Biomedical News

Penetration Testing Surgical Needles to ASTM F3014-14

Needle penetration force is a critical attribute used to assess a needle’s performance and usability for a given medical procedure. According to Eric Hinrichs, Principal Engineer at Ethicon and ASTM F04 member, both low and consistent needle penetration force is especially desired in the following situations:
  • The surgeon has limited space to maneuver the needle
  • The needle must pass through thick or hard tissue
  • The surgeon must maintain exact control over the needle to avoid vessels or delicate organs
Source: ASTM News

Most surgical needles are coated to enhance the needle’s durability and lubricity depending on the application. Often times needles with a coating that increases durability, decreases lubricity, and similarly, coatings that increase lubricity, decrease durability. Quantitative, comparative measurements of different needle coatings can help needle manufacturers understand how the needle may perform during use.

Despite ASTM F3014 being published in 2014, many needle manufacturers have been quantifying curved needle penetration forces for years. Unlike needles that are used in syringes, surgical suture needles are curved, allowing clinicians more flexibility to close wounds. For the past decade, Instron has worked closely with some of the leading curved needle manufacturers to develop a specialized curved needle test system.

Currently, ASTM F04 is working on a future standard to help guide needle manufacturers on how to select the most appropriate needle penetration medium. As part of the current standard, it is imperative that the needle is able to pass through the selected medium consistently over time to simulate the needle’s use in surgery.

In addition to optimizing needle lubricity and durability by better understanding needle penetration force, needle manufacturers must also optimize other material properties such as needle strength and rigidity. When optimizing needle strength, manufacturers are also trying to make the needle as slender as possible, and rigid enough to resist bending, but ductile enough to resist breaking. Similarly, ASTM F1874-98 (2011) outlines a standard method for bend testing of surgical needles to help quantify the yield bend moment of a needle and maximum bending of a needle. Testing to meet both standards are possible on Instron’s curved needle test system.

Quantifying the Frictional Forces of Guidewire and Catheters Taken in a Tortuous Path

The femoral artery is among the easiest and safest ways to gain access to the human heart. For example, when patients require a coronary angioplasty, a procedure used to open clogged or blocked heart arteries, access to the heart is obtained through the femoral artery. Generally, this procedure entails locating the femoral artery, insertion of an angiography needle, insertion of a guidewire through the angiography needle, removal of the angiography needle and insertion of a catheter along the wire. The guidewire is then used to guide the catheter to the blocked or clogged artery. The catheter will have a deflated balloon on its tip and a stent could be placed around the deflated balloon. The stent is navigated through the body to the area of the clogged or blocked artery where the balloon is inflated, expanding the stent. After the stent is deployed and the artery is opened, the balloon is deflated and the catheter and guidewire are pulled out of the body.

As one could imagine, the paths taken by the guidewire and catheter have many twists and turns, thus considered a tortuous path. Both catheters and guidewires can be coated and lubricated to reduce frictional forces along this tortuous path and subsequently reduce the force required to push and pull the catheters and guidewires through the body.

Working together with the Ghent University, Instron developed a simplified way to use a standard 5944 universal testing machine to simulate the action of a surgeon inserting the catheter into a patient. The purpose of this simulation is to quantify the frictional forces associated with the tortuous path.

The testing machine is mounted horizontally and uses a pneumatic grip to push the catheter into the tortuous path that simulates an artery. After the catheter is pushed through the path, the pneumatic grip releases the catheter, the crosshead returns to its original starting point, the pneumatic grip re-closes on the catheter, and the cycle continues. The catheter pushing mechanism can be sped up or slowed down to better simulate the actions of a surgeon.

University of Ghent     University of Ghent

The use of a universal testing system to quantify frictional forces during surgical procedures is not limited to testing guidewires and catheters. Other non-surgical applications that require the measurement of frictional forces include endoscopy, rhinoscopy, colonoscopy, and others.

Flexural Testing of Guidewire to Simulate Real-life Conditions

A wide range of industries need to perform mechanical tests in order to gain information about the properties of the materials they design, manufacture, or study. This could be anything from a component of an airplane to an orthopedic device in your body. Each material can differ enormously in both the conditions under which it can survive and how it might change throughout its lifecycle. It is essential for a testing machine to be able to reproduce real-life conditions to fully understand a material’s capacities and limitations. In addition, it is beneficial if one machine can be easily set up for materials with different shapes, sizes, and stiffness. Hence, versatility is key in material testing. 

In an example of testing a non-linear biomedical guidewire, a specimen was positioned on a 3-point bend fixture fitted to an ElectroPuls E1000 machine. The machine was set up with a 250N Dynacell load cell to run load peaks of 1N and 11N in compression at a frequency of 10Hz.

BioNews Dynamic Bend Test

Two special features of the WaveMatrix™ software were used to ensure accuracy and control throughout the duration of the test.
  1. The Automated Tuning Wizard uses a simple ramp waveform to measure the stiffness of the load string. This determines the gain settings to optimize the performance and control of the machine for the chosen specimen material and geometry. In just a few clicks, the machine is tuned and ready for testing. 
  2. Attaining load peaks is essential when it comes to testing non-linear specimens, but it can be a challenge. Another feature within our software called Advanced Amplitude Control ensures that the load peaks are met for each cycle and the desired load of tension is achieved. Without this, load peaks would likely drop below the desired load of tension as the test progresses. This feature ensures control even when the stiffness of the specimen changes.
The graph below shows the sinusoidal waveform of the non-linear guidewire specimen. The load peaks are consistently reached to high accuracy. This showcases the fact that the ElectroPuls can provide excellent control even whilst testing challenging materials to reproduce real-life conditions.

Non Linear Specimens Graph

Interview with Ghent University

Instron has partnered with Ghent University in Belgium for a number of years, providing materials testing equipment to meet the University’s wide array of testing requirements.

We had the pleasure of interviewing Dr. Matthieu De Beule, Assistant Professor at Ghent University. Dr. De Beule’s lab focuses on biofluid, tissue, and sold mechanics for medical applications.

“We really try to bring simulation technology from bench, meaning from device development, to bed, meaning clinical practice. One of the key aspects for doing this is model validation. Model validation is where our Instron equipment is of upmost importance.” ~ Dr. Matthieu De Beule
Read more about the full interview here.

Testing Catheters at Body Temperature—Does Temperature Really Matter?

Testing a material at body temperature compared to ambient temperature can have a significant effect on its mechanical properties. This is especially the case with polymeric materials.

To quantify the effect temperature has on polymeric medical tubing, we ran tensile tests on 40 extruded polyethylene catheters. 20 specimens were tested in near ambient conditions at 28°C (82.4°F) and the remaining 20 specimens were tested at body temperature or 37°C (98.6°F). A BioBox was used to accurately maintain these temperatures and the relative humidity was kept constant for this testing between 25 and 30%.

The results: Testing polyethylene catheters at 37°C produced a lower modulus, lower maximum force, and higher extension at break when compared to average results obtained from testing at 28°C.

Temperature Graph
Mean Result ±1 Standard Deviation 
  Modulus (MPA) 26.34  ±  0.45
19.5 ± 0.48
  Maximum Force (N) 16.62 ± 0.54
15.02 ± 0.42
  Extension at Break (mm) 525.12 ± 35.10
532.22 ± 32.98