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Attarilar, et al.
the 3D printer machine, the .STL file is converted into G applications. This thematic review provides some insights
file through slicing the designed model into 2D horizontal into the realization of this purpose.
cross-section arrays in a size range of 25 – 100 μm.
Then, the first layer of the 3D object is formed by the x-y 2. 3DP process techniques
movement of the printer head. Finally, the rest of the object ASTM Committees grouped different types of AM into
was created through the incessant movement of the printer seven main categories based depending on the material
head in the z-direction; hence, the desired morphology addition method and working procedure (Figure 3). In
can be deposited layer by layer on the first basal sheet as fact, each of these seven main methods has its pros and
a substrate . However, this printing procedure is highly cons according to the main objective of fabricating a 3D
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dependent on the 3DP machine. The general production printed specimen. A right method is essential and it is
procedure is represented schematically in Figure 2. generally selected according to the following parameters:
3DP can utilize various types of materials such as ABS Material type (plastic, metal alloys, ceramics, sand, and
plastic, PLA, polyamide (nylon), glass filled polyamide, wax), material state (liquid, powder, wire, etc.), material
SLA materials (epoxy resins), silver, titanium, steel, wax, compatibility, and its availability, consolidation type
photopolymers and polycarbonate, cells, hydrogels, etc. (polymerizing, laser melting or sintering, fusing, UV
Among these materials, metallic materials are of great curing, etc.), desired feature size, resolution, throughput,
importance in the biomedical field. The metallic materials and speed . In biomedical 3DP extrusion , thermal
[13]
[15]
used in AM technology must adhere to two crucial inkjet and laser-assisted techniques are commonly
requirements: First, they must have good weldability to used. The most common techniques for metal 3DP are
prevent crack formation during solidification; second, the powder bed fusion or melting methods, among which
raw metallic material should be prepared in the form of the selective laser melting (SLM) and electron beam
spherical powder with a size of tens micrometers range to melting (EBM) are very popular and they are the most
satisfy the acceptable packing density and homogeneity widely used 3DP methods in the world. Direct energy
requirements of the AM manufactured part. About 50 deposition uses metal feedstock and a laser to fabricate
metallic alloys can be used in AM manufacturing, and they parts. Vat photopolymerization selectively cures a vat
are mostly Ti-, Ni-, Al-, and Cu-based alloys, tool steels, of liquid photopolymer through targeted light-activated
stainless steels, Co-Cr alloys, and some precious and polymerization to produce 3D printed components. All
refractory metals . More than 80% of all used implants the various methods are well-classified and represented
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in medicine are metallic ones and they are categorized into in Figure 3 and the detailed information about each of the
two different groups: Bio-degradable and non-degradable methods is included in following sections.
metallic implants . Biodegradable metals include iron,
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magnesium, zinc, and calcium. Considering the excellent 2.1. Vat photopolymerization
advantages of 3DP, this technology will have a great SLA is the first patented and commercialized AM process
impact and an increase of its applications, especially in which uses a vat photopolymerization technique, and the
the biomedical field, is expected in near future. Therefore, 3D objects are generated in this process by selectively
a comprehensive understanding of the recent methods and curing a vat of liquid photopolymer through targeted
techniques opens up a new horizon for optimum design light-activated polymerization. The SLA, digital light
and fabrication of more advanced materials for implant processing (DLP), continuous, direct light processing

Figure 2. Schematic representation of the 3D printing process (Reprinted from 3D Printing Technology in Nanomedicine, 1 edition,
st
Ashish, Ahmad N, Gopinath P, et al, 3D Printing in Medicine: Current Challenges and Potential Applications, pp 1-22, Copyright (2019),
with permission from Elsevier) .
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