Carl Mendonça, Ultrapolymers, outlines polymer choice considerations for successful plastics device components.
Numerous studies have pointed to growth in ageing populations coupled with greater demand for healthcare in the coming decades. As solutions to deal with increasing demand for treatment – and medical devices - are sought, the challenges for device designers are plentiful. One of these challenges is to use materials that meet increasing legislative demands, are cost-effective, user-friendly and also meet increasing environmental demands.
When it comes to polymer choice for device components, compliance with evolving regulatory requirements for risk management needs to be considered alongside competitive and innovative drivers. New therapies and treatment advances mean therapy delivery technology has to evolve to match. Polymer technology similarly evolves with new grade introductions with improved properties such as lubrication, antimicrobial content, glass/metal replacement capabilities etc.
The Medical Device Regulation (MDR) and In-Vitro Diagnostics Regulation (IVDR) bring a higher degree of scrutiny as greater traceability and risk management become necessary. The polymer (combination) chosen should meet or exceed the renewed legal requirements. Intensified communication between all stakeholders to clearly set out performance expectations of the chosen material(s) becomes key. Disclosure of information about formulation consistency, consistency of supply, change management or notification of change becomes increasingly valuable or even a prerequisite for correct material selection. These discussions will highlight possibilities, limitations and risk management options for all stakeholders. In light of the above, a polymer should vary as little as possible – careful consideration should be given to the controls in place at each stage to minimise variance – communication again being key.
Discussions at the very start of a new project design (or even a modification of an existing product) on suitable polymer choice should consider all requirements of the polymer performance and compare these to available polymer types and grades to arrive at a shortlist for further consideration. Discussion with technical support advisors from the polymer industry will greatly aid this process. A study by RAPRA showed that just under 50% of product failures investigated could be attributed to the material selection process. Hence the earlier the stage at which materials are considered (preferably the product design stage), the better the chance of an optimal choice.
Material choice consideration should include all parties from designer to material supplier, toolmaker, moulder and end user. This establishes ‘must have’ and ‘nice to have’ lists of material properties. The ‘must have’ list should be challenged to ensure that the designer/end user is convinced of the absolute necessity. Factors to consider include physical requirements, colour, sustainability, processing requirements, environment of use, specifications, approvals, assembly or secondary operations, etc. Responses will determine if an amorphous or semi-crystalline material is more suitable. Amorphous materials tend to have more constant physical properties, better dimensional stability over temperature variation and generally better transparency.
Semi-crystalline materials tend to have better chemical resistance, higher stiffness and wear resistance, as well as other properties. If the part is to be coloured, then how this is achieved needs careful consideration to ensure consistency.
Physical requirement considerations include final use conditions – single impact or repeated, operating temperature, stiffness requirements etc. Will a standard grade meet the requirements or will a modified grade be required? If modified, will the material meet regulatory requirements? Is the part under load over an extended period – does creep performance need to be considered?
Chemical resistance can really only be tested on the final design and with the relevant chemicals. Time, temperature and concentration will determine performance as well as conditions of test – if the part is under stress (load) or strain (extension), chemical resistance can be affected. Cleaning solutions also need to be considered for potential effect on material performance. Although chemical resistance tables and information are available, it is always best to test using real conditions, as leachable or extractable elements could also affect performance in the final application.
This article aims to provide a starting point for rounded discussions about product design and application requirements such that all stakeholders contribute to the decision-making process on material selection coupled with part design. All parties should evaluate the importance of influencing factors from their own aspect as well as others. Only then can a consensus be sought to progress towards a successful outcome.