Quantitative Determination of the Hydrophobicity of Nanoparticles

Analytical techniques for the characterization of nanoparticles for mRNA delivery

Nanotechnology-assisted RNA delivery has gotten a tremendous boost over the last decade and made a significant impact in the development of life-changing vaccines and therapeutics. With increasing numbers of emerging lipid- and polymer-based RNA nanoparticles progressing towards the clinic, it has become apparent that the safety and efficacy of these medications depend on the comprehensive understanding of their critical quality attributes (CQAs). However, despite the rapid advancements in the field, the identification and reliable quantification of CQAs remain a significant challenge. To support these efforts, this review aims to summarize the present knowledge on CQAs based on the regulatory guidelines and to provide insights into the available analytical characterization techniques for RNA-loaded nanoparticles. In this context, routine and emerging analytical techniques are categorized and discussed, focusing on the operation principle, strengths, and potential limitations. Furthermore, the importance of complementary and orthogonal techniques for the measurement of CQAs is discussed in order to ensure the quality and consistency of analytical methods used, and address potential technique-based differences.

Size-dependent photocatalytic inactivation of Microcystis aeruginosa and degradation of microcystin by a copper metal organic framework

Water eutrophication has led to increasingly serious algal blooms (HABs) that pose significant threats to aquatic environmental and human health. Differently sized copper metal organic frameworks (Cu-MOFs), including Cu-MOF-1 (30 nm), Cu-MOF-2, (40 nm), Cu-MOF-3 (50 nm), and Cu-MOF-4 (1 µm×100 nm), were synthesized. Their performance in inactivating Microcystis aeruginosa and degrading microcystin was assessed at the concentration of 0-60 mg/L under visible light irradiation for 6 h. The photocatalytic antialgal activity of Cu-MOF-4 was 10.5%, 14.2%, and 31.2% higher than that of Cu-MOF-3, Cu-MOF-2, and Cu-MOF-1; the efficacy in photocatalytic degradation of microcystin induced by Cu-MOFs also exhibited significant size-dependent efficiency, where Cu-MOF-4 was 2.6-, 1.8-, and 2.0-fold of Cu-MOF-3, Cu-MOF-2, and Cu-MOF-1, respectively. Cu-MOF-4 had greater performance than other Cu-MOFs could attributed to: 1) Cu-MOF-4 is easier to interact with algal cells due to its lower surface negative charge and higher hydrophobicity, resulting in more photocatalyst-algae heteroaggregates formation; 2) Cu-MOF-4 had greater electron-hole pairs separation ability, thus exhibiting higher reactive oxygen species (ROS) production; 3) Cu-MOF-4 had greater hydrostability than other Cu-MOFs, leading to more sustained ROS generation. Additionally, the reusability of Cu-MOF-4 was also greater than other Cu-MOFs.

Theoretical basis and experimental verification for evaluating the distribution of engineered nanoparticles in water-oil system

The distribution of nanoparticles between aqueous and organic phases is universally considered as the starting point in predicting the fate and bioavailability of engineered nanoparticles in the environment. However, the theoretical basis for determining the distribution of nanoparticles in the immiscible water-oil system remains unclear. Here, for the first time, theoretical calculations were conducted to illustrate the underlying mechanism. It was suggested that the distribution of nanoparticles was largely controlled by the surface charge, particle size and surface hydrophobicity, and the water-oil interface was not the favorable phase for nanoparticles until a size threshold (10 nm) was met and the particle surface became amphiphilic. The theoretical results were verified by the experimental approaches of different nanoparticles distributed in the water-octanol mixture. The neutralization of a charged surface led to enhanced distribution into octanol for hydrophobic nanoparticles (e.g., aqueous C₆₀), yet it had little effect on hydrophilic nanoparticles (e.g., fullerol). More nanoparticles were trapped at the water-oil interface when size grew larger (e.g., Ag-CIT and Au-CIT with citrate) and the surface rendered amphiphilic by polymeric coatings (e.g., Ag-PVP with polyvinylpyrrolidone), though larger hydrophobic nanoparticles like aqu-nC₆₀ tended to stay in the octanol. The surface charge and hydrophobicity may have an important impact on the path-dependent distribution of nanoparticles in water- octanol system. The mechanistic insights based on theoretical calculations and experimental approaches will facilitate the accurate prediction of the distribution of engineered nanoparticles in biological and environmental systems.

