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Sweet Self-Assembly


Published on Dec 13, 2018

Abstract

The "Sweet Self-Assembly" program focuses on the creation of macrocapsules using self-assembly techniques. Participants make edible macrocapsules using techniques similar to those being used in laboratories to make nanocapsules or “smart drugs”.

Aim

Self-assembly can be used to create new materials including nanocapsules.

Goals

As a result of participating in this program, visitors will be able to:

1. Identify self-assembly as a process by which molecules and cells form themselves into specific, ordered structures under the right conditions.

2. Acknowledge that self-assembly can be used by scientists to create objects on the nano-scale.

3. Understand that nano is very, very small.

4. Discover that scientists are using self-assembly to create nanocapsules which can be less harmful than regular medicines.

Program-Specific Background

Alginate Beads

Sodium alginate, a seaweed extract, is a common thickening agent found in products such as syrups, Cool Whip®, ice cream and fruit filled snacks. Calcium chloride is a type of salt. When the two solutions come into contact, a chemical reaction occurs. Alginate molecules are long and stringy and have multiple negative ions. Sodium (Na+) bonded to the alginate has a positive charge which balances out the negative charge of the alginate. When the sodium alginate solution is dropped into the calcium chloride bath, calcium ions (Ca2+) replace the sodium ions. This reaction causes the long chains of alginate molecules to form a gel and self-assemble around the filler ingredient (which is combined in with the sodium alginate solution) creating capsules or beads. This process is used extensively in molecular gastronomy, a new branch of cooking. In molecular gastronomy, chefs will mix a variety of favors to create “fake caviar.”

Self-Assembly and Nanotechnology

Through scientific innovation, nanotechnologists now have the ability to move and arrange atoms. Though an amazing feat, this process remains a time-consuming and impractical solution towards building macroscale quantities of nanoscale objects. To streamline this process, scientists are experimenting with a process called self-assembly.

Common in the natural world, self-assembly is a process by which molecules and cells organize themselves into functional structures. This happens millions of times a day in a variety of ways. In fact, all living things, including human beings, contain structures that are self-assembled. A prime example in humans is the construction of DNA. Genetic codes and sequences guide the process of self-assembly, which occurs under specific conditions.

Nanotechnologists use self-assembly to make the manufacturing of nanomaterials fast and cheap. The trick to self-assembly lies in the understanding how specific conditions like temperature and pressure affect how molecules interact as the conditions are often unique to each self-assembly process. Scientists can use molecules’ natural tendencies to bond in very specific patterns under certain conditions to build smaller, more complex, and greater quantities of structures.

Nanocapsules

Self-assembly is being used extensively in the creation of nanocapsules. A nanocapsule is any nanoparticle that has an outside shell and a corresponding hollow interior. Ranging in size, these capsules are often submicroscopic, but constructed from millions of nanoparticles. The interior can be filled with a number of different substances. These nanocapsules, also referred to as “smart drugs,” can be used to create a more targeted drug delivery system. The capsules are created with specific chemical receptors that will only bind to specific cells. This breakthrough allows medicine to go directly to the diseased cells without affecting the healthy cells. It also allows for lower dosages of medicine as it will go directly to the needed source. This could result in as much as a 10,000-fold decrease in drug doses. With such a decrease, the harmful side effects of treatments such as chemotherapy could be greatly minimized.

Materials

• Sodium Alginate (Food Grade)

• Calcium Chloride (Food Grade)

• Blender

• Four Bowls – alginate, water, calcium chloride, and water rinse

• Flavoring (Ice Cream Toppings, snow cone flavors, etc)

• Food Coloring (Optional – To intensify color)

• Strainers

• Eye Droppers or Needleless Syringes

• Meter Stick

Procedure

Step 1:

Making the solutions:

Mixture 1:

Mix ½ teaspoon of sodium alginate powder and 1 cup of water in a blender. Blend until the sodium alginate powder has fully dissolved.

