Dielectric Elastomer Energy Harvesting and its Application to Human Walking

Human walking requires sophisticated coordination of muscles, tendons, and ligaments working together to provide a constantly changing combination of force, stiffness and damping. In particular, the human knee joint acts as a variable damper, dissipating greater amounts of energy when the knee undergoes large rotational displacements during walking, running or hopping. Typically, this damping results from the dissipation, or loss, of metabolic energy. It has been proven to be possible however; to collect this otherwise wasted energy through the use of electromechanical transducers of several different types which convert mechanical energy to electrical energy. When properly controlled, this type of device not only provides desirable structural damping effects, but the energy generated can be stored for use in a wide range of applications. A novel approach to an energy harvesting knee joint damper is presented using a dielectric elastomer (DE) smart material based electromechanical transducer. Dielectric elastomers are extremely elastic materials with high electrical permittivity which operate based on electrostatic effects. By placing compliant electrodes on either side of a dielectric elastomer film, a specialized capacitor is created, which couples mechanical and electrical energy using induced electrostatic stresses. Dielectric elastomer energy harvesting devices not only have a high energy density, but the material properties are similar to that of human tissue, making it highly suitable for wearable applications. A theoretical framework for dielectric elastomer energy harvesting is presented along with a mapping of the active phases of the energy harvesting to the appropriate phases of the walking stride. Experimental results demonstrating the energy harvesting capability of a DE generator undergoing strains similar to those experienced during walking are provided for the purpose of verifying the theoretical results. The work presented here can be applied to devices for use in rehabilitation of patients with muscular dysfunction and transfemoral prosthesis as well as energy generation for able-bodied wearers.

Effects of Treatment for Cervical Disc Degenerative Disease in Military Populations

Numerous clinical and biomechanical evaluations of cervical disc replacement and anterior cervical discectomy and fusion as treatment of cervical disc herniation have been performed. Military patients represent a unique patient population as they may be subject to large external forces in theatre. Military patients are more susceptible to degenerative disease of the cervical spine, and if treated with single-level bony fusion, the treated level may be subject to large forces postoperatively. Literature reviews were conducted to determine patient outcomes following cervical disc replacement compared to bony fusion surgery; compare cadaver studies that evaluated the two conditions; and finite element modeling studies. In the civilian population, patients treated with each type of surgery have clinical improvement that is at least equivalent in the 2- and 5-year follow-up periods. Based on the finite element and cadaver biomechanical studies, semiconstrained devices, ProDisc-C and Prestige, are less mobile and a larger load is placed on the core of the device in comparison to the more mobile and unconstrained Bryan disc.

A Numerical Approach of Estimating Dental Implant Healing Process Using Resonance Frequency Analysis (RFA)

This paper investigates primary stability of dental implant that indicates the process of bone-implant integration. This integration is known to happen at the boundary of the bone and dental implant contact surface. The resonance frequency of dental implant is used as the parameter for this investigation due to its high sensitivity to boundary condition variations. In this study, resonance frequency analysis (RFA) of the jaw-implant structure is carried out using finite element modeling. The FEM analyses are conducted in ANSYS modal analysis simulation environment. The FEM model of the structure includes titanium implant, Cancellous and cortical bone. Different implant-bone interface conditions are studied for this investigation. Various boundary conditions were studied to identify natural frequencies of jaw-implant structure. Our analysis shows that the resonance frequency of the implant increases during the healing period and reaches a plateau when the implant-bone interface was fully integrated. The results show that RFA could be suggested as a non-invasive, reliable and accurate diagnostic method for early assessment of the healing stages.

Experimentally Validated Computational Simulation of Lumbar Spine Intervertebral Disc Puncture

Back pain is a debilitating medical condition, often with an unclear source. Over time, back pain can affect the work and lifestyle of an individual by reducing job productivity and time spent on enjoyable activities. Discography of the intervertebral disc (IVD) is often used to diagnose pathology of the disc and determine if it may be a source for chronic back pain. It has recently been suggested that discography may lead to IVD degeneration, and has been a cause of controversy among spine care physicians. Using the results from a cadaveric experimental model, a finite element model was first validated. Then, a study was conducted to better understand the changes caused by discography on human spine mechanics. An anatomically accurate L3-L5 lumbar spine model was developed using computed tomography scans. Discography was simulated in the model as an area in the disc affected by needle puncture. The material properties in the nucleus pulposus were adjusted to match experimental data both before and after puncture. The results show that puncture of the IVD leads to increased deformation as well as increased stresses in the disc. Pressure in the nucleus pulposus found to decrease after puncture, and was calculated in the course of this study. Puncturing the IVD changes disc mechanics and may lead to progressive spine issues in the future such as disc degeneration. While discography has been the gold standard to determine if the disc was a source of back pain in patients for many years, the potential long-term degenerative effects of the procedure are only now coming into light, and must be closely examined.

Spatially Controllable Deposition of Electrospray Microparticles

Electrospray has been widely used in micro/nanotechnology which deposit micro/nanoscale particles on planar surfaces. However, in conventional electrospray approach the distribution of these particles patterned on the collecting surface is poorly controlled. This work introduces a programmable patterning method of electrospray, which microparticles are sprayed on micropatterned collecting chips. By manipulating the local electrical field using a combination of activated and floating electrodes, a good spatial contrast of microparticle patterning is obtained. In addition, the size-dependent contrast enhancement is demonstrated using a series of electrode arrays with different electrode patterns. Combined with encapsulation technique, this unique electrospray method promises potential applications in the field of functional cell/tissue engineering.

