Distance Profiles Research Articles

Compression of High Grafting Density Opposing Polymer Brushes Using Molecular Dynamics Simulations in Explicit Solvent

Opposing polymer brush layers at high grafting density were examined under confinement and characterized with respect to structure and interaction forces using molecular dynamics simulations in an explicit solvent. The brush system underwent a static compression, where the system is simulated at several discrete separation distances. These simulations are all at the same solvent chemical potential as a non-interacting reference state to produce a realistic compression. Normal pressure-distance profiles were generated and compared to density profiles at each separation distance to determine structure-property relationships. Significant interpenetration of brush layers occurred at high compression, to the extent that each brush reached the opposing surface. Higher interpenetration corresponded to a sharp increase in the pressure-distance curve, suggesting a correlation between interpenetration and interaction forces. We find clear differences from literature values using implicit solvent techniques.

Diffusivities and atomic mobilities in fcc_A1 Ni–X (X=Ge, Ti and V) alloys

Based on three groups of Ni/Ni–9at% Ge diffusion couples, interdiffusion coefficients were determined in the face-centered (fcc_A1) Ni–Ge alloys at 1173, 1273 and 1373K by means of the Boltzmann–Matano method coupled with electronic probe microanalysis (EPMA) technique. On the basis of various critically-reviewed experimental diffusivities as well as the available thermodynamic descriptions, atomic mobilities in fcc_A1 Ni–X (X=Ge, Ti and V) alloys were assessed by means of DIffusion Controlled TRAnsformation (DICTRA) software package. For the self-diffusivities in dynamically unstable fcc_A1 Ge, Ti and V, a semi-empirical correlation was employed. Moreover, the first-principles calculations were also used to calculate the activation energy for self-diffusion in fcc_A1 Ge. Comprehensive comparison between the calculated and the measured diffusivities shows that most of the experimental data can be reproduced by the atomic mobilities obtained in the present work. In addition, the reliability of the currently obtained atomic mobilities in fcc_A1 Ni–X (X=Ge, Ti and V) alloys were further validated by comparing the model-predicted concentration–distance profiles and the experimental ones.

Ultrasound Versus Landmark-guided Femoral Vein, Artery Access in Pediatric Cardiac Catheterization

Background: To investigate the effects of rosuvastatin on cardiac function and serum MPO, MMP-9 in patients with chronic heart failure. Methods: From Nov. 2010 to Dec. 2011, 60 patients with CHF hospitalized at the Department of Cardiology in the Second Hospital of Hebei Medical University was selected, including 26 cases of ischemic heart disease, 34 cases of non-ischemic heart disease.And after admission were randomly divided into control group and the statin group (rosuvastatin 10mg/day). (N1⁄430 cases). The levels of MPO and MMP9, 6-minute walking distance, echocardiography (the size of heart chambers, LVEF) and blood lipids profiles were measured at baseline and 7-10days, 6weeks after treatment. Results: Six weeks after treatment, LVEF (%), the 6-minute walking distance of statin group and the 6 minutes walking distance of control group was significantly increased than before treatment (44.17O12.91 vs 38.75O14.4, 437.12O46.17 vs 356.10O42.60, 433.82O58.66 vs 379.33O61.81, p < 0.05). In addition, 6 weeks after treatment, the indexes of LV, LA, RA in statin group were significantly reduced than before treatment (62.35O9.75 vs 63.92O9.98, 39.92O6.11 vs 42.19O5.66, 34.92O4.35 vs 38.13O5.85, p< 0.05))after 7-10 days and 6 weeks of treatment, serum MMP-9 level in statin group decreased significantly compared with that of control group((42.70O14.41 vs 73.55O32.30, 47.78O22.29 vs 69.22O21.66, p< 0.05). After 6 weeks

