Fabrication Of Three-dimensional Large-size Glass Microfluidic Devices Based On Ultrafast Laser Direct Writing And Carbon Dioxide Laser-assisted Packaging

Currently,there is an increasing demand for customized manufacturing of large-size and high-precision microchannel devices in many fields such as lab on chips,organs on chips,and flow chemistry.In particular,compared with the traditional two-dimensional microfluidic structures,three-dimensional(3D)microfluidic structures provide superior performance for the functional manipulation of fluids.As one of the widely used substrates in laboratory research and industrial application of microfluidic technology,fused silica glass has excellent advantages in terms of its high chemical stability,low thermal expansion coefficient,wide transmission spectral range,and good biocompatibility.Ultrafast laser direct writing is one of the most representative technologies for three-dimensional microfabrication of fused silica.3D controllable microchannels with arbitrary configurations can be flexibly fabricated in fused silica by ultrafast laser direct writing assisted selective chemical etching.However,for the practical fabrication of centimeter-scale 3D fused silica microfluidic devices,some technical barriers still exist.Firstly,it is still difficult to directly fabricate 3D glass microchannels with arbitrary length and uniform size by conventional ultrafast laser-assisted chemical etching,due to its inherent limitation of etching selectivity.Secondly,for the fabrication of large-size closed glass microfluidic structures,additional fabrication procedures such as aligning,stacking,and bonding of the substrates are needed,which leads to the pressure resistance of microchannels being limited by the bond strength and mechanical strength of bonding materials.In particular,the bonding process has high requirements for the flatness and smoothness of glass surfaces.In addition,for current microfabrication methods simultaneous fabrication of centimeter-scale glass objects with external arbitrary shapes and 3D embedded microchannels with high aspect ratios on/in a single substrate remains challenging.To address these issues,this thesis focuses on the exploration of the advanced fabrication technology of 3D large-size glass microfluidic devices with a high pressure-resistant performance by combining ultrafast laser microfabrication and carbon dioxide(CO₂)laser microprocessing.The main achievements are as follows:(1)A manufacturing method of 3D large-size glass microfluidic devices with high pressure-resistant performance have been proposed,which is based on ultrafast laser-assisted selective chemical etching and defocusing CO₂ laser-induced localized sealing of the extra-access ports.The proposed method enables customized centimeter-scale manufacturing of 3D fused silica microfluidic devices.Controllable sealing of extra-access ports on the sample surface with arbitrary shape can be achieved,which has no requirements on the shape and surface smoothness of glass structures.(2)The optimized process of CO₂ laser-induced sealing of the extra-access ports has been systematically studied.By optimizing the spatial size of the microchannel structure as well as the CO₂ laser processing parameters such as laser power and defocusing distance,the extra-access ports can be almost eliminated and a nearly perfect main channel can be obtained with unlimited length.,Meanwhile,the stress distribution around the extra-access ports can also be controlled.As compared with PDMS bonding,this improved approach allows the robust formation of a sealing layer with a tunable depth and controllable thickness,which exhibits superior mechanical strengths in harsh environments.With this technique,an all-glass microfluidic droplet generator is manufactured and its function has been verified,showing great potential for developing high-throughput,customized microfluidic devices in the microdroplet production and micro/nano emulsification.(3)The influence parameters on the processing accuracy(including model accuracy,optical accuracy,and etching accuracy)of ultrafast laser-assisted 3D glass subtractive printing have been analyzed and the possible improved methods are demonstrated.The hybrid femtosecond and picosecond laser microprocessing approach is proposed to improve the structuring accuracy of glass surfaces while ensuring the etching rate in 3D glass subtractive printing.With this approach,the high-precision fabrication of a microcell culture cage is demonstrated.(4)Large-scale fabrication of freeform all-glass microfluidic networks encapsulated in 3D printed macro-scale objects have been demonstrated by a combination of ultrafast laser 3D subtractive glass printing and CO₂ laser-induced port sealing.With the developed technique,a 3D fused silica hand model with a size of?3cm×2.7 cm×1.1 cm in which the blood vessel network is encapsulated is designed and manufactured.It shows the great potential for developing new 3D organs-on-a-chips and multifunctional bionic microfluidic systems.