A hybrid coating of polydopamine and nano-hydroxyapatite enhances surface properties of 3D printed poly(lactic-co-glycolic acid) scaffolds

Polydopamine (pDA)-based surface modification is a promising method to enhance the surface conditions of biomaterials and facilitate cell-material interactions. Traditionally, the pDA is coated before anchoring secondary bioactive factors, which requires an extra step and limits the availability of pDA on the surface, impeding the efficacy of pDA itself in enhancing cell function. In this study, for the first time, nano-hydroxyapatite (nHA) particles were immobilized on 3D printed poly(lactic-co-glycolic acid) (PLGA) scaffolds with a single step during dopamine polymerization. Unique micro-/nano-pores were produced during incubation of the PLGA substrate with Tris-HCl. Surprisingly, PLGA controls and pDA demonstrated higher surface roughness than nHA and pDA-nHA groups. The coating processes did not alter the strut width (cross-sectional area from top view). No visible differences in coating thickness were observed among groups. Both nHA and pDA alone increased the hydrophilicity of the PLGA surface, and the hybrid pDA-nHA coating further improved the hydrophilicity. The mechanical properties were not different between groups. Only the hybrid pDA-nHA coating showed increasing cell numbers from day 1 to 3 and day 3 to 5. Cell number on hybrid pDA-nHA scaffolds on day 5 was greatest among experimental groups, while cell number on pDA was the lowest at all timepoints. These results collectively highlight a novel, single-step method of self-polymerized, dopamine-induced nHA deposition for enhancing the surface properties of and cell-material interactions with 3D printed PLGA scaffolds, demonstrating the efficacy of pDA-based hybrid coatings in functionalizing polymer substrates for bone tissue engineering.