A New Tissue Resonator Indenter Device and Reliability Study

Knowledge of tissue mechanical properties is widely required by medical applications, such as disease diagnostics, surgery operation, simulation, planning, and training. A new portable device, called Tissue Resonator Indenter Device (TRID), has been developed for measurement of regional viscoelastic properties of soft tissues at the Bio-instrument and Biomechanics Lab of the University of Toronto. As a device for soft tissue properties in-vivo measurements, the reliability of TRID is crucial. This paper presents TRID’s working principle and the experimental study of TRID’s reliability with respect to inter-reliability, intra-reliability, and the indenter misalignment effect as well

An applied investigation of viscosity–density fluid sensors based on torsional resonators

Real-time viscosity and density measurements give insight into the status of many chemical and biochemical processes and allow for automated controls. In many applications, sensors that enable the real-time measurements of fluid properties use resonant elements. Such sensors measure induced changes in the element’s resonance frequency and damping that can be related to the fluid properties. These sensors have been widely researched, though they are not yet commonly used in industrial processes. This study investigates two resonant elements to measure the viscosity and density of Newtonian fluids. The first is a probe-style viscosity-density sensor, and the second is a non-intrusive tubular viscosity sensor. These two sensors were investigated using analytical, numerical, and experimental methods. In the analytical method, the sensors’ resonance frequencies and bandwidths were predicted based on reduced-order models for both structure and fluid. In the numerical method, the interaction of the resonant element with the fluid was investigated by means of computational fluid dynamics (CFD). Experiments were conducted for validation, to evaluate the sensors’ capabilities, and understand cross-sensitivity effects between viscosity and density. This work successfully modeled and validated the two different torsional resonant element sensors, namely the probe-style viscosity-density sensor and the tubular viscosity sensor against experiments. There are two key output parameters, i.e., resonance frequency and bandwidth. Using these parameters, it is possible to predict fluid viscosity and density. Overall, this work demonstrates the potential of numerical modeling for the development of torsional resonance sensors. These findings directly affect the development of the future generation of fluid viscosity and density sensors

On the Application of Mechanical Vibration in Robotics-Assisted Soft Tissue Intervention

Mechanical vibration as a way of transmitting energy has been an interesting subject to study. While cyclic oscillation is usually associated with fatigue effect, and hence a detrimental factor in failure of structures and machineries, by controlled transmission of vibration, energy can be transferred from the source to the target. In this thesis, the application of such mechanical vibration in a few surgical procedures is demonstrated. Three challenges associated with lung cancer diagnosis and treatment are chosen for this purpose, namely, Motion Compensation, tumor targeting in lung Needle Insertion and Soft Tissue Dissection: A robotic solution is proposed for compensating for the undesirable oscillatory motion of soft tissue (caused by heart beat and respiration) during needle insertion in the lung. An impedance control strategy based on a mechanical vibratory system is implemented to minimize the tissue deformation during needle insertion. A prototype was built to evaluate the proposed approach using: 1) two Mitsubishi PA10-7C robots, one for manipulating the macro part and the other for mimicking the tissue motion, 2) one motorized linear stage to handle the micro part, and 3) a Phantom Omni haptic device for remote manipulation. Experimental results are given to demonstrate the performance of the motion compensation system. A vibration-assisted needle insertion technique has been proposed in order to reduce needle–tissue friction. The LuGre friction model is employed as a basis for the study and the model is extended and analyzed to include the impact of high-frequency vibration on translational friction. Experiments are conducted to evaluate the role of insertion speed as well as vibration frequency on frictional effects. In the experiments conducted, an 18 GA brachytherapy needle was vibrated and inserted into an ex-vivo soft tissue sample using a pair of amplified piezoelectric actuators. Analysis demonstrates that the translational friction can be reduced by introducing a vibratory low-amplitude motion onto a regular insertion profile, which is usually performed at a constant rate. A robotics-assisted articulating ultrasonic surgical scalpel for minimally invasive soft tissue cutting and coagulation is designed and developed. For this purpose, the optimal design of a Langevin transducer with stepped horn profile is presented for internal-body applications. The modeling, optimization and design of the ultrasonic scalpel are performed through equivalent circuit theory and verified by finite element analysis. Moreover, a novel surgical wrist, compatible with the da Vinci® surgical system, with decoupled two degrees-of-freedom (DOFs) is developed that eliminates the strain of pulling cables and electrical wires. The developed instrument is then driven using the dVRK (da Vinci® research kit) and the Classic da Vinci® surgical system

Development of high-Q micromechanical cell mass sensor (optimizing parameters for in-plane mass sensors)

