Leverage Multiple Materials in Medical Device Design

Every medtech company has its own issues to overcome. Parts are failing. Manufacturing labor costs are too high. Product development is at a standstill. Time to market is slow because the production process is overly complicated. Design innovation can create help manufacturers overcome these issues.

Incorporating multimaterial components into a medical device design can lead to innovative results. Multimaterial components can offer a host of product benefits over one-material designs:

You can create a cutting-edge device by leveraging multiple materials that offer unique benefits over a one-material design, but choosing the right combination of materials and manufacturing methods is a complicated endeavor. Finding the right balance of quality, cost, and capability in materials and suppliers is essential to success.

Reviewing existing designs and well-known methodologies is a good starting point when developing a medical device using multiple materials. When brainstorming for your product, expand the process by considering design ideas from outside medtech. Talking through the solutions created for different products with diverse uses can help generate new ideas.

Reviewing what has been done before can help you get started, but true innovation will come from considering each material and assembly method and their unique benefits. Through this process, you might come up with a unique combination of materials that offers the necessary features to meet your design specifications.

Materials Selection

How can you leverage multiple materials to take full advantage of their benefits? When selecting the ideal material combination for a new component, there are many important things to consider.

Material Compatibility. First and foremost, the materials chosen for an assembly must be compatible with each other. If the assembly is an overmolded application, the materials must be able to bond together. Another consideration is stability—if the materials are pressed together in an assembly for years, will chemical reactions lead to a degradation of properties?

General Performance. The selected materials must hold up to the demands of your application and the stresses of everyday use. Tension, compression, tear, and creep are just some of the forces that could impact your component’s performance.

Chemical Resistance. Components are used in different environments and are exposed to a multitude of elements. The environment must be thoroughly considered in order to select the appropriate material.

Product Life Cycle. Implantable devices designed to stay in the human body for the life of the patient are exposed to various fluids, acids, and lipids and cannot break down from this contact.

Cost. It is important to create the correct balance of performance, quality, and cost. For example, creating a complex overmolded device that provides greater performance than the product requires but at a higher cost can limit the success of an otherwise great design. By determining an appropriate sale price while analyzing quality and performance requirements, you can set a target budget per piece that will help you choose the most cost-effective materials and assembly method.

When developing a medical device design, it is important to consider the component’s use and other design requirements to ensure a successful outcome. A supplier with a thorough understanding of the application’s rigors and a broad knowledge of materials can guide you to make the proper choices in material, design, and manufacturing method.

A supplier with niche capabilities can leverage its experience to combine materials that don’t traditionally work together. It is critical to select a supplier with a willingness to experiment to find the ideal combination of materials to meet product design requirements.

Multimaterial Assembly Methods

Once you’ve discovered which materials have the features that match your design specifications, it’s time to determine which production method will be most effective in meeting your project goals.

Mechanical Assembly. Mechanical assembly uses screws, fasteners, built-in snap features, post-and-sockets, and other similar connections to assemble disparate materials. There are few limitations in the types of materials that can be combined this way.

Mechanical assembly has a few advantages:

One medical device company needed to modify an existing product design for a polycarbonate dental packaging cap and vial. The existing cap was screwed into place onto the vial using a threaded design. This prevented the company from automating its packaging process, as the equipment would either overtorque and crack the cap or under-torque, causing the cap to fall off during shipment. The company worked with a contract partner to resolve this issue by creating a threaded design that snapped into place but could still be unscrewed normally. The end customer experienced no change in the function of the vial, while the device company saved tens of thousands of dollars in labor costs.

Chemical Assembly. Chemical assembly leverages adhesives to bond two materials. The adhesive must be chemically compatible with both substrates while creating a sufficient bond. The adhesive must also be able to withstand all of the environmental rigors of the end application. Successful chemical assembly production requires a manufacturer with intimate knowledge of adhesive and material compatibility, as well as rigorous testing and experimentation to confirm a successful bond.

Chemical assembly offers these benefits:

One medical device compay used chemical assembly to create a disposable Y-body connector used to mix and apply a two-component surgical adhesive. The complex assembly consisted of seven separate components, including two molded plastic luer fittings, two check valves, a plastic molded Y-body connector, a coextruded silicone tube (composed of silicone coextruded over a metal wire), and a molded silicone tip. Each of the silicone and plastic components were molded, the tube was extruded, and each part was chemically adhered together.

Thermal Assembly. Multiple methods of thermal assembly, including spin, ultrasonic and vibrational welding, and heat staking, can be used to bond thermoplastic materials. These methods create strong chemical bonds by melting the plastic material together.

Thermal assembly offers these benefits:

For example, ultrasonic welding can be used to develop a three-piece check valve consisting of a two-component plastic housing and an internal rubber valve. The completed assembly creates a hermetic seal with a chemical bond between the two housing components, removing the risk of leakage or failure of the check valve.

Overmolding. Overmolding, or multimaterial molding, involves molding a material over a previously formed part. The substrate can be nearly any rigid material, such as plastic or metal. However, the temperature requirements for the overmolding process and the chemical compatibility of the materials can create certain limitations. When molding a thermosetting silicone over a thermoplastic material, the thermoplastic must have a high enough melting temperature to remain solid while overmolding with the thermoset material. This greatly limits the pool of thermoplastic substrates that can be used in this type of design.

By leveraging overmolding, medical device manufacturers can take advantage of these inherent benefits:

One company developed a micromolded neurostimulation lead that involved two layers of overmolding. The first overmolding was a tiny nitinol metal ring overmolded with an implantable polyether ether ketone material. The overmolding was then primed and overmolded again with an implantable-grade silicone seal on one end. The component measured only 0.080 in. in diameter and weighed less than 1 g, adding to the project’s complexity.

Conclusion

When developing a new product design or enhancement, consider all available material options to maximize the functionality of the component. A good supplier can help your team work through your essential questions and determine the best material and manufacturing method for your product design. Collaborating with an expert partner can help you decide which assembly method is the correct path to take in manufacturing your multimaterial device to achieve the performance benefits, cost reductions, or other project goals you may have.

Ken Kostecki is the southeast territory sales manager for MRPC (Butler, WI), a single-source provider of medical device components and assemblies, specializing in cleanroom molding. He holds a bachelor’s degree in composite materials engineering from Winona State University and an MBA from the University of Wisconsin, Whitewater. He can be reached at [email protected].