A REVIEW: FORMULATION OF HYDROGEL

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Patel et al. World Journal of Pharmacy and Pharmaceutical Sciences

A REVIEW: FORMULATION OF HYDROGEL

Disha Patel*, Prof. Bhavna Joshi, Dr. Umesh Upadhyay

1Vii Semester B-Pharm, Sigma Institute of Pharmacy, Bakrol, Ajwa, Vadodara -390019

(Gujarat, India).

2Assistant Professor, Sigma Institute of Pharmacy, Bakrol, Ajwa, Vadodara -390019

(Gujarat, India).

3Principal, Sigma Institute of Pharmacy, Bakrol, Ajwa, Vadodara -390019 (Gujarat, India).

ABSTRACT

Thermo sensitive hydro gel formulation contains polymeric materials.

Hydrogels are hydrophilic, highly water swell able polymer networks

which capable to converting chemical energy into mechanical energy

and vice versa. They can be tailored regarding their chemical nature

and physical structure, sensitiveness to external stimuli and

biocompatibility. Hydrogel are water swollen polymeric material and

that able to maintain a distinct three dimensional structure. Hydrogels

are sensitive to different environmental stimuli like pH, temperature,

ion, electric signals, light, pressure, antigen specific, enzyme sensitive,

and glucose levels. Hydrogel used in delivery of drug through various

routs like ophthalmic parentral drug, oral, nasal TDDS and also in

NDDS like in nanoparticles. Now a day’s stimuli sensitive hydrogels are also used in

administration of DNA.

1. INTRODUCTION

Hydrogels are a hydrophilic polymers that can swell in water and hold a large amount of

water and maintaining the structure.[1]

Approaches of dosage form designs require a carrier

which should be biocompatible and bio sensitive like hydrogels.[2]

A three-dimensional

network was formed by cross linking polymer chains.[1]

The cross- linking polymeric these

structures insoluble in water due to anionic interaction and hydrogen–bonding. Cross linking

can be provided by covalent bonds, van der Waals interactions, or physical entanglements.

Hydrogels can protect the drug from hostile environments.[3]

Hydrogen bonding these

WORLD JOURNAL OF PHARMACY AND PHARMACEUTICAL SCIENCES

SJIF Impact Factor 7.632

Volume 9, Issue 11, 938-957 Review Article ISSN 2278 – 4357

*Corresponding Author

Disha Patel

Vii Semester B-Pharm,

Sigma Institute of

Pharmacy, Bakrol, Ajwa,

Vadodara -390019(Gujarat,

India).

Article Received on

04 Sept. 2020,

Revised on 24 Sept. 2020,

Accepted on 14 October 2020

DOI: 10.20959/wjpps202011-17625


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structures biological fluids in large amount at least 10-20 times of their molecular weight,

thus become swollen.[2]

Drug release in response to external stimuli, and are most

investigated. Hydrogels having such ‘sensor’ properties can undergo reversible volume phase

transitions or sol-gel phase transitions upon changes in the environmental condition such

These properties of polymers play important role in drug delivery.[4]

Hydrogels have been

used extensively in the development of the smart drug delivery systems.[5]

The hydrophilicity

of the network is due to the presence of hydrophilic groups such as -NH2, -COOH, -OH, -

CONH2, -CONH -, and -SO3H. In order to design hydrogels with the desired performance

and structure, determination and characterization of hydrogel network parameters are very

significant. morphological and thermal, we have discussed some important characterization

techniques physicochemical, morphological and structural, and thermal such as infrared

spectroscopy, X-ray diffraction analysis, atomic force microscopy, electron microscopy,

thermal gravimetric analysis, differential scanning calorimetric, etc., and the applications of

hydrogels with patents were discussed.[55-57]

2. Classification of hydrogel

2.1 Classification based on generations

2.2.1 First generation hydrogel

A class of hydrogels introduced in approximately 1900 is described as colloidal gel of

inorganic salt,[5]

which is formulated through the polymerization of water‐soluble monomers

with multifunctional cross‐linkers or with hydrophilic polymers through cross‐linking.[6]

During this time, materials having high swelling ability and good mechanical properties were

developed. Chemical structures of few first‐generation hydrogels are shown in Figure.[6]

Fig 1: First generation hydrogel.[6]


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2.2.2 Second generation hydrogel

The factors included heat, pH, ionic strength, light, and concentration of specific monomer in

the solution. These specific environmental factors can be controlled to alter proper-ties such

as drug release, gel formation, biodegradability, and dissolution.[6]

