2.hydrogels

Presented By: SANDEEP MOLLIDAINM.Pharmacy (pharmaceutical technology)Dept. of pharmaceutical technology.Vsp.

CONTENTS

•Introduction•Classification of Hydrogels•Advantages of Hydrogels•Disadvantages of Hydrogels•Types of Hydrogels •Monomers Used In The Synthesis of Synthetic Hydrogels•Method of Preparation of Hydrogels•Characterization of Hydrogels•Common Uses For Hydrogels•Pharmaceutical Applications of Hydrogels•Summary and conclusions•References•Acknowledgement

2

Introduction:

Hydrogel is a network of polymer chains that are

hydrophilic, water insoluble, sometimes found as a

colloidal gel in which water is the dispersion medium.

Hydrogels are highly absorbent natural or synthetic

polymers.

Definition:

3

Introduction:

Hydrogels are crosslinked polymer networks that absorb

substantial amounts of aqueous solutions.

Hydrogels can contain over 99.9% water.

Hydrogels are three-dimensional, hydrophilic, polymeric

networks capable of imbibing large amounts of water or

biological fluids.

4

Introduction:

The networks are composed of homopolymers or

copolymers, and are insoluble due to the presence of

chemical crosslinks (tie-points, junctions), or physical

crosslinks, such as entanglements or crystallites.

The high water content of the materials contributes to

their biocompatibility.

5

Introduction:

These crosslinks provide the network structure and

physical integrity.

These hydrogels exhibit a thermodynamic

compatibility with water which allows them to swell in aqueous media.

6

Classification Of Hydrogels:

7

Advantages of Hydrogels :

Hydrogels possess a degree of flexibility very similar

to natural tissue, due to their significant water content.

Entrapment of microbial cells within Hydrogel

beads has the advantage of low toxicity.

Environmentally sensitive Hydrogels have the

ability to sense changes of pH, temperature, or the

concentration of metabolite and release their load as

result of such a change.8

Advantages of Hydrogels:

Timed release of growth factors and other nutrients

to ensure proper tissue growth.

Hydrogels have good transport properties.

Hydrogels are Biocompatible.

Hydrogels can be injected.

Hydrogels are easy to modify.

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Disadvantages of Hydrogels:

Hydrogels are expensive.

Hydrogels causes sensation felt by movement of the maggots.

Hydrogels causes thrombosis at Anastomosis sites.

The surgical risk associated with the device implantation and retrieval.

Hydrogels are non-adherent; they may need to be secured by a secondary dressing.

Hydrogels are expensive.

Hydrogels causes sensation felt by movement of the maggots.

Hydrogels causes thrombosis at Anastomosis sites.

The surgical risk associated with the device implantation and retrieval.

Hydrogels are non-adherent; they may need to be secured by a secondary dressing.

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Disadvantages of Hydrogels:

Hydrogels used as contact lenses causes lens

deposition,hypoxia, dehydration and red eye

reactions.

Hydrogels have low mechanical strength

Difficulty in handling.

Difficulty in loading.

Difficulty in Sterilization11

Types of Hydrogels :

Natural Polymers

e.g.: Dextran, Chitosan, Collagen, Dextran Sulfate

Disadvantages:

Low mechanical Strength.

Batch variation.

Animal derived materials may pass on viruses.12

Types of Hydrogels :

Synthetic Polymers

e.g.:Poly (vinyl alcohol)

Disadvantages:

Low biodegradability

Can include toxic substances

13

Hydrogels can be used in different types of controlled release systems.

These are classified according to the mechanism controlling the release of drug from the device as

- Diffusion controlled systems.- Swelling controlled system.- Chemically controlled system.- Environmental responsive systems.

Classification Of Hydrogel Based Systems:

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Diffusion is the most common mechanism controlling release.

In hydrogel based drug delivery system. There two types : -Reservoir devices. -Matrices devices

Diffusion is the most common mechanism controlling release.

In hydrogel based drug delivery system. There two types : -Reservoir devices. -Matrices devices

Diffusion Controlled Release Systems:

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Reservoir devices:

They consists of polymeric membrane surrounding a core containing a drug .

Typically reservoir devices are capsules, cylinders, slabs or spheres.

Rate limiting step for drug release is diffusion through the outer membrane of the device.

Reservoir devices:

They consists of polymeric membrane surrounding a core containing a drug .

Typically reservoir devices are capsules, cylinders, slabs or spheres.

