Cryogenic transmission electron microscopy (cryo-TEM) for studying the morphology of colloidal drug delivery systems

3D micromixer for nanoliposome synthesis: a promising advance in high mass productivity

This paper addresses an important breakthrough in the high mass production of liposomes by microfluidics technology. We investigated the synthesis of liposomes using a high flow rate microfluidic device (HFR-MD) with a 3D-twisted cross-sectional microchannel to favor chaotic advection. A simple construction scaffold technique was used to manufacture the HFR-MD. The synthesis of liposomes combined the effects of high flow and high concentration of lipids, resulting in high mass productivity (2.27 g of lipid per h) which, to our knowledge, has never been registered by only one microdevice. We assessed the effects of the flow rate ratio (FRR), total flow rate (TFR), and lipid concentration on the liposome physicochemical properties. HFR-MD liposomes were monodisperse (0.074) with a size around 100 nm under the condition of an FRR of 1 (50% v/v ethanol) and TFR of 5 ml min^-1 (expandable to 10 ml min^-1). We demonstrated that the mixing conditions are not the only parameter controlling liposome synthesis using experimental and computational fluid dynamics analysis. A vacuum concentrator was used for ethanol removal, and there is no further modification after processing in accordance with the structural (SAXS) and morphological (cryo-TEM) analysis. Hence, the HFR-MD can be used to prepare nanoliposomes. It emerges as an innovative tool with high mass production.

Development and Delivery Systems of mRNA Vaccines

Since the outbreak of SARS-CoV-2, mRNA vaccine development has undergone a tremendous drive within the pharmaceutical field. In recent years, great progress has been made into mRNA vaccine development, especially in individualized tumor vaccines. mRNA vaccines are a promising approach as the production process is simple, safety profiles are better than those of DNA vaccines, and mRNA-encoded antigens are readily expressed in cells. However, mRNA vaccines also possess some inherent limitations. While side effects such as allergy, renal failure, heart failure, and infarction remain a risk, the vaccine mRNA may also be degraded quickly after administration or cause cytokine storms. This is a substantial challenge for mRNA delivery. However, appropriate carriers can avoid degradation and enhance immune responses, effector presentation, biocompatibility and biosafety. To understand the development and research status of mRNA vaccines, this review focuses on analysis of molecular design, delivery systems and clinical trials of mRNA vaccines, thus highlighting the route for wider development and further clinical trials of mRNA vaccines.

Cryogenic Electron Microscopy Methodologies as Analytical Tools for the Study of Self-Assembled Pharmaceutics

Many pharmaceutics are aqueous dispersions of small or large molecules, often self-assembled in complexes from a few to hundreds of molecules. In many cases, the dispersing liquid is non-aqueous. Many pharmaceutical preparations are very viscous. The efficacy of those dispersions is in many cases a function of the nanostructure of those complexes or aggregates. To study the nanostructure of those systems, one needs electron microscopy, the only way to obtain nanostructural information by recording direct images whose interpretation is not model-dependent. However, these methodologies are complicated by the need to make liquid systems compatible with high vacuum in electron microscopes. There are also issues related to the interaction of the electron beam with the specimen such as micrograph contrast, electron beam radiation damage, and artifacts associated with specimen preparation. In this article, which is focused on the state of the art of imaging self-assembled complexes, we briefly describe cryogenic temperature transmission electron microscopy (cryo-TEM) and cryogenic temperature scanning electron microcopy (cryo-SEM). We present the principles of these methodologies, give examples of their applications as analytical tools for pharmaceutics, and list their limitations and ways to avoid pitfalls in their application.

Nuclear Magnetic Resonance Spectroscopy: A Multifaceted Toolbox to Probe Structure, Dynamics, Interactions, and Real-Time In Situ Release Kinetics in Peptide-Liposome Formulations

Liposomal formulations represent attractive biocompatible and tunable drug delivery systems for peptide drugs. Among the tools to analyze their physicochemical properties, nuclear magnetic resonance (NMR) spectroscopy, despite being an obligatory technique to characterize molecular structure and dynamics in chemistry as well as in structural biology, yet appears to be rather sparsely used to study drug-liposome formulations. In this work, we exploited several facets of liquid-state NMR spectroscopy to characterize liposomal delivery systems for the apelin-derived K14P peptide and K14P modified by Nα-fatty acylation. Various liposome compositions and preparation modes were analyzed. Using NMR, in combination with cryo-electron microscopy and dynamic light scattering, we determined structural, dynamic, and self-association properties of these peptides in solution and probed their interactions with liposomes. Using ³¹P and ¹H NMR, we characterized membrane fluidity and thermotropic phase transitions in empty and loaded liposomes. Based on diffusion and ¹H NMR experiments, we localized and quantified peptides with respect to the interior/exterior of liposomes and changes over time and upon thermal treatments. Finally, we assessed the release kinetics of several solutes and compared various formulations. Taken together, this work shows that NMR has the potential to assist the design of peptide/liposome systems and more generally drug delivery systems.

Nanostructured lipid carriers enhances the safety profile of tretinoin: in vitro and healthy human volunteers' studies

Aim: To enhance the tretinoin (TRE) safety profile through the encapsulation in nanostructured lipid carriers (NLC). Materials & methods: NLC-TRE was developed using a 2³ experimental factorial design, characterized (HPLC, dynamic light scattering, differential scanning calorimetry, x-ray diffraction analysis, transmission electron microscopy, cryo-transmission electron microscopy) and evaluated by in vitro studies and in healthy volunteers. Results: The NLC-TRE presented spherical structures, average particle size of 130 nm, zeta potential of 24 mV and encapsulation efficiency of 98%. The NLC-TRE protected TRE against oxidation (p < 0.0001) and promoted epidermal targeting (p < 0.0001) compared with the marketed product, both 0.05% TRE. The in vitro assay on reconstructed human epidermis and the measurement of transepidermal water loss in healthy volunteers demonstrated an enhanced safety profile in comparison to the marketed product (p < 0.0002). Conclusion: The NLC-TRE enhances the epidermal targeting and safety profile of TRE, representing a potential safer alternative for the topical treatment of skin disorders using TRE.

