Haptic manipulation of deformable CAD parts with a two-stage method

Real-time interaction between a designer and a deformable mock-up in Virtual Reality environments is a promising paradigm to evaluate design feasibilities. In this paper we focus on the haptic-aided deformation verification process of industrial deformable parts by combining small deformations and relatively large rigid-body motions. First, concerning the modelling process of small deformations, we propose a two-stage method extended from the linear modal analysis. In this two-stage method, modal deformation sub-spaces are pre-computed in an off-line phase, and real-time deformations are quickly reproduced by superimposing the responses of certain modes which are selected depending on interaction requirements. Based on this two-stage method, we propose a mesh analysis method to enrich the off-line pre-computations corresponding to different anticipated interaction scenarios. Furthermore, we apply a real-time division scheme which divides the deformation response process into two separate modules, so that stable haptic interactions are guaranteed. Second, concerning the purpose of global deformation verifications, we combine relatively large rigid-body motions resulting from the integration of classical motion equations and small deformations resulting from the aforementioned two-stage method. We have implemented the two-stage method to model small deformations and rigid-body motions. Real-time experiments are carried out by coupling a single haptic device with a simulation framework and experimental results validate the deformation accuracy on one hand, and demonstrate a good and stable haptic interaction experience on the other.     

(E)US elastography: current status and perspectives

(Endo)sonographic real-time elastography is a new method to describe the mechanical properties of tissue. Similar to colour flow Doppler ultrasonography, a region of interest is defined. The relative stiffness of the tissues within this area is described by colours superimposing on the B-mode image. Real-time elastography can be performed with linear scanners for transcutaneous use, rigid endocavitary probes and with flexible echoendoscopes. The probes can be used to compress the tissue. The elasticity modulus is calculated from the resulting deformation of the tissue. In endoscopic ultrasound, arterial and cardiac pulsations or respiratory movements cause the deformation of the tissue that is used for the calculation. Several studies have demonstrated that real-time elastography is feasible and improves the diagnostic accuracy for tumours of the breast, the prostate, the cervix, and the thyroid gland. Endosonographic elastography has been employed in the examination of lymph nodes and the pancreas. For the differentation between benign and malignant lymph nodes, the accuracy is reported to be 85 % to 90 %. Therefore, the method seems to be useful to select lymph nodes suitable for biopsy. The elastographic pattern of malignant tumours of the pancreas is different from that of the normal pancreas, but similar to that of chronic pancreatitis due to the same biomechanical architecture. Therefore, the early diagnosis of cancer within chronic pancreatitis will probably not be improved by elastography. In summary, (endo)sonographic real-time elastography is a promising new method. Nevertheless, prospective studies are needed to define useful applications and the clinical significance of the method.     

Gastrointestinal tract modelling in health and disease

The gastrointestinal （GI） tract is the system of organs within multi-cellular animals that takes in food, digests it to extract energy and nutrients, and expels the remaining waste. The various patterns of GI tract function are generated by the integrated behaviour of multiple tissues and cell types. A thorough study of the GI tract requires understanding of the interactions between cells, tissues and gastrointestinal organs in health and disease. This depends on knowledge, not only of numerous cellular ionic current mechanisms and signal transduction pathways, but also of large scale GI tissue structures and the special distribution of the nervous network. A unique way of coping with this explosion in complexity is mathematical and computational modelling; providing a computational framework for the multilevel modelling and simulation of the human gastrointestinal anatomy and physiology. The aim of this review is to describe the current status of biomechanical modelling work of the GI tract in humans and animals, which can be further used to integrate the physiological, anatomical and medical knowledge of the GI system. Such modelling will aid research and ensure that medical professionals benefit, through the provision of relevant and precise information about the patient＇s condition and GI remodelling in animal disease models. It will also improve the accuracy and efficiency of medical procedures, which could result in reduced cost for diagnosis and treatment.     

