Silicone Rubber Model Research Articles

High-sensitivity liquid-metal-based contact lens sensor for continuous intraocular pressure monitoring

Intraocular pressure (IOP) is a crucial physiological indicator for the diagnosis and treatment of glaucoma. The current infrequent IOP measurement during an office visit is insufficient to characterize the symptoms. Here, an LC resonator strain sensor in a contact lens, composed of a stretchable inductance coil using liquid metal and a chip capacitor, was developed for real-time IOP monitoring. The lens sensor was operated on the basis of ‘mechanical-electrical’ principle. The rising IOP will increase the curvature radius of the cornea and stretch the inductance coils through the cornea and tear film, leading to a decrease in resonant frequency. The theoretical model of the whole process has been established and explored. The sensor has been scientifically designed and fabricated to be ultra-soft, comfortable, safe without leakage and has a stable signal. The sensor was calibrated on two silicone rubber model eyeballs, respectively, showing linear and stable responses. An experiment on porcine eyes in vitro was conducted. The sensor can track IOP changes and shows much higher sensitivity than the current mainstream lens sensors, which is even an order of magnitude higher than the existing inductive sensor. The high-sensitivity and ultra-flexible liquid-metal-based lens sensor is a promising approach for 24 h continuous IOP monitoring in clinics.

Dielectric spectroscopy of aluminium hydroxide particles filled silicone rubber and dielectric model analysis with modified numerical solutions

In numerical solutions of Hanai equation widely used in heterogeneous systems, the uncertainty of conductivity at high frequency affects the accuracy of phase parameters results (permittivity and conductivity of components). To overcome this limitation, broadband dielectric spectroscopy of eight groups of silicone rubber (SR) was measured at a frequency from 10−1 Hz to 105 Hz and at a temperature from 0 °C to −40 °C. An obvious relaxation peak related to the interface between aluminium hydroxide (ATH) and SR was observed and confirmed. Based on the interfacial polarization, phase parameters of ATH and SR were calculated by modified numerical solutions, which was verified by other information. It was found that with the increase of ATH concentration, polarization strength increased and relaxation time decreased, which indicated that the number of charges accumulated at the interface increased in interfacial polarization process and the Debye length of interface decreased. Because of the surface conductivity around ATH, the conductivity of ATH is higher than that of SR. This paper is beneficial for the studies on the interface properties of ATH filled silicone rubber and provides supports for studying the electrical parameters of particles dispersed in continuous medium systems without physical transition or chemical changes with enhanced accuracy.

Novel Three-Dimensional Coordinate System to Analyze Alveolar Molding Effects of Pre-Surgical Nasoalveolar Molding on Infants With Non-Syndromic Unilateral Cleft Lip and Palate.

The aim of this study is to establish a stable 3-dimensional (3D) coordinate system for investigating the alveolar molding effects of pre-surgical nasoalveolar molding (PNAM) on non-syndromic unilateral cleft lip and palate (UCLP) patients, basing on the Frankfort Horizontal (FH) plane.Twenty-one non-syndromic UCLP neonates who sought medical advice in the department of Orthodontics, from 2016.5 to 2017.10 were enrolled in the present study. All neonates were subjected to PNAM before the cleft lip repair. The treatment duration was 75.76 days. Silicone rubber models were obtained and scanned using a 3D laser scanner pre- and post-PNAM treatment. A 3D coordinate system based on the FH reference plane was built utilizing Rhino3D software to record the landmark 3D coordinates, to measure the distance, angle, and length variables. The Paired Student's t test and the Pearson correlation coefficient were used to calculate reproducibility and reliability of the landmark localization for repeated measurements. Changes of the measurement variables were analyzed by the Paired Student's t test.This study revealed a high reproducibility and reliability for most of the landmarks. By the end of PNAM treatment, the cleft gap was reduced with the malformation of alveolar segments aligned normally and the anterior points of both alveolar segments were rotated to the cleft side.Utilizing the FH plane to set up a rigorous and stable 3D system is meaningful. PNAM therapy is effective in reducing the severity of the maxillary deformity not only on the non-cleft side, but also on the cleft side.

