Are you interested in raising & experimenting with silk worms? This instructable is for you! As a part of my graduate school research I had a chance to experiment with raising and creating fabric with silk worms.
Silk used in design:
Silkworms are the oldest domesticated insect and have been a source of design, economy and trade for thousands of years. Silkworms spin silk, a protein fiber known for its strength, sheen and pure white color. They are also disarmingly cute creatures and easy to raise and nurture.
Silkworms have also become an intense area of research in the past 15 years due to silk's unique material properties. Silk is being developed as a biomaterial for electronic, optical and mechanical implants (see the lab of Fiorenzo Omenetto of Tufts for more). The silkworm has also been synthetically engineered to produce silk with altered properties, including fluorescent silk and super-strong spider silk.
With this context, my colleagues at MIT created the Silk Pavilion, a structure woven by 6500 silkworms over the course of 2 weeks. The purpose of the project was to use silkworms to directly fabricate a product, in this case a hemispherical dome. This approach contrasts with existing silk design, which uses a traditional textiles process. Perhaps in the future, synthetic biology will enable a more advanced form of silk worm domestication. Silkworms could be engineered to produce varied types of materials; perhaps the location of the silk deposition could be controlled via light guides, sound or other means.
Brief bio background
The Bombyx Mori silkworm life cycle is approximately 8 weeks in length and is comprised of several stages: egg, larva, pupa, and adult (moth).
The silkworm creates a cocoon at the end of the larval stage. The cocoon is a single, unbroken strand of silk that is approximately a kilometer in length. The silkworm spins the cocoon using a single spinneret organ. Two glands inside the worm produce the two components of liquid silk, which become a solid fiber upon contact with each other and air. Interestingly, various parts of the silk cocoon appear to have different material properties, suggesting that the silk worm can vary the deposition of the two silk components to create fibers of different properties (research article). How sophisticated!
After creating a cocoon, the silkworm pupates, emerges from the cocoon, and lives a brief life, which includes mating and laying eggs. Silkworm moths cannot fly.
What's in this Instructable:
(1) A brief description of how to purchase and raise silkworms. This is covered in more depth by other sources.
(2) How to make silkworms weave flat surfaces instead of cocoons.
(3) How to provide basic location control using heating.
(4) How to use silkworms to create a composite layup
Step 1: Buying silkworms & supplies
Silkworms are available for purchase on several online stores: silkworm shop, mulberry farms, coastal silkworms. I purchased silkworms and food from the Silkworm shop.
Each of these websites offers silkworms of various sizes: small, medium, and large. The size indicates the worm maturity. Larger worms are nearly ready to spin silk, requiring approximately 7-14 days of feeding before spinning. Smaller worms require more time to feed and grow. My preference is to purchase the mature, larger silkworms.
Silk worms eat a LOT of food. For 25 large silkworms, you will need to purchase about 2-4 lbs of food to raise them to cocoon stage. Silkworms exclusively consume Mayberry leaves. Each of the online retailers also supplies a Mayberry puree.
Step 2: Raising silkworms.
There are several great places online to read about raising silkworms:
A few of my personal tips and tricks on how to raise silkworms:
(1) Wear nitrile gloves. Silk worms poop a lot. You'll be a lot happier handling them while wearing gloves.
(2) Silkworms do well at room temperature (70 degrees and above) - but cannot survive at lower temperatures.
(3) Feed the silkworms regularly. It helps to break the Mayberry food into smaller bites that are easier to consume by the worms. Add more food to the container whenever it becomes empty. The silkworms eat surprising amounts of food in the larva stage as they are growing.
(4) Use multiple growing containers. Plastic containers work well with sides of at least 5-6 inches. Silk worms seem to eat and grow and different rates.
(5) It can be helpful to move silkworms to new containers as they grow larger. This is also a good way of keeping the silkworms in a new clean location.
(6) Use a plastic grating (video) on the bottom of your container. This helps the silk worm poop to fall through to the bottom of the container, keeping it away from the silk worms and their food.
(7) When a silkworm begins to spin silk, immediately separate them from the others and begin to use them. Allowing silkworms to spin silk within their growth containers becomes a huge, poopy mess. It's not fun.
(8) Be patient. Depending on the size of the silk worms, it may take 1-2 weeks before they are ready to spin silk.
