Interference from Proteins and Surfactants on Particle Size Distributions Measured by Nanoparticle Tracking Analysis (NTA)

Critical parameters to standardize the size and concentration determination of nanomaterials by nanoparticle tracking analysis

The size and concentration are critical for the diagnostic and therapeutic applications of nanomaterials but the accurate measurement remains challenging. Nanoparticle tracking analysis (NTA) is widely used for size and concentration determination. However, highly repeatable standard operating procedures (SOPs) are absent. We adopted the "search-evaluate-test" strategy to standardize the measurement by searching the critical parameters. The particles per frame are linearly proportional to the sample concentration and the measured results are more accurate and repeatable when the concentration is 108-109 particles/ml. The optimal detection threshold is around 5. The optimal camera level is such that it allows clear observation of particles without diffractive rings and overexposure. The optimal speed is ≤ 50 in AU and ∼ 10 μl/min in flow rate. We then evaluated the protocol using polydisperse polystyrene particles and we found that NTA could discriminate particles in bimodal mixtures with high size resolution but the performance on multimodal mixtures is not as good as that of resistive pulse sensing (RPS). We further analyzed the polystyrene particles, SiO2 particles, and biological samples by NTA following the SOPs. The size and concentration measured by NTA differentially varies to those determined by RPS and transmission electron microscopy.

Engineered Exosomes Loaded with Triptolide: An Innovative Approach to Enhance Therapeutic Efficacy in Rheumatoid Arthritis

OBJECTIVES

Exosomes are small, membrane-bound vesicles secreted by cells into the extracellular environment. They play a crucial role in various biological processes, including immune response, cell-to-cell signaling, and tumor progression. Exosomes have attracted attention as potential targets for therapeutic intervention, drug delivery, and biomarker detection. In this study, we aimed to isolate exosomes from human RA fibroblasts (hRAF-Exo) and load them with triptolide (TP) to generate engineered exosomes (hRAF-Exo@TP).

METHODS

Transmission electron microscopy, particle size analysis, and western blotting for protein detection were employed to characterize hRAF-Exo. Furthermore, a murine model of collagen-induced arthritis (CIA) was employed to observe the distinct affinity of hRAF-Exo@TP towards the afflicted area.

RESULTS

Cellular experiments demonstrated the inhibitory effect of hRAF-Exo@TP on the proliferative activity of human RA fibroblasts. Additionally, it exhibited remarkable selectivity for lesion sites in a CIA mouse model.

CONCLUSION

Exosomes loaded with TP may enhance the therapeutic effects on RA in mice. Our study provides a promising avenue for the treatment of RA in the future.

Two-dimensional water-molecule-cluster layers at nanobubble interfaces

HYPOTHESIS

Bulk nanobubbles (NBs) have high surface charge densities and long lifetimes. Despite several attempts to understand the lifetime of NBs, their interfacial layer structure remains unknown. It is hypothesized that a specific interfacial layer exists with a hydrogen bond network that stabilizes NBs.

EXPERIMENTS

In situ infrared reflectance-absorption spectroscopy and density functional theory were used to determine the interfacial layer structure of NBs. Furthermore, nuclear magnetic resonance spectroscopy was used to examine the interfacial layer hardness of bubbles filled with N2, O2, and CO2, which was expected to depend on the encapsulated gas species.

FINDINGS

The interfacial layer was composed of three-, four-, and five-membered ring clusters of water molecules. An interface model was proposed in which a two-dimensional layer of clusters with large electric dipole moments is oriented toward the endohedral gas, and the hydrophobic surface is adjacent to the free water. The interfacial layer hardness was dependent on the interaction with the gas (N2 > O2 > CO2), which supports the proposed interface model. These findings can be generalized to the structure of water at gas-water interfaces.