Rate limiting step for drug release is diffusion through the outer membrane of the device.


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Draw backs:

In the event that the outer membrane ruptures the entire content of the device are delivered instantaneously .

While preparing these device care must taken to ensure that the device doesn't contain pin holes or defects that may lead to rupture.

Draw backs:

In the event that the outer membrane ruptures the entire content of the device are delivered instantaneously .

While preparing these device care must taken to ensure that the device doesn't contain pin holes or defects that may lead to rupture.


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Matrix devices:

In matrix devices the drug is dispersed through out the 3D structure of the hydrogel.

Release occur due to diffusion of the drug through out the macro molecular mesh or water filled pores.

Matrix devices:

In matrix devices the drug is dispersed through out the 3D structure of the hydrogel.

Release occur due to diffusion of the drug through out the macro molecular mesh or water filled pores.


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In these release drug systems the drug is dispersed within a glassy polymer .

Up on contact with biological fluid, the polymer begins to swell.

As the penetrant enters the glassy polymer, the glass transition temperature of the polymer is lowered allowing for relaxations of the macro molecular chains.

Swelling Controlled Release Systems:

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They are of two types:

Erodible drug delivery system -In erodible system drug release occurs due to

degradation or dissolution of the hydrogel.

Pendent chain system -In pendent chain system drug is affixed to the

polymer back bone through degradable linkages. -As these linkages degrade drug is released

They are of two types:

Erodible drug delivery system -In erodible system drug release occurs due to

degradation or dissolution of the hydrogel.

Pendent chain system -In pendent chain system drug is affixed to the

polymer back bone through degradable linkages. -As these linkages degrade drug is released

Chemically Controlled Release Systems

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It is also known as degradable or absorbable release system, can be either matrix or reservoir type.

In reservoir type devices the membrane erodes significantly and drug is released by diffusion mechanism.

Zero order release can be obtained by this system.

It is also known as degradable or absorbable release system, can be either matrix or reservoir type.

In reservoir type devices the membrane erodes significantly and drug is released by diffusion mechanism.

Zero order release can be obtained by this system.

Erodible Drug Delivery System

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This system consists of linear homo/co-polymers with drug attached to the back bone chains.

The drug is released from the polymer by hydrolysis or enzymatic degradation of these linkages.

This system consists of linear homo/co-polymers with drug attached to the back bone chains.

The drug is released from the polymer by hydrolysis or enzymatic degradation of these linkages.

Pendent Chain System

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Stimuli-sensitive Swelling-controlled Release Systems

Environmentally-sensitive hydrogels have the ability

to respond to changes in their external environment.

They exhibit dramatic changes in their swelling

behavior, network structure, permeability or

mechanical strength in response to changes in the

pH or ionic strength of the surrounding biological

fluid, or temperature.

Environmentally-sensitive hydrogels have the ability

to respond to changes in their external environment.

They exhibit dramatic changes in their swelling

behavior, network structure, permeability or

mechanical strength in response to changes in the

pH or ionic strength of the surrounding biological

fluid, or temperature. 23

Stimuli-sensitive Swelling-controlled Release Systems

Other hydrogels have the ability to respond to

applied electrical or magnetic fields, or to changes

in the concentration of glucose.

Because of their nature, these materials can be used

in a wide variety of applications, such as separation

membranes, biosensors, artificial muscles, chemical

valves and drug delivery devices.24

pH-Sensitive Hydrogels:

Hydrogels exhibiting pH-dependent swelling

behavior contain ionic networks contain either

acidic or basic groups.

In aqueous media of appropriate pH and ionic

strength, these groups ionize, and develop fixed

charges on the gel.

Hydrogels exhibiting pH-dependent swelling

behavior contain ionic networks contain either

acidic or basic groups.

In aqueous media of appropriate pH and ionic

strength, these groups ionize, and develop fixed

charges on the gel.

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As a result of the electrostatic repulsions, the

uptake of solvent in the network is increased.

Ionic groups, such as carboxylic or sulfonic acid, show sudden or gradual changes in their dynamic

and equilibrium swelling behavior as a result of

changing the external pH.

26


In these gels, ionization occurs when the pH of the

environment is above the pKa of the ionizable group.

As the degree of ionization increases (increased

system pH), the number of fixed charges increases,

resulting in increased electrostatic repulsions between

the chains.

This, in turn, results in an increased hydrophilicity of

the network, and greater swelling ratios. 27


Conversely, cationic materials contain groups such as amines.

