Presence Of Shear Stress Research Articles

Hypothesizing the interplay of thrombus formation, wall enhancement, and perifocal edema as predictive factors for rupture in brain AVMs

The presence of shear stress within intracranial AVMs (arteriovenous malformations) due to high flow, perinidal angiogenesis, intranidal aneurysms, and biological factors are presumed risk factors for rupture. However, emerging imaging and histological evidence suggests that risk factors for AVM rupture may extend beyond the classical understanding. The presence of perifocal edema at the time of rupture, luminal thrombosis, and vessel wall enhancement on vessel wall MRI elucidate the possibility of an underlying inflammatory process within AVMs, which may predispose them to instability and eventual rupture. We hypothesize that for some AVM ruptures, the occurrence of thrombosis within vascular outpouchings of the AVM initiates a cascade of events, including local hypoxia, inflammation, breakdown of the blood–brain barrier and wall matrix degradation, which is evident from the presence of perifocal edema and vessel wall enhancement observed on imaging. These changes might ultimately raise the risk of AVM rupture and subsequent hemorrhage. Understanding this inflammatory component offers promising insights into AVM pathogenesis and may facilitate the development of preventive strategies to mitigate rupture risk.

P67: An Evaluation of Aspirin and Platelet Activation in the Presence of Shear Stress

Background: Mechanical circulatory support (MCS) causes high levels of shear stress, which could lead to complications such as platelet activation and thrombosis. Aspirin is an anti-platelet drug that functions through COX-1 inhibition, however, this may not be sufficient to reduce activation via mechanical stimuli. As such, this study evaluated the efficiency of Aspirin to reduce the downstream effects of platelet functioning and the impact this may have on shear stress-induced thrombosis. Methods: Human blood was treated with and without Aspirin (4.5 μg/mL) and subjected to VAD-like shear stress for 4 hours. Platelets were analyzed by flow cytometry, using CD42b and CD62P, to assess multifactorial parameters. Positive events were normalized and assessed for platelet activation, granularity (size), as well as the number of platelet-platelet aggregates and platelet-derived extracellular vesicles (EVs). Results: Aspirin moderately reduced platelet activation and platelet granularity compared to the untreated control, suggesting little to no protective effects against mechanical stimulation. However, the presence of Aspirin had a greater effect on reducing the number of platelet aggregates and platelet-derived EVs in the presence of VAD-like shear stress. Conclusion: The use of Aspirin (and COX-1 inhibition) may prove ineffective for reducing platelet activation by mechanical stimuli in high-risk patients. However, Aspirin may impair the downstream formation of pro-thrombotic platelet aggregates and EVs, thereby reducing the risk of thrombosis in MCS patients. As Aspirin is observed to provide some protection, further research into combination therapy with additional anti-platelet drugs is needed to overcome the negative impact of mechanical stimulation.

Recombinant human plasma gelsolin reverses increased permeability of the blood–brain barrier induced by the spike protein of the SARS-CoV-2 virus

BackgroundPlasma gelsolin (pGSN) is an important part of the blood actin buffer that prevents negative consequences of possible F-actin deposition in the microcirculation and has various functions during host immune response. Recent reports reveal that severe COVID-19 correlates with reduced levels of pGSN. Therefore, using an in vitro system, we investigated whether pGSN could attenuate increased permeability of the blood–brain barrier (BBB) during its exposure to the portion of the SARS-CoV-2 spike protein containing the receptor binding domain (S1 subunit).Materials and methodsTwo- and three-dimensional models of the human BBB were constructed using the human cerebral microvascular endothelial cell line hCMEC/D3 and exposed to physiologically relevant shear stress to mimic perfusion in the central nervous system (CNS). Trans-endothelial electrical resistance (TEER) as well as immunostaining and Western blotting of tight junction (TJ) proteins assessed barrier integrity in the presence of the SARS-CoV-2 spike protein and pGSN. The IncuCyte Live Imaging system evaluated the motility of the endothelial cells. Magnetic bead-based ELISA was used to determine cytokine secretion. Additionally, quantitative real-time PCR (qRT-PCR) revealed gene expression of proteins from signaling pathways that are associated with the immune response.ResultspGSN reversed S1-induced BBB permeability in both 2D and 3D BBB models in the presence of shear stress. BBB models exposed to pGSN also exhibited attenuated pro-inflammatory signaling pathways (PI3K, AKT, MAPK, NF-κB), reduced cytokine secretion (IL-6, IL-8, TNF-α), and increased expression of proteins that form intercellular TJ (ZO-1, occludin, claudin-5).ConclusionDue to its anti-inflammatory and protective effects on the brain endothelium, pGSN has the potential to be an alternative therapeutic target for patients with severe SARS-CoV-2 infection, especially those suffering neurological complications of COVID-19.

