Development of the Telemetrical Intraoperative Soft Tissue Tension Monitoring System in Total Knee Replacement with MEMS and ASIC Technologies

The alignment of the femoral and tibial components of the Total Knee Arthoplasty (TKA) is one of the most important factors to implant survivorship. Hence, numerous ligament balancing techniques and devices have been developed in order to accurately balance the knee intra-operatively. Spacer block, tensioner and tram adapter are instruments that allow surgeons to qualitatively balance the flexion and extension gaps during TKA. However, even with these instruments, the surgical procedure still relies on the skill and experience of the surgeon. The objective of this thesis is to develop a computerized surgical instrument that can acquire intra-operative data telemetrically for surgeons and engineers. Microcantilever is chosen to be used as the strain sensing elements. Even though many high end off-the-shelf data acquisition components and integrated circuit (IC) chips exist on the market, yet multiple components are required to process the entire array of microcantilevers and achieve the desired functions. Due to the size limitation of the off-chip components, an Application Specific Integrated Circuit (ASIC) chip is designed and fabricated. Using a spacer block as a base, sensors, a data acquisition system as well as the transmitter and antenna are embedded into it. The electronics are sealed with medical grade epoxy

Integrated microcantilever fluid sensor as a blood coagulometer

The work presented concerns the improvement in mechanical to thermal signal of a microcantilever fluid probe for monitoring patient prothrombin time (PT) and international normalized ratio (INR) based on the physical measurement of the clotting cascade. The current device overcomes hydrodynamic damping limitations by providing an internal thermal actuation force and is realised as a disposable sensor using an integrated piezoresistive deflection measurement. Unfortunately, the piezoresistor is sensitive to thermal changes and in the current design the signal is saturated by the thermal actuation. Overcoming this problem is critical for demonstrating a blood coagulometer and in the wider field as a microsensor capable of simultaneously monitoring rheological and thermal measurements of micro-litre samples. Thermal, electrical, and mechanical testing of a new design indicates a significant reduction in the thermal crosstalk and has led to a breakthrough in distinguishing the mechanical signal when operated in moderately viscous fluids (2-3 cP). A clinical evaluation has been conducted at The Royal London Hospital to measure the accuracy and precision of the improved microcantilever fluid probe. The correlation against the standard laboratory analyser INR, from a wide range of patient clotting times(INR 0.9-6.08) is equal to 0.987 (n=87) and precision of the device measured as the percentage coefficient of variation, excluding patient samples tested < 3 times, is equal to 4.00% (n=64). The accuracy and precision is comparable to that of currently available point-of-care PT/INR devices. The response of the fluid probe in glycerol solutions indicates the potential for simultaneous measurement of rheological and thermal properties though further work is required to establish the accuracy and range of the device as a MEMS based viscometer

Nanoelectromechanical Sensors based on Suspended 2D Materials

The unique properties and atomic thickness of two-dimensional (2D) materials enable smaller and better nanoelectromechanical sensors with novel functionalities. During the last decade, many studies have successfully shown the feasibility of using suspended membranes of 2D materials in pressure sensors, microphones, accelerometers, and mass and gas sensors. In this review, we explain the different sensing concepts and give an overview of the relevant material properties, fabrication routes, and device operation principles. Finally, we discuss sensor readout and integration methods and provide comparisons against the state of the art to show both the challenges and promises of 2D material-based nanoelectromechanical sensing.Comment: Review pape

