David A. Belforte
New technique produces prototypes of implants and the instruments used by surgeons to place them in patients’ bodies
DePuy Spine, founded in 1895 in Warsaw, IN, as DePuy Manufacturing, is the first commercial manufacturer of fiber splints to set orthopedic fractures. In 1993, DePuy and Biedermann Motech (Germany) jointly formed DePuy Motech to develop, manufacture, and market spinal implants. The 1998 purchase of Cleveland-based AcroMed made the company the second largest spinal-device company. That same year it was acquired by Johnson & Johnson. In 1999 the company moved to Raynham, MA, where it resides today.
The company’s innovative products are used by orthopedic and spinal surgeons in surgical and nonsurgical therapies to treat patients with conditions resulting from degenerative-disease deformities, trauma, and sports-related injuries. Among the products developed and manufactured are rod, screw, and hook systems for lumbar problems and cervical- and spine-stabilization systems.
The average lead time to make many of its prototype implants and instruments is six-to-eight weeks, and products can be very costly. There is no guarantee that the item will work as intended when received, and often modifications are part of the development process. Because of the extended delivery times, it is a challenge to plan for surgeon-team meeting deadlines.
Peter Ostiguy, staff team leader, is in charge of the rapid-prototyping operation at DePuy Spine. It consists of four systems, two of which are laser-based-one for metal powders and one for polymers-and two that are inkjet machines with UV light curing of polymer materials. These units are used to produce prototypes of new implants and the instruments used by the surgeons to place these implants in patient’s bodies. After approval of the prototypes, these models are created in software for downloading to machine shops that produce the final products.
The term rapid prototyping is slowly being replaced by rapid manufacturing, as that aspect of the technology seems to be paramount today. At DePuy Spine, rapid prototyping is the process currently used because the company utilizes its equipment to produce, for the most part, prototypes that will eventually be manufactured using conventional machining practices. No instruments or implants have been used in the operating room arena to date. But, Ostiguy turns out prototype parts that are used by surgeons and engineers to visualize an eventual end product-in this case spinal implants and instruments.
DePuy Spine has been involved in rapid prototyping for 15 years. It introduced stereolithography in 1992 for making 3D CAD models, wax patterns for the foundry, and soft tooling. In 2001, the company brought in its first Objet unit, a prototyping system that uses inkjet technology that can process at high speed and allows the company to make assemblies and to do material conversions and variations.
DePuy was making a number of plastic prototypes for evaluation by project teams and the company’s design surgeons. Thus, the ability for this technology to impact the business has been proven at DePuy Spine. Its interest in new rapid-prototyping technology was stimulated with the advent of companies developing metal materials for use in medical components.
Samples from DePuy have been made in cobalt chromium (CoCr) with good success, and the company contacted Electro Optical Systems GmbH (eos), which offered its direct metal laser sintering (DMLS) machine that had the capability to produce 17-4 stainless-steel parts. In February 2007, DePuy purchased an eos M270 metal-powder unit that has been used in approximately 20 projects, producing more than 1300 parts to date.
With the eos system, an .stl file is created from CAD-no drawings are required. A work platform is generated from this file, and 17-4 stainless-steel powder distributed 20 µm thick is deposited on the platform. The laser beam sinters the powder, and the work platform is lowered. Sequential cycles eventually produce a metal part.
An early success was an instrument that was in development. The engineer was looking for some metal samples. The quote to manufacture these was $5000, with a six- to ten-week delivery time. Ostiguy, using the eos machine, built a working prototype in a little more than a week at a fraction of the cost and then proceeded to build two more iterations in less time than the earliest delivery time set by the prototype vendor.
The engineer and the team had the ability to make effective modifications so that when it was time to go to production there was complete confidence from the team that it had a robust design. These instrument samples were an important aspect in getting feedback from the surgeon in a timely manner and were utilized effectively at surgical training sessions.
From this early success there has been no turning back. Part of the success is having individuals that are talented in the removal and cleanup of the parts after they have been built. With experience in what is conducive to successful builds they have combined building the samples on the DMLS machine followed up with some postmachining. The company has been able to go from “model to metal,” reducing the need to have fully detailed drawings for development as it did in the past with earlier prototypes.
Where does DePuy go from here? It is optimistic that in the near future heat-treatable stainless-steel material will be developed, which will open a number of new avenues. As Ostiguy says, “This technology spawns a new foundation on how we design our components. In the past we ‘designed for manufacturability.’ Now we can ‘design for functionality.’ Geometric constrains have been reduced.”
BUILDING METAL MODELS
The EOSINT M 270 builds metal parts using direct metal laser sintering (DMLS), which fuses metal powder into a solid part by melting it with a focused laser beam and builds the part up additively layer by layer. Even highly complex geometries are created directly from 3D CAD data, automatically, in just a few hours, and without any tooling. It is a net-shape process, producing parts with high accuracy and detail resolution, good surface quality, and excellent mechanical properties. A wide variety of materials can be processed, ranging from light alloy steels to superalloys and composites. Available materials include stainless steels, cobalt chrome, different titanium alloys, and tool steels. Components can be built in sizes up to 9.85 × 9.85 × 8.5 in.
Positive parts are produced directly from CAD data by an application called DirectPart. The components can be prototypes, series production parts, or even spare parts. The requirements may vary from functional metal prototypes created within one day to economically manufacturing hundreds of individualized implants in biocompatible alloys each week.
DMLS is also well known as a technology for tool making, an application known as DirectTool. The direct process eliminates tool-path generation and multiple machining processes such as EDM. Tool inserts are built overnight or even in just a few hours. Also, the freedom of design can be used to optimize tool performance, for example, by integrating conformal cooling channels into the tool. Increasingly, both strategies are combined to create improved performance in shorter time. DirectTool is best known for plastic injection molding; however, the technology is also used for other tooling types, including blow molding, extrusion, die casting, and sheet metal forming.
By utilizing a fiber laser, the M 270 offers an extremely small focus diameter for improved detail resolution and part quality, while the variable-focus technology and the fast motors together ensure a very high building speed. The high intensity of the laser energy in combination with the sealed process chamber provide an optimal platform for future material and process developments, especially for building functional prototypes and end products in metal.