In the present study, swine thighbone samples with different water contents were prepared through process of dehydration. The influence of water content on the biotribological behavior of the bone tissue was studied with nanoindentation test, reciprocating sliding test and impact wear test. It is shown that the water contents had significant influence on the mechanical properties and biotribological behavior of the swine thighbone samples. In this experiment condition, with decreasing water content, the hardness and elastic modulus of the swine thighbone samples increased, while the tribological properties significantly decreased. The viscoelasticity of bone tissue decreased with decreasing water content, which mainly resulted in different wear mechanisms of the bone tissue samples under applied loading.
The mechanical behavior modeling of human soft biological tissues is a key issue for a large number of medical applications, such as surgery simulation, surgery planning, diagnosis, etc. To develop a biomechanical model of human soft tissues under large deformation for surgery simulation, the adaptive quasi-linear viscoelastic (AQLV) model was proposed and applied in human forearm soft tissues by indentation tests. An incremental ramp-and-hold test was carried out to calibrate the model parameters. To verify the predictive ability of the AQLV model, the incremental ramp-and-hold test, a single large amplitude ramp-and-hold test and a sinusoidal cyclic test at large strain amplitude were adopted in this study. Results showed that the AQLV model could predict the test results under the three kinds of load conditions. It is concluded that the AQLV model is feasible to describe the nonlinear viscoelastic properties of in vivo soft tissues under large deformation. It is promising that this model can be selected as one of the soft tissues models in the software design for surgery simulation or diagnosis.
The objective of this study was to determine the visco-hyperelastic constitutive law of brain tissue under dynamic impacts. A method combined by finite element simulations and optimization algorithm was employed for the determination of material variables. Firstly, finite element simulations of brain tissue dynamic uniaxial tension, with a maximum stretch rate of 1.3 and strain rates of 30 s–1 and 90 s–1, were developed referring to experimental data. Then, fitting errors between the engineering stress-strain curves predicted by simulations and experimental average curves were assigned as objective functions, and the multi-objective genetic algorithm was employed for the optimation solution. The results demonstrate that the brain tissue finite element models assigned with the novel obtained visco-hyperelastic material law could predict the brain tissue’s dynamic mechanical characteristic well at different loading rates. Meanwhile, the novel material law could also be applied in the human head finite element models for the improvement of the biofidelity under dynamic impact loadings.
ObjectiveTo summarize the research progress in creep characteristics of lumbar intervertebral disc.MethodsThe relevant literature at home and abroad was systematically searched. Then, the concept and structural basis of lumbar disc creep, the description of creep characteristics, and the latest progress of its influencing factors were summarized and analyzed.ResultsThe intervertebral disc is viscoelastic. After loading, the deformation increases with time. However, the degree of increase is not linear with time. That is creep, which plays an important role in buffering the load generated by human activities and absorbing energy in order to maintain stable movement of the spine. Both experimental and simulation studies can well describe the creep behavior of intervertebral disc. Various models including standard linear solid model and corresponding constitutive equations can quantify and compare the creep characteristics, which can be obviously changed by the degeneration of intervertebral disc and the mode of loading stress.ConclusionCreep is an important mechanical properties of intervertebral discs, and an in-depth understanding of the creep characteristics of lumbar intervertebral discs is of great guiding significance for the intervention and treatment of low back pain.