Injection Molding and Plastics for Medical Devices

What to Consider When Injection Molding PEEK for Medical Devices

The injection molding process allows device manufacturers to quickly convert PEEK into complex component designs. This means injection molding is effective for an array of medical devices, whether they are used inside or outside the body. Many of those devices are used in cardiovascular, trauma fixation, dental, spinal and arthroscopic applications. PEEK can also be injection molded into components for surgical instrumentation and laboratory equipment.

There are several advantages to injection molding medical plastics like PEEK. These advantages include:

  1. High production volumes – The injection molding process only takes seconds, and most of that is dedicated to cooling the material. This quick conversion time means larger production runs are possible, and this is a major reason why medical plastics are replacing metal components in single-use instruments.In some cases, the device’s design is such that it can only be produced by adhering multiple molded components together. These components can be molded in tandem, though, so the process remains time-efficient.
  2. Cost efficiency – Injection molding is also very cost efficient, especially when used for larger production runs. The process requires the production of a mold, which makes up the bulk of initial costs, but the cost to produce each part is much lower compared to machining and other component production techniques. If the production run exceeds a few hundred components, then injection molding is usually the cost-effective choice.

Injection molding is especially useful for surgical instruments and equipment, as medical facilities are tasked with controlling hospital-acquired infections, or HAIs. According to the CDC, HAIs account for nearly 100,000 deaths every year, and 22 percent of them start at the surgical site. Single-use devices help hospitals control infections by switching in a new, sterile instrument every time a different patient is treated. The cost effectiveness of injection molding medical plastics makes this possible.

There are, however, challenges that must be solved when injection molding medical plastics, including PEEK. For example:

  1. Process safety – Medical plastics and the processes they are subjected to must be verified as safe and biocompatible. PEEK’s biocompatibility has been proven using the testing protocols outlines in ISO 10993. However, it’s not enough for a polymer converter to utilize medical grade plastic because the converter’s processes must also be verified.This is done through a number of standards, but one of the most relevant is ISO 13485, which is widely considered to be the standard for medical device manufacturers and the processes they use. The ISO 13485 standard, like the ISO 9001 standard it is based on, is focused on the manufacturer’s quality management system (QMS), but it adds important language on risk management, design controls, inspections and traceability. The converter’s QMS is a critical document, formalizing its procedures and policies for achieving its quality and safety goals. With a QMS, manufacturers can quickly and reliably modify their processes to improve output.ISO 13485, being specific to the medical industry, also contains standards on proper sterilization and device handling to prevent contamination. If adhesives or other materials are needed to produce the final component, these must also be accounted for.

    Among the most important parts of ISO 13485, though, is process validation. Process validation is needed to ensure the medical plastic remains safe even after manufacturing.  A validated process, then, is one that reliably produces a safe, quality component. This is a critical part of the ISO 13485 standard because it’s generally not possible to test a manufactured medical component without destroying it.

    Patient safety is paramount, so medical device manufacturers are expected to attain and maintain ISO 13485 certification.

  2. Process control – PEEK is a high-performance polymer that possesses excellent thermal resistance. Compared to other medical plastics, then, it must be subjected to extremely high temperatures to allow for proper processing. Depending on the size and shape of the injection molding barrel and the grade of PEEK being converted, temperatures inside the barrel may range between 650- and 750-degrees Fahrenheit. That’s a large range to cover, so it may take some time for a converter to find the temperature that works best for their production needs.Further, temperature control is also needed inside the mold, usually between 170 and 400 degrees Fahrenheit, and this includes the surface temperature of the mold. This elevated temperature prevents sudden cooling, which can result in the PEEK transitioning to an amorphous state and thereby affecting the physical properties of the component.Pressure control is also an important processing variable during the injection molding process that is essential for consistent, high quality components.  Advanced molding technology utilizing in mold cavity pressure transducers are an important capability to address consistent processing of high intricate components and devices.

    Experienced polymer converters are experts at controlling multiple processing conditions, which ensures consistent output quality and reduced waste.

  3. Equipment cleanliness – PEEK is processed at temperatures that cause other medical plastics to degrade, so the injection barrel must be meticulously cleaned to prevent this contamination from affecting the finished component. Any contamination could lead to hundreds of pounds of useless PEEK – which would be an expensive mistake. If that contamination makes it to the final product, it may compromise its properties and potentially be a safety concern.To prevent this, the injection equipment must be cleaned thoroughly before PEEK is injection molded. This usually requires personnel to remove the screw and be thorough with all cleaning processes. Further, any other surface that comes in contact with the PEEK, like hoppers and drying ovens, must also be kept clean to minimize the risk of contamination.

There are several advantages and challenges associated with injection molding of medical plastics like PEEK. An expert converter is familiar with all of them, so they can make the most of the process.

 

FAQ

Q. Is injection molding or machining better for medical plastic?

A. Injection molding offers significant cost and time efficiency benefits when used in large production runs. Machining is cost-effective for small production runs (usually a few hundred components or less) and offers superior tolerances.

Q. What certification is important for medical device manufacturers?

A. ISO 13485 is built on the ISO 9001 framework but adds industry-specific language for medical device manufacturers. ISO 13485 compliance can help a medical device manufacturer to be in compliance with FDA and European medical device quality standards.

Q. What advantages does PEEK bring to medical devices?

A. As a high performance polymer, PEEK possesses several advantages. It is biocompatible, radiolucent and has excellent material and mechanical properties. When implanted, it can provide a flexural modulus similar to the body’s cortical bone, which makes the material a frontline choice for spinal implants.