Anthony Kalaijakis, Molex
Advanced technologies are driving innovations in mobile healthcare delivery - exciting diagnostic and monitoring telehealth and eHealth devices that allow physicians to reach more people more efficiently, even in remote regions of the world. Optimal patient comfort and mobility depends on packaging more features into thinner, smaller devices. Developing reliable devices that perform seamlessly in non-traditional healthcare environments beyond the confines of clinical settings presents unique challenges for medical device designers.
Compliance ensures reliability and safety
Medtech is a highly regulated industry with stringent medical-grade guidelines for high-density medical devices used in home healthcare telemetry and portable applications. Regulations apply to material sourcing, manufacturing, and packaging processes. A number of industry regulatory and environmental ratings exist for electronic components, including U.S. Food and Drug Administration (FDA) registration, ISO 13485, ISO 10993, RoHS, and REACH. Suppliers may additionally adhere to ISO 9001 quality management and ISO 14001 environmental management regulations.
FDA and other industry specifications, including AAMI-53 and global safety standard IEC60601, UL/CSA, are critical medtech design criteria. FDA classification and general controls are based on the intended device use, and take into account potential risk to the patient. A Class II and III device will require stricter definitions for performance and risk management than a lower risk Class I device. Registered manufacturers adhere to stringent quality systems, including inspections, tracking, and traceability criteria. Supplier FDA registration provides added assurance of the quality and safety of the electronic components used in disposable, portable, and wearable medical devices.
Navigating the interconnect maze
Connectors are ubiquitous in devices across medical modalities, including imaging, therapeutic, minimally invasive surgical devices, implanted electronics, patient monitors, and sensors. Choosing interconnect technologies for a given application is a critical first step. In past designs, numerous connectors might have been required for multifunctional devices.
Today’s connector options often combine copper power and signal, fiber optics, fluid or gas connections, even an RF antenna interface, all packaged in a single integrated interface. The right connectors can yield overall lower cost for the manufacturer, a more compact package, and improve healthcare provision. So it is important to successfully navigate the connector technology maze.
Before identifying connector styles, a designer needs to initially identify each connection type, whether board-to-board, wire-to-board, wire-to-wire, panel mount, or inline termination, in addition to receptacle through-hole or surface mount terminations. Criteria should specify number and type of interface contacts, as well as the associated cable configurations.
Whether a cable is intended for an ECG, defibrillator, power, analogue, digital, bandwidth, fibre optic, or some combination, will determine the cable diameter, length, shape, and material options. In every design there are packaging size constraints, in addition to manufacturer preferences for the desired physical size of the end product and branding requirements, such as logo marking and serialization for tracking.
Connector specifications depend primarily on the intended use of a device in real-world environments. Application functions, plus any potential for misuse, jointly inform the physical properties desired in the connectors. Design demands are significantly higher in a portable device intended to allow a patient freedom of mobility.
Portable medical devices must meet design specifications more akin to smart phones than traditional medical equipment used in clinical settings. Mating cycles for medtech device connections may range from a single-use connector in a disposable sensor to tens of thousands of mating cycles in an MRI coil or portable glucose monitor worn by a mobile patient 24/7.
Devices worn or carried by patients must be built to perform under a very wide range of conditions. A range of temperatures and humidity levels exist in real-life settings, such as patient homes, where shock, vibration, and accidental drops also occur more often than in clinical settings where equipment is handled by professionals. (See Figure 1)
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Fig. 1 – Circular connectors with medical-grade plastic housings have proven an economical option in a wide range of portable diagnostic and patient monitoring equipment
Connector mechanical specifications
A range of durable materials is suitable for lightweight portable and wearable medtech devices. Connector contact bases and platings are typically metal, with medical-grade plastic or metal body housing and strain reliefs. Gold plated contacts generally work best in harsh environments. While tin is more economical, gold plating offers the most reliable contact and mating cycles. Nickel-palladium-to-gold is also proven and accepted within the industry.
A properly designed device with regular un-mating of connector interfaces allows visual inspection to reduce debris build-up. If contaminants are observed they can be eliminated before impacting performance. Medical device sterilization, specifically exposure to sterilized wipes, gamma radiation, ethylene gas, autoclave, and Sterrad process, also factor into material selection and design. Each sterilization method presents different exposure levels, chemicals, reactivity, and risks to connector integrity. Medtech applications typically require connectors resistant to fluid ingress, with most requiring an IP6 or IP7 rating level. (See Figure 2)
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Fig. 2 – High-performance and affordable custom-off-the-shelf circular connectors feature lightweight medical grade plastic housings to withstand autoclave and other sterilization processes
Medical connectors are either locking or non-locking based on how they connect to a device. In an assembly connecting a patient to a portable device, it is often desirable to have a secure locking connection to avoid unintentional disconnection. It may also be desirable for the connector to safely disconnect if an axial force is applied to avoid accidental injury to the patient, connector, or cable assembly. Even in non-locking connectors, medical cables require a positive connection between plug and receptacle. A loose connection may cause intermittent contact, resulting in unwanted noise or signal degradation, which can interfere with device performance.
