Overmolded Plastic Assemblies Improve Stent Design

Working with Phillips Plastics, Medtronic has developed a new delivery system for AAA ("abdominal aortic aneurysm") endovascular surgery to deploy stent grafts through a patient's arteries. The delivery system also provides a new platform for Medtronic Vascular's endovascular product lines that will be fully implemented after completion of all clinical trials and gaining approvals in the U.S. and Europe.

The Xcelerant delivery system provides doctors an ergonomic tool for precisely deploying stent grafts. A unique gear reduction system in the handle of the delivery system and a release that disengages the gearing provides a convenient, ergonomic method for doctors to use slow, controlled or rapid deployment of the stent material.

The Xcelerant system is designed for volume manufacturing, and the handheld unit snaps together to simplify the final assembly steps. The design eliminates all mechanical fasteners, minimizes gluing operations, and uses overmolded plastic parts to create a strong industrial design.

Designed for Manufacturing
Medtronic Vascular chose to outsource a range of services for this project including industrial design, CAD design, design for manufacturability, SLA, rapid tooling, mold development, qualification and assembly. Phillips Plastics (www.phillipsplastics.com) collaborated on the design and worked through details of mold development, qualification, and completion of finished assemblies.

A modular design allows customization to accommodate different anatomies and is suited for a broad range of patients. The self-expanding, thin-wall polyester graft material, supported by diamond-shaped elements, supplies high radial force for reliable, secure sealing without barbs, hooks, or balloons. Markers on the stent graft material aid in accurate stent graft placement.

Xcelerant Delivery System
The Xcelerant delivery system has a nose cone with a long, tapered shape for easier arterial access. The soft, compliant tapered tip increases flexibility for negotiating differing anatomies, and a lubricious coating on the inner wall of the graft cover helps reduce deployment forces and facilitates deployment of the stent grafts. The deployment handle allows precise, controlled withdrawal of the stent graft cover and features a smooth, intuitive motion.

"A key advantage of Xcelerant delivery system is that it offers a disposable handle," says Scott Doig, Product Development Manager responsible for the Xcelerant program at Medtronic. "Our current AneuRx product has a reusable handle that has to be snapped on, and the user must autoclave it after every case. Xcelerant provides an integrated handle that is totally disposable. Each catheter comes with a handle, and the physician can just dispose of the entire unit after each case."

The unit is designed with overmolded plastic assemblies that snap together. There are no fasteners required for assembling the product, reducing the number of operators on the line and making the line much simpler.

Simplifying Assembly
There are many overmolded plastics parts used in the design, and extruded tubes with plastic parts overmolded onto them. To achieve the ergonomic design and the scalability requirements of the company's various product lines, simplifying assembly and eliminating the need for fasteners was an important design goal. The product is designed for multiple French sizes in order to accommodate the requirements of individual product lines and maintain totally scalability in the platform.
One design objective was to carefully design the subassemblies, so Medtronic could reduce final assembly operations on the line and outsource manufacturing responsibilities to Phillips Plastics for these molded assemblies.

"That's one reason why we chose to overmold as many parts as possible," Doig says. On previous projects, Medtronic would have an extruded tube, molded a part, and glued it on. But overmolding provided a method for snapping the entire assembly together by creating junctions between the mechanized handle and the extrusions.