Hydrogels

Hydrogels are naturally occurring or synthetic polymer materials that display very diverse chemical and physical properties. These polymers are interlocked molecular networks that are either physically or chemically crosslinked to form 3D networked tissues that contain large amounts of water. In this article, there is further information about these. 

What are Hydrogels?

These super-soft, transparent materials shrink or swell when they come into contact with water (absorption and desorption), and they can hold a large volume of water without losing their structural integrity.

Hydrogels were introduced for biological use in 1960. To be recognised as hydrogel, water must compose at least 10% of its total mass and volume.

The Hydrogels’ ability to absorb water comes from hydrophilic functional groups attached to the polymeric backbone, whereas the resistance to dissolution comes from cross-links between chains of the network. Hydrogels can be made from a variety of materials, both natural and synthetic.

Natural Hydrogels including silk fibroin, hyaluronic acid, alginate, and chitosan are obtained from tissues.  Unique properties of Hydrogels include biocompatibility, biodegradability, low cytotoxicity, ability to tailor the hydrogel into an injectable gel, and similarity to physiological environments.

Although, natural Hydrogels have some limitations, for instance, neither they have strong mechanical properties nor they are easily controllable because of their batch-to-batch variation. Due to these reasons In the process of creating composite polymers, natural Hydrogels are mostly mixed with synthetic ones.

Due to their inherent biocompatibility, tunable properties, and similarity to tissue and cell environments, Hydrogels have become a highly relevant biochemical scaffold. Since the decade-long development of Hydrogels, they have evolved from static materials to “smart” responsive materials that adapt to various simulations, including pH, temperature, chemicals, electrical signals, or light.

In addition to biomedical applications, their responsive and programmable properties make them ideal for applications such as catalysts, chemical detectors, and carbon-capture absorbents.

There are types of Hydrogels: biochemical, chemical, and physical. 

• Physical gels – The gels which can convert from liquid to gel in reaction to environmental changes in pH, temperature, ionic concentration, or any other condition such as mixing of two elements.
• Chemical gels – These involve covalent bonding which introduces degradation resistance and mechanical resistance.
• Biochemical gels – the gels which contain biological agents such as amino acids or enzymes which take part in the gelation process.

How To Make Hydrogels?

The process of making Hydrogels includes 3 important processes – monomer, initiator, and cross-linker. Generally, Hydrogels can be prepared from either synthetic or natural polymers. The polymers can be crosslinked to create Hydrogels in many ways: linking polymer chains through chemical reactions. In order to generate main-chain free radicals that can form cross-link junctions, ionizing radiation is used along with physical processes like entanglements, electrostatics, crystallization, and electrostatic interactions.

In terms of their preparation methods, Hydrogels can either be homopolymers, copolymers, semi-interpenetrating networks (semi-IPN) or interpenetrating networks (IPN)

• Homopolymeric Hydrogels – are Hydrogels composed of monomers which are the building blocks of polymer networks.
• Copolymeric hydrogel – A copolymeric hydrogel is a polymer network made up of more than two monomer species arranged in a random, block or alternate configuration along the chain of the polymer.
• Interpenetrating polymeric hydrogel –  An important class of Hydrogels, multipolymer interpenetrating polymeric hydrogel (IPN), consists of two cross-linked synthetic and/or natural polymer components embedded in a network. A cross-linked polymer makes up half of a semi-IPN hydrogel, while a non-cross-linked polymer makes up the other half.

How To Use Hydrogels? 

Hydrogels are being used in many fields because of their certain structure and compatibility with various conditions to use. The property of flexibility in Hydrogels makes them possible to use in various conditions as well as the biocompatibility widens their uses in medical science.

Drug delivery

Hydrogels are good vehicles for delivering drugs into the body. Hydrogels are perfect to be used as a medium for delivering drugs into the body as they have good compatibility with living tissues and the capability to preserve immersed proteins in their natural state.

Hydrogels are composed of water, as a result, they can shrink small enough to be swallowed and expand enough in the stomach to not pass into the small intestine. Due to these properties, they are compatible to load medicine and release it in such a controlled manner.

Tissue engineering

As a medical treatment, tissue engineering seeks to replace or restore damaged, injured, or missing tissues in order to restore their anatomical structure and function. This will result in the ability to replace entire organs. Tissue engineering is based on the construction of three-dimensional scaffolds made from biomaterials which provide mechanical support and guide cell growth into new tissues or organs. Hydrogels are ideal for tissue engineering since the physical and biological properties of Hydrogels can be altered to mimic tissues.

Recently, adhesive Hydrogels are introduced to dress wounds during the surgical process. It helps in sealing the tiny wounds out so air and body fluids don’t leak. Hydrogel polymers bond to biological tissues through 3 mechanisms – physical interpretation, electrostatic attraction toward negative charge cells, and covalent bond between neighboring items. These mechanisms make adhesive super strong.

Environmental remediation 

The wastewater from many industrial processes contains heavy metals and dyes that pose a significant threat to public health and ecological systems.Scientists have found an environmentally friendly way to remove pollutants from water. It is known as the filtration of water with hydrogel material.

Contact lenses

To make contact lenses hydrogel possesses ideal properties as it contains a great deal of water, permeability towards oxygen, good mechanical properties, wettability of the surface, stability towards hydrolysis and sterilization, good optical facilities, nontoxicity, and having enough biological tolerance towards living cells.

Polymers 

Different polymers have different properties which depend on the chemical they are developed from. For instance, there are two types of POLY- (ETHENE) .

Uses of polymers:-

1. Poly(ethene) ‘polythene’ – carry bags, food wrap, shampoo bottles.
2. Poly(propene) ‘polypropylene – bucket, mat, bowl, ropes, crates
3. Poly(chloroethene) ‘PVC – Insulation for electrical wires, gutters, windows, pipes.
4. Poly(tetrafluoroethylene) ‘PFTE’ – containers at the laboratory, coating for nonstick pans.

Conclusion

In the above article we learned that too many cross-linking methods have been devised and are currently available for hydrogel synthesis. Recently, many hydrogel-based networks have been designed and tailored to meet the needs of different applications. The favorable property of these Hydrogels is their ability to swell when put in contact with an aqueous solution.