Sadao Omata

New tactile sensor like the human hand and its applications

Abstract This paper describes the development of a new type of tactile sensor which is designed to operate with a piezoelectric element employed as the sensor. Conventional tactile sensors, which consist of a strain gauge, conductive elastomer and piezoelectric polymer film, are confined solely to data acquisition relating to pressure or force. However, the new sensor proposed here is able to detect, very much like the human hand, the hardness and/or softness of an object. Several experiments have been carried out to investigate its possible applications in robotics and medicine. It is demonstrated that the visualization of tactile sensory performance using the new sensor is most useful in a robotics application; the sensor is also able to detect the hardness of an extraneous substance and that of skin.

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 Youngs 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-microm 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. Youngs 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 (Deltaf(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), Deltaf(0)/x and Youngs modulus is Deltaf(0)/x (Hz/microm)=0.2992 x Youngs 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.

Objective evaluation of Liver consistency to estimate hepatic fibrosis and functional reserve for hepatectomy

BACKGROUND The empiric evaluation of liver consistency is currently used to plan the surgical strategy. The aim of this study was to verify the feasibility of the objective measurement of liver consistency and to check its correlation with liver fibrosis and liver functional reserve. STUDY DESIGN Fifty-two consecutive patients who underwent hepatic resections in our department were enrolled. The indications for liver resection were hepatocellular carcinoma in 36 patients, metastatic liver tumors in 12 patients, and other conditions in 4 patients. Liver consistency was measured with a new tactile sensor. A fibrosis index was calculated as an expression of the percentage of fibrotic tissue. Liver consistency was compared with the degree of liver fibrosis observed in histologic specimens (fibrosis index) and with liver function parameters. RESULTS Liver stiffness showed a significant positive correlation with fibrosis index (r = 0.887, p < 0.0001). Liver stiffness also showed significant positive correlation with the indocyanine green test (r = 0.631, p < 0.0001) by a univariate analysis. The indocyanine green test and platelet count were independently and significantly associated with liver stiffness by a multiple regression analysis. In five patients, the liver stiffness values measured intraoperatively differed markedly from those expected from the indocyanine green test values. In these patients, the operative procedures were finally selected based on the liver stiffness measured with the tactile sensor and good clinical outcomes were obtained. CONCLUSIONS These results show for the first time that liver stiffness can be clinically assessed quantitatively by means of the tactile sensor. The tactile sensor adequately estimates liver stiffness and this estimation is well correlated with liver fibrosis and functional reserve. Liver consistency determined objectively in this manner may be useful for optimizing surgical decision making.

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 μm 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.

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(0) when tissue is compressed, whereas the tactile sensor evaluates the hardness/softness or change in resonance frequency Δf when a vibrating rod is attached to tissue. Both techniques can detect changes in silicone hardness/softness or in hormone-induced changes of testes, interstitial fluid. Although both F(0) and FT are significantly correlated to Δf in the experiments, it is concluded that F(0) is the most promising impression parameter to give valuable information about the hardness of living tissue as compared with Δf. The comparison indicates that the impression technique in the most easy, to interpret, non-invasive tool to assess tissue oedema so far developed.

Tactile resonance sensors in medicine.

Tactile sensors in general are used for measuring the physical parameters associated with contact between sensor and object. Tactile resonance sensors in particular are based on the principle of measuring the frequency shift, Δf, defined as the difference between a freely vibrating sensor resonance frequency and the resonance frequency measured when the sensor makes contact to an object. Δf is therefore related to the acoustic impedance of the object and can be used to characterize its material properties. In medicine, tactile resonance sensor systems have been developed for the detection of cancer, human ovum fertility, eye pressure and oedema. In 1992 a Japanese research group published a paper presenting a unique phase shift circuit to facilitate resonance measurements. In this review we summarize the current state-of-the-art of tactile resonance sensors in medicine based on the phase shift circuit and discuss the relevance of the measured parameters for clinical diagnosis. Future trends and applications enabled by this technology are also predicted.

Local elasticity imaging of vascular tissues using a tactile mapping system

This study aimed to map the elasticity of a natural artery at the micron level by using a tactile mapping system (TMS) that was recently developed for characterization of the stiffness of tissue slices. The sample used was a circumferential section (thickness, approximately 1 mm) of a small-caliber porcine artery (diameter, approximately 3 mm). Elasticity was measured with a probe of diameter 1 μm and a spatial resolution of 2 μm at a rate of 0.3 s per point, without significant sample invasion. Topographical measurements were also performed simultaneously. Wavy regions of high elasticity, layered in the circumferential direction, were measured at the tunica media, which was identified as an elastin-rich region. The Young’s modulus of the elastin-rich region in the media was 50.8 ± 13.8 kPa, and that of the elastin-rich region of the lamina elastica interna was 69.0 ± 12.8 kPa. Both these values were higher than the Young’s modulus of the other regions in the media, including smooth muscle cells and collagen fibrils (17.0 ± 9.0 kPa). TMS is simple and inexpensive to perform and allows observation of the distribution of the surface elastic modulus at the extracellular matrix level in vascular tissue. TMS is expected to be a powerful tool in evaluation of the maturation and degree of reconstruction in the development of tissue-engineered or artificial tissues and organs.

Influence of Pelvic Floor Muscle Contraction on the Profile of Vaginal Closure Pressure in Continent and Stress Urinary Incontinent Women

PURPOSE We characterized the vaginal pressure profile as a representation of closure forces along the length and circumference of the vaginal wall. Vaginal pressure profile data were used to test the hypothesis that the strength of pelvic floor muscle contractions differs significantly between continent women and women with stress urinary incontinence. MATERIALS AND METHODS Vaginal pressure profile recordings were made in 23 continent subjects and in 10 patients with stress urinary incontinence. The recordings characterized closure forces along the entire length of the vagina and identified differences among the anterior, posterior, left and right sides of the vaginal wall. Using a novel, directionally sensitive vaginal probe we made vaginal pressure profile measurements with the women at rest and during pelvic floor muscle contraction while supine. RESULTS The nature of the vaginal pressure profile was characterized in terms of force distribution in the anterior and posterior vaginal walls, which was significantly greater than that on the left and right sides. The continent group had significant greater maximum pressure than the stress urinary incontinence group on the posterior side at rest (mean +/- SE 3.4 +/- 0.3 vs 2.01 +/- 0.36 N/cm(2)) and during pelvic floor muscle contraction (4.18 +/- 0.26 vs 2.25 +/- 0.41 N/cm(2)). The activity pressure difference between the posterior and anterior vaginal walls in the continent group was significantly increased when the pelvic floor muscles contracted vs that at rest (3.29 +/- 0.21 vs 2.45 +/- 0.26 N/cm(2)). However, the change observed in the stress urinary incontinence group was not significant (1.85 +/- 0.38 vs 1.35 +/- 0.27 N/cm(2)). CONCLUSIONS The results demonstrate that the voluntary pelvic floor muscles impose significant closure forces along the vaginal wall of continent women but not in women with stress urinary incontinence. The implication of these findings is that extrinsic urethral closure pressure is insufficiently augmented by pelvic floor muscle contraction in women with stress urinary incontinence.

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

ABSTRACT 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 Youngs 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.

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 Masons 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.