Prosthetic limbs have a rich and fascinating history, dating back to ancient civilizations. Yet, persistent challenges remain, particularly for children needing upper-limb prostheses. Growth, accessibility, and the need for devices that are both functional and aesthetically pleasing make pediatric prosthetics uniquely complex. Access to suitable prosthetics can significantly impact a child’s psychological and social development. However, the high costs, insurance limitations, and perceived fragility and complexity of traditional devices often put these solutions out of reach for many children. These obstacles have fueled a global grassroots movement to create affordable and accessible alternatives, and 3D printing has emerged as a game-changing technology. The ability to create customized, user-specific hardware through 3D printing has led to a surge in open-source, Do-It-Yourself (DIY) assistive devices, offering hope to millions worldwide. This article explores the groundbreaking research and development in 3D-printed prosthetics driven by maker communities and non-profit organizations. We will examine innovative case studies, technological advancements, training methodologies, and the evolving medical and regulatory landscape in the United States, highlighting clinical studies designed to measure the life-changing impact of these devices.
The Enduring Need for Innovation in Prosthetics
The design of prosthetics has evolved over centuries, from rudimentary replacements in ancient Egypt and Rome to sophisticated modern devices. The late 19th century marked a turning point with the invention of the Hanger Limb, developed in response to the American Civil War, ushering in an era of modern prosthetic design. Medical advancements since then have significantly reduced limb loss from traumatic injuries. Despite progress, the need for prosthetic limbs remains substantial. In 2005, approximately 1.6 million people in the United States lived with limb differences, with about 541,000 experiencing upper-limb loss. Projections indicate this number could double by 2050. While trauma remains a leading cause of upper-limb amputation, particularly among males, amputations resulting from vascular disease are also on the rise. Congenital limb differences, present from birth, also affect a significant population globally.
In the U.S., over 32,500 children have experienced major pediatric amputations. The Centers for Disease Control and Prevention estimates that around 1,500 children are born with upper-limb reductions each year. Globally, the prevalence of limb reductions varies, highlighting the widespread need for solutions that address both access and user acceptance. Alarmingly, a significant percentage of individuals with both congenital and acquired limb loss choose not to use prosthetics, even when available. Usage rates for upper-limb prosthetics range from only 37% to 56%, significantly lower than lower-limb prosthetics, which are often perceived as more essential. This disparity is particularly pronounced among children with transverse upper-limb amputations, where usage rates can be as low as 44% to 66%.
Several factors contribute to the low adoption rates of upper-limb prosthetics, including inadequate aesthetic design, excessive weight, limited insurance coverage, high costs, and challenges with device acceptance at user, provider, parental, and insurance levels. The ideal prosthetic should seamlessly blend form and function, mirroring the complexity and dexterity of the human hand. Historically, prosthetic design has strived for realism, attempting to replicate the appearance of a natural limb. However, designer Graham Pullin argues for a broader perspective, suggesting that prosthetics should not be limited to mere functionality but should embrace both aesthetics and functionality as equally important design considerations.
Limited research has explored the psychological benefits of aesthetically improved prosthetic limbs. Studies indicate that individuals with limb differences may experience lower self-esteem and heightened concerns about body image. These psychosocial factors and quality of life considerations are crucial yet still not fully understood. Research suggests that prosthetic use can improve social engagement and confidence. Furthermore, studies focusing on the user’s perspective reveal that prostheses can positively impact psychoemotional well-being. Further investigation into both the functional and aesthetic aspects of prosthetic design is essential to create more user-centered and impactful solutions.
Contemporary Challenges and the 3D Printing Revolution
3D printing has emerged as a pivotal technology in addressing the critical issues surrounding upper-limb prosthetics. It offers solutions to limited and delayed access to conventional prosthetics, paving the way for more timely and personalized care. This exploration delves into the history and impact of 3D-printed prosthetics, the populations they serve, and the challenges that have motivated their development. Ultimately, we will discuss the integration of these advancements into mainstream medical practice.
