This document summarizes the history and discovery of hydrogels. It discusses how Otto and Lim first proposed the use of PHEMA hydrogels in contact lenses in 1960. Lim synthesized some of the first hydrogel materials somewhat by accident in 1954. Since then, hydrogels have found applications in drug delivery, tissue engineering, contact lenses, and other biomedical uses due to their biocompatibility and ability to absorb large amounts of water. The document also discusses stimuli-responsive and "smart" hydrogels that can release drugs in response to environmental triggers like pH, temperature, and electric fields.

1. Name: Sayyad Ali
 Presented To Dr. Taos Khan
 Topic # Hydrogel
 Dated 27/02/1202
 COMSATS ABBOTTABAD.
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2. Hydrogel
 Introduction
 The method by which a drug is delivered can
have a significant effect on its efficacy. Some
drugs have an optimum concentration range
within which maximum benefit is derived, and
concentrations above or below this range can
be toxic or produce no therapeutic benefit at
all.
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3. • To minimize drug degradation and
loss, to prevent harmful side-effects and
to increase drug bioavailability and the
fraction of the drug accumulated in the
required zone, various drug delivery and
drug targeting systems are currently
under development
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4. • Among drug carriers one can name soluble
polymers, micro particles made of insoluble
or biodegradable natural and synthetic
polymers, Microchips, microcapsules, cells,
cell ghosts,lipoproteins, liposome’s, and
micelles. The carriers can be made slowly
degradable, stimuli-reactive (e.g., pH or
temperature-sensitive), and even targeted.
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5. • Hydrogels are water-swollen polymeric
materials that maintain a distinct three-
dimensional structure. Their
classification may be based on the source:
natural, synthetic, or hybrid hydrogels
(composed of synthetic and natural
molecules); on the basis of nature of the
crosslinking: covalent or non-covalent
(physical) gels;
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6. • On the basis of nature of the network:
homopolymer, copolymer, interpenetrating, or
double networks; physical structure: (optically
transparent), microporous, and macroporous
hydrogels, and on their fate in the organism:
degradable and non-degradable hydrogels.
Due to their high water content, most
hydrogel structures possess excellent
biocompatibility.
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7. • There is a wide variety of the design options
for the preparation of hydrogels of different
structures and properties. The traditional
methods of hydrogel synthesis were limited
in the control of their detailed structure, but
novel approaches based on genetic
engineering and hybrid hydrogels, have
considerably enhanced this research.
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8. • As a result, the application potential
of hydrogels, in addition to
traditional areas such as
biomaterials and drug delivery
systems, has expanded to other
fields, such as microfluidics and
nanotechnology.
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9. DISCOVERY
• In the early 1950s Otto and Lím from the
Prague(Czechoslovakia) Institute of
Chemical Technology initiated a research
program to design polymers for medical
use. Some merchandised polymers had been
applied in humans use previously, but this
was the first attempt to design polymers for
human use with properties to fulfill the
criteria of biocompatibility.
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10. • The target was the design of new biomaterials
for applications in ophthalmology. The main
features of their design were (included in their
grant proposal in 1952 which stated as
• (a)shape stability and softness similar to that
of the soft surrounding tissue;
• (b) chemical and biochemical stability;
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11. • c) high permeability for water-soluble
nutrients and metabolites across the
biomaterial tissue-interface.
• It is amazing that these hypotheses are
still valid for soft contact lenses.
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12. • Based on this validation, Lím started
efforts to synthesize new hydrogels.
First, he considered polymerization of
N-vinylpyrrolidone. However, it was not
available, so Lim’s first experiments
focused on partially methacryloylation of
polyvinylalcohol. Polyvinylalcohol was
chosen due to its previous use in human
implants (Ivalon et al).
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13. • Methacryloyl esters were chosen
because the structure of the polymer
reflects a pivalic (trimethyl acetic
acid) acid structure. The latter was
known to be stable to pure hydrolysis.
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14. • The polyvinyl alcohol route produced
optically clear hydrogels containing
80–90% water but these hydrogels did
not show mechanical properties
necessary for use in contact lenses.
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15. gelatine hydrogels crosslinked with partially
oxidised dextrans.
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16. 16

17. • One year later, Lím by chance identified
a novel hydrogel material. He was
synthesizing the tri ethylene glycol di
methacrylate monomer by acid
catalyzed trans esterification of methyl
methacrylate with tri ethylene glycol.
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18. • At the end of the reaction he come
across with the neutralization of the
acid, dilution with water to isolate the
water-insoluble tri ethylene glycol di
methacrylate, washing the organic layer
with water, drying and isolating the pure
product by distillation.
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19. • (One day Lím had to catch the train to
his home, so he stopped the reaction
early, and managed to add water to
separate the layers before leaving. In
the morning, he noticed that the water
layer turned into a clear hydrogel
overnight).
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20. • Obviously, it was a copolymer of tri-
ethylene-glycol, mono-methacrylate
with tri-ethylene-glycol di-
methacrylate led to the final
selection of a hydrogel.
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21. • So the existence of hydrogels dates back to
1960, when Otto and Lim first proposed the
use of hydrophilic networks of poly-
hydroxyl-ethyl methacrylate (PHEMA) in
contact lenses.
• Since then, the use of hydrogels has
extended to various biomedical and
pharmaceutical applications.
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22. • In comparison to other synthetic
biomaterials, hydrogels resemble living
tissues closely in their physical properties
because of their relatively high water
content , soft and rubbery consistency.
• Hydrogels show minimal tendency to
adsorb proteins from body fluids because
of their low interfacial tension.
