On the Effects of Residual Stress in Microindentation Tests of Soft Tissue Structures

2004 ◽  
Vol 126 (2) ◽  
pp. 276-283 ◽  
Author(s):  
Evan A. Zamir ◽  
Larry A. Taber

Microindentation methods are commonly used to determine material properties of soft tissues at the cell or even sub-cellular level. In determining properties from force-displacement (FD) data, it is often assumed that the tissue is initially a stress-free, homogeneous, linear elastic half-space. Residual stress, however, can strongly influence such results. In this paper, we present a new microindentation method for determining both elastic properties and residual stress in soft tissues that, to a first approximation, can be regarded as a pre-stressed layer embedded in or adhered to an underlying relatively soft, elastic foundation. The effects of residual stress are shown using two linear elastic models that approximate specific biological structures. The first model is an axially loaded beam on a relatively soft, elastic foundation (i.e., stress-fiber embedded in cytoplasm), while the second is a radially loaded plate on a foundation (e.g., cell membrane or epithelium). To illustrate our method, we use a nonlinear finite element (FE) model and experimental FD and surface contour data to find elastic properties and residual stress in the early embryonic chick heart, which, in the region near the indenter tip, is approximated as an isotropic circular plate under tension on a foundation. It is shown that the deformation of the surface in a microindentation test can be used along with FD data to estimate material properties, as well as residual stress, in soft tissue structures that can be regarded as a plate under tension on an elastic foundation. This method may not be as useful, however, for structures that behave as a beam on a foundation.

Author(s):  
Sebastian Halm ◽  
David Haberthür ◽  
Elisabeth Eppler ◽  
Valentin Djonov ◽  
Andreas Arnold

Abstract Introduction This pilot study explores whether a human Thiel-embalmed temporal bone is suitable for generating an accurate and complete data set with micro-computed tomography (micro-CT) and whether solid iodine-staining improves visualization and facilitates segmentation of middle ear structures. Methods A temporal bone was used to verify the accuracy of the imaging by first digitally measuring the stapes on the tomography images and then physically under the microscope after removal from the temporal bone. All measurements were compared with literature values. The contralateral temporal bone was used to evaluate segmentation and three-dimensional (3D) modeling after iodine staining and micro-CT scanning. Results The digital and physical stapes measurements differed by 0.01–0.17 mm or 1–19%, respectively, but correlated well with the literature values. Soft tissue structures were visible in the unstained scan. However, iodine staining increased the contrast-to-noise ratio by a factor of 3.7 on average. The 3D model depicts all ossicles and soft tissue structures in detail, including the chorda tympani, which was not visible in the unstained scan. Conclusions Micro-CT imaging of a Thiel-embalmed temporal bone accurately represented the entire anatomy. Iodine staining considerably increased the contrast of soft tissues, simplified segmentation and enabled detailed 3D modeling of the middle ear.


2021 ◽  
Vol 7 (2) ◽  
pp. 363-366
Author(s):  
Thomas Reuter ◽  
Christof Hurschler

Abstract Mechanical parameters of hard and soft tissues are explicit markers for quantitative tissue characterization. In this study, we present a comparison of biphasic material properties of equine articular cartilage estimated from stress relaxation (ε = 6 %, t = 1000 s) and creep indentation tests (F = 0.1 N, t = 1000 s). A biphasic 3D-FE-based method is used to determine the biomechanical properties of equine articular cartilage. The FE-model computation was optimized by exploiting the axial symmetry and mesh resolution. Parameter identification was executed with the Levenberg- Marquardt-algorithm. Additionally, sensitivity analyses of the calculated biomechanical parameters were performed. Results show that the Young’s modulus E has the largest influence and the Poisson’s ratio of ν ≤ 0.1 is rather insensitive. The R² of the fit results varies between 0.882 and 0.974 (creep model) and between 0.695 and 0.930 (relaxation model). The averaged parameters E and k determined from the creep model yield higher values in comparison to the relaxation model. The differences can be traced back to the experimental settings and to the biphasic material model.


