Barbara Bellich

Chitosan nanoparticles: preparation, size evolution and stability.

PURPOSE Characterisation of chitosan-tripolyphosphate nanoparticles is presented with the aim of correlating particle shape and morphology, size distribution, surface chemistry, and production automatisation with preparation procedure, chitosan molecular weight and loaded protein. METHODS Nanoparticles were prepared by adding drop wise a tripolyphosphate-pentasodium solution to chitosan solutions under stirring. Trehalose, mannitol and polyethylene-glycol as bioprotectants were used to prevent particle aggregation and to reduce mechanical stress during freezing and drying processes. RESULTS As a novel result, time evolution of the particle size distribution curve showed the presence of a bimodal population composed of a fraction of small particles and of a second fraction of larger particles attributed to the rearrangement of particles after the addition of tripolyphosphate. Storage for 4 weeks resulted in a slight increase in average size, due to the continuous rearrangement of small particles. Improvement of nanoparticle stability after lyophilisation and spray-drying was observed in the presence of all bioprotectants. Trehalose was the best protectant for both methods. Finally, in vivo tests using chick embryos assessed the biocompatibility of chitosan, tripolyphosphate and the nanoparticles. CONCLUSION The simple ionotropic gelation method with low-MW chitosan was effective in achieving reproducible nanoparticles with the desired physico-chemical and safety characteristics.

Microwave generated solid dispersions containing Ibuprofen.

The purpose of this study was to apply the attractive technique of the microwaves irradiation (MW) for the preparation of solvent-free solid dispersions (SD). In particular, the microwave technology has been considered in order to prepare an enhanced release dosage form for the poorly soluble drug Ibuprofen (IBU), employing PVP/VA 60/40 (PVP/VA 64) and hydroxypropyl-beta-cyclodextrin (HP-beta-CD) as hydrophilic carriers. Their physico-chemical characteristics and dissolution properties were compared to the corresponding physical mixtures and the drug alone. The results of physico-chemical characterization attested a correspondence of the solid state of the drug before and after irradiation treatment and that an amorphous form of the drug was obtained. This result, together with the presence of the hydrophilic polymers determined a remarkable enhancement of the in vitro dissolution rate of the drug suggesting that the microwave technique could be considered as a new and interesting method to prepare drug-polymer systems.

“The Good, the Bad and the Ugly” of Chitosans

The objective of this paper is to emphasize the fact that while consistent interest has been paid to the industrial use of chitosan, minor attention has been devoted to spread the knowledge of a good characterization of its physico-chemical properties. Therefore, the paper attempts to critically comment on the conflicting experimental results, highlighting the facts, the myths and the controversies. The goal is to indicate how to take advantage of chitosan versatility, to learn how to manage its variability and show how to properly tackle some unexpected undesirable features. In the sections of the paper various issues that relate chitosan properties to some basic features and to advanced solutions and applications are presented. The introduction outlines some historical pioneering works, where the chemistry of chitosan was originally explored. Thereafter, particular reference is made to analytical purity, characterization and chain modifications. The macromolecular characterization is mostly related to molecular weight and to degree of acetylation, but also refers to the conformational and rheological properties and solution stability. Then, the antimicrobial activity of chitosan in relation with its solubility is reviewed. A section is dedicated to the formulation of chitosan biomaterials, from gel to nanobeads, exploring their innovative application as active carrier nanoparticles. Finally, the toxicity issue of chitosan as a polymer and as a constructed nanomaterial is briefly commented in the conclusions.

Marine Polysaccharides in Microencapsulation and Application to Aquaculture: “From Sea to Sea”

This reviews main objective is to discuss some physico-chemical features of polysaccharides as intrinsic determinants for the supramolecular structures that can efficiently provide encapsulation of drugs and other biological entities. Thus, the general characteristics of some basic polysaccharides are outlined in terms of their conformational, dynamic and thermodynamic properties. The analysis of some polysaccharide gelling properties is also provided, including the peculiarity of the charged polysaccharides. Then, the way the basic physical chemistry of polymer self-assembly is made in practice through the laboratory methods is highlighted. A description of the several literature procedures used to influence molecular interactions into the macroscopic goal of the encapsulation is given with an attempt at classification. Finally, a practical case study of specific interest, the use of marine polysaccharide matrices for encapsulation of vaccines in aquaculture, is reported.

Chitosan-pectin hybrid nanoparticles prepared by coating and blending techniques.