Combining secondary ion mass spectrometry image depth profiling and single particle inductively coupled plasma mass spectrometry to investigate the uptake and biodistribution of gold nanoparticles in Caenorhabditis elegans

Analytical techniques capable of determining the spatial distribution and quantity (mass and/or particle number) of engineered nanomaterials in organisms are essential for characterizing nano-bio interactions and for nanomaterial risk assessments. Here, we combine the use of dynamic secondary ion mass spectrometry (dynamic SIMS) and single particle inductively coupled mass spectrometry (spICP-MS) techniques to determine the biodistribution and quantity of gold nanoparticles (AuNPs) ingested by Caenorhabditis elegans. We report the application of SIMS in image depth profiling mode for visualizing, identifying, and characterizing the biodistribution of AuNPs ingested by nematodes in both the lateral and z (depth) dimensions. In parallel, conventional- and sp-ICP-MS quantified the mean number of AuNPs within the nematode, ranging from 2 to 36 NPs depending on the size of AuNP. The complementary data from both SIMS image depth profiling and spICP-MS provides a complete view of the uptake, translocation, and size distribution of ingested NPs within Caenorhabditis elegans.

Microfluidic and hydrothermal preparation of vesicles using sorbitan monolaurate/polyoxyethylene (20) sorbitan monolaurate (Span 20/Tween 20)

Here, we present a method for preparing vesicles by combining hydrothermal emulsification with solvent diffusion (SD). The sorbitan monolaurate/polyoxyethylene (20) sorbitan monolaurate (Span 20/Tween 20) system was used as the target lipid because these lipids are cheap and advantageous for the production scale. The water-in-oil (W/O) emulsion stabilized with lipids was formed under hydrothermal conditions (240 °C under 10 MPa), followed by mixing with water that included lipids to obtain a W/O-in-water (W/O/W) emulsion. The SD for the W/O/W emulsion as a subsequent process yielded vesicles. The optimal preparation conditions were 50:50 wt% Span 20/Tween 20 as a mixing ratio (final lipid concentration 12 mM), octanoic acid as an organic solvent, 240 °C for 4 min during the hydrothermal treatment, and 4 °C for 24 h in the SD process. The diameter of the vesicles obtained was at most 100 nm, which was comparable to that of the W/O/W emulsion before SD. This suggested that the W/O/W emulsion acted as a template for vesicle formation. The number density, diameter, and membrane properties of vesicles depend on the mixing ratio of the water/oil/lipid system. Specifically, the number density of vesicles was low relative to that of vesicles prepared by the conventional method.

Challenges in the Physical Characterization of Lipid Nanoparticles

Nano-sized drug transporters have become an efficient approach with considerable commercial values. Nanomedicine is not only limited to drug delivery by means of different administration routes, such as intravenous, oral, transdermal, nasal, pulmonary, and more, but also has applications in a multitude of areas, such as a vaccine, antibacterial, diagnostics and imaging, and gene delivery. This review will focus on lipid nanosystems with a wide range of applications, taking into consideration their composition, properties, and physical parameters. However, designing suitable protocol for the physical evaluation of nanoparticles is still conflicting. The main obstacle is concerning the sensitivity, reproducibility, and reliability of the adopted methodology. Some important techniques are compared and discussed in this report. Particularly, a comparison between different techniques involved in (a) the morphologic characterization, such as Cryo-TEM, SEM, and X-ray; (b) the size measurement, such as dynamic light scattering, sedimentation field flow fractionation, and optical microscopy; and (c) surface properties, namely zeta potential measurement, is described. In addition, an amperometric tool in order to investigate antioxidant activity and the response of nanomaterials towards the skin membrane has been presented.

Application of Fundamental Techniques for Physicochemical Characterizations to Understand Post-Formulation Performance of Pharmaceutical Nanocrystalline Materials

Nanocrystalline materials (NCM, i.e., crystalline nanoparticles) have become an important class of materials with great potential for applications ranging from drug delivery and electronics to optics. Drug nanocrystals (NC) and nano co-crystals (NCC) are examples of NCM with fascinating physicochemical properties and have attracted significant attention in drug delivery. NCM are categorized by advantageous properties, such as high drug-loading efficiency, good long-term physical stability, steady and predictable drug release, and long systemic circulation time. These properties make them excellent formulations for the efficient delivery of a variety of active pharmaceutical ingredients (API). In this review, we summarize the recent advances in drug NCM-based therapy options. Currently, there are three main methods to synthesize drug NCM, including top-down, bottom-up, and combination methods. The fundamental characterization methods of drug NCM are elaborated. Furthermore, the applications of these characterizations and their implications on the post-formulation performance of NCM are introduced.

