Photopolymerization of hydrogels using UV LED system was highly efficient with the aid of synthesized water soluble photoinitiator.

The three-dimensional of hydrogel networks within nm range can microscopically be considered as “porous”mesh. This feature may imply that hydrogel networks possess sieving characteristics; i.e. exclusion of solutes or molecules based on size. In this study the network and sieving characteristics of poly(N-isopropylacrylamide) (PNIPAAm) hydrogels were investigated. PNIPAAm hydrogels were prepared via free radical using N-isopropylacrylamide (NIPAAm) as main monomers and N,N‘-methylenebisacrylamide (MBAAm) as crosslinkers. As the composition of the hydrogels was varied, the mesh sizes of the resulting hydrogels were in the range of 4.0 to 11.0 nm. These data were obtained from swelling experiments. Dextrans as test solutes with molecular weight in the range of 4 to 2000 kg/mol were used in partitioning experiments to investigate the sieving of the hydrogel networks. The partitioning data indicated that of hydrogel networks excluded the solutes which were bigger than its mesh sizes. The experimental results not only show a good correlation of sieving coefficient on the size basis but also nicely fitted to the partition data estimated from the Ogston model. Undoubtedly, PNIPAAm hydrogel networks possessed sieving characteristics to separate molecules exclusively and selectively as a function of size.

Recent trends show that the UV LED light source can greatly reduce environmental effect without compromising performance as compared to conventional UV mercury-based lamp (UV Hg) system. In this study, the possibility of using UV LED technology for photopolymerization of polyacrylamide (PAAm) hydrogels is presented. This has strongly drives the needs for suitable water-soluble photoinitiator formulation. Specifically, the photoinitiator must possess characteristic wavelength within UV LED range as UV LED emits monochromatic light sources only (365 nm or 385 nm). Here, the commercially available photoinitiator Oligo [2-hydroxy-2-methyl-1-[4-(1-methylvinyl) phenyl] propanone] (Chivacure 300) was chosen. However, Chivacure 300 has limited solubility in water. Hence, addition of tetrahydrofuran (THF) at various ratios was required. The results demonstrated that 9.5:0.5 ratio of water/THF was the minimum ratio needed for the solubility of Chivacure 300. After the synthesis of PAAm hydrogels, almost complete conversion of hydrogels was achieved (> 80 %). The highest conversion was achieved with formulation of Chivacure 300 in 9.5:0.5 ratio of water/THF. At this ratio, the hydrogels obtained were transparent. With increasing ratio of THF in water, the appearance of hydrogels gradually changed to cloudy. Indeed, UV LED technology can be used to polymerize PAAm hydrogels with comparably high conversion to conventional UV Hg system.

Double network (DN) hydrogels have drawn considerable attention as innovative materials possessing both high water content as well as improved mechanical properties. In this study, DN hydrogels were formed from a combination of two hydrogel networks. The first network composed of acrylamide (AAm) andN’,N’-methylenebisacrylamide (MBAAm). AAm and MBAAm were covalently crosslinked via photopolymerization simultaneously with/without the presence of the second network pre-gel mixture; physically crosslinked gelatin-calcium carbonate (GCa). The mechanical properties characterization of the hydrogels revealed that tensile strength, Young’s modulus and elongation at break increased with the increasing amount of second network component; i.e. GCa. These data could confirmed that the polyacrylamide (PAAm)-GCa DN hydrogels possessed ‘stretchability’ character. Overall, PAAm-GCa DN hydrogels had shown better mechanical strength than the PAAm single network hydrogels. We foreseen that DN hydrogels are highly potential to be developed as artificial muscles.