(647a) Peg Hydrogels with Tunable Biodegradation Rate for Sustained Delivery of Platelet-Rich Plasma for Treatment of Osteoarthritis

Knee osteoarthritis (KOA), a disease caused by chronic inflammation and wearing of articular cartilage, affects over 50 million Americans. Sustained delivery of platelet-rich plasma (PRP) is a promising KOA therapy and has the potential to slow, reverse or halt its progression. PRP is a concentrated assortment of growth factors and cytokines derived from the patient’s own platelets and is currently used in the clinic as a direct injection in the knee. However, such bolus injections have shown mixed results due to a rapid clearance of the growth factors. Here, we tested the therapeutic effects of a sustained PRP release from polyethylene glycol (PEG) hydrogels on primary articular chondrocytes.

Poly(ethylene glycol) (PEG) has been studied widely for the design of biodegradable hydrogel networks because of its exceptional biocompatibility and inertness. For temporal control of PRP release, we first designed and characterized PEG hydrogels with a wide range of properties. We made hydrogel using a combination of multiarm PEG-acrylate (PEGAc) of varying molecular weight and number of arms and three categories of dithiol crosslinkers, namely, ester-containing, non-ester-containing and crosslinkers with neighboring functional groups of different electronegativities. By changing these parameters, we obtained hydrogels with controlled degradation ranging from 10 h to 32 d and mesh size in the range of 9-14 nm. Uniquely, the hydrogel storage moduli could be controlled by the dithiol crosslinker chemical identity independent of the degradation time or mesh size. Further in vitro biocompatibility testing showed suitability for PRP delivery.

We then tested the PEG hydrogels for encapsulation and release of PRP. Specifically, to model the release of multicomponent PRP through PEG hydrogels, we examined bulk diffusion of total PRP proteins and model proteins having a hydrodynamic radius and molecular weight in a range corresponding to the growth factors found in PRP. Model proteins or PRP at 2-10% w/v were encapsulated during gelation of the hydrogels. Our results indicated that protein size and hydrogel degradation controlled diffusion of all proteins and secondary structure of proteins encapsulated during gelation remained unaffected post-release. Multiplex analysis showed release of therapeutically relevant proteins from PRP (endothelial derived growth factor (EGF) and platelet derived growth factor (PDGF)) at all time points until complete degradation of the hydrogels. Further investigation of the mechanism of protein release from high PRP concentration containing hydrogels using fluorescence correlation spectroscopy (FCS) indicated anomalous diffusion which may be due to protein crowding or protein-protein interactions. PRP released from hydrogels promoted the proliferation of human dermal fibroblast (HDF) cells, indicating retained bioactivity upon encapsulation and release. PRP releasates/ fractions collected at specific time intervals also showed increased proliferation in HDF cells comparable to that of a bolus PRP injection.

Lastly, we evaluated the therapeutic effects of sustained release of PRP from PEG hydrogels on primary articular chondrocytes. We examined the release profiles of different PRP fractions and their effects on chondrocyte proliferation, expression of anabolic and catabolic gene transcripts post-treatment with PRP fractions released at different time from the PEG hydrogel. We also examined the effect of the released PRP on glycosaminoglycan (GAG) production in cartilage explants. We observed a sustained release of several growth factors including EGF and PDGF for PRP-loaded PEG gels. In particular, PRP released from hydrogel promoted chondrocyte growth in vitro with different fractions showing differential ability to promote chondrocyte proliferation correlating to their growth factor content. PRP released from the PEG gels also led to significant reduction in gene expression for genes related to matrix degradation and upregulation of anti-inflammatory genes. Treatment of cartilage explants with different fractions of released PRP showed an increase in GAG production. Taken together, these results indicate that sustained delivery of PRP from PEG hydrogels had a significant beneficial effect on chondrocytes, in terms of cell proliferation and matrix production, as compared to a bolus PRP dose or no PRP.