Design of Health Technologies Medical Sensors

1. Design of Health TechnologiesMedical Sensors EEG Electroencephalogram Biosensors: • EEG Electroencephalogram • Hernia Repair (Herniorrhaphy) • Diabetes / Implantable insulin pumps • Implantable Cardioverter defibrillator (ICD) • Glucose monitoring • Other systems

2. Advanced Sensing Systems Biosensors: • EEG Electroencephalogram • Hernia Repair (Herniorrhaphy) • Diabetes / Implantable insulin pumps • Implantable Cardioverter defibrillator (ICD) • Glucose monitoring • Other systems

3. EEG Electroencephalogram (Monitoring Brain waves) • Brain cells communicate by producing tiny electrical impulses. In an EEG, electrodes are placed on the scalp over multiple areas of the brain to detect and record patterns of electrical activity and check for abnormalities. • You apply between 16 and 25 metal discs (electrodes) in different positions on your scalp which are held in place with a paste. The electrodes are connected by wires to an amplifier and a recorder. • EEG is used to help diagnose the presence and type of seizures, to look for causes of confusion, and to evaluate head injuries, tumors, infections, degenerative diseases, and metabolic disturbances that affect the brain. • It is also used to evaluate sleep disorders and to investigate periods of unconsciousness. The EEG may be done to confirm brain death in a comatose patient.

4. Hernia Repair (Herniorrhaphy) • A hernia occurs when part of an organ (usually the intestines)protrudes through a weak point or tear in the thin muscular wall that holds the abdominal organs in place. • Hernia repair is performed as an outpatient procedure using local or general anesthesia. First, through an incision, the segment of bowel is placed back into the abdominal cavity. Next, the muscle and fascia are stitched closed to repair the hernia. A piece of plastic mesh is often used to reinforce the defect in the abdominal wall. • A hernia occurs where any part of the body abnormally protrudes into any other area. Hernia operation Animation

5. Diabetes / Implantable insulin pumps • Implantable insulin pumps are emerginginsulin-delivery devices that can be surgically implanted under the skin of individuals with diabetes. The pump delivers a continuous basal dose of insulin through a catheter and into the patient’s abdominal cavity. • Implantable insulin pumps are devices that can be surgically implanted in individuals with diabetes as an insulin-delivery device. They are usually placed on the left side of the abdomen. • The disk-shaped pumps are about the diameter of a hockey puck but much thinner. They weight about 5 to 8 ounces when filled. The reservoir holds up to several months’ worth of insulin and is refilled via a syringe injection through abdominal tissue. Depending on the dosage of insulin, the battery in an implanted pump lasts about eight to 13 years, according to one manufacturer. Diabetes Type I and II

6. Implantable Cardioverter defibrillator (ICD) Summary • An implantable cardioverter defibrillator (ICD) is a device that is implanted in the chest to constantly monitor and correct abnormal heart rhythms (arrhythmias). The devices were developed originally to correct heart rhythms that are too fast, but recent technological advances have increased the pool of possible patients who may benefit from an ICD.  • ICDs are mainly used to treat two forms of abnormal heart rhythms, both of which occur in the ventricles, or lower pumping chambers of the heart. If the ventricles begin to beat too quickly (ventricular tachycardia), the device may emit low-energy electrical pulses that allow the heart to regain its normal rhythm. If the tachycardia progresses to a very rapid, life-threatening rhythm that causes the ventricles to quiver rather than beat (ventricular fibrillation), the device may deliver a relatively stronger jolt to reset the heart rate (defibrillation). Heart Conduction Animation

7. Implantable Cardioverter defibrillator (ICD) cont • Left Ventricular Assist Device Animation • Heart Bypass Surgery • Angiogram • Stress Test • Hypertension

