Miniaturised medical interconnects serve rapid evolution in medtech

Author : Bob Stanton, Director of Technology at Omnetics

05 February 2018

This article discusses how technological demands from hospitals, practitioners and patients is driving miniaturisation of equipment, sensors and probes – and how cable and connector manufacturers are responding.

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Micro and Nano-sized connectors connected to miniaturised flexible cable for new biomedical devices are on the rise. Detector circuit chips and processors are being moved from instrument boxes to inside the end of the cable and probe. Handheld portable ultrasound devices are being used to evaluate a wide range of internal organs, from blood clot analysis to cancer testing. New sensor chips are used in medical clinics for processing minute blood cells to provide immediate data during doctor visits.

Circuit processor chips in the brain are being used to help amputees move prosthetic legs or hands. From over-the-counter pharmacy products to neuromodulation implants, we are seeing an evolution of micro-signal processing for monitors to assist and repair damage to the human body. Digital displays are becoming portable and are being shared with the patient in real time.

A good example of a miniature interconnect is the use of Micro circular connectors to enable quick-change probes and sensors in the medical diagnostics world. The insert portion of a miniature circular connector is overmoulded to a design that serves as a connector and handle for a small electronic probe.

In this case, the end of the probe contains a thermistor that changes electrically with temperature. A surgeon can insert the probe into the body and monitor the temperature of the patient’s blood and tissue. The data is captured and printed in real time onto a display or paper strip-chart. This gives the physician early warning information to help with intervention and avoid the risk of potential reactions during the procedure. The connector inserts can be pre-wired with varying contact systems spaced as narrow as .635mm and moulded to various materials. Smaller diameter cables that have been ruggedised and covered with bio-safe materials can be specified. Manufacturing is usually carried out in medical-quality clean rooms.

Medical interconnect device reliability and quality are highly important in the development of new miniaturised connectors. This begins with the use of highly reliable elements. When planning ahead for use in dynamic patient service environments, connector designers often choose the spring-pin and socket system.

This assures proven reliability and performance over wide ranges of shock, vibration and thermal changes. Spring pins are made of BeCu (beryllium-copper alloy), with high tensile strength (17,200ksi) that withstands the rigours of use and abuse. Pin and socket elements selected also pass extreme plating tests specified for reliability. The metal coating begins with a strong nickel-plated barrier which is then coated with 50 micro-inches of gold.

Afterwards, they are inserted into miniature insulator housings, moulded from LCP (liquid crystal polymer). This format offers the highest level of reliability testing in medical, military and aerospace industries. Cables and wire systems most often use Teflon® insulated wiring that is carefully laser-stripped to avoid nicking. The cables and wires are crimped into the back section of the pin system, netting higher long term reliability than soldering to the wire. The pin-and-wire set are inserted into ruggedised LCP insulator bodies and epoxied in place. Insulators are sometimes customised to the designer’s criteria for specialty units.

Additional solutions for enabling portable and miniature medical devices include combining two miniaturised cables into one. Since designs often require lower current flow and voltage, cable can be used that offers both power and signal within one medical-rated interconnect. UL and safety ratings are also improved with insulation and properly keyed connectors, because they cannot be mismated in the wrong sockets. Power is controlled within the same cable and is well isolated from outside operating room electromagnetic noise. Many new medical instruments provide imaging for doctors and radiologists.

Such imaging systems generate and transmit high amounts of digital data. The newer circuits often run at digital circuit speeds of up to 5 Gigabits/second. These speeds require high speed digital connectors with special wiring that provide high resolution imaging and reduce delay time for the medical practitioner.

In addition, new medical products are expanding device portability and daily patient use outside of the service environment. Cables and connectors are being designed for patient wear, data collection and subsequent data sharing with the medical practitioner. New flat cable and connector systems are being employed to fit into personal clothing and provide data monitoring of key biometric data. These are similar to body monitoring devices designed for NASA and military ground troops.

New electronics used in prosthetic limb devices are necessarily miniaturised and very rugged. The highly flexible, yet wear-resistant, cables are jacketed and wired, and are increasingly in demand for use in soft robotic exosuits. Medical exoskeleton systems are being tested to assist in initial rehabilitation, and in some cases, longer term patient support for walking (for instance, for patients born with spina bifida).

Additionally, we see medical equipment in ambulances often exposed to both extremely hot and cold temperatures when the vehicle is parked. During service, they often experience rough handling, high strength pulls and sharp bends in cables. The connectors must withstand many repeated connections and disconnections during use. Miniature spring pin-to-socket technology serves that need well.

Microminiature and Nanominiature connector and cable systems are rapidly expanding their capability, while miniaturising in size and weight. The advent of high density, low voltage chip technology has provided opportunities for fast and reliable systems to serve the evolving medical field. New materials and methods of connector and cable design can now handle very high speed digital signals – within minute spaces – that simultaneously reduce size and weight, while increasing signal integrity and system ruggedness.

Customised variations of current miniature connectors can be very rapidly developed and shared with medical device designers using computer models. When approved, manufacturing data is automatically routed to machining equipment and manufacturing labs for first-article builds.

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