Adhesion of Mussel Foot Protein-3 to TiO2 Surfaces: the Effect of pH

The underwater adhesion of marine mussels relies on mussel foot proteins (mfps) rich in the catecholic amino acid 3,4-dihydroxyphenylalanine (Dopa). As a side chain, Dopa is capable of strong bidentate interactions with a variety of surfaces, including many minerals and metal oxides. Titanium is among the most widely used medical implant material and quickly forms a TiO2 passivation layer under physiological conditions. Understanding the binding mechanism of Dopa to TiO2 surfaces is therefore of considerable theoretical and practical interest. Using a surface forces apparatus, we explored the force-distance profiles and adhesion energies of mussel foot protein 3 (mfp-3) to TiO2 surfaces at three different pHs (pH 3, 5.5 and 7.5). At pH 3, mfp-3 showed the strongest adhesion force on TiO2, with an adhesion energy of ∼-7.0 mJ/m(2). Increasing the pH gives rise to two opposing effects: (1) increased oxidation of Dopa, thus, decreasing availability for the Dopa-mediated adhesion, and (2) increased bidentate Dopa-Ti coordination, leading to the further stabilization of the Dopa group and, thus, an increase in adhesion force. Both effects were reflected in the resonance-enhanced Raman spectra obtained at the three deposition pHs. The two competing effects give rise to a higher adhesion force of mfp-3 on the TiO2 surface at pH 7.5 than at pH 5.5. Our results suggest that Dopa-containing proteins and synthetic polymers have great potential as coating materials for medical implant materials, particularly if redox activity can be controlled.

Adhesion of mussel foot proteins to different substrate surfaces.

Mussel foot proteins (mfps) have been investigated as a source of inspiration for the design of underwater coatings and adhesives. Recent analysis of various mfps by a surface forces apparatus (SFA) revealed that mfp-1 functions as a coating, whereas mfp-3 and mfp-5 resemble adhesive primers on mica surfaces. To further refine and elaborate the surface properties of mfps, the force-distance profiles of the interactions between thin mfp (i.e. mfp-1, mfp-3 or mfp-5) films and four different surface chemistries, namely mica, silicon dioxide, polymethylmethacrylate and polystyrene, were measured by an SFA. The results indicate that the adhesion was exquisitely dependent on the mfp tested, the substrate surface chemistry and the contact time. Such studies are essential for understanding the adhesive versatility of mfps and related/similar adhesion proteins, and for translating this versatility into a new generation of coatings and (including in vivo) adhesive materials.

Efficient Reuse Distance Analysis of Multicore Scaling for Loop-Based Parallel Programs

Reuse Distance (RD) analysis is a powerful memory analysis tool that can potentially help architects study multicore processor scaling. One key obstacle, however, is that multicore RD analysis requires measuring Concurrent Reuse Distance (CRD) and Private-LRU-stack Reuse Distance (PRD) profiles across thread-interleaved memory reference streams. Sensitivity to memory interleaving makes CRD and PRD profiles architecture dependent, preventing them from analyzing different processor configurations. For loop-based parallel programs, CRD and PRD profiles shift coherently across RD values with core count scaling because interleaving threads are symmetric. Simple techniques can predict such shifting, making the analysis of numerous multicore configurations from a small set of CRD and PRD profiles feasible. Given the ubiquity of parallel loops, such techniques will be extremely valuable for studying future large multicore designs. This article investigates using RD analysis to efficiently analyze multicore cache performance for loop-based parallel programs, making several contributions. First, we provide an in-depth analysis on how CRD and PRD profiles change with core count scaling. Second, we develop techniques to predict CRD and PRD profile scaling, in particular employing reference groups [Zhong et al. 2003] to predict coherent shift, demonstrating 90% or greater prediction accuracy. Third, our CRD and PRD profile analyses define two application parameters with architectural implications: C core is the minimum shared cache capacity that “contains” locality degradation due to core count scaling, and C share is the capacity at which shared caches begin to provide a cache-miss reduction compared to private caches. And fourth, we apply CRD and PRD profiles to analyze multicore cache performance. When combined with existing problem scaling prediction, our techniques can predict shared LLC MPKI (private L2 cache MPKI) to within 10.7% (13.9%) of simulation across 1,728 (1,440) configurations using only 36 measured CRD (PRD) profiles.

