On the Stability of Pickering and Classical Nanoemulsions: Theory and Experiments

Fortification of Sunflower Oil by Nanoemulsions Containing Vitamin-D3: Formation, Stability, and Release

This study addresses the challenge of stabilizing vitamin D3, an unstable, fat-soluble vitamin, whose efficacy is diminished by environmental factors. The objective was to encapsulate vitamin D3 using pectin (1%-3% w/w) and whey protein concentrate (WPC) (1%-2% w/w) at varying ratios, facilitated by Tween 80 surfactant (0.5% and 2.5% w/w), through high-pressure homogenization to create oil-in-water (O/W) nanoemulsions. Optimization of the preparation conditions for both aqueous and oil phases was conducted using an experimental design. Characterization and stability of the nanoemulsions were assessed using scanning electron microscopy (SEM), dynamic light scattering (DLS), and Fourier transform infrared spectroscopy (FTIR). Release kinetics of vitamin-D3 into sunflower oil were monitored using high-performance liquid chromatography (HPLC) under various conditions. The optimal encapsulation was achieved with a 30:70 oil-to-aqueous phase ratio, comprising 27.5% oil and 2.5% surfactant in the oil phase, and 1% WPC and 2% pectin in the aqueous phase. The nanoemulsion demonstrated stability over 60 days of storage, with a z-average particle size of 98.2 nm. HPLC analysis indicated a 90% recovery of encapsulated vitamin-D3 in sunflower oil. These findings suggest the promising approach of the developed nanoemulsion for enhancing the bioavailability and shelf life of vitamin-D3 in food applications.

High thermal conductive and photothermal phase change material microcapsules via cellulose nanocrystal stabilized Pickering emulsion for solar harvesting and thermal energy storage

Phase change materials (PCMs) are promising for thermal energy storage due to their high latent enthalpy and constant phase change temperature. However, organic PCMs suffer from leaking, low thermal conductivity, and flammability. Herein, high thermal conductivity, photothermal and flame-proof docosane microcapsules with melamine-formaldehyde (MF) and polypyrrole (PPy) (C22-CMFP) were reported with cellulose nanocrystal (CNC) stabilized Pickering emulsion droplets as templates through in-situ polymerization. CNCs showed outstanding C22 Pickering emulsifying ability with the presence of NaCl and provided ideal templates for C22 microcapsules. The obtained C22-CMFP microcapsules displayed high enthalpy (205.7 J/g), C22 core ratio (86.1 %), and stability. The C22-CMFP microcapsules retained an outstanding enthalpy remaining ratio (98.9 %) after 100 times cooling/heating cycles and could tolerate 100 °C for 12 h without leaking due to the robust hybrid CMFP shell. PPy significantly improved the thermal conductivity and photothermal conversion efficiency of C22-CMFP microcapsules. The C22-CMFP microcapsules exhibited a high thermal conductivity of 0.683 W/(m·K). The maximum temperature of C22-CMFP microcapsules under light irradiation for 18 min was 60.4 °C. Moreover, C22-CMFP microcapsules showed superb flame-proof properties. This study provides a facile approach to fabricate high enthalpy, stable, thermal conductive, photothermal, and flame-proof PCM microcapsules for solar harvesting and thermal energy storage.

Sub-micron colloidosomes with tuneable cargo release prepared using epoxy-functional diblock copolymer nanoparticles

HYPOTHESIS

Pickering emulsions stabilized using epoxy-functional block copolymer nanoparticles should enable the formation of sub-micron colloidosomes that are stable with respect to Ostwald ripening and allow tuneable small-molecule cargo release.

EXPERIMENTS

Epoxy-functional diblock copolymer nanoparticles of 24 ± 4 nm were prepared via reversible addition-fragmentation chain transfer (RAFT)-mediated dispersion polymerization of methyl methacrylate (MMA) in n-dodecane. Sub-micron water-in-n-dodecane Pickering emulsions were prepared by high-pressure microfluidization. The epoxy groups were then ring-opened using 3-aminopropyltriethoxysilane (APTES) to prepare cross-linked colloidosomes. The colloidosomes survived removal of the aqueous phase using excess solvent. The silica shell thickness could be adjusted from 11 to 23 nm by varying the APTES/GlyMA molar ratio. The long-term stability of the colloidosomes was compared to precursor Pickering emulsions. Finally, the permeability of the colloidosomes was examined by encapsulation and release of a small molecule.

FINDINGS

The Pickering emulsion droplet diameter was reduced from 700 to 200 nm by increasing the salt concentration within the aqueous phase. In the absence of salt, emulsion droplets were unstable due to Ostwald ripening. However, emulsions prepared with 0.5 M NaCl are stable for at least one month. The cross-linked colloidosomes demonstrated much more stable than the precursor sub-micron emulsions prepared without salt. The precursor nanoemulsions exhibited complete release (>99 %) of an encapsulated dye, while higher APTES/GlyMA ratios resulted in much lower dye release, yielding nearly impermeable silica capsules that retained around 95 % of the dye.

