What makes something hydrophilic

Hydrophilic substances have the ability to absorb and hold water. Hydrogels are a type of hydrophilic polymers that are widely utilized in sanitary products, biomedical engineering, bioseparation, agriculture, food processing, and oil recovery, to mention a few.

The characteristic property of these hydrogels is to absorb water and swell. Hydrophilic hydrogels also have a soft character along with biocompatibility. Hydrogels are copolymers or homopolymers that are prepared by crosslinking of monomers. These monomers have an ionizable group or a functional group that can be ionized. Hydrogels may contain weakly basic groups like substituted amines, or weakly acidic groups like carboxylic acid, or strong basic and acidic groups like quaternary ammonium compounds and sulfonic acids.

All these ionic groups make the hydrogels hydrophilic. Polyacrylates and sodium polyacrylates are superabsorbent hydrophilic hydrogel polymers that are used in making diapers.

These superabsorbent hydrogels can hold water equivalent to times their own weight. Hydrophilic hydrogels are similar to the extracellular matrix and for this reason, they are widely being explored for making artificial tissue scaffolds.

Due to biocompatibility, hydrophilic hydrogels are widely used in biomedical applications. Gelatin is one of the widely used hydrophilic hydrogels. Gelatin is most commonly used for preparing capsules.

The hydrophilic hydrogel also helps to hasten the wound healing process and hence they are widely used as a wound-healing agent. Hydrophilic hydrogels are superabsorbent materials that are also widely used in drug-delivery systems, tissue repairing, and cosmetics.

Hydrophilic super porous hydrogels are used as disintegrants or super disintegrants in a tablet for achieving fast drug release from the tablet. Hydrophilicity is a critical criterion for the absorption of a drug molecule. It is a well-established fact that for the absorption of a drug in the human body, the drug should be in a solubilized state.

Hydrophilic drugs tend to easily dissolve and are solubilized, thereby enabling drug absorption. Thus, hydrophilic drugs having suitable permeability have a higher probability of getting absorbed in the body easily and exert their therapeutic effects. Hydrophilic substances are coated onto the surface of medical devices to reduce bacterial adhesion onto the surface of the medical device. Hydrophilic polymers like, polyvinylpyrrolidone PVP , polyurethanes, polyacrylic acid PAA , polyethylene oxide PEO , and polysaccharides are widely used as anti-fouling coatings on medical devices like catheters, stents.

As soon as any medical device is placed in the body, the deposition of the protein layer is initiated. Over a period of time, this layer becomes very thick and can result in serious side effects viz. Hence, it is necessary to circumvent the formation of the protein layer on the surface of the medical device. Hydrophilic polymers act as an anti-fouling agent and thereby resist the build-up of this protein layer over the surface of the medical device. Additionally, these hydrophilic polymers help to reduce the coefficient of friction thereby enabling ease of installation of the medical device in the body.

For a similar reason, but in a different application, hydrophilic polymers or surfaces are used in parts of the marine structure that are used underwater. Due to compatibility with water, hydrophilic surfaces face reduced friction underwater, thereby aiding in their easy movement underwater.

Hydrophilic polymers are used as an anti-fouling agent on the filtration membranes in reverse osmosis RO filtration. Polymers like cross-linked poly ethylene glycol PEG , Triethylene glycol dimethyl ether triglyme , Cellulose-based, etc are used in RO filtration membranes.

Being hydrophilic in nature, these polymers allow filtration of water through them and concurrently resist the development of a bacterial layer over them.

Fluoride acid treatment to dental implants is carried out to increase the hydrophilicity of the dental implants. This results in reduced healing time, the easy establishment of the implant, and also a firm anchoring of the implant. If there are no local regions of high or low electron density in the molecule, it is called hydrophobic Greek for "water-fearing". This term arises because hydrophobic molecules do not dissolve in water.

If a molecule has areas where there is a partial positive or negative charge, it is called polar, or hydrophilic Greek for "water-loving". Polar molecules dissolve easily in water. Improvements in hydrophilic and hydrophobic surfaces could provide ketchup bottles where the condiment just glides right out, glasses that never fog up, or power plants that wring more electricity from a given amount of fuel. Photo courtesy of Rong Xiao and Nenad Miljkovic.

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