Construction of ‘smart’ surfaces with polymer functionalized silica nanoparticles

Silica nanoparticles (SiNPs) coated with the pH responsive poly(2-(diethylamino)ethyl methacrylate) (PDEAEMA) shells have been synthesized in different sizes using surface-initiated atom transfer radical polymerization (ATRP). A mixture of the PDEAEMA functionalized SiNPs (20 and 128 nm) was found to efficiently change the surface property of a substrate. The surface properties were investigated at different ratios of functionalized SiNPs. Moreover, fluorescent-doped SiNPs with PDEAEMA were also prepared to study the adsorption/desorption behavior of the SiNPs on the substrates at different pHs. A Surface Forces Apparatus (SFA) was used to measure the interactions between PDEAEMA surfaces in aqueous solutions of different pHs, and the force–distance profiles directly indicate that the intermolecular interactions of PDEAEMA are pH sensitive. At pH < pKa (∼7.3) steric repulsion dominates while at pH ≥ pKa the hydrophobic attraction between PDEAEMA molecules plays a critical role in their molecular behaviors in solutions and on surfaces. Our results provide a new insight into the fundamental understanding and development of environmentally responsive and multifunctional surfaces and nanomaterials.

Computational study of atomic mobilities in Al–Zr solid solutions and the growth of ZrAl3 intermetallic phase

Based on the thermodynamic description, experimental diffusion coefficients and empirical relations, the atomic mobilities of Al and Zr in fcc_Al, bcc_Zr and hcp_Zr phases have been optimized. From the comparisons between the calculated and measured diffusion coefficients, it can be seen that most of the experimental data are reproduced well. A good prediction was also made in the composition–distance profile of the diffusion zone in the Zr/Zr-2.8wt% Al diffusion couple. Introducing the concept of “average interdiffusion coefficient”, the growth of ZrAl3 intermetallic phase with a narrow homogeneity range in Zr/Al diffusion couples was simulated using the obtained atomic mobility parameters. Meanwhile the average interdiffusion coefficients were assessed and their temperature dependence was then established. The difference in the average interdiffusion coefficients of the ZrAl3 phase based on separate experiments was also explained.

Subsurface characterization using seismic refraction and surface wave methods: a case of Lagos State University, Ojo, Lagos State

This study contains the finding of geophysical investigations conducted at the proposed science complex site at Lagos State University, Ojo, Lagos, Nigeria. Surface wave and seismic refraction tests are non-invasive seismic techniques and have been used to determine the shear wave velocity profile of soil deposits. The methods provide a simplified characterization of subsurface in two-dimensional (2D) (distance and depth) profiles. Seismic records obtained were processed/analyzed by Seis-Imager software to obtain one-dimensional shear wave velocity (Vs) distribution. Multiple Vs obtained were integrated and used to construct two-dimensional Vs map. The measured P- and S-wave velocities were also used to estimate Poisson’s ratio, rigidity modulus, and N-values. The study had shown that the area investigated composed mainly of loose sediments (clay formation) to the depth of 12 m with P-wave velocity ranging between 125 and 205 m/s and corresponding S-wave velocity between 60 and 100 m/s. The results presented in this study will be vital information for the engineers in construction of the proposed science complex.

Inhibitor-induced conformational shifts and ligand-exchange dynamics for HIV-1 protease measured by pulsed EPR and NMR spectroscopy.

