Characterization of Tissue Thermal Conductivity During a Tissue Joining Process

Electrosurgical vessel sealing, a tissue joining process, has been widely used in surgical procedures, such as prostatectomies for bleeding control. The heat generated during the process may cause thermal damages to the surrounding tissues which can lead to detrimental postoperative problems. Having better understanding about the thermal spread helps to minimize these undesired thermal damages. The purpose of this study is to investigate the changes of tissue thermal conductivity during the joining process. We propose a hybrid method combining experimental measurement with inverse heat transfer analysis to determine thermal conductivity of thin tissue sample. Instead of self-heating the tissue by the thermistor, we apply an external cold boundary on the other side of the tissue sample to stimulate a higher temperature gradient without denaturing the tissue in comparison to the heated method. The inverse heat transfer technique was then applied to determine the tissue thermal conductivity. Tissue thermal conductivity at different levels (0%, 25%, 50%, 75%, and 100%) of the joining process was measured. The results show a decreasing trend in tissue thermal conductivity with increasing joining level. When the tissue is fully joined, an average of 60% reduction in tissue thermal conductivity was found.

Combat Helmet Design Incorporating Multiple Ballistic Threats, Brain Functional Areas and Injury Considerations

Combat helmet protection zone parametric design is presented for small arms and explosive device ballistic threat notional spatial distributions. The analysis is conducted using a computer aided design software application developed to evaluate ballistic threats, helmet design parameters, and a standard set of common brain injuries associated with head impacts. The analysis helps to define the helmet trade space, facilitates prototyping, and supports helmet design optimization. Direct head impacts and helmet impacts, with and without helmet back face contact to the head, are tabulated. Head strikes are assumed to produce critical or fatal penetrating injuries. Helmet back face deflections and impact generated projectile-helmet-head motions are determined. Helmet impact obliquity is accounted for by attenuating back face deflection. Head injury estimates for ten common focal and diffuse head injuries are determined from the back face deflections and the head injury criteria. These, in turn, are related to the abbreviated injury score and associated radiographic dimensional diagnostic criteria and loss of consciousness diagnostic criteria from the trauma literature.

A Sensitivity Study of the Porcine Head Subjected to Bump Impact

Understanding load transfer to the human brain is a complex problem that has been a key subject of recent investigations [4–6]. Because the porcine is a gyrencephalic species, having greater structural and functional similarities to the human brain than other lower species outlined in the literature, it is commonly chosen as a surrogate for human brain studies [7]. Consequently, we have chosen to use a porcine model in this work. To understand stress wave transfer to and through the brain, it is important to fully characterize the nature of the impact (i.e. source, location, and speed) as well as the response of the constituent tissues under such impact. We suspect the material and topology of these tissues play an important role in their response. In this paper, we report on a numerical study assessing the sensitivity of model parameters for a 6-month old Gottingen mini-pig model, under bump loading. In this study, 2D models are used for computational simplicity. While a 3D model is more realistic in nature, a 2D representation is still valuable in that it can provide trends on parameter sensitivity that can help steer the development of the 3D model. In this work, we investigate the variation of skull and skin thickness, evaluate material variability of the skull, and consider the effects of nasal cavities on load transfer. Eighty simulations are computed in LS-DYNA and analyzed in MATLAB. The results of this study will provide useful knowledge on the necessary components and parameters of the porcine model and therefore provide more confidence in the analysis. This is an essential first step as we look toward bridging the gap between correlates of injury in animal and human models.

Numerical Analysis of Texture Tactics on Skin by Using of the Model of Periodic Micro Unit

Various mechanical effects occur in the human skin when it touches the texture which has micrometric scale. Since these mechanical effects in the skin are complicated, their study is necessary. The purpose of this study is to ascertain these mechanical effects by applying numerical analyses for a detailed discussion. In particular, the analysis confirms the differential effects in the skin due to a periodic variation of the texture. By the modeling situation that the texture touches the skin, a stress in the position of skin sensory organs is examined. As a result of the analysis, von Mises stresses at a shallow position of skin showed characteristic effects in the case of a large texture period. It is inferred that these effects occur with a texture period greater than a certain boundary value. Stress values at deep positions of skin are substantially equal without depending on the pressure position of the skin surface. In other words, skin sensory organs of the deep position have a wide receptive field in the numerical analysis of this paper, and this result matches with results of previous researches.

