Optimisation of a Brownian dynamics algorithm for semidilute polymer solutions

Simulating the static and dynamic properties of semidilute polymer solutions with Brownian dynamics (BD) requires the computation of a large system of polymer chains coupled to one another through excluded-volume and hydrodynamic interactions. In the presence of periodic boundary conditions, long-ranged hydrodynamic interactions are frequently summed with the Ewald summation technique. By performing detailed simulations that shed light on the influence of several tuning parameters involved both in the Ewald summation method, and in the efficient treatment of Brownian forces, we develop a BD algorithm in which the computational cost scales as O(N^{1.8}), where N is the number of monomers in the simulation box. We show that Beenakker's original implementation of the Ewald sum, which is only valid for systems without bead overlap, can be modified so that \theta-solutions can be simulated by switching off excluded-volume interactions. A comparison of the predictions of the radius of gyration, the end-to-end vector, and the self-diffusion coefficient by BD, at a range of concentrations, with the hybrid Lattice Boltzmann/Molecular Dynamics (LB/MD) method shows excellent agreement between the two methods. In contrast to the situation for dilute solutions, the LB/MD method is shown to be significantly more computationally efficient than the current implementation of BD for simulating semidilute solutions. We argue however that further optimisations should be possible.Comment: 17 pages, 8 figures, revised version to appear in Physical Review E (2012

FORMULATION AND EVALUATION OF PRONIOSOMAL GEL-BASED TRANSDERMAL DELIVERY OF ATORVASTATIN CALCIUM BY BOX–BEHNKEN DESIGN

Objective: The aim of this study was to investigate the combined influence of three independent variables in the preparation of atorvastatin proniosomes by coacervation-phase separation method. Methods: On the basis of the preliminary trials, a 3-factor, 3-level Box–Behnken design was employed to study the effect of cholesterol, soya lecithin, and Span 60 independent variable on dependent variables (particle size and % entrapment efficiency). Transmission electron microscopy analysis of optimized formulation has demonstrated the presence of individual proniosomes in spherical shape. Results: Atorvastatin optimized proniosomal formulation F2 shown better particle size and % entrapment efficiency, and also, the drug release was 99.72% within 24 h in slow and controlled manner when compared with control. Kinetic analysis of drug release profiles showed that the drug release was followed by zero-order manner with Korsmeyer–Peppas model, which implies super case II release kinetics. The particle size and zeta potential of the optimized atorvastatin proniosomal gel were found to be 65.72 and −10.5, respectively. The optimized batch of proniosomes was used for the preparation of atorvastatin-based proniosomal hydrogel by incorporating hydrated proniosomes to carbopol matrix to enhance the stability and viscosity of the system. Conclusion: The enhanced skin permeation, for a prolonged period of time, may lead to improved efficacy and better patient compliance. This study suggests that proniosomal gel-containing atorvastatin could perform therapeutically better effects than the conventional formulations

The viscosity radius in dilute polymer solutions: Universal behaviour from DNA rheology and Brownian dynamics simulations

The swelling of the viscosity radius, $\alpha_\eta$, and the universal viscosity ratio, $U_{\eta R}$, have been determined experimentally for linear DNA molecules in dilute solutions with excess salt, and numerically by Brownian dynamics simulations, as a function of the solvent quality. In the latter instance, asymptotic parameter free predictions have been obtained by extrapolating simulation data for finite chains to the long chain limit. Experiments and simulations show a universal crossover for $\alpha_\eta$ and $U_{\eta R}$ from $\theta$ to good solvents in line with earlier observations on synthetic polymer-solvent systems. The significant difference between the swelling of the dynamic viscosity radius from the observed swelling of the static radius of gyration, is shown to arise from the presence of hydrodynamic interactions in the non-draining limit. Simulated values of $\alpha_\eta$ and $U_{\eta R}$ are in good agreement with experimental measurements in synthetic polymer solutions reported previously, and with the measurements in linear DNA solutions reported here.Comment: 19 pages, 14 figures, two column, Supporting Information added, to appear in Macromolecule

Shear thinning in dilute and semidilute solutions of polystyrene and DNA

The viscosity of dilute and semidilute unentangled DNA solutions, in steady simple shear flow, has been measured across a range of temperatures and concentrations. For polystyrene solutions, measurements of viscosity have been carried out in the semidilute unentangled regime, while results of prior experimental measurements in the dilute regime have been used for the purpose of data analysis, and for comparison with the behaviour of DNA solutions. Interpretation of the shear rate dependence of viscosity in terms of suitably defined non-dimensional variables, is shown to lead to master plots, independent of temperature and concentration, in each of the two concentration regimes. In the case of semidilute unentangled solutions, defining the Weissenberg number in terms of a concentration dependent large scale relaxation time is found not to lead to data collapse across different concentrations. On the other hand, the use of an alternative relaxation time, with the concentration dependence of a single correlation blob, suggests the existence of universal shear thinning behaviour at large shear rates.Comment: 24 pages, 13 figures, supplementary material (see ancillary directory), to appear in Journal of Rheolog

Dip coating of forsterite-hydroxyapatitie-poly (ɛ-caprolactone) nanocomposites on Ti6Al4Vsubstrates for its corrosion prevention

