David Stirling, group chief executive officer, Zotefoams explains how thermoforming could offer medical device manufacturers the flexibility to design and produce a variety of custom thermoformed applications in a cost effective manner.
The medical device industry remains one of the world’s most heavily regulated sectors, with ever growing demands that require new, technologically advanced equipment and applications. Consequently, now more than ever, medical device manufacturers are relentlessly seeking innovative, cost effective and most importantly, quality controlled technologies and processes to remain competitive.
Typical manufacturing processes, such as injection or blow moulding, are being surpassed by alternative solutions that offer greater production benefits with lower costs. One process in particular that is attracting significant interest for medical devices is thermoforming.
Thermoforming is the process by which heat is applied to a thermoplastic material, which, along with the subsequent application of pressure or vacuum, enables three dimensional shapes to be produced from a flat sheet.
In vacuum forming, a sheet of thermoplastic material is clamped into a frame and shuttled into an oven. The hot sheet is then either stretched over the mould, also known as a male moulding tool, or inside the mould, otherwise known as a female moulding tool. It is then drawn by vacuum to a desired shape. Compression moulding on the other hand sees the material heated in an oven before being transferred to a press outfitted with a cold or near ambient temperature mould, the material then cools under pressure.
Thermoforming has become the production process of choice for many manufacturers due to its high quality finish that produces quality on a par with injection moulding, but with a faster turnaround time and lower tooling costs. It is compatible with a variety of materials, including polystyrene, polyvinyl chloride and polyethylene (PE), each offering unique properties for custom thermoformed solutions.
When selecting materials for thermoforming medical support applications, such as prosthetics, it is vital manufacturers consider the potential risks, particularly if the device will be in direct contact with the human body, and evaluate how the manufacturing method may, or may not, alter the components of a material and ensure they comply with rigorous industry requirements.
Zotefoams, a British manufacturer of closed-cell PE, polyvinylidene difluoride (PVDF) and nylon (PA6) foams for demanding industrial applications, has increasingly recognised the properties of its polyolefin foam range that can provide a more advanced, sophisticated element to thermoforming. Zotefoams claims its polyolefin product, Plastazote, is the most cited thermoplastic foam material within medical literature.
Most foams today are chemically blown, with the plastic heated and mixed with a blowing agent to produce expansion. This process is more difficult to control reliably than physical expansion and can result in a product with variable densities and different properties in different directions. The chemical blowing agent is then released over time, producing odour and potential fogging.
However, the notable mechanical characteristics of Zotefoams’ PE-based foam ultimately stems from Zotefoams’ unique manufacturing technology that uses only pure nitrogen to expand foams. This three stage, environmentally friendly process ensures the production of pure, chemically inert foams, with uniform cell structure and regular cell walls due to the free environment in which they are expanded in. The process takes place without the use of a mould and very little in built stress, and with little tendency to distort during conversion; both of these features make the foam easy to process and fabricate.
Compared with other thermoformable materials, these PE products offer excellent chemical resistance and meet recognised industry standard, ISO 10993. Being cross-linked, PE can maintain its structure even at temperatures above its softening point, enabling thermoforming techniques to be used with a combination of heat and pressure and warranting the production of more complex shapes for a wide variety of medical healthcare applications, including podiatric, prosthetics and orthotics. It can also be used as a form of protection for diagnostic medical devices as it allows optimum impact resistance for sensitive or fragile parts whilst maintaining purity if the packaging is cut, as no shedding occurs.
Together with the right material, thermoforming can offer medical device manufacturers a cost effective solution with the flexibility to design and produce a variety of custom thermoformed applications. From rigid plastics to soft touch foams, this cutting edge process allows manufacturers to transform advanced, raw materials into highly protective, industry compliant medical devices.