Addressing Prosthetic Limb Abandonment
Patient expectations and goals significantly influence their satisfaction and continued use of prosthetic devices. A device with advanced features, like articulated fingers, raises user expectations regarding comfort and performance. Factors contributing to device rejection vary based on amputation type, gender, and age. Individuals with congenital limb loss are more likely to abandon devices in adulthood, while women with acquired limb loss are more prone to rejection than men. Prosthesis abandonment is a widespread concern across all demographics, stemming from issues related to sensory feedback, appearance, function, control, comfort, and durability. These are all critical areas demanding further research and improvement in prosthetic design and user acceptance.
A comprehensive review of over 200 research articles revealed pediatric rejection rates ranging from 38% for passive devices, 45% for body-powered devices, and 32% for electric devices. Adult rejection rates are similarly concerning, with 39% for passive, 26% for body-powered, and 23% for electric devices. Long-term data on myoelectric devices remains limited. These high rejection rates underscore the urgent need for innovative approaches to enhance user affinity and improve outcomes.
The Power of Appearance and Design
Individuals with limb differences can face social stigma and discrimination due to their perceived impairment. Prosthetic limbs can play a crucial role in mitigating this stigma. Integrating art and design into prosthetic development can further empower users. Sociologist Erving Goffman’s theory suggests that stigma can lead individuals with disabilities to adopt compensatory behaviors to conceal their difference. This might manifest as hiding a prosthetic limb in photographs or social situations.
Historically, children’s prosthetics were often limited to body-powered hooks or passive, skin-toned devices. Even today, these options remain common, despite advancements in technology. Current trends emphasize normalization and reducing the stigma associated with prosthetic limbs. Early prosthesis users have reported feeling empowered through various means, fostering both social engagement and personal acceptance of their limb difference. This acceptance is a complex and deeply personal journey. Modern materials now enable the creation of more natural-looking prosthetics. Researchers have developed silicone elastomer gloving materials and advanced motors to achieve a more realistic appearance without adding excessive weight. While aiming for natural aesthetics is valuable, art-inspired designs can offer individuals with disabilities a powerful means of self-expression and boost self-esteem.
Our research suggests that blending aesthetic design with functional prosthetics, including designs that move beyond traditional human forms, can positively impact social identity and interactions. This is a key area of ongoing investigation.
Enhancing Function and Control
Modern bionic prosthetics offer three primary control methods: body-powered systems utilizing cable movements, button-press controls, and electromyography (EMG). Each method offers a unique user experience, with varying degrees of intuitiveness and functionality. Body-powered devices require gross body movements to control the prosthesis, while button-press systems offer more direct control but can be less intuitive. Prosthetic selection is typically based on individual needs, experiences, and functional requirements. However, children often have limited input in this process. Furthermore, long-term studies comparing outcomes for children fitted with prosthetics versus those without are scarce.
Body-powered prosthetics are frequently prescribed in the U.S. and often considered more robust than myoelectric devices. They provide users with physical feedback, while myoelectric devices primarily offer visual feedback. Due to robustness concerns, training complexities, and technical limitations like weight, body-powered devices are often preferred by professionals and users. Control schemes using skin movement or button presses can lead to unintended activations, creating a frustrating user experience.
Electromyography (EMG) stands out as a promising control method. It measures the electrical signals produced by muscle contractions. EMG sensors, combined with signal processing and filtering circuits, can capture a user’s intended movements by detecting muscle contractions. This filtered signal can then control the prosthetic hand’s movements. Many advanced prosthetic systems utilize multiple EMG sensors placed on different muscle groups to capture a range of signals for more nuanced control, interpreting various limb motions.
A Paradigm Shift in Prosthetic Limb Design
The internet’s ability to facilitate digital sharing of 3D design models has fostered a thriving global maker community. A carpentry accident in 2011 sparked a global collaboration to restore dexterity to a carpenter who lost several fingers. Richard Van As, the carpenter, teamed up with special effects artist Ivan Owen. This collaboration resulted in the world’s first 3D-printed upper-extremity prosthetic device in 2012. The designs were made open-source, allowing the global maker community to reproduce and refine them. This body-powered device used wrist flexion to activate finger movement, marking a significant milestone in accessible prosthetic design.
