The concept of an autonomic self-healing material, where initiation of repair is integral to the material, is now being considered for engineering applications. This bio-inspired concept offers the designer an ability to incorporate secondary functional materials capable of counteracting service degradation whilst still achieving the primary, usually structural, requirement. Most materials in nature are themselves self-healing composite materials. This paper reviews the various self-healing technologies currently being developed for fiber reinforced polymeric composite materials, most of which are bioinspired; inspired by observation of nature. The most recent self-healing work has attempted to mimic natural healing using more detailed study of natural processes. A perspective on current and future self-healing approaches using this biomimetic technique is offered. The intention is to stimulate debate and reinforce the importance of a multidisciplinary approach in this exciting field.

1. SELF HEALING POLYMER COMPOSITES:
MIMICKING NATURE TO ENHANCE
PERFORMANCE
-Seminar By:
Abhijith Achuthakumar
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2. INTRODUCTION
Need for continual improvement in material performance is a common
feature of any modern engineering endeavors.
 A key focus of current scientific research is the development of
bioinspired material systems.
A great many natural materials are themselves self-healing composite
materials.
Lightweight, high strength, high stiffness fibre reinforced polymer
composite materials are leading contenders as component materials to
improve the efficiency and sustainability of many forms of transport.
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3.  The healing potential of living organisms and the repair strategies in
natural materials is increasingly of interest to designers seeking lower
mass structures with increased service life.
 It is simple observation that many natural systems can self-heal.
 it is equally simple observation that animals usually achieve this via a
‘bleeding’ mechanism.
 A clear distinction is whether the natural mechanism has been simply
observed or whether it has been studied and specific functional points
mimicked.
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4. SELF HEALING STRATEGIES IN
ENGINEERING STRUCTURES
BIO-INSPIRED SELF HEALING APPROACHES:
 One area of interest is the fusion of the failed surfaces.
 Polymeric materials possessing selective cross-links between polymer
chains that can be broken under load and then reformed by heat.
 In certain instances, polymeric material hosts a second solid-state
polymer phase that migrates to the damage site under the action of
heat .
 Possibility of using nanoparticles dispersed in polymer films to
deposit at a damage site.
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5. MICROENCAPSULATION:
 The third area of interest is based upon a biological ‘bleeding’
approach to repair, i.e. microcapsules and hollow fibres.
 Microencapsulation self-healing involves the use of a
monomer, dicyclopentadiene (DCPD), stored in urea-formaldehyde
microcapsules dispersed within a polymer matrix.
 A key advantage of this approach is the ease with which they can be
incorporated within a bulk polymer material.
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6.  When the microcapsules are ruptured by a crack, the monomer is
comes into contact with a dispersed particulate catalyst, thus initiating
polymerization & repair.
 Its disadvantage is the necessity for capsule rupture & the need for
catalyst.
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7. HOLLOW FIBRES:
 Self-healing using hollow fibres embedded within an engineering
structure, is similar to the arteries in a natural system.
 Here the self-healing material acts as the structural fibres.
 The key advantage is that the fibres can be located to match the
orientation of the surrounding reinforcing fibres thereby minimizing
Poisson ratio effects.
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8.  The fibres can be placed at any location within the stacking sequence
to address specific failure threats .
 A few disadvantages are the relatively large diameter of the fibres
compared to the reinforcement, the need for fibre fracture etc.
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9. BIOMIMETIC SELF-HEALING APPROACHES:
 The challenge for the future is the evolution of ‘engineering self-
healing’ towards a biomimetic solution.
 To date, the autonomous healing materials in engineering structures
have been distributed randomly throughout the structure or spaced
evenly through the composite laminate structure.
 In nature the network is tailored for a specific function with the
healing medium often being multifunctional.
 In the first man-tailored work, the key failure interfaces were
identified and then the hollow fibre self-healing network was designed
for a specific composite component and operational environment.
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10. VASCULAR NETWORKS
 Biological organisms have a highly developed, multifunctional
vascular network.
 This network supplies fluid to an area from a point reservoir, giving a
branching network.
 Over years, the branching & size of vessels have evolved to minimize
the power required to distribute and maintain the supporting fluid
within many other constraints.
 Future of self healing relies on the development of a continuous
healing network embedded within a composite laminate.
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11.  This mimiced network has to deliver healing agent from reservoirs to
damaged sites to permit repair of all types of composite material
modes.
 The healing agent needs to be replenished & renewed during the life
of the structure.
 It must restore matrix material properties & structural efficiency of
fractured fibres.
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12. HEALING AGENT
 Mammalian blood clotting has evolved around a series of chemical
reactions & their inactive precursors known as Clotting
factors, triggered in the form of a 'waterfall' of reactions.
 It is initiated by a damage that breaches endothelial cells & culminates
in the production of fibrin.
 In addition to rapid injury response, system malfunction is extremely
rare.
