JMIR Publications

ABSTRACT

Background:

Despite considerable advancements in prosthetic technology, 12–53% of lower limb amputees abandon their prostheses. This statistic underscores the urgent need for solutions that address persistent challenges such as discomfort, sweating, maceration, and dissatisfaction with conventional materials. Prosthetic comfort is central to user satisfaction and long-term adherence, and strongly influences mobility and quality of life. Particularly, the interface between the residual limb and prosthetic socket remains a major source of dissatisfaction due to fit and load transfer requirements. While existing silicone liners provide suspension and load distribution, the thick insulating silicone material traps sweat and causes skin irritation, hygiene issues and dermal injuries that are intensified by hot and humid climates. As such, there is a need for alternative interface materials with improved breathability, moisture regulation, and tunable mechanical properties.

Objective:

This study presents the design, fabrication and evaluation of Flexoknit, a digitally-informed transtibial prosthetic interface that integrates skin-strain analysis with computer numerical control (CNC) knitting to deliver patient-specific material customization. This proof-of-concept interface liner will be compared with the conventional silicone liner in terms of its overall mass and usability (i.e. user’s range of motion, walking tests, thermal regulation).

Methods:

This study employed an experimental, mixed-methods design to develop, characterise, and evaluate Flexoknit, a transtibial prosthetic interface created through computer numerical control (CNC) multi-material knitting and informed by residual-limb skin-strain patterns. The study comprised three major phases: 1.Digital design and fabrication of multi-material knitted structures, including yarn selection, stitch programming, and interface construction. 2.Material and fabric characterisation involving thermal analysis, mechanical testing, and moisture management assessment of the knitted samples. 3.User testing to evaluate mobility, suspension, thermal and moisture comfort, and overall user satisfaction compared with a conventional silicone liner.

Results:

The exploration of multi-material knits comprising of thermoformable yarn and spandex yarns with different stitch combinations generated distinct stiffness grades with nearly order-of-magnitude differences that were indicated by uniaxial tensile tests. The spatial layout of these graded zones applies biomechanical insights from Lines of Non-Extension (LoNEs), aligning high-stiffness regions with areas of minimal skin strain and low-stiffness regions with areas of greater deformation. User testing demonstrated a 22.5% improvement in total range of motion, a 37.5% reduction in interface mass, and improved thermal regulation in hot, humid environments compared with a conventional silicone liner. The user walked unaided and performed sit-to-stand movements after a brief adjustment period, reporting positive comfort and usability feedback.

Conclusions:

Overall, this work establishes Flexoknit as a promising direction for future prosthetic development—one that integrates principles of biomechanics, textile engineering, and digital fabrication to create user-centered interface solutions. Further research is warranted to refine structural performance, evaluate long-term durability, and validate the design across diverse user groups and real-world conditions.