Binary Dispersions Research Articles

Molecular dynamics, physical and thermal stability of neat amorphous amlodipine besylate and in binary mixture

In this paper, a stable amorphous solid dispersion of an antihypertensive drug, amlodipine besylate (AMB) was prepared by entrapping it in a polymer matrix, polyvinyl pyrrollidone, in different weight ratios (AMB/PVP 05:95, 10:90, 20:80, 30:70). The glass forming ability of all binary dispersions were studied by means of differential scanning calorimetry and found good correlation between experimental Tg and Fox Flory's prediction. By considering the daily dosage limit of 5 mg, a weight ratio of 05:95 was further considered for the study. The structures of neat and binary of AMB were characterized by density functional theory, Fourier transform infrared spectroscopy, Fourier transform Raman spectroscopy and UV–visible spectroscopy. Further, detailed molecular dynamics of both pure and binary were investigated using broadband dielectric spectroscopy to judge the physical stability of the amorphous dispersions. Translation-rotation coupling of AMB possibly explains the dual conductivity and dipolar nature of the secondary relaxation in neat AMB. Thus, the binary dispersion of AMB with commercially acceptable weight ratio with strong glass forming behaviour and better shelf life was prepared and characterized for practical applications.

Fluorescence enabled direct visual observation for diagnosis of ultrafiltration membrane fouling by bi‐disperse submicron particle suspensions

AbstractWhilst direct observation (DO) methodologies can describe back‐transport of supra‐micron particles, present technologies are unable to discriminate submicron particles, which are primarily responsible for membrane fouling. In this study, we therefore introduce a fluorescence enabled direct visual observation (RLF‐DVO) methodology to permit visual characterisation of submicron particle transport during cross‐flow filtration. Particle discrimination was achievable for particle diameters exceeding 0.25 µm; however, this was dependent upon particle concentration and the cross‐flow velocity employed. Nevertheless, this is considerably below the detection limit of current techniques (around 3 µm). During filtration of a binary dispersion comprised of submicron particles, deposition was observed before a change in transmembrane pressure was detected, which underpins the important role of DO for fouling diagnosis. Based on observations made during this study, recommendations are proposed that will further improve resolution. Importantly, this study demonstrates RLF‐DVO can provide real‐time description of submicron particle transport during cross‐flow filtration.

Enhanced Biopharmaceutical Performance of Rivaroxaban through Polymeric Amorphous Solid Dispersion.

Rivaroxaban (RXB) is an orally active direct inhibitor of the activated serine protease Factor Xa, given as monotherapy in the treatment of venous thromboembolism (VTE). It has been characterized in vitro as a substrate for the active, nonsaturable efflux via P-gp transporter, limiting its high permeability. Therefore, the role of P-gp inhibiting polymers in enhancing the biopharmaceutical performance of RXB by preparing polymeric amorphous solid dispersion and subsequent improvement in solubility and permeability was investigated. Initially, solubility parameter and Flory-Huggins interaction parameter were determined for miscibility studies between drug and polymers. Binary dispersions were prepared by dissolving drug with polymers eudragit S100, eudragit L100, and soluplus in common solvent (5% v/v water in tetrahydrofuran) using spray dryer. Prepared binary dispersions were analyzed by differential scanning calorimetry (DSC), microscopy, powder X-ray diffractometry (PXRD), Fourier transform infrared spectroscopy (FTIR), dynamic vapor sorption (DVS), and solution nuclear magnetic resonance (NMR) spectroscopy. Superior performance of binary dispersions was observed upon dissolution and solubility studies over micronized active pharmaceutical ingredient. Amorphous solid dispersion (ASD) prepared with soluplus showed 10-fold increase in apparent solubility and maintenance of supersaturation for 24 h compared to the crystalline RXB. Further, pharmacokinetic study performed in animals was in good correlation with the solubility data. Increases of 5.7- and 6.7-fold were observed in AUC and Cmax, respectively, for ASDs prepared with soluplus compared to those with crystalline RXB. FTIR and NMR spectroscopy unveiled the involvement of N-H group of RXB with C═O group of polymers in intermolecular interactions. The decreased drug efflux ratio was observed for ASDs prepared with eudragit S100 and soluplus in Caco-2 transport study suggesting improvement in the absorption of RXB. Hence, the present study demonstrates ASD using soluplus as a promising formulation strategy for enhancing the biopharmaceutical performance of RXB by increasing the solubility and circumventing the P-gp activity.

