Stacking the Deck

SYGNUS allows simple integration into the casting header of the IPG that CCC produces. It has helped reduce the header volume while keeping a good insulation between contacts.

For years, manufacturers of pacemakers, defibrillators, neurostimulators, and other active implantables have been feeling extraordinary pressure from shareholders and other funding sources to quickly move from prototype to design and build. As a result, many device makers have begun searching for opportunities to integrate or systemize in order to make the most of precious time and capital. In addition, for an increasing number, this search is leading straight to the header cavity where housing of the critical lead interface takes place.

Active implantables, also known collectively as implantable pulse generators, or IPGs, have been around in their most basic form since the 1950s. These small bundles of electronics, batteries, and wires, positioned within the body and used to send electrical pulses to nerves and organs, found their earliest application in the treatment of cardiac-related conditions such as bradycardia (slow heart rhythm) and tachycardia (fast, irregular heart rhythm). However, by 1960, less than a decade after their inaugural use, IPGs were also in use to deliver pain-reducing, life-improving therapies to the deep brain and spinal cord as well.

In recent years, there have been exponential advancements in the design and efficiency of IPGs, resulting in the emergence of additional use. Seeking to deliver new modalities of pain management to an aging population (nearly 28% of Americans will turn 65 in the next decade), a fresh crop of manufacturers, fueled by entrepreneurial spirit and venture capital, have been introducing breakthrough technologies for the treatment of angina, epilepsy, and even hearing loss. Once a “dumb” unit designed only to deliver, today’s IPG has evolved into a device that can, in some cases, predict seizures by sensing microvolt fluctuations in brain wave activity – and potentially stop them before they begin.

Nevertheless, as the number of new players in the IPG marketplace has grown, so too have investors’ demands for faster, less resource-intensive development of innovative devices and new therapies. The answer for some manufacturers has been to look within their designs for opportunities to systemize and integrate.
 

Top-Down Approach
One area identified by many OEMs as ideal for integration is the device header. This implantable-grade plastic or silicone enclosure at the top of the IPG is hermetically sealed to the can – the metal housing in which the electronics and battery reside – and it can make up as much as 25% of the overall device volume. All of the critical connections that drive the IPG’s functions originate in the header connector cavity – where transmission of power is through multi-channel connections – going out as signals from the battery and electronics to the lead, and ultimately out to the body. Electrical contacts inside the header ensure that the transmission of the right signals occur through the right channels on the lead, and that the seals between those contacts are isolated against both bodily fluids and electrical cross talk that may otherwise cause false positives, improper stimulation, or general malfunctioning of the device.

In the half-century or so since the introduction of the first IPG, this dual need for connecting and sealing has remained constant. However, some of the tools engineers use to meet that need have changed significantly.
 

Connection Progression
In the early days of IPGs, the setscrew was the primary method for fastening and connection. Used in series along the header, it provided both mechanical retention and electrical contact. However, as device functionality improved and the need for multiple connections grew from four, to six, to as many as 16 in some neurostimulators, the process of tightening each setscrew during the surgical process became less and less viable. While it acknowledged the continued need for a setscrew to ensure absolute retention of the lead in the device header, the medical community demanded alternatives, and several new types of contact technologies began to emerge.
 

Among the first of these to supplant the multiple setscrew setup was the Multi-Beam contact – resembling a leaf spring ribbon inside a can – which was designed, manufactured, and introduced by Medtronic and is still widely used today. Constructed of stainless steel, titanium, and MP35N, the Multi-Beam offers cost-effective electrical connectivity. However, its relatively low number of contact points (six to eight) can mean higher contact resistance, which may result in reduced battery and device service life. In addition, the Multi-Beam has inherent size limitations, and its leaf springs have linear force curves that can result in variations of insertion and extraction forces.

The Canted-coil spring, a contact technology developed around the same time as the Multi-Beam, offered designers yet another alternative to the setscrew. Designed by Bal Seal Engineering Inc., the spring was first employed in an IS-1 ring connection, but it soon evolved into a spring/housing combination that could provide a desirable weld surface. The combination, which became known as the Bal Conn, continues to be specified by many of today’s device makers, due in large part to its ability to provide very low electrical resistance in a limited space. The Bal Conn’s Platinum-Iridium spring allows for low, highly-controllable insertion and extraction forces, and its spring coils provide multi-point conductivity. While it can help conserve header real estate, the Bal Conn is best suited for challenges that cannot be met by off-the-shelf solutions.

The ImplanTac Contact Socket is a more recent IPG interconnect offering. Its manufacturer, Hypertronics, describes the design as a basket of wires that positions lengths of wire strung at an angle to the socket’s axis. This contact offers low electrical resistance and low insertion/extraction forces, but its construction limits it to a set axial length, which can be prohibitive for OEMs seeking to reduce package size or pack more contacts into the connector cavity.
 

Stuck in the Middle
Unlike their contact counterparts, the seals used to provide fluidic and dielectric isolation inside the device header have not evolved all that much. Generally, they have been (and continue to be) molded from implantable-grade silicone, a material with properties that are widely known and accepted in the implantable world. Silicone is soft and malleable, so it flows easily into and around non-uniform surfaces while retaining the ability to seal. It is also relatively inert, so it is less likely to react with the metals used to form the contacts and lead.
 

The SYGNUS system allows a simple integration into the casting header; it has a reduced size, a controlled pitch, and adjustable  numbers of contact per row.

