Experimental characterization and constitutive modeling of the biomechanical behavior of male human urethral tissues validated by histological observations

This work aims at observing the mechanical behavior of the membranous and spongy portions of urethrae sampled on male cadavers in compliance with French regulations on postmortem testing, in accordance with the Scientific Council of body donation center of Grenoble. In this perspective, a thermostatic water tank was designed to conduct ex vivo planar tension tests in a physiological environment, i.e., in a saline solution at a temperature of \(37 \pm 1\) \({^{\circ }}\hbox {C}\). In order to observe the anisotropy of the tissues, the samples were tested in two directions. Tests consisting of a series of load–unload cycles of increasing amplitudes were performed to highlight their viscous behavior. The results were then discussed according to the microstructure of tissue, which was investigated using different staining methods and histological analysis. The observed behaviors were then fitted using an anisotropic hyperelastic or a visco-hyperelastic matrix–fiber model.     

Mechanics of the urethral duct: tissue constitutive formulation and structural modeling for the investigation of lumen occlusion

Urinary incontinence, often related to sphincter damage, is found in male patients, leading to a miserable quality of life and to huge costs for the healthcare system. The most effective surgical solution currently considered for men is the artificial urinary sphincter that exerts a pressure field on the urethra, occluding the duct. The evaluation of this device is currently based on clinical and surgical competences. The artificial sphincter design and mechanical action can be investigated by a biomechanical model of the urethra under occlusion, evaluating the interaction between tissues and prosthesis. A specific computational approach to urethral mechanics is here proposed, recalling the results of previous biomechanical experimental investigation. In this preliminary analysis, the horse urethra is considered, in the light of a significant correlation with human and in consideration of the relevant difficulty to get to human samples, which anyway represents the future advance. Histological data processing allow for the definition of a virtual and a subsequent finite element model of a urethral section. A specific hyperelastic formulation is developed to characterize the nonlinear mechanical behavior. The inverse analysis of tensile tests on urethra samples leads to the definition of preliminary constitutive parameters. The parameters are further refined by the computational analysis of inflation tests carried out on the entire urethral structure. The results obtained represent, in the light of the correlation reported, a valid preliminary support for the information to be assumed for prosthesis design, integrating surgical and biomechanical competences.     

Experimental and modeling investigation of the mechanism of synaptic vesicles recycling

Under the condition of microelectrode recording and fluorescence microscopy with dye FM 1-43 the research of exo-/endocytosis of synaptic vesicles in motor nerve terminals (NT) of frog cutaneous pectoris and white mice diaphragm muscles during high frequency stimulation (20 imp/s) was carried out. A mathematical modeling allowed us to conclude that the obtained experimental data can be explained in the following framework. Three pools of synaptic vesicles are involved in neurotransmitter release in the frog motor NT. Recovery of these pools is provided by endocytosis of two types: fast endocytosis with limited capacity and slow endocytosis. Fast-reconstructing vesicles refill the mobilization pool and slow endocytosis recovers the reserve pool. Our modeling investigation has revealed in frog NT independent recruiting of reserve and mobilization pools to the neurotransmitter secretion, i.e. this pools work concurrently. Experimental data, obtained on mice preparations, are well described with the framework of two-pools model including single type of endocytosis (fast endocytosis).     

Biomechanical modeling of refractive corneal surgery

The aim of refractive corneal surgery is to modify the curvature of the cornea to improve its dioptric properties. With that goal, the surgeon has to define the appropriate values of the surgical parameters in order to get the best clinical results, i.e., laser and geometric parameters such as depth and location of the incision, for each specific patient. A biomechanical study before surgery is therefore very convenient to assess quantitatively the effect of each parameter on the optical outcome. A mechanical model of the human cornea is here proposed and implemented under a finite element context to simulate the effects of some usual surgical procedures, such as photorefractive keratectomy (PRK), and limbal relaxing incisions (LRI). This model considers a nonlinear anisotropic hyperelastic behavior of the cornea that strongly depends on the physiological collagen fibril distribution. We evaluate the effect of the incision variables on the change of curvature of the cornea to correct myopia and astigmatism. The obtained results provided reasonable and useful information in the procedures analyzed. We can conclude from those results that this model reasonably approximates the corneal response to increasing pressure. We also show that tonometry measures of the IOP underpredicts its actual value after PRK or LASIK surgery.     

3D Mechanical properties of the layered esophagus: experiment and constitutive model

The identification of a three dimensional constitutive model is useful for describing the complex mechanical behavior of a nonlinear and anisotropic biological tissue such as the esophagus. The inflation tests at the fixed axial extension of 1, 1.125, and 1.25 were conducted on the muscle and mucosa layer of a porcine esophagus separately and the pressure-radius-axial force was recorded. The experimental data were fitted with the constitutive model to obtain the structure-related parameters, including the collagen amount and fiber orientation. Results showed that a bilinear strain energy function (SEF) with four parameters could fit the inflation data at an individual extension very well while a six-parameter model had to be used to capture the inflation behaviors at all three extensions simultaneously. It was found that the collagen distribution was axial preferred in both layers and the mucosa contained more collagen, which were in agreement with the findings through a pair of uniaxial tensile test in our previous study. The model was expected to be used for the prediction of stress distribution within the esophageal wall under the physiological state and provide some useful information in the clinical studies of the esophageal diseases.     