An electrospun PGS/PU fibrous scaffold to support and promote endothelial differentiation of mesenchymal stem cells under dynamic culture condition

Shear stress is one of the dominant mechanical stimuli present in a vessel wall and an important regulator of endothelial cells functions. It has been shown that shear stress can derive endothelial differentiation of mesenchymal stem cells (MSCs). Engineering a vascular basement membrane thus requires a scaffold that is not only biocompatible but also able to withstand shear stress and support endothelial differentiation of MSCs in the presence of shear stress. In this study, we fabricated an electrospun poly(glycerol sebacate) (PGS)/polyurethane (PU) fibrous scaffold and characterized its physical properties, mechanical properties, and platelet adhesion and hemolysis induction. The developed PGS/PU indicated desirable hydrophilicity (∼41°), an elastic modulus (∼27 MPa) close to that of the Saphenous vein, and no significant level of hemolysis (∼0.03%) and platelet adhesion. The PGS/PU was next seeded with MSCs and implemented in a custom-made bioreactor for applying shear stress (magnitude: ∼15 dyn/cm2, duration: 24 h). Investigating the endothelial-specific gene expression in the presence of shear stress revealed that expression levels of VEGF R-2, VWF, and PCAM-1 significantly increased for the cells seeded on the PGS/PU scaffold compared to those seeded on a glass coverslip. It is thereby concluded that the developed PGS/PU fibrous scaffold can support and significantly promote the endothelial differentiation of MSCs in the presence of shear stress without the need for any growth factors. The findings of this study could provide insights into engineering a functional vascular basement membrane in vitro for vascular tissue engineering applications.

Research on Tunnel Surrounding Rock Failure and Energy Dissipation Based on Cyclic Impact and Shear Loading

Aiming at the cyclic impact deformation and failure of tunnel surrounding rock under shear stress, a self-developed rotation-impact simulation test platform was used to determine the number of failures, stress-strain curves, and energy in the process of cyclic impact failure. The failure process of rock under different impact velocities and shear stresses has been systematically studied. Results show that, under the same impact speed, the shear stress will increase with the increase in the rotation speed, but an upper limit will exist. When the rotation speed reaches this upper limit, the shear stress will no longer increase. The presence of shear stress will reduce the number of impacts required for rock failure. When the impact speed is 7.2 m/s, the number of impacts at the maximum rotation speed is 60% of the static state. When the impact velocity is 16.8 m/s, this value is only 33.3%. At the same impact velocity, the stress-strain curves under different rotation speeds do not change significantly, but with the increase in the rotation speed, the slope of the elastic stage of the stress-strain curve gradually decreases, and the corresponding stress of the rock sample decreases when the maximum strain is reached. With the increase in shear stress, the crushing specific energy required for rock failure gradually decreases. The greater the impact velocity, the more obvious the impact of shear stress on energy dissipation. In the tunnel process, when the surrounding rock is subjected to impact loads from different directions, only the axial strain analysis will have certain safety hazards, and timely support and reinforcement work are required.

Von Willebrand Factor Facilitates Intravascular Dissemination of Microsporidia Encephalitozoon hellem.

