What do Orbeez, Jell-O, and the inside of a diaper have in common? You probably already know the answer based on the article’s title, but in case you don't, they're made out of hydrogels!

What is a Hydrogel?

A hydrogel is a three-dimensional structure of several connected polymer chains that retain water. To simplify, it's a material where molecules link up to form chains, and those chains link up to each other to serve as a semipermeable barrier that allows the water inside to move semi-naturally, depending on the elasticity of the chains.

History

Hydrogels aren’t new; in fact, they were around even before World War I, since 1894. They were regarded as a “colloid gel” when a scientist described the substance as derived from an inorganic salt. It wasn’t until the 1960s that hydrogels gained significant attention when chemists O. Wichterle and D. Lim developed and sold the world’s first synthetic hydrogel, pHEMA, as commercial contact lenses.

Ever since then, their invention has not only made lasting impacts on the optometry field but also on the study of hydrogels and their diverse applications in a multitude of industries, especially biomedical.

Hydrogels in Medicine

Because of hydrogels’ hydrophilic properties and biocompatibility (suitable to be in contact with tissue or a body system), scientists have been able to utilize them for wound dressings and tissue regeneration.

In a medical setting, hydrogels are thin, transparent, and stretchable sheets that provide a moist environment. This optimizes the healing process, as it has been observed to speed up the production of blood vessels, tissues, and necessary collagen.

Hydrogels’ flexible structure allows them to fit easily into any crevice of the body, protecting wounds from external infections and diseases. And because of their semi-permeability, hydrogels can be injected with growth factors and stimulants that seep into the wound at a controlled rate, thus speeding the healing process even more.

Because of their characteristics of being customizable and adaptable, hydrogels are rivaled by traditional fabric dressings like gauze, which can dry out wounds and damage newly developed tissue upon removal.

Since hydrogels have been proven to accelerate skin tissue growth, they have been utilized as scaffolds to regenerate other types of tissue, ranging from bones and cartilage to other organs. A scaffold’s framework mimics the extracellular matrix (ECM) of tissue, allowing the damaged area to integrate seamlessly with the cells in the tissue. The moist environment that hydrogels provide is a breeding ground for cells, allowing them to multiply, differentiate into their appropriate cell type, migrate, and stitch together until it forms tissue. Thanks to hydrogel’s biodegradability, they decompose and exit the body via excretion once their purpose has been served.

Despite the success hydrogel scaffolds can have in saving lives, they have limitations. Their poor mechanical strength makes the scaffold sensitive to external and internal stress, making them prone to tearing. Because of hydrogels’ semi-permeability, they’re susceptible to swelling in an aqueous environment, which can compromise their efficiency. Additionally, hydrogel scaffolds often fail in complex tissues where multiple distinct ECMs are present with different types of cells, compared to simpler tissues. Lastly, the scaffold’s overly simplified microvascular system can fail in delivering nutrients to newly created cells, rendering them necrotic or “dead.”

Indeed, scientists have a long way to go before hydrogels become a trusted household name for families and hospitals. Until then, let’s appreciate their ability to save us from the mess of a baby’s bottom while we enjoy a nice cup of Jell-O.