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This chapter is dedicated to the design, processing, and performance of metal matrix composites (MMCs) with applications in biomaterials. These composites, through the utilization of appropriate reinforcements, possess the capability to integrate the high strength and ductility of metals with bioactive and biodegradable materials, resulting in multifaceted and enhanced properties. In addition to presenting innovative solutions in material composition and more diversity in the use of reinforcements, it focuses on developing improved techniques, methods and applying new materials to maximize the benefits of MMCs in the field of biomaterials. These strategies, outlined in detail, represent the most efficient and innovative approaches to enhance the performance of biomaterials. Also, historical development and current trends of MMCs for biomedical applications were studied. The chapter aims to bridge the gap between materials science and biomedical engineering, and to show the advantages and challenges of MMCs as an important biomaterials for hard tissue replacement and regeneration. The chapter also discusses the criteria and requirements for selecting and designing MMCs as biomaterials.
Shahid Rajaee Teacher Training University, Tehran, Iran
Soroush Parvizi*
Shahid Rajaee Teacher Training University, Tehran, Iran
*Address all correspondence to: parvizi@sru.ac.ir, soroush.parvizi@gmail.com
1. Introduction
Significant advancements have been made in the development of biomaterials for medical applications throughout three generations. In the early 1930s, stainless steel and cobalt-chromium alloys were introduced, and in the 1940s, polymers were accepted as biomaterials. The first total-hip prosthesis was released in 1938, and the first blood vessel made up of vinyon and copolymer was introduced in 1952. In the following years, vascular grafts, total-hip replacement, heart valves, and artificial hearts were invented in 1953, 1958, 1960, and 1976, respectively. Figure 1 displays the different generations’ goals from 1940 to 2021 [1].
Figure 1.
The evolution of biomaterials science and technology [1].
Biomaterials should have excellent physical and mechanical properties and be biocompatible, biofunctional, bioadhesive, corrosion-resistant, and bone conductive. They should also have a low friction coefficient and wear rate. The properties of biomaterials are briefly described in Table 1.
Mechanical properties
Sufficient hardness to increase wear resistance
Implant material should have the same elastic modulus as the surrounding bone to avoid stress-shielding.
High fatigue strength helps to increase the lifetime of materials under cyclic loading.
Tribological properties
High wear resistance reduces debris and inflammation.
Low friction is key to prevent implant loosening and ensure its stability and longevity while avoiding complications and expenses.
Rough surfaces provide an improved healing process and osseointegration.
Biocompatibility
It ensures compatibility to prevent any damage or negative effects on the human or animal body, such as inflammation or infection.
Corrosion resistance
High corrosion resistance is necessary for both biocompatibility and mechanical strength.
Hemo-capability
The testing of blood-device interactions is crucial to prevent issues caused by polymorphism.
Osseointegration
Medical implants need to integrate well with tissues and allow for safe removal after healing.
Nontoxicity and cell viability
Use non-toxic substances for maximum cell viability.
Table 1.
Properties that are essential for biomaterials.
Biomedical materials encompass a broad spectrum, containing ceramics, metals, polymers, and composites. Metallic biomaterials are highly reliable when it comes to mechanical performance in medical applications. They are often used for creating surgical implants and other load-bearing clinical applications. Alloys and metal matrix composites are widely used in the medical field. While metals themselves are not biofunctional, they can be coated with apatite or biopolymers to become bioactive and biocompatible. Furthermore, metals have many dental applications, including stents, stent grafts, bone fixation, and hip implants.
Biodegradable metallic materials have become increasingly important in the field of biomedical applications in recent years. On the other hand, in the case of metal materials, their inherent structure, general properties, preparation techniques, and biocompatibility pose considerable challenges for modification. Moreover, biodegradable metals are prone to excessive degradation, leading to compromised mechanical integrity—a limitation that hinders their practical utility as biomaterials. To address these issues, degradable metals serve as promising foundational materials for creating metal matrix composites. By skillfully combining biodegradable metals with other materials, we can develop robust and functional biodegradable metallic matrix composites suitable for various biomedical applications. This chapter overviews metal matrix composites and their potential as biomaterials for various hard tissue applications [2]. Metal matrix composites (MMCs) consist of a metal matrix reinforced by another material, such as ceramics [3] or polymers. MMCs have been widely used in various engineering applications due to their superior mechanical, thermal, and electrical properties. MMCs have recently attracted attention as potential biomaterials for hard tissue applications, such as orthopedic, dental, and cardiovascular implants.
