Development of a hybrid scaffold for cartilage tissue generation
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There exists a need for a biocompatible polymer system of appropriate degradation properties for use in the production of tissue-engineered cartilage replacement implants. The implant consists of a layer of cartilage grown using autogenous chondrocyte cells on a porous calcium phosphate base for anchoring in situ. This implant would serve to improve the current treatments for wear and age-related degradation of articular cartilage. Pilot dissolution studies of the biodegradable polymers Polyvinyl Alcohol (PVA), Polycaprolactone (PCL), and Polyethylene Glycol (PEG), provided strong evidence supporting the use of PVA and PEG, not PCL, in film preparation. Results indicate that the dissolution of PVA rapidly exceeds that required for this application while the dissolution of PCL is not fast enough. The results of a literature review indicate that PEG dissolves faster than PCL, but not PVA. Consequently, a co-polymer hydrogel film of PVA and PEG, to fully degrade in 10 hours, was prepared to serve as a support for the in vitro seeding of cartilage-producing chondrocyte cells onto the artificial bone scaffold base. In preparing the film, the concentration of the PVA and PEG stock solutions, the composition of PVA and PEG (by mass % ratio) in the film, and the thickness of the film were defined to be the design variables. The degradation properties of the film are hypothesized to be influenced by the design variables, such that the degradation rates can be engineered by manipulating these parameters. A full factorial DOE was applied to determine the significance of the design variables and their interaction on the degradation rate. To determine degradation rate, in vitro dissolution studies of the hydrogel film were conducted in Earle’s balanced salt solution at 37oC. Upon optimizing the degradation rate, it was theoretically determined that an optimized film of 50wt% PVA, 50wt% PEG, and thickness of 3mm dissolves by 88.19 % in 10 hours. Validation testing indicated that the optimized film was prematurely perforated at approximately 22 minutes of immersion in EBS at room temperature suggesting failure by bulk dissolution, which was later confirmed through investigation and identification of a heterogeneous, multi-phase microstructure under transmitting light microscope.