Surface patterning of protein matrix basement by thermal imprinting

Abstract

In order to hourly monitor the variation of specific cell growth, a grid mesh for the recording of adhesion positions on the surface of glass slides and dishes is printed. However, since the focal length of a lens, used for making observation, changes with the film thickness when using a protein matrix basement membrane, the surface of the basement membrane and the bottom glass plate cannot simultaneously be observed. In one way to address this problem, the author considered patterning fine structures directly on the surface of the protein matrix basement membrane by employing a thermal imprinting technology. As a mold, a 100-μm-wide grid and images of area-numbers were processed using laser lithography and reactive-ion-etching on a 1-inch Si wafer. For a gelatinous protein, we chose a mixture basement membrane BioCoat Matrigel, which was coated on a 35-mm-diameter dish. A protein thin layer was gelled on a dish according to the manufacturer's specs; the dish was then placed on the bottom loading stage of our thermal nanoimprint system. After that, a Si mold was pressed against a Matrigel matrix basement by a servo motor of the thermal nanoimprint system for 30---90 s at a press force of 1 kN. And then the mold was then released from the Matrigel without cooling when a press time reached to a set value. When an imprint temperature was 75 °C, an imprinted pattern could barely be observed. On the other hand, if the mold was heated up to 100 °C or more, the imprinted grid mesh and the printed number on the Matrigel could be clearly observed. However, a heating at 125 °C seemed to have discolored white a part of the protein. Therefore, under our experimental conditions, it can be said that the optimal heating temperature exists around 100 °C. Although in the past, in conventional thermal nanoimprint lithography, a thermoplastic bearing a glass transition temperature has been targeted, the work presented here sets an example of direct patterning on biological materials such as proteins.