A Combined FEM/Genetic Algorithm for Vascular Soft tissue Elasticity Estimation

Tissue elasticity reconstruction is a parameter estimation effort combining imaging, elastography, and computational modeling to build maps of soft tissue mechanical properties. One application is in the characterization of atherosclerotic plaques in diseased arteries, wherein the distribution of elastic properties is required for stress analysis and plaque stability assessment. In this paper, a computational scheme is proposed for elasticity reconstruction in soft tissues, combining finite element modeling (FEM) for mechanical analysis of soft tissues and a genetic algorithm (GA) for parameter estimation. With a model reduction of the discrete elasticity values into lumped material regions, namely the plaque constituents, a robust, adaptive strategy can be used to solve inverse elasticity problems involving complex and inhomogeneous solution spaces. An advantage of utilizing a GA is its insistence on global convergence. The algorithm is easily implemented and adaptable to more complex material models and geometries. It is meant to provide either accurate initial guesses of low-resolution elasticity values in a multi-resolution scheme or as a replacement for failing traditional elasticity estimation efforts.     

Ultrasound and color Doppler in nephrology. Technology and applications

Advances in digital technology in the last decades have led to a fast development of ultrasound technology. Ultrasound information originating from stationary structures or red blood cells moving into the vessels can be visualized with different imaging modalities. Conventional B-mode sonography provides anatomical details based on acoustic impedance differences. Gray-scale sonography represents the structural echoes as brightness points. Based on the Doppler effect, vascular scattering can be represented as spectral wave velocity depending on time (velocity/time curve), or as dual-scale color mapping depending on the changes in average blood velocity. The flow-in is depicted in red and the flow-out in blue. The analysis of the vascular scattering enhanced by infusion of contrast agents is the basis of contrast-enhanced harmonic imaging. The perfusional pattern of tissues allows the differential diagnosis of expansive lesions. Tissue strain analysis provides a new dimension of diagnostic information. It is used in elastographic imaging to describe relative physical tissue stiffness properties. Tissue stiffness information is complementary to and independent of the acoustic impedance information provided by B-mode imaging as well as the vascular flow information provided by Doppler imaging. Adjacent tissue elements may appear identical using conventional B-mode or Doppler imaging. When stress (axial force) is applied to tissues, they show different degrees of deformation. Comparing the baseline and stress image information, each tissue element may be labeled by its relative stiffness. A lighter shade indicates relatively soft tissue (elastic), while a darker shade indicates relatively stiff tissue (non-elastic).     

Nanomechanical Mapping of Hard Tissues by Atomic Force Microscopy: An Application to Cortical Bone

Force mapping of biological tissues via atomic force microscopy (AFM) probes the mechanical properties of samples within a given topography, revealing the interplay between tissue organization and nanometer-level composition. Despite considerable attention to soft biological samples, constructing elasticity maps on hard tissues is not routine for standard AFM equipment due to the difficulty of interpreting nanoindentation data in light of the available models of surface deformation. To tackle this issue, we proposed a protocol to construct elasticity maps of surfaces up to several GPa in moduli by AFM nanoindentation using standard experimental conditions (air operation, nanometrically sharp spherical tips, and cantilever stiffness below 30 N/m). We showed how to process both elastic and inelastic sample deformations simultaneously and independently and quantify the degree of elasticity of the sample to decide which regime is more suitable for moduli calculation. Afterwards, we used the frequency distributions of Young’s moduli to quantitatively assess differences between sample regions different for structure and composition, and to evaluate the presence of mechanical inhomogeneities. We tested our method on histological sections of sheep cortical bone, measuring the mechanical response of different osseous districts, and mapped the surface down to the single collagen fibril level.     