Arriving at Integration
Traditionally, producers of IPGs have had little choice but to undergo the costly, iterative, and time-consuming job of purchasing electrical contacts and designing, creating, and testing their own isolation seals for the critical lead interface. By some industry accounts, this process can tack as much as six months onto the development of a new device.

However, a new kind of plug-and-play connector technology, slated for formal introduction this month, may make the process obsolete – at least for some smaller OEMs and startups focused on emerging therapies.

The concept behind this technology is relatively simple. First, take a proven electrical contact platform and package it with isolation seals that can guard against fluid infiltration and prevent signal leakage. Then, test the components for insertion and extraction forces, conductivity, electrical resistance, seal isolation, and other criteria, so that a manufacturer can confidently integrate the entire connector system into its device design and move closer to the ultimate goal of market introduction.

Bal Seal Engineering has developed an example of this approach, which effectively pairs seals and contacts in a pre-tested, compact, and scalable package. Marketed under the trade name SYGNUS, this solution is built around the Canted-coil spring technology and is thought to be the world’s first seal-integrated contact system.

The SYGNUS system combines the tiny springs made from Platinum-Iridium, metal housings of MP35N, and implantable-grade silicone isolation seals in a configuration that forms a dense connector stack to accommodate lead diameters ranging from 0.90mm to 3.20mm. Since a version of the seal/contact combo is engineered to the recently-ratified four-pole standard (IS-4 and DF-4) for cardiac health management devices (a proximal cap serves as the datum, and a distal cap completes the footprint), the company says SYGNUS gives manufacturers the ability to dedicate resources to therapy and function improvements, instead of component procurement or development.

“There has definitely been a growing need for this kind of solution,” says Bal Seal Business Development Manager Bill Nissim. “To some companies, especially those facing venture capital deadlines and clinical trial windows, choosing a system like [SYGNUS] provides a level of freedom that could mean the difference between success and failure. Similarly, from a patient’s perspective, it might be one of the factors that determine whether or not a breakthrough therapy ever makes it to market.”

Cardiac IPG device makers who have recently tested and adopted the new standardized seal/contact technology cite reliability, safety, and ease of implementation as primary reasons for their choice. Moreover, in a move that mirrors their CHM counterparts, designers of active implantables used in the delivery of neuromodulation therapies are now eyeing the same kind of stack solution – engineered to even smaller, more contact-dense specifications – for the very same reasons.

For now at least, this new focus on systemization – especially of the contact/seal variety – is more prevalent among small, agile manufacturers whose organizations do not afford for the vertical integration common to the industry giants. However, it may not be long before even the heavy-hitters discover the benefits of specifying pre-packaged, pre-tested connecting solutions for their devices.
 

Q&A with CCC:
With the introduction of SYGNUS, the integrated implantable seal/contact system for use in cardiac and neuromodulation devices Today’s Medical Developments caught up with a representative of CCC Medical Devices, a company that has already started using it.

In the following Q&A, CCC Business Development Manager, Oscar de Oliveira, explains his company’s decision to use the integrated seal and contact stack, and how that decision has affected technology and yield at CCC.

TMD: What does CCC Medical Devices do?
CCC: We are a medical device company offering design and manufacturing contract services, with more than 40 years of experience with implantable medical devices and systems. CCC’s customers are research institutions and medical device companies, and we design and develop devices and systems for many medical fields, including neurostimulation, heart failure, obesity, diabetes, blood pressure control, sleep apnea, patient monitoring, and many others.

TMD: What are some of the major challenges CCC faces in the development of IPGs?
CCC: The biggest challenge is to implement all the required features while minimizing the power consumption and the size of the device, and maximizing the product reliability.

TMD: Did CCC identify a need for a header connection solution that integrated seals and contacts? What was driving this need?
CCC: Neurostimulation therapies require delivering electrical pulses to the body, using leads with several electrodes as the interface. The IPG header must be able to connect the lead’s contacts to the internal circuit and it must be as small as possible in order to decrease the total volume of the device. From an electrical point of view, the header has to ensure a suitable seal between each pair of connectors. These factors led us to need a connection solution that could provide easy integration to the header, suitable sealing and small size, in order to minimize the size of the device and optimize its manufacture.

TMD: What led you to choose the SYGNUS Implantable Contact System as a possible solution?
CCC: The SYGNUS system allows a simple integration into the casting header; it has a reduced size, a controlled pitch, and an adjustable number of contacts per row. In addition, the silicone seal not only ensures electrical insulation between each pair of contact, but also helps eliminate epoxy leakage that could occur during header casting.

TMD: How does CCC use the SYGNUS system?
CCC: We pre-assemble it in one stack with the correct number of contacts and with an end cap and a connector block with setscrew for the lead mechanical fixation. Then it is welded to the device and goes through the epoxy header casting process.

TMD: How does SYGNUS solve the size challenges you described earlier?
CCC: The IPG header volume is usually 1/4 to 1/5 of the total IPG volume, so any solution that helps to reduce the IPG header will have an important impact on the IPG size. The SYGNUS system has helped us to reduce the header volume while keeping a good insulation between contacts.

TMD: As a result of using this system, what is the biggest benefit to CCC?
CCC: The biggest benefits of the use of the SYGNUS system are the IPG header size optimization, and the improvement of the assembly process and the product yield.

Bal Seal Engineering Inc.
Foothill Ranch, CA
sygnusconnects.com
balseal.com
 

CCC Medical Devices
ccc.com.uy