Hyaluronic acid (HA) is a polysaccharide located in the extracellular matrix of soft tissues. Extensive studies have been done to develop hyaluronic acid-based biomaterials for tissue engineering and other applications. Electrospun hyaluronic acid fibers were produced by dissolving hyaluronic acid in aqueous ammonia and dimethyl formamide solutions [12Bre]. Fibers with diameters of 39 ± 12 nm were
obtained. In another study, pure hyaluronic acid was dissolved using a combination of deionized water, formic acid, and dimethylformamide (25/50/25) and nanofibers with average diameters of 100 nm were obtained [11 Liu]. Addition of formic acid increased chain entanglements and viscosity and allowed the formation of nanofibers. However, the membranes obtained were unstable and dissolved in aqueous media. To overcome this deficiency, electrospun hyaluronic acid membranes were cross-linked with ethyl-3-(3-dimethylaminopropyl) carbodiimide hydrochloride (EDC) [09Xu2]. Although the cross-linked materials showed signifi­cant improvement in stability when treated in water, they were not stable in PBS. To further improve the stability of the membranes in PBS, gelatin was blended with hyaluronic acid with the aim to increase the amine groups and therefore obtain better cross-linking. Membranes containing HA and gelatin were cross-linked with EDC/NHS and found to be stable in PBS at 37 °C for up to 28 days. Unlike previous reports that suggested that HA was cytotoxic, membranes produced from HA/gelatin were cytocompatible and the degradation of the membranes could be controlled from 1 to 30 days. Three-dimensional HA nanofibrous scaffolds were developed using thiolated HA derivative 3,3′-dithiobis(propanoicdihydrazide) (DTPH) with the addition of PEO to assist fiber formation [06Ji]. Scaffolds were further cross-linked with the addition of poly(ethylene glycol)-diacrylate (PEGDA) conjugate. Later, PEO was extracted from the scaffolds using water to obtain HA-DTPH nanofibrous scaffolds. Fibroblasts were found to attach and spread on the scaffolds suggesting that the scaffolds could be useful for cell encapsulation and tissue regeneration [06Ji]. Figure 58.13 depicts the growth of cells on the scaffolds.

Macro- and nanofibrous hyaluronic acid/collagen blend fibers were made into scaffolds using electrospinning and leaching technique [08Kim]. Sodium hydroxide and N, N-dimethyl formamide were used as a solvent mixture to electrospun the fibers in the form of 3D nanofibrous scaffolds shown in Fig. 58.14. Fibers with average diameters between 226 and 357 nm were developed and the average tensile strength of the scaffolds varied between 267 and 432 kPa. Salt leaching resulted in the formation of macroporous and nanoporous (Fig. 58.15) HA scaffolds that were suggested to be suitable for tissue engineering.