Vocal fold tissue failure: preliminary data and constitutive modeling

In human voice production (phonation), linear small-amplitude vocal fold oscillation occurs only under restricted conditions. Physiologically, phonation more often involves large-amplitude oscillation associated with tissue stresses and strains beyond their linear viscoelastic limits, particularly in the lamina propria extracellular matrix (ECM). This study reports some preliminary measurements of tissue deformation and failure response of the vocal fold ECM under large-strain shear The primary goal was to formulate and test a novel constitutive model for vocal fold tissue failure, based on a standard-linear cohesive-zone (SL-CZ) approach. Tissue specimens of the sheep vocal fold mucosa were subjected to torsional deformation in vitro, at constant strain rates corresponding to twist rates of 0.01, 0.1, and 1.0 rad/s. The vocal fold ECM demonstrated nonlinear stress-strain and rate-dependent failure response with a failure strain as low as 0.40 rad. A finite-element implementation of the SL-CZ model was capable of capturing the rate dependence in these preliminary data, demonstrating the model's potential for describing tissue failure. Further studies with additional tissue specimens and model improvements are needed to better understand vocal fold tissue failure.     

Experimental study and constitutive modeling of the viscoelastic mechanical properties of the human prolapsed vaginal tissue

In this paper, the viscoelastic mechanical properties of vaginal tissue are investigated. Using previous results of the authors on the mechanical properties of biological soft tissues and newly experimental data from uniaxial tension tests, a new model for the viscoelastic mechanical properties of the human vaginal tissue is proposed. The structural model seems to be sufficiently accurate to guarantee its application to prediction of reliable stress distributions, and is suitable for finite element computations. The obtained results may be helpful in the design of surgical procedures with autologous tissue or prostheses.     

Biomechanical modeling and optimal control of human posture

The present work describes the biomechanical modeling of human postural mechanics in the saggital plane and the use of optimal control to generate open-loop raising-up movements from a squatting position. The biomechanical model comprises 10 equivalent musculotendon actuators, based on a 40 muscles model, and three links (shank, thigh and HAT-Head, Arms and Trunk). Optimal control solutions are achieved through algorithms based on the Consistent Approximations Theory (Schwartz and Polak, 1996), where the continuous non-linear dynamics is represented in a discrete space by means of a Runge-Kutta integration and the control signals in a spline-coefficient functional space. This leads to non-linear programming problems solved by a sequential quadratic programming (SQP) method. Due to the highly non-linear and unstable nature of the posture dynamics, numerical convergence is difficult, and specific strategies must be implemented in order to allow convergence. Results for control (muscular excitations) and angular trajectories are shown using two final simulation times, as well as specific control strategies are discussed.     

3D biomechanical properties of the layered esophagus: Fung-type SEF and new constitutive model

Biomechanics and Modeling in Mechanobiology - Background and Purpose: Most current studies on the passive biomechanical properties of esophageal tissues directly use the exponential strain energy...     

Experimental investigation and modeling of oscillatory behavior in the continuous culture of Zymomonas mobilis

The mechanism causing oscillation in continuous ethanol fermentation by Zymomonas mobilis under certain operating conditions has been examined. A new term, "dynamic specific growth rate," which considers inhibitory culture conditions in the recent past affecting subsequent cell behavior, is proposed in this article. Based on this concept, a model was formulated to simulate the oscillatory behavior in continuous fermentation of Zymomonas mobilis. Forced oscillation fermentation experiments, in which exogenous ethanol was added at a controlled rate to generate oscillatory behavior, were performed in order to obtain estimates for the model parameters and to validate the proposed model. In addition, data from a literature example of a sustained oscillation were analyzed by means of the model, and excellent agreement between the model simulation and experimental results was obtained. The lag in the cells' response to a changing environment, i.e., ethanol concentration change rate experienced by the cells, was shown to be the major factor contributing to the oscillatory behavior in continuous fermentation of Zymomonas mobilis under certain operating conditions. (c) 1997 John Wiley & Sons, Inc. Biotechnol Bioeng 56: 99-105, 1997.     