These groups ionize in media which are at a pH below the pKb of the ionizable species.

Thus, in a low pH environment, ionization increases, causing increased electrostatic repulsions.

The hydrogel becomes increasingly hydrophilic and will swell to an increased level.

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Temperature-sensitive Hydrogels:

Temperature-sensitive hydrogels have gained considerable attention due to the ability of the hydrogels to swell or deswell as a result of changing the temperature of the surrounding fluid.

Widely used in on±off drug release regulations, biosensors and intelligent cell culture dishes.

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Thermosensitive hydrogels can be classified as

positive or negative temperature-sensitive systems.

A positive temperature-sensitive hydrogel has an

upper critical solution temperature (UCST).

Such hydrogels contract upon cooling below the

UCST.

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Negative temperature-sensitive hydrogels

have a lower critical solution temperature (LCST).

These hydrogels contract upon heating above the

LCST.

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Other Stimuli-sensitive Hydrogels:

Several stimuli, other than pH and temperature, can

trigger drug release from a depot.

These include physical stimuli, such as light,

magnetic field , electric current and ultrasound ,

which can be applied to the systems externally.

Chemical stimuli, like ionic species , certain

chemical substances and biological compounds.

Several stimuli, other than pH and temperature, can

trigger drug release from a depot.

These include physical stimuli, such as light,

magnetic field , electric current and ultrasound ,

which can be applied to the systems externally.

Chemical stimuli, like ionic species , certain

chemical substances and biological compounds.

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Monomer abbreviation

Monomer

HEMA Hydroxyethyl methacrylate

HEEMA Hydroxyethoxyethyl methacrylate

HDEEMA Hydroxydiethoxyethyl methacrylate

MEMA Methoxyethyl methacrylate

MEEMA Methoxyethoxyethyl methacrylate

Monomers Used In The Synthesis Of Synthetic Hydrogels:

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Monomer abbreviation

Monomer

EG Ethylene glycol

EGDMA Ethylene glycol dimethacrylate

NVP N-vinyl-2-pyrrolidone

AA Acrylic acid

PEGMA PEG methacrylate

Monomers Used In The Synthesis Of Synthetic Hydrogels:

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Method Of Preparation Of Hydrogels:Crosslinking

Isostatic Ultra High Pressure

Nucleophilic Substitution Reaction

Using Gelling Agents

Use Of Irradiation

Freeze Thawing 35

Crosslinking:

Linear polymers

Crosslinking

Chemical compoundsIrradiation

Monomers used in the preparation of the ionic polymer network contain an ionizable group, gets ionized, or undergoes substitution after the polymerization is completed.

36

By using Cross Linkers:

Purpose To impart sufficient mechanical strength to these polymers

Examples

Cross linkers prevent burst release of the medicaments.

Glutaraldehyde, Calcium chloride

Presence of residue.

Advantage

Drawbacks

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Isostatic Ultra High Pressure :

Suspension of natural biopolymers (starch)

ultrahigh pressure of 300-700 MPa

5or 20 min

gelatinization of starch molecules occur.

IUHP brings about changes in the morphology of the polymer.Where as heat-induced gelatinization (40 to 52°C) causes a change in ordered state of polymer.

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Nucleophilic Substitution Reaction:

Methacyloyl chloride 2-dimethylamino ethylamine.

Nucleophilic substitution.

N-2-dimethyl amino ethyl-methacryalmide (DMAEMA)

(a pH and temperature sensitive.)

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By Using Gelling Agents:

Examples

Glycophosphate. 1-2 Propanediol.Glycerol. Mannitol.

Drawbacks

Turbidity. Presence of negative charged moieties pose problem of interaction with the drug.

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Use Of Irradiation:

Irradiation method processing is costlyMechanical strength of such Hydrogels is less.

Advantages

Drawbacks

Irradiation method is convenient. Hydrogels prepared by microwave irradiation are more porous than conventional methods.

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Freeze Thawing:

Opaque in appearance

Little swelling capacity.

Advantage

Drawbacks

Sufficient mechanical strength.

Good Stability.

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Characterization Of Hydrogels:

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Atomic Force Microscope

Atomic Force Microscopy (AFM):

A Multimode Atomic Force Microscope form Digital Instrument is used to study the surface morphology of the hydrogels.

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X-ray Diffraction:

Used to understand whether the polymers retain their crystalline structure or they get deformed during the pressurization process

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FTIR (Fourier Transform Infrared Spectroscopy)

Any change in the morphology of Hydrogels changes their IR absorption spectra.

