Characterization of submicron systems via optical methods

Measuring the electrophoretic mobility and size of single particles using microfluidic transverse AC electrophoresis (TrACE)

The ability to measure the charge and size of single particles is essential to understanding particle adhesion and interaction with their environment. Characterizing the physical properties of biological particles, like cells, can be a powerful tool in studying the association between the changes in physical properties and disease development. Currently, measuring charge via the electrophoretic mobility (μep) of individual particles remains challenging, and there is only one prior report of simultaneously measuring μep and size. We introduce microfluidic transverse AC electrophoresis (TrACE), a novel technique that combines particle tracking velocimetry (PTV) and AC electrophoresis. In TrACE, electric waves with 0.75 to 1.5 V amplitude are applied transversely to the bulk flow and cause the particles to oscillate. PTV records the particles' oscillating trajectories as pressure drives bulk flow through the microchannel. A simple quasi-equilibrium model agrees well with experimental measurements of frequency, amplitude, and phase, indicating that particle motion is largely described by DC electrophoresis. The measured μep of polystyrene particles (0.53, 0.84, 1, and 2 μm diameter) are consistent with ELS measurements, and precision is enhanced by averaging ∼100 measurements per particle. Particle size is simultaneously measured from Brownian motion quantified from the trajectory for particles <2 μm or image analysis for particles ≥2 μm. Lastly, the ability to analyze intact mammalian cells is demonstrated with B cells. TrACE systems are expected to be highly suitable as fieldable tools to measure the μep and size of a broad range of individual particles.

Particle Detection and Characterization for Biopharmaceutical Applications: Current Principles of Established and Alternative Techniques

Detection and characterization of particles in the visible and subvisible size range is critical in many fields of industrial research. Commercial particle analysis systems have proliferated over the last decade. Despite that growth, most systems continue to be based on well-established principles, and only a handful of new approaches have emerged. Identifying the right particle-analysis approach remains a challenge in research and development. The choice depends on each individual application, the sample, and the information the operator needs to obtain. In biopharmaceutical applications, particle analysis decisions must take product safety, product quality, and regulatory requirements into account. Biopharmaceutical process samples and formulations are dynamic, polydisperse, and very susceptible to chemical and physical degradation: improperly handled product can degrade, becoming inactive or in specific cases immunogenic. This article reviews current methods for detecting, analyzing, and characterizing particles in the biopharmaceutical context. The first part of our article represents an overview about current particle detection and characterization principles, which are in part the base of the emerging techniques. It is very important to understand the measuring principle, in order to be adequately able to judge the outcome of the used assay. Typical principles used in all application fields, including particle–light interactions, the Coulter principle, suspended microchannel resonators, sedimentation processes, and further separation principles, are summarized to illustrate their potentials and limitations considering the investigated samples. In the second part, we describe potential technical approaches for biopharmaceutical particle analysis as some promising techniques, such as nanoparticle tracking analysis (NTA), micro flow imaging (MFI), tunable resistive pulse sensing (TRPS), flow cytometry, and the space- and time-resolved extinction profile (STEP^®) technology.

Assessment of active pharmaceutical ingredient particle size in tablets by Raman chemical imaging validated using polystyrene microsphere size standards

Particle size is a critical parameter for controlling pharmaceutical quality. The aim of this study was to assess the size of the micrometer-scale active pharmaceutical ingredients (API) in tablets using Raman chemical imaging and to understand the effects of formulation on particle size. Model tablets containing National Institute of Standards and Technology traceable polystyrene microsphere size standards were developed to determine the binarization threshold value of Raman chemical images for API particle sizing in specific formulations and processes. Three sets of model tablets containing 5, 10, and 15 μm polystyrene microspheres, used to mimic API, were prepared using a commercial tablet formulation (Ebastel tablets, mean API particle size was about 5 μm). Raman mapping with a 50× objective (NA, 0.75) was applied to tablet cross-sections, and particle size of polystyrene microspheres was estimated from binary images using several binarization thresholds. Mean particle size for three sets of polystyrene microspheres showed good agreement between pre- and postformulation (the slope = 1.024, R = 1.000) at the specific threshold value ((mean + 0.5σ) of the polystyrene-specific peak intensity histogram), regardless of particle agglomeration, tablet surface roughness, and laser penetration depth. The binarization threshold value showed good applicability to Ebastel tablets, where the API-specific peak intensity histogram showed a pattern similar to that of polystyrene microspheres in model tablets. The model tablets enabled determination of an appropriate binarization threshold for assessing the mean particle size of micrometer-scale API in tablets by utilizing the unique physicochemical properties of polystyrene microspheres.

