Material matters – and we offer a large choice of different materials, ranging from a wide variety of polymers, via glass or silicon, to ceramics or metals. All materials have their pros and cons, regarding costs or geometrical freedom, for example, polymers are dominating.
Materials in Microfluidics
Historically, microfluidics and the use as lab-on-a-chip for applications in life sciences or analytical sciences started with technologies being available from semiconductor industries. Consequently, since these technologies were available and allowed for micro-structuring, they were used for the first microfluidic devices. Materials that were applicable to be structured by technologies used in semiconductor industries were glass and silicon. First microfluidic devices, besides ink jet printer heads for non-life science microfluidics, were made from glass and silicon, reaching back to the 1970s with Stephen Terry’s gas chromatograph integrated on a silicon wafer, which was functional but rather expensive. These semiconductor manufacturing technologies have been available at many engineering institutes, thus these disciplines pioneered in microfluidics due to the availability of elaborate and usually expensive technologies.
Another manufacturing technology arose by simply taking the micro-structured silicon devices made by the semiconductor technologies and replicating the structures into a soft polymer in a process called casting (often also referred to as “soft lithography”), just by pouring the liquid polymer onto the silicone matrix, hardening it, and removing the soft polymer replicate. This process can be repeated may times, and besides the one-time investment in the silicon master, it is – from an equipment point of view – an extremely low-cost technology. The material used for this process is a special kind of silicone, usually PDMS (Polydimethylsiloxane).
Later on, a merger of conventional fabrication technologies, for e.g. standard life science plastic lab ware, namely injection molding, with micro-technology took place. The challenge that had to be overcome to make this technology available for microfluidics was in a first instance the generation of the micro-structured master in metals that withstands, depending on the feature sizes, several thousand to several hundred thousand replication cycles. After the replication, assembling technologies needed to be developed. The adoption of industrial replication technologies in combination with the wide variety of commercially available polymers enables a most cost efficient fabrication together with the widest design freedom and is the reason for the current progress made in the commercialization of microfluidic devices.