Physically, it represents the stiffness of a material within the elastic range when tensile or compressive loads are applied.
The elastic modulus of a material is generally calculated by the bending test, because deflection can be easily measured in this case as compared to very small elongation in compressive or tensile load.
[3][page needed] Hardness is a measure of plastic deformation and is defined as the force per unit area of indentation or penetration.
As said above, biomaterials sample are very small, therefore micro- and nano-scale hardness tests (Diamond Knoop and Vickers indenters) are used.
According to Griffith's theory of fracture in tension, the largest flaw or crack will contribute the most to the failure of a material.
For example, hydroxyapatite and other calcium phosphates bioceramics are important for hard tissue repair because of their similarity to the minerals in natural bone, and their excellent biocompatibility and bioactivity, but they have poor fatigue resistance and strength.
Although wear is commonly reported in orthopaedic applications such as knee and hip joint prostheses, it is also a serious and often fatal experience in mechanical heart valves.
The selection of biomaterials for wear resistance unfortunately cannot rely only on conventional thinking of using hard ceramics, because of their low coefficient of friction and high modulus of elasticity.
The development of fatigue fracture and wear resistant biomaterials looks into the biocomposites of two or more different phases such as in interpenetrating network composites.
Of equal importance are the tools developed to predict fatigue fracture/wear using new methodologies involving in vitro tests, computational modelling to obtain design stresses and fracture/wear maps to identify mechanisms.
Viscoelasticity, a material property characterized by the extrusion of dual solid and liquid-like behaviors, is typically found in an array of polymer-based biomaterials, including those used in biomedical devices as well as in clinical settings.
From polymer-based surface coatings on drug-eluting stents to entangled tissue networks that have load-bearing capabilities and hydrogels that possess complex crosslinks, all of these examples display viscoelastic behavior.
Viscoelasticity is often described in terms of its time-dependent material properties associated with its characteristic stress relaxation time.
There are modeling programs employed to probe the material behavior over an array of temperatures and applied frequencies, as well as to decrease the potential for complexity in synthesizing polymers at the industrial level and for commercial use.
For example, in polymeric grafts that act as replacements for tissues, the viscoelastic response is necessary to be mimicked to ensure ample biocompatibility and structural stability over the life-span of the material.
In comparison to other tissue, articular cartilage itself begins to enlarge when subjected to unloading and this puts the microstructure of the material into a state of tension.
Furthermore, when a mechanical load is applied to the tissue, the fluid is forced out of the porous membranes of the biomaterial which exacerbates permanent deformation, while simultaneously stifling viscous flow and decreasing energy in the material overall.
Overall, the viscoelastic characteristics and the viscous attributes in the liquid phase play a role in the dynamic behavior of tissue, and tissue-based materials.