Ostwald ripening of beta-carotene nanoparticles

Controlling drug nanoparticle formation by rapid precipitation

Nanoparticles are a drug delivery platform that can enhance the efficacy of active pharmaceutical ingredients, including poorly-water soluble compounds, ionic drugs, proteins, peptides, siRNA and DNA therapeutics. To realize the potential of these nano-sized carriers, manufacturing processes must be capable of providing reproducible, scalable and stable formulations. Antisolvent precipitation to form drug nanoparticles has been demonstrated as one such robust and scalable process. This review discusses the nucleation and growth of organic nanoparticles at high supersaturation. We present process considerations for controlling supersaturations as well as physical and chemical routes for modifying API solubility to optimize supersaturation and control particle size. We conclude with a discussion of post-precipitation factors which influence nanoparticle stability and efficacy in vivo and techniques for stabilization.

Block copolymer nanoparticles as nanobeads for the polymerase chain reaction

New sequencing technologies based on massively parallel signature sequencing (MPSS) have been developed to reduce the cost of genome sequencing. In some current MPSS platforms, DNA-modified micrometer-scale beads are used to template the polymerase chain reaction (PCR). Reducing the size of the beads to nanoscale can lead to significant improvements in sequencing throughput. To this end, we have assembled polymeric nanobeads that efficiently template PCR, resulting in DNA-decorated "nanobeads" with a high extent of functionalization.

Controlled antisolvent precipitation of spironolactone nanoparticles by impingement mixing

Continuous antisolvent precipitation of spironolactone nanoparticles were performed by impingement mixing in this work. In the range of Reynolds numbers (Re) 2108-6325 for the antisolvent water stream and 1771-5313 for the solvent stream, i.e. acetonic drug solution, 302-360 nm drug nanoparticles were achieved. Increasing drug concentration from 25 to 50 and 100 mg/ml led to a significant size increase from 279.0±2.6 to 302.7±4.9 and 446.0±17.3 nm, respectively. "Two-step crystallization" was first observed for spironolactone in the water/acetone system: the drug was precipitated initially as spherical cluster, which rearranged into ordered cuboidal nanocrystals finally. The nanoformulation showed faster dissolution rate in comparison with the raw drug. By combining the impingement mixing and an on-line spray drying, a fully continuous process may be developed for mass-production of dried drug nanoparticles.

Fluorescent polymeric nanoparticles: aggregation and phase behavior of pyrene and amphotericin B molecules in nanoparticle cores

The state of aggregation of compounds, especially drugs, in the cores of nanoparticles (NPs) formed by rapid precipitation is a significant unresolved issue. The state can control the dissolution kinetics from the NP, bioavailability, and chemical stability of the compound. A block-copolymer-directed rapid precipitation process is used to form ≈100 nm NPs comprising mixtures of hydrophobic species including fluorescent probe molecules. Fluorescence measurements are used to probe the state of aggregation and dynamics of rearrangement of pyrene (Py), Hostasol Yellow (HosY), and amphotericin B (AmpB) in NP cores. The Flory-Huggins theory of mixing is used to predict the miscibility or phase separation of the fluorophores from the host NP core material (polystyrene, cholesterol, or polycaprolactone). For Py, excimer fluorescence shows an initial microphase separation in the polystyrene core. Over time the Py redistributes more uniformly with a decrease in excimer and increase in monomer fluorescence. The Flory-Huggins theory predicts the miscibility. For HosY, the fluorescence quenching is not time-dependent, thus indicating stability of the microphase-separated fluorophores, which is consistent with the Flory-Huggins theory calculations. For the drug compound AmpB, the amphiphilic character of the molecule creates unusual "anti-Ostwald" ripening behavior in which the size distribution decreases and narrows over time, and the fluorescence demonstrates an increased ordering in the NP core over time--opposite to the behavior observed for Py.

Statistical analysis of low molecular mass heparin nanoencapsulation

The objective of this study was to use Box-Behnken design (BBD) to investigate the influence of formulation variables on the properties of heparin-loaded poly(lactic-coglycolic acid) (PLGA)-polymethacrylate-RLPO (E-RLPO) nanoparticles (NP) in terms of mean diameter (as size) and drug encapsulation efficiency. The NPs were prepared by the double emulsion solvent evaporation method. The independent variables were: X1 - polymer mass ratio (PLGA:E-RLPO) in the oil phase, X2 - concentration of polyvinyl alcohol (PVA) as emulsion stabilizer, and X3 - volume of the external aqueous phase (W2). Particle size (analyzed by dynamic light scattering) and encapsulation efficiency (EE, estimated by spectrophotometry) were the investigated responses. The polynomial equation obtained from regression analysis of the reduced model (p = 0.0002, F = 25.7952 and R2 = 0.96) provided an excellent fit. The optimal size for the NP was found to be 134.2 ± 16.5 nm with formulation variables of 48.2:61.8, 0.321 (%,m/V) and 263 mL for X1, X2 and X3, respectively. Probably, due to electrostatic interaction between the negatively charged drug and the positively charged E-RLPO, the percent EE of heparin was between 74.4 ± 6.5 % (lowest value) and 92.1 ± 5.3 % (highest value). The data suggest that BBD is a useful tool in rational design of heparin-loaded NPs.

