The source codes can be found here:
1 => Standard Viscoelasticity -> Arruda-Boyce solid + Newtonian fluid
2 => Standard Viscoelasticity -> Gent solid + Newtonian fluid
3 => Single element benchmarking
A demonstration:
(a) showing experiment setup with hydrogel electrodes (b) showing the modeling in simulation (c) experimental and simulation results for canbon grease electrodes (d) for hydrogel electrodes
I hope these codes can also be used for educational purposes, other than research.