Microfluidic contact lenses for unpowered, continuous and non-invasive intraocular pressure monitoring

Intraocular pressure (IOP) is a crucial physiological indicator of the visual system and play a key role in the diagnosis and treatment of glaucoma. However, the current handheld single measurement tools for IOP sensing cannot meet the future demands for glaucoma management. Thus, here we present the microfluidic contact lens sensors that could provide unpowered, continuous and non-invasive IOP monitoring. The microfluidic contact lens is comprised of a sensing layer of the micropatterned soft-elastomer and a hard plastic reference layer. The devices use the annular sensing chamber filled with the dyed liquid and a sensing microchannel as the IOP transducer. Resulting from the volume variance of the sensing chamber and caused by the deformation of the sensing layer under pressure, the IOP signal is detected as the displacement change of the dyed liquid’s interface in the sensing channel, and in which, the displacement change can be optically observed by using the smart-phone camera. Based on the silicone rubber model eyeball, the sensing mechanism of the devices with different design parameters (the position of the sensing chambers and the dimension of the sensing channels) are explored by using the theoretical analyses and experimental investigations. The characteristics of these microfluidic contact lens sensors are tested, in which, the maximum sensitivity of the device (with the sensing chamber of 8.5 mm in diameter and the sensing channel of 100 × 40 um in size) can be achieved to 0.708 mm/mmHg in a working range of 0˜40 mmHg. Also, cyclical tests were conducted and indicated that the devices had a good reversibility and Long-term stability. Furthermore, the device (with the sensing chamber of 5.0 mm in diameter and the sensing channel of 150 × 40 um in size) was test on the porcine eyes ex vivo, showing a sensitivity of 0.2832 mm/mmHg in a range of 8˜32 mmHg and, the device had a good reproducibility to its IOP change. This work provides a promising approach for unpowered, continuous and non-invasive monitoring of IOP.

Soft wearable contact lens sensor for continuous intraocular pressure monitoring

Intraocular pressure (IOP) is a primary indicator of glaucoma, but measurements from a single visit to the clinic miss the peak IOP that may occur at night during sleep. A soft chipless contact lens sensor that allows the IOP to be monitored throughout the day and at night is developed in this study. A resonance circuit composed of a thin film capacitor coupled with a sensing coil that can sense corneal curvature deformation is designed, fabricated and embedded into a soft contact lens. The resonance frequency of the sensor is designed to vary with the lens curvature as it changes with the IOP. The frequency responses and the ability of the sensor to track IOP cycles were tested using a silicone rubber model eye. The results showed that the sensor has excellent linearity with a frequency response of ∼8kHz/mmHg, and the sensor can accurately track fluctuating IOP. These results showed that the chipless contact lens sensor can potentially be used to monitor IOP to improve diagnosis accuracy and treatment of glaucoma.

Opened end-to-side technique for end-to-side anastomosis and analyses by an elastic true-to-scale silicone rubber model

The end-to-side anastomosis is frequently used in microvascular free flap transfer, but detailed rheological analyses are not available. The purpose of this study was to introduce a new modified end-to-side (Opened End-to-Side, OES-) technique and compare the resulting flow pattern to a conventional technique. The new technique was based on a bi-triangulated preparation of the branching-vessel end, resulting in a "fish-mouthed" opening. We performed two different types of end-to-side anastomoses in forty pig coronary arteries and produced one elastic, true-to-scale silicone rubber model of each anastomosis. Then we installed the transparent models in a circulatory experimental setup that simulated the physiological human blood flow. Flow velocity was measured with the one-component Laser-Doppler-Anemometer system, recording flow axial and perpendicular to the model at four defined cross-sections for seven heart cycles in each model. Maximal and minimal axial velocities ranged in the conventional model between 0.269 and -0.122 m/s and in the experimental model between 0.313 and -0.153 m/s. A less disturbed flow velocity distribution was seen in the experimental model distal to the anastomosis. The OES-technique showed superior flow profiles distal to the anastomosis with minor tendencies of flow separation and represents a new alternative for end-to-side anastomosis.

