Design–Engineering Synergy in Healthcare: Developing a Human-Centered Self-Injection System for Infertility Treatment

Abstract

Infertility treatment often requires patients to self-administer hormonal injections, creating significant physical, logistical, and psychological burdens. While medical technologies have improved pharmacological efficacy and safety, design aspects addressing usability, portability, and emotional distress remain underexplored. This study presents Blloom, a compact self-injection device that integrates ergonomic, thermal, and emotional considerations designed through an interdisciplinary design-thinking framework. This study identified critical user needs related to self-injection anxiety, medication refrigeration, and treatment-related stigma through in-depth, multi-method qualitative design research. The resulting prototype is characterized by one-handed operation, concealed needle delivery, and built-in passive cooling (2–8 °C for up to 8 h). Formative evaluations with patients and clinicians confirmed its improved usability, emotional comfort, and contextual compatibility. At this prototypical stage, medication- and container-specific compatibility, as well as long-term reliability, require further bench testing and clinical validation. Process analysis further revealed how designer–engineer collaboration evolved from empathic exploration to implementation-driven convergence. The findings demonstrate how human-centered design can mitigate the multidimensional burdens of infertility treatment and provide a replicable framework for interdisciplinary innovation in self-managed healthcare devices.

1. Introduction

Infertility imposes economic and accessibility challenges, as well as considerable psychological and behavioral burdens on both patients and their partners. The recurring cycles of expectation and disappointment during treatment, fear of self-injection, and the requirement for strict refrigeration profoundly affect patients’ everyday routines and emotional stability.

In recent years, the demand for infertility treatments has risen sharply in many countries—including South Korea—amid growing concerns over declining birth rates [1], as shown in Figure 1. Most infertility therapies involve patients self-administering ovulation-inducing hormone injections into the abdomen at prescribed times each day. Throughout this process, pain, complex preparation steps, and the inconvenience of storage and portability frequently undermine aspects including usability, adherence to treatment, and the overall patient experience. The World Health Organization (WHO) reports that one in six adult couples worldwide experience infertility, identifying it as a major public health concern [2]. Infertility is a global health issue that transcends income levels, with high medical costs, social stigma, and psychological distress as its primary accompanying burdens. A photograph of a newborn surrounded by 1616 IVF needles captures this problem with effectively [3].

However, existing research on medical devices remains largely centered on safety and technical efficiency, with relatively little attention devoted to design approaches that incorporate user experience (UX) perspectives. While medical technologies have long prioritized pharmacological efficacy and technical safety, recent scholarship underscores that usability, emotional comfort, and human-centered design are equally critical in achieving effective and sustainable healthcare outcomes. The design of medical devices is shifting from purely engineering-driven optimization toward integrated frameworks that balance technical reliability with UX and empathy. Studies published in Designs have demonstrated how design thinking methodologies and interdisciplinary collaboration can enhance both the functional and emotional performance of healthcare products [4,5,6,7]. In service design discourse, dignity has been articulated as a core principle that reframes user experience beyond functionality toward respect and autonomy [8]. Moreover, recent human-centered design frameworks applied to wearable medical devices have illustrated how empathetic and context-aware processes can mitigate psychological burdens and improve user engagement in treatment routines.

The application of design thinking in healthcare device innovation continues to evolve, as researchers emphasize user needs and systemic innovation across practice contexts [9]. The specific objective of this study is to systematically analyze user burdens and potential risks occurring during the self-injection stage of infertility therapy and to propose “Blloom”, an integrated device combining cooling and injection assistance. The two letters “ll” in “Blloom” represent the two lines on a pregnancy test—the sign of a positive result.

Many IVF patients repeatedly test during the waiting period, hoping to see those lines. The product brand name, Blloom, shows support for patients undergoing infertility treatment and embodies the hope symbolized by the pregnancy test’s two lines.

Through a user-centered design and prototyping process, this study aims to address existing usability gaps and contribute to the development of more empathetic and human-centered medical devices.

1.1. Our Process

The Double Diamond model systematizes the creative process of problem exploration, definition, development, and delivery through alternating phases of divergence and convergence and has been widely applied in social and healthcare design contexts [10,11,12,13,14]. Since its introduction by the UK Design Council in 2004, the framework has evolved into a universal methodology for public, industrial, and social innovation practices. This structured framework has been expanded in recent design research to include iterative reframing and co-creative dialog across disciplines, reinforcing its utility in complex public and healthcare contexts [15].

However, within the context of medical device development, the Double Diamond model often faces limitations in integrating with engineering-oriented development processes. Design collaboration studies highlight the inherent friction and eventual convergence between design and engineering teams in healthcare innovation projects [16]. Differences in disciplinary language, priorities, and roles between designers and engineers can result in parallel rather than collaborative workflows, hindering the full realization of human-centered innovation.

This study employed the Double Diamond process—comprising the Discover, Define, Develop, and Deliver phases, as shown in Figure 2—as the overarching framework for design and analysis.

• Discover/Define: Qualitative research and task analysis were conducted to identify user needs and constraints, leading to the derivation of key human factor (HF) requirements.
• Develop: Based on these findings, iterative product design and prototyping were carried out, with design alternatives evaluated from usability and safety perspectives.
• Deliver: The final stage involved performance and usability validation using functional prototypes, converging the outcomes toward a product-ready solution suitable for real-world implementation.

1.2. Current Status of Self-Injection Devices

Self-injection devices are generally classified into pen injectors, auto-injectors, and on-body delivery systems. The ISO 11608 [17] series defines the requirements and testing methods for bolus delivery needle-based injection systems (NISs), establishing standardized criteria for their safety and performance. Technological development in this field has primarily focused on drug stability, injection accuracy, and needle safety, leading to continuous advancement in pen- and auto-injector designs. However, patients continue to experience difficulties related to their limited ease of use, operational complexity, and the lack of portability, as medications must be maintained within the recommended temperature range of 2–8 °C. The self-injection device market has evolved mainly within the therapeutic domains of rheumatoid arthritis and diabetes, while no specialized solutions currently exist for infertility treatment.

Table 1. A comparative analysis of currently available self-injection devices.

