1. Molecular Dynamics of Water Responsive
Polymers and Applications.
By
Koushik .B
4th
year B.Tech Chemical Engineering
SSN College of Engineering
ACKNOWLEDGEMENT
The internship opportunity I had with Applied Mechanics Department, IIT
Madras was a great platform for learning and professional development.
Therefore, I consider myself as a very lucky individual as I was provided
with an opportunity to be a part of it. I am using this opportunity to express
my deepest gratitude and special thanks to Dr. Pijush Ghosh who guided me
2. and kept me on the correct path and allowed me to carry out my project at
their esteemed organization.
I express my deepest gratitude to Ms. Amrita Rath, for taking part in useful
decision & giving necessary advices and guidance. I choose this moment to
acknowledge her contribution gratefully.
I perceive this opportunity as a big milestone in my career development. I
will strive to use the gained skills and knowledge in the best possible way,
and I will continue to work on their improvement, in order to attain the
desired career objectives.
ABSTRACT
Chitosan is a linear polysaccharide, which is generally found in shrimp’s
shells. Chitosan has significant applications in commercial and biomedical
sector. It is observed that the chitosan film undergoes deformation due to
water uptake, where the surface hydrophilicity undergoes changes. The
report deals with the study of this self-folding property of chitosan in the
presence of water. The chitosan films used in the study were prepared by the
process of deacetylation of chitin where HAP or glutaraldehyde was mixed
with 1:1 v/v glacial acetic acid. The parameters used in the study are,
deformation of those samples at different time intervals and variation of
deflection angles.
Keywords: Polysaccharides, hydrophilicity, deacetylation.
INTRODUCTION
3. Chitosan is a polysaccharide that is obtained from chitin, which is found in
the hard outer skeleton of shellfish, crab, lobster and shrimp.
It is composed of randomly distributed β-(1-4)-linked D-glucosamine
(deacetylated unit) AMD N-acetyl-D-glucosamine (acetylated unit).
MANUFACTURE
Chitosan is a chemically processed form of chitin, which is the structural
element in the exoskeleton of crustaceans (such as crabs and shrimp) and cell
walls of fungi. It is done so by deacetylation of chitin. The degree of
deacetylation (%DD) can be determined by NMR spectroscopy, and the
%DD in commercial chitosans ranges from 60 to 100%. On average, the
molecular weight of commercially produced chitosan is between 3800 and
20,000 amu (atomic mass units). A common method for the synthesis of
chitosan is the deacetylation of chitin using sodium hydroxide in excess as a
reagent and water as a solvent. This reaction pathway, when allowed to go to
completion (complete deacetylation) yields up to 98% product. In the project
done, two varied samples of chitosans, cross linked polymers and HAP
polymers are used. The chitosan films used in the study were prepared by
mixing HAP or glutaraldehyde with 1:1 v/v glacial acetic acid.
APPLICATIONS
4. Chitosan has a wide range of uses in pharmaceutical, agricultural and
commercial sector. It can be used as a soluble dietary fiber, a
biopesticide, a seed treatment, an anti – bacterial agent and also in
cosmetic and fabric industry. Though controversial, there are instances
where chitosan has been used to treat obesity, high cholesterol, and
Crohn’s disease. It is claimed that it might block absorption of dietary
fat and cholesterol to support the former situation.
The agricultural and horticultural uses for chitosan are primarily for
plant defense and yield increase. Here the glucosamine polymer
influences the biochemistry and molecular biology of the plant cell. In
the case of plant defense, it acts as ecologically friendly bio pesticide
substance that boosts the innate ability of plants to defend themselves
against fungal infections. Whereas in the other case, chitosan increases
photosynthesis, promotes and enhances plant growth, stimulates
nutrient uptake, increases germination and sprouting, and boosts plant
vigor.
The commercial uses include those of water filtration, as a fining agent
in wine making and as a polyurethane coating etc.
Whereas in the case of pharmaceutical industry, it is used as hemostatic
agent in bandages. Also chitosan's properties allow it to be used in
transdermal drug delivery. The popular usage includes transportation of
insulin.
SELF FOLDING PROPERTY
Self-folding broadly refers to self-assembly processes wherein thin films or
interconnected planar templates curve, roll-up or fold into three dimensional
(3D) structures such as cylindrical tubes, spirals, corrugated sheets or
polyhedral.
Self-folding methods are important for drug delivery applications since they
provide a means to realize 3D, biocompatible, all-polymeric containers with
5. well-tailored composition, size, shape, wall thickness, porosity, surface
patterns and chemistry. Self-folding is also a highly parallel process, and it is
possible to encapsulate or self-load therapeutic cargo during assembly. A
variety of therapeutic cargos such as small molecules, peptides, proteins,
bacteria, fungi and mammalian cells have been encapsulated in self-folded
polymeric containers.
Self-folding can occur spontaneously when 2D planar structures are released
from a substrate, typically on dissolution of a sacrificial layer, or in response
to stimuli such as electrical signals, pH, temperature, magnetic fields or
chemicals.
