Properties Of Human Soft Tissues Research Articles

A Minimalistic, Synthetic Cell‐Inspired Metamaterial for Enabling Reversible Strain‐Stiffening

AbstractStrain‐stiffening, i.e. the nonlinear stiffening of a material in response to a strain, is an intrinsic feature of many biological systems, including skin, blood vessels, and single cells. To avoid a mismatch in mechanical properties, synthetic materials in contact with such biological systems should also be strain‐stiffening. Conventional strain‐stiffening materials are either highly dependent on the applied strain‐rate, or only available for a limited stiffness regime. Both aspects limit the applicability of these materials. In contrast, living cells employ a dynamic strain‐stiffening mechanism that is based on the cross‐linking of cytoskeletal fibers in response to external stress. This strain‐stiffening of the cytoskeleton is mimicked in a mechanical metamaterial by a minimalistic structure consisting of parallel slats connected to backbones. Herein, it is demonstrated experimentally that the structures can be adapted such that the strain required for stiffening, the final stiffness, as well as the degree of stiffening can be tuned, particularly by combining several strain‐stiffening elements. These properties make the structure promising for the development of devices that should resemble the mechanical properties of human soft tissues, e.g., skin‐integrated flexible electronics and blood vessel grafts.

Development of Dummy Based on Impedance Properties of Human Soft Tissue Using a Nonlinear Viscoelastic Model

Securing human safety in a physical human–robot interaction (pHRI) has been extensively studied to allow for the expansion of robotic applications. Dummies with the same impedance properties as those of human soft tissues are suitable substitutes for the validation of the safety assurance of the pHRI experiment. This study demonstrated the development process of dummies with high biofidelity. A psychophysiological experiment was designed to replicate the clamping scenario, and the center of the palm, thenar eminence, and forefinger pad were selected as three soft tissues of the human hand to be impacted to obtain the dynamic response of the contact force. A nonlinear five-element viscoelastic model was developed to quantify the viscoelasticity of the three soft tissues through curve fitting of the contact force. Subsequently, three dummies were fabricated using a polyurethane resin material. The biofidelity of the dummies was examined via a parametric comparison with the soft tissues and curve comparisons to examine whether the steady-state force and the dynamic response of the contact force were located within the corresponding ranges enclosed by the calibration curves of the soft tissues. All three dummies showed high biofidelity in the case where the steady-state force exceeded approximately 5 N, even though they have different nonlinearity of elasticity from that of soft tissues.

A Novel Concept for Unidirectional Communication With an Active Implant Based on Deliberately Produced Human Body Signals.

A new patient-friendly and discrete approach to build a unidirectional communication path with active implants based on deliberately produced human body signals is presented. The application for which this approach is intended is an artificial urinary sphincter implant, the closure mechanism of which is wirelessly actuated in the event of micturition need. Conventional implant communication methods can be associated with limitations regarding technological implementation and usability, and are used by medical professionals only. In order to enable patients to discretely and directly communicate with their implant without the need for an external handheld device, the feasibility of a communication approach based on manually applied 'knocking' signals on abdominal tissue is examined in the presented work. A gelatin-based phantom model is used to mimic vibro-acoustic properties of human soft tissue in vitro. A piezoelectric element and an electret microphone are applied as sensors for signal detection at the implantation site and are investigated with respect to their suitability for the intended application. Clinical Relevance- The presented implant communication method can contribute to urinary incontinence therapy by enabling patients to discretely and user-friendly actuate their artificial sphincter implant and can provide a basis for future research into new implant communication technologies.

Fluorescence microscope observation of the structure of a calcium alginate hydrogel

Abstract Calcium alginate hydrogels are used in a wide range of applications in the food, medical, pharmaceutical, and cosmetic industries. I have studied a calcium alginate hydrogel as an ultrasound phantom material. This hydrogel is formed using sodium alginate, calcium sulfate dihydrate, trisodium phosphate 12-hydrate, glycerol, and water, and mimics the ultrasound properties of human soft tissue. In this study, the structure of the calcium alginate hydrogel was observed with a fluorescence microscope after staining with the calcium indicator calcein. Two types of hydrogel structures, tape-like and thread-like, were observed by this method. The thread-like structures were rare in the hydrogel, which made them more difficult to find than the tape-like structures. These structures were several micrometers in diameter and longer than the tape-like structures, which were several micrometers to several tens of micrometers wide. The thread-like structures spread out in three dimensions, and existed singly or in aggregates. The outer shape of the aggregated thread-like structures resembled the shape of the tape-like structures, which suggested that the tape-like structures were made up of thread-like structures. The tape-like and thread-like structures are thought to contribute to retention of water, which is the main component of a hydrogel, by surrounding it.

