Poly(ethylene glycol) (PEG) hydrogels have a chemically and physically tied filament self-ensemble structure, high water adsorption, and biodegradability, which makes it a favorable substrate for biomedical application. The addition of cell adhesion sequences as dangling ends allows for engineering substrates for controlled cell growth. While PEG has been used extensively in tissue engineering there have been few attempt to accurately model its properties.
A coarse-grained model is developed for an entangled cross-linked PEG, which includes dangling ends, and is used to characterize PEG's mechanical properties. Dangling ends can be peptide groups intentionally added to make PEG favorable for cell interactions or they can result from the polymerization process. Our model includes four adjustable parameters; percent of a peptide group (YPep), percent of dangling ends (YDE), the average number of persistence lengths between two entanglements (NE), and the average number of persistence lengths between two cross-links (NC).
Molecular and chemical process information such as NE, NC, YPep, and YDE are used as input parameters to create a numerical ensemble of number of persistence length(s) between entanglements and cross-links, and connecting vectors between entanglements during the preparation step of the model. Different deformation fields at equilibrium are applied to the prepared ensemble to analyze the stress-strain behavior of system in the dynamic step of the modeal. It is assumed that cross-link points and average position of entanglements are deformed affinely. Entanglements are allowed to move along polymer chains; therefore polymer chains are able to create new entanglements or disentangle from each other. The effects of dangling ends and peptide group on mechanical properties are studied under different deformation fields. This model is currently being compared to experimental data. The results indicate that dangling ends and peptide group reduce the mechanical strength that is dominated by cross-links.