Multilayered pore-closed PLGA microsphere delivering OGP and BMP-2 in sequential release patterns for the facilitation of BMSCs osteogenic differentiation.

Bone tissue regeneration may be more effectively administrated by controlled release of multiple biofactors, given that bone healing comprises a cascade of biological events controlled by numerous cytokines and growth factors (GFs). Here, we propose a novel microcarrier with the capability to sequentially deliver dual biofactors for better controlling the bone regeneration process. First, osteogenic growth peptide (OGP) was incorporated in porous poly(lactic-co-glycolic) acid (PLGA) microspheres by a simple solution dipping method and subsequent pore-closing treatment. Then, a multilayered polyelectrolyte coating ((HA-CS)2 -Hep-BMP-2-Hep-(CS-HA)2 ) was prepared on the surface of such OGP-loaded pore-closed PLGA microspheres by layer-by-layer assembly. Results showed that the OGP release was minimal (<17.1%) in the first 15 days but accelerated remarkably thereafter, while at least 60.3% of the bone morphogenetic protein-2 (BMP-2) load was released in the first 15 days and only very slow release was observed subsequently. Further in vitro cell experiments showed that the dual-biomolecule-loaded microspheres elicited more cells with extremely elongated cellular morphology, much higher alkaline phosphatase level and upregulated expression of osteocalcin. Such a dual loading of OGP and BMP-2 had a more positive impact on bone marrow mesenchymal stem cells proliferation and osteogenic differentiation compared with either OGP or BMP-2 alone, suggesting potential synergistic benefit of the sequential release of multiple peptide-based biofactors in a coordinated manner. Overall, this dual delivery system may provide a therapeutic strategy sequentially targeting multiple events (or mechanisms) during bone healing, which is believed to benefit the regenerative repair of bone defects. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 106A: 95-105, 2018.