Biological evaluation of polydopamine and chitosan composite coatings on the 3D printed porous biphasic calcium phosphate scaffold

A current, gradually growing trend is to use bioactive ceramics to develop new bone scaffolds to replace traditional bone implants. Biphasic calcium phosphate (BCP), a mixed material of hydroxyapatite and tricalcium phosphate, has limited osseointegration ability. Therefore, improving the bioactivity and osteoinductive ability of BCP scaffolds through various surface modification methods is an important issue. Polydopamine (PDA) coating, chitosan (CS) coating, and their composite coatings have been previously reported to individually possess a good ability to improve scaffold bioactivity, but few comparisons between them and the optimal coating sequence of PDA and CS have been reported. Herein, we fabricated a BCP scaffold by using a self-made 3D printer, sintered the scaffold, and then prepared PDA, CS, PDA/CS and CS/PDA coatings by solution immersion. Afterwards, the surface morphology, element composition and proportion, compressive strength and surface contact angle of the five groups of scaffolds were characterized. Finally, the adhesion, proliferation and osteogenesis-related gene expression levels of MC3T3-E1 on the five groups in vitro were evaluated in detail. The results showed that the five types of scaffolds were fabricated successfully and that the PDA/CS and CS/PDA coatings had different surface morphologies. The compressive strengths of the composite-coating groups were higher than those of the single-coating groups and the BCP group. The CCK-8 experiment revealed that the composite coatings can promote the initial adhesion and proliferation of cells. The detection results of three osteogenesis-related genes (OCN, COL-1 and Runx-2) proved that the composite coatings had a synergistic effect in promoting osteodifferentiation and that the CS/PDA coating had the greatest effect in improving cell viability and promoting osteogenic differentiation.