Applicability of OECD TG 201, 202, 203 for the aquatic toxicity testing and assessment of 2D Graphene material nanoforms to meet regulatory needs

Tests using algae and/or cyanobacteria, invertebrates (crustaceans) and fish form the basic elements of an ecotoxicological assessment in a number of regulations, in particular for classification of a substance as hazardous or not to the aquatic environment according to the Globally Harmonised System of Classification and Labelling of Chemicals (GHS-CLP) (GHS, 2022) and the REACH regulation (Registration, Evaluation, Authorisation and Restriction of Chemicals, EC, 2006). Standardised test guidelines (TGs) of the Organisation for Economic Co-operation and Development (OECD) are available to address the regulatory relevant endpoints of growth inhibition in algae and cyanobacteria (TG 201), acute toxicity to invertebrates (TG 202), and acute toxicity in fish (TG 203). Applying these existing OECD TGs for testing two dimensional (2D) graphene nanoforms may require more attention, additional considerations and/or adaptations of the protocols, because graphene materials are often problematic to test due to their unique attributes. In this review a critical analysis of all existing studies and approaches to testing used has been performed in order to comment on the current state of the science on testing and the overall ecotoxicity of 2D graphene materials. Focusing on the specific tests and available guidance's, a complete evaluation of aquatic toxicity testing for hazard classification of 2D graphene materials, as well as the use of alternative tests in an integrated approach to testing and assessment, has been made. This information is essential to ensure future assessments generate meaningful data that will fulfil regulatory requirements for the safe use of this "wonder" material.

Self-assembled aluminum oxyhydroxide nanorices with superior suspension stability for vaccine adjuvant

The suspension stability of aluminum-based adjuvant (Alum) plays an important role in determining the Alum-antigen interaction and vaccine efficacy. Inclusion of excipients has been shown to stabilize antigens in vaccine formulations. However, there is no mechanistic study to tune the characteristics of Alum for improved suspension stability. Herein, a library of self-assembled rice-shaped aluminum oxyhydroxide nanoadjuvants i.e., nanorices (NRs), was synthesized through intrinsically controlled crystallization and atomic coupling-mediated aggregations. The NRs exhibited superior suspension stability in both water and a saline buffer. After adsorbing hepatitis B surface antigen (HBsAg) virus-like particles (VLPs), human papillomavirus virus (HPV) VLPs, or bovine serum albumin, NR-antigen complexes exhibited less sedimentation. Further mechanistic study demonstrated that the improved suspension stability was due to intraparticle aggregations that led to the reduction of the surface free energy. By using HBsAg in a murine vaccination model, NRs with higher aspect ratios elicited more potent humoral immune responses. Our study demonstrated that engineered control of particle aggregation provides a novel material design strategy to improve suspension stability for a diversity of biomedical applications.

Evaluating Nanoparticle Hydrophobicity Using Analytical Membrane Hydrophobic Interaction Chromatography

Nanoparticle hydrophobicity is a key factor controlling the stability, adhesion, and transport of nanoparticle suspensions. Although a number of approaches have been presented for evaluating nanoparticle hydrophobicity, these methods are difficult to apply to larger nanoparticles and viruses (>100 nm in size) that are of increasing importance in drug delivery and gene therapy. This study investigated the use of a new analytical hydrophobic interaction chromatography method employing a 5.0 μm pore size polyvinylidene fluoride membrane as the stationary-phase in membrane hydrophobic interaction chromatography (MHIC). Experimental data obtained using a series of model proteins were in good agreement with literature values for the hydrophobicity (both experimental and computational). MHIC was then used to evaluate the hydrophobicity of a variety of nanoparticles, including a live attenuated viral vaccine, both in water and in the presence of different surfactants. This new method can be implemented on any liquid chromatography system, run times are typically <20 min, and the experiments avoid the use of organic solvents that could alter the structure of many biological nanoparticles.