Mechanical Behavior of Biomaterials

J. Paulo Davim, J. Paulo Davim

• Publisher: Woodhead Publishing
• Year: 2019
• Print ISBN:
  9780081021743
• eBook ISBN:
  9780081021750
• Topic: Technology & Engineering
• Subtopic: Materials Science
• Index: Technology & Engineering

Mechanical Behaviour of Biomaterials focuses on the interface between engineering and medicine, where new insights into engineering aspects will prove to be extremely useful in their relation to the biomedical sciences and their applications. The book's main objective focuses on the mechanical behavior of biomaterials, covering key aspects, such as mechanical properties, characterization and performance. Particular emphasis is given to fatigue, creep and wear, fracture, and stress and strain relationships in biomaterials. Chapters look at both experimental and theoretical results. Readers will find this to be an essential reference for academics, biomechanical researchers, medical doctors, biologists, chemists, physicists, mechanical, biomedical and materials engineers and industrial professionals. - Presents contributions from international experts - Provides insights at the interface of disciplines, such as engineering and the medical and dental sciences - Presents a comprehensive understanding on the mechanical properties of biomaterials - Covers surface and bulk properties

1

Tribology of materials for biomedical applications

Prasanta Sahoo*; Suman Kalyan Das*; J. Paulo Davim^† * Jadavpur University, Kolkata, India
^† Department of Mechanical Engineering, University of Aveiro, Aveiro, Portugal

Abstract

With recent advancements in medical science, there have been improvements in the quality of human life. The discoveries in the field of materials has positively impacted the development of prosthetics and implants, which are becoming more biocompatible as well as durable. To gain knowledge of the tribological characteristics of these materials, namely friction, wear, and corrosion, is significant in order to further enhance their durability, leading to a decrease in the frequency of surgical replacement and a more normal life for the patient. Hence, this chapter explores the tribological implications of various materials employed in biomedical applications.

Keywords

Biomedical; Materials; Tribology; Friction; Wear; Corrosion; Implant; Coating

1.1 Introduction

A long healthy life—in recent years we have come a long way towards fulfilling this age-old dream of mankind, thanks to advancements in modern medicine. But this very success creates a host of new challenges for medicine. Our increasingly aging population has produced a rise in age-related ailments. Our diet is different from that of our grandparents, resulting in obesity and metabolic disorders. Also, the trend towards high-risk recreational sports persists, with potential hazards ranging from fractures to severe internal injuries. Present-day and future medicine must confront these changes in modern society.

Since ancient times, humans have attempted to restore the functionalities of body parts stricken with trauma or disease. The human body and its associated biological systems are unique. Commonly available materials in their raw forms, when directly interacting with these biological systems, may result in various side effects and damage to the human body. Hence, some special materials have been identified, called biomaterials, that are both compatible with living tissue and provide the necessary engineering functions. Metals and alloys, ceramics, and polymer-based materials are often used in implants and other medical devices. Fig. 1.1 illustrates some of the metallic implants and bone fixation devices available.

Fig. 1.1 Examples of metallic implants and bone fixation devices [1]. (A) From https://www.lawyersandsettlements.com/images/articles2/hip17-article.webp. (B) From https://upload.wikimedia.org/wikipedia/commons/a/a9/Claviculafraktur_lateral_6mo_platte.webp. (C) From https://upload.wikimedia.org/wikipedia/commons/3/3c/External_fixator_xray.webp. (D) From https://upload.wikimedia.org/wikipedia/commons/0/00/Stainless_steel_and_ultra_high_molecular_weight_polythene_hip_replacement_(9672239334).webp. (E) From http://www.iran-daily.com/content/imgcache/file/132951/0/image_650_365.webp.

The science of tribology is not limited to mechanical machinery; it also finds application in the medical field. The human body possesses a wide variety of sliding and frictional interfaces, mainly in the joints. Moreover, the friction between the eyelids and eyeball, skin friction, etc. also fall under the scope of tribology. Hence, a separate domain, called biotribology, has been developed to deal with the application of tribological principles, such as friction, wear, and lubrication between interacting surfaces in relative motion, to medical and biological systems [2]. According to www.nature.com, “Biomedical materials are biomaterials that are manufactured or processed to be suitable for use as medical devices (or components thereof) and that are usually intended to be in long-term contact with biological materials.” Study of the tribological aspects of biomedical materials is equally important, as such study deals with reducing friction and wear, thus resulting in the greater longevity of biomedical implants and devices. This reduces the complications associated with repeated surgeries. Besides, as more cases of younger implant patients are appearing, increasing the longevity of implants has become very significant. Typical examples of tribology in biomedicine include the following:

• ● Tribology of natural synovial joints and artificial replacements
• ● Wear of dental implants
• ● Wear and replacement of heart valves
• ● Lubrication of pump in total artificial hearts
• ● Ocular tribology and tribology of contact lenses
• ● Wear of screws and plates in bone fracture repair
• ● Friction of skin and interaction with clothing

Finally, with growing knowledge of the tribological aspects of biomedicine, the quality of human life is expected to improve.

1.2 Desired properties in biomaterials for medical applications

Materials to be used within the living human body, and supposed to coexist with living tissue and other organic matter without any degradation, should possess unique combinations of properties, some of which are given in the following list [3]:

• ● Biocompatibility: The biomaterial should be compatible with living systems and not cause any bodily harm, which includes any negative effects a material can have on the components of a biological system (bone, extra- and intracellular tissues, and ionic composition of plasma).
• ● Nontoxic: The material should not be toxic to living cells and organisms. Toxicity can be of two types: genotoxic (which can alter the DNA of the genome) or cytotoxic (causes damage to individual cells). Failure to comply with both biocompatibility as well as nontoxicity can lead to rejection of implants and other serious health conditions.
• ● Mechanical properties: The material should have a low modulus combined with high strength to prolong the service period of the implant and prevent loosening, thereby preventing the need for revision surgery. Moreover, stress shielding (reduction in bone density as a result of removal of typical stress from the bone by an implant) can be prevented by matching the modulus of elasticity of biomaterials to that of bone, which varies from 4 to 30 GPa.
• ● High wear resistance: The material should have a high wear resistance and exhibit a low friction coefficient when sliding against body tissues. An increase in the friction coefficient or a decrease in the wear resistance can cause the implant to loosen. Moreover, the wear debris generated can cause inflammation destructive to the bone supporting the implant.
• ● High corrosion resistance: The human body is not an environment that one would consider hospitable for an implanted metal alloy: a highly oxygenated saline electrolyte at a pH of around 7.4 and a temperature of 37°C [4]. Moreover, the abundant presence of chlorine ions in the body fluids results in aggravated corrosion scenarios for metals. An implant made of a biomaterial with a lo...

Table of contents

• Cover image
• Title page
• Table of Contents
• Copyright
• Contributors
• About the editor
• Preface
• 1: Tribology of materials for biomedical applications
• 2: Designing and analysis of the femoral neck for an artificial hip joint prosthesis
• 3: Mechanical properties of the optic nerve head
• 4: Metallic biomaterials—A review
• 5: Mechanical behavior of selective laser melting-produced metallic biomaterials
• 6: Machining of a biomaterial with dual negative tool geometry
• Index