By Sean Fenske, Editor-in-Chief
 
The orthopedics industry is traditionally associated with metals. Whether implants, instrumentation, or trays, the industry leverages metal as a primary component for fabrication. With increasing benefits found in plastics, however, injection molding of orthopedic devices is growing in interest.
 
Furthermore, when considering plastics for implants, there is the potential to realize additional benefits. These can be provided through bioresorbable materials. Since use of these types of plastics may add complexity to the molding process, it is critical to work with an expert molding provider who has experience with these materials.
 
To address the use of plastics for orthopedic implants, whether bioresorbable or not, Robert Schwenker, VP of sales, specialty molding and medical tubing at Spectrum Plastics Group, took time to respond to a number of questions on the topic. In this Q&A, he addresses materials, molding considerations, and factors to keep in mind when specifying the process for orthopedic implants.
 
Sean Fenske: When it comes to orthopedics, are more manufacturers exploring the use of molding for implants?
 
Robert Schwenker: There is definitely a continued trend toward injection molded solutions in implantable products. In markets with strong growth, like Sports Medicine, the number of surgeries is growing, which is creating the need for more products in the field. At a certain volume, molded solutions are much more economical than machined solutions in both labor and material usage, so as the number of surgeries increases, there are greater inquiries for molded solutions. We are also seeing a move into other component areas like spacers, clips, and fastener devices, which is adding to the need for implantable components. In many cases, smaller parts are a better fit for injection molding.
 
Fenske: What are the key considerations to keep in mind when selecting molding for orthopedic implants?
 
Schwenker: Many customers who are looking for injection molding solutions are often coming from a machined component in the early prototype stage. To convert these designs to an injection molded part does require some changes that may seem minor, but are critical to the long-term manufacturability of a part. These may require slight changes in material or part design, as well as the overall process. Engaging in a design for manufacturability session with our engineers is an important first step in the process to limit the impact to the final part geometry and still make it moldable. During this process, we can also help to understand the required strength and performance of the application to assist in part design and material selection. More material formulations are entering the market and providing more options for implants, but these can also impact design considerations.
 
Fenske: What materials are often used for orthopedics and what benefits do they offer?
 
Schwenker: In medical injection molding, implantable products are often manufactured with PEEK, PLA/PLGA, and polyethylene. PEEK is notable for its strength; as such, it is used as a metal replacement and commonly indicated for long-term implants. PLA/PLGA are bioresorbable, and polyethylene is easily moldable and has little impact on the human body. We continue to work with a variety of different, highly-engineered resins in deployment devices and tools. There is a trend to move away from metal components and introduce more plastics into product design, still providing excellent strength while potentially reducing the cost of a device. Spectrum has had great success with polyarylamide, PAEK, as well as polysulphones in developing cost-effective solutions for customers.
 
Fenske: How does working with bioresorbable materials for orthopedic implants affect the molding process?
 
Schwenker: Bioresorbable materials require extensive expertise in handling, processing, and knowledge to mold successfully as they have very high viscosity, and excessive shear can destroy the integrity of the material. Even in mold design, it is important to have design engineers that understand how the product behaves throughout the runner system. Beyond that, the entire molding process, from the time the material enters the door until it leaves in a foil pouch, needs to be manufactured in a controlled environment and managed in a robust quality system.
 
Fenske: What are the key factors to consider when specifying a bioresorbable material for an implant?
 
Schwenker: Obviously, the key benefit to a bioresorbable product is that it will eventually be absorbed into the patient. The targeted absorption rate—whether it is 12 months or four years—is often the primary factor and depends on the application. The actual geometry of a part plays a critical role as well. Spectrum has developed laser processing technology to drill microports into components to help create a porous framework that will allow for more consistent absorption without damaging overall strength. With bioresorbable products, materials and part design go hand-in-hand.
 
Fenske: What aspects do manufacturers often overlook when it comes to using molding technologies and materials for orthopedic implants?
 
Schwenker: It is very easy to focus solely on the product and mold design, and assume once these aspects are determined, the problem is solved. The reality is all the peripheral aspects of production are just as important. The recent years have demonstrated the importance of managing supply chains, whether it is to manage inventories of bioresorbable products with a specific shelf life or to use advanced planning techniques to source metal components with long lead times. Then on the other side, products continue to get smaller and more precise. Investments in measurement techniques and the ability to detect potential failure modes is also critical. The quality systems around molding implant products contribute to the real value and safety of the product. In the end, it is important to have a company culture that understands every single one of our products will have a positive impact on someone’s life, but they need us to be excellent.
 
Fenske: Do you have any additional comments you’d like to share based on any of the topics we discussed or something you’d like to tell orthopedic device manufacturers?
 
Schwenker: While injection molding will continue to be a core manufacturing capability, it is clear new materials and technologies like additive manufacturing and laser processing are changing the manufacturing landscape rapidly. While many aspects of the medical markets can be reluctant to change, these new capabilities are also driving a renewed sense of innovation. We continue to invest in these technologies so we can have a comprehensive solution portfolio, which allows for more collaboration. In the end, this is a partnership with all the stakeholders and we feel fortunate to be part of this industry.
 
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