Tissue Engineering Using Ceramics and Polymers

Aldo R. Boccaccini, P.X. Ma

• Publisher: Woodhead Publishing
• Year: 2014
• eBook ISBN: 9780857097163
• Edition: 2
• Topic: Biological Sciences
• Subtopic: Biotechnology
• Index: Biological Sciences

The second edition of Tissue Engineering Using Ceramics and Polymers comprehensively reviews the latest advances in this area rapidly evolving area of biomaterials science. Part one considers the biomaterials used for tissue engineering. It introduces the properties and processing of bioactive ceramics and glasses, as well as polymeric biomaterials, particularly biodegradable polymer phase nanocomposites. Part two reviews the advances in techniques for processing, characterization, and modeling of materials. The topics covered range from nanoscale design in biomineralization strategies for bone tissue engineering to microscopy techniques for characterizing cells to materials for perfusion bioreactors. Further, carrier systems and biosensors in biomedical applications are considered. Finally, part three looks at the specific types of tissue and organ regeneration, with chapters concerning kidney, bladder, peripheral nerve, small intestine, skeletal muscle, cartilage, liver, and myocardial tissue engineering. Important developments in collagen-based tubular constructs, bioceramic nanoparticles, and multifunctional scaffolds for tissue engineering and drug delivery are also explained. Tissue Engineering Using Ceramics and Polymers is a valuable reference tool for both academic researchers and scientists involved in biomaterials or tissue engineering, including the areas of bone and soft-tissue reconstruction and repair, and organ regeneration. - Second edition comprehensively examines the latest advances in ceramic and polymers in tissue engineering - Provides readers with general information on polymers and ceramics and looks at the processing, characterization, and modeling - Reviews the latest research and advances in tissue and organ regeneration using ceramics and polymers

Part I

General issues: materials

Outline

1 Ceramic biomaterials for tissue engineering

2 Polymeric biomaterials for tissue engineering

3 Bioactive ceramics and glasses for tissue engineering

4 Biodegradable and bioactive polymer/inorganic phase nanocomposites for bone tissue engineering (BTE)

1

Ceramic biomaterials for tissue engineering

J. Huang, University College London, UK

S. Best, University of Cambridge, UK

Abstract:

This chapter reviews the range of ceramics currently used in skeletal repair and tissue regeneration and covers the bioinert, bioactive and resorbable ceramics, glasses and glass ceramics. The scope of the chapter includes the relationships between microstructure (crystalline and non-crystalline) and properties (mechanical properties, surface properties, biocompatibility and bioactivity). The processing (porous tissue engineering scaffolds and surface modification) of bioceramics is also considered. Based on the stringent requirements for clinical application, prospects for the development of advanced ceramic materials for tissue engineering are highlighted for the future.

Key words

bioceramics; hydroxyapatite; bioactive glasses; mechanical properties; biocompatibility; bioactivity

1.1 Introduction

Ceramic materials, such as porcelain, cement and glass, have been part of everyday life for thousands of years; advanced ceramics have been used in recent times in telecommunications, the environment, energy, transportation and health. Generally speaking, ceramic materials are solid materials composed of inorganic, non-metallic substances, exist as both crystalline and non-crystalline (amorphous) compounds, and glasses and glass-ceramics (partially crystallised glasses) are subclasses of ceramics.

A biomaterial is a non-viable material used in a medical device; intend to interact with biological systems (Williams, 1987). Various engineering materials, including ceramics, metal (alloys), polymer and composites, have been developed to replace the function of the biological materials. The focus of this chapter is to consider ceramics used in biological applications, now generally referred to as bioceramics, and their applications in implants and in the repair and reconstruction of diseased or damaged body parts. Most clinical applications of bioceramics relate to the repair of the skeletal system, comprising bone, joints and teeth, and to augment both hard and soft tissue. According to the types of bioceramics and host tissue interactions, they can be categorised as either bioinert or bioactive, the bioactive ceramics may be resorbable or non-resorbable, and all these may be manufactured either in porous or dense in bulk form, or granules or coatings.

The chapter begins by introducing various ceramics used in medical applications, including bioinert ceramics (i.e. alumina and zirconia), and bioactive ceramics (i.e. calcium phosphates, bioactive glasses and glass-ceramics). To understand the nature and formation of ceramic structures, it is essential to have an understanding of the atomic arrangements, the forces between atoms and the location of atoms in a crystalline lattice. The difference between crystalline and non-crystalline materials with the examples of hydroxyapatite ceramics and bioactive glasses, the most widely applied bioceramics, is discussed in Section 1.2. The properties of a ceramic are determined by its microstructure (e.g. grain size and porosity). A brief summary of the common techniques for characterisation of the microstructure of ceramics is included in Section 1.3. This is followed by a review of the properties of ceramics, particularly mechanical properties, surface properties, biocompatibility and bioactivity, which are crucial for the biological application of the ceramics. Alumina and zirconia have excellent mechanical properties for the load-bearing applications, while the bioactivity of glass and ceramics leads to the potential for osteoconduction. A brief review of the processing of ceramics with an example of hydroxyapatite (HA) is presented in Section 1.5. The processing of porous ceramics scaffolds and surface modification of surface using coating and thin film deposition is also discussed. The chapter finishes with a summary highlighting the importance of understanding of the clinical requirement and relationships between processing, microstructure and properties, which will help to develop better ceramic materials for tissue engineering.

