Titanium-magnesium composites have garnered increased attention as a
promising partially degradable biomaterial. These composites merge the
bioactivity of magnesium with the robust mechanical properties of titanium.
This article addresses the drawbacks of conventional mechanically alloyed
titanium-magnesium alloys for bioimplants and highlights three effective methods
for preparing titanium-magnesium composites for bioimplants through melt techniques:
infiltration casting, powder metallurgy, and hot rotary swaging. We outline the
advantages and limitations of each method. The composites were assessed for mechanical
properties and degradation behavior, evaluating their feasibility as bio-implants,
and discussing potential future developments. This review aims to provide a
conceptual and practical toolkit for designing titanium-magnesium composites
that can locally biodegrade.
Contact us to discuss your requirements of
titanium woven wire mesh distributor.
Our experienced sales team can help you identify the options that best suit your needs.
Introduction
Tissue injury is an inevitable element of human experience. Certain injuries may
not heal on their own, necessitating the implantation of hard tissue repair
components to assist healing (Zhang L. et al., 2019). Autologous bone grafts
are the optimal choice for restoration due to no rejection and high success rates
(Rodriguez-Merchan, 2022). However, limitations in material availability and shape
adjustment pose challenges for widespread use. Synthetic bone repair materials are
increasingly drawing attention as a solution to these limitations, aided by computer
aided design and numerical simulations (Zach et al., 2014). Metals, ceramics, and
polymers are common in hard tissue replacement materials. Most plastic surgery devices
and dental implants rely on metallic materials, including temporary and permanent
implants (Taddei et al., 2004; Chen and Liu, 2016). Despite numerous industrial
metals, only a select few meet bio-implant requirements for development, given
the inherent harsh conditions of the human body. Existing implants widely used
in orthopedic applications include Ti-based alloys (Liu et al., 2019; Yan et al.,
2019), stainless steel (Brooks et al., 2017; Teo et al., 2021), and cobalt-based
alloys (Mas Ayu et al., 2019). Despite their extensive use, these metal implants
suffer notable biological drawbacks such as corrosion, which leads to the release
of allergenic/toxic Ni and Cr ions into bodily fluids. The release of these ions prompts
adverse inflammatory and immune responses (Wong and Man, 2018).
Titanium offers advantages such as low density and high strength, with a dense oxide
film forming on its surface when it contacts air or oxygen-containing mediums (Tang
et al., 2018). Titanium alloys are extensively utilized in biomedical applications due
to their excellent biocompatibility and mechanical properties (Fan et al., 2021).
Magnesium, a light metal with a density similar to human bone (1.74 g/cm3 vs. 1.75 g/cm3)
(Zhou H. et al., 2021), boasts superior mechanical compatibility, biocompatibility,
and degradability, making it suitable for a wide range of biomedical uses. Magnesium
promotes calcium deposition, aiding bone formation (Makkar et al., 2018).
The respective shortcomings of titanium and magnesium materials hinder their broad
utilization. Titanium's disadvantage lies in its Young’s modulus (E), which, though
lower than other metals, still markedly differs from human bone, causing “stress shielding”
(Chen and Thouas, 2015). Consequently, past studies aimed to reduce the E of biomedical
titanium materials. The β-phase titanium has a low E, making the increase of β-phase content
in titanium alloys a significant research focus (Koizumi et al., 2018; Aguilar et al.,
2019; Pellizzari et al., 2020). Porous titanium structures are also explored to reduce E
effectively (Khodaei et al., 2018). However, introducing heavy β-phase stabilizing
elements increases the risk of cytotoxicity from metal ion release (Yu et al., 2015) and
patient allergies post-implantation (Fage et al., 2016). Therefore, porous titanium is
considered effective to avoid “stress shielding.” Altering porous structure porosity
allows E adjustment to match human bone tissue, while also facilitating nutrient movement
and cell proliferation (Meenashisundaram et al., 2020). But as titanium is biologically
inert, surface modifications are necessary to induce human bone tissue formation (Su et al.,
2020), complicating preparation and raising production costs. Magnesium and its alloys'
rapid degradation in the human body is another concern (Bütev Öcal et al., 2020), leading
to increased local pH and rapid hydrogen precipitation. High-purity Mg alloys degrade slower
but possess low mechanical strength, making them unsuitable for implants. Alloying improves
magnesium's corrosion resistance, with alloys like AZ91D, WE43, and ZK60 lasting longer
in the human body than pure magnesium (Witte et al., 2005; Asri et al., 2017).
Considering the inherent drawbacks of Ti-based and Mg-based materials, titanium-magnesium
composites for partially biodegradable implants have intrigued researchers recently.
