09.25.06
Rapid Prototyping Keeps Pace With Brisk Orthopedic Changes
New technology enhances the conceptual phase of product development, changes manufacturing
Frank Celia
In any creative endeavor, the planning stage is a key element. In any process, to create something where nothing before existed requires preparation, with an eye toward anticipating and averting potential problems.
This certainly is true for medical product development, where large sums of money hang in the balance and schedules are tight. A small error early in the process can have devastating consequences further down the line. Thus, at-tention to detail is rigorous in the conceptual and design phases, or at least as rigorous as possible given time and financial constraints. Because of such limitations, design engineers often confine their efforts to avoiding catastrophes and getting the design “good enough,” rather than striving for absolute perfection.
CNC equipment assists Gauthier Biomedical in creating rapid prototypes of devices and instruments. Photo courtesy of Gauthier Biomedical. |
The technology used to create rapid prototypes is considerably sophisticated, perhaps even revolutionary. Many feel that these technologies eventually will find a home in mainstream manufacturing processes. In experimental trials, for example, prototyping methods have been used to create customized orthopedic implants. Surgeons also use rapid prototyping to produce accurate physical models of their surgery cases on which they can practice prior to the actual surgery. Such trial runs significantly reduce complications and surgery times, physicians say.
Rapid Prototyping Defined
The term “rapid prototyping” is somewhat amorphous, most commonly used to describe a host of related technologies. In general, the term means methods that form objects by adding and bonding materials layer by layer. These processes also may be called additive fabrication, 3-D printing, solid free-form fabrication or layered manufacturing. The basic idea is to form an object without building a mold, creating an elaborate machine setup or engaging in a final assembly. The object is created from the inside out, one layer at a time—thus, the term “additive fabrication” as one layer is added upon the previous.
The manufacturing area at Donatelle has dedicated personnel and equipment for rapid prototyping. Photo courtesy of Donatelle. |
At this point, most of the rapid prototyping that occurs in orthopedics is of the subtractive variety. To a large extent, orthopedic devices and instruments are made from metal, and additive processes are usually best accomplished in non-metallic materials. However, some shops that service orthopedic clients do provide additive fabrication. Others may subcontract out for these services, when necessary.
Following are some of the most common additive fabrication methods.
Stereolithography (SLA). The object is created in vat of liquid plastic, based on a computer-aided design (CAD) program. The software breaks the CAD model down into thin layers, usually five to 10 layers per millimeter. One layer at a time, the 3-D printer’s laser “paints” the object, exposing the liquid plastic in the tank and hardening it, until the model is complete.
One company offering this service is Mack Prototype, based in Garner, MA. “The part will be very close, not as much as machining or molding, but it is going to give a very close representation of the client’s design,” said Ric Perry, president of the company. In orthopedics, this process is often used to create an instrument prototype to test its ergonomics, he noted. “We do this so a doctor can hold [an instrument] and decide whether it has the right feel. Sometimes that is the first step, deciding if the part is ergonomically correct.”
Selective laser sintering (SLS). Similar to SLA, this process has the advantage of offering a choice from a wider variety of materials, including polymers such as nylon and polystyrene and metals such as steel and titanium. SLA employs a high-powered laser to fuse small particles of plastic, metal or ceramic powders into a 3-D object, one layer at a time. Again, the device takes its information from a CAD file and selectively fuses the powdered material by scanning cross sections on the surface of a powder bed, each layer on top of the previous. Material properties produced by this method can be comparable to those produced from conventional manufacturing methods, and sometimes 100% density can be achieved, which is rare among prototyping methods.
Mack Prototype also offers SLS but has found that often it is easier to simply machine the part. With today’s advanced technology, all the materials that could go into producing a SLS prototype can be machined very quickly, and the machined prototype will mimic the properties of a manufactured part more closely. “We can machine all those materials and the client can take the part to a higher level of testing, before it goes into production,” explained Perry.
this 3-D CAD software program, SolidWorks, is used before building a functional prototype. CAD has become quite popular in orthopedic prototyping. Photo courtesy of Gauthier Biomedical. |
Fused deposition modeling (FDM). An extrusion nozzle is supplied with material from a plastic filament or metal wire that is unwound from a coil. The nozzle, which is heated to melt the material, can be turned off or on to control the flow and is guided by a computer to move horizontally or vertically. In this way, the process builds layer after layer of the prototype. Parts and devices created by this method are slightly more functional than those built by other methods, in part because the plastics used can be of engineering grade. But again, FDM parts are still not as functional or as detailed as a machined part, and it is often easier to machine a prototype instead, according to Perry, although he added that FDM does have its place in the prototyping arena.
