What are hydrogels?
Hydrogels are a group of materials that usually contain a large amount of water and only a small number of other substances, which we classify as polymers. These polymers are long molecular chains that can be joined together by a chemical reaction or physical interactions to form a three-dimensional network – in our case, a hydrogel network. It is like tying strings together. We can knot them (polymers) firmly and systematically (by chemical reaction) or crumple them (by physical interaction). We can easily imagine that both such networks will have completely different properties – just like chemically or physically crosslinked hydrogels. The properties of the net will also vary depending on how many places and how regularly we weave it together, as well as what strings (stiff or elastic) we use to weave it. In the case of hydrogels, this depends on which molecular chains we use – i.e. polymers.
oyenlab.org
If the three-dimensional network is so-called hydrophilic, i.e. formed by water-soluble polymers, it can absorb a large amount of water without dissolving. This insoluble material, formed by a polymer network and water, is then called a (polymeric) hydrogel. But we also know three-dimensional polymer networks that contain a different solvent instead of water (organogels) or no solvent at all (various rubbers and resins). Hydrogels can also be prepared by chaining and cross-linking low-molecular substances, so-called monomers – repeating subunits of emerging long polymer chains. A rich selection of building units – polymers and monomers – along with countless cross-linking and modification reactions and hydrogel preparation methods allows us to create hydrogels with different to unique properties that will exactly meet our requirements for their intended applications, whether in the food industry or perhaps in medicine.
Many hydrogels can be found in nature: our tissues are actually complex hydrogels, but we can also prepare them synthetically from chemically modified natural polymers or from synthetic polymers. The best-known examples of hydrogels include aspic, gummy bears or soft contact lenses.
istock.org
Soft contact lenses are indeed synthetic hydrogels. The very first such hydrogel was made in 1953 at the University of Chemistry and Technology (which is our university) by chemical cross-linking of 2-hydroxyethyl methacrylate (HEMA) with ethylene glycol dimethacrylate (EGDMA). It was a PhD student of Prof. Wichterle, later professor Drahoslav Lím, who invented the material.
The resulting three-dimensional hydrophilic polymer network retained a large amount of water, and because it was transparent, Prof. Wichterle thought that this hydrogel was suitable for the preparation of soft contact lenses. The very first such lenses were prepared by casting in silicone molds, which turned out to be a less-than-optimal solution. A few years later, in 1961, Prof. Wichterle built the first so-called lens machine using centrifugal casting methods. The machine was made with the help of Merkur, which was a construction kit for children, a bicycle dynamo, and a bell transformer.
The patent of soft contact lenses was sold by the state of Czechoslovakia to the USA. Prof. Wichterle held about 180 other patents and published around 200 scientific articles during his lifetime. All this even though he was imprisoned by the Nazis and the communist regime treated him badly.
google.com
Articles and videos popularizing the topic
This long-lasting hydrogel could be used to replace damaged human tissues [VIDEO]
New hydrogel that doesn't dry-out [VIDEO]
Revolutionary gel is five times stronger than steel [ARTICLE]
People
Prof. Otto Wichterle (*1913 - †1998)
co-inventor of the first synthetic hydrogel based on PHEMA (with Prof. Drahoslav Lím), inventor of soft hydrogel contact lenses
wikipedia.org
Prof. Karel Dušek (*1930 - †2020)
devoted his life to studying the formation, structure, and properties of cross-linked polymers and polymer gels, more
imc.cas.cz
Prof. Jian Ping Gong
co-inventor of double-network hydrogels, I had the privilege to work in her lab as a postdoc
altair.sci.hokudai.ac.jp/g2
Common synthetic hydrogels generally have relatively poor mechanical properties – for example, a contact lens breaks relatively easily – and cannot compete with complex materials that we know from nature, such as tissues. This is because they are made up mostly of water and a simple polymer network that lacks possibilities for mechanisms through which mechanical energy could be dissipated (transformed into other types of energy).
Prof. Gong found that if the hydrogel is made up of two independent polymer networks, it is mechanically much stronger than the contributions of the individual networks would account for. This synergistic effect has become the subject of intensive research.
Dr. Daniel Rudolf King (*1988 - †2022)
I met Dan in Prof. Gong's lab. He was a very talented scientist and always a great companion. I will never forget.
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