Formation and Properties of Silk Thin Films

As an immobilization matrix cast fibroin silk films exhibit useful properties including stability to most solvents, biological compatibility, phase transition for the physical entrapment of reactive molecules, and the capablity to retain high activity of the entrapped molecules. However, in the casting process there is limited control over the density, thickness and the orientation of the polymer chains. The Langmuir-Blodgett (LB) technique can enhance the control of the membrane structure and allow improved control over membrane properties. We have formed natural silk films using the Langmuir technique. Silk fibroin, regenerated from Bombyx mori cocoons, formed stable LB thin films as indicated from pressure/area isotherms. Multiple layers of the silk fibroin were deposited on a number of substrates and basic information about the physical properties of the LB films were obtained with transmission electron microscopy (TEM) and ellipsometry data. Preliminary analysis of electron diffraction data from the film indicates a polycrystalline structure consistent with the known structure of silk. Infrared spectrometric analysis of these silk films using attenuated total reflectance (ATR) gave wavenumbers for amide I, II, III and V bands, which are in agreement with the silk II conformation reported for cast silk membranes.