Fundamental Biomaterials: Metals

Sabu Thomas, Preetha Balakrishnan, M.S. Sreekala, Sreekala Meyyarappallil Sadasivan

• Publisher: Woodhead Publishing
• Year: 2018
• Print ISBN: 9780081022054
• eBook ISBN: 9780081022061
• Topic: Technology & Engineering
• Subtopic: Materials Science
• Index: Technology & Engineering

Fundamental Biomaterials: Metals provides current information on the development of metals and their conversion from base materials to medical devices. Chapters analyze the properties of metals and discuss a range of biomedical applications, with a focus on orthopedics. While the book will be of great use to researchers and professionals in the development stages of design for more appropriate target materials, it will also help medical researchers understand, and more effectively communicate, the requirements for a specific application. With the recent introduction of a number of interdisciplinary bio-related undergraduate and graduate programs, this book will be an appropriate reference volume for students. It represents the second volume in a three volume set, each of which reviews the most important and commonly used classes of biomaterials, providing comprehensive information on materials properties, behavior, biocompatibility and applications. - Provides current information on metals and their conversion from base materials to medical devices - Includes analyses of types of metals, discussion of a range of biomedical applications, and essential information on corrosion, degradation and wear and lifetime prediction of metal biomaterials - Explores both theoretical and practical aspects of metals in biomaterials

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Metallic biomaterials

State of the art and new challenges

Dr. J. Wilson, Department of Bioelectronics and Biosensors, Alagappa University, Karaikudi, Tamilnadu, India

Abstract

Biomedical applications of macro-, micro-, and nanomaterials are exponentially increasing every year due to their analogy to various cell receptors, ligands, structural proteins, and genetic materials. Among the various biomaterials available, metallic-based implant materials can provide scaffolds for excellent tissue/bone/organ repair that are needed to save and prolong the human being’s life. This review will therefore highlight recent advancements on metallic bioimplants with their advantages and limitations based on nanotechnology.

Keywords

Osseointegration; bioabsorbability; biomaterial; alloy

Acknowledgement

The author J. Wilson would like to thank DST-SERB, BRNS and UGC for financial assistance.

1.1 Introduction

With the rapid improvement of standards of living and progress of society the people are facing social pressure, which is accompanied by increased rates of occurrence of various diseases and thus limiting their life. With the broad application and swift improvement of microtraumatic intervention treatment, the implantation of biomaterials is recognized to be one of the most efficient strategies to save and prolong the life of the human community [1]. The wide use of antimicrobial and other antibiotic agents has led to a profound increase in difficulties to undertake neurosurgical, orthopedic, and cardiovascular treatment which adds additional financial pressure on the healthcare patients [2]. Hence the biomaterials are essential, nevertheless they tend to cause certain limitations such as mechanical failure, infection, and immunogenic reactions to implanted biomaterials. Remarkable research efforts have been demonstrated to the improvement of biomaterials to continue the physiological processes and functions critical to sustaining life [3].

1.2 Types of biomaterials

In ancient times, gold wires were used as a scaffold to tie an artificial tooth to its neighboring teeth. In the early 1900s bone plates were successfully used to repair bone fractures and to accelerate their healing. Later in the 1950–60s, blood vessel replacement was performed using hip joints and artificial heart valves. Generally, the biomaterials can be classified into the following types:

1.2.1 Metals

As a class of materials, metals are the most widely known scaffold for load-bearing implants. For instance, some of the most common orthopedic surgeries hold the choice of using metallic implants. These vary from simple wires, screws to fracture fixation plates, total joint prostheses for hips, ankles, knees, shoulders, and so on. Moreover, in orthopedics, metallic implants are chosen in cardiovascular surgery, maxillofacial surgery, and as dental materials. The most commonly employed metals and alloys used for medical device applications are stainless steel, titanium and titanium alloys, cobalt-based alloys, and tantalum-based alloys [4].

1.2.2 Polymers

A wide variety of polymers have been utilized as biomaterials in the medical field. Their applications range from facial prostheses to tracheal tubes, kidney, liver parts, heart components, dentures, to hip and knee joints. Also, polymeric biomaterials are added in the preparation of medical adhesives, sealants, and coatings for a variety of functions. The physical behavior of polymers possesses a close similarity to soft tissue which is useful to repair skin, tendon, cartilage, and vessel walls, as well as drug delivery and so on. Polyethylene is used for replacing joint prostheses, while polycaprolactone has been utilized in resorbable sutures, screws and plates for fracture fixation purposes [5].

1.2.3 Ceramics

Traditionally, ceramic materials were used as restorative materials in dentistry. These materials range from crowns, cements, and dentures. Some ceramic scaffolds are demonstrated in joint replacement augmentation and bone repair. However, their poor fracture toughness severely limits their applications for load-bearing applications [6].

1.2.4 Composites

The most successful composite biomaterials used in the field of dentistry are restorative materials and dental cements. Carbon-reinforced polymer and carbon–carbon composites are of great attraction for joint replacement and bone repair because of their low elastic modulus levels. However, composite materials are extensively utilized for prosthetic limbs, where their combination of low density/weight and high strength result in them being supreme scaffolds for such applications [7].

