|The surgical staple cartridge pictured here contains a liquid crystal polymer material. Image courtesy Celanese/Shutterstock.|
Liquid crystal polymer (LCP) thermoplastics have a Christian Bale kind of reputation in the polymers universe: Gifted, but difficult. At the co-located Medical Design & Manufacturing (MD&M) West and PLASTEC West event in Anaheim, CA, earlier this month, Don DeMello, Field Development Engineer, Medical Business Unit, at Celanese (Irving, TX) sought to set the record straight on this material, and explain what it brings to the realm of medical device design.
LCPs are used extensively in consumer electronics because of the tight-tolerance designs the material enables and its high strength and stiffness. When the tooling and production process have been configured appropriately, LCPs can significantly accelerate cycle times and measurably improve productivity, which offsets the relatively higher cost of the material compared with other engineering resins. These advantages are readily transferable to the design and manufacture of medical devices, notably drug-delivery systems and wearables, according to DeMello.
Here are six takeaways from DeMello’s presentation that may help inform the material selection process when developing next-generation medical devices.
- High shear is required to achieve the high flow potential of LCP. “Low heat of fusion allows for rapid cycle times,” said DeMello. “Sometimes, you’re only limited by how fast you can open and close the press.” The material freezes off quickly, making it relatively flash free, and, unlike other materials, it flows well under shear without degradation. Moreover, “it can be processed in conventional equipment once the tooling and process have been appropriately designed. And contrary to conventional wisdom, LCP can be “easy to work with,” said DeMello.
- You can design wall sections down to 0.3 mm, even smaller, using LCPs, according to DeMello. It’s amazingly stiff and strong—with a tensile strength of 185 MPa (27,000 psi) and a modulus of up to 30,000 MPa (4,400,000 psi) with specialty grades—making it suitable for some metal replacement applications, but it is also used for lightweighting purposes and to free up real estate in devices for other important functions. This is especially valuable in wearables, added DeMello, where size truly does matter, not just for the obvious reason that the product is designed to be worn but also because “patients want the device to be inconspicuous.”
- When working with LCP, medical device designers should prepare themselves for a paradigm shift. “Typically, you design to certain values, such as tensile strength, modulus and so forth,” said DeMello. “With LCP, the design itself drives the material properties. As you go to thinner walls, you increase the strength and stiffness of the part. You want to take advantage of those behaviors, and that requires a change in mindset. Design engineers are not used to thinking that material properties can change as the design changes, but with LCP, they do,” said DeMello.