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Materials Science in Additive Manufacturing Preparation and modification of porous Ti

Figure 6. Schematic diagram of gel injection molding.

in the mixture, resulting in a reduction in porosity, with produce porous titanium with an anisotropic structure. The
the compressive strength of the sintered samples ranging Young’s modulus and yield stress of porous titanium were
from 24.4±6.8 to 79.1±6.5 MPa. 1 – 7.5 GPa and 10 – 110 MPa, respectively. The length-
diameter ratio of titanium mesh affects the compression
Parts with high quality, complex shape, and uniform
aperture distribution can be prepared by gel injection properties of porous titanium. A higher length-diameter
ratio of the pore increases the Young’s modulus and yield
molding. The mold required by this process is inexpensive stress of titanium mesh.
and is suitable for preparing large-size and high-precision
porous medical implant materials. Compared with the powder sintering method to
prepare porous titanium, the product prepared by the
3.2. Fiber braiding method fiber sintering method has better plasticity and impact
Fiber sintering refers to the technique of winding or resistance, and the porosity can reach more than 90%.
arranging metal fibers into the desired structure and then The products prepared by this method have been widely
placing them in a reducing atmosphere so that the contact used in cardiovascular and cerebrovascular scaffolds and
points between the fibers are thoroughly combined and other fields, but the prominent drawbacks lie in their shape
sintered to obtain porous titanium alloys. This method has limitations and the low bonding strength at the titanium
been widely used in preparing cardiovascular scaffolds and wire connection in the complex service environment of the
titanium mesh. human body.
The pore characteristics of metal fibers can be adjusted 3.3. Additive manufacturing method
by changing the winding mode, length, diameter, and Additive manufacturing, also known as 3D printing, has the
length-diameter ratio. Liu et al. utilized a commercial advantage of manufacturing medical implants quickly and
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pure titanium wire with a diameter of 0.27 mm as raw accurately. The products of which can not only achieve
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material, wound it along a rod with a diameter of 1.5 mm, specific mechanical properties but also shape compatibility,
and uniformly stretched the helical spring section prepared which was otherwise not possible between traditional
to maintain a particular pitch. The stretched coil spring universal internal implants and the human body. At present,
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wire was then wound together to form a pre-compacted the common methods for 3D-printing medical titanium
sample, as shown in Figure 7A. Using bisphenol A glycyl alloys are selective laser sintering (SLS), electron beam
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methacrylate (BisGMA) as a binder, the free cross-wire melting technology (EBM), selective laser melting technology
nodes in wound porous titanium were fixed to enhance (SLM), and direct ink writing (DIW) technology. 61
its strength, and the BisGMA-reinforced porous titanium
material with a porosity of 40 – 55% was prepared. Its 3.3.1. SLS/EBM/SLM
elastic modulus and yield strength were 0.4 – 1.4 GPa and As shown in Figure 8A and B, the principle of electron
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12.9 – 52.5 MPa, respectively. Wang et al. took NiTi wire beam melting molding technology and selective laser
as raw material, used a mold to arrange NiTi regularly, sintering/melting technology is preparing a construct
and added Nb powder at the connection points of each using melted metal powder in a layer-by-layer fashion
cross line for sintering, forming a NiTi porous scaffold using electron beam or laser as heat source in vacuum or
(Figure 7B). The strain of the elastic test scaffold reached inert gas environment. The specific working process is as
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27%, and the remaining strain remained close to zero follows: pre-laying powder, high-energy electron beam/
after unloading, showing good superelasticity. Li et al. laser deflection after focusing on producing high energy,
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superimposed titanium mesh with different apertures scanning the powder layer in a local small area to produce
(300 μm, 551 μm, 697 μm) layer by layer (Figure 7C) to high temperature and even melting, continuous scanning
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Volume 3 Issue 1 (2024) 8 https://doi.org/10.36922/msam.2753