Hypothesics Lab Report

Part 2 of the laboratory hypothesizes that different PEG precursor combinations will have an effect on the modulus of the material due to the differences in mesh structure. Unlike part 1, part 2 focuses on variation in mesh structure due to the polymerization of 2, 4, and 8 arm PEGnorb with 2 and 4 arm PEG thiol, rather than the impact of polymerization time. Table II displays the precursor combinations, the resulting hydrogel modulus, and the mesh size of experimental groups 1-2, 4-5, and 7-8. Figure 2 (a) and (b) display the modulus of each group and the mesh size of select groups, respectively. Although trivial, the minimum modulus displayed in Figure 2 (a) is group 1, a combination of 2 arm PEGnorb, or PEG 2k, and PEGdithiol, or 2SH, of

The mesh size is a measurement, in nanometers, of the space in between crosslinks within the mesh network. It is hypothesized that meshes with low mesh size will have high Young’s moduli. The reasoning for this hypothesis is that it is expected that closely packed and highly crosslinked meshes will be able to resist deformation better than meshes that are not. The hydrogel with the lowest mesh size is experimental group 8, the combination of PEG 20k with 4SH (Mw = 10kg/mol), of 13.8 nm. The modulus of experimental group 8 is 77.2 ± 2.06 kPa, which is the highest modulus of the precursor combinations. The hydrogel with the highest mesh size is group 7, the combination of PEG 20K with 2SH, of 39.6 nm. The modulus for group 7 is 38.2 ± 3.24 kPa. As hypothesized, the combination resulting in the lowest mesh size had the highest modulus, suggesting that mesh size is inversely proportional to modulus. The combination resulting in the lowest mesh size does not have the lowest modulus, however, its modulus is still far lower than that of group 8. The second lowest mesh size is that of group 2, the combination of PEG 2k and 4SH (Mw = 10kg/mol), at 14.3 nm. The modulus of group 2 is 34.5 ± 2.72 kPa, which is much smaller than that of group 8. However, when relating mesh size to modulus it is important to recall how precursor structure influences the amount of bonds that can be made. Group 2 is the combination of 2 arm PEGnorb with 4 arm PEG thiol, while Group 8 is 8 arm PEGnorb with 4 arm PEG thiol. The previous observation relating mesh network structure and the amount of arms can be attributed for the large difference between the moduli of groups 2 and