gms | German Medical Science

Objectives: Tissue adhesives may aid in the treatment of cartilage defects for improved cartilage integration. However, many fail to satisfy the demand for adequate adhesion strength on wet tissue surfaces and to facilitate sufficient cell migration and extracellular matrix (ECM) deposition at the defect site. Here, we present a poly(2-alkyl-2-oxazoline) (POx)-based adhesive, equipped with mussel-inspired adhesion moieties and tunable degradability. Lateral cartilage integration was evaluated in an in vitro defect model in a biomechanical push-out test and long-term tissue culture.

Methods: POx polymers were synthesized with different catechol functionalization degrees. The adhesive catechol group was attached to the side chain either with a stable amide- or with a hydrolyzable ester-linkage (0, 25 and 50% of total POx content) to obtain adhesives with different degradability. Under oxidative conditions, POx precursor solutions were reacted with fibrinogen to form an adhesive hydrogel. To evaluate the integrative potential the adhesives were applied at the defect interface of a disc/ring in vitro model that were generated from porcine articular cartilage blocks. Using a biomechanical push-out device, adhesive strength was determined as measure for cartilage integration 1 day after application and after culture for up to 3 weeks. Fibrin served as control for immediate bonding strength. Biocompatibility was tested with MTT staining. Cell invasion and ECM development at the defect site was analyzed histologically and immunohistochemically.

Results and conclusion: Using the combination of POx and fibrinogen as cartilage adhesive, immediate bonding strengths (up to 20.08 ± 3.57 kPa) were obtained, consistently exceeding that of fibrin glue (7.64 ± 3.95 kPa). A higher catechol functionalization of POx led to increased immediate bonding strengths. No cytotoxic effects were observed for any tested POx adhesive. Modification of POx with hydrolyzable ester-linkages did not significantly influence immediate bonding strength but adhesive degradability and long-term integration success. Adhesives solely consisting of POx with stable amide-linkages lacked degradation and showed no cell invasion or ECM deposition. In strong contrast, incorporation of 25 and 50% POx with ester-linkages allowed for glue degradation and resulted in enhanced cell invasion. Strong deposition of cartilage-specific ECM was observed in histology and immunohistochemistry, especially as demonstrated for glycosaminoglycans and collagen II, bridging the defect after 21 days.

Our study demonstrated catechol-modified POx in combination with fibrinogen to function as a promising biocompatible adhesive with tunable adhesion strength. Enhancing the degradability of POx adhesives by ester-linkages particularly improved long-term integration in a cartilage defect model in vitro.

Acknowledgement: Funding from EU, grant #309962 (HydroZONES).