Static and dynamic mechanical behavior of biomaterials in dry and simulated physiological conditions
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Biomateriaalien staattinen ja dynaaminen mekaaninen käyttäytyminen kuivassa ja simuloidussa fysiologisessa olosuhteissa
Mechanical testing is one of the fundamental procedures when determining the properties of materials. Biomaterials, when used as temporary or permanent replacements of biological tissues inside the human body, demand particularly the characterization of mechanical properties. One of the main requirements is that the biomaterials behave mechanically as similarly to the original tissue and are mechanically compatible with the surrounding tissue after implantation. Since the human body is constantly in motion, the implanted biomaterials are subjected to different fluctuating forces, the prior knowledge of how the biomaterials behave not just during static loading but dynamic as well, is extremely important. The aim of this thesis was to study the mechanical behavior of different polymer based biomaterials by subjecting them to static and dynamic loadings and also to two different environments, dry ambient laboratory and physiologically simulated condition consisting of aqueous and 37 °C environment. The stress-strain behavior as well as static and dynamic stress relaxation and creep behaviors were considered among other things. The study revealed that in order to produce reliable mechanical properties of biomaterials intended to be used in the human body, mechanical tests should be conducted in 37°C and at least in aqueous media. Introducing water and warmer environment in tests result in more elastic and flexible behavior of the tested materials. While static tests can be used to determine basic mechanical properties, more extensive knowledge can be obtained by also dynamically loading the samples. Because of the viscoelasticity of polymers, careful design of mechanical tests is important since different parameters such as testing speeds may give different results.