The advantages of MMCs as biomaterials include the following:
They can combine metals’ high strength and ductility with the biocompatibility and bioactivity of ceramics or polymers.
They can offer tailored degradation rates and corrosion resistance by adjusting the composition and microstructure of the matrix and the reinforcement.
They can reduce the stress-shielding effect and improve osseointegration by matching the elastic modulus and porosity of the native tissue.
They can provide multifunctional properties, such as antibacterial, anti-inflammatory, and drug delivery capabilities, by incorporating bioactive agents or nanoparticles into the matrix or the reinforcement.
However, there are also some challenges and limitations associated with MMCs as biomaterials, such as:
The fabrication of MMCs with complex shapes and delicate structures can be difficult and costly, requiring advanced processing techniques and equipment.
The interface between the matrix and the reinforcement can be prone to cracking, delamination, or debonding, affecting the mechanical integrity and biocompatibility of the MMCs.
The biodegradation and biocorrosion of MMCs can generate harmful by-products or gas bubbles, causing inflammation, infection, or tissue damage.
Therefore, the design and optimization of MMCs for biomaterials require careful consideration of the material selection, processing methods, and performance evaluation. In this chapter, we will review the current state-of-the-art and prospects of MMCs for biomaterials, focusing on the following aspects:
The common metals, ceramics, and polymers used as the matrix and the reinforcement of MMCs for biomaterials.
There are various processing techniques for fabricating MMCs for biomaterials, including casting, infiltration, powder metallurgy, and additive manufacturing.
The applications and challenges of MMCs for biomaterials in different hard tissue domains, such as bone, cartilage, tooth, and blood vessels.
2. Design of metal matrix composite for biomedical applications
Over the past two decades, MMCs have undergone development with the aim of enhancing the properties of biodegradable materials intended for biomedical applications. An MMC typically comprises a metal matrix, with principal constituents including metals such as Mg, Zn, and stainless steel. Additionally, it involves a reinforcement component, with examples being hydroxyapatite and tricalcium phosphate. Among the commonly employed metal matrices for orthopedic implant applications are Fe, Zn, and Mg [4]. The performance of a metal matrix can be enhanced through a practical approach, such as the utilization of MMCs, achieved by selecting suitable reinforcements. Additionally, optimizing the properties of MMCs in interaction with surrounding tissues involves careful consideration of factors like the proper selection of constituents, reinforcement size, concentration, and the fabrication method. The design of MMCs for biomedical applications involves the selection of the matrix, reinforcement, and structure, which are critical to the properties of the composite.
2.1 Matrix
The matrix is the base material that forms the matrix of the composite. The matrix should be biocompatible, corrosion-resistant, and have good mechanical properties. The choice of the metal matrix and the reinforcement depends on the application’s requirements. Some of the most common metals used as matrices are titanium, stainless steel, magnesium, cobalt-chromium, zinc, and their alloys. These metals have different biomedical applications, as summarized in Table 2.
Metals and alloys
Advantages
Disadvantages
Titanium
High strength-to-weight ratio, excellent corrosion resistance, good biocompatibility, low elastic modulus
High cost, poor wear resistance, low bioactivity
Stainless steel
High strength, good wear resistance, low cost
High elastic modulus, poor corrosion resistance, low biocompatibility
Magnesium
Low density, high specific strength, good biodegradability, high bioactivity
Low corrosion resistance, high hydrogen evolution, low mechanical stability
Cobalt-chromium
High strength, high wear resistance, good corrosion resistance, good biocompatibility
High elastic modulus, high cost, potential toxicity
Zinc
Low elastic modulus, good biodegradability, good bioactivity, low cost
Low strength, low corrosion resistance, high hydrogen evolution
Table 2.