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23. • Further, the ability of molecules of
different sizes to diffuse into (drug
loading) and out of (drug release)
hydrogels allows the possible use of dry or
swollen polymeric networks as drug
delivery systems for
oral, nasal, buccal, rectal, vaginal, ocular
and parenteral routes of administration.
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24. Hydrogel can be delivered by any of the following routs
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25. • Because of these qualities it gained
different names like ‘intelligent gels’ or
‘smart hydrogels. The smartness of any
material is the key to its ability to
receive, transmit or process a
stimulus, and respond by producing a
useful effect.
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26. Hydrogels are ‘smart’ or ‘intelligent’ in the
sense that they can recognize the
predominant stimuli and respond by
displaying changes in their physical or
chemical behavior, resulting in the release of
entrapped drug in a controlled manner.
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27. • Some hydrogels undergo continuous or
discontinuous changes in swelling that are
mediated by external stimuli such as changes
in pH, temperature, ionic strength, solvent
type, electric and magnetic fields, light, and
the presence of chelating species.
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28. • The majority of stimuli responsive
hydrogels were created using conventional
(traditional) methods of synthesis of a
relatively small number of synthetic
polymers, especially (meth) acrylate
derivatives and their copolymers.
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29. • In 1968, Dusek and Patterson
theoretically predicted that changes in
external conditions might result in abrupt
changes of the hydrogel’s degree of
swelling.
• Indeed, 10 years later, Tanaka and others
have verified the theory by experimental
observations
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30. Pathways of solid polymer degradation(General)
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31. Cont.… pathways of degradation
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32. Basic difference in gel and hydrogel
• Both gels and hydrogels might be similar
chemically, but they are physically distinct.
• D. Jordan suitably described gels as ‘The colloidal
condition, the gel, is one which is easier to recognize
than to define
• Technically, gels are semi-solid systems
comprising small amounts of solid, dispersed in
relatively large amounts of liquid, having more
solid-like than liquid-like character.
Sometimes, hydrogels are also described as
aqueous gels because of the prefix ‘hydro’.
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33. • Although the term ‘hydrogel’ implies a
material already swollen in water, while in a
true sense hydrogel is a cross-linked network
of hydrophilic polymers. They possess the
ability to absorb large amounts of water and
swell, while maintaining their three-
dimensional (3D) structure.
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34. • hydrogels display swelling in aqueous
media for the same reasons that an
analogous linear polymer dissolves in
water to form an ordinary polymer
solution. Thus, the feature central to the
functioning of a hydrogel is its inherent
cross-linking.
• Conventional gels can also develop small
levels of cross-links as a result of a gain in
energy under the influence of shear
forces, but these are reversible
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35. • Because of the above quality hydrogels is a
polymer network, these polymers produce
systems that extend a range of
rigidities, beginning with a sol and
increasing to jelly, gel and hydrogel.
Thus, hydrogel, sometimes referred to as
xerogel, is a more rigid form of gel
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36. Future perspectives
• An interesting characteristic about many
responsive hydrogels is that the mechanism
causing changes in network structure can be
entirely reversible in nature.
• This conveys elastic deformability with
‘shape-memory’ behaviors so that hydrogels
return back to their original shape at the
end of initiating stimuli.
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37. • Keeping in view this quality The Jiang’s
laboratory developed a tunable
(adjustable) liquid lens that permits
autonomous focusing. The design was
based on a temperature-sensitive
hydrogel.
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38. • All the scientific evidences seem to indicate
that the basic and translational research in
hydrogels has a bright future.
• Numerous new designs, e.g. involving protein
domains containing non-recognized amino
acids, successful attempts has done to control
the morphology of self-assembling peptide
fibers, artificial glycoproteins for controlling
cell responses , hydrogels play a key role in
the building material for the
microchemotaxis and for all the above
phenomena.
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39. • It has a role in the enhancement of the
use of DNA recognition motifs, and an
improved synthetic method can be
established with hydrgel(Genetic
Engineering).
• An outstanding example of the
potential of stimuli-sensitive hydrogels
in the development of
bionanotechnology products is the
design of optical systems that do not
require mechanical components.
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40. Application of hydrogel
• New researchers have demonstrated that a gel
composed of small, woven protein fragments
can successfully carry and release proteins of
different sizes to different targets in the body.
• It is enabling the delivery of drugs such as
insulin and trastuzumab (A monoclonal
antibody (protein) often used to treat breast
and ovarian cancer), hormones, growth factors
as well as eye medications.
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41. • Furthermore, one can control the rate of release of
active ingredients from hydrogel by changing the
density of the gel, allowing for continuous drug
delivery over a specific period of time.
• A newly introduced gel, known as a "nanofiber
hydrogel scaffold," enables, over hours, days or even
months, a gradual release of the proteins from the
gel, and the gel itself is eventually broken down into
harmless amino acids (the building blocks of
proteins).
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42. • Peptide hydrogels are ideally suited for drug
delivery as they are pure, easy to design and
use, non-toxic, bio-absorbable, and can be locally
applied to a particular tissue.
• Depending on the size and density of the mesh, it
can carry protein molecules between 14,000 and
150,000 daltons (a unit of molecular weight).
• Earlier work showed that the hydrogels could also
carry smaller molecules, between 300 and 900
daltons. " So it can deliver both small molecules
and big molecules,".
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43. REFERENCES
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being exposed to an exciting new research field, it was possible to witness soccer and movie stars
visiting Prof. Wichterle and trying to get a free sample of soft contact lenses that were not commercially
available at that time.
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Thank you
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