The adsorption processes and how the protein adsorption takes place on metal oxides are described here.....

1. JUSTIN K GEORGE
ME CHEMICAL ENGINEERING
15MCH003
GUIDE – Dr. KANHAIYA JETHANI
DEPARTMENT OF CHEMICAL ENGINEERING
AISSMS COE PUNE -01

2. Contents
• Adsorption : Basics
• Spontaneity & Exothermicity
• Classification Of Adsorption
• Adsorption Isotherms
• Thermodynamics of Protein Adsorption
• Protein Structure
• Protein Coating
• Protein Transport and Adsorption Kinetics
• Biomaterials - medical implants
• Metal oxides as biocompatible coatings
• Mediator of the interaction between foreign materials and cells
• Role of protein adsorption in the biocorrosion and tribological
processes
• Conclusion
• References

3. ADSORPTION : BASICS
Adhesion of atoms, ions, or molecules from a gas, liquid, or dissolved solid
to a surface.
ADSORBENT the substance on which surface the adsorbate is adsorbed.
ADSORPTION is a spontaneous process i.e.
ADSORPTION is an exothermic process i.e.

4. SPONTANEITY & EXOTHERMICITY
Any process can be represented thermodynamically under constant T & P by
Adsorption is a SPONTANEOUS process, there is a decrease in the free
energy of the system .
For SPONTANEITY ............. at const T &P
As translational freedom of adsorbate is reduced when it is adsorbed , thus
ΔS < 0 or negative.
As for Spontaneity , ΔG < 0 , hence ΔH should be negative i.e ΔH < 0.

5. CLASSIFICATION OF ADSORPTION
Molecules and atoms can attach to surface in two ways .
1. PHYSICAL ADSORPTION
2. CHEMICAL ADSORPTION
Physisorption ( Physical Adsorption) - Van der Waals interaction between
the adsorbate & the substrate (weak).
Energy released is the same order of magnitude as the enthalpy of
condensation.
Chemisorption (Chemical Adsorption) -Chemical Bond ( usually covalent )

7. ADSORPTION ISOTHERMS
Adsorption -studied through graphs known as Adsorption Isotherm.
The amount of adsorbate on the adsorbent as a function if its
pressure (gas) or concentration (liquid) at constant T.
According to Le Chatlier’s principle, on application of excess pressure ,
the equilibrium will shift in the direction where
number of molecules decreases.
In the given Adsorption Isotherm , after saturation
pressure Ps adsorption does not increases.

8. Types of Adsorption Isotherms

9. 1.FREUNDLICH ISOTHERM
Isothermal variation of adsorption of a quantity of gas adsorbed by unit
mass of solid adsorbent with pressure is Freundlich Adsorption Isotherm
x/m = adsorption per gram of adsorbent ie, the amount
of adsorbate (x) by the weight of the adsorbent (m).
P is Pressure, k and n are constants.
Taking the logarithms of Freundlich Isotherm :
Freundlich Isotherm gives the relationship of
adsorption with pressure at lower values,
Limitation : Failed to predict adsorption capacity
at higher pressure .

10. 2.LANGMUIR ISOTHERM
Based on different assumptions one of which is that dynamic equilibrium
exists between adsorbed gaseous molecules and the free gaseous
molecule.
................
The extent of surface coverage is normally expressed as the
fractional coverage, θ
The rate of change of surface coverage due to adsorption is proportional to
the partial pressure p of gas & the number of vacant sites N(1 − θ ), where
N is the total number of sites, ka & kd rate constants for adsorption &
desorption
................
The rate of change of θ due to desorption is proportional to the number of
adsorbed species, Nθ
...................

11. At equilibrium there is no net change (that is, the sum of these two
rates is zero), and solving for θ gives the Langmuir Isotherm, where
K = (ka / kd)
....................
At lower pressure, Kp is so small that factor (1 + Kp ) in denominator can
almost be ignored & Langmuir equation reduces to :
At higher pressure , Kp is so large that factor ( 1 + Kp) in denominator is
nearly equal to Kp & Langmuir equation reduces to :
Limitation : Valid at low Pressures only

12. 3.TEMKIN ISOTHERM
An assumption of the Langmuir isotherm is the independence and
equivalence of the adsorption sites.
Deviations from the isotherm can often be traced to the failure of these
assumptions.
The enthalpy of adsorption often becomes less negative as θ increases,
which suggests that the energetically most favourable sites are
occupied first.
Temkin Isotherm takes into account all the indirect adsorbate-adsorbate
interactions on adsorption isotherms
...............

