Repair of an osteochondral defect by sustained delivery of BMP-2 or TGFβ1 from a bilayered alginate-PLGA scaffold

Abstract

Regeneration of cartilage defects can be accelerated by localized delivery of appropriate growth factors (GFs) from scaffolds. In the present study we analysed the in vitro and in vivo release rates and delivery efficacies of transforming growth factor-β1 (TGFβ1) and bone morphogenetic protein-2 (BMP-2) from a bilayered system, applied for osteochondral defect repair in a rabbit model. A bone-orientated, porous PLGA cylinder was overlaid with GF containing PLGA microspheres, dispersed in an alginate matrix. Four microsphere formulations were incorporated: (a) blank ones; (b) microspheres containing 50 ng TGFβ1; (c) microspheres containing 2.5 µg BMP-2; and (d) microspheres containing 5 µg BMP-2. Release kinetics and tissue distributions were determined using iodinated ((125) I) GFs. Bioactivity of in vitro released BMP-2 and TGFβ1 was confirmed in cell-based assays. In vivo release profiles indicated good GF release control. 20% of BMP-2 and 15% of TGFβ1 were released during the first day. Virtually the total dose was delivered at the end of week 6. Significant histological differences were observed between untreated and GF-treated specimens, there being especially relevant short-term outcomes with 50 ng TGFβ1 and 5 µg BMP-2. Although the evaluation scores for the newly formed cartilage did not differ significantly, 5 µg BMP-2 gave rise to higher quality cartilage with improved surface regularity, tissue integration and increased collagen-type II and aggrecan immunoreactivity 2 weeks post-implantation. Hence, the bilayered system controlled GF release rates and led to preserved cartilage integrity from 12 weeks up to at least 24 weeks.

Comparative, osteochondral defect repair: Stem cells versus chondrocytes versus Bone Morphogenetic Protein-2, solely or in combination

“…1a) was prepared as previously described (Reyes et al, 2012). Briefly, the bone-directed layer (Fig.…”

“…Microsphere preparation BMP-2 loaded microspheres were prepared by a double emulsion (w/o/w) method (Hernández et al, 2012). Briefly, the first emulsion was made by vortexing 200 µL of a BMP-2 (180 μg) solution in 0.07 % poly-vinyl alcohol (PVA) with 2 mL of a PLGA (Resomer ® RG504) methylene chloride solution (50 mg/mL).…”

“…Accordingly, scaffolds may be loaded with GFs such as bone morphogenetic protein (BMP)-2 and TGF-b1 (Sellers et al, 1997;Sellers et al, 2000;Holland et al, 2005;Holland et al, 2007;Reyes et al, 2012), seeded with chondrocytes or MSCs Qi et al, 2011;Ito et al, 2012), or employed with combinations of both GFs and cells (Im and Lee, 2010;Wang et al, 2010). To date, only few studies compare MSCs and chondrocytes in cartilage defect repair.…”

“…This study compares osteochondral defect repair in rabbits upon implantation of allogeneic chondrocyte-versus MSC-seeded, alginate/ PLGA tri-layer scaffolds, both without BMP-2 and under controlled release of the alginate-embedded, microsphereencapsulated BMP-2. A relatively low dose of 5 µg of BMP-2 and its release kinetics from this system had been optimised for cartilage repair in a preceding study (Reyes et al, 2012). BMP-2 was liberated into the defect for approximately 6 weeks (previously determined by local 125 I-BMP-2 monitoring).…”

Controlled Release Strategies for Bone, Cartilage, and Osteochondral Engineering—Part II: Challenges on the Evolution from Single to Multiple Bioactive Factor Delivery

“…Reyes et al 142 analyzed osteochondral regeneration postimplantation of a bilayered scaffold loaded with BMP-2 or TGF-b1 and observed that the higher concentration of BMP-2 gave rise to higher quality cartilage with improved surface regularity 2 weeks postimplantation.…”