2016 ◽  
Vol 22 ◽  
pp. 101-117 ◽  
Author(s):  
Stephan Lautenschlager

AbstractIn the last two decades, advances in computational imaging techniques and digital visualization have created novel avenues for the study of fossil organisms. As a result, paleontology has undergone a shift from the pure study of physically preserved bones and teeth, and other hard tissues, to using virtual computer models to study specimens in greater detail, restore incomplete specimens, and perform biomechanical analyses. The rapidly increasing application of these techniques has further paved the way for the digital reconstruction of soft-tissue structures, which are rarely preserved or otherwise available in the fossil record. In this contribution, different types of digital soft-tissue reconstructions are introduced and reviewed. Provided examples include methodological approaches for the reconstruction of musculature, endocranial components (e.g., brain, inner ear, and neurovascular structures), and other soft tissues (e.g., whole-body and life reconstructions). Digital techniques provide versatile tools for the reconstruction of soft tissues, but given the nature of fossil specimens, some limitations and uncertainties remain. Nevertheless, digital reconstructions can provide new information, in particular if interpreted in a phylogenetically grounded framework. Combined with other digital analytical techniques (e.g., finite element analysis [FEA], multibody dynamics analysis [MDA], and computational fluid dynamics [CFD]), soft-tissue reconstructions can be used to elucidate the paleobiology of extinct organisms and to test competing evolutionary hypotheses.


Author(s):  
Islam Talaat Khalil Attia ◽  
Ali Mahmoud Emran ◽  
Elhafez Abd Elgafez Megahed ◽  
Mamdouh Fouad Lashin

Background: Ulnar-sided wrist pain is a common cause of upper- extremity disability. Presentation can vary from acute traumatic injuries to chronic degenerative conditions. Carful clinical examination should be done, there are some provocative tests for some pathologies which induce pain when the patient has the specific pathology for the test. MRI of the wrist is often challenging because the components of the wrist have complex anatomy of bone and soft tissues, with ligaments and cartilage which are small sized structures measuring millimeters. MRI is a one of advanced imaging techniques that play an important role in evaluating the wrist and is a useful examination modality because of its multiplanar, multisequence capability and its excellent resolution of soft tissue structures. MRI is particularly advantageous for assessing occult bone lesions and soft tissue structures around the wrist such as cartilages, tendons, ligaments and nerves. Aim: The aim of this study is to assess the role and accuracy of clinical tests and MRI in diagnosis of chronic ulnar-sided wrist pain causes. Patients and Methods: This is a prospective study and was conducted on a 50 adult patients complaining from chronic ulnar side wrist pain. They were attended to Orthopedic Department of Tanta University Hospitals over a period of 6 months starting from November 2019 till May 2020. Results: MRI gave positive finding in most of patients (92%), while negative in about (8%) of cases, this means that there are some pathologies need more investigations to be diagnosed. Most of Clinical tests also gave a help in diagnosis of the cause of the pain especially ulnocarpal stress test, fovea sign test, ECU synergy test and piano key test which by statistics showed significant results but LT ballottement test had insignificant results so LTL pathology can't be diagnosed by clinical tests only but needs more investigations as MRI. So some pathologies can be diagnosed clinically as ECU tenosynovitis, but other pathologies need more investigations like MRI like LTL tear, also some pathologies need more investigations. Conclusion: Most of clinical tests give significant results in diagnosis of chronic ulnar-sided wrist pain except for some pathologies like LTL tear needs more investigations, also MRI has important role and gives significant results in diagnosis.


2012 ◽  
Vol 58 (4) ◽  
pp. 477-501
Author(s):  
M. Nagórska

AbstractIn the flexible road pavement design a mechanistic model of a multilayered half-space with linear elastic or viscoelastic layers is usually used for the pavement analysis.This paper describes a domain selection for the purpose of a FE model creating of the linear elastic layered half-space and boundary conditions on borders of that domain. This FE model should guarantee that the key components of displacements, stresses and strains obtained using ABAQUS program would be in particular identical with those ones obtained by analytical method using VEROAD program.It to achieve matching results with both methods is relatively easy for stresses and strains. However, for displacements, using FEM to obtain correct results is (understandably) highly problematic due to infinity of half-space. This paper proposes an original method of overcoming these difficulties.


2019 ◽  
Vol 2019 ◽  
pp. 1-12 ◽  
Author(s):  
Maziar Ramezani ◽  
Stefan Klima ◽  
Paul Le Clerc de la Herverie ◽  
Jean Campo ◽  
Jean-Baptiste Le Joncour ◽  
...  

