Everyone’s heard they should “think big” in the plastic injection molding industry. While that may be true when talking about profit or volume, that attitude doesn’t really apply to plastic injected-molded medical devices. The operative term in this specialized niche is “think small”, as in physical size of the devices themselves. Whether worn outside the body, or implanted within, size matters — as in small size.
Think about it: these devices have to be light enough and compact enough not to weigh down or crowd out the area of the body they’re associated with.
According to a recent report, the global market for plastic injection molded medical devices is expected to reach $42 billion by 2026, up from $31.6 billion in 2020.
Plastic medical mask
Four types of injection molding utilized in medical devices
1. Thin wall molding
“Thin Wall Molding” simply means the process by which medical devices can be manufactured to ensure light-weight — and light-weight translates to patient comfort. Generally speaking, thin wall molding produces walls thinner than 1mm.
This technique doesn’t require any special plastic injection molding equipment — conventional plastic injection molding machinery will do — but does require certain resins, such as LCP, polypropylene, nylon and silicone. These materials allow walls to retain their structural integrity even though they are much thinner than normal.
Thin walls are often found in micro-surgical tools and wearable devices, but are also common in invasive equipment like endoscopes and catheter ablation tools.
2. Gas-assisted injection molding
When parts are produced with conventional plastic injection molding techniques, there’s a risk that “sink marks” can result, making the finished product look marred and potentially structurally weaker. Sink marks occur when thick areas of a mold cool more slowly than thin areas after the resin is injected. Without enough pressure to pack these thicker areas tightly against the walls, uneven distribution produces a “sunken” appearance.
Gas-assisted injection molding can remedy this problem by pumping gas (usually nitrogen) through channels built into the mold.
3. 3D printing
While 3D printing method can sometimes be utilized to print actual injection molds, it’s most often used to create prototypes to test a plastic injection mold design before it goes into production.
However, for certain medical device parts, metal isn’t necessary to create a mold. In that case, 3D printing can be used to create molds out of plastic instead.
4. Liquid silicone injection molding
While surface-born staph infections are the bane of hospitals everywhere, some medical devices are particularly vulnerable. Tubes, respiratory masks and gloves, for example, require hygienic levels far above other plastic medical devices.
Liquid silicone injection molding is ideal for devices like these because of the chemical resistance of this rubber-like substance. Also required is a clean production room that allows no ambient air, with its attendant dust and moisture, to make contact with the mold or the product itself as it cools.
Silicone is also biologically inert, meaning it doesn’t interact with biological tissue and can be implanted safely in the body.
And there you have it: the “Big Four” plastic injection molding methods that are healthy for both patients and the profits of plastic medical device manufacturers.
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