Cryo-field emission scanning electron microscopy imaging of a rigid surfactant mesophase

Lyotropic liquid crystals for parenteral drug delivery

The necessity for long-term treatments of chronic diseases has encouraged the development of novel long-acting parenteral formulations intending to improve drug pharmacokinetics and therapeutic efficacy. Lately, one of the novel approaches has been developed based on lipid-based liquid crystals. The lyotropic liquid crystal (LLC) systems consist of amphiphilic molecules and are formed in presence of solvents with the most common types being cubic, hexagonal and lamellar mesophases. LC injectables have been recently developed based on polar lipids that spontaneously form liquid crystal nanoparticles in aqueous tissue environments to create the in-situ long-acting sustained-release depot to provide treatment efficacy over extended periods. In this manuscript, we have consolidated and summarized the various type of liquid crystals, recent formulation advancements, analytical evaluation, and therapeutic application of lyotropic liquid crystals in the field of parenteral sustained release drug delivery.

Formation of Self-Assembled Mesophases During Lipid Digestion

Lipids play an important role in regulating bodily functions and providing a source of energy. Lipids enter the body primarily in the form of triglycerides in our diet. The gastrointestinal digestion of certain types of lipids has been shown to promote the self-assembly of lipid digestion products into highly ordered colloidal structures. The formation of these ordered colloidal structures, which often possess well-recognized liquid crystalline morphologies (or “mesophases”), is currently understood to impact the way nutrients are transported in the gut and absorbed. The formation of these liquid crystalline structures has also been of interest within the field of drug delivery, as it enables the encapsulation or solubilization of poorly water-soluble drugs in the aqueous environment of the gut enabling a means of absorption. This review summarizes the evidence for structure formation during the digestion of different lipid systems associated with foods, the techniques used to characterize them and provides areas of focus for advancing our understanding of this emerging field.

Liquid crystal delivery of ciprofloxacin to treat infections of the female reproductive tract

Infections of the female reproductive tract are a major cause of morbidity and mortality in humans, requiring significant investment to sustain treatment and representing a major challenge to health. The increasing prevalence of bacterial resistance, and an almost complete absence of new antibiotic therapies for the past five decades, mean there is a desperate need for novel approaches to the treatment of bacterial infections. Within the present study, we demonstrate the effective ex vivo treatment of bacterial infection of the female reproductive tract using a controlled-release, liquid crystal-based platform. Liquid crystal encapsulation of ciprofloxacin significantly enhanced its bactericidal efficacy and reduced cell toxicity. Liquid crystal structures are low-cost, simple to manufacture and provide a sustained-release profile of encapsulated ciprofloxacin. Treatment of Escherichia coli infected reproductive tract epithelial cells and whole organ cultures with liquid crystal encapsulated ciprofloxacin proved to be an effective strategy for reducing bacterial load and reproductive tract inflammatory responses to infection. These data suggest that such an approach could provide an efficacious treatment modality for enhancing the effectiveness of current antibiotic therapies.

Colloidal aspects of dispersion and digestion of self-dispersing lipid-based formulations for poorly water-soluble drugs

Self-dispersing lipid-based formulations, particularly self-microemulsifying drug delivery systems (SMEDDS) have gained an increased interest in recent times as a means to enhance the oral bioavailability of poorly water-soluble lipophilic drugs. Upon dilution, SMEDDS self-emulsify in an aqueous fluid and usually form a kinetically stable oil-in-water emulsion or in some rare cases a true thermodynamically stable microemulsion. The digestion of the formulation leads to the production of amphiphilic digestion products that interact with endogenous amphiphilic components and form self-assembled colloidal phases in the aqueous environment of the intestine. The formed colloidal phases play a pivotal role in maintaining the lipophilic drug in the solubilised state during gastrointestinal transit prior to absorption. Thus, this review describes the structural characterisation techniques employed for SMEDDS and the recent literature studies that elucidated the colloidal aspects during dispersion and digestion of SMEDDS and solid SMEDDS. Possible future studies are proposed to gain better understanding on the colloidal aspects of SMEDDS and solid SMEDDS.

Shear-Induced Transformation of Polymer-Rich Lamellar Phases to Micron-Sized Vesicles

In the present work, we study the shear-induced transformation of polymer-rich lamellar phases into vesicles. The evolution of vesicle size is studied by different scattering techniques, rheology, and microscopy methods. The lamellar phase found in the system D₂O/ o-xylene/ Pluronic PE9400/C₈TAB can be fully transformed to multilamellar vesicles (MLVs) by applying shear. The size of the MLVs is proportional to the inverse square root of the shear rate. Hence, the polymer-based quaternary system behaves similar to lamellar phases based on small surfactant molecules. Additionally, we found a growth effect leading to a size increase of the vesicles after shearing was stopped.

