Measuring Strain Distributions in the Anterior Cruciate Ligament Using Ultrasound

Optimal prevention and treatment strategies of anterior cruciate ligament (ACL) injury can be realized with a detailed understanding of how physiological factors impact the ACL. A noninvasive, in vivo method that assesses the ACL’s mechanical integrity is needed to help clarify this multi-factorial pathophysiology. We investigated the use of the noninvasive, in vivo technique, ultrasound strain elastography (USE) (1), to distinguish between normal and injured ACLs. USE is used as a diagnostic tool in oncological (2), hepatic (3), and cardiovascular (4) applications. This technique uses ultrasonic RF data to track tissue motion in order to estimate strain within the tissue.

Increasing Storage Modulus, Contact Angle and Surface Tension of Airway Mucus Increases Clearance by Simulated Cough Through a Model Trachea

Altered surface and viscoelastic material properties of mucus during respiratory diseases have a strong influence on its clearance by cilia and cough. Combined effects of the surface properties (contact angle and surface tension) and storage modulus with relatively unchanged viscosity on displacement of the simulated mucus aliquot during simulated cough through a model adult human trachea is investigated. For the mucus simulants used in this study contact angle and surface tension increase significantly as storage modulus increase while viscosity remains practically unchanged. Displacement of mucus simulant aliquots increased significantly with increasing storage modulus (and contact angle) at a given cough velocity in the range between 5 meters/second (m/s) and 30 m/s with duration 0.3 s. Results suggest that the interactive effects of elasticity and surface properties may help facilitate mucus displacement at low cough velocities.

Three-Dimensional High Resolution Scaffold Fiber Architecture and Morphology in Tissue Engineered Heart Valve Tissue

Engineered heart valve tissue (EHVT) has received much attention as a potential pediatric valve replacement therapy, offering prospective long-term functional improvements over current options. A significant gap in the literature exists, however, regarding estimating tissue mechanical properties from tissue-scaffold composites. Detailed three-dimensional structural information prior to implantation (in vitro) and after implantation in (in vivo) is needed for improved modeling of tissue properties. As such, a novel high-resolution imaging technique will be employed to obtain three-dimensional microstructural information. Analysis techniques will be used to fully quantify constituents of interest including scaffold, collagen, and cellular information and to develop appropriate two-dimensional sectioning sampling protocols. It is the intent of this work to guide modeling efforts to better elucidate EHVT tissue-specific mechanical properties.

The Influence of Trabecular Microstructure on Mechanical Properties and the Pullout Strength of Suture Anchors

Suture anchors provide soft-tissue fixation, often tendons and ligaments, to bone. The most common type of surgery in which suture anchors are used is in rotator cuff repairs, where the anchor is implanted into the humerus to create a point of fixation for the supraspinatus.[1–2] Pullout strength, or the force necessary to pull the anchor from the bone, has been previously used as a metric to compare suture anchor performance. In investigating suture anchor performance, it has been suggested that pullout strength is positively correlated to bone mineral density (BMD).[2]

The Role of Nuclear Stiffness and Resilience in Mechanotransduction

Mechanical force is found to be increasingly important during development and for proper homeostatic maintenance of cells and tissues. The nucleus occupies a large volume fraction of the cell and is interconnected with the cytoskeleton. Here, to determine the direct role of the nucleus itself in converting forces to changes in gene expression, also known as, mechanotransduction, we examine changes in nuclear mechanics and gene reorganization associated with cell fate and with extracellular force. We measure mechanics of nuclei in many model cell systems using micropipette aspiration to show changes in nuclear mechanics. In intact cells we characterize the rheological changes induced in the genome organization with live cell imaging and particle tracking, and we suggest how these changes relate to gene expression.

Critical Design Condensation Locations in Facial Masks

Facial masks are the main interface between patients and breathing supportive devices. Condensation in these masks causes serious breath disturbance which could be life threatening. Based on temperature-driven mass and heat transfer formulations, a computer simulation fluid dynamic model is developed to compute the condensation rate and locations of a typical breathing facial mask. Condensation measurements are taken to validate the model. The effects of mask geometry and shape on condensation are elaborated on.

