Boogers, snot, and loogies—mucus doesn’t usually inspire pleasant thoughts. Even the word “mucus” grosses people out. Despite our unpleasant reactions to this slimy substance, mucus is a superhero in our battle to maintain a healthy internal environment (our microbiome) and to keep our bodies functioning smoothly. In this resource, you will learn about mighty mucus and use slime as a model to explore some amazing properties of this vital, albeit icky, substance.

The Lowdown On Mucus

Mucus is not a waste product or just fuel for a sneeze. Even when we are blowing our noses, mucus is providing a valuable service. We have mucus all over our bodies—our eyes, noses, throats, lungs, digestive tract, and even genitalia. It is estimated that we create one gallon of mucus a day, and yes we are swallowing mucus all the time.

How Does Mucus Help Us Out?

1. Mucus acts as a physical barrier, trapping unwanted particles from entering our bodies and flushing them from our body. Think runny nose!
2. Mucus moisturizes tissues in our body, acting as a lubricant. Without mucus, we couldn’t blink, swallow, or even poop!
3. Mucus can defend against infection by facilitating the movement of antibodies or white blood cells to sites of infection, and even altering the behavior of pathogens!
4. Mucus helps house the human body’s massive microbiome, even working to ‘tame’ it, making sure normally beneficial microbes don’t go rogue.

What Is Mucus Made Of?

One of the researchers uncovering the amazing properties of mucus is Katharina Ribbeck, biochemist and principal investigator at the Laboratory for Biological Hydrogels at MIT. Ribbeck’s lab group has shown that mucus can interfere with bacterial behavior, preventing communication with other bacteria and even attachment to surfaces. Mucus also fosters and houses microbial communities that help our bodies in a variety of ways. Their work has shown that cervical mucus of pregnant women can potentially be used as a predictor for preterm labor, much of which is shown in its physical properties. Whoa!

Ribbeck was on Science Friday to discuss some of the seriously cool science behind mucus.

Mucus is a type of slime. Below are three different synthetic slime recipes that you can use to model mucus. Although these slime recipes are relatively safe, please create slime with the supervision of an adult. We recommend using gloves if you have sensitive skin.

Slime #1: Gelatin Slime

Ingredients

— ½ cup water (125 mL)
— 3 packs gelatin (approx. 7 g)
— ¼ light corn syrup (62.5 mL)

Directions

1. Heat water (do not boil) and mix in gelatin with a spoon.
2. Let mixture cool slightly, then gently mix in light corn syrup.
3. Use your spoon to stretch and play with your slime!

Slime #2: Classic Borax Slime

Ingredients

— ¼ tsp borax powder (found with laundry products)
— ½ cup clear washable PVA school glue (like Elmer’s Glue™)
— 1 cup of water divided into ½ cups

Directions

1. Dissolve the borax powder into ½ cup of warm water.
2. Separately, mix ½ cup of clear glue with ½ cup of water.
3. Pour borax-water mixture into glue-water mixture and stir with a spoon. It will be clumpy.
4. Remove from bowl and knead the mixture together until you achieve desired slime consistency.

Slime #3: Contact Solution Slime

Ingredients

— 1 ½ tbsp contact lens solution (one that contains boric acid and sodium borate)
— ½ tsp baking soda
— 2 tbsp water
— 6 oz clear washable PVA school glue (like Elmer’s Glue™)

Directions

1. Empty the entire 6 oz container of glue into a bowl.
2. Add baking soda and water and mix thoroughly.
3. Slowly add a ½ tbsp of contact lens solution, while stirring. Then mix/knead the mixture.
4. Repeat the previous step until the desired consistency is reached.

Want to make it more icky looking? Add food coloring during the initial step of any recipe to alter the color of your slime. A little goes a long way.

Slime Reflection

For each slime recipe, reflect on the following questions:

• — What does your slime feel like?
• — When you pull your slime upwards does it stretch or break?
• — How watery does your slime seem?
• —How easily does your slime flow or pour? Does it have a low viscosity (pours easily) or a high viscosity?
• —Rub your slime between your hands. Does it reduce friction between your hands (lubricate) or increase it?
• —Try plopping your slime onto a dusty or dirty surface. Does it capture small particles or leave them behind?
• —BONUS: How could you quantify how moist your slime is?

Challenge: After learning more about the mucus related research of Ribbeck and her lab group at MIT, which slime recipe do you think is the “best” model of mucus? Justify your choice using information you learned about mucus above.

Scientific models are simplified representations of a system that can help us to explain and make predictions regarding phenomena. You are going to use slime as a model to explore the mucus system in different bodily areas and functions.

Mucus produced in different cavities and surfaces in the body varies widely. The mucus layer over your eye is not the same as the one secreted in your nose. Mucus even changes based on life events or changes in health. Ever had a runny nose? Also, remember the cervical cancer example discussed at the beginning of this activity.

Think about the different ways that mucus helps you, or put another way, the functions it performs in your body. How might the characteristics (e.g, viscosity, moisture, stickiness) of that mucus be different in each of those scenarios?

Create Your Mucus Models

Using information from Katharina’s Science Friday interview, the video above, and the collection of mucus resources below identify three functions or properties of mucus you want to model.

Choose a slime recipe that you think would best model the mucous function you are trying to demonstrate. Manipulate the recipe (by incorporating more or less of different ingredients) to achieve the viscosity or consistency you think would best support a particular function.

Mucus Model Reflection

For each of your three models, reflect on the following questions:

• — What property or function of mucus were you trying to model?
• — What consistency or viscosity were you trying to create?
• — How did you alter the recipe to create your model?
• — How did this change model for this function of mucus effectively?
• — What are the limitations of your model?

Meet the giant larvacean and its house built of snot! Humans are not the only organisms that create biological hydrogels like mucus. In fact, many marine organisms have a mucus layer the keeps them healthy and some even serve ecological functions. Giant larvacean are solitary free-swimming marine animals that use mucus to trap food!

Learn more about the giant larvacean from The House That Snot Built Science Friday segment. After exploring more about how giant larvaceans create their snot houses. Think about your three slime recipes:

• — How you would model a marine mucus that can function as a filter?
• — How would you test that model?

• — Why Do We Have Snot? (MIT Explains)
• — How Mucus Keeps Us Healthy
• — Mucus: The Body’s Unsung Hero
• — Everything You Didn’t Want To Know About Snot
• — What Is Your Snot Saying?
• — Mucus, Our Body’s Silent Defender

Also, check out Katharina Ribbeck’s lab at MIT.

4-LS1-1 From Molecules to Organisms: Structures and Processes
Construct an argument that plants and animals have internal and external structures that function to support survival, growth, behavior, and reproduction.

MS-LS1-3 From Molecules to Organisms: Structures and Processes
Use argument supported by evidence for how the body is a system of interacting subsystems composed of groups of cells.

Science and Engineering Practices

• — SEP 2: Developing and using models
• — SEP 6: Constructing explanations and designing solutions