Embedment of liposomes into chitosan physical hydrogel for the delayed release of antibiotics or anaesthetics, and its first ESEM characterization.

This work describes the characterization of an original liposomes/hydrogel assembly, and its application as a delayed-release system of antibiotics and anaesthetics. This system corresponds to drug-loaded liposomes entrapped within a chitosan (CS) physical hydrogel. To this end, a suspension of pre-formed 1,2-dipalmitoyl-sn-glycero-3-phosphocoline liposomes loaded with an antibiotic (rifampicin, RIF), an anaesthetic (lidocaine, LID), or a model fluorescent molecule (carboxyfluorescein, CF), was added to a CS solution. The CS gelation was subsequently carried out without any trace of chemical cross-linking agent or organic solvent in the final system. Liposomes within the resulting gelled CS matrix were characterized for the first time by environmental scanning electron microscopy. The release of drugs from the assembly was investigated by fluorescence or UV spectroscopy. The cumulative release profiles of RIF and LID (and also CF for comparison) were found to be lower from the "drug-in-liposomes-in-hydrogel" (DLH) assembly in comparison to "drug-in-hydrogel" (DH) system.

Self-crosslinked fibrous collagen/chitosan blends: Processing, properties evaluation and monitoring of degradation by bi-fluorescence imaging.

Porous collagen/chitosan scaffolds with different Collagen:Chitosan (Coll:Ch) ratios were prepared by freeze-drying followed by self-crosslinking via dehydrothermal treatment (DHT) and characterized as biomaterials for tissue engineering. Cy7 and Cy5.5 fluorochromes were covalently grafted to collagen and chitosan, respectively. Thus, it was possible, using optical fluorescence imaging of the two fluorochromes, to simultaneously track their in vivo biodegradation, in a blend scaffold form. The fluorescence signal evolution, due to the bioresorption, corroborated with histological analysis. In vitro cytocompatibility of Coll:Ch blend scaffolds were evaluated with standardized tests. In addition, the scaffolds showed a highly interconnected porous structure. Extent of crosslinking was analyzed by convergent analysis using thermogravimetry, Fourier Transform Infrared Spectroscopy and PBS uptake. The variations observed with these techniques indicate strong interactions between collagen and chitosan (covalent and hydrogen bonds) promoted by the DHT. The mechanical properties were characterized to elucidate the impact of the different processing steps in the sample preparation (DHT, neutralization and sterilization by ß-irradiation) and showed a robust processing scheme with low impact of Coll:Ch composition ratio.

Macro-hydrogels versus nanoparticles by the controlled assembly of polysaccharides.

The controlled assembly of oppositely charged chitosan (CS, Mw ∼ 33 × 10(3) to 600 × 10(3)g mol(-1)) and dextran sulfate (DS, Mw = 1.3 × 10(6)g mol(-1)) or heparin (HP, Mw = 1.8 × 10(4)g mol(-1)) led either to nanoparticles or macro-hydrogels, at room temperature. The control over the electrostatic attractive interactions was achieved using 2 mol L(-1) NaCl in the polyion solutions and subsequent dialysis to let the assembly occur. Macrohydrogels formed with an excess of polyanion. In the presence of an excess of polycation, colloidal gels were exclusively obtained. At salt concentrations lower than 1 mol L(-1), the spontaneous gelation provided macro-hydrogels, whatever the polyion in excess. Rheology measurements showed a similar elastic behaviour for CS-DS and CS-HP hydrogels, though CS-HP hydrogels appeared less cohesive. SAXS experiments revealed an aggregate morphology with internal and surface structure depending on the degree of acetylation (DA) of chitosan.

Controlling the complexation of polysaccharides into multi-functional colloidal assemblies for nanomedicine.

The controlled assembly of oppositely charged polysaccharides led to colloids stable in physiological media, capable of encapsulating a molecular drug and of sorbing proteins at their interface. Two types of particles were obtained: both chitosan-dextran sulfate (CS-DS) and chitosan-heparin (CS-HP) stable over 30 days in PBS at 25 and 37°C. At gastric pH 1.2, these particles remained stable over 3 days, enough for a stomach transit. The structural analysis by small angle X-ray scattering (SAXS) showed that CS-DS surface was semi-rough and chains inside particle exhibited rod-like conformation. Moreover, the particle interfaces could efficiently be functionalized with anti-OVA or anti-α4ß7 antibodies, in PBS, with the conservation of the antibody bioactivity over at least 8 days. Finally, during the assembly process, a molecular model drug, AMP, could be encapsulated with a loading efficiency up to 72% for CS-DS particles and 66% for CS-HP. All these data establish that the controlled assembly process under equilibrium conditions lead to colloids well suited for the targeted nanodelivery of drugs.