Nano-interventions for neurodegenerative disorders

With an increase in lifespan and changing population demographics, the incidence of central nervous system (CNS) diseases is expected to increase significantly in the 21st century. Contrary to common belief, it is recognized that neurodegenerative diseases may be multisystemic in nature and this presents numerous difficulties for the potential treatment of these disorders. This review focuses on applications in the nano-delivery of therapeutic agents across the blood-brain barrier. We explore various types of nanoparticles, ranging from polymerics to liposomes. A brief discussion of the pharmacokinetic parameters and specific targeting strategies of these nanoparticles follows, presenting suggestions for the mechanisms of cellular and intracellular uptake and possible toxicity considerations of nanoparticles.

Stabilization of the nitric oxide (NO) prodrugs and anticancer leads, PABA/NO and Double JS-K, through incorporation into PEG-protected nanoparticles

We report the stabilization of the nitric oxide (NO) prodrugs and anticancer lead compounds, PABA/NO (O(2)-{2,4-dinitro-5-[4-(N-methylamino)benzoyloxy]phenyl} 1-(N,N-dimethylamino)diazen-1-ium-1,2-diolate) and "Double JS-K" 1,5-bis-{1-[(4-ethoxycarbonyl)piperazin-1-yl]diazen-1-ium-1,2-diol-2-ato}-2,4-dinitrobenzene, through their incorporation into polymer-protected nanoparticles. The prodrugs were formulated in block copolymer-stabilized nanoparticles with sizes from 220 to 450 nm by a novel rapid precipitation process. The block copolymers, with polyethylene glycol (PEG) soluble blocks, provide a steric barrier against NO prodrug activation by glutathione. Too rapid activation and NO release has been a major barrier to effective administration of this class of compounds. The nanoparticle stabilized PABA/NO are protected from attack by glutathione as evidenced by a significant increase in time taken for 50% decomposition from 15 min (unformulated) to 5 h (formulated); in the case of Double JS-K, the 50% decomposition time was extended from 4.5 min (unformulated) to 40 min (formulated). The more hydrophobic PABA/NO produced more stable nanoparticles and correspondingly more extended release times in comparison with Double JS-K. The hydrophobic blocks of the polymer were either polystyrene or polylactide. Both blocks produced nanoparticles of approximately the same size and release kinetics. This combination of PEG-protected nanoparticles with sizes appropriate for cancer targeting by enhanced permeation and retention (EPR) and delayed release of NO may afford enhanced therapeutic benefit.

Protected peptide nanoparticles: experiments and brownian dynamics simulations of the energetics of assembly

Soluble peptides, susceptible to degradation and clearance in therapeutic applications, have been formulated into protected nanoparticles for the first time through the process of kinetically controlled, block copolymer directed rapid precipitation using Flash NanoPrecipitation. Complementary Brownian dynamics simulations qualitatively model the nanoparticle formation process. The simulations corroborate the hypothesis that the size of nanoparticles decreases with increasing supersaturation. Additionally, the influence of the polymer-peptide interaction energy on the efficiency of nanoparticle protection by polymer surface coverage is elucidated in both experiments and simulations.

Modeling of formation of nanoparticles in reverse micellar systems: Ostwald ripening of silver halide particles

There are many possible size enhancement processes that affect the formation of nanoparticles in reverse micelles, such as coagulation and Ostwald ripening, and different physical systems are likely to follow one or more of these mechanisms depending upon the properties of the system. It has been suggested that silver halide particles, prepared from a reverse micellar system of AgNO3 and KCl in NP-6/cyclohexane solution, increase in size due to Ostwald ripening (Kimijima, K.; Sugimoto, T. J. Phys. Chem. B 2004, 108, 3735), which occurs due to the dependence of the solubility of the particles on the particle size so that the larger particles grow at the expense of smaller particles. This study provides a modeling framework to quantitatively analyze the ripening process of nanoparticles produced in reverse micellar systems.

Thermodynamic limits on drug loading in nanoparticle cores

Recently, biodegradable nanoparticles based on block copolymers have attracted attention as effective drug delivery vehicles. Maximizing the amount of drug loaded into particle is the desired goal, but loadings of only between 3 to about 25 wt% drug (for paclitaxel) are found experimentally. The reasons for the low loading and variability in loading have not been fully explained. In this study, a model is presented that quantitatively explains the observed phenomena. The thermodynamic model of drug loading is based on the molar free energy of the drug, which depends on the block copolymers size (entropic term), the interaction parameter between the drug and the hydrophobic core (enthalpic term), and the pressure-volume work to load the particle. The pressure-volume work, related directly to the interfacial tension between the core and the corona region, has not been previously considered with respect to drug loading. To validate the model, calculations were compared with experimental results for organic solutes, including paclitaxel, loaded into poly(ethylene glycol)-b-poly(epsilon-caprolactone), PEG-b-PCL block copolymer micelles. The model developed was found to predict the loading values in close agreement with experiments reported in the literature.

