Search

Measurements of the swelling pressure ω and shear modulus Gs in a set of poly(vinyl acetate) networks swollen to different degrees in toluene and in acetone are reported, using solutions of the uncross-linked polymer to obtain deswelling under known conditions of osmotic pressure. The swelling pressure can be completely described by the difference between two terms, each of which is a simple power law in the polymer volume fraction φ. Identification of the subtractive term with that related to the elastic free energy of the network gives the volume elastic modulus Gv. The shear modulus Gs, obtained from mechanical measurements at constant volume, and Gv are found to coincide for these samples, and neither deviates measurably from a one-third power law dependence on φ, up to values of φ in excess of 0.4. The remaining term in the swelling pressure of the networks behaves like the mixing term in a polymer solution, obeying good solvent scaling predictions as a function of concentration in both diluents. Its magnitude, however, is substantially smaller than the osmotic pressure of an equivalent uncross-linked solution of infinite molecular weight. The difference between the cross-linked and uncross-linked states conflicts with the assumption that the two mixing free energies are identical. [ABSTRACT FROM AUTHOR]

Polymer networks with sparse chemical crosslinks are composed in general of deeply interpenetrating coils. The microscopic statistical features of such gels are defined by three characteristic lengths: Rt, the separation between the end (junction) points of each component coil; Rs, the distance between two spatially nearest neighbor junction points; and ξ, the polymer–polymer correlation length. These distances are related through R2t =AR3s/ξ, where A is a numerical constant that depends upon the network structure. While Rt varies extremely weakly with polymer volume fraction φ, and ξ depends strongly on φ as predicted by scaling theory, only Rs deforms affinely (i.e., as φ-1/3) upon swelling. The swelling pressure in such a system consists of two parts, mixing and elastic. The mixing part for each coil contains a factor (Rt0/Rt)2 to allow for correlations in the concentration, where Rt0 is the unperturbed end-to-end distance. This situation is the same as for polymer solutions. For the elastic part of the swelling pressure, experimental observations are described that prove the following equivalences, in lightly crosslinked polyvinyl acetate gels: (1) the shear modulus is equal to the volume elastic modulus; (2) the ratio of the shear modulus of a gel swollen in a theta diluent to that of the same gel swollen to the same degree in a good solvent is a constant equal to the ratio of the corresponding temperatures, T/θ. It is concluded that the individual component coils make no significant contribution to the network elasticity, the latter being provided only by the mutual folding of the interpenetrating coils. [ABSTRACT FROM AUTHOR]

Abstract: Because the boronic acid moiety reversibly binds to sugar molecules and has low cytotoxicity, boronic acid-containing hydrogels are being used in a variety of implantable glucose sensors under development, including sensors based on optical, fluorescence, and swelling pressure measurements. However, some method of glucose selectivity enhancement is often necessary, because isolated boronic acid molecules have a binding constant with glucose that is some 40 times smaller than their binding constant with fructose, the second most abundant sugar in the human body. In many cases, glucose selectivity enhancement is obtained by incorporating pendant tertiary amines into the hydrogel network, thereby giving rise to a hydrogel that is zwitterionic at physiological pH. However, the mechanism by which incorporation of tertiary amines confers selectivity enhancement is poorly understood. In order to clarify this mechanism, we use the osmotic deswelling technique to compare the thermodynamic interactions of glucose and fructose with a zwitterionic smart hydrogel containing boronic acid moieties. We also investigate the change in the structure of the hydrogel that occurs when it binds to glucose or to fructose using the technique of small angle neutron scattering. [Copyright &y& Elsevier]

Abstract: A double Pulsed Gradient Spin Echo (d-PGSE) MR experiment was used to measure and assess the degree of local diffusion anisotropy in brain gray matter, and in a novel “gray matter” phantom that consists of randomly oriented tubes filled with water. In both samples, isotropic diffusion was observed at a macroscopic scale while anisotropic diffusion was observed at a microscopic scale, however, the nature of the resulting echo attenuation profiles were qualitatively different. Gray matter, which contains multiple cell types and fibers, exhibits a more complicated echo attenuation profile than the phantom. Since microscopic anisotropy was observed in both samples in the low q regime comparable to that achievable in clinical scanner, it may offer a new potential contrast mechanism for characterizing gray matter microstructure in medical and biological applications. [Copyright &y& Elsevier]

