Plasma Etching of Silk Fibroin: Experiments and Models

Abstract

Silk fibroin biopolymer is anisotropically etched using oxygen and argon/oxygen plasma. At room temperature, silk removal rates are 0.25 µm min−1. Scanning electron micrographs show that silk fibroin is a heterogeneous material for which plasma etching reveals a silk backbone structure as the matrix is more quickly volatilized. A simple physical model of silk etching accurately predicts the etch rate without any fitting parameters. The model and experimental data show that atomic oxygen, in the absence of ion bombardment, only slowly etches silk (<0.017 µm min−1) and does not spontaneously etch silk fibroin backbone structures. Rather, the silk constituents must be removed by first covering the surface with adsorbed atomic oxygen which is then simultaneously desorbed through energetic ion bombardment.