	Regular Style	Pen-Type Syringe	Auto Syringe	Patch Type
Syringe	Image retrieved from http://tradeindia.com/products/premium-quality-glass-and-plastic-syringes-with-needles-8497648.html (accessed on 27 February 2026)	Image retrieved from https://handok.co.kr/product/detail?idx=249 (accessed on 27 February 2026)	Image retrieved from https://www.druginfo.co.kr/detail/sideEffect.aspx?pid=215833 (accessed on 27 February 2026)	Image retrieved from https://eopatch.com/main/main.html (accessed on 27 February 2026)
Product Features	Manual medication transfer required.	Cartridge-based medication with button dial operation.	Built-in automatic injection mechanism.	Adheres to skin for slow, automatic drug delivery.
Why it is Unsuitable for Infertility Treatment	Poor portability; needs refrigeration. Complex injection process; requires skill. Hygiene and exposure concerns outdoors.	Vertical injection prone to shaking and creates risk of bruising. Exposure and privacy concerns during outdoor use. Requires separate cooler for medication storage and transport.	Potential mechanical failures and high cost. Typically large and heavy, limiting portability.	Continuous delivery limits immediate injection. Limited attachment sites; discomfort with long wear.

Note. Columns indicate device types; rows describe the administration format, key features, and the main reasons for limited suitability in infertility self-injection.

shows the reasons why the existing solutions are not sufficiently suitable for infertility treatment in terms of portability and maintaining the recommended temperature range. A comparative analysis of currently available self-injection devices reveals persistent gaps between technical performance and emotional usability. While pen-type and auto-injectors offer basic convenience and reliability, they often expose users to visible needles or require preparatory steps that amplify procedural anxiety. Patch-type devices show promise in minimizing needle phobia and increasing discretion but are limited in terms of medication type, dose volume, or cooling constraints.

Across categories, few products address the combined needs of mobility, thermal stability, and psychosocial comfort, underscoring a market opportunity for integrated, emotionally considerate solutions.

1.3. Lack of Solutions to the Emotional and Procedural Burdens of Infertility Treatment

While several studies have sought to mitigate the burdens of infertility treatment—primarily through educational interventions or emotional support tools (see Table 2)—few have translated these insights into tangible changes in product design or clinical practice. To date, UX research has largely remained separate from device engineering, leaving a gap in addressing the intertwined psychological and procedural challenges of self-injection [18,19]. This study addresses that gap by proposing an integrated design–engineering approach that reconceptualizes self-injection as both a technical task and an emotionally fraught experience requiring holistic design intervention [20].

During infertility treatment, users experience multiple physical and psychological burdens, including those relating to medication storage, injection procedures, and emotional anxiety. These challenges extend beyond a simple medical act, evolving into a comprehensive UX issue that permeates the entire treatment process. Needle phobia has been reported in 20–50% of adolescents and 20–30% of adults and is closely associated with avoidance behaviors [21]. Therefore, interaction designs that minimize needle visibility play a crucial role in reducing patients’ psychological distress.

In addition, rFSH (recombinant follicle-stimulating hormone) cartridges must be stored within a temperature range of 2–8 °C and discarded within 28 days after opening, according to labeling guidelines. Thus, maintaining the proper temperature during transport and waiting periods is directly linked to the continuity and safety of treatment. Injection failures or improper medication storage not only reduce treatment adherence but also lead to fragmentation of patients’ daily lives through repeated negative experiences.

Table 2. Summary of previous studies on infertility treatment.

Previous Studies	Regular Style Pen-Type Syringe	Auto Syringe Patch Type
Brady et al., 2020 [22]	Adopting a self-management-oriented approach can enhance the woman’s sense of autonomy and locus of control, broaden their scope of choice, and contribute to reducing the overall burden on healthcare systems.	Self-management interventions can contribute to alleviating healthcare resource constraints by decreasing the need for frequent clinical visits.
Brew et al., 2023 [23]	The average cost of a single in vitro fertilization (IVF) cycle is estimated at USD 15,000–20,000, with repeated attempts often exceeding USD 40,000. Due to limited insurance coverage, infertility treatment remains financially inaccessible for low-income or uninsured individuals.	Within the United States, the combination of high treatment costs and limited accessibility serves as a significant barrier to care for many individuals and families affected by infertility.
Domar et al., 2018 [24]	Approximately 65% of patients undergoing IVF discontinue treatment before achieving a live birth, underscoring the importance of identifying the factors that lead insured women to terminate in vitro fertilization (IVF) therapy prematurely.	The psychological burden, or the so-called “burden of care,” has been identified as the leading cause of treatment discontinuation, irrespective of insurance status. Moreover, discontinuation of IVF treatment appears to be influenced more by cumulative mental and emotional fatigue than by economic limitations.
Verhaak et al., 2007 [25]	Symptoms of anxiety and depression commonly emerge during patients’ adaptation to in vitro fertilization (IVF) treatment.	There is a clear need to reduce the psychological burden experienced by patients.
Gameiro et al., 2012 [26]	The primary reasons for treatment discontinuation include delays in scheduling and the psychological and physical burdens experienced during treatment.	Simplification of treatment procedures and enhancement of usability are required.
McLenon and Rogers, 2019 [21]	Injection-related fear is reported in approximately 20–30% of the adult population.	There is a need for needle concealment and simplification of the injection procedure.

Table 2. Summary of previous studies on infertility treatment.

