Enhanced osteogenesis of hydroxyapatite scaffolds by coating with BMP-2-loaded short polylactide nanofiber: a new drug loading method for porous scaffolds

Porous hydroxyapatite (HA) is widely used in porous forms to assist bone defect healing. However, further improvements in biological functions are desired for meeting complex clinical situations such as impaired bone regeneration in poor bone stock. The extracellular matrix (ECM) of human tissues is characterized by nanofibrous structures and a variety of signal molecules. Emulating these characteristics are expected to create a favorable microenvironment for cells and simultaneously allow release of osteogenic molecules. In this study, short polylactide fibers containing BMP-2 were prepared by electrospinning and coated on porous HA scaffolds. The coating did not affect porosity or pore interconnectivity of the scaffold but improved its compressive strength markedly. This fiber coating produced burst BMP-2 release in 1 day followed by a linear release for 24 days. The coating had a significantly lower rat calvarial osteoblasts (RCOBs) adhesion (vs. uncoated scaffold) but allowed normal proliferation subsequently. Bone marrow stem cells (MSCs) on the coated scaffolds expressed a significantly increased alkaline phosphatase activity relative to the uncoated ones. After implantation in canine dorsal muscles, the coated scaffolds formed significantly more new bone at Weeks 4 and 12, and more blood vessels at Week 12. This method offers a new option for drug delivery systems.