Microstructural characteristics of surfactant assembly into a gel-like mesophase for application as an oil spill dispersant

HYPOTHESIS

Polyoxyethylene (20) sorbitan monooleate (Tween 80) can be incorporated into the gel-like phase formed by L-α-phosphatidylcholine (PC) and dioctyl sulfosuccinate sodium salt (DOSS) for potential application as a gel-like dispersant for oil spill treatment. Such gel-like dispersants offer advantages over existing liquid dispersants for mitigating oil spill impacts.

EXPERIMENTS

Crude oil-in-saline water emulsions stabilized by the surfactant system were characterized by optical microscopy and turbidity measurements while interfacial tensions were measured by the spinning drop and pendant drop techniques. The microstructure of the gel-like surfactant mesophase was elucidated using small angle neutron scattering (SANS), cryo scanning electron microscopy (cryo-SEM), and ³¹P nuclear magnetic resonance (NMR) spectroscopy.

FINDINGS

The gel-like phase consisting of PC, DOSS and Tween 80 is positively buoyant on water and breaks down on contact with floating crude oil layers to release the surfactant components. The surfactant mixture effectively lowers the crude oil-saline water interfacial tension to the 10^-2 mN/m range, producing stable crude oil-in-saline water emulsions with an average droplet size of about 7.81 µm. Analysis of SANS, cryo-SEM and NMR spectroscopy data reveals that the gel-like mesophase has a lamellar microstructure that transition from rolled lamellar sheets to onion-like, multilamellar structures with increasing Tween 80 content.

Self-assembled structures formed during lipid digestion: characterization and implications for oral lipid-based drug delivery systems

There is increasing interest in the use of lipid-based formulations for the delivery of poorly water-soluble drugs. After ingestion of the formulation, exposure to the gastrointestinal environment results in dispersion and digestion processes, leading to the production of amphiphilic digestion products that form self-assembled structures in the aqueous environment of the intestine. These structures are crucial for the maintenance of drug in a solubilized state prior to absorption. This review describes the structural techniques used to study such systems, the structures formed in assembled 'equilibrium' compositions where components are combined in expected ratios representative of the endpoint of digestion, structures formed using dynamic in vitro 'non-equilibrium' digestion models where the composition and hence structures present change over time and observations from ex vivo aspirated samples. Possible future directions towards an improved understanding of the structural aspects of lipid digestion are proposed.

Understanding nanoparticle cellular entry: A physicochemical perspective

Understanding interactions between nanoparticles (NPs) with biological matter, particularly cells, is becoming increasingly important due to their growing application in medicine and materials, and consequent biological and environmental exposure. For NPs to be utilised to their full potential, it is important to correlate their functional characteristics with their physical properties, which may also be used to predict any adverse cellular responses. A key mechanism for NPs to impart toxicity is to gain cellular entry directly. Many parameters affect the behaviour of nanomaterials in a cellular environment particularly their interactions with cell membranes, including their size, shape and surface chemistry as well as factors such as the cell type, location and external environment (e.g. other surrounding materials, temperature, pH and pressure). Aside from in vitro and in vivo experiments, model cell membrane systems have been used in both computer simulations and physicochemical experiments to elucidate the mechanisms for NP cellular entry. Here we present a brief overview of the effects of NPs physical parameters on their cellular uptake, with focuses on 1) related research using model membrane systems and physicochemical methodologies; and 2) proposed physical mechanisms for NP cellular entrance, with implications to their nanotoxicity. We conclude with a suggestion that the energetic process of NP cellular entry can be evaluated by studying the effects of NPs on lipid mesophase transitions, as the molecular deformations and thus the elastic energy cost are analogous between such transitions and endocytosis. This presents an opportunity for contributions to understanding nanotoxicity from a physicochemical perspective.

Polyglycerol fatty acid ester surfactant-based microemulsions for targeted delivery of ceramide AP into the stratum corneum: formulation, characterisation, in vitro release and penetration investigation

