Formation and Characterization of Ultrathin Films Containing Amyloidogenic Proteins

Abstract

Ultrathin films are useful for coating materials and controlling drug delivery processes. Here, we explore the use of two-dimensional amyloidal networks as biodegradable ultrathin films. In a first step, we have studied the lateral aggregation and fibril formation of insulin that is adsorbed at and confined within planar polyelectrolyte multilayers containing poly(diallyldimethylammonium chloride) (PDDA), poly(styrenesulfonic acid) (PSS), and hyaluronic acid (Hyal). Si-PDDA-PSS-(Ins-PSS)x and Si-PDDA-PSS-(Ins-Hyal)x multilayers have been prepared and characterized in the hydrated state by using X-ray reflectometry, ATR-FTIR spectroscopy and confocal fluorescence microscopy. The obtained data demonstrate a successful build-up of insulin-polyelectrolyte multilayers on silicon wafers that grow strongly in thickness upon insulin adsorption on PSS and Hyal layers. The secondary structure analysis of insulin, based on the insulin infrared amide I’ band, indicates intermolecular β-sheet formation within the multilayers at 70 °C and pH = 2, i.e. at conditions that promote amyloid fibrils rich in β-sheet contents. However, insulin that is incorporated in polyelectrolyte multilayers rather forms amorphous aggregates as can be inferred from confocal fluorescence images. Only when insulin is the top-layer, formation of a fibrillar network can be observed after adding seeds to the buffer solution.