Microsporidia are a group of spore-forming, fungus-related pathogens that can infect both invertebrates and vertebrates including humans. The primary infection site is usually digestive tract, but systemic infections occur as well and cause damages to organs such as lung, brain, and liver. The systemic spread of microsporidia may be intravascular, requiring attachment and colonization in the presence of shear stress. Von Willebrand Factor (VWF) is a large multimeric intravascular protein and the key attachment sites for platelets and coagulation factors. Here in this study, we investigated the interactions between VWF and microsporidia Encephalitozoon hellem (E. hellem), and the modulating effects on E. hellem after VWF binding. Microfluidic assays showed that E. hellem binds to ultra-large VWF strings under shear stress. In vitro germination assay and infection assay proved that E. hellem significantly increased the rates of germination and infection, and these effects would be reversed by VWF blocking antibody. Mass spectrometry analysis further revealed that VWF-incubation altered various aspects of E. hellem including metabolic activity, levels of structural molecules, and protein maturation. Our findings demonstrated that VWF can bind microsporidia in circulation, and modulate its pathogenicity, including promoting germination and infection rate. VWF facilitates microsporidia intravascular spreading and systemic infection.

Late-stage Calcific Aortic Valve Disease Within an Aortic Valve-on-a-chip Model

Objective: Calcific aortic valve disease (CAVD) is a progressive disease ranging from aortic sclerosis to severe aortic stenosis. Current treatments include total valve replacement and drug interventions tailored to other cardiovascular diseases. In late-stage CAVD, glycosaminoglycans (GAGs), such as chondroitin sulfate (CS), deposit in the fibrosa layer. Here we utilize 3D microfluidic devices to study the effects of shear stress, CS, and endothelial cells on calcification in an aortic valve fibrosa model to understand CAVD progression. Methods: Valve-on-a-chip devices were fabricated utilizing a wafer mold, soft lithography, and corona discharge. Devices have a flow channel and 3D matrix reservoir of collagen-only healthy controls or with 1mg/mL or 20mg/mL CS. Porcine aortic valve interstitial cells (PAVIC) are embedded within and endothelial cells (PAVEC) seeded onto the matrix. Steady shear stress at 1dyne/cm2 and 20dyne/cm2 was applied using a peristaltic pump at 37°C and 5%CO2. Alizarin Red S (ARS) was used to assess calcific nodule formation after 14-day cultures. Results: PAVIC/PAVEC co-cultures with increasing shear stress and GAGs exhibit increased calcification compared to static controls (Figure 1). Quantitatively, ARS increased as shear stress increased, regardless of GAGs. In the presence of CS, analysis of nodules indicated that nodule size decreased with shear stress, however it increased the total average percent area stained. Valve-on-a-chip models with PAVIC-only show decreased calcium deposition when compared to co-cultures. Conclusions: In vitro calcification increases in the presence of shear stress, PAVEC, and increased concentrations of GAGs. Further studies will identify the chemical composition of nodules and to understand early-CAVD pathophysiology. Given that CAVD has no targeted therapies, the creation of a physiologically-relevant test-bed of the aortic valve will lead to contributions in new therapeutics.

Investigating the use of equivalent elastic approach to identify the potential location of bending-induced interface debonding under a moving load

Poor interface bonding conditions reduce the bearing capacity of asphalt pavements and lead to several distresses. In particular, the association between localized interface debonding and near-surface longitudinal cracking was detected by field observations in the United States. Prediction of potential location and extent of localized interface debonding is important to preclude near-surface cracking. However, there is limited information regarding the onset of localized interface debonding induced by bending. Since interface debonding location and extent may depend on pavement structure, material properties, and loading conditions, a practical approach is needed. Several researchers adopted an equivalent elastic approach to overcome the complexity of modeling the viscoelastic responses of asphalt when evaluating the impact of multiple factors. Therefore, this study focused on determining whether the equivalent elastic approach can be used to identify the potential location of bending-induced localized interface debonding without a significant loss of accuracy. The viscoelastic and equivalent elastic analyses were conducted using 3-D finite element models developed to simulate an asphalt pavement subjected to a moving load. The 3-D equivalent elastic analysis appeared to be sufficient to accurately determine the potential location and extent of localized debonding induced by bending, which are mainly controlled by presence of shear stress in combination with low confinement on the horizontal interface plane. Furthermore, localized debonding was found to likely occur along a strip in the longitudinal direction which resembles a plane-strain problem. This study substantiated that future research efforts can focus on the transverse cross-section when assessing the impact of localized debonding.