Previous Studies	Regular Style Pen-Type Syringe	Auto Syringe Patch Type
Brady et al., 2020 [22]	Adopting a self-management-oriented approach can enhance the woman’s sense of autonomy and locus of control, broaden their scope of choice, and contribute to reducing the overall burden on healthcare systems.	Self-management interventions can contribute to alleviating healthcare resource constraints by decreasing the need for frequent clinical visits.
Brew et al., 2023 [23]	The average cost of a single in vitro fertilization (IVF) cycle is estimated at USD 15,000–20,000, with repeated attempts often exceeding USD 40,000. Due to limited insurance coverage, infertility treatment remains financially inaccessible for low-income or uninsured individuals.	Within the United States, the combination of high treatment costs and limited accessibility serves as a significant barrier to care for many individuals and families affected by infertility.
Domar et al., 2018 [24]	Approximately 65% of patients undergoing IVF discontinue treatment before achieving a live birth, underscoring the importance of identifying the factors that lead insured women to terminate in vitro fertilization (IVF) therapy prematurely.	The psychological burden, or the so-called “burden of care,” has been identified as the leading cause of treatment discontinuation, irrespective of insurance status. Moreover, discontinuation of IVF treatment appears to be influenced more by cumulative mental and emotional fatigue than by economic limitations.
Verhaak et al., 2007 [25]	Symptoms of anxiety and depression commonly emerge during patients’ adaptation to in vitro fertilization (IVF) treatment.	There is a clear need to reduce the psychological burden experienced by patients.
Gameiro et al., 2012 [26]	The primary reasons for treatment discontinuation include delays in scheduling and the psychological and physical burdens experienced during treatment.	Simplification of treatment procedures and enhancement of usability are required.
McLenon and Rogers, 2019 [21]	Injection-related fear is reported in approximately 20–30% of the adult population.	There is a need for needle concealment and simplification of the injection procedure.

While prior self-injection research (e.g., Lange et al., 2014 [27]; Elkefi et al., 2023 [28]) has focused on ergonomic optimization, no study has integrated passive refrigeration and concealment design within infertility treatment devices. This study bridges this gap by using a Double Diamond-driven interdisciplinary approach.

2. Methods

2.1. Discover Phase

This study aimed to design a self-injection device that alleviates the physical and emotional burden experienced by patients undergoing infertility treatment, based on an in-depth understanding of their treatment experiences. The design outcome was derived by applying the Double Diamond design process.

2.1.1. Conducting Desk Research

This research involved a comprehensive review of the existing literature and prior studies to analyze the global landscape of infertility treatment and the characteristics of patients’ experiences. The WHO [3] reports that one in six adult couples worldwide experiences infertility, while the average success rate of in vitro fertilization (IVF) remains as low as 30–40%. Patients typically undergo more than seven treatment cycles, each costing approximately USD 12,000–20,000 in the United States. These figures highlight that infertility treatment extends beyond a medical procedure, representing a complex process intertwined with economic, emotional, and social burdens.

2.1.2. Mapping the User Journey

As shown in Figure 3, the infertility treatment process is structured into five stages—trying to conceive → diagnosis → artificial insemination (AI) → in vitro fertilization (IVF) → successful pregnancy—which are visualized to illustrate patients’ experiential and emotional transitions across each touchpoint. Patients perform self-injections up to three times per day and as many as three injections per treatment cycle, maintaining this routine for over a month. Some medications require refrigeration at 2–8 °C to ensure their stability. Repeated tests and medical procedures lead to accumulated physical fatigue and exacerbate anxiety and psychological pressure related to treatment outcomes.

The infertility treatment journey is further analyzed and visualized according to the same sequence of stages, emphasizing UX and emotional fluctuations throughout the process. Patients repeatedly perform self-injections—up to three times daily and up to three per treatment cycle—for periods exceeding one month, while certain medications must be stored under refrigeration at 2–8 °C. Such repetitive injection routines, together with continuous examinations and procedures, intensify both physical exhaustion and emotional distress associated with the uncertainty of pregnancy success. Through this analysis, four major problem domains were identified within the patient experience: discomfort during self-injection, challenges in medication storage, mobility constraints, and emotional anxiety. Product design for stigmatized health conditions must consider how form, portability, and symbolic cues influence users’ willingness to adopt and carry devices publicly [14].

2.1.3. Mapping Key Stakeholders

The stakeholders involved in infertility treatment were structured along two axes (as illustrated in Figure 4): core vs. supplementary and direct vs. indirect involvement. The major stakeholders include infertility patients, spouses and families, medical professionals, hospitals, pharmaceutical companies, and governmental and insurance institutions. Patients directly experience the physical, emotional, and financial burdens associated with ongoing treatment, while spouses and families provide emotional and financial support. Medical professionals are responsible for clinical care, consultation, and the accompanying emotional labor, whereas hospitals and pharmaceutical companies supply the necessary infrastructure and medications. Governmental and insurance systems play a decisive role in sustaining treatment by offering financial subsidies and policy support. This stakeholder interaction analysis revealed that patients’ experiences are dynamically mediated within a multi-layered network of interdependent actors.

2.1.4. Analyzing Online Patient Communities

Authentic user expressions were collected from Naver Cafes and KakaoTalk open chatrooms—two of the most prominent online communities in South Korea—and the everyday contexts of infertility patients were further observed via YouTube vlogs. Recurrent statements such as “I tend to stay home because of infertility treatment,” “The cooler bag is too large to carry around,” and “I feel anxious about injecting myself in public restrooms due to hygiene concerns” were frequently identified. Through this analysis, three core pain points were derived from the infertility patient experience: social isolation, limited portability, and anxiety toward external environments.

2.1.5. Conducting In-Depth Interviews

Interviews were conducted with a total of nine infertility patients via a combination of phone calls, video conferences, and in-person sessions (see

Table 3. Participant profiles for in-depth interviews.

Participant No.	Age	Interview Method	No. of Treatment Cycles	Current Status
1	41~45	Phone	33 IVF	Unsuccessful
2	41~45	Video call	11 IVF	Successful
3	31~35	In-person	3 AI; 1 IVF	Successful
4	36~40	Questionnaire	5 IVF	Successful
5	31~35	Questionnaire	8 IVF	Successful
6	36~40	In-person	9 IVF	In treatment
7	31~35	In-person	2 IVF	Successful
8	36~40	Phone	2 IVF	In treatment
9	31~35	In-person	3 AI; 2 IVF	Successful

). Participants had undergone an average of 14 treatment cycles.

