Electronic medical implant technology is getting better and safer, promising a larger market for commercialization soon and giving patients greater hope for improved treatment. Prodded by consumer and regulatory concerns about effectiveness and safety, the industry and academia are forging ahead with new products. Some are in the pipeline for approval by the U.S. Food and Drug Administration (FDA), and others are in FDA-approved clinical trials.
Many medical implants use microelectromechanical-systems (MEMS) technology, which is finding its way into a vast number of new applications thanks to advances in smart phone, wireless, Internet, and energy harvesting technologies (see “Consumer-Focused MEMS Embarks On The Internet Of Things”). The global microelectronic medical implant market, including accessories and supplies, was estimated at $16.3 billion last year and is projected to grow to $24.8 billion by 2016 according to BCC Research. The fastest growing segment is neuro-stimulators with a projected compound annual growth rate (CAGR) of 10.5%.
Neural stimulators are used in a variety of implant applications, such as pain management, cochlear stimulation, drug delivery, and brain studies of neurological diseases. Many of these implants are being honed to be more biocompatible with the human body so they can last longer and produce fewer side effects. They’re also smaller so they can be minimally invasive to bodily functions and more practical. And, they’re being designed to dissipate less power so they can operate on less energy or in some cases harvested energy.
These issues are extremely important to designers and users of medical implants, particularly in orthopedic, spinal pain management, cardiovascular, retinal, cochlear, and drug-delivery applications. A relatively small number of implant failures has led to FDA recalls due to patient injuries and subsequent litigation (see “How Safe Are Medical Implants?”).
Eyeing MEMS
One of the most challenging areas in which microelectronic technology is being brought to bear for a better understanding of how implants interact with the body is in human vision. Razi Haque, a researcher at the University of Michigan’s Wireless Integrated MicroSensing and Systems (WIMS2) Research Center and president of Structured Microsystems Inc., points out that “the biggest challenge for an ophthalmic device is size.”
Haque has demonstrated a technique that enables millimeter-scale microsystems with highly integrated components for intra-ocular pressure-sensing applications. He is working on a microsystem measuring 1.5 by 2 by 0.5 mm that includes the battery, ASIC, and antenna. This housing sits on top of and is interconnected with a MEMS pressure sensor.
Haque’s work has attracted interest from others working in this area, and he may commercialize it with the right partners. “I believe that although there are no FDA-approved intra-ocular pressure sensors at present, this will change in the next few years because of increasing interest in micro-devices and the potential to improve treatment and treatment options.”
Now in clinical trials, the Triggerfish intra-ocular MEMS pressure sensor from Switzerland’s Sensimed AG employs a wireless pressure sensor from STMicroelectronics as a retinal implant that enables better management of glaucoma patients via earlier diagnosis and treatment that is optimally tailored to the individual patient (Fig. 1).
1. The Triggerfish intra-ocular device from Sensimed uses a wireless pressure sensor from STMicroelectronics as a retinal implant that enables better management of glaucoma patients. The smart contact-lens sensor acts as a transducer, antenna, and mechanical support for additional readout electronics. (courtesy of STMicroelectronics)
The smart contact-lens sensor acts as a transducer, antenna, and mechanical support for additional readout electronics. The patient wears a receiver around the neck. Powered via RF waves, the lens does not need to be connected to a battery. The embedded components are positioned in the lens so they don’t interfere with the patient’s vision.
Retinal implants are a prime area of research and testing for helping those patients with sight maladies like retinitis pigmentosa and macular degeneration. This year, a major breakthrough occurred when a retinal implant made by Germany’s Retina AG was tested with totally blind patients who were able to obtain “rudimentary” eye vision.
Surgeons implanted the 3-mm2, 15,000-pixel microchip at Oxford University’s John Radcliff Hospital and Kings College Hospital in the United Kingdom (Fig. 2). The chip is controlled by a circuit behind the patient’s ear and connected via a cable. The patients were able to differentiate rough outlines of shapes such as straight lines and curves and distinguish light from darkness, although this capability was for a limited distance and range of viewing.
2. Retina AG has tested a retinal implant on totally blind patients who were able to obtain “rudimentary” vision. The 3-mm2, 15,000-pixel microchip is controlled by a circuit behind the patient’s ear and connected via a cable. The patients could differentiate rough outlines of shapes such as straight lines and curves and distinguish light from darkness, although this capability was for a limited distance and range of viewing. (courtesy of Retina AG)
The Stanford University School of Medicine is taking a different approach with a retinal prosthesis powered by solar energy. Researchers there have devised specially designed goggles equipped with a miniature camera and a pocket PC to process visual data streams.
Improving Hearing
Cochlear implants are another large area benefiting from advances in microelectronics. There are no FDA-approved fully implantable total cochlear implants in which the neural stimulus, amplifier, audio processor, speaker, and power source are placed within the human body. All commercially available deices use an electrode array implanted in the cochlea.
