Читать книгу Materials for Biomedical Engineering - Mohamed N. Rahaman - Страница 100

The engineering properties of a material depends on its microstructure and, consequently, in the design and creation of biomaterials, we are concerned not just with the material itself but with its microstructure also. Microstructure refers to the structure of a material at a scale of approximately 0.1–100 μm, such as the nature of the phases present in the material, the quantity of each phase and its distribution. Unless specifically emphasized, structure at a nanoscale is often included within the realm of microstructure. A phase is defined as a region of material with uniform physical and chemical properties. As biomaterials are solids, we are essentially concerned with one or more solid phases, crystalline or amorphous, and, if present, porosity.

Controlling the microstructure of a biomaterial to achieve a desired combination of properties for a particular application is an important area of biomaterials science. Inadequate microstructural control often leads to unpredictable properties, which can lead to catastrophic failure and, for biomaterials used as implants for example, to serious complications for the patient. A large variety of methods are available to create biomaterials with the requisite shape and microstructure, but robotic methods, referred to as rapid prototyping, additive manufacturing or, more commonly, three‐dimensional printing (3D printing), have been used increasingly in recent years. These robotic methods provide unprecedented control of the shape and microstructure of a biomaterial, particularly when a high degree of complexity is required.

Microstructures are commonly examined in a microscope, such as an optical microscope or an electron microscope, depending on the scale of resolution required. Often, metals and ceramics are etched using a thermal or chemical treatment to reveal the grain boundaries or the phases within the solid. The microstructures of biomaterials are numerous, varying from simple to more complex and, thus, it is not possible to describe them all. Instead, we discuss microstructural features relevant to the design and creation of biomaterials in two broad categories, namely dense biomaterials and porous biomaterials.