Vítor Manuel Gomes Correia. Development of piezoresistive sensors for biomedical applications. Universidade do Minho Escola de Engenharia - PDF

Universidade do Minho Escola de Engenharia Vítor Manuel Gomes Correia Development of piezoresistive sensors for biomedical applications Vítor Manuel Gomes Correia UMinho 2013 Development of piezoresistive

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Universidade do Minho Escola de Engenharia Vítor Manuel Gomes Correia Development of piezoresistive sensors for biomedical applications Vítor Manuel Gomes Correia UMinho 2013 Development of piezoresistive sensors for biomedical applications Março de 2013 Universidade do Minho Escola de Engenharia Vítor Manuel Gomes Correia Development of piezoresistive sensors for biomedical applications Tese de Doutoramento Engenharia Electrónica Industrial e de Computadores Trabalho efectuado sob a orientação do Professor Doutor José V. Gerado Rocha Professor Doutor Senentxu Lanceros-Mendez Março de 2013 Acknowledgements First words to be written During the journey of my PhD, several people have contributed in the most different ways to make this moment possible. So, I cannot conclude this relevant step of my life without expressing my gratitude and my appreciation to all those that directly and indirectly have contributed to the development of this work throughout all these years and that helped me to grow as a person and as a professional. My first acknowledgment is for my supervisor Prof. Gerardo Rocha, for encouraging me in the continuation of my academic career and for the opportunity to accompany him all these years as a teacher and as a friend. Thank you for your friendship. To my co-supervisor, Prof. Senentxu, for giving me the opportunity of being a part of a fantastic research group due to scientific knowledge, work methodology, ideas, availability, shared knowledge and most of all, the friendship revealed over all these years. Thank you for your friendship and sharing of experiences. I would like to mention my colleagues/friends of Electroactive Smart Materials group for helping me along this time, always with a constructive and mutual aid spirit. In particular to Marcos Martins for his help in simulations; Vítor Sencadas for his help in the biomechanical tests; Armando for his help with the depositions techniques; Silvia Reis, Cristina and Helder for their support and friendship. I want to thank the financial support by the Foundation for Science and Technology- FCT under grant SFRH/BD/48708/2008. To colleagues and researchers at Cetemmsa for the excellent reception and availability during my stay for the development of printed sensors. I would like to thank the researchers at the Instituto de Biomecánica de Valencia (IBV) for the excellent reception and availability during my stay for the development of biomechanical tests. I also acknowledge the INL- International Iberian Nanotechnology Laboratory for their support. III Very special thanks to my parents for everything that have done for me, for all you tried to do and for all that will be done for me. What I am today I owe it to you. I want to thank to my brothers Ramiro, Ana and Rui for the support, inspiration and motivation they gave me. Lastly but most important of all, I thank to my wife Goreti that has been always my support, my refuge, my inspiration, my joy and my love. Love you! :) IV I dedicate this work to Goreti, my brothers and my parents, Thanks V Abstract In the last decades there has been an increase in sensing systems applied in a variety of situations with a large variety of sensor ranges. This represents a growing area with high potential. One of the areas of sensor development that require a great deal of attention is the area of sensor for biomedical applications and biosensors. These sensors have to overcome a number of challenges and limitations inherent to the environment where they are introduced. These difficulties lead to the necessity of using new materials and new techniques for their construction together with the more traditional materials, e.g. silicon based, which have already proven their potential in this area. Among the various materials, polymers have proven to be a good choice, due to a set of advantages such as simple processing, flexibility and facility of being obtained in different shapes. Therefore it is interesting to fabricate polymer based piezoresistive sensors for functional coatings of implantable hip prosthesis. These sensors will allow coating the prosthesis and provide new functionalities to the implants such as the possibility to measure forces and deformations between the prosthesis and the bone and therefore improving the postoperative diagnostic. In this works, a model of hip prosthesis with coated sensors was developed. For this purpose, flexible piezoresistive sensors have been developed that allow being implanted. Strain sensors were fabricated based on thin films of n + -nc-si.h by the technique of hot-wire chemical vapor deposition at a temperature of 150 ºC on a polymeric