Antimicrobial Cocktail For Implant Coating And Regenerative Tissue Scaffolds

Objective: Infections related to wound, implant and dental inflammation are major problems in the military. With micro-organisms developing resistance to antibiotics, it is becoming increasingly more difficult to treat these infections using traditional methods.  To develop a localized broad spectrum antimicrobial delivery system that can be incorporated into implant coating or regenerative tissue scaffolds for periodontal tissue regeneration.

Method: The antimicrobial cocktail was prepared with silver nanoparticles (AgNPs), and rifampicin and tobramycin loaded liposomes. AgNPs were synthesized by reducing silver nitrate with sodium borohydrate (NaBH4) and adding polyvinyl alcohol or 1% sodium citrate.  Liposomes were prepared using a dried lipid film, and were loaded with tobramycin or rifampicin. The size of AgNPs and liposomes were determined by nanoparticle size analyzer and characterized by Transmission Electronic Microscopy (TEM). Nanosystems were stored at 4°C for long term stability and functionality testing. Two sets of bacteria, one involving wound infections (Acinetobacter baumannii, two strains of Staphylococcus aureus (includes MRSA), Pseudomonas aeruginosa, and Proteus mirabilis) and dental pathogens (Aggregatibacter actinomycetemcomitans, streptococcus mutans, Porphyromonas gingivalis, Treponema denticola, and Tannerella forsythia) were used for evaluation of antibacterial activity using minimum inhibitory concentration at 50% inhibition (MIC₅₀).

Result: The average size of AgNPs was 59 ± 5 nm.  Liposomes ranged from 250-470 nm. AgNPs and antibiotic loaded liposomes maintained long term stability at 4°C without changing antibacterial activity for at least six months. The cocktail of AgNPs and antibiotics loaded liposomes increased the antimicrobial activities by three to nine times depending on the micro organism compared to antimicrobial activities of individual nanosystem. 

Conclusion: Our nanosystem cocktail showed wide spectrum antibacterial activity against ten strains involved in either wound infections or dental infections. 

This work was funded under Work Unit Numbers G1009 and G1026 at the Naval Medical Research Unit San Antonio, Texas