Advantages and disadvantages of metal matrices of MMCs.
Mg-based material: Since 1878, medical applications have employed Mg-based materials, including both pure and alloyed ones. The human body completely degrades magnesium (Mg) after use, making it a biodegradable material. Materials that are mechanically strong, biocompatibility, bioactivity, and biodegradability are necessary for patients with bone injuries, dental issues, critical wounds, and coronary artery conditions during the healing process. Magnesium-based materials are chosen and designed according to the particular application. For instance, Mg-based materials are utilized in the development of cardiovascular stents, which achieve the necessary angiographic outcomes within 4 months through safe and complete dissolution. The optimal duration for coronary stents to complete arterial vessel remodeling and degrade while maintaining mechanical integrity is typically 6–12 months. Additionally, there are several Mg-based biodegradable bone implants for orthopedic purposes displayed in Figure 2 [5]. The medical field considers magnesium to be an essential element due to these applications.
Figure 2.
(A) The WE43 alloy screw used in the tibia fracture model of beagle dogs. (B) The HP Mg screw used to fix goat femoral neck fractures. The blue arrow indicates the femoral head. (C) The Mg2Ag intramedullary nails for femoral fractures in mice. (D) The innovative Mg/Ti hybrid fixation device (blue arrow) to fix tibial fractures in rabbits. Scale bar: 10 mm [5].
Zinc matrix composites: Researchers Yang and colleagues [6] have successfully developed a new orthopedic implant material by creating pure zinc (Zn) matrix composites reinforced with hydroxyapatite (HAp) using spark plasma sintering (SPS). HAp is a bioceramic known for its bioactivity, which promotes bone ingrowth, cell osseointegration, and proliferation. Its crystallographic and chemical structures are similar to those found in natural bone. The study found that ZnHAp composites exhibited enhanced biocompatibility and adaptable degradation rates both in vivo and in vitro. However, Zn matrix composites have a significant drawback—low mechanical strength. Further research is required to improve its mechanical properties.
Iron-based metal matrix composites: Due to their superior degradation rate compared to iron and stainless steel, iron-based metal matrix composites are a common choice for biomaterials [2, 3]. In a study conducted by Ulum et al. [7], a sequence of biomaterial composites was fabricated using reinforcements like b-tricalcium phosphate (TCP), HAp, or a mix of TCP-HAp into an iron matrix. The presence of these bioceramics helped enhance the degradation rate of the composites. According to Ulum et al. [7], MMCs displayed greater bioactivity than pure iron and iron alloys in vivo. A composite consisting of iron matrix and bioceramic reinforcement such as calcium silicate was prepared by Wang et al. [8] and their recommendations were made. The use of these composites could lead to the creation of biodegradable bone implants with improved biomedical performance, making them a practical approach.
Cobalt-chromium alloys: Cobalt-chromium alloys are used in load-bearing applications, including ankle joints, because of their exceptional wear resistance. Compared to stainless steel and Ti alloys, these alloys have a higher wear resistance. They are categorized into two groups: wrought and cast alloys. Wrought alloys are chosen over cast alloys for medical implants due to their greater strength. However, it is not desirable to have a high Ni content in wrought alloys. However, nanoparticles of a size of 20–60 nm are released from these implants every year, ranging from 1012 to 1014. In the case of prosthetic hip joints such as MoM implants, the growth of known organisms results in infection, inflammation, and disintegration, but the medical implications of this result still need more clarification. According to other research, high levels of Co and Cr in the serum can cause implants to loosen and corrosion products can be harmful [9]. The failure of Co-Cr alloys as hip implants can be attributed to a high level of toxicity.
Titanium: The high tensile strength, lightweightness, and biocompatibility of titanium make it a great choice for orthopedic applications. Ti and its alloys have high corrosion resistance and are nonmagnetic. However, the tribological properties of Ti alloys require improvement. The chemical and mechanical properties of Ti, which have been upgraded, can be obtained in grades 4 (G4Ti) and 5 (Ti-6Al-4V). To decrease Ti′s elastic modulus for implant applications while maintaining its strength, nontoxic elements such as Nb, Ta, Mo, and Zr are included [1]. These rare earth elements (Nb, Ta, Zr, and Mo) are expensive, so recent studies have suggested using Mn, Fe, Al, Cr, and Sn to reduce the cost of Ti-based medical implants.
