SP0151 MICROFABRICATION TECHNOLOGIES FOR CARTILAGE REPAIR

Abstract

Background: Cartilage trauma is a major risk factor for the development of post-traumatic osteoarthritis. Treatment options are limited, are ineffective in the long run or come with disadvantages. Hence unconventional new strategies need to be explored to address this problem. Objectives: In this lecture, I will present three strategies that are currently explored in my lab and that rely on the integration of biology with micro- and nanotechnologies to solve this problem. Results and Methods: In a first strategy, we invested in the development of injectable and in situ gelating hydrogels that can be used as fillers of a cartilage defect stimulating its regeneration. We developed a panel of natural polymer (e.g. hyaluronic acid, dextran, heparin, gelatin, collagens) – tyramine conjugates which crosslink in a macromolecular network in an enzymatic reaction. The reaction is fast, can be tuned and using this method a wide variety of extracellular matrix mimics can be engineered. Moreover, the crosslinking reaction fixates the gel in the surrounding tissue through covalent bonding between tyramine residues in the hydrogel with tyrosine residues in extracellular matrix proteins, effectively acting as a glue. The hydrogel can be applied during an arthroscopic procedure. We tested the potential of the hydrogel to facilitate the repair of an acute focal cartilage defect in an equine chondral defect model and evaluated the repair process after 2 weeks, 3 months and 7 months. We compared the repair of a hydrogel-filled defect with the microfracture procedure, a frequently used but largely ineffective procedure due to the formation of fibrous cartilage instead of hyaline cartilage. After two weeks massive cell ingrowth in the hydrogel was observed. This continued and after 3 months hydrogel treated defects resulted in near complete defect filling with predominantly hyaline cartilage and without noticeable reactions in the subchondral bone. This was in marked contrast to the defects treated with microfracture, which showed a massive response in subchondral bone and the formation of fibrous tissue. The repair was consolidated after 7 months. Defect filling might be a viable solution for treatment of focal cartilage defects to prevent early onset, post-traumatic osteoarthritis. In a second strategy, we use the same material platform for cell delivery in the joint. Co-injection of cells with the in situ gelating hydrogels might be beneficial in the repair of particularly large (osteo)chondral defects. We have developed microfluidic-based systems for the encapsulation of 10-15 cells in microgels of approximately 100μm or even at the single cell level in microgels with a diameter of 30μm slightly larger than the cell itself. We postulated that encapsulation of Mesenchymal Stromal Cells (MSCs) could prolong the retention time in the joint after an intra-articular injection over “naked” MSCs and may, therefore, improve the therapeutic benefit of these cells. We tested this hypothesis in a rat model and indeed showed that, while “naked” near infrared labeled MSC rapidly disappeared from the injected joint, encapsulated cells remained present up to 4 months. We are currently exploring its potential to improve the therapeutic efficacy of the MSCs. In a third strategy, we use the material platform in combination with cytokine neutralizing antibodies to generate easily injectable microgels that can sequester pro-inflammatory cytokines from the synovial fluid. Rather than using conventional antibodies, we rely on the variable domain of single chain, heavy chain-only antibody fragments such as found in Camelidae. These antibody fragments can be easily produced using recombinant DNA technology and are open for a wide variety of chemical reactions without impacting its biological activity. These microgels can effectively neutralize cytokines in cell assays in vitro and are currently explored for its potential to neutralize cytokines in synovial fluid and after intra-articular injection. Conclusion: In conclusion, the integration of biology with microfabrication technologies has the potential to generate the next generation of therapies for the treatment of cartilage defects and osteoarthritis. Disclosure of Interests: None declared