Page 195 - IJB-9-4

International Journal of Bioprinting b-Ti21S TPMS FGPs produced by laser powder bed fusion

and mechanical properties similar to human bone . columnar structure oriented along the building direction.
[1]
Among the various biomaterials, metallic ones offer an This alloy exhibits lower Young’s modulus of 52 GPa with
ideal combination of mechanical and biological properties, a variation of less than 20% due to the texture, A good
making them suitable for long-lasting implants. Commonly mechanical strength of around 830 MPa, an extraordinary
used metallic materials in the orthopedic and dental fields fracture elongation of 21%, and a lower cytotoxicity
are 316L, Co-based alloys, tantalum alloys, and titanium compared to Ti-6Al-4V .
[17]
alloys . Thanks to the excellent combination of high
[2]
specific strength, high corrosion resistance, enhanced The human bone is composed of the external dense
biocompatibility, and elastic modulus (110–52 GPa), cortical part and the internal porous, namely trabecular
[1]
titanium alloys are particularly suitable biomaterials for one . The cortical bone confers high strength, while the
implants. The most common titanium alloy used in the trabecular bone promotes the vascularization and flow of
orthopedic field is the standardized Ti-6Al-4V extra- nutrients for continued bone remodeling. The stiffness
low interstitial (ELI) thanks to its excellent mechanical of bones varies depending on their location. Cortical
[3]
properties and biocompatibility. However, the release of bone has an elastic modulus ranging from 4 to 30 GPa,
metal ions such as Al and V can lead to severe metabolic while trabecular bone has a modulus between 0.1 and 4
bone diseases and neurological disorders [4-6] . Additionally, GPa. However, the elastic modulus of the Ti21S alloy is
V ions are cytotoxic . Furthermore, to achieve the desired still higher compared to that of human bone, which can
[4]
mechanical performances, a post-thermal treatment must cause a stress shielding effect. This occurs when the higher
typically be applied to transform martensite into a less brittle stiffness of the implant material prevents the transfer of
a + b microstructure. The presence of undesirable elements, mechanical stress to the surrounding bone, resulting in
the need for a further thermal treatment, and the very high bone resorption and implant loosening. To prevent this
elastic modulus of Ti-6Al-4V have led to the development effect and promote bone tissue growth, a prosthetic device
of the second generation of titanium alloys, based on with both high strength and low modulus similar to bone
the b phase microstructure. These novel biomaterials is preferred. One solution to reduce the bulk stiffness of the
result in a decreased elastic modulus and a reduction of implant is to create a porous structure that more closely
[19]
the harmful elements with good strength and corrosion matches the stiffness of the surrounding bone . Design
resistance already after the additive manufacturing (AM) and optimization of cellular structures to merge optimal
production process [7,8] . Three wrought b titanium alloys mechanical properties and osteointegration are a core issue
are standardized, namely Ti-15Mo , Ti-12Mo-6Zr-2Fe , of recent studies in the engineering biological field [1,19,20-25] .
[10]
[9]
and Ti-15Mo-5Zr-3Al . The body-centered cubic (bcc) The production of complex and even smaller cell
[11]
structure of b phase permits to obtain a lower stiffness geometries is made possible thanks to AM processes, such
thanks to its low intrinsic elastic modulus with additional as laser powder bed fusion (LPBF), selective laser sintering
good mechanical properties and extraordinary corrosion (SLS), and selective electron beam melting (SEBM), which
resistance and biocompatibility. Unfortunately, b Ti-15Mo is also known as electron beam powder bed fusion. Energy
is characterized by a low strength compared to Ti-6Al-4V sources, such as laser in LPBF and SLS and electron beam in
and a strong tendency to the brittle w phase precipitation . SEBM, are used to selectively melt or sinter layers of metal
[12]
[26]
To achieve higher mechanical strength, the addition of powders to form the cellular structure . The optimization
other elements is necessary. The b Ti-12Mo-6Zr-2Fe alloy of the processing parameters namely power, scan speed,
in the as-built condition shows higher mechanical strength hatch spacing, layer powder thickness, and chamber
compared to Ti-15Mo but also higher elastic modulus similar environment are of fundamental importance to obtain
[27]
to Ti-6Al-4V due to unwanted a phase precipitation inside a nearly defect-free component . Otherwise, internal
II
b microstructure [13,14] . A decrease in the elastic modulus is defects such as lack of fusion, keyhole porosity, and cracks
achieved by changing the scanning strategy and application can form. Manufacturing imperfections due to the printing
of a postsolution heat treatment which permits a significant process, namely variation of the cross-section, excess of
increase in the intensity of the {100}<001> texture leading material at the junction between struts or ligaments, and
to an elastic modulus of around 75 GPa . For Ti-15Mo- strut waviness, can modify the final mechanical response of
[13]
5Zr-3Al, an elastic modulus of 80 GPa and a strength the cellular structure [18,28,29] . The mechanical properties of a
around 900 MPa, with the latter being close to the one of porous metal are also affected by the unit cell architecture
Ti-6Al-4V, can be achieved by the alloy . Recent studies and the ratio between the density of the structure and the
[15]
have highlighted the promising performances of a un- density of the material, namely the relative density. During
standardized metastable b alloy (b-Ti21S) with the chemical an external compression load, the cellular structures may
composition of Ti-15Mo-3Nb-3Al-0.2Si (wt.%) [16-18] . undergo deformation as a result of stretching, bending, and
It displays a b phase microstructure with a textured twisting of the struts and ligaments. The elastic modulus E

Volume 9 Issue 4 (2023) 187 https://doi.org/10.18063/ijb.729