Water plays a primary role as a solvent in biomaterials, dissolving both inorganic salts and large organic molecules with nearly equal efficiency. As the majority component of most living organisms, water is the first molecule to contact biomaterials in clinical applications. Water's unique properties are due to its ability to self-associate through hydrogen bonding networks, allowing it to dissolve many solutes and participate actively in biological processes. The behavior of water near surfaces and its role in biology are important topics in biomaterials science given water's interactions with biomaterials and influence on their biocompatibility.

1. Role of water in Biomaterials
· The primary role water plays in biomaterials is as a solvent
system.
· Water is the “universal ether” as it has been termed (Baier and
Meyer, 1996), dissolving inorganic salts and large organic
macromolecules such as proteins or carbohydrates (solutes) with
nearly equal efficiency (Pain, 1982).
· Water is an active participant in biology, which simply could
not and would not work the way it does without the special
mediating properties of water.
· Moreover, it is widely believed that water is the first molecule
to contact biomaterials in any clinical application (Andrade et
al., 1981; Baier, 1978).
· This is because water is the majority molecule in any
biological mixture, constituting 70 wt % or more of most living
organisms, and because water is such a small and agile
molecule, only about 0.25 nm in the longest dimension.
· Consequently, behavior of water near surfaces and the role of
water in biology are very important subjects in biomaterials
science.
· Self-association confers unique properties on water, many of
which are still active areas of scientific investigation even after
more than 200 years of chemical and physical research applied
to water (Franks, 1972).
WATER SOLVENT PROPERTIES
A
C
B
D
FIG. Atomic structure of water illustrating (A) tetrahedral
bonding arrangement wherein hydrogen atoms (H, light-colored

2. spheres) are Lewis acid centers and the two lone-pair electrons
on oxygen (O, dark-colored spheres) are Lewis base centers that
permit water to hydrogen bond with four nearest-neighbor water
molecules; (B) electron density map superimposed on an
atomic-radius sphere model of water providing a more authentic
representation of molecular water; (C) approximate molecular
dimensions; and (D) five water molecules participating in a
portion of a hydrogen-bond network.
· Hydrogen bonds in water are relatively weak 3–5 kcal/mole
associations with little covalent character (Iassacs et al., 1999;
Marshall, 1999).
· Hydrogen bonds are quite transient in nature, persisting only
for a few tens of picoseconds (Berendsen, 1967; Luzar and
Chandler, 1996).
· Modern molecular simulations suggest, however, that more
than 75% of liquid-water molecules are interconnected in a
three-dimensional (3D) network of three or four nearest
neighbors at any particular instant in time (Robinson et al.,
1996).
· In chemical terminology, less self-associated water has a
greater chemical potential than more self associated water.
· This is why water ice with a complete crystalline network i s
less dense than liquid water and floats upon unfrozen water, a
phenomenon with profound environmental impact.
· Water is amphoteric in this sense because, as illustrated in
Figs. 1A and 1D, it can simultaneously share and donate
electron density. Hydrogen atoms (the Lewis acids) on one or
more adjacent water molecules can accept electron density from
the unshared electron pairs on the oxygen atom (the Lewis
bases) of another water molecule.
· In this manner, water forms a 3D network through Lewis acid–
base self-association reactions.
· In chemical terminology, less self-associated water has a
greater chemical potential than more self-associated water.
· Interestingly, more self-associated water with a relatively
more complete 3D network of hydrogen bonds must be less

3. dense (greater partial molar volume) than less self-associated
water because formation of linearly directed hydrogen bonds
takes up space (Fig. 1C), increasing free volume in the liquid.
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WHAT IS MEANT HYDROPHOBICITY ?
Hydrophobicity comes also from the greek word Hydro(water)
and Phobicity (fear) it refers to the physical property of a
material that repels a mass of water.
· Some of the common natural Hydrophobic materials are
waxes, oil and fats.
The evaluation of hydrophobicity is made through water contact
angle measurements.
A water droplet would be spherical so the water
contact angle will be significantly high.
• At the molecular level, the hydrophobic effect is important in
driving protein folding formation of lipid bilayers and micelles,
insertion of membrane proteins into the nonpolar lipid
environment and protein-small molecule interactions.
Substances for which this effect is observed are known as
hydrophobes.HYDROPHOBIC EFFECT
The hydrophobic effect represents the tendency of water to
exclude non-polar molecules. The effect originates from the
disruption of highly dynamic hydrogen bonds between
molecules of liquid water.HYDROPHILIC COATING
Hydrophilic coatings wet the surface very easily, and maintain
the wetness for longer time. Thus, using hydrophilic
coatings eliminates the need for additional lubricants.
MSEG-402-Vijay 10SUPER HYDROPHOBIC
COATING
The process of coating the surface of a material with
hydrophobic property material in order to avoid sticking of
liquids on that surface.
This is absolutely unique way of coating unlike conventional

