Micro Tactile Sensor Research Articles

Effects of stamp properties on transfer-print and its application to fabricate a micro-tactile sensor

Effects of stamp properties on transfer-print and its application to fabricate a micro-tactile sensor

Sensitivity improvements of a resonance-based tactile sensor

Resonance-based contact-impedance measurement refers to the application of resonance sensors based on the measurement of the changes in the resonance curve of an ultrasonic resonator in contact with a surface. The advantage of the resonance sensor is that it is very sensitive to small changes in the contact impedance. A sensitive micro tactile sensor (MTS) was developed, which measured the elasticity of soft living tissues at the single-cell level. In the present paper, we studied the method of improving the touch and stiffness sensitivity of the MTS. First, the dependence of touch sensitivity in relation to the resonator length was studied by calculating the sensitivity coefficient at each length ranging from 9 to 40 mm. The highest touch sensitivity was obtained with a 30-mm-long glass needle driven at a resonance frequency of 100 kHz. Next, the numerical calculation of contact impedance showed that the highest stiffness sensitivity was achieved when the driving frequency was 100 kHz and the contact-tip diameter of the MTS was 10 μm. The theoretical model was then confirmed experimentally using a phase-locked-loop-based digital feedback oscillation circuit. It was found that the developed MTS, whose resonant frequency was 97.030 kHz, performed with the highest sensitivity of 53.2 × 106 Hz/N at the driving frequency of 97.986 kHz, i.e. the highest sensitivity was achieved at 956 Hz above the resonant frequency.

Surface density mapping of natural tissue by a scanning haptic microscope (SHM)

To expand the performance capacity of the scanning haptic microscope (SHM) beyond surface mapping microscopy of elastic modulus or topography, surface density mapping of a natural tissue was performed by applying a measurement theory of SHM, in which a frequency change occurs upon contact of the sample surface with the SHM sensor – a microtactile sensor (MTS) that vibrates at a pre-determined constant oscillation frequency. This change was mainly stiffness-dependent at a low oscillation frequency and density-dependent at a high oscillation frequency. Two paragon examples with extremely different densities but similar macroscopic elastic moduli in the range of natural soft tissues were selected: one was agar hydrogels and the other silicon organogels with extremely low (less than 25 mg/cm3) and high densities (ca. 1300 mg/cm3), respectively. Measurements were performed in saline solution near the second-order resonance frequency, which led to the elastic modulus, and near the third-order resonance frequency. There was little difference in the frequency changes between the two resonance frequencies in agar gels. In contrast, in silicone gels, a large frequency change by MTS contact was observed near the third-order resonance frequency, indicating that the frequency change near the third-order resonance frequency reflected changes in both density and elastic modulus. Therefore, a density image of the canine aortic wall was subsequently obtained by subtracting the image observed near the second-order resonance frequency from that near the third-order resonance frequency. The elastin-rich region had a higher density than the collagen-rich region.

Flexible Microtactile Sensor for Normal and Shear Elasticity Measurements

This paper presents a tactile sensor capable of measuring Young's modulus and shear modulus of elasticity for polymers, soft tissue, and other materials. The sensor is built by using polydimethylsiloxane as the structural material. A number of sensing cells of different stiffnesses are used in each sensor. The Young's modulus of the targeted object can be measured based on the relative deflections of adjacent sensing cells. The shear modulus measurement is enabled by using a quad-electrode structure in each sensing cell. Experimental results show sensing resolutions of 0.1 MPa for Young's modulus measurement in the range of 0.1-1 MPa and 0.05 MPa for shear modulus measurement ranging from 0.05 to 0.2 MPa. The flexible tactile sensor can be integrated on the end effector of robotic arms to achieve tactile sensing feedback. The proposed sensing technology can also be utilized for fast measurement of both Young's modulus and shear modulus for industrial applications that involve measuring mechanical properties of materials.

Fabrication and performance assessment of a novel stress sensor applied for micro-robotics

An innovative tactile sensor is analyzed and verified by intensive experiments. By using micro-cantilever beams, on which the strain gauge layers (Pt/Ti) are deposited, the corresponding induced strains can be detected and converted into electric resistance change, with respect to either applied normal stress or shear stress. The four micro-cantilever beams are allocated in the fashion such that any adjacent beams are perpendicular to each other to decouple any potential measure discrepancy due to non-ideal orthogonality. In addition, the micro-cantilever beams are curled before hands so that they can concurrently detect normal stress and shear stress. To be protected from being damaged by strong stress, the curled cantilever beams are covered up by elastomer material. Therefore, the micro-tactile sensor can detect normal stress up to 250 kPa and shear stress up to 35 kPa. Besides, since the elastomer is made of PDMS, which is of high bio-compatibility, the tactile sensor can be used to directly contact with human body. By taking the design and fabrication parameters into account, the curled micro-cantilever beams, which is of multi-layer structure by polymer/Pt/Ti/Si, can be produced with high yield rate. Finally, the efficacy of the tactile sensor is verified by experiments via a micro-manipulator, a high-resolution microscope and a force sensor for calibration.