2.2.2.1 pH‐Sensitive Hydrogels

All the pH-sensitive polymers contain pendant acidic (e.g. carboxylic and sulfonic acids) or

basic (e.g. ammonium salts) groups that either accept or release protons in response to

changes in environmental pH.[7]

pH sensitive hydrogels used to encapsulate proteins in

acrylamide polymer cross-linked with bisacrylamide acetal cross linkers. pH in various

tissues and cellular compartments shown in table 1.[8]

Table 1: Ph in various tissues and cellular compartments.[8]

Tissue/cellular compartment pH

Blood 7.35–7.45

Stomach 1.0–3.0

Duodenum 4.8–8.2

Colon 7.0–7.5

Early endosome 6.0–6.5

Late endosome 5.0–6.0

Lysosome 4.5–5.0

2.2.2.3 Temperature‐Responsive Hydrogels

Many polymers exhibit a temperature-responsive phase transition property. The structures,

LCST AND UCST of some of those polymers are shown in fig. 4 and table 2 respectively.[7]

Fig. 4: Structures of some temperature-sensitive polymers.[7]


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Table 2: Lcst and ucst of several typical thermosensitive polymers.[7]

Polymer LCST ⁰C

Poly(N- isopropylacrylamide) (PNIPAM) 32

Poly(N,N-diethylacrylamide) (PDEAM) 25

Poly(N-ethylmethacrylamide) (PNEMAM) 58

Poly(methyl vinyl ether) (PMVE) 34

2.2.3 Third generation hydrogel

Although the effect of temperature and pH on the properties of hydrogels was studied

extensively from 1970 to 1990, however in the mid‐1990s, other physical factors like

self‐assembly process, cross‐linking through enzymes, and stereose-lective interaction

became the focus of many research activities. In this era, focus shifted toward investigating

and developing complex materials, which were ste-reochemically active in nature like

polyethylene glycol–polylactide (PEG–PLA) and cyclodextrins.[9-12]

Special focus was laid

on the mechanical strength and elasticity of hydrogels synthesized during this period.[13]

These hydrogels are more advantageous as in situ they provide enhanced opportunity for

homo-geneous mixing of cells and proteins with the polymeric solutions before hydro-gel

formation.[14]

They are formed in the body after injection of reacting precursors in the

body.[15]

Hydrogels are a special class of cross‐linked polymers that have the capability to

hold water molecules within the spaces present among the polymeric chains. They are agents

with high water content synthesized using cross‐linked poly-mers and are very important as

they can provide sustained, local delivery of various therapeutic agents. Hydrogels having the

strength to retain more than 95% water within their structure are termed superabsorbent and

are able to show high compatibility with living tissues due to this large extent of water. These

gels can be biodegradable and can be classified into different groups such as ionic or neutral

hydrogels, physically or chemically cross‐linked, stimuli‐responsive hydrogels, and natural or

synthetic hydrogels. Stereo complexed nano hydrogels were considered more innovative

because of their potential in the controlled release of proteins, encapsulation of living cells

for a long period of time (up to 15 days), and biocompatibility.[16-18]

Although the first report

about them was published in 1957, not too much interest was shown in this period; however,

from 1990 onward, numerous reports were filed about their synthesis, characterization, and

utilization.[19-20]

Poly‐l‐lactic acid (PLLA) and poly‐d‐lactic acid (PDLA) are examples of

optically active polymers having the same chemical structure but with different chiralities. In

solid form, PLLA forms the left‐handed helix, while PDLA furnishes the right‐handed helix.

This polymer is crystalline in nature, and both helices are densely packed due to the presence


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of van der Waals forces, which unite the two helices together to give birth to a stereocomplex

polymer. In such polymers stereocomplex crys-tals are formed at shorter distance toward

polylactide (PLA) block lengths, and finally aqueous solutions of both mix together through

cross‐linking to furnish a hydrogel. Nowadays, both PLLA and PDLA are complexed

together to prepare injectable hydrogel.Researchers are presently focused on the enhancement

of mechanical perfor-mance of hydrogels with potential applications in many areas; however

in this chapter, special attention will be focused on drug delivery applications of nanohy-

drogels. Researchers are now involved in synthesizing topological hydrogels and double

hydrogels.[21]

Nanoscale dispersion of layered silicates or clay polymer network technique is

now in operation to synthesize nanohydrogels with improved properties. Acrylamide

(AAm)‐based monomers together with synthetic hec-torite clay, laponite as a physical

cross‐linker can be used to prepare nanocompos-ite hydrogel, replacing the traditional

chemical cross‐linker.[22]