Introduction. Computational modeling of the human pelvis using the finite elements (FE) method has become increasingly important to understand the mechanisms of load distribution under both healthy and pathologically altered conditions and to develop and assess novel treatment strategies. The number of accurate and validated FE models is however small, and given models fail resembling the physiologic joint motion in particular of the sacroiliac joint. This study is aimed at using an inverted validation approach, using in vitro load deformation data to refine an existing FE model under the same mode of load application and to parametrically assess the influence of altered morphology and mechanical data on the kinematics of the model. Materials and Methods. An osteoligamentous FE model of the pelvis including the fifth lumbar vertebra was used, with highly accurate representations of ligament orientations. Material properties were altered parametrically for bone, cartilage, and ligaments, followed by changes in bone geometry (solid versus 3 and 2 mm shell) and material models (linear elastic, viscoelastic, and hyperelastic isotropic), and the effects of varying ligament fiber orientations were assessed. Results. Elastic modulus changes were more decisive in both linear elastic and viscoelastic bone, cartilage, and ligaments models, especially if shell geometries were used for the pelvic bones. Viscoelastic material properties gave more realistic results. Surprisingly little change was observed as a consequence of altering SIJ ligament orientations. Validation with in vitro experiments using cadavers showed close correlations for movements especially for 3 mm shell viscoelastic model. Discussion. This study has used an inverted validation approach to refine an existing FE model, to give realistic and accurate load deformation data of the osteoligamentous pelvis and showed which variation in the outcomes of the models are attributed to altered material properties and models. The given approach furthermore shows the value of accurate validation and of using the validation data to fine tune FE models.


Author(s):  
C. P. Arun

Soft tissues hollow structures are capable of collapsing not only under their own power but also able to employ movements of their neighbors to aid their function of propelling content. An intensive study of collapsible hollow structures is a recent development and no general law recognising this convenient coupling of the dynamics of neighboring organs is available in the literature. The literature on whole organ physiology was analysed and examples of neighboring organs providing assistance to soft tissue structures was collected. We offer the title Covenant of NOA to the arrangement that soft tissue structures have with their neighbors. The calf muscle pump and parturition are obvious examples of NOA. From examining videocystometric recordings, we are able to offer, as the latest to a long list of known NOAs, the assistance of the pelvic diaphragm to the urinary bladder that aids the latter in emptying completely. The modeling of soft tissue hollow organs as functioning somewhat in isolation must be considered antediluvian. Very often, soft tissue structures come in pairs to implement NOA: it is time we too hearkened to the Covenant of NOA.


Author(s):  
V. N. Druzhinin ◽  
V. G. Suvorov ◽  
A. N. Cherny ◽  
S. N. Troynakov ◽  
U. T. Tukhtaev

