Polyvinylidene fluoride - based MEMS tactile sensor for minimally invasive surgery

Minimally invasive surgery (MIS) procedures have been growing rapidly for the past couple of decades. In MIS operations, endoscopic tools are inserted through a small incision on human's body. Although these procedures have many advantages such as fast recovery time, minimum damage to human body and reduced post operative complications, it does not provide any tactile feedback to the surgeon. This thesis reports on design, finite element analysis, fabrication and testing of a micromachined piezoelectric endoscopic tactile sensor. Similar to the commercial endoscopic graspers, the sensor is teeth like in order to grasp slippery tissues. It consists of three layers; the first layer is a silicon layer of teeth shapes on the top and two supports at the bottom forming a thin plate and a U-Channel. The second layer is a patterned Polyvinylidene Fluoride (PVDF) film, and the third layer is a supporting Plexiglas. The patterned PVDF film was placed on the middle between the other two layers. When a concentric load is applied to the sensor, the magnitude and the position of the applied load are obtained from the outputs of the sensing elements which are sandwiched between the silicon supports and the Plexiglas. In addition, when a soft object/tissue is place on the sensor and load is applied the degree of the softness/compliance of the object is obtained from the outputs from the middle PVDF sensing elements, which are glued to the back of the thin silicon plate. The outputs are related to the deformation of the silicon plate which related to the contacting object softness. The sensor has high sensitivity and high dynamic range as a result it can potentially detect a small dynamic load such as a pulse load as well as a high load such as a firm grasping of a tissue by an endoscopic grasper. The entire surface of the tactile sensor is also active, which is an advantage in detecting the precise position of the applied point load on the grasper. The finite element analysis and experimental results are in close agreement with each other. The sensor can potentially be integrated with the gasper of a commercially available endoscopic graspe

Tactile Sensing System for Lung Tumour Localization during Minimally Invasive Surgery

Video-assisted thoracoscopie surgery (VATS) is becoming a prevalent method for lung cancer treatment. However, VATS suffers from the inability to accurately relay haptic information to the surgeon, often making tumour localization difficult. This limitation was addressed by the design of a tactile sensing system (TSS) consisting of a probe with a tactile sensor and interfacing visualization software. In this thesis, TSS performance was tested to determine the feasibility of implementing the system in VATS. This was accomplished through a series of ex vivo experiments in which the tactile sensor was calibrated and the visualization software was modified to provide haptic information visually to the user, and TSS performance was compared using human and robot palpation methods, and conventional VATS instruments. It was concluded that the device offers the possibility of providing to the surgeon the haptic information lost during surgery, thereby mitigating one of the current limitations of VATS

Force Sensing Surgical Grasper with Folding Capacitive Sensor

Minimally-invasive surgery (MIS) has brought many benefits to the operating room, however, MIS procedures result in an absence of force feedback, and surgeons cannot as accurately feel the tissue they are working on, or the forces that they are applying. One of the barriers to introducing MIS instruments with force feedback systems is the high cost of manufacturing and assembly. Instruments must also be sterilized before every use, a process that can destroy embedded sensing systems. An instrument that can be disposed of after a single use and produced in bulk at a low cost is desirable. Printed circuit micro-electro-mechanical systems (PCMEMS) is an emerging manufacturing technology that may represent an economically viable method of bulk manufacturing small, single-use medical devices, including surgical graspers. This thesis presents the design and realization of a PCMEMS surgical grasper that can fit within a 5 mm trocar, and can accurately measure forces in 3 axes, over a range of +/-4 N. The designed instrument is the first PCMEMS grasper to feature multi-axis sensing, and has a sensing range twice as large as current PCMEMS devices. Experimental results suggest that the performance of the sensing system is similar to conventionally-manufactured MIS instruments that use capacitive force transducers. The techniques applied in this thesis may be useful for developing a range of PCMEMS devices with capacitive sensors. Improvements to the design of the grasper and sensing system are suggested, and several points are presented to inform the direction of future work related to PCMEMS MIS instruments

Design and development of new tactile softness displays for minimally invasive surgery

