Simultaneous synthesis of hydroxyapatite/chitosan composite from crab shells and its polycaprolactone-blended scaffolds for enhanced bone regeneration

Abstract

Although the hydroxyapatite–chitosan reinforced poly(ε-caprolactone) composite (PCL/HA–CS) is vital for bone regeneration, it is still predominantly synthesized from various non-biological sources, while natural bioresources, such as crab shell, containing essential precursors, are discarded as waste, causing environmental pollution. Here, we present a sustainable strategy to fabricate bone scaffolds by directly converting crab shells into a HA–CS composite via a one-pot process, followed by blending with PCL. The resulting HA–CS composite, containing 78.37% nano-sized HA, exhibited strong antibacterial activity without cytotoxic effects, with minimum inhibitory concentrations of 2.5 mg mL⁻¹ and 5 mg mL⁻¹ for S. aureus and E. coli, respectively, and corresponding minimum bactericidal concentrations of 5 mg mL⁻¹ and 10 mg mL⁻¹. When combined with PCL, the biogenic material demonstrated balanced mechanical strength, biocompatibility, and excellent mineralization under in vitro conditions. A formation mechanism was also proposed, in which the amine groups of CS interact with HA, while residual hydroxyl groups form interfacial bonds with PCL, enabling uniform distribution of HA–CS within the polymer matrix. Moreover, the biodegradation rate (ν) of PCL/HA–CS during the first four weeks could be linearly tuned by adjusting the HA–CS content, following a linear relationship: ν (%/day) = 0.0108 [HA–CS] (%) + 0.1133. This controllability enables better synchronization between scaffold degradation and new bone formation, addressing a major limitation of conventional PCL-based scaffolds. Overall, crab shell waste offers a promising and eco-friendly route to generate high-performance scaffolds for bone tissue engineering.