Self-assembled mRNA vaccines

mRNA vaccines have evolved from being a mere curiosity to emerging as COVID-19 vaccine front-runners. Recent advancements in the field of RNA technology, vaccinology, and nanotechnology have generated interest in delivering safe and effective mRNA therapeutics. In this review, we discuss design and self-assembly of mRNA vaccines. Self-assembly, a spontaneous organization of individual molecules, allows for design of nanoparticles with customizable properties. We highlight the materials commonly utilized to deliver mRNA, their physicochemical characteristics, and other relevant considerations, such as mRNA optimization, routes of administration, cellular fate, and immune activation, that are important for successful mRNA vaccination. We also examine the COVID-19 mRNA vaccines currently in clinical trials. mRNA vaccines are ready for the clinic, showing tremendous promise in the COVID-19 vaccine race, and have pushed the boundaries of gene therapy.

Polymeric micelles in drug delivery: An insight of the techniques for their characterization and assessment in biorelevant conditions

Polymeric micelles, i.e. aggregation colloids formed in solution by self-assembling of amphiphilic polymers, represent an innovative tool to overcome several issues related to drug administration, from the low water-solubility to the poor drug permeability across biological barriers. With respect to other nanocarriers, polymeric micelles generally display smaller size, easier preparation and sterilization processes, and good solubilization properties, unfortunately associated with a lower stability in biological fluids and a more complicated characterization. Particularly challenging is the study of their interaction with the biological environment, essential to predict the real in vivo behavior after administration. In this review, after a general presentation on micelles features and properties, different characterization techniques are discussed, from the ones used for the determination of micelles basic characteristics (critical micellar concentration, size, surface charge, morphology) to the more complex approaches used to figure out micelles kinetic stability, drug release and behavior in the presence of biological substrates (fluids, cells and tissues). The techniques presented (such as dynamic light scattering, AFM, cryo-TEM, X-ray scattering, FRET, symmetrical flow field-flow fractionation (AF4) and density ultracentrifugation), each one with their own advantages and limitations, can be combined to achieve a deeper comprehension of polymeric micelles in vivo behavior. The set-up and validation of adequate methods for micelles description represent the essential starting point for their development and clinical success.

Liquid Crystalline Phases for Enhancement of Oral Bioavailability

Liquid crystalline phases (LCPs) are generated upon lipolysis of ingested lipids in the gastrointestinal tract. The breaking off and subsequent evolution of LCPs produce more advanced vesicular and micellar structures which facilitate oral absorption of lipids, as well as co-loaded drug entities. Owing to sustained or controlled drug release, bioadhesiveness, and capability of loading drugs of different properties, LCPs are promising vehicles to implement for enhancement of oral bioavailability. This review aims to provide an overview on the classification, preparation and characterization, in vivo generation and transformation, absorption mechanisms, and encouraging applications of LCPs in enhancement of oral bioavailability. In addition, we comment on the merits of LCPs as oral drug delivery carriers, as well as solutions to industrialization utilizing liquid crystalline precursor and preconcentrate formulations.

Computational and Experimental Approaches to Investigate Lipid Nanoparticles as Drug and Gene Delivery Systems

Lipid nanoparticles (LNPs) have been widely applied in drug and gene delivery. More than twenty years ago, DoxilTM was the first LNPs-based drug approved by the US Food and Drug Administration (FDA). Since then, with decades of research and development, more and more LNP-based therapeutics have been used to treat diverse diseases, which often offer the benefits of reduced toxicity and/or enhanced efficacy compared to the active ingredients alone. Here, we provide a review of recent advances in the development of efficient and robust LNPs for drug/gene delivery. We emphasize the importance of rationally combining experimental and computational approaches, especially those providing multiscale structural and functional information of LNPs, to the design of novel and powerful LNP-based delivery systems.

Nondestructive production of exosomes loaded with ultrathin palladium nanosheets for targeted bio-orthogonal catalysis

The use of exosomes as selective delivery vehicles of therapeutic agents, such as drugs or hyperthermia-capable nanoparticles, is being intensely investigated on account of their preferential tropism toward their parental cells. However, the methods used to introduce a therapeutic load inside exosomes often involve disruption of their membrane, which may jeopardize their targeting capabilities, attributed to their surface integrins. On the other hand, in recent years bio-orthogonal catalysis has emerged as a new tool with a myriad of potential applications in medicine. These bio-orthogonal processes, often based on Pd-catalyzed chemistry, would benefit from systems capable of delivering the catalyst to target cells. It is therefore highly attractive to combine the targeting capabilities of exosomes and the bio-orthogonal potential of Pd nanoparticles to create new therapeutic vectors. In this protocol, we provide detailed information on an efficient procedure to achieve a high load of catalytically active Pd nanosheets inside exosomes, without disrupting their membranes. The protocol involves a multistage process in which exosomes are first harvested, subjected to impregnation with a Pd salt precursor followed by a mild reduction process using gas-phase CO, which acts as both a reducing and growth-directing agent to produce the desired nanosheets. The technology is scalable, and the protocol can be conducted by any researcher having basic biology and chemistry skills in ~3 d.

Liquid crystalline nanoparticles for drug delivery: The role of gradient and block copolymers on the morphology, internal organisation and release profile

Amphiphilic polymers represent one of the main class of stabilizers for non-lamellar lyotropic liquid crystalline nanoparticles, being essential for their formation and stability. In the present study, poly(ethylene oxide)-block-poly(ε-caprolactone) (PEO-b-PCL) block copolymers and poly(2-methyl-2-oxazoline)-grad-poly(2-phenyl-2-oxazoline) (MPOx) gradient copolymers were incorporated as stabilizers in liquid crystalline nanoparticles prepared from glyceryl monooleate. The polymers were chosen according to their high biocompatibility and promising stealth properties, in order to develop safe and efficient drug delivery nanosystems. The physicochemical characteristics and fractal dimension of the resultant nanosystems were obtained from light scattering techniques, while their micropolarity and microfluidity from fluorescence spectroscopy. The effect of temperature, serum proteins and ionic strength on the physicochemical behavior was monitored. Their morphology was assessed by cryo-TEM, while their thermal behavior by microcalorimetry and high-resolution ultrasound spectroscopy. Their properties were dependent on the stabilizer chemistry and topology (block/gradient copolymer) and its concentration. Subsequently, resveratrol, as model hydrophobic drug, was loaded into the nanosystems, the entrapment efficiency was calculated and in vitro release studies were carried out, highlighting how the different stabilizer can differentiate the drug release profile. In conclusion, the proposed copolymers broaden the toolbox of polymeric stabilizers for the development of liquid crystalline nanoparticles intended for drug delivery applications.