Разработка инновационных материалов для судебной экспертизы

In the production of experimental studies related to the modeling of the behavior of human soft tissues in such widespread types of forensic examinations as forensic ballistic, tracological, forensic examination of cold and throwing weapons, forensic medical-use bioimitators. Human corpses, animal carcasses, and their living individuals are used as such objects, but in recent decades, with the development of chemistry and chemical technology, various artificial substitutes have become increasingly widespread – colloidal systems based on gelatin, soap, mixtures of petroleum petrolatum, as well as specialized compositions. Among the main advantages of using soft tissue substitutes are the following: visibility of the results obtained, availability of synthetic materials, uniformity of structure, reproducibility of experimental results with a statistically reliable amount, as well as, if necessary, the possibility of varying mechanical parameters for physical modeling of the characteristics of human biological tissues within the framework of an expert experiment. The paper proposes a technology for obtaining a reusable synthetic compound that allows modeling the properties of human soft tissues. The synthetic compound provides the transfer of general patterns of morphology of the formed gunshot injuries, similar to gunshot wounds on biological materials.

Thermal Properties of Human Soft Tissue and Its Equivalents in a Wide Low-Temperature Range

Thermal Properties of Human Soft Tissue and Its Equivalents in a Wide Low-Temperature Range

Bimodal microwave and ultrasound phantoms for non-invasive clinical imaging

A precise and thorough methodology is presented for the design and fabrication of bimodal phantoms to be used in medical microwave and ultrasound applications. Dielectric and acoustic properties of human soft tissues were simultaneously mimicked. The phantoms were fabricated using polyvinyl alcohol cryogel (PVA-C) as gelling agent at a 10% concentration. Sucrose was employed to control the dielectric properties in the microwave spectrum, whereas cellulose was used as acoustic scatterer for ultrasound. For the dielectric properties at microwaves, a mathematical model was extracted to calculate the complex permittivity of the desired mimicked tissues in the frequency range from 500 MHz to 20 GHz. This model, dependent on frequency and sucrose concentration, was in good agreement with the reference Cole–Cole model. Regarding the acoustic properties, the speed of sound and attenuation coefficient were employed for validation. In both cases, the experimental data were consistent with the corresponding theoretical values for soft tissues. The characterization of these PVA-C phantoms demonstrated a significant performance for simultaneous microwave and ultrasound operation. In conclusion, PVA-C has been validated as gelling agent for the fabrication of complex multimodal phantoms that mimic soft tissues providing a unique tool to be used in a range of clinical applications.

Validation System for Digital Stethoscopes

Abstract Stethoscope auscultation is a diagnostic method widely used by medical professionals. With the introduction of digital stethoscopes, auscultation sound analysis has been objectified, which led to an increased interest in the field. Until today, however, no standard to assess the acoustical properties of stethoscopes is available. Some approaches use phantoms mimicking the properties of human soft tissue. In most cases, however, the properties of the phantoms have not been analyzed with respect to environmental variables. In our work, we propose a stethoscope characterization system for the frequency range between 50 Hz and 2.5 kHz with a small financial footprint. We analyzed its frequency behavior over temperature, time and position on the phantom and derived quantitative recommendations for environmental variables. Finally, the frequency response of a commercial digital stethoscope was characterized at different pressure levels. We conclude that the presented system is capable to stably and reproducibly assess the transfer function of digital stethoscopes. We hope that future stethoscope designs will be characterized with respect to their acoustical properties.

