Team:UCLA/Project/Spinning Silk

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          <h1>Processing Silk</h1>
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          <h2>Preparation for Silk Materials</h2>
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          <h2>Spinning Silk</h2>
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          <p>In order to form fibers from silk, soluble silk protein solutions must be  much like how they are in natural spider spinnerets. The majority of spinning methods entail pushing, or extruding, silk solution through very thin channels. During this extrusion, shear forces on the silk solution cause the amino acids of the proteins to align in a way that allows the strong beta sheets of the silk structure to form. Multiple proteins are similarly aligned, causing separate proteins to interact and form larger structures.
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The standard method that we are using to produce silk fibers is syringe extrusion, in which a syringe pump forces silk dope through a small-diameter tube into a liquid coagulation bath. This method most directly emulates the process that spiders use. In a natural spider spinneret, silk solution produced in the spider's glands are forced through small-diameter spinnerets, and expelled as solid threads.
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[PICTURE of syringe extrusion set up]
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Another method that we are investigating is centrifuge extrusion, in which a column with a small-diameter channel is loaded with silk dope, and placed into a centrifuge tube containing the coagulation solution. The loaded column and tube are then centrifuged at high speeds, and the resulting centrifugal force extrudes the dope through the channel into the coagulation bath, causing a fiber to form.
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A final method for fiber production that we worked with is rotary jet spinning. Rotary jet spinning is very similar to centrifuge extrusion, in that the dope is spun at very high speeds and centrifugal force pushes the dope out of the channel. However, in rotary jet spinning, the dope is loaded into a reservoir that is mounted vertically onto a motor shaft. This method does not allow for the usage of a coagulation bath, as the reservoir holding the dope must be spun in air. If the reservoir were to be spun in a liquid bath, the resultant turbulence in the bath would cause structural instability and destroy the apparatus.
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          <h2>Post-Spin Stretch</h2>
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          <p>A very important part of creating fibers from expressed recombinant silk is the stretching of the fiber after it has been extruded. This can be observed in actual spiders, who tug on the silk threads they produce in order to stretch them. This stretching not only results in longer lengths of threads to work with, it confers extra strength and elasticity to the fibers.
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<h1> <font size="5"> SILK SPINNING </font> </h1>
 
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<p>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.
 
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<p> 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. </p>
 
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<p> 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.
 
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Revision as of 02:14, 17 October 2014

iGEM UCLA




























Processing Silk

Preparation for Silk Materials



Spinning Silk

In order to form fibers from silk, soluble silk protein solutions must be much like how they are in natural spider spinnerets. The majority of spinning methods entail pushing, or extruding, silk solution through very thin channels. During this extrusion, shear forces on the silk solution cause the amino acids of the proteins to align in a way that allows the strong beta sheets of the silk structure to form. Multiple proteins are similarly aligned, causing separate proteins to interact and form larger structures. The standard method that we are using to produce silk fibers is syringe extrusion, in which a syringe pump forces silk dope through a small-diameter tube into a liquid coagulation bath. This method most directly emulates the process that spiders use. In a natural spider spinneret, silk solution produced in the spider's glands are forced through small-diameter spinnerets, and expelled as solid threads. [PICTURE of syringe extrusion set up] Another method that we are investigating is centrifuge extrusion, in which a column with a small-diameter channel is loaded with silk dope, and placed into a centrifuge tube containing the coagulation solution. The loaded column and tube are then centrifuged at high speeds, and the resulting centrifugal force extrudes the dope through the channel into the coagulation bath, causing a fiber to form. [SCHEMATIC of extrusion column] [PICTURE of actual extrusion column in centrifuge tube A final method for fiber production that we worked with is rotary jet spinning. Rotary jet spinning is very similar to centrifuge extrusion, in that the dope is spun at very high speeds and centrifugal force pushes the dope out of the channel. However, in rotary jet spinning, the dope is loaded into a reservoir that is mounted vertically onto a motor shaft. This method does not allow for the usage of a coagulation bath, as the reservoir holding the dope must be spun in air. If the reservoir were to be spun in a liquid bath, the resultant turbulence in the bath would cause structural instability and destroy the apparatus. [PICTURE of rotary jet spinner]

Post-Spin Stretch

A very important part of creating fibers from expressed recombinant silk is the stretching of the fiber after it has been extruded. This can be observed in actual spiders, who tug on the silk threads they produce in order to stretch them. This stretching not only results in longer lengths of threads to work with, it confers extra strength and elasticity to the fibers.

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