Purdue University School of Chemical Engineering GRADUATE SEMINAR SERIES Dr. Deborah E. Leckband Reid T Milner Professor of Chemical Sciences Department of Chemistry University of Illinois at Urbana "Thermally Responsive Polymers In Biotechnology: New Perspectives On An Old Problem" Tuesday, April 1, 2014 9:00-10:30 A.M. FRNY G140 Refreshments at 8:30 AM in Henson Atrium, FRNY Hall Abstract. The temperature-dependent solubility of poly(N-isopropyl acrylamide) is exploited to reversibly switch polymer interactions with proteins and cells at the lower critical solution temperature (LCAT) near 32°C. Two notable applications are cell sheet engineering and thermally programmed protein separations. Both applications hinge on achieving reversible bioadhesion to PNIPAM coatings, but a fundamental challenge has been the identification of polymer design parameters that impact reversible bioadsorption above and below the LCST. For decades, the assumption has been that thermally triggered polymer collapse and reswelling are essential for thermally reversible bioadhesion. I will present evidence that contradicts this view, but provides an alternative model consistent with current data. Surface force measurements, neutron reflectivity, and AFM imaging characterized the brush architecture as a function of the chain density, chain molecular weight, and temperature. The latter findings were in turn compared with temperature-dependent protein (and cell) adsorption and release. Qualitative comparisons of the experimental trends with theories for polymer brushes and their interactions with proteins in good and poor solvents suggests an alternative model for thermally-switchable bioadsorption, as well as design guidelines for tailoring the performance of PNIPAM coatings in these biological applications. Bio: Deborah Leckband pioneered the use of force measurements to quantify biomaterial surface properties at the molecular scale and their impact on material performance in biotechnology and the clinic. She investigated a range of materials, including water-soluble polymers, membranes, and immobilized proteins. Findings resulted in novel insights regarding how molecular scale surface forces impact many applications including drug delivery, biofouling, biosensing, and fundamental biological issues such as cell-cell cohesion. Her studies of biomaterials, in particular, often transformed long-held views on mechanisms underlying bioadhesion and how to control them.