Enhanced MSC chondrogenesis following delivery of TGF-β3 from alginate microspheres within hyaluronic acid hydrogels in vitro and in vivo

Mesenchymal stem cells (MSCs) are being recognized as a viable cell source for cartilage repair and members of the transforming growth factor-beta (TGF-beta) superfamily are a key mediator of MSC chondrogenesis. While TGF-beta mediated MSC chondrogenesis is well established in in vitro pellet or hydrogel cultures, clinical translation will require effective delivery of TGF-beta s in vivo. Here, we investigated the co-encapsulation of TGF-beta 3 containing alginate microspheres with human MSCs in hyaluronic acid (HA) hydrogels towards the development of implantable constructs for cartilage repair. TGF-beta 3 encapsulated in alginate microspheres with nanofilm coatings showed significantly reduced initial burst release compared to uncoated microspheres, with release times extending up to 6 days. HA hydrogel constructs seeded with MSCs and TGF-beta 3 containing microspheres developed comparable mechanical properties and cartilage matrix content compared to constructs supplemented with TGF-beta 3 continuously in culture media, whereas constructs with TGF-beta 3 directly encapsulated in the gels without microspheres had inferior properties. When implanted subcutaneously in nude mice, constructs containing TGF-beta 3 microspheres resulted in superior cartilage matrix formation when compared to groups without TGF-beta 3 or with TGF-beta 3 added directly to the gel. However, calcification was observed in implanted constructs after 8 weeks of subcutaneous implantation. To prevent this, the co-delivery of parathyroid hormone-related protein (PTHrP) with TGF-beta 3 in alginate microspheres was pursued, resulting in partially reduced calcification. This study demonstrates that the controlled local delivery of TGF-beta 3 is essential to neocartilage formation by MSCs and that further optimization is needed to avert the differentiation of chondrogenically induced MSCs towards a hypertrophic phenotype. (C) 2011 Elsevier Ltd. All rights reserved.