(9) When silkworms begin spinning, they don't stop. When you see a silkworm spinning, immediately apply them to your design. Fortunately, once the worms begin spinning silk, they rarely poop.
Step 3: The silk worm is spinning... now what?
So, the silk worm is now spinning... what should you do?
Here are a few possibilities:
Step 4: Spinning: Surfaces vs. Cocoon
Silkworms naturally create cocoons. But it's also possible for them to spin silk on surfaces.
When given a flat surface, a spinning silkworm deposits silk on the flat surface. The images above demonstrate the concept. The silkworm moves around on the surface, trying to find a corner or large post area to create a cocoon. Given none such areas, the worm continues to spin as it is searches, depositing silk on the surface. (Image credit: Carlos Uribe Gonzalez, Jared Laucks, Markus Kayser).
Tips for spinning silk on surfaces:
Step 5: Experiment: Temperature guided deposition
I was curious whether silk worms preferred heated or cooled areas for depositing silk. If so, perhaps temperature gradients could be used to guide silk deposition on a surface.
To test this, I hacked together a simple platform (pictured above) to create a temperature gradient. The platform was made of soda-lime glass covered with paper. Glass was selected because it is a mild insulator. A strong insulator, such as silicone and many plastics, would create a very sharp gradient. If the platform were made of a thermal conductor, such as aluminum or other metals, the entire platform would be the same temperature. Other materials with similar thermal conductivities should work as well.
(List: Thermal conductivity of common materials).
For the heat source, I used a scrap 10 W power resistor. [List of power resistors on digikey that should work] and connected it to a DC power supply. To attach the power resistor to the glass, I waterjetted a press-fit hole into the bottom of the glass and then carefully pressed in the power resistor. This really was overkill. If you're interested in doing this, use a high-temperature adhesive (high conductivity & resistant to heat) where you would simply glue the power resistor to the surface of the glass. Other types of temperature sources should work just as well
For the actual experiment, I placed 3-5 spinning worms on the surface for two days. I took the temperature of the plate using a FLIR camera. As can be seen in the thermal images, the heat pattern is oval-like due to the rectangular shape of the power resistor. The temperature gradient ranged from a hot core (around 140C) to room temperature.
The worms deposited silk in greater density near regions close to the heat source - but not too close. The heat appeared to create a sort of "campfire-effect" that attracted worms to warm regions. The surface in these regions - according to the FLIR - was around 40-80 C. The experiment was repeated twice. The room temperature was not controlled. My intuition is that if the room was very warm (perhaps 28-32C or 80 to 90F), then this effect would go away.
We didn't go any farther with this experiment. But one could imagine scaling up this approach: a surface with a controllable temperature gradient that guides silk worms to deposit silk in "programmed" locations.
Step 6: Technique: Silk worm composite layup
[The original write-up for this part of the project can be found here].
Perhaps silkworms could be used to lay-up fibers for a composite? Silk worms could be use to "print" fibers onto a surface and then a resin could be used to bind the fibers together into a strong, hard material.
Making a layup surface:
The silkworms need a surface to deposit their silk. I decided to design a simple wave in Rhino and milled a wax surface using the tabletop Shopbot.
Harvesting the silk:
I propped up the wax surface using a paper cup and put them both inside of a large blue bowl. The bowl captured any potential escapees that jumped off the wax surface.
I left the worms on the wax wave for about 2 and a half days. The worms applied more silk to the edges of the wax block.
[want to learn how to do a composite layup? This is a good step-by-step image tutorial. Vacuum bagging tutorial.]
I applied a very small amount of resin on top of the silk fiber layup. (Approximately 10-20 drops) and gently smoothed it around for an even coating. [Entropy Resin Super Sap 100 works well] Then I put the wax, fibers and resin into a vacuum bag, covered with cotton padding and vacuumed the piece overnight.
The results can be seen in the images above.
The finished piece was thin and flexible, yet retained the geometry of the wax wave. The edges of the layup were noticeably stronger and stiffer where the silkworms had deposited more fiber.
Overall the process created a material that was flexible and strong. The piece was noticeably stronger along the edges of the piece where the silkworms deposited more silk. It's unclear how much of the strength and flexibility of the piece came from the resin vs the samples. In a very simple negative control, I made small rectangular pieces of resin, which were brittle and snapped easily. So, the silk did something! But its unclear how the material would perform compare to another natural fiber, such as burlap.