Computational Fluid Dynamics Simulation of the Blood Flow in the Circle of Willis

The blood supply for the brain is born by four arteries, that is, two internal carotid arteries and two vertebral arteries. They are mutually connected at the cerebral base, and form a closed arterial circle, called the circle of Willis, so that the safety of the brain blood supply is increased. However their anastomoses show a very wide variety of atypism. If some of anastomses are very thin, or even do not exist, the safety of the blood supply is not secured. This is particularly important when some diseases such as cerebral thrombosis occurs and the blood flow supply stops unilaterally. Redistribution of the blood supply in such cases is thought to be strongly affected by geometrical configuration of the anastomoses. It is also known that cerebral aneurysms, which may induce serious cerebrovascular diseases, preferentially occur at the circle of Willis. Complex blood flow pattern has been suspected of having an influence on this preference. This is again dependent on complex geometry of the circle.

Design, Build, and Test of a Permanently Implanted Prosthetic Hand

The feasibility of a permanently implanted prosthetic hand was evaluated from both an internal biocompatibility and exterior mechanics point of view. A literature review of the issues involved in permanent implantation of a percutanious device was performed in the areas of bone interaction and fixation and neural interface control. A theoretical implant was designed for a 90th percentile male, using a HA-G-Ti composite material to provide a permanent base to which the hand could attach. Using a radial implant length of 1.87 inches and an ulna implant length of 1.32 inches, the simulated implant could withstand a push out force of 10.260 pounds. Using nerve guidance channels and microelectrode arrays, a Regenerative Neural Interface was postulated to control the implant. The use of Laminin-5 was suggested as a method of preventing the lack of wound closure observed in percutanious devices. The exterior portion of a permanent artificial hand was analyzed by the construction of a robotic hand optimized for weight, size, grip force and wrist torque, power consumption and range of motion. Using a novel dual drive system, each finger was equipped with both joint position servos as well as a tendon. Fine grip shape was formed using the servos, while the tendon was pulled taunt when grasping an object. Control of the prosthetic hand was performed using a distributed network of micro-controllers. Each finger’s behavior was governed by a master/slave system where input from a control glove was processed by a master controller with joint servo and tendon instructions passed to lower-level controllers for management of hand actuators. The final weight of the prototype was 3.85 pounds and was approximately 25% larger than the 90th percentile male hand it was based on. Grip force was between 1.25 and 2 pounds per finger, depending on amount of finger flexion with a wrist lifting torque of 1.2 pounds at the center of the palm. The device had an average current draw of 3 amps in both normal operation and tight grasping. Range of motion was similar to that of the human model. Overall feasibility of the device is examined and factors involved in industrial implementation are discussed.

Development and Verification of a Dynamic TKR Model

The success of current total knee replacement (TKR) devices is contingent on the kinematics and contact mechanics during in vivo activity. Indicators of potential clinical performance of total joint replacement devices include contact stress and area due to articulations, and tibio-femoral and patello-femoral kinematics. An effective way of evaluating these parameters during the design phase or before clinical use is via computationally efficient computer models. Previous finite element (FE) knee models have generally been used to determine contact stresses and/or areas during static or quasi-static loading conditions. The majority of knee models intended to predict relative kinematics have not been able to determine contact mechanics simultaneously. Recently, however, explicit dynamic finite element methods have been used to develop dynamic models of TKR able to efficiently determine joint and contact mechanics during dynamic loading conditions [1,2]. The objective of this research was to develop and validate an explicit FE model of a TKR which includes tibio-femoral and patello-femoral articulations and surrounding soft tissues. The six degree-of-freedom kinematics, kinetics and polyethylene contact mechanics during dynamic loading conditions were then predicted during gait simulation.

Biomechanical Analysis of Soft Tissue Neck Injury During Pedestrian Fall

Pedestrians sustain serious injuries when impacted by vehicles [1]. Various biomechanical studies have focused on pedestrian injuries due to direct contact with the vehicle and environment [1–5]. Similar studies on the injuries to the pedestrian due to indirect force such as inertial load are limited [6]. One of the most susceptible regions of the human body to inertial loading is the neck component (cervical spine). The cervical spine connects the head and upper torso, and provides mobility to the head. Direct loading to the head and/or upper torso subjects the cervical spine to indirect loading. For example, in a pedestrian lateral fall on the shoulder, the cervical spine flexes laterally due to inertial loading from the head and upper torso, and may injure its soft tissue components. The purpose of this study is to delineate the biomechanics of the soft tissue neck injury during the pedestrian lateral fall due to vehicular impact using the anthropometric test device.

Reduction of Flow Rate Into a Saccular Aneurysm After Stenting

Stents, wire-frame structures, are very effective devices in the treatment of vascular diseases, such as stenoses and aneurysms. One-third of patients who have stent placements develop restenosis over a six-month period, with the cause thought to be hemodynamic-related. The use of stent grafts to treat aneurysms often leads to exclusion of smaller vessels adjacent to the aneurysm from the circulation, and success of this procedure may therefore depend on the size of small vessels being occluded. An open stent is preferred to preserve the blood supply to neighboring vessels, but is considered to be less effective in aneurysm thrombosis and in reducing the pressure inside the aneurysm.