Lipid-Based Nanoformulations for Drug Delivery: An Ongoing Perspective

Oils and lipids help make water-insoluble drugs soluble by dispersing them in an aqueous medium with the help of a surfactant and enabling their absorption across the gut barrier. The emergence of microemulsions (thermodynamically stable), nanoemulsions (kinetically stable), and self-emulsifying drug delivery systems added unique characteristics that make them suitable for prolonged storage and controlled release. In the 1990s, solid-phase lipids were introduced to reduce drug leakage from nanoparticles and prolong drug release. Manipulating the structure of emulsions and solid lipid nanoparticles has enabled multifunctional nanoparticles and the loading of therapeutic macromolecules such as proteins, nucleic acid, vaccines, etc. Phospholipids and surfactants with a well-defined polar head and carbon chain have been used to prepare bilayer vesicles known as liposomes and niosomes, respectively. The increasing knowledge of targeting ligands and external factors to gain control over pharmacokinetics and the ever-increasing number of synthetic lipids are expected to make lipid nanoparticles and vesicular systems a preferred choice for the encapsulation and targeted delivery of therapeutic agents. This review discusses different lipids and oil-based nanoparticulate systems for the delivery of water-insoluble drugs. The salient features of each system are highlighted, and special emphasis is given to studies that compare them.

Innovations in Nanoemulsion Technology: Enhancing Drug Delivery for Oral, Parenteral, and Ophthalmic Applications

Nanoemulsions (NEs) are submicron-sized heterogeneous biphasic liquid systems stabilized by surfactants. They are physically transparent or translucent, optically isotropic, and kinetically stable, with droplet sizes ranging from 20 to 500 nm. Their unique properties, such as high surface area, small droplet size, enhanced bioavailability, excellent physical stability, and rapid digestibility, make them ideal for encapsulating various active substances. This review focuses on recent advancements, future prospects, and challenges in the field of NEs, particularly in oral, parenteral, and ophthalmic delivery. It also discusses recent clinical trials and patents. Different types of in vitro and in vivo NE characterization techniques are summarized. High-energy and low-energy preparation methods are briefly described with diagrams. Formulation considerations and commonly used excipients for oral, ocular, and ophthalmic drug delivery are presented. The review emphasizes the need for new functional excipients to improve the permeation of large molecular weight unstable proteins, oligonucleotides, and hydrophilic drugs to advance drug delivery rapidly.

Nanoemulsions of betulinic acid stabilized with modified phosphatidylcholine increase the stability of the nanosystems and the drug's bioavailability

Betulinic acid (BA) is a natural compound with significant potential for treating various diseases, including cancer and AIDS, and possesses additional anti-inflammatory and antibacterial properties. However, its clinical application is limited because of its low solubility in water, which impairs its distribution within the body. To overcome this challenge, nanoemulsions have been developed to improve the bioavailability of such poorly soluble drugs. This study investigated modified phosphatidylcholine (PC), where some fatty acids were replaced with conjugated linoleic acid (CLA) to stabilize BA nanoemulsions. The modified PC was used to prepare nanoemulsions with droplet sizes of up to 45 nanometers. These nanoemulsions maintained stability for 60 days at room temperature (25°C±2°C) and under refrigeration (5°C±1°C), with no signs of instability. Nanoemulsions stabilized with CLA-modified PC achieved a higher drug encapsulation rate (93.5±4.3 %) than those using natural PC (82.8±4.2 %). In an in vivo model, both nanoemulsion formulations significantly increased BA absorption, with CLA-modified PC enhancing absorption by 21.3±1.3 times and natural PC by 20±2.3 times compared to the free drug. This suggests that nanoemulsions with modified PC could improve the stability and efficacy of BA in clinical applications.

Effect of Temperature, Oil Type, and Copolymer Concentration on the Long-Term Stability of Oil-in-Water Pickering Nanoemulsions Prepared Using Diblock Copolymer Nanoparticles

