(123d) Investigation of Stem Cell Responses to Dynamic Surface Topography

Chemistry, mechanics, and topography of a biomaterial strongly regulate the interaction of cells such as attachment and proliferation.  Specifically, topographical cues are shown to strongly influence nuclear organization/focal adhesions and alter cell alignment and hence function.However, the majority of reports on surface topography have focused on static micro/nano-patterns and the use of dynamic patterns is limited, potentially due to limited material systems for such studies.  However, the native tissue environment is dynamic and dynamic changes in the microenvironment play critical roles in many biological events such as tissue regeneration, wound healing, fibrosis and tumor progression.  In this work, we developed a dynamic PDMS patterning system and investigated the effect of pattern switching on nuclear orientation and stem cell behavior.  PDMS surface patterns were prepared via strain induced buckling by stretching a surface and exposing to UV ozone for 30 min. In the stretched state the PDMS was flat, whereas lamellar patterns formed when the strain was released.  hMSCs attached and spread randomly on the pre-stretched films; however, cells attached and aligned themselves to track the pattern shape on the pre-released substrates. After 1 day, cells had a random range of nuclei orientation from 10^o to 90^o for pre-stretched substrates whereas for pre-released substrates almost 80% of the cells had nuclei orientation ≤ 10º, which remained constant after 7 days.  Dynamic studies (switching after 1, 3, and 7 days of culture) showed that the nuclear orientation of the cells on the pre-released films changed significantly from aligned to completely random when the film was stretched and that nuclear orientation went from random to aligned when stretched films were released. This study demonstrates that the strain responsive PDMS surface patterns can be used as a powerful tool to dynamically control the cell and nuclear alignment. This dynamic control over cell nuclei provides a novel platform to investigate the relationships between cellular differentiation and nuclear morphology. Ongoing long term studies are enabling us to study the influence of matrix generation of aligned and random cells, and the effect of switching on pre-formed matrix.