Читать книгу Materials for Biomedical Engineering - Mohamed N. Rahaman - Страница 31

Charts provide a succinct way to show a direct comparison of material properties. As a mechanical function is often a major consideration in many biomedical applications, charts that compare mechanical properties can be useful at the outset of materials selection and design. Several types of mechanical properties are available and, depending on the application, some properties can be more important than others. Figure 1.5 shows one type of material property chart, which depicts the measured strength versus elastic modulus for the primary classes of synthetic materials and for selected natural materials. The properties of the synthetic materials shown in Figure 1.5 (and in most mechanical property charts) are those for the dense materials, that is, the materials have zero or near zero porosity. As the presence of porosity lowers the mechanical properties of a material, one approach to modifying the properties of strong synthetic materials in order to achieve more optimal properties for use as biomaterials is to incorporate a controlled amount of porosity into them. In comparison, incorporation of a strong phase into polymers to form a composite provides a way to improve their mechanical properties.

Figure 1.5 Strength versus elastic modulus for the three major classes of synthetic materials used as biomaterials (ceramics, metals, and polymers). The range shown for each class of material is approximate and for the dense (or almost dense) material (zero or close to zero porosity). The presence of porosity in these materials will lead to a reduction in these and other mechanical properties. The properties of some human tissues are shown for comparison.