A semi-structured interview protocol was used to explore participants’ experiences of infertility treatment and self-injection. The guiding questions included:

• Treatment Experience: “Can you describe any memorable difficulties or discomfort you experienced during infertility procedures, medication intake, or diagnostic tests?”
• Medical Device Usability: “Have you ever felt that the instructions or operation methods of medical devices (e.g., injection devices) were unclear or insufficient?”
• Self-Injection Experience: “When performing self-injections, have you experienced confusion about dosage, medication type, or injection procedures? Can you describe that moment?”
• Information Delivery: “Did you feel that the information provided by hospitals or pharmacies (e.g., dosage, order, duration) was sufficient and easy to understand?”
• Personal Coping Strategies: “Have you developed any personal strategies to reduce pain, anxiety, or mistakes during injections (e.g., changing needles, labeling medications)?”
• Time and Schedule Conflicts: “Have you ever had to modify or cancel work, appointments, or travel plans due to treatment schedules?”
• Public or Workplace Context: “Have you experienced discomfort or anxiety when administering medication (e.g., injections or vaginal suppositories) outside the home, such as at work or in public places?”
• Storage and Portability: “How do you usually store your medications, especially those requiring refrigeration? Have you experienced inconvenience when carrying medication outside the home?”
• Disposal Routine: “How do you dispose of used needles and syringes? Have you ever experienced uncertainty, inconvenience, or safety concerns related to disposal?”
• Overall Improvement Needs: “If you could improve any aspect of the current treatment or self-injection process, what would you change?”

The interviews revealed common challenges among patients, including emotional burdens such as anxiety, stress, and social isolation; physical fatigue resulting from repeated injections and procedures; and difficulties in balancing daily life and work due to the need for refrigerated storage of medications.

2.1.6. Performing Role-Playing Simulations

In the preceding research phase, desk research, a user journey map, a stakeholder map, analysis of online communities for infertility patients, and in-depth interviews were conducted to explore patients’ experiences and challenges from multiple perspectives. However, as these approaches were limited to indirect observation and verbal data, it was difficult for the team to directly perceive and empathize with patients’ concrete discomforts. To gain an experiential understanding of the situations patients face and to identify a commonly shared core pain point, the team conducted self-injection scenario experiments in various public settings, including bathroom sinks, buses, bus stops, and park benches, as demonstrated in Figure 5.

When performing the procedure while carrying a bulky cooler bag like those used by actual infertility patients during outings, the team observed that the burden of public attention, concerns about hygiene, inconvenience due to the need to use both hands, and psychological pressure to complete the injection quickly occurred simultaneously. Through this process, it was verified that existing self-injection devices are not adequately suited to patients’ real-life contexts and that the discomforts previously described only in emotional terms could be identified more concretely at the behavioral (task) level.

2.2. Define Phase

In this phase, key user pain points were identified using an affinity diagram, and the final How Might We (HMW) questions were formulated through processes of problem redefinition, design ideation clustering, and design requirements.

2.2.1. Identifying Key User Pain Points

User statements collected during the Discover phase, including interview summaries and role-playing observation notes, were segmented into individual Post-it units. Through three iterative affinity diagram sessions, the team reorganized the data into meaningful clusters while examining causal relationships and contextual links among categories. The classification process employed a grid structure consisting of “statement basis, memo, and design implication.” Ultimately, eight key pain points and corresponding user needs were derived through team consensus:

• Pain and anxiety from repeated injections: Daily injections cause physical pain and psychological anxiety, undermining patients’ ability to maintain treatment adherence.
• Fatigue from hospital visits: The entire hospital process (including scheduling, waiting, and consultation) is perceived as highly challenging and, when combined with the self-injection routine, amplifies overall treatment fatigue.
• Disposal after use: A lack of clear information regarding the timing and method of disposal leads to confusion, and some patients express concern that the drugs or syringes might be mistaken for controlled substances.
• Persistent uncertainty: The waiting period for pregnancy results after each treatment cycle generates tension and frustration, causing patients to perceive the entire treatment as an anxiety-inducing and distressing experience.
• Stigma and diminished self-perception: Due to social stigma surrounding infertility, patients often attempt to conceal their injection behavior, leading to decreased self-efficacy and withdrawal from social interactions.
• Disruption of daily routine: Requirements such as refrigerated storage, transportation, and time management for injections disrupt daily patterns, creating a sense of separation between everyday life and treatment.
• Procedural and cognitive burden: Complex steps such as drug mixing, dosage adjustment, and injection angle management are challenging for non-experts, leading to heightened anxiety during administration.
• Unhygienic and confined injection environments: Patients frequently need to self-inject in confined or unsuitable spaces such as restrooms or vehicles during daily activities, causing both hygiene concerns and physical discomfort.

2.2.2. Redefining the Core Problem

The current self-injection process for infertility treatment involves complex procedures of medication refrigeration, preparation, administration, and disposal, intertwined with social stigma and psychological anxiety. As a result, it is difficult for patients to perform injections naturally within their daily routines, leaving them continuously exposed to physical pain, emotional distress, and potential risks of misuse.

Accordingly, this study aimed to design a UX that seamlessly integrates infertility treatment into everyday life. Two core design directions were established—lifestyle compatibility (anywhere/anytime/one-hand) and injection reliability (safe/clean/certain)—emphasizing both the adaptability of treatment within daily contexts and the assurance of safe and reliable administration.

2.2.3. Clustering and Refining Design Ideas

Alleviation of social and psychological burden: The injection experience is recontextualized into an everyday-friendly routine that does not require concealment of the act, achieved through the integration of the injector with clothing or accessories and the reduction in public visibility.

• Intuitiveness and safety in preparation: Minimizing user burden through automation of drug mixing and setup, combined with an injection site design that reduces visual exposure.
• Resolution of disposal and hygiene issues: Ensuring safety and hygiene with a compact, modular disposal system, a disguised outer case, and a secure sealing structure.
• Enhanced routine compatibility: Improving ease of execution in daily contexts through a structure that allows one-handed administration anywhere.
• Reduction in uncertainty during injection: Providing users with a sense of confidence through multimodal feedback that indicates progress and completion, as well as emotional support elements.
• Exploration of alternative delivery methods: Examining the potential of non-injection drug delivery approaches, such as transdermal patches and microneedle systems.

These insights informed the functional and emotional design targets of the Blloom prototype, leading to the integration of concealed injection, ambient portability, and passive cooling—features that directly address the anxiety, spatial limitations, and social stigma identified during user research.

2.2.4. Deriving Design Requirements

Through the above process, specific design requirements were identified to guide the development of an infertility self-injection device that enables treatment to be seamlessly integrated into everyday life, comprising the following:

• A self-injection process operable with one hand;
• A needle-concealed structure;
• An integrated cooling module with intuitive temperature visibility;
• Sensory feedback indicating injection completion;
• A user environment that shields external visibility.