Is Synthetic Composite Bone a Substitute for Natural Bone in Screw Bending Tests?

Composite replica bones have been used extensively for biomechanical studies. These studies normally rely upon the overall tensile, compressive, and bending strength of large replica bones, such as the tibia and femur. In this study, highly localized behavior of composite bone was scrutinized by examining the material’s response to cortical screws in bending. Of interest was localized deformation of the composite material as compared to the response of natural bone under similar loading conditions. Cortical screw deflection in a laminated composite bone was compared to deflection in a bovine bone under quasi-static loading. The laminated composite bone consisted of short glass fiber reinforced epoxy as a cortical bone substitute, while polyurethane foam was used as a cancellous bone substitute. A new laser projection method was used to make comparative measurements of the slope of the screw head near to the applied load. Initial results indicate that composite bone is a reliable substitute for natural bone in quasi-static studies of cortical screw deflection.

Nonlinear Dynamic Viscoelastic Model for Osteoarthritic Cartilage Indentation Force

Biomechanical properties and dynamic response of soft tissues as articular cartilage remains issues for attention. Currently, linear isotropic models are still used for cartilage analysis in spite of its viscoelastic nature. Therefore, the aim of this study was to propose a nonlinear viscoelastic model for cartilage indentation that combines the geometrical parameters and velocity of the indentation test with the thickness of the sample as well as the mechanical properties of the tissue changing over time due to its viscoelastic behavior. Parameters of the indentation test and mechanical properties as a function of time were performed in Laplace space where the constitutive equation for viscoelasticity and the convolution theorem was applied in addition with the Maxwell model and Hayes et al. model for instantaneous elastic modulus. Results of the models were compared with experimental data of indentation tests on osteoarthritic cartilage of a unicompartmental osteoarthritis cases. The models showed a strong fit for the axial indentation nonlinear force in the loading curve (R2 = 0.992) and a good fit for unloading (R2 = 0.987), while an acceptable fit was observed in the relaxation curve (R2 = 0.967). These models may be used to study the mechanical response of osteoarthritic cartilage to several dynamical and geometrical test conditions.

Nano-Watt Heat Flux Sensor Considering Contact Resistance at Thermopile Junctions

This paper presents design and fabrication procedures for nano-Watt resolution of heat flux sensor. To enhance the resolution, a contact resistance of thermopile is especially focused. CMOS (Complementary Metal-Oxide Semiconductor-compatible) process was used for deposition of gold and chromium which are composed of thermopile. The most important part of thermopile is the contact region of the junctions which generate electrical noises as well as thermoelectric power. The effect of contact conditions at junction point was investigated. The fabricated sensor has 100 thermocouples connected in series and its active junction is on the membrane which directly affects the sensitivity. Developed sensor system provides 0.0629V/nW of sensitivity and 1nW of high resolution.

Ultrasound Viscoelastic Imaging of Breast Lesions: A Practical Hybrid Freehand Technique for Data Acquisition

Ultrasound imaging of the breast is a standard method in breast cancer screening, along with mammography. The viscoelastic properties of soft tissue can provide supplementary information for radiologist to consider in their assessment of pathology and tissue characterization. Measuring these properties generally entails acquiring a time sequence of ultrasound images and calculating parametric data from it. As images are necessarily accumulated over time, acquisition is limited by the frame rate and memory capacity of the ultrasound machine, and practical considerations such as movement from the clinicians hands and patient breathing. This paper describes a technique for hybrid-freehand imaging of viscoelasticity (HYFIVE). It involves acquiring a time sequence of images making use of a simple purpose built canister enclosure for the ultrasound probe which allows for a stable and accurate manipulation of applied forces, without the need of motors, sensors or other sophisticated and costly parts. A sequence of ultrasound strain images was computed and a first order Kelvin-Voigt tissue model fit to the resulting strain vs. time curves to obtain parametric data related to tissue stiffness and viscosity. Experiments were conducted on both gelatin phantoms and clinical patient data.

Specific Treatments for Improving the Quality of Life in Rheumatologic Affections and Osteoporosis

The analysis and implementation of modern treatments for the patients diagnosed with osteoporosis, degenerative rheumatic affections and peripheral circulatory disorders have become a healthy priority for the society. These treatments have the goal to raise the bone mineral density of the skeleton, reducing joints pain and inflammation while improving and maintaining joints function. This paper presents a conservative treatment of patients from Recovery Clinical Hospital of Felix Spa, diagnosed with degenerative and rheumatoid affections. The treatment is complex and involves balneal-physical-kinetic recovery therapy that must be periodical repeated at every six months to perform. Ankylosing spondylitis was been evaluated by BASFI-BASDAI scores, while the gonarthrosis with Artroflex by SF-36 of quality life scale and Lequesne index. In addition, a vibration treatment combined with balneal-conservative treatment was been proposed to reduce the therapy time and improved the quality live of patients. The vibration system comprises a vibration bed with adjusting control of signal by a digital frequency convertor, and a command panel system for measuring and processing of data. Because the vibration trial is in incipient experiment stage, it was been applied first on Wistar rats, due to increase the calcium mass of bones. The results of all treatments were emphasized the efficiency of balneal cure in rheumatic affections.