Urethral dysfunction is a common complication of diabetes mellitus, spinal cord injury, vaginal childbirth, and pelvic trauma. Stress urinary incontinence (SUI) is the involuntary loss of urine due to the inability of the urethral sphincter to maintain a tight seal during the storage phase and is a condition that physically and emotionally affects 25 million American women annually [1]. There are currently several treatments for SUI including surgery, Kegel exercises, and electrical stimulation, each accompanied by limited effectiveness and/or complications [2–3]. We believe that regenerative medicine techniques, applied to the native urethra, may aid in improving the function and support of the diseased urethra. Thus, we have begun the development of a tissue engineered urethral wrap (TEUW) for placement as a cuff around the native urethra and integration with the host tissue. The goal of this work was to explore structural and mechanical effects following implantation of a TEUW.

Current methods of atlantoaxial stabilization rely on screw fixation. Screw placement may be transarticular, or C1 lateral mass screws in combination with pedicle or pars screws at C2. These techniques can put the vertebral artery at risk. There is also dissection around the ganglion of the second cervical nerve root, which can lead to significant bleeding or postoperative pain.

In the last two decades, decellularized native aortic valve (AV) has been investigated as tissue engineered heart valve (TEHV) replacements due to their potential to develop into a viable valve. [1] Decellularization removes major immunogenic cellular components. After repopulated with recipient’s cells, TEHV can be readily used because of the necessary functional design. [2] However, several problems with this approach have been identified, such as insufficient cell infiltration, mechanical deterioration, formation of fibrous sheath on implantation, and reduced orifice area after surgery. [3]

Endoscopes are used in medicine to inspect inside the body without having to perform open surgery on the patient. The current gold standard for screening and diagnosing colorectal cancer and inflammatory bowel disease is the colonoscopy. This procedure uses a flexible endoscope to inspect the wall of the large intestine, from the rectum to the caecum, for cancerous or precancerous lesions. This screening is very important since early detection of colon cancer is 85–95% successfully treated. Unfortunately, there is only a 30% compliance rate for colonoscopies in the United States. This lack of compliance is due largely in part to the uncomfortable nature of the procedure, caused by the fact that the stiff scope is difficult to manipulate in the non-rigid colon, leading to “looping” of the scope (see Fig. 1), and that the clinician is essentially navigating in near blind conditions during the procedure.

Tissue engineering provides a means to create fully functional tissue-equivalents that can grow, repair and remodel in vivo . Our laboratory’s approach to fabricating artery- and heart valve-equivalents utilizes cell-seeded fibrin gels. However, even after 4–5 weeks of static incubation, the mechanical properties of these constructs are below those of native tissue. Previous studies in our laboratory have shown a significant role of mechanical stretching in improving properties of collagen-based tissue constructs (Isenberg and Tranquillo, 2003). We examined the effects of cyclic distention (CD) of cell-seeded fibrin-based tubular constructs (TC) and valve-equivalents (VE) after five weeks of culture. We used human dermal fibroblasts and porcine valve interstitial cells as the cell sources. Circumferential strain amplitudes from 2.5% to 15% were applied to evaluate the effects of CD on remodeling of the TC. We further hypothesized that during long-term conditioning, cells adapt to CD of constant strain amplitude, diminishing the remodeling into tissue. We tested this hypothesis by applying step-wise incremental CD (ICD) from 5%–15% strain amplitude and compared this group to a set of samples subject to CD of constant strain amplitude in this range. Based on the outcome of the cyclic distension study with tubular constructs, we applied CD to VE in a novel bioreactor.

It is usually assumed, in both clinical and experimental settings, that blood velocity profiles in the common carotid artery (CCA) are fully-developed. This allows for a simpler estimation of CCA flow rates or wall shear stresses (WSS) from limited velocity data, such as peak velocities acquired using Doppler ultrasound (DUS) [1]. However, the assumption of a long, straight CCA may be incorrect, as the CCA does possess some curvature [2], which may alter the velocity profile from the assumed Poiseuille or Womersley shapes, and thus lead to incorrect inferences about flow rate or WSS. Consequently, this may have an impact on our understanding and diagnoses of cardiovascular related diseases. The aim of this study was to characterize the real shape of CCA velocity profiles in vivo.

Cellular mechanics involves the ability of cells to sense and respond to external forces. The type of deformations that cells undergo such as stretching, compression or shearing depends on physiological conditions such as how muscle deforms during movement. Using a custom fabricated stretching device, we focused on investigating how statically applied mechanical stretch affects syndecan-4, focal adhesion complexes and phosphorylated focal adhesion kinase (p-FAK). These results have potential implications in a variety of fields including biophysics, mechanotransduction, and cellular structure.

