Force Relaxation Research Articles

Adapted protocol of rate of force development and relaxation scaling factor for neuromuscular assessment in patients with knee osteoarthritis

BackgroundThe linear relationship between muscle torque and rate of torque rise/relaxation during rapid muscle contractions has been recently introduced as a novel measure of muscle quickness, termed rate of torque development/relaxation scaling factor (RTD-SF/RTR-SF). Because the standard assessment protocol includes potentially painful muscle contractions, the first purpose of this study was to validate an adapted RTD-SF/RTR-SF protocol for knee extensor muscles that utilizes lower submaximal intensities and can be used in knee osteoarthritis patients. MethodsA cross-sectional study was performed on a group of healthy controls (n = 24) who underwent the standard RTD-SF/RTR-SF protocol (20–80% of maximum) and the knee osteoarthritis group (n = 24) who underwent the adapted protocol (20–60% of maximum). We calculated the RTD-SF, RTR-SF and the linearity (r2) for both relationships, based on both protocols in controls. ResultsThe validity of the adapted protocol was acceptable (intraclass correlation coefficient = 0.77–0.93), with low within-participant variation (coefficient of variability <10%) for both outcome measures. Compared with the control group, the knee osteoarthritis group had similar RTD-SF, but lower linearity of RTD-SF (0.90 vs. 0.82). The RTR-SF (8.0/s vs. 6.7/s) and its linearity (0.87 vs. 0.73) were significantly reduced. Comparing the affected and the unaffected leg in the knee osteoarthritis group, the unaffected leg had greater maximal torque (96.2 vs. 84.1 Nm) and higher linearity for RTD-SF (0.86 vs. 0.80) and RTR-SF (0.82 vs. 0.73). ConclusionsWe confirmed the validity of the adapted RTD/RTR-SF protocol and its sensitivity to impairments associated with knee osteoarthritis.

Characterization of the Viscoelastic Properties of Ovarian Cancer Cells Membranes by Optical Tweezers and Quantitative Phase Imaging

Author(s): Lu, T; Anvari, B | Abstract: Ovarian cancer is the deadliest gynecological cancer in women. It is a highly metastatic disease with pelvis, regional lymph nodes, and peritoneal cavity as major sites for tumor deposits. Mechanical properties of ovarian cancer cells can play a major role in metastasis as the cells detach from the ovaries and undergo deformation during the metastatic process. Herein, we have characterized the viscoelastic properties of the plasma membrane of normal epithelial (IOSE364) and cancerous (SKOV3) ovarian cells by optical tweezers and quantitative phase imaging. Using optical tweezers, we obtained time-resolved force profiles associated with membrane tethers pulled from the cells. We used quantitative phase imaging to measure the diameter of membrane tethers, and subsequently, estimated the membrane bending modulus and membrane tension in the tether. Our results indicate that the force (190 ± 76npN) (mean ± standard deviation) required to separate the membrane of SKOV3 cells from the cytoskeleton was significantly lower (p = 0.0004) than the force (350 ± 81npN) for IOSE364 cells. The mean stiffness (2.8 ± 0.8npN/μm) of membrane tethers pulled from SKOV3 cells was significantly lower (p = 0.032) than the value for IOSE 364 cells (3.7 ± 0.8npN/μm). Mean value of the force relaxation characteristic time associated with diffusive flow of lipids was also significantly lower (p = 0.018) for SKOV3 membranes (12.9 ± 6.9ns) as compared to the value for IOSE 364 membranes (20.4 ± 6.2ns). Similarly, the mean value of the membrane bending modulus for SKOV3 cells [(0.51 ± 0.23) × 10–18nJ] was significantly lower (p = 0.007) than the value for IOSE364 cells [(1.29 ± 0.32) × 10–18nJ]. Overall, our results suggest that the membranes of SKOV3 cells are less resistant to mechanical deformation. Increased membrane susceptibility to mechanical deformation may be a facilitating factor in the metastatic behavior of cancerous ovarian cells. Characterization of membrane biomechanics may provide a useful diagnostic biomarker for assessment of the metastatic potential of ovarian cancer, and a target for development of therapeutics.

