20 March 2007 Laser-assisted modification of polymers for microfluidic, micro-optics, and cell culture applications
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Laser-assisted patterning of polymers is investigated for the direct fabrication of polymeric lab-on-a-chip devices in microsystem technology for capillary electrophoresis chips in bio-analytical applications. In many cases the laser process induces a chemical, physical and topographical change in the laser treated surface. This material modification significantly influences the lab-on-a-chip-functionalities. We will present our current research results in laser-assisted modification of polystyrene (PS) and polymethylmethacrylate (PMMA) with respect to applications in micro-optics, micro-fluidics and cell culture applications. For this purpose the refractive index change, the wettability and the adsorption of proteins and the adhesion of animal cells were investigated as function of laser- and processing parameters. The possible change of surface chemistry was characterized by X-ray photoelectron spectroscopy. The local UV-laser-assisted formation of chemical structures suitable for improved cell adhesion was realized on two- and three-dimensional PS and polycarbonate (PC) surfaces. Above and below the laser ablation threshold two different mechanisms were detected. In one case the produced debris was responsible for improved cell adhesion, while in the other case a photolytical activation of the polymer surface including a subsequent oxidization in oxygen or ambient air leads to a highly localized alteration of protein adsorption from cell culture media and increased cell adhesion. The highly localized control of wettability on polymeric surfaces was investigated for PS and PMMA. In the case of PS the dynamic advancing contact angle could be adjusted between 2° and 150°. This was possible for a suitable exposure dose and an appropriate choice of processing gas (helium or oxygen). A similar but not so significant effect was observed for PMMA below the laser ablation threshold. For PMMA the dynamic advancing contact angle could be adjusted between nearly 50° and 80°. The adjustment of wettability for microfluidic application will be discussed. For the integration of integrated optical waveguides in micro-fluidic devices new approaches for a rapid manufacturing of optical singlemode waveguides made of PMMA were investigated. For this purpose a high repetition excimer laser radiation source was used in combination with a flexible mask technology. The waveguides were characterized for the visible optical range and for 1559 nm. The obtained structures reveal absorption losses of 0.7 dB/cm in the visible range.
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W. Pfleging, W. Pfleging, R. Adamietz, R. Adamietz, H. J. Brückner, H. J. Brückner, M. Bruns, M. Bruns, A. Welle, A. Welle, "Laser-assisted modification of polymers for microfluidic, micro-optics, and cell culture applications", Proc. SPIE 6459, Laser-based Micro- and Nanopackaging and Assembly, 645907 (20 March 2007); doi: 10.1117/12.700208; https://doi.org/10.1117/12.700208


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