There exists a strong correlation between the behavior of a cell, its physical properties, and its surrounding environment. Biomechanics has led to an improved understanding of the way diseases evolve and their progression cycle, providing methods targeted towards curing these diseases. Moreover, many studies have been carried out on the progression that occur to cell biophysics. More particularly, these studies on the mechanics of individual cells have pointed to their coordination and cycle, which helps us understand cellular metabolic and physiological process better. Development of more precise, versatile and reliable measurement tools and techniques will provide a greater understanding of cellular behavior and biophysical properties. Micromechanical systems (MEMS) technology can provide these tools – for analyzing single cells and give important and useful information about their biophysical properties. In modern research, the ability to reliably investigate and understand these cellular properties requires measurement devices that provide high sensitivity, high throughput, and adaptability to include multiple on-chip functionalities. Many MEMS-based resonant sensors have been extensively studied and used as biological and chemical sensors. However, previous works have shown that there are several technology limitations that inhibit application of various mass sensors to mass measurement and analysis, including insufficient cell capture efficiency, media perfusion for long term growth, cell adhesion and cell movement/spreading. The primary objective of this work is to theoretically characterize and compare the characteristics of resonant sensors vibrating in-plane (lateral mode) and out-of-plane (transversal) and note the improvement when the microcantilever is excited in the in-plane direction. Our current out-of-plane resonant sensor while more effective than regular micro cantilevers, are less efficient as a sensing platform due to an additional liquid resistance exerted by the surrounding liquid. This work highlights the design of a relatively high-Q (quality factor) laterally vibrating mass sensor. It includes a review of other sensor geometries iteratively considered. A theoretical analysis and modelling of our optimal in-plane mass sensors are carried out

Development of novel dynamic indentation techniques for soft tissue applications

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2007.Includes bibliographical references (leaves 141-149).Realistic material models to simulate the behavior of brain tissue at large deformations and high strain rates are necessary when designing equipment to protect against ballistic impacts. Acquiring experimental data for brain tissue response is critical to developing appropriate models. Current in vivo and in situ procedures for testing the material behavior of soft tissues are dominated by indentation techniques. The major challenge for this testing configuration is in finding a unique solution to the "inverse problem" i.e., obtaining material properties that are uniquely defined by the indentation force-displacement response. Much of the information related to the interplay between shear and bulk compliance in the deformation field beneath the indenter is lost when capturing the single force-displacement output. To address this challenge, we propose a material testing technique that follows the well- proven path of conventional indentation methods, but also enriches the signal by acquiring displacement data for an offset, passive surface tracking sensor. We present the results of a finite element (FE) study to demonstrate that the addition of a secondary sensor can help to discern between materials with varying degrees of compressibility. To this end, a large displacement in vivo dynamic indentation surface tracking (DIST) tool was designed and manufactured. This tool incorporates the secondary sensor concept to measure the force-displacement response of brain tissue at strain rates up to 1000%/s. The technique is applied in vitro to measure the response of porcine brain tissue. To select an appropriate constitutive framework for porcine brain tissue in vitro, uniaxial compression tests measuring the corresponding lateral stretch response are performed.(cont.) A three-dimensional large deformation constitutive model for brain tissue is developed. The model accounts for the observed features of the material response including non-linearity, conditioning, hysteresis, and strain-rate dependence. The model is incorporated into an FE simulation of the brain indentation tests performed with the DIST tool. The effectiveness of the DIST as a material-testing tool is assessed.by Asha Balakrishnan.Ph.D

Nanoscale mechanical and electrical properties of low-dimensional structures

In this thesis, we mainly study the mechanical, electrical and electromechanical properties of low-dimensional structures of advanced materials, in particular two-dimensional (2D) materials and compound semiconductor (CS) structures and devices. Given the scarcity of methods for direct nano-mapping of physical properties of complex three-dimensional (3D) multilayer CS and 2D materials heterostructures, we adapted and developed suitable optical methods and functional scanning probe microscopies (SPM) approaches based in atomic force microscopy (AFM). These allowed us to successfully investigate the behaviour of one- and two dimensional (1D and 2D) free oscillating structures, such as AFM cantilevers, tuning forks (TF), Si3N4 membranes and graphene drums using the optical laser Doppler vibrometry (LDV) and dynamic AFM modes, finding governing relations of the dynamic behaviour in real-life systems and comparing these with modelling. In addition to the existing ultrasonic SPM, such as force modulation and ultrasonic force microscopy (FMM and UFM), we developed a new method called modulation ultrasonic force microscopy (M-UFM), which allows for nonlinear local excitation and the probing of membrane vibrations. Furthermore, we probe mechanical, electrical and thermal properties of supported layers and heterostructures of diverse transition metal dichalcogenides (TMDCs) and franckeite, understanding their intrinsic surface and subsurface nanostructure. In the final part of this thesis, we explored the feasibility of combining nano-sectioning via Beam Exit Cross-sectional Polishing (BEXP) and the material sensitive SPM analysis for the investigation of defects in CS structures, such as multiple quantum wells (MQW) and nanowires (NWs), and 2D material heterostructures. We applied this methodology to investigate the propagation of material defects, such as antiphase domains in CS, and their effects on the morphology, nanomechanics and electric properties in MQW structures, and to directly observe reverse piezoelectric domains inside individual GaN NWs