Based on these insights, the final HMW statement was defined: “How might we help infertility patients perform self-injections safely and comfortably without disrupting their daily routines or attracting unwanted attention?”

2.3. Develop Phase

Based on the HMW question derived from the Define phase, this study established three key design goals.

2.3.1. Establishing Design Goals

Goal 1: Discreet injection

The device was designed with a compact and slim form that can be easily carried in a bag or pouch, enabling patients to administer injections comfortably in everyday environments, such as public transportation, workplaces, or cafes. During the design phase, a disposable syringe was disassembled, and its internal components, including the plunger, cylinder, and needle connection, were analyzed. We then realized that, instead of a conventional vertical injection structure, a horizontal cartridge insertion system could achieve our goal of creating a discreet injection device. By fixing the plunger inside the main body and allowing only the cartridge to be replaced, we minimized the overall volume of the device while ensuring stable drug delivery.

Goal 2: One-handed injection

Conventional self-injection requires one hand to lift the skin and the other to inject, making public use challenging. To address this, the injector shell includes an apparatus that gently secures the skin, eliminating the need for manual pinching. When placed against the abdomen, the device naturally holds the skin in position, enabling a stable one-handed injection with a single button press.

Goal 3: Portability and suitability for female users

Considering the primary user group, female patients, the device dimensions were designed to fit the average adult female hand size (width: 7–8 cm; length: 16–17 cm). The overall profile was kept thin and flat to fit comfortably in the hand, while the injection button and cartridge slot were clearly distinguished to balance operability and portability.

During the Develop phase of the Double Diamond design process, low-fidelity prototyping, participatory design sessions, and form factor and mechanism design were carried out to propose a feasible concept while achieving the three main design goals.

2.3.2. Developing Low-Fidelity Clay Prototypes

To achieve our design goals, clay prototypes of various sizes and forms were created as our first low-fidelity physical prototypes. The clay prototypes were made by directly holding and simulating injection motions. They were intended to evaluate operability and usability. To determine the optimal button position, the location was adjusted so that it could be pressed with different fingers, such as the thumb and index finger, in order to to identify the most stable and intuitive control point. Models with different cross-sectional shapes, including cylindrical, oval, and flat forms, were produced, as shown in Figure 6, and could be used to compare and assess portability and grip comfort in everyday use.

A 3D CAD model was developed based on the optimal form derived from the clay prototypes, and the actual size and handling were verified using 3D printing.

2.3.3. Conducting Participatory Design Sessions

A participatory design session was organized to incorporate the real experiences of both users and experts into the design process. The session included one infertility patient, two nurses, two engineers, and two designers, lasting approximately three hours (

Table 4. Participant profiles for participatory design sessions.

Participant No.	Participant Group	Domain Background	Expertise Type
1	Individual with infertility experience	Engineering	Academic
2	Engineering faculty	Engineering	Clinical
3	Nursing professional	Healthcare	Clinical
4	Nursing professional	Healthcare	Student
5	Engineering student	Engineering	Student
6	Engineering student	Engineering	Student
7	Design student	Design	Student
8	Engineering student	Design	Student

).

The procedure consisted of four stages: self-injection role playing, sharing of discomfort experiences, ideation and clay prototyping, and voting and validation. Figure 7 depicts how this session was conducted.

The key insights from the session were as follows:

• Dose tracking: Reflecting the nurses’ feedback that “unlike insulin, infertility injections require remembering how many doses have been administered,” the need for a transparent cylinder and a dosage-tracking window was identified.
• Portability: The infertility patient emphasized that “a device meant to be used only at home is unrealistic,” highlighting the importance of compact sizing comparable to a pencil case.
• Hygiene procedure: All participants agreed that skin disinfection is essential and reached a consensus that this step should remain user-initiated.
• Feedback: Based on the comment that “I need feedback confirming that the medication has been fully delivered,” a mechanical feedback structure at the end of the plunger was proposed.

Prior research has shown that self-injection usability is significantly influenced by intuitive affordances and interface clarity. For example, formative studies on pen-type injectors revealed that structured visual cues and one-handed operation can reduce errors and cognitive load during administration [27]. Our findings mirror this pattern: users consistently favored Blloom’s concealed needle, simplified single-button interface, and compact size, which enabled discreet and stable use. Therefore, we decided to maintain the concept of a small, flat form factor that can be discreetly used under clothing and set 3D-modeling-based prototype development as the next step.

This session also clarified that we needed to incorporate a mechanical feedback feature that confirms when the medication has been fully delivered. One infertility patient remarked, “I feel like I could inject at my office desk instead of hiding in the restroom now.” This insight suggests that the proposed prototype has the potential to shift injection behavior from hidden, private spaces to more open, everyday environments, highlighting its impact on UX and behavioral change.

3. Results

3.1. Refining the Form Factor and Engineering the Mechanism

Several form factors were produced using 3D printing based on the form validated using the clay models (Figure 8). We evaluated button accessibility, grip comfort, and overall handling by manually testing various form factors and then selected the most comfortable shape through a preliminary vote. Based on usability findings, the chosen form factor was further refined and prototyped, and a rounded, pebble-like form with a single button was ultimately selected through repeated comparative evaluations. This design decision aimed to soften the cold, sharp image of conventional syringes and provide a gentle and reassuring UX.

This usability-driven form factor, however, required a critical engineering decision. The conventional vertical injection architecture had to be reconfigured into a horizontal layout to realize a flat, palm-sized device suitable for one-handed use. This transition introduced strict constraints on the device’s overall scale, particularly its height, as internal components—including the needle path and force transmission mechanisms—needed to be rearranged without compromising functional reliability. Such usability-driven structural reconfigurations and scale-related constraints have been widely discussed in the medical device engineering literature, where ergonomic requirements directly influence system architecture and feasibility [4,6]. As a result, scale—especially the vertical dimension—became a central point of negotiation between designers and engineers, shaping subsequent mechanism selection and structural refinement within a human-centered medical device design framework [7].

