Medical Device Principles: Batteries and Power

While medical device technology continues to grow more and more advanced, one component that seems to be lagging behind is battery technology. As you know, batteries are what makes all of our electronic devices portable. One of the specs I look at when researching a notebook computer, cell phone, or mp3 player is the battery life. With current technology, you can increase the battery life easily, but at the expense of size, as more power requires a larger battery. Recently, Apple switched their MacBook notebook line to an internal, non-replaceable battery so that a larger battery can be placed inside the notebook.

With medical devices, especially implants, battery and power is extremely crucial. A company can develop the world's most advanced implant that can prevent many problems, but if the battery needs to be replaced often, then much of the advantage is lost. This is even more important to senior citizens, whose risk of complications under general anesthesia increase with age.

The power system utilized can vary from device to device, however, how can medical devices as a whole be made to deliver results without needing their batteries replaced frequently? Here are a few technologies, current, future, and even fictional, that may be the answer:

• Conventional: a battery is attached to the device itself. It is very low-maintenance, however, as mentioned above, minor surgery must be performed to replace the battery. This system is most suitable for implants with low power applications.
• RF: this system uses an implanted receiver with control circuitry powered by an external source. Power is sent from an external source (e.g. belt-worn battery pack) wirelessly to the receiver using RF energy. This system eliminates the need to replace an internal battery, however, the external power source must be worn in close proximity to the receiver in order to receive power.
• RF + rechargeable: the newest type of system utilizes the battery feature of a conventional system with the wireless telemetry of an RF system to recharge the battery. The external power source is worn for a few hours every few weeks to recharge the battery. The battery must eventually be replaced, however, rechargeable systems last longer than conventional systems.
• Biomechanical: also known as "power-walking", there have been a few research projects that utilize the movement of our limbs while walking to generate electricity. It's only enough electricity to power small handheld devices like a cell phone or GPS, but it might be enough to power a medical implant. One company called Lightning Packs develops electricity-generating backpacks that use the body's vertical movement, similar to how a pedometer works. The latest is a study from the University of Michigan, Simon Fraser University in Canada, and the University of Pittsburgh that uses an electricity-generating knee brace.
• Nuclear: in the late Michael Crichton novel, The Terminal Man, the main character, a man suffering from violent epilepsy, has electrodes implanted in his brain to control the seizures. The electrodes are powered by a plutonium pack in his shoulder, which theoretically, would last his entire lifetime and would be removed after his death. This system would eliminate the need for any maintenance, however, as the world is still a little hesitant to embrace nuclear energy to power our cities, plutonium to power our implants will probably be left to the pages of fiction for a while. (In case you were wondering, the main character's computer "takes over" his personality and he goes crazy in the end. Read it. The book is amazing and Michael Crichton was a genius!)

Music Drives Lab-on-Chip

In college, I wrote a research paper about the development of Lab-on-chip technologies. Lab-on-chip is exactly what it sounds like. It combines all the functions of a medical laboratory and conducts tests on samples of blood, urine, or any biological fluid, on a device the size of a credit card.

Not to get too technical, but basically the volume of fluid collected is small enough that it takes on special properties that allow it to be moved, heated, and manipulated faster, cheaper, and more accurately. (E-mail me if you'd like to read my paper).

Typically, small amounts of electricity or air are required to move the samples around the lab-on-chip device. The electrical connections and air hoses can take up significant space and eliminate the advantages of a small device (see the above image of a lab-on-chip). However, a study from the University of Michigan showed that "music" can move these samples. It's actually tones at specific frequencies and amplitudes that drive the samples. The channels in the device are of varying lengths and widths, therefore, different frequencies can move samples in different channels because of the varying air pressures the sound waves produce.

Lab-on-chip devices are amazing. The goal is that these devices will be used for many different tests in the physician's office or even at home. Such devices would even be great in poor, undeveloped countries where resources and trained personnel are limited. If this sound-based engine or a similar technology really works, lab-on-chip devices will truly be portable!

Learn More: In New U-M Lab-On-A-Chip Device, Music Is The Engine [via Medical News Today]

FOCUS on...Visual Prostheses (Part 2)

In Part 1, we looked into how vision is achieved and how damage to the retina by two common diseases impairs one's vision. While there aren't any cures for such diseases, implants are being developed to help those with age-related macular degeneration (AMD) and retinitis pigmentosa (RP) live easier lives.

