Comparison and characterization of potential protein delivery systems: poly(2-hydroxyethyl methacrylate) and 4-arm poly(ethylene glycol)/heparin hydrogels
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Synthetic and natural hydrogel materials have been widely used in applications such as contact lens, wound dressings, and tissue engineering scaffolds because they have an ability to hold a large amount of water and this provides an environment similar to a natural cellular matrix system in human body. Hydrogels can also be easily engineered to deliver small molecule drugs or large macromolecules such as proteins and growth factors. Hydrogels can serve as skin wound treatment to deliver therapeutic agents to the localized site without causing off-targeted side effects. In order to perform its duty maximally, the hydrogel should be able to retain a sufficient amount of the drug and release it in active form in a controlled manner. A protein used in this study as a drug is keratinocyte growth factor(KGF) and it is known to enhance wound healing rate by stimulating the migration and proliferation of keratinocyte cells for reepithelialization. In this study, the efficiency of two types of hydrogel materials will be examined with KGF to determine their viability as potential protein delivery systems. First, poly(2-hydroxyethyl methacrylate) (HEMA) hydrogel is already widely used as contact lens material and it is known to uptake proteins via a diffusion mechanism. The second material is heparin immobilized amine-functionalized star-shaped poly(ethylene glycol) (starPEG/heparin) hydrogel. It is known to uptake protein via electrostatic interaction and also via large pores. The maximum water content and swelling ratio of each hydrogel were tested using the gravimetric equilibrium swelling test. Then the fluorescence dye labeled KGF was used to test maximum protein uptake capability. To understand the general trend and factors that contributed to the results, focused ion beam scanning electron microscopy (FIB-SEM) was used to image surface of hydrogels, and Fourier-transform infrared spectroscopy(FTIR) and X-ray photoelectron spectroscopy(XPS) were used to analyze crosslinking degree and elements and functional groups on the hydrogel surface.