These composites aim to overcome the disadvantages of current permanent and non-permanent
implants. Initial research focused on feasibility as orthopedic load-bearing implants
(Li et al., 2015), showing mechanical and fatigue properties comparable to Grade 4 Ti
(Balog et al., 2017). Therefore, titanium-magnesium composites are viable for dental
implants and other applications such as bioinspired fish scales (Liu X. et al., 2021),
indicating broad application prospects.
This paper reviews recent research and developments of titanium-magnesium composites in
biomedical materials. It covers three main sections: first, preparation methods of
titanium-magnesium composites, detailing three suitable preparation techniques; second,
summarizing their mechanical properties and effects of all phases and alloying elements
on these properties; and third, discussing corrosion properties influenced by material
ingredients and volume ratio. This review aims to present the current state and limitations
of titanium-magnesium composites as biomaterials and their future potential, ultimately
providing a toolkit for designing locally degradable titanium-magnesium composites.
Processing methods
Alloying Ti with Mg is a common strategy for preparing titanium-magnesium alloy. However,
there are two significant challenges in the traditional preparation of titanium-magnesium
alloys. Titanium has a high melting point (1668°C), significantly higher than magnesium's
boiling point (1070°C). Furthermore, magnesium's role as solute atoms in the titanium
matrix is limited by low solid solubility (0.9 at.% magnesium in titanium at room temperature
and 0.02 at.% titanium in magnesium) (Yao et al., 2022). Hence, conventional melting methods
face difficulties in alloying titanium and magnesium. Mechanical alloying extends the solid
solubility, with ball milling tests showing potential for enhancing solid solubility of
magnesium in titanium (Liang and Schulz, 2003; Cai et al., 2018). However, the low magnesium
content limits the influence on titanium-magnesium alloys, prompting interest in infiltration
casting, powder metallurgy, and hot press forging preparation methods.
FIGURE 1. Titanium-magnesium binary phase diagram.
Infiltration casting
Infiltration casting is a liquid-state fabrication method, in which a porous preform
is impregnated in a molten matrix metal to fill the pores. Techniques such as mechanical
winding, powder metallurgy, and 3D printing are employed to prepare porous titanium,
followed by filling with molten magnesium, forming a titanium-magnesium composite
(Li et al., 2015; Esen et al., 2016; Meenashisundaram et al., 2020). Li et al. (2015)
created cylindrical porous titanium preforms using a 2D titanium mesh woven into a 3D
material. Molten Mg infused the porous titanium, forming the titanium-magnesium composite
material after cooling. Their research showed that the composite’s stiffness improved
compared to entangled titanium, though only matched pure magnesium's strength. Esen et al.
(2016) achieved better mechanical properties using Ti and Ti-6Al-4V skeletons by loose powder
sintering and capillary penetration of molten magnesium. Meenashisundaram et al. (2020) used
3D inkjet printing to mix titanium powder and polyvinyl alcohol, preparing porous titanium
parts, followed by pressureless infiltration of molten magnesium. 3D printing enables faster
and more cost-effective manufacturing of net shapes for biomedical implants, increasing
precision, fit, and load distribution (Yi et al., 2021). Infiltration casting offers
simple operation, low manufacturing costs, and large-scale production. Its drawback is
low bonding strength of the titanium-magnesium interface, requiring improvement in
solution wettability and fluidity.
FIGURE 2. The schematic diagram of preparing titanium-magnesium composites
by infiltration casting.
Powder metallurgy
Powder metallurgy for preparing titanium-magnesium composites involves using titanium
and magnesium powders as raw materials, mixed, pressed, and sintered through ball milling.
The schematic diagram of preparing titanium-magnesium composites by powder metallurgy
is shown in Figure 3. Powder metallurgy offers low sintering temperature, ease of operation,
low energy consumption, and high precision. Sintering—a critical part—directly affects
mechanical properties. It can be done through spark plasma sintering (SPS), microwave
sintering, atmosphere sintering, etc. SPS technology is fast, low-temperature, energy-efficient,
and environmentally friendly (Hu et al., 2020). Ouyang et al. (2020) prepared titanium-magnesium
composites using SPS with commercial titanium and Mg-3Zn powders. The composites achieved
higher than 98% relative density. However, low Mg content in SPS-prepared composites
results in independent pores after degradation rather than continuous channels. Avoiding
oxides during preparation, Ibrahim et al. (2020) achieved Ti-xMg at temperatures below 450°C.
Powder metallurgy offers quick, efficient preparation, but faces challenges such as raw
material oxidation during sintering and weak interfacial bonding due to lack of metal compound
formation at interfaces.
FIGURE 3. The schematic diagram of preparing titanium-magnesium composites
by powder metallurgy.
