Assessment of osteogenesis for 3D-printed polycaprolactone/hydroxyapatite composite scaffold with enhanced exposure of hydroxyapatite using rat calvarial defect model

In the polycaprolactone/hydroxyapatite scaffold fabricated by the melting-extrusion-type 3D-printing system, hydroxyapatite (bioceramic) particles are usually covered by a thin-film polycaprolactone (thermoplastic polymer) layer because of the rheological characteristics of the melting-extrusion process. The original bioactive characteristics of the bioceramic particles can be disrupted by this thin-film thermoplastic polymer. Therefore, in this study, an alkaline erosion process was employed to eliminate the thin-film polycaprolactone layer to expose the hydroxyapatite particles. To investigate the influence of the enhanced exposure of hydroxyapatite on cell response and bone regeneration, the polycaprolactone scaffold, polycaprolactone scaffold with alkaline erosion, and polycaprolactone/hydroxyapatite scaffold were compared with the polycaprolactone/hydroxyapatite scaffold with alkaline erosion. Furthermore, to identify the characterization of the 3D-printed composite scaffold for hydroxyapatite's exposure, the morphology, pore size, porosity, mechanical compressive modulus, in-vitro cell response, and in-vivo bone regeneration were assessed. Consequently, the proposed alkaline erosion for the exposure of hydroxyapatite did not change the structural characteristics of the 3D-printed scaffolds, such as the pore size, porosity, and mechanical property. Additionally, we verified that the exposure of hydroxyapatite particles on the scaffold's surface promoted the bone-regeneration ability of the scaffold because of enhanced osteoconduction by hydroxyapatite's exposure.