Jean-Luc Six

Biodegradable nanoparticles made from polylactide-grafted dextran copolymers

Polysaccharide-covered polyester nanoparticles were prepared using the emulsion/solvent evaporation process. The core of the nanoparticles was made either of PLA or of a blend of polylactide and polylactide-grafted dextran copolymer in various proportions. The surface of the nanoparticles was covered by dextran chains via the use of water-soluble polylactide-grafted dextrans as polymeric stabilizers during the emulsification step. The characteristics of the nanoparticles (size, surface coverage, thickness of superficial layer, colloidal stability) were correlated to the structural parameters (length and number of polylactide grafts) of the copolymers as well as to their surface active properties. The complete biodegradability of the nanoparticles was evaluated by considering the rate of hydrolysis of polylactide grafts in phosphate buffer and the rate of enzymatic degradation of dextran backbone by dextranase.

Physicochemical evaluation of PLA nanoparticles stabilized by water-soluble MPEO-PLA block copolymers.

Different water-soluble MPEO-PLA diblock copolymers with various alpha-methoxy-omega-hydroxyl polyethylene (MPEO) and poly(lactic acid) (PLA) block lengths have been synthesized. Their surface-active properties were evidenced by surface tension (water/air) measurements. In each case the surface tension leveled down above a critical polymer concentration, which was attributed to the formation of a dense polymer layer at the liquid-air interface. The applicability of copolymers as emulsion stabilizers in the preparation of PLA nanospheres by an o/w emulsion/evaporation technique was then investigated. Four copolymers presenting sufficient water solubility and good surfactive properties were used to prepare PLA nanospheres with MPEO chains firmly anchored at the particle surface. The effect of polymer concentration in emulsion on particle size and surface coverage was examined. Whatever the copolymer characteristics, it was found that the optimal concentration to obtain a large amount of MPEO at the particle surface was similar (around 2 g/l). The effect of the copolymer composition on MPEO layer characteristics and on colloidal stability was also evaluated. The conformation of MPEO blocks at the PLA particle surface is discussed in relation to the layer thickness and the surface area occupied per molecule.

Evaluation of intra-articular delivery of hyaluronic acid functionalized biopolymeric nanoparticles in healthy rat knees.

The aim of this study is to evaluate the toxicity of nanoparticles of poly(D,L-lactic acid) (PLA) or poly(D,L-lactic-co-glycolic acid) (PLGA) covered by chemically esterified amphiphilic hyaluronate (HA) which will be used for intra-articular injection as a drug carrier for the treatment of arthritis (RA) and/or osteoarthritis (OA). PLA and PLGA are FDA approved polymers that are already used for the preparation of nano or microparticles. HA is a natural polysaccharide already present in the articulations known to interact with the CD44 receptors of the cells (especially chondrocytes). Therefore, we can envisage that the HA covering can improve the interactions between the cells and the nanoparticles, leading to better targeting or biodistribution. The knee of healthy male rats was injected one to two times weekly, with various concentrations of nanoparticles encapsulating Dextran-FITC. The synovial membranes and the patellae were collected aseptically and histologically analyzed to assess the effects and localization of the nanocapsules in the knee joint. We did not observe significant modifications in the synovial membranes (weak hyperplasia) or patellae integrity after local administration of nanodevices into the rats. While we found some nanoparticles in the synovial membrane, none were detected in the patellae. Moreover, the histological observations for patellae were confirmed by radiosulfate intake, which depicted no decrease in proteoglycans biosynthesis in nanoparticles treated animals. Concerning the safety towards synovial membranes, we also had a look at the inflammatory response after injections of nanoparticles covered by amphiphilic HA or polyvinyl alcohol (PVA) by monitoring the mRNA expression levels of some specific early cytokines (IL-1β and TNF-α). Once again, no differences were observed between the control rats and the rats treated with nanoparticles. Considering these preliminary results obtained in healthy rats, we can establish that neither the amphiphilic HA-covered PLGA nanoparticles nor their degradation products induce major modifications of articular tissues functions, while injected into the knee of healthy rats. These results should be confirmed in OA or RA rat models, in order to confirm that nanoparticles do not worsen already altered (degenerative or inflamed) articular tissues. Once confirmed, such tuneable nanoparticles could be proposed as a safe drug delivery system for the treatment of articular disease, allowing a wide range of encapsulating molecules.

