Microfluidics has properties that make it attractive as practical and feasible tools in biotechnology areas. The knowledge of several possibilities of materials is an important aspect for developing new microfluidic designs with proper applications. The characteristics and properties of the materials used are quite relevant aspects for the desired microfluidic platforms. Commercial microfluidic devices are primarily etched and/or molded from mechanically sturdy and chemically durable materials, such as glass, polydimethylsiloxane (PDMS), and thermoplastics. Glass- and polymer-based microfluidics in biochemical analyses and related applications has made the spectacular success. Not far behind this, the investigation of microfluidic systems in other classes of materials has been rapidly growing.
Early miniaturized total analysis systems (μTAS) devices were fabricated from silicon and glass using clean-room techniques that were translated to microfluidic device fabrication. This was largely a choice of convenience and necessity (early microfluidics focused largely on electrophoretic phenomena where glass is a preferred material), but not a long-term solution for cell biology research. Silicon is opaque to visible and ultraviolet light, making this material incompatible with popular microscopy methods. Glass and silicon are both brittle materials, they have non-trivial bonding protocols for closing microchannels, and in general they require expensive, inaccessible fabrication methods. These materials were well suited for some applications (for example, electrophoresis), but were ultimately limited in their growth potential. Cheaper, more accessible materials and fabrication methods were needed to fuel the growth of microfluidic technology development and adoption.
PDMS is an optically transparent, gas- and vapor-permeable elastomer. PDMS was first used in 1998 for the fabrication of more complex microfluidic devices and helped soft lithography become the most widely adopted method for fabricating microfluidic devices. Adoption of the material can be attributed to several key factors, including (1) the relatively cheap and easy set-up for fabricating small numbers of devices using PDMS in a university setting; (2) the ability to tune the hydrophobic surface properties to become more hydrophilic; (3) the ability to reversibly and (in some cases) irreversibly bond PDMS to glass, plastic, PDMS itself, and other materials; and (4) the elasticity of PDMS, which allows for easy removal from delicate silicone molds for feature replication. However, perhaps most importantly, the elasticity of PMDS allows for valving and actuation, which has led to a plethora of microfluidic designs and publications.
Despite all the beneficial properties of PDMS that enabled its rapid adoption amongst university engineers, there are several limitations to implementing the material in biomedical research. For example, PDMS has been shown to absorb small molecules, which can affect critical cell signaling dynamics. Thus, polystyrene may be preferred over PDMS for many cell biology applications, particularly because biologists have a long history of using polystyrene for cell culture. Furthermore, the use of polystyrene mitigates or eliminates many material property issues associated with PDMS, including the bulk absorption of small molecules and evaporation through the device, and polystyrene makes handling and packaging easier for use in collaborations.
In addition to thermoplastic materials, there has been substantial progress in using destructible, cheap materials such as paper, wax, and cloth for point-of-care applications in low-resource settings. These materials have the benefit of being cheap and easily incinerated, making them ideal choices for settings where safe disposal of biological samples is challenging. Currently, there is increasing activity in developing microfluidic paper-based analytical devices (μPADs). These μPAD devices are expansions on tried-and-tested lateral-flow assays (for example, pregnancy strip test) and operate by passively wicking biological samples through patterned hydrophilic regions using capillary forces.
Fig.1 Materials other than PMDS are being used for microfluidic device design. (Sackmann, 2014)
A microfluidic biomaterial is a biomaterial (most commonly, a hydrogel such as alginate or type I collagen) that contains a microscale channel that can sustain fluid flow. The material should be compatible with the culture of cells within the bulk of the material. Microfluidic biomaterials possess many advantages for potential biological applications. First, and most importantly, these materials are inherently able to sustain fluid flow. As a result, immediate perfusion is possible, which is desirable when the biomaterial contains embedded cells to which nutrients are to be delivered and from which metabolites are to be removed. Second, the transport of substances and/or cells to and from the biomaterial can be tailored with the geometry of the microfluidic network. Third, because the sizes and locations of microfluidic channels are chosen by design, the microfluidic geometry within the biomaterial is well-controlled and reproducible. Fourth, microfluidic biomaterials contain micrometer-scale channel widths that are particularly well-suited for replicating the geometry of microvessels and other tubular structures that are desired in engineered tissues.
Fig.2 Strategies for forming microfluidic biomaterials and representative implementations. (Tien, 2021)
Different materials have different applications in microfluidic development and every material has its unique purpose. What is important is to choose appropriate materials corresponding to your final purpose in microfluidic development. Creative Biolabs has been focusing on microfluidics over years and is experienced in this field. We have established a comprehensive one-stop microfluidic solution platform and provide a variety of microfluidic-based services including but not limited to:
If you are interested in any one of our services or you have any questions about microfluidics, please don’t hesitate to contact us for more information.
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