Introduction: NANO-INDENTATION has recently been employed as a powerful tool for determining the mechanical properties of biological tissues on NANO and micro scales. A majority of soft biological tissues such as ligaments and tendons exhibit viscoelastic or time-dependent behaviors. The constitutive characterization of soft tissues is among very important subjects in clinical medicine and especially, biomechanics fields. Periodontal ligament plays an important role in initiating tooth movement when loads are applied to teeth with orthodontic appliances. It is also the most accessible ligament in human body as it can be directly manipulated without any surgical intervention.From a mechanical point of view, this ligament can be considered as a thin interface made by a solid phase, consisting mainly of collagen fibers, which is immersed into a so-called ground substance. However, the viscoelastic constitutive effects of biological tissues are seldom considered rigorous during NANO-INDENTATION tests.Methods: In the present paper, a mathematical contact approach is developed to enable determining creep compliance and relaxation modulus of distinct periodontal ligaments, using constant–rate INDENTATION and loading time histories, respectively. An adequate curve-fitting method is presented to determine these characteristics based on the NANO-INDENTATION of rigid Berkovich tips. Generalized Voigt-Kelvin and Wiechert models are used to model constitutive equations of periodontal ligaments, in which the relaxation and creep functions are represented by series of decaying exponential functions of time.Results: Time-dependent creep compliance and relaxation function have been obtained for tissue specimens of periodontal ligaments.Conclusion: To improve accuracy, relaxation and creep moduli are measured from two tests separately. Stress relaxation effects appear more rapidly than creep in the periodontal ligaments.

The scientific importance of NANOcomposites is being increased due to their improved properties. This paper is divided into two parts. First, Al-Al2O3 NANOcomposite was produced by using ball milling technique followed by cold compaction and sintering. Microstructure and morphology studies were done through SEM, TEM, and EDX analyses on the produced powder. The mechanical properties of the produced composite were determined by the tensile test. Also, NANO-INDENTATION experiment was conducted on the produced composite to determine its hardness. Second, a 2-D axisymmetry model was implemented in ANSYS software to simulate the NANO-INDENTATION experiment on pure aluminum and Al-Al2O3 NANOcomposite. A conical indenter with 70.3o was considered in simulations. The results show that, a homogenous distribution of the reinforcement in the matrix was achieved after 20 h milling. The elastic modulus, yield strength, and the hardness of the produced composite were increased compared to the pure metal. The finite element (FE) simulation results showed a good agreement with the experimental results for NANO-INDENTATION experiment. The scatter of the FE results from the experimental results in the pure metal was smaller than that observed for the NANOcomposite.

Discovering the mechanical properties of biological composite structures at the NANO-scale is much interesting today. Top Neck mollusk shells are amongst biomaterials NANO-Composite that their layered structures are composed of organic and inorganic materials. Since the NANO INDENTATION process is known as an efficient method to determine mechanical properties like elastic modulus and hardness in small-scale, so, due to some limitation of considering all peripheral parameters; particular simulations of temperature effect on the atomic scale are considerable. The present paper provides a molecular dynamics approach for modeling the NANO-INDENTATION mechanism with three types of pyramids, cubic and spherical indenters at different temperatures of 173, 273, 300 and 373K. Based on load-INDENTATION depth diagrams and Oliver-Far equations, the findings of the study indicate that results in the weakening bond among the bilateral atoms lead to reduced corresponding harnesses. Whenever, the temperature increases the elastic modulus decrease as well as the related hardness. Moreover, within determining the elastic modulus and hardness, the results obtained from the spherical indenter will have the better consistency with experimental data. This study can be regarded as a novel benchmark study for further researches which tend to consider structural responses of the various Bio-inspired NANO-Composites.

The elasticity modules of the micro/NANOparticles, especially biological particles are measured using different tools such as atomic force microscopy. The tip of the atomic force microscopy as an indenter has different shapes such as spherical, conical and pyramidal. In the contact of these tips and biological cells, avoiding the cell damage is a necessity. The goal of this paper is investigation and comparison of different tips’ geometries. Different tip’ s geometries and their related theories were collected and proposed. To generalize theories’ application for any kind of particle (even non-biological particles) some of simplifying assumptions used in these theories, such as tip rigidity, were removed. Simulation of the force-INDENTATION depth was done for gold NANOparticle and observed that if simplifying assumptions were not removed there would be big errors in calculating the elasticity module of some particles. Then, simulations were done for two yeast and mouse embryo cells. For both cells, in general, the geometry of the curve group, the geometry of the pyramidal group and finally the geometry of the conical group were positioned from the highest to the lowest places. For hyperbolic, conical and pyramidal tips, the important parameter was semi vertical angel. To observe its effect, different magnitudes of this parameter were simulated. According to observed results in three investigated geometries and for both cells, bigger semi vertical angel created higher curves and this means in bigger angels the possibility of cell damage is higher.

NANO-INDENTATION test is one of the most common method to study the material post-yielding behavior providing a suitable material model. Nowadays, this test is also used to investigate the pressure-dependent behavior and other mechanical behaviors of bone. Different material models such as Johnson-Cook, von-Mises, Drucker-Prager, and Hill models have been presented to consider the anisotropy, pressure dependency, strain rate, and temperature dependency of cortical bovine bones similar to human bone in tension and compression. In the present study, using the Arbitrary Eulerian-Lagrangian (ALE) finite element method in Abaqus software with appropriate contact conditions, the material flow and the results of bone pile-up was well predicted with an error of less than 1%. Also, suitable parameters of the extended Drucker-Prager model for predicting post-yielding bovine cortical bone behavior were presented such that the force-displacement curve of test, showed less than 5% deviation from the experimental results. The friction angle 46°, , and zero-degree dilation angle along with the frictional contact conditions between the tool and the bone with a coefficient of 0. 3 provided the best parameters to predict post-yielding behavior. It was also shown that changing the angle of dilation from zero to 10 degrees can increase the maximum force applied to the bone up to 40%.