The Rise of 3D Printed Prosthetic Arms
The open-source availability of the Robohand and Ivan Owen’s designs had a profound global impact on accessibility technology. Inspired by the potential, researchers and makers worldwide contacted the designers, eager to contribute. The effectiveness of collaborative design and production led to the formation of numerous maker communities and non-profit organizations dedicated to improving local access to prosthetics, including e-NABLE, Enable Community Foundation, Robohand, and Limbitless Solutions. These groups encompass both individual designers and university-based research teams from institutions like Rochester Institute of Technology (RIT), Creighton University, University of Central Florida (UCF), and the University of Washington at Bothell. Additive manufacturing techniques range from affordable home-built 3D printer kits to industrial-grade machines. While much of the initial focus was on body-powered devices, some groups are advancing research into electromyographically actuated devices for individuals with more extensive limb loss, utilizing biosensors and electromechanical motors.
Custom sizing, achieved through volumetric scaling or precise parametric adjustments, enables rapid and iterative prosthetic production. With the expanding range of 3D printing materials and colors, users can personalize their devices with custom color schemes, enhancing engagement and ownership. In 2014, the “Prosthetists Meet 3D Printers” conference at Johns Hopkins Hospital brought together makers and medical professionals to discuss the potential of 3D printing to improve access and quality of prosthetic care. This event, along with the e-NABLE web platform, facilitated crucial collaborations between designers, medical experts, and individuals with limb differences.
Collaborative design efforts, often utilizing cloud-based software like Autodesk Fusion 360, have fostered group support and accelerated advancements in functionality, robustness, and user-driven feedback. The e-NABLE network has made significant contributions, shared through open-source repositories like Thingiverse.com. These readily available designs have dramatically improved prosthetic accessibility for children globally, fueled by the proliferation of affordable 3D printers in schools, libraries, and homes.
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Robohand, an early 3D-printed prosthetic hand design available open-source, illustrating the potential of DIY assistive devices.
Figure 1. The Robohand assistive device, first made available for 3D printing globally via Thingiverse. Image from the Food and Drug Administration.
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Figure 2. The Raptor reloaded hand by Enable available for download via Thingiverse. (a) Exploded view of design and user assembly methods. (b) Completed assembly of device.
This global collaboration has accelerated prototyping. A visual representation of the design evolution and the growth of global chapters is available on the e-NABLE website. The maker movement’s integration with university research has further propelled the field. Researchers are working to standardize production and establish best practices through data-driven analysis. The work of Jorge M. Zuniga, initially at Creighton University and now at the University of Nebraska, exemplifies this effort. His research has advanced the implementation of additive manufacturing in biomedical research and its translation to clinical settings. The Cyborg Beast hand, a wrist-powered design building upon earlier work, has gained significant traction among children with limb differences due to its improved integration and ease of assembly.
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The Cyborg Beast 3D-printed prosthetic hand designed by Jorge M. Zuniga, demonstrating personalized cosmetic finishes and community-driven design improvements.
Figure 3. The Cyborg Beast by Creighton University’s Jorge M. Zuniga and available on Thingiverse. (a) Personalized assembled device. (b) A group of assembled hands featuring different cosmetic treatments.
Jon Schull, a founder of the e-NABLE movement, and his team at RIT have made substantial contributions, developing new body-powered forearms and hands controlled by elbow or wrist movement. This work has also led to innovative educational approaches incorporating project-based learning using 3D printers and global design networks.
Appearance – Cooperative Expression
3D printing empowers greater individual customization of prosthetic devices. As the collaborative network of developers expands, user-driven design becomes increasingly central. To enhance user affinity for bionic designs, end-user participation is prioritized. Our research team has termed this approach “cooperative expression,” drawing from participatory design methodologies like cooperative inquiry.
