A pinch elastometer for soft tissue (original) (raw)
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A Novel Elastometer For Soft Tissue
WIT transactions on engineering sciences, 2005
A novel device has been designed to allow a surgeon to determine the medium strain (5-25%) compressive properties of highly extensible soft tissue during a surgical procedure. The motivation for the instrument is the need for accurate knowledge of the elastic properties of vaginal tissue in vivo during corrective surgery for incontinence in women. Studies have shown that a surgical technique that adjusts the elastic nature of vaginal tissue can reduce urge and stress incontinence symptoms. The success of the surgical technique would be greatly enhanced by the introduction of an objective measure of the stiffness of vaginal tissue. The compressive deformation is achieved by folding and pinching (indenting) the tissue between two circular cylinders. The applied load and indentation depth are used to estimate the elastic properties of the sampled tissue. A linear material model has been developed and tested against commercially available elastomers. The limits of application of the lin...
Medical Engineering & Physics, 2008
We have developed a device entitled the 'Tissue Elastometer' (TE) for evaluating the Young's modulus of soft tissues. Soft tissue specimens are compressed between the object plate of an electronic balance and a linearly actuated indenter with a small rounded tip. The hardware of the device was designed such that a deformation model for semi-infinite media is applicable for calculating the Young's modulus of test specimens from their collected force-displacement data. Force-elongation measurements were performed on long strips of cured silicone mixtures to produce calibrated, tissue-mimicking test samples for the TE in a Young's modulus range of 10-400 kPa. When tested with the TE, the Young's moduli of the silicone samples demonstrated accuracy to within 1-10% of their calibrated values. Testing on excised tissue samples (fresh store-bought poultry breast; bovine liver, kidneys, hind shanks; porcine) was also performed, and a repeatability of elasticity measurements was demonstrated in the range of 8-14%. Results indicate that the TE can be effectively used in laboratory and clinical environments to evaluate the elasticity modulus of tissues.
Automatic characterization of soft tissues material properties during mechanical tests
Muscle Ligaments and Tendons Journal
Introduction: The estimation of the non-linear viscoelastic characteristics of human soft tissues, such as ligaments and tendon, is often affected by the implemented procedure. This study aims at developing and validating a protocol, associated with a contactless and automatic procedure, enabling the determination of the material behavior and properties of any soft tissues. Methods: Several markers were drawn onto the soft tissue specimen analyzed under uniaxial tensile test. An automatic contactless procedure, that uses a camera for recording the position of the markers during the test, was developed to compute the displacement, and the force applied, enabling the calculation of the true-stress/strain curve of the material. Young's modulus and Poisson's ratio can be calculated, on demand, for selected regions of interest of the soft tissues. The repeatability and reproducibility of the procedure were analyzed. The procedure was initially tested and verified on an artificial silicone material and later applied for investigating the mechanical behavior of a pig Achilles tendon and of a human patellar tendon. Results: The procedure show a high repeatability, independent by the operator, reliability and accuracy for the tested synthetic material (with a maximum error of 3.7% for Young's modulus). Additionally, the developed protocol was also suitable for the analysis of animal and human soft tissues. Conclusion: A protocol to automatically and accurately determine material properties in soft tissues was developed, tested and validated. Such approach could successfully be implemented for the mechanical characterization of any biological soft-tissue. Level of evidence: V.
Automatic Characterization of soft tissue material properties during mechanical tests
2019
Background: The determination of the non-linear viscoelastic characteristics of human soft tissues, such as ligaments and tendon, is often affected by the procedure implemented. This study aims at developing and validating a protocol, associated with a contactless and automatic procedure, enabling the determination of the material behavior and properties of soft tissues. Methods: Several markers were drawn onto specimens analyzed under a uniaxial tensile test. An automatic contactless procedure that uses a camera for recording the position of the markers during the test and later computes the displacement with the force applied to calculate the true-stress/strain curve of the material. Young's modulus and Poisson's ratio can be calculated, on demand, for selected regions of interest of the soft tissues. The repeatability and reproducibility of the procedure were analyzed. The procedure was initially tested and verified on an artificial silicone material and later applied for investigating the mechanical behavior of a pig Achilles tendon and on a human patellar tendon. Results: The procedure resulted repeatable, independently by the operator, reliable and accurate for the tested synthetic material (with a maximum error of 3.7% for Young's modulus). Additionally, the developed protocol was also suitable for the analysis of animal and human soft tissues. Conclusion: A protocol to automatically and accurately determine material properties in soft tissues was developed, validated and tested. Such approach could successfully be implemented for the mechanical characterization of any biological soft-tissue.
