Measuring elastic properties of thin biological films using capillary wrinkling

Imprinting of soft biological cells to create microenvironments for cell culture has gained significant importance in studying biological processes. Developments in soft lithography techniques have caused a decrease in the size of these imprinted biological cells. Where pattern sizes were in the range of 50 um, they are now being fabricated in the range of 1 um. However, there has been very little work done to characterize the elastic properties of these imprinted gels at this scale. In this work, we attempt to use an unique technique that uses the wrinkling that occurs when a floating thin film is subject to a normal loading force. A previous study has reported the use of this metrology method to measure elastic properties of floating thin polystyrene films by counting the number and length of wrinkles that are created when subjected to radial stresses from a droplet of water. In this case, we extend this theory to study wrinkle formation in floating polystyrene films coated with biological cells, and fibronectin. Also, we attempt to study capillary wrinkling in biological films such as agarose and Matrigel™. Wrinkles are induced in thin films of these materials by applying a droplet of fluid on the film surface. Using an appropriate scaling relationship, the elastic properties of these films may be obtained. The dependence of these elastic properties on gel aspect ratios, concentration, and, film floating media will be discussed.