**3.4 Injection molding**

*Contemporary Developments and Perspectives in International Health Security - Volume 1*

Photolithography is one of the earliest and still one of the most popular methods

In softlithography, the reverse master is designed and fabricated in such a way as to have protruding patterns on its surface. It can be the positive or negative image of a target LoC. Silicon, PMMA, or a chemical-coated PDMS can be made to bear the master image. One of the benefits of softlithography is that it can be used to fabricate LoCs with three-dimensional microfluidics channels and also to form microstructures, including channels, and submacrostructures, including cell-culture chambers [29, 30, 35]. Softlithography technique is convenient, straightforward to apply, accessible to a wide range of users, and low-cost nonphotolithographicbased approach for micro and nanofabrication. Some softlithography techniques are: microcontact printing (μCP), microtransfer molding (μTM), replica molding (REM), micromolding in capillaries (MIMIC), and solvent-assisted micromolding (SAMIM). **Table 3** compares the advantages and disadvantages of conventional

Microembossing, also known as microtransfer molding or hot-embossing, is the process by which the configuration of microfluidic channels is transferred onto

Definition of patterns Rigid photomask Elastomeric stamp or mold

Planar surface Two-dimensional structures

Resolution 100 nm From 30 nm to 1 μm

*Comparison between photolithography and softlithography [21–24, 29, 30, 33–35].*

**Photolithography Softlithography**

SAMs on Au and SiO2 SAMs on Au, Ag, Cu, GaAs, Al, Pd, and SiO2

> Precursor polymers Polymer beads Sol-gel materials Conducting polymers Colloidal materials Organic and inorganic salts Biological macromolecules

Both planar and nonplanar Both two-dimensional and threedimensional structures

Photoresists Photoresists

for fabricating LoCs. The photolithography and etching method for fabricating mask and LoCs relies on the traditional photo developing method. The process involves using negative or positive photoresists. Photoresists are exposed to high intensity UV-wavelengths through masks and spin coated. In photolithography, there are mask and mask-less methods. Mask-less photolithography can be achieved by methods whereby light is spatially modulated and light patterns can be manipulated at every pixel. In photolithography, before etching with chemicals, a UV resist can be used to spin coat chemicals and focused UV light can be beamed onto the

**3.1 Photolithography**

photoresist [34].

**3.2 Softlithography**

**3.3 Microembossing**

Materials that can be patterned directly

Surfaces and structures that

can be patterned

photolithography and softlithography [29].

**200**

**Table 3.**

In injection molding fabrication protocol, the injection of molten thermoplastic involves under high pressure into a heated closed master mold, followed by cooling until the thermoplastic solidifies, and subsequent demolding the replica from the master mold. For industrial scale manufacturing of macroscopic objects in thermoplastics that has been adopted for micromanufacturing, injection molding is a well-established technique [32].