Nocturnal pulse oximetry indicators in the evaluation of obstructive sleep apnea syndrome in outpatients with concomitant diseases of the upper respiratory tract and overweight

By using mathematical modeling, to evaluate the impact of upper respiratory tract diseases, retro- and micrognathia, and body mass index (BMI) on nocturnal pulse oximetry indicators (oxygen saturation level and oxygen desaturation index) in outpatients examined for suspected obstructive sleep apnea syndrome (OSAS). The study enrolled 260 subjects with a mean age of 47.8±12.0 years. All the examinees underwent outpatient pulse oximetry screening during nocturnal sleep because of suspected OSAS. Multislice spiral computed tomography was carried out to assess the paranasal sinuses and nasal septum. BMI was calculated. Variance factor analysis using an original programming application intended to create binary and ternary dispersion complexes was employed as a main mathematical tool. There were statistically significantly sets of risk factors for OSAS: nasal septum deviation + increased BMI + male gender = 68.66%; chronic allergic rhinitis + increased BMI + male gender = 63.09%; retromicrognathia + increased BMI + male ganger = 59.48%; and chronic tonsillitis + increased BMI + male gander = 60.88%. Higher BMI and male gender are a most statistically significant set of risk factors. Pulse oximetry screening during nocturnal sleep in snoring patients with suspected OSAS in combination with an assessment of age, sex, BMI, ENT comorbidity, retro- and micrognathia can predict the severity of the disease and serve as a basis for elaborating an OSAS screening program.

Tpeak-Tend dispersion as a predictor for malignant arrhythmia events in patients with vasospastic angina

BackgroundTpeak-Tend interval (Tp-e interval) in electrocardiogram (ECG) has been reported to predict malignant arrhythmia events (MAE) in ST-segment elevation myocardial infarction and ion channelopathy. Tp-e interval and other ECG parameters as predictors for MAE was evaluated in patients with vasospastic angina (VA). Methods and resultsSixty-two patients with VA (Non-MAE group) and 20 patients with VA complicated by MAE (MAE group) were enrolled in our Division of Cardiology between January 2010 and December 2015. Continuous variables were analyzed by t-test and categorical variables by Chi-square analysis. Patients with MAE showed greater QTc (corrected QT interval) dispersion (P=0.005), Tp-ec (corrected Tp-e) interval (P=0.001), Tp-ec dispersion (P<0.001) and Tp-e/QT ratio (P<0.001) than those in non-MAE groups when ST-segment elevated. After elevated ST-segment returned, there were no significant differences in these ECG parameters between two groups (All P>0.05). At univariate binary logistic regression analysis QTc dispersion (odds ratio(OR)=1.133; P=0.013), Tp-ec (OR=1.058; P=0.003), Tp-e/QT (OR=1.403; P=0.001), and Tp-ec dispersion (OR=1.497; P=0.004) were significantly associated with MAE. At multivariable logistic regression analysis, Tp-ec dispersion remained a predictor of MAE. Receiver operating characteristic (ROC) curve analysis showed that only AUC (Area under curve) of Tp-ec dispersion had significant difference with those in QTc dispersion (P<0.001), Tp-ec (P=0.003), and Tp-e/QT ratio (P=0.012), respectively. ConclusionsQTc dispersion, Tp-ec, Tp-e/QT and Tp-ec dispersion were significantly increased in VA patients with MAE than those without MAE when coronary spasm was onset. Prolonged Tp-ec dispersion was the best discriminators and a strong independent predictor of MAE in VA patients.

