Bioceramic Coatings for Medical Implants

Trends and Techniques

Robert B. Heimann, Hans D. Lehmann

• Publisher: Wiley-VCH
• Year: 2015
• Print ISBN: 9783527337439
• eBook ISBN: 9783527684007
• Edition: 1
• Topic: Technology & Engineering
• Subtopic: Materials Science
• Index: Technology & Engineering

Reflecting the progress in recent years, this book provides in-depth information on the preparation, chemistry, and engineering of bioceramic coatings for medical implants. It is authored by two renowned experts with over 30 years of experience in industry and academia, who know the potentials and pitfalls of the techniques concerned. Following an introduction to the principles of biocompatibility, they present the structures and properties of various bioceramics from alumina to zirconia. The main part of the work focuses on coating technologies, such as chemical vapor deposition, sol-gel deposition and thermal spraying. There then follows a discussion of the major interactions of bioceramics with bone or tissue cells, complemented by an overview of the in-vitro testing methods of the biomineralization properties of bioceramics. The text is rounded off by chapters on the functionalization of bioceramic coatings and a look at future trends. As a result, the authors bring together all aspects of the latest techniques for designing, depositing, testing, and implementing improved and novel bioceramic coating compositions, providing a full yet concise overview for beginners and professionals.

1
Bioceramics – A Historical Perspective

Synopsis

In this chapter, we will attempt to trace briefly the long and sometimes anfractuous history of important bioceramics including coatings. Emphasis will be put on the bioinert ceramics alumina and zirconia, as well as on bioactive, that is osseoconductive calcium phosphates.

1.1 Alumina

Alum (potassium aluminium sulfate, KAl(SO₄)₂·12H₂O) was already known in antiquity (‘sal sugoterrae’ of Pliny), and widely utilised in dying of wool, as a coagulant to reduce turbidity in water, and as a medicine to remedy various ailments based on its astringent, haemostatic and antibiotic nature. In 1754, the German (al)chemist Andreas Sigismund Marggraf (1709–1782) was first to isolate aluminium oxide (‘Alaunerde’) from alum but was unable to determine its exact composition (Marggraf, 1754, 1761). Between 1808 and 1810, Sir Humphrey Davy tried unsuccessfully to reduce the oxide to metallic aluminium, a feat that was accomplished later by Oerstedt (1825) by heating aluminium chloride with potassium amalgam.

Aluminium oxide (alumina) has also been known since ancient times and several isolated uses have been reported for emery (smirgel), an impure corundum occurring, for example, on the Greek island of Naxos. Gorelick and Gwinnett (1987) have shown that emery was likely employed as an abrasive for drilling of hardstone beads and cylinder seals during ancient Mesopotamian times. In addition, finely ground emery powder was arguably used by the famous Greek sculptor Pheidias as a separation medium to avoid adhesion of heated glass sheets to clay-based moulds. The corrugated glass sheets thus obtained were likely designed to be clothing folds adorning the himation (ancient Greek cloak) of the giant statue of Zeus in his Olympia temple (Heilmeyer, 1981).

The unique mechanical and thermal properties of alumina have spurred its utilisation as high temperature-, wear- and corrosion-resistant ceramics. Besides this, its first application as biomaterial was suggested by Rock (1933) in a Deutsches Reichspatent, followed by a patent issued to Sandhaus (1966) for the use of alumina for dental and jaw implants. However, it was only after the groundbreaking paper by Boutin (1972) that alumina took off on its worldwide triumphal course as a suitable ceramic material for femoral balls of hip endoprostheses.

Figure 1.1 shows the development of bioinert and bioactive ceramics (Rieger, 2001). In 1920, tricalcium phosphate (TCP) was suggested as a bioresorbable ceramic material for filling of bone gaps that, however, was unable to bear extended loads (Heughebaert and Bonel, 1986). Alumina entered the scene around 1930 (Rock, 1933) and was subsequently much improved in terms of its compressive strength and fracture toughness by painstaking engineering of its purity and ever decreasing grain size down to the nano-scale level. This development led to orthopaedic structural ceramic products such as Ceraver-Osteal® (Boutin, 1972), Keramed® (Glien, Kerbe and Langer, 1976), Frialit® (Griss and Heimke, 1981), and finally the family of Biolox® ceramics by Feldmühle, later CeramTec companies (Dörre and Dawihl, 1980, see also Clarke and Willmann, 1994) as well as BIONIT® manufactured by Mathys Orthopädie GmbH (Bettlach, Switzerland). The current high-end product of CeramTec is Biolox® delta, a zirconia-toughened alumina (ZTA) alloy reinforced with chromia as a crack arrester (see Chapter 4.1.1).