 This is achieved by the rapid removal of activated enzymes upon
fibrin production & action of endothelial cells.
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13.  Biomimetic hollow fibre self-healing mimics mammalian self-healing
in that a liquid healing agent leaks from a region of mechanical
damage.
 In mammals the immediate response is the need to arrest bleeding;
whereas in biomimetic self-healing the rapid response is to restore
some degree of structural integrity or prevent crack propagation.
 Haemostatic system functions through almost 80 coupled biochemical
reactions & this enormous complexity limits its degree to be
mimicked.
 Synthetic self-healing resin needs to be developed to duplicate the
blood clotting approach.
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14.  Self-healing in man-made structures requires intimate contact of 2 part
resin systems:
1)A resin & a hardener 2)A resin & a catalyst
 In resin & hardener type, the efficiency of healing depends on the
extent of their mixing, i.e., molecular transfer across the boundary.
 In resin & catalyst type, the chemical reactions spread at the damaged
site & beyond it as well, using up the resin supply.
 It is desirable to develop a resin system that mimics the clotting of
blood to allow multiple ,localized repair events.
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15. COMPARTMENTALISATION
 A cut to a tree, triggers the formation of internal impervious boundary
walls that develops over time to protect the tree from damage.
 This defense mechanism is termed compartmentalisation & is the
main healing mechanism that protects them from pathogen infection
through wounds.
 It is a 2 part process:
1)A chemical boundary is active in the short term to protect against
pathogens present at the time of injury.
2)A long term formation of a barrier zone giving continued protection
from pathogens.
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16.  A parallel concern in the use of composite materials, is the effect of
environmental attack on damaged structure.
 Moisture ingress reduces strength of these structures over time.
 A biomimetic system for producing an impervious internal boundary
in a damaged structure helps to avoid the secondary risk of moisture
ingress.
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17. RECOVERY AFTER YIELD
 Nature offers alternative healing strategies to repair brittle
materials, in the form of materials that regain strength after yielding.
 An example is: Mussel Byssal thread.(Gains back an amount of its
modulus).
 A better damage tolerance strategy is to adopt a hybrid composite
material that mimics the safety strategies observed in living
organisms.
 This method, although not self-healing, helps develop an elastic-
plastic behavior in composite materials.
 This approach can be furthered, if the yielded fibres & the matrix
material, could then be healed to regain its original stiffness.
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18. REINFORCEMENT REPAIR
 Self healing in fibre reinforced composites has been primarily focused
on polymer matrices as typical impact damage is primarily in the
matrix.
 However, reinforcing phase provides majority of strength & stiffness
within any composite & it is this component that would benefit from a
self-healing capability.
 The natural process of bone healing is a complicated process, where
the initially 'woven' bone is remodeled & replaced by mature 'lamellar'
bone.
 The process takes around 18 months, that can be accelerated on
application of an axial load at fracture site.
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19. CONCLUSION
 The problem of damage initiation, propagation & tolerance has
limited the acceptance of composite materials in all engg. disciplines.
 Nature has developed materials with healing potential over years.
 Self healing approaches applied in composite materials to-date are
primarily bio-inspired.
 More recent advance is the study of natural healing to allow
biomimetic self-healing.
 Tailored placement of healing components & adoption of biomimetic
vascular networks are very active topics on the same.
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20.  Biomimetic healing agents are a requirement closely linked to the
adoption of vascular networks.
 Compartmentalisation is a bridge between self-healing & engg
damage tolerance philosophy; particularly applicable to the problem
of moisture ingress.
 Post yield recovery offers self-healing for overloading in primary
direction.
 Reinforcements extend the concept of healing beyond repair of matrix
dominated failure modes.
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21. REFERENCES
 R.S Trask, H R Williams & I P Bond 2007 SELF HEALING
POLYMER COMPOSITES: Mimicking nature to enhance
performance U.K: University Of Bristol, Bristol. BS8 1TR
Department of Aerospace Engineering.
 S. R. White, N. R. Sottos, P. H. Geubelle, J. S. Moore, M. R.
Kessler, S. R. Sriram, E. N. Brown & S. Viswanathan 2008
Autonomic healing of polymer composites University of Illinois
Department of Aeronautical and Astronautical
Engineering, Department of Theoretical and Applied
Mechanics, Department of Chemistry, Urbana-
Champaign, Urbana, Illinois 61801, USA
 Y. C. Yuan, T. Yin, M. Z. Rong, M. Q. Zhang 2008 Self healing in
polymers and polymer composites. Concepts, realization and
outlook: A review Zhongshan University, Key Laboratory for
Polymeric Composite and Functional Materials of Ministry of
Education, OFCM Institute, School of Chemistry and Chemical
Engineering, Guangzhou 510275, P. R. China ;Materials Science
Institute, Guangzhou 510275, P. R. China
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