Regulation of Silk Material Structure by Temperature-Controlled Water Vapor Annealing

Abstract

We present a simple and effective method to obtain refined control of the molecular structure of silk biomaterials through physical temperature-controlled water vapor annealing (TCWVA). The silk materials can be prepared with control of crystallinity, from a low content using conditions at 4°C (alpha-helix dominated silk I structure), to highest content of ~60% crystallinity at 100°C (beta-sheet dominated silk II structure). This new physical approach covers the range of structures previously reported to govern crystallization during the fabrication of silk materials, yet offers a simpler, green chemistry, approach with tight control of reproducibility. The transition kinetics, thermal, mechanical, and biodegradation properties of the silk films prepared at different temperatures were investigated and compared by Fourier transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC), uniaxial tensile studies, and enzymatic degradation studies. The results revealed that this new physical processing method accurately controls structure, in turn providing control of mechanical properties, thermal stability, enzyme degradation rate, and human mesenchymal stem cell interactions. The mechanistic basis for the control is through the temperature controlled regulation of water vapor, to control crystallization. Control of silk structure via TCWVA represents a significant improvement in the fabrication of silk-based biomaterials, where control of structure-property relationships is key to regulating material properties. This new approach to control crystallization also provides an entirely new green approach, avoiding common methods which use organic solvents (methanol, ethanol) or organic acids. The method described here for silk proteins would also be universal for many other structural proteins (and likely other biopolymers), where water controls chain interactions related to material properties.

Silk-based resorbable electronic devices for remotely controlled therapy and in vivo infection abatement

“…The cast-and-peel process was used, as previously reported (23). All samples were treated to be water insoluble through a vapor annealing process (16,17), which also helped to stabilize the drug within the crystallized silk matrix (24)(25)(26). Fig.…”

“…Silk protein biomaterials have degradation rates that depend on crystallinity (e.g., beta-sheet content) and molecular weight of films used to support the electronic device. The lifetime of the devices can be specifically adjusted, chosen via the crystallinity of the silk (16,17), yet operation in an in vivo environment imposes additional challenges because of mechanical handling, sterilization, and mechanical stability at the biopolymer-device interface.…”

Implantable, multifunctional, bioresorbable optics

“…S1 and S2). The dissolution time of the MPA films can be tuned by controlling the degree of crystallinity during the silk protein self-assembly process by regulating the water content within the film through an annealing step (15)(16)(17). This approach can be used to allow rapid to slow degradation of the device, depending on the application (SI Appendix, Fig.…”

Toward Biodegradable Mg–Air Bioelectric Batteries Composed of Silk Fibroin–Polypyrrole Film

“…This allows the fibroin chain to self-assemble into a structure with reduced β-sheet content, thus resulting in a rapid biodegradation rate. [22] SF-PPy film prepared by chemically coating a PPy layer only onto top side of silk support showed a bilayer structure with a total thickness of ~60 µm (Figure 1a). The glossy black PPy coating was composed of particles/aggregates Fourier-transform infrared spectra equipped with attenuated total reflectance (ATR-FTIR) and Raman spectroscopy were used to further characterize SF-PPy film structure.…”

“…They were consistent with the previously reported water-annealed silk films. [22,26] The PPy-modified side of SF-PPy film showed only PPy characteristic peaks due to its complete coverage on the silk substrate. It exhibited absorption peaks of C-N absorption at around 1293 cm -1 , PPy ring breathing at 1150 cm -1 and C-H in plane bending modes at about 1025 cm -1 .…”