Hydrothermal processing of 3D-printed calcium phosphate scaffolds enhances bone formation in vivo: a comparison with biomimetic treatment

Abstract

Hydrothermal (H) processes accelerate the hydrolysis reaction of α-TCP compared tothe long-establishe dbiomimetic (B) treatments. They are of special interest for patient-specific 3D-printed bone graft substitutes, where the manufacturing time represents a critical constraint. Altering the reaction conditions hasimplications forthe physicochemical propertiesof the reaction product. However, the impact of the changes produced by the hydrothermal reaction on the invivo performancewas hitherto unknown.The present study compares the bone regeneration potential of 3D printed α-TCP scaffolds hardened using these two treatments in rabbit condyle monocortical defects. Although both consolidation processes resulted in biocompatible scaffolds with osseointegrative and osteoconductive properties, the amount of newly formed bone increased by one third in the hydrothermal vs the biomimetic samples. B and H scaffolds consisted mostly of high specific surface area calcium deficient hydroxyapatite (38 and 27 m2/g respectively), with H samples containing also 10 wt. %β-TCP. The shrinkage produced during the consolidation process was shown to be very small in both cases, below 3%, and smaller for H than for B samples. The differences in the in vivo performance were mainly attributed to the distinct crystallisation nanostructures, which proved to have a major impact on permeability and protein adsorption capacity, using BSA as a model protein, with B samples being highly impermeable. Given the crucial role that soluble proteins play in osteogenesis, this is proposed to be a relevant factor behind the distinct in vivo performances observed for the two materials.