Abstract: Insight in the osmotic behavior of degrading hydrogels is of great importance in the design of biodegradable hydrogels for biomedical applications. This study compares the degradation behavior of PEG-HEMA (hydroxyethylmethacrylated polyethylene glycol) and dex-HEMA (hydroxyethylmethacrylated dextran) hydrogels. The degradation of PEG-HEMA gels takes several months to over a year, while that of dex-HEMA gels takes only days or weeks. The faster degradation kinetics of dex-HEMA networks can be attributed to stabilization of the keto–enol form by hydroxyl groups. Upon degradation of PEG-HEMA and dex-HEMA hydrogels, respectively, free PEG and free dextran chains are produced. We investigated the effect of unattached PEG and dextran chains on the swelling pressure of the degrading gels. It is found that low molecular weight free chains significantly increase the swelling pressure. However, the contribution of higher molecular weight free chains (M w >10kDa) is similar to that of the network chains. [Copyright &y& Elsevier]

Presents a correction to the article 'Elastic Free Energy in Swollen Polymer Networks.'

Background: NT-proXNP, a new natriuretic peptide analyte, incorporates information about the concentrations of both N-terminal pro-atrial and pro-brain natriuretic peptides (NT-proANP, NT-proBNP). We aimed to investigate whether NT-proXNP is a reliable indicator of the cardiac index (CI) and the hemodynamic state in neonates and infants undergoing an open heart surgery. Methods: We enrolled 26 children under the age of 1 year into this prospective study. All patients underwent an elective cardiac operation with cardiopulmonary bypass (CPB) to achieve complete biventricular repair. Peri-operative hemodynamic parameters were assessed by transpulmonary thermodilution and natriuretic peptide levels were recorded. Results: The NT-proXNP level correlated significantly with the simultaneously measured NT-proANP level ( r=0.60, P<0.001), but more strongly with the NT-proBNP level ( r=0.89, P<0.001) and the arithmetic sum of both ( r=0.88, P<0.001). NT-proXNP had a strong correlation with CI ( r=−0.85, P<0.001), the stroke volume index ( r=−0.80, P<0.001) and the global ejection fraction ( r=−0.67, P<0.009) throughout the post-operative period. Conventionally measured parameters such as heart rate, mean arterial pressure and pulse-pressure product exhibited weaker correlations with CI than NT-proXNP. Among laboratory values, creatinine levels correlated significantly with CI ( r=−0.77, P<0.001) and NT-proXNP ( r=0.76, P<0.001) during the post-operative period. A post-operative NT-proXNP level of 3079 pmol/l was diagnostic for CI <3 l/min/m2 with 89% sensitivity and 90% specificity (area under the curve: 0.91 ± 0.05). Conclusion: NT-proXNP is a good marker of cardiac output following pediatric cardiac surgery and might be a useful tool in the recognition of a low output state. [ABSTRACT FROM AUTHOR]

Background: Long-term outcomes after percutaneous coronary intervention (PCI) with contemporary drug-eluting stents, as compared with coronary-artery bypass grafting (CABG), in patients with left main coronary artery disease are not clearly established.Methods: We randomly assigned 1905 patients with left main coronary artery disease of low or intermediate anatomical complexity (according to assessment at the participating centers) to undergo either PCI with fluoropolymer-based cobalt-chromium everolimus-eluting stents (PCI group, 948 patients) or CABG (CABG group, 957 patients). The primary outcome was a composite of death, stroke, or myocardial infarction.Results: At 5 years, a primary outcome event had occurred in 22.0% of the patients in the PCI group and in 19.2% of the patients in the CABG group (difference, 2.8 percentage points; 95% confidence interval [CI], -0.9 to 6.5; P = 0.13). Death from any cause occurred more frequently in the PCI group than in the CABG group (in 13.0% vs. 9.9%; difference, 3.1 percentage points; 95% CI, 0.2 to 6.1). In the PCI and CABG groups, the incidences of definite cardiovascular death (5.0% and 4.5%, respectively; difference, 0.5 percentage points; 95% CI, -1.4 to 2.5) and myocardial infarction (10.6% and 9.1%; difference, 1.4 percentage points; 95% CI, -1.3 to 4.2) were not significantly different. All cerebrovascular events were less frequent after PCI than after CABG (3.3% vs. 5.2%; difference, -1.9 percentage points; 95% CI, -3.8 to 0), although the incidence of stroke was not significantly different between the two groups (2.9% and 3.7%; difference, -0.8 percentage points; 95% CI, -2.4 to 0.9). Ischemia-driven revascularization was more frequent after PCI than after CABG (16.9% vs. 10.0%; difference, 6.9 percentage points; 95% CI, 3.7 to 10.0).Conclusions: In patients with left main coronary artery disease of low or intermediate anatomical complexity, there was no significant difference between PCI and CABG with respect to the rate of the composite outcome of death, stroke, or myocardial infarction at 5 years. (Funded by Abbott Vascular; EXCEL ClinicalTrials.gov number, NCT01205776.). [ABSTRACT FROM AUTHOR]

