Microvisk develops versatile viscometer

Engineers have developed a cheaper and more convenient solution to measure the effectiveness of blood clotting.

Anti-coagulant medications that delay the formation of blood clots are administered to prevent thrombosis and embolism in many medical disorders. For patients with these conditions, the time that their blood takes to clot needs to be monitored regularly so that the drug dosage can be optimised.

The Prothrombin Time/International Normalised Ratio (INR) test works by introducing a biochemical substance called thromboplastin to a blood sample that starts the same series of clotting reactions that occur when a blood vessel is ruptured in the body. The clot changes the blood from a free-flowing solution to a gel-like substance with a markedly different viscosity – and the time it takes this change in viscosity to occur is then measured.

The disposable strip features a cantilever comprising a pair of polyamide strips, each with a different co-efficient of expansion

Traditionally, however, such tests have either been conducted in a lab using automated optical analysis techniques, or by manually monitoring chemical reaction rates. Now, engineers at North Wales-based Microvisk have developed an automated system that will rapidly test the clotting time of blood either while at home or at a doctor’s surgery.

’What makes our system truly unique is that we look at the actual blood-clotting process itself by measuring the change in the viscosity from one blood state to another,’ said John Curtis, Microvisk’s chief executive.

At first glance, the Microvisk system appears relatively simple – it comprises a small disposable strip onto which blood is placed and a handheld reader into which it is inserted for analysis.

The strip itself, however, is an active component crucial to the operation of the system. It contains a small amount of thromboplastin to initiate the clotting reaction and a micro-machined cantilever that is responsible for sensing the change in the viscosity of the blood over time. The cantilever itself, which is held rigid at one end and flexes at the other, comprises a pair of polyamide strips that each have a markedly different co-efficient of expansion. Sandwiched between these two polyamide layers are a heater and a piezo-resistive element.

The Microvisk system consists of a small disposable strip and a reader

When a sample of blood is placed on the strip, the small amount of dried thromboplastin contained on it is made soluble and the blood starts to coagulate. Once placed inside the reader, the heating element on the strip is thermally cycled, which causes the cantilever to oscillate due to the markedly different co-efficients of expansion of each of the polyamide strips.

As the blood becomes more viscous, it presents more of a resistive effect to the oscillating cantilever, causing a corresponding change to the output from the piezo-resistive layer between the polyamide strips.

By measuring the changes in resistance in the piezo-resistive layer due to the increase in blood viscosity, the handheld reader can calculate the time it takes the blood to change from a solution to a gel – which the unit then converts and displays.

’Because the system can test a small volume of whole blood, it can make the Prothrombin Time test less intrusive, removing the need for a laboratory to perform a similar analysis,’ said Curtis.

The company has undertaken trials that have confirmed that the $1,200 (£770) system is as accurate and produces results that are as reproduceable as a traditional system that costs between £35,000-£65,000.

Microvisk now plans to commercialise the technology by developing two different systems: one will be targeted at point-of-care use and one for home use.

But the applications for the technology go far beyond the medical field. Curtis said that the sensor could also one day become an invaluable tool in industrial environments.