Hydrogels photo-crosslinking by 266 nm pulsed laser radiation

In the last years, efforts have been made for the development of smart wound dressings with enhanced efficiency in the treatment of major skin wounds. The requirements of an ideal wound care system are: capability of the long-term release of medicine, to maintain high humidity at the wound site, non-toxicity, to be removed without affecting the wound, to allow the exchange of gases and water vapor, to be impermeable to bacteria and cost-effective. A solution for an ideal wound dressing are hydrogels These are formed from polymers, natural or artificial, and can offer optimized therapeutic action and controlled release of the drugs. They can be formed via photopolymerization, solution polymerization/cross-linking, bulk polymerization, suspension polymerization, or inverse-suspension polymerization. The hydrogels obtained by polymers exposure to UV radiation offer the advantages of temporal and spatial control, free of chemical additives, and simultaneously sterilization is obtained. This method produces free radicals in polymer solution due to UV laser interaction with a photoinitiator. This study is addressing the hydrogel formation by photocrosslinking gelatin chains functionalized with methacrylate groups when Irgacure 2959 was used as a photoinitiator. The solution was exposed to the fourth harmonic of an Nd:YAG laser at energies between 0.25 and 1 mJ. The crosslinking process was monitored in real-time by laser-induced fluorescence and offline by UV-Vis and FTIR absorption spectroscopy. The dimerization reaction was evaluated at intermediate times; the changes from dilute to the semi-dilute polymer solution and to fully crosslinked hydrogel were monitored. Additionally, the photodegradation of Irgacure 2959 was investigated in the same condition used to form the hydrogels. Its photodegradation was evaluated at 1 min, 5 min, 10 min, 20 min, and 30 min. The photodegradation of Irgacure 2959 was evidenced by the fluorescence spectra changes in peak intensity and peak wavelength, the UV-Vis absorption spectra, where the absorbance band of Irgacure 2959 vanished and a new band at shorter wavelengths appeared. Also, the FTIR spectra analysis showed the degradation of the photosensitizer and facilitated photoproducts identification. (author)