From the September 2017 issue of HealthCare Business News magazine
Compared to other material testing that can take weeks or months to perform, the four-step test is relatively simple and quick and takes just 24 hours to complete. Developed to ensure replicable, reliable and accurate results, the testing protocol is based on modified ASTM standards. Steps one through three are based on modified ASTM D543 standards, and the fourth step is based on modified ASTM D4812 standards. The test is designed to mimic failures from typical usage conditions to better understand why commonly used plastics fail. It does not require specialized equipment other than what is typically found in most manufacturing testing labs:
• Step 1: Select the appropriate jig and choose a strain level that most appropriately reflects environmental stress cracking.
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Step 1: Select the appropriate jig
• Step 2: Load flex bars onto the jig, and be sure to load control samples.
Step 2: Load flex bars onto the jig
• Step 3: Apply chemicals to flex bars using presoaked pieces of cotton. Enclose the entire sample jig in a plastic bag to prevent evaporation, and leave it at room temperature for 24 hours.
Step 3: Apply chemicals to the flex bars
• Step 4: Perform reverse side impact test.
Step 4: Perform reverse side impact test
Step four’s reverse side impact test is the true differentiating step. A material may or may not exhibit visually apparent changes after the first three steps. However, varying degrees of cracking and crazing become noticeable and significant after the reverse side impact test is performed. Simply put, step four offers a more accurate assessment of how a material will hold up in real-world settings. For better accuracy in interpreting results, testers should document the impact strength of exposed and control samples to calculate the percentage of reverse side impact strength retention. A higher retention means better reliability after exposure.
Testing helps select the best materials
As awareness of surface compatibility issues increases, health care facilities are likely to raise concerns to device manufacturers and become more vocal about their material requirements. These specifications may well find their way into equipment RFQs and RFIs. Protocols like the four-step test can offer manufacturers a valuable tool that can be applied to materials they are considering in equipment design. It may also assist in making retrofits to current production lines.
Procedures like the four-step test make it evident that, especially in light of new disinfectant protocols to reduce HAIs, certain plastics are better suited for many medical device applications. By analyzing test results, manufacturers can make more confident choices in material selection for device housings.
About the authors: Yubiao Liu, Ph.D., is a medical application development scientist at Eastman Chemical Company. Danielle Augustin-Glenn, Ph.D., is a research scientist at Clorox Healthcare.
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