Selective Laser Sintering

Additive Manufacturing for Medical Devices

The use of additive manufacturing (AM) techniques to produce medical devices is growing at a rapid pace, and it’s easy to see why. Additive manufacturing allows manufacturers to lower production costs by reducing waste and decrease time to market by simplifying (or eliminating) tooling and equipment. Employing AM technologies also makes it possible to produce patient-specific designs and devices with complex geometries, and to do so at a lower cost than traditional manufacturing methods.

 The terms “rapid prototyping” and “additive manufacturing” are often used interchangeably. But rapid prototyping can refer to a variety of methods – including additive manufacturing – by which models are produced for demonstration, proof of concept, and feasibility testing. The term additive manufacturing specifically refers to a production method that involves “building up” a part by adding layers of material.

It’s important to note that medical devices produced via additive manufacturing techniques can be validated, but the method and requirements for validation should be addressed during the initial product development.

There are many additive manufacturing technologies used for the development and production of medical devices, and each technology is designed for specific metals or resins. The combination of the AM process and its suitable materials often drives the decision of which technology to use for a given device or purpose. But when choosing which additive manufacturing technology to use, or even whether AM is appropriate for a given product, it’s important to consider the implications that it will have on the entire product development and release process, from prototyping to production.

Processes and Materials

Stereolithography

Stereolithography, (SL) is an additive manufacturing technique in which an ultraviolet (UV) laser cures, or hardens, a liquid plastic. The stereolithography apparatus (SLA) creates the part, layer by layer, by submerging a metal platform into a vat of photopolymer (liquid plastic that is hardened with light). The platform is lowered by an amount equal to the thickness of the first layer, and the UV laser traces the pattern of the initial layer onto the surface of the liquid. The platform is then lowered by the thickness of the next layer, and the laser again traces the pattern of that layer on the surface of the resin, curing it and joining it to the layer below. It’s important to note that for objects with thin walls or other delicate structures, the SL process requires supports during manufacturing. These supports are removed after the completion of the build.

There are three resins that are particularly well suited for producing medical devices with stereolithography, and each one has unique benefits for specific applications.

  • BioClear: This resin produces parts that are clear, strong, and water-resistant. BioClear is USP VI certified, and is primarily used for medical applications that are non-implant and have limited contact with the body, such as device prototypes or dental drill guides.
  • Watershed XC 11122: The unique feature of Watershed XC 11122 is that it creates parts that are nearly colorless, with an appearance and mechanical properties similar to commonly used clear thermoplastics such as polycarbonate. Watershed has excellent water resistance and is dimensionally stable.
  • ProtoGen O-XT 18420: This is an ABS-like photopolymer that has excellent chemical resistance and can withstand a wide range of temperature and humidity levels. Its white color makes it easy to see details, making it preferable for applications such as surgical planning models.

Light Fixture made form Stereolithography (SLA)

Sterolithography 3D Printed prototype

Stereolithography has relatively high accuracy and feature definition, combined with isotropic material properties. It is widely used in the development process to evaluate form, fit, and function. It is also a good choice for patterns to support low-volume production methods such as resin casting and investment casting.

Selective Laser Sintering

In the selective laser sintering (SLS) process, a laser heats a powdered material – usually plastic, ceramic, or glass – to just below its melting point, hardening and bonding it to create a 3D structure. Similar to the stereolithography technique, SLS builds the part on a platform, which lowers incrementally as the laser create layers that form the part. In contrast to stereolithography, SLS typically does not require support structures, even for thin, fragile parts.

Surgical cutting block of a human heart created from nylon using Selective Laser Sintering

Selective Laser Sintering

A common use of SLS technology in medical device manufacturing is to produce patient-specific surgical cutting blocks (also referred to as surgical cutting guides). While SLS can be used with a variety of materials, nylon is often the material of choice in these types of applications.  SLS produces high-precision parts and geometries that are nearly impossible to obtain by other methods, and nylon provides a robust part with a high melting point.

Electron Beam Melting and Direct Metal Laser Sintering

The electron beam melting (EBM) process manufactures parts by melting powdered metal with an electron beam (unlike SLS, which heats the powdered material to just below its melting point). Manufacturing with EBM technology takes place in a vacuum to avoid scattering of the electron beam, and the vacuum environment helps eliminate impurities trapped in the metal. Parts produced with EBM technology are also stress-free and have high yield strength.

While EBM technology is suitable for a wide range of metals and alloys – aluminum stainless steel, titanium and cobalt chrome – the most commonly used materials for medical devices are titanium and stainless steel. The US Food and Drug Administration (FDA) has approved titanium implantable devices produced via EBM.

Another additive manufacturing technology that uses metal to produce parts is direct metal laser sintering (DMLS). This process is essentially the same as selective laser sintering, but DMLS builds the part from powdered metal rather than plastic, ceramic, or glass. Like EBM technology, DMLS can be used with stainless steel and titanium, making it a suitable option for medical devices.

 Choose the Right Partner

In 2016, the FDA addressed the topic of producing medical devices through additive manufacturing technology, with its draft guidance document, Technical Considerations for Additive Manufactured Devices. While this document covers two main areas – “Design and Manufacturing Considerations” and “Device Testing Considerations” – it is not meant to be a comprehensive guide.

As a manufacturer, navigating the possibilities for additive manufacturing of medical devices can be overwhelming. But a development partner who is comfortable with all the materials and technologies available can help you make the best decisions regarding technical and performance requirements, validation methods, and time-to-market objectives.

Vaupell, Inc., a division of Sumitomo Bakelite (TYO: 4203) provides complete product development services for medical device manufacturers. Our team can assist in design for manufacturability, project engineering, 3D printing, and injection molding expertise for medical device projects from concept to commercialization. Our innovation center located in Hudson, NH can assist in concept, feasibility, and short-run production builds. Scale-up and commercial launch are supported in our ISO 13485 registered facilities in MA and MI.

Vaupell has in-house capability for SLA, SLS, DMLS, metals and plastics machining, prototype tooling building, and injection molding. Connect with us to learn more about how we can assist you in your next line extension or product development project.

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Vaupell Holdings is a group company of Sumitomo Bakelite Co. Limited.