Mechanical properties of soft human tissues under dynamic loading

In this study, both the dynamic shear (torsion) and axial compressive responses of porcine lung tissue were examined using modified Kolsky bar techniques. High-rate compression data were collected using a Kolsky bar with a hollow transmission bar on annular specimens at strain rates between 1000–3000 s−1. The radial deformation of the annular specimen was recorded on a modified single loading Kolsky bar using high-speed imaging capabilities. The collected images and analysis of boundary movement indicated inhomogeneous specimen deformation induced by radial inertia, which significantly altered the desired uniaxial stress state in such high-rate compression test techniques. A novel torsion experimental technique was developed to obtain the dynamic pure shear behavior of lung tissue at shear strain rates above 500 s−1 without inertia effects. The pure shear response was found to be two orders of magnitude weaker than the uniaxial compressive response when compared by equivalent stress–strain relations.

Quantifying 3-Dimensional Soft-to-Hard Tissue Response After Class III Orthognathic Surgery: A Hybrid Cone-Beam Computed Tomography-Stereophotogrammetric Analysis.

On the dynamic shear failure of Ti-6Al-4V in different test specimen geometries

We have constructed an apparatus which enables one to measure, simultaneously, the shear modulus, the viscosity, and the surface pressure of a monomolecular film on water under a hydrostatic compression. It is particularly suitable for measurements of the static shear modulus of insoluble monolayers. A capillary wave generator/detector system was also incorporated to determine the surface pressure. The trough is a Teflon cup 12.7 cm (5.4 in.) in inner diameter with sloping interior sides. As the cup is raised, while maintaining the water elevation fixed, the film is uniformly compressed. A rotor suspended at the center from a fine torsion fiber is used to measure the mechanical properties (surface viscosity and/or surface shear modulus). To measure the quasistatic shear properties, the cup is rotated through a small angle and the residual deflection of the rotor determined. Dynamic shear response is probed by studying transient torsional oscillations following a sudden angular displacement of the torsion fiber. There are no barrier seals and circular symmetry is maintained at all times. The apparatus has a resolution of 5×10−4 surface poise of shear viscosity and 1×10−4 dyn/cm of static shear modulus.

Soft tissue response and facial symmetry after orthognathic surgery

Nickel-containing alloys commonly are used in medical and dental applications that place them into long-term contact with soft tissues. The release of Ni ions from these alloys is disturbing because of the toxic, immunologic, and carcinogenic effects that have been documented for some Ni compounds. In particular, Ni ions in solution recently have been shown to cause expression of inflammatory mediators, such as interleukin-1beta (IL-1beta), tumor necrosis factor-alpha (TNF-alpha), and intercellular adhesion molecules (ICAMs) from keratinocytes, monocytes, and endothelial cells. However, the ability of the solid alloys themselves to induce these inflammatory effects has not been demonstrated. An in vitro system was used to determine if Ni-containing biomedical alloys could cause secretion of either IL-1beta or TNF-alpha from monocytes or expression of ICAMs on endothelial cells. Pure nickel, titanium, and three biomedical alloys-18-8 stainless steel, NiTi, and Rexillium III-were evaluated. First, it was determined whether or not the alloys or pure metals could cause cytotoxicity to THP-1 human monocytes or human microvascular endothelial cells (HMVECs) by measuring the succinic dehydrogenase (SDH) activity of the cells. Then, using identical conditions of exposure, the secretion of IL-1beta or TNF-alpha from monocytes or ICAM-1 expression on the HMVECs was determined. Only pure nickel suppressed (by 48% compared to Teflon controls) the SDH activity of the HMVECs or THP-1 monocytes. No alloy or metal caused the HMVECs to express ICAM-1, but the NiTi alloy caused a significant (ANOVA/Tukey) secretion of IL-1beta from the THP-1 monocytes. Secretion of TNF-alpha induced by NiTi was detectable but not statistically significant. The levels of IL-1beta secretion from monocytes were sufficient to induce ICAM-1 expression on HMVECs. The release of Ni from the NiTi was a logical suspect in causing the IL-1beta secretion by monocytes, but its role was not confirmed since other alloys, such as Rexillium III, released the same quantities of Ni yet did not activate the THP-1 monocytes. Within the limitations of in vitro conditions, our results indicate that NiTi alloys pose a risk of promoting an inflammatory response in soft tissues by activating monocytes. Further study is needed to substantiate this finding in vivo.