Participatory design is a research field focused on the direct involvement of users in the design process. Initially applied to workplace computer systems, it is now being adapted to engage children in the development of low-tech design prototypes. Cooperative inquiry, a brainstorming technique within participatory design, emphasizes collaborative exploration. Key dimensions of child-designer partnerships include the child’s relationship with adult participants, their interaction with the technology, and the inquiry’s goals. Cooperative inquiry is a flexible method for technology development. Researchers have successfully used it to involve children with special learning needs and adults in software design, empowering children to personalize their experience. Studies using cooperative inquiry report increased emotional engagement and a greater sense of project ownership among children.
Our team is applying a modified participatory design approach, “cooperative expression,” to the aesthetic design of bionic limbs to improve user affinity. This approach customizes the visual appearance of 3D-printed bionic limbs. Recipients can artistically personalize interchangeable sleeves through an interactive website. They can compare 3D designs, select preferred options, and further customize colors and effects. Artists create initial aesthetic frameworks, including color palettes and customizable zones, to streamline choices and encourage exploration beyond typical preferences.
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Infographic outlining the cooperative design process for 3D-printed prosthetics, emphasizing user participation and interdisciplinary manufacturing.
Figure 4. Overview of design process and methodology from design generation, user participation, and interdisciplinary manufacturing.
This user-centered design process integrates the end-user from initial concept to final product. While structural and mechatronic components are standardized, digital designers create 3D representations of artistic shells. An interactive web portal enables users to customize colors, effects, and regions of the sleeve, visualizing their personalized design. Artistic designs may be adjusted based on user portal interactions to optimize the human-machine interface. Production involves 3D printing, surface preparation, priming, automotive finishing techniques, and painting. Artists translate user selections from the portal, enhancing visual effects during painting. The completed system undergoes validation before fitting. This process ensures active user involvement before production and fitting, fostering an emotional connection to the prosthetic limb.
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Figure 5. (Left) Example interactive web page for children to customize color and effect regions during the design process, and how user participation can be translated to (Right) the final design with artistic input from art team and production teams. Sleeve design made in partnership with Riot Games.
The design process offers “empowerment classes” of interchangeable aesthetic sleeves: Warrior, Shadow, Ethereal, and Serenity. These classes represent distinct personalities and emotional affinities. Artists create inspired 3D models aligned with these classes, and collaborations with external artists have expanded the design catalog. This variety and interchangeability empower children to express themselves, potentially increasing device affinity, reducing social stigma, and promoting long-term engagement, ultimately improving user performance. Future research will evaluate the impact of this approach on psychosocial development and stigma reduction.
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Examples of artistic sleeves for 3D-printed prosthetics, representing 'Warrior,' 'Ethereal,' 'Serenity,' and 'Shadow' empowerment classes, enhancing user expression.
Figure 6. 3D-printed electromyographic actuated limb device with interchangeable artistic covers from Limbitless Solutions at the University of Central Florida. (a) Warrior class, (b) Ethereal class, (c) Serenity class, and (d) Shadow class.
Function – Electromyography
Research has demonstrated that a 16-sensor EMG system can predict a user’s intended control with 86% accuracy after two days of training. This system was tested with a 25-year-old male transradial amputee. The system learns to interpret EMG input based on movements mimicking pre-amputation actions. Complexity increases with multiple EMG inputs controlling multiple outputs. Each monitored muscle region requires intentional activation, sometimes simultaneously, which can be overwhelming, especially for children, potentially contributing to device rejection.
Our 3D-printed prosthesis utilizes a single EMG sensor, simplifying daily calibration and use. On-board signal processing correlates muscle contraction intensity or the number of contractions to actuate different hand gestures, including individual finger movements. Addressing the limitations of current EMG devices presents opportunities to refine both design and training methodologies.
Control – Gamification and Training
Single-surface EMG provides multi-gesture control, enabling users to control their prosthetics through contraction intensity and patterns. Due to control complexity, a custom video game-based training system was developed to provide a safe and engaging learning environment. The game system captures filtered EMG input and uses it as a multifunction controller or analog input. Training systems incorporating game mechanics similar to real-arm actions, like punching, have shown improved usability scores with EMG control.
Our team’s training game, Magical Savior of Friends (MSOF), is a side-scrolling game where players control a magical character who performs superpower attacks and defenses based on muscle contraction amplitude. After calibration, players learn to vary contraction magnitude to control in-game actions. Calibration sets low, medium, and maximum thresholds. Low threshold calibration eliminates noise. Gestures trigger distinct superpower attacks.
