Design and integration of an instrumented knee prosthesis

Total knee arthroplasty is nowadays one of the most important orthopedic surgery. It consists of a procedure in which parts of the knee are replaced by a prosthesis. The largest indication for total knee arthroplasty is osteoarthritis, a knee disease that can cause the cartilage of the femur and tibia to wear away, so that the bones rub together with use. The major risk factors for osteoarthritis are aging and obesity. Both the life expectancy and the obesity rate are increasing in the developed countries, thus the number of estimated total knee arthroplasties is growing over the years. Although over one million of prosthetic joints are implanted every year in the developed countries, none of them contains sensors to help the orthopedic surgeons in improving the precision of the replacement surgery. The goal of this study is to design an electronic system to be embedded inside a total knee prosthesis, in order to measure the force applied to it and its kinematics. Providing the orthopedic surgeons with quantitative data on the biomechanics of the prosthetic knee can help them in improving the implant precision and, as a consequence, could reduce the risk of an early revision surgery. In the frame of this thesis, we worked with the F.I.R.S.T. prosthesis by Symbios Orthopedie SA, that was instrumented with sensors and electronics to measure, process and transmit force and kinematics data to an external reader. The constraints in the design have been established by the medical doctors and the prosthesis manufacturer and the technical solutions adopted are presented. In order to simplify a future approval for human tests, we decided to keep the shape of the knee artificial joint. To achieve that, we put all the sensors and the electronics inside the middle part of the prosthesis, constituted of a polyethylene insert located between the metallic parts of the artificial joint and whose function is to reduce the rubbing. An original encapsulation was designed to guarantee the bio-compatibility of the instrumented prosthesis and to avoid a potentially dangerous contact between the electronics and the human body. This should be ensured even in case of extreme wearing of the polyethylene insert, that can occur some years after the prosthesis implant and is one of the main indications for a revision surgery. The sensors were tested by using mechanical simulators of the knee joint and validated by means of reference sensors. Different demonstrators have been designed, from the first, with only the sensors located inside the prosthesis and all the electronics fabricated in a large-scale outside of it, to the last miniaturized versions, that can be entirely embedded inside the prosthesis. Moreover, an autonomous sensor for balancing the ligaments tension during the knee replacement surgery was designed, fabricated and tested. Such a device could be an important help for the medical doctors during the surgery to improve the precision of the implant and, being not-implantable, could easily obtain an approval for human clinical trials

Development of piezoresistive sensors for biomedical applications

Tese de doutoramento em Engenharia Electrónica Industrial e de ComputadoresIn 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. 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.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 mm2 per sensor. 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 mm2, 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.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. 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 sensores obtidos foram construídas matrizes de 4 x 5 sensores que apresentam uma área ativa de 1.8 x 1.5mm2 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 mm2, 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. 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

Biomedical Engineering

Biomedical engineering is currently relatively wide scientific area which has been constantly bringing innovations with an objective to support and improve all areas of medicine such as therapy, diagnostics and rehabilitation. It holds a strong position also in natural and biological sciences. In the terms of application, biomedical engineering is present at almost all technical universities where some of them are targeted for the research and development in this area. The presented book brings chosen outputs and results of research and development tasks, often supported by important world or European framework programs or grant agencies. The knowledge and findings from the area of biomaterials, bioelectronics, bioinformatics, biomedical devices and tools or computer support in the processes of diagnostics and therapy are defined in a way that they bring both basic information to a reader and also specific outputs with a possible further use in research and development

Polymeric Microsensors for Intraoperative Contact Pressure Measurement

Biocompatible sensors have been demonstrated using traditional microfabrication techniques modified for polymer substrates and utilize only materials suitable for implantation or bodily contact. Sensor arrays for the measurement of the load condition of polyethylene spacers in the total knee arthroplasty (TKA) prosthesis have been developed. Arrays of capacitive sensors are used to determine the three-dimensional strain within the polyethylene prosthesis component. Data from these sensors can be used to give researchers a better understanding of component motion, loading, and wear phenomena for a large range of activities. This dissertation demonstrates both analytically and experimentally the fabrication of these sensor arrays using biocompatible polymer substrates and dielectrics while preserving industry-standard microfabrication processing for micron-level resolution. An array of sensors for real-time measurement of pressure profiles is the long-term goal of this research. A custom design using capacitive-based sensors is an excellent selection for such measurement, giving high spatial resolution across the sensing surface and high load resolution for pressures applied normal to that surface while operating at low power

An implantable micro-system for neural prosthesis control and sensory feedback restoration in amputees

