When a new material is rolled out for use in medical device applications, at least two questions are posed from the get-go: Can the material withstand various sterilization techniques? And can it be molded or extruded? Ensinger (Washington, PA) was tasked with answering the second question when Sabic Innovative Plastics (Pittsfield, MA) approached it to determine the extrudability of its Ultem HU1004 material, a polyetherimide (PEI) resin used to manufacture a variety of medical devices and components.

In the following conversation, Bruce Dickinson, marketing manager at Ensinger, discusses the advantages of using Ultem HU1004 and details the process by which the material's extrudability was tested and confirmed.

MPMN: Please say a few words about the properties of Ultem HU1004. What kind of material is it and how does it differ from other materials used in medical device components?

Dickinson: Ultem HU1004 belongs to a group of materials that generally exhibit good temperature and chemical resistance. But what's unique about it is that it was developed specifically for Sterrad sterilization applications, a sterilization technique that uses hydrogen peroxide vapor and a gas plasma. A relatively new form of sterilization, Sterrad allows medical device manufacturers to sterilize their products without the introduction of high heat and moisture levels. Thus, medical devices that incorporate such components as electronics can survive this sterilization process.

However, the drawback for plastics that have historically been used in the medical device industry, including polyphenylene sulfide (PPS) or polyphenolsulfone (PPSU), is that colors added to the materials degrade after repeated Sterrad cycles. Ultem HU1004, in contrast, retains its color much better than other medical device plastics. That's its main selling point.

MPMN: Describe the extrusion trials. What were you trying to demonstrate?

Dickinson: When Ensinger's resin suppliers bring new materials to us, they are familiar with the target end-use market. In many cases, their ultimate objective is to sell their materials to injection molders. Thus, many of the properties exhibited by a product such as Ultem HU1004 will be of interest to companies performing injection molding. However, before a product becomes an injection-molded part, it is often machined from a stock shape. To ensure that the resin can be extruded into a stock shape while maintaining all of its required physical properties, we subject it to a series of extrusion trials.

In our trials, we were trying to establish that the material can be extruded because that's part of the development process that many companies undergo when they develop new medical devices. This process starts with small quantities of stock-shape material. While this stage may be followed by an injection-molding stage using huge quantities of the material, this frequently does not happen. Moreover, if a material will be used to produce tens of thousands rather than hundreds of thousands of parts, it may remain as an extrudable stock-shape item.

MPMN: What steps were involved in your extrusion trials?

Dickinson: In such cases, we typically run a test extrusion process. This process involves extruding the material into 2-in.-diam rod, which is easier to process than plate. Then, if this process is successful, we extrude the material into plate and examine it to ensure that it is free of such flaws as inclusions or bubbles. That's the procedure we followed in this case.

MPMN: Given the results of the trials, how is the material being used in medical device applications?

Dickinson: The results of the extrusion trials showed that we could potentially carry this grade of Ultem. However, because it is relatively new, we are not prepared to keep it in stock just yet. Meanwhile, we are testing the material in conjunction with some medical device OEMs, and if they agree with us that the material is beneficial, we will begin to keep it in stock based on their requirements. Potential applications could include handles for surgical drills or other components that are manufactured from machined parts. The bottom line is, such components must be able to withstand sterilization.

Bob Michaels is senior technical editor at UBM Canon.

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