Once the form factor was chosen, the next step was to work on the mechanism to make it feasible. The mechanism was developed through a series of iterations described in Figure 9. From a human factors engineering standpoint, ergonomic injectors that require minimal grip strength and cognitive processing are more acceptable to first-time users. A recent study emphasized the importance of anthropometric compliance and safety affordances in auto-injector design [28].

Our engineers aligned this by proposing a single-handed mechanism and fail-safe alignment features that reflected the following principles:

• Dual button + longitudinal wedge: In this mechanism, two buttons are pressed sequentially to move the wedge, which then positions and fixes the cartridge at the injection height. Safety can be improved by separating the insertion and injection steps; however, the multi-step operation introduces complexity, making intuitiveness a key challenge.
• Spring-loaded holder: This mechanism uses stored spring energy to insert the needle, allowing the user to inject the medication with a single button press once the spring is activated. However, recompressing the spring via button movement adds structural complexity.
• Lateral wedge + rack and pinion + height lock: This design combines lateral wedges with a rack-and-pinion mechanism to maintain a constant needle angle. Adding a height lock system enhances needle stability during repeated use. Nevertheless, improved stability increases structural complexity, manufacturing difficulty, and potentially enlarges the overall product size.
• Pear-shaped cam: In this configuration, four pear-shaped cams rotate to move the cartridge downward. The cams enable stable needle descent as they rotate from 0° to 90°, but once the cartridge reaches its lowest position, it cannot maintain height if the cam rotates further due to a single peak distance. Consequently, a new cam design was required to sustain the needle position during injection.
• Semi-circle cam: This mechanism uses a semi-circular cam to lower the cartridge to its minimum position and maintain that height throughout the injection process. Because insertion and injection occur in a single motion, usability is significantly improved. However, potential wear from repeated use must be considered.

All structural dimensions were designed based on the average hand size of adult women in South Korea, and the semi-circle cam mechanism was ultimately adopted. The button width was also optimized according to the average female finger width (1.6–1.8 cm) [29].

3.2. Validating the Prototype Through Subject Matter Expert Review

The final prototype integrated a passive cooling unit (maintaining 2–8 °C for up to 8 h), a concealed needle actuator with one-button operation, and an automatic tissue-lifting mechanism. The form was optimized for discreet carrying in daily-use bags. These features were then subjected to formative evaluation. Before progressing further in the Develop phase, the low-fidelity prototypes, evolved through the definition of the form factor and mechanism design, were subjected to initial validation by subject matter experts (SMEs). “Subject matter experts (SMEs)” are people with specialized knowledge or talent that are needed by agile development teams and usually refer to SMEs who are “outside” the team [30].

The prototype was reviewed by a multidisciplinary panel of subject matter experts to supplement user-centered insights with clinical and regulatory perspectives. This included a professor of medical device usability engineering at Yonsei University College of Medicine with over 20 years of industry and regulatory experience; an obstetrician–gynecologist at CHA Bundang Medical Center with more than 10 years of clinical experience specializing in infertility; a public health consultant with a doctoral degree and prior roles in clinical research organizations (CROs) and biotechnology startups; and two senior engineers from a global consumer product engineering company, comprising a Senior Engineering Manager (with 14 years of experience) and a Head of Engineering (with 13 years of experience).

Their evaluations provided critical feedback on device classification, medication compatibility, the safety of the automated tissue-lifting mechanism, and the clinical relevance of refrigerated storage integration. The key insights from these expert interviews included the following:

• The device should be classified as a composite medical device integrating storage and administration functions, not a simple injector.
• A 2 mL dose capacity with compatibility for multiple infertility medications was identified as clinically appropriate.
• While manual skin pinching is standard practice, an automated lifting mechanism could enhance injection accuracy and user safety.

In this study, we consider compatibility within a dedicated Blloom cartridge format that accommodates commonly used subcutaneous fertility treatment injectables up to a 2 mL dose capacity. Accordingly, the current prototype is not directly interchangeable with commercially available pen injectors or standard syringes.

These evaluations underscored Blloom’s feasibility as a combination product and emphasized the need to align usability innovations with clinical protocols and regulatory frameworks in future development stages.

3.3. Evaluating Usability Through a Design Thinking Workshop

To further examine the usability and contextual fit of the final Blloom prototype, we conducted a design thinking workshop with two participant groups: (1) clinical experts, including four nurses and one preventive medicine specialist, and (2) three individuals with lived experience of infertility treatment, including one partner of a woman undergoing infertility treatment. The clinical expert group evaluated the prototype from a medical and practice-oriented perspective, focusing on whether the interaction flow and device concept were acceptable within typical injection routines. Separately, participants with infertility experience interacted directly with the prototype to reflect on its practicality and perceived comfort in real-world use, as illustrated in Figure 10.

The two groups were engaged in separate sessions to minimize bias and prevent experiential participants from being overly influenced by expert opinions. Feedback was collected via guided discussions and hands-on walkthroughs of the prototype, as shown in Figure 10. In addition, all clinical experts independently completed a System Usability Scale (SUS) assessment using a five-point response format. This approach enabled us to capture both overall perceived usability and more granular feedback, including process-related pain points, perceived advantages, satisfaction with specific functions and design elements, and step-by-step usability issues. The workshop also provided an opportunity to gather concrete improvement suggestions directly from both experts and users with lived experience. The evaluation focused on the ease of one-handed operation, the clarity of the injection sequence, the perceived safety of the concealed needle mechanism, and emotional comfort during use.

3.4. Proposing the Final Blloom Self-Injection System

This study finalized the integrated self-injection device Blloom via iterative prototyping and user feedback. The key features of Blloom are summarized in Figure 11, with illustrated user scenes.

The designer–engineer collaboration established four main benefits for users.

• Enhanced portability: The device adopts a thin, flat form factor that fits easily into a bag or pouch, reducing the total volume of supplies carried during treatment-related outings by approximately 85%.
• Simplified, one-handed operation: A button-based, single-action mechanism enables injections without multi-step preparation. An integrated plunger with tissue-grip functionality supports stable, intuitive one-handed use.
• Discreet, safe use in everyday contexts: The device is designed for natural, unobtrusive administration under clothing (e.g., lower abdomen/waistline), allowing patients to inject without drawing attention in public settings.
• Built-in insulated storage: An internal cooling module maintains medication within the recommended temperature range (2–8 °C) for up to 8 h, enabling safe transport and storage without a separate cooler bag.

