3D printing is a great tool to make medical implants, and materials have a significant influence on the quality of the final product. This blog focuses on materials for metal 3D printing implants.
3D Printing medical implants is a new tool to complement an already very advanced medical device industry. 3D printing is becoming more common with manufacturing high-value medical implants, which require osseointegration and/or patient-specific shapes.
Beyond geometry, it is especially important to figure out what material is used in the 3D printing of the implant. For metals, a metallurgical process and metallurgy are what make it beautiful.
Materials for metal 3D printing implants: feedstock is the key
The 3D printable material or ‘feedstock’ starts as a powder and needs to be well known from the beginning, in contrast to the usual machining process, where a solid metal block is carved using the ‘milling’ process. The 3D printing process melts the powder to form the implant, which opens a myriad of variables that can change the material microstructure and chemical composition.
Feedstock characterization comes in place to avoid uncertainties in the final product, each character has an influence on different aspects of the final implant.
Materials for metal 3D printing implants: Left in the Dust!
The 3D printing processes for metal implants start by making the feedstock. The powder makers get a solid material and break them into small particles in a process called ‘atomization’. There are several ways to make it happen, but the best method for 3D printing feedstock is ‘plasma atomization’.
To make a long story short, ‘plasma atomization’ is a process where a flow of melted metal passes towards a high-pressure gas torch with a sun-like temperature, creating a zillion small metal droplets that cool down and solidify while falling. This happens inside a tank that collects these droplets thru a bottom-funnel and is sieved to be separated by grain size, which typically ranges from 5 to 105 microns.
Materials for metal 3D printing implants: Are you in good shape?
Powder bed fusion relies on powder spread over a platform in a very even way to be melted in the contour of the implant, so the shape and size of the powder grains are very important in the quality of this “bed”. Uneven powder spreading generates difficulties in the powder spreading system which also leaves spaces for undesired porosity and oxygen contamination in the final product.
Powder bed fusion using Laser or Electron Beam as a heat source is the most used 3D printing process for metal implants. Variations in handling, quality control, and safety limitations related to powder size and flowability. Therefore, inspecting the powder in relation to these parameters is important to have a stable, precise, and safe process. On a more mundane aspect, the smaller the powder particle size, the higher its price.
Materials for metal 3D printing implants: Chemical composition
Chemical composition determines biocompatibility, microstructure, and subsequently mechanical properties of the implant. Perhaps the biggest difference between 3D printing and other processes is the fact that the material’s chemical properties change during the process. Different chemical elements have different melting and boiling points so the vaporization rates are different for each element in the alloy, so this must be compensated in the feedstock.
How we handle, blend, sieve the powder, and clean the part impacts the quantity of humidity and contamination in the feedstock. Therefore, most implant makers having strict control over the powder before and after the building process. This allows implant makers to control humidity and oxygen during printing, which has a direct influence on the mechanical properties of the resulting implant.
Materials for metal 3D printing implants: Like in cheese, better check the texture and quantity of holes.
Morphology and composition have a direct effect on the final implant microstructure. The microstructure has great importance in the implant strength. The smaller the material crystals are, the more grains there are, and consequently more internal boundaries. Internal boundaries lead to bigger resistance to the atom’s mobility, which is related to strength.
When material failures, normally happen by cracking, cracks are generally initiated by irregular pores, rounded pores usually do not initiate cracks, so control feedstock is mandatory to control the process-induced porosity and cracking.
3D printing medical implants are trending. The beautiful pieces of metal that look like cyber limbs or mimic nature are very compelling images, but material science cannot be left behind or we risk the benefits these incredible implants can bear.
About the Author:
Fabio Sant’Ana has a Precision Mechanics degree and a Business Administration Bachelor’s, born and raised in São Paulo he has 25 years of experience in helping companies to acquire and take full advantage of 3d Machining and Additive Manufacturing Equipment. Entrepreneur and knowledge avid is a member of standards organizations ASTM F42 Additive Manufacturing, ABNT CEE-261 Manufatura Aditiva e ABNT CB-26 Odonto-Médico-Hospitalar. CAD/CAM, Surface Modelling, and EBM specialist is passionate in connect people and companies to the right tools to accomplish the mission.