Single polymer adsorption in shear: flattening versus hydrodynamic lift and corrugation effects

The adsorption of a single polymer to a flat surface in shear is investigated using Brownian hydrodynamics simulations and scaling arguments. Competing effects are disentangled: in the absence of hydrodynamic interactions, shear drag flattens the chain and thus enhances adsorption. Hydrodynamic lift on the other hand gives rise to long-ranged repulsion from the surface which preempts the surface-adsorbed state via a discontinuous desorption transition, in agreement with theoretical arguments. Chain flattening is dominated by hydrodynamic lift, so overall, shear flow weakens the adsorption of flexible polymers. Surface friction due to small-wavelength surface potential corrugations is argued to weaken the surface attraction as well.Comment: 6 pages, 4 figure

Conformations, Transverse Fluctuations and Crossover Dynamics of a Semi-Flexible Chain in Two Dimensions

We present a unified scaling description for the dynamics of monomers of a semiflexible chain under good solvent condition in the free draining limit. We consider both the cases where the contour length $L$ is comparable to the persistence length $\ell_p$ and the case $L\gg \ell_p$. Our theory captures the early time monomer dynamics of a stiff chain characterized by $t^{3/4}$ dependence for the mean square displacement(MSD) of the monomers, but predicts a first crossover to the Rouse regime of $t^{2\nu/{1+2\nu}}$ for $\tau_1 \sim \ell_p^3$, and a second crossover to the purely diffusive dynamics for the entire chain at $\tau_2 \sim L^{5/2}$. We confirm the predictions of this scaling description by studying monomer dynamics of dilute solution of semi-flexible chains under good solvent conditions obtained from our Brownian dynamics (BD) simulation studies for a large choice of chain lengths with number of monomers per chain N = 16 - 2048 and persistence length $\ell_p = 1 - 500$ Lennard-Jones (LJ) units. These BD simulation results further confirm the absence of Gaussian regime for a 2d swollen chain from the slope of the plot of $\langle R_N^2 \rangle/2L \ell_p \sim L/\ell_p$ which around $L/\ell_p \sim 1$ changes suddenly from $\left(L/\ell_p \right) \rightarrow \left(L/\ell_p \right)^{0.5}$, also manifested in the power law decay for the bond autocorrelation function disproving the validity of the WLC in 2d. We further observe that the normalized transverse fluctuations of the semiflexible chains for different stiffness $\sqrt{\langle l_{\bot}^2\rangle}/L$ as a function of renormalized contour length $L/\ell_p$ collapse on the same master plot and exhibits power law scaling $\sqrt{\langle l_{\bot}^2\rangle}/L \sim (L/\ell_p)^\eta$ at extreme limits, where $\eta = 0.5$ for extremely stiff chains ($L/\ell_p \gg 1$), and $\eta = -0.25$ for fully flexible chains.Comment: 14 pages, 18 figure

Effect of Adsorbing and Nonadsorbing Polymer on the Interaction Between Colloidal Particles

In this paper it is described how a recent theoretical model can be applied to a system of two colloidal particles in the presence of adsorbing and nonadsorbing polymer. It turns out that in the case of adsorption the most suitable boundary condition is restricted equilibrium, in which a constant amount of polymer is in local equilibrium inside the gap between two particles. At a low polymer dose the formation of bridges gives rise to bridging flocculation, at higher amounts of polymer steric stabilization occurs due to the mutual repulsion of two extended polymer layers. If the polymer does not adsorb on the particles, full equilibrium applies in which the chemical potentials of solvent and polymer in the gap are the same as in the equilibrium bulk solution, The depletion of polymer near the surface may lead to depletion flocculation in not too concentrated polymer solutions. In very concentrated systems the thickness of the depletion zone is relatively small, and the attraction between the particles becomes too weak to overcome the particle entropy, Then the system is restabilized

Delocalization transition of the selective interface model: distribution of pseudo-critical temperatures

According to recent progress in the finite size scaling theory of critical disordered systems, the nature of the phase transition is reflected in the distribution of pseudo-critical temperatures $T_c(i,L)$ over the ensemble of samples $(i)$ of size $L$. In this paper, we apply this analysis to the delocalization transition of an heteropolymeric chain at a selective fluid-fluid interface. The width $\Delta T_c(L)$ and the shift $[T_c(\infty)-T_c^{av}(L)]$ are found to decay with the same exponent $L^{-1/\nu_{R}}$, where $1/\nu_{R} \sim 0.26$. The distribution of pseudo-critical temperatures $T_c(i,L)$ is clearly asymmetric, and is well fitted by a generalized Gumbel distribution of parameter $m \sim 3$. We also consider the free energy distribution, which can also be fitted by a generalized Gumbel distribution with a temperature dependent parameter, of order $m \sim 0.7$ in the critical region. Finally, the disorder averaged number of contacts with the interface scales at $T_c$ like $L^{\rho}$ with $\rho \sim 0.26 \sim 1/\nu_R$.Comment: 9 pages,6 figure

Hexadecylphosphocholine, a new ether lipid analogue. Studies on the antineoplastic activity in vitro and in vivo.

