On Household Hydrogels

Hello, everybody! My friend N.Tesla has invited me to place some science here. So you know I’m not some hobo off the street (donations always accepted), I’m Vincent Stoddle, a chemical engineer about to go to graduate school for my Ph.D. I want to go into drug delivery using nanotechnology but I’m fascinated by anything in the nanotech area as well as in biology.

 

I thought it would be interesting to show how today’s research is connected to the stuff in your pantry, garden, and bathroom. So a lot of drug companies are working on extending the release of drugs, or trying to target certain places in the body. Some methods are using hydrogels to hold onto the drug until it reaches the designated location and then release it either by diffusing out the drug, or by dissolving the gel itself. This is actually one of the many treatments for cancer that are being studied right now. “But Vincent,” you may ask, “Why would such a smart and awesome material be in my house, and can I be curing cancer with it?” Well my friend, it’s because hydrogels were already in your house before they were being used for this research, and no, you can’t cure cancer with your household hydrogels.

Okay, I’m getting ahead of myself. Before we can go listing off the hydrogels in your house, it might help to know what a hydrogel is. It’s a plastic that is very hydrophilic. This means it will interact very strongly with water and will dissolve in it. “But Vincent,” you may ask, “Why would I want a plastic that dissolves in water?” Well my friend, a hydrogel has two main components: a polymer and a cross-linker. A polymer is a compound made up of many repeating units that usually form long chains. This makes up the bulk of the hydrogel and determines its properties, while the cross-linker binds the whole mess together. The cross-linker is usually in a very low concentration so it doesn’t affect the properties of the hydrogel. So the polymer is highly soluble in water and the water tries to surround the polymer strands and push them apart, but the cross-linker keeps the polymer strands together in one solid piece.

This is exactly what it looks like under a microscope

This is exactly what it looks like under a microscope Source

By changing the polymer, cross-linker, and the ratio of the two, you can create many different hydrogels with a wide variety of properties, which would explain why they’re on your dessert plate and in your bathroom.

Dat Jiggle

Dat Jiggle Source

Your first, and most delicious, household hydrogel is Gelatin which is a mix of peptides and proteins that are derived from collagen in animal connective tissue and skin. Proteins are folded chains made of peptides which are just amino acids which are important biological molecules.  When you boil the gelatin you break apart the proteins into strands which are open to more interaction with the water and to cross-linking between peptides. It creates this mesh of peptides and proteins that hold all the water in the bowl. As the gelatin cools the peptides bond together and form the hydrogel with very flexible bonds with a lot of space in between them to hold water. This is what gives gelatin its jiggle and volume. The peptides are very good at holding the water which is why you usually don’t see the gelatin leaking juice unless you heat it up which breaks the peptide bonds.

So soft and wet.

So soft and wet. Source

Now if you’re one of those 35 million people reading this while wearing contacts, then you already know about our second household hydrogel. Yes, soft contact lenses are nothing more than very flexible, very leaky, and very transparent hydrogels. The newer ones are made from silicone as the polymer, because they allow more oxygen to pass through. The problem though is that it makes them stiffer and not able to hold as much water, since they have to leave space for the oxygen to pass through. There are some lenses that have tried to fix this by reducing the amount of cross-linking in the lenses and allowing more water to fit in.  All this is controlled while retaining the ability to be shaped to change your vision. Now along the lines of drug delivery, these are actually being looked at for transport of some eye medicines. Soon you won’t even need eye drops! Just more contacts.

So the next type of hydrogel can be found in two places in your home. I’ll give you a hint, it doesn’t always smell good, and if you don’t handle it right, then it can get really messy. Give up? Well this hydrogel is usually kept in its dry form since they want to absorb a lot of water very quickly.

I don't need it. I don't need it.

I don’t need it. I don’t need it. Source

Still not get it? Okay, the first place you’ll find superabsorbent polymer is in your potting soil. Yep they want to hold onto a large amount of water so that you don’t have to water your plants every 4 hours. The same polymer is also in your baby’s diaper. Yep, what better way to contain a spill than to soak it up into a hydrogel that works better than, like, 1000 thirsty sponges. Just watch this video and see for yourself. So the next time you’re running low on Huggies, just put your kid in the garden and let ’em run free.

You could even try stuffing one into the other.

You could even try stuffing one into the other.

So whether you’re a gardener, a parent, a Jell-o connoisseur, or just blind, then you’re loving your own household hydrogels.

-V.Stoddle

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