Theoretical analysis for dynamic contact angle hysteresis on chemically patterned surfaces

A dynamic wetting problem is studied for a moving thin fiber inserted in fluid and with a chemically inhomogeneous surface. A reduced model is derived for contact angle hysteresis by using the Onsager principle as an approximation tool. The model is simple and captures the essential dynamics of the contact angle. From this model, we derive an upper bound of the advancing contact angle and a lower bound of the receding angle, which are verified by numerical simulations. The results are consistent with the quasi-static results. The model can also be used to understand the asymmetric dependence of the advancing and receding contact angles on the fiber velocity, which was observed recently in the physical experiments reported in the work of Guan et al. [“Asymmetric and speed-dependent capillary force hysteresis and relaxation of a suddenly stopped moving contact line,” Phys. Rev. Lett. 116, 066102 (2016)].

Evidence for abnormal deformational reserve in hypertrophic obstructive cardiomyopathy on exercise: is this a true fingerprint?

Abstract Hypertrophic obstructive cardiomyopathy (HOCM) is characterized by muscle hypertrophy and fibrosis, interfering with force generation and relaxation. Abnormal ventricular (LV) myocardial deformation have been demonstrated in patients with HOCM at rest, but there is lack of data regarding the deformational mechanics in exercise in obstructive HCM. Aims To assess the adaptability of LV deformational behaviour to physical exercise in HOCM patients as compared to healthy controls and to examine if Deformational Imaging (DMI) can provide additional information. Methods 28 obstructive HOCM (age 51.2±14.2yrs; 16 men, LVOT-obstruction 56±19mmHg at rest or on Valsalva maneuver) and 32 control subjects (50.9±6.8 yrs, 19 men from the MAGYAR-PATH Registry) underwent bicycle stress Echo (ESE) with full conventional 2D- and Doppler TTE, 2D- and 3D-Speckle Tracking Analysis (DMI) and 3D-Full Volume assessment both at rest and on submaximal ESE. Results At rest, the HOCM group had lower GLS (−14.6±4.5 vs 18.4±2.6%, p&amp;lt;0.01) but higher CS (−32.9±5.1 vs 28.8±2.3%) and Twist (9.9±2.6 vs 6.1±2.2°) than in control subjects. Exercise induced an increase in all strains in control subjects but less in HOCM (GLS: −21.4±3.5 vs 15.1±3.0% and CS: −33.9±3.6 vs 34.1±4.2% in controls). The increase of LV twist was blunted in HOCM (Δ1.2 vs Δ3.6° in controls). The PSS was more pronounced in HOCM on ESE (46.6±12.0 vs 21.2±9.6%, AUC: 0.71 for predicting HOCM), the UTR was slower (118±2.1 vs 133.1±14.1°/s) and occurred later in HOCM. The MD of Strain increased in HOCM on ESE (Δ85.1 vs Δ8.1ms in controls). The Twist had positive correlation with LVOT-obstruction (R2=0.54, p&amp;lt;0.01) and inverse correlation with UTR (R2=−0.72, p&amp;lt;0.02). The UTR/Twist ratio diminished only in HOCM on exercise (−6.0±0.8 vs −13.1±2.5 1/s). The MD, the PSS on ESE and the UTR/Twist ratio predicted the HOCM deformation phenotype accurately (AUC: 0.72, cut-off 6.0 1/s). Conclusions The HOCM patients had attenuated Strain and Rotational response on exercise implying impaired deformational adaptability with post-systolic shortening and pronounced mechanical dispersion of peak Strain on exercise which was more accurate to identify the HOCM phenotype than other Echo-indices. These findings support evidence for reduced systolic-diastolic coupling efficiency in HOCM patients on exercise which can contribute to the development of exercise-related breathlessness, dynamic LVOT-obstruction and arrhythmias in patients with HOCM. These distinct deformational patterns on exercise can help in the differential diagnosis of patients with LV hypertrophy of unknown aetiology with good sensitivity and specificity and can also aid in the risk stratification workup in HOCM. DMI Predictors for HOCM Funding Acknowledgement Type of funding source: Public hospital(s). Main funding source(s): Milton Keynes University Hospital Research Founding

Stress fibres are embedded in a contractile cortical network.