There is wealth of data from experimental and numerical methods of analysing and modelling soft connective tissues of joints. In recent years, the advances in computational and technological capabilities allowed for several aspects of the function and mechanical behaviour of soft connective tissues of joints to be explored. However, the nature of soft tissue poses a great challenge in characterizing its material behaviour in a repeatable and physiologically or clinically relevant manner. This review article attempts to present, critique, and suggest experimental and numerical methods that are associated with the function and mechanical response of soft connective tissues of joints.

Soft tissue seal around implants ensures stable osseointegration and a long-term survival of dental implants. Different surface modification and decontamination for implant abutments were endorsed in order to improve peri-implant soft tissue healing, such as laser, plasma spray, acid etching, and steaming. The aim of this study was to evaluate the response of peri-implant soft tissue to titanium abutments treated with Erbium-doped: Yttrium-Aluminum-Garnet (Er:YAG) laser versus plasma spray. Twenty-four patients who required implant placement in the maxillary arch participated in this study. Patients were divided into three groups, abutments treated with Er:YAG laser versus cold plasma spray and untreated abutments. Fourteen days following the implant abutment insertion, soft tissue peri-implant biopsies were taken for histological, histochemical, and immunohistochemical evaluation. Scanning electron microscopy was done for the abutments; plaque index (PI) and gingival index (GI) were assessed 14 days and 3 months following final restoration. Regarding the histological results, the least mean inflammatory cell count was in the plasma group (174.09 ± 40.67), followed by the laser group (654.27 ± 85.95) and the control group (852.00 ± 117.98), with statistically significant differences between them. The mean area fraction of collagen fibers showed the highest value in the plasma group (9.73 ± 1.91), followed by the laser group (3.25 ± 0.49), while the lowest value was found in the control group (1.17 ± 0.51). The immunohistochemical expression of E-cadherin was significantly higher and uniformly distributed in the plasma group (42.4 ± 11.2%) followed by the laser group (15.4 ± 4.07%) and the control group (6.8 ± 1.7%). SEM analysis of healing abutments showed fibroblast-like cells, which were more developed with dense fibers in the plasma group; laser group fibers showed fewer and more delicate fibers than the plasma group, while no fibers were detected in the control group. Within the limitations of this feasibility study, the present data concluded that plasma spray and Erbium: YAG laser can be used for abutment surface treatment to achieve better peri-implant soft tissue healing. Clinically and histologically, plasma spray showed a better effect on the peri-implant soft tissues by reducing the inflammatory reaction, promoting collagen fiber formation, higher fibroblast-like cell attachment, and upregulating E-cadherin expression than Erbium: YAG laser and control groups.

The response of hard and soft oral tissues to prolonged uninterrupted wearing of a removable partial prosthesis in a Nigerian patient is discussed. To our knowledge only one case has been reported in the literature. In this case additional mucosal changes to the reported caries-free pattern is discussed.

The interaction of ultrasound waves with human tissues is complex, and it is inevitable that simplifying physical and mathematical modelling must be invoked to aid our understanding of the processes involved. For pulse-echo methods, finite (bounded) transducers are used to generate three-dimensional (3-D) pulses which travel into the 3-D inhomogeneous medium that is tissue. For soft tissues, it is reasonable to disregard shear wave propagation, but attenuation of the ultrasound pulse is marked, and must be included. Moreover, since attenuation rises in a near-linear fashion with frequency, the shape of the pulse changes as it traverses tissue. Scattered waves are generated by tissue inhomogeneities (density, elasticity and absorption), and are coherently detected.

A detailed understanding of non-targeted normal tissue response is necessary for the optimization of radiation treatment plans in cancer therapy. In this study, we evaluate the ability of electrical impedance spectroscopy (EIS) to non-invasively determine and quantify the injury response in soft tissue after high dose rate (HDR) irradiation, which is characterized by large localized dose distributions possessing steep spatial gradients. The HDR after-loading technique was employed to irradiate small volumes of muscle tissue with single doses (26–52 Gy targeted 5 mm away from the source). Impedance measurements were performed on 29 rats at 1, 2 and 3 month post-irradiation, employing 31 frequencies in the 1 kHz to 1 MHz range. Over the first 3 months, conductivity increased by 48% and 26% following target doses of 52 Gy and 26 Gy 5 mm from the HDR source, respectively. Injury, assessed independently through a grid-based scoring method showed a quadratic dependence on distance from source. A significant injury (50% of cells atrophied, necrotic or degenerating) in 1.2% of the volume, accompanied by more diffuse injury (25% of cells atrophied, necrotic or degenerating) in 9% of the tissue produced a conductivity increase of 0.02 S m−1 (8% over a baseline of 0.24 S m−1). This was not statistically significant at p = 0.01. Among treatment groups, injury differences in 22% of the volume led to statistically significant differences in conductivity of 0.07 S m−1 (23% difference in conductivity). Despite limitations, the success of EIS in detecting responses in a fraction of the tissue probed, during these early post-irradiation time-points, is encouraging. Electrical impedance spectroscopy may provide a useful metric of atrophy and the development of fibrosis secondary to radiation that could be further developed into a low-cost imaging method for radiotherapy monitoring and assessment.