substrate, using the lithographic technique to construct the various layers of the sensors. The sensor has a gauge factor of -28 for low frequency deformation cycles. Sensors with larger flexibility were also developed though inkjet printing technique. Various configurations and materials were used to evaluate which materials are most appropriate for these types of sensors. Sensors with a gauge factor of approximately 2.5 for an active layer of PeDOT were obtained. A sensor matrix of 4 x 5 sensors was fabricated with an active area of 1.8 x 1.5 mm 2 per sensor. VII These sensors were subjected to a set of electromechanical tests to evaluate its performance in situations close to end use. So the prosthesis was coated with the various sensors, cemented and subjected to deformation cycles for three levels of force according to standard ISO7206. An adaptive system read-out electronic circuit was developed and built that allows reading piezoresistive sensors with different characteristics. This system allows measuring a matrix of 8x8 sensors, but can be scaled to a large number of sensors. The readable range of the system is between 50 Ω and 100 kω according to the needs of the sensors being implanted. The total area of the circuit is 135 mm 2, according to the requirements of a circuit to be used in in-vivo applications. An energy management system was also implemented that allows to activate and deactivate parts of the circuit when they are not needed, reducing the energy consumption. The system was validated by measuring a matrix of sensors with different characteristics. Finally, simulations were performed in order to evaluate the best options for the development of a wireless communications system. Three possible operation frequency ranges were used for three types of standard antennas. The communication system was introduced into a model simulating the characteristics of the various layers that constitute the human body. These simulations allow evaluate the frequency range most appropriate for implantable devices, the most appropriate antenna and the best location within the body. So the frequency chosen for the implementation was 868 Mhz for a Inverted- F antenna (IFA). In conclusion, the key elements for the implementations of an instrumented hip prosthesis were development and validated. The developed and/or simulated elements, including sensors, circuits for reading and communication system can also be used in other applications due to characteristics. VIII Resumo Nas últimas décadas, tem-se registado um aumento do número de sistemas de sensorização, aplicados aos mais diversos meios e grandezas. Esta é uma área em claro crescimento e ainda com elevado potencial. Uma das áreas de desenvolvimento de sensores que tem recebido uma grande atenção é a área dos sensores para aplicações biomédicas e os biossensores, com claros benefícios para o ser humano. Estes novos sensores necessitam, no entanto, de ultrapassar um grande número de desafios e restrições inerentes ao ambiente onde estes serão introduzidos, estas dificuldades levam à necessidade de utilizar novos materiais e novas técnicas para a sua construção junto com os mais tradicionais, e.g. baseados em silício, que tem já provado o seu interesse nesta área. Entre os diferentes materiais, os polímeros têm demonstrado ser uma boa escolha, devido ao conjunto de vantagens que apresentam, como o seu processamento simples, flexibilidade e facilidade de serem obtidos em diferentes formas, dai a sua escolha para fabricar sensores piezoresitivos implantáveis para o revestimento funcional de uma prótese de anca. Estes sensores permitem revestir a prótese, dando assim novas funcionalidades aos implantes, tais como permitir medir força e deslocamentos entre a prótese e o osso e melhorar o diagnóstico pós-operatório. Neste trabalho foi desenvolvido um modelo de prótese de anca com implementação de sensores. Para atingir esse objectivo, foram desenvolvidos sensores piezoresitivos flexíveis que permitam ser implantados. Assim foram fabricados sensores de deformação baseados em filmes finos de n + -nc-si.h pela técnica de hot-wire chemical vapor deposition a uma temperatura de 150ºC sobre um substrato polimérico. Recorreu-se a técnica de litografia para construir as várias camadas do sensor. Os sensores apresentam um gauge factor de -28, para ciclos de baixa frequência em testes de four-point-bending. Foram ainda desenvolvidos sensores com uma maior flexibilidade através da técnica de inkjet printing. Para esse desenvolvimento foram usadas várias configurações e materiais, para avaliar quais os materiais mais adequados para este tipo de sensores. Na caracterização destes sensores obteve-se um gauge factor de aproximadamente 2.5 para uma camada ativa de PeDOT. Com os melhores IX sensores obtidos foram construídas matrizes de 4 x 5 sensores que apresentam uma área ativa de 1.8 x 1.5mm 2 por sensor. Estes sensores foram sujeitos a um conjunto de ensaios electromecânicos, para avaliar o seu desempenho em situações próximas da utilização final. Desta