Contractile actomyosin networks are responsible for the production of intracellular forces. There is increasing evidence that bundles of actin filaments form interconnected and interconvertible structures with the rest of the network. In this study, we explored the mechanical impact of these interconnections on the production and distribution of traction forces throughout the cell. By using a combination of hydrogel micropatterning, traction-force microscopy and laser photoablation, we measured the relaxation of traction forces in response to local photoablations. Our experimental results and modeling of the mechanical response of the network revealed that bundles were fully embedded along their entire length in a continuous and contractile network of cortical filaments. Moreover, the propagation of the contraction of these bundles throughout the entire cell was dependent on this embedding. In addition, these bundles appeared to originate from the alignement and coalescence of thin and unattached cortical actin filaments from the surrounding mesh.

Impact of Film Stress and Film Thickness Process Control on GaAs-TiAu Metal Adhesion

The fabrication of GaAs-based optoelectronic ridge-waveguide devices requires deposition of a topside-contact metallization for proper device operation. Fabrication delays occurring during the processing of TiAu-contact pads have been linked to poor adhesion and metal blister formation, factors that negatively affect the final device yield. In this study, we examined sputter-deposited Ti and Au films to determine the impact of film-thickness process control and film stress as measured by wafer bow. We theorized that competing stress relaxation forces between the Ti and Au films would produce a post-deposition change in wafer bow, which affects the Au film, setting the stage for blister creation. We now report the development of a reduced-stress sputter-deposited TiAu-contact metallization and demonstrate the utility of the modified process with fabrication of blister-free ridge-waveguide devices with high device yield.

MEMS device for applying shear and tension to an epithelium combined with fluorescent live cell imaging

Mechanical forces play important roles in the biological function of cells and tissues. While numerous studies have probed the force response of cells and measured cell-generated forces, they have primarily focused on tensile, but not shear forces. Here, we describe the design, fabrication, and application of a silicon micromachined device that is capable of independently applying and sensing both tensile and shear forces in an epithelial cell monolayer. We integrated the device with an upright microscope to enable live cell brightfield and fluorescent imaging of cells over many hours following mechanical perturbation. Using devices of increasing stiffness and the same displacement input, we demonstrate that epithelia exhibit concomitant higher maximum resistive tensile forces and quicker force relaxation. In addition, we characterized the force response of the epithelium to cyclic shear loading. While the maximum resistive forces of epithelia under cyclic shear perturbation remained unchanged between cycles, cyclic loading led to faster relaxation of the resistive forces. The device presented here can be applied to studying the force response of other monolayer-forming cell types and is compatible with pharmacological perturbation of cell structures and functions.

Understanding the mechanics of closure is key to optimal midurethral sling technique

The animal experiments and prototype midurethral sling operations demonstrated that the sling provided new collagen to reinforce weak pubourethral ligaments (PUL). The now strengthened PULs were able to restore the contractile power of the 3 oppositely-acting directional closure forces. By contraction, these three forces exponentially altered the intraurethral resistance to flow when they closed the urethra to sustain continence. Relaxation of the forward force allowed the two posterior forces to uninhibitedly open the posterior urethral wall just prior to detrusor contraction, to facilitate evacuation of urine. The aim of this work is to examine the mechanics of the component anatomical structures which contribute to these functions, to analyse how subtle details impact on the actual surgical technique of the midurethral sling operations to optimize success, contribute to complications and how to prevent and fix them.

