Development of hydroxyapatite reinforced alginate–chitosan based printable biomaterial-ink

Abstract

This study reports synthesis of sodium alginate/ chitosan/ hydroxyapatite (HAp) based biomaterial-ink. An ionic interaction between polyanionic alginate and polycationic chitosan has been observed that forms a physical gel. The dispersion of HAp has been achieved through ultra-sonication, and stability of HAp in the hydrogel system has been achieved through hydrogen bonding with chitosan. Post printing crosslinking has been carried out with a 10 w/v % aqueous calcium chloride (CaCl2) solution. The combinations of biomaterial-ink have been characterized through Attenuated Total Reflectance-Fourier transform infrared spectroscopy (ATR-FTIR), Scanning Electron Microscope (SEM), contact angle measurements. Further, the inks were characterized to estimate the printability and rheological responses. ATR-FTIR study confirms the ionic interaction between alginate and chitosan and identifies the presence of HAp in the biomaterial-ink. SEM morphology depicted the post-printing shape retention ability of the bioprinted constructs and revealed the structure’s rough morphology. All the biomaterial-ink combinations depicted hydrophilic nature as confirmed by the contact angle measurements. Rheological studies of the printable ink with hydroxyapatite revealed shear thinning properties and acceptable viscosity, essential for extrusion during bioprinting. The biomaterial-ink comprised only sodium alginate, and chitosan also displayed shear thinning abilities and showed lower working viscosity resulting in poor printability. The addition of hydroxyapatite to the hydrogel revealed acceptable post-printing structural stability. However, beyond 0.2% by weight of HAp imparts brittleness in the final structure. The linear viscoelastic regime, elastic modulus, and viscous modulus of the inks have been determined through the oscillatory strain sweep test. Creep recovery study, essential for predicting material behaviour immediately after ejection from the nozzle, indicated the material’s viscoelastic behaviour. The power law model has been used to estimate the flow index that predicted shear thinning abilities of the biomaterial-ink, and a correlation between the experimental and theoretical model was established. Herschel–Bulkley empirical model was used to determine yield stress (minimum stress required for extrusion from the nozzle) of the biomaterial-ink. Rheological studies and printability studies indicated Ink 5% 2% 0.1% as a promising combination for tissue engineering applications.