Designing for Polymer Additive Manufacturing of Medical Devices

A quick guide to production of medical devices through polymer additive manufacturing

Medical products that work smoothly, and efficiently, in the hands of the end-user; that meet the requirements of the physician and the patient; and that can be delivered quickly and yet cost less without compromising quality, are at the crux of most medical device manufacturers’ objectives. As a result, every medical designer spends time and money at the innovation stage on adding, refining and optimising features.

Everyone in the medical device manufacturing industry is starting to understand that additive manufacturing enables the design of intricate, complex geometries while reducing material consumption and, where polymers are concerned, weight. But, learning to design for additive manufacturing, and optimizing your designs to capture all the benefits, including mass customization, means unlearning everything you were taught about conventional design. If you believe your device could be produced through additive manufacturing, here are a few plus points to think about.

Design freedom:

The foundation of performance is based on design, and with additive manufacturing your designs are no longer dictated by geometry and process.

A major constraint of traditional manufacturing is the “manufacturability” of complex components. Traditionally, you broke down these components, created tools or moulds for each resultant part, and then reassembled them into the required component.

With additive manufacturing, you’re done with thinking about subtraction. Think instead about addition. You can consolidate multiple part components into a single part, saving time and costs and producing a more functional result. The added benefits? With polymer additive manufacturing, not only are you optomising topology, but you’re also light-weighting the part, too.

Accuracy:

Today’s polymer additive manufacturing technology is highly accurate. In fact, tolerances fall between 0.0762 and 0.3mm for Paragon’s polymer additive manufacturing technologies, with production repeatability guidelines of up to ±40μm for our Carbon M2 printers. In many instances, this obviates the need to produce gauges, jigs and fixtures for quality assurance, saving time and cost. If accuracy is an issue, these can be 3D printed at a fraction of a cost of machined tools.

Print bed optimization:

Part layout on the print bed is crucial to the production process. There are several factors for consideration here, and this is where great support from your manufacturing partner is paramount.

Lay a part flat on the print bed and you’ll get the fastest print, but space won’t necessarily be optimized. Line up your component parts vertically, and while you may achieve visual perfection straight off the printer, your compromise is probably part strength. Your best option for strength, accuracy and visual conformity is to print the parts on their side.

However, depending upon the technology you opt for, you will also need to consider your support structure positioning, and how to nest your parts on the bed to ensure the most efficient use of the print bed.

For the Digital Light Synthesis process, you’ll need support structures, especially where there are overhangs in your design features. The software associated with this technology should generate support structures automatically; however, it’s not a one size fits all approach, and you need to think about making sure your supports are minimal in quantity but offer maximum functionality. This is where your chosen production partner can help, especially when design and development is part of the package.

Achieving optimal production efficiency in terms of quantity and speed also comes from nesting parts on the print bed. Your production team will know which parts, and even parts of the parts are self-supporting; and which require supports.

Materials and compliance:

Medical materials need to be safe, biocompatible and meet standards set by ISO10993, the FDA, various PMAs and other notified bodies.

Fortunately for medical device designers, the developers of our AM technologies have your needs uppermost. Medical materials for Digital Light Synthesis and MJF have specifically been designed to incorporate sterilization, chemical resistance, impact strength, abrasion resistance, tensile strength, rigidity and even translucency. Each material has undergone stringent testing and has a place on the FDA Master Access File.

When designing your device for additive manufacture, you can now think about incorporating silicones, elastomers, flexible and rigid polyurethanes. If you are thinking about impact resistance, lattice structures created with resilient elastomeric polyurethanes; or silicone for a softer touch. Structures such as single use surgical instruments, devices for physiotherapy or cutting guides requiring biocompatibility, abrasion-resistance, sterilizability and impact strength can be constructed from a medical grade polyurethane; and even PA 11 Nylon.

Finishing processes:

Regardless of what the photographs might show you, parts straight off the printer are rarely ready for immediate use. Every part you create through polymer additive manufacturing will require post-production processing, so it’s imperative you think about the dimension specifications for the final part. This is especially true for patient-matched devices such as orthotics and prosthetics where scans have been used to dictate the final intended outcomes.

Digital Light Synthesis produced parts are black, white or grey. Dyeing or colouring parts could cause them to lose their integrity. PA 11 Nylon, used in Multi Jet Fusion, on the other hand, takes up colour exceptionally well and integrity is not compromised.

Postproduction processing will also use various methods to improve the looks of surfaces. PolyShot Surfacing of MJF-produced parts, for example, improves the surface texture to give a smooth, satin-like finish. DLS-produced parts will still retain some optical layering which can be removed with specific polishing processes. Check with your production team just how they intend to finish the part. You don’t want to polish away any structural strength.

Communicating through design and development:

A good production team will be with you every step of the way through the design and development process. They have produced many parts; don’t be afraid to ask for their opinion, and certainly don’t be afraid to state when you think things are not going as smoothly as you like. They are there to support you from beginning to end and through every iteration in between.