Maria Marlow

Surface modification of microspheres with steric stabilizing and cationic polymers for gene delivery.

In this paper, we describe surface modification of poly( D,L-lactide- co-glycolide) (PLG) microspheres, intended for DNA vaccine application, with two functionalities: a steric stabilizing component, provided by poly(vinyl alcohol) (PVA) and a cationic component, aimed at subsequent DNA surface loading. The cationic functionality arises from polycations, such as PEI, poly( L-lysine), trimethyl chitosan, and (dimethylamino)ethyl methacrylate, introduced into the water phase of classical oil-in-water (o/w) solvent evaporation method of PLG microsphere fabrication. By systematic evaluation of production variables, a system was produced with balanced properties in terms of microsphere size appropriate for uptake by antigen presenting (e.g., dendritic) cells, colloidal stability, and relatively high DNA loading. The polycation (PEI) molecular weight and preparation concentration were both found to increase the surface polycation content and DNA binding capacity; however, they lead to an increased tendency for aggregation, particularly when the microsphere size was decreased. DNA loading of almost 100% efficiency was achieved under optimized conditions in physiologically acceptable buffers, resulting in a surface DNA loading appropriate for vaccine purposes. A further increase in surface DNA loading was however associated with an increase in the particles negative potential, indicating the surface presence of DNA charges not neutralized by the polycation and hence potentially not protected from in vivo enzymatic degradation. The internalization of surface-loaded DNA into the target cells was confirmed by monitoring fluorescent DNA after the microspheres were endocytosed by the cells in culture.

Formation of fluorinated nonionic surfactant microemulsions in hydrofluorocarbon 134a (HFC 134a)

A structurally related series of fluorinated nonionic oxyethylene glycol surfactants of the type C(m)F(2m+1)(CH(2))(n)O[(CH(2)CH(2)O)(p)H], denoted C(m.n)E(p) (where m=4, 6, or 7, m=1 or 2, and p=4 or 6) were synthesized and their surface behavior in aqueous solution was characterized. The ability of these surfactants to form water-in-hydrofluorocarbon (HFC) propellant 134a microemulsions suitable for use in the aerosolized delivery of water-soluble drugs has been investigated. Phase studies showed that, regardless of the composition used, clear one-phase systems could not be prepared if a fluorinated nonionic surfactant was used alone, or in combination with a short or medium fluorocarbon alcohol cosurfactant. Clear one-phase systems could, however, be prepared if a short-chain hydrocarbon alcohol, such as ethanol, n-propanol, or n-pentanol, was used as cosurfactant, with the extent of the one-phase region increasing with decreased chain length of the alcohol cosurfactant. Light-scattering studies on a number of the hydrocarbon-alcoholcontaining systems in the propellant-rich part of the phase diagram showed that only systems prepared with C(4.2)E(6) and propanol contained microemulsion droplets (all other systems investigated were considered to be cosolvent systems).

A quantitative assessment of inhaled drug particle-pulmonary surfactant interaction by atomic force microscopy

To date limited consideration has been given to the physical interaction between inhaled drug particles and pulmonary surfactant (PS). This study combines atomic force microscopy (AFM) with a Langmuir-Blodgett (LB) approach to quantify the force of adhesion between micronised budesonide particles and simulated PS monolayers. A LB approach was used to prepare Survanta monolayers at pre-determined surface pressures and AFM was employed to facilitate their visualisation. Adhesion measurements between drug particles and PS monolayers were executed via AFM. Contact angle measurements were performed to probe material wetting characteristics, the data confirmed that budesonide is hydrophobic and Survanta films at increasing surface pressure exhibit a rising hydrophobic character. AFM revealed that PS properties were governed by applied surface pressure and that the degree of interaction of budesonide was greater at higher surface pressure, where packing of the lipid film was increased; consistent with the point of exhalation. This correlates well with the accepted inhaler technique. The increasing hydrophobicity of the PS film, on increased pressure, was believed to be the primary reason for increased interaction with the hydrophobic budesonide. Surface chemistries of the drug particles and PS interface are considered to be important for inhaled drug delivery.

Gelation properties of self-assembling N-acyl modified cytidine derivatives

In this study we report the synthesis of new cytidine derived gelators possessing acyl chains of different lengths. These low molecular weight gelators were shown to form self-supporting gels at 0.5% (w/v) in binary systems of aqueous miscible polar organic solvent and water. The representative gels were studied using rheology and their fibrillar structure confirmed by TEM imaging and FTIR. We further demonstrated the use of these gels as potential drug delivery platforms by monitoring release characteristics of both high and low molecular weight fluorescently labelled tracers.

Fluorinated ionic surfactant microemulsions in hydrofluorocarbon 134a (HFC 134a).