Label-free discrimination of extracellular vesicles from large lipoproteins

Extracellular vesicles (EVs) are increasingly gaining interest as biomarkers and therapeutics. Accurate sizing and quantification of EVs remain problematic, given their nanometre size range and small scattering cross-sections. This is compounded by the fact that common EV isolation methods result in co-isolation of particles with comparable features. Especially in blood plasma, similarly-sized lipoproteins outnumber EVs to a great extent. Recently, interferometric nanoparticle tracking analysis (iNTA) was introduced as a particle analysis method that enables determining the size and refractive index of nanoparticles with high sensitivity and precision. In this work, we apply iNTA to differentiate between EVs and lipoproteins, and compare its performance to conventional nanoparticle tracking analysis (NTA). We show that iNTA can accurately quantify EVs in artificial EV-lipoprotein mixtures and in plasma-derived EV samples of varying complexity. Conventional NTA could not report on EV numbers, as it was not able to distinguish EVs from lipoproteins. iNTA has the potential to become a new standard for label-free EV characterization in suspension.

Pharmaceutical Development of Nanostructured Vesicular Hydrogel Formulations of Rifampicin for Wound Healing

Chronic wounds exhibit elevated levels of inflammatory cytokines, resulting in the release of proteolytic enzymes which delay wound-healing processes. In recent years, rifampicin has gained significant attention in the treatment of chronic wounds due to an interesting combination of antibacterial and anti-inflammatory effects. Unfortunately, rifampicin is sensitive to hydrolysis and oxidation. As a result, no topical drug product for wound-healing applications has been approved. To address this medical need two nanostructured hydrogel formulations of rifampicin were developed. The liposomal vesicles were embedded into hydroxypropyl methylcellulose (HPMC) gel or a combination of hyaluronic acid and marine collagen. To protect rifampicin from degradation in aqueous environments, a freeze-drying method was developed. Before freeze-drying, two well-defined hydrogel preparations were obtained. After freeze-drying, the visual appearance, chemical stability, residual moisture content, and redispersion time of both preparations were within acceptable limits. However, the morphological characterization revealed an increase in the vesicle size for collagen-hyaluronic acid hydrogel. This was confirmed by subsequent release studies. Interactions of marine collagen with phosphatidylcholine were held responsible for this effect. The HPMC hydrogel formulation remained stable over 6 months of storage. Moving forward, this product fulfills all criteria to be evaluated in preclinical and clinical studies.

Precision size and refractive index analysis of weakly scattering nanoparticles in polydispersions

Characterization of the size and material properties of particles in liquid suspensions is in very high demand, for example, in the analysis of colloidal samples or of bodily fluids such as urine or blood plasma. However, existing methods are limited in their ability to decipher the constituents of realistic samples. Here we introduce iNTA as a new method that combines interferometric detection of scattering with nanoparticle tracking analysis to reach unprecedented sensitivity and precision in determining the size and refractive index distributions of nanoparticles in suspensions. After benchmarking iNTA with samples of colloidal gold, we present its remarkable ability to resolve the constituents of various multicomponent and polydisperse samples of known origin. Furthermore, we showcase the method by elucidating the refractive index and size distributions of extracellular vesicles from Leishmania parasites and human urine. The current performance of iNTA already enables advances in several important applications, but we also discuss possible improvements.

Emerging Challenges and Innovations in Surfactant-mediated Stabilization of Biologic Formulations

Biologics may be subjected to various destabilizing conditions during manufacturing, transportation, storage, and use. Therefore, biologics must be appropriately formulated to meet their desired quality target product profiles. In the formulations of protein-based biologics, one critical component is surfactant. Polysorbate 80 and Polysorbate 20 remain the most commonly used surfactants. Surfactants can stabilize proteins through different mechanisms and help the proteins withstand destabilization stresses. However, the challenges associated with surfactants, for instance, impurities, degradation, and potential triggering of adverse immune responses, have been encountered. Therefore, there are continued efforts to develop novel surfactants to overcome these challenges associated with traditional surfactants. Meanwhile, surfactants have also found their use in formulations of newer and novel modalities, namely, antibody-drug conjugates, bispecific antibodies, and adeno-associated viruses (AAV). This review provides an updated in-depth discussion of surfactants in the above-mentioned areas, namely mechanism of action of surfactants, a critical review of challenges with surfactants and current mitigation approaches, and emerging technologies to develop novel surfactants. In addition, gaps, current mitigations, and future directions have been presented to trigger further discussion and research to facilitate the use and development of novel surfactants.