Combinatory interpretation of protein corona and shear stress for active cancer targeting of bioorthogonally clickable gelatin-oleic nanoparticles.

Nanoparticle-protein interactions under conditions mimicking physiology determine how nanoparticles (NPs) will behave inside blood vessels and, therefore, the overall outcome of the drug-delivery system. Here, for the first time, we explore the effects of bio-mimicking shear stress and protein corona conditions on novel active targeting of clickable fattigation nanoparticles (NPs) for cancer therapy. Active targeting dibenzocyclooctyne-functionalized biocompatible gelatin-oleic NPs (GON-DBCOs) via a bioorthogonal click reaction were prepared by the desolvation method for delivery of docetaxel (DTX) to lung and breast cancer models. The effect of shear stress (5 dyne/cm2) and human serum albumin (HSA) protein corona on the cellular behavior of NPs was explored under a dynamic microfluidic system in lung (A549) and breast (MCF-7) cancer cell lines. The developed drug-loaded NPs had a particle size of 300nm, a narrow size distribution, positive zeta potential, high encapsulation efficacy (72.4%), and spherical morphology. The particle size of the protein corona-coated NPs increased to 341nm with a negative zeta potential. The inhibitory dose (IC50) increased approximately 3- and 42-fold in A549 and MCF-7 cells, respectively, under dynamic microfluidic conditions compared to static conditions. Cellular uptake was significantly decreased in the presence of shear stress and a protein corona, compared with static conditions, in both lung (A549, **p<0.01) and breast (MCF-7, *p<0.05) cancer cell lines. Clathrin-and energy-dependent pathways were found to be involved in the cellular uptake of NPs. This study could serve as a vital tool for the evaluation of NPs under aggressive bio-mimicking conditions comprising shear stress and a protein corona to predict the in vivo performance of NPs and support the preclinical and clinical translation of NP drug delivery systems.

Understanding controversies in the \u03b1-\u03c9 and \u03c9-\u03b2 phase transformations of zirconium from nonhydrostatic thermodynamics

Significant debate has been noted in the α-ω and ω-β phase transformations of zirconium. The initial pressure of the α-to-ω transformation at room temperature has been reported to vary from 0.25 to 7.0 GPa, while the hydrostatic transformation is believed to occur at approximately 2.2 GPa. Shear stress is commonly considered as a key factor leading to the discrepancy. However, the principal mechanisms previously proposed concluded that the phase transformation pressure would be decreased in the presence of shear stress. The experimental results of the α-ω transformation in zirconium are contrary to this conclusion. In the ω-β phase diagram of zirconium, the dT/dP along the phase boundary near the α-ω-β triple-point was reported to be either positive or negative, but no theoretical explanation, especially a quantitative one, has been proposed. This article aimed to quantitatively investigate and explain the controversies reported in the α-ω and ω-β phase transformations of zirconium by applying a new nonhydrostatic thermodynamic formalism for solid medium, which has recently been proposed and is capable of quantitatively estimating the impact of shear stress on phase transformations in solids.

LRFD for Lateral-Torsional Buckling Resistance of Cellular Beams

Cellular beams are those that present sequential web openings along the span, and are produced by thermal cutting and welding. Studies addressing the lateral-torsional buckling resistance curve of cellular beams according to the American standard are scarce. The objective of the present study is to investigate the lateral-torsional resistance in cellular beams, considering the Load and Resistance Factor Design. To this end, geometrical and material nonlinear analyses are conducted. The cellular beams are simply supported, with fork supports at the ends, and subjected to three types of loading: uniform bending, mid-span concentrated load and uniformly distributed loads. The geometric parameters of cross section and unrestrained length are varied. Results are compared with the nominal and design flexural strength. Failure modes are associated with non-dimensional lateral-torsional stiffness. Considering the application of uniform bending moment, failure modes such as LTB and WDB + LTB occurred. In contrast, considering the presence of shear stress, failure modes such as the Vierendeel mechanism, WPB, and WPB + LTB occurred. It was concluded that when compared with the numerical model results, the design flexural strength was ineffective under inelastic buckling regime, a situation in which interaction of modes of failure can occur. When considering only the pure lateral-torsional bucking, the Load Resistance Factor Design variation was observed. This variation presented an average value equal to 0.83, differing from the procedure in question by approximately 7.8%.

