Introduction
Handheld medical devices must perform reliably across a wide range of device specifications and end-user environmental conditions. Mechanical and signal integrity of cable components are especially critical for achieving high performance, accuracy, durability, longevity, and user satisfaction. As handheld devices continue to shrink while simultaneously incorporating higher data rates, advanced imaging, sensing, and digital control, the demands placed on interconnects have increased significantly.
Medical cables are exposed to extreme wear and tear in most clinical environments. They are repeatedly coiled and uncoiled, stepped on, pulled, twisted, and rolled over by carts and equipment. Repeated sterilization cycles—often involving high temperatures, pressure, moisture, and aggressive chemicals—further stress both the physical and electrical integrity of the cable. Common equipment examples include endoscopic cameras, electrosurgical devices, medical foot switches, lithotripters, laser and energy-based treatment devices, magnet therapies, pulse oximetry systems, and ultrasound equipment.
To ensure cables perform as expected throughout their service life, cable manufacturers subject designs to extensive validation testing that evaluates mechanical durability, electrical performance, and environmental resistance. Material selection plays a central role in maintaining this integrity. A wide range of insulation, shielding, and jacketing materials are available for medical electronics, and the optimal solution is rarely driven by a single requirement. Performance factors influencing material selection include biocompatibility, disinfection and sterilization compatibility, revision control assurance, regulatory compliance, aesthetics, flexibility, durability, signal performance, and cost. Subtle differences in priority can result in significant changes in cable design, performance, manufacturability, and overall lifecycle cost.
Physical and Mechanical Properties
Insulation compounds that can be reliably extruded to very small wall thicknesses—such as fluoropolymers—are generally less flexible than elastomeric materials. Conversely, highly flexible compounds such as silicone rubber cannot typically be extruded to extremely thin dimensions. As medical devices continue to demand smaller cable diameters and tighter bend radii, balancing flexibility with dimensional control has become increasingly challenging.
Shielding method selection further affects mechanical performance. Foil tape, applied helically, effectively forms a continuous tube around the cable and provides 100% shielding coverage. However, foil shields lack natural flex points, making them comparatively stiff. While thin foil can wrinkle and form localized flex points, the overall construction remains less flexible. Braided shields, woven similarly to shoelaces, can flex naturally in all directions and offer excellent durability in dynamic applications, though their coverage is inherently less than 100%. Hybrid shielding designs—combining foil and braid—are increasingly used to balance EMI performance, flexibility, and durability in compact medical cables.
Conductor construction also plays a significant role in flexibility and fatigue resistance. Finer conductor stranding and specialized alloy selections can improve flex life with minimal impact on overall cable size. Advances in conductor metallurgy and stranding techniques now allow for improved fatigue resistance without sacrificing electrical performance.
Additional mechanical considerations include:
- Flex life: Typically measured using defined test cycles (e.g., 10,000 cycles at a 1-inch bend radius, with failure defined by loss of continuity). Flex life can be improved through optimized conductor alloys, cable geometry that minimizes internal abrasion, long-flex-life compounds, and application-specific testing. New England Wire Technologies employs customized flex-testing equipment, including machines that replicate real-world handling such as wrapping and unwrapping a cable around a simulated hand to mimic clinical use and storage.
- Cut-through resistance: Jacket durability against nicks and cuts is essential in high-traffic environments. Rugged jacket compounds can improve resistance, though tradeoffs with flexibility and diameter may be required.
- Tensile strength: Cables are frequently pulled, often abruptly. Integrating strength members such as aramid fibers, Kevlar®, high-strength alloys, or stainless steel can significantly increase resistance to stretching and breakage, especially in handheld devices subjected to repeated handling.
- Skin feel: User interaction remains an important consideration. Some materials are rejected due to tackiness that causes uncomfortable drag on skin, while others may be overly slippery and prone to sliding off sterile surfaces. Surface texturing, matte finishes, and advanced low-friction coatings are commonly used to fine-tune tactile performance.
