How Flex-Life Testing Helps Medical Cable Assemblies Maintain Performance After Repeated Bending

Medical devices are put into use in clinical practice and repeatedly exercised in a variety of different ways. Robotic surgical arms undergo thousands of bends and twists, while ultrasound probes are repeatedly re-angled during lengthy procedures and endoscopes navigate tortuous anatomical pathways. If not properly managed, these mechanical stresses can degrade electrical performance over time, potentially leading to equipment failure, signal artifacts, and premature cable replacement. At Hotten, we take every measure to ensure that our medical cable assemblies deliver reliable, long-term performance in clinical environments – this is why we use a full flex-life test as an absolute design verification test. This article examines four key aspects of flex-life testing that help ensure reliable performance under real-world clinical conditions.

Simulating Real-World Clinical Motion Profiles

This simple bend test does not replicate the multi-axis motion required in healthcare environments and typically involves repeated bending around a fixed mandrel. Hotten's flex-life testing procedures are customised to simulate the use of each type of device. We have developed test rigs for our robotic wire harnesses that simulate the compound motions—including torsion, bending, and axial translation—experienced at the articulation points of surgical robotic arms. In endoscopic systems, gimbal mechanisms help stabilize the camera cable while allowing the camera to rotate through 360° around a pulley. The tests performed on these types of cables are known as "roll-on" cable flex tests. We conduct flex cycles to the required qualification level. For example, when qualifying a cable for 50,000 cycles, we compare the test parameters with data from actual clinical use.This approach provides a realistic representation of clinical use and helps verify long-term reliability in the field.

Real-Time Electrical Performance Monitoring During Flexing

A cable may withstand 1,000,000 mechanical cycles without visible mechanical damage while still experiencing degradation in electrical performance (such as an increase in insertion loss, drift in impedance or crosstalk) without any mechanical damage. Electrical performance can be evaluated at defined intervals during the flex-life test to identify changes in cable performance. At the same time, we measure the DC resistance, capacitance, characteristic impedance (TDR) and high-frequency attenuation within the required frequency range of a test sample bent several times. Special monitoring of phase stability and skew between differential pairs is performed for our high frequency transmitting cables and harnesses (ICE – intracardiac echo; IVUS – intravascular ultrasound) This real-time data enables us to identify the onset of performance degradation rather than detecting failure only after it occurs,and to set end-of-life thresholds conservatively to help ensure that the signal integrity of the device is maintained during its service life.

Multi environment flex conditioning – temperature & sterilizations

In clinical environments, cables are rarely flexed under controlled room-temperature conditions. Operating rooms may be cooled for cardiac surgery or warmed for long oncological surgeries and cables may also be flexed immediately after high-temperature autoclave sterilization or chemical disinfection, when residual moisture may still be present. At Hotten, flex-life testing can be conducted across a range of temperatures (0°C – 60°C) and humidity levels in our environmental chambers with controlled conditions. Only cable designs qualified to withstand these combined mechanical and environmental stresses are offered for clinical applications, minimizing failure in the field under these combination environmental stresses.

Failure Mode Effects Analysis (FMEA); Continuous Design Improvement

Flex-life testing is not simply a pass-or-fail verification method; it is also a tool for identifying design improvements. If a test sample fails due to conductor fracture, shield damage, or insulation abrasion, our engineering team conducts a detailed failure analysis of the test sample, using microscopy, cross-sectional analysis, and impedance profiling techniques. If, for example, a cable breaks at the end of the strain relief at the connector overmold, we change the geometry of the strain relief and test once again. For example, a dental sensing cable may be replaced if it exhibits increased attenuation after 30,000 cycles, or the conductor material or construction may be reviewed to improve flexibility and fatigue resistance. Through this continuous improvement process, Hotten develops more than 300 new cable specifications each year and incorporates the resulting knowledge into future designs. All changes will undergo additional flex-life testing and each design iteration further improves product performance and reliability.

Conclusion

Ultimately, flex-life testing is more than a quality assurance tool; it helps bridge the gap between laboratory testing and real-world clinical use. Whether it's for use in an ultrasound probe or a robotic harness, our medical cable assemblies at Hotten are designed to maintain reliable performance through the repeated bends, twists, and tensile stresses encountered in daily hospital use. Supported by a 10,000 m² facility, more than 40 production units, and annual production exceeding 144 million meters, Hotten translates flex-life testing data into durable, reliable cable solutions, so that healthcare providers can focus on their patients and not the failure of the cable.