Microfluidics relates to design and study of devices which move or analyze tiny amount of liquid, smaller than a droplet. Microfluidic devices have microchannels ranging from submicron to few millimeters. To compare, human hair is about 100 micron thick. Microfluidics has been increasingly used in the biological sciences, because precise and controlled experiments can be conducted at lower cost and faster pace. Lab-on-a-Chip devices use microfluidics for applications such as Point-of-Care testing of diseases, or Organ-on-a-Chip studies.
Microfluidics systems work by using a pump and a chip. Different types of pump precisely move liquid inside the chip with the rate of 1 μL/minute to 10,000 μL/minute. For comparison, a small water drop is ~10 microliter (μL). Inside the chip there are microchannels that allow the processing of the liquid such as mixing, chemical or physical reactions. The liquid may carry tiny particles such as cells or nanoparticles. The microfluidic device enables the processing of these particles, for example trapping and collection of cancer cells from normal cells in blood.
A microfluidic chip is a device that enables tiny amount of liquid to be processed or visualized. The chip is usually transparent and its length or width are from 1cm (0.5″) to 10cm (4″). The chip thickness ranges from about 0.5mm(1/64″) to 5mm (1/4″). Microfluidic chips have internal hair-thin microchannels that are connected to outside by means of holes on the chip called inlet/outlet ports. Micorfluidic chips are made from thermoplastics such as acrylic, glass, silicon, or a transparent silicone rubber called PDMS.
Microfluidic chips are usually made by making thin grooves or small wells on surface of a layer, and then enclosing those features by means of a second layer to form microchannels or chambers. Channels need to be leak-proof thus the layers must to be properly bonded. Depending on material choice, the channels are made via soft lithography, hot embossing, injection molding, micro-machining, or etching. 3D printing may be used for producing microfluidic chips, although it has serious limitations in terms of minimum feature size, surface roughness, optical transparency, or choice of material.
There are several reasons to use microfluidics. First, to make use of small size scale in the range of microns. For every 3D shape type, e.g. a rectangular channel or chamber, the ratio of surface area to volume increases as size decreases. This makes it favourable for microchannels to captures targets such as cells, germs or nanoparticles. Alternatively, Magnetic or Electric fields are more effective at short distance, making microfluidics ideal for sensing or detecting. Ability to visualize and characterize small objects such as living cells is another advantage of microfluidics. Microfluidics is also used to miniaturize or integrate conventional laboratory practices by making lab on a chip devices to save cost or reduce time.
Microfluidics has application in most experimental science and engineering. Examples are molecular and cell biology research, genetics, fluid dynamics, micro-mixing, Point of Care Diagnostics, Lab on a Chip, Tissue engineering, Organ on a Chip, drug delivery device, fertility testing and assistance, synthesis of chemicals or proteins.