Over recent years, mobile health (mHealth) technologies have become integral to contemporary wellness promotion, with more than 350,000 health applications available globally [1]. Wellness applications represent prevalent mHealth tools designed to promote healthy lifestyle behaviors, such as improved diet and physical activity [2]. In Australia, approximately 88% of the population owns a smartphone [3], offering significant opportunities for large-scale digital health interventions.

Despite this proliferation, sustained engagement remains a critical challenge. Meta-analyses report dropout rates exceeding 43% across mHealth interventions for chronic disease management [4]. Among young adults aged 18 to 34 years, defined by the Australian Communications and Media Authority as digital natives [5], engagement barriers are particularly pronounced due to inadequate personalization [6], cultural insensitivity [7], and a lack of theoretical grounding in application design [8]. Building on the completed phase 1 (systematic literature review of 32 studies, expert consultations [n=6], formative research with young adults [n=20], and rapid review of user interface [UI] or user experience [UX] design practices [35 studies]) and phase 2 (wireframe development and preliminary evaluation using interactive Figma prototypes refined through iterative expert feedback), the MiCARE progressive web application (PWA) aims to address these gaps through a theory-driven, user-centered approach.

Young adults face rising chronic disease risks, particularly prediabetes, which affects approximately 374 million adults globally [9] and can be reversed through early lifestyle intervention [10]. Sedentary behavior compounds these risks, with adults spending an average of 8.8 hours per day sedentary across European countries [11], while Australians sit for approximately 8 hours per day [12]. Poor dietary habits further exacerbate health risks, with nearly half of Australian adults (49%) failing to consume recommended fruit servings and more than 90% not meeting vegetable intake guidelines [13].

Despite these challenges, digital wellness solutions offer unique advantages for young adults, including flexible access to tailored tools and seamless integration into daily routines [14]. However, most commercially available applications lack evidence-based design and theoretical grounding [8,15], compromising personalization and cultural relevance and resulting in poor sustained engagement.

The MiCARE framework synthesizes multitheoretical models to address engagement gaps: self-determination theory (SDT) [16], which emphasizes autonomy, competence, and relatedness as core constructs underpinning intrinsic motivation; the CARE (compassion, assistance, respect, and empathy) framework [17], which guides culturally sensitive engagement through compassion, assistance, respect, and empathy; user-centered design (UCD) principles [18], which emphasize iterative co-design and responsiveness to user preferences; inclusive design principles [19], which ensure equitable access and representation for diverse populations; design science research methodology (DSRM) [20,21], which provides a systematic approach to developing and evaluating information systems artifacts; and task-technology fit (TTF) [22] and Unified Theory of Acceptance and Use of Technology (UTAUT) [23], frameworks for assessing technology acceptance and sustained use.

Prior systematic work established the foundation for MiCARE development. A systematic literature review of 32 studies identified key engagement barriers, including high dropout rates [24,25], inadequate personalization [26,27], environmental constraints [7,28], and cultural or language barriers [29,30]. Facilitators included cultural tailoring [29,30], personalized feedback [25,31], user-friendly design [32,33], and peer support [34,35].

Building on these findings, a 3-step UCD process included systematic literature review (32 studies), expert consultations (n=6), formative research with young adults (n=20), and rapid review of UI and UX design practices (35 studies). This process generated 5 design objectives: empathy-driven interaction, equity-focused accessibility, culturally sensitive personalization, incremental goal setting, and intuitive onboarding. User preferences identified during earlier formative design research with young adults indicated that 55% preferred grid layouts, 65% favored large-button interactions, and 50% preferred minimalist interface designs, informing the feature specifications.

While conceptual frameworks for digital health interventions are well established [36,37], the technical translation from theory to deployable software constitutes a critical knowledge gap [38]. Published studies typically present either fully developed interventions without implementation details or propose frameworks without functional prototypes. For example, LeSeure et al [29] developed the DiaFriend mobile app for type 2 diabetes management but noted that “the backend is incomplete and requires expert collaboration for full functionality.” Similarly, Curtis et al [39] documented UCD processes for a childhood weight management app but provided limited technical specifications, constraining reproducibility. This implementation gap is particularly problematic for resource-constrained research settings. Comprehensive technical documentation enables future researchers to adapt proven implementations rather than rebuilding from conceptual frameworks, thereby accelerating evidence-based innovation in digital health [40].