Hexadecylphosphocholine (He-PC) is a new compound synthesized according to the minimal structural requirements deducted from studies with other ether lipids. In vitro studies on He-PC revealed remarkable antineoplastic activity on HL60, U937, Raji and K562 leukemia cell lines. In addition, He-PC, applied orally, showed a superior effect in the treatment of dimethylbenzanthracene-induced rat mammary carcinomas when compared to intravenously administered cyclophosphamide. After oral application He-PC was well absorbed from the intestine and metabolized in the liver by phospholipases C and D. During a 5-week treatment no hematotoxic effects were detected. In a clinical pilot study on breast cancer patients with widespread skin involvement, topically applied He-PC showed skin tumor regressions without local or systemic side effects

Validation of the Dutch translation of the quality of recovery-15 scale

BACKGROUND: The 15-item Quality of Recovery-15 (QoR-15) scale is strongly recommended as a standard patient-reported outcome measure assessing the quality of recovery after surgery and anesthesia in the postoperative period. This study aimed to validate the Dutch translation of the questionnaire (QoR-15NL). MATERIALS AND METHODS: An observational, prospective, single-centre cohort study was conducted. Patients who underwent surgery under general anesthesia completed the QoR-15NL (preoperatively (t1) and twice postoperatively (t2 and t3)) and a visual analogue scale (VAS) for general recovery at t2. A psychometric evaluation was performed to assess the QoR-15NL's validity, reliability, responsiveness, reproducibility and feasibility. RESULTS: Two hundred and eleven patients agreed to participate (recruitment rate 94%), and 165 patients were included (completion rate 78%). The QoR-15NL score correlated with the VAS for general recovery (rs = 0.59). Construct validity was further demonstrated by confirmation of expected negative associations between the QoR-15NL and duration of surgery (rs = -0.25), duration of Post Anesthesia Care Unit stay (rs = -0.31), and duration of hospital stay (rs = -0.27). The QoR-15NL score decreased significantly according to the extent of surgery. Cronbach's alpha was 0.87, split-half reliability was 0.8, and the test-retest intra-class coefficient was 0.93. No significant floor- or ceiling effect was observed. CONCLUSION: The QoR-15NL scale is a valid, easy-to-use, and reliable outcome assessment tool with high responsiveness for patient-reported quality of recovery after surgery and general anesthesia in the Dutch-speaking population. The QoR-15NL's measurement properties are comparable to the original questionnaire and other translated versions. TRIAL REGISTRATION: not applicable

Prehabilitation to prevent complications after cardiac surgery - A retrospective study with propensity score analysis

BACKGROUND: The rising prevalence of modifiable lifestyle-related risk factors (e.g. overweight and physical inactivity) suggests the need for effective and safe preoperative interventions to improve outcomes after cardiac surgery. This retrospective study explored potential short-term postoperative benefits and unintended consequences of a multidisciplinary prehabilitation program regarding in-hospital complications. METHODS: Data on patients who underwent elective cardiac surgery between January 2014 and April 2017 were analyzed retrospectively. Pearson’s chi-squared tests were used to compare patients who followed prehabilitation (three times per week, at a minimum of three weeks) during the waiting period with patients who received no prehabilitation. Sensitivity analyses were performed using propensity-score matching, in which the propensity score was based on the baseline variables that affected the outcomes. RESULTS: Of 1201 patients referred for elective cardiac surgery, 880 patients met the inclusion criteria, of whom 91 followed prehabilitation (53.8% ≥ 65 years, 78.0% male, median Euroscore II 1.3, IQR, 0.9–2.7) and 789 received no prehabilitation (60.7% ≥ 65 years, 69.6% male, median Euroscore II 1.6, IQR, 1.0–2.8). The incidence of atrial fibrillation (AF) was significantly lower in the prehabilitation group compared to the unmatched and matched standard care group (resp. 14.3% vs. 23.8%, P = 0.040 and 14.3% vs. 25.3%, P = 0.030). For the other complications, no between-group differences were found. CONCLUSIONS: Prehabilitation might be beneficial to prevent postoperative AF. Patients participated safely in prehabilitation and were not at higher risk for postoperative complications. However, well-powered randomized controlled trials are needed to confirm and deepen these results

Adsorption transition of a self-avoiding polymer chain onto a rigid rod

The subject of this work is the adsorption transition of a long flexible self-avoiding polymer chain onto a rigid thin rod. The rod is represented by a cylinder of radius R with a short-ranged attractive surface potential for the chain monomers. General scaling results are obtained by using renormalization group arguments in conjunction with available results for quantum field theories with curved boundaries [McAvity and Osborn 1993 Nucl. Phys. B 394, 728]. Relevant critical exponents are identified and estimated using geometric arguments.Comment: 19 pages, 4 figures. To appear in: J. Phys.: Condens. Matter, special issue dedicated to Lothar Schaefer on the occasion of his 60th birthda

Adsorption of Multi-block and Random Copolymer on a Solid Surface: Critical Behavior and Phase Diagram

The adsorption of a single multi-block $AB$-copolymer on a solid planar substrate is investigated by means of computer simulations and scaling analysis. It is shown that the problem can be mapped onto an effective homopolymer adsorption problem. In particular we discuss how the critical adsorption energy and the fraction of adsorbed monomers depend on the block length $M$ of sticking monomers $A$, and on the total length $N$ of the polymer chains. Also the adsorption of the random copolymers is considered and found to be well described within the framework of the annealed approximation. For a better test of our theoretical prediction, two different Monte Carlo (MC) simulation methods were employed: a) off-lattice dynamic bead-spring model, based on the standard Metropolis algorithm (MA), and b) coarse-grained lattice model using the Pruned-enriched Rosenbluth method (PERM) which enables tests for very long chains. The findings of both methods are fully consistent and in good agreement with theoretical predictions.Comment: 27 pages, 12 figure

Universal Scaling, Entanglements, and Knots of Model Chain Molecules

By identifying the maximally random jammed state of freely jointed chains of tangent hard spheres we are able to determine the distinct scaling regimes characterizing the dependence of chain dimensions and topology on volume fraction. Calculated distributions of (i) the contour length of the primitive paths and (ii) the number of entanglements per chain agree remarkably well with recent theoretical predictions in all scaling regimes. Furthermore, our simulations reveal a hitherto unsuspected connection between purely intramolecular (knots) and intermolecular (entanglements) topological constraints