Atherosclerosis is a disease characterized by arterial plaques that include several components of which the necrotic core has been recognized as an important indicator of the likelihood of plaque rupture [1]. In the present study, the relation of hemodynamic wall shear stress (WSS) to necrotic core localization in the left coronary artery of patients was investigated using intravascular ultrasound (IVUS) and computational fluid dynamics (CFD). An innovative 3D measuring technique was developed and was successfully used to reconstruct coronary arteries in patients based on angiographic images and echo ultrasound slices from IVUS. The reconstruction includes lumen, external elastic membrane (EEM) and spatial distribution of plaque components such as fibrous tissue, necrotic core and calcium. WSS distribution in the vessel segment was computed by CFD, and the relative locations of necrotic core and WSS were determined. Results to date support the hypothesis that a greater necrotic core in coronary plaques is associated with areas of low WSS. The methodology developed has implications for the study of plaque progression and the prediction of likelihood of plaque rupture.

Head fold morphogenesis constitutes the first discernible epithelial folding event in the embryonic development of the chick. It arises at Hamburger and Hamilton (HH) stage 6 (approximately 24 hours into a 21-day incubation period) and establishes the anterior extent of the embryo [1]. At this stage, the embryonic blastoderm is composed of three germ layers (endoderm, mesoderm, and ectoderm), which are organized into a flat layered sheet that overlies the fibrous vitelline membrane (VM). Within this blastodermal sheet, a crescent-shaped head fold develops just anterior to the elongating notochord, spanning across the embryonic midline at the rostral end of neural plate. At the crest of this fold, the bilateral precardiac plates fuse in a cranial to caudal direction and give rise to the primitive heart tube and foregut [2, 3]. An understanding of head fold morphogenesis may thus offer insight into how embryonic tissues are arranged to make ready for proper cardiac formation.

Certain serious illnesses, including pneumonia and the acute respiratory distress syndrome (ARDS), can lead to fluid accumulation in the lung and obstruction of the small pulmonary airways. Fluid in the lungs inhibits gas exchange and patients may require mechanical ventilation, which can expose the lung to mechanical stresses that exacerbate the existing injury and result in additional fluid accumulation. Recent improvements in ventilation protocols (e.g. low lung volume ventilation) have improved ARDS treatment, but mortality rates remain high (30–40%).

Cardiovascular and lung diseases are the leading causes of death and disability worldwide. There are many therapies available for their treatment such as simple lifestyle changes, medicines, and surgical intervention or corrections. For the cases where the above treatments do not alleviate the patients’ conditions, the use of artificial devices may be the only option to treat or replace the diseased organ(s). However, the consideration of blood containing biomedical devices may introduce a prolonged contact between the blood and inorganic surfaces which induces variety of blood damages including hemolysis due to the creation of non-physiological mechanical shear stress field. Hemolysis is the release of hemoglobin from the red blood cells (RBC) as a result of the rupture of RBC membrane due to these unavoidable mechanical effects. For that reason, characterization of fluid dynamics and hemolytic performance is the key step to evaluate the design of biomedical devices.

The mechanical properties of cells have been of great interest to scientists from early studies which suggested that mechanical stress-induced alterations in cell shape and structure are critical for control of many cell functions. Although various loading tests of a cell have been designed to understand the cellular mechanical properties, the heterogeneous intracellular structure such as cytoskeletons brings about difficulties in interpreting experimental data.

A well known “Polonaise” pattern of epiblast cell movements accompanies formation of the amniote primitive streak (PS), which is the organizing center for gastrulation. Although the movements observed in classical (text book) and modern studies appear similar, the biophysical mechanisms driving these movements are unknown. In comparison to studies of dynamic cellular movements during PS formation, and more generally, gastrulation, there is a relative paucity of data regarding movement of the extracellular matrix (ECM) lying adjacent to the ventral surface of the epiblast. Electron microscopy and immunofluorescence studies demonstrated decades ago the presence of a nascent basement membrane-like structure, which we refer to as the sub-epiblastic ECM (SE ECM), containing, at least, fibronectin [1] and collagen [1]. Using ultrastructural markers, Sanders [2] found that the SE ECM is transported medially to the PS with the epiblast cells. Almost two decades later, Bortier et al. [3] grafted radiolabeled quail cells into the epiblasts of chicken blastoderms, and concluded that whole groups of epiblast cells slide across (move relative to) the SE ECM — thus, contradicting Sanders’ earlier findings.