8. Vitamins and Minerals • Vitamins and minerals are naturally occurring nutrients found in foods that are needed by the body for normal functioning and overall health. These essential nutrients must be obtained from the diet because the body cannot manufacture them. They are often referred to as micronutrients because they are needed in small amounts by the body. A lack of any of the essential micronutrients from the diet may lead to deficiencies, compromising the ability to function and impairing health. There is also a risk of toxicity with certain micronutrients when too much are consumed daily. • Several vitamins and minerals, as well as some phytochemicals, are classified as antioxidants. Recently, antioxidants have received a lot of attention for their possible role in disease prevention due to their ability to reduce cellular damage caused by free radicals. However, further research is needed. In addition, some researchers claim that certain vitamins and minerals are helpful in the prevention and/or treatment of various heart–related conditions. There is also a substance called coenzyme Q–10 that acts like an antioxidant vitamin. Scientists and researchers know the roles the following vitamins and minerals play in our bodies, and this group may have heart–healthy effects: • Vitamin and Mineral Animation

9. Magneto-elastic sensors (Grimes) The magneto-elastic material resonates at a characteristic frequency when excited by a magnetic field.

10. Magneto-elastic sensors The magneto-elastic ribbon is made of a commercial sheet called Metglas. The polymer is a custom co-polymer made by the Grimes group. It is believed to work because glucose bonds to sites on polymer chains that separate them from other chains. This allows the polymer to absorb water.

11. Magneto-elastic sensors Its frequency response (in air) shows a sharp peak which is determined by the density of the polymer layer

12. Magneto-elastic sensors Resonant frequency in a liquid is lower, and the peak is not as sharp.

13. Magneto-elastic sensors Frequency response in water varies with the glucose concentration, in an almost perfectly linear curve.

14. Sensor measurement The electronics are simple. A sharp spike is applied to a driving coil, and a response is measured in a sense coil.

15. Sensor measurement The magnetic spike is short, about 3 gauss for 16 micro-seconds (earth’s magnetic field is about 0.5 gauss, and a refrigerator magnet about 10 gauss). The pickup coil measures sensor activity for a further 8 milli-seconds. The response is transformed with an FFT to determine the frequency peak. This should be easy to do with a small, battery-powered device. Because the sensor’s response is quite slow (tens of minutes to respond), it is enough to take readings every few minutes.

16. Biosensor status There are many promising systems on the horizon, but the only commercially-deployed biosensors are glucose monitors (~$4B). 3 main types: Single Use: Disposable sensing material, often “static” measurement. Cheap and portable, but low sensitivity and accuracy. Intermittent Use: Often use hydrodynamics – generally much better performance from sensing a moving fluid. Its still a challenge to move these out of the lab and onto a chip.

17. Biosensor status Continuous (In Vivo) Sensors: Very economical, but very hard to calibrate and may suffer from unknown amount of drift.

18. Biosensor design We give a brief introduction to micro-fluidic sensor design. While these were originally fabricated in silicon using MEMS techniques, the trend is toward glass and plastic as the substrate. Both glass and many plastics allow optical measurements, but silicon is opaque to visible light. Glass and plastic are also more resistant to contamination from the chemicals used in the measurement.

19. Biosensor design Surface immobilization: The first step is sensing is creating a selective surface to react to the sensed agent

20. Biosensor design Bead immobilization: A variation that uses beads to increase relative surface area.

21. Biosensor design Detection: Several methods, including resonant frequency of MEMS cantilevers. But amperometry (current measurement) is the most widely used approach. Typical mechanisms for current flow include redox cycles between the target group and variants.

22. Biosensor design Optical Detection: A 2D array of agent/antigen reactions produces fluorescent traces:

23. Biosensor design Magnetic Detection: The antibodies are immobilized on a surface and magnetic beads bind to sites where the analyte is attached.

24. Enzyme-Linked Immunosorbent Assay

25. Reuse Most immunosensors use bound antibodies and immobilization. Removing the bound species can be difficult without destroying the sensors. Methods and results vary, but a recent detector for Chagas disease used glycine-HCl to wash the sensor, and reported efficacy for more than 30 cycles.

26. Biosensor design Systems-on-a-chip: are promising but coming slowly. Biosensing still seems a long way from commercial viability. But there are some promising prototypes:

27. Discussion Questions • It may be a while before we have highly integrated sensors for many pathogens (and economics dictates that they will come for first-world diseases first). Can you think of telemedicine/information tools to help facilitate traditional (but simple) lab methods? • Sensors for medical diagnosis may always be a difficult economic proposition. Can you think of other models that might work? E.g. home testing?