Namely, Liu et al. fabricated a COP-based microfluidic channel via CO2 laser ablation using pulse mode at a maximum frequency of 1kHz, whereas a Gaussian-like profile was left on the surface of the COP plate as the COP melted, decomposed, and evaporated. They concluded that the main parameters affecting the profile of the microchannel included the power and scan speed of the laser, as well as the focusing accuracy of the laser and the mechanical transmission system 59 . CO2 laser ablation was also adopted to pattern PC and polylactic acid (PLA) sheets with the desired micro-features , and to create microchannel arrays in PET foils . Laser ablation is also possible via desktop CO2-free laser cutters to create the sheets and membranes with the desired geometries . Commercially available laser systems are flexible approaches for rapid redesign of channel geometries and are usually cheaper than some other techniques such as injection molding, which requires metal molds or photolithography -a process that needs to be conducted in a cleanroom. The main drawbacks of laser ablation technique are the poor quality of the surface finish and its incapability for the fabrication of complex microchannel designs . Further, the cut profile in conventional laser cutters is only limited to Gaussian-shaped profile or through cuts (Figure ) . Formation of bulge along the scan route is another common problem associated with laser cutting technique 66 . Chai et al. showed that high thermal resistant thermoplastic polymers such as polyformaldehyde (POM) can be CO2 laser cut without formation of bulges and carbide residue, and the channel depth and width are easily adjustable by changing the scan speed and laser energy (Figure ) . Covering PMMA substrates by photoresist or PDMS is another way to tackle the bulge formation 68 .