Formation of gold nanoparticles upon chitosan leading to formation and collapse of gels

Abstract

In this article we have demonstrated the formation of chitosan–gold hydro gels that collapse in time. The mechanism for the formation and collapse in time is proposed. The gels were characterized using scanning electron microscopy (SEM), attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR), rheometry and X-ray diffraction (XRD). The formation of the gels is hypothesised to be due to the electrostatic interaction between the AuCl₄⁻ and the NH₃⁺ in the protonated chitosan. The collapse of the gel is attributed to the reduction of Au(III) to Au nanoparticles on the chitosan surface. The formation and the subsequent collapse of the gel were unique to gold under the experimental conditions. A model is proposed for the formation and the collapse of the gel. We coin the term “self collapsing gels” for these kinds of gels. The gels were tested for their abilities to be used for the encapsulation of drugs using insulin. This self collapsing nature of the gels combined with biocompatibility may benefit drug delivery research as encapsulants for the controlled release of drugs.