Hot rotary swaging
Hot rotary swaging is an incremental shaping process used to modify the cross-sections of
rotationally symmetric metal objects like rods, tubes, and wires, and link various materials
or components. It reduces grain-size in metals, improving mechanical properties, and has been
used for demanding materials and alloys (Chi et al., 2019; Kunčická et al., 2020; Strunz et al.,
2020). Esen et al. (2013) used titanium and magnesium powders to create composites with varying
Mg volume fractions, followed by 1-hour annealing at 600°C for homogeneous microstructure. The titanium-magnesium
composites prepared by this method had high density and good plasticity but required careful handling to
prevent magnesium powder oxidation reactions during processing.
FIGURE 4. The schematic diagram of preparing titanium-magnesium composites
by hot rotary swaging.
FIGURE 5. SEM micrograph of titanium-magnesium composites containing 80
vol% Mg (A) MgO layers and EDS line scan taken along white line and (B)
titanium-magnesium interface and EDS line scan across titanium and magnesium (Esen et al., 2013).
Producing titanium-magnesium composites is challenging, especially using traditional techniques.
The three methods discussed—powder metallurgy, infiltration casting, and hot rotary swaging—
have successfully prepared titanium-magnesium composites, each offering unique advantages. Powder
metallurgy may result in magnesium volatilization during the process, altering initial design content.
Hot rotary swaging achieves high magnesium content composites but may generate oxides (MgO) due to reactions
with oxygen during processing. Infiltration casting allows mass production and control over porosity,
pore size, and distribution through 3D printing technology, producing composites suitable
for replacing bone in different parts. In addition to these techniques, emerging technologies
like laser rapid solidification are considered promising for creating metastable structures
and alloys with low miscibility due to their rapid cooling rates.
Mechanical properties
Ti and Ti-6Al-4V are commonly used as support structures for preparing titanium-magnesium
composites (Wang et al., 2011; Esen et al., 2020). CP-Ti, an α titanium alloy, is used for
dental applications or porous coatings, rather than joint implants, due to low mechanical
strength at room temperature (Chen and Thouas, 2015). Ti-6Al-4V, a widely used bio-applicable
Ti-based α+β alloy, offers better mechanical properties. Al and V elements in Ti-6Al-4V,
however, are cytotoxic; Al ions may depress bone growth and risk Alzheimer's disease (Tamilselvi
et al., 2006; Li et al., 2014). Research on Ti-based alloys focuses on changing chemical compositions
to replace problematic components and creating bone-like alloys (Kunčická et al., 2017).
β-type titanium alloys containing β-phase stabilizers (Mo, Zr, Ta) possess lower modulus of
elasticity and higher toughness than Ti-6Al-4V (Zhang Y. S. et al., 2019). They exhibit
higher corrosion resistance in the human body compared to (α+β) titanium alloys like Ti-6Al-4V
(Carman et al., 2011). Incorporating rare metal elements complicates β-titanium alloy preparation,
increasing raw material costs (Narita et al., 2012). Low-cost β-titanium alloys are in development
for large-scale biomedical applications (Gepreel and Niinomi, 2013). Most titanium-magnesium composites
use pure titanium for safety and cost-effectiveness.
Porous titanium and titanium alloy structures possess significantly reduced mechanical properties
compared to bulk materials. However, completely filled internal pores with magnesium improve
composite properties, though still less than bulk titanium and titanium alloys. Recent studies suggest
titanium-magnesium composites with spatially aligned structures enhance stress transfer, delocalize
damage, and arrest cracking, improving strength and ductility (Zhang et al., 2022). Extensive research
shows titanium-magnesium composites' mechanical properties meet human implant requirements, with
ultimate compressive strength (UCS) as a key factor. UCS of titanium-magnesium composites prepared
by different processes is higher than human bone, and UCS decreases with increasing magnesium content,
given magnesium's lower mechanical properties and non-alloyed titanium-magnesium interfaces. Titanium
tends to exhibit ductile fracture mode while magnesium shows typical brittle fracture (Ouyang et al., 2020).
Studies indicate that composites prepared with hydrogenated-dehydrogenated titanium powder exhibit
better mechanical properties than those prepared with plasma atomized titanium powder due to TiO2's
strengthening effect (Ibrahim et al., 2020). Adding rare metal elements complicates β-titanium alloy
preparation and increases raw material costs (Narita et al., 2012). Other methods to improve mechanical
properties include optimizing the preparation process. Lai et al. (2022) found that microwave sintering
significantly improved UCS, and Ouyang et al. achieved UCS as high as 1346.3 MPa with SPS-fabricated
composites due to nanograin size microstructure (Ouyang et al., 2020).
Comments
Please Join Us to post.
0