Formation of coil or helix which is indicative of cross linking is evident by appearance of bands near 1648 cm-1

FTIR

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Rheology:

Hydrogels are evaluated for viscosity under constant temperature (4°C) by using Cone Plate viscometer.

Cone plate viscometer47

Swelling Behavior:

The Hydrogels are allowed to immerse in aqueous

medium or medium of specific pH to know their

swellability. of these polymeric networks.

These polymers show increase in dimensions related

to swelling.

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Swelling degrees (SDs) of hydrogels were measured

at 370 C. The fresh made samples (wet) were weighted

and immersed in buffer solutions with different pH

values. These samples were gently wiped with filter

paper to remove the surface solution when taken out

from the solutions, then weighted and returned to the

Same container at pre-determined time intervals.

Swelling Behavior:

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Swelling Behavior:

The SD was calculated as follows:

W0 = Weight of the original Hydrogel

Wt = is the weight of hydrogel at various swelling times

SD (%)= (Wt/Wo)×100

Picture of a swollen Hydrogel50

In-vitro Release Study For Drugs:

Since Hydrogels are the swollen polymeric networks,

interior of which is occupied by drug molecules,

therefore, release studies are carried out to understand

the mechanism of release over a period of application

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In-vitro Release Study For Drugs:

Dissolution media: Buffer solution with various pH values.

R.P.M: 90 rpm.

Temperature : 370C.

Sink condition is maintained by replacing the buffer periodically.

Dissolution apparatus

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Physical, Chemical And Toxicological Properties Of Hydrogels:

Factors affecting swelling of hydrogels.

Mechanical properties.

Cytotoxicity and in-vivo toxicity.

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Factors Affecting Swelling Of Hydrogels:

It is defined as the ratio of moles of crosslinking

agent to the moles of polymer repeating units.

The higher the crosslinking ratio, the more

crosslinking agent is incorporated in the hydrogel

structure.

Crosslinking ratio

54


Highly crosslinked hydrogels have a tighter

structure, and will swell less compared to the same hydrogels with lower crosslinking ratios.

Crosslinking hinders the mobility of the polymer

chain, hence lowering the swelling ratio.

Crosslinking ratio

55


The chemical structure of the polymer may also

affect the swelling ratio of the hydrogels.

Hydrogels containing hydrophilic groups swell to a

higher degree compared to those containing

hydrophobic groups..

Chemical Structure

56


Hydrophobic groups collapse in the presence of

water, thus minimizing their exposure to the water

molecule.

As a result, the hydrogels will swell much less

compared to hydrogels containing hydrophilic

groups.

Chemical Structure

57


Swelling of environmentally-sensitive hydrogels

can be affected by specific stimuli.

Swelling of temperature-sensitive hydrogels can be

affected by changes in the temperature of the

swelling media.

Chemical Structure

58


Ionic strength and pH affect the swelling of ionic

strength- and pH-sensitive Hydrogels, respectively.

There are many other specific stimuli that can affect the swelling of other environmentally-responsive

Hydrogels.

Chemical Structure

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Mechanical properties:

Mechanical properties of hydrogels are very

important for pharmaceutical applications.

The integrity of the drug delivery device during

the lifetime of the application is very important to

obtain FDA approval, unless the device is

designed as a biodegradable system.

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A drug delivery system designed to protect a

sensitive therapeutic agent,such as protein, must

maintain its integrity to be able to protect the protein

until it is released out of the system.

Changing the degree of crosslinking has been

utilized to achieve the desired mechanical property

of the hydrogel.

61


Increasing the degree of crosslinking of the system

will result in a stronger gel.

However, a higher degree of cross-linking creates a

more brittle structure.

Hence, there is an optimum degree of crosslinking

to achieve a relatively strong and yet elastic

hydrogel. 62


Copolymerization has also been utilized to achieve

the desired mechanical properties of hydrogels.

Incorporating a co-monomer that will contribute

to H-bonding can increase the strength of the

hydrogel.

63

Cytotoxicity And In-vivo Toxicity:

Cell culture methods, also known as cytotoxicity

tests, can be used to evaluate the toxicity of

hydrogels.

Three common assays to evaluate the toxicity of

hydrogels include

-extract dilution. -direct contact.-agar diffusion.

64


Most of the problems with toxicity associated with

hydrogel carriers are the unreacted monomers, oligomers and initiators that leach out during application.

