gms | German Medical Science

Objectives: Cartilage treatment strategy is dependent on amongst others the lesion severity. Development and evaluation of cartilage treatment strategies in different defect geometries in pre-clinical models need to address defects ranging from fissures and cartilage only lesions to large defects involving subchondral bone.

Aim of this study was to modify a previously published osteochondral model (Schwab et al. 2016) by creating standardized cartilage defects with an automated device to mimic partial thickness and full thickness defects. Matrix assisted cell free and cell loaded treatments were compared to investigate the influence of surrounding tissue and defect depth on cartilage regeneration in ex vivo model.

Methods: Artificial Tissue Cutter (ARTcut®) is a computerized numerical controlled device for automated wounding of soft and hard tissues or tissue engineered products. Sensor controlled drilling allows creation of reproducible defects with standardized geometry. In this study, chondral defects, 4mm in diameter and 1mm in depth, were created with ARTcut® in cartilage of porcine osteochondral explants (8mm diameter x 5mm height). Lesions were left untreated, filled with cell free or chondrocyte loaded collagen I hydrogel isolated form rat tail and cultured for 4 weeks in ex vivo culture platform with tissue specific media. Live-dead staining was performed to investigate cell viability (day 0 & day 28). Cartilage regeneration was evaluated by (immune-) histological stainings and quantification of proteoglycan (GAG) content in hydrogels.

Results and Conclusion: Implementation of ARTcut® allows creation of chondral defects with a defined depth, measured from the surface of superficial layer of the explant. Live-dead staining did not show evidence of necrotic tissue formation due to drilling. Instead, invasion of cells into cell free hydrogel was observed after 4 weeks ex vivo culture. These cells originated from cartilage. Total number of cells migrated in chondral defects was less compared to full thickness defects. Invaded cells showed an elongated morphology which will be further analyzed for cartilage phenotypic markers. Chondrocytes in cell loaded approach synthesized cartilage matrix, shown by Safranin-O staining and immunohistological staining for collagen II and aggrecan and absence of collagen I and X. GAG/DNA content increased at day 28 to 5-fold (21.7 µg/µg) compared to day 0 (4.38 µg/µg).

ARTcut® represents an innovative device for creation of cartilage defects with varying geometries in osteochondral model to mimic different lesion severities and thus stages in degenerative joint disease. Comparison on chondral and osteochondral defects allows to study influence of opening subchondral bone on cartilage regeneration in ex vivo model.