Hierarchical Engineering Model of the Human Body

Engineers and scientists are able to understand and analyze the behavior of complex engineering systems in a wide range of critical technologies through hierarchical modeling followed by simulation of the model operation. This process results in a high fidelity integrated model as each level in the hierarchy is modeled in sufficient detail. The overall objective of this effort is to develop a sophisticated hierarchical model of the human body, followed by simulation of the model operation. In this initial research phase, the feasibility of the concept is explored and a framework for the model is described. A six-level model consisting of the whole body as a system, system of systems, organs, tissues, cells, and molecules is proposed and described. This paper explains that the human body is amenable to such hierarchical modeling and describes the benefits that can be achieved. The systems in the body deal with numerous processes: electrical, chemical, biochemical, energy conversion, transportation, pumping, sensing, communications, and so on. Control volume models for the organs in the body capture the mass and energy balance and chemical reactions. Tissue can be represented similar to structural components made of various biomaterials. Cells can be represented as a manufacturing and maintenance workforce assisted by molecular reactions. Following the representation of a healthy body, simulation runs by inserting faults and/or deficiencies in the operational parameters into the model could reveal the causes for specific diseases and illnesses. Such modeling and simulation will benefit medical, pharmaceutical, nutritional specialists, and engineers in designing, developing, and delivering products and services to enable humans to lead healthy lives.

Temporal Variation Characteristics of Analysis Accuracy in Two-Dimensional Ultrasonic-Measurement-Integrated Blood Flow Analysis

A two-dimensional ultrasonic-measurement-integrated (2D-UMI) blood flow analysis system was developed for easy acquisition of an intravascular hemodynamics, which feeds back Doppler velocity obtained by an ultrasonic measurement to a numerical blood flow simulation for clinical application. In previous study, ultrasonic measurement and 2D-UMI simulation were performed to clarify the analysis accuracy for real flow field. Additionally, spatial variation characteristics of analysis accuracy was clarified by comparison of velocity vectors between 2D-UMI and 3D-CFD analysis results corresponding to an experimental flow. However, temporal variation of analysis accuracy of 2D-UMI analysis result has not been examined in spite of essential information for reduction of experimental measurement error due to speckle noise. The aim of this study was to clarify temporal variation characteristics of analysis accuracy of each velocity component obtained in 2D-UMI blood flow analysis. Comparisons of Doppler velocity V and (u, v) velocity profiles between measurement data, 2D-UMI, and 3D-CFD analysis results were performed, and their time variations were discussed. As a result, it was clarified that temporal variation of Doppler velocity error for measurement data became larger with increasing feedback gain. Temporal variations of u and v velocity component errors for 3D-CFD analysis result showed the same tendency as that of Doppler velocity in feedback gain.

Is the Maturation of Arteriovenous Fistulas a Mechanical or Biological Problem?

During the maturation the high pressure blood from the artery inflows directly to the vein, extends its diameter, and finally the blood flow rate in the vein is even 500-times greater than normal one. The changes of the wall shear stress (WSS) in the vein are thought to play a key role in the remodelling of its wall. However, this process is still not well understood. The aim of this paper is to show an innovative approach for modelling of the vein deformation during the maturation process of a-v fistulas. Dilation of the vein was modelled as two-step complex biomechanical process. The obtained results concerning final diameter of the vein are compared with average diameter obtained for large group of patients. Moreover, this study shows the changes in the flow rate and the WSS that occur after maturation in the patient-specific fistula.

