Synthesis and Evaluation of Composite CS-AgNPs Microspheres

Objectives: To develop novel composite microsphere consisting of biopolymer chitosan (CS) and silver nanoparticles (AgNPs) used as dental filler material.
Methods: A spray freeze drying process was employed to synthesize the composite microspheres. AgNPs colloid was prepared by dropping reducing agent with appropriate concentration into silver salt solution containing certain concentration of Chitosan. The obtained CS-AgNPs colloid solution was sprayed into liquid nitrogen to form CS-AgNPs composite microsphere and further freeze-dried in a lyophilizer. The microstructure of prepared CS-AgNPs microspheres were characterized using Scanning electron microscope (SEM), UV-Visible spectrophotometer (UV-Vis), and X-ray diffraction (XRD). Minimum inhibitory concentrations (MIC) and Minimum bactericidal concentration (MBC) of the CS-AgNPs composite microspheres were tested on S. mutans (ATCC 25175) and E. faecalis (ATCC 29212). The biocompatibility of CS-AgNPs composite microspheres was investigated with MTT assay on gingival epithelial cell.
Results: SEM observation showed that porous composite microspheres were successfully synthesized and the diameter of microspheres was in a range from 5 microns to 20 microns. XRD diffraction pattern was consistent with typical metallic silver crystalline. The peaks in UV-Vis spectra appeared between 405 nm and 429 nm, that confirmed the XRD result. The MIC and MBC of CS-AgNPs composite microspheres for S. mutans were 4 µg/mL and 8 µg/mL, while the MIC and MBC for E. faecalis were 128 µg/mL and 256 µg/mL, respectively. MTT results showed that 8 µg/mL had no cytotoxicity on epithelial cell but 128 µg/mL was toxic.
Conclusions: Novel porous CS-AgNPs composite microspheres were synthesized with the spray freeze drying process. These CS-AgNPs composite microspheres showed a great anti-microbial effects on S. mutans and E. faecalis, indicating its potential application as anti-microbial fillers used in dental materials.