Development of Bioadhesive Microcapsules as a New Cellular Treatment for the Diffuse Cartilage Lesions

<b>Introduction: </b>Cartilage structures can be damaged causing two types of injuries: focal; the lesion is restricted to a concrete zone or diffuse; the lesion affects a broad area of the articular cartilage. This type of lesions appears due to the reduced self-healing capacity of articular cartilage. Diffuse damage is much more difficult to treat, usually restricted to palliative care or systemic anti-inflammatory treatments. This type of diffuse lesions have a high prevalence as the common type of degenerative processes.<br/>More recently, cell-based approaches using autologous chondrocytes or mesenchymal stem cells (MSCs)¹ have been tested and it can even be found in some clinics. However, the efficacy of such cell-based treatment is controversial². In general terms, the applied cells stay in the injection site only for short periods of time, so their regenerative potential is greatly reduced. The most promising approach is the combination of such cells with a biomaterial-based carrier that can play that role.<br/>The general objective of the project, in order to resolve the previous task, is the development of bioadhesive and injectable cell microcarriers with the ability to regenerate the articular cartilage. This aim is materialized in the fabrication of multibiofunctional capsules that are able to promote the cell cargo with selective adhesion and location on the articular surface. To do so, special attention is paid to the cell-material interaction on both the inner and outer surface of the capsule by means of the inclusion of specific cell adhesion domains and sequences that promote the adhesiveness to collagen II and chondroitin sulfate.<br/>The microcapsules are based on a novel kind of biomaterials, named Recombinamers that are polypeptide materials obtained by recombinant DNA technology. In particular, the core composition of the microcarrier is the Elastin-like Recombinamers (ELRs)³.<br/><b>Experimental methods: </b>Recombinant DNA techniques have proven to be very powerful tools for the development of novel protein-based biomaterials. This class includes ELRs, which are protein-based polypeptides that comprise repetitive units of the Val−Pro−Gly−X−Gly (VPGXG)n pentapeptide, in which X (guest residue) could be any amino acid except<br/>L-proline. ELRs are inspired by elastin, showing excellent biocompatibility, and they exhibit thermo-responsiveness in aqueous media.<br/>The cloning and molecular biology for gene construction were performed using standard genetic-engineering methods. Production was carried out by recombinant techniques using Escherichia coli as the cell system. Purification was performed by several cooling and heating purification cycles (Inverse Transition Cycling) following centrifugation; the ELRs obtained in this manner were dialyzed against MilliQ water and lyophilized.<br/><b>Results and discussion</b>:<b> </b>Genetic engineering methods allowed the synthesis of the genetic construct capable of synthesizing the desired biomaterial. Biopolymer adhesion to the hyaline-cartilage matrix was demonstrated measuring the adhesion forces between our biomaterial and surfaces with collagen II and chondroitin-sulfate versus control surfaces and quartz-microbalance.<br/>Tailored layer-by-layer (LbL) approaches allowed the encapsulation of cell spheroids of autologous chondrocytes and MSCs.<br/>In vitro and ex vivo assays were performed using cartilage explants from patients surgically intervened, this type of analysis showed the derivatized ELR adhesion efficacy to the articular surface and the final liberation of cell spheroids encapsulated hoping to demonstrate the cartilage regeneration.<br/><b>Conclusion: </b>In conclusion, a novel protein-based biomaterial with adhesion to the hyaline-cartilage matrix was synthetized. Besides, cell spheroids were encapsulated by the polymer.<br/>Hence, in this study could be possible overcome the limitations of the current treatments used in diffuse cartilage lesions and suppose an advance in regenerative medicine.