Characterization ofmicrochannels fabricatedwith laser for microfluidic
applications
Due to the numerous applications it presents, the microfluidics field has
experienced enormous developments in the past few years. Lab-on-a-chip,organ-on-a-chip, point of care devices, cell capture, chemical and biologicalanalysis are some of the examples for direct microfluidic applications.
Regarding uses, microfluidic devices have different geometries which canbe as complex as needed, but one of the basic structures that comprisethese microfluidic device is the microchannel.
Several materials have been reported for the fabrication of the microchannel,
and the suitability of one or another depends on the fabrication technique.
Some of these materials are polymers, silicon or glass. Examples ofmanufacturing techniques are soft-lithography, photolithopgraphy orthermofusing techniques. But when using soda lime glass as material
which was chosen due to its robustness, chemical resistance, transparency
and low cost- direct laser writing presents itself as one of the most suitable
techniques. It is accurate and versatile, generating very complex geometries
quickly. Moreover, due to its non-contact nature, there is no contaminantand does not require clean room facilities. When working in micron
dimensions for this application, it is crucial to have a very good image ofthe topography to ensure its quality, as well as all the information about theCASE STUDY CHARACTERIZATION OF MICROCHANNELS FABRICATED WITHLASER FOR MICROFLUIDIC APPLICATIONSPhotonics4Life is a researchgroup in the Optics Area of theApplied Physics Department ofthe Universidade de Santiago deCompostela (Spain). One of its
research areas is dedicated to thefabrication of different microfluidicdevices by laser processing. These
devices simulate blood vessel
networks and cellular behaviours
in vascular pathologies suchas micro-tumours, formationof atherosclerotic plaques andaneurysms for performing
preclinical in vitro models. Authors:
M.Teresa Flores-Arias and María
Aymerich.

1channel dimensions. In this report, the structures manufactured by directlaser writing are fully characterised by means of confocal microscopy.

■ Measurements
Microchannels were fabricated over soda lime glass by direct laser writing.
The laser employed was a Rofin Nd:YVO4 system, with 20 ns pulse
duration and 1064 nm central wavelength. The setup was composed by agalvanometer system that addresses the beam and allows the fabrication ofcomplex structures with no need of sample movement. The laser beam was
focused over the substrate surface by using a lens of 100 mm focal lengththat ensures a working area of 80x80 mm2. Soda lime glass was obtained
from a local supplier.
In order to obtain a proper aspect ratio of the structures, several laser scans
were applied to the sample. Therefore, a study of the evolution of thetopography was performed. Microchannels with scans from one to ten times
were manufactured. Using Sensofar S neox 3D optical profiler, a confocal
image of the structured area was captured using a 20X magnification
objective. The surface profile was generated and the evolution of the depthof microchannels with the laser scans was depicted (Figure 1).
Figure [1] Confocal image of several
microchannels with different laser scans,from one (left) to ten (right). The profile of thechannels is also generated.

Roughness value of the microchannel walls are a critical value to know since
it should be low enough for microfluidic applications. Thanks to Sensofar S
neox 3D optical profiler and SensoMAP analysis software, it was possible toobtain roughness values from small areas. The topography of the bottom ofa microchannel with eight laser scans, obtained with a 50X magnification
objective, was selected for the study (Figure 2).

Figure [2] 3D topography of one microchannel fabricated with laser and the roughness

parameters of the bottom of the channel, according to ISO 25178.

2

CASE STUDY CHARACTERIZATION OF MICROCHANNELS FABRICATED WITHLASER FOR MICROFLUIDIC APPLICATIONSThanks to the versatility and accuracy of laser direct writing, several
microfluidic devices can be manufactured. Here we show some 3D confocal
topographies of some of those examples obtained with a 20X objective(Figure 3).

Figure [3] 3D confocal topographies detail some examples of microfluidic devices performedwith laser over soda lime glass.

■ Conclusions
Thanks to the S neox, 3D optical profiler from Sensofar, it was possible toeasily characterise the topography of the microchannels fabricated withlaser technologies. The evolution of the profile of the structures with thelaser scans was analysed by using the confocal technique with a 20X
magnification objective.
Moreover, in combination with the SensoMAP analysis software, theroughness parameters of the manufactured channels were calculated. In
this case, a 50X magnification objective was employed when acquiring theconfocal topography.
In conclusion, by using the S neox, 3D optical profiler, each structure can beperfectly characterised in dimensions and roughness.

CASE STUDY CHARACTERIZATION OF MICROCHANNELS FABRICATED WITHLASER FOR MICROFLUIDIC APPLICATIONS

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