4. Discussion

4.1. Evaluating Blloom’s Contribution to the Medical Device Market

Fear of needles and anxiety over procedural correctness are among the most cited barriers in self-managed therapies. Disposable auto-injector studies have highlighted how design-related use errors—particularly those stemming from ambiguous feedback or inadequate handling space—undermine user trust and adherence [31]. In contrast, Blloom’s design reframed this experience by minimizing user exposure to the needle and enabling flexible injection locations, thereby reducing treatment-associated stress.

While the formative evaluation of Blloom highlights its effectiveness in alleviating usability and emotional burdens associated with infertility self-injection, several nuanced implications warrant further discussion. First, the promising user feedback—centered on reduced anxiety, enhanced discretion, and intuitive operation—suggests that design thinking can tangibly improve patient agency in stigmatized medical routines. However, this also raises a methodological consideration: the empathic design insights, though deeply contextualized, are inherently situated within a limited cultural and clinical cohort. Consequently, the generalizability of these insights to broader, multi-ethnic, or low-resource contexts remains an open question for translational research.

Second, clinicians’ recognition of Blloom as a viable training aid underscores its pedagogical potential. Nevertheless, this feedback also reveals a latent opportunity space: the device could be developed further as a transitional tool for patients newly entering self-administered care, particularly in assisted reproductive technologies (ARTs). Such use cases may require differentiated interaction models or modular components tailored to varying skill levels and treatment regimens. While the current prototype does not yet include features such as tactile feedback or dose visibility, future iterations could incorporate such elements to enhance device familiarity and self-efficacy, particularly among novice users. Prior studies have shown that these features can significantly improve patient trust and reduce misuse in pen-type injectors [32].

Finally, while the integration of cooling, concealment, and ergonomic design demonstrates how interdisciplinary collaboration can reconcile technical constraints with emotional intelligence, market deployment introduces regulatory, cost, and manufacturing challenges not yet addressed in this prototypical phase. Therefore, the design thinking process must be extended beyond ideation and validation to include strategic planning for clinical trials, reimbursement frameworks, and adoption within diverse healthcare infrastructures.

Given the invasive nature of self-injection, we explicitly considered use-related safety risks at the task level and translated them into design requirements. Key risks include (1) anxiety-driven hesitancy or incomplete administration, mitigated by needle concealment and a simplified single-action operation; (2) contamination risk in constrained everyday environments, mitigated by minimizing handling steps and enclosing the cartridge during use; and (3) uncertainty about completion, which motivates the addition of clearer confirmation feedback in future iterations. These considerations will be further formalized through risk management and usability engineering in subsequent development stages.

4.2. Analyzing Designer–Engineer Collaboration Within the Double Diamond Framework

Analyzing team dynamics across the Double Diamond process enables a deeper understanding of how designer–engineer interdisciplinary collaboration impacts the final product and the prioritization of user needs under technical constraints, an increasingly relevant issue in healthcare innovation. The following summary (also detailed in

Table 5. Designer–engineer collaboration triggers across the Double Diamond phase.

Timeline in Double Diamond		Basis for Trade-Off
Discover Designer-initiated convergence	Conducted comprehensive identification of infertility patients’ pain points through desk research and online community analysis.	Actual user voices collected through user research. Real pain points of infertility patients identified from online sources such as mom communities, KakaoTalk open chats, YouTube vlogs, and blogs.
	Significant time was required to reach a compromise on which of the two major pain points identified through user research should be prioritized.	The designer acknowledged an initial lack of understanding of engineering capabilities. Through continuous learning and technical review, both sides reached mutual understanding and consensus. A collaborative attitude was established through deep dialog and empathy between designers and engineers.
Define Designer-initiated convergence	Visualized various issues and user needs related to infertility patients’ injection experiences through an ideation board. Among multiple pain points, discussions focused on key challenges, such as “being able to inject without worrying about others’ gaze” and “storing medication without a cooler bag.”	The problem definition eventually converged on “concealment and simplification of injection” and “improvement of storage and portability” → the engineer proposed feasible technical solutions → the team agreed on pain points that could be realized in a working prototype. Based on repeatedly confirmed user needs—such as injection concealment, reduced refrigeration burden, and hygienic simplicity—the team finalized key pain points.
	After the Define phase, designers generated a wide range of conceptual ideas.	Rather than relying solely on external validation, the team maintained an open and receptive mindset, finding a balance between ideation and practical convergence → result: a repetitive cycle of divergence, validation, and convergence throughout collaboration.
Develop Reciprocal negotiation phase	During the prototyping process, the inclusion of a cooling function emerged as a central point of debate.	Expert consultation provided additional justification for the need for a cooling function. During prototyping, the team restructured the internal layout to secure space for the cooling module, resolving technical constraints. Consequently, the cooling function was successfully integrated, becoming a defining key feature of the product.
	In the same phase, engineers proposed a design operating with two buttons, which became a topic of contention.	User research data ultimately served as the decisive basis for design decisions, leading to consensus on prioritizing user needs. The number of buttons was finalized based on human factor guidelines.
	Designers sought to reduce the product’s size, while engineers preferred to increase its dimensions for structural feasibility.	The product size was determined according to average female hand dimensions referenced from human factor standards.
Deliver Reciprocal negotiation phase	At the final output stage, defining the criteria for product completeness became a key discussion point.	Through the collaboration process, the team recognized a multi-layered definition of completeness, balancing design refinement and engineering robustness. This cross-disciplinary coordination resulted in a shared understanding of completeness as the alignment of UX and performance standards.

) captures how designer–engineer collaboration evolved at each step of the Double Diamond design process.

Discover: Designers explored a broad set of issues grounded in patient experience, while engineers initially adopted a defensive posture based on feasibility constraints. Although conflict emerged, repeated sharing of user research and online community evidence clarified actual pain points and enabled convergence. User data functioned as a shared language and as the basis for agreement.

Define: Tension intensified around problem definition and requirements. Designers proposed solutions (e.g., an HCG test kit concept), whereas engineers cautioned against non-implementable ideas. Negotiation around feasibility narrowed the scope to validated needs (e.g., pain mitigation and refrigerated storage convenience), which were adopted as the final problem definition.