Injectable PLA-based in situ forming implants for controlled release of Ivermectin a BCS Class II drug: solvent selection based on physico-chemical characterization

In situ forming implants (ISI) prepared from biodegradable polymers such as poly(d,l-lactide) (PLA) and biocompatible solvents can be used to obtain sustained drug release after parenteral administration. The aim of this work was to study the effect of several biocompatible solvents with different physico-chemical properties on the release of ivermectin (IVM), an antiparasitic BCS II drug, from in situ forming PLA-based implants. The solvents evaluated were N-methyl-2-pyrrolidone (NMP), 2-pyrrolidone (2P), triacetine (TA) and benzyl benzoate (BB). Hansen’s solubility parameters of solvents were used to explain polymer/solvent interactions leading to different rheological behaviours. The stability of the polymer and drug in the solvents were also evaluated by size exclusion and high performance liquid chromatography, respectively. The two major factors determining the rate of IVM release from ISI were miscibility of the solvent with water and the viscosity of the polymer solutions. In general, the release rate increased with increasing water miscibility of the solvent and decreasing viscosity in the following order NMP>2P>TA>BB. Scanning electron microscopy revealed a relationship between the rate of IVM release and the surface porosity of the implants, release being higher as implant porosity increased. Finally, drug and polymer stability in the solvents followed the same trends, increasing when polymer-solvent affinities and water content in solvents decreased. IVM degradation was accelerated by the acid environment generated by the degradation of the polymer but the drug did not affect PLA stability.

Polysaccharide-covered nanoparticles with improved shell stability using click-chemistry strategies

Dextran-covered PLA nanoparticles have been formulated by two strategies. On one hand, dextran-g-PLA copolymers have been synthesized by click-chemistry between azide-multifunctionalized dextran (DexN3) and alkyne end-functionalized PLA chains (α-alkyne PLA); then nanoprecipitated without any additional surfactants. On the other hand, DexN3 exhibiting surfactant properties have been emulsified with unfunctionalized or α-alkyne PLA, which are dissolved in organic phase with or without CuBr. Depending on the o/w emulsion/evaporation process experimental conditions, dextran-g-PLA copolymers have been produced in situ, by click chemistry at the liquid/liquid interface during the emulsification step. Whatever the process, biodegradable core/shell polymeric nanoparticles have been obtained, then characterized. Colloidal stability of these nanoparticles in the presence of NaCl or SDS has been studied. While the physically adsorbed polysaccharide based shell has been displaced by SDS, the covalently-linked polysaccharide based shell ensures a permanent stability, even in the presence of SDS.

Amphiphilic photosensitive dextran-g-poly(o-nitrobenzyl acrylate) glycopolymers.

Among all photosensitive monomers reported in the literature, o-nitrobenzyl acrylate (NBA) was selected in this present study. Two strategies were compared to produce azido-terminated poly(o-nitrobenzyl acrylate) (PNBA) using controlled Single Electron Transfer-Living Radical Polymerization (SET-LRP). In a parallel way, dextran (Dex) was modified by the introduction of several alkynyl-terminated hydrophobic chains. Finally, an Huisgen-type Copper (I)-catalyzed Azide-Alkyne Cycloaddition (CuAAC) click-chemistry was carried out to produce amphiphilic Dex-g-PNBA glycopolymers with different number and length of PNBA grafts. 2D DOSY (1)H NMR was used to prove the formation of such glycopolymers. Preliminary study on Dex-g-PNBA self-assembly was done by measuring the critical water content (CWC) above which Dex-g-PNBA started to auto-organize themselves to produce nano-objects. Finally, under UV irradiation, PNBA grafts turn into poly(acrylic acid) ones giving light-sensitive properties to such amphiphilic Dex-g-PNBA. Such properties were evaluated and compared with those of PNBA.

