¹Universitätsmedizin Göttingen, Klinik für Unfallchirurgie, Orthopädie und Plastische Chirurgie, Göttingen, Deutschland

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Objectives and questions: Osteoarthritis (OA) is a degenerative joint disease characterized by the progressive breakdown of articular cartilage (AC) and structural changes in the subchondral bone (SB). Cartilage-bone marrow microchannel connectors (CMMCs) establish a direct link between AC and SB, facilitating potential biochemical and mechanical interactions. Recent studies indicate that CMMC morphology changes during OA progression, potentially affecting cartilage homeostasis and regeneration. However, the specific role of CMMC alterations in mesenchymal stem cell (MSC) differentiation and cartilage formation remains unclear.

This study aims to design a bioreactor system that allows to evaluate how different CMMC porosities influence MSC chondrogenesis and extracellular matrix (ECM) composition.

Material and methods: Human bone marrow MSCs SCP1 cells were encapsulated in polyethylene glycol diacrylate (PEGDA)-based (6,000 Mn) hydrogels and chondrogenically differentiated for 14 days. Additionally, a 3D alginate-based cell culture system was tested to pre-differentiate MSCs for two weeks prior to the bioreactor run.

A novel 3D bioreactor system was created to simulate varying properties of fluid mechanical forces and subchondral porosities. The bioreactor was designed to provide controlled mechanical stimulation and nutrient exchange, closely mimicking the knee joint environment. Polyetherimide (PEI) was selected as casing material due to its autoclavability and resistance to alcohol-based disinfectants. To investigate the impact of CMMC porosity on chondrogenesis, membranes with different porosities were created in titanium foils by laser beam cutting: 1.2% (healthy cartilage), 8% (early-stage OA), and 30% (late-stage OA).

Results: A resusable bioreactor design was further optimized to function as a closed system, reducing the potential for leakage and contamination. A model for the subchondral porosity was successfully produced at micrometer scale. Threedimensional culture of MSCs in chondrocyte differentiation conditions resulted in a significant upregulation of aggrecan, collagen type II (hCol2A1), collagen type X (hColX), and SRY-box transcription factor 9 (SOX9).

Discussion and conclusions: We have created a model system that models the CMMC-properties of different OA stages. This will allow to determine if and how CMMC-related structural changes contribute to chondrogenesis. Understanding the role of CMMC porosity in MSC chondrogenesis could offer new insights into OA pathogenesis and potential cartilage repair strategies.

References

[1] Taheri S, Winkler T, Schenk LS, Neuerburg C, Baumbach SF, Zustin J, Lehmann W, Schilling AF. Developmental Transformation and Reduction of Connective Cavities within the Subchondral Bone. Int J Mol Sci. 2019 Feb 12;20(3):770. DOI: 10.3390/ijms20030770