Last year, more than 50 million surgical procedures were performed in the United States. As that number grows each year, the quantity of and preference for minimally invasive surgeries is also increasing. Key factors driving this trend, compared to traditional open surgery, include lower associated costs for both doctor and patient, an increased number of people insured domestically and abroad, improving healthcare infrastructure in developing countries, shorter recovery times, and a reduced overall impact on the patient.
The emergence of a specialized device—the medical guidewire—is enabling this shift in procedures. While historically used in coronary procedures, the guidewire has become an integral part of a growing number of medical procedures with its use steadily increasing and expanding into more and more medical specialties. (See Figure 1)
A guidewire is a thin, flexible, medical wire inserted into the body to guide a larger instrument, such as a catheter, central venous line, or feeding tube. The process of catheterization was noted as early as the 18th century. The first modern applications were used as early as 1844 for the cardiac catheterization of animals, and then in 1929 on humans, when the process was tested by Dr. Werner Forssmann, a German physician. He proved to his doubting colleagues that it was possible to access the heart with a wire by carrying out the procedure on himself, and, in the process, received the 1956 Nobel Prize in Medicine for developing that technique for cardiac catheterization. Over the years, the guidewire has become more sophisticated, smaller, and made from a variety of materials, thus presenting a range of challenges in the production of guidewires.
The market for guidewires is now global and growing. According to a 2014 research report published by Grand View Research, “Global guidewires market is expected to reach $2.19 billion by 2020. Growing prevalence of target diseases coupled with growing geriatric population base is expected to drive guidewire demand over the next six years.”
The materials used to make guidewires have varied over the years but today they primarily consist of stainless steel and Nitinol (nickel titanium). Some wires are also coated with Teflon® or parylene.
The consistent change in materials presents challenges in the production of guidewires, which are typically manufactured on grinding machines. These grinding machines must be able to keep up with regular material changes and the associated technical requirements. Different abrasives, such as cubic boron nitride (CBN), diamond, and various grades of vitrified abrasives are used in grinding and regulating wheels to offer greater flexibility in materials, making grinding machines more relevant for a longer period of time, and protecting a manufacturer’s investment.
Guidewire production also relies on material handling solutions to automate the process and maximize a machine’s throughput. One such grinding system uses a dual-carriage, linear motor, part-feed system that allows wires to be fed into the grinding machine continuously with no loss of linear positional resolution, dramatically increasing the precision of the ground wire. Instead of using traditional sensors that can degrade over time and limit the speed of the process, the dual-carriage linear motor allows the machine to adjust and react in real time. This allows for shorter grind times and higher levels of accuracy in the diameter and length of the wire over unlimited lengths.
Diameter requirements of guidewires are only getting smaller as guidewires are introduced into more medical specialties, such as in neurological surgeries. This further pushes manufacturers of precision grinding systems to innovate in order to handle smaller and more accurate wire specifications. Some machines on the market today are capable of grinding guidewires with a diameter resolution down to 0.1 microns, or 0.000004 inches, while grinding the required shapes into the wire.
The Introduction of Grinding
In the production of guidewires, shapes such as tapers, angles, and arcs have to be formed into the wire which decide its maneuverability and torque. These features are dependent upon what other components will be connected to the wire which acts as a transport vehicle of these components to the treatment area. Initially, shapes were formed into the wire using chemical etching, a very slow process which, as the name suggests, required the use of chemicals to form the wire. In 1966, the process of centerless grinding was used for the first time to create a simple taper into a stainless steel wire, providing a faster solution and eliminating the need for chemicals.
Centerless grinding utilizes a grinding wheel and a control wheel. The control wheel rotates the work piece as the grinding wheel cuts into it. The part is not held by centers, hence the term centerless. This process insures excellent roundness and diameter control and can be automated to produce wires at an even higher rate. The process soon replaced chemical etching as the most efficient and accurate way to form guidewires. Centerless grinders have helped guidewire manufacturers regain more control over their production requirements.
