Magnesium Composite Materials and Applications

Magnesium Composite Materials

Magnesium-based composite material is used in biomedical applications. The chemical composition matrix material and reinforcement being considered are very crucial factors due to the fact that most material for industrial applications is enormously toxic in the human body environment. The material should possess good mechanical properties and should be biocompatible, especially for biomedical applications.

Generally, a biodegradable biomedical implant must be nontoxic or carcinogenic and it should be compatible with the human body environment. In addition, it is ideal if nutritional minerals like magnesium, zinc, and calcium are present in the implants (see Table 14.3). In order to maintain the mechanical integrity and load-bearing capacity of the implant, the material should possess convenient dissolution rate or measured corrosion rate until healing the surrounding tissues. The load-bearing properties may not be necessary once the healing takes place. Along these lines, pure magnesium, magnesium alloys, and composites are utilized as productive biomedical and biodegradable implants, which are important to control the corrosion rate in a physiological environment (Andrej et al., 1999).

Biodegradable composite material consists of a biodegradable metal matrix and biodegradable reinforcement. Magnesium-based micro composites and Nanocomposites have been developed to achieve the required mechanical properties, corrosion resistance, non-toxicity, and biocompatibility. Many researchers have taken abundant opportunities to develop magnesium biodegradable composites for

TABLE 14.3

Compositions of Alloying Elements through Chemical Analysis for Selection of Matrix Materials (Frignani et al., 2006)

Matrix

Nominal Element Component (wt %)

Trace Elements (Max) (wt%)

Al

Zn

Mn

Ca

Li

Nd

Zr

Y

Fe

Cu

Si

Ni

Be ppm

AZ31

3.5

1.4

0.3

0.003

0.008

1.2

0.001

5-15

AZ91

9.5

0.5

0.3

0.004

0.025

0.05

0.001

5-15

AM60

6.0

0.2

0.2

0.004

0.008

0.05

0.001

5-15

LAE442

4.0

4.0

2.0

Heavy metallic rare elements

WE43

3.2

0.5

4.0

Heavy metallic rare elements

biomedical applications. Magnesium composites have excellent biodegradability and biocompatibility when compared to other metals. The selection of reinforcements plays a very important role in the metal matrix composites to improve its properties. The development of biodegradable composites, both matrix and reinforcement, has to be bioinert, bioactive, and biodegradable while healing the tissue without losing its mechanical integrity.

Mostly ceramic-based reinforcements are used in composites because of their bioactive, bioinert, and biocompatibility in the biological environment. If metallic- based reinforcements are used, they can create a toxic environment due to their lack of biocompatibility in the biological environment. Whenever ceramic-based reinforcements are used in composites, those are called bioceramic composites. The main advantage of bioceramic composites is their low chemical reactivity, corrosion resistance, and biocompatibility. The very early first ceramic reinforcements use in biomedical applications was alumina (Al20,) and zirconium (ZrO,). To be specific, the important feature of these two reinforcements is their enormously low- reaction kinetics. Other ceramic reinforcements exhibit faster reaction kinetics and create toxicity. Bioactive composites come in contact with physiological fluids and have chemical reactions toward tissue to repair or reform the tissue. The reinforcement particle size may improve the grain refinement to increase the properties of the composite. In their current generation, calcium phosphate ceramic reinforcements are focused to generate orthopedic implants and dental implants. HAP is used to improve the bonding between the implant and the orthopedic bone due its outstanding bioactive and biocompatible property. The properties of bioceramic reinforcements are given in Table 14.4.

Applications

Biodegradable magnesium implants have been available in the market since the year 2010with the trade name Magnezix. A pow-der metallurgy method was used for the first CE-certified biodegradable screw- (Seitz et al., 2016). This screw is approved for fixation of bone and fragments, and its mechanical properties were

TABLE 14.4

Properties of Bioceramic Reinforcements

Reinforcement

Characteristics

Applications

Alumina(Al,03)

Bioinert, biocompatible, high hardness, high strength, corrosion resistant, and stress shielding

Femoral head, porous coatings for femoral stems, bone screws, and plates

ZirconiafZrO,)

High fracture toughness, high flexural strength, low Young’s modulus, biocompatible, bioinert, nontoxic

Artificial knee, bone screws, and plates

Bioglass

Biocompatible, bioactive, brittle, and nontoxic

Artificial bone and dental implants

Hydroxyapatite(Hap)

Bioabsorbable. bioactive, biocompatible, similar composition to bone, good osteoconductive properties

Femoral knee, femoral hip. tibial components, acetubular cup

more appropriate when compared with other implant materials. The ultimate tensile strength of Magnezix is greater than 290 MPa, the elastic modulus is about 45 GPA, and its yield strength is greater than 260MPa. The elongation is up to 8% and pre- clinical studies were conducted from year 2010-2012.

