MEMS or microelectromechanical systems use micro-sized components as sensors transducers and actuators. These are currently found in cars, gaming devices, smartphones, and environmental testers. Many of these same MEMS are used in the medical field, for example, the MEMS and neural sensors found in smartphones are also found in pacemakers. It has been used in the medical field is called bio MEMS. Bio-MEMS currently on the market include a therapeutic system for diabetics which not only monitors glucose levels with an internal sensor. But also, provides a precise amount of insulin when needed via a cannula and a micro-sized needle inserted below the skin. Another bio MEMS that has been on the market for quite a while is the cochlear implant. The cochlear implant uses an electrode array implanted inside the ear to stimulate the eardrum when it receives audio vibrations from an external transmitter. The possibilities for these in the future are endless tissue engineering is a huge field that is working toward the development of artificial organs and organ tissue to help alleviate some of the problems surrounding organ failure and organ donations. The development of drug delivery systems is another huge market. Several types of in vivo drug delivery systems are currently being tested but we're still working on perfecting components with high selectivity and specificity. Such components include micro-sized liposome vesicles to carry drugs throughout the bloodstream to a specific cancerous tissue where it attaches releases its drug and destroys the cancerous tissue.
So what exactly are bio MEMS? In general, bio MEMS are MEMS that are used in the medical field. For example, pacemakers and defibrillators use some of the same sensors that are found in cars smartphones, and cameras. These devices perform a medical or biological function therefore they are BioMEMS. Other types use biological components to perform a medical function or application. Applications for these devices exist in diagnostics and therapeutics detection and analysis drug delivery or cell culture. In addition, new emerging markets have made bio MEMS the largest and most diverse application of MEMS devices.
MEMS Cell Culture Array. This array creates a microenvironment for growing cells in vitro and in parallel, allowing for the analysis of multiple cell growth conditions. A diagram of how it works is on the left. The constructed array is shown with a SEM image on the right. [Developed by and courtesy of BioPOETS Lab, UC-Berkeley] 1
BioMEMS Sensor Placement
Bio-MEMS are currently found in laboratories in the field in doctor’s offices and surgical rooms. However, they are also found in and on the patient. Bio-MEMS sensor placement on a patient depends on the device and its application. A sensor can be topical meaning applied to the skin or placed in the mouth. It can be externally connected meaning in vitro or it can be in vitro with an internal or in vivo component. It can also be fully implanted making it totally in vivo. Let's talk about some examples. One familiar topical sensor is the thermometer used for measuring body temperature. Thick film disposable thermistors and infrared thermometers have largely replaced the mercury thermometer. It is very non-invasive and perfect for delicate situations because it goes virtually unnoticed by the patient.
Externally Connected BioMEMS
The diabetic therapeutic system that you saw earlier and this retinal prosthesis are examples of externally connected BioMEMS. The retinal prosthesis contains a micro-sized electrode array implanted on the retinal tissue in the back of the eye. The patient wears glasses that contain a video camera receiver and transmitter that process and send optical signals to the array. Stimulating the individual electrodes which in turn stimulate the cells below the retina. This stimulation travels up the optic nerve to the brain which interprets the signal and provides a rough visual. This BioMEMS has given some blind people a somewhat useful representation of what they are looking at.
Fully implantable devices or in vivo bio MEMS have numerous possibilities, but few of these devices have made it to market mainly due to biocompatibility issues. And plantable bio MEMS that have been on the market for years are defibrillators and pacemakers. Another in vivo devices currently on the market is that pill camera used for endoscopy and colonoscopies. This pill about the size of a large vitamin tablet contains its light source battery, camera, lens, and transmitter. The patient swallows the pill in the morning and goes about his daily routine. During the day the pill travels through the entire gastrointestinal tract recording color images at a rate of two frames per second. The images are transmitted from the pill to a receiver that the patient wears on his belt. At the end of the day, the patient returns the receiver to the clinic where the images are then downloaded and analyzed. The pill is expelled without the patient even being aware of it. Other emerging implantable devices include neural implants and probes spinal cord stimulators to treat intractable pain and pressure sensors for monitoring cardiovascular pressures eye pressures.
BioMEMS Lab-on-a-Chip (LOC)
The other category of bio MEMS uses biological molecules as a component. In biology, we learned that some biomolecules can detect and bind with other biomolecules, like an antibody detecting and binding to a specific virus. This characteristic of biomolecules has enabled the development of biosensors. An example of a biosensor is the home pregnancy test that employs certain antibodies with an attached reporter group a specific protein produced during pregnancy and that becomes present in the urine. Another example is the glucometer a diagnostic biosensor that monitors blood glucose levels of diabetics from a single drop of blood. The pregnancy test and the glucometer are types of microfluidic BioMEMS is referred to as a lab on a chip. LOC test for one or more biomolecules within a small sample of bodily fluid. In the development and testing phases are LOCs that can accurately test for many analytes or different biomolecules from one small sample. This image has shown microfluidic MEMS in this cell culture array. This array uses micro-sized chambers and channels to create optimal environments for cell cultivation. This array creates microenvironments for growing cells in parallel allowing for the analysis of multiple cell growth conditions. The environment and cell growth are controlled by several other micro components within this system. The Internet of Things or IoT connects devices such as bio MEMS monitoring systems to the Internet enabling the gathering and management of information from those devices. This information in turn offers the opportunity for more efficient and effective health benefits. Examples of IoT devices are this electrocardiogram biosensor and the pacemaker. The ECG patch contains electrodes and circuitry that monitor measure and collect data regarding the patient's heart and activity. This data is transmitted wirelessly to the patient's smartphone or computer. Today's pacemakers are designed to send collected data wirelessly to a transmitter-receiver device that sits next to the patient's bed and is hooked up to the phone line. Every night while the patient sleeps the data is collected. This collected data is sent periodically to the doctor’s computer without the patient's knowledge of any transmission.
BioMEMS are systems that use MEMS, or biomolecular components to sense, analyze, measure, or actuate. This is a brief overview of some of the thousands of BioMEMS being used in the medical field today and others in development and testing. The MEMS market for medical applications is currently approximately two point 1 billion dollars and is projected to grow at double-digit rates for the next decade. With the current market of 2.1 billion, we think it's safe to say that bio MEMS devices are already impacting every aspect of our lives. Ultimately these systems promise to significantly improve medical care on a global scale.
References1 Bionanotechnology: Lessons from Nature. Goodsell, D. S. Wiley-Liss, Inc., Hoboken, New Jersey (2004)