Materials and Micromachining Methods

Inquiry

Through manipulating fluids using microfabricated channel and chamber structures, microfluidics is a powerful tool to realize high sensitivity, high speed, high throughput, and low-cost analysis. A significant feature of microfluidics is that the material of the device dominates its functions. To realize certain functions, attention should be paid to choosing the suitable material for the device as it endows the inherent property of the device and determines the applicable microfabrication approaches.

Many materials have been developed over the past decades that are appropriate for transformation into microfluidic biomaterials. The suitable techniques for fabricating microfluidic devices often depend on the materials and specific application of the device and include micromachining, soft lithography, embossing, in situ construction, injection molding, and laser ablation.

Inorganic Materials

The first-generation microfluidic device was prepared in silica and glass owing to their resistance to organic solvents, ease in metal depositing, high thermoconductivity, and stable electroosmotic mobility, although many other chip materials have been introduced afterward. Silicon materials often find use when semiconductor characteristics or devices are needed, and glass is the best material for sensitive optical detection or high voltage applications.

An example of a hybrid glass/PDMS device with a well and single channel for embryo culture. Fig.1 An example of a hybrid glass/PDMS device with a well and single channel for embryo culture. (Beebe, 2002)

Rigid Polymers

The vast variety of polymers offers great flexibility in choosing the most suitable materials for different needs. Compared with inorganic materials, polymers are easy to access and inexpensive to microfabricate and therefore have become the most commonly used microchip materials. According to their properties, polymers are classified into elastomers, thermosets, and thermoplastics.

Hydrogels

Microchannels can be built in the hydrogels for the delivery of solutions, cells, and other substances. They are highly porous with controllable pore sizes, allowing small molecules or even bioparticles to diffuse through. Most hydrogels are gelled at mild conditions in aqueous solutions; thus, they can be molded from masters made of almost any material insoluble in water. In contrast to the ease in molding, the bonding is challenging. Reported bonding strategies include (1) melting a thin layer of the bonding surface by heating or chemicals right before attaching and (2) utilizing a second linking agent at the interface.

Papers

Paper is a highly porous matrix made of cellulose, excellent in wicking liquids. The fabrication of paper-based microfluidic devices is simple. In general, any method that generates hydrophobic patterns on paper is feasible. The reported methods can be divided into two groups. Lithographic processes apply polymer solution to a paper and subsequently, remove the formed coating from certain regions where channels are defined. In contrast, the printing (cutting) methods directly generate hydrophobic barriers without pre-exposure of the channel area to reagents.

3D Printing (3DP)

3DP is a relatively new approach to fabrication, and many 3DP methods have been successful in forming fluidic channels, including fused deposition modeling (FDM), PolyJet (PJ), stereolithography (SLA), and more.

Hybrid and Composite Materials

The materials mentioned above can be modified or combined into one hybrid chip to fabricate more powerful devices for specific aims.

Table 1. Applications of microfluidic systems made of different materials. (Ren, 2013)

Applications of microfluidic systems made of different materials.

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Referencse

  1. Beebe, D. J.; et al. Physics and applications of microfluidics in biology. Annual review of biomedical engineering. 2002, 4(1), 261-286.
  2. Ren, K.; et al. Materials for microfluidic chip fabrication. Accounts of chemical research. 2013, 46(11), 2396-2406.

For Research Use Only. Not For Clinical Use.

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