Measurements of Mean Velocity and Turbulent Statistics in a Centrifugal Blood Pump

An estimated 150,000 patients in the Western World require heart transplantation every year, while only 4,000 (2.5%) of them actually receive a donor heart [1]. This lack of available donors for heart transplantation has led to a large effort since the 1960s to develop an artificial mechanical heart as an alternative to heart transplant. Most end stage cardiac failures result from cardiac disease or tissue damage of the left ventricle. After this failure, the ventricle is not strong enough to deliver an adequate supply of oxygen to critical organs. A left ventricular assist device (LVAD) is a mechanical pump that does not replace the native heart, but rather works in concert with it. An LVAD can effectively relieve some strain from a native heart, which has been weakened by disease or damage, and increase blood flow supplied to the body to maintain normal physiologic function. The inlet to the LVAD is attached to the native left ventricle, and the output of the assist pump rejoins the output of the native heart at the aorta, as shown in Figure 1. Blood flow from both the aortic valve and the assist pump combine and flow through the body. The clinical effectiveness of LVADs has been demonstrated; however, all of the currently available pumps have a limited life because of either the damage that they cause to blood or their limited mechanical design life.

Vitrification Solutions for the Cryopreservation of Tissue-Engineered Bone

Osteoblast (OB)-seeded hydroxyapatite (HA) scaffold cortical bone substitutes are being developed at Michigan State University. Preservation methods need to be developed to preserve such living products to ensure a steady supply for transplantation. Theoretically vitrification is an attractive method for the cryopreservation of tissue-engineered bone because it can eliminate the destructive effect of ice formation [1]. However, relatively fast cooling and warming rates are required to avoid damage associated with ice crystallization and relatively high concentrations of cryoprotective agents (CPAs) are required to achieve a glassy (vitrified) state. These rapid rates of temperature change may not be possible as tissue-engineered structures become larger. In addition to cell damage, rapid rates may also cause destructive thermo mechanical damage to the scaffold itself. Slower rates can be used to achieve the vitrified state but this requires higher CPA concentrations, which are more toxic. As a means of studying the interactive determinants of an optimal vitrification process for osteoblasts, we have undertaken thermal analysis of a variety of vitrification solutions of interest using differential scanning calorimetry (DSC) to determine the critical cooling and warming rates. The toxicity dynamics and tendency for the scaffolds to be damaged mechanically by the vitrification process are also examined. Glycerol and dimethyl sulfoxide at a concentration of 40% were studied with and without an ice blocker. Two vitrification “cocktails” (VS55 and VEG) over a concentration range of 80% to 100% were studied with and without an ice blocker. On the basis of these studies 95% VEG with ice blocker was least toxic and yielded the highest recovery (∼90%) for OBs vitrified in liquid suspension. Vitrification does not seem to be detrimental to the bending strength of high density (low porosity) HA scaffolds, but lower density HA scaffolds break more easily after vitrification in some instances.

Superimposed Oscillations Enhance the Clearance of Mucus Simulant at Low Air Flows in a Rigid Tracheal Model

Clearance of mucus by the beating action of cilia is the primary means of removing inhaled particulates and airway debris from airways in healthy people. However many pulmonary diseases are associated with impaired mucociliary clearance mechanisms. For these patients, cough is the default airway clearance mechanism. Unfortunately most pulmonary disease patients can only produce low expiratory flow rates and have difficulty coughing for this reason.

Shape Optimization of Femoral Components of an Artificial Hip Prosthesis Using the Three-Dimensional P-Version Finite Element Study and the In Vitro Measurement of Strain in the Bone Cement

Though Total Hip Arthroplasty (THA) is being performed with greater frequency every year for patients with endstage arthritis of hip, mechanical fatigue of bone cement leading to damage accumulation is implicated in the loosening of cemented hip components. This fatigue failure of bone cement has been reported to be the result of high tensile and shear stresses at the bone cement. The aim of this study is to design the optimum shape of femoral component of a THA that minimizes the peak stress value of maximum principal stress at the bone cement and to validate the FEM results by comparing numerical stress with experimental ones. The p-version three-dimensional Finite Element Method (FEM) combined with an optimization procedure was used to perform the shape optimization. Moreover the strain in the cement mantle surrounding the cemented femoral component of a THA was measured in vitro using strain gauges embedded within the cement mantle adjacent to the developed femoral stem to validate the optimization results of FEM.

Crash Test Software Analysis

The development of highly advanced computer simulation software packages has enabled design engineers to more effectively integrate safety features into their designs. Designs can be tested long before any physical construction ever begins. This saves money, allowing more extensive testing to be performed, and it also saves time, expediting the process of moving concept to reality. In the automotive industry, such software can be especially useful, since computer simulations can be run over and over again, making it possible to observe the effects of adjusting single variables in dynamic situations. This has opened the door for testing of non-typical occupants. Restraints and safety devices are no longer designed to suit the needs of the average person; they can be tailored to account for all body types, or even for the disabled.