Comparative evaluation of amoxicillin loading and release behavior from waste-derived hydroxyapatite synthesized by solid-state and wet chemical routes

This study presents a comparative analysis of amoxicillin loading and release behaviors of hydroxyapatite (HAp) synthesized by two methods, solid-state reaction (S-HAp1000) and wet chemical precipitation (W-HAp1000) using waste chicken eggshells as the calcium source and calcination at 1000 °C for 2 hours. Structural and morphological characterization revealed significant differences: S-HAp1000 exhibited a biphasic composition with 75.5% HAp and 24.5% β-TCP based on Rietveld refinement, larger crystallite size (88 nm), and higher amoxicillin entrapment efficiency (11.63%), while W-HAp1000 exhibited 99.6% phase-pure HAp, smaller crystallite size (83 nm), and lower entrapment efficiency (7.28%). Drug release in simulated body fluid (SBF) at pH 7.4 and 4.0 showed that W-HAp1000 released 62.96% and 79.18% of amoxicillin respectively, compared to 44.66% and 66.01% for S-HAp1000. Release kinetics revealed that amoxicillin release from S-HAp1000 followed an anomalous (non-Fickian) transport mechanism at physiological pH (7.4), which shifted toward a diffusion-controlled (Fickian) mechanism under acidic conditions (pH 4.0). In contrast, W-HAp1000 exhibited a concentration-dependent, zero-order release profile at pH 7.4, transitioning to a case II transport mechanism, characterized by matrix relaxation or erosion at pH 4.0. W-HAp1000 also showed broader antibacterial activity, inhibiting both <i>S. aureus</i> and <i>E. coli</i>, whereas S-HAp1000 was only effective against <i>S. aureus</i>. These findings suggest that synthesis methodology significantly influences the drug delivery performance of HAp for osteomyelitis therapy.