MEMS Piezoresistive Micro-Cantilever Arrays for Sensing Applications

In several application fields there is an increasing need for a diffused on-field control of parameters able to diagnosis potential risks or problems in advance or in early stages in order to reduce their impact. The timely recognition of specific parameters is often the key for a tighter control on production processes, for instance in food industry, or in the development of dangerous events such as pollution or the onset of diseases in humans. Diffused monitoring can be hardly performed with traditional instrumentation in specialised laboratories, due to the time required for sample collection and analysis. In all applications, one of the key-points for a successful solution of the problem is the availability of detectors with high-sensitivity and selectivity to the chemical or biochemical parameters of interest. Moreover, an increased diffused on-field control of parameters can be only achieved by replacing the traditional costly laboratory instrumentations with a larger number of low cost devices. In order to compete with well-known and established solution, one of main feature of new systems is the capability to perform specific tests on the field with fast response times; in this perspective, a fast measurement of reduced number of parameters is to be preferred to a straightforward “clone” of laboratory instrumentation. Moreover, the detector must also provide robustness and reliability for real-world applications, with low costs and easiness of use. In this paradigm, MEMS technologies are emerging as realisation of miniaturised and portable instrumentation for agro-food, biomedical and material science applications with high sensitivity and low cost. In fact, MEMS technologies can allow a reduction of the manufacturing cost of detectors, by taking advantage of the parallel manufacturing of large number of devices at the same time; furthermore, MEMS devices can be potentially expanded to systems with high level of measurement parallelism. Device costs are also a key issues when devices must be for “single use”, which is a must in application where cross-contamination between different measurement is a major cause of system failure and may cause severe consequences, such as in biomedical application. Among different options, cantilever micro-mechanical structures are one of the most promising technical solution for the realisation of MEMS detectors with high sensitivity. This thesis deals with the development of cantilever-based sensor arrays for chemical and biological sensing and material characterisation. In addiction to favourable sensing properties of single devices, an array configuration can be easily implemented with MEMS technologies, allowing the detection of multiple species at the same time, as well as the implementation of reference sensors to reject both physical and chemical interfering signals. In order to provide the capability to operate in the field, solution providing simple system integration and high robustness of readout have been preferred, even at the price of a lower sensitivity with respect to other possibilities requiring more complex setups. In particular, piezoresistive readout has been considered as the best trade-off between sensitivity and system complexity, due to the easy implementation of readout systems for resistive sensors and to their high potential for integration with standard CMOS technologies. The choice has been performed after an analysis of mechanical and sensing properties of microcantilever, also depending of technological options for their realisation. As case-studies for the development of cantilever devices, different approaches have been selected for gas sensing applications, DNA hybridisation sensing and material characterisation, based on two different technologies developed at the BioMEMS research unit of FBK (Fondazione Bruno Kessler - Center for Materials and Microsystems, Trento). The first process, based on wet-etching bulk micromachining techniques, has provided 10 µm-thick silicon microcantilevers while the second technology, based on Silicon-On-Insulator (SOI) wafer, has provided a reduction of device thickness, thus resulting in an increase of sensitivity. Performances of devices has been investigated by analytical and numerical modelling of both structures and readout elements, in order to optimise both fabrication technology and design. In particular, optimal implant parameters for the realisation of piezoresistors have been evaluated with process simulation with Athena Silvaco simulation software, while ANSYS has been used to analyse the best design for devices and the effect of some technology-related issues, such as the effect of underetch during the release of the beams or residual stresses. Static and modal analysis of cantilever bending in different conditions have been performed, in order to evaluate the mechanical performances of the device, and later results have been compared with the experimental characterisation. With regard to gas sensing applications, the development has been oriented to resonant sensors, where the adsorption of analytes on a adsorbent layer deposited on the cantilever leads to shift of resonance frequency of the structure, thus providing a gravimetric detection of analytes. The detection of amines, as markers of fish spoilage during transport, has been selected as a case-study for the analysis of these sensors. The sensitivity of devices has been measured, with results compatible with the models. Cantilever structures are also suitable for bioaffinity-based applications or genomic tests, such as the detection of specific Single Nucleotide Polymorphisms (SNPs) that can be used to analyse the predisposition of individuals to genetic-based diseases. In this case, measurements are usually performed in liquid phase, where viscous damping of structures results in a severe reduction of resonance quality factor, which is a key-parameter for the device detection limit. Then, cantilever working in “bending mode” are usually preferred for these applications. In this thesis, the design and technologies have been optimised for this approach, which has different requirements with respect to resonant detectors. In fact, the interaction of target analytes with properly functionalised surfaces results in a bending of the cantilever device, which is usually explained by a number of mechanism ranging from electrostatic and steric interaction of molecules to energy-based considerations. In the case of DNA hybridisation detection, the complexity of the molecule interactions and solid-liquid interfaces leads to a number of different phenomena concurring in the overall response. Main parameters involved in the cantilever bending during DNA hybridisation has been studied on the basis of physical explanations available in the literature, in order to identify the key issues for an efficient detection. Microcantilever devices can play a role also in thin film technologies, where residual stresses and material properties in general need to be accurately measured. Since cantilever sensors are highly sensitive to stress, their use is straightforward for this application. Moreover, apart from their sensitivity, they also have other advantages on other methods for stress measurements, such as the possibility to perform on-line measurements during the film deposition in an array configuration, which can be useful for combinatorial approaches for the development of thin film materials libraries. In collaboration with the Plasma Advanced Materials (PAM) group of the Bruno Kessler Foundation, the properties of TiO2 films deposited by sputtering has been measured as a case study for these applications. In addiction to residual stress, a method for measuring the Young’s modulus of the deposited films has been developed, based on the measurement by means of a stylus profilometer of beam stiffness increase due to TiO2 film. The optimal data analysis procedure has been evaluated in order to increase the efficiency of the measurement. In conclusion, this work has provided the development of MEMS-based microcantilever devices for a range of different applications by evaluating the technological solutions for their realisation, the optimisation of design and testing of realised devices. The results validate the use of this class of devices in applications where high sensitivity detectors are required for portable analysis systems

