Effect of hemocompatibility on the surface properties of Si incorporated diamond like carbon films.

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Effect of hemocompatibility on the surface
properties of Si incorporated diamond like carbon
films.

• R. K. Roy, S. J. Park, K.-R. Lee, D. K. Han,
  J.-H. Shin,
• Future Technology Division, Korea Institute of
  Science and Technology
• Biomaterials Research Center, Korea Institute
  of Science and Technology,
• Dept. Radiology, Asan Medical Center

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Contents
1. Introduction 2. Experimental 3. Results and
Discussion Surface energetics relation
Wettability Blood biomaterial interfacial
tension Activated partial thromboplastin time
(aPTT) Protein adsorption tests Platelet
adhesion and activation XPS analysis 4.
Conclusion
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1. Introduction

• A medical device in cardiovascular application
  faces the following problems
• Thrombogenicity formation of blood clots
• Cytotoxity release of metal ions
• Stability in long term use delamination and
  spallation
• during compressive and tensile forces of
  medical implants

In this respect, diamond like carbon (DLC) has
emerged as a promising coating material for
cardiovascular application due to its superior
tribological, inert and hemocompatible
properties.
Heart valve

• To get rid of delamination and improve
  hemocompatibility,
• it is necessary to
• dope the surfaces of biomaterials with certain
  elements
• use an interlayer which improves its adhesive
  properties

• Improved hemocompatibility is denoted by
• higher albumin/ fibrinogen ratio
• higher clotting times
• low platelet adhesion and activation

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2. Experimental
Coatings Si incorporated DLC
films. Synthesis method Capacitively coupled rf
plasma assisted chemical vapor deposition.
Precursor gases Benzene, silane. Substrates
Si, nitinol. Bias voltage
- 400 V System pressure 1.33
Pascal Deposition time 12 mins Ar cleaning
- 400 V, 0. 49 Pa, 15 mins.
Interlayer Si of thickness 5 nm to ensure
better adhesion.
Surface modification treating the Si
incorporated DLC films with plasma of various
gases like O, N, H and carbon tetrafluoride at -
400 V, 1.33 Pa, 10 mins.
Schematic diagram of RF PACVD system.
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3. Results and Discussion
Surface Energetics Relations
Youngs equation
(1)
where, ? is the contact angle between liquid and
solid, are the free energies of the
liquid and solid against their saturated vapor,
is the free energy of the interface between
liquid and solid, is the equilibrium
pressure of adsorbed vapor of the liquid on the
solid.
(2)
(3)
where the superscript d and p refer to the
dispersion and polar force components.
(4)
(5)
,
,
,
,
where
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Wettebility
Coatings/ substrates Water contact angle (degree) Formamide contact angle (degree)
O2 treated SiDLC 13.4 1.3 5.0 1.2
Si 35.3 2.7 12.0 1.5
N2 treated SiDLC 42.7 3.7 10.2 1.3
H treated SiDLC 67.2 1.8 45.7 1.4
SiDLC 70.1 3.0 49.5 1.4
Nitinol 76.6 1.1 51.2 0.7
CF4 treated SiDLC 88.4 2.9 68.0 0.5
Liquid al ßl ?lv (ergs/cm2)
Water 4.67 7.14 72.8
Formamide 6.28 4.32 58.2
Water contact angles of various surfaces
Coatings a ß
SiDLC 5.4 0.5 3.3 0.6
SiDLC (CF4 treated) 5.0 0.4 2.0 0.5
SiDLC (N2 treated) 5.6 0.2 5.2 0.3
SiDLC (O2 treated) 4.2 0.1 7.3 0.1
SiDLC (H2 treated) 5.5 0.3 3.5 0.4
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Surface energy of plasma treated Si incorporated
DLC films
Coatings Total Surface Energy (nJ/cm2)
SiDLC 39.7 8.9
SiDLC (CF4 treated) 29.1 5.8
SiDLC (N2 treated) 58.8 6.1
SiDLC (H2 treated) 42.1 6.0
SiDLC(O2 treated) 71.0 1.1
Interfacial tensions between the implant (phase
1) and blood plasma (phase2) are given by
(6)
a (dyne/cm)1/2 ß (dyne/cm)1/2
Human blood 3.3 6.0
Human Fibrinogen 4.97 6.35
Human serum albumin 5.6 5.8
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Activated Partial Thromboplastin Time (aPTT)
The aPTT determines the ability of blood to
coagulate through the intrinsic coagulation
mechanism. It measures the clotting time from the
activation of factor XII through the formation
of fibrin clot.
Incubation time 30 mins and 1 hour in platelet
poor plasma (PPP).
A higher aPTT was noted in case of O plasma
treated SiDLC films.
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Plasma Protein Adsorption
The plasma protein adsorption tests were done by
treating the samples with albumin and fibrinogen
solution and measuring the absorbances through
ELISA (Enzyme linked immunosorbent assay)
analysis.
Incubation time 5 mins, 60 mins.
The O and carbon tetraflouride plasma treated
SiDLC films showed increased rate of albumin
adsorption with time, while H plasma treated
SiDLC films minimized rate of fibrinogen
adsorption.
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Platelet Adhesion and Activation
Incubation time in fresh human platelet rich
plasma (PRP) 2 hours
Si
SiDLC (N treated)
SiDLC (H treated)
These results show that the adherence and
activation of platelets is less in case of O and
H plasma treated SIDLC films, compared to N
plasma treated SiDLC films and Si substrate.
SiDLC (O treated)
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X-Ray Photoelectron Spectroscopy (XPS) studies
C-C bonds are present in all the films. F-F,
C-N and Si-O bonds are seen on the surface of
carbon tetraflouride, N and O plasma treated
SiDLC films.
Bonding structure of carbon and fluorine show low
polarizability, which gives rise to the low
surface energy and increased hydrophobicity of
carbon tetrafluoride treated SiDLC films. Si-O
and C-N bonds are polar in nature, which results
in higher polar component in the surface energy
of O and N plasma treated SiDLC films.
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4. Conclusions
The plasma treatment of the Si incorporated DLC
films with various gases like N,O,H and carbon
tetrafluoride has a considerable effect on its
hemocompatibility and surface property. The O
plasma treated SiDLC films have shown higher
aPTT, higher albumin adsorption and minimized
platelet adhesion and activation. The H plasma
treated SiDLC films have reduced fibrinogen
adsorption. The XPS studies revealed the
presence of C-N, Si-O and F-F bonds in case of
N,O and carbon tetrafluoride treated SiDLC films.
The oxygen and H plasma treated SiDLC films can
serve as effective coating on endovascular SMART
nitinol stents.