forma foi revestida uma prótese com os diferentes sensores, cimentada e sujeita a ciclos de deformação para três níveis de força, segundo a norma ISO7206. Foi desenvolvido e construído um sistema de leitura adaptável que permite medir sensores piezoresistivos com diferentes características entre eles. Este sistema permite medir uma matriz de 8x8 sensores, mas pode ser escalada para um número maior de sensores. A gama de leitura do sistema varia entre 50 Ω e 100 kω, de acordo com as necessidades dos sensores a serem implementados. A área total deste circuito é de 135 mm 2, de acordo com as necessidades de um circuito a ser utilizado em aplicações in-vivo. Foi também implementado um sistema de gestão de energia que permite ativar e desativar partes do circuito quando estas não são necessárias, permitindo, desta forma, reduzir os consumos de energia. O sistema foi validado através da medição de uma matriz de sensores com diferentes características. Finalmente, foram realizadas simulações de forma a avaliar as melhores opções para o desenvolvimento do sistema de comunicação sem fios. Foram usadas três possíveis gamas de frequência de operação para três tipos de antenas standard. O sistema de comunicação foi introduzido num modelo simulando as características das várias camadas que constituem o corpo humano. Estas simulações permitem aferir a gama de frequências mais adequadas para os dispositivos implantáveis, a antena mais adequada e a sua melhor localização, pois foi verificado como as várias camadas que constituem o corpo humano influenciam a comunicação. Assim, a frequência escolhida para a implementação foi de 868 MHz e a antena foi a IFA. Em conclusão, os elementos principais para a implementação de uma prótese de anca instrumentada, foram desenvolvidos e validados. Os elementos desenvolvidos e/ou simulados, incluindo os sensores, circuitos de leitura e sistema de comunicação, poderão igualmente ser utilizados em outras aplicações devido às suas boas características. X Table of contents Acknowledgements... III Abstract... VII Resumo... IX Table of contents... XI List of figures... XIV List of tables... XVIII List of symbols... XIX List of abbreviations... XXI 1. Introduction Implantable sensors Polymeric materials for strain and pressure sensors Piezoresistive sensors Metallic Crystal silicon semiconductor Polymer-based sensors Polymeric sensors productions technics Electronic interface and communications systems for biosensors Objectives Structure and methodology References Piezoresistive silicon thin film senor array for biomedical applications Introduction Experimental Hot-wire chemical vapor deposition XI Sensor array fabrication Results and discussion Conclusions References Piezoresistive sensors for force mapping of hip-prostheses Introduction Experimental Results and Discussion Conclusions References Development of inkjet printed strain sensors Introduction Experimental details Inkjet printed and inks Electrical conductivity measurement Electro-mechanical characterization Results and discussion Single sensor development Single sensor characterization Sensor array and matrix developed Electro-mechanical sensor array and matrix characterization Smart prosthesis development Conclusions References Adaptive Sensor Interface Circuit for Piezoresistive Sensor Arrays Introduction XII Adaptive system architecture Circuit implementation Firmware design Experimental work and results Conclusions References Ultra-High Band Radiowave Propagation Analysis for implanted Biosensors Communication System Introduction Modeling and analysis Computational technique Antenna models Human body model Results and discussion Conclusions References Conclusions and future work Conclusions Future work XIII List of figures Figure Zig-Zag pattern format for a metallic sensor Figure Piezoresistive intrinsic effect, intermolecular connections variation by a mechanical deformation Figure Production of polymer films using a bar-coating method Figure Production of polymer films using a spin-coating method Figure Inkjet printing main classification: a) multi deflection continuous inkjet and b) drop on demand inkjet Figure Schematic representation of the continuous inkjet printing (CIJ) technology operation mode Figure Schematic representation of the thermal inkjet technology operation mode Figure Schematic representation of the piezoelectric drop on demand inkjet technology operation mode Figure Piezoresistive response, under 4-point bending loading cycles of one nc-si:h microresistor with dimensions W L= μm 2 and thickness 120 nm on a 125 μm thick polyimide substrate. a) Optical micrograph of sensor and metallic leads; b) Sensor resistance, R (left axis) and vertical displacement of loading bars, z (right axis) as a function of time; c) Sensor resistance, R, as a function of strain, ε, calculated from data in b) using eq. (2.2). The slope is the GF ( 28.1) Figure Time-domain results of the dynamic actuation of large-area sensors. Each piezoresistor, RS, in the sensor is part of a Wheatstone bridge circuit in a