Synthesis and characterization of Gelatin-Hydroxyapatite nanohybrid composites

Abstract
Gelatin-based nanocomposites have gained significant attention as sustainable and multifunctional biomaterials due to their natural origin, biocompatibility, and tuneable properties, making them strong candidates for advanced structural applications, such as matrix fillers and functional coatings in porous substrates like leather. But, pure gelatin suffers from limited mechanical strength, thermal instability, and rapid solubility in aqueous environments, necessitating structural reinforcement. Nano-calcium hydroxyapatite (CaP) is a well-established inorganic additive that enhances the mechanical, thermal, and structural performance of gelatin matrices; however, its tendency to agglomerate in gelatin limits uniform dispersion, and consequently restricts its reinforcement capabilities. This study focuses on the synthesis and characterization of a novel nanohybrid composite, integrating gelatin nano-emulsion as the biopolymer matrix with different weight ratios of nano-CaP colloidal suspension (CaP10% and CaP20%) as the reinforcing phase. Various characterization techniques were used to evaluate the influence of nano-CaP on interfacial interaction and effect on microstructure. Fourier transform infrared spectroscopy and X-ray diffraction results show calcium hydroxyapatite as the main phase (75%) in the nanohybrid composite while scanning electron microscope confirmed its intimate contact and homogenous dispersion. The 10% CaP loading provided a better physical and thermo response, including a higher glass transition temperature (220 °C), and increased hydrophobicity (45% increase in water contact angle). These enhancements in properties are attributed to the homogenous dispersion of nano-CaP in the nanogelatin matrix and the strong interfacial interaction between the particle surfaces and the nanogelatin molecule. Overall, the results demonstrate the potential of colloidal nano-CaP suspension as a dual-function agent for cross-linking and thermo-mechanical reinforcement in gelatin-based nanocomposites.