Cyclic Expansion/Compression of the Air–Liquid Interface as a Simple Method to Produce Silk Fibers

Self‐assembly of recombinant spider silk protein at air–liquid interfaces is used as a starting point to produce homogeneous fiber bundles. The film that is formed on a silk protein solution in a vertically placed syringe is subjected to repeated controlled extension and compression by an oscillating vertical motion. Thereby, a precise breakup of the film can be achieved, followed by transport and roll‐up against the syringe wall prior to extraction. Advantages of the method are that it 1) is simple to use; 2) requires a small volume of protein solution (1 mL) at relatively low concentration (1 mg mL−1); 3) can be performed under sterile conditions; 4) does not require any use of coagulants; and 5) is compatible with the addition of viable cells during the process, which thereby are integrated uniformly throughout the fiber. A recombinant spider silk protein is assembled into a fiber by vertically oscillating the protein solution in a syringe. The silk fiber consists of compressed films formed at the air–liquid interface, which in turn is composed of nanofibrils where the protein is mainly in a β‐sheet structure.