The SYGNUS implantable contact system from Bal Seal Engineering, Inc. is visible in the header of this IPG, used to deliver neurostimulation therapy. Image courtesy of CC Medical Devices.

For years, manufacturers of neurostimulators and other active implantables have been feeling extraordinary pressure from shareholders and other funding sources to move more quickly from design stage to production. As a result, many device makers have begun searching for opportunities to integrate components as subsystems in order to make the most of precious time and capital. And for an increasing number, this search is leading straight to the header cavity, where the critical lead interface is housed.

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). By 1960, less than a decade after their inaugural use, IPGs were successfully employed to deliver pain-reducing, life-improving therapies to the deep brain and spinal cord.

In recent years, exponential advances have been made in the design and efficiency of IPGs, and many more uses have emerged. 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 simple 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.

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

A top-down approach

The SYGNUS integrated seal/contact assembly is designed for compliance with ISO’s IS-4 and DF-4 standards. Pre-tested seals and contacts form a stack and canted-coil spring elements provide electrical connectivity and mechanical holding.

One area identified by many OEMs as ideal for integration is the device header. This implantablegrade plastic or silicone enclosure at the top of the IPG is hermetically sealed to the “can,” or 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 power is transmitted through multi-channel connections as signals from the battery and electronics to the lead, and ultimately out to the body. Electrical contacts inside the header ensure that the right signals get transmitted through the right channels on the lead, and seals between those contacts isolate against both bodily fluids and electrical “crosstalk” 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, the dual need for connecting and sealing has remained constant. But some of the tools engineers use to meet that need have changed significantly.

The 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. But 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.

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