Discipline: Biological Sciences
Subcategory: Biomedical Engineering
Jamila Perkins - Syracuse University
Co-Author(s): Alex Jannini, Justin Sheplock, Dr. James Henderson PhD, Dr. Julie Hasenwinkel PhD Syracuse University, Syracuse,NY
Hydrogels are cross-linked polymer networks that are capable of containing anywhere from 50%-90% water; however, they are typically mechanically weak and brittle, which may limit their applications. Double network synthesis techniques can be used to strengthen hydrogels by independently crosslinking two different types of hydrogels within the same volume. In this method, a strong polyelectrolyte is covalently cross-linked using UV-photopolymerization and then swollen in a monomer solution containing a ductile, neutral monomer. The double network is formed during a second round of UV-photopolymerization.  Our lab has synthesized double networks of methacrylated hyaluronic acid (MHA) (the rigid network) and poly(dimethyl acrylamide)(PDMAM) (the ductile network) similar to those developed by Chen et al., and studied the effect of the concentration and crosslinking ratio ratio of the MHA network on double network properties. The goal is to understand the effect of these compositional variables in order to form double networks with optimal properties for desired applications.
To study these variables, a 2^2 factorial design with a centerpoint was devised to investigate whether the concentration of MHA and/or crosslink ratio of poly(ethyleneglycol diacrylate) (PEGDA) to MHA, and the interaction of the two variables, affected the mechanical properties, and whether or not that affect was linear. Tensile, tearing, and swelling studies were conducted and the max stress, elongation at break, Young’s Modulus, tearing energy, and maximum swelling ratio were analyzed. The analysis found that tensile and swelling properties were linear responses while the tearing energy was found to be nonlinear. The tensile test data possessed a directly proportional trend wherein as the wt% and crosslinking ratio increased the maximum stress was increased, but the ductility of the gels was sacrificed. The swelling study showed an inversely proportional relationship between the variables and the swelling ratio ‘Q’ meaning that when the crosslinking ratio and wt% increased, the swelling ratio decreased. In the trouser tearing test the normalized force was found to be similar for all compositions except the 2wt% 4:1 gel which had a sharp increase in the amount of energy required to propagate the tear. Based on this information, a central composite design (CCD) has been created to further investigate the linearity (or lack thereof) between the variables. Once the CCD is complete there will a better understanding of the type of nonlinear response the tearing energy has and the significance of the responses. A future project would be to create a new CCD that tests the effects of both the brittle network variables and the ductile network variables on the mechanical properties of the hydrogels.
Funder Acknowledgement(s): This project is sponsored by: NSF HRD 1712733and NSF-IGERT grant DMR-DGE-1068780. The authors would also like to thank the Syracuse Biomaterials Institute, LSAMP, and WiSE programs.
Faculty Advisor: Dr. Julie Hasenwinkel, firstname.lastname@example.org
Role: I completed the synthesis and analysis of the data from the mechanical tests performed for the centerpoint data of the 2^2 factorial design. Upon completion I moved on to mechanical testing of the central composite design data points; which was an additional four data points. The mechanical tests completed were the tensile test, the trouser tearing test and swelling studied. All data analysis was completed by me. The data interpretation was a joint effort between myself and the PhD student.