Ceramics in Biology and Medicine

Abstract

A comprehensive definition of a biomaterial was provided at the National Institutes of Health (NIH) Consensus Development Conference on the Clinical Applications of Biomaterials in the United States.

1 People and History

Duchateau, Alexis (1714–1792) was the pharmacist in Paris who made the first porcelain dentures in ~1770.

Dubois de Chémant, Nicolas (1753–1824) wrote a dissertation on artificial teeth describing the advantages using mineral paste to make replacement teeth. He escaped to England from the French Revolution and later obtained porcelain paste from Wedgwood.

Gluck, Themistocles (1853–1942) is generally regarded as the inventor of artificial biomaterials (ivory was a favorite).

Hench, Larry (born 1938) developed Bioglass® in 1969. He is Emeritus Professor of Materials at Imperial College, London.

Hippocrates (460–370 BCE). One of his aphorisms can be translated as: those diseases which medicines do not cure, iron cures; those which iron cannot cure, fire cures; and those which fire cannot cure, are to be reckoned wholly incurable. Modern hyperthermia treatment uses ferrite nanoparticles to locally generate heat.

2 Exercises

• 35.1 Briefly compare and contrast the suitability of metals, ceramics, and polymers for use in biomedical applications. In your answer, consider the following factors: biocompatibility, mechanical properties, and ease of processing.

• 35.2 Alumina (Al₂O₃) ceramic implants are required to have a small grain size (<4.5 m). (a) Why do you think a small grain size is important? (b) How does the addition of MgO to the powder mixture help to keep the grain size small? (c) Are there any other ways that could be used to limit the extent of grain growth?

• 35.3 Explain why tetragonal zirconia polycrystal (TZP) and Mg-partially stabilized zirconia (PSZ) ceramics have higher toughness than alumina ceramics.

• 35.4 The Weibull modulus of an alumina bioceramic is given as 8.4. (a) What does a value of m = 8.4 imply? (b) For an implant made out of a metal, the value of m ~ 100. What implications would this have for lifetime predictions for the metal component compared to the alumina component? (c) How does the value of m affect the design of a component for a load-bearing application?

• 35.5 The composition of Bioglass® 45S5 is 45% SiO₂, 24.5% Na₂O, 24.4% CaO, and 6% P₂O₅. (a) Classify each of the oxide constituents of 45S5 as either network formers, modifiers, or intermediates. (b) What would the composition of Bioglass® 45S5 be in mol%? (c) Explain briefly how the structure of 45S5 differs from the silicate glasses described in Chapter 7 and what implications this difference has on the properties of 45S5.

• 35.6 The substitution of ions in the hydroxyapatite (HA) structure can change the lattice parameters of the unit cell. Explain how you think the substitution of Ca²⁺ for the following ions would change both the ${a}$ and ${c}$ lattice parameters: Sr²⁺, Ba²⁺, Pb²⁺, Mg²⁺, Mn²⁺, and Cd²⁺.

• 35.7 According to ASTM Standards [American Society for Testing and Materials (1990) Annual Book of ASTM Standards, Section 13, F 1185–1188], the acceptable composition for commercial HA is a minimum of 95% HA, as established by X-ray diffraction (XRD) analysis. Describe how XRD can be used to determine phase proportions in a mixture.

• 35.8 We mentioned that in steel fibers/bioactive glass composites it was important that there was chemical interaction between the two components to ensure stress transfer during loading. We have just formed a bioceramics company and want to hire you as a consultant. We want you to determine whether such interactions have occurred in a composite we have just made. What analytical technique or techniques would you use for your evaluation? Explain the reasoning behind your answer and some of the pros and cons of the technique or techniques you chose.

• 35.9 One of the advantages of plasma spraying for producing HA coatings on metallic implants is that the substrate temperature can be kept relatively low. What possible mechanisms can lead to a loss in the mechanical strength of a metal if it is exposed to high temperatures? (You can limit your discussion to the cases of Ti alloys and stainless steel).

• 35.10 Explain why the mechanical properties of turbostratic carbons such as LTI are different from those of graphite. Both are forms of carbon and are chemically identical.

• 35.11 We can use several definitions of a biomaterial. Discuss at least three that have been proposed and explain why you prefer the one given here.

• 35.12 Explain why HA and TCP behave differently in the body.

• 35.13 Name the two main types of bone. Say where they are found in the body and why.

• 35.14 Why is stress shielding a problem for prostheses?

• 35.15 Why is alumina used as the femoral ball, and why is so much work aimed at improving this device?

• 35.16 What is a bioactive ceramic, and why has Bioglass been so successful?

• 35.17 Discuss the composition and structure of Cerabone and explain why it was so designed.

• 35.18 Write down the general formula for HA and state its percentage in bone by weight and volume. How does its structure relate to its properties?

• 35.19 Discuss why thermal spraying is the preferred method for producing HA and TCP coatings.

• 35.20 Summarize and justify five uses for nanobioceramics.