Double electron-electron resonance (DEER) spectroscopy was utilized to investigate shifts in conformational sampling induced by nine FDA-approved protease inhibitors (PIs) and a nonhydrolyzable substrate mimic for human immunodeficiency virus type 1 protease (HIV-1 PR) subtype B, subtype C, and CRF_01 A/E. The ligand-bound subtype C protease has broader DEER distance profiles, but trends for inhibitor-induced conformational shifts are comparable to those previously reported for subtype B. Ritonavir, one of the strong-binding inhibitors for subtypes B and C, induces less of the closed conformation in CRF_01 A/E. (1)H-(15)N heteronuclear single-quantum coherence (HSQC) spectra were acquired for each protease construct titrated with the same set of inhibitors. NMR (1)H-(15)N HSQC titration data show that inhibitor residence time in the protein binding pocket, inferred from resonance exchange broadening, shifting or splitting correlates with the degree of ligand-induced flap closure measured by DEER spectroscopy. These parallel results show that the ligand-induced conformational shifts resulting from protein-ligand interactions characterized by DEER spectroscopy of HIV-1 PR obtained at the cryogenic temperature are consistent with more physiological solution protein-ligand interactions observed by solution NMR spectroscopy.

In silico modeling and experimental evidence of coagulant protein interaction with precursors for nanoparticle functionalization

The design of novel protein–nanoparticle hybrid systems has applications in many fields of science ranging from biomedicine, catalysis, water treatment, etc. The main barrier in devising such tool is lack of adequate information or poor understanding of protein–ligand chemistry. Here, we establish a new strategy based on computational modeling for protein and precursor linkers that can decorate the nanoparticles. Moringa oleifera (MO2.1) seed protein that has coagulation and antimicrobial properties was used. Superparamagnetic nanoparticles (SPION) with precursor ligands were used for the protein–ligand interaction studies. The molecular docking studies reveal that there are two binding sites, one is located at the core binding site; tetraethoxysilane (TEOS) or 3-aminopropyl trimethoxysilane (APTES) binds to this site while the other one is located at the side chain residues where trisodium citrate (TSC) or Si60 binds to this site. The protein–ligand distance profile analysis explains the differences in functional activity of the decorated SPION. Experimentally, TSC-coated nanoparticles showed higher coagulation activity as compared to TEOS- and APTES-coated SPION. To our knowledge, this is the first report on in vitro experimental data, which endorses the computational modeling studies as a powerful tool to design novel precursors for functionalization of nanomaterials; and develop interface hybrid systems for various applications.

Effect of dissolved calcium on the removal of bacteriophage PRD1 during soil passage: The role of double-layer interactions

The objective of this work was to investigate and obtain quantitative relations for the effects of Ca(2+) concentration on virus removal in saturated soil and to compare the experimental findings with predictions of the DLVO theory. In order to do so, a systematic study was performed with a range of calcium concentrations corresponding to natural field conditions. Experiments were conducted in a 50-cm column with clean quartz sand under saturated conditions. Inflow solutions were prepared by adding CaCl(2,) NaCl and NaHCO(3) to de-ionized water. Values of pH and ionic strength were fixed at 7 and 10mM, respectively. Bacteriophage PRD1 was used as a conservative model virus for virus removal. The samples were assayed using the plaque forming technique. Attachment, detachment and inactivation rate coefficients were determined from fitting breakthrough curves. Attachment rate coefficients were found to increase with increasing calcium concentration. Results were used to calculate sticking efficiency, for which an empirical formula as a function of Ca(2+) was developed. Numerical solutions of the Poisson-Boltzmann equation were obtained to evaluate the effect of Ca(2+) on the double-layer interactions between quartz and PRD1. Based on these results, the DLVO interaction energies were calculated. It turned out that the experimental findings cannot be explained with the distance profiles of the DLVO interaction. The discrepancy between theory and experiment can be attributed to underestimation of the van der Waals interactions, chemisorption of Ca(2+) onto the surfaces, or by factors affecting the double-layer interactions, which are not included in the Poisson-Boltzmann equation. When abruptly changing from inflow solution containing Ca(2+) to a Ca(2+)-free solution, pronounced mobilization of viruses was observed. This indicates virus removal is not irreversible and that chemical perturbations of the groundwater can cause a burst of released viruses.