Add in 4 tablespoons of selected flavor. Blend again.

Let sit for 15-30 minutes to remove air bubbles.

Mixture 2:

Measure 2 ¼ cups of warm water into a large bowl or plastic container. Dissolve ¾ teaspoon of calcium chloride into the water and stir.

Procedure and Discussion:

Today, we are using self-assembly to make capsules. Have you ever heard of self-assembly? No? Well, you might not have heard of it, but you wouldn’t be here without it. Self-assembly is a process by which molecules and cells organize themselves into functional structures. It happens naturally millions of times a day and creates things like snowflakes, viruses and even you. Let’s do a yummy experiment, so we can learn more about this process.

Procedure

Try This!

1. Fill a pipette or needleless syringe with the alginate solution.

2. Put a few drops in the water bowl. Ask the visitors what they see.

3. Put the strainer into the calcium chloride solution.

4. Slowly squeeze out small drops of the alginate solution into the strainer while it is submerged in the calcium chloride bath.

5. Results: Sodium alginate beads will form immediately upon impact with the calcium chloride solution.

6. Rinse the beads in a clean water bath before allowing consumption

What's Going On?

What happened when the sodium alginate solution hit the water bath? Nothing, right? The solution dropped to the bottom and spread out. Okay, now what happened when the sodium alginate solution hit the calcium chloride solution? That’s right; it created little balls or capsules. Now, I’m sure you are asking yourself, “What is sodium alginate and calcium chloride and how do they do that?”

Sodium Alginate is a seaweed extract used as a common thickening agent. You eat it all the time in food like Cool Whip®, syrup and ice cream. Calcium chloride, the stuff we mixed in the water for our ‘bath’, is basically a type of salt, but different from table salt. When the two come into contact, a chemical reaction occurs that causes the sodium alginate to self-assemble around the filler ingredient and create the nice, round capsules you see. And since we used food-grade chemicals with our [insert flavor], they are safe to eat. Want to give one a try?

The cool thing is that scientists are using this same process in a lab to make really, really, really, really small nanocapsules. Have you ever heard of nano? Nano is just a measurement that means really, really small. How small is nano? Well, a nanometer is one-billionth of a meter. That means it is one billion times smaller than this meter stick here (show meter stick). Do you think you could break this stick in a billion pieces? It would be pretty tough and the pieces would be really, really tiny. Nano is tiny!

Scientists are actually in labs creating capsules just like we did here but on a much smaller scale. It would be really hard to make something you can’t see with your eyes, right? Well, scientists are using that process we talked about, self-assembly, to make things come together like they want them to. They set the right conditions and voila, they have really, really tiny capsules with medicine inside. These capsules are so small that we can’t even see the individual capsules with our eyes.

They have made these capsules even more special by “programming” them with special chemical receptors that stick only to sick cells. Currently, some medicines are really strong and can harm healthy cells as well as the sick cells. This is one of the reasons why treatments like chemotherapy for cancer are so hard on the body. With these nanocapsules, the medicine will only go to and affect the sick cells. Also, since the medicine goes straight to where it needs to go, they can use less medicine which is a really good thing. Just imagine, these really, really tiny nanocapsules which you can’t individually see with your eyes can make you better, faster.

Conclusion:

Self-assembly can help us make some really great things, like our yummy big capsules or really tiny nanocapsules that can help sick people get better. As long as scientists set the right conditions, they can make these capsules quickly and easily. It’s amazing that something so small could make a major impact one day on medicine!

References:

1. Maddox, Dianne Maddox. 2005. Science on the Edge: Nanotechnology. Blackbirch Press.

2. Johnson, Rebecca L. 2006. Nanotechnology. Lerner Publications Company.

3. http://www.nanonet.go.jp/english/kids/k-make/organization.html

4. http://www.sciencemuseum.org.uk/antenna/nano/skin/131.asp





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