Hydrogels are water-swollen, cross-linked polymeric structures produced by reactions of monomers or by hydrogen bonding. This hydrogels used in various applications of tissue enginerring, drug delivery, Easy to modify Biocompatible. Hydrogels acts as a barriers during tissue injury in order to prevent restenosis or thrombosis.

1. Article Written and Published at
www.worldofchemicals.com

2. INTRODUCTION
 Hydrogels are water-swollen, cross-linked polymeric structures
produced by reactions of monomers or by hydrogen bonding.
Hydrogels are composed of two constituents. One constituent is
hydrophilic polymers like polyvinyl alcohol, sodium
polyacrylate, acrylate polymers and copolymers, while the
second constituent is water.
 Hydrogels possess the hydrophilic quality which makes them a
good analog for natural tissues and they even tend to mimic the
flexibility and other textural qualities of biological media.
 Cross linked structure of hydrogels is characterized by junctions
or tie points, which may be formed from strong chemical
linkages (such as covalent and ionic bonds), permanent or
temporary physical entanglements, microcrystallite
formation, and weak interactions (such as hydrogen bonds).
 Hydrogels under mechanical stress can exhibit a range of
responses from rapid, elastic recovery following an applied
stress or strain to a time-dependent recovery approaching
viscous behaviour

3. Advantages
 Effective in hydrating wound surfaces and liquefying necrotic
tissue on the wound surface
 Non-adherent and can be removed without trauma to the
wound bed
 "Soothing" effect promotes patient acceptance
 Easy to modify
 Biocompatible
 Good transport properties
 Hydrogels provide suitable semi-wet, three-dimensional
environments for molecular-level biological interactions
 Hydrogel mechanical properties are highly tunable, for example
elasticity can be tailored by modifying cross-link densities
 Hydrogels can be designed to change properties (e.g. swelling/
collapse or solution-to-gel transitions) in response to externally
applied triggers, such as temperature, ionic strength, solvent
polarity, electric/magnetic field, light, or small (bio) molecules.

4. Disadvantages
 Low mechanical strength
 Hard to handle
 Difficult to load
 Hydrogels are the first biomaterials designed for use in the human
body. Applications of hydrogels include
 Tissue Engineering (TE)
 Synthetic extracellular matrix
 Implantable devices
 Biosensors
 Materials controlling the activity of enzymes
 Phospholipid bilayer destabilizing agents
 Soft contact lenses
 Pills/Capsules
 Bioadhesive carriers
 Implant coatings
 Electrophoresis gels
 Chromatographic packing material

5. Hydrogels as barriers
 To improve the healing response following
tissue injury, hydrogels have been used as
barriers in order to prevent restenosis or
thrombosis. Restenosis thickening can be
reduced by forming a thin hydrogel layer
intravascularly via the process of interfacial
photopolymerization.
 The process behind the restenosis
thickening is by preventing
platelets, coagulation factors and plasma
proteins from contacting the vascular wall.

6. Hydrogels in drug delivery
 Hydrogels are often used as localized drug
storehouses because they are
hydrophilic, biocompatible, and their drug
release rates can be controlled and triggered
intelligently by interactions with bio-molecular
stimuli.
 Characteristics of hydrogels like drug delivery
capability and barrier role can be used
simultaneously to deliver therapeutic agents.
 Hydrogels formed on the inner surface of
blood vessels via interfacial
photopolymerization have been utilized for
intravascular drug delivery.

7. Current research work
 1] Shyni Varghese’s at University of California, San Diego
has developed smart, self-healing hydrogels that binds in
seconds to achieve extensive applications including
medial sutures, targeted drug delivery, industrial sealents
and self-healing plastics.
 Self-healing is one of the most fundamental properties of
living tissues that allows them to sustain repeated
damage. To achieve the self-healing capacity of hydrogels
Varghese's laboratory scientists performed computer
simulations to modify the side chain molecules of
hydrogels.
 These computer simulations revealed that the ability of
hydrogel to self-heal depended critically on the length of
the side chain molecules, or fingers, and that hydrogels
having an optimal length of side chain molecules exhibited
the strongest self-healing.

8. Current research work
 [2] Professor Langer's group at the Massachusetts Institute of
Technology contributed their work towards hydrogel at the tissue
engineering level and reviewed the use of microengineered hydrogels
for tissue engineering applications.
 Microengineered hydrogels are hydrogels with dimensions as small as
a few tens of nanometre. These can be prepared by emulsification,
photolithography, microfluidic synthesis and micromolding. Applications
of microengineered hydrogels may be classified into two categories:
"top-down tissue engineering" and "bottom-up tissue engineering".
 Top-down tissue engineering approach controls the microscale features
of large pieces of hydrogels, whereas bottom-up tissue engineering
approach generates scaffolds by assembly of small functional units.
 Microengineered hydrogels can potentially be applied in tissue
engineering to recreate the complexities of in vivo tissue constructs
either by engineering the microvasculature and cellular organization in
large microscale scaffolds, or by assembling the building blocks in the
shape of microgel tissue units to generate larger structures.

9. Other Reference
 [1] © From University of California, website -
http://www.jacobsschool.ucsd.edu/news_event
s/releases/release.sfe?id=1175
 [2] © From Massachusetts Institute of
Technology, website -
http://web.mit.edu/doylegroup/pubs/LabChip_
Panda_08.pdf
 [3] By Brandon V. Slaughter, Shahana S.
Khurshid, Omar Z. Fisher, Ali
Khademhosseini, and Nicholas A.
Peppas, Hydrogels in Regenerative
Medicine, Available from -
http://www.tissueeng.net/lab/papers/hydrogels
%20in%20regenerative%20medicine.pdf