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Materials Science in Additive Manufacturing MAM for orthopedic bone plates: An overview

Table 2. Summary of orthopedic bone plate materials
Material category Specific materials Pros Cons References
Practical plate • Stainless steel 316L • High mechanical strength • Stiffness mismatch with bone [52-54,60]
material • Titanium alloy Ti-6Al-4V • Corrosion resistance • Low fatigue life
• Biocompatibility
Low-modulus alloy • Ti−35Nb−7Zr−5Ta • Resembles cortical bone modulus • Inconsistency in the fabrication process [7,61]
(β-Ti alloys) • Ti-35Zr-28Nb • Low toxicity • Mechanical property deviations
• Good mechanical attributes
• Corrosion resistance
Smart alloy • Ni-Ti • Low stiffness • Not mechanically superior [43,48,60]
• Biocompatibility • Nickel release concerns
• Super-elasticity
Biodegradable metal • Iron-based • Good mechanical strength • Uncontrollable degradation rate [28,64-71]
• Magnesium-based • Enhances bone formation • Hydrogen gas formation (magnesium)
• Zinc-based
Bioceramic and • Nano-hydroxyapatite • Biocompatibility • Insufficient bone healing support [15,27,52,72,73]
polymer • Polyetheretherketone • Biodegradability • Low mechanical strength
• Drug loading capability

that of cortical bones. For instance, Young’s modulus for corrosion resistance. However, a notable challenge in this
316L SS ranges between 190 and 205 GPa and for Ti6Al4V domain is the sensitivity of these alloys to AM parameters.
between 110 and 112 GPa, while cortical bone has a For instance, variations in energy density can lead to
much lower modulus ranging between 11.6 and 20.8 GPa. significant changes in the mechanical properties of TNZT
Similarly, while 316L SS has a yield strength of 343 – 535 samples . Similarly, scanning strategies during the AM
[61]
MPa and an ultimate tensile strength of 557 – 661 MPa, process have been observed to influence the porosity and
Ti6Al4V displays higher values, with a yield strength of modulus of the resultant implants .
[63]
795 – 1051 MPa and an ultimate tensile strength of 860 Another intriguing development is the incorporation
– 1116 MPa. In comparison, the cortical bone’s yield of titanium into the nickel-titanium (NiTi) shape memory
strength is between 53.4 and 132.4 MPa, and its ultimate alloy. Boasting low stiffness, superior biocompatibility, and
tensile strength is between 72.8 and 175.2 MPa [55-59] . superelastic properties, NiTi alloys present a strong case
This disparity can hinder beneficial mechanical cues, for orthopedic applications, especially in fracture plates.
potentially affecting the healing process or even leading Recent studies have underscored the potential of these
to conditions like osteoporosis . Notably, due to to the alloys, highlighting their consistency and mechanical
[27]
superior strength and reduced stiffness of Ti6Al4V bone appropriateness for bone plate manufacturing [43,48] .
plates compared to 316 L SS, they are becoming a popular However, there are concerns regarding the release of nickel
alternative to traditional plates. However, they still faced (Ni) elements into the human body .
[60]
challenges like poor fatigue properties, which can result in
plate loosening or fractures . It is evident that while metals such as stainless steel and
[60]
titanium-based alloys offer robust mechanical support for
Addressing the stiffness mismatch in orthopedic
implants calls for exploring materials with a more bone healing, their finite lifespan poses another challenge.
appropriate modulus. A promising avenue has been the These materials often necessitate subsequent removal
development of biocompatible β-Ti alloys, especially surgeries. Consequently, the spotlight is shifting toward
with the incorporation of β stabilizing alloy elements biodegradable or smart materials, which not only support
such as molybdenum (Mo), niobium (Nb), silicon (Si), bone healing but also degrade over time, obviating the
need for removal.
tantalum (Ta), tin (Sn), and zirconium (Zr). The alloys,
Ti−35Nb−7Zr−5Ta (TNZT) and Ti-35Zr-28Nb (TZN), The evolution of materials for orthopedic implants now
have garnered particular attention due to their modulus emphasizes biodegradable options. Such materials should
being akin to that of cortical bone . A study by Li et al. ideally exhibit adequate mechanical strength without
[62]
[61]
illustrated the potential of TZN for bone scaffolds using inducing stress shielding. They should also degrade at a
selective laser melting (SLM). Although the mechanical rate that aligns with the bone healing process, ensuring
properties varied based on the employed porosity structures, continuous mechanical support . In addition, it is
[64]
the scaffolds showcased promising biocompatibility and imperative that these materials avoid elements such as Al,

Volume 2 Issue 4 (2023) 6 https://doi.org/10.36922/msam.2113