Application of asymmetric flow-field flow fractionation to the characterization of colloidal dispersions undergoing aggregation

The characterization of complex colloidal dispersions is a relevant and challenging problem in colloidal science. In this work, we show how asymmetric flow-field flow fractionation (AF4) coupled to static light scattering can be used for this purpose. As an example of complex colloidal dispersions, we have chosen two systems undergoing aggregation. The first one is a conventional polystyrene latex undergoing reaction-limited aggregation, which leads to the formation of fractal clusters with well-known structure. The second one is a dispersion of elastomeric colloidal particles made of a polymer with a low glass transition temperature, which undergoes coalescence upon aggregation. Samples are withdrawn during aggregation at fixed times, fractionated with AF4 using a two-angle static light scattering unit as a detector. We have shown that from the analysis of the ratio between the intensities of the scattered light at the two angles the cluster size distribution can be recovered, without any need for calibration based on standard elution times, provided that the geometry and scattering properties of particles and clusters are known. The nonfractionated samples have been characterized also by conventional static and dynamic light scattering to determine their average radius of gyration and hydrodynamic radius. The size distribution of coalescing particles has been investigated also through image analysis of cryo-scanning electron microscopy (SEM) pictures. The average radius of gyration and the average hydrodynamic radius of the nonfractionated samples have been calculated and successfully compared to the values obtained from the size distributions measured by AF4. In addition, the data obtained are also in good agreement with calculations made with population balance equations.

Long-term shelf stability of amphiphilicβ-cyclodextrin nanosphere suspensions monitored by dynamic light scattering and cryo-transmission electron microscopy

Amphiphilic beta-cyclodextrins (betaCDa) were synthesized by statistically grafting hexanoyl carbon chains on the secondary hydroxyl functions of the betaCD glucopyranosyl units. The obtained derivative was used to prepare submicronic colloidal nanosphere suspensions using a nano-precipitation method. The fresh suspensions contained particles with a diameter ranging from 60-100 nm. Taking into account that the physical stability of colloidal systems remains one of the major problems which can restrict their use in pharmaceutical particulate carrier formulations, the long-term stability of the aqueous nano-dispersions was investigated. Two complementary characterization methods, namely dynamic light scattering and cryo-transmission electron microscopy, were used to control the size distribution and morphology of the nanospheres during storage. The zeta potential was measured as well. An unexpected good physical stability of the suspensions after 3 year storage at room temperature was observed. This behaviour appears to be related to the small size and structural organization of the nanoparticles. The mean diameters determined from light scattering experiments are consistent with those measured from electron micrographs. The slight difference between the values obtained by both methods is discussed.

Particle size analysis in pharmaceutics: principles, methods and applications

Physicochemical and biopharmaceutical properties of drug substances and dosage forms can be highly affected by the particle size, a critical process parameter in pharmaceutical production. The fundamental issue with particle size analysis is the variety of equivalent particle diameters generated by different methods, which is largely ascribable to the particle shape and particle dispersion mechanism involved. Thus, to enable selection of the most appropriate or optimal sizing technique, cross-correlation between different techniques may be required. This review offers an in-depth discussion on particle size analysis pertaining to specific pharmaceutical applications and regulatory aspects, fundamental principles and terminology, instrumentation types, data presentation and interpretation, in-line and process analytical technology. For illustration purposes, special consideration is given to the analysis of aerosols using time-of-flight and cascade impactor measurements, which is supported by a computational analysis conducted for this review.