A study of knee anterior cruciate ligament biomechanics with respect to energy and relaxation

BackgroundThis research aimed to study the biomechanical properties of sheep tendon under torsion and the tendon energy absorption performance with an externally imposed initial force. MethodsTendons of nine healthy knees of sheep were investigated. In both tests, we investigated energy and relaxation at rotations of 0°, 90°, 180°, and 360°. For both tensile force and tensile displacement at a sampling period of 100 milliseconds, the maximum value of 89 N was selected as the maximum tension state for 600 s of relaxation duration for testing relaxation, and analysed of the average force of the last 30 s. FindingsThe difference of energy levels of the tendons are significant between twisted groups (180° and 360°) and untwisted group (0°) (P < 0.05); The relaxation force decreases significantly with twisted groups (90°,180°, and 360°) and untwists group (0°) (P < 0.05). The nine-group tendons show no significant difference at torsion 90° and 180° (P = 0.466). Peak force test shows significant differences between the twisted groups (90°,180°, and 360°) and untwisted group (0°) (P < 0.05). InterpretationThe torsion tendon has lower energy absorption and relaxation than the untwisted counterparts; thus, it may be more prone to damage. These results are useful for providing guidance on anterior cruciate ligament reconstruction.

Atherogenic diet-diminished endothelial glycocalyx contributes to impaired vasomotor properties in rat.

Hypercholesterolemia- and atherosclerosis-caused vasomotor property dysfunction may be involved in many clinic manifestations of atherosclerosis, including angina, acute myocardial infarction, and sudden cardiac death. However, its underlying mechanism is not clear. The endothelial glycocalyx is a protective surface layer on the endothelial cells, serving as a molecular sieve, cell adhesion modulator, and mechanosensor for blood flow. In the present study, we demonstrated by confocal microscopy in Sprague-Dawley (SD) male rats fed a 12-wk high-cholesterol diet (HC) compared with the normal diet (NC) that the dimension of the endothelial glycocalyx reduced significantly in both the common carotid artery (2.89 ± 0.41 µm and 3.25 ± 0.44 μm, respectively) and the internal sinus region (2.35 ± 0.07 µm and 3.46 ± 0.86 μm, respectively). Furthermore, we showed by real-time PCR that this dimension modification of endothelial glycocalyx may be attributed to a significant downregulation of heparan sulfate proteoglycan (HSPG)-related genes, including syndecan-3, glypican-1, and EXT1, not resulting from an enhanced shedding of sulfated glycosaminoglycans (sGAGs) from the vessel wall to the plasma. Meanwhile, the mean contraction and relaxation forces of the common carotid artery with responses to norepinephrine (NE) and acetylcholine (ACh) decreased ~0.34- and 0.13-fold, respectively, accompanied by a lower level of nitric oxide (NO) release. These findings suggest that the atherogenic high cholesterol diet diminished endothelial glycocalyx and disturbed the local NO release, thus contributing to the impaired vasomotor properties of the vessel.NEW & NOTEWORTHY Twelve-week high-cholesterol (HC) diet reduces the thickness of the endothelial glycocalyx in Sprague-Dawley (SD) male rats, which is mainly attributed to a downregulation of heparan sulfate proteoglycan-related genes (syndecan-3, glypican-1, EXT1), not resulting from an enhanced shedding of sulfated glycosaminoglycans (sGAGs) into the plasma. HC-diminished glycocalyx may disturb its mechanotransduction of local shear stress, lower nitric oxide (NO) release, and impair vasomotor responses to norepinephrine (NE) and acetylcholine (ACh).

Mobility in immersed granular materials upon cyclic loading

We study the mobility of objects embedded in an immersed granular packing and subjected to cyclic loadings. With this aim, we conducted uplift experiments whereby a horizontal plate is embedded in the packing and subjected to a vertical cyclic force oscillating between zero and a maximum amplitude. Tests performed at different cyclic force frequencies and amplitudes evidence the development of three mobility regimes whereby the plate stays virtually immobile, moves up steadily, or slowly creeps upwards. Results show that steady plate uplift can occur at lower force magnitudes when the frequency is increased. We propose an interpretation of this frequency-weakening behavior based on force relaxation experiments and on the analysis of the mobility response of theoretical viscoelastoplastic mechanical analog. These results and analysis point out inherent differences in mobility response between steady and cyclic loadings in immersed granular materials.

