Ultrafast laser micro/nano processing for microfluidic and tissue engineering apllications

Summary form only given: This paper reviews our work on the application of ultrafast pulsed lasers for the biomimetic micro/nano processing of materials surfaces and controlling materials properties via this process. A unique aspect of this approach is that the material modifications can occur over many different length scales, adding complexity to the surface and a new dimension to surface optimization. As a result, direct irradiation of materials by ultrafast laser pulses often induces modifications leading to complex micro and nanoscale surface structures, which are often found to have different and by far superior properties to those of the bulk materials. It is shown that the artificial surfaces obtained by femtosecond (fs) laser processing of Si in reactive gas atmosphere exhibit roughness at both micro and nanoscales that mimics the hierarchical morphology of natural surfaces[1]. Along with the spatial control of the topology, defining surface chemistry provides materials exhibiting notable wetting characteristics which are potentially useful for open microfluidic applications. Depending on the functional coating deposited on the laser patterned structures we can achieve artificial surfaces that are: (a) of extremely low surface energy, thus water repellent and self-cleaned[1]; (b) responsive, i.e show the ability to change their surface energy in response to different external stimuli such as light, electric field and pH [2,3]. The implementation of laser engineered hierarchical surfaces for the development of biomimetic tissue scaffolds is additionally presented. Cell culture experiments performed with the fibroblast NIH/3T3 cell line [4] as well as with primary neuronal cultures [5] showed that it is possible to preferentially tune cell adhesion and growth, through choosing proper combinations of surface topography and chemistry. Furthermore combinations of the scaffolds obtained with well-defined biological nanostructures in a "scaffold on scaffold" forma- - t are investigated. It is found that cell adhesion properties can be effectively tuned by chemical functionalization of the 3D structures obtained with well-defined cell-binding peptides, for example Arg-Gly-Asp-Cys (RGDC). It is concluded that the laser textured 3D micro/nano Si surfaces with controllability of roughness ratio and surface chemistry can advantageously serve as a novel means to elucidate the 3D cell-scaffold interactions for tissue engineering applications.