Despite an influential shortcoming of minimally invasive sugary (MIS), which is the lack of tactile feedback to the surgeon, MIS has increasingly been used in various types of surgeries. Restoring the missing tactile feedback, especially information which can be obtained by the palpation of tissue, such as detection of embedded lump and softness characterization is important in MIS. The present study aims to develop tactile feedback systems both graphically and physically. In graphical rendering approach, the proposed system receives signals from the previously fabricated piezoelectric softness sensors which are integrated with an MIS grasper. After processing the signals, the tactile information is displayed by means of a color coding method. Using the graphical images, the softness of the grasped objects can visually be differentiated. A physical tactile display system is also designed and fabricated. This system simulates non-linear material properties of different soft objects. The system consists of a linear actuator, force and position sensors and processing software. A PID controller is used to control the motion of a linear actuator according to the properties of the simulated material and applied force. Graphical method was also examined to render the tactile information of embedded lumps within a soft tissue/object. The necessary information on the size and location of the hidden features are collected using sensorized MIS graspers. The information is then processed and graphically rendered to the surgeon. Using the proposed system surgeons can identify presence, location and approximate size of hidden lumps by grasping the target object with a reasonable accuracy. Finally, in order to determine the softness of the grasped object, another novel approach is taken by the design and fabrication of a smart endoscopic tool equipped with sensors for measuring the applied force and the angle of the grasper jaws. Using this method, the softness/compliance of the grasped object can be estimated and presented to the surgeo

Optical Microsystems for Static and Dynamic Tactile Sensing: Design, Modeling, Fabrication and Testing

Minimally invasive surgical operations encompass various surgical tasks ranging from conventional endoscopic/laparoscopic methods to recent sophisticated minimally invasive surgical techniques. In such sophisticated techniques, surgeons use equipment varying from robotic-assisted surgical platforms for abdominal surgery to computer-controlled catheters for catheter-based cardiovascular surgery. Presently, the countless advantages that minimally invasive surgery offers for both patients and surgeons have made the use of such surgical operations routine and reliable. However, in such operations, unlike conventional surgical operations, surgeons still suffer from the lack of tactile perception while interacting with the biological tissues using surgical instruments. To address this issue, it is necessary to develop a tactile sensor that can mimic the fingertip tactile perceptions of surgeons. In doing so and to satisfy the needs of surgeons, a number of considerations should be implemented in the design of the tactile sensors. First, the sensor should be magnetic resonance compatible to perform measurements even in the presence of magnetic resonance imaging (MRI) devices. Currently, such devices are in wide-spread use in surgical operation rooms. Second, the sensor should be electrically-passive because introducing electrical current into the patients’ body is not desirable in various surgical operations such as cardiovascular operations. Third, the sensor should perform measurements under both static and dynamic loading conditions during the sensor-tissue interactions. Such a capability of the sensor ensures that surgeons receive tactile feedback even when there is continuous static contact between surgical tools and tissues. Essentially, surgeons need such feedback to make surgical tasks safer. In addition, the size of the sensor should be miniaturized to address the size restrictions. In fact, the combination of intensity-based optical fiber sensing principles and micro-systems technology is one of the limited choices that address all the required considerations to develop such tactile sensors in a variety of ways. The present thesis deals with the design, modeling, manufacturing, testing, and characterizing of different tactile sensor configurations based on detection and integration methods. The various stages of design progress and principles are developed into different design configurations and presented in different chapters. The main sensing principle applied is based on the intensity modulation principle of optical fibers using micro-systems technology. In addition, a hybrid sensing principle is also studied by integrating both optical and non-optical detection methods. The micromachined sensors are categorized into five different generations. Each generation has advantages by comparison with its counterpart from the previous generation. The initial development of micromachined sensors is based on optical fiber coupling loss. In the second phase, a hybrid optical-piezoresistive sensing principle is studied. The success of these phases was instrumental in realizing a micromachined sensor that has the advantage of being fully optical. This sensor measures the magnitude of concentrated and distributed force, the position of a concentrated force, the variations in the force distribution along its length, the relative hardness of soft contact objects, and the local discontinuities in the hardness of the contact objects along the length of the contact area. Unlike most electrical-based commercially-available sensors, it performs all of these measurements under both static and dynamic loading conditions. Moreover, it is electrically passive and potentially MRI-compatible. The performances of the sensors were experimentally characterized for specific conditions presented in this thesis. However, these performances are easily tunable and adjustable depending upon the requirements of specific surgical tasks. Although the sensors were initially designed for surgical applications, they can have numerous other applications in the areas of robotics, automation, tele-display, and material testing