Furthermore, rigorous evaluation of theory-driven wellness applications remains limited. While the TTF [22] and UTAUT [23] provide validated frameworks for assessing technology adoption, few studies systematically apply these models to evaluate user experience outcomes in preventive health contexts [38]. The integration of multiple theoretical perspectives (SDT, CARE, UCD, and inclusive design) with evaluation frameworks (TTF and UTAUT) addresses calls for theory-driven development [36,37] and rigorous evaluation methodologies [40] in digital health.

This paper presents a protocol for a 9-month project with the following aims:

We hypothesize that a theory-driven, user-centered digital health platform will demonstrate high usability, perceived usefulness, and user satisfaction among young adults, supporting sustained engagement with wellness content over a 3-month evaluation period. This study assesses formative usability and feasibility to identify design strengths, usability issues, and refinement priorities, informing subsequent development and larger-scale evaluation.

The development and evaluation of the platform adopt a co-design, user-centric methodological approach [40], weighing all stakeholders’ experiential needs and preferences equally. The implementation process follows the DSRM [20,21], integrating behavioral theory (SDT and CARE framework) with UCD principles [18] and inclusive design [19] to optimize uptake and use of the digital platform.

Integrating digital health technologies into practice has the potential to impact current practices [41]. The design process is guided by multiple theoretical frameworks, including SDT for motivation and autonomy, CARE for empathetic engagement, UCD for iterative co-design, and inclusive design for accessibility, ensuring theoretical fidelity throughout development. The evaluation uses the TTF [22] and the UTAUT [23] frameworks to match stakeholder expectations and digital literacy to the final platform design. The evaluation follows established usability testing guidelines [42], with sample sizes appropriate for identifying usability issues and achieving qualitative saturation [43].

The study uses a mixed methods approach across 2 phases conducted over 9 months. An overview of the study design is shown in Figure 1. Phase 1 [44] (systematic literature review, expert consultations, formative research, and UI and UX review) and phase 2 (wireframe development and prototype evaluation, which has been accepted for publication) have been completed, providing the theoretical and design foundation for the subsequent phases. Phase 3 (October 2025 to March 2026) has commenced and is currently underway, involving the technical implementation of the MiCARE platform. Phase 4 (April 2026 to June 2026) will follow the completion of phase 3 and will focus on formative usability and feasibility evaluation with 20 university-affiliated young adults from La Trobe University (Bundoora and Bendigo campuses). This single-site, convenience sample supports heuristic usability discovery and design validation.

The stakeholder group for this study consists of young adults aged 18 to 34 years affiliated with La Trobe University. Participants will be recruited from La Trobe University (Bundoora and Bendigo campuses) through advertisement posters and email invitations.

Participants will be eligible for inclusion in the study if they meet the following criteria: (1) adults aged 18 to 34 years; (2) ownership of a computer or smartphone with stable internet connectivity; (3) ability to read, write, and understand English; and (4) willingness and ability to provide informed consent.

Participants will be excluded from the study if they meet any of the following criteria: (1) individuals with compulsive exercise behaviors or a history of disordered eating, as wellness content could be triggering; (2) inability to commit to a 3-month study duration; and (3) lack of basic digital literacy skills necessary to navigate web applications.

Technical implementation data will be documented through (1) sprint logs that record implementation decisions and rationale, (2) a clinical verification report for chatbot responses, (3) expert panel feedback on accessibility compliance, and (4) development timeline.

Following completion of phase 3, a systematic formative usability and feasibility evaluation will be conducted with young adults (n=20) over a 3-month period. The evaluation uses the TTF [22] and UTAUT [23] frameworks as descriptive and exploratory organizing lenses.