Figure 1.1 Application of bioceramics in medical devices: 100 years of history. (Adapted from Rieger (2001), and adjusted to current developments.)

Evaluation of biocompatibility resulted chiefly from clinical experience (Boutin, 1972; Hulbert, Morrison and Klawitter, 1972; Griss et al., 1973; Griss, 1984; Mittelmeier, Heisel and Schmitt, 1987) supported by in vitro cytotoxicity testing (for example Catelas et al., 1998; Nkamgueu et al., 2000, and many other contributors).

1.2 Zirconia

Zirconium dioxide was first extracted from the mineral zircon (zirconium silicate, ZrSiO₄) by the German chemist Martin Heinrich Klaproth (1743–1817) in 1787, using the yellowish orange-coloured, transparent gemstone jacinth (hyacinth) from Ceylon as starting material. Zircon has been known to man for a very long time; its name presumably originated from the Arabian word ‘zargun’, meaning ‘gold-coloured’ that etymologically is related to the ancient Persian words ‘zarenu’ (gold) and ‘gauna’ (colour) (Vagkopoulou et al., 2009). In 1824, the Swedish chemist Jöns Jakob Berzelius (1779–1848) was first to isolate metallic zirconium by reduction of K₂ZrF₆ with potassium.

For the following 150 years, zirconium as well as zirconia were considered mere scientific curiosities without any substantial technological merits apart from limited utilisation of zirconia in heavy-duty bricks for high temperature applications and for special glasses (Morey, 1938) with a high index of refraction. It was only in 1969 that the first scientific study of the outstanding biomedical properties of zirconia emerged (Helmer and Driskell, 1969). Subsequently, it was discovered that alloying zirconia with oxides such as yttria, calcia, magnesia and others was able to stabilise its tetragonal modification thus halting the structurally and mechanically deleterious phase transition from the tetragonal to the monoclinic phase (Garvie and Nicholson, 1972). This discovery allowed using the so-called transformation toughening of zirconia to produce ceramics with unsurpassed crack resistance (‘ceramic steel’) (Garvie, Hannink and Pascoe, 1975). Still later, it was found that even unalloyed microcrystals of zirconia could be stabilised against transformation if the tetragonal high temperature phase has a reduced surface free energy with respect to the monoclinic low temperature structure (Garvie, 1978). These partially stabilised tetragonal zirconia polycrystalline ceramics (TZP) are characterised by a structure of high density, small grain size and high purity that jointly elicit strength and fracture toughness unusually high for a ceramic material. Consequently, such ceramics were employed to fashion femoral ball heads starting by the mid-eighties of the past century (Cales and Stefani, 1995, Figure 1.1) and, later, to make dental parts of all kinds including dental roots, inlays and veneers.

Starting in the 1980s, besides structural and mechanical investigations of zirconia (see, for example Rühle, Claussen and Heuer, 1983), studies on its biocompatibility moved into the limelight as evidenced, for example, by the pioneering work of Garvie et al. (1984), Christel et al. (1989) and Hayashi et al. (1992). Their work triggered a virtual avalanche of research that used increasingly sophisticated evaluation techniques of material properties. In addition, studying the in vitro and in vivo biomedical performance of zirconia in contact with biofluid and tissues established zirconia as a viable bioceramics (for example Piconi and Maccauro, 1999; Piconi et al., 2003; Fini et al., 2000; Clarke et al., 2003; Thamaraiselvi and Rajeswari, 2004; Manicone, Ros...

Table of contents

• Cover
• Related Titles
• Title Page
• Copyright
• Table of Contents
• Preface
• Glossary
• Chapter 1: Bioceramics – A Historical Perspective
• Chapter 2: Socio-Economic Aspects and Scope of Bioceramic Materials and Biomedical Implants
• Chapter 3: Fundamentals of Interaction of Bioceramics and Living Matter
• Chapter 4: Structure and Properties of Bioceramics Used in Orthopaedic and Dental Implants
• Chapter 5: Technology of Coating Deposition
• Chapter 6: Deposition, Structure, Properties and Biological Function of Plasma-Sprayed Bioceramic Coatings
• Chapter 7: Characterisation and Testing of Bioceramic Coatings
• Chapter 8: Future Developments and Outlook
• Appendix Relevant Scientific Journals/Book Series with Bioceramic Content
• Index
• End User License Agreement