Acrylic bone cement is a porous biomaterial with many applications across both the medical and dental fields. In orthopaedics, it is used in the fixation of artificial implants where it forms a mechanical bond between the implant and the surrounding tissue. Bone cement is prepared during surgery by mixing a polymer powder and a liquid monomer. The mixture is then inserted into the body in a dough-like state, setting around the implant. Due to the manner in which the cement is prepared and inserted, the material tends to contain defects. Porosity arises in the cement due to trapped air and evaporation of the monomer during the mixing process. Larger defects of various shapes occur as a result of trapped debris, incomplete filling of the space, premature solidification and shrinkage: these are all similar to causes of defects in castings and injection-mouldings [1]. Even without these defects, stress concentrations can arise due to protrusion of bone into the cement as well as the geometry of the hip implant. High stresses can occur in the cement close to the femoral stem, the magnitudes of which are dependant of the cross-section of the stem and other design features [2].

The primary goal of tissue engineering is to develop a biological, mechanically-robust, and anti-thrombogenic vascular graft to replace diseased or damaged tissue and organs [1]. For example, researchers have incorporated smooth muscle cells (SMCs) into extracellular matrix to provide a living, functional conduits with the intended purpose of replacing SMC-containing tubes, such as the blood vessel, urethra, esophagus, intestine, etc. Although the preferred source is autologous cells to avoid immunological rejection, adult SMCs are difficult to obtain and expand. An alternative source of autologous cells could be bone marrow derived stem cells (BMSCs), which differentiate toward mesenchymal and hematopoietic lineages [2].

Modeling pulsatile flow past heart valves remains a relatively unexplored but critical area. Due to the geometric complexity and the interaction between the flowing blood and the heart valve leaflets, existing numerical techniques that require domain discretization, such as finite element methods or finite difference techniques, cannot fully represent the moving and deforming boundaries present in an operating valve. Our aim is to develop a technique to model the flow through heart valves which includes the interaction between the blood flow and the valve leaflets using the radial functions method (RFM). The RFM is a meshless technique that fully accounts for moving and deforming surfaces and thus is well suited to model the blood flow and its interaction with leaflet motion. Here we present a 2D fluid structure interaction (FSI) model of the blood flow through a bileaflet mechanical heart valve (MHV).

In studies on nervous tissues, researchers have investigated the relationship between tracer distributions, infusion pressure, flow rate, and tissue properties to optimize and implement infusion techniques [1]. Intratumoral infusion studies have also measured pressure gradients in vitro and determined how drug delivery depends on intrinsic tissue structures [2]. Measuring pressure gradients allows for the calculation of tissue transport properties such as hydraulic conductivity. This property is necessary for modeling extracellular flow and convective transport through tissues. However, it remains a challenge to measure in vivo pressure gradients due to difficulties in measuring small changes in pressure over short distances and the invasive nature of these experiments. Porous media models of infusion predict exponential decay of the pressure profile in tissues [3], but experimental studies to validate these results in biological tissue or hydrogels are lacking. In this study, we measured the pressure within a hydrogel at different distances from an infusion source. The measured pressure gradient was used to estimate hydraulic conductivity of the hydrogel. Eventually, the developed infusion-pressure testing system may be used to characterize hydraulic conductivity of biological tissues.

Cerebral aneurysms are a mayor cause of hemorrhagic stroke which is a highly significant and devastating disease. Currently there is an increased interest in using endovascular devices for flow diversion such as stents, for treating intracranial aneurysms [1]. Several studies have proven that the geometry and position of the stent in its deployed state play a mayor role in the way the blood flow is diverted. The design of flow diverters and the selection of the most appropriate device for a given aneurysm require a computational model to study the changes in the blood flow patterns after stenting. In this paper an innovative methodology for virtual deployment of stents within patient-specific anatomical models is presented. One remarkable property of this technique is the ability to easily interchange different stent designs within the same model in order to perform fast comparative characterizations.

Cryosurgery, the minimally-invasive destruction of undesirable tissues by freezing, is an attractive technique for treating diseases where tight control over lesion size and minimal scar tissues are crucial, such as cancer and dermatologic disorders (1, 2). Unlike hyperthermic (high temperature) treatments, cryosurgery maintains the integrity of the extracellular matrix (ECM) while destroying the cells of the tissue. The undamaged ECM results in a unique wound healing process, which, compared to most injuries, leads to a better tissue recovery. Thus, cryosurgery has been of great interest in many clinical fields and has been studied extensively. However, numerous questions remain.