The relationship that exists between structure and function is a unifying theme in my varied biomembrane-based research activities. It applies equally well to the lipid as to the protein component of membranes. With a view to exploiting information that has been and that is currently being generated in my laboratory, as well as that which exists in the literature, a number of web-accessible, relational databases have been established over the years. These include databases dealing with lipids, detergents and membrane proteins. Those catering to lipids include i) LIPIDAT, a database of thermodynamic information on lipid phases and phase transitions, ii) LIPIDAG, a database of phase diagrams concerning lipid miscibility, and iii) LMSD, a lipid molecular structures database. CMCD is the detergent-based database. It houses critical micelle concentration information on a wide assortment of surfactants under different conditions. The membrane protein data bank (MPDB) was established to provide convenient access to the 3-D structure and related properties of membrane proteins and peptides. The utility and current status of these assorted databases will be described and recommendations will be made for extending their range and usefulness.

In the present study, we report the effects of cooling ejaculated and epididymal bovine sperm from the same animals with and without a cryoprotective agent, glycerol. Water transport data during freezing of ejaculated and epididymal bovine sperm cell suspensions were obtained at a cooling rate of 20 °C/min under two different conditions: i) in the absence of cryoprotective agents, CPAs; and ii) in the presence of 0.7 M glycerol. Using previously published values, the bovine sperm cell was modeled as a cylinder of length 39.8 μm and a radius of 0.4 μm with an osmotically inactive cell volume, V b , of 0.61V o , where V o is the isotonic cell volume. The subzero water transport response is analyzed to determine the variables governing the rate of water loss during cooling of bovine spermatozoa, i.e. the membrane permeability parameters (reference membrane permeability, L pg and activation energy, E Lp ). The predicted best-fit permeability parameters ranged from, L pg = 0.021 to 0.038 μm/min-atm and E Lp = 27.8 to 41.1 kcal/mol. The subzero water transport response and consequently the subzero water transport parameters are not significantly different between the ejaculated and epididymal bovine spermatozoa under corresponding cooling conditions. If this observation is found to be more generally valid for other mammalian species as well, then the sperm extracted from the testicles of an animal during post-mortem can also be optimally cryopreseved using procedures similar to those derived for ejaculated sperm.

Motive . The motivation of the current study is to investigate the response of vesicles to applied electric fields, with potential applications in electroporation-mediated molecular delivery [3]. In this technique, an applied field transiently permeabilizes the cell membrane to gain access to the cytoplasm, and deliver active agents such as genes, RNA, proteins into the cell. Although widely applied in classical and emerging areas such as drug delivery and stem cell research, current electroporation techniques suffer from low efficiency and high cell death [4]. The present work is a step towards understanding the complex fundamental processes involved in electroporation, and possibly improving it via parametric optimization. For this purpose we use vesicular cellular mimics as our model to provide good controllability, and to focus on the dynamics of the lipid membrane. Our preliminary results show extreme elongation of the vesicles under high-strength, short-duration DC pulses. Such deformation may significantly affect electroporation, and hence the efficiency of molecular delivery.

Hemodialysis (HD) remains the primary treatment modality for the management of renal failure patients. Hemodialysis membranes play an important role in renal replacement therapy (RRT). HD is an extracorporeal blood clean process where the major mass transfer mechanism is diffusion. This therapy is mainly effectual for low molecular weight (LMW) solutes (such as urea and creatinine) removal or clearance for which diffusive mass transfer is a swift process. There is an increase in the removal of middle molecular weight (MMW) solutes (such as β2-microglobulin) when high flux membranes are available. Hemodiafiltration (HDF) is a treatment where the convective mass transfer accolades with diffusive mass transfer to increase the solute clearance efficacy, specifically for MMW solutes. The convective mass transfer is reliant on the amount of fluid exchanged. Toxin removal efficiency of HDF significantly depends on the porosity, pore size, pore distribution and surface area of the membrane [1, 2] . Although newly developed high flux polysulfone membranes have high MMW solute clearance, the non-uniform pore size and pore distribution is the main contributors to the albumin loss. Previous studies by Huang et al. [3] , showed that nanoporous alumina sheet membranes have uniform pore size (∼ 10nm), high hydraulic permeability, uniform pore distribution and excellent pore structure with uniform channels. It was predicted that these membranes would have high molecular removal capacity. Therefore, in this study, experiments were performed to generate the data of intrinsic membrane properties such as hydraulic permeability, sieving coefficient and solute diffusive permeability for the alumina tubular membranes. Results were also compared to current polyethersulfone (PES) dialysis membranes.

Geobacter sulfurreducens is a δ-proteobacterium capable of electron transfer to extracellular compounds and surfaces [1] that has possible technological applications in microbial-based sensors, bioremediation of contaminated environments and harvesting electricity from waste organic matter [2]. Further development of many of these applications requires stabilization and preservation of bacteria as thin films on surfaces. One method of encapsulating bacteria in thin films is through the use of porous latex coatings [2]. However, during the formation of these films, the bacteria are exposed to osmotic stresses.

