Bone Repair Biomaterials

Regeneration and Clinical Applications

Kendell Pawelec, J. A. Planell

• Publisher: Woodhead Publishing
• Year: 2018
• ISBN:
  9780081024522
• Edition: 2
• Topic: Technology & Engineering
• Subtopic: Materials Science
• Index: Technology & Engineering

Bone Repair Biomaterials: Regeneration and Clinical Applications, Second Edition, provides comprehensive reviews on materials science, engineering principles and recent advances. Sections review the fundamentals of bone repair and regeneration, discuss the science and properties of biomaterials used for bone repair, including metals, ceramics, polymers and composites, and discuss clinical applications and considerations, with chapters on such topics as orthopedic surgery, tissue engineering, implant retrieval, and ethics of bone repair biomaterials. This second edition includes more chapters on relevant biomaterials and a greatly expanded section on clinical applications, including bone repair applications in dental surgery, spinal surgery, and maxilo-facial and skull surgery.

In addition, the book features coverage of long-term performance and failure of orthopedic devices. It will be an invaluable resource for researchers, scientists and clinicians concerned with the repair and restoration of bone.

• Provides a comprehensive review of the materials science, engineering principles and recent advances in this important area
• Presents new chapters on Surface coating of titanium, using bone repair materials in dental, spinal and maxilo-facial and skull surgery, and advanced manufacturing/3D printing
• Reviews the fundamentals of bone repair and regeneration, addressing social, economic and clinical challenges
• Examines the properties of biomaterials used for bone repair, with specific chapters assessing metals, ceramics, polymers and composites

1

Introduction to the challenges of bone repair

Kendell M. Pawelec University of Michigan, Ann Arbor, MI, United States

Abstract

Within the body, the bone plays many key roles, everything from a support structure, to a protective shell, to a metabolic source of ions. While bone can normally adapt to the changing demands of its environment, when the system breaks down, it can be devastating to the individual and society. The majority of the population will experience an ailment related to bone in their lifetime, as the result of trauma or disease. These appear in the orthopedics, dentistry, maxillofacial, and spinal regions. Collectively, these conditions account for a large amount of healthcare spending, and negatively impact society by reducing productivity and lowering the quality of life. In many cases, surgery is required to repair the affected area, often utilizing implants. Important barriers to current bone repair implants are the management of infections, improvement of fixation in unhealthy bone, and integration of bone and implant. Biomaterials are poised to play a unique role in solving these issues.

Keywords

Biomaterials; Bone; Epidemiology; Healthcare; Socioeconomic

1.1. Introduction

The musculoskeletal system has many key functions, from structural to metabolic. Playing a major role in the musculoskeletal system, bone is a complex tissue which is highly responsive to its environment. It is made up of around 25%–30% protein, mainly collagen type I, with a calcium phosphate ceramic, namely hydroxyapatite, making up the remaining 65%–70% of the dry mass. As a composite structure, with a remarkable hierarchical architecture, bone has unique mechanical properties allowing individuals to perform a wide range of activities [1]. To achieve these mechanics, two distinct types of bone exist within the body: cortical and trabecular bone. Cortical bone is a dense form of bone, which appears at the outer edges of long bones. Trabecular bone, on the other hand, is a very porous structure, made up of small compartments, known as trabeculae. Bone will remodel in response to mechanical cues throughout life by depositing mineral on concave surfaces of the bone and removing it from convex surfaces areas. In addition, the orientation and spacing of trabeculae is impacted by the mechanical load on the bone and adapts to changes in that loading. Factors such as the individual’s weight, physical activities, and gait play a role in determining the loading experienced by the skeletal system. This fulfills its most obvious function, as structural support for an individual, which not only aides in locomotion, but also protects sensitive tissues, such as the spinal cord and brain. Loss of bone’s structural features results in fragility of the bone and increases the risk of fractures and other trauma.

In addition to structure, bone serves as a reservoir for many important metabolic ions, such as calcium and phosphates. These ions play important roles in signaling and in molecular energy storage. To regulate the level of ions systemically, bone must interact with many other organs within the body, such as muscle, kidneys, and liver [2]. This interaction is accomplished through hormones, either secreted from other organs, such as vitamin D and estrogen, or secreted from bone tissue, such as osteocalcin [3–5]. For example, osteocalcin is released in the blood, and when activated, it has a wide range of effects on muscle activity and insulin secretion [2,5]. The interconnection of many systems can manifest in chronic diseases, such as diabetes, liver disease, or kidney disease. In these cases, bone architecture is affected, reducing the structural stability of bone [2,6].

To maintain bone tissue, several cell types are active within the bone niche. Most importantly, these include osteoblasts, osteoclasts, osteocytes, and mesenchymal stem cells. Osteoblasts function primarily to deposit bone. Their activity is offset by osteoclasts, large multinucleated cells, which are responsible for bone resorption [7]. Maintaining a tight balance between the two cell types is critical for the homeostasis of bone. When either resorption or deposition dominates, negative consequences result. Osteocytes, the most prevalent cell type, are found within the bone’s mineralized tissue. They form an interconnected network within the tissue and are believed to be derived from osteoblasts which become embedded in the matrix, and which undergo terminal differentiation. Given their position inside of the bone tissue, osteocytes are responsible for mechanical sensing in the bone, and can secrete factors which regulate osteoblast and osteoclast function [8]. Mesenchymal stem cells are located within the bone marrow, serving as a source for progenitor cells. It is their relative abundance and ease of proliferation which have made these stem cells interesting targets for cell therapies within the musculoskeletal system.

