Microfluidics: enabling 'micro' medical technologies
23 August 2017
With all the discussion about the personalisation of medicine and what can be achieved by having access to the latest gadgets, it is easy to overlook the underlying technologies that make these devices possible. Microfluidics is an enabling technology that underpins many medical devices such as implantable biosensors and portable diagnostic bioassays and is already having an impact on the development of portable medical devices, point of care tests and diagnostics for low resource settings.
From the macro- to the micro-scale
Microfluidic technology is used in a broad spectrum of devices, but the fundamental principle is that it relies on controlling the movement of fluids in very small spaces, in devices that aim to miniaturise standard laboratory procedures. The advantages of miniaturisation in this context are:
- Devices can be designed to make optimal use of small quantities of biological material
- Small volumes of reagents are needed
- Users can carry out many experiments at once and have more precise control over the conditions in which chemical reactions take place
Portability is an important feature of many of these devices, opening up the accessibility of diagnostics to different clinical situations and patient groups.
Central to many of these devices is a microfluidic chip (or chips) measuring just a few centimetres or even millimetres that can be made from a variety of materials such as glass, silicon or polymers. A microfluidic chip contains channels, valves and/or wells in which chemical reactions can take place. A chip can function as a standalone device or as part of larger devices with additional pieces of equipment to control the fluid flow and to measure outputs and provide readouts.
Testing in low-resource health systems
Disposable microfluidic devices that have easy to read outputs have the potential to be transformative in low-resource settings where access to medical testing laboratories can be patchy or non-existent. They can be made of a single layer or folded layers of paper or cloth, with wax or other materials used to create channels. Devices made of soft material like paper are cheaper to manufacture and store, less fragile, and require little or no specialist equipment to use. Fluid moves through these devices by wicking or capillary action and can be designed to display a colour change that indicates the result of the experiment or test.
One example is of a chip that measures levels of liver enzymes to indicate liver damage in HIV and TB patients. A drop of the patient's blood is placed on the paper chip and the blood plasma wicks through the layers on the chip that are impregnated with different reagents. Elevated levels of two enzymes that indicate liver damage give colour readouts on the back of the chip, which can be read by eye by trained healthcare workers. This approach means that a patient does not have to wait for a test result from a centralised laboratory and if action is needed they can be treated more quickly. The chips themselves are relatively cheap, and once they have been used, can be easily disposed of by incineration.
Point of care testing
Another area with great potential for microfluidic technologies are point of care diagnostics devices in frontline medical situations such as accident and emergency departments or GP surgeries. One device currently available and already trialled in a London hospital can be used for the early detection of sepsis (blood poisoning) in patients, allowing prompt treatment. Although the point of care device is more expensive than the laboratory test, sepsis is cheaper to treat the earlier it is caught. Such decentralised testing enable clinicians to act early and while the costs of the test may be higher, these must be weighed against the patient benefit, both in terms of swifter treatment decisions and improved access to testing.
While these uses are extremely promising, there are challenges. Manufacturing microfluidic chips is not a trivial undertaking - the process can require stringent clean room conditions or some steps to be undertaken by hand. These restrictions can be challenging when scaling up from the research laboratory to industry, which in turn affects which materials and processes can be used to create commonly used devices. The cost of materials and manufacturing is also an important consideration. While microfluidic chips themselves are small, extending miniaturisation throughout the device – for example the equipment needed to supply reagents to a chip, to move fluid around the chip, or to measure results – can be difficult.
The research community also talk of finding a 'killer application' that will propel microfluidic technologies into the mainstream. This is a technological advance in the development of microfluidic technology that will allow any laboratory process to be miniaturised while matching or improving performance over current practice. Time will tell if such a transformative technology will be developed thus making the 'lab on a chip' universal, rather than for specific applications.
From health testing to robotics
From the development of more accessible diagnostics to a soft octobot controlled by a microfluidic circuit, this technology will continue to be central to many of the innovative healthcare devices currently being developed, despite the many technical challenges. As these challenges are overcome, medical devices that make use of microfluidic technologies will become more common in hospital units and in GP surgeries, and will have an impact on the delivery of healthcare in low- and middle-income countries.