Pellet-fed continuous-silk-fibre 3D/4D printing of PLA/bamboo-charcoal bio-composites with shape recovery and thermomechanical stability

• A pellet-fed material-extrusion platform with integrated continuous-fibre co-deposition. • Synergistic BC and continuous silk fibre reinforcement boosts tensile strength by 213%. • 3-point bending strength of PLA/BC/CSF is 247% higher than PLA. • Reduced burning rates by 63% (PLA/BC/CSF), 47% (PLA/CSF), and 30% (PLA/BC). • PLA/BC/CSF exhibits higher stiffness/strength and the fastest shape recovery. • While PLA exhibits creep/sag. PLA/BC/CSF retains the geometry. A pellet-fed extrusion platform with integrated continuous-fibre co-deposition is presented, enabling 3D/4D printing of bio-composites directly from pellets, avoiding a separate filament-making step, thereby reducing time, energy, and material waste. A polylactic acid/bamboo-charcoal/continuous-silk-fibre (PLA/BC/CSF) system was formulated to overcome PLA’s low strength, thermal creep, and flammability. With 3 wt% BC, PLA tensile strength increased by 28%; with CSF, tensile strength reached 108 MPa (+213% vs PLA). Three-point bending strength rose + 247% over PLA (+200% vs PLA/BC; +40% vs PLA/CSF). The burning rate decreased by 63% relative to PLA, evidencing improved flame resistance. Under 70 °C and constant load, PLA/BC/CSF beams retained geometry whereas PLA sagged, confirming superior thermo-mechanical stability. Architected honeycomb and trapezium meta -composites printed from PLA/BC/CSF exhibited quasi-constant force, and quasi-zero stiffness plateaus with energy dissipation and shape recovery (full after 25% compression; 85% recovery after 45% upon heat activation), supporting reuse and overload protection. The approach delivers a low-cost, lower-energy route to continuous-fibre bio-composites and demonstrates printable, recoverable components for logistics and automotive use (e.g., pallets, chassis inserts, dashboard face-parts), advancing sustainable additive manufacturing and circular-economy goals.