Introduction

Despite the development of biomaterials with different properties and new ways to biofabricate scaffolds, the repair of cartilage lesions remains a challenge. Cell-material interactions determine the final result, in cell-free as well as cell containing procedures, but we do not fully understand these interactions and how they influence cartilage regeneration. We have evaluated several materials for their effects on cell migration, cartilage tissue formation as well as inflammation using in vitro and in vivo assays.

Content

METHODS:

Different hydrogels and scaffolds and modifications of their physical and chemical properties were used. In vitro assays were performed to study migration of human Bone marrow-derived Mesenchymal Stromal Cells (BMSCs) and the capacity of the materials to support cartilage tissue formation. For in vivo evaluation bovine osteochondral tissue biopsies were harvested in which a defect was created that we filled with the materials and implanted subcutaneously in athymic mice. uCT and histology were performed to analyse cell ingrowth, tissue repair and inflammatory reaction.

RESULTS:

Migration of BMSC into a hydrogel in vitro depended on stiffness and composition of the hydrogel and could be stimulated by addition of chemokines such as PDGF-BB. Inflammatory cytokines as well as factors secreted by macrophages also stimulated migration of BMSCs in vitro.

The formation of cartilage tissue was also hydrogel composition dependent. In the semi-orthotopic osteochondral defect model in vivo, migration of cells from the bone (marrow) side was obvious and depended on the biomaterial used. Induction of an inflammatory process by the material is not necessarily bad for the repair response, as long as the inflammation resolves since inflammatory factors impair chondrogenesis. Loading factors such as PDGF-BB, BMP-2 or antiMiR221 in the material could stimulate the repair process.

It remains a challenge to prevent ossification of the newly generated cartilage in an osteochondral defect using a cell-free procedure. We have demonstrated that cartilage, even mature articular cartilage, secretes angiogenic factors and the integrity of the cartilage matrix was demonstrated to be key for prevention of vessel ingrowth in a bone environment.

DISCUSSION & CONCLUSIONS:

The in vitro and in vivo models are useful to study materials for capacity to stimulate cartilage repair. More fundamental knowledge of how the physical properties and the composition of materials influence cell behaviour is important to improve cartilage regeneration. To regenerate a functional osteochondral unit choices related to embedding the right cells or attract the right cells at the right moment, preventing vessels from entering the cartilage part and rebuilding a functional interface between bone and cartilage will be the challenges for the future.

References

Presented work will be based on previously published work of the group:

Fahy N et al. Human osteoarthritic synovium impacts chondrogenic differentiation of mesenchymal stem cells via macrophage polarisation state. Osteoarthritis Cartilage. 2014;22(8):1167

Sivasubramaniyan K. et al. Bone Marrow-Harvesting Technique Influences Functional Heterogeneity of Mesenchymal Stem/Stromal Cells and Cartilage Regeneration. Am J Sports Med. 2018;46(14):3521

Lolli A et al. Hydrogel-based delivery of antimiR-221 enhances cartilage regeneration by endogenous cells. J Control Release. 2019;309:220

Vainieri ML, et al. Evaluation of biomimetic hyaluronic-based hydrogels with enhanced endogenous cell recruitment and cartilage matrix formation. Acta Biomater. 2020;101:293

Nossin Y et al. The Releasate of Avascular Cartilage Demonstrates Inherent Pro-Angiogenic Properties In Vitro and In Vivo. Cartilage. 2021 Dec;13(2_suppl):559S-570

Andres Sastre et al. A new semi-orthotopic bone defect model for cell and biomaterial testing in regenerative medicine. Biomaterials 2021 Dec;279:121187

Muntz I et al, The role of cell-matrix interactions in connective tissue mechanics. Phys Biol. 2021- epub

Acknowledgments

TargetCaRe (HORIZON2020-MSCA-2014-ITN nr 642414); CarBon (HORIZON2020-MSCA-2016-ITN nr 721432); Hunter (NWO Perspectief P15-23); NanoScores (Eurnanomed3 JTC-2017 nr ENMIII 077-2); AO Foundation (AO-OCD consortium TA1711481); Medical Delta Regenerative Medicine 4D programme; Convergence Health and Technology Impuls program