Photopolymers lack of stability in the long-time period. The combination of medical imaging and SLA has been used to fabricate models or moulds for the preparation of implants in cranial surgery [ 29 , 32 ], customized heart valves [ 33 ], ear-shaped implants [ 34 ], and aortas [ 35 ].
Dental applications are increasing [ 36 ] as well as the fabrication of tissue engineering scaffolds [ 37 , 38 ], thanks also to the development of biodegradable macromers and resins [ 39 ]. This technology was developed by Scott Crump in the late eighties of last century, and it was marketed in the 90s by Stratasys company, of which Crump was the co-founder [ 40 ].
Stratasys holds this trade name for FDM even if the patent expired in For this reason, the subsequent printer manufacturers exploiting the same extrusion principle have coined the alternative acronym of FFF fusion filament fabrication. FDM printers build parts layer-by-layer using a thermoplastic filament that is heated to a semiliquid state, extruded, and deposited on the printing bed along with a computer-controlled path [ 41 ]. The FDM filaments come in two standard sizes with a diameter of 1. As for all AM processes, the smaller is the thickness of the layer, the higher is the part accuracy but also the longer the manufacturing time.
Thanks to the solid material that feeds the 3D printer, multiple extruders can be used to combine diverse materials with different properties e. Lactic acid-based polymers, including PLA and PCL, have biocompatible and biodegradable properties, and hence are extensively used for medical and pharmaceutical applications.
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These biocompatible materials enable manufacturers of medical devices to rely on the FDM technique to produce devices that can be used safely for clinical trials and for low-volume productions of end-use parts. Polymethyl methacrylate PMMA filament was used for 3D-printing of porous patient-tailored implants for craniofacial reconstructions and orthopedic spacers [ 42 ].
On modified FDM printers [ 43 , 44 ], the possibility to directly extrude polymeric compounds from pellet feedstocks offers the potentiality to extend the range of materials for biomedical applications. However, there is no evidence of specific case studies so far. Laser powder bed fusion L-PBF , also known as selective laser melting SLM , is an AM process that uses a high-energy density laser, usually an ytterbium fibre laser, to fuse selected areas on a single layer according to the processed data and create 3D metal parts layerwise.
The building process begins with laying a fine metallic powder layer on a substrate plate in a controlled inert environment. After selective melting, the building platform is lowered, and a new layer is applied. The process is repeated until the part build height is reached. The laser beam focus is controlled by a galvanometer, and the movement of the beam is controlled by an F-theta lens. In L-PBF, laser power, scanning speed, hatching distance, and layer thickness are the common process parameters adjusted to optimize the process. These parameters affect the volumetric energy density that is available to heat up and melt the powders, mechanical properties, and surface roughness of the parts produced [ 45 ].
The alloys currently available for this process include stainless steel, cobalt chromium Co-Cr alloys , Ni-based alloys, aluminium Al-Si-Mg alloys , and titanium Ti6Al4V alloy. Compared with the cast and forged components, a part produced by the L-PBF process has excellent mechanical properties, thanks to characteristics of grain refinement, extended solid solubility, chemical homogeneity, reduction in quantity, and size of phase segregation [ 46 ].
However, due to the Marangoni convection induced by high thermal capillary forces, the melt pool may be unstable causing microstructures uncontrollability [ 47 ]. Therefore, to meet the current clinical requirements in parts of Ti6Al4V produced by L-PBF, heat treatment is needed to adapt the physiochemical properties and to homogenize the metal microstructures, trying to possibly improve the cytocompatibility in vitro.
In this case, the energy of an electron beam is used to melt the powder, after a preheating phase of the powder layer. The mechanic of an EBM system mixes the hardware of a welding machine and the operating base of an electron microscope [ 48 ]. If compared to the previous model A-machines , the Q-machines have a camera, Q-Cam, which takes a picture of each layer after the melting phase. With the aid of image-processing software, the machine provides a report about the final quality of the printed parts. In this way, defects or errors can be detected and recognised immediately, without the need for additional part inspection after production.
