Effects of transforming growth factor β1 released from biodegradable polymer microparticles on marrow stromal osteoblasts cultured on poly(propylene fumarate) substrates

Recombinant human transforming growth factor β1 (TGF-β1) was incorporated into microparticles of blends of poly(DL-lactic-co-glycolic acid) (PLGA) and poly(ethylene glycol) (PEG) to create a delivery vehicle for the growth factor. The entrapment efficiency of TGF-β1 in the microparticles containing 5% PEG was 40.3 ± 1.2% for a TGF-β1 loading density of 6.0 ng/1 mg of microparticles. For the same loading, 17.9 ± 0.6 and 32.1 ± 2.5% of the loaded TGF-β1 was released after 1 and 8 days, respectively, followed by a plateau for the remaining 3 weeks. Rat marrow stromal cells showed a dose response to TGF-β1 released from the microparticles similar to that of added TGF-β1, indicating the activity of TGF-β1 was retained during microparticle fabrication and after TGF-β1 release. An optimal TGF-β1 dosage of 1.0 ng/mL was determined through a 3-day dose response study for maximal alkaline phosphatase (ALP) activity. The TGF-β1 released from the microparticles loaded with 6.0 ng TGF-β1/1 mg of microparticles for the optimal dosage of TGF-β1 enhanced the proliferation and osteoblastic differentiation of marrow stromal cells cultured on poly(propylene fumarate) substrates. The cells showed significantly increased total cell number, ALP activity, and osteocalcin production with values reaching 138,700 ± 3300 cells/cm², 22.8 ± 1.5 x 10^-7 μmol/min/cell, and 15.9 ± 1.5 x 10^-6 ng/cell, respectively, after 21 days as compared to cells cultured under control conditions without TGF-β1. These results suggest that controlled release of TGF-β1 from the PLGA/PEG blend microparticles may find applications in modulating cellular response during bone healing at a skeletal defect site. (C) 2000 John Wiley and Sons, Inc.