In this work, the prototype of an electronic bi-directional interface between the Peripheral Nervous System (PNS) and a neuro-controlled hand prosthesis is presented. The system is composed of two Integrated Circuits (ICs): a standard CMOS device for neural recording and a High Voltage (HV) CMOS device for neural stimulation. The integrated circuits have been realized in two different 0.35μm CMOS processes available fromAustriaMicroSystem(AMS). The recoding IC incorporates 8 channels each including the analog front-end and the A/D conversion based on a sigma delta architecture. It has a total area of 16.8mm2 and exhibits an overall power consumption of 27.2mW. The neural stimulation IC is able to provide biphasic current pulses to stimulate 8 electrodes independently. A voltage booster generates a 17V voltage supply in order to guarantee the programmed stimulation current even in case of high impedances at the electrode-tissue interface in the order of tens of k­. The stimulation patterns, generated by a 5-bit current DAC, are programmable in terms of amplitude, frequency and pulse width. Due to the huge capacitors of the implemented voltage boosters, the stimulation IC has a wider area of 18.6mm2. In addition, a maximum power consumption of 29mW was measured. Successful in-vivo experiments with rats having a TIME electrode implanted in the sciatic nerve were carried out, showing the capability of recording neural signals in the tens of microvolts, with a global noise of 7μVrms , and to selectively elicit the tibial and plantarmuscles using different active sites of the electrode. In order to get a completely implantable interface, a biocompatible and biostable package was designed. It hosts the developed ICs with the minimal electronics required for their proper operation. The package consists of an alumina tube closed at both extremities by two ceramic caps hermetically sealed on it. Moreover, the two caps serve as substrate for the hermetic feedthroughs to enable the device powering and data exchange with the external digital controller implemented on a Field-Programmable Gate Array (FPGA) board. The package has an outer diameter of 7mm and a total length of 26mm. In addition, a humidity and temperature sensor was also included inside the package to allow future hermeticity and life-time estimation tests. Moreover, a wireless, wearable and non-invasive EEG recording system is proposed in order to improve the control over the artificial limb,by integrating the neural signals recorded from the PNS with those directly acquired from the brain. To first investigate the system requirements, a Component-Off-The-Shelf (COTS) device was designed. It includes a low-power 8- channel acquisition module and a Bluetooth (BT) transceiver to transmit the acquired data to a remote platform. It was designed with the aimof creating a cheap and user-friendly system that can be easily interfaced with the nowadays widely spread smartphones or tablets by means of a mobile-based application. The presented system, validated through in-vivo experiments, allows EEG signals recording at different sample rates and with a maximum bandwidth of 524Hz. It was realized on a 19cm2 custom PCB with a maximum power consumption of 270mW

Restoring Fine Motor Skills through Neural Interface Technology.

Loss of motor function in the upper-limb, whether through paralysis or through loss of the limb itself, is a profound disability which affects a large population worldwide. Lifelike, fully-articulated prosthetic hands exist and are commercially available; however, there is currently no satisfactory method of controlling all of the available degrees of freedom. In order to generate better control signals for this technology, and help restore normal movement, it is necessary to interface directly with the nervous system. This thesis is intended to address several of the limitations of current neural interfaces and enable the long-term extraction of control signals for fine movements of the hand and fingers. The first study addresses the problems of low signal amplitudes and short implant lifetimes in peripheral nerve interfaces. In two rhesus macaques, we demonstrate the successful implantation of regenerative peripheral nerve interfaces (RPNI), which allowed us to record high amplitude, functionally-selective signals from peripheral nerves up to 20 months post-implantation. These signals could be accurately decoded into intended movement, and used to enable monkeys to control a virtual hand prosthesis. The second study presents a novel experimental paradigm for intracortical neural interfaces, which enables detailed investigation of fine motor information contained in primary motor cortex. We used this paradigm to demonstrate accurate decoding of continuous fingertip position and enable a monkey to control a virtual hand in closed-loop. This is the first demonstration of volitional control of fine motor skill enabled by a cortical neural interface. The final study presents the design and testing of a wireless implantable neural recording system. By extracting signal power in a single, configurable frequency band onboard the device, this system achieves low power consumption while maintaining decode performance, and is applicable to cortical, peripheral, and myoelectric signals. Taken together, these results represent a significant step towards clinical reality for neural interfaces, and towards restoration of full and dexterous movement for people with severe disabilities.PhDBiomedical EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/120648/1/irwinz_1.pd

Advances in Integrated Circuits and Systems for Wearable Biomedical Electrical Impedance Tomography

