Synthesis of photo-switchable hydrogels and investigation of various properties

Hydrogels are known as polymer networks with hydrophilic groups or domains that have the ability to swell in an aqueous medium. They are capable of holding large amount of water in their three-dimensional networks, from 10-20 % up to thousands of times to their dry weight in water. Although they have high affinity for water, they are prevented from dissolving due to the chemical or physical bonds formed between the polymer chains. Hydrogels have gained a great importance in the last few decades due to their biocompatibility, biodegradability, high functionality and wide range of applications. Natural and synthetic polymers can be used to prepare hydrogels. In both cases, there are some drawbacks and advantages. Although hydrogels made from natural polymers may not provide sufficient mechanical properties, they have advantages like low toxicity, high biocompatibility and biodegradability. On the other hand, synthetic hydrogels provide better mechanical properties, long service life and high capacity of water absorption. They can be modified to gain biocompability, degradability and functionality. Both natural and synthetic polymer based hydrogels possess a degree of flexibility similar to natural tissues due to thier large amount of water content. It is possible to design and produce polymer networks with molecular-scale control over structure such as cross-linking density and with tailored properties, such as biodegradation, mechanical strength and chemical and biological response to stimuli. In response to small changes in environmental parameters such as temperature, pH, ionic strength, electric and magnetic field; they undergo an abrupt volume phase transition. Hydrogels can be classified on different bases such as source, polymer composition, and configuration, type of cross-linking, appearance and electrical charge. Hydrogels prepared by photopolymerization have been investigated for a number of applications such as drug delivery, coatings, biosensors, drug delivery systems and tissue engineering. Recently photopolymerization systems offer wide range of materials for these applications with improved biocompability or biodegradability. Photopolymerization has several advantages; fast curing rates at room temperature, minimal heat production and control during polymerization. The main aim of this study is synthesis of an acrylamide based industrial hydrogel using with amoniumpersulphate (APS) / tetramethylethylenediamine (TEMED) initiators, diacrylated Irgacure-2959 (DAI) as a crosslinker according to free radical polymerization. Later, various properties before and after decomposition of hydrogels which contains a UV decomposable crosslinker (DAI) added into the industrial hydrogel formulations were investigated. Swelling behaviors and mechanical resistance properties of crosslinked hydrogels are different from each other due to the chemical structure and crosslinking density of polymeric structure. It means addition of the photodecomposable crosslinker into the conventional hydrogel formulations will effect entire properties of hydrogels. Therefore, swelling behaviours of acrylaime based UV decomposable and conventional hydrogels was determined in different time intervals. Diacrylated Irgacure-2959 (DAI) was characterized by Gas Chromatography- Mass Spectroscopy (GC-MS); mechanical properties and Fourier Transform Infrared Spectroscopy (FTIR). Thermal properties were investigated by Thermogravimetric Analyzer (TGA). Also morphological studies of all hydrogels were carried out by using Scanning Electron Microscopy (SEM).