One of the most well-known and well-developed projects comes from the Department of Ophthalmology and the Department of Biomedical Engineering at my alma mater, the University of Southern California. Led by Dr. Mark Humayun and Dr. James Weiland, with teams from USC, Caltech, UC Santa Cruz, and the National Science Foundation, with Second Sight Medical Products, Inc., the 10-year old project consists of a glasses-mounted camera, an implanted wireless receiver, and a small electrode array attached to the back of the retina. The camera captures an image and converts it into an electric signal, which is sent to the receiver implanted inside the eye. The receiver sends the signal to the electrode array, which emits electrical pulses perceived by the user as small points of light.

Current research includes developing an intraocular camera which would be placed into the space that the (now-useless) lens occupies. Users of the current glasses-mounted camera must move their heads to scan an object. An intraocular camera will allow users to move their eyes to scan an object in a more natural manner. Another ongoing project is increasing the number of electrodes on the array. The first model (Argus I) had 16 electrodes, allowing the user to basically see only a 4x4 field of pixels. The latest model has 60 electrodes, allowing the user to see much greater detail.

Other notable approaches include the Implantable Miniature Telescope (IMT), developed by Dr. Isaac Lipshitz with VisionCare. The IMT takes one's central field of vision and enlarges it up to 3x. In this way, the image is not focused on the damaged part of the retina but is projected over other healthy parts of the retina, which reduces the blind spot that those with AMD suffer from.

Another unique approach is the Artifical Silicon Retina, developed by Drs. Alan and Vincent Chow. The ASR is implanted in the sub-retinal space in the eye and the unique composition of the device converts light into electrical current without the need of any external devices, basically mimicking the function of photoreceptors. However, it is shown that the device is not theoretically practical for neural stimulation. Moreover, Optobionics, the company that developed the ASR, ceased operations in May 2007.

Visual prostheses are exciting devices with numerous engineering challenges to overcome. The physiology of the eye only allows for an implant no larger than 5mm. The curvature of the eye presents challenges in developing electrode arrays with equal retinal stimulation. And as with almost any implant, there are issues of power and telemetry requirements. However, there is so much devoted to researching visual prostheses that we will undoubtedly have some amazing "bionic eyes" in the near future.

Learn More:

Wikipedia entry on visual prostheses

U.S. Department of Energy webpage on the Artificial Retina Project (USC project)

FOCUS on...Visual Prostheses (Part 1)

"FOCUS on..." will be a periodic DeviceLine feature in which a specific part of the body or disease will be highlighted. Basic anatomy and physiology or pathology will be covered, followed by current research and companies that are developing devices."

We've come a long ways in helping visually-impaired people to see. Maybe not as far as Star Trek's Geordi LaForge, who even in early part of his career had far superior vision than most of his crewmates even with his VISOR, but technological advancements have given blind people opportunities for greater independence. In the near future, Braille could very well become less common as prostheses are being developed to allow people to see the real world around them.

Overview of Vision: Vision is accomplished by a coordination of motor and sensory systems in the eye. Ocular muscles move your eye to the desired target. Light reflected off this target enters the eye. The amount of light that enters is adjusted by the pupil, which changes in shape to allow more or less light to enter. The cornea refracts the light, while the lens also refracts the light and focuses the light more precisely through the eye. The image is then projected in an inverted fashion onto the retina, which contain specialized cells called photoreceptors. These photoreceptors are responsible for changing light into electrical signals that are sent to the brain.

Diseases of the Eye: Patients who use visual prostheses are usually diagnosed with age-related macular degeneration (AMD) or retinitis pigmentosa (RP). Both are related to damage to the retina.

AMD is the leading cause of blindness in western countries and is typically caused by abnormal deposits called drusen between the retina and the blood vessels in the back of the eye. The result is a slow, increasing loss of one's center of vision. Those with AMD never go totally blind, however, their perception is greatly impaired, as shown in the photo on the right. There is currently no cure, and laser treatment is the only current option available.

RP is a genetic eye condition that is the leading cause of inherited blindness. RP results in slow degradation of the photoreceptors in the retina, and can lead to total blindness. Those who suffer from RP typically begin to lose their peripheral vision, giving them tunnel vision that gets smaller and smaller over time (shown on left). There's currently no cure for RP.