Measurement of Young's Modulus of Vocal Folds by Indentation

To assess the accuracy of the indentation method for stiffness measurements and to estimate the Young's modulus of the vocal fold using this technique. Basic science. Indentation tests were performed using a range of indenter diameters and indentation depths on single- and double-layer silicone rubber models with various cover-layer thicknesses with known geometry and Young's moduli. Measurements were repeated on intact vocal folds and isolated muscle and cover-layer samples from three cadaveric human larynges. Indentation on single-layer rubber models yielded Young's moduli with acceptable accuracy when the indentation depth was equal to or smaller than the indenter diameter, and both were smaller than the physical dimensions of the material sample. On two-layer models, the stiffness estimation was similarly influenced by indenter diameter and indentation depth, and acceptable accuracy was reached when indentation depth was much smaller than the height of the top cover layer. Measurements on midmembranous vocal fold tissue revealed location-dependent Young's moduli (in kPa) as follows: intact hemilarynx, 8.6 (range=5.3-13.1); isolated inferior medial surface cover, 7.5 (range=7-7.9); isolated medial surface cover, 4.8 (range=3.9-5.7); isolated superior surface cover, 2.9 (range=2.7-3.2); and isolated thyroarytenoid muscle, 2.0 (range=1.3-2.7). Indenter diameter, indentation depth, and material thickness are important parameters in the measurement of vocal fold stiffness using the indentation technique. Measurements on human larynges showed location-dependent differences in stiffness. The stiffness of the vocal folds was also found to be higher when the vocal fold structure was still attached to the laryngeal framework compared with that when the vocal fold was separated from the framework.

Swirling flow pattern in a non-planar model of an interposition vein cuff anastomosis

One of the main causes of long-term failure of ePTFE grafts is the development of anastomotic intimal hyperplasia which leads to graft thrombosis. Experimental studies with bypass grafts have shown an inverse relationship between mean wall shear stress and intimal hyperplasia. The geometry of the anastomosis has a strong influence on the flow pattern and wall shear stress distribution. The aim of this in vitro study was to investigate the influence of non-planarity in a model of a distal anastomosis with interposition vein cuff, an anastomosis configuration that is increasingly being used because of improved clinical results. Laser Doppler anemometer measurements were carried out in silicone rubber models of interposition vein cuff anastomoses with planar and non-planar inflow. The pulsatile flow waveforms were typical of those found in femoro-infrapopliteal bypass. Axial and radial velocities were measured in the proximal and distal outflow segments. As expected a symmetrical helical flow pattern (Dean flow) was evident in the planar model. The model with non-planar inflow, however, gave rise to swirling flow in both the distal and proximal artery outflow segments for during the systolic phase. In patients, the anastomosis is usually non-planar. Since the configuration depends in part upon the tunnelling of the graft, this may be altered to some extent. Non-planar anastomotic configurations induce a swirling flow pattern, which may normalise wall shear stress, thereby potentially reducing intimal hyperplasia.

D108 脳動脈瘤内部の流動パターンのIn Vitro PIV計測とCFD解析

This paper presents PIV results and CFD results obtained for in vitro flow behaviors in a cerebral aneurysm. Non-pulsating flow, Re=700, is investigated as a first step. The MRI data acquired from an actual patient are reconstructed into a digital three-dimensional model, from which a transparent silicone rubber model suitable for flow visualization is fabricated by using a rapid-prototyping technique. A commercial CFD code based on the finite volume method is utilized. The PIV measurement, realized by the index matching technique, has revealed that the flow velocity in the aneurysm is low, that there is a recirculation zone in the center of the aneurysms and that the flow in the bleb is stagnant. These features are in agreement with the CFD result, which shows in addition that the wall shear stress is high at the entrance and the exit of the aneurysm but low on its internal wall.

Modeling endoleaks and collateral reperfusion following endovascular AAA exclusion.

To investigate the effect on intrasac pressure of stent-graft deployment within a life-size silicone rubber model of an abdominal aortic aneurysm (AAA) maintained under physiological conditions of pressure and flow. A commercial bifurcated device with the polyester fabric preclotted with gelatin was deployed in the AAA model. A pump system generated physiological flow. Mean and pulse aortic and intrasac pressures were measured simultaneously using pressure transducers. To simulate a type I endoleak, plastic tubing was placed between the aortic wall and the stent-graft at the proximal anchoring site. Type II endoleak was simulated by means of side branches with set inflow and outflow pressures and perfusion rates. Type IV endoleak was replicated by removal of gelatin from the graft fabric. With no endoleak, the coated graft reduced the mean and pulse sac pressures to negligible values. When a type I endoleak was present, mean sac pressure reached a value similar to mean aortic pressure. When net flow through the sac due to a type II endoleak was present, mean sac pressure was a function of the inlet pressure, while pulse pressure in the sac was dependent on both inlet and outlet pressures. As perfusion rates increased, both mean and pulse sac pressures decreased. When there was no outflow, mean sac pressure was similar to mean aortic pressure. In the presence of both type I and type II endoleaks, mean sac pressure reached mean aortic pressure when the net perfusion rate was low. In vitro studies are useful in gaining an understanding of the impact of different types of endoleaks, in isolation and in combination, on intrasac pressure after aortic stent-graft deployment.

