Fused Granular Fabrication of Biodegradable Lightweight Knee Orthoses: Printability of Poly(lactic Acid)/Poly(butylene Adipate-Co-Terephthalate)/Bamboo Fiber Composites

Conventional knee orthoses (KOs) are fabricated from petroleum-based plastics and are difficult to recycle, while filament-based fused deposition modeling is limited by low deposition efficiency and weak interlayer strength for large load-bearing devices. Herein, the authors reported fused granular fabrication (FGF) of lightweight, biodegradable KOs from poly(lactic acid)/poly(butylene adipate-co-terephthalate)/bamboo fiber (PLA/PBAT/BF) composites. Composites with 2, 6, and 10 wt.% BF were melt-compounded using zinc acetate as a transesterification catalyst and directly granule-printed. Rheological and morphological analyses revealed that increasing BF loading raised melt viscosity and elasticity, albeit with local fiber aggregation. Tensile strength decreased from 37.0 to 26.0 MPa with fiber addition, whereas notched impact strength improved from 7.2 to 11.6 kJ/m2, attributed to fiber pull-out, interfacial debonding, and matrix plastic deformation. A demonstration KO weighing only 243 g was printed. Printability depended strongly on nozzle temperature and speed: at 40 mm/s, all BF loadings failed, whereas 10 wt.% BF achieved defect-free printing at 220 °C and 30 mm/s. An optimal processing window of 10 wt.% BF, 190–220 °C, and 30 mm/s yielded tough, lightweight, biodegradable, custom-fit orthoses, demonstrating promising potential for rehabilitation applications.