Clear and Flexible Thin Films for Simultaneous Mechanical Loading and Imaging of Cells

Cultured neurons undergo morphological changes when placed under a tensile load. Stretch can occur during growth or joint movement, but can also have damaging effects during surgery or limb lengthening. To study the cellular mechanics governing these responses, we have previously studied the effects of applied stretch on axons of cultured rat sensory neurons. Our initial device required the inversion of a flexible membrane, on which neurons were seeded, in close proximity to a glass cover slip to allow for high resolution microscopy during stretch. This design proved to be generally effective, yet provided limited access to the cells due to substrate inversion. To enable solution exchange or drug delivery to cells during experimentation, an optically clear and flexible substrate compatible with current devices and optical microscopy techniques is necessary. We present a method to integrate thin films made from polydimethylsiloxane (PDMS) into a cell stretching device. PDMS is a cheap silicone elastomer which is optically clear and biocompatible. The polymer was spun at high speeds on custom-made polycarbonate sheets to create films of a specific thickness, which was dictated to be compatible with the maximum working distance of the microscope objective (typically <200 microns). The thin films have shown to equally distribute tensile loading when uniaxial strain is applied through a cell stretcher. In addition, the optically clear property coupled with the appropriate thickness of the film enabled real time imaging of neuronal cells and the analysis of the cytoskeletal component actin in response to tensile loading. The upright film provides easy access to cells for drug delivery or other chemical reagents. Future applications include films with microfluidic constructed channels for localized drug delivery to cells.