One-Pot Synthesis of Biocompatible Silver Nanoparticle Composites from Cellulose and Keratin: Characterization and Antimicrobial Activity

A novel, simple method was developed to synthesize biocompatible composites containing 50% cellulose (CEL) and 50% keratin (KER) and silver in the form of either ionic (Ag+) or Ag-0 nanoparticles (Ag(+)NPs or Ag(0)NPs). In this method, butylmethylimmidazolium chloride ([BMIm(+)Cl(-)]), a simple ionic liquid, was used as the sole solvent and silver chloride was added to the [BMIm(+)Cl(-)] solution of [CEL+KER] during the dissolution process. The silver in the composites can be maintained as ionic silver (Ag+) or completely converted to metallic silver (Ag-0) by reducing it with NaBH4. The results of spectroscopy [Fourier transform infrared and X-ray diffraction (XRD)] and imaging [scanning electron microscopy (SEM)] measurements confirm that CEL and KER remain chemically intact and homogeneously distributed in the composites. Powder XRD and SEM results show that the silver in the [CEL+KER+Ag+] and [CEL+KER+Ag-0] composites is homogeneously distributed throughout the composites in either Ag+ (in the form of AgClNPs) or Ag NPs form with sizes of 27 +/- 2 or 9 +/- 1 nm, respectively. Both composites were found to exhibit excellent antibacterial activity against many bacteria including Escherichia coli, Staphylococcus aureus, Pseudomonas aeruginosa, methicillin-resistant S. aureus (MRSA), and vancomycin-resistant Enterococus faecalis (VRE). The antibacterial activity of both composites increases with the Ag+ or Ag-0 content in the composites. More importantly, for the same bacteria and the same silver content, the [CEL+KER+AgClNPs] composite is relatively more toxic than [CEL+KER+Ag(0)NPs] composite. Experimental results confirm that there was hardly any Ag NPs release from the [CEL+KER+Ag(0)NPs] composite, and hence its antimicrobial activity and biocompatibility is due not to any released Ag NPs but rather entirely to the Ag(0)NPs embedded in the composite. Both AgClNPs and Ag(0)NPs were found to be toxic to human fibroblasts at higher concentration (>0.72 mmol), and for the same silver content, the [CEL+ICER+AgClNPs] composite is relatively more toxic than the [CEL+KER+Ag(0)NPs] composite. As expected, by lowering the Ag(0)NPs concentration to 0.48 mmol or less, the [CEL+KER+Ag(0)NPs] composite can be made biocompatible while still retaining its antimicrobial activity against bacteria such as E. coli, S. aureus, P. aeruginosa, MRSA, and VRE. These results, together with our previous finding that [CEL+KER] composites can be used for the controlled delivery of drugs such as ciprofloxacin, clearly indicate that the [CEL+KER+Ag(0)NPs] composite possesses all of the required properties for it to be successfully used as a high-performance dressing to treat chronic ulcerous infected wounds.