Laponite forms disk‐like particles having a thickness of 1 nm and a

diameter of 25 nm when sus-pended in water. These nanoparticles with negative charge

density bear the capa-bility to serve as multifunctional cross‐linkers for different

applications.[23]

2.2 Classification Based on Source

Based on source hydrogels can be classified into two groups: hydro-gels synthesized from

synthetic sources (synthetic hydrogels) and hydrogels iso-lated from natural sources like

cellulose, collagen, CS, fibrin, matrigel, agarose, alginate, hyaluronic acid (HA), gelatin

cellulose, and chalkstone (natural hydro-gels).[24-26]

2.3 Classification of Interpenetrating Network Hydrogels

2.3.1 Homopolymeric Hydrogel

Hydrogels derived from a single species of monomer are termed homopolymeric hydrogels,

which is the basic structural unit of any polymer network.[27-28]

Polyvinyl alcohol (PVA), PEG, polyvinylpyrrolidone (PVP), and polyacrylic acid (PAA) are

the polymers used to synthesize homopolymeric hydrogels. Hence are widely used as

efficient materials for controlled release of drugs.[29]

2.3.2 Copolymeric Hydrogel

Hydrogels composed of two types of monomer in which at least one is hydro-philic in nature

are called copolymeric hydrogel. Triblock poly(ethylene glycol)–poly(ε‐caprolactone)–


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poly(ethylene glycol) (PECE) is a biodegradable co polymeric hydrogel that can be used for

the development of drug delivery systems.[30]

2.3.3 Semi‐interpenetrating Hydrogels

If one linear polymer is allowed to penetrate into the other polymer, which is already

cross‐linked without the need of chemical bond, it is called semi‐IPN hydrogel. This hydrogel

effectively responds to pH changes and temperature variations.[31]

PVP, PEO, polyether are example for the preparation of semi-interpenetration hydrogel.[32-36]

2.4.4 Interpenetrating hydrogels

IPN hydrogels are defined as the combination of two polymeric compounds in which one is

either synthesized or cross‐linked immediately with the other.[37]

3. Release mechanism of bio therapeutic molecules from

Temperature sensitive hydrogels

The release mechanisms of compounds from hydrogel, the drug release mechanisms can be

classified as: (i) passive diffusion, (ii) erosion of hydrogels, and (iii) Chemical control. The

most important and common release mechanism of thermo-sensitive hydrogels is passive

diffusion, and different sizes of biotherapeutic molecules which entrapped in the gel matrix

that can diffuse freely which depending on the size of the mesh of the gel matrix.The

behavior is influenced by several parameters which including the degree of cross-linking, the

chemical structure of monomer and the intensity of external stimuli. The typical mesh size of

temperature-sensitive hydrogels as reported ranges from 5 to 100 nm in swollen state which

is much larger than most small molecule drugs. Thus, the diffusion of these drugs is free in a

swollen state, while macromolecules such as oligonucleotides, peptides and proteins will

exhibit sustained release unless the structure andmesh size of the swollen hydrogel are

properly designed to achieve the desired diffusion rate. In the case of erosion-controlled

mechanism, the release of biotherapeutic molecules is depending on the rate of erosion.

Finally, chemical controlled release is determined by the chemical reactions in the gel matrix,

including polymeric chain cleavage by hydrolysis or enzymatic degradation, or reversible/

irreversible reactions that occur between the polymer network and the release of the drug.[38]


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4. Method of preparation of hydrogel

4.1. Solubility

Normally the hydrogel content of a given material is estimated by measuring its insoluble

part in dried sample after immersion in deionized water or 48 h at room temperature. The

sample should be prepared at a dilute concentration (typically ~ 1%) to ensure that hydrogel

material is fully dispersed in water. The gel fraction is then measured as follows:

Gel Fraction (hydrogel %) = (Wd/Wi)*100

Where, Wi is the initial weight of dried sample and Wd is the weight of the dried insoluble

part of sample after extraction with water.[39]

Gelling agent; Eg, glycophosphate1-2propanediol, glycerol, trehalose, mannitol etc used in

the preparation of hydrogels. Usually the problem of turbidity and presence of negative

charged moieties.[2]

4.2 Use of water and critical conditions of drying

Aerogels of carbon have been prepared by super critically controlling the drying

conditions.eg: Aerogels of resorcinol formaldehyde hydrogels. The method is expensive but

leads to formation of which are associated with this method pose problem of interaction with

the drug xerogels with good mechanical strength.[2]