Reduced Order Modeling and Experimental Investigation of Acoustic Particle Manipulation in Complex 3D Geometries

A reduced order computational model and imaging experiments are presented as a combined method to investigate migration and trapping of microscale particles within an ultrasonic droplet generator. Use of two-dimensional (2D) cross-sectional representations of the three-dimensional (3D) device enables observation of acoustic focusing phenomena that are otherwise visually inaccessible. Our approach establishes relationships between system operating parameters and particle retention due to acoustic radiation forces that arise during atomization of heterogeneous particle suspensions. The droplet generator consists of a piezoelectric transducer for ultrasonic actuation, a resonant fluid-filled chamber, and an array of microscopic pyramidal nozzles. 2D visualization chips were produced through anodic bonding of glass to microfluidic reservoirs deep reactive ion etched in silicon. Open nozzle orifices of the 3D microarray were sealed in its 2D representation to facilitate filling and testing. Finite element analysis was used to model the harmonic response of the 2D assembly from 500 kHz to 2 MHz. The average nozzle tip pressure amplitude across the 2D array was then used to identify operating frequencies that correspond to optimal droplet ejection from the 3D device (ejection modes). The pressure field at these resonant frequencies predicts the equilibrium distribution of polymeric beads suspended in the reservoirs of the 2D chips. To qualitatively assess the accuracy of the model results, visualization experiments were performed at the first three ejection modes of the system (fn1 ≈ 620–680 kHz, fn2 ≈ 1.14 MHz, and fn3 ≈ 1.63 MHz) using 10 μm polystyrene beads. The model demonstrates a remarkable ability to capture the overall shape, as well as specific details of the terminal particle distributions, defined as the state with no further movement toward a pressure node or antinode. Finally, time course trials of acoustic focusing of heterogeneous particle suspensions were used to observe the influence of particle volume on the magnitude of the acoustic radiation force. A mixture of 5 μm and 20 μm diameter polystyrene beads was subjected to a standing acoustic field in the 2D chips. Particle position was recorded at 5 ms intervals until an equilibrium distribution was achieved. As expected, the larger beads focused much more rapidly than smaller beads, acquiring their final positions in seconds (versus 10s of seconds for the 5 μm particles). The method and results reported here serve as building blocks toward translation of an existing ultrasonic droplet generator into a high-throughput particle separation and isolation platform.

Development of a Force Sensing Instrument Assisted Soft Tissue Mobilization Device

Instrument assisted soft tissue mobilization (IASTM) is a form of massage using rigid manufactured or cast devices. The delivered force, which is a critical parameter in massage during IASTM, has not been measured or standardized for most clinical practices. In addition to the force, the angle of treatment and frequency play an important role during IASTM. As a result, there is a strong need to characterize the delivered force to a patient, angle of treatment, and stroke frequency. This paper proposes a novel mechatronic design for a specific instrument from Graston Technique® (Model GT-3), which is a frequently used tool to clinically deliver localize pressure to the soft tissue. The design uses a 3D load cell, which can measure all three force components force simultaneously. The overall design is implemented with an IMUduino microcontroller chip which can also measure tool orientation angles and provide computed stroke frequency. The prototype of the mechatronic IASTM tool was validated for force measurements using an electronic plate scale that provided the baseline force values to compare with the applied force magnitudes measured by the device. The load cell measurements and the scale readings were found to be in agreement within the expected degree of accuracy. The stroke frequency was computed using the force data and determining the peaks during force application. The orientation angles were obtained from the built-in sensors in the microchip.

CFD Analysis Comparing Steady Flow and Pulsatile Flow Through the Aorta and its Main Branches

A computational fluid dynamics (CFD) study has been done comparing pulsatile and non-pulsatile blood flow through the aortic arch and its main branches. The pulsatile flow was to mimic the blood flow due to a beating heart and the non-pulsatile or steady flow was to mimic cardiopulmonary bypass (CPB). The purpose of the study was too narrow in on possible reasons CPB may contribute to the development of atherosclerosis. The main focus of the study was to look at the wall shear stress (WSS) values due to their close association with the development of atherosclerosis. In addition velocity and pressure data were also analyzed. The results of this study showed a stark contrast between the WSS values between the CPB model and the beating heart model. The CPB model did not have any points of oscillating WSS combined with the fact that there were regions of very high and very low constant WSS values in comparison with the beating heart analysis suggests that there may be potential for atherosclerotic development or plaque buildup within the artery. The beating heart model showed a range of WSS values within the aorta that were much lower overall compared with the CPB model.