Low-Frequency Ultrasonic Tomography: Mathematical Methods and Experimental Results

This paper describes investigation of the possibilities of low-frequency ultrasonic tomography in medicine. The main application is the development of tomographic methods for differential diagnosis of breast cancer. To solve the inverse problem, a mathematical model is used that describes both the phenomena of diffraction and refraction and the absorption of ultrasound in an inhomogeneous medium. The algorithms developed for reconstructing the velocity structure were evaluated using the test bench for experimental studies. Broadband ultrasonic sources in the 50–600 kHz range were used for sounding. A Teledyne Reson TC4038 hydrophone with a sensitivity of approximately 4 µV/Pa and a frequency range of 10–800 kHz was used as a receiver. A Teledyne Reson VP1000 preamplifier was used to amplify the signals. The studies were carried out on phantoms with acoustic parameters close to the properties of human soft tissues. A layerwise model was used to reconstruct the three-dimensional velocity structure. The sound speed cross-sections reconstructed from the experimental data have a resolution of approximately 2 mm, while the central wavelength is approximately 4 mm. An important result of the work is an experimental confirmation of the correspondence of the model to physical processes.

Acoustic Characterisation of Konjac Glucomannan Gel as a Medical Phantom

Acoustic properties are the main criteria to evaluate the compatibility of tested materials as a medical phantom. We determined the acoustic properties of konjac glucomannan (KGM) gel to verify its compatibility as a medical phantom. The acoustic properties measurement employed ultrasonic insertion technique and utilized two identical transducers of 5 MHz center frequencies. One KGM gel block with 5.62 mm thickness was used as sample to determine its longitudinal speed, acoustic impedance and attenuation coefficient at three different water temperatures; (21.5 ± 0.1), (22.5 ± 0.1) and (23.5 ± 0.1) °C. Findings indicated that its longitudinal speed and acoustic impedance increased from (1495 ± 1) to (1499 ± 1) m s-1 and (1.555 ± 0.001) to (1.559 ± 0.001) × 106 kg m-2 s-1 as the water temperature increased from (21.5 ± 0.1) to (23.5 ± 0.1) °C. It also indicated that its attenuation coefficient varied around (0.1303 ± 0.0107) to (0.1373 ± 0.0103) dB cm-1 with increasing water temperature. KGM gel is compatible to be a medical phantom since its acoustic properties are comparable to the acoustic properties of human soft tissue.

Biomechanical Characterization of Human Soft Tissues Using Indentation and Tensile Testing.

Regenerative medicine aims to engineer materials to replace or restore damaged or diseased organs. The mechanical properties of such materials should mimic the human tissues they are aiming to replace; to provide the required anatomical shape, the materials must be able to sustain the mechanical forces they will experience when implanted at the defect site. Although the mechanical properties of tissue-engineered scaffolds are of great importance, many human tissues that undergo restoration with engineered materials have not been fully biomechanically characterized. Several compressive and tensile protocols are reported for evaluating materials, but with large variability it is difficult to compare results between studies. Further complicating the studies is the often destructive nature of mechanical testing. Whilst an understanding of tissue failure is important, it is also important to have knowledge of the elastic and viscoelastic properties under more physiological loading conditions.This report aims to provide a minimally destructive protocol to evaluate the compressive and tensile properties of human soft tissues. As examples of this technique, the tensile testing of skin and the compressive testing of cartilage are described. These protocols can also be directly applied to synthetic materials to ensure that the mechanical properties are similar to the native tissue. Protocols to assess the mechanical properties of human native tissue will allow a benchmark by which to create suitable tissue-engineered substitutes.

Study on the application of shear-wave elastography to thin-layered media and tubular structure: Finite-element analysis and experiment verification

