Medical Device Torsion Testing

In addition to axial and multi-modal loading in vivo, medical devices often experience torsion and bending during use. For some orthopedic devices such as bone screws, the torsional loading is imposed during the implantation, and the device needs to resist failure during the applied torsion. In some fixation devices, the head is designed to shear off at a predetermined torque so that it does not remain within the implantation site. For intravascular applications, the device often experiences torsional loading post implantation.

例如，外围指示中使用的支架移植物可以由于正常的肢体运动而体验扭转。用于主动脉修复的设备有时可能由于躯干扭曲而经历扭转装载。多年来，元素已经表现了数百个扭转测试应用程序，并为这些应用程序开发了一个测试夹具和技术的工具箱。

元件has many test systems that were designed to perform torsional testing. Most of our BOSE/TA ELF3300s, Instron ElectroPuls E3000s, and MTS systems are equipped with torsion stages to provide rotational motion to single or multiple specimens. This rotational motion can be used independently or in concert with the axial systems for multi-modal fatigue.

Specifications for torsional tests typically include the rate of rotation (deg/s), rotational frequency (Hz), peak torque (N*m), or peak rotation (deg). This testing can be used for fatigue, validation and functional testing, destructive testing, and material characterization. Results typically take the form of cycles at fractures, max rotation at fracture, max torque at fracture, or a simple torque vs. angular displacement curve.

We can develop and implement torsion testing fixtures for a variety of devices, including:

• 医用骨螺钉插入/移除和断裂扭矩表征
• Spinal disc implant fatigue testing
• Torsional modulus characterization of fine l wire
• Combined cantilevered and pure bend testing of peripheral stents
• 折射率和仪表电缆的纯弯曲
• Rotational fracture testing of dental picks
• Validation of surgical tools
• SFA gait testing (tension/bending/torsion)

Bone Screw Testing

ASTM F543-13 is a test method used to measure the torsional yield strength, maximum torque and breaking angle of bone screws under standard conditions. Element carried out ASTM F543-13 and ISO 6475:1989 compliant Fiducial Bone Screw insertion and removal torque testing using the rotational stage of a BOSE/TA ELF3300AT.

使用具有可调节力缸的一对线性轴承用于对样品施加光滑，恒定的轴向压力，而旋转级提供了所需的角度位移（驱动扭矩）以将螺钉嵌入模拟骨材料块中。以旋转角与扭矩和轴向载荷的形式收集数据。

元件also performed the accompanying ultimate torsional strength testing, holding the screw stationary and applying a measured angular displacement to the driving head until fracture occurred.

Surgical Tool Testing

元件has tested a wide variety of surgical tools and accessories in addition to the actual implants. Surgical tools need to be able to withstand rotational forces during use and are often tested to simulated forces they will experience during routine use in the operating room to observe any fracture, disassembly or damage during testing.

The torque-to-fracture testing described was performed on an Instron ElectroPuls E3000 tester with a modular torsion stage and torque cell. Data was provided in the form of a continuous torque vs. angle plot and a maximum torque value. MDT also performed the accompanying axial force, multiple orientation 3-point bend, and suture pull tests for this device series. Tests were performed on the entire device as well as on device components.

Peripheral Stent Testing

组合的悬臂/弯曲测试（WAG BEND）测试使用BOSE / TA ELF3300AT的旋转级进行。样品中的恒定生理温度和压力通过加热的平均压力罐和静止歧管的盐水再循环来维持，该固定歧管为弯曲提供“基部”。通过使用架空高速摄像机和尺寸分析软件验证弯曲半径和运动。各种样品直径，长度和弯曲角度/半径可容纳在最多N = 12个样品的运行中。

SFA Testing

元件has carried out many SFA gait motion tests on a variety of peripheral devices in compliance with ASTM 2942-13. The SFA tester mounted on a BOSE/TA ELF3300AT uses both the axial and rotational actuators to apply cyclical tension, torsion, and local bending to the samples over test runs of many millions of cycles. Physiological pressure and temperature in the samples are maintained by a mean-pressure heated saline recirculation system.

Conclusion

总的说来,importance of torsion testing for many different types of medical devices is paramount. Element's torsion test instruments coupled with several decades of torsion testing expertise have resulted in the design of a variety of torsion fixtures and test protocols for many challenging applications.

Contact us todayto discuss how torsion testing may complement your medical device mechanical testing and regulatory submission data.