A total of 20 young adults aged 18 to 34 years will be recruited from La Trobe University (covering both rural and urban areas) through advertisement posters placed in common areas and follow-up emails to those expressing initial interest. The recruitment time frame will span 3 months, allowing sufficient time to reach the target sample size and follow up with potential participants. Sample sizes are informed by established usability testing guidelines [42,47] and qualitative saturation guidelines [43], which suggest that 15 to 20 participants can identify approximately 90% of usability issues. If the recruitment target is not achieved, the recruitment period may be extended.

An online screening survey (10‐15 min) administered via QuestionPro (a platform licensed by La Trobe University) will determine eligibility. Potential participants will receive an email invitation with a link to the survey, accessible on various devices. Survey responses will be reviewed by authorized research personnel to confirm eligibility. Eligible participants will complete an initial survey (30‐45 min) collecting baseline data on familiarity with digital applications, current use patterns of similar applications, and expectations for the web application interface. This will be followed by accessing the web application via a provided link, with guidance from the research team if needed. Participants will be assigned a unique ID code for logging into the web application instead of using email or personal information.

Over the 3-month study period, participants will regularly interact with the web application’s interface and features, including navigating information pages, using the reminder system, using the goal-setting feature, and engaging with gamification elements. Weekly interaction is expected to be 15 to 30 minutes per week. These interactions will help evaluate usability and user satisfaction aspects of the design. Midway through the study (after 1.5 months), participants will complete a mid-study survey (30 min) providing feedback on their experience with the interface and specific design elements. At the end of the study, participants will complete a final survey (30 min) evaluating overall user experience and satisfaction with the web application design.

Real-time use analytics will be extracted from Firebase, including retention rates, feature interactions, navigation patterns, and session duration. These data will be analyzed descriptively to contextualize self-reported findings. Over the 3-month period, participants are expected to dedicate approximately 6 to 9 hours in total.

Survey instruments have been developed based on the TTF [22] and UTAUT [23] constructs, assessing usability, usefulness, and satisfaction.

The TTF [22] and UTAUT [23] are used as organizing frameworks to structure data collection and interpretation.

The TTF [22] assesses the degree to which technology assists individuals in performing their tasks. For MiCARE, TTF evaluation examines the alignment between young adults’ wellness self-management needs and the platform’s features. Key constructs include task characteristics (eg, goal setting and information seeking), technology characteristics (eg, feature functionality and interface design), fit between tasks and technology, and performance impacts (eg, ease of wellness management).

The UTAUT [23] identifies factors influencing technology adoption. For MiCARE, UTAUT evaluation examines performance expectancy (perceived usefulness), effort expectancy (ease of use), social influence (peer recommendations), facilitating conditions (technical support and accessibility), and behavioral intention (likelihood of continued use).

To support transparent interpretation and inform progression decisions, the following a priori success thresholds are defined:

Failure to meet these thresholds will prompt targeted design refinements prior to further evaluation. Meeting these thresholds will justify progression to a larger, more diverse sample evaluation.

Findings will be disseminated through (1) peer-reviewed journal publications in digital health, human-computer interaction, and health informatics venues; (2) conference presentations at workshops focusing on digital health, user experience design, and preventive health; (3) summary reports provided to participants highlighting key user experience insights; and (4) recommendations shared with La Trobe University and the broader digital health community.

The research team comprises transdisciplinary specialists in digital health innovation, implementation science, software engineering, human-computer interaction, and health informatics.

This protocol documents the systematic technical implementation and formative usability evaluation of MiCARE, a theory-driven PWA designed to support wellness engagement among young adults. Through comprehensive specifications grounded in multiple theoretical frameworks—SDT [16], the CARE framework [48], UCD [18], inclusive design [19], DSRM [20,21], TTF [22] and UTAUT [23]—we demonstrate a replicable methodology for translating multitheoretical frameworks into functional digital health interventions and conducting early-stage usability assessment.

The implementation methodology prioritizes transparency through web technologies, replicability through standardized architectural patterns, and accessibility through WCAG compliance [46]. By documenting code-level design rationale alongside theoretical foundations, this work provides digital health researchers and developers with a practical template for translating engagement frameworks into deployable interventions.