914 硬さ測定用カテーテルに関する基礎的研究

This paper describes the development of a catheter sensor for measurement of stiffness of the blood vessel wall. The basic sensor is constructed with a piezoelectric transducer (PZT), which acts as the tactile sensor and employs the phase shift principle. Two type of catheter sensor were developed. One type was built with a contact tip angle at 45 degrees in order to emit ultrasonic waves directly to the inside wall. The objective of the construction of the other type was to miniaturize its outside diameter as much as possible. Different concentrations of silicone gum and rubber models of blood vessels were used for measurements. Result show that the sensors could distinguish between silicone gum samples of different levels of hardness and determine the hardness/softness of neoplasm in blood vessel model. Thus, the catheter sensor developed here may prove very useful for inner measurements of blood vessels and may also be useful in detecting intraluminal obstruction due to tumor presence.

Flexible tubular replicas of abdominal aortic aneurysms.

The aim of this study was to manufacture life-size, flexible, tubular replicas of human abdominal aortic aneurysms and the associated vasculature, suitable for use in a training simulator for endovascular procedures. Selective laser sintering was used to create a geometrically correct master model for each of ten anatomical variations. The masters were used to generate flexible latex replicas. The use of the replicas in the training simulator was demonstrated. In total ten silicone rubber models were produced. When connected into the training simulator and perfused at arterial pressure it was possible to deploy an endovascular stent under fluoroscopic control and to perform angiography. The study has shown that conventional rapid prototyping technology can be used to manufacture flexible, radiolucent replicas which provide a realistic training environment for endovascular procedures.

Experiments on Particle Deposition in the Human Upper Respiratory System

ABSTRACT In this study, the deposition of particles (0.3 μm to 2.5 μm in diameter) within a silicone rubber model of the human upper respiratory system was studied. The domain of the respiratory tract under investigation begins at the entrance (nostrils and mouth) and continues through to the second generation of the tracheobronchial airways (main bronchi). The particle deposition efficiency of the sample respiratory system was computed by measuring particle concentration at the inlet and outlet of the model. The regional deposition patterns of fluorescent particles (0.3 μm to 0.7 μm in diameter) was examined by measuring the fluorescent intensity with a fluorescence spectrophotometer. For simulated oral inhalation, the deposition efficiency of the oral cavity (0.9%-5.4%) is approximately the same as that of the oropharynx-trachea region (0.8%-4.8%). During simulated nasal inhalation, the deposition efficiency of the nasal region (20%-43.6%) is greater than the values of the nasopharynx-trachea region (2....

A silicone rubber mould of the heart

The macroscopical structure of the ventricular myocardium has been an unsolved problem since the XVIth century, when Anatomy started as an authentic science. Since then the spatial organization of the myocardial fibres has represented, as Pettigrew says, "an arrangement so unusual and perplexing, that it has long been considered as forming a kind of Gordian knot in Anatomy. Of the complexity of the arrangement I need not speak further than to say that Vesalius, Albinus, Haller and De Blainville, all confessed their-inability to unravel it". What is shown in the present paper is the result of an anatomical work, developed over 43 years, by means of which it has been shown that the ventricular myocardial mass consists of a band, curled in a helical way, which extends from the pulmonary artery to the aorta. This is illustrated by a silicone rubber model cast from an actual unrolled myocardial band.

The evaluation of a biexponential model for description of intercompartmental fluid shifts in compressed oedematous tissue

A parametric model was fitted to force curve data gained by a non-invasive impression method that measures force and fluid translocation during mechanical compression of the skin. The ability of the model parameters to estimate highand low-viscosity fluid flow in compressed areas were evaluated in a silicone rubber model and in six patients with chronic pitting oedema. Different softnesses of silicone rubber gave significantly different parameter values. The flow properties of the silicone model could be analysed in detail with the suggested model. Parameter analysis showed a higher fraction of low-viscosity fluid for oedema than for reference sites. The model parameters could be interpreted in softness values according to an international standard for consistency (ISO 2137). The suggested parametric model gave reliable and detailed information about high- and low-viscosity fluid flow and can be used to estimate intercompartmental fluid shifts in oedematous tissue.

