An expansive range of materials are available with injection moulding, making it easier to produce medical equipment that adheres to the strict biosafety and chemical stability criteria of the medical sector. Techniques such as thin wall moulding and gas-assisted injection moulding enable the production of both practical and aesthetically appealing parts.

Jack Rulander is a senior R&D engineer at Protolabs. He works on introducing new technologies to the company's digital manufacturing process for injection molding. Rulander has nearly 20 years of experience in the plastics engineering industry.

During material shortages, substitution options are available based on desired material properties and the intended function of produced parts. (An extensive list is available on the Protolabs website.) Each lesser-known plastic could work as a replacement for commonly used plastics such as acrylonitrile butadiene styrene (ABS), polycarbonate (PC), and polypropylene (PP).

Known by its trade name Xarec, the plastic alternative is the first syndiotactic polystyrene (SPS) resin. The innovative structure allows for a variety of highly sought after characteristics. SPS is resistant to hydrolysis; chemically resistant to corrosion by various acids and alkalis, including automobile oil and antifreeze; and also resistant to heat. It also features a low specific gravity, reducing the weight and cost of parts. SPS is a fit for electronic components for various hybrid electric vehicles, as well as an essential component for everyday home appliances. Furthermore, it is viewed as a sound environmental choice.

PPS features a very high melting point and poor solubility, requiring special processing to manufacture parts out of the resin. But in the end, PPS has outstanding heat and chemical resistance, good dimensional stability, and high tensile and structural strength due to its aromatic ring structure. Parts made with PPS also feature flame-retardant capabilities and exceptional electrical properties, making it a widely used polythioether. Common applications include electrical and electronic parts, and mechanical parts in automobiles and precision engineering.

The indelible imprint of injection moulding in medical manufacturing underscores its pivotal role in delivering efficient, high-quality, and cost-effective solutions to the industry. As the medical field continues to evolve, the synergy between injection moulding and emerging technologies like 3D printing is poised to drive innovation further, ensuring the continual enhancement of patient care and medical advancements.

We know it’s frustrating when a material supply is low — especially when you’ve designed molded parts for a specific plastic — but hopefully these alternatives can help you bridge your part design and manufacturing past the material gap.

Perhaps intriguingly is the fact that 3D printing and injection moulding are not exclusive of one another. Injection moulding is frequently preceded by 3D printing, which assists with prototyping and even helps create moulds for the injection moulding process.

This resin is an amorphous, transparent, and pale-amber high-performance thermoplastic that exhibits good melt stability, which permits fabrication by conventional thermoplastic processing methods. PSU also has outstanding mechanical, electrical, and thermophysical properties, as well as excellent chemical and hydrolytic stability. The characteristics come together to make the resin a tremendous fit for components that are exposed to steam and hot water, like plumbing components, sterilizable plastic parts for medical devices, and membranes for water treatment, gas separation, and more.

Semi-aromatic polyamides like PPA are often a cost-effective alternative to the more expensive, fully aromatic aramids. Featuring a combination of aromatic and aliphatic groups, PPA greatly reduces moisture absorption, which results in few dimensional changes and more stable properties. The material is a great fit for products that must withstand prolonged exposure to harsher chemicals and higher temperatures. With that, common applications are motor parts, coolant pumps, bearing pads, resonators, and more.

The disruptions have combined to create a significant material shortage, increasing prices or downright halting the production of plastic-based components. Fortunately, the tremendous innovation we have seen in material development provides options for product developers willing to explore alternatives for commonly used resins.

PPO touts excellent tensile and impact strength while showing resistance to many chemicals, including steam and water; however, it is sensitive to stress cracking. PPO also poses a problem with melt processing because of its high glass-transition temperature. With that, it is often blended with high-impact polystyrene (HIPS) to be used in applications across the automotive and electronics industry, including pump parts, fan impellors, catalyst supports, and more.

Liquid silicone injection moulding: This produces pliable, durable parts in high volume, and is used in fabricating tubes and respiratory masks requiring high levels of hygiene and chemical resistance.

A plastic resin shortage hasn't slowed down operations at Protolabs’ injection molding facility in Rosemount, MN. Image courtesy Protolabs.

Since the need for devices and components in the medical sector is always increasing, injection moulding stands out for its effectiveness and capacity to handle large-scale orders. The method is best suited for high-volume production, making it the preferred method for mass-producing medical components. That said, even though 3D printing is hailed for having cheaper initial costs in small-scale production, its cost advantage diminishes as production volume rises.

Well-suited for products with straightforward shapes, injection moulding delivers unrivalled precision and finish quality. For medical applications such as moving machine parts or implantable devices, the procedure gives a vital smoother finish.

Supply-chain disruptions have left no part of our industry untouched over the last year. While there is light at the end of the tunnel in our fight against COVID-19, it is apparent the fallout will continue for some time. The impact is only heightened with the recent Suez Canal blockage and a shipping container shortage.

Gas-assisted injection moulding: In certain medical device applications, gas-assist moulding can provide solutions that conventional injection moulding can’t. The process consists of injecting a pressurised gas into the mould cavity after the initial plastic injection, expelling the molten plastic and forming hollow areas within the final product. It is suited to the manufacturing of complex parts without visual blemishes, for instance, tube- or rod-shaped parts which typically include handles and foot pedals, as well as large, cover-shaped structural parts e.g. side panels and covers for medical devices.

Luke Smoothy, founder and director, Get It Made, delves into why injection moulding still holds the sceptre in the medical industry and highlights the key benefits it brings.

Thin wall moulding: A specialised form of conventional injection moulding that focuses on the mass production of ultra-thin (less than 1mm) and light plastic parts to make material cost savings. This is used to create portable medical devices enabling clinicians and patients to transport and operate them more easily - such as wearable devices, micro surgical tools, and invasive equipment like catheter ablation tools and endoscopes.

In the realm of medical device manufacturing, the tussle between traditional injection moulding and modern 3D printing technologies continues. However, injection moulding has held its ground firmly, especially when high-volume production, cost-effectiveness, and precision are all paramount.