Bio-MEMS - MEMS for Biomedical Applications

Continuous monitoring of physiological parameters of patients is important medical requirement in many cases especially when patients are in critical state. One of the important physiological parameters is blood pressure. In our country 1 out of every 8 persons above 30 year of age suffer from high blood pressure. In extreme cases continuous monitoring of blood pressure is required. Similarly continuous intraocular pressure (IOP) measurement is required in Glaucoma which is one of major reason for blindness. The conventional methods used by the medical practitioners for measurement of blood pressure referred to as extracorporeal methods like blood pressure cuff kit, tonometer (for IOP measurement) are not very suitable for continuous monitoring. These systems are not portable (sometimes big in size), are expensive, require expertise to operate, and are not very comfortable for patients for continuous measurement (imagine a BP cuff kit tied to patient all the time). There is a need for very small size, light weight, implantable systems for continuous measurement, and that is how MEMS come into pictures. MEMS are used for a large number of commercial applications today and one of them is biomedical. MEMS used in biomedical applications are referred to as Bio-MEMS. Fig. 1 shows Bio-MEMS sensor for IOP measurement.

Fig. 1 Bio-MEMS for IOP measurement (Source: Ref. 3)

MEMS is an acronym for Micro Electro Mechanical Systems. MEMS have micro electronic circuitry built with mechanical system and its size vary from few hundred nanometres to upto millimetres. They are extremely lightweight, small, fast, low cost devices and therefore are used in a large number of portable applications including biomedical. It is estimated that Bio-MEMS market is over $5 Billion today. The very first Bio-MEMS sensors that were developed and put to use were actually the pressure sensors for different measurements like disposable blood pressure, intracranial pressure (ICP), intraocular pressure (IOP), intrauterine pressure etc. The most common types of pressure sensors used are capacitive sensors. A range of sensing elements could be used that deform with applied pressure and transduction mechanism is used for measuring resulting strain or deflection. Capacitive sensors have many important benefits like high sensitivity, low power consumption, electrical stability, usable in different gases or liquid media, better temperature performance, less sensitive to drift and robust structure etc.

Other than pressure sensors there are many other types of Bio-MEMS sensors available for different applications like MEMS Inertial Sensors for defibrillators and pacemakers, MEMS based hearing aid transducers, MEMS based needles for drug delivery, MEMS based surgical tools etc. Some of the manufacturers of MEMS sensors for biomedical applications are CardioMEMS, NXP semiconductors, GE, Omron, Sensimed AG and Silicon Microstructures.

Mr. Amit Monga - Asst. Professor (ECE), Chitkara University, H.P.

References

1. A. Monga and R. Vig "An Ultra Miniature MEMS Capacitor for Arterial Pressure Measurement", Journal of The Institution of Engineers (India): Series B, vol. 93, Issue 4, pp 271-275, December 2012 ISSN: 2250- 2106
2. R. Puers, "Capacitive sensors: how and when to use them", Invited paper, Sensors & Actuators A, Vol.37-38, pp.93-105, 1993.
3. https://electroiq.com/2013/10/mems-devices-for-biomedical-applications/