By Daniel Ratzlaff, Product Line Manager, Smiths Interconnect

The medical market is increasingly being impacted by mega trends such as expanding global markets, extreme demands by COVID-19, ageing population, and, where possible, product reusability, addressing the key growing issues of both waste and limitations on recycling to minimise environmental impact. All these trends drive the need for high-quality and affordable medical devices that should meet the economic needs and local demands.

Reuse is key

In some cases, where reusing medical products increases the risk of spreading disease, it is still desirable to have low-cost, reliable, yet disposable devices that can be used on one patient only. However, because now hospitals and clinicians must factor in cost and waste concerns, it is becoming more critical to minimise the disposable portion of the medical system to as small a part as possible, with the remainder being reusable as much as it is feasible. This makes financial sense and minimises environmental waste.

A perfect example are the disposable catheters used in electrophysiology. This is a minimally-invasive procedure that maps and treats arrhythmias by feeding the catheter through a small incision (typically in the groin area) into a blood vessel to the heart, allowing quicker patient recovery, with fewer complications, compared with traditional open-heart methods. The catheters themselves are often single-use devices.

The extension cables connecting these catheters to the system traverse the border between the sterile field (where the patient is) and the external system, which is in an unsterile area away from the patient. These cables are typically reused, which reduces the costs of each procedure, but are then sterilised between patients.

A leading medical device manufacturer was recently looking for an alternative to standard high-cost autoclave compatible connector offerings for a new range of electrophysiology catheters it was developing. Key connector requirements were small size, ease of use, ruggedness and resistance to autoclave sterilisation, in a package accommodating multiple contacts and ensuring signal reliability from the external system through the extension cable, to the tip of the catheter, and back.

Additional features

There are many connector options for autoclavable connectors, but this device maker required additional features, such as low mating forces and low contact resistance, in a package that would be easy and intuitive for medical personnel to use whilst focusing their attention on the procedure and patient care.

Multiple paths were explored, including development of a custom connector, but the existing Smiths Interconnect circular plastic D Series met many of the requirements within the current package.

However, the current solution would not survive autoclaving. A review was conducted to evaluate all features and the required application specifications. The existing solution used hyperboloid contacts, providing compliance with device electrical requirements (high cycle life for the system-side receptacle/low contact resistance) and the durability and reliability to survive the harsh chemicals and temperatures associated with the required sterilisation processes.

The system-side panel-mount receptacle contained the hyperboloid contacts whilst the cost-effective plug used male pins to ensure longer device life and an affordable cable solution. The existing high-strength polymer, used for the plug and receptacle and widely accepted within the medical industry, was evaluated against alternative materials for ease of use, availability, chemical resistance and mechanical robustness, as well as the ability to maintain the same features and aesthetics of the original materials.

A perfect fit

Ultimately, polyetherimide was chosen as the replacement material for all plastic components. Connectors using the new material were then built and subjected to autoclave, electrical and mechanical testing to ensure survivability and consistent electrical properties before and after testing. The tests included 20 pre-vacuum autoclave cycles at 135°C for four minutes each, then the connectors were mated and unmated 200 times to ensure no substantial changes in performance had occurred. Finally, the dielectric withstanding voltage was measured on each tested connector pair, confirming that the insulators continued to meet the design specification. At the end of the testing, the new connectors functioned without any noticeable impact to their mechanical or electrical performance.

By performing a material analysis and selecting the correct polymer, the features of the existing D series connectors were maintained, consisting of high mating cycle life on the system side that increases the MTBF (mean time between failures), a simple, user-friendly, push-button latching system that ensures that the connectors stay dependably mated during the procedure, and low mating and de-mating forces. Additionally, new benefits emerged, including high-temperature resistance, improved mechanical properties, lower water absorption and improved chemical resistance to harsh environments and sterilisation protocols (including steam autoclaving), all critical to address emerging trends in today’s medical market and needed for the customer’s application.

This solution was also economical, since new materials could be applied across the D series platform, already available in three standard sizes, without impacting contact density, the ability to intermate with existing D series designs, or the integration of existing contact technologies, including crimp and poke contacts for automation and reduced assembly time. This allowed for a mix of disposable and reusable solutions in the same family, which afforded the customer flexibility to integrate reusable receptacles with disposable and reusable plugs for the same system, or any other combination, depending on its applications.

Proven heritage

For many years, D Series connectors have a proven heritage in medical devices and applications used globally; from disposable catheters to the mating cables, to bedside patient monitors, patient-worn therapeutic devices, and rugged automatic external defibrillators, which are critical to first responders. They have now been updated to meet the market requirements for reusability and sterilisation in both manufacturing and hospital settings by implementing a new material without affecting existing key features critical to previous applications of the product or reducing their cost-effectiveness.