Stabilized polymeric nanoparticles for controlled and efficient release of bifenthrin

BACKGROUND

Nanoparticle formulations of pesticides have been proposed to produce a better spatial distribution of the pesticide on leaf surfaces, which provides better efficiency. Nanoparticles are well studied for drug delivery and sustained release but not in the agricultural sciences, because of the difficulty in generating stable pesticide nanoparticles with controlled particle size distribution and because the processes to generate nanoparticles are usually costly. In this paper, a model pesticide, bifenthrin, has been prepared in nanoparticle form by using the Flash NanoPrecipitation process. The process involves rapid micromixing to effect supersaturation, and polymer assembly to control particle size.

RESULTS

A multi-inlet vortex mixer (MIVM) was developed to provide rapid micromixing, high supersaturation and rapid nucleation and growth of bifenthrin nanoparticles. Several polymeric stabilizers were tested. With an increase in pesticide loading from 50 to 91%, nanoparticle size increased from 100 to 200 nm. The stability of the nanoparticle dispersions was followed for more than 12 days. The steric stability caused by the corona structure of the hydrophilic block of the polymers prevents nanoparticles aggregation. Ostwald ripening is responsible for the slow particle size growth observed.

CONCLUSION

Flash NanoPrecipitation using an MIVM provides a cost-effective process to produce stable pesticide nanoparticle suspensions. Nanoparticle size depends on supersaturation, pesticide loading and type of polymer. Nanoparticle pesticides potentially provide higher efficiency, better uniformity of coverage for highly active compounds and less exposure to workers, relative to compounds solubilized in organic solvents.

Clinical toxicities of nanocarrier systems

Toxicity of nanocarrier systems involves physiological, physicochemical, and molecular considerations. Nanoparticle exposures through the skin, the respiratory tract, the gastrointestinal tract and the lymphatics have been described. Nanocarrier systems may induce cytotoxicity and/or genotoxicity, whereas their antigenicity is still not well understood. Nanocarrier may alter the physicochemical properties of xenobiotics resulting in pharmaceutical changes in stability, solubility, and pharmacokinetic disposition. In particular, nanocarriers may reduce toxicity of hydrophobic cancer drugs that are solubilized. Nano regulation is still undergoing major changes to encompass environmental, health, and safety issues. The rapid commercialization of nanotechnology requires thoughtful environmental, health and safety research, meaningful, and an open discussion of broader societal impacts, and urgent toxicological oversight action.

Formation of block copolymer-protected nanoparticles via reactive impingement mixing

Reactive impingement mixing was employed to produce polymer-protected nanoparticles. Amphiphilic block copolymer was formed in situ by reactive coupling of hydrophobic and hydrophilic blocks. Simultaneously, a hydrophobic compound and the copolymer coprecipitated to form nanoparticles in the range of 100 nm. Specifically, beta-carotene was stabilized by the amphiphilic diblock copolymer, formed from the reaction of an amino-terminated hydrophilic block, poly(ethylene glycol) (PEG-NH2), with an acid chloride-terminated hydrophobic block, either poly(epsilon-caprolactone) (PCL-COCl) or polystyrene (PS-COCl). Spherical particles were observed by scanning and cryogenic transmission electron microscopy. Process conditions, including feed concentration of beta-carotene and feed concentrations of polymeric stabilizers, had little or no effect on average particle sizes over the range studied. Further, for Reynolds numbers greater than 500 the feed flow rates also had no effect. The effect of glass transition temperature (Tg) of the hydrophobic polymer on morphology and particle formation mechanism is discussed.

Mechanistic insight into domain formation and growth in a phase-separated Langmuir-Blodgett monolayer

The mechanism of the formation and growth of phase-separated domains in mixed arachidic acid (C19H39COOH) (AA) and perfluorotetradecanoic acid (C13F27COOH) (PA) monolayer films was investigated through a combination of surface pressure-area isotherm measurements and atomic force microscope (AFM) imaging. In the mixed AA-PA monolayer system, distinct discontinuous domains consisting primarily of AA form spontaneously in a surrounding continuous matrix enriched in PA. By varying the monolayer deposition conditions, including temperature, surface pressure, and the mechanical agitation of sample solutions, it was determined that phase-separated nuclei are formed initially in the bulk sample solution and further growth of domains proceeds on the subphase surface via an Ostwald ripening process involving the diffusion of AA from the matrix to the discontinuous domains. In addition, selective dissolution of the arachidic acid followed by in situ AFM imaging has allowed the visualization of the fusion of AA to the phase-separated domains and has highlighted some unusual pattern formation that occurs at low subphase temperatures.