13. 4.BET ISOTHERM
Most widely used isotherm dealing with multilayer adsorption is BET
Isotherm.
Under the condition of high P & low T , thermal energy of gaseous
molecules decreases & more & more gaseous molecules would be
available per unit surface area of adsorbent and this leads to multilayer
adsorption.
p* is the vapour pressure above a layer of adsorbate
that is more than one molecule thick & which
resembles a pure bulk liquid ,
Vmon is the monolayer coverage vol.,
When c >> 1,
the BET isotherm takes the simpler form

14. Protein Structure
Proteins are polymeric
chains of amino acids.
Amino acids have a central
carbon atom attached to a
hydrogen, a carboxyl group
(COOH) and an amine
group (NH2)
Each of the 20 standard
amino acids have a one-
letter symbol. A sequence
of three symbols, as shown
for RNA (right) is called a
codon

15. Surface and Protein Domains

16. PROTEIN COATING
Adsorption of proteins to a surface creates a new surface
-
-
-
-
-
-
-
-
+ =
Surface Protein Solution New Surface

18. Surface features and their interactions with proteins:
• Topography: greater texture means greater interaction
• Composition: Chemistry governs types of interactions
• Hydrophobicity: hydrophobic surfaces bind more protein
• Heterogeneity: non-uniform surfaces have many different
types of domains to interact with proteins
• Potential: surface charge affects charge distributions of ions
in solution and proteins

19. Surfsolprotads GGGG
STHG


For a reaction to spontaneously occur, the change in Gibbs
free energy, G, must be <0:
Thermodynamics of Protein
Adsorption

20. Protein Transport and Adsorption Kinetics
Four main types of
protein transport:
1. Diffusion
2. Thermal convection
3. Flow (convective
transport)
4. Coupled transport
(combinations of 1-3)
A concentration gradient drives
diffusion, while a temperature gradient
creates thermal convection

21. Initial adsorption rate is high on a
clean surface
Rate slows as surface becomes
covered
Further adsorption occurs as
molecules rearrange to create new
free surface

22. Biomaterials - medical implants
Surface modification of biomaterials can improve the
performance and lifetime of current metallic implantable devices.
Three basic surface characteristics to improve the
biocompatibility of the medical implants;
a) high bio-corrosion resistance
b) chemical inertness
c) bioactivity
Metals and their alloys are widely used for Implants in the dental ,
orthopedic and cardiovascular fields,

23. Metal oxides as biocompatible coatings
Metal oxide coatings represent a potential surface modification
to enhance the biocompatibility and other biological-related
properties, such as the biocorrosion resistance.
Metal and metallic alloys extensively used due to the properties
of their native oxides
The native oxide layer is a chemically passive surface which
confers corrosion resistance and less reactive to the biological
media.

24. Mediator of the interaction between
foreign materials and cells
First events occurring when a foreign material comes in contact
with a biological media is the adsorption of a protein layer.
The adsorbed proteins act as a translator between the surface
properties of the material and the cell receptors.

25. Role of protein adsorption in the
biocorrosion and tribological processes
There are two processes which are important for the development
of modified biomaterial surfaces;
 Corrosion
 Tribology.
The adsorption of proteins can either decrease the corrosion and
ion release rates or enhance them, depending on the adsorbed
proteins and their interaction with the surface and the liquid
medium.
Tribological issues are quite important for the moving parts in
artificial joint implants.Protein adsorption process as a
mechanism to improve the tribological response, which involves
friction and wear

26. CONCLUSION
 Adsorption process spontaneous & exothermic process.
 Proteins are comprised of discrete building blocks (amino
acids).
 Protein adsorption on metal oxides acts very important
process.
 Protein adsorption studies helps to make an insight about
the behaviour of the protein system.
 Medical implants used to correct unintended physiological
responses by the body (bio-response).
 Protein adsorption study helps to design the medical
implants.

27. • Protein Adsorption of Ultrafine Metal Oxide and Its Influence on Cytotoxicity
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• A look into the interaction of metal oxide thin films with biological media: Albumin
and Fibrinogen adsorption , Mater. Res. Soc. Symp. Proc. Vol. 1376
• An overview of protein adsorption on metal oxide coatings for biomedical
implants P. Silva-Bermudez, S.E. Rodil, Surface & Coatings Technology 233 (2013)
147–158Protein
• Adsorption to Surface Chemistry and Crystal Structure Modification of Titanium
Surfaces ,Ryo Jimbo1, Mikael Ivarsson , Anita Koskela, Young-Taeg Sul2, Carina B.
Johansson
• A comparative study of fibrinogen adsorption onto metal oxide thin films, Applied
Surface Science ·October 2013.
REFERENCES