Shear-wave elastography (SWE) enables the noninvasive and quantitative evaluation of the mechanical properties of human soft tissue. Generally, shear-wave velocity (CS) can be estimated using the time-of-flight (TOF) method. Young’s modulus is then calculated directly from the estimated CS. However, because shear waves in thin-layered media propagate as guided waves, CS cannot be accurately estimated using the conventional TOF method. Leaky Lamb dispersion analysis (LLDA) has recently been proposed to overcome this problem. In this study, we performed both experimental and finite-element (FE) analyses to evaluate the advantages of LLDA over TOF. In FE analysis, we investigated why the conventional TOF is ineffective for thin-layered media. In phantom experiments, CS results estimated using the two methods were compared for 1.5 and 2% agar plates and tube phantoms. Furthermore, it was shown that Lamb waves can be applied to tubular structures by extracting lateral waves traveling in the long axis direction of the tube using a two-dimensional window. Also, the effects of the inner radius and stiffness (or shear wavelength) of the tube on the estimation performance of LLDA were experimentally discussed. In phantom experiments, the results indicated good agreement between LLDA (plate phantoms of 2 mm thickness: 5.0 m/s for 1.5% agar and 7.2 m/s for 2% agar; tube phantoms with 2 mm thickness and 2 mm inner radius: 5.1 m/s for 1.5% agar and 7.0 m/s for 2% agar; tube phantoms with 2 mm thickness and 4 mm inner radius: 5.3 m/s for 1.5% agar and 7.3 m/s for 2% agar) and SWE measurements (bulk phantoms: 5.3 m/s ± 0.27 for 1.5% agar and 7.3 m/s ± 0.54 for 2% agar).

Stable and Flexible Materials to Mimic the Dielectric Properties of Human Soft Tissues

Emerging biomedical applications require realistic phantoms for validation and testing of prototype systems. These phantoms require stable and flexible tissue-mimicking materials with realistic dielectric properties in order to properly model human tissues. To create a tissue-mimicking material to fulfill these needs, carbon powder and urethane rubber mixtures were created, and the dielectric properties were measured using a dielectric probe. Both graphite and carbon black were tested. Mixtures of graphite and urethane (0% to 50% by weight) provided relatively low permittivity and conductivity, suitable for mimicking fatty tissues. Mixtures of carbon black and urethane (0% to 15% by weight) provided a broad range of suitable properties. Samples with 15% carbon black had permittivity and conductivity similar to higher-water-content tissues, however the cured samples were not mechanically suitable for moulding into complex shapes. Finally, mixtures of graphite, carbon black, and urethane were created. These exhibited a range of dielectric properties and can be used to mimic a variety of soft tissues. The mechanical properties of these samples were tested and presented properties that exceed typical phantom requirements. This tissue-mimicking material will be useful when creating thin, flexible, and robust structures such as skin layers.

Collaborative Simulation of Soft-Tissue Deformation for Virtual Surgery Applications

A key challenge of collaborative surgical simulation is to maintain a high level of state consistency among the distributed users under the limitation of network transmission capacity. In this paper, a framework integrating a scalable deformable model and an extensible communication protocol is proposed to meet this challenge. The parameters of the deformable model are obtained by making reference to the biomechanical properties of human soft tissues. Efficient collaboration is achieved by developing the communication protocol and implementing a series of network management approaches, including service management, computation policies, coupling control, token control and availability mechanism. A prototype has been developed by using the client-server network architecture. Experimental results demonstrate that this framework can support collaborative surgical simulation with acceptable network latencies.

Breast ultrasound imaging phantom to mimic malign lesion characteristics

Ultrasound (US) phantoms are used to simulate the main acoustic properties of human soft tissues and are usually applied in guided biopsy training and equipment calibration. In this work it is presented an ultrasound phantom that mimics breast lesions with irregular edge, which is a typical feature related to malignancy. The phantom matrix was made of a mixture of water, agar, glycerine and graphite and PVC powders and the lesions were of silicon and polyacrylamide. The mimicking properties were US attenuation, propagation speed and density. The images obtained were visually compatible to malignant and benign lesions and are meant to be used as references for evaluation of segmentation algorithms for image processing.

Quantifying dynamic mechanical properties of human placenta tissue using optimization techniques with specimen-specific finite-element models

