INTRODUCTION:

As demonstrated by Lee. K. won, and Park, the term ‘hydrogel’ was originally used in an article that was authored in 1894. The substance explained there was actually a colloidal gel formed of chemical salt instead of hydrogel as we know it now. It is noteworthy to observe that the term’s history has been continuously lengthy¹.

A Hydrogel is three-dimensional (3D) network of hydrophilic polymers that expands in water without changing its structure due to physical or chemical cross-linking between individual polymers chains¹.

In any case, poly hydroxyl-ethyl methacrylate (PHEMA) hydrogel was initial inter-connecting substance described in the literature. It had all the usual hydrogen feature, the most notable of which being a strong affinity for water. Hydrogels are actually the first material designed for use inside the patient; this material was developed considerably later, in 1960, with the audacious idea of using it in applications involving permanent interaction with human tissues. Hydrogel are resistant to disintegration because of cross-links between network chains², and they can absorb water because of hydrophilic functional group affixed to the structural unit of polymer. Numerous substances, both manmade and natural, meet carboxyl (COOH-), and hydroxyl groups (OH-)³. Physical, chemical, or a mix of the two crosslinking techniques can be used to create polymeric hydrogels.

Types of hydrogels:

The hydrogels are categorized into various group based on-

1. Categorizing based on sources:

a. Organic hydrogels:

These are also known as natural hydrogels. Natural hydrogels exhibits strong cell adhesion, biodegradability, and biocompatibility. Proteins like collagen, gelatin, and lysozyme (LYZ) and polysaccharides like hyaluronic acid (HA), alginate, and chitosan (Cts) are these are the main categories of organic polymers that are utilized to make organic hydrogels.

b. Synthetic hydrogels:

These are more beneficial than organic hydrogels since they be made to possess a significantly greater variety of physical and chemical properties than those around in the nature. Hydrogels derived from polyethylene glycol (PEG) are frequently employed in therapeutic context due to their non-toxicity, reliability, and poor antibodies.

c. Composite hydrogels:

These gels are created by combining organic as well as synthetic polymer of hydrogels. A range of organically occurring biopolymer, such as dextran, collagen, and chitosan, have been combined with synthetic polymers, such as poly (N-isopropyl acrylamide) and polyvinyl alcohol, to combine the benefits of synthetic and organic hydrogels⁴.

2. Categorization based on the makeup of polymers

a. Homo-polymeric hydrogels:

Also known as polymers made up of just one type of species of monomer, homo-polymeric hydrogel are the fundamental structure components of all polymer network. The cross-linked skeleton of homo-polymer is affected by the kind of monomer and polymerization process. To make homopolymers, poly (2-hydroxyethyl methacrylate, or poly HEMA) can be used as a monomer, benzoin isobutyl ether as the Ultra-Violet (UV) sensitive starter, and polyethylene glycol dimethacrylate as an interconnecting agent. After being prepared in de-ionized water, the film was exposed to UV light for 20 minutes at a distance of 11 mm from the source (λ =253.7 nm). The film was then fully sank in the water for a full day to get rid of any potentially dangerous or chemicals which are failed to react that could living tissue. Since they encourage appropriate would healing, they can also be used to manufacture fake skin and burn bandages in addition to spectacles. Also used in the creation of synthetic cartilage, bone marrow and nerve card cell recovery, and scaffolds that encourage cell adherence⁵.

b. Copolymeric hydrogels:

They consist of multiple distinct monomer species, each including a hydrophilic component. These monomers are randomly arranged in an irregular sequence along the linkages of polymeric matrix. By starting the polymerization oof BLG N- carboxyanhydride with diamine group at the end of poly (ethylene oxide) chains of poloxamer, a thermoplastic co- polymeric hydrogel based on y-benzyl L-glutamate (BLG) and poloxamer are created. Hydrogel were described for the drug delivery applications and were sensitive to pH and temperature.

c. Multipolymer interpenetrating polymeric hydrogel (IPN):

Comprising two distinct interconnecting synthetic and/or organic polymer components, the network system of this fundamental family of hydrogels is known as multipolymer interpenetrating polymeric hydrogels (IPN). The two parts of semi- IPN hydrogel are cross-linked polymers. Because networks segment continually connect, the IPN appoarch can achieve limited phase separation and overcomes thermodynamic incompatibility. It is thought that the topography and mass morphology’s sustainability guaranteed by the interlocked structure of inter-locked IPN component^{6, 7}.

