Research

Glycosaminoglycan (GAG) Biomaterials for Protein Delivery
and Cell Differentiation

The Temenoff laboratory has demonstrated the power of modification of a key component of the extracellular matrix (GAGs) to affect protection and release of growth factors as well as influence mesenchymal stem cell (MSC) differentiation. To accomplish this, our lab has developed multiple families of GAGs with controlled sulfation patterns and further modified them to be crosslinkable for inclusion in hydrogel and microparticle biomaterials.

To investigate interactions between GAGs and therapeutic growth factors, we have explored the ability of several heparin species with controlled desulfation to protect the growth factor Bone Morphogenetic Protein-2 (BMP-2) from denaturation. Overall results suggest that desulfation may be needed at only one position to maintain the ability for the GAG to complex and protect the growth factor within a biomaterial carrier, while simultaneously reducing the anti-coagulatory effects of heparin (which are also sulfation-pattern dependent) to make future heparin-based biomaterials safe for in vivo growth factor delivery applications.

In terms of interactions with cells, we have shown that level of sulfation in crosslinked GAG-based hydrogels can affect mesenchymal stem cell differentiation towards chondrocytes in the presence of the chondrogenic growth factor TGF-β1. To further increase the amount of GAG available to interact with cells, a novel means of coating the surface of cells with GAGs has also been developed in our laboratory.

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Repair of Tendon Overuse Injuries

The Temenoff laboratory is interested in both knowing more about how ligaments and tendons are damaged, as well as designing new repair strategies for these tissues. In recent studies, we have used a rat model of an overuse injury to supraspinatus (rotator cuff) to demonstrate that damage occurs in the area of tendon insertion to bone. A novel multiplex zymography assay (developed in the Platt laboratory) was employed to determine activity of the cathepsin family of highly collagenolytic proteases. In overuse groups, increased cathepsin activity was seen in the insertion region, whereas little difference was observed in the remainder of the tendon. Moreover, collaborations with clinicians from Emory University allowed investigation of end stage disease (torn rotator cuff) in humans, where active cathepsins were also present. These results provide important information on a yet unexplored mechanism (protease-mediated ECM degradation) for tendon degeneration that may operate alone or in conjunction with other biochemical changes to contribute to chronic tendon degeneration leading to rotator cuff tear.

In terms of repair, MSCs have been suggested as a potential cell source for tendon/ligament tissue engineering to overcome the current limitation of lack of autologous fibroblasts. However, how best to deliver these cells to encourage engraftment remains unknown. In response, our laboratory has developed poly(ethylene glycol) hydrogel carriers with controlled degradation times due to altered susceptibility to hydrolysis. Three hydrogel formulations, including non-degrading, slower degrading (degraded in ~10 days) and faster degrading (degraded in ~5 days) hydrogels were selected for studies with MSCs in tendon tissue explants that had been treated with collagenase as a reproducible model of degenerate tendon. Quantitative analysis of the resulting histology images indicated that cell delivery from the hydrogels was dependent on the degradation rate. Based on these results, these hydrogels provide a versatile biomaterial platform to control cell delivery in injured tendons.

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