Forced peeling and relaxation of neurite governed by rate-dependent adhesion and cellular viscoelasticity

Tight connection between neural cells and their micro-environment is crucial for processes such as neurite outgrowth and nerve regeneration. However, characterizing neuron adhesion remains challenging because of its rate-dependent nature as well as its coupling with the viscoelastic cellular response. In this study, by conducting successive forced peeling and relaxation tests on the same neurite, we managed to extract both adhesion and viscoelastic characteristics of neural cells simultaneously for the first time. Specifically, well-developed neurites were peeled away from the substrate by an atomic force microscopy (AFM) probe under different loading rates and then held at a fixed separation distance for relaxation. A computational model was also developed to explain the observed peeling-relaxation response, where the neurite was treated as a standard linear viscoelastic material while a viscous-regularized cohesive law was introduced to represent neuron–substrate adhesion. Our combined experimental and simulation results indicated that the adhesion energy is of the order of 0.04–0.1 mJ∕m2, albeit being strongly rate-dependent, and relaxation takes place inside neurite with a characteristic time of ∼3 s. These findings could be critical for our physical understanding and modeling of different adhesion-mediated processes like neuron migration and synapse formation in the future.

Mechanical properties of a biodegradable self-expandable polydioxanone monofilament stent: In vitro force relaxation and its clinical relevance.

Biodegradable stents are promising treatments for many diseases, e.g., coronary artery disease, urethral diseases, tracheal diseases, and esophageal strictures. The mechanical properties of biodegradable stent materials play a key role in the safety and efficacy of treatment. In particular, insufficient creep resistance of the stent material could result in premature stent collapse or narrowing. Commercially available biodegradable self-expandable SX-ELLA stents made of polydioxanone monofilament were tested. A new, simple, and affordable method to measure the shear modulus of tiny viscoelastic wires is presented. The important mechanical parameters of the polydioxanone filament were obtained: the median Young's modulus was [Formula: see text] = 958 (922, 974) MPa and the shear modulus was [Formula: see text] = 357 (185, 387) MPa, resulting in a Poisson's ratio of ν = 0.34. The SX-ELLA stents exhibited significant force relaxation due to the stress relaxation of the polydioxanone monofilament, approximately 19% and 36% 10 min and 48 h after stent application, respectively. However, these results were expected, and the manufacturer and implanting clinician should be aware of the known behavior of these biodegradable materials. If possible, a biodegradable stent should be designed considering therapeutic force rather than initial force. Additionally, new and more advanced biodegradable shape-memory polymers should be considered for future study and use.

Experimental Study on the Performance of GFRP–GFRP Slip-Critical Connections with and without Stainless-Steel Cover Plates

Composite structures have become increasingly popular in civil engineering due to many advantages, such as light weight, excellent corrosion resistance and high productivity. However, they still lack the strength, stiffness, and convenience of constructions of fastener connections in steel structures. The most popular fastener connections in steel structures are slip-critical connections, and the major factors that influence their strength are the slip factors between faying surfaces and the clamping force due to the prevailing torque. This paper therefore examined the effect that changing the following parameters had on the slip factor: (1) replacing glass fiber reinforced plastic (GFRP) cover plates with stainless-steel cover plates; (2) adopting different surface treatments for GFRP-connecting plates and stainless-steel cover plates, respectively; and (3) applying different prevailing torques to the high-strength bolts. The impact on the long-term effects of the creep property in composite elements under the pressure of high-strength bolts was also studied with pre-tension force relaxation tests. It is shown that a high-efficiency fastener connection can be obtained by using stainless-steel cover plates with a grit-blasting surface treatment, with the maximum slip factor reaching 0.45, while the effects of the creep property are negligible.

