Dispersible chitosan particles showing bacteriostatic effect against Streptococcus mutans and their dental polishing effect.

Nontoxic and biodegradable chitosan is potentially useful in various applications. We prepared submicron chitosan particles with high dispersibility in aqueous solution utilizing the electrostatic interaction phase separation method described in a previous report, but using citric acid as the polyvalent anionic compound instead of sodium sulfate. The submicron chitosan particles showed significant antibacterial activity and anti-adhesive action against Streptococcus mutans, even at around neutral pH. However, chitosan granules showed no antibacterial activity under the same conditions. The addition of the chitosan particles to dental polishing paste provided stainless steel discs (the same hardness as dental enamel) with a smoother surface than polishing paste without additives. In view of their submicron size and antibacterial activity, chitosan particles could potentially be multifunctional components of oral and dental cleaning materials.

Preparation and characterization of dispersible chitosan particles with borate crosslinking and their antimicrobial and antifungal activity.

We synthesized new dispersive chitosan particles at circumneutral pH. Particles composed of a chitosan-borate complex were synthesized by a method consisting of two simple steps: mixture and dialysis. As this method does not employ reagents such as organic solvents or surface-active agents and does not require heat treatment, it has a minimal negative impact on the environment. Crosslinking of the reaction of glucose and boric acid at ordinary temperature and pressure led to the formation of composite particles. Stereoscopic microscopy and investigation of the particle size distribution by dynamic light scattering (DLS) revealed that particles ranging in size from submicrons to several microns with high dispersibility in water were obtained. Even after heat treatment at 80°C for 12h, the particles maintained their composite formation, indicating that they have high thermal stability. Chitosan powders demonstrated inadequate antimicrobial properties at circumneutral pH, but the particles of the chitosan-borate complex had antimicrobial properties against the gram-negative bacterium, Escherichia coli, and the gram-positive bacterium, Staphylococcus aureus, as well as the fungi Aspergillus niger and Fusarium solani. These results indicated that the particles of the chitosan-borate complex had a broad antimicrobial spectrum at circumneutral pH.