**2. Rapid prototyping of microfluidic chips**

In recent years, microfluidic devices find many advanced applications in chemical analysis [22], polymerase chain reaction (PCR) [23], biological analysis [24], and chemical synthesis [25]. Main rapid prototyping methods of fabricating microfluidic chips include PDMS casting, micromachining, and 3D printing, etc.

### **2.1 PDMS casting**

PDMS casting is also named soft lithography. The polydimethylsiloxane (PDMS) is a kind of silicon-based organic polymer material that has been widely used in microfluidic devices by rapid prototyping [26]. PDMS casting fabrication process is typically divided into the following steps (see **Figure 1**): molds developing, PDMS casting, curing and releasing, bonding, and integration [14]. A master mold needs to be prepared firstly, where SU-8 epoxy resin usually is applied as the mold material [27]. The standard PDMS compositions are composed of silicon elastomer base and the curing reagent in a ratio of 10:1. The uncured PDMS is poured into the mold, followed by curing at 70–80 °C for an hour. After releasing PDMS from the mold, PDMS microfluidic chips can be obtained [28]. The post-process of PDMS

**35**

**Figure 2.**

*Prototyping and Production of Polymeric Microfluidic Chip*

chip fabrication approaches by the PDMS casting process.

CO2 assistance can realize microstructuring in polymer materials.

on the microfluidic chip [19].

**2.2 Micro machining**

**Figure 1.**

*Process steps of PDMS casting.*

casting usually includes bonding and integration. Bonding can reduce the hydrophobicity of the PDMS chip to encapsulate its microchannel. To enhance the bonding strength of chips with other materials, adjusting bonding process parameters and surface modification by using oxygen plasma to form O-Si-O covalent bonds at the interface of PDMS microfluidic channels are commonly used [29]. Finally, some microsensors, microheaters and microfluidic pumps are integrated onto microfluidic chip for diversified performance [18]. **Figure 2** shows the practical microfluidic

Although PDMS casting is a rapid prototyping process for disposable microfluidic chip fabrication, it is a complex process with many drawbacks. The microfluidic chip fabricated by PDMS casting has insufficient mechanical strength, non-conductivity, and non-magneticity. Also, under high temperature, high voltage, and pressure conditions, it is not easy to integrate other precision components

The microfluidic chip fabricated by micro machining, such as femtosecond laser or endmill, has relatively high accuracy and can be used repeatedly [20]. Combing with computer numerical control (CNC), micro machining can rapidly and accurately construct devices at several microns scale [21]. However, microchannels obtained from micro milling are too rough to use as a microfluidic chip, especially for the machining of polymer materials [22]. However, compared with micro milling, laser micro machining with improved accuracy can perform the direct writing ablation of polymers such as PMMA, PC, etc. Direct-write laser machining with UV and

*PDMS casted microfluidic chip: PDMS substrate with microchannels (a); enclosing of microchannel (b, e, f); PDMS molding(g); PDMS curing (c, h); substrate integration to fluid pump (d); SWB was applied for prototyping PDMS (I; forces in reversible bonded microdevice (j), mold characterization and cross-section (k) [30].*

*DOI: http://dx.doi.org/10.5772/intechopen.96355*

*Prototyping and Production of Polymeric Microfluidic Chip DOI: http://dx.doi.org/10.5772/intechopen.96355*