Modified polyethylenimines as non viral gene delivery systems for aerosol therapy: effects of nebulization on cellular uptake and transfection efficiency

This study examined the effect of nebulization on the cellular uptake and transfection efficiency of polyplexes from four polyethylenimine (PEI) modifications: branched 25 kDa PEI (bPEI), linear 22 kDa PEI (linPEI), pegylated PEI (pegPEI) and biodegradable PEI (bioPEI). Polyplexes were aerosolized with air-jet and ultrasonic nebulizers. The aerosol was collected and used to determine complex size and zeta potential. Fluorescence-assisted cell sorting (FACS) was used to quantify the cellular association of polyplexes in primary alveolar cells (AEC), A549 cells and primary bronchial cells (BEC). Confocal laser scanning microscopic images provided information about the internalization of polyplexes. Transfection efficiencies of polyplexes were quantified via measurement of luciferase expression. All polymers were stable during nebulization, although size increases were observed after air-jet nebulization. FACS studies showed a two- to three-fold increase in polyplex association with BEC compared to A549 cells, while polyplex association with AEC was negligible. BPEI, linPEI and bioPEI polyplexes were internalized, while pegPEI polyplexes remained predominately attached to the cellular membrane. Luciferase expression was detected only in BEC and A549 cells with transfection efficiencies approximately one order of magnitude higher in BEC. All PEI modifications investigated were suitable for aerosol therapy, although cell type and polymer structure significantly influenced the uptake and transfection efficiency of the polyplexes.

Biochemical characterization of an inhibitor of Escherichia coli UDP-N-acetylmuramyl-l-alanine ligase

UDP-N-acetylmuramyl-l-alanine ligase (MurC) is an essential bacterial enzyme involved in peptidoglycan biosynthesis and a target for the discovery of novel antibacterial agents. As a result of a high-throughput screen (HTS) against a chemical library for inhibitors of MurC, a series of benzofuran acyl-sulfonamides was identified as potential leads. One of these compounds, Compound A, inhibited Escherichia coli MurC with an IC(50) of 2.3 microM. Compound A exhibited time-dependent, partially reversible inhibition of E. coli MurC. Kinetic studies revealed a mode of inhibition consistent with the compound acting competitively with the MurC substrates ATP and UDP-N-acetyl-muramic acid (UNAM) with a K(i) of 4.5 microM against ATP and 6.3 microM against UNAM. Fluorescence binding experiments yielded a K(d) of 3.1 microM for the compound binding to MurC. Compound A also exhibited high-affinity binding to bovine serum albumin (BSA) as evidenced by a severe reduction in MurC inhibition upon addition of BSA. This finding is consistent with the high lipophilicity of the compound. Advancement of this compound series for further drug development will require reduction of albumin binding.

Application of dynamic laser scattering to the quality control of injectable drugs: polymer formation in ampicillin solution

OBJECTIVE

To assess the usefulness of dynamic laser scattering for monitoring the stability of ampicillin after reconstitution from commercially available vials with respect to the polymer formation and potency.

METHODS

Polymer formation and the remaining potency of the reconstituted ampicillin solution were estimated using dynamic laser scattering and high-performance liquid chromatography.

RESULTS

The laser light-scattering submicron particle analyser was sufficiently sensitive for detecting both monomer and polymer aggregates with the average diameter of 1.1 +/- 0.2 and 7.3 +/- 1.7 nm, respectively, in the ampicillin solution. Polymer formation was dependent on both the storage temperature and the storage period, but it was detected, even when no precipitates were visible and when loss of potency was less than 10% of the initial value following storage at 4 or -15 degrees C.

CONCLUSION

Submicron particle analysis using scanning electron microscopy, when used in combination with high-performance liquid chromatography, provides a useful method for studying polymer formation in antibiotic solutions and for the quality control of antibiotic injections during storage.

Top ten considerations in the development of parenteral emulsions

The development of parenteral emulsions continues to play an important role in the formulation and delivery of many drugs. In addition to solubilization and stabilization applications, appropriately designed parenteral emulsions are effective delivery systems for sustained release and targeting of drugs. Control of the strict requirements of globule size and surface charge is important in the design and ultimate stability of the formulation. This review highlights the important issues and suggests strategies to assist the scientist in the development, manufacture and stability of this essential dosage form.