Cutting edge electronics are affording tremendous strides in the effectiveness of today’s advanced medical devices. The ability to reduce the size of these sophisticated components is a significant factor behind this success. This article highlights medical device technologies that are enhancing the quality of healthcare due in no small part to advances in electronics miniaturization.
By Mike Rice
John Hopps invented the world’s first cardiac pacemaker in 1950. It was about the size of a television set and quite cumbersome to use. Later that decade, Wilson Greatbatch filed his own patent describing a much smaller implantable version of this life-saving device. In so doing, he not only opened the door to better overall cardiac rhythm management, but also spawned a market for implantable cardiac devices that is estimated to be almost $10 billion in 2006.1
Today, facing clinical demand for much faster progress, medical device designers are drawing on innovations in numerous fields to improve the diagnostic, monitoring, and therapeutic capabilities of next generation devices. These innovations can improve treatment and care for millions of patients worldwide, and manage, alleviate, and cure an increasing range of ailments and conditions. This article showcases the many components of medical design that continue to impact the innovation and miniaturization in this field, from the increasing popularity of MEMS technology to how battery design is changing long-term patient care.
MEMS Sensors Improve Pacemaker Performance
Micro electro-mechanical systems (MEMS) technology is an important enabler of today’s rapid expansion in the number and types of implantable devices available. Just one example are the next generation implantable devices that extend the monitoring of events and responses within the human body far beyond the simple detection of bradycardia, or excessively slow heart-rate. Today’s pacemakers use MEMS sensors to detect patient exercise levels and adjust the pacing rate to meet the increased demand for cardiac output.System-on-Chip IP
To realize the full potential of implantable device innovation, advances in additional supporting technologies are also required. Suitable signal conditioning electronics are required, as well as optimal implementation techniques either on the same chip or separately from the MEMS sensor. However, medical device innovators often do not have this kind of expertise in-house. Partnerships with chip design and fabrication providers willing to devote resources to this specialized and rapidly growing technology sector can deliver access to valuable IP such as proven interfaces to established MEMS technologies.Other IP for new implantable devices include turnkey IP for transient surge suppression, meeting a worldwide implantable medical device standard. This standard mandates that device designers include circuitry to protect the sensitive front-end electronics of implantable devices from current delivered from an external defibrillator.
Further benefits delivered by a specialist semiconductor provider may include expertise in flexible circuit design, space-saving die packaging, and miniaturized assembly techniques.
RF Communications
The availability of highly miniaturized, low-power RF devices and specialized communication protocols is also changing the way patients and their caregivers manage chronic conditions such as diabetes and heart failure. Data retrieval from older implantable devices has typically been achieved using inductive communication between the implant and an external controller. This usually required periodic visits to the physician office. |
| A typical RF transceiver block diagram |
Modern wireless communication now allows the patient to upload data and download new programs over a landline or cellular connection. To support this innovation, the FCC has allocated the Medical Implant Communications Service band of frequencies (402-405 MHz) for implanted medical devices to communicate with external devices. This band has very good characteristics for use within and around the human body, enabling the best possible signal range and data integrity at anticipated bit rates.
Power Consumption and Battery Technology
The fundamental objective for an implantable device is to maximize the patient’s healthy and active lifetime. Consistent with this objective is the need for low overall power consumption and hence long battery life. Developments in electronic design and fabrication, as well as enhancements to implantable battery technologies are both vitally important in this context.Ultra low power IC design involves many specialized techniques that require extensive experience to perfect. Careful management of duty cycles at the system level, including assiduously turning off parts of the circuit when not in use, can contribute significantly to reducing the overall power budget. Chip designers may also individually optimize circuits to achieve the most power-efficient system architecture. Specialty chip producers also leverage extensive familiarity with fabrication processes to optimize parameters such as leakage current from CMOS transistors in the steady state, as well as transistor switching losses.
Among the most interesting power saving innovations to emerge recently, is a quick-start oscillator for RF communication applications. This unique IP allows data transmission to begin extremely quickly, thereby eliminating the usual protracted startup sequence that wastes valuable power. The design and manufacture of the quick-start IP has enabled AMI Semiconductor (AMIS) to partner with a developer of a wireless implantable sensor for blood glucose monitoring. The total average current drain from the battery is less than 3 µA. The AMIS SoC includes a 32 kHz oscillator, current and voltage references, high-precision analog-to-digital converter (ADC), digital filtering and sensor bias running at 100% duty cycle, and a low-duty RF section.
Battery technologists, for their part, are seeking new bio-compatible solutions that will deliver greater energy density for longer battery life. The concept of rechargeable batteries for implantable applications is also now delivering workable solutions. One example includes a lithium-ion rechargeable battery manufactured by Quallion. Specifically developed for use in implantable electronics, this is currently being used by Advanced Bionics Inc. to power a new implantable neurostimulator called the Bion. This device also incorporates sophisticated microelectronics, a stimulator, and bidirectional communications within a cylindrical package only 3.2 mm in diameter. Insertion is highly non-invasive compared to a traditional implantable pulse generator (IPG). This combination of cutting-edge technologies that enable the Bion will allow a wide range of so far untreated and under-treated conditions to be monitored, controlled, alleviated, and possibly cured using neurostimulation.
A much longer-lasting source of power could be the human body itself. Development of biothermal power sources, for example, is focusing on the use of thermoelectric materials, using nanoscale-based, thin-film technologies to convert the human body’s natural thermal energy into electrical power. Whereas current Lithium-based battery technologies have a lifetime of five-to-seven years, Biophan Technologies Inc. suggests a biothermal power source could last up to 30 years.
Revitalizing the Grandfather of Implantables
It is fitting that the technologies now underpinning the latest implantable devices are also enabling significant enhancements in the devices that jump-started the implantable revolution back in the 1950s—heart pacemakers. A traditional pacemaker or implantable cardioverter defibrillator (ICD) is implanted near the collarbone, with transvenous leads that are inserted into the heart. By contrast, Interventional Rhythm Management, Inc. recently received a series of patents for an implantable intravascular defibrillator. The IRM device, built in a form factor similar to that of a drinking straw, will be unobtrusively anchored in a large vessel in the abdomen. The implantation procedure is minimally invasive and similar to that required to perform angioplasty or to insert a stent.This is a significant step forward for pacemakers and ICDs, made possible by the gamut of electronic technologies now available to developers of medical devices. These include state-of-the-art semiconductor integration techniques, advances in low power design, chip scale semiconductor assembly including stacked-die technology, cutting edge RF and antenna technology, and high-energy-density bio-compatible battery technologies.
ONLINE
For additional information on the technologies and products discussed in this article, see the following websites:
www.amis.com/applications/medical
www.quallion.com
www.advancedbionics.com
References
1 Harris Nesbitt 2005 MedTech OutlookMike Rice is the medical marketing and business development manager at AMI Semiconductor, 2300 Buckskin Rd., Pocatello, ID 83201. He is responsible for overseeing the corporate strategy for business development in targeted medical semiconductor markets. Rice brings more than 20 years of medical and technology industry experience to AMIS. He can be reached at 425-605-2652 or mike_rice@amis.com.