Because it produces parts and devices that function well, FDM often is employed in non-prototyping modalities. It is, for example, the manufacturing method being used in the RepRap Project, an ambitious and experimental undertaking in the United Kingdom that seeks to develop a prototyping machine that can replicate itself. The designers of the RepRap Project hope to do for manufacturing what desktop publishing and the Internet have done for the written word.
Solid Ground Curing. This process is similar to SLA in that it builds a product in layers of plastic. However, it is quicker because the layers are hardened all at once instead of one at a time.
Ink Jet Printing. In ink jet printers that work on paper, tiny drops of ink are shot on the page to produce images. In the rapid prototyping version, the same concept is applied, except the droplets are made of a liquid-to-solid compound, and they are shot on a three-dimensional object. This process is relatively fast but does not produce a prototype with a great deal of functional ability.
'If They Win, We Win’
Many machine shops and manufacturing service providers have added rapid prototyping facilities in response to the needs of their customer—OEMs and small start-ups that require more flexibility and speed in their prototyping needs. Donatelle, based in New Brighton, MN, has dedicated equipment and personnel for the sole purpose of rapid prototyping. “This way, we are not vying for production resources,” said Dana E. Schramm, director of engineering. “This is a separate group of people who are really fine-tuned just to deliver parts quickly at a prototype level.”
Staunton, VA-based IncisionTech, which specializes in bone saws and their components, is in a similar situation. The company does not consider itself primarily a prototype shop, but so many clients wanted the service that it began to provide such offerings.
“They want to see this new shape or size, and they want to be trying it out by next week,” said Chip Harvill, director of sales and marketing. “What you might have is a surgeon who has a lot of purchasing power, and that surgeon may want a saw with 13-and-a-half teeth per inch, rather than the standard saw, which has 12. Everyone has his or her own ideas about what will help to produce the best surgery.”
IncisionTech can produce very small runs—as few as five or 10 parts. The company’s rapid prototyping capabilities are relatively new, having been added in the past year or so. The company has gone so far as to add its own “incision lab,” which can analyze the physical attributes of a cutting edge. This gives the company’s engineers some idea of the edge’s quality before the part undergoes functional testing.
New England Precision Grinding (NEPG) Inc. also has added rapid prototyping to its list of services within the past year. “We see it as a way to attract new business,” said Rick Desrosiers, manager of sales and marketing for the Holliston, MA-based company. By working with engineers from many different medical device companies and helping them in the early stages of device development, the company builds a bond and intimate product knowledge that can be carried into production manufacturing, he noted. Though NEPG’s rapid prototyping facilities do turn a profit, making money is not the primary focus.
“Our rapid prototyping center was designed to help our customers develop superior products and get them to market faster than the competitors,” Desrosiers said. “The quicker they can introduce a better product, the better their chances of capturing market share and succeeding. If they win, we win.”
Other Uses
One innovation that has sprung from rapid prototyping techniques is the creation of accurate physical models that surgeons can practice on before surgery. One company capitalizing on this trend is Medical Modeling LLC of Golden, CO.
To begin the process, the patient’s parameters are scanned via two-dimensional computed tomography technology. This information is shipped to the company and, within about a week, the designers (employing SLA technology) can produce a highly accurate replica of the bone structure, which can be used in the surgical planning process. Research has concluded that surgeons spent an average of 17% less time in the operating room when using a model for cases in spinal, maxillofacial and craniofacial surgery. The company also noted that the models reduce anesthesia time and enhance implant sizing.
In another novel use of rapid prototyping technology, researchers at the University of Texas in Austin used SLS to create a casting mold for a one-of-a-kind, custom-made femur implant.
Some Challenges, Too
The increasing demand for prototyping in the orthopedics world is obviously good for business and enhances innovation, but it also increases the amount of customer service and communication that must occur between OEMs and their service providers. “You really need to flesh things out with the customer,” said Bob Lamson, vice president of business development for Medway, MA-based MicroGroup a manufacturer with expertise in tubing components. “We specialize in dealing with a lot of very complex components here, so we need to dig into the details. That is where the devil is.”
Gauthier Biomedical in Grafton, WI manufactures orthopedic instruments and handles, such as ratcheting screwdriver handles and torque limiting/torque measuring instruments. This means that ergonomics is an important aspect of the finished part. Additive fabrication can help customers get a feel of an instrument before machining and hard tooling come into play. Customers expect much shorter lead times than they did in the past, according to Michael T. Gauthier, president of the company. “A lot of times, customers think we have product waiting on the shelf in stock to ship them, but that is not always the case,” he said. Like other companies, Gauthier has set aside computer numerically controlled (CNC) instruments and allocated employees to create prototypes quickly.
Most people believe the rapid prototyping field will continue to grow at pace with the orthopedics market, if not faster. “The reason there is so much growth in this field,” said Mack Prototype’s Perry, “is you have an opportunity to go through three, four or even five design iterations and get the very best possible design, instead of just a design that will work.”