Transparency of the microfluidic device, resolution and precision of the microchannels, and bonding strength are important parameters that should be taken into consideration when an appropriate bonding method is selected. Thermal fusion bonding is a very fast technique to bond thermoplastic layers. However, it requires high pressure and temperature, which hinders its potential for the low-cost mass production of microfluidic devices. Deformation of channels after thermal diffusion bonding is also very plausible as this process is usually performed at temperature above the Tg. Furthermore, in this process, the layers cannot be bio-functionalized prior to bonding as the high temperate used in this method would denature immobilized proteins and eliminate functional groups. Thus, the functionalization process should be performed after channel bonding which can be more challenging considering the limited access to the inner surface of the channel after bonding.