R. K. Roy *, S. J. Park*, K.-R. Lee*, D. K. Han**, J.-H. Shin+,

1. 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

2. 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

3. 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

4. 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.

5. 3. Results and Discussion Surface Energetics Relations: Young’s equation: (1) where, θ 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

6. Wettebility: Water contact angles of various surfaces:

7. Surface energy of plasma treated Si incorporated DLC films: Interfacial tensions between the implant (phase 1) and blood plasma (phase2) are given by: (6)

8. 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.

9. 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.

10. 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)

11. 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.

12. 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.