Screening of drug-sericin solid dispersions for improved solubility and dissolution

The aim of present attempt deals with preparation of binary dispersion of sericin, waste of sericulture industry in order to enhance solubility and dissolution of poorly soluble drugs. Solid dispersions (SDs) of BCS-II drugs were prepared by spray drying, solvent evaporation, ball milling and physical mixing in ratio of drug:sericin (1:0.5, 1:1, 1:1.5, 1:2, 1:2.5 and 1:3). Further, SDs were investigated by solubility, ATR-FTIR, XRD, DSC, micromeritics and tablettability, surface morphology and in-vitro dissolution. Results demonstrated that, sericin improves solubility of drugs by 8–10 fold. The ATR-FTIR showed the slight shifting/broadening of principle peaks corresponding to NH and OH. Spray dried (1:2w/w) SDs showed maximum reduction in crystallinity of drugs indicating drug was molecularly distributed and was in amorphous state. Spray dried SDs of meloxicam showed better compressibility and compactibility. The microphotograph of spray dried SDs of lornoxicam and meloxicam showed bowl shaped and blend of bowl and spherical particles respectively, while spray dried SDs of felodepine showed spherical shape. The spray dried SDs (1:2w/w) displayed better dissolution performance than other methods Conclusively, sericin offers a hydrophilic matrix to deliver poor water soluble drugs and its aerodynamic shape may show a great potential for various drug deliveries.

Mucoadhesive amorphous solid dispersions for sustained release of poorly water soluble drugs

The oral delivery of mucoadhesive patches has been shown to enhance the absorption of large molecules such as peptides. We hypothesized that this mechanism could have utility for poorly soluble small molecules by utilizing a mucoadhesive polymer as the matrix for an amorphous solid dispersion. Binary dispersions of itraconazole and carbomer (Carbopol 71G) were prepared utilizing a thermokinetic mixing process (KinetiSol Dispersing) and the physicochemical properties were investigated by powder X-ray diffraction, calorimetry, and liquid chromatography. Adhesion of the dispersions to freshly excised porcine intestine was investigated with a texture analyzer. Minitablets were compressed from the optimal dispersion and further investigated in vitro and in vivo in rats. Thermokinetic mixing successfully processed amorphous dispersions up to 30% drug loading and each dispersion exhibited works of adhesion that were approximately an order of magnitude greater than a negative control in vitro. Ethylcellulose (EC) coated and uncoated minitablets prepared with the 30% drug load dispersion were delivered orally to rats and exhibited sustained release characteristics, with overall bioavailability greater for the uncoated minitablets compared to the EC-coated minitablets, similar to the rank order observed in our in vitro dissolution experiments. Necropsy studies showed that minitablets delivered with enteric-coated capsules targeted release to the distal small intestine and adhered to the intestinal mucosa, but the rat model presented limitations with respect to evaluating the overall performance. Based on the in vitro and in vivo results, further investigations in larger animals are a logical next step where fluid volumes, pH, and transit times are more favorable for the evaluated dosage forms.

Multiscale directed self-assembly of composite microgels in complex electric fields.

This study explored the application of localized electric fields for reversible directed self-assembly of colloidal particles in 3 dimensions. Electric field microgradients, arising from the use of micro-patterned electrodes, were utilized to direct the localization and self-assembly of polarizable (charged) particles resulting from a combination of dielectrophoretic and multipolar forces. Deionized dispersions of spherical and ellipsoidal core-shell microgels were employed for investigating their assembly under an external alternating electric field. We demonstrated that the frequency of the field allowed for an exquisite control over the localization of the particles and their self-assembled structures near the electrodes. We extended this approach to concentrated binary dispersions consisting of polarizable and less polarizable composite microgels. Furthermore, we utilized the thermosensitivity of the microgels to adjust the effective volume fraction and the dynamics of the system, which provided the possibility to dynamically "solidify" the assembly of the field-responsive particles by a temperature quench from their initial fluid state into an arrested crystalline state. Reversible solidification enables us to re-write/reconstruct various 3 dimensional assemblies by varying the applied field frequency.

