Advancements in medical technology and material science have created new engineering challenges for medical devices used in minimally invasive interventional procedures. Medical device companies are making devices that are smaller (less invasive), more complex, and multifunctional, which require more precision and tighter tolerances from their contract manufacturers. For example, in the extrusion market, device companies continue to develop complex new designs for single products that require co-extrusion, multi-lumen, multidurometer segments, or variable coil/braid reinforcements.

Fig. 1 – Advanced technology, such as this etch-free EFEP co-extrusion from Teleflex Medical OEM, impact medical device design. (Photos and illustration are: ©2012 Teleflex Incorporated. All rights reserved. Used with permission.)
As challenging as these expectations are, what is perhaps hardest to design into new products is low cost. The medical industry expects more technology and function, but at a lower price point. Device companies are continuously looking for ways to save money on their new launches; some have even initiated corporation-wide global initiatives with goals to reduce costs over the next several years.

Increasingly complex designs, materials, tooling, and prototyping all drive up costs — yet cost savings must still be engineered into the final product, without compromising quality or function. One way to do this is by improving efficiencies that speed up the manufacturing process (automation, for example) and reduce waste. Another method is to work with a partner skilled in the practice of designing for manufacturability, that is, engineering products and processes that eliminate certain steps, such as finishing and assembly. For example, overmolding, multi-shot molding, and other injection-molding technologies can bond different materials together in a single step, thereby reducing assembly steps. More sophisticated process control and validation, such as robotics or sensors and visual systems, can monitor manufacturing process parameters in real time, observe the ejection of product from molds or extruders, and inspect final products in microscopic detail — all of which reduce production costs.

Yet another cost-control method medical device companies are taking seriously is aligning themselves with vertically-integrated outsource partners, like Teleflex Medical OEM (Kenosha, WI), that can provide expert, single-source, concept-to-completion services that meet all their design, production, and regulatory needs. This greatly facilitates communication and decision-making while improving quality control, waste management, and speed to market. Any catheter provider that wants to be a key part of the supply chain must provide integrated design, engineering, material selection, prototyping, testing, validation, manufacturing, assembly, packaging, and labeling capabilities — and also know the regulatory landscape in detail.

Miniaturization is Huge

Fig. 2 – Devices are becoming smaller and more complex. Case in point, PTFE tubing with braid reinforcement and multi-lumen design.
Driven by the proliferation of minimally- invasive surgical procedures, devices continue to become smaller — which requires more innovative processes for design and production. It is much more difficult working with the tighter specifications that miniaturized products require. For example, tubing can have interior diameters as small as 0.004 inch ±0.0005 inch with walls as thin as 0.005 inches. Catheter sizes can be as small as 1 Fr – that size is for a braid reinforced catheter, not just a simple extruded tube.

Microcatheters, one of the most common miniaturized products, are ideal for diagnostic and therapeutic neuroradiology or occlusive therapies. Outside diameters are as small as 0.026 inches, interior diameters 0.014 inches, and minimum wall thicknesses are 0.005 inches. Liner and outer jacket materials, braid or coil reinforcement, durometer and stiffness, variable shaft diameter, embedded marker bands, and thin-wall construction can all be customized according to use. Microcatheters are available with flat or round wire and coilreinforced configurations. Flat wire is generally used for thinwalled applications where performance is critical. Coiled shafts are more flexible and kink-resistant, but may not provide the same torque and push capabilities as a braided shaft.

Microcatheters are often used in delicate neurovascular cerebral procedures for the treatment of strokes and aneurysms, so very high precision manufacturing is required. Building a catheter, regardless of size, is often an “inside out” process where the inner liner (most likely polytetrafluoroethylene, or PTFE) is layered with the coil or braid support, followed by bonding with the outer shaft.

The big challenge is that each layer has its own specifications and tolerances, which collectively add up (“tolerance stacking”) to meet the specifications and tolerances determined for the final product — a key consideration during material selection. Manu fac turing and process controls are tightly controlled, and because the final product is essentially microscopic, rigorous inspection and control systems are required to detect the smallest imperfections.

Medical Design Briefs Magazine

This article first appeared in the August, 2012 issue of Medical Design Briefs Magazine.

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