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- Quality in metal AM
This chapter describes quality issues and regulations for AM applications in the medical industry, thereby addressing all AM value chain positions.
Keywords: AM in the medical industry, regulations, materials, metrology & inspection
- AM applications in the medical industry
- Post process
- Further reading
1. AM applications in the medical industry
The follow medical applications are most commonly manufactured with AM technology:
- Tissue grafts
- Patient specific planning model
- Patient specific implants
- Patient specific guides
For applications of additive manufacturing in the medical industry we address the following articles:
- 3D opportunity in medical technology (Deloitte University Press, 2014)
- Medical applications of Additive Manufacturing Technologies in general, Sirris 2011
- A detailed five-year review of medical device additive manufacturing research and its potential for translation to clinical practice, scientific article, Stephenson (2015)
- Metal AM applications in the medical industry (Danut Dragoi, 2016)
Medical AM applications are medical devices. Requirements of medical devices strongly depend on the specific application. Requirements can be functional, usability and technical requirements. Key aspect within the medical field is the required biocompatability of medical devices.
More information on biocompatability of metal AM medical applications: Biocompatability of metals in the human body: the ultimate bio-corrosion scenario (Hansen, 2008)
For generic standards concerning AM we refer you to chapter 'application: regulations and requirements'.
The developed ISO standards for AM can be found here, ASTM standards for AM can be found here and CEN standards for AM can be found here. These initiatives work in collaboration, the developed standards complement each other. ISO 13485 is required for manufacturers of medical devices.
The following standards are relevant for the use of titanium in the medical industry:
- ASTM F1472 – wrought/forged Ti-6Al-4V
- ASTM F136 – wrought/forged Ti-6Al-4V ELI
- ASTM F2924 – Additively Manufactured Ti-6Al-4V
- ASTM F2885 – MIM’ed Ti-6Al-4V
- ASTM F1108 – Cast and HIP’ed Ti-6Al-4V
Several more AM and application specific regulations need compliance when producing medical implants. Examples are:
- ASTM F1295-11: Standard Specification for Wrought Ti6Al7Nb alloy for surgical implant applications
- ISO 5832-3 Implants fur Surgery – Metallic Materials – Part 3: Wrought T6Al4V alloy
- ASTM F3001-14 “Standard Specification for Additive Manufacturing Titanium-6-Aluminium-4 Vanadium ELI (Extra Low Interstitial) with Powder Bed Fusion
An overview of AM manufactuared materials and their applications are described by Hansen (2008), and include:
- Titanium (Ti6Al4V, Ti6Al4V ELI)
- Cobalt Chrome (CoCr, CoCrMo, CoCrW
- Oxidised zirconia and niobium
- Stainless steel and alloys
- Ultra high MW Polyethylene, polypropylene, Palm C, Nylon 12
It should be noted that manufacturing of implantable devices in the orthopaedics business is largely limited to those materials that are currently approved for use by regulatory bodies and will always be limited to materials that are proven to be both biocompatible and safe for use.
The article of Hansen (2008) reviews the corrosion of AM metals in the human body.
Design considerations for the metal AM medical applications are discussed in (Sing et al, 2015).
The key aspect of AM medical applications is customization. Quality during design can therefore very well be discusses per case, as in the chapter 'Intramedullary Nail'. Generic quality issues for design for AM can be studied in chapter 'Design'.
A trend in the medical field is that the AM machine will be more and more qualitfied by the OEM. This means service providers do not need to obtain certification for the machine themselves.
Although many process parameters can be monitored, certification requirements are mainly limited to laser spot monitoring.
8. Post processing
Generic post processing steps and quality issues are described in chapter 'Post processing', and can be applied to the medical industry. In post processing steps, before mentioned standards should be taken into consideration.
Initial inspection after primary manufacture concentrates upon the functional aspects of the product and is largely to ensure that the part conforms to the design and is within pre-determined physical and mechanical tolerances. An inspection of the surface finish may also be made at this point should it be required for specific product lines.
Products that pass these quality criteria then undergo secondary processing and finishing before cleaning and packaging prior to sterilization and any final inspection of the product.
Measurement and methods of inspection vary from product to product. However, all products must conform to the design that has received regulatory approval. Tests are then designed in order to control the critical quality attributes for the individual product.
The products are also supplied with a kit of specialised tools that are used during surgery in conjunction with the device. Some devices are also used during surgery in conjunction with other products (e.g. screws). It is important that the device maintains compatibility with these additional tools and products. Tests typically include visual inspection, measurement of physical tolerances, mechanical testing, porosity, surface finish and sterility.
10. Further reading
The following website can be visited for more information about quality in AM for the medical industry: