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  • Subject area(s): Engineering
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  • Published on: 7th September 2019
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The term “hydrogel” dates back to 1894 and was actually the first biomaterial made for human use. Hydrogels are known to absorb water and are most commonly used for diapers. Back then, it was a colloidal gel that was made with inorganic salts but developed much later into what we describe as a hydrogel. Hydrogels are cross linked polymers that often contain carboxylic acid groups. Polymers are composed of repeating structural units called monomers. “Covalent bonds hold the atoms in the polymer molecules together and secondary bonds then holds groups of polymer chains together to form the polymeric material” (“Polymer Structure”). The polymer chains typically exist in the shape of randomly coiled molecules that contain negative charges. The negative charges along the polymer chain resist each other and attract water (“Products from Oil”). The most typical hydrogel property and actually the first was a polyhydroxyethylmethacrylate (C6H10O3)n. The “n” means there are many more.

Over the years, the development of hydrogels changed and increased constantly over the years; which can be split into three generations. Claimed by L’Hocine Yahia, first generation hydrogels deal with a wide range of cross linking procedures that involves the chemical modification of a monomer or polymer with an initiator. “The general aim is to develop material with high swelling, good mechanical properties and relatively simple rationale” (L’Hocine Yahia). Second generation hydrogels had the capabilities to respond to specific stimuli, such as pH, temperature, or concentration of specific molecules in solution (L’Hocine Yahia). And finally, the third generation of hydrogels which focuses on the investigation and development of stereo complexed materials and hydrogels being cross linked by other physical interactions (L’Hocine Yahia). To this day, the progress of hydrogels continues to increase, which could possibly change the future for human use.

According to gcsescience.com, hydrogels can hold up to five hundred times its own weight of pure water. When their surroundings begin to dry out, the hydrogels gradually dispense  up 95% of their stored water and repeats the absorbing process when exposed to water again (Megan) Hydrogels are very responsive to pH, temperature, and salt concentration, which causes the change of structure in the polymer chains. Just by adding salt, it can have a significant effect on the amount of water hydrogels can hold. “The negative charges along the chain repel each other less in the presence of the sodium ions and so the chain becomes more coiled up” (“Products from Oil”). The coiled up structure of the chain actually squeezes out the water from the hydrogel.

Some current uses of hydrogels are soft contact lens, diapers, wound dressings, and drug delivery systems (“Products from Oil”). Currently, there is a research on utilizing hydrogels to develop smart windows in order to keep heat out but still let light in. Although the swelling of hydrogels in heat poses as a flaw. Yes there are currently “smart glass” on the market, but they block out the light. Luckily, researchers have found a solution for smart windows. “A novel thermally responsive hydrogel (TRH) has been demonstrated by confining poly(ethylene oxide), poly(propylene oxide), and poly(ethylene oxide) triblock-copolymer (EPE) molecules into the pores of polymer framework” (“Thermally Responsive Composite Hydrogel via Self-Assembly for Smart Window Applications\"). Claimed by Hindawi, “the transmittance of TRH can reach almost zero when the temperature is above 30°C. It is found that the TRH based smart window can complete a phase separation process in 1 min using a 12 V DC power source or in 4 mins using a 9 V battery.” Smart windows can revolutionize and change how much we spend on electricity and reduce the consumption of energy.

There is also a current research on utilizing hydrogels to possibly create the future Band-Aid. Jennifer Chu says that “the key to the design is a hydrogel matrix designed by Xuanhe Zhao, the Robert N. Noyce Career Development Associate Professor in MIT’s Department of Mechanical Engineering. The hydrogel, which Zhao detailed earlier this month, is a rubbery material, mostly composed of water, designed to bond strongly to surfaces such as gold, titanium, aluminum, silicon, glass, and ceramic.” This hydrogel-based Band-Aid can imitate the physiological and mechanical properties of the human body. It contains electronic sensors, reservoirs, and drug delivery channels. The sensors can sense an abnormal temperature at certain regions of the body which activates the drug delivery channels to deliver a specific type of medicine to the body. The Band-Aid of the future could possibly help a lot on treating burns or other skin conditions.

Hydrogels are quickly developing in the biomedical industry. Researchers are hoping to find a way to harness hydrogels to quickly heal wounds. Developing this new type of hydrogel may have the ability to rebuild blood vessels in order to speed up the healing process of wounds. It may even prevent scarring.

People typically do not know the term “hydrogel” or maybe even heard of it. We actually use hydrogels in our everyday lives. Diapers, contact lenses, and even in agriculture. Hydrogels have been around for centuries and has developed to be a revolutionary biomaterial for human use.

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