Abstract
Hyaluronic acid (HA) is a natural polysaccharide with promising applications in modern cosmetic and nutricosmetic products due to its high-water affinity, which is essential for skin hydration, as well as its biocompatibility, biodegradability, non-toxicity, and non-immunogenic nature. In this study, we investigated and optimized the method of crosslinking for formulating novel HA hydrogel films. We used Pentaerythritol Tetra-acrylate (PT) as the cross-linking agent over a range of pH values and used different cross-linking methods (Ultraviolet (UV) radiation, microwaving, and oven heating). The efficacy of the cross-linking reaction was evaluated using swelling studies and Fourier transform infrared (FTIR) spectroscopy for the characterization of the xerogel HA-PT film formulations. We found that HA-PT cross-linked hydrogels are produced under alkaline conditions (pH 11) but not under neutral or acidic conditions. Cross-linked HA-PT xerogel films using UV-irradiation showed excessive swelling indicative of inadequate cross-linking. The oven and microwaving methods produced HA-PT films with high cross-linking density. FTIR data suggest formation of ester bond between the carbonyl of the HA and hydroxyl group of the PT acrylate group. Overall, the oven method was considered better and easier than UV-radiation/microwave methods because it is safer, user-friendly and eco-friendly, and can process larger batches.
Highlights
Cross-linked hydrogels are three-dimensional (3D) networks of polymer chains, containing hydrophilic groups or domains that can uptake and retain significant amounts of water [1].The cross-linking bond can be classified as chemical (Type 1 hydrogels) or physical (Type 2 hydrogels)
We found that Hyaluronic acid (HA)-Pentaerythritol Tetra-acrylate (PT) cross-linked hydrogels are produced under alkaline conditions but not under neutral or acidic conditions
Chemical crosslinking enhances the mechanical stability of hydrogels, which leads to hydrogel film formulations [2]
Summary
Cross-linked hydrogels are three-dimensional (3D) networks of polymer chains, containing hydrophilic groups or domains that can uptake and retain significant amounts of water [1]. The cross-linking bond can be classified as chemical (Type 1 hydrogels) or physical (Type 2 hydrogels). Chemical cross-linking involves stable covalent bonds and is, irreversible. Physical cross-linking involves a network of molecular entanglements, and/or secondary forces including ionic, hydrogen bonding, or hydrophobic interactions. These interactions can be reversed/broken by changes in physical conditions or on application of stress [1]. Water uptake and water holding capacity are the most important characteristics of cross-linked Type 1 hydrogels
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