2021
The rupture of the cap tissue layer of a fibroatheroma in human coronary vessels is considered the key event leading to the formation of a thrombus and myocardial infarction, resulting in more than half a million deaths in the US every year. In this study, we are interested in investigating the biomechanics of different elastomer materials that can be used as laboratory models to replicate coronary arteries’ ultimate tensile stress (0.2 - 2.08 MPa). To this end, we developed a biomechanical testing system that allows us to characterize the material properties of small samples with high accuracy and precision. We built and validated the performance of the instrument’s subsystems (displacement, strain rate, gram-force readings, temperature control, gripping mechanism, and strain measurement) to ensure that the data being collected is accurate. With our developed tensile system, we test several Polydimethylsiloxane (PDMS) elastomers (silicone) to find a suitable laboratory model to rep...
Independent testing of soft tissue visco-elasticity using indentation and rotary shear deformations
Studies in health technology and informatics, 2003
Numerous techniques exist to measure the mechanical properties of soft tissues in vivo, such as mechanical stretching, indentation or shearing, as well as elastographic methods employing ultrasound or other imaging modes. Many groups have reported properties which do not necessarily correspond with each other due to differences in choice of technique, tissue model or other variations. This work deliberately makes use of the two independent modes of indentation and rotary shear, on the same material samples, employing similar modeling approximations, to attempt to determine the common, underlying material properties. This paper introduces the ROSA-2 rotary shear instrument, and presents its mechanical characteristics, as well as presenting validation experiments that were performed to verify non-slip contact with tissue. Measurements made with it are compared with those acquired with the TeMPeST l-D indentation instrument. Initial testing showed reasonably agreement when testing sili...
An Instrumented Probe for Mechanical Characterization of Soft Tissues
Biomedical Microdevices, 2001
Characterizing the mechanical properties of biological tissues is very important for research in biology, physiology and biomechanics, and even in clinical practice. Different techniques exist to perform accurate measurements of the mechanical parameters of tissues, but most instruments require that the biological sample is excised and prepared by drying and fixation. New and more versatile instruments capable of measuring the
Review of Experimental Techniques used to study the Dynamic Behavior of Soft Tissues
Advances in Intelligent System Research (iCMMD-2016 Proceddings), 2017
This review is intended to highlight and discuss the various experimental techniques used to obtain the mechanical behavior of soft tissues at varying strain rates. A variety of techniques used to obtain the mechanical properties of soft tissues and soft materials from low to intermediate and high rates of strain are summarized. These techniques include quasi-static, intermediate and dynamic strain rate setups. Split Hopkinson Pressure Bar (SHPB) technique with some modifications is commonly used for testing soft materials at high strain rates up to 104 s-1. Article searches were performed on impact biomechanics, orthopaedic and biomechanical publications in databases: PubMed, Scopus, ScienceDirect, Compendex, MEDLINE and EMBASE. The discrepancies on the use of conventional SHPB in the dynamic soft tissues testing were highlighted. This review explains the use of conventional SHPB technique for the characterization of soft tissues under compressive and tensile loading. The discrepan...
Medical image analysis, 2010
Soft tissue characterization with the inverse finite element method (FEM) optimization algorithm plays an important role in developing a physical model for medical simulations. However, tissue characterization that takes into account comprehensive boundary conditions for large deformations remains a challenge due to computational complexities and a lack of experimental data. In this study, soft tissue experiments on porcine livers were performed to measure the surface deformation and force response of soft tissues resulting from indentation loading depending on various indentation depths and two different tip shapes. Measurements were carried out with a three-dimensional (3D) optical system and a force transducer. Using the surface deformation and force response results, we estimated the maximum radius of influence, which can be utilized to determine the minimal required soft tissue model size for the FEM simulation. Considering the influence of the boundary conditions, the model wa...
Compression-dependency of soft tissue bioimpedance for in-vivo and in-vitro tissue testing
The present study determines the effect of compression over bioimpedance of healthy soft tissue (in-vitro and in-vivo). Electrical impedance spectroscopy (EIS) is a promising tissue characterization and tumor detection technique that uses tissue impedance or admittance to characterize tissue and identify tissue properties as well as cell structure. Variation in EIS measurements while applying pressure suggests that compression tends to affect soft tissue bioimpedance. Moreover, the displacements in tissue caused by applied compression may provide useful information about the structure and state of the tissue. Thus combining the changes to the electrical properties of tissue resulted by applied compression, with the changes in tissue displacements caused by applied compression, and consequently measuring the effect that electrical and mechanical properties have on each other, can be useful to identify tissue structure. In this study, multifrequency bioimpedance measurements were performed on in-vitro and in-vivo soft tissue at different pressure levels. Increasing compression on the in-vitro tissue results in an increase in both extracellular resistance and membrane capacitance while it causes a reduction in the intracellular resistance. However, as the compression over the in-vivo samples increases, the intracellular and extracellular resistance increase and the membrane capacitance decreases. The in-vivo measurements on human body are also tested on contra-lateral tissue sites and similar tissue impedance variation trends are observed in the contra-lateral sites of human body. The evidence from these tests suggests the possibility of using this EIS-Pressure combined measurement method to improve tumor detection in soft tissue. Based upon the observations, the authors envision developing an advanced model based upon the Cole model, which is dependent on tissue displacements.