Biomimetic shear stress and nanoparticulate drug delivery

Fluidic shear stress generated by fluid flow in human body contributes to the interactions between nanoparticles (NPs) and cells and may affect cellular distribution and delivery of NPs. Furthermore, different NPs properties may differently influence the cellular delivery and targeting of NPs under the in vivo dynamic environments. Thus, we reviewed and discussed how fluidic shear stress affects to drug delivery and cellular distribution of diverse NPs under the biomimetic microfluidic shear stress. Among different physicochemical properties of NPs, size, shape, material type and surface functionality, and surface charge of NPs are critical factors to cellular uptake in presence of fluidic shear stress in dynamic cellular environment. From previous studies, it suggested that fluidic shear stress stimulated specific endocytosis and prompted cell signaling pathway. The cellular interactions between NPs and cells in drug delivery should be carefully investigated in presence of shear stress which is one of critical factors to show the difference of in vitro and in vivo drug distribution and therapy. The shear-activated drug delivery using NPs were also the scope of this review.

Enhanced directional cell migration induced by vaccinia virus on a microfluidic-based multi-shear cell migration assay platform.

Virus-induced cell migration plays important roles in the direct and rapid spread of virus particles. As cell migration is also regulated by shear stress, it is necessary to explore the cell migration behavior influenced by multiple factors including a virus and shear stress. In this report, a three-layer microfluidic chip with symmetric channels was designed and fabricated to investigate vaccinia virus-induced cell migration in different shear stress environments. Regular "exclusion zones" without cell damage were formed by microvalves. The results showed that infected cells were more elongated and tended to migrate along the flow direction compared to the random cell migration under static conditions. Meanwhile, shear stress enhanced the natural directional persistence and accelerated the velocity of infected cell migration. Moreover, reduced peripheral lamellae and the axial lamella being confined to the flow direction were responsible for the increased directionality of cell migration under shear stress. Interestingly, in the presence of shear stress, the Golgi complex reoriented and relocated behind the nucleus and aligned to the flow direction in infected migratory cells accompanied by the rearrangement of the cytoskeleton. Our report reveals the cell migration behavior in the multi-environment of virus infection and shear stress based on the microfluidic cell migration assay platform. It helps us to deeply understand the interactions between the virus, host cells, and surrounding microenvironment.

Shear stress increases cytotoxicity and reduces transfection efficiency of liposomal gene delivery to CHO-S cells.

Animal cells in suspension experience shear stress in different situations such as in vivo due to hemodynamics, or in vitro due to agitation in large-scale bioreactors. Shear stress is known to affect cell physiology, including binding and uptake of extracellular cargo. In adherent cells the effects of exposure to shear stress on particle binding kinetics and uptake have been studied. There are however no reports on the effect of shear stress on extracellular cargo delivery to suspension cells. In this study, we have evaluated the effect of shear stress on transfection of CHO-S cells using Lipofectamine 2000 in a simple flow apparatus. Our results show decreased cell growth and transfection efficiency upon lipoplex assisted transfection of CHO-S while being subjected to shear stress. This effect is not seen to the same extent when cells are exposed to shear stress in absence of the lipoplex complex and subsequently transfected, or if the lipoplex is subjected to shear stress and subsequently used to transfect the cells. It is also not seen to the same extent when cells are exposed to shear stress in presence of liposome alone, suggesting that the observed effect is dependent on interaction of the lipoplex with cells in the presence of shear stress. These results suggest that studies involving liposomal DNA delivery in presence of shear stress such as large scale transient protein expression should account for the effect of shear during lipoplex assisted DNA delivery.

