Table 4.
Main materials used for microfluidic chip fabrication
| Materials/features | Silicon/glass | Polymers | Paper | |||
|---|---|---|---|---|---|---|
| Elastomers | Thermosets | Thermoplastics | Hydrogels | |||
| Examples | – | PDMS | SU-8 | PMMA, polystyrene | ||
| Microfabrication techniquea | Wet and dry etching | Casting | Photolithography | Thermomoulding | Photolitography, printing | |
| Resolution limit | < 100 nm | < 1 μm | < 100 nm | ~ 100 nm | ~ 10 μm | ~ 200 μm |
| Mechanical stability | Very high | Low | High | Medium | Low | Very low |
| Chemical stability | Very high | Low | High | Low | Low | Low |
| Solvent compatibility | Very high | Low | High | Medium to high | Low | Medium |
| Thermostability | Very high | Medium | High | Medium to high | Low | Medium |
| Hydrophobicity | Hydrophilic | Hydrophobic | Hydrophobic | Hydrophobic | Hydrophilic | Amphiphilic |
| Optical transparency | No/High | High | High | Medium to high | Medium to low | low |
| Oxygen permeabilityb | < 0.01 | ∼500 | 0.03–1 | 0.05–5 | > 1 | > 1 |
| Scalability | Medium | Lowc | Low | High | N/A | High |
| Cost | High | Medium | Medium to high | Medium to low | low | Low |
| Main advantages | Excellent chemical, mechanical and thermal resistance High thermal-conductivity | Once the high-resolution mould is made, multiple devices can be fabricated outside the clean room | Low cost | |||
| Rubber-like elasticity (useful to form pumps and valves Low investment cost | High aspect ratio features High optical transparency | Low cost in mass production | ||||
| Main disadvantages |
Expensive Laborious and time-consuming fabrication |
Low melting point Tendency to adsorb reagents |
Sample evaporation Low sensitivity | |||
| Only suitable for research prototyping | High cost | High investment cost Insufficient gas permeability | ||||
| Applicability |
Capillary electrophoresis; Analytical and micro-reaction devices |
Cell-based studies; Clinical and veterinary diagnostics and POC devices or ‘organs-on-chips’ devices |
Platforms requiring high chemical/thermal stability; Moulds for elastomers | Mass-scale production of conventional microfluidic devices | Colorimetric analysis; Mass-scale production | |
aphotosensitive glass can be considered as thermoset
bOxygen permeability is beneficial to long-term living cells studies, but the loss of water may lead to a shift in pH and disturb the chemical analysis
cOnly suitable for research prototyping because is difficult to scale up (cost per unit does not decrease) [204]