But there are companies that sell FDA-approved cochlear implants commercially where a fine-wire flexible implant is placed within the cochlea and the rest of the circuitry is placed behind the ear and elsewhere. Last year, Austria-based MED-EL introduced in the U.S. the Maestro cochlear implant system, which uses the world’s smallest titanium wire cochlear implant and extends battery life up to 50% (Fig. 3).
3. The Maestro cochlear implant system from MED-EL uses the FDA-approved Flex electrode arrays, which uses exclusive wave-shaped wires. The arrays feature paired electrode contacts that are tapered on the apical end to better match the shape of most cochlea. The system includes the cable array, a control panel, the speaker, and audio processor, which is worn behind the ear (a). The array wire is implanted within the cochlea (b). (courtesy of MED-EL)
This year, MED-EL announced FDA approval of its Flex24 and Flex28 (24 nm and 28 nm, respectively) electrode arrays, which use the company’s exclusive wave-shaped wires. The arrays feature paired electrode contacts for seven basal channels and single-electrode channels for five apical channels that are narrower and more flexible than straight wire designs. They’re also tapered on the apical end to better match the shape of most cochlea.
“The greater the cochlea coverage, the more natural is the sound,” explains Ingeborg Hochmair, MED-EL’s founder, CEO, and head of worldwide operations. “Manufacturing the very thin wires, which are a mixture of platinum and iridium, and the silicone is a major innovation for us.”
Australia-based Cochlear Americas Inc. and Advanced Bionics Corp. both use a flexible wire implant in the cochlea as well. Cochlear’s Nucleus 5 has what the company claims is the industry’s first and only sound processor that uses AutoPhone technology. It provides automatic phone detection for an easier phone connection that requires no buttons to push.
Advanced Bionics says its Neptune freestyle design audio processor for its cochlear implant lets its wearers choose how to wear it—in their hair, on their arm, under the collar, or in their pocket. The company says it’s waterproof and the industry’s first and only swimmable processor.
“A challenge for cochlear and neural implants is obtaining the necessary flexibility and being compatible with standard surgical techniques,” explains Angelique C. Johnson, a researcher with the University of Michigan’s WIMS2 Research Center. “It must also have long-term survivability.” Johnson has formed a new company, called MEMStim, to commercialize a self-curling monolithically backed high-density 128-site cochlear electrode array with two patents on this work.
The array features a stiffness-controlling ringed channel for stylet wire placement and a self-curling parylene substrate capable of pre-curving the array to within a 0.5-mm radius of curvature. A 32-site array with irridium-oxide sites on 250-µm centers is realized along with a four-channel stimulation ASIC capable of driving multi-polar site configurations with bi-phasic pulses of up to 500 µA/channel.
An advanced off-stylet (AOS) method allows a straightened wire to be inserted first into the cochlea. The array does not contact the outer cochlear wall, mitigating the effects of too much implant stiffness. A cochleostomy shows how the ring-backed array is first inserted and then turned around the first turn of the array (Fig. 4).
4.The University of Michigan developed the discrete-ringed pre-curved parylene arrays for a cochlear implant. A thin vapor is deposited as a masking layer of parylene (a), which is etched out to form a channel (b). Channel walls are then coated with parylene, and the overlap opening is sealed off (c). A layer of parylene completely seals the channel (d). Selective masking and etching follows (e). Then, the exposed regions of the tunnel are etched (f). The final step is the release of the entire array from the carrier wafer (g). A ring-backed array is inserted through cochleostomy (h) and around the first turn of the cochlea (i). (courtesy of the University of Michigan’s WIMS2 Research Center)
An exciting development that may bode well for hearing-implant patients comes from work at the University of Utah. Demonstrations there on cadavers have shown that a speaker can be embedded in the ear to benefit those suffering from hearing loss and deafness, along with other electronics like the processor and power source, which are embedded under the skin of the skull. The only thing to be worn externally is a charging circuit behind the ear to recharge the implant’s battery.
The work is being performed by Darrin J. Young, an associate professor of electrical and computer engineering at the University of Utah, and USTAR, the Utah Science Technology and Research initiative. Young conducted the study with Mark Zurcher and Wen Ko, his former electrical engineering colleagues at Case Western University in Cleveland, Ohio, and with ear-nose-throat physicians Maroun Semaan and Cliff Megarian of University Hospital’s Case Medical Center. The present prototype of the microphone is 2.5 by 6.2 mm and weighs 25 mg (less than one-thousandth of an ounce) and will be reduced in the future to 2 by 2 mm.
Sound moves through the ear canal to the eardrum, which vibrates. The eardrum is connected to the hammer, anvil, and stirrup bones. An attached accelerometer sensor detects those vibrations at the umbo part of the ear. These vibrations are then processed and sent to the electrodes in the cochlea (Fig. 5). Research has shown that the sound can be more efficiently transmitted if the anvil is removed.