Fig. 3: Hydrogel preparation block diagram.[40]


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4.3 Use of Cross linkers

4.3.1 Physical cross-linking

There has been an increased interest in physical or reversible gels due to relative ease of

production and the advantage of not using cross-linking agents. These agents affect the

integrity of substances to be entrapped (e.g. cell, proteins, etc.) as well as the need for their

removal before application. Careful selection of hydrocolloid type, concentration and pH can

lead to the formation of a broad range of gel textures and is currently an area receiving

considerable attention, particularly in the food industry.[41]

Fig. 4: Schematic representation of the steps involved in preparation of hydrogel.[41]

The physical hydrogels (also called self-assembling hydrogels) are formed when

macromolecules self-assemble through non-covalent, secondary molecular interactions such

as hydrophobic, electrostatic, and H-bonding. In physically cross-linked gels, dissolution is

prevented by physical interactions, which exist between different polymer chains (Fig.5).[42]

Fig. 5: Representation of physical cross linking of hydrogel.[42]

4.3.2 Chemical cross-linking

Chemical cross-linking covered here involves grafting of monomers on the backbone of the

polymers or the use of a crosslinking agent to link two polymer chains. The cross-linking of

natural and synthetic polymers can be achieved through the reaction of their functional


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groups (such as OH, COOH, and NH2) with cross-linkers such as aldehyde (e.g.

glutaraldehyde, adipic acid dihydrazide). There are a number of methods reported in literature

to obtain chemically cross-linked permanent hydrogels. Among other chemical cross-linking

methods, and hydrophobic interactions, (incorporating a polar hydrophilic group by

hydrolysis or oxidation followed by covalent crosslinking crosslinking) are also used to

obtain chemically cross-linked permanent hydrogels. The following section reviews the

major chemical methods (i.e. crosslinker, grafting, and radiation in solid and/or aqueous

state) used to produce hydrogels from a range of natural polymers.[43]

In chemically cross-linked gels, covalent bonds are present between different poly-mer

chains. Usually chemical modifications are performed to produce cellulose derivatives either

by esterification or etherification.[44]

Chemical cross-linking isa highly versatile method to

create hydrogels with good mechanical stability. However, the cross-linking agents used are

often toxic compounds, which will be extracted from the gels before they are utilized

(FIG.6).[45]

Fig. 6: Represantation of chemical cross linking of hydrogel.[45]

4.4 Use of Nucleophilic substitution reaction

Nuclrophilic group are electron rich center so they used for preparing hydrogels. A pH and

temperature sensitive hydrogel viz. hydrogel of N-2-dimethylamino ethylmethacrylamide

(DMAEMA) has been prepared using nucleophilic substitution reaction between methacyloyl

chloride and 2-dimethylamino ethylamine.[2]


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4.5 Isostatic ultra high pressure (IUHP)

Polymerization is done by subjecting monomer to ultra-high pressure at constant temperature.

Suspension of natural biopolymers (eg.-starch) are subjected to ultra-high pressure of 300-

700 MPa for 5 to 20 minutes in a chamber which brings about changes in the morphology of

the polymer i.e. gelatinization of starch molecules occur. Temperature in the chamber varies

from 40 to 52 C.[2]

4.6 Freeze thawing

Freeze thawing method imparts sufficient mechanical strength and stability to the hydrogels

except that they are opaque in appearance with little swelling capacity S. Mohammad et al.,

prepared freeze-thawed PVA/kaolinite nano composite hydrogels. Freeze-thawed nano

composite hydrogels were prepared on the basis of polyvinyl alcohol (PVA) containing 0, 5,

10, and 15 wt% of kaolinite (based on the dried hydrogel). The micro-structure of nano

composite was investigated using the X-ray diffractometry (XRD) and transmission electron

microscopy (TEM) techniques. Intercalated morphology was observed for all prepared nano

composite hydrogels. The effect of kaolinite on the mechanical properties of PVA/kaolinite

nano composite hydrogels was studied using uniaxial tensile test (ASTM D-1822-99),

dynamic mechanical thermal analysis (DMTA), and hardness measurement. Remarkable

increases on the tensile modulus and tensile strength were observed for the nano composite

hydrogels, e.g. 228 and 131% increases were achieved in tensile modulus and tensile strength

by incorporating 15% wt of kaolinite into PVA hydrogel, respectively. The DMTA test was

performed in the compression mode, using disc-shaped samples with a diameter of 11 mm

and a thickness of 5 mm. It was shown that the storage modulus of PVA hydrogel increases

by increasing the kaolinite content.[46]

4.7 Use of irradiation

Irradiation method is suitable as well as convenient but the processing is costly along with

the poor mechanical strength of the product. High energy radiation like gamma and electron

beam has been used to prepare the hydrogels. The irradiation of aqueous polymer solution

results in the formation of radicals on the polymer chains, resulting in the formation of macro

radicals. Recombination of macro radicals on different chains results in the formation of

covalent bonds, and finally a cross linked structure is formed.[46]


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4.8 Grafting

Grafting involves the polymerisation of a monomer on the backbone of a preformed polymer.

