Synthesis of Novel Antimicrobial Chlorhexidine Particles for Biomedical Application

Aims: To synthesize and characterize calcium, strontium, zinc and fluoride containing CHX particles and incorporate them into gels for antibacterial applications, as well as explore the surface crystallisation of the particles. Methods: Novel chlorhexidine (CHX) particles were synthesized by mixing CHX diacetate (CHXD) with CaCl2, SrCl2, ZnCl2, NaF or NaCl-NaF mixtures to harvest CHX-CaCl2 / CHX-SrCl2 / CHX-ZnCl2 / CHX-ZnCl2 / CHX-NaF / CHX-NaF-NaCl particles, which were characterized using; SEM, FTIR, XRD and UV-Vis. Antibacterial ability was evaluated by incubating three major sub-gingival bacteria (Porphyromonas gingivalis, Fusobacterium nucleatum and Aggregatibacter actinomycetemcomitans) and cytotoxicity was measured using mouse fibroblast L929 cells. Alkaline phosphatase activity and bone-like mineral nodules expression of MC3T3-E1 cells were carried out. The synthesized CHX-CaCl2, CHX-SrCl2 and CHX-ZnCl2 particles (1%) were incorporated into HPMC gels or used for surface coating via a rinse method. A CHX digluconate (1%) HPMC gel and Corsodyl® were used as comparison gels. Gels were immersed in deionized water, phosphate-buffered saline (PBS) and artificial saliva (AS) to characterize drug release behaviour. The released samples were examined against P. gingivalis (strain 381) using the zone of inhibition method. The synthesized CHX-CaCl2 particles were coated on the surface of the human teeth and medical devices including polymethyl methacrylate denture base, a regular neck implant (∅3.3mmRN, 8mm, lot RA221, Straumann) and orthodontic brackets (Victory Series, 3M Unitek, Monrovia, Calif). The coated bracket was immersed in AS to characterize drug release kinetics. Results: The CHX-CaCl2, CHX-SrCl2 and CHX-ZnCl2 particle sizes were controlled via processing time and temperature and were as safe as CHXD, with antibacterial activity against a range of oral pathogens. CHX-ZnCl2 particles gave pH-responsive release of Zn2+ ions. XRD and FTIR indicated a unique crystal structure for the novel particles (CHX-CaCl2 / CHX-SrCl2 / CHX-ZnCl2 / CHX-ZnCl2 / CHX-NaF / CHX-NaF-NaCl) compared with CHXD. Alkaline phosphatase activity and bone-like mineral nodules of MC3T3-E1 cells were not significantly promoted in the CHX-SrCl2 and CHX-ZnCl2 particles when compared with the cell only group. CHX release of CHX-CaCl2 / CHX-SrCl2 / CHX-ZnCl2 gels was via a sustained release throughout the assay period in all mediums (PBS and DW). The CHX digluconate gel in contrast showed phases of burst CHX release in DW and PBS. All test and comparison gels displayed lower cumulative CHX release when immersed in PBS compared to deionised water. Dialysates from novel CHX HPMC gels (PBS) exhibited inhibition of P. gingivalis at all time points. Corsodyl® gel failed to inhibit P. gingivalis at 2 weeks. SEM / digital images revealed rapid crystallisation of dendritic CHX-CaCl2 on teeth, titanium implants and brackets. The amount of CHX loaded into the CHX-CaCl2 particles and coated onto brackets was controlled by adjusting the concentration of CHXD. Conclusions: Novel CHX particles containing calcium/strontium/zinc and fluoride were synthesized, which had a sustained drug release and were effective against a range of oral pathogens, with reduced cytotoxicity, and a smart pH-responsive drug/ ion release. Novel CHX particles were incorporated into gels or surface-coated on a range of medical devices and teeth, showing sustainable and antimicrobial efficacy. These particles show great potential for the prevention or reversal of caries and infections in Medicine and Dentistry