PROCESSING Silk materials
Silk is an excellent substance, but it can't do anything until it has been processed. The materials processing team works on making functional fibers and hydrogels from the recombinant silk proteins produced by the other teams. Currently, our focus is on creating silk fibers and hydrogels, as well as characterizing their respective mechanical and chemical properties.
Silk is originally produced in spiders as proteins in liquid solution. It’s not until this solution is passed through the spider’s spinneret that the silk comes together as a fiber that can be woven into webs and fabrics. A major part of our project revolves around emulating this natural process using laboratory methods to convert liquid silk solutions into durable threads. We will be using two different methods of spinning silk fibers, to see the benefits and drawbacks of each method.
The first method is directly inspired by the natural spinneret structure of spiders. In spiders, liquid silk solution is passed from silk glands and forced, or extruded, through tiny openings at the end of the spinnerets. This process compacts the silk proteins, and forces them to organize into solid threads. In a similar fashion, we can use a syringe to force silk solution through a needle into a liquid bath that promotes coagulation. The resulting fiber can then be drawn through additional chemical baths that stretch it and improve its elasticity. The end result is a silk thread much like one that would be produced in a real spider spinneret.
The second method adds an additional mechanical element to the process. This process draws inspiration not only from the spider spinneret, but also from a machine that we know and are familiar with – a cotton candy machine. In a machine called a Rotary Jet Spinner (RJS), a reservoir with a spinneret-like nozzle is filled with liquid silk solution. This reservoir is then spun at extremely high speeds, up to 20,000 revolutions per minute. The centrifugal force of this rotation extrudes the solution through the nozzle at a uniform rate, causing compaction and solid arrangement of the silk proteins. As the thread is ejected from the nozzle, any remaining liquid is evaporated, resulting in a solid fiber that is collected on a wall surrounding the reservoir.
A hydrogel is a 3-dimensional polymer matrix that suspends water within itself, and has applications in tissue engineering, drug delivery, and tissue implantation, to name a few. Hydrogels created from other polymers for these purposes have already been studied for decades, but silk is remarkable in that it evokes no immune response. This makes it particularly suited for use within the human body.
Silk hydrogels can be created in a wide variety of ways. Some methods include using sonication, electricity, or even ultraviolet radiation to coagulate the liquid silk into a gel. Our team primarily utilizes acids and vortexing to create the gels.