Medical injection molding is a common method for manufacturing devices, products, and supplies used throughout the industry. Products made from medical-grade plastics are used in diagnostic devices, operating rooms, consumer-use products, dental applications, and medical laboratories worldwide. Safety, functionality, reliability, patient comfort, and ease of use are all concerns when developing a medical product; plastics have long been relied on to deliver these.

Injection Molding Processes

Injection molding is a formative method used to produce high-quality plastic medical products. The plastic is melted and injected at pressure into the injection molding tool. The cavity of the tool determines the shape of the finished component. For some plastics, annealing or curing may be necessary once injection molding is complete.

Annealing is a heat treatment method that helps to eliminate stress in the plastic caused by the manufacturing process. It can also improve dimensional stability and increase crystallinity in semi-crystalline and crystalline polymers. Curing is necessary for thermoset plastics to develop the optimum properties of the polymer.

When more complex products are desired, insert molding and overmolding can be used. These processes are used to seamlessly combine two materials into one product. Both processes are commonly used when manufacturing medical products.

Medical insert molding is a manufacturing process that enables injection molders to encase pre-formed, often metal, components in durable plastic to aid in product assembly. This method is widely used for various medical products that require threaded inserts, bushings, electrical contacts, spring-loaded clips, pins, blades, or magnets. A more robust and permanent bond between metal and plastic will form once it cools if the metal insert has a knurled, ribbed, or abraded surface.

Products suitable for insert molding include those that:

  • Require disassembly or maintenance access: This simplifies the process by eliminating the need for separate fasteners or adhesives. Examples include equipment casings, housings, and medical devices.
  • Demand precise insert placement: Insert molding ensures accurate alignment and functionality, crucial for applications like male/female connectors and high-precision assemblies.
  • Benefit from joining high-load-bearing parts: The strong bond created by insert molding makes it ideal for components that need to withstand significant stress, such as structural elements.
  • Integrate conductive features: This allows for the seamless incorporation of conductive components like pins and contacts, ensuring reliable connections in electronics like monitors, power supplies, and medical equipment.
  • Seek permanent attachment and durability: Insert molding offers a robust and lasting solution for applications requiring long-term performance, such as surgical and dental instruments.

Medical overmolding is a two-step molding formative process where two plastics or two different colors are molded together, one on top of the other. A common use for overmolding is to mold a soft-touch material over a harder plastic. Overmolding can provide both functional and aesthetic properties to a product.

This process provides greater flexibility in design. With traditional injection molding, you have the properties of one material to work with. Overmolding gives you the advantage of having additional material attributes to work with. Functionally, overmolding can be used to make tools more ergonomic and comfortable in the hand. It can provide shock absorption, impact resistance, watertight seals, noise and vibration dampening, chemical resistance, and non-slip grips.

Choosing the most suitable injection molding process will depend on the product design and materials. It is essential to ensure all materials used are compatible with one another.

Medical Grade Plastics

Medical-grade plastics are materials designed to meet the stringent requirements of medical applications. These materials are used in a variety of medical devices, equipment, and packaging, from complex tight tolerance applications to simple containers and housings. The characteristics that distinguish medical-grade plastics from commodity plastics include biocompatibility, sterilizability, chemical resistance, physical and mechanical properties, regulatory compliance, and consistency and reliability.

  • Biocompatibility means the plastic must not cause any adverse reactions when it comes into contact with the body. They must be non-toxic, non-carcinogenic, and not cause irritation or allergic reactions.
  • Sterilizability means they must be able to withstand repeated sterilization without degrading, losing structural integrity, or altering the chemical composition, whether the sterilization is autoclaving, gamma radiation, ethylene oxide gas, or electron beam radiation. While not all medical products are sterilized, this is a critical consideration for those that are.
  • Chemical resistance means the plastic must not degrade in contact with chemicals, including organic solvents, acids, bases, alcohols, and other substances. This will ensure that the plastic will not break down or interfere with the application, such as results from point-of-care diagnostic tests.
  • Physical and mechanical properties of the plastic are important for medical products that require strength, flexibility, or durability. The material must maintain these characteristics under varying conditions they may be exposed to, such as high stress or high heat applications.
  • Regulatory compliance is mandatory for medical products. Any plastic used to produce a medical product must not violate any FDA regulations.
  • Consistency and reliability should be given. The production of medical-grade plastic products must follow strict quality control procedures to ensure every product meets quality requirements and can be manufactured consistently, particularly for products where variability can impact safety or efficacy.

Some commonly used plastics for medical products include PEEK (Polyetheretherketone), PE (Polyethylene), PC (Polycarbonate), polyamide (PA), and acrylonitrile butadiene styrene (ABS).

Choosing the Right Partner for Your Medical Injection Molding

Working with an injection molding company isn’t just about finding any provider; it’s about partnering with one with extensive experience in launching medical products. This expertise is crucial because seasoned molders understand the critical nature of medical products, particularly regarding time to market and product quality. They will approach your product with this in mind, guiding you seamlessly from the design phase through production.

Experienced medical injection molders also know that certain products require using plastics with specific properties like high-temperature or sterilization compatibility. However, not every molder is equipped to handle high-performance and engineered plastics. Your chosen molder should offer expertise in material selection and ensure compatibility and functionality of these materials.

It’s not just understanding the materials but having the processes you need. Insert molding and overmolding have become increasingly essential. Whether it’s adding a plastic handle to a surgical tool or incorporating a soft-touch grip on a knob, your molder must possess the capabilities to execute these intricate processes flawlessly.

Medical Injection Molding with Ensinger

Developing medical products demands precision, control, and unwavering quality. At Ensinger Precision Components, we deliver essential solutions for your most critical projects. Our extensive portfolio of high-performance medical-grade materials allows us to help you find the perfect fit for your demanding applications, with guaranteed traceability down to the raw material level.

Are you ready to find a solution for your medical product challenges? Contact Ensinger today. Let’s discuss your project and how we can help you make a tangible difference in patients’ and medical professionals’ lives.