Plasma-Assisted Hydroxyapatite/Chitosan Bionanocomposite Films with Improved Thermal Stability, Biomineralization and Optical Absorption Properties

Hydroxyapatite (HAp) is a well-known precursor for synthesizing different bionanocomposite products for biomedical applications. For the first time, we aimed to evaluate the effects of plasma surface functionalization of HAp nanoparticles (NPs) on the chemical, physical, and bio-functional properties of chitosan films using experimental and computational evaluations. Atmospheric air plasma process was conducted on HAp NPs at two different air pressures (650 and 1300 mTorr) and four different exposure times (1, 3, 6, and 9 min), followed by fabrication of HAp/chitosan bionanocomposites. Fourier transform infrared (FTIR) spectra proved that the position of bands at 1639 and 1037 cm⁻¹ were shifted to 1635 and 1031 cm⁻¹ due to the interaction between chitosan amine groups and HAp phosphate groups. Quantum mechanical and molecular dynamic (MD) simulations were used to understand the interactions between chitosan and HAp. Density functional theory (DFT) calculations were used to explore the electronic properties of untreated and plasma-treated HAp (T-HAp). MD simulations using the PCFF force field were used to investigate the interactions of HAp/chitosan and T-HAp/chitosan bionanocomposites. According to the results from thermal gravimetric analysis (TGA), the duration of HAp NP plasma treatment is a significant factor in the weight loss properties for the resultant HAp/chitosan bionanocomposites. The overall reflectance % properties of films prepared with T-HAp NP samples decreased, confirming the potential applications for skin tissue protection against solar UV radiation. The bioactivity of the bionanocomposite films was also studied by examining the HAp formation by incubating in simulated body fluid.