Development of tactile sensors for simultaneous, detection of normal and shear stresses

A novel tactile sensor is analyzed and verified by intensive experiments. By using micro-cantilever beams, on which the strain gauge layers (Pt/Ti) are deposited, the corresponding induced strains can be detected and converted into electric resistance change, with respect to either applied normal stress or shear stress. The four micro-cantilever beams are allocated in the fashion such that any adjacent beams are perpendicular to each other to decouple any potential measurement discrepancy due to non-ideal orthogonality. In addition, the micro-cantilever beams are curled beforehand so that they can concurrently detect normal stress and shear stress. To be protected from being damaged by strong stress, the curled cantilever beams are embedded by elastomer material. Therefore, the micro-tactile sensor can detect normal stress up to 250 kPa and shear stress up to 35 kPa. Besides, since the elastomer is made of PDMS, which is of high bio-compatibility, the tactile sensor can be used to directly contact with human body. By taking the design and fabrication parameters into account, the curled micro-cantilever beams, which are composed by four layers: polymer/Pt/Ti/Si, can be produced with high yield rate. Finally, the efficacy of the tactile sensor is verified by experiments via a micro-manipulator, a high-resolution microscope and a force sensor for calibration.

A micro-tactile sensor for in situ tissue characterization in minimally invasive surgery

This study presents and characterizes a micro-tactile sensor that can be integrated within MIS graspers. The sensor is capable of measuring contact forces and characterizing softness. The grasping forces are distributed normally, though in some cases concentrated loads also appear at the contact surfaces. In the latter case, the position of the concentric load can also be determined. This enables the sensor to detect hidden anatomical features such as embedded lumps or arteries. The microfabricated piezoelectric-based sensor was modeled both analytically and numerically. In a parametric study the influence of parameters such as length, width, and thickness of the sensor was studied using a finite element model. The sensor was microfabricated and tested using elastomeric samples. There is a good conformity between the experimental and theoretical results.

Elasticity Measurement of Zona Pellucida Using a Micro Tactile Sensor to Evaluate Embryo Quality

To enable improved success rates of IVF, we developed the technology to optimize embryo selection with the highest implantation potential while ensuring no damage to embryos using zona elasticity as the selection criterion. In this communication we outline the biomechanics and safety of zona pellucida (ZP) elasticity measurement using the micro tactile sensor (MTS) system and demonstrate the specific changes in ZP elasticity during oocyte maturation, fertilization, and early embryo development. Zona hardening was demonstrated mechanically following fertilization at the pronuclear (PN) stage, and Young's modulus decreased gradually as the embryo developed. Evaluation of the quality of expanded blastocysts (EPB) showed that the quality of EPBs could also be evaluated from elasticity parameters. Furthermore, the observations indicated that ZPs of embryos generated in vivo were significantly harder than those of embryos generated in vitro at each stage. Preliminary results also indicated that denuded oocytes matured in vitro did not show zona hardening following parthenogenetic activation by strontium chloride, suggesting that sufficient maturation and consequent oocyte activation may be evaluated by increases in ZP elasticity. We conclude that MTS-elective single embryo transfer can be applied to human assisted reproductive technology to enable embryo quality evaluation in both early embryos and EPBs.

Reliable ovum evaluation system by engineering technology, micro tactile sensor (MTS) system for elective single embryo transfer (ESET) on human ART

Elective single embryo transfer is the best way to reduce the risk of multiple pregnancy in IVF. Quantitative criteria with precision mechanical sensing are required for further reliable diagnosis. We tried to develop reliable ovum evaluation system by engineering technology (Murayama et al, Human Cell 2006;19:119–125).

Mouse zona pellucida dynamically changes its elasticity during oocyte maturation, fertilization and early embryo development

A change in the elasticity of mouse zona pellucida was quantitatively evaluated during oocyte maturation, fertilization and early embryo development. Young's modulus of zona pellucida of germinal vesicle (GV), metaphase-II (MII), pronuclear (PN), 2cell, 4cell, 8cell, morulae (M) and early blastocyst (EB) stages was measured using a micro tactile sensor (MTS) and a chamber exclusively designed for the measurement. The MTS has very high sensitivity and a deformation of only 5 microm was sufficient to calculate the Young's modulus and the oocyte/embryo maintained its original spherical shape during the measurement. The Young's modulus of GV, MII, PN, 2cell, 4cell, 8cell, M and EB was 22.8+/-10.4 kPa (n=30), 8.26+/-5.22 kPa (n=74), 22.3+/-10.5 kPa (n=66), 13.8+/-3.54 kPa (n=41), 12.6+/-3.34 kPa (n=19), 5.97+/-4.97 kPa (n=6), 1.88+/-1.34 kPa (n=8) and 3.39+/-1.86 kPa (n=4), respectively. Experimental results clearly demonstrated that the mouse zona pellucida hardened following fertilization. Interestingly, once the zona pellucida hardened at the PN stage, it gradually softened as the embryo developed (i.e. it was found that the zona hardening is a transient phenomenon). Furthermore, the zona pellucida of the GV oocyte was as hard as that of the PN embryo and became soft as it matured to the MII stage. In addition, the safety of the MTS measurement for oocytes and embryos was discussed both theoretically and experimentally.

