The Intricacies of Injection Molding in Medical Devices

The injection molding manufacturing process enables the mass production of components. By injecting molten substances into a mold (or “mould” in the United States), it operates. As a mass production method, it is frequently employed to create thousands of identical products. Injection molding is utilized with thermoplastic and thermosetting polymers more frequently than with metals, glasses, elastomers, and confections.

In this blog, we will take a look at the basics of the injection molding process and its usage in manufacturing medical devices. First off, let’s have a look at how injection molding actually works.            

How does Injection Molding Work?

First Stage – Fabricating the Mould

The initial phase of injection molding involves the fabrication of the mold. The majority of molds are precision machined from metal, typically aluminum or steel, to match the specifications of the product they will manufacture.

Second Stage – Conforming the Shape of Mold

After the mold-maker has fabricated the mold, the component material is introduced into a heated cylinder and agitated through a helical-shaped screw. The material in the barrel is melted by heating bands, and the molten metal or plastic is then poured into the cavity of the mold, where it cools and solidifies to conform to the shape of the mold.

Reducing Cooling Time

By utilizing cooling lines circulating water or oil from an external temperature controller, the chilling time can be decreased. Mold tools are affixed to plate molds (also known as “platens”). When the material has solidified, the plate molds detach, allowing ejector pins to remove the component from the mold.

Third Stage – Combining Separate Materials

A two-shot mold is a form of injection molding that permits the combination of distinct materials in a single component. By employing this methodology, one can soften plastic products with a velvety feel, add colors, or create items boasting distinct performance attributes.

Types of Injection Molding:

There are different varieties of injection molding, such as:

  • Gas-assisted injection molding,
    • Uses nitrogen gas injected into the mold after partial solidification to create hollow sections or reduce material use in thick-walled parts.
  • Micro injection molding,
    • Produces small and intricate parts with high precision, ideal for applications in electronics and medical devices.
  • Reaction injection molding,
    • Involves the reaction of two liquid components to create a polyurethane or polyurea part, commonly used for automotive parts.
  • Die casting,
    • Utilizes metal molds to produce intricate, high-integrity metal components with high precision.
  • Cube molding,
    • Allows for multiple molds on each face of a cube, increasing production efficiency.
  • Thin-walled injection molding,
    • Ideal for producing lightweight parts with thin walls while maintaining structural integrity.
  • Liquid silicone rubber injection molding, etc.
    • Uses liquid silicone rubber as the material, suitable for producing flexible and heat-resistant parts.

What Materials are Normally Used in Injection Molding?

The commonest materials used in injection molding are thermosetting polymers and thermoplastics. However, some other materials are also used, such as elastomers, glass, metals, and confections, etc.

Common Plastics Used in Injection Molding

Some of the commonly used plastics in injection molding are:

  1. Polycarbonate:

This impact-resistant, durable plastic exhibits minimal shrinkage and excellent dimensional stability. It is an optically clear transparent plastic offered in various grades, can deliver a superior aesthetic finish and exhibiting commendable resistance to heat.

  • Polybutylene Terephthalate (PBT):

PBT’s favorable electrical characteristics render it well-suited for utilization in power components and automotive applications. Depending on the amount of glass fill, the strength can range from moderate to high; unfilled varieties are rigid and flexible. In addition to displaying fuels, oils, lipids, and numerous solvents, PBT is incapable of absorbing flavors.

  • Aliphatic Polyamides (PPA):

A wide variety of PPAs (or nylons) exist, each possessing distinct advantages. In broad terms, nylons exhibit superior strength, resistance to high temperatures, and chemical resistance. Certain nylons are resistant to abrasion, possess excellent hardness and rigidity, and have a high impact resistance.

  • Acrylonitrite Butadiene Styrene (ABS)

It is a tough and impact-resistant plastic with applications in various industries. It is resistant to acids and bases, high dimensional stability, and is resistant to shrinkage as well.

  • Perfluoroalkoxy (PFA):

It is a fluoropolymer with thermal resistance, creep resistance at higher temperatures, and resistance against a wider range of chemicals as well.