Cooperative deformation of mineral and collagen in bone at the nanoscale

In biomineralized tissues such as bone, the recurring structural motif at the supramolecular level is an anisotropic stiff inorganic component reinforcing the soft organic matrix. The high toughness and defect tolerance of natural biomineralized composites is believed to arise from these nanometer scale structural motifs. Specifically, load transfer in bone has been proposed to occur by a transfer of tensile strains between the stiff inorganic (mineral apatite) particles via shearing in the intervening soft organic (collagen) layers. This raises the question as to how and to what extent do the mineral particles and fibrils deform concurrently in response to tissue deformation. Here we show that both mineral nanoparticles and the enclosing mineralized fibril deform initially elastically, but to different degrees. Using in situ tensile testing with combined high brilliance synchrotron X-ray diffraction and scattering on the same sample, we show that tissue, fibrils, and mineral particles take up successively lower levels of strain, in a ratio of 12:5:2. The maximum strain seen in mineral nanoparticles (approximately 0.15-0.20%) can reach up to twice the fracture strain calculated for bulk apatite. The results are consistent with a staggered model of load transfer in bone matrix, exemplifying the hierarchical nature of bone deformation. We believe this process results in a mechanism of fibril-matrix decoupling for protecting the brittle mineral phase in bone, while effectively redistributing the strain energy within the bone tissue.     

Study on the Actuating Performance of an Embedded Macro Fiber Composite Considering the Shear Lag Effect

Macro fiber composite (MFC), which are new ultrathin piezoelectric smart materials, are mostly applied in the fields of shell structure deformation and vibration control. Among others, the application of embedded MFCs in sandwich structures has received wide attention. Currently, its actuating force formula is primarily acquired based on the Bernoulli–Euler Model, which does not consider the shear lag effect and actuating force of MFC ends. To study the actuating performance of an MFC in a sandwich structure, according to its action characteristics, the MFC is divided into upper and lower actuating units without any interaction between to two under the condition of plane strain, and the shear lag effect is considered between the units and the top and bottom of the sandwich structure. The actuating force of the MFC ends is obtained by considering its influence on the bending deformation of the sandwich structure, which deduces the actuating force formula of the embedded MFC. In contrast to ANSYS piezoelectric simulation, the distribution of the MFC interior normal stress is similar to the result from ANSYS piezoelectric simulation, and there is a very small deviation between the MFC end and central normal stress and the result from ANSYS piezoelectric simulation. Taking the end deflection of the sandwich structure with an embedded MFC as an example, the actuating force simulation of the MFC considering the shear lag effect is compared with the ANSYS piezoelectric simulation and actuating force simulation based on the Bernoulli–Euler model. The result indicates that the actuating force simulation of the MFC considering the shear lag effect is closer to the ANSYS piezoelectric simulation, which proves the rationality and necessity of considering the shear lag effect and end actuating force of the MFC.     

Magnetic resonance imaging of the lumbar spinous processes and adjacent soft tissues: normal and pathologic appearances

The spinous processes and intervening soft tissues of the lumbar region may be involved by degenerative, inflammatory, neoplastic, and traumatic processes resulting in low back pain. While conventional radiography and computed tomography have proven useful in the demonstration of abnormalities affecting the spinous processes, they are of limited utility in the evaluation of the intervening soft tissues, which are the predominant site of initial pathologic involvement. To explore the potential role of magnetic resonance imaging (MRI) in the assessment of the spinous processes and adjacent ligaments, a retrospective review of 55 consecutive examinations of the lumbar spine was performed. The normal and pathologic appearances of the region on both T1 and T2 weighted images were characterized, and the optimal imaging variables for demonstration of the spinous processes and adjacent soft tissues were determined with subsequent prospective application to new cases. Correlative examination of cadaveric sections and dried specimens was also performed to facilitate understanding of anatomical relationships visualized by MRI. Based upon the results of this investigation, MRI is the procedure of choice in the evaluation of disease processes affecting the spinous processes and intervening ligaments, primarily owing to the ability to image directly in the sagittal plane and its superior soft tissue contrast discrimination capability.     