CHITOSAN IN THE PRESENCE OF WATER
It has been observed that, chitosan samples undergo the same self – folding
phenomenon in the presence of water. In this case, this effect is observed due
to the differential surface hydrophilicity after water is absorbed by the
polymer when exposed to it.
The deformations of different chitosan samples used are as follows:
1. CCLCSHAP200 (Successive images at a time interval of 5sec)
6. CLCSHAP300 (Successive images at a time
interval of 5sec)
2. CLCSHAP500 (Successive images at a time interval of 5sec)
9. 4. PURE SAMPLE
The deflection angle of a chitosan sample in the folding phenomenon is the
angle subtended by the tangent at the extreme point of the sample with
respect to the horizontal.
10. The deflection of the different samples and the rate of change of those angles
at different time intervals are as follows:
1. CLCSHAP200
2. CLCSHAP300
3. CLCSHAP500
11. 4. CSHAP10
5. PURE SAMPLE
Rate of Diffusion studies
Fick's first law relates the diffusive flux to the concentration under the
assumption of steady state. It postulates that the flux goes from regions of
high concentration to regions of low concentration, with a magnitude that is
proportional to the concentration gradient (spatial derivative), or in simplistic
terms the concept that a solute will move from a region of high concentration
to a region of low concentration across a concentration gradient.
Log(qT/qE)= nlog(T)+log(K)
Where,
12. qT= mass of water at time T.
qE= mass of water at time =infinity.
n is a constant of proportionality, which decides the type of diffusion.
Time Wt1 Wt2 Wt3 DIff1 Diff2 DIff3
0 3.3 3.5 3.6
10 7.14 7.3 7.22 3.84 3.8 3.42
20 8.68 8.74 8.58 5.38 5.24 4.98
30 8.9 9.02 8.94 5.6 5.52 5.34
40 9.24 9.16 9.08 5.94 5.66 5.48
50 10.16 10.18 9.88 6.86 6.68 6.28
60 11.15 10.88 10.66 7.85 7.38 7.06
70 11.27 11.15 11.2 7.97 7.65 7.6
80 11.33 11.32 11.39 8.03 7.82 7.79
90 11.37 11.37 11.31 8.07 7.87 7.71
SUPER ABSORBING POLYMERS
Sodium polyacrylate is an example of a super-absorbing polymer. It is
a cross-linked (network) polymer that contains sodium atoms. It
absorbs water by a process called osmosis.
When the (sodium-containing) polymer is placed in contact with water,
there is a tendency for the sodium to distribute equally between the
network and the water.
That means, some of the sodium atoms want to leave the network and
move to the water. When these sodium atoms leave, they are replaced
with water molecules. Water swells the polymer network to try to keep
the sodium concentration balanced between the polymer and the water.
The cross-links that connect the chains together prevent them from
dissolving/breaking apart in the water. Sodium polyacrylate can absorb
13. 800 times its weight in distilled water, but only 300 times its weight in
tap water, since tap water contains some sodium, calcium and other
mineral salts.
SWELLING MEASUREMENTS
Each sample was placed into distilled water for swelling at room
temperature. Swelling process was controlled by weighting. The ability
for swelling was expressed as the swelling ratio, W, in which M1 and
M2 are the weights of swollen and dry samples:
W = M1/M2
Effect of additional temperature treatment at the temperatures 120, 150,
180 °C after complete water evaporation on swelling ability was
measured.
FOLDING PATTERNS ON HYDROGELS
OBSERVATIONS
The following conclusions can be drawn from these readings:
1. The deflection is seen more in Pure sample and CSHAP10, where there
are chances for a deflection of 180 degrees or more.
14. 2. In the case of cross linked polymers, as the concentration of chitosan
increases, the folding property subtly decreases.
3. The folding process is slower in cross linked polymers (which in this
project took around a time interval of 30sec), whereas in the case of pure
sample and HAP polymer, its comparatively faster (took around 10sec to
deflect completely).
4. In the case of cross linked polymers, the chances of getting a deflection
angle as supplementary is comparatively less.
5. The rate of change of deflection angle decreases after a particular time.
Which is obvious, as the sample gradually slows down the deformation and
returns to its original state in the reverse process.
Future Scope
To study the different surface patterns on the chitosan films.
To study whether inert gases like nitrogen, helium can be absorbed in
chitosan films.
To coat temperature resistant materials on the film surface to study
folding characteristics at elevated temperatures.
Work on the implementation chitosan in its potential applications.
REFERENCES:
1. https://en.wikipedia.org/wiki/Chitosan
2. http://www.researchgate.net/publication/6437739_Water_Absorption_a
nd_Degradation_Characteristics_of_Chitosan-
Based_Polyesters_and_Hydroxyapatite_Composites
3. http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3462897/#R88
4. http://www.webmd.com/vitamins-supplements/ingredientmono-625-
chitosan.aspx?activeingredientid=625&activeingredientname=chitosan
http://www.drugs.com/npc/chitosan.html
