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Ionov, L. ; Synytska, A. ; Stamm, M. ; Diez, S.
Temperature-induced size-control of bioactive surface patterns

Micropatterned surfaces are widely used for biotechnological applications such as cell culture, bioanalytics, and tissue engineering. Although many approaches exist to fabricate sophisticated surface patterns, for example based on microcontact printing, electron beam lithography, or dip-pen lithography, they are almost entirely limited to producing fixed patterns that cannot be intentionally modified under physiological conditions. However, patterns that could be generated or modified on demand in aqueous environment would tremendously extend the applicability of structured surfaces. In order to achieve such in-situ treatment in a localized manner a number of optical and electrochemical techniques have been proposed. However, most of the optical strategies use UV illumination, which is often harmful to biological species.
Here we demonstrate a new method to produce bioactive surfaces with patterns whose size can be changed in response to variation of the environmental conditions, rather than local treatment. Our design is based on the patterned surface-immobilization of thermoresponsive poly-(N-isopropylacrylamide) (PNIPAM) polymer chains. In aqueous environments, PNIPAM (homopolymer) chains undergo reversible collapse or swelling above or below the Low Critical Solution Temperature (LCST = 33 °C), respectively. However, the LCST can be gradually increased or decreased by incorporation of additional hydrophobic or hydrophilic comonomers, respectively. Likewise, the LCST can be tuned by varying the ratio of both added comonomer types. Using this principle, we fabricated a surface containing lateral LCST gradients by laying down opposing gradients of hydrophilic and hydrophobic PNIPAM-copolymers. Across this surface, polymers whose LCST is above or below the actual temperature of the surrounding were collapsed or swollen, respectively. We further showed that changes in ambient temperature could alter the size of the area in which a particular polymer was collapsed or swollen . By embedding functional proteins into the switchable polymer layers we demonstrated the temperature-induced size-control of bioactive surface patterns.

Polymeric Materials: Science and Engineering 1001



October 2009


Polymer Interfaces