Abstract The glymphatic system is a recently discovered transport system, mediated by cerebral spinal fluid (CSF), that clears metabolic and cellular waste products in the brain. This system's function in the brain is analogous to that of the lymphatic system in the rest of the mammalian body. It is hypothesized that CSF clears harmful chemicals from the brain by flowing through interstitial spaces in the brain during sleep. While there is growing recognition of the critical role the glymphatic system plays in maintaining normal brain health and in explaining pathology, there are few noninvasive imaging methods that measure and characterize the efficacy of glymphatic transport in vivo. In this study we designed, constructed, and tested a glymphatic transport magnetic resonance imaging (MRI) flow phantom, which combines regions that mimic CSF-filled ventricles and brain interstitial space. We tested high- and low-q space diffusion MRI and diffusion tensor imaging (DTI) acquisitions to determine if they could detect, measure, and map interstitial glymphatic flows. The results suggest that, under certain flow conditions, diffusion-weighted MRI can detect the enhanced mixing that occurs during glymphatic clearance. [ABSTRACT FROM AUTHOR]

A silicon oil-filled glass capillary array is proposed as an anisotropic diffusion MRI phantom. Together with a computational/theoretical pipeline these provide a gold standard for calibrating and validating high-q diffusion MRI experiments. The phantom was used to test high angular resolution diffusion imaging (HARDI) and double pulsed-field gradient (d-PFG) MRI acquisition schemes. MRI-based predictions of microcapillary diameter using both acquisition schemes were compared with results from optical microscopy. This phantom design can be used for quality control and quality assurance purposes and for testing and validating proposed microstructure imaging experiments and the processing pipelines used to analyze them. [ABSTRACT FROM AUTHOR]

Background: Patients with obstructive left main coronary artery disease are usually treated with coronary-artery bypass grafting (CABG). Randomized trials have suggested that drug-eluting stents may be an acceptable alternative to CABG in selected patients with left main coronary disease.Methods: We randomly assigned 1905 eligible patients with left main coronary artery disease of low or intermediate anatomical complexity to undergo either percutaneous coronary intervention (PCI) with fluoropolymer-based cobalt-chromium everolimus-eluting stents (PCI group, 948 patients) or CABG (CABG group, 957 patients). Anatomic complexity was assessed at the sites and defined by a Synergy between Percutaneous Coronary Intervention with Taxus and Cardiac Surgery (SYNTAX) score of 32 or lower (the SYNTAX score reflects a comprehensive angiographic assessment of the coronary vasculature, with 0 as the lowest score and higher scores [no upper limit] indicating more complex coronary anatomy). The primary end point was the rate of a composite of death from any cause, stroke, or myocardial infarction at 3 years, and the trial was powered for noninferiority testing of the primary end point (noninferiority margin, 4.2 percentage points). Major secondary end points included the rate of a composite of death from any cause, stroke, or myocardial infarction at 30 days and the rate of a composite of death, stroke, myocardial infarction, or ischemia-driven revascularization at 3 years. Event rates were based on Kaplan-Meier estimates in time-to-first-event analyses.Results: At 3 years, a primary end-point event had occurred in 15.4% of the patients in the PCI group and in 14.7% of the patients in the CABG group (difference, 0.7 percentage points; upper 97.5% confidence limit, 4.0 percentage points; P=0.02 for noninferiority; hazard ratio, 1.00; 95% confidence interval, 0.79 to 1.26; P=0.98 for superiority). The secondary end-point event of death, stroke, or myocardial infarction at 30 days occurred in 4.9% of the patients in the PCI group and in 7.9% in the CABG group (P<0.001 for noninferiority, P=0.008 for superiority). The secondary end-point event of death, stroke, myocardial infarction, or ischemia-driven revascularization at 3 years occurred in 23.1% of the patients in the PCI group and in 19.1% in the CABG group (P=0.01 for noninferiority, P=0.10 for superiority).Conclusions: In patients with left main coronary artery disease and low or intermediate SYNTAX scores by site assessment, PCI with everolimus-eluting stents was noninferior to CABG with respect to the rate of the composite end point of death, stroke, or myocardial infarction at 3 years. (Funded by Abbott Vascular; EXCEL ClinicalTrials.gov number, NCT01205776 .). [ABSTRACT FROM AUTHOR]