In the applications of bioheat transfer, cells and tissues are exposed to various stresses from high and low temperatures, freezing, drying and chemicals, and resultantly they are damaged and dead However, the mechanism of cell damage and death due to the stresses is not sufficiently understood quantitatively. Also, mathematical model of cell damage and death for the prediction of cell lethality and viability is undeveloped. The prediction could contribute to design and optimization of the relevant devises and processes.

Flipchip assembly is the direct electrical connection of the device die on the substrates or circuit boards using conductive stud bumps. Stud bumps help in the reduction of the number of bond wires and weight, and improve performance. Ueno et al. [1] fabricated copper column bumps with a diameter of 75 μm, a height of 50 μm and a pitch of 200 μm. Ni/Au bumps were also fabricated using electroless plating method with a pitch of 50 μm [2]. Tomita et al. [3] successfully fabricated tip capped copper column bumps with a height of 5 μm that were spaced 100 μm apart. Lead free solder bumps have been fabricated using pure-tin (Sn), tin-bismuth (80wt%Sn:20wt%Bi), tin-copper (99.3wt%Sn:0.7wt%Cu), tin-silver (96.5wt%Sn:3.5wt%Ag), and tin-silver-copper (93.8wt%Sn:3.5wt%Ag:0.7wt%Cu) alloys with a diameter of 200 μm and a pitch of 400 μm [4]. Low cost gold bumps have also been fabricated on polymer substrates with dimensions of 40 μm in diameter, 41 μm in height and a pitch of 100μm [5]. More recently Chu et al. [6] have demonstrated the use of cylindrical indium solder bumps with 80 μm diameter for optical interconnect and microwave applications.

In the United States, it is estimated that in 2008 approximately 1.2 million people will suffer a new or recurrent myocardial infarction. In 2005, the latest full year for which statistics are available, 16 million Americans (7.3% of the population) had some form of coronary heart disease. Loss of myocardium as a result of myocardial infarction increases wall stress locally and globally and triggers adaptive responses at the molecular, cellular, and tissue levels. These adaptive responses can lead to left ventricular dilation and congestive heart failure. Accurate non-invasive evaluation of myocardial structural degeneration (damage) and left ventricular remodeling following an infarct would have both prognostic and therapeutic value clinically.

Mechanical integrity of arteries is vital for maintaining compensatory mechanisms under physiologic conditions, and changes in vessel structure (and consequently, vessel mechanical properties) are hallmarks of the progression of pathologic states. Oxidative stress can (1) induce endothelial dysfunction by interfering with nitric oxide (NO) signaling pathways relevant to vasodilation/vasoconstriction of arteries, and (2) alter atherosclerotic plaque composition by oxidation of constituents or by interruption of reverse cholesterol transport from plaques.

Much attention has been given to the motions of and the forces and moments exerted upon the cervical spine during rear-end collisions, often in the interest of understanding so-called whiplash injuries in low-speed collisions and serious or fatal neck injuries in higher speed collisions. In contrast, lumbar spine loads are seldom recorded in rear-end collisions. For example, it has become common to place instrumented anthropomorphic test devices (ATDs) in vehicles during FMVSS 301 Fuel System Integrity rear-end impacts. Since the mid-1990s, upper neck loads have been measured during these tests, and, more recently, lower neck load data have been collected as well [1]. Lumbar spine loads, in contrast, are generally not recorded [1].

Proteoglycans and Type II collagen represent the two major biochemical constituents of articular cartilage. Collagen fibrils in cartilage resist the swelling pressure that arises from the fixed charges of the glycosaminoglycans (GAGs), and together they give rise to the tissue’s unique load bearing properties. As articular cartilage exhibits a poor intrinsic healing capacity, there is significant research in the development of cell-based therapies for cartilage repair. In some of our tissue engineering studies, we have observed a phenomenon where chondrocyte-seeded hydrogel constructs display cracking in their central regions after significant GAG content has been elaborated in culture. A theoretical analysis was performed to gain greater insights into the potential role that the spatial distribution of proteoglycan and collagen may play in this observed response.

Skeletal muscles’ primary function is the application of force to its bony origins and insertions. There are various models of muscle function that generally assume a uniform behavior from origin to insertion during force generation even though the structure and activation is complex. Engineering strains within skeletal muscles, though, have been shown to be non-uniform [1]. We have developed methods to quantify Lagrangian finite strains using cine phase-contrast magnetic resonance imaging (CPCMRI) and post-processing algorithms [2] and have described them during cyclic motion in the supraspinatus and biceps brachii. Principal and maximum in-plane shear strains can be identified at the scale of millimeters throughout the contracting and elongating muscle.