While seemingly simple and fun, the game provides meaningful training for complex multi-gesture hand states. Preliminary results show significant improvement in contraction accuracy after just one hour of gameplay. Gamification offers a low-pressure environment for practice and feedback, crucial for improving myoelectric prosthesis control. Simulation through gaming effectively trains prosthesis users. This work is expanding to offer prosthesis users new opportunities to engage with games they might otherwise be unable to play.
Comfort and Durability
3D printing, like any manufacturing process, has advantages and limitations. It offers personalized medicine and rapid prototyping, proving effective in clinical settings. While beneficial for procedure planning, concerns about the safety of 3D-printed parts exist. Professionals optimizing designs based on material properties must understand the manufacturing process’s impact. Tests on 3D-printed ABS plastic show variable mechanical properties depending on print orientation, with strengths ranging from 10% to 73% of injection-molded samples. Layer printing method affects deviation from material standards, but optimization can improve reliability and predictability. Consistent standards and best practices are essential for reliable 3D-printed medical components. FDA guidelines recommend workflow and documentation for part tracking in case of failure. Understanding part vulnerabilities can preemptively minimize risks. With realistic loading expectations and manufacturing considerations, 3D printing can produce stable, resilient, lightweight, and cost-effective parts.
Discussion of Regulatory Framework
While significant progress has been made in advancing 3D printing techniques for prosthetics, reviews of current studies highlight areas for continued development. An independent review of 314 studies indicated a trend towards case studies rather than randomized controlled trials. Areas needing further attention include study power, statistical rigor, reliable outcome measures, and recruitment clarity. The review emphasized the need for rigorous efficacy and effectiveness evaluations to provide healthcare professionals with the evidence needed for informed patient care decisions.
To further advance the field and quantify the impact of our 3D-printed electromyographically actuated multi-gesture arms, a clinical trial is underway in collaboration with Oregon Health & Science University and the University of Central Florida. This study, deemed non-significant risk, involves twenty participants aged 6 to 17 in a year-long trial with four assessments. Assessments are designed to measure quality of life (using the Children’s Hand-Use Experience Questionnaire (CHEQ) and PedsQL) and myoelectric control (using the Assessment of Capacity for Myoelectric Control (ACMC)).
CHEQ, designed for ages 6-18, uses a four-category scale to assess a child’s hand function and limitations. It uses nested questions to evaluate independent task completion and hand usage patterns, providing a baseline understanding of how limb difference impacts daily life.
PedsQL is a validated 23-question survey for parents and children assessing health-related quality of life over the past month. It covers physical, emotional, social, and school functioning, with responses translated into scores out of 100%.
ACMC is a Rasch rating scale assessing prosthetic arm function through 30 items evaluating gripping, holding, releasing, and coordination during tasks like meal preparation and LEGO assembly. Occupational therapists assess performance, documenting participant feedback. Study findings will inform design and methodology improvements.
Conclusions
The future of 3D printing and collaborative design in prosthetics is promising, with rapid iteration and user-centered designs. However, robust clinical assessments are still needed. Our clinical trial of 3D-printed EMG-controlled bionic limbs, using well-defined outcome metrics, aims to contribute to the field and assess readiness for wider adoption. Continued validation of design and performance will improve technology translation and design methods. User-centered design and cost reduction have the potential to revolutionize functional prosthetic accessibility, particularly for pediatric patients.
Acknowledgments
The authors thank the Limbitless Solutions team for their contributions. We appreciate the support of Riot Games and 343 Industries for their sleeve designs.
Author Contributions
Conceptualization: A.M., P.S., A.C.; Writing – Original Draft: A.M., P.S., with support from J.S., M.D., D.C., A.K., I.W., A.C.; Writing – Review & Editing: All authors.
Funding
This research received no external funding.
Conflicts of Interest
The authors declare no personal conflict of interest but disclose that Limbitless Solutions has received support from Stratasys (3D printer manufacturer).
