Читать книгу Materials for Biomedical Engineering - Mohamed N. Rahaman - Страница 108

In this chapter, we discussed how atoms pack in three dimensions to form solids, defects in crystalline solids and microstructure of materials, which, along with atomic bonding (Chapter 2), are the structural features that control the properties of a material.

 Packing of atoms in solids is divided into two broad classes, crystalline, and amorphous.

 The vast majority of metals and ceramics are not composed of a single crystal but, instead, are polycrystalline, composed of a large number of small crystals called grains. Atomic packing defects composed of point defects, line defects (dislocations) and grain boundaries exert a strong effect on the physical and mechanical properties of crystalline solids.

 Inorganic glasses are amorphous but when subjected to a controlled heat treatment, some glasses can be converted to glass‐ceramics, which often have better properties than their parent glasses.

 The majority of polymers are amorphous but under appropriate conditions, some polymers develop a semicrystalline structure composed of crystalline and amorphous regions. Whether a polymer is amorphous or semicrystalline has a strong influence on their properties.

 We discussed more recently discovered allotropes of carbon, such as graphene, carbon nanotubes, and fullerenes, which are receiving considerable interest for use in biomedical applications due to their unique properties.

 As the engineering properties of materials are dependent on their microstructure, the ability to control the microstructure of a biomaterial is important for achieving a desired combination of properties for a particular application.