(116ab) Smart Biomaterials and Surface Engineering

Conventional cell detachment agents such as proteolytic enzymes can irreparably damage cellular structure and consequent function. In order to address this issue an alternative method of cell harvesting has been developed using smart or stimuli responsive polymers as a substratum for the cultivation of cells with a view to tissue engineering.

Thermoresponsive polymers are a type of smart polymer that are environmentally sensitive and undergo drastic phase transition in response to a small temperature change. By exploiting this unique property of poly-(N-isopropylacrylamide) (pNIPAm) and poly-(ethylpyrrolidone methacrylate) (pEPM) it is possible to detach cell sheets in which the cell to cell junctions remain in-tact. This opens up possibilities for tissue damage repair such as corneal or spinal damage repair.

pNIPAm and pEPM have a lower critical solution temperature (LCST) of 32ºC and 34ºC, respectively, above which the polymers are insoluble in water and below which the solubility is favored. This hydrophobic to hydrophilic conversion is exploited in cytotechnology by culturing fibroblasts (3T3 cells) on polymer films over the LCST and detaching from the substrates below the LCST once the cells have grown to confluence.

Biological characterization was achieved by seeding cells and capturing images of cell proliferation and their subsequent detachment using thermal control. Physical characterization of fabricated films was achieved using AFM, SEM, FTIR, and confocal microscopies.

In general, cells seeded on spin coated pNIPAm and solvent casted pEPM grew to confluence. Cell detachment via cold treatment took approximately 20 minutes for spin coated pNIPAm and 70 minutes for solvent casted pEPM. The solvent casting film preparation method yields films in the micrometer range while spin coating produces much thinner films in nanometer range. A common side effect of the spin coating process is the edge bead effect. This does not seem to have any adverse affect for cell growth and detachment. pNIPAm and pEPM show great promise for cell harvesting methodologies.