Preparation and evaluation of chitosan–hydrophobic silica composite microspheres: Role of hydrophobic silica in modifying their properties

Abstract

Biodegradable microspheres used as controlled release systems are important in pharmaceutics. Chitosan biopolymer represents an attractive alternative to other biomaterials because of its significant physicochemical and biological behaviors. Chitosan microspheres are expected to become promising carrier systems for drug and vaccine delivery, especially via oral, mucosal and transdermal routes. Controlling the swelling rate and swelling capacity of the hydrogel and improving the fragile nature of microspheres under acidic conditions are the key challenges that need to be overcome to allow the use of chitosan microspheres for controlled or sustained release specially via these non-invasive administration routes. There have been many studies on the modification of chitosan microsphere structures with cross-linkers, blends with various kinds of polymers and new organic-inorganic hybrid systems in order to obtain some improved properties. In this work, microspheres composed of chitosan and nanosized hydrophobic silica commercialized under the name Aerosil R972 were generated by a method consisting of two steps: first, preparation of a macroscopically homogeneous chitosan-hydrophobic silica dispersion by an optimized procedure, and then drying. Spray drying was the technique used here. FTIR spectroscopy, X-ray powder diffraction, differential scanning calorimetry, thermal gravimetric analysis, Scanning Electron Microscopy (SEM) and high resolution Transmission Electron Microscopy (TEM) were used to characterize the microspheres, besides acid stability, moisture sorption capacity, release properties and biological assays. The chitosan-hydrophobic silica composite microspheres showed improved thermal degradation, lower water affinity, better acid stability and ability to retard rifampicin (drug model) release under simulated gastric conditions. In vitro biocompatibility studies indicated low cytotoxicity and low capacity to activate cell production of the proinflammatory mediator nitric oxide, encouraging further studies on the use of the new chitosan-hydrophobic silica composite microspheres as drug carrier systems via oral or nasal routes.

Structure and Properties of Functionalized Porous Silica Hybrid Materials

“…In acidic media the W values are higher, than these of hybrid weight in neutral solution and can be associated with swelling behavior of CS units into solutions with different pH [35]. In acidic conditions the CS units expanded, as a result of which penetration of water molecules is, favor [36]. In both media the swelling tests presented that with increasing of the organic amount the weight of the hybrid materials also increase.…”

Biopolymer colloids for controlling and templating inorganic synthesis

“…Starting from a colloidal suspension of laponite particles, Shi et al [ 4 ] reported the preparation of a nanocomposite matrix of chitosan and clay that was applied as a glucose biosensor. Very recently, da Costa Neto et al [ 5 ] prepared chitosan/silica composite microspheres by mixing an aqueous solution of the biopolymer with commercial nanosized silica particles. The obtained microparticles were dried afterwards.…”

Special issue on innovative processes and materials

“…Melt crystallization as a purification route respectful of environmental constraints is examined in reference [14] and a crystallization process performed in a continuous reactor for synthesis purpose is presented in paper [18]. Spray-drying is the process used in both papers [15] and [16] but for two different purposes.…”

“…In reference [15], the spray drying of oil-in water emulsions, containing hydrophilic carriers, is used to encapsulate lipophilic compounds into powders while in paper [16], spray drying is performed to produce chitosan-hydrophobic silica composite microspheres. A complementary analysis is reported on a pneumatic drying process [17].…”