- Sterilization resistance: Autoclave sterilization is particularly harsh and can degrade low-temperature plastics such as polyethylene, thermoplastic polyurethane, and PVC, while also accelerating oxidation of copper conductors. To counter these effects, high-temperature-resistant and corrosion-resistant materials—such as silicones, fluoropolymers, and silver-plated conductors—are often required. While these materials are more expensive, collaboration between engineers, suppliers, and end users can sometimes identify lower-cost alternatives that still meet defined sterilization cycles. Chemical disinfectants can also leach plasticizers from jacket materials, leading to brittleness, deformation, or discoloration, making early discussion of cleaning protocols essential.
Signal and Power Integrity
As handheld medical devices increasingly integrate high-resolution imaging, digital sensing, and real-time data processing, maintaining signal integrity has become more complex. Prototyping is especially valuable for identifying the optimal balance between shielding effectiveness, impedance control, attenuation, and mechanical flexibility.
Prototypes can often be produced while the medical device itself is still under development, allowing design teams to establish electrical benchmarks early. Achieving maximum shielding and signal resolution is relatively straightforward when size and flexibility are not constrained; however, handheld devices rarely allow such compromises. Deep knowledge of material behavior, dielectric properties, and cable geometry is essential to optimizing performance.
New England Wire Technologies can rapidly mockup material combinations and manufacturing processes, producing prototypes whose electrical parameters—such as impedance stability, crosstalk, and attenuation—can be measured and refined. This iterative approach enables faster redesign decisions and reduces risk as data rates and bandwidth requirements continue to increase.
Biocompatibility
Standard industrial cables often use compounds containing irritants or additives that are unsuitable for continuous human contact. Many fire-retardant additives fall into this category, making UL-listed cable designs more challenging for medical applications. Biocompatibility requirements apply to the complete device and include all materials and assembly processes.
Biocompatibility classifications depend on device type (surface-contacting, externally communicating, or implantable) and duration of contact (limited, prolonged, or permanent). Communicating these requirements clearly to a knowledgeable supplier helps optimize material selection and shortens qualification timelines by avoiding both under- and over-specification.
Material suppliers may certify compounds for food contact or compliance with standards such as ISO 10993-5 cytotoxicity testing. Some suppliers maintain FDA Drug Master Files (DMFs) containing confidential formulation and process details that can support device submissions. In many cases, suppliers offer parallel industrial and medical-grade material families with similar performance but different documentation, revision control, and traceability requirements. While medical-grade materials carry higher costs, they provide critical assurance for regulated applications.
Design for Manufacturability
Premature cable failure remains a significant challenge for handheld medical devices. Insufficient tensile strength, inadequate fatigue resistance, or internal conductor movement caused by repeated coiling can lead to early failure. These risks can often be mitigated through optimized conductor construction, added strength members, and data-driven testing during the prototyping phase.
Design for manufacturability (DFM) brings the cable supplier into the design process early, enabling collaboration on material selection, construction, and processing methods. This approach reduces downstream design changes and production issues. New England Wire Technologies specializes in challenging short-run designs, refining both product and process to meet each customer’s unique requirements.
DFM has become increasingly important as medical device manufacturers push toward smaller, more complex designs with higher data bandwidth and tighter tolerances. Sterilization compatibility must be validated under real-world packaging and bulk-processing conditions. DFM also includes developing customized test methods that replicate actual end-use environments, such as coiling and uncoiling, flex, torsion, combined flex/torsion, crush resistance, and accelerated aging.
Prototyping remains a critical stage in ensuring that the final cable design meets both performance and manufacturability goals. Early prototypes allow design teams to identify weaknesses, validate thin-wall constructions, and confirm tight electrical tolerances before full-scale production. Multiple prototype iterations may be required but investing in this phase yields long-term benefits in reliability, lead-time consistency, and product longevity.
Conclusion
Evaluating cable design options early—working closely with an experienced cable manufacturer—is the most effective way for medical device manufacturers to optimize mechanical and signal integrity while controlling lifecycle costs. A DFM-driven approach can significantly increase initial assembly yields and extend product life by years in some applications. Including the cable manufacturer early in the design process and investing in targeted prototyping and testing can generate substantial returns within the first year, followed by long-term cost savings driven by improved performance, durability, and customer satisfaction.
This article was contributed by Tom Paquet, Design Engineer.