Spider silk is one of the most remarkable natural materials, with exceptional properties such as high strength, elasticity, and biocompatibility.
However, harvesting spider silk from spiders is difficult and inefficient, as spiders are territorial and cannibalistic.
Therefore, scientists have been looking for ways to produce spider silk artificially, using methods such as genetic engineering, chemical synthesis, or biomimetic spinning.
One of the most promising approaches is to use genetically modified silkworms, which are already widely used for producing silk fibers commercially.
Silkworms have many advantages over spiders, such as large-scale rearing, high productivity, and easy manipulation of their genes.
Moreover, silkworms secrete a protective layer of glycoproteins and lipids on their silk fibers, which helps them resist degradation from environmental factors.
How silkworms were engineered to produce spider silk
The study was led by Junpeng Mi, a PhD candidate at the College of Biological Science and Medical Engineering at Donghua University.
The researchers used a combination of CRISPR-Cas9 gene editing technology and microinjections to introduce spider silk protein genes into the DNA of silkworms.
The spider silk protein genes were derived from two species of spiders: Nephila clavipes and Araneus ventricosus.
The researchers chose these genes because they encode for the major ampullate spidroin (MaSp), which is the main component of dragline silk, the strongest and toughest type of spider silk.
To start, the researchers injected hundreds of thousands of fertilized silkworm eggs with the spider silk protein genes and then screened them for successful integration using fluorescence microscopy.
Silkworms that had the spider silk protein genes in their genome showed red fluorescence in their eyes, indicating that the gene editing had worked.
Then, the researchers reared the transgenic silkworms and collected their cocoons. They extracted the silk fibers from the cocoons using a forced reeling method, which involves boiling the cocoons in water and then pulling out the fibers manually.
They analyzed the fibers using various techniques, such as scanning electron microscopy, Fourier transform infrared spectroscopy, and tensile testing.
What are the benefits and applications of spider silk from silkworms
The researchers found that the transgenic silkworms produced fibers that contained both silkworm silk proteins and spider silk proteins.
The ratio of spider silk proteins to silkworm silk proteins varied depending on the type and number of spider silk protein genes inserted into the silkworms.
The highest ratio achieved was about 35%, which means that more than one-third of the fiber was composed of spider silk proteins.
Moreover, the researchers found that the spider silk proteins enhanced the mechanical properties of the fibers.
The fibers produced by the transgenic silkworms were six times tougher than the Kevlar used in bulletproof vests and had a higher breaking strength and elongation than normal silkworm silk fibers.
The fibers also had a higher thermal stability and water resistance than normal silkworm silk fibers.
The researchers concluded that their study demonstrated a feasible and scalable technique for producing spider silk fibers using genetically modified silkworms.
According to the researchers, they envision various applications for spider silk fibers from silkworms, such as surgical sutures, bulletproof vests, smart textiles, biomedical devices, and aerospace materials.
They said that their technique could be further improved by optimizing the expression and secretion of spider silk proteins in silkworms, as well as by modifying other genes related to fiber quality and performance.
The study was supported by grants from the National Natural Science Foundation of China, the Shanghai Municipal Science and Technology Commission, and Donghua University.