So, a good understanding the toxicity of the

monomers and initiators used is very important.

65


Approaches to solve this problem:

Modifying the rate of polymerization in order to

achieve a higher conversion

Extensive washing of the resulting hydrogel.

Formation of hydrogels without any initiators to

eliminate the problem of the residual initiator.

66


Commonly used technique to eliminate the problem

of the residual initiator is by using gamma irradiation.

Hydrogels can be made without the presence of

initiators by using thermal cycle to induce

crystallization. The crystals formed act as physical

crosslinks and are able to absorb the load applied to

the hydrogels.

Commonly used technique to eliminate the problem

of the residual initiator is by using gamma irradiation.

Hydrogels can be made without the presence of

initiators by using thermal cycle to induce

crystallization. The crystals formed act as physical

crosslinks and are able to absorb the load applied to

the hydrogels.67

Common Uses For Hydrogels:

68

Pharmaceutical Applications Of Hydrogels:

Peroral Drug Delivery

Drug Delivery In The Oral Cavity

Drug Delivery in the G.I.T

Ocular Delivery

Transdermal Delivery

Subcutaneous Drug Delivery

Hydrogels To Fix Bone Replacements

Tissue Engineering

Protein Drug Delivery

Topical Drug Delivery

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Drug delivery through the oral route has been the

most common method in the pharmaceutical

applications of hydrogels.

In peroral administration, hydrogels can deliver

drugs to four major specific sites; mouth, stomach,

small intestine and colon.

Peroral Drug Delivery:

70

By controlling their swelling properties or

bio-adhesive characteristics in the presence of a

biological fluid, hydrogels can be a useful device

for releasing drugs in a controlled manner at these

desired sites.


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Additionally, they can also adhere to certain specific

regions in the oral pathway, leading to a locally increased drug concentration, and thus, enhancing

the drug absorption at the release site.


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Drug delivery to the oral cavity can have versatile

applications in local treatment of diseases of the

mouth, such as periodontal disease, stomatitis,

fungal and viral infections,and oral cavity cancers.

Long-term adhesion of the drug containing hydrogel

against copious salivary flow, which bathes the oral

cavity mucosa, is required to achieve this local drug

delivery.

Drug Delivery In The Oral Cavity:

73

Drug Delivery in the G.I.T:

Ease of administration of drugs. Availability of large surface area for drug absorption

High patient compliance.

First pass metabolism.

Pre-systemic metabolism.

Advantages with oral route

Drawbacks with oral route

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Drug Delivery in the G.I.T:

Hydrogel-based devices can be designed to deliver

drugs locally to specific sites in the GI tract. E.g.,: Specific antibiotic drug delivery systems for the

treatment of H.pylori infection in peptic ulcer disease

These Hydrogels protect the insulin in the harsh, acidic

environment of the stomach before releasing the drug

in the small intestine. 75

Ocular Delivery :

Effective tear drainage; blinking &Low permeability

of the cornea.

Limited absorption due to rapid elimination leading

to poor ophthalmic bioavailability.

Due to the short retention time, a frequent dosing

regimen is necessary for required therapeutic

efficacy.

Drawbacks with ocular route

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Ocular Delivery :

Silicone rubber Hydrogel composite ophthalmic

inserts extended the duration of the Pilocarpine to

10 hr, compared to 3 hr when Pilocarpine nitrate was

dosed as a solution.

Hydrogels in Ocular Delivery

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Ocular Delivery :

In-situ forming Hydrogels are attractive as an ocular

drug delivery system because of their facility in

dosing as a liquid,and long term retention property as

a gel after dosing.

Hydrogels in Ocular Delivery

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Ocular Delivery :

Swollen Hydrogels can deliver drugs for long duration.

Easy to remove.

Patient compliance is high.

Advantages

79

Transdermal Delivery :

Drug delivery to the skin has been generally used to treat skin diseases or for disinfections

of the skin.

Transdermal route is employed for systemic

delivery of drugs.

Purpose

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The possible benefits of transdermal drug delivery

are - drugs can be delivered for a long duration.

- drugs can be delivered at a constant rate.

- drug delivery can be easily interrupted on

demand by simply removing the devices.

- drugs can bypass hepatic first-pass

metabolism.81


Furthermore, because of their high water content,

swollen hydrogels can provide a better feeling for

the skin in comparison to conventional ointments

and patches.

82

Subcutaneous delivery:

Subcutaneously inserted exogenous materials may

more or less evoke potentially undesirable body

responses, such as inflammation, carcinogenecity

and immunogenecity.

