Vk 100

CO₂ laser micro-machining is an efficient and cost-effective method of producing a wide range of polymeric microfluidic devices^{22 (link)}. The pre-fabricated epoxy resin cast chips (3 mm thick) were micro-machined using a commercial bench top CO₂ laser (Universal Laser System, VLS 3.5, USA) with a maximum power of 30W (Fig. 1a). The micro-channel pattern was designed by using CorelDraw©X5 2010 software, a computer-aided design (CAD) tool, associated with the laser cutter. Vector mode was adopted for cutting lines widths below 200 μm. The design was plotted on eight lines with different colors at a time due to the ability of the plotter to accommodate eight different laser settings in one pass (Fig. 1b). Varying laser settings were employed to optimize the micro-patterning process where average power (P) ranged from 1.8 to 3.6W and scanning speed (S) ranged from 5 to 20 mm/s. The quality characteristics for the resulting micro-channels include the width, depth, and surface roughness (Ra) of the micro-channels and bulge heights was assessed using 3D laser microscope (Keyence VK- × 100). Each experiment was conducted three times, and then the average and standard deviation were calculated.Figure 1

Schematic representation of CO₂ laser ablation process (a) and eight-line design (b).

Surface morphology of the irradiated areas were analyzed by a scanning electron microscope (SEM, Quanta 450 FEG, FEI, Hillsboro, OR, USA). Atomic force microscopy (AFM, ICON, Bruker, Madison, WI, USA) and 3D laser scanning confocal microscope (VK100, Keyence, Osaka, Japan) were utilized to measure the topography of the hierarchical structure.