3. Types of hydrogel in accordance with biodegradability:

a. Biodegradable hydrogels ( recyclable):

Hydrogels breakdown naturally. Among the several biodegradable polymers present in nature are agar, fibrin, and chitosan. Poly (aldehyde gluronate), polyanhydrides, and poly (N- isopropyl acryamide).

b. Not - recyclable hydrogels:

Numberous vinylated minutes and macropratical are used to create non- biodegradable hydrogels including 2-hydroxyethylmethacrylate (HEMA), methoxylpolyethyleneglycol (MPEG), 2-hydroxypropyl methacrylate (HPMA), and acrylamide (AAm) ⁸.

4. Categorization according to physical structure:

The following is how it is categorization of hydrogel is depended upon their chemical makeup and physical connections:

A. Undefined (Non- crystalline / amorphous).

B. Semi crystalline: a complicated mixture of definite.

5. Categorization according to interconnection:

Two types of hydrogel can be distinguished based on the characteristics of inner- connecting linkages:

· Chemically interconnected connections provides enduring relationship.

· In physical networks, transient junctions can be generated via polymer chain entanglements, hydrophobic or hydrogen bonding interactions or both ⁹.

6. Classification based on physical appearance :

· Matrix

· Film

· Microsphere

7. Classification according to connection of electrical charges:

A. Ampholytic electrolytes, or amorphous electrolytes, have both base and acid group in them.

B. Ionic that have positive and negative states.

C. Nonionic (Netural).

D. Polybetaines that have both positive and negative group are known as zwitter ions ¹⁰.

8. Classification on the bases of configuration:

The following categories of hydrogel can be developed according to their chemical and physical characteristics:

A. Permanent gel: Whenever it comes to being permanent or chemical gels, hydrogen bond - which replace stronger and more resilient covalent connections -raised questions. Their rising balance is shown by the cross-link density and the polymer water activity coefficient ¹¹.

B. Physical gel: When secondary factor like as hydrophobic contacts, hydrogen bond, or ionic forces hold the networks together, they are called physical or reversible gels. To stop dissolving, the various polymer gel are physically cross-linked. Any one of these reversible relationship could be disrupted by stress or environment changes ¹².

9. Release controller:

· Time controlled hydrogels.

· Intelligent or stimulus -induced hydrogels¹³.

Current and emerging application of hydrogels:

1. Biocompatibility:

Research on hydrogel biocompatibility started in the 1960s. The concept of biocompatibility postulate that complex responses arise from the interaction of biological component with the human body. The research team demonstrated the high biocompatibility of hydrogel by injecting them into the experimental body and using them to treat bone and joint injuries without inducing inflammatory response.

2. Biodegradability:

By interacting with the biological environment, materials that are biodegradable can undergo a sequence of events that eventually lead to their progressive degradation into monomers or low molecular weight molecules. Surgical implant at the forefront of medical technology, interventional therapy and in vivo drug delivery are major issues in the profession right now, But major safety issue are by the drug delivery system complex metabolism and the interventional materials rejection. Biodegradable and high-performing hydrogel can be created by modifying combining hydrogels, since they are biocompatible substances.

3. Medical dressing:

The most common conditions seen in hospitals are trauma and trauma infection. Medical dressings can help wounds heal by absorbing wound exudate fluid and serving as a protective barrier over wounds. Because of their excellent flexibility, biocompatibility, and capacity to absorb liquids and generate a most environment for tissue regeneration, hydrogel dressings are a perfect choice for medical dressings. Furthermore, the hydrogels slip-elastic nature effectively reduces the risk of subsequent damage from wound adhesion.

4. Medication administration:

Medication administration are technologically advanced devices designed to deliver therapeutic drugs with precision and/or under regulated distribution. Because hydrogel may use to store medication, regulate the medication distribution rate and drive its release, manage its hardness and strength of formulation, promote decomposition, and hide the smell of pharmaceutical, they are more advantageous when it comes to medication distribution and carriers.

5. Pulp regeneration:

By implanting pulp stem cells that have been cultured in vitro. The application of tissue engineering techniques to pulp regeneration involves the use of a biocompatible, absorbable, and degradable biological scaffold. Through this process, pulp stem cells are stimulated to create pulp-like tissue and pulp-dentin complexes, which are subsequently utilized to repair injured pulp tissue and return it to its normal physiological state.

6. Cardiac repair:

One of the main conditions endangering people’s health is myocardial infarction. Heart failure results from the large-scale necrosis and scarring of myocardial cells following myocardial infarction. The use of direct heart transplantation as a cardiac repair procedure is influenced by rejections reaction and donor numbers, notwithstanding the procedure’s poor success rate. Although cardiac repair via cell transplantation is a more effective treatment for heart failure, this strategy has not been widely used in practice because cells do not retain well after transplantation¹⁴.

