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

Synthetic and bio-artificial tactile sensing: a review

This paper reviews the state of the art of artificial tactile sensing, with a particular focus on bio-hybrid and fully-biological approaches. To this aim, the study of physiology of the human sense of touch and of the coding mechanisms of tactile information is a significant starting point, which is briefly explored in this review. Then, the progress towards the development of an artificial sense of touch are investigated. Artificial tactile sensing is analysed with respect to the possible approaches to fabricate the outer interface layer: synthetic skin versus bio-artificial skin. With particular respect to the synthetic skin approach, a brief overview is provided on various technologies and transduction principles that can be integrated beneath the skin layer. Then, the main focus moves to approaches characterized by the use of bio-artificial skin as an outer layer of the artificial sensory system. Within this design solution for the skin, bio-hybrid and fully-biological tactile sensing systems are thoroughly presented: while significant results have been reported for the development of tissue engineered skins, the development of mechanotransduction units and their integration is a recent trend that is still lagging behind, therefore requiring research efforts and investments. In the last part of the paper, application domains and perspectives of the reviewed tactile sensing technologies are discussed

The Development of an in Vivo Spinal Fusion Monitor Using Microelectromechanical (Mems) Technology to Create Implantable Microsensors

Surgical fusion of the spine is a conventional approach, and often last alternative, to the correction of a degenerative painful spinal segment. The procedure involves the surgical removal of the intervertebral disc at the problematic site, and the placement of a bone graft that is commonly harvested from the patients iliac crest and placed within the discectomized space. The surrounding bone is expected to incorporate and remodel into the bone graft to eventually provide an immobilized site. Spinal instrumentation often accompanies the bone graft to provide further immobility to the targeted site, thus augmenting the fusion process. However, the status of a fusion and the incorporation of bone across a destabilized spinal segment are often difficult for the surgeon to assess. Radiographic methods provide static views of the fusion site that possess excessive limitations. The radiographic image cannot provide the surgeon with information regarding fusion integrity when the patient is mobile and the spine is exposed to multiple motions. Fortunately, technological advances utilizing microelectromechanical system technology (MEMS) have provided insight into the development of miniature devices that exhibit high resolution, electronic accuracy, miniature sizing, and have the capacity to monitor long-term, real-time in vivo pressures and forces for a variety of situations. However, numerous challenges exist with the utilization of MEMS devices for in vivo applications.This work investigated the feasibility of utilizing implantable microsensors to monitor the pressure and force patterns of bone incorporation and healing of a spine fusion in vivo. The knowledge obtained from this series of feasibility tests using commercially available transducers to monitor pressures and forces, will be applied towards the development of miniature sensors that utilize MEMS technology to monitor real-time, long-term spine fusion in living subjects. The packaging, radiographic, and sterilization characteristics of MEMS sensors were eva

The Development of an in Vivo Spinal Fusion Monitor Using Microelectromechanical (Mems) Technology to Create Implantable Microsensors

Surgical fusion of the spine is a conventional approach, and often last alternative, to the correction of a degenerative painful spinal segment. The procedure involves the surgical removal of the intervertebral disc at the problematic site, and the placement of a bone graft that is commonly harvested from the patients iliac crest and placed within the discectomized space. The surrounding bone is expected to incorporate and remodel into the bone graft to eventually provide an immobilized site. Spinal instrumentation often accompanies the bone graft to provide further immobility to the targeted site, thus augmenting the fusion process. However, the status of a fusion and the incorporation of bone across a destabilized spinal segment are often difficult for the surgeon to assess. Radiographic methods provide static views of the fusion site that possess excessive limitations. The radiographic image cannot provide the surgeon with information regarding fusion integrity when the patient is mobile and the spine is exposed to multiple motions. Fortunately, technological advances utilizing microelectromechanical system technology (MEMS) have provided insight into the development of miniature devices that exhibit high resolution, electronic accuracy, miniature sizing, and have the capacity to monitor long-term, real-time in vivo pressures and forces for a variety of situations. However, numerous challenges exist with the utilization of MEMS devices for in vivo applications.This work investigated the feasibility of utilizing implantable microsensors to monitor the pressure and force patterns of bone incorporation and healing of a spine fusion in vivo. The knowledge obtained from this series of feasibility tests using commercially available transducers to monitor pressures and forces, will be applied towards the development of miniature sensors that utilize MEMS technology to monitor real-time, long-term spine fusion in living subjects. The packaging, radiographic, and sterilization characteristics of MEMS sensors were eva

The Development of an in Vivo Spinal Fusion Monitor Using Microelectromechanical (Mems) Technology to Create Implantable Microsensors