Considerations in the design and sensitivity optimization of the micro tactile sensor

Although miniaturization has been considered the only technology with which to increase sensitivity of tactile sensors, we recently developed the micro tactile sensor (MTS) that performs with high sensitivity without microfabrication. In this study, we examined design and sensitivity optimization of the MTS using theory based upon Mason's equivalent circuit. The touch probe, which is attached to the lead zirconate titanate (PZT) element, was expressed as a purely inductive circuit component. Resonance frequency was calculated as a function of the length of the touch probe, and sensitivity was predicted to be dependent on the length. Furthermore, many kinds of MTS were fabricated with different touch probe lengths, and actual sensitivity was measured as phase shift between nonloaded and loaded conditions. And, from the consideration of theory and experimental data, a sensitivity coefficient was proposed and found to be useful.

Development of Tactile Mapping system for the stiffness characterization of tissue slice using novel tactile sensing technology

In this study, we modified our previously developed Micro-Tactile Sensor (MTS) not only to measure elasticity with high sensitivity but also to detect the instant of contact. First, modal analysis of the MTS was undertaken using finite element analysis to find a frequency where longitudinal and rotational vibration modes exist. Second, the MTS oscillated using these two types of vibration, and its basic performance was assessed. While the resonance mode of major longitudinal vibration shifted in an indentation and elasticity dependent manner, a disappearance of the rotational vibration upon contact resulted in abrupt change in resonance frequency which was used to signal touch detection. Last, using the modified MTS, we developed Tactile Mapping technology and used it to obtain a contour image and topographical Young's modulus information for a slice of porcine heart with coronary artery.

Fabrication of micro tactile sensor for the measurement of micro-scale local elasticity

Abstract In the recent past, atomic force microscopy (AFM) has been successfully applied to local elasticity measurement especially in biological fields. However, inevitable use of a cantilever results in difficulties in measurements and in sample preparation. Furthermore, the high cost of AFM systems prevents their widespread industrial and clinical use. In this paper, characteristics of local elasticity are evaluated by a new type of micro tactile sensor (MTS) developed with inexpensive and simple technology. MTS technology is based on simple ultrasonic contact sensing, and its high sensitivity is appropriate for micro-scale measurement. The sensor consists of a piezoelectric transducer and a needle-shaped 10-μm transduction point made with a glass needle. High stability and resolution are accomplished by applying a novel phase shift method. Young’s modulus of objects can be derived by analyzing the change in resonance frequency of the system. Using silicone samples with different degrees of Young’s modulus, a calibration equation for the MTS was calculated. Results show that with this novel MTS technology, micro-scale local elasticity measurement can be made without using conventional cantilever probes.

Micro-mechanical sensing platform for the characterization of the elastic properties of the ovum via uniaxial measurement

Stiffness is an important parameter in determining the physical properties of living tissue. Recently, considerable biomedical attention has centered on the mechanical properties of living tissues at the single cell level. In the present paper, the Young’s modulus of zona pellucida of bovine ovum was calculated using Micro Tactile Sensor (MTS) fabricated using piezoelectric (PZT) material. The sensor consists of a needle-shaped 20-μm transduction point made using a micro-electrode puller and mounted on a micro-manipulator platform. Measurements were made under microscopic control, using a suction pipette to support the ovum in the same horizontal axis as the MTS. Young’s modulus of ovum was found to be 25.3±7.94 kPa ( n=28). This value was indirectly determined based on calibration curves relating change in resonance frequency (Δ f 0) of the sensor with tip displacement for gelatin at concentrations of 4%, 6%, and 8%. The regression equation between the rate of change in resonance frequency (versus sensor tip displacement), Δ f 0/ x and Young’s modulus is Δ f 0/ x (Hz/μm)=0.2992×Young’s modulus (kPa)−1.0363. It is concluded that a reason that the stiffness of ovum measured in the present study is approximately six times larger than previously reported, may be due to the absence of large deformation present in of existing methodologies.

912 マイクロスケールタクタイルマッピング法の開発

In the recent past, atomic force microscopy (AFM) has been successfully applied to local elasticity measurement especially in the biological fields. However, inevitable use of cantilever results in difficulties in measurements and in sample preparing. Furthermore, the high cost of AFM systems prevents their widespread use. In this paper, characteristics of local elasticity are evaluated by Micro Tactile Sensor (MTS) developed with inexpensive and simple technology. MTS technology is based on simple ultrasonic contact sensing, and its high sensitivity is appropriate for micro scale measurement. High stability and resolution are accomplished by applying a novel phase shift method. Using this new MTS technology, Tactile Mapping of the slice preparation of prostate cancer (PC3) was performed.