Calibrated liposomal release of the anti-mitotic agent BI-2536 increases the targeting of mitotic tumor cells

Cancer drugs which are specifically targeted at mitosis have generally under-delivered as a class. One likely reason is that only a small percentage of cancer cells in a tumor are actually dividing at any moment. If this is the case, then prolonged bioavailability in the tumor should significantly increase the efficacy of antimitotic agents. Here, we show that if the Plk1 inhibitor BI 2536 is co-encapsulated in a liposome with a pair of anions, its release rate is dependent on both the identity and stoichiometry of the anions. We created a library of liposomes with varying release rates using this approach and found that liposomal drug release rates correlated inversely with in vitro cancer cell killing. Xenografted mice treated with a single dose of slow-releasing liposomal BI 2536 experienced tumor volume decreases lasting 12 days and complete responses in 20% of mice. Treatment with two doses a week apart increased the response rate to 75%. This approach, which we termed Paired Anion Calibrated Release (PACeR), has the potential to revive the clinical utility of antimitotic cancer drugs which have failed clinical trials.

Recombination Monophosphoryl Lipid A-Derived Vacosome for the Development of Preventive Cancer Vaccines

Recently, there has been an increasing interest for utilizing the host immune system to fight against cancer. Moreover, cancer vaccines, which can stimulate the host immune system to respond to cancer in the long term, are being investigated as a promising approach to induce tumor-specific immunity. In this work, we prepared an effective cancer vaccine (denoted as "vacosome") by reconstructing the cancer cell membrane, monophosphoryl lipid A as a toll-like receptor 4 agonist, and egg phosphatidylcholine. The vacosome triggered and enhanced bone marrow dendritic cell maturation as well as stimulated the antitumor response against breast cancer 4T1 cells in vitro. Furthermore, an immune memory was established in BALB/c mice after three-time preimmunization with the vacosome. After that, the immunized mice showed inhibited tumor growth and prolonged survival period (longer than 50 days). Overall, our results demonstrate that the vacosome can be a potential candidate for clinical translation as a cancer vaccine.

Application of Cryogenic Transmission Electron Microscopy for Evaluation of Vaccine Delivery Carriers

Cryogenic transmission electron microscopy (Cryo-TEM) enables visualizing the physicochemical structure of nanocarriers in solution. Here, we demonstrate the typical applications of Cryo-TEM in characterizing archaeosome-based vesicles as antigen carriers, including the morphology and size of vaccine carriers. Cryo-TEM tomography, incorporated with immunogold labeling for identifying and localizing the antigens, reveals the antigen distribution within archaeosomes in three dimensions (3D).

Hybrid Biopolymer and Lipid Nanoparticles with Improved Transfection Efficacy for mRNA

Hybrid nanoparticles from lipidic and polymeric components were assembled to serve as vehicles for the transfection of messenger RNA (mRNA) using different portions of the cationic lipid DOTAP (1,2-Dioleoyl-3-trimethylammonium-propane) and the cationic biopolymer protamine as model systems. Two different sequential assembly approaches in comparison with a direct single-step protocol were applied, and molecular organization in correlation with biological activity of the resulting nanoparticle systems was investigated. Differences in the structure of the nanoparticles were revealed by thorough physicochemical characterization including small angle neutron scattering (SANS), small angle X-ray scattering (SAXS), and cryogenic transmission electron microscopy (cryo-TEM). All hybrid systems, combining lipid and polymer, displayed significantly increased transfection in comparison to lipid/mRNA and polymer/mRNA particles alone. For the hybrid nanoparticles, characteristic differences regarding the internal organization, release characteristics, and activity were determined depending on the assembly route. The systems with the highest transfection efficacy were characterized by a heterogenous internal organization, accompanied by facilitated release. Such a system could be best obtained by the single step protocol, starting with a lipid and polymer mixture for nanoparticle formation.

Microemulsion Microstructure(s): A Tutorial Review

Microemulsions are thermodynamically stable, transparent, isotropic single-phase mixtures of two immiscible liquids stabilized by surfactants (and possibly other compounds). The assortment of very different microstructures behind such a univocal macroscopic definition is presented together with the experimental approaches to their determination. This tutorial review includes a necessary overview of the microemulsion phase behavior including the effect of temperature and salinity and of the features of living polymerlike micelles and living networks. Once these key learning points have been acquired, the different theoretical models proposed to rationalize the microemulsion microstructures are reviewed. The focus is on the use of these models as a rationale for the formulation of microemulsions with suitable features. Finally, current achievements and challenges of the use of microemulsions are reviewed.

