gms | German Medical Science

Objectives: Osteoarthritis (OA) is a degenerative joint disease causing loss of articular cartilage and structural damage in all joint tissues. Cartilage has only minimal intrinsic regenerative capacity due to the lack of vascularization and innervation. It remains challenging to identify successful long-term treatment options for articular cartilage defects occurring during OA progression. Therefore, methods to support the native structural properties of articular cartilage are highly anticipated. The aim of this study was to infiltrate zwitterionic monomer solutions into ex vivo human OA-cartilage explants to replace lost proteoglycans, and to encapsulate isolated human OA-chondrocytes within hydrogels to investigate the effects of different hydrogels on chondrocytes viability.

Methods: Chondrocytes and cartilage explants were isolated from knee joints of OA-patients undergoing total knee replacement surgery. Chondrocytes were cultivated in monolayers and cartilage explants were kept under sterile conditions until further use. Three different monomer solutions were synthesized to hydrogels: i) methacryloyloxyethyl-phosphorylcholine (MPC)-60, ii) MPC30, and iii) a novel sulfobetaine-methacrylate (SBMA)-based monomer solution. Cartilage explants were infiltrated with either MPC60, MPC30 or SBMA while protected from light at different time points (1 – 30min and 24h), and then polymerized with visible light. OA-chondrocytes were embedded in the respective monomers, subsequently polymerized with visible light, and cultivated for 1, 3 and 7 days. Successful infiltration and polymerization of hydrogel-containing OA-cartilage explants were analysed by Fourier-transform infrared spectroscopy, Scanning electron microscopy and immunofluorescence. Viability of hydrogel-containing OA-cartilage explants and hydrogel-embedded OA-chondrocytes was measured by live/dead cell staining and CellTiter-blue assay, respectively.

Results and conclusion: In general, cytotoxic effects of all three monomer solutions were observed, as well as a time-dependent infiltration behaviour into the OA-cartilage explants accompanied by increasing cell death and penetration depth. Interestingly, hydrogels were mainly deposited inside the chondrocytes, partially co-localized with cell nuclei, and chondrocyte-lacunae. Viability of OA-chondrocytes embedded in hydrogels was time-dependently decreased, with more viable cells embedded in SBMA compared to MPC60 or MPC30. The successful deposition of zwitterionic hydrogels within OA-cartilage identifies the infiltration method as a potential future therapeutic option for the repair/replacement of OA-cartilage suprastructure. Due to the toxic effects of the monomer-solutions, the focus should be on sealing the OA-cartilage surface, instead of complete infiltration. An alternative treatment option for focal cartilage defects could be the usage of hydrogels as bionic for cell-based 3D-bioprintable-hydrogels.