Brownian motion-based nanoparticle sizing-A powerful approach for in situ analysis of nanoparticle-protein interactions

A key hurdle toward effective application of nanoparticles (NPs) in biomedicine is still the incomplete understanding of the biomolecular adsorption layer, the so-called protein corona, which inevitably forms around NPs when they are immersed in a biofluid. NP sizing techniques via the analysis of Brownian motions offer a powerful way to measure the thickness of the protein corona in situ. Here, the fundamentals of three techniques, dynamic light scattering, fluorescence correlation spectroscopy, and nanoparticle tracking analysis are briefly summarized. Then, experimental procedures for the determination of binding curves are presented in a tutorial fashion. Nanoparticle sizing experiments are illustrated with a selection of recent results on the interactions of transferrin with hydrophilic and hydrophobic polystyrene nanoparticles, and key insights gained from this work are discussed.

Nanomedicines - Tiny particles and big challenges

After decades of research, nanotechnology has been used in a broad array of biomedical products including medical devices, drug products, drug substances, and pharmaceutical-grade excipients. But like many great achievements in science, there is a fine balance between the risks and opportunities of this new technology. Some materials and surface structures in the nanosize range can exert unexpected toxicities and merit a more detailed safety assessment. Regulatory agencies such as the United States Food and Drug Administration or the European Medicines Agency have started dealing with the potential risks posed by nanomaterials. Considering that a thorough characterization is one of the key aspects of controlling such risks this review presents the regulatory background of nanosafety assessment and provides some practical advice on how to characterize nanomaterials and drug formulations. Further, the challenges of how to maintain and monitor pharmaceutical quality through a highly complex production processes will be discussed.

Separation, Characterization and Discriminant Analysis of Subvisible Particles in Biologics Formulations

Background:

The presence of subvisible particles (SVPs) in parenteral formulations of biologics is a major challenge in the development of therapeutic protein formulations. Distinction between proteinaceous and non-proteinaceous SVPs is vital in monitoring formulation stability.

Methods:

The current compendial method based on light obscuration (LO) has limitations in the analysis of translucent/low refractive index particles. A number of attempts have been made to develop an unambiguous method to characterize SVPs, albeit with limited success.

Results:

Herein, we describe a robust method that characterizes and distinguishes both potentially proteinaceous and non-proteinaceous SVPs in protein formulations using Microflow imaging (MFI) in conjunction with the MVAS software (MFI View Analysis Suite), developed by ProteinSimple. The method utilizes two Intensity parameters and a morphological filter that successfully distinguishes proteinaceous SVPs from non-proteinaceous SVPs and mixed aggregates.

Conclusion:

he MFI generated raw data of a protein sample is processed through Lumetics LINK software that applies an in-house developed filter to separate proteinaceous from the rest of the particulates.

Using Image Attributes to Assure Accurate Particle Size and Count Using Nanoparticle Tracking Analysis

Nanoparticle tracking analysis (NTA) obtains particle size by analysis of particle diffusion through a time series of micrographs and particle count by a count of imaged particles. The number of observed particles imaged is controlled by the scattering cross-section of the particles and by camera settings such as sensitivity and shutter speed. Appropriate camera settings are defined as those that image, track, and analyze a sufficient number of particles for statistical repeatability. Here, we test if image attributes, features captured within the image itself, can provide measurable guidelines to assess the accuracy for particle size and count measurements using NTA. The results show that particle sizing is a robust process independent of image attributes for model systems. However, particle count is sensitive to camera settings. Using open-source software analysis, it was found that a median pixel area, 4 pixels², results in a particle concentration within 20% of the expected value. The distribution of these illuminated pixel areas can also provide clues about the polydispersity of particle solutions prior to using a particle tracking analysis. Using the median pixel area serves as an operator-independent means to assess the quality of the NTA measurement for count.