Definition, Classification, Technical Features, Manufacturing, Preparation And Applications of Polymer Hydrogels
Published on: Mar 4, 2016
Transcripts - Polymer hydrogels
By Amit Gomey
Under the Guidance Of
Dr. A.K. Jana
• Classifications of hydrogels
• Technologies adopted in hydrogel preparations
• Drug Delivery
What is Polymer?
• The word polymer has been derived from the Greek words polys
(meaning many) and meros (Part or unit). The polymers (e.g.
proteins and celluloses) form the basic building block of life.
• Polymers are substances whose molecules have high molar masses
and are composed of a large number of repeating units. There are
both naturally occurring and synthetic polymers. Among naturally
occurring polymers are proteins, starches, cellulose, and latex.
What is hydrogels?
Hydrogel products constitute a group of polymeric materials, the
hydrophilic structure viz. amino, carboxyl and hydroxyl groups, in the
polymer chains of which renders them capable of holding large
amounts of water in their three-dimensional networks.
The ability of hydrogels to absorb water arises from hydrophilic
functional groups attached to the polymeric backbone, while their
resistance to dissolution arises from cross-links between network
Technical Features Of Hydrogels
• The highest absorption capacity in saline.
• Desired rate of absorption depending on the application
• The highest absorbency under load (AUL).
• The lowest soluble content and residual monomer.
• The highest durability and stability in the swelling environment and
during the storage.
• The highest biodegradability without formation of toxic species
following the degradation.
• pH-neutrality after swelling in water.
• Colorlessness, odorlessness, and absolute non-toxic.
• Photo stability.
• Re-wetting capability (if required) the hydrogel has to be able to give
back the imbibed solution or to maintain it; depending on the
application requirement (e.g., in agricultural or hygienic
• High cost
• Low mechanical strength
• Can be hard to handle
• Difficult to load with drugs/nutrients
• May be difficult to sterilize
• Non Adherent
Classification Of Hydrogels
Based on source:
(a) Natural and
Based on polymeric composition:
(a) Homopolymeric hydrogels
(b) Copolymeric hydrogels
(c) Multipolymer interpenetrating polymeric hydrogel
Based On Configuration :
(a) Amorphous (non-crystalline).
(b) Semi-crystalline: A complex mixture of amorphous and crystalline
Based On Type Of Cross-linking:
(a) Physical Nature and
(b) Chemical Nature
Based On Physical Appearance:
Based on presence or absence of electrical charge located on the
(a) Nonionic (neutral)
(b) Ionic (including anionic or cationic)
(c) Amphoteric electrolyte (ampholytic)
Technologies Adopted In Hydrogel Preparation
The polymerization techniques have been listed below:
• Bulk Polymerisation
• Solution polymerization/cross-linking
• Suspension polymerization
• Grafting to a support
• UV Polymerisation
• Bulk hydrogels can be formed with one or more types of monomers.
• Usually, a small amount of cross-linking agent is added in any
• The polymerization reaction is normally initiated with radiation,
ultraviolet, or chemical catalysts.
• High rate of polymerization and degree of polymerization occur
because of the high concentration of monomer.
• In solution copolymerization/cross-linking reactions, the ionic or
neutral monomers are mixed with the multifunctional crosslinking
• The polymerization is initiated thermally by UV-irradiation or by a
redox initiator system.
• The prepared hydrogels need to be washed with distilled water to
remove the monomers, oligomers, cross-linking agent, the initiator,
the soluble and extractable polymer, and other impurities
• In this technique, the monomers and initiator are dispersed in the
hydrocarbon phase as a homogenous mixture.
• The viscosity of the monomer solution, agitation speed, rotor design,
and dispersant type mainly governs the resin particle size and shape.
• The dispersion is thermodynamically unstable and requires both
continuous agitation and addition of a low hydrophilic–lipophilic-
balance (HLB) suspending agent.
• Done to add strength to structure of hydrogels as bulk
polymerisation give weak structured hydrogels.
• Technique involves the generation of free radicals onto a stronger
support surface and then polymerizing monomers directly onto it as
a result a chain of monomers are covalently bonded to the support.
• Ionizing high energy radiation, like gamma rays and electron beams,
used as an initiator to prepare the hydrogels of unsaturated
• Results in the formation of radicals on the polymer chains.
• Recombination of the macro-radicals on different chains results in a
cross-linked structure is formed.
Following are the method for the synthesis of hydrogels:
• Synthesis of hydrogels from monomers
• Synthesis of hydrogels from prepolymers
• Synthesis of hydrogels from polymers
Synthesis of hydrogels from monomers
• Copolymerization of hydrophilic monomers and polyfunctional
comonomers, acting as crosslinkers, leads to the formation of
hydrophilic network structures.
• Commonly used monomers are hydrophilic (meth) acrylates and
• Polymerization of vinyl monomers is most frequently initiated via
radical initiators. By the use of redox initiator, radicals are
Synthesis of hydrogels from prepolymers
• Prepared by crosslinkage of low molecular weight hydrophilic
polymers or oligomers.
• The reaction of α, ω-hydroxyl poly (ethylene glycol) with a
diïsocyanate in the presence of a triol as crosslinker.
• The reaction leads to the formation of crosslinked hydrophilic
Synthesis of hydrogels from polymers
• Chemical cross linkage of hydrophilic polymers results in the
formation of a hydrogel.
• Preparation of stationary phases for gel filtration chromatography.
• Other polymers like gelatine and agarose can form hydrogels upon
cooling from an aqueous solution. The gel formation is due to helix-
formation and association of the helices, forming junction zones
• Peroral Drug Delivery
• Drug Delivery in the Oral Cavity
• Drug Delivery in the GI Tract
• Rectal Delivery
• Ocular Delivery
• Transdermal Delivery
• Subcutaneous Delivery
• Protein Drug Delivery
• Drug Delivery
• Hydrogel for Gene Delivery
• Novel Hydrogel for Controlled Drug Delivery
• Tissue Engineering
• Soft Contact Lenses
• Cosmetology: Implanted into breast accentuate them for aesthetic
reasons. Implants have silicon elastomer shell and are filled with
hydroxyl propyl cellulose polysaccharide gel.
• Hydrogel for Gene Delivery: Modification of hydrogel composition
leads to effective targeting and delivery of nucleic acids to specific
cells for gene therapy.
• Novel Hydrogel for Controlled Drug Delivery: HYPAN is the novel
hydrogel having properties useful for controlled drug delivery.
• Tissue Engineering: Micronized hydrogels used to deliver
macromolecules (phagosomes) into cytoplasm of antigen-presenting
cells. This property is also utilized in cartilage repairing. Natural
hydrogel materials used for tissue engineering include agarose,
methylcellulose and other naturally derived products.
• Soft Contact Lenses
Hydrogels are an interesting class of materials that can be prepared by
a variety of methods. The properties of these materials depend on their
building blocks and the preparation procedures and can be largely
varied. They can be classified on the basis of source, cross-linking and
configurations. Hydrogels serve a broad range of applications,
including biomaterials, matrices for drug delivery and scaffolds for
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