Mechanical properties of biomaterials

Mechanical properties of biomaterials
For any material to be classified for biomedical application there are many requirements must be met , one of these requirement is the material should be mechanically sound; for the replacement of load bearing structures, the material should possess equivalent or greater mechanical stability to ensure high reliability of the graft.
The physical properties of ceramics depend on their microstructure, which can be characterized in terms of the number and types of phases present, the relative amount of each, and the size, shape, and orientation of each phase.
Elastic Modulus
Elastic modulus is simply defined as the ratio of stress to strain within the proportional limit. Physically, it represents the stiffness of a material within the elastic range when tensile or compressive load are applied. It is clinically important because it indicates the selected biomaterial has similar deformable properties with the material it is going to replace. These force-bearing materials require high elastic modulus with low deflection. As the elastic modulus of material increases fracture resistance decreases. The Elastic modulus of a material is generally calculated by bending test because deflection can be easily measured in this case as compared to very small elongation in compressive or tensile load. However, biomaterials (for bone replacement) are usually porous and the sizes of the samples are small. Therefore, nanoindentation test is used to determine the elastic modulus of these materials. This method has high precision and convenient for micro scale samples. Another method of elastic modulus measurement is non-destructive method such as laser ultrasonic technique. It is also clinically very good method because of its simplicity and repeatability since materials are not destroyed. An ultrasonic technique has been developed for measuring the elastic moduli of bioceramic coatings applied to titanium orthopaedic implants.