NiTi shape memory alloy (SMAs): Newly, researchers have shown significant interest in a distinct alloy composed of nearly equiatomic ratios of nickel and titanium—referred to as nickel-titanium (NiTi) shape memory alloy (SMA) [10, 11]. This alloy has garnered attention due to its remarkable shape memory and superelastic properties. The NiTi SMA was called “Nitinol” after the U.S. Ni-Ti-Naval Ordnance Laboratory. Nitinol is lightweight and exhibits high strength and corrosion resistance, shape-changing capabilities, no cytotoxicity, and even relatively lower cost than gold-cadmium SMAs [12].
2.2 Reinforcement
Magnesium-based MMCs can be reinforced with hydroxyapatite (HAp), calcium phosphate (CaP), or bioactive glass (BG) to form a protective layer of calcium phosphate on the surface of magnesium [13]. This not only improves corrosion resistance but also promotes bone formation and integration. Similarly, iron-based MMCs can be reinforced with poly(lactic acid) (PLA), poly(glycolic acid) (PGA), or polycaprolactone (PCL) to slow down the rate of Fe degradation. This is achieved by creating a barrier layer that reduces ion diffusion and water penetration. Additionally, zinc-based MMCs can be reinforced with HAp, CaP, or BG to enhance the mechanical strength of zinc [6]. This improves load transfer and interfacial bonding between the metal matrix and the reinforcement. Expected reinforcements used in biomedical MMCs include ceramic particles, carbon fibers, and graphene.
MMCs possess a unique combination of mechanical and biocompatible properties, making them an ideal material for biomedical applications. These composites can be further strengthened by reinforcing them with HAp, calcium phosphate (CaP), or bioactive glass (BG). This helps form a protective layer of calcium phosphate on the surface of magnesium, enhancing their corrosion resistance and promoting bone formation and integration. Similarly, iron-based MMCs can be reinforced with poly (lactic acid) (PLA), poly (glycolic acid) (PGA), or polycaprolactone (PCL) to slow down the rate of Fe degradation. A barrier layer is created to reduce ion diffusion and water penetration, which helps enhance the material’s durability. Moreover, zinc-based MMCs reinforced with HAp, CaP, or BG can enhance their mechanical strength by improving load transfer and interfacial bonding between the metal matrix and the reinforcement. In biomedical MMCs, ceramic particles, carbon fibers, and graphene are expected reinforcements that offer superior mechanical and biological properties.
2.3 Structure and properties
The term “structure” in composite materials refers to how the matrix and reinforcement are arranged. It’s crucial to design the structure to optimize the composite’s properties, such as strength, stiffness, and toughness. In biomedical MMCs, particulate, fiber, and laminate structures are commonly used.
The matrix, reinforcement, and structure determine the properties of the composite. When it comes to biomedical MMCs, it is essential to customize the properties to the specific application. For instance, MMCs used in orthopedic implants should have high strength and stiffness, while MMCs used in dental implants should have good wear resistance and biocompatibility. The critical characteristics of metal biomaterials are shown in Figure 3. The most common biomedical alloys are based on Fe, Co, Ti, and Mg.
Figure 3.
Properties and advantages of metallic biomaterials.
In conclusion, the design of MMCs for biomedical applications is a complex process that involves the selection of the matrix, reinforcement, and structure. The properties of the composite should be tailored to the specific application to ensure optimal performance.
Metal-based composites can be made using two types of fabrication methods: conventional and advanced. Traditional methods include casting, powder metallurgy, diffusion bonding, and mechanical alloying. Although these methods are relatively simple and low-cost, they may result in defects such as porosity, segregation, or residual stress in the composite. On the other hand, advanced methods such as friction stir processing, laser surface alloying, spark plasma sintering, and electrochemical deposition can produce high-quality composites with fine microstructures, uniform distribution, and strong interfacial bonding. However, these methods may require sophisticated equipment and high energy consumption.
