 different evaluation tools used. The first area, regarding QOL, seems to hint at the fact that CAP may have a statistically significant impact on QOL. Within QOL, social inclusion, rights, emotional wellbeing and self-determination are the most positively impacted areas hinting at the fact that these products may open areas of participation to the students. The second area, related to function, shows that CAP are effective in helping students take mar in more activities. As such, competence and adaptability seem to be highly impacted with a lesser impact on self-esteem. The third and final area, tied to the satisfaction of teachers and students’ aids, shows a high level of satisfaction. Specifically, responsibility, empathy and functional quality seem to be more highly rated than other areas.

An iterative design process provided as a continued service that ensures proper communication and education to the staff helps ensure that the implemented products are designed to meet the needs and abilities of each specific case and stay relevant and in use. Within this design process, 3D printing is a powerful tool that makes the design process a low-cost endeavor where many different designs and adjustments can be created cheaply and quickly.

3D printing to create CAP in the context of inclusive education schools or special educational needs and disability schools seems to be a tool with great potential to broaden the participation opportunities of children that may otherwise not be able to participate in a comfortable manner or at all in many different activities such as painting or in routines regarding toileting.

These conclusions hint at the fact that 3D printing may be a useful tool to facilitate the creation of CAP, the benefits of which seem statistically significant, but which may be further clarified with the help of more specific tools and different, more scientifically strict studies that may contain blinding processes as well as control groups. These more specific tools may need to be developed, translated and implemented to gather more specific and tailored results that may point to improvements in the design process or to each specific type of device implemented.