Effects of shear stress on the cellular distribution of polystyrene nanoparticles in a biomimetic microfluidic system

Effects of shear stress on the intracellular uptake of nanoparticles were originally investigated using a calibrated biomimetic microfluidic system (BMS) that mimics the dynamic environment of cells. Positively or negatively charged polystyrene nanoparticles (PSNs) were chosen as a model. PSNs were delivered to HEK 293T and MS1 cell lines using a BMS. To evaluate intracellular uptake of PSNs under static and dynamic conditions (0.5, 1.0, 3.0 dyne/cm2), the fluorescence intensity of intracellular PSNs was measured by flow cytometric analysis and confocal laser scanning microscopy. When delivering cationic PSNs to cells, the intracellular uptake increased as the exposure time and PSN concentration increased under both static and dynamic conditions. Under dynamic conditions, the intracellular uptake of cationic PSN was highly increased in both HEK 293T and MS1 cell lines compared to static conditions. However, intracellular uptake of cationic PSNs was maximized when shear stress was at 0.5 dyne/cm2 and then gradually decreased as the magnitude of fluidic shear stress increased to 3.0 dyne/cm2. Contrarily, the anionic PSNs showed no significant difference of cellular uptake in presence of shear stress. Thus, shear stress should be considered to investigate the cellular distribution of various nanoparticles and drug delivery systems.

Comparison of the uptake of methacrylate-based nanoparticles in static and dynamic in vitro systems as well as in vivo

Polymer-based nanoparticles are promising drug delivery systems allowing the development of new drug and treatment strategies with reduced side effects. However, it remains a challenge to screen for new and effective nanoparticle-based systems in vitro. Important factors influencing the behavior of nanoparticles in vivo cannot be simulated in screening assays in vitro, which still represent the main tools in academic research and pharmaceutical industry. These systems have serious drawbacks in the development of nanoparticle-based drug delivery systems, since they do not consider the highly complex processes influencing nanoparticle clearance, distribution, and uptake in vivo. In particular, the transfer of in vitro nanoparticle performance to in vivo models often fails, demonstrating the urgent need for novel in vitro tools that can imitate aspects of the in vivo situation more accurate. Dynamic cell culture, where cells are cultured and incubated in the presence of shear stress has the potential to bridge this gap by mimicking key-features of organs and vessels. Our approach implements and compares a chip-based dynamic cell culture model to the common static cell culture and mouse model to assess its capability to predict the in vivo success more accurately, by using a well-defined poly((methyl methacrylate)-co-(methacrylic acid)) and poly((methyl methacrylate)-co-(2-dimethylamino ethylmethacrylate)) based nanoparticle library. After characterization in static and dynamic in vitro cell culture we were able to show that physiological conditions such as cell–cell communication of co-cultured endothelial cells and macrophages as well as mechanotransductive signaling through shear stress significantly alter cellular nanoparticle uptake. In addition, it could be demonstrated by using dynamic cell cultures that the in vivo situation is simulated more accurately and thereby can be applied as a novel system to investigate the performance of nanoparticle systems in vivo more reliable.

On the energetics of tensile and shear void coalescences

This paper investigates the mechanisms of tensile and shear void coalescences in ductile materials from energetics perspective. By examining and comparing the elastic and plastic energies of a voided cell throughout its deformation history, the onset of and final coalescence can be distinctly established. This energy-based approach offers a single unified method and criterion for determining the occurrences of both mechanisms. This paper also reports a novel micromechanics model that considers general stress states described by three macroscopic normal stresses and one macroscopic shear stress. Detailed formulation of the model is presented that includes the homogenization-based derivation and implementation of a 4×4 orthogonal transformation matrix, which relates the macroscopic deformation rate of the cell to displacement rates of non-physical degrees-of-freedom (DOFs), and the polar decomposition of the macroscopic deformation gradient tensor which admits the explicit determination of the logarithmic strain measures and rotation angle.In terms of stress ratios, ρ1(=Σ11/Σ22),ρ2(=Σ12/Σ22),ρ3(=Σ33/Σ22), it is analytically shown that multiple macroscopic stress states {ρ1,ρ2,ρ3} can exist that result in the same stress triaxiality T and Lode parameter L. Specifically, it is shown that for a prescribed pair of T and L and in the absence of shear stress, at most six stress states {ρ1,0,ρ3} are possible. On the other extreme in the presence of shear stress, an infinite number of stress states is possible, due to the existence of Mohr's circle for this stress state. This model, together with the proposed energy-based criteria, is used to examine void coalescence under multiple stress-state conditions for any given T and L. Numerical results have shown that the presence of shear stress has a significant effect of reducing the effective strains for the onset of and final void coalescences. In addition, a relationship has also been established between shear angle and effective strain at the onset of shear void coalescence.