Impression technique for the assessment of oedema: comparison with a new tactile sensor that measures physical properties of tissue

To measure tissue oedema, the impression technique and a new tactile sensor technique are compared and evaluated in a silicone rubber model and in an in vivo rat testis model. The principles of the two techniques differ in that the impression technique evaluates interstitial fluid flow FT and peak force F(O) when tissue is compressed, whereas the tactile sensor evaluates the hardness/softness or change in resonance frequency delta f when a vibrating rod is attached to tissue. Both techniques can detect changes in silicone hardness/softness or in hormone-induced changes of testis interstitial fluid. Although both F(O) and FT are significantly correlated to delta f in the experiments, it is concluded that F(O) is the most promising impression parameter to give valuable information about the hardness of living tissue as compared with delta f. The comparison indicates that the impression technique is the most easy to interpret, non-invasive tool to assess tissue oedema so far developed.

Sound transmission to the human fetus

A common noninvasive test for fetal well-being involves transmitting an audio-frequency acoustic signal into the amniotic fluid by means of a mechanical vibrator, which is applied to the mother’s abdomen close to the fetal head. This test has been simulated in the laboratory, using a silicone rubber model uterus of spherical shape filled with water. The outside of the model was excited by an impedance head and a load-distributing contact disk. Mechanical impedance measurements were compared with similar measurements on volunteer subjects at about 30 weeks’ pregnancy, and showed similar trends as a function of frequency. The model was then used to establish a transfer function between the exciting force and the acoustic pressure in the water-filled cavity. A simple theoretical model is presented which accounts for the main features observed experimentally. Results indicate that commercial fetal stimulators can produce intrauterine sound pressures as high as 30 Pa rms (180 Pa peak pressure) close to the point of excitation. The actual level depends on the thickness of the subcutaneous fat layer which couples the vibrator to the uterus.

Some flow visualization and laser-Doppler-velocity measurements in a true-to-scale elastic model of a human aortic arch--a new model technique.

Flow studies were done in an elastic true-to-scale silicone rubber model of an aortic arch to study further hemodynamic influences on atherosclerosis. The model was prepared from a cast of a young woman. A revised model technique was used. The model had a compliance similar to that of the human aortic arch. Velocity measurements were done in the model with a two component laser-Doppler-anemometer in steady and pulsatile flow using a calcium chloride solution with a viscosity of eta = 3.18 mPas and density of rho = 1.28 kg/m3 at 20 degrees C. The time average Reynolds numbers over a whole cycle in the ascending aorta was Re = 1350. The Womersley parameter for pulsatile flow was a = 20. The pulse wave velocity in the ascending aorta was about c = 5.4 m/sec. The secondary flow behavior was discussed for steady and pulsatile flow. Reverse flows were found, especially along the inner radius of the aortic arch in the descending aorta in steady and pulsatile flow and also in small areas of the ascending aorta and at the branches of the aortic arch. The formation of atherosclerotic plaques at preferred local flow regions is discussed.

Correlation of laser-Doppler-velocity measurements and endothelial cell shape in a stenosed dog aorta.

Laser-Doppler-velocity measurements were carried out in an elastic 1:1 true-to-scale silicone rubber model of a dog aorta with stenosis. The model was constructed from a cast of a severely stenosed dog aorta (71% of its area). The stenosis in the dog aorta was prepared by wrapping a cotton band around the aorta. This band was tightened until the presence of a thrill or a bruit was felt distal to the band. Twelve weeks later the animal was sacrificed and a cast was prepared from the aorta. From this vascular cast, the cross-sectional area was calculated. Endothelial cell geometry and orientation was studied using computerized analysis to determine the cell area and shape index. An elastic silicone rubber model was prepared from the cast to measure the velocity profiles and to estimate the local wall shear stress. Velocity measurements were done at steady and pulsatile flow using a Newtonian aqueous-glycerol solution and a non-Newtonian blood-like fluid. From those velocity measurements the velocity gradients near the wall were determined and the shear stress calculated. The flow distal to the stenosis separates from the wall at physiological conditions. The endothelial cells are smaller and more elongated in the throat; distal to the stenosis they are larger and rounder. The shape index distribution along the stenosed aorta is correlated with the level of wall shear stress. It is shown that even low changes in the wall shear stress have an influence on the orientation of the endothelial cells.

Holographic contouring of the surface topography and study of the contact rigidity of rough surfaces

An investigation carried out using the immersion method of holographic contouring is reported. When properly adjusted this method allows the construction of contour maps of the surfaces with contour intervals Δz ranging from 1 μm to several millimetres. Measurements were carried out on metal surfaces and silicone rubber models.