The edible mussel Lithophaga lithophaga is considered as one of the most important human food sources in Alexandria, Mediterranean Sea. The present study is designed to determine the seasonal bioaccumulation levels of Cd, Co and Pb in the whole soft tissues as well as different tissues of Lithophaga lithophaga. Results revealed that the seasonal bioaccumulation levels of Cd, Co and Pb in date mussel were below the permissible limits or other reported values from other regions of the Mediterranean. On the other hand, the order of metals accumulation level in different tissues was as follows: digestive gland>remaining soft tissues>gonads. The present study confirmed the role of digestive gland as a concentration center for heavy metals. Moreover, total protein content and stress protein responses of the whole soft tissues were evaluated. The total protein content was arranged in the following order: summer>autumn>spring>winter. Five novel stress proteins appeared in summer. The histological and ultrastructural studies of the digestive gland of Lithophaga lithophaga collected in summer and spring showed marked histopathological alternations.

Quantitative assessment of the biomechanical properties of limb soft tissues has become more important during the last decade because of the introduction of computer-aided design and computer-aided manufacturing (CAD/CAM) and finite element analysis to the prosthetic socket design. Because of the lack of a clinically easy-to-use apparatus, the site and posture dependences of the material properties of lower limb soft tissues have not been fully reported in the literature. In this study, an ultrasound indentation system with a pen-size hand-held probe developed earlier by the authors was used to obtain the indentation responses of lower limb soft tissues. Indentation tests were conducted on normal young subjects with four females and four males at four sites with three body postures. A linear elastic indentation solution was used to extract the effective Young's modulus from the indentation responses. The determined modulus ranged from 10.4 to 89.2 kPa for the soft tissues tested. These results were in a similar range as those reported in the literature. The thickness of the lower limb soft tissues varied slightly with body posture changes. The Young's modulus determined was demonstrated to be significantly dependent on site, posture, subject and gender. The overall mean modulus of male subjects was 40% larger than that of female subjects. No significant correlation was established between the effective Young's modulus and the thickness of entire soft tissue layers.

The characteristic highly nonlinear, time-dependent, and often inelastic material response of soft biological tissues can be expressed in a set of elastic-viscoplastic constitutive equations. The specific elastic-viscoplastic model for soft tissues proposed by Rubin and Bodner (2002) is generalized with respect to the constitutive equations for the scalar quantity of the rate of inelasticity and the hardening parameter in order to represent a general framework for elastic-viscoplastic models. A strongly objective integration scheme and a new mixed finite element formulation were developed based on the introduction of the relative deformation gradient-the deformation mapping between the last converged and current configurations. The numerical implementation of both the generalized framework and the specific Rubin and Bodner model is presented. As an example of a challenging application of the new model equations, the mechanical response of facial skin tissue is characterized through an experimental campaign based on the suction method. The measurement data are used for the identification of a suitable set of model parameters that well represents the experimentally observed tissue behavior. Two different measurement protocols were defined to address specific tissue properties with respect to the instantaneous tissue response, inelasticity, and tissue recovery.

Cohesion and internal friction angle are the two material parameters used in the Coulomb model to predict rock failure in many rock engineering applications. Although these two parameters have been extensively quantified under static conditions using the direct shear or the triaxial compression methods, the effect of dynamic loading on these parameters is not yet clear. A dynamic punch shear method was proposed by Huang et al. (Rev Sci Instrum 82:053901. https://doi.org/10.1063/1.3585983 , 2011) to measure the dynamic cohesion of rocks, and the dependence of cohesion on the loading rate has been revealed. To further investigate the effect of dynamic loading on the internal friction angle and thus the complete dynamic shear response of rocks, this method is extended in this study to include the normal stress by applying lateral confinement to a disc specimen. The confinement is realized by enclosing the specimen assembly in a 1.5 inch diameter Hoek cell. The dynamic load is applied by a split Hopkinson pressure bar system, which is modified to ensure that the specimen assembly remains intact in the Hoek cell during pressurization by applying a static axial pre-stress. Three groups of green sandstone specimens under confinements of 0, 10 and 20 MPa are tested with different loading rates. The results show that the dynamic shear strength exhibits significant rate dependency and it thus increases with the loading rate and the normal stress. The dynamic cohesion increases with the loading rate, while the internal friction angle remains constant.