Electrical impedance tomography (EIT) is an impedance mapping technique that can be used to image the inner impedance distribution of the subject under test. It is non-invasive, inexpensive and radiation-free, while at the same time it can facilitate long-term and real-time dynamic monitoring. Thus, EIT lends itself particularly well to the development of a bio-signal monitoring/imaging system in the form of wearable technology. This work focuses on EIT system hardware advancement using complementary metal oxide semiconductor (CMOS) technology. It presents the design and testing of application specific integrated circuit (ASIC) and their successful use in two bio-medical applications, namely, neonatal lung function monitoring and human-machine interface (HMI) for prosthetic hand control. Each year fifteen million babies are born prematurely, and up to 30% suffer from lung disease. Although respiratory support, especially mechanical ventilation, can improve their survival, it also can cause injury to their vulnerable lungs resulting in severe and chronic pulmonary morbidity lasting into adulthood, thus an integrated wearable EIT system for neonatal lung function monitoring is urgently needed. In this work, two wearable belt systems are presented. The first belt features a miniaturized active electrode module built around an analog front-end ASIC which is fabricated with 0.35-µm high-voltage process technology with ±9 V power supplies and occupies a total die area of 3.9 mm². The ASIC offers a high power active current driver capable of up to 6 mAp-p output, and wideband active buffer for EIT recording as well as contact impedance monitoring. The belt has a bandwidth of 500 kHz, and an image frame rate of 107 frame/s. To further improve the system, the active electrode module is integrated into one ASIC. It contains a fully differential current driver, a current feedback instrumentation amplifier (IA), a digital controller and multiplexors with a total die area of 9.6 mm². Compared to the conventional active electrode architecture employed in the first EIT belt, the second belt features a new architecture. It allows programmable flexible electrode current drive and voltage sense patterns under simple digital control. It has intimate connections to the electrodes for the current drive and to the IA for direct differential voltage measurement providing superior common-mode rejection ratio (CMRR) up to 74 dB, and with active gain, the noise level can be reduced by a factor of √3 using the adjacent scan. The second belt has a wider operating bandwidth of 1 MHz and multi-frequency operation. The image frame rate is 122 frame/s, the fastest wearable EIT reported to date. It measures impedance with 98% accuracy and has less than 0.5 Ω and 1° variation across all channels. In addition the ASIC facilitates several other functionalities to provide supplementary clinical information at the bedside. With the advancement of technology and the ever-increasing fusion of computer and machine into daily life, a seamless HMI system that can recognize hand gestures and motions and allow the control of robotic machines or prostheses to perform dexterous tasks, is a target of research. Originally developed as an imaging technique, EIT can be used with a machine learning technique to track bones and muscles movement towards understanding the human user’s intentions and ultimately controlling prosthetic hand applications. For this application, an analog front-end ASIC is designed using 0.35-µm standard process technology with ±1.65 V power supplies. It comprises a current driver capable of differential drive and a low noise (9μVrms) IA with a CMRR of 80 dB. The function modules occupy an area of 0.07 mm². Using the ASIC, a complete HMI system based on the EIT principle for hand prosthesis control has been presented, and the user’s forearm inner bio-impedance redistribution is assessed. Using artificial neural networks, bio-impedance redistribution can be learned so as to recognise the user’s intention in real-time for prosthesis operation. In this work, eleven hand motions are designed for prosthesis operation. Experiments with five subjects show that the system can achieve an overall recognition accuracy of 95.8%

Master of Science

thesisControl of a prosthetic device for amputees should be as natural as possible for optimal integration into daily use. A commonly used source of signal for the control of a prosthetic is the amputee's own electrical activity in muscles, known as electromyogram (EMG) readings. In order for these signals to be correctly interpreted to control the prosthetic, the intended effect of the signals must be understood. A device capable of applying forces and measuring the responses of a finger along a single axis was created with the purpose of gathering data about the mechanical behavior of the hand and relating it to the corresponding EMG signals. Using force and displacement sensors, each device can quantify the behavior of a fingertip. The device is designed such that multiple can be combined into an array for testing several fingers at once, which allows the gathering of complex force and motion data for an entire hand. Data gathered with this device are presented, in which the EMG data are used to predict force, and compared with the actual force. This initial comparison shows the device's ability to gather data which can improve understanding of the relation of EMG signals to complex motion of the fingers, which in turn will lead to a more natural control of prosthetic hands

A Closed-Loop Bidirectional Brain-Machine Interface System For Freely Behaving Animals

A brain-machine interface (BMI) creates an artificial pathway between the brain and the external world. The research and applications of BMI have received enormous attention among the scientific community as well as the public in the past decade. However, most research of BMI relies on experiments with tethered or sedated animals, using rack-mount equipment, which significantly restricts the experimental methods and paradigms. Moreover, most research to date has focused on neural signal recording or decoding in an open-loop method. Although the use of a closed-loop, wireless BMI is critical to the success of an extensive range of neuroscience research, it is an approach yet to be widely used, with the electronics design being one of the major bottlenecks. The key goal of this research is to address the design challenges of a closed-loop, bidirectional BMI by providing innovative solutions from the neuron-electronics interface up to the system level. Circuit design innovations have been proposed in the neural recording front-end, the neural feature extraction module, and the neural stimulator. Practical design issues of the bidirectional neural interface, the closed-loop controller and the overall system integration have been carefully studied and discussed.To the best of our knowledge, this work presents the first reported portable system to provide all required hardware for a closed-loop sensorimotor neural interface, the first wireless sensory encoding experiment conducted in freely swimming animals, and the first bidirectional study of the hippocampal field potentials in freely behaving animals from sedation to sleep. This thesis gives a comprehensive survey of bidirectional BMI designs, reviews the key design trade-offs in neural recorders and stimulators, and summarizes neural features and mechanisms for a successful closed-loop operation. The circuit and system design details are presented with bench testing and animal experimental results. The methods, circuit techniques, system topology, and experimental paradigms proposed in this work can be used in a wide range of relevant neurophysiology research and neuroprosthetic development, especially in experiments using freely behaving animals