“We had previously outsourced the type of work these machines are capable of doing,” said Jim Boldig, project engineer for Custom Wire Technologies, Port Washington, WI, a contract manufacturer of fine and micro fine wire parts for medical OEMs. “By adding these machines, we now have the vertical integration to allow Custom Wire Technologies to produce complete assemblies and be competitive in the marketplace. Additionally, this gives us the ability to reduce our overall lead time to our customers.” (See Figure 2)
Advanced Options and Additional Features
Since the introduction of that first centerless grinder for guidewires, their design has evolved to offer an increasing array of shapes and tapers for the growing number of medical specialties. Longer and more complex shapes including multitapers, parabolic, flat features, and threads are required (see diagram). To achieve such a complex variety of shapes requires even more sophisticated grinding systems.
In addition to traditional centerless grinding systems, machines with outer diameter (OD) technologies are also available. OD systems use a narrower wheel and the wire is fed through a hydrostatic bushing, making even more complex wire shapes possible. Some of these machines also feature a centerless mode, which incorporates the best of both worlds, maintaining absolute length and diameter control, but allowing for greater speed and material removal using a wider wheel. By offering both OD and centerless modes in one machine, manufacturers receive even more possibilities and capabilities.
Grinding machines are able to meet the stringent requirements of the medical industry in accuracy, surface finish, and complex design features. They allow guidewire manufacturers to produce wires 30 times more accurate and with more flexibility in wire feature creation, all at faster rates than traditional methods.
To make these machines even more efficient, advanced grinding systems also offer various levels of automation, “the most appealing feature of centerless grinders,” said Boldig. “These machines have been well designed and built to nearly eliminate an operator entirely. It has given us the ability to have one operator oversee three machines. This frees up additional workforce for other projects.”
Simple interface platforms, such as easy-to-follow touch screens, also allow less skilled operators to run the machines. User configurable shape profiles stored in libraries allow users to choose from an array of wire shapes, with the ability to add custom shapes. Systems are available in different languages, with CE certification, to provide for a global customer base. (See Figure 3)
As the capabilities of grinding machines for medical guidewires increase, so do the additional features available for these machines, allowing even greater flexibility across specialties and a growing range of options for guidewire manufacturers. Peripheral component integration such as spool feeders, cutters and retractors, inline gauging, and grit blasters expand the machines’ capabilities and eliminate the need for secondary processes.
Spool feeders, cutters, and retractors allow the wire to be pulled directly from a spool to the desired length, where it is then cut and automatically fed to the machine. Some wire cutters even allow the wire to be cut after grinding, which provides the ability to grind multiple short parts out of one long wire in one feeding operation, reducing cycle time.
Wire extractors pull finished guidewires out of the grind zone using gripper mechanisms that then place the wires in the receiving tray. There are even high speed programmable part extractors that offer programmable positioning and allow for the fast grinding of double-ended grinds and faster part extraction, further reducing cycle time.
With a grit blaster, parts can be sandblasted in line with the grinding process, eliminating additional handling and a secondary operation. These additional features allow manufacturers to, in essence, create a machine that works specifically for their process, depending on the end guidewire application.
To provide even more flexibility in applications, some grinders can produce other surgical tools, such as catheters and orthopedic pins, in addition to guidewires.
“We have found orthopedic pins to be a good fit for our contract manufacturing abilities. We now have the ability to manufacture a wide range of devices, not just guidewires, and this is because these machines are adaptable,” said Boldig. “These machines are unique in their abilities. We have been able to manufacture parts we may never have taken the opportunity to try before.”
As the medical industry pushes the frontiers of surgical procedures and the need for minimally invasive surgeries increases, guidewire production must stay on pace to meet those needs. That requires processes that can handle the most desirable materials, with the necessary shapes, at a rate of production that makes the most economic sense. Today’s centerless and OD grinders, matched with their available accessories, supply this ever-advancing industry with a reliable and precise solution.
This article was written by Mark Bannayan, Vice President, Glebar Company, Ramsey, NJ. For more information on Glebar Company, visit http://info.hotims.com/55596-164 . For information on Custom Wire Technologies, Port Washington, WI, visit http://info.hotims.com/55596-191 .