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 Ag⁰ nanoparticles (Ag⁺NPs or Ag⁰NPs). 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 (Ag⁰) 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+Ag⁰] composites is homogeneously distributed throughout the composites in either Ag⁺ (in the form of AgClNPs) or Ag⁰NPs form with sizes of 27 ± 2 or 9 ± 1 nm, respectively. Both composites were found to exhibit excellent antibacterial activity against many bacteria including <i>Escherichia coli</i>, <i>Staphylococcus aureus</i>, <i>Pseudomonas aeruginosa</i>, methicillin-resistant <i>S. aureus</i> (MRSA), and vancomycin-resistant <i>Enterococus faecalis</i> (VRE). The antibacterial activity of both composites increases with the Ag⁺ or Ag⁰ 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+Ag⁰NPs] composite. Experimental results confirm that there was hardly any Ag⁰NPs release from the [CEL+KER+Ag⁰NPs] composite, and hence its antimicrobial activity and biocompatibility is due not to any released Ag⁰NPs but rather entirely to the Ag⁰NPs embedded in the composite. Both AgClNPs and Ag⁰NPs were found to be toxic to human fibroblasts at higher concentration (>0.72 mmol), and for the same silver content, the [CEL+KER+AgClNPs] composite is relatively more toxic than the [CEL+KER+Ag⁰NPs] composite. As expected, by lowering the Ag⁰NPs concentration to 0.48 mmol or less, the [CEL+KER+Ag⁰NPs] composite can be made biocompatible while still retaining its antimicrobial activity against bacteria such as <i>E. coli</i>, <i>S. aureus</i>, <i>P. aeruginosa</i>, 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+Ag⁰NPs] composite possesses all of the required properties for it to be successfully used as a high-performance dressing to treat chronic ulcerous infected wounds