Processing-structure relationships of poly(ethylene glycol)-modified liposomes

Revealing cholesterol effects on PEGylated HSPC liposomes using AF4-MALS and simultaneous small- and wide-angle X-ray scattering

Liposome development is of great interest owing to increasing requirements for efficient drug carriers. The structural features and thermal stability of such liposomes are crucial in drug transport and delivery. Reported here are the results of the structural characterization of PEGylated liposomes via small- and wide-angle X-ray scattering and an asymmetric flow field-flow fractionation (AF4) system coupled with differential refractive-index detection, multi-angle light scattering (MALS) and dynamic light scattering. This integrated analysis of the exemplar PEGylated liposome formed from hydrogenated soy phosphatid-yl-choline (HSPC) with the addition of cholesterol reveals an average hydro-dynamic radius (R h) of 52 nm with 10% polydispersity, a comparable radius of gyration (R g) and a major liposome particle mass of 118 kDa. The local bilayer structure of the liposome is found to have asymmetric electronic density profiles in the inner and outer leaflets, sandwiched by two PEGylated outer layers ca 5 nm thick. Cholesterol was found to effectively intervene in lipid chain packing, resulting in the thickening of the liposome bilayer, an increase in the area per lipid and an increase in liposome size, especially in the fluid phase of the liposome. These cholesterol effects show signs of saturation at cholesterol concentrations above ca 1:5 cholesterol:lipid molar ratio.

Ultra-small angle neutron scattering to study droplet formation in polyelectrolyte complex coacervates

Associating soft matter such as surfactants, polymers, proteins, and liposomes, may form structures with dimensions not readily accessible by optical methods. Scattering methods can provide detailed information about the mechanism of associative phase separation including nucleation density, size, and shape. Ultra-small angle neutron scattering, a reciprocal space method, provides sensitivity to submicron to micron-scale structures in a non-invasive manner and described in the context of nucleation and growth of dilute droplets formed by a temperature jump into the meta-stable region of polyelectrolyte complex coacervates.

PEGylation and surface functionalization of liposomes containing drug nanocrystals for cell-targeted delivery

Liposomal formulations have important therapeutic applications in anti-cancer treatments but current formulations suffer from serious side effects, high dosage requirements and prolonged treatment. In this study, PEGylated azide-functionalized liposomes containing drug nanocrystals were investigated with the aim of increasing the drug payload and achieving functionalization for targeted delivery. Liposomes were characterized using cryogenic transmission electron microscopy (cryo-TEM), dynamic light scattering (DLS), small and ultra-small angle neutron scattering (SANS/USANS) and small and wide angle X-ray scattering (SAXS/WAXS). Cryo-TEM experiments revealed the dimensions of the nanocrystal-loaded liposomes and the change of shape from spherical to elongated after the formation of nanocrystals. Results from SANS/USANS experiments confirmed the asymmetric particle shape. SAXS/WAXS experiments confirmed that the crystalline drug only occurred in freeze-thawed samples and correlated with a new unidentified polymorphic form of ciprofloxacin. Using a small molecule dye, dibenzocyclooctyne (DBCO)-cy5, specific conjugation between DBCO groups and surface azide groups on the liposomes was confirmed; this indicates the promise of this system for tumour-targeted delivery.

Poly-phosphocholinated Liposomes Form Stable Superlubrication Vectors

We have prepared phosphatidylcholine (PC) vesicles (liposomes) incorporating a novel lipid/poly-phosphocholine conjugate. This both stabilizes the liposomes against aggregation (for example, during storage or when being delivered) and allows them to act as very efficient lubricating elements readily attaining superlubric performance (defined as coefficient of friction μ < 10^-2) via hydration lubrication at physiological salt concentrations and pressures. In contrast, vesicles sterically protected by poly(ethylene glycol) chains (PEGylation), which is the general method of choice, while being equally stable to aggregation are much poorer lubricants under these conditions, which is attributed to the relatively poor hydration of the PEG. Our approach enables the use of PC liposomes as stable superlubrication vectors in potential biomedical applications.

Fabrication and Characterization of Hybrid Stealth Liposomes

Next-generation liposome systems for anticancer and therapeutic delivery require the precise insertion of stabilizing polymers and targeting ligands. Many of these functional macromolecules may be lost to micellization as a competing self-assembly landscape. Here, hybrid stealth liposomes, which utilize novel cholesteryl-functionalized block copolymers as the molecular stabilizer, are explored as a scalable platform to address this limitation. The employed block copolymers offer resistance to micellization through multiple liposome insertion moieties per molecule. A combination of thermodynamic and structural investigations for a series of hybrid stealth liposome systems suggests that a critical number of cholesteryl moieties per molecule defines whether the copolymer will or will not insert into the liposome bilayer. Colloidal stability of formed hybrid stealth liposomes further corroborates the critical copolymer architecture value.