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Engineering Plastics Deliver Cost/Performance Advantages as Metal-Replacement Option

In terms of logistics, radiofrequency identification (RFID) technology for plastic parts is under evaluation and is already used in some segments of the healthcare industry. Plastics in general will allow RFID technology to function perfectly, while aluminum will create strong interference, making its use difficult. RFID tracking combined with high-performance plastics is already used successfully in other industries such as aircraft catering trolleys. For RFID applications, cost-effective high-performance plastics with strong mechanical properties are being targeted for multiple-use applications as a replacement for aluminum.

Understanding Plastic Design and Material Selection

Resin suppliers continue to develop new materials with improved mechanical properties to facilitate the replacement of metal in healthcare applications. However, perceptions play a key role in metal-to-plastics conversion, since most designers still tend to think in terms of direct part-to-part replacement. As a result, development of plastic parts can require several cycles of “make it and break it” which add both cost and length to the overall development time. To shorten that cycle, designers need to understand material properties and redesign accordingly. High-performance plastics don’t have the same mechanical properties as metals, so part design will need to be adapted to plastics, paying special attention to part thickness, equivalent stiffness, use of ribs and radius. Designers must also manage tolerances and make use of computer-aided engineering (CAE).

Material selection is critical in order to avoid under- or over-specifying the proper material requirements. The application will fail if under-specified, while costs will run too high if the product is over-specified. When considering thermoplastics over metal, several criteria must be evaluated, including:

  • biocompatibility
  • primary function of the instrument or device
  • product service life
  • size of production run

The first step in material selection for healthcare applications is assessing biocompatibility requirements and determining whether the part will be in contact with body fluids and for how long. Thebiocompatibility requirementswill define the first group of materials to evaluate for the metal to plastic conversion. Every country has its own legislation, but a standardized test method, ISO 10993, is followed by the healthcare industry in the U.S. and Europe.

Another key factor in material selection is determining the primary function of the instrument or device. For example, devices or instruments subjected to considerable mechanical forces such as traction, compression and shear will typically need to be molded from highly reinforced (glass or carbon fiber filled) plastics such as PEEK. Meanwhile, applications that require greater dimensional stability and tighter tolerances will lean more towards unreinforced engineering plastics such as PPSU.

Understanding the device’s service life and its single-use or reusable status will again narrow the potential material candidates. A key factor to consider will be the sterilization method and how it will affect material properties, and thus the device performance. This is important because a material often times is selected for one specific property, and sterilization can often affect that performance attribute, particularly in reusable applications. An often used method is steam sterilization, which exposes devices to steam at 134°C for approximately 18 minutes. This amount of heat in a steam environment is harmful to many plastics, particularly after repeated exposures. But high-performance plastics such as PPSU, PAEK and PEEK will withstand repeated sterilizations without adversely affecting performance. Competitive materials such as polyamides (nylons) suffer a strong decrease in mechanical performance in just a few sterilizations and will not be recommended for use in instruments or devices that require repeated steam sterilization. Another important consideration is that these high-performance plastics require resistance to highly aggressive cleaning and disinfecting agents that are applied to the instruments or devices before sterilization.