While both AMD and RP currently don't have any cures, there are treatments being developed in the form of implantable prosthetic devices.

Tomorrow in Part 2, we'll look into some of the devices being developed for treatment of AMD and RP and the companies behind them, as well as engineering challenges for future devices.

Company Spotlight: Intuitive Surgical

Today we highlight a Sunnyvale, CA-based company called Intuitive Surgical. Founded in 1995, Intuitive Surgical's flagship product is the da Vinci surgical system.

The da Vinci system uses robotics and the latest 3-D visualization technology to simplify many minimally-invasive surgical procedures. The system consists of a surgeon's console, a patient-side cart, a vision system, and a number of proprietary surgical instruments controlled by the surgeon on the console.

So far, the da Vinci system has been successfully used in urologic, laproscopic, gynecologic, and throracoscopic surgical procedures.

This product definitely extends the boundaries of traditional surgery. Large movements by the surgeon are translated to much smaller movements at the site of surgery, which allows for more precise techniques and is also more forgiving at unexpected movements by the surgeon's hands. While Intuitive's focus is not pure "robotic surgery", robot-assisted surgical units such as the da Vinci system certainly makes the surgeon's job a little less stressful.

Learn more: http://www.intuitivesurgical.com/index.aspx

Implantable Device for Cancer Monitoring

Dr. Michael Cima, Ph.D., a professor of Material Science and Engineering at the Massachusetts Institute of Technology (MIT) has developed an implantable device which can continually monitor the progress of cancer in the body.

Currently, the process of monitoring the growth and treatment of a tumor involves a biopsy. Biopsies are accurate, however, they can only give the condition of a tumor at a certain point in time and must be repeated multiple times to track the progress.

Dr. Cima's device utilizes nanoparticles that will clump a certain way, depending on the target molecules that enter through a polycarbonate membrane. The clumping can be detected using MRI, a much less invasive test.

The current in vivo version of the device tests for cancerous biomarkers (specifically the levels of the human hormone chorionic gonadotropin, however, the device can be modified to test for pH changes, oxygen levels, and the effectiveness of chemotherapy agents.

Learn more: http://www.physorg.com/news167335574.html [via PhysOrg.com]

The Medical Device Industry

I thought it would be appropriate for DeviceLine's first entry to discuss briefly about the medical device industry in general.

My direct experience in the industry is very limited, but from what I've learned, the area of research in which medical devices typically are born out of (usually the discipline of biomedical engineering), came primarily from an application of electrical engineering to the field of medicine. Most programs are not much older than 40 years old. With that said, as the field of electrical engineering has changed much since the 1970's, especially with the development of the integrated circuit and digital electronics.

Medical devices have also undergone a dramatic change too, becoming increasingly smaller and smaller. However, with the developments in genetic engineering, will medical devices completely disappear?

I think medical devices won't be going anywhere for a while and that the industry will continue to grow and demand will continue to increase.

First off, genetic engineering can never replace medical tools. Surgical tools, imaging modalities, and diagnostic devices are such tools that will always utilize electronics. I think as the baby boomer generation grows, there will be a greater demand for these tools in the office and in the home.

Also, genetic engineering is still too new of a technology. I'm really excited about the developments in tissue engineering, however, there are still too many hurdles that genetic engineering has to overcome. Many are concerned about the ethical issues related to stem cell research. Many of the products so far have proven more costly and not superior than their medical device counterparts, something consumers are hesitant to invest in this economy. Finally, as very new technology that involves living tissue, genetic and tissue engineering may have some unique FDA regulations to clear.

Do I want genetic and tissue engineering to one day replace implantable medical devices? Yes! And I think they will someday. Until then, medical devices will play the role of enhancing the lives of its users. For now, we'll have to live with creating "six million dollar men" before we create "frankensteins".

Welcome to DeviceLine!

Welcome to DeviceLine! There are a lot of amazing medical devices out there, and I hope to highlight some of the current products, as well as up and coming products. We'll also be discussing biotech/pharmaceutical products a bit, however, our main focus will be medical devices.

This blog is a work in progress, so please excuse the bugs as I tweak the layout over the next few weeks. Thanks and enjoy!