Characterization of hydroxyphenol-terminated alkanethiol self-assembled monolayers: Interactions with phosphates by chemical force spectrometry

Tannins and humic substances, commonly referred to as natural organic matter (NOM), constitute an important component of natural water and soil systems. These species contain numerous hydroxyl and carboxyl functional groups whose reactivity is strongly dependent on both the quantity and location of these moieties on the aromatic ring. In the present study, self-assembled monolayers (SAMs) of 4-(12-mercaptododecyl)benzene-1,2-diol (o-hydroxyphenol-terminated); 5-(12-mercaptododecyl)benzene-1,3-diol (m-hydroxyphenol-terminated); bis(11-thioundecyl) hydrogen phosphate (monoprotic phosphate); and 11-thioundecyl dihydrogen phosphate (diprotic phosphate) were prepared and characterized using X-ray photoelectron spectroscopy (XPS), attenuated total reflectance infrared spectroscopy (ATR-IR), and water contact angle measurements. The interactions between phenolic groups with phosphates were examined as a function of pH using the chemical force spectrometry (CFS) technique. The observations are discussed in the context of hydrogen bonding and electrostatic repulsion interaction between corresponding species. Adhesion force profiles of hydroxyphenol isomers interacting with monoprotic phosphate are dominated by ionic H-bonding; however the strength of o-hydroxyphenol interactions is significantly higher. The difference in location of hydroxyl groups on the interface also results in significantly different force–distance profiles for the isomeric hydroxyphenols when interacting with diprotic phosphate.

Toward optimal fragment generations for ab initio protein structure assembly

Fragment assembly using structural motifs excised from other solved proteins has shown to be an efficient method for ab initio protein-structure prediction. However, how to construct accurate fragments, how to derive optimal restraints from fragments, and what the best fragment length is are the basic issues yet to be systematically examined. In this work, we developed a gapless-threading method to generate position-specific structure fragments. Distance profiles and torsion angle pairs are then derived from the fragments by statistical consistency analysis, which achieved comparable accuracy with the machine-learning-based methods although the fragments were taken from unrelated proteins. When measured by both accuracies of the derived distance profiles and torsion angle pairs, we come to a consistent conclusion that the optimal fragment length for structural assembly is around 10, and at least 100 fragments at each location are needed to achieve optimal structure assembly. The distant profiles and torsion angle pairs as derived by the fragments have been successfully used in QUARK for ab initio protein structure assembly and are provided by the QUARK online server at http://zhanglab.ccmb. med.umich.edu/QUARK/.

Molecular Interactions of a Polyaromatic Surfactant C5Pe in Aqueous Solutions Studied by a Surface Forces Apparatus

Studies on molecular mechanisms of polyaromatic surfactants in stabilizing water-in-oil (W/O) or oil-in-water (O/W) emulsions are of great scientific and practical importance. A polyaromatic surfactant N-(1-hexylheptyl)-N'-(5-carboxylicpentyl) perylene-3,4,9,10-tetracarboxylic bisimide (C5Pe) with well-defined molecular structure containing fused aromatic rings and heteroatoms similar to asphaltene molecules, was used in this study in an attempt to understand molecular interaction mechanisms of heavy oil components in aqueous solutions. A surface forces apparatus (SFA) was used to directly measure the molecular interactions of C5Pe. Solution pH, salt concentration and Ca(2+) addition showed a strong impact on molecular interactions between C5Pe adsorbed on mica surfaces. The repulsion observed between the two adsorbed C5Pe molecular layers was shown to have a steric and electrosteric origin. The force-distance profiles at short separation distances under high compression force were well fitted with the Alexander-de Gennes (AdG) model. At pH ≥ 4, the repulsive forces measured over a long separation distance under low compression force were shown to deviate from the AdG model but could be fitted with the Derjaguin-Landau-Verwey-Overbeek (DLVO) theory, indicating an electrostatic origin of the observed repulsion due to ionization of -COOH groups. Adhesion between two C5Pe surfaces was shown to decrease sharply with increasing solution pH and salt concentration, being attributed to the decrease in surface hydrophobicity and hence hydrophobic attraction. Addition of Ca(2+) ions induced the formation of large C5Pe aggregates due to strong bonding of Ca(2+) with -COOH groups, leading to a longer range steric repulsion. Our results provide a new insight into the molecular interactions of polyaromatic surfactants at oil-water interfaces and in complex aqueous solutions.

