Medical connection systems are used to transmit power, data, and control signals to and from medical devices. They can be found in numerous clinical settings—surgical devices such as hand tools; therapeutic equipment; and diagnostic equipment such as EEG, ECG, EKG and EMG machines. They are also common in portable medical devices.
What is a Medical Connector?
Connectors encompass more than just wires. Fiber-optic connection systems are employed for control signals, biomedical sensing, endoscopic imaging, and visible light transmission. Many medical connectors are incorporated into complex harnesses intended for one-time use (Figure 1).
Figure 1:Disposable cable for spinal surgery monitoring. (Source: ATL Technology)
When designing connectors for medical use, many factors must be considered, including FDA classification of the medical device, base electrical requirements including voltage and current, EMC and shielding requirements, and environmental requirements for specifying appropriate materials.
FDA Classification and Applicable Standards for Medical Device Connectors
The U.S. Food & Drug Administration (FDA) classifies medical devices based on the risks associated with use of the device. Devices are classified into one of three categories: Class I (lowest risk), Class II (higher risk), and Class III (highest risk). The level of regulatory control increases with the classification. The European Union, Canada, and other countries have similar regulations.
In addition, the FDA has a classification category for the manufacturing process itself (FDA 21 CFR 820) to ensure medical standards of quality.
For medical electronic equipment, IEC 60601 is a series of technical standards for the safety and effectiveness of medical electrical equipment; compliance with IEC 60601-1 is a requirement for FDA approval of new devices.
Formal risk management methodologies are now an integral part of the regulatory process. Manufacturers now look closer at the risks of every component and material used in their devices, then document those risks for FDA inspection. ISO 14971 is the ISO standard for the application of risk management to medical devices. The connector used in an FDA-classified device must meet the appropriate requirements, even though the manufacturer of the device itself is ultimately responsible for certification and risk assessment.
Medical Connector Cables: Operational Requirements
The most important requirement for connectors, of course, is safety for both patients and medical personnel, followed by ease of use. Since they are used in hospitals and other clinical settings, they should be designed to be easily manipulated using surgical gloves.
Push-pull designs are preferred with an audible click to indicate successful engagement. Connectors and cables can also be color-coded to ensure they are plugged into the proper receptacles. Unique mechanical coding can guarantee the correct connector is plugged into its proper mating connector.
In many cases, the patient connector is attached to a probe or similar device intended for one-time use, but the mating connector on the instrument itself should be robust enough to withstand as many as 10,000 mating cycles.
Since many physiological signals are very small—a typical electrocardiogram (ECG or EKG) signal has a peak amplitude, before amplification, of around 1 mV—it is important that the electrical characteristics remain consistent over the lifetime of the product. The low signal levels may also mandate EMC protections such as shielding. The rise of portable equipment as well as in-home devices has only increased the need for both robustness and ease of use.
Environmental Considerations
Medical connectors must withstand various medical sterilization processes including autoclave, STERRAD®, Ethylene Oxide (EtO), gamma and chemical sterilization. Connectors on assemblies intended for disposable use normally come in sealed packages, having already been sterilized at the factory; the mating receptacles on the equipment, though, are reused and so must be sterilized in place. These are often supplied with soak caps to protect the contacts during sterilization.
A medical interconnect system must also be sealed against water and dust and other potential hazards, so it should carry the appropriate IP rating when mated to the matching receptacle. Each IP number is independent; the first one indicates resistance against dust intrusion (levels 1 – 6), and the second indicates resistance against liquids (levels 1 - 8). For example, an IP67 system has the highest level of protection against dust (6) and can withstand immersion in up to 1 m of water for up to 30 minutes (7).
Medical Connector Materials
As mentioned, a heat and chemical-resistant material is needed for medical connectors. PPSU, PSU and PEI are three thermoplastic high-performance plastics that feature a combination of thermal, electric and mechanical properties that make them suitable for medical use.
- High upper-temperature limit for use in air (+180 °C, +170 °C and +150 °C continuously for PPSU 1000, PEI 1000 and PSU 1000 respectively)
- High mechanical strength, rigidity and creep resistance over a wide range of temperatures
- Excellent resistance to hydrolysis (suitable for repeated steam sterilization)
- High ductility, even at low temperatures
- Harmless in physiological terms (suitable for contact with food)
- Very high-dimensional stability
- Translucent, non-optical quality (except for PPSU, which is black)
- Very resistant to energy-rich radiation (gamma and X-rays)
- Good electric insulation properties and positive dielectric behavior
Trends in Medical Connectors
With the rise in portable and in-home medical equipment, size and weight have become increasingly important. Miniature connectors are making their appearance, but with the smaller size means that increased attention must be paid to ISO 14971 risk management factors such as clearance and creepage for higher-voltage signals.
Hybrids are another trend in connectors. Of course, electrical signals are vitally important, but many medical devices require “umbilical” connections that include fluid lines, and fiber-optic connections in addition to wires. To make sure everything is hooked up correctly, RFID tagging is often another required feature. Specialized manufacturers are able to fill this need by incorporating multiple connectors, cables and fluid lines into a single custom assembly.
This capability is available in standard products, too. For example, the Hybrid Circular MT Cable and Receptacle System from Molex (Figure 2 below) combines optical and electrical solutions in one connector. This multi-functional connector provides options for three configurable MT ports by leveraging the existing circular MT optical connector and receptacle design. Applications include cardio-thoracic surgery equipment, diagnostic equipment, electro-surgical equipment and similar devices.
Figure 2: The MediSpec Hybrid Circular MT Connector System. (Source: Molex)
Medical Connectors from Arrow
Multiple Arrow manufacturers offer connection systems designed for the exacting medical market, including Molex, TE Connectivity and Amphenol.
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