Advancements in optics and digital imaging tools have often led to new insights into tissue structure. Newly available computer controlled lcd polarizing filters have provided unprecedented control over light waveforms and structure. Inexpensive digital cameras have many times greater color sensitivity. Our goal is to apply these new technologies to quantitative imaging of aortic valve structures in-situ. We have developed a new elliptically polarized light imaging system (EPLIS) and technique for imaging aortic valve tissues. This new technique reveals takes advantage of the birefringent property of collagen to reveal multi-layered collagen fiber and membrane valve structures that were previously unknown . Using digital imaging correlation (DIC) image analysis software (developed in-house), the new imaging technique allows direct measurement of the internal deformations of aortic valve specimens during controlled loading. We present our imaging and analysis techniques, along with time-lapse images showing the complex structure of the aortic valve and direct measurements of deformations under controlled loads.

The actin cytoskeleton provides mechanical support for the cell and influences activities such as cancer metastasis and chemotaxis. While their mechanical responses have been studied in vivo and in vitro , understanding the link between these two forms remains challenging. To explore this gap and further understand cell structure, we reconstructed the cell cytoskeleton in a membrane-like spherical liposome to mimic the cellular environment; this enables an artificial “cell like” system. Through this approach, we are pursuing a path to compare in vitro mechanics from a polymer physics perspective of individual actin filaments with the in vivo mechanics of a living cell [1]. A living cell contains many organelles, which are in a highly packed environment and require significant organization to function. The actin cytoskeleton provides both structural and organizational regulation that is essential for cellular response. Here, we first encapsulated G-actin into giant unilamellar vesicles through an electroformation technique and then polymerized them into actin filaments (F-actin) within individual vesicles. To probe their conformation, we visualized these vesicles with fluorescence and laser scanning confocal microscopy. We then used a tapping mode atomic force microscopy to determine the mechanical properties of these cell-like systems. These results provide insight into a wide range of fields and studies including polymer physics, cell biology, and biotechnology.

In the present study, we report the effects of cooling ejaculated and epididymal rhesus monkey ( Macaca mulatta ) sperm in the presence of extracellular. Water transport data during freezing of ejaculated and epididymal sperm cell suspensions were obtained at a cooling rate of 20 °C/min in the absence of any cryoprotective agents. Additional water transport data was obtained from ejaculated sperm at a cooling of 5 °C/min without CPAs and at 20 °C/min in the presence of 0.7M of glycerol, as well. Using previously published values, the bovine sperm cell was modeled as a cylinder of length 73.83 μm and a radius of 0.32 μm with an osmotically inactive cell volume, V b , of 0.772V o , where V o is the isotonic cell volume. The subzero water transport response is analyzed to determine the variables governing the rate of water loss during cooling of bovine spermatozoa, i.e. the membrane permeability parameters (reference membrane permeability, L pg and activation energy, E Lp ). The predicted best-fit permeability parameters ranged from, L pg = 0.0023 to 0.0029 μm/min-atm and E Lp = 10.6 to 45.5 kcal/mol. The subzero water transport response and consequently the subzero water transport parameters are not significantly different between the ejaculated and epididymal macaque spermatozoa under corresponding cooling conditions.

In a typical cryopreservation protocol, the system to be preserved is first equilibrated with chemicals known as cryoprotective agents (CPAs). CPAs have been shown to alleviate cell damage from either the solute effects or the formation of intracellular ice during the subsequent freezing process. Thus, an extensive body of literature reporting the effects of CPAs on cellular systems has been accumulated over the last 50 years; detailing largely experimental interactions between cell systems and chemicals. Recent advances in computational methodology now offer an additional dimension in our ability to understand the molecular interactions between cell membranes, idealized as lipid bilayers and CPAs at atomistic scales. Computer simulations provide unique capabilities for analyzing biomembrane properties from atomistic perspective with a degree of detail that is hard to reach by other techniques. The excellent agreement with the experiment obtained in various molecular dynamics (MD) studies [1] on simple model membranes has raised the confidence in applying the molecular dynamics simulations to even more complex systems. Dimethylsulfoxide (DMSO) is one of the most widely used solvents in cell biology and cryopreservation. During a typical cryopreservation protocol the DMSO composition of aqueous buffers inside and outside of the cell is known to differ considerably. To model and understand the structural changes in cell membranes in such a situation we performed MD simulations of an idealized lipid bilayer membrane which separates two aqueous reservoirs with and without DMSO. Zwitterionic dimyritoylphosphatidylcholine (DMPC) lipid bilayers was chosen as the model membrane.