A comparative histological study of certain nematodes

Summary A histological and anatomical study has been made of the digestive tract, excretory system, and somatic musculature of examples of the following families: Oncholaimidae, Rhabdiasidae, Strongylidae, Heterakidae, Oxyuridae, and Dorylaimidae. The excretory systems of these groups presents one of the most varied pictures of nemic anatomy. While as yet it is too early to draw conclusions, this system will probably furnish one of the best clews to the relationships of the various groups. The evolution of the musculature from the platymyarian to the coelomyarian form has probably occurred several times in the course of nemic development. It is interesting chiefly from the fact that those nematodes with the more simple platymyarian type of musculature could not have arisen from a more specialized type, thus acting as a check on relationship arrived at by other means. Despite the large number of articles dealing with the anatomy of nematodes, we have but skimmed the surface, and we must obtain information regarding the internal structure of every family of nematodes before conclusions will bear much weight.Abbreviations ac accessory organ - amp ampulla - amph amphid - amph gl amphidial gland - an anus - bas m basal membrane - blb? pseudobulb - blb bulb - bm basal membrane - b cl cell body - cl? cell whose function is unknown - cl b cell body - ch dsl dorsal chord - cl int intestinal chord - cl lat lateral chord - cl ren renette cell - cl nrv nerve cell - ch vnt ventral chord - carp body of gland - crd cardia - dct duct - dct ej ejaculatory duct - det ex excretory duct - det en connective duct - dct gl cdl duct of caudal gland - ct subv duct of subventral gland - dct gl dsl duct of dorsal galnd oviduet - dct gl subn duct of subventral gland - dct ov oviduct - dsl gl rct dorsal rectal gland - dsl on dorsal tooth - ej ovejector - el elevation - emb embryo in uterus - ex cr external leaf crown - ex lat longitudinal excretory gland - fbr amph amphidial nerve fibril - gl dsl oe dorsal gland - gl dsl ncl nucleus of dorsal gland - gl dsl dorsal gland - gl ex excretory gland - gl marg marginal gland - gl oe esophageal gland - gl ej ejaculatory gland - gl subv oe subventral esophageal gland - gl subd subdorsal gland - gl subv subventral gland - gl subv rct subventral rectal gland - gnd gonad - gng cl ganglion cell - gr granule - gl rct rectal gland - int intestine - int cr internal leaf crown - lat longitudinal duct - lb lip - lob gl lobe of gland - lob gl ds lobe of dorsal gland - lob gl subv lobe of subventral gland - l subv on right subventral tooth - marg fbr marginal fibers - msc fibular part of muscle - msc oe esophageal muscle - msc pl sarcoplasm - msc sph sphincter muscle - ncl nucleus - ncl brg cl nucleus bridge cell - ncl brg oe nucleus esophagus muscle - ncl gl dsl nucleus of dorsal gland - ncl gl subv. nucleus of subventral gland - ncl marg marginal nucleus - ncl p peripheral nucleus - ncl msc cl nucleus of muscle fibers - ncl oe esophageal nucleus - ncl b cl nucleus in cell body - ncl cl ren nucleus of renette cell - ncl gl dsl nucleus of dorsal gland - ncl o msc nucleus of ordinary muscle fibers - nvr r nerve ring - oe esophagus - or orifice - org? organ of unknown function - or amph opening of amphid - or dsl gl orifice of dorsal gland - or subv gl opening of subventral gland - oe msc n esophageal muscle nucleus - ov oviduct - p. ex excretory pore - ph pharynx - ppl papilla - pre ppl preanal papilla - pre rct pre rectum - ren renette - ret d retractor dorsalis - ret reticulum - rct rectum - r subv on right Subventral tooth - s, rv reservoir - rv? possible reservoir - set seta - sp spicule - st Stabehensaum - subd msc subdorsal muscle - trm termination of duct - trm ov blind end of ovary - t p tunica propria - ut uterus - valv valve - valv int intestinal valve - valve ret valve reticulum - vlv vulva     

Biomechanical characteristics of human ankle-joint muscles

Equivalent biomechanical characteristics of human ankle-joint muscles have been determined by impact and vibration tests. The estimate of the stiffness and damping coefficients has yielded, respectively, (2.67 +/- 0.48) X 10(4) N X m-1 and (811.58 +/- 201.3) N X s X m-1 by impact actions, n = 126; (1.49 +/- 0.35) X 10(4) N X m-1 and (430.1 +/- 36.1) N X s X m-1 -by vibration actions, n = 7. The characteristics of the ankle-joint muscles of subjects representing different kinds of sports have proved to be different.     

Region-specific constitutive modeling of the plantar soft tissue

Recent research has shown that hyperelastic properties of the plantar soft tissue consisting of adipose tissue and fibrous septa change from region to region. However, relatively little research has been conducted to develop analytical or computational models to describe the region-specific behavior of the plantar soft tissue. The objective of the research is to develop a region-specific constitutive model of the plantar soft tissue. Plantar soft tissue specimens were dissected from six regions [subcalcaneal (CA), sublateral (LA), subnavicular (Nav), 1st, 3rd, and 5th submetatarsal (M1, M3, M5)] from cadaveric foot samples, and a picrosirius red staining technique was used to visualize the collagen fibers in fibrous septa. The volume fractions of adipose tissue and fibrous septa and the volume fractions of the principal orientations of the fibrous septa were calculated with the intensity gradient method. Region-specific constitutive models were then developed in finite element analysis considering the microstructure of the plantar soft tissue. The hyperelastic region specific material properties of the plantar soft tissue were validated with experimental unconfined compression tests and indentation tests from the literature. The results show that the models give reasonable predictions of the stiffness of the soft tissue within a standard deviation of the tests. The region-specific constitutive models help to explain how changes in the constituents are related to mechanical behavior of the soft tissue on a region specific basis.