Morphology and microstructural analysis of bioactive-loaded micro/nanocarriers via microscopy techniques; CLSM/SEM/TEM/AFM

Efficient characterization of the physicochemical attributes of bioactive-loaded micro/nano-vehicles is crucial for the successful product development. The introduction of outstanding science-based strategies and techniques makes it possible to realize how the characteristics of the formulation ingredients affect the structural and (bio)functional properties of the final bioactive-loaded carriers. The important points to be solved, at a microscopic level, are investigating how the features of the formulation ingredients affect the morphology, surface, size, dispersity, as well as the particulate interactions within bioactive-comprising nano/micro-delivery systems. This review presents a detailed description concerning the application of advanced microscopy techniques, i.e., confocal laser scanning microscopy (CLSM), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and atomic force microscopy (AFM) in characterizing the attributes of nano/microcarriers for the efficient delivery of bioactive compounds. Furthermore, the fundamental principles of these approaches, instrumentation, specific applications, and the strategy to choose the most proper technique for different carriers has been discussed.

Liposomes for Antibiotic Encapsulation and Delivery

When antibiotics are administered, orally or intravenously, they pass through different organs and layers of tissue on their way to the site of infection; this can cause dilution and/or intoxication. To overcome these problems, drug delivery vehicles have been used to encapsulate and deliver antibiotics, improving their therapeutic index while minimizing their adverse effects. Liposomes are self-assembled lipid vesicles made from at least one bilayer of phospholipids with an inner aqueous compartment. Liposomes are attractive vehicles to deliver antibiotics because they can encapsulate both hydrophobic and hydrophilic antibiotics, they have low toxicity, and they can change the biodistribution of the drug. Furthermore, liposomes have been approved by regulatory agencies. However, most developmental and mechanistic research in the field has been focused on encapsulation and delivery of anticancer drugs, a class of molecules that differ significantly in chemistry from antibiotics. In this critical Review, we discuss the state of knowledge regarding the design of liposomes for encapsulation and delivery of antibiotics and offer insight into the challenges and promises of using liposomes for antibiotic delivery.

Effects of sodium chloride on rheological behaviour of the gemini-like surfactants

The gemini-like surfactants have been constructed by compounding N-erucamidopropyl-N,N-dimethylamine (UC22AMPM) and o-phthalic acid (o-PA), m-phthalic acid (m-PA), or p-phthalic acid (p-PA), and are denoted as o-EAPA, m-EAPA, and p-EAPA, respectively. It is well known that inorganic salts have significant effects on surfactant aggregates, and herein the effects of sodium chloride (NaCl) on gemini-like surfactants is explored by rheological and dynamic light scattering measurements, and cryo-TEM. It is found that the viscoelasticity of the EAPA systems first increases and then decreases with an increase of the NaCl concentration. And the optimal NaCl concentrations for these three systems are in the order of o-EAPA < m-EAPA < p-EAPA due to different spacer distances between the two carboxyl groups in the phthalic acid. Similar trends in the N,N-dimethyl oleoaminde-propylamine (DOAPA) and o-PA, m-PA, or p-PA systems were also observed. The results show that an appropriate NaCl concentration will promote gemini-like surfactants to form wormlike micelles (WLMs). Upon further increasing the NaCl concentration, the WLMs transform into vesicles. Excessive NaCl concentration will cause the surfactant systems to reach their cloud point and make the surfactants precipitate out. The mechanism of the effects of NaCl is that Cl- reduces the electrostatic repulsion between the headgroups of the surfactants. This work is helpful in understanding the effects of inorganic salts on the surfactants and this study is useful for exploring the practical applications of gemini-like surfactants.

Recent advances of characterization techniques for the formation, physical properties and stability of Pickering emulsion

Recently, there have been increasing demand for the application of Pickering emulsions in various industries due to its combined advantage in terms of cost, quality and sustainability. This review aims to provide a complete overview of the available methodology for the physical characterization of emulsions that are stabilized by solid particles (known as Pickering emulsion). Current approaches and techniques for the analysis of the formation and properties of the Pickering emulsion were outlined along with the expected results of these methods on the emulsions. Besides, the application of modelling techniques has also been elaborated for the effective characterization of Pickering emulsions. Additionally, approaches to assess the stability of Pickering emulsions against physical deformation such as coalescence and gravitational separation were reviewed. Potential future developments of these characterization techniques were also briefly discussed. This review can act as a guide to researchers to better understand the standard procedures of Pickering emulsion assessment and the advanced methods available to date to study these emulsions, down to the minute details.

Quantitative Structural Analysis of Polystyrene Nanoparticles Using Synchrotron X-Ray Scattering and Dynamic Light Scattering

A series of polystyrene nanoparticles (PS-1, PS-2, PS-3, and PS-4) in aqueous solutions were investigated in terms of morphological structure, size, and size distribution. Synchrotron small-angle X-ray scattering analysis (SAXS) was carried out, providing morphology details, size and size distribution on the particles. PS-1, PS-2, and PS-3 were confirmed to behave two-phase (core and shell) spherical shapes, whereas PS-4 exhibited a single-phase spherical shape. They all revealed very narrow unimodal size distributions. The structural parameter details including radial density profile were determined. In addition, the presence of surfactant molecules and their assemblies were detected for all particle solutions, which could originate from their surfactant-assisted emulsion polymerizations. In addition, dynamic light scattering (DLS) analysis was performed, finding only meaningful hydrodynamic size and intensity-weighted mean size information on the individual PS solutions because of the particles' spherical nature. In contrast, the size distributions were extracted unrealistically too broad, and the volume- and number-weighted mean sizes were too small, therefore inappropriate to describe the particle systems. Furthermore, the DLS analysis could not detect completely the surfactant and their assemblies present in the particle solutions. Overall, the quantitative SAXS analysis confirmed that the individual PS particle systems were successfully prepared with spherical shape in a very narrow unimodal size distribution.