quarter-bridge configuration. In a) the output voltage of the sensor (the unbalanced V out of the bridge) is displayed. In b) a detail of graph a), between 49 and 51 s, is zoomed in. In c) the constant amplitude, variable frequency excitation voltage, Vexcitation, driving the mechanical oscillator (see text) is shown for the time interval [49,51] s. In d) the signal amplitudes and their ratio ( 1 : 0.54 : 0.15 ) XIV given by three piezoresistors in the sensor (channels 1 to 3) located at different distances from the clamped edge of the sensor Figure a) Readout circuit for a 4 4 sensor array. The switches are connected in the right position for reading R11. In this case, a voltage is applied to R11 and its current is measured. R12, R13 and R14 are shunted, so their currents are null. b) Block diagram of the sensor electronic interface Figure a) Image of the hip-joint prosthesis in the stress-strain experimental setup, and b) inclination angles and of the axis of the prosthesis Figure Block diagram of the electronic signal acquisition and recording of the output sensors signal Figure Simulated stress distribution for the hip-joint prosthesis with solicitation along y. The horizontal rectangle indicates the placement of the cement Figure Piezoresistive response for the commercial metallic sensors performed with a maximum force of 2300 N and: a) 0.5 Hz, b) 5 Hz Figure Piezoresistive response for the commercial metallic sensors performed with at 1 Hz for: a) 1300 N and b) 4000 N Figure Piezoresistive measurement for the ni-s:h microresistor performed with a maximum force of 2300 N and: a) 0.5 Hz, b) 1 Hz, c) 5 Hz and d) detail of the electrical output of sensor S22 of figure c Figure Electrical circuit used to obtain the value of the sensor resistance (Rx) Figure Electrical circuit used to obtain the value of the multi-sensor resistance (R x ). Here R 1 to R 3 are the resistances of the bridge, V S is the voltage supply, V G is the differential voltage between the bridge terminals, G is the gain of the amplifier and Out is the output voltage corresponding to V G * G Figure Schematics of the 4-point bending test used for the electromechanical evaluation of the sensors. z is the vertical displacement of the piston, d is the sample thickness and a is the distance between the two bending points. The sensors are placed at the bottom surface of the substrate XV Figure 4.3 a) Projected pattern for Strain gauge sensor, b) defects at the middle of the printed lines, c) defects at the end of the printed lines, d) final result of strain gauge sensor, e) Desired pattern for the interdigitated conductive layer for piezoresistive sensors, f) excess of material at the end of the lines, g) short-circuit between the lines and h) final result of the interdigitated printed pattern. All bar scales correspond to 0.5 mm Figure 4.4 a) Representation of the homogeneity problems arising with the deposition of the PeDOT layer, b) final PR sensor based on PeDOT and c) semiconductor sensor based on TIPS-Pentacene Figure 4.5 a) Representative cyclic deformation applied to a sample of strain gauge b) PR sensor with the corresponding resistance variation as a function of time and c) relative change in electrical resistance due to mechanical deformation, for several up-down cycles applied to a sample Figure 4.6 a) Design of the array pattern, b) final result of the printed array, c) design of the different layers needed for the printing of the sensor matrix and d) printed sensor matrix Figure 4.7 a) representative cyclic strain applied to an array of sensors and the corresponding electrical variation over time and b) representative cyclic strain applied to a sensor matrix and electrical response of 3 sensors within the matrix Figure 4.8 a) Picture of the hip-prosthesis with the implemented sensors in the stress-strain experimental setup, b) PR measurement for the PeDot PR sensors performed with a maximum force of 4000 N, c) sensor response to 1000 cycles and c) prosthesis displacement and sensor amplitude response as a function of the applied force Figure Block diagram of the adaptive multi-sensor interface circuit Figure Schematic of the adaptive interface circuit. The sensors are connected between the terminals of analog switch IC1 and IC Figure Algorithm construction to determine the calibration parameters of the adaptive circuit for a particular sensor XVI Figure Circuit consumption in the various operation states Figure a) Mechanical and electrical experimental setup of the hip-joint prosthesis; b) Sensor characteristics used to validate the adaptive multi-sensor interface circuit and c) Electrical and mechanical response of the instrumented hip-joint prosthesis for a maximum mechanical load of 4 kn Figure 5.6 a) Picture of the sensor matrix using in the experimental setup and b) mechanical deformation signal and amplitude response of three sensors Figure Radiation pattern and return loss for a dipole antenna in free space for a frequency of 868MHz Figure Radiation
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