Surface modification processes and applications are discussed for biomedical sector. Ti, Co-Cr and various implants are considered. The techniques involved are Micro arc Oxidation, Electron Beam Deposition, Plasma Immersion Ion Implantation, Gas Nitriding and many more for corrosion and wear resistance, biointegration, fatigue resistance.

1. Surface modification techniques in
biomedical sector
Term paper presentation for
Surface Modification
Metallurgical and Materials Engineering
IIT Kharagpur

2. Introduction
● A biomaterial is any matter, surface, or construct that interacts with
biological systems.
● Natural or synthetic.
● Metallic, ceramic or polymer.
Metallic steel, Cobalt and Titanium based alloys
Ceramic titania (TiO2), titanium carbide (TiC), titanium nitride
(TiC), bioglass, hydroxyapatite (HA), silicon carbide
(SiC)
Polymer polyethylene terephthalate,
polytetrafluoroethylene, ultrahigh molecular weight
polyethylene (UHMWPE) and lactide-co-glycolide

3. Surface modification of biomaterials
● Bio-integration is the ideal outcome expected of an artificial implant.
● Phenomena occurring at the interface between the implant and host
tissues does not induce any deleterious effects.
● Bulk properties for mechanical strength
● Surface properties for biocompatibility

4. Objectives of surface modification of biomaterials
As biomedical devices are subject to extremely high clinical requirements, a
thorough surface modification process is needed prior to implantation
process into the human body. The objectives of surface modification are:
1.Increase bioactivity, cell growth and tissue attachments after implantation
2.Increase hardness of implant to reduce wear rate especially in articulation
joint applications
3.Introduce passive layer to prevent excessive ion release into body
environment
4.Promote antibacterial effect
5.Increase fatigue strength of implants

5. Biomaterial applications
Hard tissue replacements
hip and knee joint implant replacement.
Schematic diagram of
the screw-shaped
artificial tooth.

6. Cardiac and cardiovascular applications
Artificial heart valve: Ring and struts
made up of Ti alloys, disc made of
pyrolitic carbon
Artificial vascular stents: Ni-Ti alloys
used due to shape memory effect

7. Osteosynthesis
Bone screw and bone plate

8. Electron Beam Deposition
● Electron beam deposition of Ti on Co-Cr substrate.
● Co-Cr has better mechanical properties compared to Ti.
● But Ti has better biocompatibility.
● So surface coating of Ti on Co-Cr substrate
● 10 × 10 × 2 mm3
● Coating thickness:
10microns
● Coating rate: 0.1nm/sec
● substrate holder: 10rpm
Electron beam Deposition of Ti on Co-Cr

9. Electron Beam Deposition
Co-Cr substrate Ti coating on Co-Cr substrate

10. Micro-Arc Oxidation
● Anodic oxidation technique.
● Plasma modifies oxide structure.
● The excellent biocompatibility of Ti is due to a thin TiO2 layer which
forms spontaneously in air.
● Ti coated Co-Cr substrate is oxidised electrochemically by MAO.
● Electrolyte containing Ca & P.
● 0.15M calcium acetate monohydrate and 0.02M glycerol phosphate
calcium salt.
● MAO requirements: Passivation at anode side & oxide should be stable in
electrochemical environment.
Ti coated Co-Cr
MAO treated after Ti coating
MAO

11. Micro-Arc Oxidation
TiO2 by MAO on Ti coated on Co-Cr substrate
SEM secondary electron cross sectional
image
● 3 to 5 microns
● Repeated dielectric
breakdown makes the TiO2
layer rough and porous
● Ca and P ions incorporated
into the TiO2 layer
BSE images of MAO treated specimen.

12. Ion implantation process
● Ion implantation is a procedure in which ions of a material are
accelerated in an electric field and bombarded into the solid substrate
surface.
● Ions implanted: Nitrogen, oxygen, carbon
● Two types of ion implantation process are:
(a)Conventional beam line ion implantation (b)Plasma immersion ion implantation (PIII) method

13. ● In beam line ion implantation, the target is totally isolated from the ion
beam generation.
● In PIII, the target is an active part of the ion generation through bias
voltage. ● Specimen is surrounded by a high-density
plasma and pulse biased to a high negative
potential. Ions generated in the overlying
plasma are accelerated and implanted into
the surface.
● Energy of ions keV to MeV.
● Low substrate temperature.
● metal and non-metallic ion simultaneously
implanted on titanium alloy.
● Ca and Mg ion implanted into titanium
alloy for increasing the bone integration.
schemiatic of PIII
Ion implantation process

14. Ion-beam assisted deposition
● Ion-beam assisted deposition (IBAD) is a vacuum deposition process that
combines physical vapor deposition (PVD) with ion-beam bombardment.
Schematic drawing of the polyfunctional IBAD system
and the process of IBAD

15. IBAD
● Biocoating with higher adhesive strength than traditional coating
techniques.
● Low substrate temperature.
Applications:
● hydroxyapatite coating preparation.
● DLC film and C–N film: chemically inert, extreme high hardness and low
friction coefficient are their attractive.
● silver coating is that it prevents bacteria attachment to the biomaterial
surface.
Ion-beam assisted deposition

16. Laser Surface Modification
● A 3kW CO2 laser emitting with a wavelength of 10.6 mm
● series of optical units deliver the CO2 laser beam to the workpiece
through the laser head
● The defocused CO2 laser beam was traversed a single time along the x
axis
● The fumes produced were removed with an extraction system
● CO2 process gas with 2 bar pressure was used to shield the laser optics
and assist the surface treatment.