Nanostructured Lipid Carriers: A Groundbreaking Approach for Transdermal Drug Delivery

Nanostructured lipid carriers (NLCs) are novel pharmaceutical formulations which are composed of physiological and biocompatible lipids, surfactants and co-surfactants. Over time, as a second generation lipid nanocarrier NLC has emerged as an alternative to first generation nanoparticles. This review article highlights the structure, composition, various formulation methodologies, and characterization of NLCs which are prerequisites in formulating a stable drug delivery system. NLCs hold an eminent potential in pharmaceuticals and cosmetics market because of extensive beneficial effects like skin hydration, occlusion, enhanced bioavailability, and skin targeting. This article aims to evoke an interest in the current state of art NLC by discussing their promising assistance in topical drug delivery system. The key attributes of NLC that make them a promising drug delivery system are ease of preparation, biocompatibility, the feasibility of scale up, non-toxicity, improved drug loading, and stability.

Combined Magnetoliposome Formation and Drug Loading in One Step for Efficient Alternating Current-Magnetic Field Remote-Controlled Drug Release

We have developed a reproducible and facile one step strategy for the synthesis of doxorubicin loaded magnetoliposomes by using a thin-layer evaporation method. Liposomes of around 200 nm were made of 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) and iron oxide nanoparticles (NPs) with negative, positive, and hydrophobic surfaces that were incorporated outside, inside, or between the lipid bilayers, respectively. To characterize how NPs are incorporated in liposomes, advanced cryoTEM and atomic force microscope (AFM) techniques have been used. It was observed that only when the NPs are attached outside the liposomes, the membrane integrity is preserved (lipid melt transition shifts to 38.7 °C with high enthalpy 34.8 J/g) avoiding the leakage of the encapsulated drug while having good colloidal properties and the best heating efficiency under an alternating magnetic field (AMF). These magnetoliposomes were tested with two cancer cell lines, MDA-MB-231 and HeLa cells. First, 100% of cellular uptake was achieved with a high cell survival (above 80%), which is preserved (83%) for doxorubicin-loaded magnetoliposomes. Then, we demonstrate that doxorubicin release can be triggered by remote control, using a noninvasive external AMF for 1 h, leading to a cell survival reduction of 20%. Magnetic field conditions of 202 kHz and 30 mT seem to be enough to produce an effective heating to avoid drug degradation. In conclusion, these drug-loaded magnetoliposomes prepared in one step could be used for drug release on demand at a specific time and place, efficiently using an external AMF to reduce or even eliminate side effects.

Controlling the size and shape of liposomal ciprofloxacin nanocrystals by varying the lipid bilayer composition and drug to lipid ratio

Drug nanocrystals precipitated inside liposomes are of increasing interest in liposomal drug delivery. For liposomal nanocrystal formulations, the size and shape of the drug nanocrystals can influence the apparent drug release properties, providing opportunities for developing tailored liposomal drug release systems. Small angle X-ray scattering (SAXS) and quantitative transmission electron microscopy (TEM) can be used to analyse the size distributions of the nanoparticles. In this study, by changing the fluidity of the membrane through the use of different membrane phospholipids with varying cholesterol content, the impact of lipid phase, fluidity and permeability on the size distribution of ciprofloxacin nanocrystals were investigated using standard TEM and SAXS as orthogonal techniques. The results show that the phospholipid phase behaviour has a direct effect on the nanocrystal size distribution, where shorter and thinner nanocrystals were formed in liposomes made from hydrogenated soy phosphatidylcholine (HSPC) and 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) phospholipids with higher phase transition temperatures than 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) and 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC) with lower transition temperatures. This is mainly due to the phase behaviour of the liposome during nanocrystal formation. The addition of cholesterol that reduces fluidity and permeability of the DOPC liposomes was also shown to restrict the growth of the ciprofloxacin nanocrystals. Moreover, increasing the drug loading of the liposomes made from HSPC and DPPC produced longer and wider nanocrystals. The findings open new opportunities to tailor nanocrystal size distributions, as well as the aspect ratio of the enclosing liposomes with potential to alter drug release and in vivo behaviour.

Small-scale preparation of perfluorocarbon-nanoemulsions utilizing dual centrifugation

BACKGROUND

Perfluorocarbon-nanoemulsions (PFC-NE) made of PFC and phospholipids (PL) by homogenization are optimal for in vivo-¹⁹F labelling of monocytes and subsequently of inflamed tissues in magnetic resonance imaging (MRI). Necessary requirements for in vivo use of PFC-NE are sterility, suitable droplet sizes and the absence of immune activating liposomes, which are a typical byproduct of the homogenization process.

METHODS AND RESULTS

To meet these requirements, we developed an aseptic in-vial preparation technique for PFC-NE based on dual centrifugation (DC) by testing different PFC/phospholipid ratios as well as the application of additives. Two different PFC, perfluorooctylbromide (PFOB) and perfluoro-15-crown-5-ether (PFCE), were investigated. Particle sizes were assessed by dynamic light scattering and NE morphology by cryoTEM. DC homogenization was optimal when using an excess of PL (8.7 % (m/m) of utilized PFC, z-ave: 180 nm, pdi: 0.2). A purification approach by centrifugation was implemented to remove liposomes formed from the excess of PL during homogenization. The purification success was proven by phospholipid assay and PFC quantification via density and sound velocity measurements.

CONCLUSION

DC in combination with a short centrifugation is a fast and reliable way of small-scale aseptic PFC-NE production for ¹⁹F MRI passive-targeting experiments of monocytes and inflamed tissues.