Freeze Dried Quetiapine-Nicotinamide Binary Solid Dispersions: A New Strategy for Improving Physicochemical Properties and Ex Vivo Diffusion.

Improving the physicochemical properties and oral bioavailability of quetiapine fumarate (QF) enabling enhanced antipsychotic attributes are the main aims of this research. The freeze dried solid dispersion strategy was adopted using nicotinamide (NIC) as highly soluble coformer. The prepared dispersions were characterized using scanning electron microscopy (SEM) differential scanning calorimetry (DSC), Fourier transform infrared spectroscopy (FTIR), and X-ray diffraction (XRD). Static disc intrinsic dissolution rate and ex vivo diffusion through intestinal tissues were conducted and compared to pure quetiapine fumarate. The results demonstrated a highly soluble coamorphous system formed between quetiapine fumarate and nicotinamide at 1 : 3 molar ratio through H-bonding interactions. The results showed >14-fold increase in solubility of QF from the prepared dispersions. Increased intrinsic dissolution rate (from 0.28 to 0.603 mg cm−2 min−1) and faster flux rate through duodenum (from 0.027 to 0.041 mg cm−2 h−1) and jejunum (0.027 to 0.036 mg cm−2 h−1) were obtained. The prepared coamorphous dispersion proved to be effective in improving the drug solubility and dissolution rate and ex vivo diffusion. Therefore, binary coamorphous dispersions could be a promising solution to modify the physicochemical properties, raise oral bioavailability, and change the biopharmaceutics classification (BCS) of some active pharmaceutical ingredients.

Binary Complex Based on Zein and Propylene Glycol Alginate for Delivery of Quercetagetin.

Propylene glycol alginate (PGA) was found to be able to dissolve in aqueous ethanol solution and applied to interact with zein to form a noncovalent binary complex by the antisolvent coprecipitation method at pH 4.0. Quercetagetin (Q) was employed to explore the Q-delivery potential of Zein-PGA binary complex. A fruit tree-like microstructure was observed for Zein-PGA binary complex as its "branches" were closely adsorbed by zein particles. A solid sponge-like entity was formed after lyophilization of Zein-PGA binary complex colloidal dispersion. A synergistic effect was found between zein and PGA on improving the entrapment efficiency and loading capacity of Q. The incorporation of Q at a high concentration induced a significant effect on the tertiary structure of zein. Electrostatic attraction, hydrogen bond, and hydrophobic effects were mainly involved in the interactions between zein and PGA. Schematics with four possible structures were proposed to explain the formation mechanism of composites.

Interaction and formation mechanism of binary complex between zein and propylene glycol alginate

The anti-solvent co-precipitation method was used to fabricate the zein-propylene glycol alginate (PGA) binary complex with different mass ratios of zein to PGA (20:1, 10:1, 5:1, 2:1 and 1:1) at pH 4.0. Results showed that attractive electrostatic interaction between zein and PGA occurred and negatively charged binary complex with large size and high turbidity was formed due to the charge neutralization. Hydrogen bonding and hydrophobic effects were involved in the interactions between zein and PGA, leading to the changed secondary structure and improved thermal stability of zein. Aggregates in the irregular shape with large size were obviously observed in the AFM images. PGA alone exhibited a fine filamentous network structure, while zein-PGA binary complex showed a rough branch-like pattern and the surface of “branch” was closely adsorbed by lots of spherical zein particles. Q in zein-PGA binary complex dispersions presented the improved photochemical and thermal stability. The potential mechanism of a two-step process was proposed to explain the formation of zein-PGA binary complexes.