Polymers with novel topologies by ring-opening metathesis polymerization of macromonomers

This paper reviews the possibilities of engineering novel macromolecular topologies via alivingo ring-opening metathesis polymerization (ROMP) of miscellaneous macromonomers. It is shown that multibranched polystyrene poly(ethylene oxide) and polybutadiene poly-macromonomers of varying compactness and branch number can be prepared by ROMP of corresponding macromonomers, provided the macromonomers carry an end-standing norbornene unsaturation. Janus-type ar-chitectures are also accessible by this technique: such entirely novel topologies can be obtained by sequential ROMP of two different macromonomers whereas their statistical copolymerization affords heteroarmed macro-molecules. Advantage has also been taken of the versatility of this technique to prepare compact polymeric architectures that behave like unimicellar systems: structures whose inner part and outer layer are chemically different can be derived through homopoly-merization of macromonomers that are themselves block copolymers.

Synthesis of α‐ and ω‐norbornenyl‐polybutadiene macromonomers and their ring‐opening metathesis polymerization

Norbornene-ended polybutadiene (PBu) macromonomers have been prepared via two different routes: a-norbornenyl-polybutadiene was derived from a norbornene-containing carbanionic initiator, whereas ω-norbornenyl samples were obtained through deactivation of living polybutadienyl anions by a norbornene-based deactivator. Out of four alkylidene complexes tried, the molybdenum alkylidene complex that contains two alkoxide ligands was found to be the most suitable initiator for the ring-opening metathesis polymerization of these macromonomers.

Are in situ formulations the keys for the therapeutic future of S-nitrosothiols?

S-nitrosoglutathione (GSNO) and S-nitroso-N-acetylpenicillamine (SNAP) were formulated into in situ forming implants (ISI) and microparticles (ISM) using PLGA and either N-methyl-2-pyrrolidone (NMP) or triacetin. Physicochemical characterization was carried out, including the study of matrix structure and degradation. A strong correlation between drug hydrophobicity and the in vitro release profiles was observed: whatever the formulation, GSNO and SNAP were completely released after ca. 1 day and 1 week, respectively. Then, selected formulations (i.e., SNAP-loaded NMP formulations) demonstrated the ability to sustain the vasodilation effect of SNAP, as shown by monitoring the arterial pressure (telemetry) of Wistar rats after subcutaneous injection. Both ISI and ISM injections resulted in a 3-fold extended decrease in pulse arterial pressure compared with the unloaded drug, without significant decrease in the mean arterial pressure. Hence, the results emphasize the suitability of these formulations as drug delivery systems for S-nitrosothiols, widening their therapeutic potential.

Synthesis and In vivo Studies of Protein C-loaded Nanoparticles with PEO Modified Surfaces

Protein C-loaded nanoparticles coated with monomethoxypoly (ethylene oxide) (MPEO) were prepared by double emulsion/solvent evaporation using water-soluble biocompatible copolymers of MPEO and polylactide, as surfactants of the secondary emulsion. The nanoparticle preparation was optimized to obtain the best yield of encapsulated protein C and provide the greatest retention of its biological activity. The nanoparticles were characterized in terms of size, zeta potential, and thickness of the MPEO external layer. Protein C-loaded nanoparticles were injected into the bloodstream of guinea pigs and the protein concentration in plasma is measured as a function of time. After a rapid release corresponding to 20% of the injected protein, the protein plasma concentration progressively decreased and reached a value close to zero after 5 h. Consequently, the in vivo fate of the fluorescent nanoparticles coated with or without MPEO is studied. The uncoated nanoparticles were rapidly captured by the circulating granulocytes while the coated ones were not. The histological analysis of the spleen, 1 hour after injection, showed that the MPEO-coated particles were retained in this organ, while the uncoated ones were not captured.