Design Optimization of a Mechanical Heart Valve for Reducing Valve Thrombogenicity: A Case Study With ATS Valve

Flow past mechanical heart valves (MHV) in mechanical circulatory support devices including total artificial hearts and ventricular assist devices, is primarily implicated in thromboembolism due to non-physiological flow conditions where the elevated stresses and exposure times are sufficiently high to cause platelet activation and thrombus formation. Mitigation of this risk requires lifelong anticoagulation therapy and less thrombogenic MHV designs should therefore be developed by device manufacturers [1].

Development and Biomechanical Characterization of a Novel Bilayer Vascular Graft

Vascular grafts are currently used to treat cardiovascular diseases such as arthrosclerosis by bypass surgery and as vascular access in hemodialysis [1]. There are a number of types of grafts including autologous vessels (such saphenous vein), synthetic grafts (such as expanded polytetrafluoroethylene) and tissue engineered blood vessels. Currently synthetic grafts are most commonly used as blood vessel replacements and there are a number of problems associated with them. One main impediment is that these grafts are not suitable for small-diameter (less than 6mm) vessel replacement [1, 2], due to high occlusion rates. The major concern over the other alternatives such as autologous vessels and tissue engineered products is their availability. Thus, new approaches to constructing biomimetic small-diameter blood vessel equivalents, that are immediately available, may address the unmet demand in this area. Therefore, we have designed a novel bilayer vascular construct which is made up of a nanofibrous intimal-equivalent as thromboresistant vessel lumen and a mimetic extracellular matrix (ECM) as medial-equivalent for smooth muscle cells (SMC) from native artery to invade and remodel the ECM.

The Effects of Geometry and Static Boundary Conditions on Microvessel Outgrowth in a 3D Model of Angiogenesis

We reported previously that, in addition to mechanical strain, a constrained boundary condition alone can alter the organization of microvessel outgrowth during in vitro angiogenesis [1]. After 6 days of culture in vitro, microvessels aligned parallel to the long axis of rectangular 3D collagen gels that had constrained edges on the ends. However, unconstrained cultures did not show any alignment of microvessels. The ability to direct microvessel outgrowth during angiogenesis has significant implications for engineering prevascularized grafts and tissues in vitro, therefore an understanding of this process is important. Since there is direct relationship between the ability of endothelial cells to contract 3D gels and matrix stiffness [2], we hypothesize that some constrained boundary conditions will increase the apparent matrix stiffness and in turn will limit gel contraction, prevent microvessel alignment, and reduce microvessel outgrowth. The objective of this study was to compare microvessel growth and alignment under several different static boundary conditions.

The Use of a Cellular Strain Injury Criterion and Diffusion Tensor Imaging in a Computational Model of Traumatic Brain Injury

With the increase in the number of soldiers sustaining traumatic brain injury from military incidents and the recent attention on sports related traumatic brain injury, there has been a focused effort to develop preventative and treatment methods for traumatic brain injury (TBI). Traumatic brain injury is caused by mechanical loading to the head, such as from impacts, sudden accelerations, or blast loading, and the pathology can range from focal damage in the brain to widespread diffuse injury [1]. In this study, we investigate the injury mechanisms of diffuse axonal injury (DAI), which accounts for the second largest percentage of deaths due to brain trauma [2]. DAI is caused by sudden inertial loads to the head, and it is characterized by damage to neural axons. Despite the extensive research on DAI, the coupling between the mechanical loading to the head and the damage at the cellular level is still poorly understood. Unlike previous computational models that use macroscopic stress and strain measures to determine injury, a cellular injury criterion is used in this work as numerous studies have shown that cellular strain can be related to the functional damage of neurons. The effectiveness of using this cellular injury criterion to predict damage in a finite element model of DAI is investigated.