Elucidation of Physicochemical Conditions for Acellular Mineralization on Surface Activated 3D-Printed PLA Scaffolds

Bioapatite formation is a gradual process that involves the nucleation and crystallization of calcium phosphate minerals. The Gibbs free energy change (ΔG) is the precipitation driving force for hydroxyapatite formation. In vitro acellular mineralization over scaffolds has been studied widely in the context of the surface chemistry of the scaffolds for acting as a nucleation site. This study aims to optimize the physicochemical conditions for bone mimetic hydroxyapatite crystal growth in vitro through acellular mineralization on 3D-printed thermoplastic scaffolds. The hydrophobic 3D-printed poly(lactic acid) (PLA) scaffolds were oxygen plasma-treated to introduce -OH and -COOH groups. These functional groups can act as nucleation sites for hydroxyapatite crystal formation. Acellular mineralization was performed in DMEM media under varied pH, Ca:P ratio, ionic strength, and % CO₂ conditions. pH 9 and Ca:P ratio 2.1 were found to accelerate the process of carbonated hydroxyapatite formation on the scaffolds. When used in combination, there was a significant increase in the formation of crystallized carbonated hydroxyapatite on these scaffolds, as shown by the intense XRD peak for the 300 plane. These conditions can be used for depositing biomimetic hydroxyapatite on 3D-printed PLA scaffolds to increase their osteointegration and, thus, enhance their potential for clinical translation.