Metal matrix composite biomaterials (MMCBs) consist of a metal matrix reinforced with another material, such as ceramics or polymers. MMCBs are used for biomedical applications because they combine metals’ mechanical strength and biocompatibility with the bioactivity and biodegradability of other materials. Some of the fabrication methods of MMCBs are as follows:
3.1 Casting
Casting is forming a solid object by pouring molten metal into a mold cavity and allowing it to solidify. Casting is used to produce biomedical components such as implants, prostheses, surgical instruments, and dental devices. Some of the advantages and disadvantages of the casting method for biomedical applications are:
Advantages:
It can produce complex shapes and geometries that are difficult or impossible to achieve by other methods.
It can use various biocompatible metals and alloys, such as titanium, stainless steel, cobalt-chromium, and magnesium.
It can reduce material waste and machining costs by producing near-net-shape components.
Disadvantages:
It requires high temperatures and pressures, which can cause oxidation, evaporation, and contamination of the materials.
It can result in defects such as porosity, shrinkage, cracks, and inclusions, which can compromise the mechanical properties and biocompatibility of the components.
It can have limited dimensional accuracy and surface finish, which may require post-processing and polishing.
3.2 Powder metallurgy
This method involves mixing metal and reinforcement powders [14], compacting them into a desired shape, and sintering them at high temperatures to form a solid composite.
Advantages: It can produce complex shapes, control the composite’s porosity and microstructure, and use various materials1.
Disadvantages: It requires high temperatures and pressures, which can cause oxidation and degradation of the materials, resulting in residual stresses and defects in the composite.
3.3 Solid-state diffusion bonding
This method involves placing metal and reinforcement sheets or foils in a stack, applying pressure and heat, and allowing them to bond through atomic diffusion.
Advantages: It can produce high strength and ductility composites and avoid melting and oxidation of the materials.
Disadvantages: It requires high temperatures and pressures, which can cause deformation and distortion of the composite, resulting in interfacial reactions and diffusion of the materials.
3.4 Liquid infiltration
This method involves infiltrating a porous reinforcement preform with molten metal, either by capillary action or by applying pressure.
Advantages: It can produce composites with high density and uniform distribution of the reinforcement, and it can use low-cost and low-melting-point metals.
Disadvantages: High temperatures and pressures can cause the composite’s thermal expansion mismatch and cracking, resulting in chemical reactions and wetting problems between the metal and the reinforcement.
3.5 Spray deposition
This method involves spraying molten metal droplets onto a substrate or a reinforcement preform, forming a composite layer.
Advantages: It can produce composites with fine microstructure and low porosity and use a wide range of materials.
Disadvantages: It requires high temperatures and pressures, which can cause oxidation and evaporation of the materials, resulting in poor bonding and delamination of the composite.
3.6 Vapor-phase deposition
This method involves depositing metal vapor onto a substrate or a reinforcement preform, forming a composite layer.
Advantages: It can produce high purity and low defect density composites and use high-melting-point metals.
Disadvantages: It requires high temperatures and pressures, which can cause thermal stress and cracking of the composite, resulting in high cost and low productivity.
3.7 3D printing
One of the fabrication methods for metal matrix composite used in biomaterials is 3D printing.
Advantages include flexible process, direct molding, and precise shape control.
Disadvantages: high cost, complex wetting behavior, and accumulation of liquid metal. Therefore, 3D printing of metal matrix composite requires carefully selecting materials and techniques to achieve the desired properties and performance [15].
Biomaterials hold extraordinary significance for human civilization. Since 4000 years ago, Egyptians and Romans utilized materials such as gold and iron for dental purposes, and wood to replace the toe [16]. In today’s world, thanks to advances in knowledge, biomaterials play a vital role in various aspects of the human body. They serve diverse purposes, acting as stents in blood vessels, forming artificial joints like knees, and hips, contributing to dental applications, and enabling heart valve replacements. These materials significantly contribute to enhancing and restoring various bodily functions, showcasing their versatility and paramount importance in the field of medical science [17]. Figure 4 provides a concise overview of the diverse applications of biomaterials within the human body.