A FEEDBACK-BASED DYNAMIC INSTRUMENT FOR MEASURING THE MECHANICAL PROPERTIES OF SOFT TISSUES

In this paper, a novel feedback-based dynamic instrument integrated into a Minimally- Invasive-Surgery (MIS) tool to evaluate the mechanical impedance of soft tissues is presented. This instrument is capable of measuring viscoelasticity of tissues if specific boundary conditions are known. Some important advantages of the proposed instrument are that it is robust and simple in comparison to other similar instruments as it does not require magnitude information of plant’s displacement output and no force sensor is used. The precision and accuracy of the measurements of the proposed instrument for soft tissues is noticeably higher than similar instruments, which are not optimized to work with soft tissues. The proposed dynamic instrument is designed to detect the frequency shifts caused by contacting a soft tissue using an improved phase-locked loop feedback system (closed loop). These frequency shifts can then be used to evaluate the mechanical properties of the tissue. The closed-loop method works fast (with an approximate resonance-frequency-shift rate of 15 Hz per second), and is capable of measuring dy­ namic mechanical properties of viscoelastic tissues, while previous focus was mostly on static/quasi-static elastic modulus. The instrument is used to evaluate the equivalent stiffness of several springs and cantilever beams, mass of reference samples, and also the frequency shifts of several phantoms with injected tumors, noting that these frequency shifts can be used to measure the viscoelasticity of the tissues. It is also shown that the instrument can be used for tumor localization in these phantoms

Experimental and theoretical analysis of a novel flexible membrane tactile sensor

In this study, we report the development of a new multi tactile sensor, capable of detecting 2D surface texture image, measuring contact-force, and identifying the difference between stiffness of sensed objects. The designed tactile sensor consists of a chamber and a membrane with a mesa structure. The detecting principle is a combination of membrane deflection and piezoresistante effects. A major advantage of the designed system is that it can be easily miniaturized and micromachined. As a result, it is suitable for using in medical applications, especially in minimally invasive surgery (MIS). © 2008 Science Publications

OPTICAL-BASED TACTILE SENSORS FOR MINIMALLY INVASIVE SURGERIES: DESIGN, MODELING, FABRICATION AND VALIDATION

Loss of tactile perception is the most challenging limitation of state-of-the-art technology for minimally invasive surgery. In conventional open surgery, surgeons rely on their tactile sensation to perceive the tissue type, anatomical landmarks, and instrument-tissue interaction in the patient’s body. To compensate for the loss of tactile feedback in minimally invasive surgery, researchers have proposed various tactile sensors based on electrical and optical sensing principles. Optical-based sensors have shown the most compatibility with the functional and physical requirements of minimally invasive surgery applications. However, the proposed tactile sensors in the literature are typically bulky, expensive, cumbersome to integrate with surgical instruments and show nonlinearity in interaction with biological tissues. In this doctoral study, different optical tactile sensing principles were proposed, modeled, validated and various tactile sensors were fabricated, and experimentally studied to address the limitations of the state-of-the-art. The present thesis first provides a critical review of the proposed tactile sensors in the literature with a comparison of their advantages and limitations for surgical applications. Afterward, it compiles the results of the design, modeling, and validation of a hybrid optical-piezoresistive sensor, a distributed Bragg reflecting sensor, and two sensors based on the variable bending radius light intensity modulation principle. The performance of each sensor was verified experimentally for the required criteria of accuracy, resolution, range, repeatability, and hysteresis. Also, a novel image-based intensity estimation technique was proposed and its applicability for being used in surgical applications was verified experimentally. In the end, concluding remarks and recommendations for future studies are provided

Design, Modeling, Fabrication and Testing of a Piezoresistive-Based Tactile Sensor for Minimally Invasive Surgery Applications

Minimally invasive surgery (MIS) has become a preferred method for surgeons for the last two decades, thanks to its crucial advantages over classical open surgeries. Although MIS has some advantages, it has a few drawbacks. Since MIS technology includes performing surgery through small incisions using long slender tools, one of the main drawbacks of MIS becomes the loss of direct contact with the patient’s body in the site of operation. Therefore, the surgeon loses the sense of touch during the operation which is one of the important tools for safe manipulation of tissue and also to determine the hardness of contact tissue in order to investigate its health condition. This Thesis presents a novel piezoresistive-based multifunctional tactile sensor that is able to measure the contact force and the relative hardness of the contact object or tissue at the same time. A prototype of the designed sensor has been simulated, analyzed, fabricated, and tested both numerically and experimentally. The experiments have been performed on hyperelastic materials, which are silicone rubber samples with different hardness values that resemble different biological tissues. The ability of the sensor to measure the contact force and relative hardness of the contact objects is tested with several experiments. A finite element (FE) model has been built in COMSOL Multiphysics (v3.4) environment to simulate both the mechanical behavior of the silicone rubber samples, and the interaction between the sensor and the silicone rubbers. Both numerical and experimental analysis proved the capability of the sensor to measure the applied force and distinguish among different silicone-rubber samples. The sensor has the potential for integration with commercially available endoscopic grasper