Separating nanoparticles by surface charge group using pH-controlled passivated gel electrophoresis

ABSTRACTBecause ionically stabilized colloids in aqueous dispersions have net surface charges that depend on pH, it is potentially possible to separate mixtures of nanospheres having identical radii, yet different types of stabilizing surface charge groups, efficiently using passivated gel electrophoresis (gel-EP). To demonstrate this, we separate a binary dispersion of polystyrene nanospheres that have nearly identical radii and surface group densities, yet different types of anionic stabilizing surface charge groups: sulfate and carboxylate. We achieve an efficient separation by adjusting the pH of the running buffer to lie between the pKa values of these charge groups, resulting in significantly different protonation and, consequently, different electrophoretic propagation velocities of the nanospheres. The measured steady-state propagation velocities of both types of anionic nanoparticles as a function of pH can be fit well by an equilibrium model of pH-dependent protonation of anionic surface charge groups. Thus, pH-controlled passivated gel-EP opens a route for separating similarly sized charged colloidal objects that are stabilized by a variety of different surface charge groups.

Confined tube flow of low viscosity emulsions: Effect of matrix elasticity

This study is addressed to the effect of the elasticity of the continuous phase on confined flow of low viscosity emulsions, a topic of interest in several applications. A Newtonian silicone oil was used as the dispersed phase, while three different water-based fluids, a Newtonian and two Boger fluids, were used as the continuous phase. All the fluids have the same viscosity (ca. 0.05 Pa s). Emulsions were prepared by feeding the two phases to a T-junction followed by a membrane. When the continuous phase was a Boger fluid, the average drop size of the so obtained emulsions was higher (as compared to the Newtonian continuous phase) and a bimodal distribution was observed. Such lower mixing efficiency for a Boger continuous phase is in line with the result for an isolated droplet that breakup is hindered by matrix elasticity. High-speed microscopy visualization of the emulsions flowing through a microcapillary allowed one to determine the velocity profiles and the droplet spatial distribution as a function of the shear rate. In all the experiments, the formation of a droplet-rich core and of a droplet-devoid wall region Δ was observed, with a significant enhancement when the continuous phase was a Boger fluid (where values of Δ as high as 37% of capillary radius were found). So, confinement here refers to the fact that, although the droplets are much smaller than capillary radius, the droplet-free layer takes up a significant fraction of the capillary radius. The observed nonhomogeneous droplet spatial distribution was not due to a transient entry effect, as shown by imaging the emulsions flow at different sections from the capillary inlet, but can be explained by a balance between collision-induced drop diffusion and wall lift force. The former acts to homogenize droplet spatial distribution, while the latter tends to push droplets away from the wall and is enhanced by matrix elasticity. These effects lead to the accumulation of larger droplets around the center of the channel, while smaller droplets are pushed toward the periphery. The velocity profiles for the Boger continuous phase were flat in the droplet-rich core, thus suggesting that the confined emulsions behave as a Bingham fluid. The corresponding yield stress was determined by data fitting of the velocity profiles and rather large values were so obtained. This result is consistent with the high values, close to the maximum packing for spherical particles in binary dispersions, of the droplet volume fraction in the core, which were estimated by measuring the thickness of the droplet-devoid annular region as a function of the applied flow rate and making a volume balance. Overall, the results of this work bear strong analogies with the confined flow of other concentrated suspensions of deformable particles, such as red blood cells in microcirculation, where the formation of a cell-free layer at the wall, which is referred to as margination, has important pathophysiological implications. These findings suggest that low viscosity emulsions with an elastic matrix under confined flow can be used as a tunable model system of biomedical relevance.

Optimising Drug Solubilisation in Amorphous Polymer Dispersions: Rational Selection of Hot-melt Extrusion Processing Parameters.

