Only in the fictional land of Oz does water cause witches to melt. In the real world, water is essential to life and a valuable resource. Scientifically known as H2O, it is used to irrigate crops and even to enlarge/swell biomaterial gels (more on that later). As a biomaterials scientist, I’m particularly interested in the different properties and applications of smart gels. When a colleague here at CCRM recently forwarded an article to me about a new smart biomaterial gel, and asked “why haven’t we made anything like this yet?” the metaphorical light bulb lit up and we will now be brainstorming applications and products in this field.
The properties of this new gel are opposite from what you would expect or are used to seeing in your everyday life. For example, when you heat frozen food, it thaws or melts and becomes softer. Ice, when heated, goes from a solid to its liquid form. (Apparently that’s what happened to that nasty witch.)
The smart biomaterial gel featured in the article, created by polymer chemists from the Netherlands, gets more rigid when it is heated. The Dutch scientists call their smart material a super gel, and they have spent two years trying to explain why it has this unusual property and how best to utilize it. Their intended application for the super gel was in electronics and non-biological systems, but as so often happens, they stumbled upon a way to make it biologically relevant.
The synthetic part is comprised of a polyisocyanopeptide (a stiff polymer) with polyethylene glycol (PEG) tails. PEG is a familiar polymer in the biomaterial world, and is well known for its ability to solubilize in water, and to increase the hydrophilicity (affinity for water) of whichever compound it is attached to. Here, the scientists are able to adjust the temperature at which the gel stiffens by tailoring the length of the PEG tails. When in gel form, more than 99% of the material is water.
The inventors have big plans for the super gel, and believe it will be used in hospitals sooner rather than later. At room temperature the super gel can easily be injected into the body, and once in the body it becomes rigid and can be used to support cell growth, or slowly release drugs locally over a long period of time. They even envision it being applied as a wound dressing. For example, the super gel can be injected while cold to a burn or cut, and then once applied, it would reach body temperature and seal the wound.
Needless to say, in the biomaterials community there are quite a few research groups working on similar ideas. It didn’t take me long to find another article (curiously, also in Wired) about a gel-based wound healing biomaterial. This other gel releases a compound, which is called antisense DNA, to help avoid the development of unsightly scars. By releasing the osteopontin (a protein found in bone) antisense DNA, they reduced the levels of osteopontin near the wound, and thus were able to speed up tissue reconstruction and the regeneration of blood vessels.
The gels discussed in this post are just two examples of a wider class of biomaterials known as hydrogels: gels containing mostly water. Anything containing mostly water is considered biocompatible, and thus a very popular and robust biomaterial. Hydrogel properties, such as mechanical strength and degradability, are tailorable because you can alter these properties by simply increasing/decreasing the water content or material content. It is also easy to load drugs and other small therapeutic compounds into hydrogels during the swelling process. More on the tricks and trades of hydrogel swelling in a future post, but for now think of hydrogels as super-sponges that are capable of absorbing water and anything suspended within it.
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