Tissue deformation spatially modulates VEGF signaling and angiogenesis

Physical forces play a major role in the organization of developing tissues. During vascular development, physical forces originating from a fluid phase or from cells pulling on their environment can alter cellular signaling and the behavior of cells. Here, we observe how tissue deformation spatially modulates angiogenic signals and angiogenesis. Using soft lithographic templates, we assemble three-dimensional, geometric tissues. The tissues contract autonomously, change shape stereotypically and form patterns of vascular structures in regions of high deformations. We show that this emergence correlates with the formation of a long-range gradient of Vascular Endothelial Growth Factor (VEGF) in interstitial cells, the local overexpression of the corresponding receptor VEGF receptor 2 (VEGFR-2) and local differences in endothelial cells proliferation. We suggest that tissue contractility and deformation can induce the formation of gradients of angiogenic microenvironments which could contribute to the long-range patterning of the vascular system.     

Numerical Modeling of a New Type of Prosthetic Restoration for Non-Carious Cervical Lesions

The paper considers a new technology for the treatment of non-carious cervical lesions (NCCLs). The three parameterized numerical models of teeth are constructed: without defect, with a V-shaped defect, and after treatment. A new treatment for NCCL has been proposed. Tooth tissues near the NCCLs are subject to degradation. The main idea of the technology is to increase the cavity for the restoration of NCCLs with removal of the affected tissues. The new treatment method also allows the creation of a playground for attaching the gingival margin. The impact of three biomaterials as restorations is studied: CEREC Blocs; Herculite XRV; and Charisma. The models are deformed by a vertical load from the antagonist tooth from 100 to 1000 N. The tooth-inlay system is considered, taking into account the contact interaction. Qualitative patterns of tooth deformation before and after restoration were established for three variants of the inlay material.     

Sensitive detection of cell-derived force and collagen matrix tension in microtissues undergoing large-scale densification

Mechanical forces generated by cells and the tension of the extracellular matrix (ECM) play a decisive role in establishment, homeostasis maintenance, and repair of tissue morphology. However, the dynamic change of cell-derived force during large-scale remodeling of soft tissue is still unknown, mainly because the current techniques of force detection usually produce a nonnegligible and interfering feedback force on the cells during measurement. Here, we developed a method to fabricate highly stretchable polymer-based microstrings on which a microtissue of fibroblasts in collagen was cultured and allowed to contract to mimic the densification of soft tissue. Taking advantage of the low-spring constant and large deflection range of the microstrings, we detected a strain-induced contraction force as low as 5.2 µN without disturbing the irreversible densification. Meanwhile, the microtissues displayed extreme sensitivity to the mechanical boundary within a narrow range of tensile stress. More importantly, results indicated that the cell-derived force did not solely increase with increased ECM stiffness as previous studies suggested. Indeed, the cell-derived force and collagen tension exchanged dramatically in dominating the microtissue strain during the densification, and the proportion of cell-derived force decreased linearly as the microtissue densified, with stiffness increasing to ∼500 Pa. Thus, this study provides insights into the biomechanical cross-talk between the cells and ECM of extremely soft tissue during large-extent densification, which may be important to guide the construction of life-like tissue by applying appropriate mechanical boundary conditions.