The polymer chains are activated by the action of chemical reagents, or high energy radiation

treatment. The growth of functional monomers on activated macro radicals leads to branching

and further to cross linking (FIG.7).[46]

Fig. 7: Grafting of a monomer on performed polymeric backbone leading to infinite

branching and cross linking.[46]

5. Characterization of hydrogel

Fig. 8: properties of hydrogel


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1. Homogeneity

Homogeneity is determined by visual inspection after the gel shave been set in the

container.[47]

2. pH

pH can be determined by using digital pH meter.[47]

3. Clarity

The clarity is determined by visual inspection against white background.[47]

4. Viscosity

Viscosity of formulation can be checked by Brookfield viscometer (Capcalc V2.2) using

model 1x with cone number 01, at an angular velocity of 5 RPM and shear rate of 66.66 for

time interval of 10 sec. at respective gelation temperature for formulation.[49]

5. Gel strength

A sample of 5 gm of formulation is gelled at 37°C. A weight of 3.5 gm is placed on the gel

surface. The gel strength is then determined by the time in seconds required by the weight to

penetrate 0.5 cm in the gel. The gel strength is then reported.[50]

6. Spread ability

Spread ability can be determined by wooden block and glass slide apparatus. Weights about

20 gm are added to the pan and the time can be noted for upper slide (movable) to separate

completely from the fixed slide. The normal range of spread ability is 5-7 gm.cm/sec.[50]

Spread ability is can be calculated by using the formula:

S = ML/T

Where,

S = Spread ability (gm.cm/sec.).

M = Weight tied to upper slide.

L = Length of the glass slide.

T = Time taken to separate the slide completely from each other.

7. Bioadhesive strength

Bioadhesive strength can be determined by measuring the force required to detach the

formulation from cellophane membrane by using wooden block and glass slide apparatus. 1

gm of gel is taken on glass slide wrapped with cellophane membrane. The movable glass


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slide is placed on fixed slide and intimate contact is provided. Two minute contact time is

given to ensure intimate contact between membrane and formulation. The weight is added in

the pan until slides get detached.[48]

The bioadhesive force, expressed as the detachment stress in dyne/cm2 is determined by the

formula:

Detachment stress = m·g/A

Where, m = Weight required to detach two glass slides from each other (gm).

g = Acceleration due to gravity (980 cm/s2).

A = Area of membrane exposed (cm2).

8. PPL (Plane Polarized Light) imaging

Investigation of the gels for the presence of liquid crystals can be done by examination under

polarized light microscope (Lawrence and Mayo, London) equipped with cross polarizer and

attached todigital Nikon Coolpix P6000 camera and monitor. A small quantity of the sample

is placed on a clean glass slide. The existence of birefringence is verified by observation

under crossed polar employing magnification of 20X and 40X.Photomicromicrographs of

these samples are taken.[51]

9. Drug content

A specific quantity (100 mg) of developed gel is taken separately and 100 mg of gel is

dissolved in 100 ml phosphate buffer solution having pH 7.4. The volumetric flasks

containing gel solutions are shaken for 2 hrs. By using mechanical shaker in order to get

complete solubility of drug. Solution is filtered and estimated spectrophotometrically using

phosphate buffer solution of pH 7.4 as blank.[50]

6. Applications of hydrogels

Fig. 9: Application of hydrogel.[41]


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6.1 Applications of hydrogels in drug delivery

Hydrogels have been used for the development of controlled delivery systems for a long time.

When the drug bearing hydrogel comes in contact with aqueous medium, water penetrates

into thesystem and dissolves the drug. The diffusion of the drug through the hydrogels may

be affected by the property (viz. pH sensitivity, light sensitivity, pressure sensitivity) of the

hydrogel depending on the chemistry of the hydrogels and has been used successfully to

design delivery systems which may release drug at a suitable environment.[41]

6.2 Applications of hydrogels in tissue engineering

Tissue engineering (TE) is a multidisciplinary approach and involves the expertise of

materials science, medical science and biological science for the development of biological

substitutes (tissue/organ). It is emerging as an important field in regenerative medicine. It has

got three basic component namely, cells/tissues, scaffolds and implantation and/or grafting.

