The development of a new orthopedic device from drawing board to manufacturing typically takes months. Involving high-precision design work, and subject to FDA approval, the process leaves little room for error. Rapid prototypes (RP) help speed the refining of designs and verification of manufacturability, but high costs have usually precluded companies from building orthopedic prototypes in-house. Fortunately, recent RP technologies have eliminated this issue.

For example, Orchid Design, Holt, MI, (orchid-orthopedics.com/design), with design centers in Conneticut and Tenessee, which works with orthopedic OEMs to develop implants, instrumentation, and minimally invasive devices, used to outsource its RP because it couldn't afford the high-end equipment. “The RP service bureau's work was fine, but each prototype cost thousands of dollars and turnaround times were as high as several weeks,” says Orchid Business Development Manager Brian McLaughlin.

As a result, the company used RP sparingly, where time and budget permitted. In most cases, the company worked off CAD drawings to refine designs and then developed metal samples downstream. Often, this was sufficient, says McLaughlin. But sometimes design flaws didn't emerge until late in the development process, when they were expensive and time-consuming to fix.

The advent of droplet-based deposition, derived from ink-jet technology, has allowed the development of compact, cost-effective 3D printers such as the Alaris30 from Objet, Billerica, MA, (objet.com) that fits in an office environment. The machine uses the company's photopolymer materials to build prototypes of orthopedic devices from CAD models, which in turn, can be generated from CT or MRI data. This allows fixtures to be customized for each patient. Since the fixtures fit well, they reduce patient discomfort, encourage healing, and last longer than traditionally developed implantables.

Basically, the 3D printer's jetting head slides back and forth along the X-axis, depositing a single, ultra-thin layer of photopolymer resin onto the build tray. Immediately after building each layer, bulbs alongside the jetting bridge emit UV light, curing and hardening each layer. This step eliminates the additional post curing required by other RP technologies. The internal jetting tray moves down slightly and the jet heads continue building the model, layer-by-layer, until it is complete.

“The Alaris30 lets us print high-resolution prototypes in a matter of hours,” says McLaughlin. “Better yet, it now makes sense for us to produce prototypes for every project. This practice has boosted the quality and manufacturability of our designs.”

For example, prototypes can highlight potential areas of difficulty such as undercuts that are too small. This lets the company easily tweak the design before it goes to the customer for review or to metal machining.

Additionally, sometimes customers change designs after seeing prototypes. “Providing customers something solid to see and touch, rather than just CAD renderings or drawings, makes products less abstract,” says McLaughlin.

Doing rapid prototyping in-house has been particularly helpful for determining the functional requirements for the small parts commonly used in orthopedics.

In one case, a customer visited Orchid with an idea for a new spinal device. The firm spent a few days creating the CAD drawings and then printed the first 3D prototype. A few changes to the design required the printing of a revised prototype a day later. With prototype in hand, the customer successfully communicated the design to investors and founded the start-up that same day.

While spending eight days from concept to funding might not be typical, says McLaughlin, it demonstrates the value of high-quality, working prototypes. “A CAD printout just isn't as compelling,” he says. “According to the customer, having a physical, working prototype was definitely a factor in landing funding so quickly.”

In another example, the firm worked with a customer on the design of a plate for fractures. Using a 3D CAD model generated from CT and MRI data, the designers printed 10 bones with different surface geometries and five prototype plates to see which plate would be most versatile on different kinds of surfaces. “Outsourcing the prototypes would have cost at least $3,000 and taken weeks,” says McLaughlin. “We did all the printing in-house in a couple of days. In fact, we now routinely print lots of bones when working on a project to double-check design and fit. This would have been too cost-prohibitive in the past.”

How to build functional medical devices

Another rapid technology called laser sintering allows the manufacturing of functional orthopedic devices and supplies. For example, technology from EOS in Novi, MI, (eos.info) uses a high-end laser to fuse small particles of powdered materials. These include medical-grade stainless steel, titanium, cobalt chrome, and a variety of plastics based on polyamide, which is biocompatible and resistant to most chemicals. Additionally, a special PEEK material, considered one of the highest performing thermoplastic polymers, can now be processed by laser sintering.

One example involved a laser-sintered orthesis made of polyamide for German professional racing cyclist Michael Teuber. Compared to his existing leg brace, the orthesis is lighter, stronger, and more durable. Generated from CAD data, the device is also tailored exactly to Teuber‘s body, and thus can serve both as a support for his lower leg and as a shoe. The structure of the orthesis also optimizes ventilation of the leg and foot. Wearing the device helped Teuber win a gold medal in the 2008 Beijing Paralympics.

Building biocompatible implants

Another company, ExOne LLC in Irwin, PA, (exone.com) is experimenting with the 3D printing of pyrophoric metal powders to build orthopedic implants as well as engineered lattice structures. The process fuses titanium and magnesium materials, which in powder form are highly flammable. According to the firm, this method is more cost-effective than laser sintering or electron beam melting.

Of great interest, the metals are biomaterials. According to Howard Kuhn of the company, biomaterials can have either a biocompatible or bioresorbable quality depending on the function of the implant in the body. Biocompatible implants use titanium, to which the human body will not react. The material is used for functional implants that typically survive the life of the patient without degrading. Examples include hip implants and biomedical screws. Titanium is the primary metal used in biocompatible implant creation because it is corrosion-resistance and can interface with tissue.

In contrast, bioresorbable implants use materials which degrade in the body over time. The body eventually replaces the material with living tissue. Current tissue-engineering strategies are focused on the restoration or replacement of pathologically altered tissues by transplanting living cells in combination with supportive scaffolds made of various biomaterials. This opens a broad range of applications for bioresorbable materials. Facial scaffolds to repair the jaw or skull are a typical example. Magnesium is the primary metal used in these applications because it is easily corroded by the body, allowing the implant to be replaced by natural tissue.