1.1.1 Bioinert ceramics

Alumina and zirconia have been used as an important alternative to surgical metal alloys in total hip prostheses and as tooth implants. The main advantages of using ceramics over the traditional metal and polymer devices are lower wear rates at the articulating surfaces and the release of very low concentrations of ‘inert’ wear particles. For example, using femoral heads of alumina ceramic bearing against alumina cup sockets significantly reduces wear debris when against ultrahigh molecular weight polyethylene cups. Excessive wear rates can contribute to loosening and eventual implantation failure. Alumina ceramics have been used successfully for many years. Zirconia ceramics have advantages over alumina ceramics in terms of higher fracture toughness and higher flexural strength, combined with a relatively lower Young’s modulus (Table 1.1). Therefore, zirconia ceramics were developed for bearing surfaces in total hip prostheses. However, concerns about in-service failures (particularly the premature fracture of a batch of ceramic femoral heads) resulted in a Food and Drug Administration (FDA) recall. For this reason, the use of zirconia for strengthening and toughening of alumina matrix composites has been developed. One example is Biolox® delta (CeramTec), which has FDA approval for use in femoral head components.

Table 1.1

A summary of mechanical properties of various biomaterials (Kokubo, 1991; Hench and Andersson, 1993; Hulbert, 1993; Hench and Best, 2004)

Materials	Density (g cm^− 3)	Hardness (Vickers, HV)	Young’s modulus (GPa)	Bending strength (MPa)	Compressive strength (MPa)	Fracture toughness KIC (MPa m^1/2)
Bioglass® 45S5	2.66	458	35	40–60		0.4–0.6
A-W glass-ceramic	3.07	680	118	215	1080	2.0
Sintered HA	3.156	500–800	70–120	20–80	100–900	0.9–1.3
Alumina	3.98	2400	380–420	595	4000–4500	4–6
Zirconia (TZP)	6.05	1200	150	1000	2000	7
Zirconia (Mg-PSZ)	5.72	1120	208	800	1850	8
Ti6Al4V	4.43	340	110	900	970	~ 80
316 stainless steel	8		200	540–1000*		~ 100

*Tensile strength.

Nanotechnology has also been applied to improve the properties of implant materials with the aim of extending the longevity of implant devices in the body, with no revision surgery necessary at the later time. To improve the fracture toughness of alumina ceramics, nanophase alumina with grain size of 23 nm were synthesised. The modulus of elasticity of nanophase alumina decreased by 70% (Webster et al., 1999). The fracture toughness of alumina can then be controlled through the use of nanophase formulations; furthermore, enhanced biological responses of osteoblast cells to the nanophase materials were found, indicating the improved osseointegration potential for nanophase alumina (Webster et al., 2000).

Alumina and zirconia have good biocompatibility, and adequate mechanical strength, but are relatively biologically inactive (nearly inert) and lack direct bonding with host tissue. Bioactive materials are conceptually different from bioinert materials in that chemical reactivity is essential. A series of bioactive ceramics, glasses and glass-ceramics are capable of promoting the formation of bone at their surface and of creating an interface, which contributes to the functional longevity of tissue.

1.1.2 Bioactive ceramics

Bioactive ceramics include several major groups, such as calcium phosphate ceramics, bioactive glasses and glass-ceramics.

Calcium phosphate ceramics

Calcium phosphates are the major constituent of bone mineral. Table 1.2 lists several calcium phosphates with their chemical formula and Ca/P ratio (from 0.5 to 2). These calcium phosphates can be synthesised by mixing calcium and phosphate solution under acid or alkaline conditions. Only certain compounds are useful for implantation in the body: compounds with a Ca/P ratio less than 1 are not suitable for biological implantation due to their high solubility.

Table 1.2

Ca/P ratio of various calcium phosphates (Aoki, 1991)

Name	Abbreviation	Formula	Ca/P ratio
Tetracalcium phosphate	TTCP	Ca4O(PO4)2	2.0
Hydroxyapatite	HA	Ca10(PO4)6(OH)2	1.67
Tricalcium phosphate (α,α′,β,γ)	TCP	Ca3(PO4)2	1.50
Octacalcium phosphate	OCP	Ca8H2(PO4)6•5H2O	1.33
Dicalcium phosphate dihydrate (brushite)	DCPD	CaHPO4•2H2O	1.0
Dicalcium phosphate (montite)	DCP	CaHPO4	1.0
Calcium pyrophosphate (α,β,γ)	CPP	Ca2P2O7	1.0
Calcium pyrophosphate dihydrate	CPPD	Ca2P2O7•2H2O	1.0
Heptacalcium phosphate	HCP	Ca7(P5O16)2	0.7
Tetracalcium dihydrogen phosphate	TDHP	Ca4H2P6O20	0.67
Calcium phosphate monohydrate	CPM	Ca(H2PO4)2•H2O	0.5

The most extensively used synthetic calcium phosphate ceramic for bone replacement ...

Table of contents

• Cover image
• Title page
• Table of Contents
• Copyright
• Contributor contact details
• Woodhead Publishing Series in Biomaterials
• Foreword
• Preface
• Part I: General issues: materials
• Part II: General issues: processing, characterisation and modelling
• Part III: Tissue and organ regeneration
• Index