Magnesium-based biomaterials were used to develop cardiovascular stents and achieve necessary angiographic results. The practical time period for coronary stents to full remodeling process of major vessels and degrading with optimal mechanical integrity is from 6 to 12 months (El-Omar et al., 2001).

Magnesium-based biodegradable stents are used in biomedical applications to recover the function of injured vascular arteries as shown in Figure 14.1. Additionally,

Cardiovascular stent expanded view (Peuster et ah, 2006)

FIGURE 14.1 Cardiovascular stent expanded view (Peuster et ah, 2006).

Magnesium-based biodegradable orthopedic implants (Peuster et al„ 2006)

FIGURE 14.2 Magnesium-based biodegradable orthopedic implants (Peuster et al„ 2006).

various degradable bone implants for orthopedic applications such as screws (Mg- Ca 0.8 alloy), plates (ZEK 100), nails (LAE442 alloy), laryngeal surgery clips (Mg), wound closing instruments, and dental implants are shown in Figure 14.2. These applications demonstrate magnesium as one of the main important elements in the medical area. In Table 14.5, the applications, advantages, and disadvantages of implant materials are detailed.

Types of Reinforcements

14.2.3.1 Alumina (Al203)

Alumina powder has specific characteristics of high hardness and high abrasion resistance. This reinforcement has excellent wear and friction behavior along with surface energy and surface smoothness. A 1,0, has a hexagonal structure; the aluminum ions have octahedral interstitial sites, which give the thermal stability of the composite. The abrasion resistance, mechanical strength, and chemical interactions of alumina make it recommended as a ceramic reinforcement for manufacturing of dental and bone implant material composites.

14.2.3.2. Zirconia (ZrO2)

Zirconia is a biomaterial that has a high mechanical strength, fracture toughness, and excellent biocompatibility. This type of ceramic-based reinforcement gives several advantages of biomedical-based implant materials. Addition of this reinforcement improves the composite strength and thermal stability, as well as reduces the toxicology.

TABLE 14.5

Biomedical Implant Materia Applications, Advantages, and Disadvantages (Wong et al., 2007)

Material

Advantages

Disadvantages

Applications

316L stainless steel

Excellent fabrication property, toughness, easily available and low cost, acceptable biocompatibility

High modulus, poor wear and corrosion resistance

Bone plates, screws, pins, and wires, etc.

Co-Cr alloys

Corrosion resistant, high fatigue strength and wear

Expensive and difficult to manufacture Stress shielding effect, high modulus, toxic due to Cr. Co, and Ni ion release

Bone plates, wires, and hip replacements

Ti alloys

Lower modulus, corrosion resistant, lightweight, and biocompatible

Poor wear resistance, poor ductility

Fixation plates, screws, nails, rods, and wires, total joint replacement

Mg composites

Biocompatibility, biodegradable, light in weight, low stress shielding effect, and low density

Hydrogen evolution during degradation

Bone screws, pins, plates, and stents

14.2.3.3. Carbon

Carbon is an element that exists in a variety of forms such as metals, polymers, and composites that may have carbon aqueous materials, which increase the fatigue strength. However, its intrinsic brittleness and low tensile strength limits its usage in load-bearing applications.

14.2.3.4. Calcium Phosphate Ceramics (CPC)

For 20 years, calcium phosphate salts have often been used as reinforcements in bio-composites for successfully replacing and augmenting bone tissue. Widely used calcium phosphate bioceramics are В-TCP and HAP. Calcium phosphates may stabilize the phase and improve the grain refinement to increase the corrosion resistance. This type of ceramic-based reinforcement has excellent bioactive, bioinert, and good biocompatibility properties.

14.2.3.5. Other Reinforcements

Si,N4 was used as a reinforcement for orthopedic implants to support bone fusion in a spiral surgery and to improve wear and longevity of prosthetic hip and knee joints. It is a hydrophilic negative charged ceramic material, which contains full of nutrients and proteins in the material. It also facilitates bone-cell adherence and integration of the material in the nearest bone. Carbon nanotubes have vast potential in manufacturing and hard tissue implants, scaffolds, micro catheters, and as substrates for neuronal enlargement disorder. Titanium-based reinforcements are used, especially for load-bearing applications due to their biocompatibility, tribological properties, mechanical properties, and corrosion resistance.

 
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