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CES Medical Polymer Selector - Case Study

Selection of plastic for medical forceps

This case study demonstrates how the CES Medical Polymer Selector, drawing on the Medical Polymer data module, could be used to establish the best material from which to make medical forceps.

The material must be USP Class VI or ISO 10993 certified, steam sterilizable, and adequately impact resistant. When applied to the medical plastics data, these criteria narrow the choice to 44 out of 628 materials.

With these constraints satisfied, the material needs to be both strong and stiff in bending, for the lowest cost and lowest volume. We can investigate these objectives through the use of a materials selection chart:

This chart, created in the CES Selector software, shows the trade-off between lowest cost and lowest volume of material. It allowed the following analysis:

• Our initial thought was to use unfilled PEEK (PEEK Classix). The chart shows PEEK is a valid option, but it is neither low cost nor low volume, so not an optimal choice
  
  
• Unfilled polypropylene copolymer is the cheapest option, but the forceps handles will need to be bulky to have adequate stiffness and strength
  
  
• The forceps could be made just one-tenth of the bulk with PEEK carbon fiber composite (e.g. Endolign). However, this material is much harder to process than other options
  
  
• Carbon fiber filled LCP (Vectra) and glass filled PPS (Fortron) offer 0.2 and 0.3 of the volume of polypropylene respectively
  
  
• An intermediate choice is PPO/PS alloy (medical grade Noryl) with about twice the bulk of LCP or PPS, but a third of the material cost

Post-script: Surgical Innovations Group chose Ticona's Fortron (40% glass filled PPS) for their forceps design. LCP-based materials gave too poor a surface finish. (source: Composites Technology, Dec 2003)