Towards Circular Ankle-Foot Orthoses : A Design-for-Disassembly Approach to Enable End-of-Life Material Recovery

Sammanfattning

Purpose: Custom-made polypropylene (PP) ankle-foot orthoses (AFOs) are among the most frequently prescribed assistive devices for lower limb conditions, yet they follow a predominantly linear lifecycle in which the PP shell is discarded as waste at end-of-life. PP is derived from finite fossil fuel reserves and carries a heavy environmental burden, making the absence of end-of-life strategies a significant resource-efficiency problem. This study investigates how Design-for-Disassembly (DfD) principles can be applied to the redesign of custom-made PP AFOs to enable material recovery at end-of-life, within the context of the Netherlands. Method: An exploratory sequential mixed methods design guided by the double diamond framework was used. Data was collected through a literature review on circular economy and DfD principles, semi-structured interviews with certified prosthetist-orthotists (CPOs) in the Netherlands, analyzed thematically, and a product analysis of existing custom-made PP AFOs. Triangulation across the three sources informed the functional requirements, guiding concept generation, evaluation through a weighted decision matrix, detailed design, and proof-of-concept prototyping. Findings: The metal rivet permanently joining the strap to the PP shell was identified as the primary design-level barrier to material recovery. The selected "anchor slot" design replaces the rivet with a geometric locking mechanism integrated into the shell, requiring no additional fastening materials. Prototype testing confirmed the locking principle and identified strap rotation under tension as an unresolved issue. Following a two-step disassembly procedure using only standard workshop tools, the PP shell can be recovered intact and free of contamination. Implications: The study demonstrates that DfD principles can be meaningfully applied to custom-made assistive technology without departing from standard fabrication methods. The anchor slot design offers a clinically grounded direction for reducing waste and retaining material value in the orthotic sector. Realizing this potential in practice, however, requires coordinated action beyond the product itself, including collection systems and recycling infrastructure aligned with national and European circular economy ambitions. Limitations: The interview sample was small, and findings should not be generalized to the broader Dutch orthotic field. Prototype testing used scaled 3D-printed models rather than full-sized vacuum-formed PP, limiting mechanical validation. The rotational behaviour identified during testing remains unresolved, and clinical testing has not been conducted. The researcher's dual role as a qualified prosthetist-orthotist and product development student is acknowledged as a potential source of bias. Conclusions: DfD principles can be applied to custom-made PP AFOs without departing from standard fabrication, and the anchor slot represents a proof-of-concept design direction. Realizing material recovery in practice will require parallel development of collection and recycling infrastructure.