The Spider: Scientist and Spinster
All these different types of silks and their different applications, but what are spider silks made of? What gives them such useful properties? Spider silk is mainly composed of large amounts of nonpolar, hydrophobic amino acids glycine and alanine but not tryptophan. The spider silk proteins are made up of repeating amino acid sequences (too complex for a sophomore chemistry student to describe or explain). It also has crystalline structures within the silk, beta sheets of nanofibers; the mixture of crystalline and elastic, semi-amorphous materials is what gives the silk such durability and strength, while still retaining flexibility and stretch/contract properties. Along with being thread, it has also been found that in vitro (prior to spinning) the silk protein can be transformed into a multitude of possible shapes: a thread, film, hydrogel, nano-fibril, capsule and a sphere.
Other than just the complexity of the silk's buildup and the genomes that code it, the actual mechanisms of spinning the silk are also hard for human bioengineers to mimic. Methods of syringe needle, microfluidics and electrospinning have experienced varying degrees of success, often lacking cost efficiency, consistent results or a product that is on par with the natural, spider spun silk. The spider itself has 5 different organs that have evolved over centuries to specialize in spinning its silk; so far, they have been able to genetically modify goats to produce milk that contains silk protein and can be drawn out, but this process is costly in regards to finances and time, while producing thread that is thicker and heavier than natural spider silk while also being less strong. The current largest piece of spider silk is a gold tinted cape made from the silk of golden orb spiders; this 11-by-4-foot cape took 83 people over a year to collect 1 million spiders and extract their silk. Scientists can only hope that with these new genetic sequencing advancements in spider research, we will be able to genetically modify other animals to produce spider silk at a much more efficient and expedited rate, or at least identify the technique of the spider and the make up of their silk, as scientists still have many theories about the spider that remain unstudied and untested.
Spider silk can be stronger than steel while still being a fraction if its weight, and in some cases, proving to be antimicrobial and anti-fungal, which have advantageous applications to use in medicine and surgery. While people have been trying to utilize silk for several years now, but progress has been slow due to the inability to identify and characterize the spider silk genes. However, recently, the Perelman School of Medicine at Pennsylvania State University have announced advancements in this field of study. The scientists and their team at Penn state were able to sequence the full genome of the golden orb-weaver spider, one of the most active silk-spinning spider species. This particular species of spider produces 28 different kinds of silk proteins. These scientists were able to to find new patterns within the genes that may be able to explain the different unique properties of different types of silk. These new DNA sequences hint at possible relation to silk strength, toughness, stretchiness and other properties, such as silk proteins being made in venom glands instead of silk glands. The pursuit for this miracle fiber has been in the works for over 50 years. Scientists hope to be able to extract these genes or decode them in order to understand how we could synthetically bioengineer a material similar to it, manipulating all the possible variations in order to create the "perfect material". Just to illustrate the complexity of this daunting task, the team at Penn was able to identify more than 14,000 likely genes: 28 hat encode spider silk proteins (spidroins), 400 short sequences that they believe relate to silk properties (high-tensile strength, flexibility, stickiness, etc) and 649 non-spidroin genes that control the production of silk, such as conversion of liquid silk from spider cells into workable fibers, a process that many biotech engineers are just beginning to find success in.
Spider silk is a highly complex biomaterial that has fascinated humanity for centuries, for many reasons: it has tensile strength (resistance to breakage under tension) comparable to steel, elasticity comparable to rubber and toughness that is two to three times that of Kevlar or Nylon. It's antimicrobial, anti-fungal, hypoallergenic and biodegradability also make it extremely versatile and useful. Spiders have an arsenal of different silks that they use to hunt, capture prey, spin webs, spin cocoons for their eggs and even make draglines (like a safety line that they use to escape from predators). Other than the obvious use of biochemistry to produce such intricate materials, spiders also use intermolecular forces. Not all spiders can spin an adhesive silk, instead using their cribellate silk to act as an "adhesive". A cribellate silk is a wooly, textured silk that is just normal silk that has been combed out to have a texture by the cribella, the spider's hind legs. It exhibits adhesive properties much like a gecko's nano-hair coated feet, through van-der-Waal forces, the spider utilizes the intermolecular attraction between molecules to become "sticky". However, this method of silk spinning is extremely time and energy consuming, which is why ecribellate spiders evolved.
Ecribellate spiders are able to spin a silk that is sticky through adhesion rather than using the adhesive properties of the nano-hairs. This sticky silk is coated in organic molecules, salts, fatty acids and small glycoproteins (protein strand with attached sugar); many scientists also propose that this silk may also be coated in small peptides, which act as metal chelators (meaning they attract metal ions and attach to them, which is why spider silk can be anti-microbial).
All these different types of silks and their different applications, but what are spider silks made of? What gives them such useful properties? Spider silk is mainly composed of large amounts of nonpolar, hydrophobic amino acids glycine and alanine but not tryptophan. The spider silk proteins are made up of repeating amino acid sequences (too complex for a sophomore chemistry student to describe or explain). It also has crystalline structures within the silk, beta sheets of nanofibers; the mixture of crystalline and elastic, semi-amorphous materials is what gives the silk such durability and strength, while still retaining flexibility and stretch/contract properties. Along with being thread, it has also been found that in vitro (prior to spinning) the silk protein can be transformed into a multitude of possible shapes: a thread, film, hydrogel, nano-fibril, capsule and a sphere.
- https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2658765/
- https://www.sciencedaily.com/releases/2017/05/170501112627.htm
- https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2658765/figure/F1/
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