The primary function of the lens of the eye, termed accommodation, is to precisely focus light onto the retina by changing curvature and corresponding refractive power. Investigators have long sought to understand the mechanism of accommodation in terms of interactions of the constituent tissues, which recently has been aided by biomechanical modeling. Such models depend heavily on accurate measurements of tissue mechanical properties and seek to predict stresses and strains. A critical component of the accommodative apparatus is the lens capsule, a bag-like membrane that encapsulates the lens nucleus and cortex and mediates tractions imposed onto this structure by the ciliary body. In addition to this physiologic process during normalcy, the lens capsule also plays a fundamental role in cataract surgery; a procedure that involves three basic steps: a quarter of the anterior lens capsule is removed via the introduction of a continuous circular capsulorhexis (CCC), the lens is broken up and suctioned out, and an artificial intraocular lens (IOL) is placed within the remnant capsular bag. Although novel IOL designs have decreased post-surgical complications, they currently lack the important feature of accommodation. Therefore, mechanical analysis of the lens capsule will allow for an understanding of its interaction with an implant that may further assist in the design of future accommodating IOLs (AIOLs). Here, we report a novel experimental approach to study in situ the regional, multiaxial mechanical behavior of both normal and diabetic human anterior lens capsules. Furthermore, we use these data to calculate material parameters in a nonlinear stress-strain relation via a custom sub-domain inverse finite element method (FEM). These parameters are then used to predict capsular stresses in response to imposed loads using a forward FEM model.

Many preservation methods have utilized sugars such as trehalose as protectants against injury during cell preservation processing, especially during drying (1–5). As mammalian cells do not synthesize trehalose, research in the mammalian cell desiccation field has focused on the development of strategies to enable trehalose delivery into the intracellular milieu. Numerous techniques have been explored ranging from microinjection (2) to the creation or utilization of membrane pores (1,3). Fluid phase endocytosis has shown great promise as an effective strategy for non-invasively delivering water-soluble materials into the intracellular space (4, 5). In this technique trehalose is transported across the cell membrane in membrane-bound cellular compartments called endosomes. Cells incubated in cell culture medium containing trehalose have been shown to take up considerable amounts of trehalose by this technique (4, 5). How much of this trehalose actually become available for protection of biomolecules during the dehydration process has yet to be determined.

Basement membranes are ubiquitous. In humans, genetic disorders in basement membranes can lead to many complications including kidney disease, skeletal muscle myopathy, hearing loss, and ocular abnormalities[1]. We hypothesize that genetic mutation of the microstructure of the lens capsule basement membrane will alter its mechanical properties. Because of its unique thickness and anatomically distinct margins, the lens capsule is the only site in the body where large-scale mechanical tests on the basement membrane can be made.

Fibroblast cells are crucial in the human body for maintenance of the extracellular matrix, including synthesizing macromolecules like collagen, and they play a critical role in wound healing of soft tissues such as skin [1]. Directing fibroblast growth is an important step in tissue engineering where the focus has gone from a top-down approach of homogeneously introducing cells into a pre-formed scaffold to a bottom-up approach in which the tissue construct is built on a cell-by-cell basis with ability to manipulate specific cell environments through location, proximity, and geometry. The ability to direct cell proliferation to encourage organized tissue formation can provide tissue engineers a means of controlling the architectural and mechanical properties of soft tissue scaffolds. This approach to functional tissue engineering represents a novel direction for the development of replacement tissues. Previous attempts of directed growth have proven successful with C2C12 mouse myoblast cells. Using laser micromachined channels in agarose hydrogel lined with a basement membrane matrix, myoblast cells were guided to align and produce myotubes [2]. The objective of the current study was to apply similar principals to direct fibroblast cell growth and proliferation, ultimately leading to their growth into three-dimensional fibers, on differentially adherent substrates. Channels (widths ranging from 60 μm to 200 μm) were laser micromachined in agarose gel to explore an optimal geometry for cellular proliferation and fiber formation. The fibroblast cells used range in size from roughly 20–30 μm. Thus, the width of each channel was chosen to explore which multiple of cell width would allow for directional alignment parallel to the channel and subsequent fiber growth. The ability to direct fibroblast cells to align and produce fibers through manipulation of their environment is critical to our laboratory’s ongoing efforts to develop three-dimensional customized tissue replacement constructs to be used in many soft tissue applications such as ligament and skin grafts.

Due to their clinical outcome high flux dialysers containing new generation of dialyser materials have been widely used for patients with chronic renal failure within the last decade [1]. Dialyser membranes are more prone to damage to to the harsh environment during high flux dialysis. Reuse of dialysers has advantages like better biocompatibility and lower cost, any damage of the dialysers membrane during reuse of the dialysers can also cause very serious clinical complications. Therefore reuse of the dialysers is an issue that has to be approached more cautiously. In this study polysulphone dialyser membranes were being investigated in terms of mechanical properties and changes in crystallinity before and after dialysis sessions. Dialysis sessions were performed on five patients with dialysis age less than two years and without any other accompanying disease at the Hemodialysis Department of Istanbul Haydarpasa Numune State Hospital.