Introduction. Timely and adequate diagnosis and treatment of degenerative-dystrophic diseases of the bone and joint apparatus, which include epicondylitis (epicondylosis), including professionally caused, continues to be a serious health problem today, since they cause significant economic damage associated with temporary and persistent disability of the active part of the world’s population. In this regard, the search for methods and methodological approaches to improve the radiation diagnosis of this disease remains relevant. The study is devoted to solution of important medical problems, including occupational diseases-optimization of X-ray of the ulnar epicondylitis based on the use of new methodological approaches quantifying the density of pathological remodeling of bone structures in the subject area, that allow to objectify the direction of changes in monitoring intensity changes in the estimated structures.The aim of the study is to improve the quality of x-ray diagnostics of ulnar epicondylitis based on a precision assessment of the optical density of bone and periarticular tissues using digital radiography.Materials and methods. A comparative analysis of the results of a comprehensive clinical and radiological examination of patients, workers of the main group (fitters and laborers machine-building plants) working age range of 30–50 years with a clinical picture of subacute phase of the ulnar epicondylitis in the absence of a pathognomonic ultrasound findings and x-ray morphological signs of the disease. X-ray studies were performed using digital low-dose x-ray diagnostic devices. Visualization, processing, analysis of medical images and comparison of results in the dynamics of research were carried out using the programs «Lins machaon doctor’s workstation». To measure the conditional optical density of bone and soft tissues, we used the ROI tool (zone of interest), which allows us to determine the desired value in areas of different dimensions. Measurements were performed on digital radiographs and computer monitor screens in the areas of interest: the lateral parts of the humerus condyles and adjacent periarticular tissues with the calculation of the average values of the optical density index (ID) and optical density gradients (IDG) relative to the density of periarticular soft tissues.Results. Analysis of the results of a posteriori osteodensitometry of the distal humerus within the framework of the developed algorithm, which includes the use of absolute and relative indicators of conditional optical density after preliminary color correction of digital x-ray images of bone and paraossal tissue structures, allowed us to expand our understanding of the topography of the distribution of mineral saturation in the condyles of at-risk individuals relative to those of the control group. It was found that the indicators of optical density of bone and paraossal tissues can be a kind of (conditional), sometimes the only indicators of the degree of severity of changes, positive or negative dynamics of pathophysiological processes. Density differences in the distal parts of the right and left humerus (bony and soft -tissue paraossal structures of the condyles) in the control group (conditional norm) in terms of absolute optical density and its gradient, regardless of the assessment area, were insignificant (statistically unreliable), although they were multidirectional. In patients with clinical signs of epicondylitis in the absence of x-ray morphologically detectable structural changes, a decrease in ID and the dynamics of its recovery at various stages of observation were revealed. Even when the ID of the actual bone structure is relatively equal, the IDG differs in different people, since it is largely determined by metabolic processes that are dynamically more labile than in the bones, and thus serve as a kind of indicator of their intensity. Taking into account the relative torpidity of perestroika processes in the structures of the bone tissue of the condyles in epicondylitis, IDG should be considered a more informative indicator of their dynamics. The importance of optical density indicators as predictors of the considered pathology is particularly evident in the process of analyzing the results of its diagnosis and development in the dynamics of observations not so much at the collective as at the individual level of assessment.Conclusions. The application of the developed methodological approach allows us to significantly expand our understanding of the topographical distribution of the density of bone and soft tissue structures of the distal humerus at various stages of examination of patients, including the early subclinical phases of possible pathology, even in the absence of visually detectable x-ray morphological changes. The use of an original algorithm for evaluating tissue density will reduce the negative role of the so-called «human factor» and thus significantly ensure the objectivity of the interpretation of research results.Funding. The study had no funding.Conflict of interests. The authors declare no conflict of interests.


2015 ◽  
Vol 137 (2) ◽  
Author(s):  
Yang Xu ◽  
Amir Rostami ◽  
Robert L. Jackson

In the current study, a semi-analytical model for contact between a homogeneous, isotropic, linear elastic half-space with a geometrically anisotropic (wavelengths are different in the two principal directions) bisinusoidal surface on the boundary and a rigid base is developed. Two asymptotic loads to area relations for early and almost complete contact are derived. The Hertz elliptic contact theory is applied to approximate the load to area relation in the early contact. The noncontact regions occur in the almost complete contact are treated as mode-I cracks. Since those cracks are in compression, an approximate relation between the load and noncontact area can be obtained by setting the corresponding stress intensity factor (SIF) to zero. These two asymptotic solutions are validated by two different numerical models, namely, the fast Fourier transform (FFT) model and the finite element (FE) model. A piecewise equation is fit to the numerical solutions to bridge these two asymptotic solutions.


Author(s):  
Bhavana Murjani ◽  
Sonali Kadam ◽  
Easwaran Ramaswami ◽  
Vijayalaxmi Nimma ◽  
Rohini Bhosale ◽  
...  

Facial reconstruction is an art and science in the field of forensics which involves construction of a recognizable face on unknown skull remains. It appears as a, metaphorically speaking “shining beacon of hope” after everything else fails for identification of the remains. Both, 2D and 3D methods of facial reconstruction have been developed for this process. The database of facial soft tissue thickness based on gender, ethnicity and age, at certain bilateral and unilateral anatomical points on skull bones, lay foundation to the process of reanimating the facial profile of a deceased. Several imaging modalities have been used for the collection of this data, in addition to the cadavers and various guidelines have been given for the reconstruction of the soft tissues, however, to construct soft tissue structures like nose, eyes, mouth and ears which take an important position in determination of the facial features is still a tedious task. This process is being researched since a century and multiple guidelines for reconstruction of the soft tissue structures are available. The face plays out based on the method used; hence selection of an appropriate method is vital. This review encompasses the various methods/guidelines derived for the reconstruction of the nose, eyes, mouth and ears of the face. In addition to the traditional methods given by Gerasimov, Krogman, Prokopec and Ubelaker, George, etc. other newer methods have been mentioned. This review also highlights assessment studies performed using the said methods in populations other than the ones they were derived from.


Sign in / Sign up

Export Citation Format

Share Document