In living tissues, various mechanical forces are ubiquitously acting on cells and their extracellular matrix (ECM), which is essential in determining the tissue’s structure and function in health and disease (1). For example, tensile forces drive the reversible transition of fibroblasts to myofibroblasts during tissue growth (2). Intracellular tensions and forces promote wound healing and direct stem cell differentiation in development and regeneration (3–5). On the other hand, ECM is known to transduce external mechanical stimuli to the cells in a highly dynamic manner during embryonic morphogenesis, cancer invasion, fibrosis, and cardiovascular disease (6–8), which is influenced by the ECM’s physical and geometrical properties such as rigidity and curvature (9, 10). In these processes, the contraction of cells and the cross-linking of collagen fibers result in considerable variation of the tissue’s elastic modulus and stress distribution (11). Although growing evidence indicates that the mechanical properties of tissues are fundamental for cellular behavior and consequent tissue functionality, the mechanical mechanisms associated with these phenomena are still largely unknown due to lacking comprehensive quantitative studies on the cell-derived forces and the ECM’s tension in tissues with various mechanical boundary conditions (10, 11).In recent years, diverse techniques have been developed to probe and characterize mechanical forces at the cellular or tissue level (12). In two-dimensional (2D) conditions, a single cell’s contractile force can be detected by measuring the cell-induced deformation of soft substrates onto which the cell is attached (13–16). The force is regulated by molecular clutch dynamics involving molecules such as integrin, talin, and vinculin (17). In three-dimensional (3D) conditions, traction force microscopy was recently used for quantifying cell-generated forces by measuring the 3D displacement of ECM surrounding the cells (18). Moreover, the contractile force of a microtissue can be determined by measuring the deflection of the flexible pillars between which the microtissue is anchored (19, 20). However, those 2D and 3D studies always detected cell/tissue forces at a stress level of higher than hundreds of Pascals since the cells respond to not only the local ECM mechanics but also the mechanical boundaries of the sensors through a positive feedback loop (21). Therefore, in very soft tissues (elastic modulus <1 kPa), such as embryo and brain (11), the cell-derived force may be overestimated because a considerable counter force exerted by the sensor with a high mechanical boundary may induce cells to generate higher endogenous force.Moreover, the limited deformation capacity of those force sensors is insufficient to track forces in tissue undergoing large-scale densification, particularly from soft to solid states, which usually happens in embryogenesis, cartilage formation, and wound closure (21–24). Although it has recently been shown that stresses in 3D developing tissues can be measured at the level of a few hundreds of Pascals by using deformable microdroplets (25, 26), this method still has a shortcoming that the microdroplets cannot sense isotropic forces during large-scale densification of soft tissues because of the microdroplets’ incompressibility (27). Thus, because of these technical limitations on the measurement of cellular forces in a greater spatial range without the interference of the mechanical boundary conditions, the magnitude and changes of cell-derived force and ECM tension in soft tissue are still unclear (1, 28).Here, we developed a force sensor based on microstrings with low spring constants and a large range of deflection to measure the cell-derived forces and ECM tension in microtissues during straining processes mimicking soft tissue densification. When 3D cultures of fibroblasts in collagen gel on the microstrings underwent long-distance contraction, the corresponding forces were detected by the deflection of the microstrings with negligible reaction force. Furthermore, tailor-made microstrings with different spring constants could achieve a large range of boundary mechanics, which allows us to explore the contribution and regulation of cellular force and collagen tension in densified microtissues under various boundary conditions. The obtained results provide insights into the interplaying roles of cellular forces, ECM tension, and mechanical boundary conditions in determining the biomechanics of very soft tissues associated with embryonic development and tissue engineering.     

Estimation of <Emphasis Type="Italic">Nonlinear</Emphasis> Mechanical Properties of Vascular Tissues via Elastography

A new method is proposed for estimation of nonlinear elastic properties of soft tissues. The proposed approach involves a combination of nonlinear finite element methods with a genetic algorithm for estimating tissue stiffness profile. A multipoint scheme is introduced that satisfies the uniqueness condition, improves the estimation performance, and reduces the sensitivity to image noise. The utility of the proposed techniques is demonstrated using optical coherence tomography (OCT) images. The approach is, however, applicable to other imaging systems and modalities, as well, provided a reliable image registration scheme. The proposed algorithm is applied to realistic (2D) and idealized (3D) arterial plaque models, and proves promising for the estimation of intra-plaque distribution of nonlinear material properties.     