The aim of this article was to construct a T-ϕ phase diagram for a model drug (FD) and amorphous polymer (Eudragit® EPO) and to use this information to understand the impact of how temperature-composition coordinates influenced the final properties of the extrudate. Defining process boundaries and understanding drug solubility in polymeric carriers is of utmost importance and will help in the successful manufacture of new delivery platforms for BCS class II drugs. Physically mixed felodipine (FD)-Eudragit(®) EPO (EPO) binary mixtures with pre-determined weight fractions were analysed using DSC to measure the endset of melting and glass transition temperature. Extrudates of 10wt% FD-EPO were processed using temperatures (110°C, 126°C, 140°C and 150°C) selected from the temperature-composition (T-ϕ) phase diagrams and processing screw speed of 20, 100 and 200rpm. Extrudates were characterised using powder X-ray diffraction (PXRD), optical, polarised light and Raman microscopy. To ensure formation of a binary amorphous drug dispersion (ADD) at a specific composition, HME processing temperatures should at least be equal to, or exceed, the corresponding temperature value on the liquid-solid curve in a F-H T-ϕ phase diagram. If extruded between the spinodal and liquid-solid curve, the lack of thermodynamic forces to attain complete drug amorphisation may be compensated for through the use of an increased screw speed. Constructing F-H T-ϕ phase diagrams are valuable not only in the understanding drug-polymer miscibility behaviour but also in rationalising the selection of important processing parameters for HME to ensure miscibility of drug and polymer.

Mechanistic insights into acyclovir-polyethylene glycol 20000 binary dispersions.

Objective:The objective of this study is to provide a mechanistic insight into solubility enhancement and dissolution of acyclovir (ACY) by polyethylene glycol20000 (PEG20000).Materials and Methods:Solid dispersions with differing ratios of drug (ACY) and carrier (PEG20000) were prepared and evaluated by phase solubility, in vitro release studies, kinetic analysis, in situ perfusion, and in vitro permeation studies. Solid state characterization was also done by Powder X-Ray Diffraction (PXRD), Differential Scanning Calorimetry (DSC), Fourier Transform Infrared spectroscopy (FT-IR) analysis and surface morphology was assessed by Polarizing Microscopic Image (PMI) analysis, Scanning Electron Microscopy (SEM), Atomic Force Microscopy (AFM), and Nuclear Magnetic Resonance (NMR) analysis.Results:Thermodynamic parameters proved the solubilization effect of carrier. The aqueous solubility and dissolution of ACY were increased in all samples. Formation of solid solution, crystallinity reduction, and absence of interaction between drug and carrier was proved by XRD, DSC, and FTIR analysis. The particle size reduction and change in surface morphology were confirmed by SEM and AFM and analysis. The permeation coefficient and amount of drug diffused was higher in samples as compared to ACY. The stability was high in dispersions, and it was proved by NMR analysis.Conclusion:The mechanical insights into the enhancement of solubility and dissolution could be used as a platform to improve the aqueous solubility for other poor water soluble drugs.

Water-assisted stable dispersal of graphene oxide in non-dispersible solvents and skin formation on the GO dispersion

Graphene oxide (GO) particles disperse well in a few polar solvents including water but do not disperse in non-polar and low dielectric constant solvents. The limitation of available solvents can restrict the application of GO compositional materials. Herein, we report that by adding small amount of water in a water-miscible solvent, the dispersity of GO can be significantly improved. The scheme works even in solvent with low dielectric constant; the water-added dioxane exhibited even better GO dispersity than pure water that is known to be the best solvent for GO dispersion to date. The method increases the spectrum of available solvents for dispersing GO particles. We also report a formation of skin layer with random birefringent wrinkles on the surface of water-dioxane binary GO dispersion. The skin layer in gel phase was partially stretchable and less rigid as compared to a fully dried GO film.