When the delicate balance within bone tissue breaks down, whether from traumatic injury or chronic disease, the effect on quality of life can be devastating. The impact is multifaceted, requiring analysis of the direct costs of healthcare and the qualitative aspects of disease, such as pain. Given the high occurrence of musculoskeletal conditions, these disorders remain a key challenge for modern medicine. Likelihood of experiencing a musculoskeletal disease increases with age, but younger populations with high activity levels, such as athletes, also carry a higher risk of disease [9,10]. This chapter seeks to outline the social and economic impact of bone repair and highlight some of the key clinical challenges which must be met. This discussion encompasses several different areas within the musculoskeletal system: orthopedics, dentistry, maxillofacial, and spinal conditions. Finally, the role of biomaterials, and the opportunities in this field are considered, along with future trends for this area.

1.2. Social and economic impact of bone repair

Diseases and trauma related to bone tissue can occur in many areas of the body. The lifetime risk for sustaining a fracture in the wrist, hip or vertebrae is estimated to be between 30% and 40% of the total population, in developed countries [11]. With the incidence of musculoskeletal trauma and disease so prevalent, the costs to society are considerable, and it has been ranked by the World Health Organization as a disease of enormous impact worldwide.

The total costs vary, depending on the specific region of the world, and access to healthcare. However, in all cases, musculoskeletal disease carries a direct and indirect cost on the individual, which filters through to society, Fig. 1.1 [12]. Direct costs, those associated with the hospital, surgery, or medications, are easy to calculate. More challenging is estimating the additional indirect and intangible costs. Indirect costs are those which result from the disease, including missed work and follow on healthcare costs. In addition, the burden of disease can also be intangible: pain and loss of mobility [13,14]. These additional costs can be devastating to the individual and have a broader economic impact. These figures are only growing as the population ages, and as the prevalence of diseases such as obesity and diabetes increases.

Figure 1.1 Many types of costs are associated with musculoskeletal disease, not all of which are readily quantifiable.

1.2.1. Orthopedics

The burden of orthopedic ailments on society is extremely high. Falling into this general category of bone-related conditions are fractures in limbs. Under most circumstances, fractures in bone will heal naturally, with little intervention, providing both ends of the fracture are aligned and in close proximity. However, there are conditions when bone must be replaced. These include cases where fractures fail to heal, when large pieces of bone are lost during trauma, or when bone tumors are removed leaving a large gap.

In addition to fractures, chronic conditions can negatively affect bone health. One such condition is osteoporosis, described as a loss of bone mass density, over 2.5 standard deviations below the average for healthy adults [11]. In addition to reduced bone density, the architecture of bone changes significantly. There is a decreased thickness in cortical bone and reduced number of trabeculae. Any alterations in bone structure will affect its ability to carry load. Reduction of the bone mass and structure increases the probability of fracture, even from very short falls. In elderly patients, especially women, osteoporosis can be associated with muscle loss (sarcopenia), as both muscle and bone are tied together through metabolic signaling [15]. When sarcopenia is present, increasing unsteadiness of mobility raises the likelihood of falls which result in a fracture [16].

Another major chronic disease, underlying many bone-related conditions which result in implants, is arthritis. Two types are known: osteoarthritis, the wearing away of bone, and rheumatoid arthritis, an autoimmune disease where cartilage is destroyed. These conditions are not limited to areas typically associated with orthopedics, but can affect any location within the body, especially the spine. Regardless, arthritis has many costs associated with it, especially due to the widespread prevalence of condition [17]. In 2003, 45 million adults (around 21% of the population) reported osteoarthritis in the United States, with over 16,500 reporting activity limitations due to the...

Table of contents

• Cover image
• Title page
• Table of Contents
• Copyright
• List of contributors
• 1. Introduction to the challenges of bone repair
• 2. Bone biology
• 3. Biomechanical aspects of bone repair
• 4. Properties and characterization of bone repair materials
• 5. Metals
• 6. Ceramics as bone repair materials
• 7. Polymers for bone repair
• 8. Natural polymers for bone repair
• 9. Cements as bone repair materials
• 10. Composite biomaterials for bone repair
• 11. Bone repair biomaterials in orthopedic surgery
• 12. Glass-ceramics for dental restoration
• 13. Biomaterial in spinal surgery
• 14. Using bone repair materials in maxillofacial and skull surgery
• 15. Long-term performance and failure of orthopedic devices
• 16. Emerging areas of bone repair materials: nucleic acid therapy and drug delivery
• 17. Retrieval, sample processing, and analyses of bone-anchored implants
• 18. Ethical considerations in bone tissue-engineered products
• Index