A poly(glycerol monomethacrylate) (PGMA) precursor was chain-extended with 2,2,2-trifluoroethyl methacrylate (TFEMA) via reversible addition-fragmentation chain transfer (RAFT) aqueous emulsion polymerization. Transmission electron microscopy (TEM) studies confirmed the formation of well-defined PGMA52-PTFEMA50 spherical nanoparticles, while dynamic light scattering (DLS) studies indicated a z-average diameter of 26 ± 6 nm. These sterically stabilized diblock copolymer nanoparticles were used as emulsifiers to prepare oil-in-water Pickering nanoemulsions: either n-dodecane or squalane was added to an aqueous dispersion of nanoparticles, followed by high-shear homogenization and high-pressure microfluidization. The Pickering nature of such nanoemulsion droplets was confirmed via cryo-transmission electron microscopy (cryo-TEM). The long-term stability of such Pickering nanoemulsions was evaluated by analytical centrifugation over a four-week period. The n-dodecane droplets grew in size significantly faster than squalane droplets: this is attributed to the higher aqueous solubility of the former oil, which promotes Ostwald ripening. The effect of adding various amounts of squalane to the n-dodecane droplet phase prior to emulsification was also explored. The addition of up to 40% (v/v) squalane led to more stable nanoemulsions, as judged by analytical centrifugation. The nanoparticle adsorption efficiency at the n-dodecane-water interface was assessed by gel permeation chromatography when using nanoparticle concentrations of 4.0, 7.0, or 10% w/w. Increasing the nanoparticle concentration not only produced smaller droplets but also reduced the adsorption efficiency, as confirmed by TEM studies. Furthermore, the effect of varying the nanoparticle concentration (2.5, 5.0, or 10% w/w) on the long-term stability of n-dodecane-in-water Pickering nanoemulsions was explored over a four-week period. Nanoemulsions prepared at higher nanoparticle concentrations were more unstable and exhibited a faster rate of Ostwald ripening. The nanoparticle adsorption efficiency was monitored for an aging nanoemulsion prepared at a copolymer concentration of 2.5% w/w. As the droplets ripened over time, the adsorption efficiency remained constant (∼97%). This suggests that nanoparticles desorbed from the shrinking smaller droplets and then readsorbed onto larger droplets over time. Finally, the effect of temperature on the stability of Pickering nanoemulsions was examined. Storing these Pickering nanoemulsions at elevated temperatures led to faster rates of Ostwald ripening, as expected.

Tween 80-Based Self-Assembled Mixed Micelles Boost Valsartan Transdermal Delivery

Valsartan (Val) is an important antihypertensive medication with poor absorption and low oral bioavailability. These constraints are due to its poor solubility and dissolution rate. The purpose of this study was to optimize a mixed micelle system for the transdermal delivery of Val in order to improve its therapeutic performance by providing prolonged uniform drug levels while minimizing drug side effects. Thin-film hydration and micro-phase separation were used to produce Val-loaded mixed micelle systems. A variety of factors, including the surfactant type and drug-to-surfactant ratio, were optimized to produce micelles with a low size and high Val entrapment efficiency (EE). The size, polydispersity index (PDI), zeta potential, and drug EE of the prepared micelles were all measured. The in vitro drug release profiles were assessed using dialysis bags, and the permeation through abdominal rat skin was assessed using a Franz diffusion cell. All formulations had high EE levels exceeding 90% and low particle charges. The micellar sizes ranged from 107.6 to 191.7 nm, with average PDI values of 0.3. The in vitro release demonstrated a uniform slow rate that lasted one week with varying extents. F7 demonstrated a significant (p < 0.01) transdermal efflux of 68.84 ± 3.96 µg/cm2/h through rat skin when compared to the control. As a result, the enhancement factor was 16.57. In summary, Val-loaded mixed micelles were successfully prepared using two simple methods with high reproducibility, and extensive transdermal delivery was demonstrated in the absence of any aggressive skin-modifying enhancers.

Chitosan-Coated Azithromycin/Ciprofloxacin-Loaded Polycaprolactone Nanoparticles: A Characterization and Potency Study

Purpose

Antimicrobial resistance is a major health hazard worldwide. Combining azithromycin (AZ) and ciprofloxacin (CIP) in one drug delivery system was proposed to boost their antibacterial activity and overcome resistance. This study aims to improve azithromycin and ciprofloxacin activity by co-encapsulating them inside chitosan-coated polymeric nanoparticles and evaluating their antibacterial activity.

Methods

The double emulsion method was employed to co-encapsulate AZ/CIP inside chitosan-coated polymeric nanoparticles. The formulations were evaluated for their nanoparticle size, size distribution, and zeta potential. Differential scanning calorimetry (DSC) analysis characterized the formula's thermal sustainability. Encapsulation efficiency was measured by HPLC and spectrophotometric analysis. Morphological studies used the Transmission Electron Microscopy (TEM). The in vitro release profiles of both AZ and CIP were monitored utilizing the dialysis membrane bag method. The micro-dilution assay assessed the antimicrobial activity against a clinical isolate of Klebsiella pneumoniae.

Results

The prepared AZ/CIP-poly-caprolactone nanoparticles were spherical; their size range was 184.0 ± 3.3-190.4 ± 5.6 nm and had high size uniformity (poly-dispersity index below 0.2). The zeta potential ranged from -21.2 ± 2.4 to -27.0 ± 2.5 mV, while chitosan-coated nanoparticles showed a positive zeta potential value ranging from 8 to 11 mV. The thermal study confirmed the amorphous state of both antibiotics inside the nanoparticles. The results of the in vitro release study indicated a slow and uniform rate of release for both drugs extended over 4-days, with a faster rate in the case of AZ. The MIC values reported for both chitosan-coated NP have been tremendously reduced by at least 15 folds of pure CIP and more than 60 folds of pure AZ.

Conclusion

The co-encapsulation of AZ/CIP into chitosan-coated polymeric nanoparticles has been successfully achieved. The produced particles showed many beneficial attributes of uniform particle sizes below 200 nm and high zeta potential values. Chitosan-coated polymeric nanoparticles extensively enhanced the antibacterial activity of both AZ/CIP against bacteria.