7. Natural Tissue Repair:

Peripheral nerve injury (PNI) affects a patient’s capacity to do daily tasks and causes loss of moto, sensory, and other autonomic functions. It also causes axonal continuity disruption, distal nerve fiber degeneration, and neuronal Using artificial biomaterials and autologous nerves for bridging repair is the classic surgical strategy to treating peripheral nerve injury (PNI); however, the restricted supply of autonomic nerves and their mismatch in size restrict its utilization.

8. Bone tissue repair:

Effective treatment strategies are necessary to encourage bone tissue regenerations and repair since anomalies in the bone caused by sickness, trauma, aging, and other illnesses are extremely harmful to the human body. Due to the lack of sources for bone grafting material, the unsoundness of donor bone tissue for allogeneic bone grafting, the risk of infection and its after effects, and other factors, bone grafting remains an essential therapy option for bone defect even though its application has been restricted¹⁵.

9. Impairment of spine nerves Repair:

It is defined as damage to the spinal cord that causes temporary or permanent changes to its function. Tetraplegia and intractable neuralgia are among the severe sequelae that affect the majority of SCI patients. Mesenchymal stem cell transplantation (MSC transplantation) is a valuable therapeutic modality for spinal cord injuries yet its limited clinical use due to a low cell transplantation survival rate.

10. Biomonitoring:

Several kinds of conductive polymer hydrogels can be created by mixing conductive fillers with various polymer matrices. Researchers are drawn to conductive hydrogels because they are a novel functional hydrogel material. They have developed capacitive sensors with conductive hydrogels on order to tract human activity.

Merites of hydrogels:

Because of hydrogel water contract they are relatively flexible, much like genuine muscles. Timely distribution of nutrient and medications. Hydrogels can be injected and biocompatible. Hydrogels are able to sense changes in pH, temperature, and metabolic concentrations and discharge of their weight in react to these alterations. Hydrogels are easily modifiable and have good transport qualities. Controllable physical properties and more efficient drug loading compound. Natural hydrogels are easily degradable and form desirable scaffolds for cell encapsulation and adhesion. Growth factors and other nutrients are released on schedule to ensure the development of natural cells. Microbiological cell entrapment in polyurethane hydrogel nanoparticle, that offers the advantages of little toxicity¹⁶.

Demerites of hydrogel:

Hydrogel’s high cost is one of its drawbacks. Hydrogel contact lens material have the following disadvantages, hypoxia, tens deposition, and red eye reaction. Challenging to sterilize. The risk associated with the surgery needed to install and remove the device. Its mechanical strength is modest¹⁷.

New approches of hydrogel:

Ø Hydrogel show’s some effect on architecture on cell activities like cell behavior, also provide tool for cell expansion. Hydrogel is type of multifaceted platform with various medico-biological administration ¹⁸.

Ø Hydrogel is use in chemotherapy, as hydrogel is present in injectable form. They are biodegradable. Features of injectable hydrogel -

a) They are thermosensitive.

b) They are pH sensitive.

c) They are photo sensitive.

d) They are dual sensitive.

Injectable hydrogel -based drugs are more effective than normal systemic drug in can certreatemen. As hydrogel released its drug at site of tumor.

Ø Hydrogel use in treatment of eyes (ophthalmology) related issues like corneal diseases, cataract surgery, fundus diseases, glaucoma¹⁹.

Ø The preservation of RNA biological activity is made possible by the distinct physiochemical characteristics of hydrogel. Hydrogel has the potential to enhance RNA stability and minimize needless loss of therapeutic agents.

Benefits of using hydrogels as a delivery system of RNA:

I. Pulsatile release of RNA on demand.

II. Multiple release are not required.

III. Extented RNA release.

IV. Local treatment at illness site.

V. Preseving the bioactivity of RNA.

VI. Less impact off target²⁰.

· Hydrogel use in cartilage repairing. New structure of hydrogel are designed to increase its mechanical properties to approach those of hyaline cartilage²¹.

· A new approached it detection of incomplete antibodies using hydrogel chromatography medium (HMC).

· The properties if hydrogen includes flexibility, suppleness, high absorption capacity when expanded, non- toxicity, compatibility with living tissues, natural break down, and mechanical properties that can be adjusted. When hydrogels warm up to temperature, they transform from liquid into a gel -like substance. Hydrogels are frequently benign to live tissues and can be injected. Hydrogel act as protective cushions for cells, allowing them to absorb nutrients and preventing damage. They also serves as a barrier to safeguard sensitive medications, guaranteeing their continued efficacy after being absorbed by the body^{22, 23}.

