Effects of transforming growth factor beta 1 released from biodegradable polymer microparticles on marrow stromal osteoblasts cultured on poly(propylene fumarate) substrates

Recombinant human transforming growth factor beta 1 (TGF-beta 1) was incorp orated 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-beta 1 in the microparticle s containing 5% PEG was 40.3 +/- 1.2% for a TGF-beta 1 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-beta 1 was released after 1 and 8 days, respectiv ely, followed by a plateau for the remaining 3 weeks. Rat marrow stromal ce lls showed a dose response to TGF-beta 1 released from the microparticles s imilar to that of added TGF-beta 1, indicating the activity of TGF-beta 1 w as retained during microparticle fabrication and after TGF-beta 1 release. An optimal TGF-beta 1 dosage of 1.0 ng/mL was determined through a 3-day do se response study for maximal alkaline phosphatase (ALP) activity. The TGF- beta 1 released from the microparticles loaded with 6.0 ng TGF-beta 1/1 mg of microparticles for the optimal dosage of TGF-beta 1 enhanced the prolife ration and osteoblastic differentiation of marrow stromal cells cultured on poly(propylene fumarate) substrates. The cells showed significantly increa sed total cell number, ALP activity, and osteocalcin production with values reaching 138,700 +/- 3300 cells/ cm(2), 22.8 +/- 1.5 x 10(-7) mu mol/min/c ell, and 15.9 +/- 1.5 x 10(-6) ng/cell, respectively, after 21 days as comp ared to cells cultured under control conditions without TGF-beta 1. These r esults suggest that controlled release of TGF-beta 1 from the PLGA/PEG blen d microparticles map find applications in modulating cellular response duri ng bone healing at a skeletal defect site. (C) 2000 John Wiley & Sons, Inc.