<i>Caesalpinia pulcherrima</i> ash as a sustainable reinforcement in metallic biomaterials for biomedical applications: a review on mechanisms, compatibility, and prospects

Abstract

Abstract Agro-waste-derived oxides are increasingly investigated as sustainable reinforcement phases in metal-matrix composites. However, their translation into biomedical metallic systems remains underexplored. Caesalpinia pulcherrima (Pride of Barbados) ash represents an oxide-bearing biomass derivative with a reported silica-rich composition. Yet, its suitability as a reinforcement in biomedical metal matrix composites (MMC) has not been systematically evaluated. This review assesses whether Caesalpinia pulcherrima ash (CPA) satisfies the chemical, mechanical, electrochemical, and biological criteria required of reinforcements in biomedical metals (316L stainless steel, Ti-6Al-4V, Cr–Co–Mn alloys, magnesium systems). It develops a transferable reinforcement-selection framework for agro-waste residues. Available evidence indicates that CPA exhibits silica-rich oxide (91%) composition and predominantly amorphous phase characteristics consistent with oxide-based reinforcement behaviour. Comparative matrix compatibility screening indicates conditional plausibility in passive-film-forming metals such as stainless steel and titanium, whereas galvanic and electrochemical uncertainties persist for magnesium systems. However, key performance metrics, including mechanical strengthening, corrosion durability in simulated body fluids, ion-release control, and cytocompatibility, have not yet been experimentally validated for biomedical MMC applications. Accordingly, the principal translational gap lies in the absence of performance-qualified validation studies. The reinforcement-selection framework proposed in this work provides a systematic pathway for screening oxide-rich agro-waste ashes based on chemical stability, matrix compatibility, strengthening mechanisms, corrosion behaviour, and biological thresholds. Future research should prioritise interface characterisation, electrochemical durability testing, mechanical qualification, and biocompatibility assessment to advance sustainable oxide reinforcements toward biomedical deployment.