The Electrochemical Surface Forces Apparatus: The Effect of Surface Roughness, Electrostatic Surface Potentials, and Anodic Oxide Growth on Interaction Forces, and Friction between Dissimilar Surfaces in Aqueous Solutions

We present a newly designed electrochemical surface forces apparatus (EC-SFA) that allows control and measurement of surface potentials and interfacial electrochemical reactions with simultaneous measurement of normal interaction forces (with nN resolution), friction forces (with μN resolution), and distances (with Å resolution) between apposing surfaces. We describe three applications of the developed EC-SFA and discuss the wide-range of potential other applications. In particular, we describe measurements of (1) force-distance profiles between smooth and rough gold surfaces and apposing self-assembled monolayer-covered smooth mica surfaces; (2) the effective changing thickness of anodically growing oxide layers with Å-accuracy on rough and smooth surfaces; and (3) friction forces evolving at a metal-ceramic contact, all as a function of the applied electrochemical potential. Interaction forces between atomically smooth surfaces are well-described using DLVO theory and the Hogg-Healy-Fuerstenau approximation for electric double layer interactions between dissimilar surfaces, which unintuitively predicts the possibility of attractive double layer forces between dissimilar surfaces whose surface potentials have similar sign, and repulsive forces between surfaces whose surface potentials have opposite sign. Surface roughness of the gold electrodes leads to an additional exponentially repulsive force in the force-distance profiles that is qualitatively well described by an extended DLVO model that includes repulsive hydration and steric forces. Comparing the measured thickness of the anodic gold oxide layer and the charge consumed for generating this layer allowed the identification of its chemical structure as a hydrated Au(OH)(3) phase formed at the gold surface at high positive potentials. The EC-SFA allows, for the first time, one to look at complex long-term transient effects of dynamic processes (e.g., relaxation times), which are also reflected in friction forces while tuning electrochemical surface potentials.

Molecular dynamics simulations of peptide adsorption on self-assembled monolayers

All-atom molecular dynamics simulations are performed to investigate the neuromedin-B peptide adsorption on the self-assembled monolayers (SAMs) of SH(CH2)10N+(CH3)2CH2CH(OH)CH2SO3− (SBT), SH(CH2)10OH and SH(CH2)10CH3. The force–distance profiles show that the surface resistance to peptide adsorption is mainly generated by the water molecules tightly bound to surfaces via hydrogen bonds (hydration water molecules); but surfaces themselves may also set an energy barrier for the approaching peptide. For the SBT-SAM, the surface first exerts a relatively high repulsive force and then a rather week attractive force on the approaching peptide; meanwhile the hydration water molecules exert a strong repulsive force on the peptide. Therefore, SBT-SAM has an excellent performance on resisting protein adsorption. For the OH-SAM and CH3-SAM, surfaces show low or little energy barrier but strong affinity to the peptide; and the hydration water molecules apply merely a repulsive force within a much narrower range and with lower intensity compared with the case for the SBT-SAM. The analysis of structural and dynamical properties of the peptide, surface and water indicates that possible factors contributing to surface resistance include the hydrogen-bond formation capability of surfaces, mobility of water molecules near surfaces, surface packing density and chain flexibility of SAMs. There are a large number of hydrogen bonds formed between the hydration water molecules and the functional groups of the SBT-SAM, which greatly lowers the mobility of water molecules near the surface. This tightly-bound water layer effectively reduces the direct contact between the surface and the peptide. Furthermore, the SBT-SAM also has a high flexibility and a low surface packing density, which allows water molecules to penetrate into the surface to form tightly-bound networks and therefore reduces the affinity between the peptide and the surface. The results show that the protein-resistant properties of the SAMs are in the decreasing order of SBT-SAM>OH-SAM>CH3-SAM, which provide mechanistic explanation on SBT materials’ excellent anti-fouling performance.

