Natural polymer-based hydrogels for cartilage regeneration

Abstract

Purpose: Cartilage is a tough, flexible tissue found throughout the body. It can become damaged because of a sudden injury, such as a sports injury, or gradual wear and tear (osteoarthritis). Injured articular cartilage has a poor regenerative capability, for this reason, tissue engineering may provide a fundamental therapeutic solution to repair cartilage injury. Human articular cartilages are composed of dense extracellular matrix and chondrocytes. One of the major components in the extracellular matrix is hyaluronic acid. The combination of hyaluronic acid with other natural polymers to prepare hydrogel scaffolds may be potentially useful in many tissue engineering applications, including cartilage regeneration. We propose the synthesis of hydrogels based on hyaluronic acid and chitosan by a new strategy of synthesis using di-isocyanates to obtain an interpenetrated network of chitosan and hyaluronic acid. Methods: Different kinds of hydrogels were synthesized using hyaluronic acid (Bioibérica, Spain), natural polymers (gelatine, chitosan) and stabilized with diisocianates. The hydrogels were charged with chondroitin sulfate (Bioibérica, Spain). Morphological Characterization: The hydrogels were characterized by scanning electron microscopy and energy dispersive X-ray microscopy in order to study the morphology and the composition of the hydrogels. Hydrogel Swelling: Dynamic swelling experiments were performed by placing discs of stabilized hydrogels in PBS at 37.0 °C, and measuring their weight gain as a function of time. Biocompatibility: Cytotoxicity in vitro assays (MTT) and cell adhesion tests (Alamar Blue) were performed on the hydrogels using different cell lines to corroborate the biocompatibility of the hydrogels. Results: All the synthesized hydrogels present a high interconnected porosity. The studied hydrogels swell around 200%. Aaround five hours equilibrium is reached and this equilibrium depend on the ratio hyaluronic acid/natural polymer increasing with the amount of hyaluronic acid present on the hydrogel. MTT assay indicated that the extracts collected at different times from the hydrogels are not cytotoxic and could be considered biocompatible. Cell adhesion assay indicates that the hydrogels support cell adhesion and proliferation, and this behaviour is better on SC-loaded hydrogels. Conclusions: Hydrogels based on hyaluronic acid and natural polymers are proposed as scaffolds for tissue engineering. The presence of interconnected porous and the good swelling properties and biocompatibility represent a great advantage for application in cartilage regeneration. The addition of drugs or glycosaminoglycan is being studied to improve the cartilage regeneration.