Manufacturing Medical Devices with Injection Molding

Injection molding is the primary method utilized to manufacture medical devices. The process consists of reshaping and molding medical-grade plastics into the intended form of the medical apparatus subsequent to their melting.

By utilizing this additive manufacturing technique, medical injection components with superior surface textures and precise dimensions are produced that are robust and long-lasting. Additionally, since many medical instruments are single-use, this method is appropriate for mass production while injection molding costs are reduced.

Why are Plastics used in Injection Molding for Medical Devices?

Medical device manufacturing industry is highly regulated across the world. This means that the products being used to manufacture medical devices should also comply with the applicable regulations and standards.

Thermoplastics, particularly those designated as “medical-grade plastics,” are exceptional materials for the production of medical injection devices due to their complete adherence to FDA regulations.

How is Injection Molding Beneficial for Medical Device Manufacturing Industry?

Compliance with Regulatory Standards

Due to regulatory compliance, components manufactured using medical injection molding are appropriate to be used in the medical industry. All equipment is obligated to adhere to a set of regulations established by the FDA encompassing safety, sterility, sanitation, and other relevant aspects.

Wide Range of Materials

Injectable molding provides machinists with an extensive selection of materials. The method is applicable to composites, fibers, plastics, and more. Nevertheless, in the context of plastic injection molding for the medical sector, the necessary materials have already been simplified. Despite this, the procedure remains compatible with the vast majority of medical-grade plastics.

Higher Volume Reproducibility

Numerous medical items are single-use, including syringes, gloves, masks, and so forth. With injection molding, the manufacturers’ requirements for having a fabrication process that can consistently produce items in large quantities gets easily fulfilled.

Standards for Regulating Injection Molding In Medical Device Manufacturing

Some of the commonest standards that regulate medical device manufacturing with injection molding are:

ISO 13485 – Medical Devices

The specifications for a quality management system (QMS) in the manufacturing of medical-grade products are delineated in ISO 13485. It is the most prevalent standard utilized in the production of medical devices. The scope of ISO 13485 extends beyond plastic injection molding to encompass the overall criteria that govern the utilization of all manufacturing processes in the production of medical equipment. This standard was established to assure the production of medical devices and equipment in a safe and effective manner while maintaining quality consistency.

 ISO 10993 – Biological Evaluation of Medical Devices

Requirements for medical device biocompatibility are the main emphasis of ISO 10993. It includes goods intended for either direct or indirect interaction with the body. Reducing the likelihood that patients may experience negative consequences from materials, such as injection-molded plastics, is the aim of ISO 10993. Materials that comply with ISO 10993 are non-toxic, do not compromise immune function, and do not have the potential to cause cancer.

 ISO 14644 – Cleanrooms and Associated Controlled Environments

ISO 14644 regulates the use of cleanrooms during medical device manufacturing. It defines the various cleanroom classes from Class 1 to Class 9, where Class 1 has the most stringent cleanliness requirements. 

Come Meet Us at TSQ & E!

Our team at TS Quality and Engineering comprises a body of professional consultants with an adequate knowledge of requirements regarding the use of injection molding in medical device manufacturing. If you are a medical device manufacturer and want to build medical devices using injection molding, then our experts can help you fulfill and implement the requirements and regulations of applicable standards, especially the ones mentioned in this blog. Reach out to us today.

About the Author

Waqas Imam

S. M. Waqas Imam is associated with TS Quality as a Regional Partner. He is also an ambassador of Medical Device Community. He is an Industrial Engineer by qualification and served the manufacturing industry since 2011. He is also IRCA CQI Lead Auditor of ISO 9001 and other management system standards. He had served as Quality Assurance and Regulatory Affairs Manager in QSA Surgical Pvt. Ltd. and Ultimate Medical Products. He managed requirements of ISO 13485:2003, EU directives, CE marking and FDA. He also served as Expert Blog Writer for 13485Academy and wrote expert articles on various topics of ISO 13485:2016.