Therefore, biocompatibility is a prerequisite that

makes materials implantable.

83


Due to their high water content, hydrogels are

generally considered as biocompatible materials.

They also provide several promising properties:

* minimal mechanical irritation upon in-vivo

implantation, due to their soft, elastic properties.

84


* Prevention of protein adsorption and cell

adhesion arising from the low interfacial

tension between water and hydrogels;

* Broad acceptability for individual drugs with

different hydrophilicities and molecular sizes

* Unique possibilities to manipulate the release of incorporated drugs by crosslinking density

and swelling. 85

Hydrogels To Fix Bone Replacements:

Provided orthopedic fasteners and replacements hip and knee replacements, etc. are coated with

Hydrogels which expand in the presence of liquids.

Swelling of such coatings causes the fastener or

replacement to be securely fixed into position once

inserted into bone material.

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Hydrogels To Fix Bone Replacements:

87

Protein Drug Delivery:

Interleukins are conventionally given as injection.

Hydrogels have the following advantages

-Better patient compliance.

-Hydrogels form insitu and release proteins

slowly

-They are biodegradable and biocompatible.

Hydrogels have the following advantages

-Better patient compliance.

-Hydrogels form insitu and release proteins

slowly

-They are biodegradable and biocompatible.88

Topical Drug Delivery:

Hydrogels are used to deliver drugs like Desonide

(synthetic corticosteroid) usually used as an anti-

inflammatory.

Hydrogels with their moisturizing properties avoids

scaling and dryness and has better patient

compliance.

89

Topical Drug Delivery:

Antifungal formulations like Cotrimazole has been

developed as Hydrogel formulation for vaginitis and

shows better absorption than conventional cream

formulations.

90

Tissue Engineering:

Microgels (micronized Hydrogels) can be used to

deliver macromolecules like phagosomes in to

cytoplasm of antigen-presenting cells.

The release is because of acidic conditions. Hydrogels

mold themselves to the pattern of membranes of the

tissues and have sufficient mechanical strength.

This property is also used in cartilage repairing

91

In The Treatment Lower Extremity Diabetic ulcers:

Diabetic ulcers are the primary cause of amputations

of the leg, foot,or toe.

NanoDOX™

A topical doxycycline Hydrogel for chronic wounds

NanoDOX™ contains 1% Doxycycline Monohydrate

Hydrogel.

Improve the topical delivery to increase local efficacy

92

Rectal Delivery:

This route has been used to deliver many types of

drugs for treatment of diseases associated with the

rectum, such as hemorrhoids.

ADVANTAGES:

This route is an ideal way to administer drugs

suffering heavy first-pass metabolism.

93

Rectal Delivery:

DRAWBACKS:

Patients compliance is less due to discomfort

arising from given dosage forms.

Substantial variability in patient’s acceptance of

treatment. this leads to variation of availability of

drugs.

94

Summary & Conclusion:

Recent developments in the field of polymer

science and technology has led to the development

of various stimuli sensitive hydrogels like pH,

temperature sensitive, which are used for the targeted

delivery of proteins to colon, and chemotherapeutic

agents to tumors.

95


Some environmental variables, such as low pH and

elevated temperatures, are found in the body.

For this reason, either pH-sensitive and/or

temperature sensitive hydrogels can be used for

site-specific controlled drug delivery.

96


Hydrogels that are responsive to specific molecules,

such as glucose or antigens, can be used as biosensors as well as drug delivery systems.

The hydrogels may be suitable as a wound

substitutes and can be used in wound healing.

97


New synthetic methods have been used to prepare

homo- and co-polymeric hydrogels for a wide

range of drugs, peptides, and protein delivery

applications.

Hydrogels are also used in regenerating

human tissue cells.

98

References:

1.Remington: The Science and Practice of Pharmacy.

Published by Lippincott Williams & Wilkins, 2005.

Twenty-First Editions. P.NO. 294,756,867,868.

2. Handbook of Pharmaceutical Excipients, A. Wade and P.J.

Weller ed., The Pharmaceutical Press, London, 1994, pp.

229–232.

3. British Pharmacopoeia 2002, the Stationary Office,

London, 2002, p. 2092–2094.

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Thank You

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2.hydrogels

Education

sensitive hydrogels

release of drug

release drug systems

diffusion controlled

erodible system drug

erodible drug delivery

pendent chain system

reservoir devices