The EBM systems work under vacuum to avoid the beam to be deflected by the air molecules. Due to the vacuum and the preheating step, the build chamber is warm during the process. Therefore, after the process, the parts need to be cooled down. At the end of the process, when the part is removed from the building chamber, a soft agglomerate of powder adheres to the surface of the built and covers it completely [ 50 ].
This agglomerate is removed by sandblasting in which the same powder of the EBM process is used in order to avoid powder contamination. After this phase of cleaning, the unused powder can be recycled several times without altering its chemical composition or physical properties, because no oxygen is present inside the building chamber during the melting process, thanks to the vacuum [ 50 ]. Because of the warm environment during the process, the part shows low residual stress as compared to laser-based L-PBF systems, which require the postprocessing of built parts by a stress-relieving treatment [ 51 ].
On the other hand, the L-PBF technique offers a better surface finish, thanks to a smaller beam size and smaller layer thickness when compared to the EBM technology [ 51 ]. However, the surface roughness resulting from the EBM process represents an advantage for medical applications. Patient-customised implants with high biocompatibility and structures with osseointegration properties have been developed and implemented [ 52 — 58 ]. A significant successful example is the large-scale production of titanium acetabular cups manufactured by two Italian companies, Lima Ltd, and Ala Ortho Srl.
The purpose of the current review is to provide a short summary that can give an overview of the AM applications in the medical field even to a reader who approaches the topic for the first time.
The main features of each AM process have been presented also by highlighting its peculiarities and differences. Numerous references have been provided to show applicative case studies, demonstrating the potentiality of AM in the medical sector. A special effort was dedicated to providing case studies which reported not only the feasibility for large-volume production but also the indication of industries which already use additive technologies as the only manufacturing system to fabricate their medical products.
The authors declare that there are no conflicts of interest regarding the publication of this paper. National Center for Biotechnology Information , U. Journal List J Healthc Eng v. J Healthc Eng. Published online Mar Author information Article notes Copyright and License information Disclaimer. Corresponding author. Manuela Galati: ti. Received Dec 21; Accepted Feb This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
Abstract Additive manufacturing AM is a disruptive technology as it pushes the frontier of manufacturing towards a new design perspective, such as the ability to shape geometries that cannot be formed with any other traditional technique. Introduction Additive manufacturing AM , also known as 3D printing, is a relatively new technology that includes a large number of processes based on the layer-by-layer strategy to fabricate components.
For all of these reasons, today AM technologies play a key role in several biomedical applications that can be resumed as follows: Equipment [ 7 — 9 ] for the production of surgical supports, instruments, and tools [ 10 ] Physical models for visualisation [ 8 ], preoperative planning [ 5 ], testing, and educational aims Fabrication of customised implants for several scopes such as prostheses [ 11 ] and devices Biostructures for scaffolds and tissue engineering In addition, since AM uses a digital file, the creation of a knowledge sharing platform, which is another pillar of the third industrial revolution, is facilitated.
From Medical Data to the 3D Model for AM Processes The literature review aims to present and discuss in detail the most representative AM technologies, covering the main research areas and case studies of applications in medicine. Open in a separate window. Figure 1.
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AM Processes for Medical Applications Nowadays, AM processes that are currently used for medical applications can be grouped into two categories according to the raw material: polymers and metals. Conclusions The purpose of the current review is to provide a short summary that can give an overview of the AM applications in the medical field even to a reader who approaches the topic for the first time.
Conflicts of Interest The authors declare that there are no conflicts of interest regarding the publication of this paper. References 1.
Gibson I. Additive Manufacturing Technologies. Berlin, Germany: Springer; Hopkinson N. Emerging rapid manufacturing processes; pp. Giannatsis J.
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Additive fabrication technologies applied to medicine and health care: a review. International Journal of Advanced Manufacturing Technology. Software framework for the creation and application of personalized bone and plate implant geometrical models.
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Zanetti E. Additively manufactured custom load-bearing implantable devices: grounds for caution. Australasian Medical Journal. Patel S. An open source 3-D printed modular micro-drive system for acute neurophysiology.