Figure 4.
Hard and soft tissue biomaterials applied to the human body [4].
Biomaterials encompass various categories, including metals, polymers, ceramics, and composites, utilized in the fabrication of implantable devices. These materials, either individually or in combination, contribute to the creation of diverse medical devices. The selection of each of these materials for use in any part of the body is carried out considering the physical and mechanical properties of each material, aiming to meet the specific needs of patients [18]. Due to the desirable mechanical properties of metals, this category of materials serves as a suitable option for applications related to hard tissues. However, despite the abundance of producible metals and alloys in the industry, only a limited number exhibit essential biocompatible properties compatible with living tissues [19]. These materials include titanium (Ti) and its alloys, stainless steels (ss), chromium and cobalt alloys (Co-Cr), and magnesium (mg) and its alloys. These materials play a vital and crucial role in meeting medical needs, especially in the fields of orthopedics and dentistry [20]. Table 3 depicts the medical applications of metal alloys.
Materials
Applications
Ti-based alloys
Fracture fixation plates, fasteners, nails, rods, screws and wires, femoral hip stems, total joint replacement (TJR) arthroplasty-hips and knees.
Stainless steel
Bone plates, bone screws, and pins, wires, etc.
Co-based alloys
Shorter term implants-bone plates and wires, total hip replacements (THR)-stem or hard-on-hard bearing system
As indicated in Table 2, metals employed within the body showcase certain limitations and vulnerabilities. Nevertheless, by employing advanced composite fabrication techniques and carefully selecting appropriate reinforcement materials, it becomes feasible to mitigate the inherent weaknesses of each metal and attain desirable properties suitable for applications in tissue repair or complete tissue replacement. These methodologies, by modifying and augmenting the mechanical, structural, and physical attributes of metals, can serve as effective solutions in the realms of medicine and health enhancement. In addition to optimizing the performance of metal materials, these interventions concurrently improve their compatibility with the human biological system. In the upcoming discussion, a more profound analysis of metals and metal matrix composites with the application of biomaterials will be provided.
4.1 Orthopedic applications
Orthopedic biomaterials are widely recognized for their high efficiency and impactful role in enhancing the mobility and quality of life for millions of individuals each year. These biomaterials are generally classified into two main application categories.
Replacement of joints that have been lost due to various factors. This application of biomaterials provides the possibility of restoring joint function to the individual.
Strengthening and repairing bone fractures. These materials are used in the healing processes to enhance bone strength and facilitate the recovery process [21].
One of the crucial applications of metals and MMCs in orthopedics is joint replacement. A joint refers to an area of the human body where two or more bones are connected. These joints bear the responsibility of supporting body weight and performing complex daily movements. Metals and metal matrix composites can provide high mechanical strength, suitable flexibility, and other necessary properties to withstand pressure. They contribute to improving joint performance, reducing weight-bearing-related issues, and enabling patients to return to their daily activities by offering the required mechanical resistance and flexibility. Figure 5 depicts a schematic of a damaged knee joint and an artificial knee joint. The artificial femur and tibia components are securely connected to the femur and tibia through careful drilling and stem insertion, with the heads exposed. This assembly is designed to mimic the natural knee’s flexibility and movement [22].
Figure 5.
Schematic diagram of (a) damaged knee joint and (b) knee joint completely replaced with biomaterials [22].
Another application of metal matrix composites in the field of orthopedics is orthopedic implants. Metals such as titanium and its alloys, 316L stainless steel, and cobalt-chromium alloys are among the materials used in the construction of orthopedic implants. These implants are preserved in the body after bone recovery. Therefore, their use comes with challenges such as interference with skeletal growth in children, increased risk of tissue infection, and weakening of surrounding bones. These issues and challenges create the need for a second surgery and implant removal after complete recovery, accompanied by higher costs and an increased risk of infection [23]. Furthermore, the lack of compatibility in the elastic modulus of these metallic implants with natural bone tissue results in the creation of protective effects against stress. This may lead to a reduction in stimulation for new bone growth and remodeling, ultimately diminishing the stability of the implant [23, 24]. Therefore, the utilization of composite materials can be a scientific approach to enhancing the performance of implants used in orthopedics [23]. These days, the use of magnesium-based composites is considered a highly suitable option for orthopedic applications due to two key features of magnesium, namely biodegradability and an elastic modulus close to the bone. By selecting appropriate reinforcements in magnesium-based composites, it is possible to enhance mechanical strength and corrosion resistance [25]. HAp, due to its chemical composition similarity with natural bone, as well as its biocompatibility and bioactivity, serves as a highly effective reinforcement in many MMCs. This reinforcing agent plays a crucial role in the development of magnesium-based MMCs used in orthopedic applications, recognized as a suitable choice for enhancing both the mechanical and biological properties of the materials [26].
