Temperature-Responsive Polymers for Biological Applications
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TEMPERATURE-RESPONSIVE POLYMERS FOR BIOLOGICAL APPLICATIONS M. Rackaitis and E. Manias Materials Science & Engineering Departmrnt, 325-D Steidle Building The Pennsylvania State University, University Park, PA 16802, U.S.A ABSTRACT Water soluble polymers with tunable lower critical solution temperature (LCST) are of increasing interest for biological applications such as cell patterning, smart drug release, DNA sequencing etc. The present study addresses control of the polymer temperature response in water by varying chemical composition of the monomer. In order to achieve this a series of polymers were designed and synthesized based on an ethyleneoxide/ethylene monomer (EO/EE). Polymers were synthesized using polycondensation reactions of difunctional m-EO and n-EE oligomers. The cloud point follows linearly the balance of hydrophobic/hydrophilic interaction and can be tailored in the range of 7 - 700C by varying the m/n composition and polymer type. Polymer grafting onto the silicon surface exhibits similar solubility behaviour. Adhesion energy measurements show that grafted polymers have solubility cloud points at the temperatures that are close to the ones of the bulk polymer solutions. INTRODUCTION Advance of biological and medical research demand of intelligent polymer materials for applications such as smart and/or controlled drug delivery [1, 2, 3], controlled cell patterning [4, 5, 6], DNA separation and sequencing [7, 8] and others. Many such applications rely on smart polymer response to the external stimuli such as pH, temperature, irradiation [9]. For example Sauer et al. [10] reports synthesis of pH sensitive nanocontainers based on poly(acrylic acid) which show a reversible pH and ionic strength dependent swelling transition in water. Reported hydrodynamic radius change is from 45 nm to 195 nm when solution pH changes from 3 to 9. Zha et al. [11] report fabrication of temperature sensitive microcontainers based on crosslinked poly(Nisopropylacrylamide) (PNIPAM). Reported change of hydrodynamic diameter is from 450 nm to 250 nm with the LCST occuring at around 32 degrees. Buchholz et al. [8] report of DNA sequencing using poly(N,N-diethylacrylamide – co – N,N-dimethylacrylamide) matrixes that significantly change viscosity upon reaching phase transition temperature. Such thermaly controlled switch eanbles acceleration of microchannel flow by 3 orders of magnitude that allows for significant improvement of sequencing efficiency of DNA analysis. Cell patterning, biorecognition and biosensor technolgy rely on the interaction of synthetic material and biological surfaces. Surfaces that undergo rapid shifts in surface properties with small external changes are of particular interest [12]. Temperature – sensitive solubility usually originates from the existence of a lower critical solution temperature (LCST) beyond which the polymer becomes insoluble in water. Such behavior is typical for the polymers that form hydrogen bonds to water [12,
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14]. Taylor and Cerankowski [14] predicted that LCST
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