Publication date: 20 April 2010
The rapidly growing market for implantable medical devices is estimated at over £25 billion is on the verge of revolutionising healthcare treatment and disease prevention by becoming interactive in nature collecting data from the body and transmitting it directly to the physician’s phone or PC.
With medical devices becoming such a prominent part of our future health care system, the reliable transmission of current via an electrical connector is a vital component to guarantee the device’s reliability, often life critical. For this reason, Hypertronics Corp, the business unit of Hypertac Group in North America manufacturing ultra reliable medical connectors for 40 years, has developed ImplantTac® contacts for use in pacemakers, neurostimulators and defibrillators as well as for more recent applications in implantable devices such as orthopaedic, visual and sensory aids, implantable patient ID and active monitoring systems (see Figure 1). This article will discuss some of the foremost medical device advancements and outline the nature of how ImplanTac® was designed to meet the critical needs of interconnect systems in medical devices.
The booming market for implantable devices began with the development of the pacemaker in 1959 when Dr. William Chardack and Dr. Andrew Gage, who were working with electrical engineer Wilson Greatbatch, came up with a viable implantable pacemaker which was patented and later acknowledged as one of the two major engineering contributions to society during the last 50 years. His company, Greatbatch, Inc. (NYSE: GB) currently manufactures vital technologies used in medical devices.
The development of the pacemaker, which provides electric signals (approx 4V) to the heart to make it beat properly, was followed in 1980 by the invention of the implantable defibrillator and over time the two were combined to an implantable cardioverter defibrillator (ICD). A defibrillator shocks a failing heart into action with a 750V pulse. While the first pacemakers were external and so large that they required the patient to move them around on a trolley, modern ones are implantable and weigh less than an ounce (25g).
The new devices used in pacing for cardiac and neuromodulation are miniaturised for portability and privacy and can handle data acquisition levels previously unimaginable. “Miniaturisation and battery life are going to lead to smaller devices being deployed for much broader ranges of medical indications,” explains Mark Manasas, Cambridge Consultants. “Previous generations of implantable devices had limited life spans due to battery life issues. Current generations are incorporating the ability to charge the devices transcutaneously.” i.e. through the unbroken skin.
Minneapolis-based Medtronic, Inc.’s senior principal mechanical engineer in Neuromodulation, David Warren Lee, explains, “The new products under development at Medtronic are either implantable or wearable devices that need to be easily concealed, and so all the components have to be smaller.” The new implantable devices are controlled by a hand held device programmed by the doctor and carried by the patient so the products also have to be robust and withstand everyday use.
This is where the critical role of the interconnect comes in. “We have to have an extremely durable, very reliable connector,” explains Lee. “It’s a medical device and it has to work.”
“The miniaturisation trend is driven by a few factors including the movement of therapy and/or monitoring from the clinic setting to the home as well as treatment for chronic conditions without a disruption in lifestyle”, explains Anthony Kalajaikas, Global Industry Director, Hypertac Hypertronics. “The next natural progression is to miniaturise the device so that it resides in the body which will require biocompatible materials.” The evolution of medical devices to implantable has driven the need for biocompatible material in all components. Commonly, interconnect companies like Hypertac Hypertronics use brass material for the connector body and beryllium copper contacts, standard in connectors. However, in developing ImplanTac®, the connector body material was changed to a biocompatible stainless steel material commonly used in medical products, 316LVM.
The selection of the contact material was more challenging as there was nothing available that matched the specifications needed in the marketplace, so for the wires Hypertac developed their own proprietary composite with a platinum contact surface. The superior mechanical and electrical spring properties of the wire are significant for the performance of the contact.
While this is the standard product, customised products with other materials such as MP35N can also be used for the same application.
The size of the contact is becoming increasingly smaller as the demand for miniaturization continues. The International Standard Organization governs the geometry and performance of the interconnect interfaces. IS-1 leads are commonly used for pacemakers and are 2.66mm in diameter, while the next generation neurostimulation products, which are often more sophisticated, require more contacts as they have more leads to connect to the device. Contact size for implantable devices can vary, and can be as small as 0.050” (1.27mm) in diameter.
The key to Hypertac’s ultra reliability is the unique contact design characterised by the Hypertac® wire basket technology (see Figure 3) which surrounds the male pin. This guarantees continuous signal integrity which is crucial in medical applications where low force and low resistance are critical. The insertion force of ImplanTac® is very low. The wire basket design creates a 360˚ contact which ensures contact reliability, eliminating electrical intermittencies and fretting which can be an issue with many connectors.
The devices have to be implanted in the body by a surgeon and in the past the set-screws that were needed to secure the device in place were commonly the cause for failure. ImplanTac® was designed to be inserted without the need for set-screws to eliminate this problem. Device failure can also be caused by contact damage during mating. Connectors that have a single wire coiled inside the contact can fail if the wire is damaged. The design of ImplanTac® uses between 6 and 10 independent wires inside each contact (depending on the size of the contact) that ensures a reliable connection even if a single wire is broken.
The implantable systems currently being development within major medical device companies will revolutionise health care in the coming decades. The National Institute of Health has predicted that in the next 20 or 30 years, nano-sized implantables that can search out and destroy cancer cells or repair tissue will be developed. The ability of recent devices to receive data from the body and store and transmit it drastically changes how we are able treat disease and monitor health.
Some new implantable devices under development are designed to reduce the use of pharmaceutical drugs to treat disease, thereby eliminating the damaging side effects. For instance, a neurostimulator called Activa® RC was recently developed at Medtronic to control the symptoms of Parkinson’s disease by delivering Deep Brain Stimulation (DBS) Therapy. Using the technology developed for pacemakers, and applying electrical impulses to an area of the brain, the symptoms of the disease such as tremors can be eliminated in many patients. The new technology is smaller and offers more advanced programming than previous models and it is also the first rechargeable DBS device.
Another implantable device, Syncromed pump, is used to inject medicine directly into the patient using a hand held device. By injecting the medication directly where it is needed in the body instead of orally, the patient only needs to use 1/100th the amount, significantly reducing side effects caused by medication.
Other new practical applications under development in areas like orthopaedics use the electrical impulse technology designed originally for pacemakers to send nerve stimulus to prosthetics and/or body parts where nerves are damaged. For example, Neurostep, currently in clinical trial, is being used to stimulate the muscles used to lift feet during walking for people who suffer from foot drop.
“The trend is towards less invasive devices and less invasive procedures,” comments Mark Manasas. “Natural Orifice Surgery (NOS) is poised to take off for the implantation of devices. Improved imaging, i.e. CT, MRI and Ultrasound are going to be much more prevalent and necessary as these procedures become less ‘open’ surgery and more ‘keyhole’ surgery.”
Advances in medical technology means that the demand for innovative and reliable applications, such as Hypertac ImplanTac™ contacts for the medical device market, is crucial and offers unlimited opportunities for quality healthcare which were previously considered impossible.
Chris Parsonage: Sales Director, Hypertac Ltd. Tel.: ++44 20 8450 8033, Email: chris.parsonage@hypertac.co.uk
