Gene delivery from responsive hyaluronic acid hydrogels for directed angiogenesis

Tissue Engineering points to maintain, restore or to improve and create new tissues. This purpose typically involves the selection of a natural or synthetic biomaterial as a scaffold to create the biological substitutes. Furthermore, angiogenesis, the growth of new blood vessels from pre-existing ones, is a critical physiological process toward the success of tissue engineering. Along with this consideration, biomaterials that possess intrinsic angiogenic potential may be better candidates for tissue engineering. In the present report, we investigated the effects on the in vitro CAM assay (Folkman et al., A simple procedure for the long-term cultivation of chicken embryos, 1974; Auerbach et al., Angiogenesis assays: a critical overview, 2003) of hyaluronic acid (HA). HA derivatives were formed by reaction of the carboxylic acid groups of the soluble natural polymer with hydrazides, via carbodiimide-mediated coupling. This intermediate product was then further reacted with a cyclic thioimidate (Traut's reagent) compound for thiolation. We herein describe a physiologically compatible strategy to prepare HA hydrogels able to i) support drug delivery, and ii) support potential in situ encapsulation of cells. In this strategy, modified hyaluronic acid was cross-linked with itself and 6% (w:v) HA hydrogels were formed under physiological conditions by air oxidation of thiols to disulfides. According to a LIVE/DEAD assay, HA hydrogel showed to support cell growth and spreading. The biomaterial scaffold was loaded with plasmid and a DNA release assay was performed. However hydrogels swollen in proteases containing media indicated that only 10% of the integrated DNA remained inside after 48hours. The angiogenic properties of the hydrogel were investigated on the chicken chorioallantoic membrane assay. In addition, we also examined the involvement of plasmid Vascular Endothelial Growth Factor (VEGF) on the CAM by integrating the signal into the hydrogel. Angiogenesis was observed around the implanted biomaterial. In addition, fluorescence microscopy of perfused animal indicated the presence of blood vessels sprouting into the hydrogel matrices. We anticipate that this HA-based hydrogel is highly tunable (Shea et al., Non-viral vector delivery from PEG-hyaluronic acid hydrogels, 2007). In addition, hydrogels with this capability for localized delivery of gene therapy vectors and controllable stability have direct applications for tissue engineering and could be useful tool for several biomedical applications (Hubbell et al., Functional biomaterials design of novel biomaterials, 2001)