5. In this proposed cochlear implant system from the University of Utah, everything is embedded within the human body except an external control and battery charging system that can be worn behind the ear. The speech processor and radio transmitter can be implanted under the skin of the skull. The embedded silicon microphone is surgically attached to the umbo. (courtesy of the University of Utah)
More Sophisticated Drug Delivery
MEMS technology is playing a significant role in the delivery and monitoring of medical drugs (see “System-Level Applications Make MEMS Ubiquitous”). More than a dozen commercially available handheld and battery-powered insulin meters and pens are on the market for consumer use. MEMS micro-needle technology also is making finger-pricking easier and faster.
The next step is an insulin pump that can be implanted on a patient’s arm as a skin patch. That’s where one notable drug-delivery mechanism, the Jewel insulin pump co-developed by Switzerland’s Debiotech and STMicroelectronics with its microfluidics MEMS technology, comes in. Introduced to the market about two years ago, it’s awaiting further FDA approval.
MEMS technology is playing a significant role in delivering and monitoring medical drugs. Proteus Biomedical’s Raisin system is designed for optimizing therapeutic benefits for those on frequent and timely medications. Conceived on the basis that patients don’t take 30% to 50% of their prescribed medications, and that the costs of hospitalization due to non-adherence total $100 billion a year, the Raisin system marries medicine and mobile computing technologies.
This integrated pharmaceutical system identifies the pill, its authenticity, and its dosage when it’s ingested. It then detects the pills and assigns time stamps. Also, it measures ECG signals, activity, and sleep and collects and presents data in real time. It then serves as a platform for data sharing, collaboration, and incentives.
The Raisin system consists of a handheld monitoring device, ingestible event markers (IEMs), and a receiver patch. The tiny marker chips, measuring less than 1 mm, have been tested as accurate at more than 99% in drug detection in multiple human clinical trials. The chips produce an ECG-like signal conducted only in the body (not RFID).
Thin-film MEMS layers on each IEM are activated and powered using stomach electrolytes. The system modulates/pulses the current flow to encode information stored in it. It then communicates this data through the body tissue, where a receiver worn on the patient’s skin detects an electric field.
Cardio and Drug Delivery Implants
Cardiac pacemakers like those made by Medtronic are best known for improving and prolonging the lives of patients with cardiac diseases. Such implants are getting smarter and more sophisticated, drawing less power than previous units. But they also require battery operation, which means surgical replacement of the battery after about six to 10 years.
Researchers at France’s CEA-Leti and five partners are combining their expertise to develop a self-powered pacemaker that’s eight times smaller than current models under the umbrella of the Heart-Beat Scavenger (HBS) Consortium. The partners include the Sorin Group, TIMA, Cedrat Technologies, Tronics, and EASII IC. They’re targeting a self-sufficient device that harvests mechanical energy from the movement of the heart, eliminating the need to replace batteries and post-implant surgical procedures.
The effort is focused on reducing the size of a cardiac pacemaker from the present 8 cm3 to just 1 cm3. This will allow the pacemaker to be attached directly to the epicardium, eliminating the need for intravenous introduction of cardiac probes.
How Safe Are Medical Implants?
Just how safe are medical implants? The answer depends on whom you’re asking. For the thousands of patients who have benefited from implants with a longer and better life, they’re fantastic. However, some patients have been injured or died as result of failure or infections.
The issue is further muddled by what many see as the Food and Drug Administration’s (FDA’s) lax attitude about approving medical device implants and acting long after failures are reported. Last year, the Institutes of Medicine, an independent advisory group, stated in a report that the FDA’s current regulatory framework for most devices is so flawed that it should be thrown out and replaced with a new system that provides a reasonable assurance of safety and effectiveness.
The FDA says that it “weighs the benefits and risks of every medical device” it reviews and that it “must balance risk with the careful evaluation of patient benefit. This promotes public health.”
Indeed, many on both sides of the debate agree that a zero-risk system would be impossible. If the FDA only approved devices that can’t cause any harm under any circumstances at all, very few devices would ever be approved. That would simply stifle medical progress and would not be beneficial to the public.
Fewer than 1% of all medical devices fail their patients in performance, a percentage that’s far fewer than the devices that don’t. “Americans should be very confident that the FDA and the medical device industry, working together, have an exemplary safety record,” says David Nexon, senior executive vice president at Advamed, a medical device trade group. He points out that “with 50,000 different implant models and devices on the market right now, about 20 of those on average find serious problems. That’s less than two-tenths of 1%.”
There’s no questioning that some implantable devices have failed and have caused agony and misery to their recipients and their families and friends, with headline-grabbing lawsuits following. That’s why researchers in the industry and academia are trying harder to perfect their inventions and the FDA is being pushed harder to scrutinize more closely industry requests for approvals.