(95e) Engineering Protein Presenting Patch Surfaces for Biological Study/Application

Cell-surface interactions under flow via specific binding depend strongly on surface functionalization and flow regime. To this end, we use micro-contact printing method in conjunction with microfluidics tools to create multifunctional patchy-surfaces with precise control over feature geometry and molecular species for the application of cancer cell detection. We then exploit the patchy surfaces to study interactions between cancer cells and selectin-functionalized surfaces in microfluidic devices. Patchy surfaces are of particular interest for cellular adhesion, as the residence time of a cell over a functionalized patch is defined by the ratio of the patch length in the direction of flow over cell streaming velocity.

To create a multifunctional surface, a micro-contact printing stamp is used to transfer octadecytrichlorosilane onto a glass surface defining active patterned regions for subsequent protein adsorption. The glass substrate is then backfilled with PEG-silane to inactivate the remaining surface. A microfluidic device is then affixed to the substrate to deliver proteins onto the active regions. The number of types of proteins and number of patches can be easily controlled simply by manipulating microfluidics design. We first demonstrated the feasibility of creating 45μm x 45μm patches of two different fluorescently labeled proteins. Using the same approach to functionalize a glass surface with two different antibodies, we were able to isolate diseased cells (colon cancer cells) from normal blood cell (leukocytes) suspension onto prescribed microdomains. Such multifuntional surfaces, we believe, could be useful in biological studies as well as development of biosensors for cancer cell detection.

We further exploit functionalized surfaces affixed to a microfluidic device as an in vitro hemodynamic flow model to study 2D cancer cell binding kinetics. In particular, a glass surface is engineered to present patches of selectin molecules, adhesion proteins involving in cancer cell metastasis. The patches are of uniform width but differing lengths in the direction of flow. Cancer cells are introduced over the patterned glass surface via microfluidic device at several different shear stresses relevant to physiological flow conditions. The cell residence time is proportional to the length of the protein patch. Our preliminary data showed that at a specific shear stress, a critical selectin patch size is required to initiate the binding event of cancer cells to seletins. We are also investigating the extent of cell binding influenced by selectin site density and selectin types (i.e., P- and L- selectins).