The pore size of the scaffolds should be >80 μm. Recently the use of resorb able hydrogels in

TE has gained much importance because

a) It is easy to process the polymers;

b) The properties of the hydrogels can be tailored very easily; and

c) Resorb able polymers like polylactic acid (PLA), polyglycolic acid (PGA), and their co-

polymers (PLA-co-PGA; PLGA) are being used for biomedical application since long

time.[48]

6.3 Applications of hydrogels in wound healing

The use of hydrogels in the healing of wounds dates back to late seventies or early eighties.

Hydrogels help in maintaining a micro-climate for biosyntheticreactions on the wound

surface necessary for cellular activities. Hydrogels may be transparent, depending on the

nature of the polymers, and provide cushioning and cooling/ soothing effects to the wound

surface. The main advantage of the transparent hydrogels includes monitoring of the wound

healing without removing the wound dressing.[52]

6.4 Application of hydrogels for gene delivery

Gene delivery is defined as the incorporation of foreign DNA particles into the host cells and

can be mediated by viral and nonviral methods. The delivery of gene into the host cells by

utilizing a virus uses the capability of a virus to incorporate its DNA into the host cells. For

the purpose retroviruses and adenoviruses have been used. These viral vectors are used as

they can provide efficient transduction and high gene expression.[53]


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.6.5 Technical Features of Hydrogel for Biomedical Applications

The technical features of hydrogel are listed as follows which is suitable for biomedical

applications.[54]

Utmost stability and constancy in a swelling environment and storage time

Utmost absorption ability (maximum equilibrium swelling)

Preferred rate of absorption, particle size, and porosity

pH-neutral, colorless, odorless, and absolutely nontoxic

Highest absorbency under load (AUL)

Photo stability, low soluble content, residual monomer, and low price

Rewetting capability of the hydrogel able to give back the imbibed solution or maintain it

as needed (e.g., in agricultural or hygiene applications)

6.6 Peroral drug delivery

The pH-sensitive hydrogels have a potential use in site-specific delivery of drugs to specific

regions of the GI tract. Hydrogels made of varying proportions of PAA derivatives and cross-

linked PEG allowed preparing silicone microspheres, which released prednisolone in the

gastric medium or showed gastro protective property. Cross-linked dextran hydrogels with a

faster swelling under high pH conditions, likewise other polysaccharides such as amide

pectins, guar gum and inulin were investigated in order to develop a potential colon-specific

drug delivery system.[58]

6.7 Rectal delivery

The rectal route may be used to deliver many types of drugs that are formulated as liquid,

semi-solid (ointments, creams and foams) and solid dosage forms (suppositories).

Conventional suppositories often cause discomfort during insertion.[1]

Marketed formulation of hydrogels

Trade Name Drug Name Used

Relday Risperidone Schizophrenia and bipolar disorder

oncogel paclitaxel Anticancer therapy

Timoptic-XE Timolol malate glucomma

Eligand Leuprolide acetate Treatment of postate cancer

POSIDUR Bupivacain Post operative pain

7. COUNCLUSION

Compared with other types of biomaterials, hydrogels have distinct properties such as high

water content, controllable swelling behavior, ease of handling, as well as biocompatibility,


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which makes them as attractive material for biomedical applications. Hydrogels, which are

three-dimensional cross-linked polymeric networks able to swell in large amounts of water,

should be considered prime candidates for carriers or matrices for cells in tissue engineering,

self-healing materials, and delivery vehicles for drugs and biomolecules. Environmentally-

sensitive hydrogels have enormous potential in various applications. Some environmental

variables, such as low pH and elevated temperatures, are found in the body.

In the future, hydrogel-based carriers can be an excellent candidate for the successful

administration of drugs at the desired rate and site in the body. Specific release rates and

dissolution profiles could be achieved with the development of new hydrogels with different

hydrophobicity/hydrophilicity and structural characteristics.

These systems could improve the delivery of more sensitive molecules and be employed in

the treatment of pathologic conditions such as diabetes or even cancer. Specifically, more

developments are expected in the use of hydrogels for delivery of therapeutic proteins and

peptides.

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A REVIEW: FORMULATION OF HYDROGEL

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