Medical Injection Molding: Guide and Best Practices

Medical injection molding is a critical process that enables designers to prototype and manufacture a wide range of products for the medical, dental, and pharmaceutical industries. Some products, like catheters, are tightly regulated, while others, such as general wellness items, have fewer requirements. Furthermore, some injection molded parts (e.g., gaskets) are not classified as medical devices but must still comply with specific material testing standards.

This guide provides essential information about medical injection molding, covering medical device classes, prototyping, material selection, and tooling—forming the foundation of effective DFM for Medical Devices and Medical Device Prototypes.

Read More About Key Components of Injection Molding Part 5: Ejection System

Understanding Medical Device Regulations

A successful project begins with understanding what constitutes a medical device and its official classification. Missteps in this area can delay new product introductions (NPI) and lead to unnecessary costs. For example, the U.S. Food and Drug Administration (FDA) classifies a manual toothbrush as a Class I medical device, but it is 510(k) exempt, meaning it does not require extensive premarket notification or testing.

Medical Device Classes

Both the FDA and the European Union’s Medical Device Regulation (MDR) categorize medical devices into three classes based on risk:

• • Class I: Low-risk devices not intended to support or sustain life (e.g., test tubes, tongue depressors).
  • Class II: Moderate-risk devices that must demonstrate reasonable safety and effectiveness (e.g., contact lenses, infusion pumps). The EU MDR further divides this into Class IIa (medium-risk) and Class IIb (medium-to-high-risk).
  • Class III: High-risk devices designed to sustain or support life, which may present an unreasonable risk of injury (e.g., implantable prostheses, pacemakers).

Quality Standards

• • ISO 13485: Specifies requirements for a quality management system for medical devices.
  • ISO 10993: Covers the biological evaluation and biocompatibility of medical devices.
  • ISO 14644: Details the standards for cleanrooms and associated controlled environments.

Prototyping and Scaling to Production

Once the regulatory pathway is clear, you will face crucial Design for Manufacturing (DFM) decisions. For prototyping, 3D printing and injection molding are both viable options. However, you must consider if the end-use material for injection molding can also be 3D printed, as this impacts the testing plan. To avoid redesigns, it is vital to prepare the part for injection molding from the start.

In some cases, you can bypass 3D printing and use prototype injection molding directly. This is often faster and more affordable than many assume. Bridge tooling can also be an effective strategy to transition smoothly from low-volume prototypes to high-volume production.

Assessing Manufacturing Readiness

While 3D printing can produce highly intricate features like lattice structures, many of these are difficult, expensive, or impossible to replicate with injection molding. To confirm your design is ready for the injection molding process, consider these DFM best practices:

• Is the wall thickness appropriate and uniform? Are ribs and gussets used for support?
• Are radii large enough to prevent defects like voids and warping?
• Have sharp corners been rounded with fillets to facilitate mold release?
• Has a sufficient draft angle been added to prevent damage during part ejection?
• Does the specified surface finish follow Society of the Plastics Industry (SPI) guidelines?
• Have part tolerances been reviewed and adjusted for the molding process?

Read More About Choosing the Best Surface Finish for Injection Molded Parts

Selecting Materials for Medical Applications

Medical injection molding often uses materials similar to other applications but may require specific medical-grade polymers that meet stringent testing standards. For instance, materials certified to meet ISO 10993 biocompatibility requirements are available, though they can be more expensive and may be unnecessary for non-implantable devices.

Common materials include:

• Polyethylene (PE): Absorbs little water and maintains its integrity during sterilization, used in items like oxygenator membranes.
• Polypropylene (PP): Offers excellent fatigue resistance, ideal for parts like the hinges on pill organizers.
• Polystyrene (PS): Supports radiation sterilization and is available in clear grades for products like blood dilution vials.
• Polyetheretherketone (PEEK): Provides high mechanical strength and is used in load-bearing implants like spinal cages.
• Thermoplastic Elastomers (TPE): Soft and elastic materials used in products like medical bandages.
• Silicone Elastomers: Includes High Consistency Rubber (HCR) and Liquid Silicone Rubber (LSR) grades that often have FDA approvals for medical use.

Choosing the Right Tooling

The choice of mold material is critical. Prototype and low-volume molds may use aluminum or softer steels, which are easier to machine but offer less precision and longevity. For high-volume production, hardened steel molds provide the best dimensional tolerance and a much longer operational life.

Production molds are optimized for fast cycle times and consistent quality over millions of cycles. In contrast, prototype molds prioritize achieving precise part quality for First Article Inspections (FAIs), with less emphasis on cycle speed, especially for pre-production volumes.

Conclusion

Successfully navigating Medical Injection Molding requires deep insight into regulatory pathways, quality standards, material science, and plastic injection mould tooling. Combining design for manufacturing solutions with the right prototyping and scale-up strategy reduces risk and accelerates market readiness. Contact us at Aprios for expert guidance and advanced manufacturing services tailored to your project.