The factors influencing the formation of water-in-134a-propellant microemulsions using the fluorinated ionic surfactants ammonium perfluorooctanoate, ammonium perfluoroheptanoate, and sodium perfluorooctanoate has been determined. None of the fluorinated ionic surfactants could be used to prepare clear, one-phase systems when used as sole surfactant, but they could be when combined with a short-chain fluoro- or hydrocarbon alcohol in surfactant:cosurfactant weight-mixing ratios (K(m)) in the range 1:2 to 2:1. When hydrocarbon alcohols were used this clear region extended over a wide range of compositions and was confirmed by means of photon correlation spectroscopy (PCS) to contain microemulsion droplets in the propellant-rich part of the phase diagram. PCS studies performed in the presence of the water-soluble drug terbutaline sulfate showed that it was possible to solubilize the drug within water-in-propellant microemulsion droplets. These studies confirm for the first time that it is possible to prepare water-in-propellant 134a microemulsions using fluorinated ionic surfactants and to solubilize water-soluble drugs within these systems.

Chain length affects pancreatic lipase activity and the extent and pH-time profile of triglyceride lipolysis.

Triglycerides (TG) are one of the most common excipients used in oral lipid-based formulations. The chain length of the TG plays an important role in the oral bioavailability of the co-administered drug. Fatty acid (FA) chain-length specificity of porcine pancreatic lipase was studied by means of an in vitro lipolysis model under bio-relevant conditions at pH 6.80. In order to determine the total extent of lipolysis, back-titration experiments at pH 11.50 were performed. Results suggest that there is a specific chain length range (C2-C8) for which pancreatic lipase shows higher activity. This specificity could result from a combination of physicochemical properties of TGs, 2-monoglycerides (2-MGs) and FAs, namely the droplet size of the TGs, the solubility of 2-MGs within mixed micelles, and the relative stability of the FAs as leaving groups in the hydrolysis reaction. During experimentation, it was evident that an optimisation of lipolysis conditions was needed for tighter control over pH levels so as to better mimic in vivo conditions. 1M NaOH, 3.5 mL/min maximum dosing rate, and 3 μL/min minimum dosing rate were the optimised set of conditions that allowed better pH control, as well as the differentiation of the lipolysis of different lipid loads.

Macroporous surface modified microparticles

Novel macroporous and surface functionalized polymeric microparticles were prepared using a modified emulsion technique. The microparticles were able to surface load DNA and have a range of potential applications in drug delivery of biologics and tissue engineering.

Surface-directed modulation of supramolecular gel properties

Supramolecular materials are widely studied and used for a variety of applications; in most applications, these materials are in contact with surfaces of other materials. Whilst much focus has been placed on elucidating factors that affect supramolecular material properties, the influence of the material surface on gel formation is poorly characterised. Here, we demonstrate that surface properties directly affect the fibre architecture and mechanical properties of self-assembled cytidine based gel films.

Self-assembling benzothiazole-based gelators: a mechanistic understanding of in vitro bioactivation and gelation

Low molecular weight gelators (LMWGs) of chemotherapeutic drugs represent a valid alternative to the existing polymer-based formulations used for targeted delivery of anticancer drugs. Herein we report the design and development of novel self-assembling gelators of the antitumor benzothiazole 5F 203 (1). Two different types of derivatives of 1 were synthesized, formed by an amide (2) and a carbamate (3a-3d) linker, respectively, which showed potent in vitro antitumor activity against MCF-7 mammary and IGROV-1 ovarian carcinoma cells. In contrast, MRC-5 fibroblasts were inherently resistant to the above derivatives (GI50 > 10 μM), thus revealing stark selectivity against the malignant cell lines over the nontransformed fibroblasts. Western blots assays demonstrated induction of CYP1A1 by 1 and its derivatives only in sensitive malignant cells (MCF-7), corroborating conservation of a CYP1A1-mediated mechanism of action. The ability to form stable gels under relatively high strains was supported by rheological tests; in addition, their inner morphology was characterized as possessing a crossed-linked nanostructure, with the formation of thick aggregates with variable widths between 1100 and 400 nm and lengths from 8 to 32 μm. Finally, in vitro dissolution studies proved the ability of hydrogel 2 to release 48% of 2 within 80 h, therefore demonstrating its ability to act as a platform for localized delivery.

Surface-Mediated Supramolecular Self-assembly of Protein, Peptide and Nucleoside Derivatives: From Surface Design to Underlying Mechanism and Tailored Functions

Among the many parameters that have been explored to exercise control over self-assembly processes, the influence of surface properties on self-assembly has been recognized as important but has received considerably less attention than other factors. This is particularly true for biomolecule-derived self-assembling molecules such as protein, peptide, and nucleobase derivatives. Because of their relevance to biomaterial and drug delivery applications, interest in these materials is increasing. As the formation of supramolecular structures from these biomolecule derivatives inevitably brings them into contact with the surfaces of surrounding materials, understanding and controlling the impact of the properties of these surfaces on the self-assembly process are important. In this feature article, we present an overview of the different surface parameters that have been used and studied for the direction of the self-assembly of protein, peptide, and nucleoside-based molecules. The current mechanistic understanding of these processes will be discussed, and potential applications of surface-mediated self-assembly will be outlined.