522-528Titanium and titanium alloys are extensively used in biomedical, cardiac and cardiovascular applications for their superb properties, such as good fatigue strength, low modulus, machinability, formability, corrosion resistance and biocompatibility. However, titanium and its alloys do not meet the majority of all clinical necessities. Due to these reasons, surface modification is frequently performed to enhance the mechanical, biological and chemical properties of titanium and alloys. In this work, nanocomposites coating of poly(ɛ-caprolactone)/hydroxyapatite/forsterite (PCL/HA/F) have been successfully deposited on the Ti6Al4V substratesby dip coating at room temperature. The coatings are prepared with various concentrations of forsterite/hydroxyapatite nanopowder (2, 4, 6 and 8 wt.%) with a fixed concentration of PCL (4 wt.%) and thus coated Ti6Al4V substrates are examined for corrosion resistance. PCL/Hydroxyapatite/Forsterite coatings are characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM), which clearly showed the formation of nanocomposites. Potentiodynamic polarization curves and electrochemical impedance spectroscopy (EIS) are used to investigate corrosion behavior of the coated substrates, which portrayed that the composite coating of PCL/HA/F substantially enhanced the corrosion resistance of Ti6Al4V alloy

Dip coating of forsterite-hydroxyapatitie-poly (ɛ-caprolactone) nanocomposites on Ti6Al4Vsubstrates for its corrosion prevention

Titanium and titanium alloys are extensively used in biomedical, cardiac and cardiovascular applications for their superb properties, such as good fatigue strength, low modulus, machinability, formability, corrosion resistance and biocompatibility. However, titanium and its alloys do not meet the majority of all clinical necessities. Due to these reasons, surface modification is frequently performed to enhance the mechanical, biological and chemical properties of titanium and alloys. In this work, nanocomposites coating of poly(ɛ-caprolactone)/hydroxyapatite/forsterite (PCL/HA/F) have been successfully deposited on the Ti6Al4V substratesby dip coating at room temperature. The coatings are prepared with various concentrations of forsterite/hydroxyapatite nanopowder (2, 4, 6 and 8 wt.%) with a fixed concentration of PCL (4 wt.%) and thus coated Ti6Al4V substrates are examined for corrosion resistance. PCL/Hydroxyapatite/Forsterite coatings are characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM), which clearly showed the formation of nanocomposites. Potentiodynamic polarization curves and electrochemical impedance spectroscopy (EIS) are used to investigate corrosion behavior of the coated substrates, which portrayed that the composite coating of PCL/HA/F substantially enhanced the corrosion resistance of Ti6Al4V alloy

DEVELOPMENT AND OPTIMIZATION OF ENZALUTAMIDE-LOADED SOLID LIPID NANOPARTICLES USING BOX–BEHNKEN DESIGN

Objective: The primary motive behind this investigation is to develop and optimize the solid lipid nanoparticles formulation of enzalutamide for the effective drug delivery. Materials and Methods: The formulation variables were optimized using design of experiments. Box–Behnken design was used for the study and the results were analyzed using response surface methodology. The prepared nanoformulation was characterized for particle size, zeta potential, surface morphology, X-ray diffractometry (XRD), in vitro drug release kinetics, and stability study. Results: The influence of formulation variables, drug-to-lipid ratio, concentration of phosphatidylcholine, and concentration of poloxamer 188 were evaluated by regression analysis. The optimized formulation (F3) was found to have the minimum particle size (253 nm) with maximum entrapment efficiency (89.72%) and drug loading (23.84%). From SEM studies, the data showed a spherical shape for enzalutamide nanoparticles with uniform and relatively narrow particle distribution. From XRD examines, it is demonstrative that the drug was not in crystalline form in nanoformulation when compared with pure drug. In vitro release studies disclosed that maximum cumulative drug release was attained by F3 (99.72%) in controlled manner. The optimized formulation of enzalutamide followed zero-order release kinetics with a strong correlation coefficient (R2 = 0.9994). Conclusion: The nanoformulation prepared under optimized conditions is in concurrence with the expected results. The SLN formulation can be used as a potential carrier for the effective delivery of enzalutamide

Universal diffusion of dendrimers in a semidilute solution of linear polymers

The static and dynamic properties of dendrimers in semidilute solutions of linear chains of comparable size are investigated using Brownian dynamics simulations. The radius of gyration and diffusivity of a wide variety of low generation dendrimers and linear chains in solution follow universal scaling laws independent of their topology. Analysis of the shape functions and internal density of dendrimers shows that they are more spherical than linear chains and have a dense core. At intermediate times, dendrimers become subdiffusive, with an exponent higher than that previously reported for nanoparticles in semidilute polymer solutions. The long-time diffusivity of dendrimers does not follow theoretical predictions for nanoparticles. We propose a new scaling law for the long-time diffusion coefficient of dendrimers which accounts for the fact that, unlike nanoparticles, dendrimers shrink with an increase in background solution concentration. Analysis of the properties of a special case of a higher functionality dendrimer shows a transition from polymer-like to nanoparticle-like behaviour.Comment: 20 pages, 14 figures, includes supplementary informatio