Evaluation of octapeptide hydrogels for cartilage tissue engineering

This thesis investigates the suitability of an octapeptide hydrogel scaffold for use in the tissue engineering of cartilage. The work has focused on two main areas; the biocompatibility of the hydrogel scaffold and the ability of the scaffold to sustain chondrocyte morphology and function. Firstly, this thesis presents a protocol for testing the biocompatibility of the FEFEFKFK hydrogel scaffold using an enzyme linked immunosorbent assay. This protocol could subsequently be used as part of the biocompatibility testing of other hydrogel scaffolds prior to in vivo use. The inflammatory potential of the hydrogel was established by encapsulating monocytes which are known to produce inflammatory mediators, within the hydrogel. The production of cytokines TNFα, IL-6 and IL-1β in response to the hydrogel was quantified using an enzyme linked immunosorbent assays. The hydrogel scaffolds tested did not insight a significant pro inflammatory response from the monocytes in any of the studies. The FEFEFKFK hydrogel was encapsulated with bovine and human chondrocytes to investigate the morphology, viability and function of chondrocytes within the hydrogel scaffold. Chondrocyte morphology and viability was assessed using a combination of optical microscopy, cell staining and confocal microscopy. It was found that both bovine and human chondrocytes were viable and maintained a normal morphology within the FEFEFKFK hydrogel up to 35 and 28 days duration respectively. However, aggregation was seen in the bovine samples after 21 days and peripheral cell death in the human samples due the degradation of the hydrogel. Chondrocyte function was evaluated by measuring the production of glycosaminoglycans from the bovine and human chondrocytes encapsulated in the hydrogel over 28 days. The production of glycosaminoglycans increased from day 7 to day 28 in the bovine chondrocyte samples and from day 7 to 21 in the human chondrocyte samples. In addition, the rheology of the hydrogel was quantified with and without chondrocytes to investigate the stiffness and degradation of the scaffold. The rheology revealed that the hydrogels were stiffer when encapsulated with chondrocytes. There was in increase in stiffness in all samples from 0-7 days. However, following this there was a gradual degradation of the hydrogel reflected by a decline in the stiffness. This thesis demonstrates that the FEFEFKFK octapeptide hydrogel supports chondrocyte viability with maintenance of normal cell morphology and function. There is no evidence of the hydrogel inciting an inflammatory response and as such it demonstrates potential for future use in vivo for cartilage engineering. The hydrogel shows degradation over time which affects the chondrocytes encapsulated within it and therefore further work needs to be carried out to improve the longevity of the hydrogel until sufficient extracellular matrix is produced to support the chondrocytes in 3 dimensions.