4.2 Dental implant applications
A dental implant is an artificial tooth root placed in the jaw to support a replacement tooth (crown) in the maxilla or mandible. The implant mimics the shape of a natural tooth root and, through a surgical procedure, gradually integrates with the bone over time to form a stable foundation for the placement of crowns. Dental implants can serve as replacements for single teeth, or multiple teeth, or provide support for partial or complete prosthetics [27]. A vast majority of dental implants are made of titanium owing to their excellent bone bonding capacity, biocompatibility, and clinical success. Titanium and its alloys are utilized as the primary materials for dental implants due to their superior mechanical properties, high resistance to corrosion, suitable biocompatibility with living tissues, and antibacterial qualities. The excellent mechanical properties of titanium make it highly suitable for withstanding loads and pressures in the oral environment [28]. In situations where the jawbone is weak or porous, enhancing its therapeutic properties becomes particularly crucial. Adding a layer of calcium phosphate compound onto the surface of titanium implants facilitates this improvement. One of the compounds used is hydroxyapatite, recognized as a primary mineral in natural teeth. Nowadays, titanium composites with hydroxyapatite coating facilitate the improved growth of the bone surrounding the implant, especially when the adjacent jawbone is compromised. The use of these composites represents an advanced approach in the field of dental implants, aiding in the acceleration and improvement of the bone integration process with the implant. Figure 5 depicts an image of a titanium-hydroxyapatite dental implant [29]. Figure 6 depicts dental implants made of Ti-HAp composite.
Figure 6.
Dental implant component made of Ti-HAp composite material [29].
Among other metal-based composites with applications in dental implants, bioactive composite metal (BIACOM) composite is noteworthy. BIACOM composite comprises an inert titanium matrix that remains permanently in place after implantation and is reinforced with magnesium. Magnesium, being a non-toxic and biodegradable metal, eventually replaces with natural tissue, enhancing osteointegration. Consequently, it is anticipated that this composite will lead to improved performance and long-term stability of dental implants. With a balanced combination of mechanical properties and biodegradability, BIACOM composite is expected to be highly suitable for various dental implant applications [30].
4.3 Cardiovascular applications
Cardiovascular issues, whether congenital or acquired, necessitate medical care, with surgical intervention sometimes being imperative. The use of stents is one of the effective therapeutic solutions for addressing cardiac issues [31]. Stents, as biological materials, are utilized to open or prevent contractions resulting from diseases such as thrombosis (blood clot formation) in vascular channels, including the heart, peripheral arteries, and veins. Figure 7 shows a schematic of a metal stent. The most common materials for stent construction include stainless steel, titanium, iron alloys, magnesium, cobalt alloys, and plastics. Nowadays, with the advancement of new biological stents, which include metallic and polymeric composites and possess high flexibility, they are biodegradable and serve as suitable alternatives to homogeneous materials. Composite stents, capable of complete absorption by surrounding tissues, contribute to the reinforcement of vascular channels. These materials also reduce the stimulation of vascular tissue, as their biocompatibility is achieved through a design based on awareness of the interaction between the stent material surface and biological tissues nearby [22].
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Written By
Sasan Ranjbar Motlagh, Zahra Alirezaei and Soroush Parvizi
Submitted: 14 February 2024Reviewed: 05 April 2024Published: 11 December 2024
Open access peer-reviewed chapter - ONLINE FIRST