Simulation of three-dimensional waves in a liquid film

A model describing long-wave dimensional perturbations in a liquid film is developed that takes into account the presence of shear stress on the interfacial surface. This model is based on the decomposition of the liquid velocity vector components in a series in linearly independent basis functions (harmonics) and does not use the assumption of self-similarity of the velocity profile. A linear analysis of the stability of film flow with respect to three-dimensional perturbations, and a numerical simulation of nonlinear waves were performed.

Liposomes equipped with poly(N-isopropyl acryl amide)-containing coatings as potential drug carriers

Polymer coated liposomes are promising drug delivery candidates. Herein, we report on the coating of liposomes with mixed films containing poly(dopamine) (PDA) and different types of poly(N-isopropyl acryl amide) (pNiPAAm). Their potential as drug carriers from solution in the presence of shear stress or in a substrate-mediated manner using macrophages is assessed. Although we found no difference in the cell mean fluorescence (CMF) when applying shear stress when employing fluorescently labeled liposomes, macrophages exposed to liposomes coated with a mixture of PDA and highly-branched pNiPAAm (LD/HB) exhibited significantly higher CMF after 2.5 h compared to liposomes coated with only PDA (LD) or with a mixture of PDA and aminated pNiPAAm (LD/pNH2). The coated liposomes did not affect the cell viability in the time frame tested, but the application of shear stress reduced the number of surface-adherent macrophages. LD, LD/pNH2 or LD/pHB could be immobilized to poly(L lysine) pre-coated silica substrates. All substrates were equally suited for macrophages to adhere. The CMF of the adhering macrophages was found to be independent of the coating of the surface-immobilized liposomes when using fluorescently labeled liposomes in the coatings. Taken together, we demonstrate that mixed PDA-based coatings can be used to affect the interaction of liposomes with macrophages with potential in drug delivery.

Lysophosphatidic Acid Induces Shear Stress–dependent Contraction in Mouse Aortic Strip In Situ

We previously reported that lysophosphatidic acid (LPA) regulates Ca²⁺ influx of fluid flow in stimulated endothelial cells and that LPA and shear stress showed increment and suppressive effects on phenylephrine-induced vasoconstriction and acetylcholine-induced vasodilatation, respectively. However, a vasoconstrictive effect of LPA alone in the presence of shear stress was not found. The present study examined the effect of LPA alone in the presence of shear stress on Ca²⁺ responses in endothelial and smooth muscle cells and contraction in mouse aortic strip using real-time 2-photon laser scanning microscopy and a custom-made parallel-plate flow chamber. Application of micromolar LPA and high shear stress elicited movement of endothelial cells after Ca²⁺ responses. The endothelial cells moved along the major axis of smooth muscle cells, a direction that was identical to that found during vasoconstriction evoked by the application of phenylephrine. The frequency of Ca²⁺ oscillations in smooth muscle cells was highest according to endothelial movement. Vasoconstriction evoked by LPA and shear stress was significantly reduced by the application of a thromboxane A₂ receptor antagonist, a cyclooxygenase inhibitor, and a thromboxane synthase inhibitor. These results suggest that micromolar LPA and high shear stress elicit vasoconstriction that is caused by Ca²⁺-dependent contraction in medial smooth muscle cells. Thromboxane A₂ may be involved in that response.