Tuning PEG-DA hydrogel properties via solvent-induced phase separation (SIPS)† Brennan Margaret Bailey, Vivian Hui, Ruochong Fei and Melissa Ann Grunlan*

This paper provides a backbone for future work that I do in the Biomaterials lab that I work in.

In tissue engineering, scaffolds are artificial structures that are capable of supporting three dimensional tissue formation. Both physical and chemical properties impact the function of the scaffold; the physical properties include storage modulus (a measure of elasticity) and morphology (pore size), while the chemical properties include swelling ratio and degradation. In theory, an efficient scaffold will have a sufficient storage modulus to maintain stress, a macro porous morphology to host seeded cells, a high swelling ratio that indicates areas of polymer rich and lean domains, and a degradation rate that parallels the rate of regeneration The scaffolds utilized are Poly(ethylene glycol) diacrylate (PEG-DA) due to their resistance to protein and cell adhesion, therefore changes in cell behavior are a result of changes in scaffold's materialistic properties. Macroporous hydrogels have previously been shown to enhance tissue formation and to enhance the degradation rate, therefore increasing the pore size is the main objective. The strategy employed to accomplish this is SIPS protocol (Solvent Induced Phase Separation), which promotes phase separation of the growing polymer chain during UV curing, due to incompatibility between the polymer chain and the solvent. The solvent used is dichloromethane (DCM), as opposed to the traditional aqueous solvent. Using the traditional aqueous solvent as a control, the storage modulus, swelling ratio, morphology, and degradation rate were experimentally tested. The storage modulus of the SIPS hydrogels increased significantly indicating the stiffness of the hydrogels increased. The swelling ratio remained the same for both conventional hydrogels and SIPS hydrogels; although this may seem unimportant, the storage modulus and swelling ratio of SIPS hydrogels can be uncoupled due to the fact that the swelling ratio increased while the swelling ratio remained the same. Uncoupling is an important characteristic for tissue engineering that indicates one material characteristic can be altered without unintentionally altering another material characteristic. Using a Scanning Electron Microscope (SEM), SIPS hydrogels indicated open porous structures, which indicate increased pore size, and as expected the degradation rate increased. As a result it can be concluded that PEG-DA scaffolds formed via SIPS, form a useful library of scaffolds to analyze the physical properties on cell behavior. 

This paper is interesting because it provides a background of the basic approaches and goals of tissue engineering, in which material characteristics of a scaffold are altered to increase the efficiency of the scaffold, in terms of supporting three dimensional tissue formation to promote tissue regeneration.

http://www.ncbi.nlm.nih.gov/pubmed/22956857