Motor-vehicle crashes are the leading cause of fetal deaths resulting from maternal trauma in the United States, and placental abruption is the most common cause of these deaths. To minimize this injury, new assessment tools, such as crash-test dummies and computational models of pregnant women, are needed to evaluate vehicle restraint systems with respect to reducing the risk of placental abruption. Developing these models requires accurate material properties for tissues in the pregnant abdomen under dynamic loading conditions that can occur in crashes. A method has been developed for determining dynamic material properties of human soft tissues that combines results from uniaxial tensile tests, specimen-specific finite-element models based on laser scans that accurately capture non-uniform tissue-specimen geometry, and optimization techniques. The current study applies this method to characterizing material properties of placental tissue. For 21 placenta specimens tested at a strain rate of 12/s, the mean failure strain is 0.472±0.097 and the mean failure stress is 34.80±12.62 kPa. A first-order Ogden material model with ground-state shear modulus ( μ) of 23.97±5.52 kPa and exponent ( α 1) of 3.66±1.90 best fits the test results. The new method provides a nearly 40% error reduction ( p<0.001) compared to traditional curve-fitting methods by considering detailed specimen geometry, loading conditions, and dynamic effects from high-speed loading. The proposed method can be applied to determine mechanical properties of other soft biological tissues.

Digital image correlation and finite element modelling as a method to determine mechanical properties of human soft tissue in vivo

The mechanical properties of human soft tissue are crucial for impact biomechanics, rehabilitation engineering, and surgical simulation. Validation of these constitutive models using human data remains challenging and often requires the use of non-invasive imaging and inverse finite element (FE) analysis. Post-processing data from imaging methods such as tagged magnetic resonance imaging (MRI) can be challenging. Digital image correlation (DIC), however, is a relatively straightforward imaging method. DIC has been used in the past to study the planar and superficial properties of soft tissue and excised soft tissue layers. However, DIC has not been used to non-invasive study of the bulk properties of human soft tissue in vivo. Thus, the goal of this study was to assess the use of DIC in combination with FE modelling to determine the bulk material properties of human soft tissue. Indentation experiments were performed on a silicone gel soft tissue phantom. A two camera DIC setup was then used to record the 3D surface deformation. The experiment was then simulated using a FE model. The gel was modelled as Neo-Hookean hyperelastic, and the material parameters were determined by minimising the error between the experimental and FE data. The iterative FE analysis determined material parameters ( μ=1.80 kPa, K=2999 kPa) that were in close agreement with parameters derived independently from regression to uniaxial compression tests ( μ=1.71 kPa, K=2857 kPa). Furthermore the FE model was capable of reproducing the experimental indentor force as well as the surface deformation found ( R 2=0.81). It was therefore concluded that a two camera DIC configuration combined with FE modelling can be used to determine the bulk mechanical properties of materials that can be represented using hyperelastic Neo-Hookean constitutive laws.

A Bernstein‐Bézier Based Approach to Soft Tissue Simulation

This paper discusses a Finite Element approach for volumetric soft tissue modeling in the context of facial surgery simulation. We elaborate on the underlying physics and address some computational aspects of the finite element discretization.In contrast to existing approaches speed is not our first concern, but we strive for the highest possible accuracy of simulation. We therefore propose an extension of linear elasticity towards incompressibility and nonlinear material behavior, in order to describe the complex properties of human soft tissue more accurately. Furthermore, we incorporate higher order interpolation functions using a Bernstein‐Bézier formulation, which has various advantageous properties, such as its integral polynomial form of arbitrary degree, efficient subdivision schemes, and suitability for geometric modeling and rendering. In addition, the use of tetrahedral Finite Elements does not put any restriction on the geometry of the simulated volumes.Experimental results obtained from a synthetic block of soft tissue and from the Visible Human Data Set illustrate the performance of the envisioned model.

A method of measuring the modulus of elasticity of human muscle tissue

An experimental method is described for estimating the mechanical properties of human soft tissues by calculating Young's modulus which was defined according to the slope of the hysteresis curve of the test subject, reflecting the dependence of its deformation on the force applied. The main causes of numerous difficulties in obtaining such data and the ways for their overcoming are considered. Experiments were made on the biceps in the isometric mode under different degrees of internal tension. It has been shown that the higher the physical development of the test subject the less the magnitude of Young's modulus. The dependence of its magnitude on the degree of muscular tension is sublinear in character in the group with good physical development and superlinear in that with poor physical development.

General characterization of the rheological properties of human soft tissues based on measurements made by the local cyclic loading method and a simple phenomenological model of these properties

General characterization of the rheological properties of human soft tissues based on measurements made by the local cyclic loading method and a simple phenomenological model of these properties