Sustainable fibre-reinforced polymer composites for biomedical applications

Fibre-reinforced polymers (FRPs) are promising alternatives to metallic and monolithic polymeric implants because their stiffness, strength and degradation can be tailored through fibre type, matrix chemistry, fibre fraction and architecture. This review examines mechanical performance, biocompatibility, and emerging design trends, and grades the evidence for each system from clinical to purely computational. Stiffness matching is the central mechanical rationale: cortical bone (~14 GPa) is ~7.9 times less stiff than Ti-6Al-4V (~110 GPa) but only ~1.3 times less stiff than carbon-fibre-reinforced PEEK (CFR-PEEK, ~18 GPa); a simplified iso-strain estimate gives implant axial load shares of ~89%, ~56% and ~32% for titanium, CFR-PEEK and a glass/sisal/chitosan sandwich (tensile modulus 6.6 GPa), respectively. Clinical evidence for CFR-PEEK in trauma remains of low certainty (nine studies, 431 patients; standardized mean difference in function 0.22, 95% CI −0.03 to 0.47). Architecture and nano-reinforcement can add measurable but system-specific gains: spatial versus planar Bouligand carbon-fibre/hydroxyapatite gave +85.6% compressive and +38.4% flexural strength, whereas 2 wt.% graphene oxide raised the modulus of a polyhydroxyalkanoate film by 36% and 0.5 wt.% cellulose nanofibre raised PLA modulus by 18.4% at a 7.4% strength loss. Natural-fibre bone-plate concepts show in-vitro cell viability up to 96.7% at 72 h and inhibition zones up to 28 mm, but no animal or clinical data, strong moisture sensitivity, and almost no fatigue data in physiological media; in 3D-printed PLA scaffolds, the compressive strength was largely unchanged after 30 days in Hanks' solution, while fatigue resistance decreased significantly. The sterilization effects are material-specific, and most advanced concepts (Bouligand, 4D, machine-learning design) remain laboratory or computational. Three priorities follow from the quantified gaps: fatigue and property retention in physiological media, degradation-matched mechanical and biological safety, and standardized evidence for clinical translation.