The Development of Equipment to Measure Mesh Erosion of Soft Tissue

Mesh erosion is a phenomenon whereby soft tissue becomes damaged as a result of contact with implants made from surgical mesh, a fabric-like material consisting of fibers of polypropylene or other polymers. This paper describes the design and construction of a testing machine to generate mesh erosion in vitro. A sample of mesh in the form of a 10 mm wide tape is pressed against soft tissue (porcine muscle) with a given force, and a given reciprocating movement is applied between the mesh and the tissue. To demonstrate the capabilities of the equipment, we measured erosion using the same mesh and tissue type, varying the applied force and the reciprocating stroke length, including zero strokes (i.e., static loading). For comparison, we also tested four other samples of polypropylene with different edge characteristics. Analysis of the results suggests the existence of three different erosion mechanisms: cutting, wear and creep. It is concluded that the equipment provides a useful and realistic simulation of mesh erosion, a phenomenon that is of great clinical significance and merits further study.     

Fabrication and Mechanical Testing of the Uniaxial Graded Auxetic Damper

Auxetic structures can be used as protective sacrificial solutions for impact protection with lightweight and excellent energy-dissipation characteristics. A recently published and patented shock-absorbing system, namely, Uniaxial Graded Auxetic Damper (UGAD), proved its efficiency through comprehensive analytical and computational analyses. However, the authors highlighted the necessity for experimental testing of this new damper. Hence, this paper aimed to fabricate the UGAD using a cost-effective method and determine its load–deformation properties and energy-absorption potential experimentally and computationally. The geometry of the UGAD, fabrication technique, experimental setup, and computational model are presented. A series of dog-bone samples were tested to determine the exact properties of aluminium alloy (AW-5754, T-111). A simplified (elastic, plastic with strain hardening) material model was proposed and validated for use in future computational simulations. Results showed that deformation pattern, progressive collapse, and force–displacement relationships of the manufactured UGAD are in excellent agreement with the computational predictions, thus validating the proposed computational and material models.     

The development and potential of acoustic radiation force impulse (ARFI) imaging for carotid artery plaque characterization

Stroke is the third leading cause of death and long-term disability in the USA. Currently, surgical intervention decisions in asymptomatic patients are based upon the degree of carotid artery stenosis. While there is a clear benefit of endarterectomy for patients with severe (> 70%) stenosis, in those with high/moderate (50-69%) stenosis the evidence is less clear. Evidence suggests ischemic stroke is associated less with calcified and fibrous plaques than with those containing softer tissue, especially when accompanied by a thin fibrous cap. A reliable mechanism for the identification of individuals with atherosclerotic plaques which confer the highest risk for stroke is fundamental to the selection of patients for vascular interventions. Acoustic radiation force impulse (ARFI) imaging is a new ultrasonic-based imaging method that characterizes the mechanical properties of tissue by measuring displacement resulting from the application of acoustic radiation force. These displacements provide information about the local stiffness of tissue and can differentiate between soft and hard areas. Because arterial walls, soft tissue, atheromas, and calcifications have a wide range in their stiffness properties, they represent excellent candidates for ARFI imaging. We present information from early phantom experiments and excised human limb studies to in vivo carotid artery scans and provide evidence for the ability of ARFI to provide high-quality images which highlight mechanical differences in tissue stiffness not readily apparent in matched B-mode images. This allows ARFI to identify soft from hard plaques and differentiate characteristics associated with plaque vulnerability or stability.     

Injecting drug use,the skin and vasculature

Damage to the skin, subcutaneous tissues and blood vessels are among the most common health harms related to injecting drug use. From a limited range of early reports of injecting-related skin and soft tissue damage there is now an increasing literature relating to new drugs, new contaminants and problems associated with unsafe injection practices. Clinical issues range from ubiquitous problems associated with repeated minor localised injection trauma to skin and soft tissue and infections around injection sites, to systemic blood infections and chronic vascular disease. The interplay of limited availability and access to sterile injecting equipment, poor injecting technique, compromised drug purity, drug toxicity and difficult personal and environmental conditions give rise to injection-related health harms. This review of injecting-related skin, soft tissue and vascular damage focuses on epidemiology and causation, clinical examination and investigation, treatment and prevention.