A mold and tool specialist helped to optimize the design of a breast coil system and biopsy device.
As Invivo Corp. (Pewaukee, WI; www.invivocorp.com) began to finalize the design of its Luminescence breast coil system and biopsy device (LBS), it consulted Nicolet Plastics Inc. (NPI; Mountain, WI; www.nicoletplastics.com), a long-time partner specializing in injection molding and mold building and tooling. The design of the LBS—which provides illumination, imaging, immobilization, and needle guidance for interventional biopsies—was particularly challenging. Not only would the disposable device need to meet high sterility standards, but it had to have good mechanical strength to provide stability and be composed of both biocompatible and flame-retardant materials that wouldn’t image during an MRI scan.
“Some components were designed ahead of time, but NPI reviewed all our specs,” explains Dean Walters, Invivo’s lead engineer for the project. “Some of the LBS’s more-complex tools had side actions, and we had to work with NPI to determine directions of pull. We couldn’t have finished the design without their input.”
A collaboration by NPI and Invivo to change the radii of certain pieces reduced the tooling costs and increased the structural integrity on several parts. Invivo was able to benefit from NPI’s expertise in both custom injection tooling and molding. “Because we have steel available in-house, we can start on the mold build quickly and often at prices that are normally associated with imported tools,” explains Mike Grobe, NPI project manager for the BBD program. “We were able to produce the Invivo tooling faster and more efficiently than could have been done using conventional tooling methods. We made 49 parts using 24 tools.”
Materials selection also benefited from NPI’s input. The original design called for materials that were not readily available; however, NPI suggested alternatives that proved to be more cost-effective without sacrificing performance. “At one point, we were struggling to find a biocompatible material for a fiducial cap,” recalls Walters. NPI found a clear rubber material that didn’t image during MRI.
NPI also assisted with the design of an LED light lens. “Invivo had a single part they wanted to mold that had to be water-clear transparent, chemically resistant, and flame retardant because there are electrical components behind it,” Grobe says. “A previous vendor had recommended a material to Invivo, but we knew it wouldn’t work because it is amber in color. After some research, we recommended using a copolyester material that is transparent and very chemically resistant.”
Walters adds, “Invivo also suggested making the lens a two-piece design with the transparent copolyester on top and a flame-retardant polycarbonate on the bottom. They bonded the pieces together with a bonding agent that did not image.”
To identify potential problems prior to mold construction, NPI used mold-flow analysis software to show the last areas of the part to fill, how the material will orient within the mold, and potential warpage and stress points. “NPI helped us develop optimal gate location and size,” Walters says. “We identified stress areas and were able to increase radii in order to eliminate those stress points and perfect the tool before the final stages. Ultimately, the product development and mold-flow analysis work we did with NPI in advance of production helped us get to market faster and to do so with less cost.”