Abdellatif Chenite

Novel injectable neutral solutions of chitosan form biodegradable gels in situ

A novel approach to provide, thermally sensitive neutral solutions based on chitosan/polyol salt combinations is described. These formulations possess a physiological pH and can be held liquid below room temperature for encapsulating living cells and therapeutic proteins; they form monolithic gels at body temperature. When injected in vivo the liquid formulations turn into gel implants in situ. This system was used successfully to deliver biologically active growth factors in vivo as well as an encapsulating matrix for living chondrocytes for tissue engineering applications. This study reports for the first time the use of polymer/polyol salt aqueous solutions as gelling systems, suggesting the discovery of a prototype for a new family of thermosetting gels highly compatible with biological compounds.

Rheological characterisation of thermogelling chitosan/glycerol-phosphate solutions

Abstract In this study we demonstrate that chitosan solutions can be neutralised up to physiological pH (∼7.2) using β-glycerol phosphate without creating immediate gel-like precipitation and furthermore that subsequent heating of these solutions induces hydrogel formation. The addition of the particular basic salt, glycerol phosphate, provides the correct buffering and other physicochemical conditions including control of hydrophobic interactions and hydrogen bonding which are necessary to retain chitosan in solution at neutral pH near 4°C and furthermore to allow gel formation upon heating to 37°C. Rheological investigation evidenced the endothermic gelation of chitosan/β-glycerol phosphate solutions and allowed the establishment of a sol/gel diagram. The gelation process appears to be governed by delicate interplay between the pH and the temperature. The role of β-glycerol phosphate is discussed in the light of relevant literature particularly those indicating the role of glycerol and polyols in the stabilisation of proteins and polysaccharides.

A thermosensitive chitosan-based hydrogel for the local delivery of paclitaxel

A novel injectable thermosensitive in situ gelling hydrogel has been developed. The system, which falls under the BST-Gel platform technology developed at Biosyntech Inc. (Laval, QC, Canada), consists of a chitosan solution (C) neutralized with beta-glycerophosphate (GP) that is liquid at room temperature but gels when heated to body temperature. We propose to use this thermosensitive hydrogel for the sustained release of paclitaxel at tumor resection sites in order to prevent local tumor recurrence. The in vitro release profiles demonstrated controlled delivery over 1 month. The initial drug loading substantially affected the release. Local delivery of paclitaxel from the formulation injected intratumorally was investigated using EMT-6 tumors implanted subcutaneously on Balb/c mice. These experiments showed that one intratumoral injection of the thermosensitive hydrogel containing paclitaxel was as efficacious as four intravenous injections of Taxol in inhibiting the growth of EMT-6 cancer cells in mice, but in a less toxic manner. Further histological analysis revealed that while the proportion of necrotic areas was similar for the C/GP/paclitaxel and the Taxol-treated tumors, a disparity between tumor-associated inflammatory cell populations may suggest differing anti-tumor mechanisms.

Effects of steam sterilization on thermogelling chitosan-based gels

A new thermogelling chitosan-glycerophosphate system has been recently proposed for biomedical applications such as drug and cell delivery. The objectives of this work were to characterize the effect of steam sterilization on the in vitro and in vivo end performances of the gel and to develop a filtration-based method to assess its sterility. Autoclaving 2% (w/v) chitosan solutions for as short as 10 min resulted in a 30% decrease in molecular weight, 3-5-fold decrease in dynamic viscosity, and substantial loss of mechanical properties of the resulting gel. However, sterilization did not impair the ability of the system to form a gel at 37 degrees C. The antimicrobial activity of chitosan against several microorganisms was evaluated after inoculation of chitosan solutions and removal of the cells by filtration. It was found that, although chitosan was bacteriostatic against the heat sterilization bioindicator Bacillus stearothermophilus, the bacteria could rapidly grow after separation from the chitosan solution by filtration. This indicated that B. stearothermophilus is an adequate strain to validate a heat sterilization method on chitosan preparations, and accordingly this strain was used to assess the sterility of chitosan solution following a 10 min autoclaving time.

125I-Iododeoxyuridine for the Treatment of a Brain Tumor Model:Selection of Conditions for Optimal Effectiveness

The intent of this study was to optimise conditions for the use of 125 IUdR in the treatment of cancer. The radiopharmaceutical plus a biomodulator, methotrexate (MTX) was delivered by intra-tumoral injection of a thermosensitive hydrogel forming a slow release depot of 125 IUdR and MTX in the tumor. Methods: The C6 rat glioblastoma was implanted intra-cranially. A chitosan polymer was used to formulate a biodegradable and biocompatible implant for controlled intra-tumoral delivery of 125 IUdR plus MTX. Results: Intratumoral implant of hydrogel loaded with 7.0 -7.4 MBq of 125 IUdR resulted in survival of 20% of treated animals to 180 days after tumor implant. Simultaneous delivery of MTX increased the number of rats that were effectively cured, to 40%. Conclusion: Using an injectable thermolabile hydrogel as vehicle for 125 IUdR delivery a higher level of tumor control was achieved in a rat glioma model than had been previously reported.

An Injectable Biomaterial for Bone Repair

The primary purpose of this study was to characterize the main features of a BCP-loaded chitosan-GP composite. The two-syringe design improves the storage conditions, facilitates the sterilization procedure and provides an easy-to-use injectable biomaterial, ensuring reproducible properties with minimal manipulation. Rheological measurements confirm that the chitosan- GP/BCP composite retains the thermosensitive properties already described for chitosan-GP hydrogels. At 37°C, the system gels within 10 minutes and reaches sufficient consistency after 30 minutes to prevent the mineral granules from migration into the surrounding tissues in vivo. The compressive force needed for the injection of chitosan-GP/BCP before gelation is approximately 6.6 N, only about 6 times that required for water and much lower than the average force that the majority of adults can exert. Morphology was investigated by environmental scanning electron microscopy (ESEM), which revealed 3-D dispersion of BCP granules embedded in chitosan-GP hydrogel. This open, porous structure affords complete access for body fluids and cells to each mineral granule immediately following implantation. The design using disposable syringes equipped with 16G hypodermic needles described here allows easy in vivo delivery of a fully injectable biomaterial containing porous scaffold that naturally enhances the osteogenic activity recognized for both chitosan and BCP.