Study on hydrogels of swelling kinetics of pH-sensitive γ-PGA/PVA

Abstract: In order to obtain non-cytotoxic hydrogel of superior water holding capacity and biocompatibility, this paper reported about the production of pH-sensitive hydrogels at different gamma poly glutamic acid (γ-glutamic acid, γ-PGA)/polyvinyl alcohol (PVA) mass radios of 3:7, 4:6, 5:5, 6:4 and 7:3 with no use of any chemical reagents. Then the properties and structure of the prepared hydrogels were characterized and the swelling kinetics of the different feed composition in different pH value (pH values of 4.0, 7.4 and 9.0)solutions were studied. The preliminary research on the drug slow-release of the prepared hydrogels were also conducted. The results showed that the γ-PGA/PVA hydrogels have the pH sensitivity and swelling-deswelling properties. With the amount of γ-PGA increasing, the swelling degree would decrease and hydrogels would show higher endurance of heat. Meanwhile, since the hydrogen bonds between γ-PGA and PVA were enhanced, the structure of the hydrogel would become more compact which would hinder the diffusion of water in the hydrogel and lead to the enhancement of its water-retention rate. The kinetic studies showed that the different pH values of solution had no effect on the initial diffusion behavior of the hydrogel which all belong to the non-Fickian diffusion model. It was also proved that different hydrogel samples in different pH values shared the same change trend of swelling rate which indicated that in the initial swelling process of γ-PGA/PVA hydrogel, the diffusion rates of water molecules and the relaxation rate of macromolecules were almost the same which also indicated that hydrogel with different components shared the same swelling kinetics process. In the same pH value environment, the water diffusion coefficient would increase along with the increase of hydrogel swelling rate, the value of characteristic constant would increase with the increasing content of PVA. The drug release study showed that 5 groups of hydrogel samples of drug embedding effect was more ideal and the embedding rates were between 70%-80%. The changes of pH value had consistent effects on the release properties of 5 groups samples. The hydrogel released rapidly in the buffer solution of pH value 7.4 with release rate of about 80%, and the release period of the buffer solution in pH value 1.2 was lengthened with final release rate of about 40%. With the increase of PGA content and the decrease of PVA content, the release rate of the drug decreased along with a lower final equilibrium release percentage and a longer release period. In addition, it was found that the drug embedding rate of the 5 groups of hydrogel samples was higher, and the performance was satisfactory. This may be due to the structure of the hydrogel containing carboxyl group, which belongs to pH sensitive hydrogel and the hydrogel in an acidic medium swelling rate and swelling degree smaller than in alkaline medium. The results provide a reference in the application of biotechnology, medical and industrial.