Surface modification of polydimethysiloxane through plasma ion implantation

Abstract

Polydimethylsiloxane (PDMS) is a silicone elastomer with many attractive properties such as machinability, low cost, and resistance to corrosion in various industrial and biomedical applications, among many others. Due to the chemically-inert nature of PDMS, modifications are necessary for the introduction of various functional groups on PDMS surfaces. One of such methods is plasma implantation. On the other hand, plasma implantation treatment can induce significant changes to the surface morphology of the samples, such as periodic rippling of surfaces in localized areas (less than hundreds of microns) that are otherwise disordered on macroscopic scales. In this project, I investigated the development of induced ripple structures formed during the plasma treatment process. It was found that a surface prepatterning step of the PDMS surface could lead to the suppression of the wavy patterns, if the implantation voltage was small. As the plasma voltage increased, the prepatterns on PDMS could guide the development of ripple growth on the surfaces, which may be used for studying the wrinkling mechanism on elastic surfaces, and for developing surfaces with designed hierarchal sub-micron or nanometer features. The effect of plasma implantation duration, and the influence of surface prepattern dimensions, were investigated. To demonstrate the applications of such ion-implanted PDMS surfaces, plasma-treated samples were used as substrates for cell culturing studies for different cell types. Processing parameters (plasma bias voltage, processing time, surface prepattern features, etc.) were varied to induce different topologies on PDMS surfaces. A systematic investigation of cell culturing on the patterned surfaces was conducted. By using MC3T3-E1cells cultured on prepatterned samples, I demonstrated the importance of controlling the surface feature sizes and the depths of prepatterned features on the cell growth processes. To illustrate the biocompatibility of these prepatterned features, cell adhesion and cell proliferation experiments were performed using both MC3T3-E1 and EAhy926 cells. In addition, to evaluate the importance of patterned surfaces in inducing cell alignment, HeLa cells were cultured on hierarchal patterns formed by high-voltage implantation of hierarchal surfaces. In summary, this work investigated the influence of surface prepatterning on the development of the topology of PDMS surfaces during plasma implantation process. Through careful control of both the surface prepatterns and the implantation conditions, a rich variety of surface features (ranging from minimal surface corrugations to the formation of hierarchal features) were obtained, demonstrating the power of combining the two techniques in the surface topology modification of elastomer surfaces. Since the surface prepatterning steps can be easily scaled for large-scale manufacturing, it should be directly applicable for industrial-scale surface modification processes. An attempt was also made to use the treated PDMS for cell studies in vitro, illustrating the possibility of interdisciplinary studies using such a material system.