Computational prediction of electrical and thermal conductivities of disklike particulate composites

The effective conductivities are determined for randomly oriented disklike particles using an efficient computational algorithm based on the finite element method. The pairwise intersection criteria of disks are developed using a set of vector operations. An element partition scheme has been implemented to connect the elements on different disks across the lines of intersection. The computed conductivity is expressed as a function of the disk density and size. It is further expressed in a power-law form with the key parameters determined from curve fitting. The particle number and the trial number of simulations vary with the disk size to minimize the computational effort in search of the percolation paths. The estimated percolation threshold agrees very well with the result reported in the literature. It has been confirmed that the statistical invariant for percolation is a cubic function of the characteristic size, and that the definition of percolation threshold is consistent with that of the equivalent system containing spherical particles. Binary dispersions of disks of different radii have also been investigated to study the effect of the size distribution. The approximate solutions in the power-law function have potential applications in advanced composites with embedded graphene nanoplatelets (GNPs).

The formation of nanocomposites as a result of evaporating droplets of dispersions of silver nanoparticles in low-volatile and binary dispersion media

The regularities of the formation of nanocomposites in the form of ring-shaped deposits during the evaporation of dispersions of cube-shaped silver nanoparticles with an average size of 70 nm on hydrophilic (glass) and hydrophobic (copper) substrates have been studied. The nanoparticles have been synthesized by the polyol method in an ethylene glycol solution. In addition, droplets of dispersions of the same nanoparticles in an ethylene glycol/ethanol mixture and water have been experimentally studied. Geometric parameters and conductivity of the formed ring-shaped deposits have been determined.

Influence of binary microgel phase behavior on the assembly of multi-functional raspberry-structured microgel heteroaggregates

We investigate the influence of microgel composition on phase behavior of binary microgel dispersions using poly(N-isopropylacrylamide) microgels cross-linked with 5mol% and 1mol% N,N′-methylenebis(acrylamide), or poly(N-isopropylmethacrylamide) microgels cross-linked with 5mol% N,N′-methylenebis(acrylamide). We then explore the dispersion phase behavior in the context of microgel deposition at a planar interface. These results are then compared to the observed assembly of microgels at curved interfaces, in the form of raspberry-like patchy particles (RLPPs) consisting of a polystyrene core surrounded by a (two-component) microgel shell. Results suggest that microgel composition has a large influence on the ability of binary dispersions to coat planar and curved interfaces. In particular, we demonstrate that binary dispersions of microgels containing higher cross-linker content exhibit decreased packing densities that are very pronounced at a curved interface. To enhance packing density we also explore the use of a two-step coating process to fabricate RLPPs with enhanced control over topography. Development of these complex vehicles is potentially beneficial in the modulation of biological systems where spatial and temporal presentation of molecules can have a large influence on cellular behavior.

Hansen solubility parameters of surfactant-capped silver nanoparticles for ink and printing technologies.

Optimal ink formulations, inclusive of nanoparticles, are often limited to matching the nanoparticle's capping agent or surface degree of polarity to the solvent of choice. Rather than relying on this single attribute, nanoparticle dispersibility was optimized by identifying the Hansen solubility parameters (HSPs) of decanoic-acid-capped 5 nm silver nanoparticles (AgNPs) by broad spectrum dispersion testing and a more specific binary solvent gradient dispersion method. From the HSPs, solvents were chosen to disperse poly(methyl methacrylate) (PMMA) and nanoparticles, give uniform evaporation profiles, and yield a phase-separated microstructure of nanoparticles on PMMA via film formation by solvent evaporation. The goal of this research was to yield a film that is reflective or transparent depending on the angle of incident light (i.e., optically variable). The nanoparticle HSPs were very close to alkanes with added small polar and hydrogen-bonding components. This led to two ink formulations: one of 90:10 vol % toluene/methyl benzoate and one containing 80:10:10 vol % toluene/p-xylene/mesitylene, both of which yielded the desired final microstructure of a nanoparticle layer on a PMMA film. This approach to nanoparticle ink formulation allows one to obtain an ink that has desirable dispersive qualities, rheology, and evaporation to give a desired printed structure.