Artificial Phospholipids and Their Vesicles

Phospholipids are at the heart and origin of life on this planet. The possibilities in terms of phospholipid self-assembly and biological functions seem limitless. Nonetheless, nature exploits only a small fraction of the available chemical space of phospholipids. Using chemical synthesis, artificial phospholipid structures become accessible, and the study of their biophysics may reveal unprecedented properties. In this article, the recent advances by our work group in the field of chemical lipidology are summarized. The family of diamidophospholipids is discussed in detail from monolayer characterization to the formation of faceted vesicles, culminating in the template-free self-assembly of phospholipid cubes and the possible applications of vesicle origami in modern personalized medicine.

Cellular uptake of self-assembled phytantriol-based hexosomes is independent of major endocytic machineries

Despite increasing interests in non-lamellar liquid crystalline dispersions, such as hexosomes, for drug delivery, little is known about their interactions with cells and mechanism of cell entry. Here we examine the cellular uptake of hexosomes based on phytantriol and mannide monooleate by HeLa cells using live cell microscopy in comparison to conventional liposomes. To investigate the importance of specific endocytosis pathways upon particle internalization, we silenced regulatory proteins of major endocytosis pathways using short interfering RNA. While endocytosis plays a significant role in liposome internalization, hexosomes are not taken up via endocytosis but through a mechanism that is dependent on cell membrane tension. Biophysical studies using biomembrane models highlighted that hexosomes have a high affinity for membranes and an ability to disrupt lipid layers. Our data suggest that direct biomechanical interactions of hexosomes with membrane lipids play a crucial role and that the unique morphology of hexosomes is vital for their membrane activity. Based on these results, we propose a mechanism, where hexosomes destabilize the bilayer, allowing them to "phase through" the membrane. Understanding parameters that influence the uptake of hexosomes is critical to establish them as carrier systems that can potentially deliver therapeutics efficiently to intracellular sites of action.

Liposomes as models for membrane integrity

Biological membranes form the boundaries to cells. They are integral to cellular function, retaining the valuable components inside and preventing access of unwanted molecules. Many different classes of molecules demonstrate disruptive properties to the plasma membrane. These include alcohols, detergents and antimicrobial agents. Understanding this disruption and the mechanisms by which it can be mitigated is vital for improved therapeutics as well as enhanced industrial processes where the compounds produced can be toxic to the membrane. This mini-review describes the most common molecules that disrupt cell membranes along with a range of in vitro liposome-based techniques that can be used to monitor and delineate these disruptive processes.

Shape and Phase Transitions in a PEGylated Phospholipid System

Poly(ethylene glycol) (PEG) polymers and PEG-conjugated lipids are widely used in bioengineering and drug transport applications. A PEG layer in a drug carrier increases hydrophilic repulsion, inhibits membrane fusion and serum opsonin interactions, and prolongs the storage and circulation time. It can also change the carrier shape and have an influence on many properties related to the content release of the carrier. In this paper, we focus on the physicochemical effects of PEGylation in the lipid bilayer. We introduce laurdanC as a fluorophore for shape recognition and phase transition detection. Together with laurdanC, cryogenic transmission electron microscopy, differential scanning calorimetry, molecular dynamics simulations, and small-angle X-ray scattering/wide-angle X-ray scattering, we acquire information of the particle/bilayer morphology and phase behavior in systems containing 1,2-dipalmitoyl- sn-glycero-3-phosphocholine:1,2-distearoyl- sn-glycero-3-phosphoethanolamine-PEG(2000) with different fractions. We find that PEGylation leads to two important and potentially usable features of the system. (1) Spherical vesicles present a window of elevated chain-melting temperatures and (2) lipid packing shape-controlled liposome-to-bicelle transition. The first finding is significant for targets requiring multiple release sequences and the second enables tuning the release by composition and the PEG polymer length. Besides drug delivery systems, the findings can be used in other smart soft materials with trigger-polymers as well.

Direct Comparison of Standard Transmission Electron Microscopy and Cryogenic-TEM in Imaging Nanocrystals Inside Liposomes

The use of electron microscopy techniques in the understanding of shape and size of nanoparticles are commonly applied to drug nanotechnology, but the type of microscopy and suitability for the particles of interest can have a significant impact on the result. The size and shape of the nanoparticles are crucial in clinical applications; however, direct comparison of the results from standard transmission electron microscopy (TEM) and cryo-TEM have rarely been reported. As a useful case for comparison, liposomal drug nanocrystals are studied here. In this study, the effect of thawing temperature on the size and shape of the ciprofloxacin nanocrystals was determined. A quantitative standard TEM assay was developed to allow for high-throughput particle size analysis. These results were compared to size and shape information obtained using the cryo-TEM method. The results showed broad agreement between the two TEM methods and that ciprofloxacin nanocrystals formed shorter and thinner crystals inside the liposomes at higher thawing temperatures. The results provide confidence in the use of standard TEM to determine the size and shape distribution of solid nanoparticles (in this case, encapsulated inside liposomes) from aqueous media without fear of sample preparation altering the conclusions.

