Preparation and characterization of bio-waste based composites reinforced by geopolymers

This study presents the development of bio-composite scaffolds for bone tissue engineering using hydroxyapatite (HA) derived from biowaste and kaolin-based materials through sustainable, low-cost approaches. The study was conducted in two parts. In the first part, a novel zero-waste wet chemical precipitation method was employed to synthesize nano-hydroxyapatite from calcined eggshells, reinforced with metakaolin (MK) in varying proportions. Characterization techniques (XRD, FTIR, SEM-EDX, and BET) confirmed successful HA formation with rod-like nanocrystals. Increasing MK content reduced crystallinity and crystallite size (37.3-21.1 nm). Cold pressing improved density, reduced porosity, and enhanced mechanical properties, achieving compressive strength (16.4 MPa) and diametral tensile strength (11.8 MPa), values within cancellous bone range. Bioactivity tests in simulated body fluid (SBF) showed progressive apatite layer formation, and antimicrobial and cytotoxicity tests indicated strong antibacterial performance and high cell viability (>95%). In the second part, hydroxyapatite extracted from bovine bones was combined with uncalcined kaolin, silica sand, and NaOH-activated geopolymeric components for injection molding. The optimized formulation (15% GP, 1.5% NaOH) exhibited favorable mechanical strength (7 MPa), porosity (55%), and Young's modulus (5.6 GPa). It also demonstrated good biocompatibility, controlled degradation in PBS and SBF, and antimicrobial efficacy. Overall, the findings confirm that both developed composites offer promising properties mechanical integrity, bioactivity, biocompatibility, and antimicrobial behavior, supporting their potential application as scaffolds for bone regeneration, particularly in trabecular bone repair.