The preparation of chitosan nanoparticles in combination with pectins, as additional mucoadhesive biopolymers, was investigated. Pectins from apple and from citrus fruit were considered; polygalacturonic acid was taken as a reference. Tripolyphosphate was used as an anionic cross-linker. Two different techniques were compared, namely the coating and the blending. Coated nanoparticles (NPs) in the ratio pectin:NPs from 2:1 to 5:1 evidenced that the size of NPs increased as the amount of pectin (both from apple and citrus fruit) was increased. In particular, for NPs coated with pectin from citrus fruit the size ranges from 200 to 260nm; while for NPs coated with pectin from apple the size ranges from 330 to 450nm. A minimum value of Z-potential around -35mV was obtained for the ratio pectin:NPs 4:1, while further addition of pectin did not decrease the Z-potential. Also blended NPs showed a dependence of the size on the ratio of the components: for a given ratio pectin:tripolyphosphate the size increases as the fraction of chitosan increases; for a low ratio chitosan:pectin a high amount of tripolyphosphate was needed to obtain a compact structure. The effect of the additional presence of loaded proteins in chitosan-pectin nanoparticles was also investigated, since proteins contribute to alter the electrostatic interactions among charged species. FT-IR and DSC characterization are presented to confirm the interactions between biopolymers. Finally, the biocompatibility of the used materials was assessed by the chorioallantoic membrane assay, confirming the safety of the materials.

Biophysical functionality in polysaccharides: from Lego-blocks to nano-particles

The objective of the paper is to show the very important biophysical concepts that have been developed with polysaccharides. In particular, an attempt will be made to relate “a posteriori” the fundamental aspects, both experimental and theoretical, with some industrial applications of polysaccharide-based materials. The overview of chain conformational aspects includes relationships between topological features and local dynamics, exemplified for some naturally occurring carbohydrate polymers. Thus, by using simulation techniques and computational studies, the physicochemical properties of aqueous solutions of polysaccharides are interpreted. The relevance of conformational disorder–order transitions, chain aggregation, and phase separation to the underlying role of the ionic contribution to these processes is discussed. We stress the importance of combining information from analysis of experimental data with that from statistical–thermodynamic models for understanding the conformation, size, and functional stability of industrially important polysaccharides. The peculiar properties of polysaccharides in industrial applications are summarized for the particularly important example of nanoparticles production, a field of growing relevance and scientific interest.

Myelography iodinated contrast media. 2. Conformational versatility of iopamidol in the solid state

The phenomenon of polymorphism is of great relevance in pharmaceutics, since different polymorphs have different physicochemical properties, e.g., solubility, hence, bioavailability. Coupling diffractometric and spectroscopic experiments with thermodynamic analysis and computational work opens to a methodological approach which provides information on both structure and dynamics in the solid as well as in solution. The present work reports on the conformational changes in crystalline iopamidol, which is characterized by atropisomerism, a phenomenon that influences both the solution properties and the distinct crystal phases. The conformation of iopamidol is discussed for three different crystal phases. In the anhydrous and monohydrate crystal forms, iopamidol molecules display a syn conformation of the long branches stemming out from the triiodobenzene ring, while in the pentahydrate phase the anti conformation is found. IR and Raman spectroscopic studies carried out on the three crystal forms, jointly with quantum chemical computations, revealed that the markedly different spectral features can be specifically attributed to the different molecular conformations. Our results on the conformational versatility of iopamidol in different crystalline phases, linking structural and spectroscopic evidence for the solution state and the solid forms, provide a definite protocol for grasping the signals that can be taken as conformational markers. This is the first step for understanding the crystallization mechanism occurring in supersaturated solution of iopamidol molecules.

Physico-chemical properties of aqueous drug solutions: From the basic thermodynamics to the advanced experimental and simulation results

The physical chemical properties of aqueous solutions of model compounds are illustrated in relation to hydration and solubility issues by using three perspectives: thermodynamic, spectroscopic and molecular dynamics simulations. The thermodynamic survey of the fundamental backgrounds of concentration dependence and experimental solubility results show some peculiar behavior of aqueous solutions with several types of similar solutes. Secondly, the use of a variety of experimental spectroscopic devices, operating under different experimental conditions of dimension and frequency, has produced a large amount of structural and dynamic data on aqueous solutions showing the richness of the information produced, depending on where and how the experiment is carried out. Finally, the use of molecular dynamics computational work is presented to highlight how the different types of solute functional groups and surface topologies organize adjacent water molecules differently. The highly valuable contribution of computer simulation studies in providing molecular explanations for experimental deductions, either of a thermodynamic or spectroscopic nature, is shown to have changed the current knowledge of many aqueous solution processes. While this paper is intended to provide a collective view on the latest literature results, still the presentation aims at a tutorial explanation of the potentials of the three methodologies in the field of aqueous solutions of pharmaceutical molecules.

Cell biothermodynamics: Can calorimetry dynamically monitor cytoplasmic water activity?

In this study, the isothermal dehydration of some biological substrates, i.e., cell monolayer, has been explored as an extension of the novel application of DSC for monitoring the dehydration changes in aqueous films of polysaccharide solutions and gels. Here we assess the possible correlation of the experimental calorimetric signal (heat flow) and changes in the water binding state using unperturbed or stressed cells as treated using hypotonic solutions or AgNO3 as aquaporin inhibitors. The experiments on unperturbed and stressed cells show the requirement for a proper setup in order to obtain reproducibility to highlight the cell dehydration patterns. The preliminary results and the analysis of the calorimetric curves proved the feasibility of the described measurements on cellular substrates and revealed a good sensitivity of the experimental response on the specific features of the system and on its actual hydration state.