Surgical fusion of the spine is a conventional approach, and often last alternative, to the correction of a degenerative painful spinal segment. The procedure involves the surgical removal of the intervertebral disc at the problematic site, and the placement of a bone graft that is commonly harvested from the patients iliac crest and placed within the discectomized space. The surrounding bone is expected to incorporate and remodel into the bone graft to eventually provide an immobilized site. Spinal instrumentation often accompanies the bone graft to provide further immobility to the targeted site, thus augmenting the fusion process. However, the status of a fusion and the incorporation of bone across a destabilized spinal segment are often difficult for the surgeon to assess. Radiographic methods provide static views of the fusion site that possess excessive limitations. The radiographic image cannot provide the surgeon with information regarding fusion integrity when the patient is mobile and the spine is exposed to multiple motions. Fortunately, technological advances utilizing microelectromechanical system technology (MEMS) have provided insight into the development of miniature devices that exhibit high resolution, electronic accuracy, miniature sizing, and have the capacity to monitor long-term, real-time in vivo pressures and forces for a variety of situations. However, numerous challenges exist with the utilization of MEMS devices for in vivo applications.This work investigated the feasibility of utilizing implantable microsensors to monitor the pressure and force patterns of bone incorporation and healing of a spine fusion in vivo. The knowledge obtained from this series of feasibility tests using commercially available transducers to monitor pressures and forces, will be applied towards the development of miniature sensors that utilize MEMS technology to monitor real-time, long-term spine fusion in living subjects. The packaging, radiographic, and sterilization characteristics of MEMS sensors were eva

MEMS Capacitive Strain Sensing Elements for Integrated Total Knee Arthroplasty Prosthesis Monitoring

Measuring the in vivo load state of Total Knee Arthroplasty (TKA) components is required to understand the structural environment and wear characteristics of the devices. The ability to acquire this information gives tremendous insight into the mechanics of the joint replacement prosthesis. Data corresponding to normal loads, in-plane loads, shear loads, load center, contact area, and the rate of loading is needed to fully understand the kinematics and kinetics of the orthopedic implant. In this research, a novel sensing system has been developed which is capable of fully characterizing three-dimensional strain and stress at a single location. Capacitance-based sensors were chosen to avoid the power loss and drift characteristics typical of resistive elements due to resistive heating effects. A design and optimization methodology has been developed by combining conformal mapping electrostatic analysis techniques with methods from micromechanics of composite materials. Results of the design and optimization technique are used to understand the behavior of the sensing system. Simulation of these systems was performed using multiphysics finite element analysis, and novel methods for fabricating the sensors were adapted from techniques for fabricating microelectromechanical systems (MEMS) using biocompatible materials. An array of six sensors was fabricated with a critical dimension of 2.25 micrometers. This array consisted of a parallel plate capacitor for measuring normal strain, two differential elements for sensing shear strain normal to the plane of the array, and three interdigitated transducer (IDT) elements for characterizing strain in the plane of the sensor. The normal strain sensor exhibited a sensitivity of 1.54×10-3 picofarads per megapascal, and the shear sensor had a sensitivity of 4.77×10-5 picofarads per megapascal. Testing results showed that all sensors had linear response to loading and insignificant drift. Multiaxial testing results illustrated the ability of the differential sensors to determine loading direction. A multiaxial, MEMS sensor array has been developed for use in orthopedic, load-measuring conditions. This system has been optimized for use in soft materials such as ultra-high molecular weight polyethylene (UHMWPE). In the future, arrays of sensors will be embedded in orthopedic components to determine the total state of stress at local positions within the component

