STUDIES ON HYALURONIC ACID AND RELATED SUBSTANCES

Oxi-HA/ADH Hydrogels: A Novel Approach in Tissue Engineering and Regenerative Medicine

Hyaluronic acid (HA) is a natural polyelectrolyte abundant in mammalian connective tissues, such as cartilage and skin. Both endogenous and exogenous HA produced by fermentation have similar physicochemical, rheological, and biological properties, leading to medical and dermo-cosmetic products. Chemical modifications such as cross-linking or conjugation in target groups of the HA molecule improve its properties and in vivo stability, expanding its applications. Currently, HA-based scaffolds and matrices are of great interest in tissue engineering and regenerative medicine. However, the partial oxidation of the proximal hydroxyl groups in HA to electrophilic aldehydes mediated by periodate is still rarely investigated. The introduced aldehyde groups in the HA backbone allow spontaneous cross-linking with adipic dihydrazide (ADH), thermosensitivity, and noncytotoxicity to the hydrogels, which are advantageous for medical applications. This review provides an overview of the physicochemical properties of HA and its usual chemical modifications to better understand oxi-HA/ADH hydrogels, their functional properties modulated by the oxidation degree and ADH concentration, and the current clinical research. Finally, it discusses the development of biomaterials based on oxi-HA/ADH as a novel approach in tissue engineering and regenerative medicine.

Periodate oxidation and macromolecular compaction of hyaluronan

Partial periodate oxidation of hyaluronan (HA) leads to ring opening of the 4-linked D-glucuronate (GlcA) residues, providing a particularly flexible element within otherwise semi-flexible chains. This leads to compaction of the chains as demonstrated by a pronounced decrease in the intrinsic persistence length, which was determined on the basis of the molecular weight dependence of radius of gyration (RG) and the intrinsic viscosity. These parameters were readily obtained using size-exclusion chromatography (SEC) with an online multi-angle laser light scattering (MALLS) detector, a viscosity detector, and a concentration-sensitive detector. The electrostatic contribution to the total persistence length increased with increasing degree of oxidation. Compared to alginates and chitosans, HA becomes less degraded during the oxidation, which is attributed to a protective effect of periodate-resistant N-acetyl-D-glucosamine (GlcNAc) residues adjacent to periodate-sensitive GlcA residues in HA.