Experimental Applications of Silk Fibroin Protein
From 10 grams of raw silk cocoons we yielded approximately 140ml of fibroin solution. We have now begun a series of experiments to understand the material properties of fibroin through various processes and applications.
Spinning
We have begun to experiment with various forms of fiber spinning using fibroin protein solution.
Electrospinning seemed like an interesting place to begin. This process involves a high voltage source as means of drawing an electrically conductive fluid out into a thin stream. As the stream is drawn toward the charged target the stream solidifies into a uniform fiber filament.
Our initial tests used a Van de Graaff generator with an approximate voltage range between 100,000 to 150,000 volts. We were able to establish a Taylor Cone at the edge of our capillary and can draw fluid toward the target from up to 40cm away but have yet to sustain a consistent enough flow to produce a continuous fiber.
Wet Spinning is something we have not yet tried but hope to. Wet spinning involves a spinneret that feeds a solution into a bath of coagulating solution, causing the polymer or protein solution to solidify as it’s drawn through it. Initial tests with HCl, ethanol, and isopropanol, have shown varying results. Isopropanol appears to be a likely candidate as it caused rapid coagulation when a droplet of fibroin was placed into it. The difficulty with this process will be fabricating a functional spinneret.
Centrifugal Spinning, a process used to make spun glass and cotton candy may be an interesting area to explore. This process involves placing molten glass, sugar, or possibly silk fibroin solution into a spinning chamber with micro-perforated walls. The centrifugal force causes the material to stream through the small holes and dry instantly in the air.
Spraying / Electrospraying is also something we hope to explore. This could be as simple as spraying the solution normally with a high-pressure diffusion nozzle. A variation of this involves a charged target to increase the efficiency of the coating.
Spin Casting is the preferred process being used by others experimenting with fibroin protein. This the method that the Ultrafast Nonlinear Optics and Biophotonics Laboratory at Tufts University has employed. This process utilizes centrifugal force on a cylindrical form to achieve a film with a uniform thickness. The thickness can be varied by adjusting the rpm’s of the spinning form. During the continuous rotation the fibroin solution air dries to form a film.
Foam – While filtering the fibroin solution to remove solids we forced the solution through different grades of fine mesh. A side effect from the filtration process was the production of very thick foam. It occurred to us that it might be possible to create different kinds of aerated solutions or foam within a mild vacuum.
Solubility – untreated silk fibroin films and filaments dissolve rapidly in water and aqueous solutions. The rate solubility can be varied by treating the fibroin in ethanol.