17. Laser Surface Modification
The three requirements generally expected of biomaterials coating are:
1) crystallinity,
2) porosity
3) adhesion.
Common advantages of laser surfacing compared to alternatives are :
● chemical cleanliness
● controlled thermal penetration and, therefore, distortion
● controlled thermal profile and, therefore, shape and location of the heat
● affected region
● less after-machining, if any, is required
● remote non contact processing is usually possible
● relatively easy to automate

18. Laser Surface Modification
At present, the lasers are being used in the following surface modifications of
the biomaterials:
● Laser patterning and microfabrication
● focusing an intense laser beam at certain spots on a surface, where the
high beam intensity causes evaporation of the material.
● By this approach, pits can be produced down to 1 mm, in the size range
of interest to match cell sizes.
● Pulsed laser deposition (PLD) of biocompatible ceramics
● thin films of biocompatible ceramics . Pulsed laser deposition is
especially well suited to the
● deposition of bone-like ceramics (e.g. hydroxyapatite (HA) and calcium
phosphates) on to metal, ceramic, semiconductor or polymer substrates
for potential application in medical implants, prosthetic devices and
biocompatible probes or sensors.

19. Laser Surface Modification
● Laser surface treatment for improving corrosion
● improvement resistance by a combination of the homogenisation of the
surface by melting, the hardening due to N incorporation and the
thickening of the oxide layer.
● improvement in pitting corrosion resistance for 316LS biograde stainless
steel.
● eliminate carbides and second phases alike, while also serving the
function of homogenising the microstructure.
● N2 induced into the laser treated surface could promote new
precipitates and as a result lowered the corrosion resistance of 316LS
stainless steel and Ti–6Al–4V alloy.
● Laser grafting
● improved surface hydrophilicity and biocompatibility of ethylene–
propylene rubber, 2-hydroxyethyl methacrylate (HEMA) and N-vinyl
pyrrolidone (NVP) have been grafted on to the surface of this polymer
using a CO2 pulsed laser at different fluence (output power J/cm2) as the
excitation source

20. High Velocity Oxygen Fuel (HVOF) coating
● thermal spray coating process
● used to improve or restore a component’s surface properties or
dimensions, thus extending equipment life
● increasing erosion and wear resistance, and corrosion protection.

21. High Velocity Oxygen Fuel (HVOF) coating
The application of hydroxyapatite (HA) coatings on Ti-6Al–4V based
prosthetics has been widely used due to the unique biocompatibility of HA.
For a long term usage, an HA coating must exhibit a high biocompatibility and
adequate mechanical properties, such as a high bond strength and an elastic
modulus value close to that of the bone. The biocompatibility and the
mechanical properties will depend on the coating microstructure, crystallinity
and phase composition.
Cross-section of the HA coating after a 7-day incubation in the SBF solution.

22. Sputtering
1. creating a gaseous plasma
2. accelerating the ions from this plasma into some source material the
source material is eroded by the arriving ions via energy transfer
3. ejected in the form of neutral particles - either individual atoms, clusters
of atoms or molecules
4. As these neutral particles are ejected they will travel in a straight line
unless they come into contact with something - other particles or a
nearby surface.
5. If a "substrate" such as a Si wafer is placed in the path of these ejected
particles it will be coated by a thin film of the source material

23. Sputtering
Schematic presentation of an apparatus for Sputtering
Calcium ion implantation where calcium ions are implanted into
biomedical titanium alloys, calcium ion mixing method where Ca is sputtered
on the surface of biomedical titanium alloys followed by Ar ion implantation,
etc. CaP precipitation is enhanced on the surface of biomedical titanium
alloys conducted with these treatments when they are implanted into living
body.

24. Gas Nitriding
● Process-
● the specimen is set in a furnace equipped with a chamber
● by using a rotary vacuum pump, the atmosphere in the chamber is
exchanged three times from air to nitrogen; purity of nitrogen gas is
higher than 99.9995%
● furnace is heated up to 1023, 1073, 1123, or 1223 K at a reduced
pressure below 0.001 MPa
● nitrogen gas is introduced into the chamber at a pressure of up to
0.100 MPa and the recording of the nitriding time is started
● specimen is kept in the nitrogen atmosphere at each temperature
for 21.6 ks
● at last furnace is cooled down to the room temperature while
maintaining the nitrogen atmosphere in the chamber.