Pin and socket selection, and the physical design of plug and receptacle, allow control over insertion and retention force. Retention force defines how firmly a receptacle holds a connector. If a connector is expected to have a high number of mate- and un-mate cycles, it is generally desirable to achieve retention force from the metallic pins and sockets.
In some instances, such as a portable defibrillator requiring a securely latched connector, it may be advisable to overmold a connector with a flexible hood to protect the latch mechanism (see Figure 3). If the retention force achieved by pin-to-socket and friction of the connector housing is insufficient, the retention force can be enhanced via design, so axial force applied to the cable is not directly applied to the removal axis of the connector. Conversely, a non-locking connector can be designed such that it can be disconnected by axial force applied to the cable. Use of right angle connectors is another approach to enhance retention and prevent accidental unmating.
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Fig. 3 - In some environments it may be advisable to overmold a connector with a flexible hood to protect the latch mechanism
Measuring retention force at pre-established intervals during mating and un-mating can confirm retention force will be maintained over the design life of a connector. Verification testing of medical connectors is essential to confirm specifications are achieved or exceeded in the final design.
Three-tier connector design solutions
Off-the-shelf connector solutions can provide medtech manufacturers a means to leverage economical technologies proven in other industries. High-performance medical circular connectors, for example, provide an economical choice with a proven contact design, durable mating force, and plastic or metal body styles to withstand sterilization. Circular connectors with a lightweight medical-grade plastic housing offer high quality electrical performance at a competitive price for many applications, such as catheters and other portable devices.
In some applications a standard off-the-shelf connector will not suffice. A custom or hybrid connector may be more appropriate for design requirements. Tooling a new connector provides the most design flexibility and comprehensive options, but comes at a higher price. Manufacturing a custom connector typically entails an injection molded hard plastic insulator into which pins and/or sockets are inserted. The assembly is overmolded with rigid material to secure the construction and provide physical strength. A second overmolded material gives the connector the color, finish, and look desired by the OEM.
Custom connectors typically demand higher upfront engineering and fabrication costs, but may be worth the investment. Design elements can be addressed with fewer compromises. A unique pin-to-socket pattern or connector shape can prevent mating by incompatible connectors, thereby ensuring patient safety. Or, the connector shape may need to closely match the device profile to optimize portability. Custom connectors may also be advisable when a variety of voltage and signal types must be carried within a single connector cable assembly—and a standard connector cannot meet the criteria.
A hybrid connector option can balance price and features. Hybrids take a proven technology, utilizing base components from a standard connector, and optimize features, without the extra cost of tooling a new connector. Hybrid connectors may incorporate robust overmolded shells for improved grip and pre-molded boots or collars for strain relief or a higher IP rating. Hybrid connectors are less costly, yet the finished product can look, feel, and feature most of the desired performance advantages of a custom connector. Additionally, designing a hybrid connector generally shortens the development schedule.
Leverage best-in-class connector technologies
Medtech manufacturers need best-in-class technologies to fill the healthcare pipeline with quality, compliant products to meet complex patient medical needs. MID (molded interconnect device)/LDS (laser direct structuring) offers 3D selective trace functionality, coupled with the flexibility of using injection molded plastics that can be soldered, plastic welded, insert molded, over-molded, and wire bonded. Addressing functionality, space, weight, and cost concerns, MID/LDS 3D custom assembly solutions streamline the manufacture of miniaturized connectors, antenna, and sensors.
The assemblies combine MID technology with LDS antenna expertise to deliver fine-pitch 3D circuitry in single compact molded devices for high density implantable and wearable patient monitors. LDS uses fewer components and improves functionality over bulkier, less ideal processors or assemblies in applications like catheters. The technology is uniquely suited to wireless remote and sensor-based patient monitoring (i.e., a glucose meter transmitting readings to a physician’s office via a remote base station connected device).
Making well-informed connector choices to streamline the design and manufacturing processes, an experienced medical component supplier can guide designers, ensuring due diligence in specifications, risk assessment, cost estimates, and test verification of fully compliant electrical, signal, and mechanical interconnects for portable and wearable medical devices.