Correlation of Nanomechanical and Mineral Properties of Human Osteoarthritic Meniscal Attachments

Meniscal horns attach the meniscus to the underlying subchondral bone. Successful meniscal replacements must maintain horn attachments of the menisci, hence recent studies have been aimed at characterizing the material properties of the ligamentous horn attachments. In order to mimic material properties in tissue engineered meniscal replacements, we must understand how these properties are influenced by mineral and matrix constituents. Additionally, understanding how osteoarthritis alters the meniscal horn attachments may elucidate appropriate design considerations of such tissue engineered replacements. Therefore, this study investigated the relationship between mechanical and mineral properties of osteoarthritic meniscal attachments.

A First Optimal Control Solution for a Complex, Nonlinear, Tendon Driven Neuromuscular Finger Model

In this work we present the first constrained stochastic optimal feedback controller applied to a fully nonlinear, tendon driven index finger model. Our model also takes into account an extensor mechanism, and muscle force-length and force-velocity properties. We show this feedback controller is robust to noise and perturbations to the dynamics, while successfully handling the nonlinearities and high dimensionality of the system. By extending prior methods, we are able to approximate physiological realism by ensuring positivity of neural commands and tendon tensions at all times.

Functional Role of the Superior Articular Facets of the Atlas in the Enhancement of Craniovertebral Junction Stability

Whiplash distortions of the cervical spine, occurring during the retraction phase of a rear end automobile accident, are known to cause posterior translation of the head relative to the chest and shoulders [1,2]. This anteroposterior shear produces sagittal plane rotation of the cervical spine which results in relative flexion between the occiput and the atlas (Fig. 1). This study demonstrates that there is a significant difference between the average angles of the anterior aspects and the posterior aspects of the superior facets of the atlas with respect to a horizontal (transverse) plane at P<0.01. We hypothesize that developmental variations in some individuals will allow excessive posterior translation of the head during rear end automobile accidents, and that this excessive motion may increase the risk of sustaining a whiplash-type injury for some individuals.

Compression Testing of 3D Polymer Fabrics for Use as Cartilage Scaffolds

The onset of osteoarthritis is characterized by damage to articular cartilage. Current treatments include pharmaceutical therapies and arthroplasty procedures. Work on a new type of device that uses orthogonal woven polymer scaffolds as a structure for tissue engineering of cartilage has been cited in the literature [1].

Fluid-Structure Modeling of Lung Epithelial Cell Deformation During the Reopening of Compliant Airways

Acute respiratory distress syndrome (ARDS) is a severe lung disease caused by a variety of direct and indirect insults. During ARDS edema fluid accumulated in the lung inhibits gas exchange between air and blood. The main treatment for ARDS is mechanical ventilation. The ventilation of fluid filled lungs involves the propagation of microbubbles over a layer of epithelial cells as shown in Figure 1. Unfortunately, experimental studies [1,3] have demonstrated that the large shear and normal stress gradients generated by microbubbles cause significant cellular deformation and injury. As a result, the mortality rates for ARDS is high (∼30–40%).

Towards Non-Invasive Pressure Assessment

In clinical practice, ultrasound is frequently applied to non-invasively assess blood velocity, blood volume flow and blood vessel wall properties such as vessel wall thickness and vessel diameter waveforms. To convert these properties into relevant biomechanical properties that are related to cardiovascular disease (CVD), such as elastic modulus and compliance of the vessel wall, local pressure has to be assessed simultaneously with vessel wall thickness and vessel diameter waveforms. Additionally, accurate estimates of vascular impedance (transfer function between pressure and blood flow) can be a valuable tool for the estimation of the condition of the vessel, e.g., to diagnose stenosis. Studies of arterial impedance in humans, however, are hampered by the lack of reliable non-invasive techniques to simultaneously record pressure and flow locally as a function of time. Local pressure assessment together with flow has great potential for improving the ability to diagnose and monitor CVD.

Effect of Mechanical Stimulation on Mesenchymal Stem Cell Seeded Cartilage Constructs

Articular cartilage is a specialized tissue with a restricted capacity for self-repair. Thus, there is a need for a functional tissue replacement product for cartilage due to the ever-increasing occurrence of cartilage injuries and osteoarthritis. Engineering a cartilage replacement construct entails a combination of source cells, cytokines/growth factors, differentiation factors, and a supportive structure to mimic the native environment [1]. An abundant source of cells, isolated from adult bone marrow, are mesenchymal stem cells (MSCs), which when isolated can be a rich cell source given their capacity for chondrogenic differentiation [2].

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.