Injectable, biodegradable scaffolds are important biomaterials for tissue engineering and drug delivery. Hydrogels derived from natural polysaccharides are ideal scaffolds as they resemble the extracellular matrices of tissues comprised of various glycosaminoglycans (GAG). Here, we report a new class of biocompatible and biodegradable composite hydrogels derived from water-soluble chitosan and oxidized hyaluronic acid upon mixing, without the addition of a chemical crosslinking agent. The gelation is attributed to the Schiff-base reaction between amino and aldehyde groups of polysaccharide derivatives. In the current work, N-succinyl-chitosan (S-CS) and aldehyde hyaluronic acid (A-HA) were synthesized for preparation of the composite hydrogels. The polysaccharide derivatives and composite hydrogels were characterized by FTIR spectroscopy. The effect of the ratio of S-CS and A-HA on the gelation time, microstructure, surface morphology, equilibrium swelling, compressive modulus, and in vitro degradation of composite hydrogels was examined. The potential of the composite hydrogel as an injectable scaffold was demonstrated by encapsulation of bovine articular chondrocytes within the composite hydrogel matrix in vitro. The results demonstrated that the composite hydrogel supported cell survival and the cells retained chondrocytic morphology. These characteristics provide a potential opportunity to use the injectable, composite hydrogels in tissue engineering applications.

Hydrogels have many different applications in the field of regenerative medicine. Biodegradable, injectable hydrogels could be utilized as delivery systems, cell carriers, and scaffolds for tissue engineering. Injectable hydrogels are an appealing scaffold because they are structurally similar to the extracellular matrix of many tissues, can often be processed under relatively mild conditions, and may be delivered in a minimally invasive manner. This review will discuss recent advances in the field of injectable hydrogels, including both synthetic and native polymeric materials, which can be potentially used in cartilage and soft tissue engineering applications.

Currently, surgical treatments for peripheral nerve injury are less than satisfactory. The gold standard of treatment for peripheral nerve gaps >5 mm is the autologous nerve graft; however, this treatment is associated with a variety of clinical complications, such as donor site morbidity, limited availability, nerve site mismatch, and the formation of neuromas. Despite many recent advances in the field, clinical studies implementing the use of artificial nerve guides have yielded results that are yet to surpass those of autografts. Thus, the development of a nerve guidance conduit, which could match the effectiveness of the autologous nerve graft, would be beneficial to the field of peripheral nerve surgery. Design strategies to improve surgical outcomes have included the development of biopolymers and synthetic polymers as primary scaffolds with tailored mechanical and physical properties, luminal "fillers" such as laminin and fibronectin as secondary internal scaffolds, surface micropatterning, stem cell inclusion, and controlled release of neurotrophic factors. The current article highlights approaches to peripheral nerve repair through a channel or conduit, implementing chemical and physical growth and guidance cues to direct that repair process.