Novel wireless RF-bioMEMS implant sensors of metamaterials

Ankara : The Department of Electrical and Electronics Engineering and the Institute of Engineering and Sciences of Bilkent University, 2010.Thesis (Ph. D.) -- Bilkent University, 2010.Includes bibliographical references leaves 301-308.Today approximately one out of ten patients with a major bone fracture does not heal properly because of the inability to monitor fracture healing. Standard radiography is not capable of discriminating whether bone healing is occurring normally or aberrantly. To solve this problem, we proposed and developed a new enabling technology of implantable wireless sensors that monitor mechanical strain on implanted hardware telemetrically in real time outside the body. This is intended to provide clinicians with a powerful capability to asses fracture healing following the surgical treatment. Here we present the proof-of-concept in vitro and ex vivo demonstrations of bio-compatible radio-frequency (RF) micro-electro-mechanical system (MEMS) strain sensors for wireless strain sensing to monitor healing process. The operating frequency of these sensors shifts under mechanical loading; this shift is related to the surface strain of the implantable test material. In this thesis, for the first time, we developed and demonstrated a new class of bio-implant metamaterial-based wireless strain sensors that make use of their unique structural advantages in sensing, opening up important directions for the applications of metamaterials. These custom-design metamaterials exhibit better performance in remote sensing than traditional RF structures (e.g., spiral coils). Despite their small size, these meta-sensors feature a low enough operating frequency to avoid otherwise strong background absorption of soft tissue and yet yield higher Q-factors (because of their splits with high electric field density) compared to the spiral structures. We also designed and fabricated flexible metamaterial sensors to exhibit a high level of linearity, which can also conveniently be used on non-flat surfaces. Innovating on the idea of integrating metamaterials, we proposed and implemented a novel architecture of ‘nested metamaterials’ that incorporate multiple split ring resonators integrated into a compact nested structure to measure strain telemetrically over a thick body of soft tissue. We experimentally verified that this nested metamaterial architecture outperforms classical metamaterial structures in telemetric strain sensing. As a scientific breakthrough, by employing our nested metamaterial design, we succeeded in reducing the electrical length of the sensor chip down to λo/400 and achieved telemetric operation across thick soft tissue with a tissue thickness up to 20 cm, while using only sub-cm implantable chip size (compatible with typical orthopaedic trauma implants and instruments). As a result, with nested metamaterials, we successfully demonstrated wireless strain sensing on sheep’s fractured metatarsal and femur using our sensors integrated on stainless steel fixation plates and on sheep’s spine using directly attached sensors in animal models. This depth of wireless sensing has proved to suffice for a vast portfolio of bone fracture (including spine) and trauma care applications in body, as also supported by ongoing in vivo experiments in live animal models in collaboration with biomechanical and medical doctors. Herein, for all generations of our RF-bioMEMS implant sensors, this dissertation presents a thorough documentation of the device conception, design, modeling, fabrication, device characterization, and system testing and analyses. This thesis work paves the way for “smart” orthopaedic trauma implants, and enables further possible innovations for future healthcare.Melik, RohatPh.D

Regulating Valvular Interstitial Cell Phenotype by Boundary Stiffness

A quantitative understanding of the complex interactions between cells, soluble factors, and the biological and mechanical properties of biomaterials is required to guide cell remodeling towards regeneration of healthy tissue rather than fibrocontractive tissue. The goal of this thesis was to elucidate the interactions between the boundary stiffness of three-dimensional (3D) matrix and soluble factors on valvular interstitial cell (VIC) phenotype with a quantitative approach. The first part of the work presented in this thesis was to characterize the combined effects of boundary stiffness and transforming growth factor-β1 (TGF-β1) on cell-generated forces and collagen accumulation. We first generated a quantitative map of cell-generated tension in response to these factors by culturing VICs within micro-scale fibrin gels between compliant posts (0.15-1.05 nN/nm) in chemically-defined media with TGF-β1 (0-5 ng/mL). The VICs generated 100 to 3000 nN/cell after one week of culture, and multiple regression modeling demonstrated, for the first time, quantitative interaction (synergy) between these factors in a 3D culture system. We then isolated passive and active components of tension within the micro-tissues and found that cells cultured with high levels of stiffness and TGF-β1 expressed myofibroblast markers and generated substantial residual tension in the matrix yet, surprisingly, were not able to generate additional tension in response to membrane depolarization signifying a state of continual maximal contraction. In contrast, negligible residual tension was stored in the low stiffness and TGF-β1 groups indicating a lower potential for shrinkage upon release. We then studied if ECM could be generated under the low tension environment and found that TGF-β1, but not EGF, increased de novo collagen accumulation in both low and high tension environments roughly equally. Combined, these findings suggest that isometric cell force, passive retraction, and collagen production can be tuned by independently altering boundary stiffness and TGF-β1 concentration. In the second part, by using the quantitative information obtained from the first part, we investigated the effects of dynamic changes in stiffness on cell phenotype in a 3D protein matrix, quantitatively. Our novel method utilizing magnetic force to constrain the motion of one of two flexible posts between which VIC-populated micro-tissues were cultured effectively doubled the boundary stiffness and resulted in a significant increase in cell-generated forces. When the magnetic force was removed, the effective boundary stiffness was halved and the tissue tension dropped to 65-87% of the peak value. Surprisingly, following release the cell-generated forces continued to increase for the next two days rather than reducing down to the homeostatic tension level of the control group with identical (but constant) boundary stiffness. The rapid release of tension with the return to baseline boundary stiffness did not result in a decrease in number of cells with α-SMA positive stress fibers or an increase in apoptosis. When samples were entirely released from the boundaries and cultured free floating (where tension is minimal but cannot be measured), the proportion of apoptotic cells in middle region of the micro-tissues increased more than five-fold to 31%. Together, these data indicate that modest temporary changes in boundary stiffness can have lasting effects on myofibroblast activation and persistence in 3D matrices, and that a large decrease in the ability of the cells to generate tension is required to trigger de-differentiation and apoptosis