Microstructures and dynamic mechanical properties of bones and implants.The trabeculae bone system - biomechanical aspects
DMTS is a powerful method for the determination of elastic and viscous properties of polymers, ceramics, composites and food, but also biomechanical materials like bones as well as artificial bone substitutes or implants.
Meanwhile, biological investigations start to determine the elastic-viscous properties of human skeletons or bones. One goal is a better understanding of Osteoporosis.
Osteoporosis is no longer a dilute illness of the human skeletal system. It can develop itself to a painful load for human life.
To get a better insight into the dynamical properties of the complex bone structures, DMTS investigations on especially prepared trabeculae bone systems of bovine (in this case calf), were carried out.
The first investigations were carried out with a low static and dynamic deformation in order to avoid irreversible changes, e.g. by breakage of micro levels.
Generally, we assume that the surroundings of the in-vivo bone systems are very close to a wet system.
Figure 1 demonstrates the preparation. In a first step, a rectangular prism was cut from the trabeculae region which was divided into two cubes with approximately identical dimensions with respect to the lumbar spine.
In order to obtain “wet” samples, the “cubes” were stored in ethylene alcohol. Therefore, the pores in the bone material were filled up with the liquid.
Figure 1: Preparation of the samples taken from bovine
The bone behaves like a sponge which is soft in the wet state and becomes stiff in the dry state. A quite reasonable explanation could be that the water in the collagen fibrillas of the trabeculae structure is removed by evaporating effects during the drying period. This causes an increase of the storage modulus E'.
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Figure 2: Storage modulus E‘ - Comparison of the wet and dried bone system