Soda-lime glass as biocompatible material to fabricate capillary-model devices by laser technologies

Microfluidic devices have been widely developed in the last decades because of the huge number of fields where they can be applied. Among all the different fabrication techniques available, laser direct writing stands out since it is a fast, accurate, versatile and non-contact method. It is particularly well-suited when working with glass, a robust and cost-efficient material. These laser advantages allow the direct fabrication of not only high quality single microchannel devices but also complex and bifurcated structures. This work establishes a roadmap for manufacturing capillary-model devices with good biocompability in soda-lime glass substrates with pulsed lasers operating in the nanosecond, picosecond and femtosecond temporal range. We determine the optimal laser parameters required for fabricating channels with a diameter:depth rate of 2:1, keeping a semi-circular section. The presence of tin doping (∼2%) in the soda-lime glass is shown to enable the fabrication with nanosecond pulses, and to improve the quality of the channels, reducing the cracking at the sides, when picosecond or femtosecond pulses were used. On the other hand, two regimes of surface roughness are found: a low roughness regime for channels fabricated with nanosecond lasers and a high roughness regime for those fabricated with pico and femtosecond lasers. Human umbilical vein endothelial cells (HUVEC) are employed for cell culturing for evaluating the biocompatibility of the channels. Structures manufactured with the nanosecond laser resulted more suitable in terms of cell adhesion than those fabricated with the picosecond and femtosecond lasers, due to the different surface roughness regimes obtained. In order to increase the biocompatibility of the channels fabricated with pico and femtosecond lasers and to improve the cell growth, a controlled post-thermal treatment is carried out for smoothing the surface