Analysis of Surgical Forces Required to Gain Access Using a Probe for Minimally Invasive Spine Surgery via Cadaveric-Based Experiments Towards Use in Training Simulators.

Virtual Reality haptic-based surgical simulators for training purposes have recently been receiving increased traction within the medical field. However, its future adoption is contingent on the accuracy and reliability of the haptic feedback. This study describes and analyzes the implementation of a set of haptic-tailored experiments to extract the force feedback of a medical probe used in minimally invasive spinal lumbar interbody fusion surgeries. Experiments to extract linear, lateral and rotational insertion, relaxation and extraction of the tool within the spinal muscles, intervertebral discs and lumbar nerve on two cadaveric torsos were conducted. Notably, mean force-displacement and torque-angular displacement curves describing the different tool-tissue responses were reported with a maximum force of 6.87 (±1.79) N at 40 mm in the muscle and an initial rupture force through the Annulus Fibrosis of 20.550 (±7.841) N at 6.441 mm in the L4/L5 disc. The analysis showed that increasing the velocity of the probe slightly reduced and delayed depth of the muscle punctures but significantly lowered the force reduction due to relaxation. Decreasing probe depth resulted with a reduction to the force relaxation drop. However, varying the puncturing angle of attack resulted with a significant effect on increasing force intensities. Finally, not resecting the thoracolumbar fascia prior to puncturing the muscle resulted with a significant increase in the force intensities. These results present a complete characterization of the input required for probe access for spinal surgeries to provide an accurate haptic response in training simulators.

Optimum cork stopper diameter for a proper wine sealing performance when modifying bottleneck diameter: a first approach

Aim of study: This study present a theoretical model that allow establishing the proper relationship between forces and diameters that take part in sealing for ensuring an adequate closure during storage time, and obtained the optimum stopper diameter for a proper sealing performance when modifying bottleneck diameter.Area of study: The proposed model is of interested to the whole cork value chain from forest owners to natural cork stoppers manufacturers.Material and methods: The optimum cork stopper diameter depends mainly on stopper quality and the compression rate applied in the bottling operation. In this study, we establish the stopper diameter when reducing bottleneck diameter, applying a compression rate of 33% when corking, and for natural cork stoppers which quality allows to recover its initial diameter to 96% after 24 h since compression.Main results: For a bottleneck diameter of 18 mm, the value of the stopper diameter should be at least of 22.3 mm, and for a bottleneck diameter of 17 mm, the value of the stopper diameter should be at least of 20.3 mm.Research highlights: These results try to solve one of the main worries of natural cork stopper manufacturers, which is the scarcity of raw cork suitable for manufacturing them. However this study is also of interested to forest owners because the increment of cork suitable for natural cork stoppers manufacturing means an increment in cork value.Key words: bottling; corking; compression force; compression rate; diameter recovery; relaxation force; relaxation ratio.Abbreviations used: Ds (Cork Stopper Diameter); Dg (Caliper Diameter the Corking Machine); Db (Bottleneck Diameter); Dr (Recovered Diameter); Fc (Compression Force); Fr (Relaxation Force); CR (Compression Rate); RR (Relaxation Ratio); RD (Diameter Recovery).

Penetration and relaxation behavior of JSC-1A lunar regolith simulant under cryogenic conditions

