Novel fibrinogen hydrogels for cell encapsulation and delivery

Introduction Hydrogels have the potential to deliver cells by injection directly to a site of injury to aid in the regeneration of damaged tissue. We have investigated a novel fibrinogen hydrogel produced using a proprietary fibrinogen polymerisation agent (FPA). When added to fibrinogen, FPA causes the polymerisation of fibrinogen into a multi-branched fibrin-like gel. The porosity of the fibrinogen hydrogels can be modified by changing the FPA concentration during gelation. The aim of this research was to investigate the potential of these novel hydrogels for encapsulation and culture of chondrocytes and mesenchymal stem cells (MSCs).

Materials and Methods Fibrinogen and fibrin hydrogels were formed by mixing solutions of 34 mg/ml fibrinogen with various concentrations of FPA or thrombin. For cell encapsulation, either bovine chondrocytes or MSCs were resuspended in fibrinogen prior to gelation. The cell encapsulated hydrogels were incubated under chondrogenic conditions for up to twenty one days. Cell viability was determined using resazurin dye and extracellular matrix (ECM) formation was assessed using 1,9-dimethylmethylene blue.

Results Chondrocytes and MSCs exhibited good survival and proliferation in all fibrinogen and fibrin hydrogels. Chondrocytes showed deposition of glycosaminoglycan's (GAGs) indicating ECM formation after twenty one days of encapsulation. In contrast, MSCs rapidly degraded and migrated out of all hydrogels after three days. Aprotinin inhibited hydrogel degradation and the deposition of GAGs could be assessed and indicated ECM formation.

Discussion The novel fibrinogen hydrogels supported cell survival and ECM formation for chondrocytes and MSCs. The MSC-induced degradation and their migration from the hydrogels was potentially due to the activation or production of a serine proteinase. This property could allow MSCs to migrate from the hydrogel into the injured tissue, and with the addition of aprotinin to the culture, greater control over the degradation of the hydrogels was provided. The fibrinogen hydrogels were comparable to commercial fibrin hydrogels, but have the additional advantage of modifying the porosity, by altering the concentration of FPAs during gelation thereby optimising the hydrogel for different cell types. In conclusion, this novel fibrinogen hydrogel has strong potential for use in cell encapsulation and delivery for the regeneration of injured tissue.