Photopolymerized Dimethacrylates Containing Antimicrobial Silver Nanoparticles Formed in situ

Objectives: Silver, a known antimicrobial agent, can be incorporated into materials to impart their bactericidal properties. The objectives of this study were to develop a method to incorporate silver nanoparticles in situ into common dimethacrylate polymers and to test the material properties as well as resistance to bacterial colonization. Methods: A homogeneous dispersion of silver salts (sliver 2-ethylhexanoate) in resin solution (BisGMA:TEGDMA 1:1 by mass) was achieved by introducing polymerizable 2-(tert-butylamino)ethyl methacrylate (TBAEMA, ≈ 1% by mass) as a coordination ligand to silver ion. The silver nanoparticles were incorporated at percentages of 0.03 % and 0.08 % (mass fraction). The free radicals generated by the photo-initiator (Irgacure 819) play a dual role: 1) polymer initiator, and 2) reducing Ag^I to Ag⁰. The degree of conversion was determined using FTIR. The presence and dispersion of silver nanoparticles was assessed by transmission electron microscopy (TEM). Bacterial growth (Streptococcus mutans) was evaluated. Results: FTIR results confirmed that the reduction of Ag^I does not decrease the vinyl conversion of the polymer and its material properties. TEM images showed well-dispersed silver nanoparticles (diameter ≈ 2 nm) in polymers with very few larger aggregates. High magnification TEM images and selected area electron diffraction further revealed that the silver nanoparticles are nanocrystalline in nature. S. mutans colonization, described in terms of object number and fraction of the surface covered, decreased markedly as the silver concentration increased. The differences for both object number and fraction covered are statistically significant from controls at both concentrations evaluated. Conclusions: A new approach was developed to incorporate silver nanoparticles in common dental monomers. At the concentrations examined, particles were of nanometer size and were well dispersed. The presence of silver nanoparticles led to a reduction in bacterial colonization.

Support: NIDCR/NIST Interagency Agreement Y1-DE-7005-01.