25. Gas Nitriding
Schematic drawing of gas nitriding process

26. Gas Nitriding
● Developed –
A biomedical, β-type titanium alloy, Ti–29Nb–13Ta–4.6Zr (TNTZ), in order to
achieve a lower Young's modulus similar to that of human hard tissues in
addition to excellent mechanical properties and good corrosion
resistance for use as structural biomaterial
● Problem –
When the titanium alloys are utilized as a material for artificial hip joints,
bone plates, etc., one of the possible risks due to wear includes the
loosening of these tools. Thus, the improvement of wear resistance is
required for biomedical titanium alloys.

27. Gas Nitriding
● Effect of Al on diffusion rate of O in TiO2 in gas nitriding -
o Depending on the oxygen partial pressure and ambient temperature,
the main point defect in TiO2 are probably oxygen vacancies under the
experimental conditions
o the inward diffusion of O is dominant in TiO2. A Ti atom is present as Ti4+
in TiO2, while Al3+ is the stable state of an Al atom. According to the
point defect theory, when Ti4+ is substituted with Al3+, an oxygen
vacancy is generated in order to satisfy the electroneutrality as follows
equation Al2O3=2Al′Ti+VO..+3OO
o it is expected to increase the diffusion rate of O ions

28. Vacuum plasma sprayed
● used to manufacture HA coatings with an approximate thickness of 40 lm
● VPS coatings were sprayed onto Ti—6Al—4V strips (80]20]2 mm) which had been
previously grit blasted with alumina grit and coated with a pure titanium bond
layer
● particles used in the manufacture of the VPS coatings were angular in nature and
had a wide size distribution
● linear increase of pushout failure load with increasing surface roughness for VPS
HA coatings

29. Vacuum Plasma Sprayed
● coatings had a comparably moderate roughness which should encourage
coating dissolution due to the large surface area exposed to the body’s
environment and allow good mechanical interlocking with bone, without
impairing the mechanical strength of the surface
● found that there is higher crystallinity and lower residual stress in the
VPS coatings, which will result in a slow rate of dissolution in vitro and in
vivo relative to the DGUN coatings

30. Detonation Gun (DGUN)
● used to manufacture HA coatings with an approximate thickness of 40 lm
● coatings were sprayed directly onto grit blasted Ti—6Al—4V with no
intervening bond layer
● Coatings were applied to one side of the substrate only
● The higher temperature which the powder particles reached during
detonation spraying should impose a higher degree of melting on the
starting powder creating a more amorphous coating
● better adhesion of the hydroxyapatite to the substrate
● higher velocity, higher energy DGUN process imposed a greater degree
of melting on the powder; but this process may be counterbalanced by
the extremely short dwell time of the particles in the plasma

31. Detonation Gun (DGUN)
● effects should combine to produce a more amorphous, more dense
coating which, despite being better adhered to the substrate will
undergo a more rapid dissolution in vitro than the VPS coatings
● detonation process resulted, to some degree, in the degradation of pure
hydroxyapatite to beta-tricalcium phosphate in the final coating
● process is a higher temperature, higher velocity technique which is
thought to impose a higher degree of melting on the ceramic starting
powder
● process producing a denser coating which had a higher proportion of the
amorphous phase with some evidence for the appearance of beta-tricalcium
phosphate
VPS vs DGUN - There was a considerable difference in the crystallinity of the
VPS and DGUN coating types

32. Conclusion
● The current applications of surface modification techniques in the field of
biomaterials and bioengineering have been described.
● It is observed that the overall trends of surface modification methods has
shifted from the use of conventional source (chemical, induction heater
and gas) to the application of advanced technology (electrolyte based,
laser, plasma and ion).
● The works on surface modifications has expanded from focusing on
tribological issues such as wear resistance, corrosion resistance and
hardness of modified layer to clinical issues such as cell growth, cell
attachment and antibacterial effects.

33. References
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Carburization and Ion Implantation Processes," [Online]. Available: www.intechopen.com.
M. H. Cheol, "Enhanced Biocompatibility of Co-Cr Implant Material by Ti Coating and Micro-Arc
Oxidation," Wiley InterScience.
F. Z. Cui , "Biomaterials modification by ion-beam processing," Surface and Coatings Technology
112 (1999), vol. 112, p. 278–285, 1999.
E. W, "Modification of mechanical and chemical surface properties of metals by plasma
immersion ion implantation," Surface and Coatings Technology, Vols. 100-101, pp. 341-352,
1998.
M. Nakai, "Surface hardening of biomedical Ti–29Nb–13Ta–4.6Zr and Ti–6Al–4V ELI by gas
nitriding," Materials Science and Engineering: A, vol. 486, no. 1–2, p. 193–201, 15 July 2008.
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hydroxyapatite for biomedical applications, Materials Science and Engineering: A Volume 396,
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Mitsuo Niinomi “Recent research and development in titanium alloys for biomedical
applications and healthcare goods”, Science and Technology of Advanced Materials, Volume 4,
Issue 5, September 2003, Pages 445–454.

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