Introducing Long Linear Acrylamide Chains to Tune the Viscous Component of a Hydrogel Brain Phantom for Blunt Impact Testing

Traumatic brain injury occurs with a blast or blunt impact to the head. To replicate blast induced brain traumatic injuries a model of the human brain needs to be established. Tuned polyacrylamide hydrogels were chosen because they replicate human brain tissue material properties while maintaining transparency. Transparency is a requirement for some of the strain diagnostics implemented, such as particle image velocimetry. The storage modulus (G’) of a material demonstrates its elasticity, and the loss modulus (G’’) represents its viscous component. Rheological tests on the polyacrylamide hydrogel reveal that the crosslinked network lacks in loss modulus compared to human brain tissue. To remedy this shortcoming, longer linear acrylamide chains are incorporated into the hydrogel to independently tune the viscous component. Introducing linear acrylamide chains acts as a dampener to the gel network since most of the chain is unable to crosslink when introduced into a polymerizing solution. Due to this the loss modulus increases as the space between cross linking is extended. These linear acrylamide chains have two main variables that can be manipulated to affect the final gel, the quantity of chains and the length of each chain. The final gels material properties are also heavily dependent on the amount of total acrylamide monomer and crosslinker that is used. The most desirable formulation developed was a 15:1 monomer to crosslinker ratio with 10.0105wt% total acrylamide content, where 15wt% of the final gel was linear chains made from 7wt% stock solution. This formulation produced a G’ of 5 kPa and a G’’ of .55 kPa. The use of linear acrylamide chains did not significantly increase the G’’, which was expected with the introduction of linear acrylamide chains. Despite this, the linear chains did show that the G’’ could be minutely adjusted using various types and quantities of linear chains.