1.2.5 Nanocomposite materials

The higher water content materials provide cell friendly microenvironments for preparing various composites. Mammadov et al. [8] suggest that polymers can mimic angiogenesis in tissue regeneration. Zhao et al. [9] demonstrated tetra sulfonatophenylporphyrin derivatives adjuvant with TiO₂ nanowhiskers for the ranostics of Rheumatoid Arthritis. Similarly, nano TiO₂ has been used for coating of orthopedic prosthetic implants [10]. The TiO₂ nanotubes-based composites have been demonstrated in the repair of articular joints, hip–knee joints, to control the wear and tear effect. The nanostructured TiO₂ coated on the surface of prosthetic implants are highly safe with improved bone mineralization and osteoblast adhesion [11]. In nanotherapeutics, various magnetic nanostructures are used to alter the cells biochemical and physiological environment by moving the charged particles into the cell by enhanced membrane permeability [12]. The hydroxyapatite-based nanocomposites are favored for the nano 3D structure formation due to the promotion of cell organization, proliferation, and allowance of free movement of nutrients to the developing tissues. Ji et al. [13] suggest that nanohydroxyapatite–chitosan–gelatin-based scaffolds are used for osteogenesis. This is also supported by Fig. 1.1.

Figure 1.1 Biomimetic spiral–cylindrical scaffold based on hybrid chitosan/cellulose/nanohydroxyapatite membrane.

1.2.6 Natural biomaterials

Interestingly, there are new materials derived from the animal and plant world being considered for use as biomaterials. One of the advantages of using natural materials for implants is because the materials are similar to those found in our body. These materials are naturally toxin-free, carry specific protein binding sites, and the biochemical reactions assist tissue healing. However, natural materials suffer from immunogenicity. Another problem faced by these natural polymers is their tendency to denature at below their melting point temperature. This severely restricts their fabrication of different sizes and shapes of implants. Natural materials include collagen, chitin, coral, cellulose, and keratin [14].

1.2.7 Nanobiomaterials

Nanobiomaterials structurally are similar to various body proteins, ligands receptors, and DNA, whose size should be in the range of 10–100 nm for better biomedical applications. The size above 100 nm may induce embolism and in between 10 to 100 nm may be utilized as better drug delivery vesicle while around 10 nm may be in biomedical imaging [15]. However, the size below 10 nm is highly toxic and reactive. This permits them to interact freely with various body receptors and quickly cross the cell membrane [16]. Nanobiomaterials are widely utilized in nanodrug delivery systems [17], gene therapies [18], cancer photodynamic therapies [19], tissue engineering [20], and orthopedic implantation [21].

1.3 Behaviors of biomaterials

Any material that has been substituted into human body should be highly acceptable to the biological system, with minimum adverse effects. And, the following various factors that concern the healing process either influence this process independently or as cofactors with other multiple factors.

1.3.1 Biocompatibility

A perfect biomaterial scaffold should not suppress the activity of normal cells and should be toxin-free during and after implantation [22]. Moreover, it should also create well induced effects that may promote adhesion and healthy cell growth in the microenvironment, composed of nanostructures. This is mainly because of a larger specific surface area of nanostructures that can promote the adsorption of proteins, cell adhesion, and growth [23]. Hence more attractive nanomaterials are being synthesized with good biocompatibility for biomedical applications [24,25].

1.3.2 Mechanical property

The scaffold should satisfy good mechanical strength and provide transfer properties. Mechanical strength of required biomaterials has a broad range density. So different geometries with different mechanical strengths have been designed to form ideal scaffolds such as nanopillars, nanofibers, nanoparticles, and nanocomposites to face the mechanical behavior challenge [26] (Table 1.1).

Table 1.1

Mechanical properties of metallic implant materials and cortical bone

Materials	Young’s modulus (GPa)	Ultimate tensile strength (MPa)	Fracture toughness (MPa $\sqrt{m}$ )
CoCrMo alloys	240	900–1540	~100
316L stainless steel	200	540–1000	~100
Ti alloys	105–125	900	~80
Mg alloys	40–45	100–250	15–40
NiTi alloy	30–50	1355	30–60
Cortical bone	10–30	130–150	2–12

1.3.3 Vesicular structure

The vesicular structure with porous diameter 200–350 μm is a necessary behavior for bone repair scaffold materials, to guarantee the transportation of oxygen and nutrients [27]. The porous biomaterial ions dissociate after implantat...

Table of contents

• Cover image
• Title page
• Table of Contents
• Copyright
• List of contributors
• 1. Metallic biomaterials: State of the art and new challenges
• 2. Nanostructured biomimetic, bioresponsive, and bioactive biomaterials
• 3. Micro- and nanopatterning of biomaterial surfaces
• 4. Bioactive metallic surfaces for bone tissue engineering
• 5. Metallic biomaterials for dental implant systems
• 6. Metallic biomaterial for bone support and replacement
• 7. Metals and alloys for biomedical applications
• 8. Biomaterials and biotechnological schemes utilizing TiO2 nanotube arrays—A review
• 9. Surface modification of Magnesium and its alloy as orthopedic biomaterials with biopolymers
• 10. Orthopedical and biomedical applications of titanium and zirconium metals
• 11. Porous tantalum: A new biomaterial in orthopedic surgery
• 12. Titanium based bulk metallic glasses for biomedical applications
• 13. Degradable metallic biomaterials for cardiovascular applications
• 14. Surface modification of metallic bone implants—Polymer and polymer-assisted coating for bone in-growth
• 15. Biocompatible coatings for metallic biomaterials
• 16. Enhancing the mechanical and biological performance of a metallic biomaterial for orthopedic applications
• 17. Interface influence of materials and surface modifications
• 18. Life cycle assessment of metallic biomaterials
• Index