Study On Structure And Properties Of N-vinylpyrrolidone Copolymer Hydrogels

The homopolymer and copolymer hydrogels of N-vinylpyrrolidone (NVP) find an extensive application in the field of biomedicine due to their good chemical stability and high biocompatibility. A series of hydrogel materials are synthesized by copolymerization of NVP and 2-hydroxyethyl methacrylate (HEMA). In this work, we have investigated the properties of the hydrogel materials in detail, the swelling behavior, different states of water in hydrogels, the transmissibility and permeability of oxygen and ions, and adsorption of bovine serum albumin (BSA) on hydrogels. The main contents and related original achievements are as follows:1. Hydrogel materials are synthesized by radical copolymerization of NVP and HEMA, with azobisisobutyronitrile (AIBN) as an initiator, reacting at 60~70癈 for 24 hours. It has been found that all of the synthetically hydrogel materials have good transparency and anti-causticity, the pH of the liquid in which hydrogels are soaked is 7.10-7.44, similar to that of human tear. It has been proved that the chain configuration in polymer is an orientation of disorder by determining the refractive index. The in vitro cytotoxicity of the hydrogel materials is examined by cell relative growth rate assay, and the cytotoxicity is up to grade 1, according to the test standard of USA, indicating that the materials have no cytotoxicity. The results show that the NVP-HEMA copolymer hydrogels have good biocompatibility, according with the requirements of the soft contact lens material.2. The swelling behavior and the effects of different percentage of the monomer of hydrogels have been investigated. It is found that the equilibrium water content (EWC) increases with the growing percentage of hydrophilic monomers, such as NVP HEMA and acrylamide (AAm). Both the dehydration speed and the EWC in hydrogel decrease after the hydrophobic monomer butyl methacrylate (BMA) is mixed with. The impact of temperature, pH and ionic intensity on hydrogels is studied in this paper. The result shows that the hydrogel materials display boththermosensitive and pH-sensitive behaviors; the sensitivity of the NVP-HEMA-AAmcopolymer is greater than that of NVP-HEMA copolymer hydrogels. The growth of the ionic strength causes the decrease of the osmotic pressure, resulting in the drop of swelling ratio.3. The different states of water in swelling hydrogels are studied by means of differential scanning calorimetry (DSC) combined with thermogravimetry (TG). It is found that the water in polymer exists in three states: free water, freezing bond water and non-freezing bond water. DSC and TG data show that the content of freezing water in hydrogel grows with increase of NVP percentage, and the non-freezing water in hydrogel increases with growth of HEMA and RMA percentages. The plasticization of the material is affected by the non-freezing water in hydrogel rather than by the freezing water.4. Two convenient apparatus are devised for testing the oxygen permeability coefficient and ion diffusion coefficient of hydrogel membranes. It is found that the transmissibility and permeability of oxygen and ions in hydrogel can be described according to the solution-diffusion model. The systematic variations in chemical structure and volume fraction of water in polymer bring about significant changes in permeability coefficients. The oxygen transmissibility (Dk/L) and ionic diffusion coefficient (P) increase as the proportion of NVP increases, hence the increase of freezing water, which is the main carrier transferring oxygen and ion in hydrogel. The relationship between ionic diffusion coefficient and hydrate degree (H) can be described in free volume theory.5 . The absorbency of bovine serum albumin (BSA) is measured by the ultraviolet spectrophotometer. A Langmuir equation can be used to describe the adsorption isotherm of BSA. The adsorption kinetics model of BSA on hydrogel is established also. Experimental result shows that the adsorption kinetics model of BSA on hydrogel obeys the Bangham equation. Adsorption...