Develop: Leadership shifted, with engineers triggering progress by proposing implementable mechanisms, demonstrating that they can move from defensive roles to proactive leadership in realization phases. Designers advocated for user-friendly size and form, and the team reached a balance between desirability and feasibility.

Deliver: Divergent emphases—designers on UX, esthetics, and detail, and engineers on structural reliability and performance—operated as complementary constraints, converging on a product that satisfies both usability and technical robustness.

The evidential basis for trade-offs became progressively explicit. Early decisions relied on qualitative statements (interviews and online comments). As the process advanced, usability tests and functional verification informed compromises and, in the final stage, objective benchmarks (e.g., human factors guidelines) anchored consensus.

The collaboration process underpinning the Blloom project can be conceptualized as a co-evolutionary and reflective collaboration model between designers and engineers. Dorst and Cross (2001) [33] described design collaboration as a co-evolution of problem and solution spaces. Our process extends this perspective by introducing iterative negotiation loops between empathic exploration (led by designers) and technical realization (led by engineers). Unlike traditional sequential workflows, the Blloom team adopted an alternating divergence–convergence structure similar to Kleinsmann and Valkenburg’s (2008) [34] model of shared understanding building, in which each disciplinary actor interprets and reframes the design problem from their own epistemic standpoint before converging through dialog and prototyping.

Furthermore, the collaboration reflected McDonnell and Lloyd’s (2009) [35] notion of reflective practice within design meetings, where iterative critique and reconstruction of concepts fostered mutual learning. This integrative dynamic is schematically represented in Table 5, depicting a recursive cycle of empathy, translation, and implementation that connects human-centered insights with engineering constraints.

Overall, the proposed model formalizes designer–engineer collaboration as a transferable framework that operationalizes human-centered design within technical product development. It illustrates how empathy-driven ideation and engineering validation can co-evolve through structured interaction, making the process applicable to broader self-managed healthcare innovations beyond the specific case of Blloom.

This trajectory evidenced a shift from voice-of-user advocacy to validation-based, rational decision making. These findings extend prior accounts (e.g., Tim Brown and the Design Council), which emphasized divergence and user-centered definition, by documenting collaboration dynamics through Develop/Deliver, where engineers assume trigger/leadership roles. For example, the integration of the tissue-lifting mechanism was initiated by engineering input during the Develop phase, while its ergonomic form and perceived safety were iteratively refined through designer-led usability feedback cycles, illustrating how conflict-triggered decisions matured into collaborative solutions.

Collaboration training should encompass role shifts and consensus-building mechanisms across all stages, not only early-phase ideation. Teaching designers to internalize technical constraints and engineers to respect design perspectives can better prepare students for real-world product development complexity.

4.3. Addressing Study Limitations

This study had several limitations that should be acknowledged when interpreting its findings. First, user research was conducted exclusively within a Korean clinical and cultural context, involving a limited sample of patients, clinicians, and subject matter experts. As such, the generalizability of insights to other demographic or healthcare settings remains uncertain.

Second, while the proposed device underwent iterative prototyping and formative usability testing, this study did not include clinical trials or regulatory validation; thus, its medical efficacy and long-term reliability are yet to be established.

Third, the collaboration dynamics between designers and engineers were analyzed within the scope of a single project, potentially limiting the transferability of the observed patterns across other design–engineering contexts. Despite these constraints, the full-cycle engagement of interdisciplinary teams and the alignment of user research with functional outcomes provide both practical design contributions and a methodological basis for future inquiry.

In addition, important trade-offs remain unresolved at this prototypical stage, including thickness and weight versus cooling duration; the manufacturability and cost implications of the cooling module; cleaning and hygiene constraints for reuse; and the long-term reliability of the tissue-lifting and cam mechanisms under repeated cycles. A clear regulatory and clinical pathway is required before any clinical deployment, including device classification, bench verification, and comparative studies against existing pen or auto-injectors.

5. Conclusions and Future Directions

This study presents Blloom as a user-centered, refrigeration-integrated self-injection device that addresses the multifaceted burdens of infertility treatment, ranging from hygienic constraints and spatial limitations to refrigeration logistics and social stigma. Through the structured application of the Double Diamond framework and design thinking methodology, we translated deep qualitative insights into an ergonomically refined and functionally feasible medical product. The final prototype demonstrated an ~80% reduction in portable volume, facilitated one-handed injection, and offered discreet usage in public settings, while maintaining temperature control within the medically recommended range for up to eight hours. Taken together, these findings suggest that Blloom’s form and function not only mitigate individual burdens but also exemplify how emotionally attuned design can normalize stigmatized treatment routines, laying the groundwork for broader application across self-managed care contexts.

Beyond its physical attributes, Blloom exemplifies how interdisciplinary collaboration between designers and engineers can evolve from disciplinary tension to synergetic realization. This shift—from empathy-driven exploration to benchmark-guided validation—traces a replicable trajectory for future medical device innovation. By embedding emotional intelligence within a technically robust form, the project affirms the potential of design thinking to optimize UX and reframe systemic inefficiencies in fertility care.

Though developed within the Korean clinical context, the findings and methodology carry broader implications. Blloom provides a transferable model for designing emotionally considerate, context-responsive, and regulation-aware devices in other stigmatized or self-managed treatment domains. In this way, the project contributes both a practical intervention and a methodological precedent for advancing human-centered innovation in healthcare. This case illustrates a replicable framework, wherein design empathy and engineering feasibility are progressively aligned through iterative negotiation, offering actionable insights for developing emotionally resonant medical products in similarly stigmatized domains.

Future work will involve transitioning Blloom from a validated concept to a clinically viable medical device. These evaluations will be essential for capturing the nuanced demands of self-injection in real-life contexts. Moreover, as the device progresses toward formal medical device certification, the Develop phase must be approached with greater methodological precision. Throughout this process, continued designer–engineer collaboration will remain indispensable, particularly in balancing human-centered insights with technical and regulatory constraints.

6. Patents

The current form factor and mechanism have been filed for patent protection in the Republic of Korea (Patent Application No. 10-2025-0117611; filed on 22 August 2025).