Ceramide AP (CER [AP]) is an integral component of the stratum corneum (SC) lipid matrix and is capable of forming tough and super stable lamellae. It may help to restore the barrier function in aged and affected skin. However, its effectiveness from conventional dosage forms is limited due to its poor solubility and penetration into the SC. Therefore, stable polyglycerol fatty acid ester surfactant (SAA)-based CER [AP] microemulsions (MEs) were formulated and characterised to enhance its solubilisation and penetration into the SC. TEGO® CARE PL 4 (TCPL4: polyglycerol-4-laurate), isopropyl palmitate (IPP) and water-1, 2 pentandiol (PeG) were used as amphiphilic, oily and hydrophilic components, respectively. The effects of HYDRIOL® PGMO.4 (HPGMO4: polyglyceryl-4-oleate) as a co-surfactant (co-SAA) and linoleic acid (Lin A) as part of the oil component on the stability and characteristics of the MEs were investigated. EPR results were used for the first time to reveal MEs nanostructures. The release and penetration behaviour of the MEs was assessed in vitro by using a multi-layer membrane model. The results obtained showed that HPGMO4 and Lin A increased stability and expanded the ME region considerably. The formulations were stable for 10 to >24 months. Dynamic light scattering (DLS) results showed that the droplets were bigger and asymmetric, which might be helpful to localise the CER into the upper layers of the epidermis. Release and penetration from the MEs was superior as compared to the hydrophilic cream (DAB). The rate and extent of CER [AP] released and penetrated from O/W MEs was better than W/O MEs.

Morphological transformations in a dually thermoresponsive coil-rod-coil bioconjugate

We report the conformational and assembly behavior of a thermoresponsive triblock biohybrid conjugate under aqueous conditions. The triblock comprises of poly(diethylene glycol methyl ether methacrylate) (PDEGMEMA) conjugated to the ends of a triple-helix forming collagen-like peptide. The circular dichroism (CD) experiment confirms the ability of the collagen-like peptide middle block to assemble as a triple helix in the hybrid conjugate. Above the LCST (~35 °C), the collapse of the thermoresponsive PDEGMEMA polymer at the ends of the peptide domain resulted in a concomitant increase in the conformational stability of the peptide domain towards thermal denaturation. Upon cooling back, the kinetic conformational refolding behavior was still observed for the peptide domain in the hybrid conjugate. Static light scattering (SLS) experiments suggested the formation of supramolecular structures upon increasing solution temperatures to above the LCST. The scattering intensity increased with increasing temperature, until at 75 °C then it was found to decrease. Cryogenic scanning electron microscopy and regular transmission electron microscopy suggested the formation of spherical aggregates that increased in size with increasing temperature up to 65 °C and a morphological transformation into fibrils was also observed at 75 °C. The synergistic effect of dual thermoresponsive behavior from the peptide and the polymer block in the triblock hybrid is suggested for the observed conformational and assembly behaviors.

Structural rearrangements and interaction within H(II) mesophase induced by cosolubilization of vitamin E and ascorbic acid

We investigated the effect of ascorbic acid (AA) cosolubilized with vitamin E (VE) on reverse hexagonal (H(II)) mesophase. The H(II) phase comprises monoolein (GMO)/d-alpha-tocopherol (VE) in a ratio of 90/10 by weight and 12.5 wt % water. The macrostructural characteristics of this system were determined by polarized light microscopy and small-angle X-ray scattering measurements. We used differential scanning calorimetry and attenuated total reflectance Fourier transform infrared to characterize the microstructure, the vibration of the functional groups, and the location of the AA guest molecule. AA was incorporated to the system in two steps: 1-4 wt % AA and 5-6 wt % AA. We compared this system to one containing tricaprylin as the oil phase, as previously reported. These measurements revealed that AA is localized first in the water rich-core and in the interface, and acts as a chaotropic molecule that decreases the water melting point. When a larger quantity of AA (5-6 wt %) is added, the system is saturated, and the AA is located in the inner cylinder and manifested by more moderate distortion. The addition of AA also causes alteration in the behavior of the GMO hydrocarbon chains and makes them more flexible. Further addition of AA caused the GMO hydrocarbon chain to be more solvated by the VE hydrocarbon chain and enabled additional migration of VE; hence a decrease in the hydrophobic melting temperature occurred (similar to tricaprylin). Increasing the amount of AA weakened the bonding between the GMO and water and created new bonds between AA and GMO and AA with water.

Shear induced formation of patterned porous titania with applications to photocatalysis

Patterned macroporous titania (TiO2) materials have been synthesized via a shear-aligned rigid crystalline surfactant mesophase. The macropores inherit the hexagonal geometry of the water channels of the template. Scanning electron microscopy (SEM) and cut-section transmission electron microscopy (TEM) images show that the macropores templated by the sheared mesophase attain considerably greater alignment than pores templated by the nonsheared mesophase. The mean pore diameter, the crystalline size of TiO2 particles, and the photoactivity of the materials increase with the increase of water content in the template. The sheared TiO2 samples exhibit higher photocatalytic activity for the degradation of Rhodamine B than the corresponding materials synthesized in the nonsheared template. The improvement in photocatalytic activity of the sheared TiO2 materials is attributed to its higher photoabsorption efficiency and the patterned channels which facilitate the diffusion and transport of reactant molecules within the frameworks. Such patterned porous materials may have promise as advanced catalytic supports and photocatalytic materials.