Few published studies document the technical translation from design specifications to functional software [38]. This protocol addresses the gap between conceptual frameworks and deployed interventions. This protocol provides comprehensive documentation of the full implementation process, enabling future researchers to adapt or extend the methodology.

The integration of behavioral theory (SDT and CARE) with implementation frameworks (DSRM, UCD, and inclusive design) and evaluation models (TTF and UTAUT) demonstrates a systematic approach to digital health development. This aligns with calls for theory-driven development in digital health [36,37] and addresses the need for rigorous evaluation methodologies [49]. This work is positioned as a design and implementation protocol accompanied by formative usability evaluation.

The JavaScript approach offers methodological advantages for research contexts. Unlike framework-dependent implementations, our approach remains interpretable without specialized knowledge, facilitating future maintenance by diverse research teams. This transparency aligns with open science principles and reproducibility standards in digital health research [50]. The Firebase-based data architecture demonstrates the practical application of serverless backend patterns in digital health research, minimizing DevOps complexity while maintaining scalability for future deployment.

Several limitations constrain interpretation and generalizability. First, the phase 4 evaluation recruits only 20 participants from a single university (La Trobe), all of whom are English-speaking, limiting external validity. This convenience, single-site, student sample supports heuristic usability discovery only and does not permit generalizable claims about acceptability, adoption, effectiveness, equity, or cultural tailoring beyond this specific setting. Accordingly, the TTF and UTAUT frameworks are applied descriptively and exploratorily only, and the study is not powered to test or validate relationships between theoretical constructs. This limitation is appropriate and expected for formative usability testing. Second, the implementation has been tested only in local development environments without deployment to production infrastructure. The planned phase 4 usability evaluation will assess real-world performance under authentic use conditions. Third, the exclusion of non-English speakers from the study is a major limitation, reducing the applicability and usability of the digital platform by culturally and linguistically diverse groups. Although the system architecture is designed to support multilingual features, only the English-language interface is deployed and evaluated in this study.

Future work will build on the MiCARE platform’s design and data from phases 3 and 4 by conducting larger-scale evaluation with more diverse samples. Emphasis will be placed on increasing user diversity by including culturally and linguistically diverse populations and individuals with varying levels of digital literacy, addressing key barriers to equitable access identified in digital divide research. Factors such as socioeconomic status, internet access, and device availability, which exacerbate the digital divide, will be assessed to optimize platform uptake and use across diverse populations. A mixed methods approach will be used, combining quantitative data with qualitative insights to evaluate implementation outcomes and user engagement. To enhance inclusivity, multilingual interface support (expanding beyond English) and simplified navigation for users with lower digital literacy will be integrated, leveraging the scalable Firebase architecture and WCAG 2.1 AA compliance established in phase 3. Recruitment will expand beyond La Trobe University to community-based settings across rural and urban Victoria, Australia, ensuring a more representative sample of young adults. Subsequent phases will incorporate powered hypothesis testing with prespecified behavioral end points and corresponding analysis plans. Findings will inform scalable deployment strategies and contribute to the evidence base for theory-driven digital health interventions, addressing the gap between conceptual frameworks and real-world implementation.

This study contributes a transparent design and implementation protocol for developing and evaluating MiCARE, a theory-driven PWA designed to foster sustained wellness engagement among young adults. By integrating SDT, CARE, UCD, inclusive design, DSRM, TTF, and UTAUT frameworks, this protocol bridges the critical gap between conceptual design and deployable digital health interventions. The systematic implementation of 6 core features, including an empathetic chatbot, learning hub, user-defined goal setting, gamification, personalized reminders, and progress dashboard, alongside a formative mixed methods usability evaluation aims to assess usability, usefulness, and satisfaction among a convenience sample of university-affiliated young adults. This work demonstrates a multitheoretical, user-centered PWA specifically tailored for preventive health engagement, addressing chronic disease risks such as prediabetes through culturally sensitive and accessible digital tools through a formative evaluation.