Extended DLVO calculations expose the role of the structural nature of the adsorbent beads during chromatography

Protein adsorption onto hydrophobic interaction chromatography supports was studied by a surface-thermodynamics approach. To gather relevant experimental information, contact angle measurements and zeta potential determinations were performed on three different commercial adsorbent beads, Phenyl Sepharose 6 Fast Flow, Toyopearl Phenyl 650-C and Source 15 Phenyl, having soft to rigid backbone structure. Similar information was obtained for a collection of model proteins, lysozyme, bovine serum albumin (BSA), polygalacturonase, aminopeptidase, chymosin, aspartic protease, beta-galactosidase, human immunoglobulin G, and lactoferrin, were evaluated in the hydrated and in the dehydrated state. Based on the mentioned experimental data, calculations were performed to obtain the (interfacial) energy versus distance profiles of nine individual (model) proteins on (commercial) beads of three different types. All of these beads harbored the phenyl-ligand onto a matrix of differentiated chemical nature. Extended Derjaguin, Landau, Verwey, and Overbeek (DLVO) calculations were correlated with actual chromatographic behavior. Typical chromatography conditions were employed. The population of model proteins utilized in this study could be segregated into two groups, according to the minimum values observed for the resulting interaction energy pockets and the corresponding retention volumes (or times) during chromatography. Moreover, trends were also identified as a function of the type of adsorbent bead under consideration. This has revealed the influence of the physicochemical nature of the bead structure on the adsorption process and consequently, on the expected separation behavior.

Real-time UV imaging of piroxicam diffusion and distribution from oil solutions into gels mimicking the subcutaneous matrix

A novel real-time UV imaging approach for non-intrusive investigation of the diffusion and partitioning phenomena occurring during piroxicam release from medium chain triglyceride (MCT) solution into two hydrogel matrices is described. Two binary polymer/buffer gel matrices, 0.5% (w/v) agarose and 25% (w/v) Pluronic F127, were applied as simple models mimicking the subcutaneous tissue. The evolution of the absorbance maps as a function of time provided detailed information on the piroxicam release processes upon the exposure of the gel matrices to MCT. Using calibration curves, the concentration maps of piroxicam in the UV imaging area were determined. Regression of the longitudinal concentration–distance profiles, which were obtained using expressions derived from Fick’s second law, provided the diffusivity and the distribution coefficients of piroxicam penetrated into the gels. The obtained MCT–agarose (pH 7.4) distribution coefficient of 1.4 was identical to the MCT–aqueous (pH 7.4) distribution coefficient determined by the shake-flask method whereas that of the MCT–Pluronic F127 system was four times less. The experimental data show that UV imaging may have considerable potential for investigating the transport properties of drug formulations intended for the subcutaneous administration.

Investigation of Thermoresponsive Nano‐Confined Polymer Brushes by AFM‐Based Force Spectroscopy

AbstractPNIPAM polymer brushes are synthesized in nanopores of track‐etched membranes. The internal structure of these nano‐confined brushes is studied by AFM force spectroscopy experiments as a function of the synthesis conditions. The approach force vs. distance profiles are fitted using the Alexander‐de Gennes model to determine the grafting density, and the worm‐like chain model is used to estimate the chain length from the retract profiles. The grafting density for brushes synthesized within 80 nm pores is ten times lower than that obtained in 330 nm pores. For the same polymerization time, the chain lengths are much lower if the synthesis is carried out in small pores. The elastic properties of the brushes are also directly related to the confinement conditions.