4. which shrink continuously during drying to produce low
porosity films.
Super hydrophobic technology makes water bounce, it stops it,
rolls it off the surface.
The surface of plant leafs, especially of the lotus flower, can
show extreme hydrophobicity to water
(large contact angels >150oC)
Surface structure 20-
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Young's equation is used to describe the interactions between
the forces of cohesion and adhesion and measure what is
referred to as surface energy.
www.ramehart.com/contactangle.htm
· A drop with a contact angle over 90° is hydrophobic.
· This condition is exemplified by poor wetting, poor
adhesiveness and the solid surface free energy is low.
Hydrophobic interactions
· Hydrophobic interactions describe the relations between water
and hydrophobes (low water-soluble molecules).
· Hydrophobes are nonpolar molecules and usually have a long
chain of carbons that do not interact with water molecules.
· The mixing of fat and water is a good example of this
particular interaction.
· The common misconception is that water and fat doesn’t mix
because the Van der Waals
· forces that are acting upon both water and fat molecules are
too weak.Causes of Hydrophobic Interactions
• American chemist Walter Kauzmann discovered that nonpolar
substances like fat molecules tend to clump up together rather
that distributing itself in a water medium, because this allow the
fat molecules to have minimal contact with water.
Hydrophobic interactions ChemWikiFormation of Hydrophobic
Interactions
· The mixing hydrophobes and water molecules is not

5. spontaneous; however, hydrophobic interactions between
hydrophobes are spontaneous.
· When hydropobes come together and interact with each other,
enthalpy increases ( is positive) because some of hydrogen
bonds that form the clathrate cage will be broken.
· Tearing down a portion of the clathrate cage will cause the
entropy to increase ( is positive), since forming it decr eases the
entropy.
According to the formula: ΔG= ΔH-TΔS
ΔH=Small positive value ΔS=Large positive value
Result :ΔG= Negative
A negative ΔG indicates that hydrophobic interactions are
spontaneous
What does the strength of Hydrophobic Interactions depend on?
In order of Effectiveness:
· Temperature
· Number of carbons on the hydrophobes
· The shape of the hydrophobesAPPLICATIONS
· A primary purpose of hydrophobic coatings such as
polytetrafluoroethylene(PTFE) or polyxylylene is to act as a
barrier against water commonly seen in automobiles
· Used in fabrication on metallic nano rod to prevent icing.
· Its is widely used in aerospace industry for providing anti -
icing coating on the surface of the aeroplane .
· Hydrophobic self cleaning glasses are installed in trafficsensor
control unit.
· We induce hydrophobic recovery after plasma treatment,
aphysical contact treatment (PCT) .
Glucose molecules have polar hydroxyl(OH) groups in them and
these attract the water to them. When sugar is in a crystal the
molecules are attracted to the water and go into solution.
Once in solution the molecules stay in solution at least in part
because they become surrounded by water molecules. This layer
of water molecules surrounding another molecule is called a
hydration shell.

6. Contact angle method
Mostly water drop on the surface
Cohesive force: molecules in a drop
Adhesive force: molecules in a drop and those on the surface
FIG. Four ways that the contact angle can be measured. (A)
Sessile drop. (B) Captive air bubble method. (C) Capillary rise
method.
(D) Wilhelmy plate method.
THE HYDROPHILIC EFFECT
• The hydrophilic solutes with biomedical relevance would
include cations such as Na+, K+, Ca2+, and Mg2+ or anions
such as Cl−, HCO3-1 and HPO4-2 .
THE SURFACE WETTING EFFECT
• It is a very common observation that water wets certain kinds
of surfaces whereas water beads up on others, forming droplets
with a finite “contact angle.”
WATER AND THE BIOLOGICAL RESPONSETO MATERIALS
It has long been assumed that the observed biological response
to materials is initiated or catalyzed by interactions with
material residing in the same thin surface region that affects
water wettability, arguably no thicker than about 1 nm.
In particular, it is frequently assumed that biological responses
begin with protein adsorption
hat biology does not “sense” or “see” bulk properties of a
contacting material, only the outermost molecular groups
protruding from a surface.
But exactly how surfaces influence "biocompatibility" of a
material is still not well understood.
Both surface energy and water theories acknowledge that the

7. principle interfacial events surfaces can promote or catalyze are
adsorption and adhesion. Adsorption of proteins and/or adhesion
of cells/tissues are known (or at least strongly suspected) to be
involved in the primary interactions of biology with materials.
Water is a very small, but very special, molecule. Properties of
this universal biological solvent, this essential medium of life
as we understand it, remain more mysterious in this century of
science than those of the very atoms that comprise it.
Self association of water through hydrogen bonding is the
essential mechanism behind water solvent properties and
understanding self association effects near surfaces is a key to
understanding water properties in contact with biomaterials.
Relationships Among Water Structure and Solvent Properties
Assignment-2
Explain any two of each surface characterization and
mechanical testing techniques for biomaterials
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