Lunar in situ resource utilization discussions have recently been focused on the presence and distribution of ice in the upper layers of surface regolith, in particular within the confines of the permanently shadowed regions. Extraction ideas - ranging from simple scooping to percussive drilling and thermal (optical) mining utilizing cold-trap volatile capture – require detailed knowledge of the mechanical properties of icy regolith as we are likely to encounter. Penetrometers provide a robust and straightforward measurement technique for determining soil properties, but previous research fails to reliably show measurement sensitivity to increasing ice content due to difficulties in experimentation at cryogenic conditions. To display the capability of a simple conical penetrometer to discern saturation levels of icy regolith simulant within an expected range, we conducted laboratory penetration and subsequent relaxation measurements of JSC-1A lunar simulant using a specially-designed cryogenic apparatus which minimizes sample temperature fluctuation as well as the thermal mismatch between the penetrating probe and tested sample. We measured penetration resistance and force relaxation behavior for JSC-1A lunar simulant under constant displacement rate penetration at ~300 mTorr pressure, ~110 K sample temperature, 170 K to 190 K probe temperature, and ice contents of 0% to 12% and 100%. Penetration resistance and relaxation behavior both showed sensitivity to ice content, with parameters of best-fit curve models offering simple empirical predictors of saturation. A critical ice content of 1% to 3%, wherein a significant increase in penetration resistance occurs, is identified as being fundamentally influenced by the filling of substantial pore space with grouting ice. A decrease in viscoelastic behavior of high ice content samples at cryogenic temperatures is noted, and inhibition of relaxation mechanisms due to activation-energy-based temperature effects is also demonstrated in dry, ice-free simulant. Additional research across the spectrum of ice saturations, temperatures, and pressure environments likely to be found in extraterrestrial environments is suggested to improve upon these results, in particular using cryogenic systems even more specialized to reduce thermal issues and increase load capacities and apparatus stiffness. Such additional information will serve to advance the potential use of these results and this technology in future exploratory missions.

Intestinal Organoids: Relaxation of Extracellular Matrix Forces Directs Crypt Formation and Architecture in Intestinal Organoids (Adv. Healthcare Mater. 8/2020)

Intestinal Organoids: Relaxation of Extracellular Matrix Forces Directs Crypt Formation and Architecture in Intestinal Organoids (Adv. Healthcare Mater. 8/2020)

Characterizing poroelasticity of biological tissues by spherical indentation: An improved theory for large relaxation

Flow of fluids within biological tissues often meets with resistance that causes a rate- and size-dependent material behavior known as poroelasticity. Characterizing poroelasticity can provide insight into a broad range of physiological functions, and is done qualitatively in the clinic by palpation. Indentation has been widely used for characterizing poroelasticity of soft materials, where quantitative interpretation of indentation requires a model of the underlying physics, and such existing models are well established for cases of small strain and modest force relaxation. We showed here that existing models are inadequate for large relaxation, where the force on the indenter at a prescribed depth at long-time scale drops to below half of the initially peak force (i.e., F(0)/F(∞) > 2). We developed an indentation theory for such cases of large relaxation, based on Biot theory and a generalized Hertz contact model. We demonstrated that our proposed theory is suitable for biological tissues (e.g., porcine liver, spleen, kidney, skin and human cirrhosis liver) with both small and large relaxations. The proposed method would be a powerful tool to characterize poroelastic properties of biological materials for various applications such as pathological study and disease diagnosis.

Numerical Study of Binary Trickle Flow of Liquid Iron and Molten Slag in Coke Bed by Smoothed Particle Hydrodynamics

In the bottom region of blast furnaces during the ironmaking process, the liquid iron and molten slag drip into the coke bed by the action of gravity. In this study, a practical multi-interfacial smoothed particle hydrodynamics (SPH) simulation is carried out to track the complex liquid transient dripping behavior involving two immiscible phases in the coke bed. Numerical simulations were performed for different conditions corresponding to different values of wettability force between molten slag and cokes. The predicted dripping velocity changes and interfacial shape were investigated. The relaxation of the surface force of liquid iron plays a significant role in the dripping rate; i.e., the molten slag on the cokes acts as a lubricant against liquid iron flow. If the attractive force between the coke and slag is smaller than the gravitational force, the slag then drops together with the liquid iron. When the attractive force between the coke and slag becomes dominant, the iron-slag interface will be preferentially detached. These results indicate that transient interface morphology is formed by the balance between the momentum of the melt and the force acting on each interface.