There is no clinically available cancer immunotherapy that exploits Langerhans cells (LCs), the epidermal precursors of dendritic cells (DCs) that are the natural agent of antigen delivery. We developed a DNA formulation with a polymer and obtained synthetic 'pathogen-like' nanoparticles that preferentially targeted LCs in epidermal cultures. These nanoparticles applied topically under a patch-elicited robust immune responses in human subjects. To demonstrate the mechanism of action of this novel vaccination strategy in live animals, we assembled a high-resolution two-photon laser scanning-microscope. Nanoparticles applied on the native skin poorly penetrated and poorly induced LC motility. The combination of nanoparticle administration and skin treatment was essential both for efficient loading the vaccine into the epidermis and for potent activation of the LCs to migrate into the lymph nodes. LCs in the epidermis picked up nanoparticles and accumulated them in the nuclear region demonstrating an effective nuclear DNA delivery in vivo. Tissue distribution studies revealed that the majority of the DNA was targeted to the lymph nodes. Preclinical toxicity of the LC-targeting DNA vaccine was limited to mild and transient local erythema caused by the skin treatment. This novel, clinically proven LC-targeting DNA vaccine platform technology broadens the options on DC-targeting vaccines to generate therapeutic immunity against cancer. [ABSTRACT FROM AUTHOR]

Abstract: Knowledge of microstructural features of nerve fascicles, such as their axon diameter, is crucial for understanding normal function in the central and peripheral nervous systems as well as assessing changes due to pathologies. In this study double-pulsed field gradient (d-PFG) filtered MRI was used to map the average axon diameter (AAD) in porcine spinal cord, which was then compared to AADs measured with optical microscopy of the same specimen, as a way to further validate this new MRI method. A novel 3D d-PFG acquisition scheme was used to obtain AADs in each voxel of a coronal slice of rat brain corpus callosum. AAD measurements were also acquired using optical microscopy performed on histological sections and validated using a glass capillary array phantom. [Copyright &y& Elsevier]

Abstract: Background: The pathway from viral myocarditis to end-stage heart failure is commonly accepted, but diagnosis of virus-mediated myocardial injury remains challenging. Virus persistency in the myocardium may accelerate ventricular failure; thus, a precise diagnosis of virus persistency may prevent the development of end-stage heart failure. Methods: We performed a systematic investigation on the sampling error of viral diagnostics in heart transplant recipients: Transmural samples from 5 regions of the explanted hearts from recipients during heart transplantation were amplified using entero-, adeno-, and herpesvirus sequences and histologic examinations performed. Results: We examined 175 myocardial samples from dilated cardiomyopathy and 100 samples from 20 forensic medicine patients. Seven patients were positive for the examined viruses: 10 positive regions for adenovirus, and 1 positive region for herpes virus DNA, but none for enterovirus. A focal myocardial pattern was detected for adenovirus. Conclusion: Our results with the patchy myocardial viral persistence may explain possible false-negative results related to virus-mediated etiology among end-stage dilated cardiomyopathy patients. Therefore, repeated endomyocardal biopsies, and multiple cardiac samples are recommended to be obtained to evaluate the etiology of heart failure, thus reducing the occurrence of end-stage heart failure and decreasing the number of patients requiring heart transplantation. [Copyright &y& Elsevier]

Diabetes mellitus is associated with endothelial and cardiac dysfunction. The cardiac hormones, the atrial natriuretic peptide (ANP) and B-type natriuretic peptide have compensatory effects in heart failure. The shunted circulation with diabetes increases the hemodynamic load of the heart, reflected in increased ANP production but the ET-systetn seems to be unaffected in these conditions.

This article focuses on a study related to vasoactive reactivity of intramural coronary resistance arteries in patients who undergoing cardiac surgery. The myocardial perfusion is mainly determined by the small coronary resistance arteries. Changes in the function of these small vessels can cause local dysfunction in the heart. These small coronary arteries have thick wall and significant spontaneous tone, which was enhanced by TXA2 agonist. The reason of the slight BK-relaxation is consistent with impaired endothelial function in these older patients with cardiac diseases.