Measuring particle size distribution of nanoparticle enabled medicinal products, the joint view of EUNCL and NCI-NCL. A step by step approach combining orthogonal measurements with increasing complexity

The particle size distribution (PSD) and the stability of nanoparticles enabled medicinal products (NEP) in complex biological environments are key attributes to assess their quality, safety and efficacy. Despite its low resolution, dynamic light scattering (DLS) is the most common sizing technique since the onset of NEP in pharmaceutical technologies. Considering the limitations of the existing sizing measurements and the challenges posed by complex NEPs both scientists and regulators encourage the combination of multiple orthogonal high-resolution approaches to shed light in the NEP sizing space (e.g. dynamic light scattering, electron microscopy, field flow fractionation coupled to online sizing detectors, centrifugal techniques, particle tracking analysis and tunable resistive pulse sensing). The pharmaceutical and biotechnology developers are now challenged to find their own pragmatic characterisation approaches, which should be fit for purpose and minimize costs at the same time, in a complicated landscape where only a few standards exist. In order to support the community, the European Nanomedicine Characterisation Laboratory (EUNCL) and the US National Cancer Institute Nanotechnology Characterization Laboratory (NCI-NCL) have jointly developed multiple standard operating procedures (SOPs) for NEP assessment, including the measurements of particle size distribution, and are offering wide access to their 'state of the art' characterisation platforms, in addition to making SOPs publicly available. This joint perspective article would like to present the NCI-NCL and EUNCL multi-step approach of incremental complexity to measure particle size distribution and size stability of NEPs, consisting of a quick preliminary step to assess sample integrity and stability by low resolution techniques (pre-screening), followed by the combination of complementary high resolution sizing measurements performed both in simple buffers and in complex biological media. Test cases are presented to demonstrate: i) the need for employing at least one high-resolution sizing technique, ii) the importance of selecting the correct sizing techniques for the purpose, and iii) the robustness of utilizing orthogonal sizing techniques to study the physical properties of complex NEP samples.

The stabilization of primitive bicontinuous cubic phases with tunable swelling over a wide composition range

In this paper we investigate the pseudo-ternary phase diagram of glycerol monooleate (GMO), a cationic lipid (DOTAP - 1,2-dioleoyl-3-trimethylammonium propane), and a "PEGylated" lipid (DOPE-PEG - 1,2-dioleoyl-sn-glycero-3-phosphoethanolamine-N-[methoxy(polyethylene glycol)-2000 kDa]) in excess water. We use small angle X-ray scattering (SAXS) and cryogenic transmission electron microscopy (Cryo-EM) to map out a phase diagram in a regime of low DOPE-PEG content (1-5 mol%), which is pertinent for the application of lipid systems as carriers of biomolecular cargo to cells. Pure GMO is known to self-assemble into bicontinuous cubic phases of the gyroid type at low water content and of the diamond type in excess water. These complex structures have numerous advantages reaching beyond drug delivery, e.g. as protein crystallization matrices, but their formulation is challenging as very small contents of guest molecules can shift the phase behavior towards other geometries such as the lamellar phase. In this work, we show that the ternary GMO/DOTAP/DOPE-PEG system allows the stabilization of bicontinuous cubic phases in excess water over a wide composition range. The symmetry of the phase can be tuned by varying the amount of PEGylated lipid, with the primitive type dominating at low DOPE-PEG content (1-3 mol%) and the diamond phase arising at 5 mol% DOPE-PEG. In addition, we found that the diamond phase is virtually non-responsive to electrostatic swelling. In contrast, primitive bicontinuous cubic lattice dimensions swell up in equilibrium to 650 Å with increased cationic lipid content.

Physical Characterization of Halofantrine-Encapsulated Fat Nanoemulsions

We report the colloidal characterization of halofantrine (Hf)-laden soybean oil fat emulsions. Hf increased the zeta potential, at all pH values, of the fat emulsions. Concomitant with this, the isoelectric point (i.e.p.) of the emulsion increased to higher pH values. The emulsion was destabilized by a small amount of Hf; interestingly, however, this was ameliorated by increasing the amount of Hf. The particle size and polydispersity of the fat emulsion reflected this with a small Hf concentration resulting in a significant increase in both particle size and polydispersity, but less so as the Hf concentration was increased. Emulsions lost stability as the pH approached the i.e.p. and this effect was greatest for the small Hf concentration emulsions. Cryogenic transmission electron microscopy showed the presence of beading or string-like behavior leading to gross distortions of the spherical shape for highly unstable emulsions. We conclude that to maintain good stability for Hf-laden soybean oil emulsions, the pH of the emulsion should be kept away from its i.e.p, and also that the drug concentration should be maintained at a relatively high value.

Remote loading of curcumin-in-modified β-cyclodextrins into liposomes using a transmembrane pH gradient

The current study provides a novel remote loading approach utilizing chemically modified cyclodextrins to incorporate hydrophobic drugs into liposomes.

Combination of Roll Grinding and High-Pressure Homogenization Can Prepare Stable Bicelles for Drug Delivery

To improve the solubility of the drug nifedipine (NI), NI-encapsulated lipid-based nanoparticles (NI-LNs) have been prepared from neutral hydrogenated soybean phosphatidylcholine and negatively charged dipalmitoylphosphatidylglycerol at a molar ratio of 5/1 using by roll grinding and high-pressure homogenization. The NI-LNs exhibited high entrapment efficiency, long-term stability, and enhanced NI bioavailability. To better understand their structures, cryo transmission electron microscopy and atomic force microscopy were performed in the present study. Imaging from both instruments revealed that the NI-LNs were bicelles. Structures prepared with a different drug (phenytoin) or with phospholipids (dimyristoylphosphatidylcholine, dipalmitoylphosphatidylcholine, and distearoylphosphatidylcholine) were also bicelles. Long-term storage, freeze-drying, and high-pressure homogenization did not affect the structures; however, different lipid ratios, or the presence of cholesterol, did result in liposomes (5/0) or micelles (0/5) with different physicochemical properties and stabilities. Considering the result of long-term stability, standard NI-LN bicelles (5/1) showed the most long-term stabilities, providing a useful preparation method for stable bicelles for drug delivery.