System Integration of Flexible and Multifunctional Thin Film Sensors for Structural Health Monitoring

Greater information is needed on the state of civil infrastructure to ensure public safety and cost-efficient management. Lack of infrastructure investment and foreseeable funding challenges mandate a more intelligent approach to future maintenance of infrastructure systems. Much of the technology currently utilized to assess structural performance is based on discrete sensors. While such sensors can provide valuable data, they can lack sufficient resolution to accurately identify damage through inverse methods. Alternatively, technologies have shown promise for distributed, direct damage detection with flexible thin film and multifunctional polymer-nanocomposite materials. However, challenges remain as significant past work has focused on material optimization as opposed to sensing systems for damage detection. This dissertation offers novel methods for direct and distributed strain sensing by providing a fabrication methodology for broadly enabling thin film sensing technologies in structural health monitoring (SHM) applications. This fabrication methodology is presented initially as a set of materials and processes which are illustrated in analog circuit primitive forms including flexible, thin film capacitors, resistors, and inductors. Three sensing systems addressing specific SHM challenges are developed from this base of components and processes as specific illustrations of the broader fabrication approach. The first system developed is a fully integrated strain sensing system designed to enable the use of multifunctional materials in sensing applications. This is achieved through the development of an optimized fabrication approach applicable to many multifunctional materials. A layer-by-layer (LbL) deposited nanocomposite is incorporated with a lithography process to produce a sensing system. To illustrate the process, a strain sensing platform consisting of a nanocomposite film within an amplified Wheatstone bridge circuit is presented. The study reveals the material process is highly repeatable to produce fully integrated strain sensors with high linearity and sensitivity. The thin film strain sensors are robust and are capable of high strain measurements beyond 3,000 μϵ. The second system developed is an array of resistive distributed strain sensors and an associated algorithm to provide an alternative to electrical impedance tomography for spatial strain sensing. An LbL deposited polymer composite thin film is utilized as the piezoresistive sensing material. An inverse algorithm is presented and utilized for determining the resistance of array elements by electrically stimulating boundary nodes. Two polymer nanocomposite arrays are strain tested under cyclic loading. Both arrays functioned as networks of strain sensors confirming the viability of the approach and computational benefits for SHM. The third system developed is a thin film wireless threshold strain sensor for measuring strain in implanted and embedded applications. The wireless sensing system is comprised of two thin film, inductor-capacitor circuits, one of which included a fuse element. The sensor is fabricated on polyimide with metal layers used to pattern inductive antennas and a strain sensitive parallel plate capacitor. A titanium thin film fuse is designed to fail, or have a large resistance increase, when a strain threshold is exceeded. Three prototype systems are interrogated wirelessly while under increasing tensile strain. One of two sensor resonant peaks disappear at a strain threshold as designed, validating the sensing approach and thin film form for use in SHM systems. The fuse approach provides a platform for various systems and sensing elements. The reference peak remains intact and is used for continuous real-time strain sensing with a sensitivity of 0.5 and a noise floor below 50 microstrain.PHDCivil EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttps://deepblue.lib.umich.edu/bitstream/2027.42/144183/1/arburt_1.pd

Design project of a low-cost data acquisition system for electromechanical testing of smart materials

This thesis aims to develop a low-cost data acquisition system to record electrical resistance and deformation data in self-sensing smart cement specimens. Subsequently, the developed system must be tested with cyclic load tests, a text file must be generated with the data obtained and said data must be analysed to extract conclusions about the performance of the system and the piezoresistive "smartness" of the materials. The most interesting application of this thesis is to implement the system designed in an intelligent cement for Structural Health Monitoring applications, where a structure can be continuously monitored to detect deformations and possible failures before they happen. For this reason, the research on this thesis’s state of the art has focused on the current applications of smart cement, current SHM systems and research about low-cost solutions. To achieve the thesis goals, fluent communication has been established between the thesis director and the author, both by exchanging emails and face-to-face meetings. In addition, face-to-face sessions have been held in the Resistance of Materials laboratory, such as preparing the test specimens and testing the data acquisition system at different points in the thesis. The results show that the developed system can record electrical resistance and deformation data and generate text files for its processing. The analysis of the obtained data also illustrates the linear relationship between the fractional change in the electrical resistance and the deformation, allowing in this way to characterize the specimens with their gauge factor and thus determine their "smartness”. To sum up, it can be established that this thesis manages to develop a low-cost system for the acquisition of reliable and replicable data and, due to its linear relationship, the cement can be considered "self-sensing" since the application of a load is translated into a change into the electrical resistance, eliminating in this way the need for off-the-shelf strain sensors in SHM systems