N,N-dimetilaminoetil metakrilat esaslı modifiye hidrojeller: Sentez, karakterizasyon ve mekanik özellikler

The development of new polymeric biomaterials for medical and pharmaceutical purposes is of great interest to life-care science and biotechnology. Multipurpose smart hydrogel systems that swell and shrink in response to environmental stimuli such as temperature, pH, ionic strength and certain chemicals have attracted much attention in the past ten years. Depending on the type of monomers incorporated in the gel structure, they can be made to respond to a variety of external stimuli leading to what are known as stimuli-responsive hydrogels which are perhaps the most extensively studied classes of intelligent hydrogels. Among researchers there has been a long-standing interest in polymer systems that demonstrate a phase transition in response to variations in solution pH and temperature. Stimuli responsive hydrogels show the reversible volume changes with pH changes and on–off switching of electric field. Since the design of biomedical devices requires better understanding of the structure - property - response relationships of hydrogels, the precise information on the swelling behavior and the mechanical properties are required in their use in actuation and sensing applications. Understanding these properties have significant impact for the design of coatings for biosensors and for actuation devices based on stimuli-responsive hydrogels. The aim of this study is to understand the swelling and elasticity behavior of acrylate-based copolymeric hydrogels under different conditions and to find quantitative correlation between the synthesis parameters and resulting physical properties. The critical questions that need to be addressed include: how the gel preparation conditions affect the macroscopic swelling properties of gels and how mechanical stability of resulting gels vary with these conditions. Thus, the experimental work of this consists two parts. In the experimental work of this thesis, the copolymeric hydrogels were prepared by free-radical crosslinking copolymerization of N,N-dimethylaminoethyl methacrylate (DMAEMA) with 2-Hydroxyethyl methacrylate (HEMA) in aqueous solution in the presence of diethylene glycol dimethacrylate (DEGDMA) as the crosslinker. It was proposed that through proper choice of monomers and other experimental conditions it is possible to tailor-make polymeric systems with specific properties. pH/temperature-induced phase transition behavior resulting from polymer-water and polymer-polymer interactions was demonstrated using poly(N,N-dimethylaminoethyl methacrylate-co-Hydroxyethyl methacrylate) P(DMAEMA-co-HEMA) copolymeric hydrogels. The extent of swelling and mechanical properties of the copolymeric P(DMAEMA-co-HEMA) hydrogels was designed by changing the preparative conditions. The swelling behavior of copolymeric hydrogels was characterized by the equilibrium swelling measurements and the results were analyzed by using Flory-Rehner theory of swelling equilibrium. Since the water adsorption characteristics of hydrogels have a significant influence on the diffusive behavior of small molecules into the gel, the swelling kinetics measurements were investigated to determine the swelling-deswelling rate of resulting gels. The diffusion of the swelling agent into the gel changes depending on the chemical composition and distribution of the hydrophobic-hdyrophilic monomer units along the macromolecular chain. The equilibrium swelling and dynamic swelling kinetics of hydrogels containing different amounts of HEMA were investigated under various experimental conditions such as temperature and pH of the swelling medium and in the presence of different types of salts. Compressive mechanical testing was performed at a state just after preparation and after equilibrium swelling in order to characterize the network structure of hydrogels such as the effective crosslinking density, the crosslinking efficiency and the number of segments between consecutive crosslinks. P(DMAEMA-co-HEMA) copolymeric hydrogels showed excellent compositional and mechanical features as well as unique tunable time-dependent swelling behavior. It was shown that these hydrogels possess tunable physicochemical properties that can be adjusted by changing copolymer composition. This work shows that the extent of the swelling ratio, the swelling mechanism, the response time and the gel strenght of acrylate-based hydrogels could be modulated by controlling the factors such as the copolymer structure, the comonomer concentration, the temperature and the pH of the swelling media. The results also support that P(DMAEMA-co-HEMA) hydrogels with improved mechanical properties can be used as a water retainer for carrying substances in pharmaceutical and biomedical applications. Keywords: N,N-dimethylaminoethyl methacrylate, hydrogel, elasticity, crosslinking, swelling, diffusion