· After severe damage, the intervertebral disc (VD) showed amazing structural and functional recovery thanks to the novel nano hybrid peptide hydrogel (NHPH) method. It promoted efficient regeneration by progressively releasing pro-regenerative cytokines, which inhibited immunological responses and created a favorable milieu in the extracellular matrix (the electrocardiogram)²⁴.

· Using hydrogel as a carrier is really helpful for studying how to regenerate pulp. It help deliver treatment precisely and creates a good environment for cells to grown back, making it easier to develop new ways to regenerate pulp²⁵.

· Hydrogels loaded with drug that fight inflammation and AID tissue regrowth can effectively improve gum health and promote periodontal regeneration in people with gum diseases²⁶.

Method of preparation of hydrogel:

The hydrogel qualities of polymer network is called hydrogel. Typically, hydrogel are prepared from hydrophilic monomer; however, hydrophobic monomers can also be utilized to deal with characteristics of resultant for a given usage. In general, hydrogel are synthesized by organic polymers or artificial polymers:

· The artificial polymers are water- resistant in nature and chemically stronger in comparison to real health.

· Natural polymer are also help in preparation of hydrogel and they provide these polymer haves appropriate active groups.

Generally, the hydrogel is synthesis process consist of 3 essential elements: monomers, starter, and inter- connecting agent. Diluted such as water or another watery solution, that can employed to control the polymerization process’s heat and the properties of the resulting hydrogels. After that, a wash is required to get rid of any contaminants from the preparation process of hydrogel²⁷.

There are following method utilized to create gel:

· Mass polymerization

· Mixture polymerization

· Suspended polymer polymerization

· Mass polymerization: hydrogel can be produced with a wide variety of vinyl monomers. One or more kind of monomers can be used to create mass hydrogels. A small amount of inter connecting reagent is typically added to all hydrogel parts. Rays, UV, lights, or artificial catalysts can typically initiate the polymerization process. The most basic method of work polymerization employees monomer solver started and common monomers. The high concentration of monomers is one factor contributing to the increase degree and rate of polymerization. When submerged in water, the crystalline, rigid, and incredibly stiff polymer matrix produced by mass polymerization of monomers hydrogels that are soft and flexible^28,29.

· Mixture/inter- connecting polymerization:

In a combination co-polymerization/inter-connecting reaction, ionized or neutral monomers are combined with a multifunctional inter-connecting reagent. One of two things can cause thermal polymerization: UV light or a redox initiator mechanism. Solution polymerization has an advantage over bulk polymerization since it uses a solvent as a heat sink. The produced hydrogel needs to be rinsed with pure water to get rid of the starter, cross-linking agent, monomers, and oligomers, among other contaminants. Phase separation and the creation of the heterogeneous hydrogel occur when the water used in polymerization exceeds the water content equal to the equilibrium swelling. For the solution-based polymer synthesis of hydrogel, ethanol, water, benzyl alcohol, and their combination are the recommended solvents^{30, 31}.

· Polymeric suspension or reverse suspended polymer: One benefit of dispersion polymerization is that it produces polymer without the need for crushing, in the form of powders, small particles, or crystals. In the method, the monomers and the catalysts are dispersed evenly throughout the hydrocarbon phase. The dispersion requires content stirring and suspension with the minimal hydrophilicity-lipophilic equilibrium (HLB) agent suspending due to its thermodynamic instability^{32, 33}.

Clinical trial summary:

We found a bunch of new clinical trials. Some involve using hydrogel on the skin, while others involve implants that aren’t injected. People are trying out different types of hydrogel for things like wound dressing, contact lenses, and patches that deliver medicine through the skin. They are testing these on various condition such as radiation burns, diabetic sore, and regular burns. Different materials used for these topical treatments include things like synthetic carbomers, chitosan, and poloxamer among others.

CONCLUSION:

Hydrogel stuff is really cool for medicine because they can copy natural body tissue and bring different medicine where they need to go. Our look at it syas that hydrogels have been changed into over 100 medical products, like for making people look better, fixing tissues, healing wound, giving support, and such. New hydrogels in coils, stents, wound patches for burns and ulcers. People are even male birth control. Some are meant to be put inside you like medicinal implants or on you like bandages.

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Received on 27.12.2024 Revised on 22.05.2025

Accepted on 05.08.2025 Published on 16.03.2026

Available online from March 18, 2026

Research J. Pharmacy and Technology. 2026;19(3):1415-1420.

DOI: 10.52711/0974-360X.2026.00204

This work is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License. Creative Commons License.