Micro-encapsulation of Particles with Chitosan
Sustainable process-product development & green chemistry
SCF as Solvent Substitutes (T1-8)
Keywords: Chitosan, DMSO, GAS, coating
Raquel Carvallo and Aydin K. Sunol
Chemical Engineering, University of South Florida, Tampa FL 33620
Coating of fine particles to produce tailored surface properties is currently a key development of supercritical fluids applications, in different areas like: Pharmaceutical, nutraceutical, cosmetic, agrochemical, electronic and specialty chemistry industries.
During the encapsulation process, the particle surface can be engineered with a specific physical, chemical, and/or biochemical properties by spreading a thin film of material on the surface of the particles. As a result, the flowability, dissolution rate, controlled release or masking, dispersability, chemical reactivity, bio-efficacy, and hydrophilicity of particles can be modified for a variety of applications.
In this work, Chitosan, a natural biodegradable polymer, is used. Chitosan is a modified carbohydrate polymer derived from chitin deacetilation. Chitin is the second most abundant polysaccharide in nature; it’s a component of the shells of crustacean.
Chitosan has some properties that make it very attractive for pharmaceutical applications like: biocompatibility, biodegrades to normal body constituents, is safe and non toxic, bacteriostatic, anticancerogen, and versatile.
The first objective of this research was to determine Chitosan solubility, since in a supercritical fluid (SCF) this the most important thermo-physical mixture property. It is required to determine the Equation of State (EOS) interaction coefficients to allow prediction of the phase distribution of the solute and this information is used to determine the appropriate conditions for process operation.
Chitosan solubility in a SCF was studied at different temperatures using static and dynamic methods; and this data is used to predict the operation conditions in the coating process.
With the static method, we used a solubility cell which was initially loaded with a known amount of solid Chitosan and DMSO an entrainer. Then the supercritical CO2 was loaded to the system with a syringe pump, the temperature was fixed and the pressure was increased with a manual syringe pump until the solute was completely dissolved in the SCF. The solubility point is visualized onto a video monitor using a camera placed against a sapphire window and the temperature and pressure of the solution are recorded on the video.
With the dynamic method, the supercritical CO2 was charged to the system with a syringe pump and compressed to the desired operating pressure. After leaving the pump, the supercritical fluid flows through a preheating column; this insures that the fluid reaches the bath temperature before it contacts the Chitosan into the extraction column. After the saturated SCF-rich phase leaves column a sample is collected and analyzed with a UV detector where the solubility can be measured as function of absorbance.
The coating method chosen is GAS or SAS: These acronyms refer to ‘Gas (or Supercritical fluid) Anti-Solvent’. In this process, the supercritical fluid is used as an anti-solvent that causes precipitation of the substrate(s) dissolved initially in a liquid solvent. In the GAS process, a batch of saturated solution containing the Chitosan is expanded several-fold by mixing with a dense gas (CO2) in a vessel. Due to the dissolution of the compressed gas, the expanded solvent has a lower solvent strength than the pure solvent. The mixture becomes supersaturated and Chitosan will precipitates over the core particles (CaO and TiO2), forming a fine coating.
The encapsulated particles are characterized using FTIR, SEM/TEM, and AFM. The release performance was modeled and experimentally verified.
Presented Monday 17, 16:40 to 17:00, in session SCF as Solvent Substitutes (T1-8).
