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1

Multifractal characteristics of titanium nitride thin films

Talu S., Stach S., Valedbagi S., Bavadi R., Elahi S. M., Talu M.

Materials Science Poland

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2015

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Vol. 33, No. 3

541--548

EN

The study presents a multi-scale microstructural characterization of three-dimensional (3-D) micro-textured surface of titanium nitride (TiN) thin films prepared by reactive DC magnetron sputtering in correlation with substrate temperature variation. Topographical characterization of the surfaces, obtained by atomic force microscopy (AFM) analysis, was realized by an innovative multifractal method which may be applied for AFM data. The surface micromorphology demonstrates that the multifractal geometry of TiN thin films can be characterized at nanometer scale by the generalized dimensions Dq and the singularity spectrum f(α). Furthermore, to improve the 3-D surface characterization according with ISO 25178-2:2012, the most relevant 3-D surface roughness parameters were calculated. To quantify the 3 D nanostructure surface of TiN thin films a multifractal approach was developed and validated, which can be used for the characterization of topographical changes due to the substrate temperature variation.

2

Numerical And Experimental Analysis Of Fracture Of Athrombogenic Coatings Deposited On Ventricular Assist Device In Micro-Shear Test

Kopernik M., Milenin A., Kąc S.

Archives of Metallurgy and Materials

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2015

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Vol. 60, iss. 2A

795--800

EN

The Polish left ventricular assist device (LVAD – RELIGA_EXT) will be made of thermoplastic polycarbonate-urethane (Bionate II) with deposited athrombogenic nano-coatings: gold (Au) and titanium nitride (TiN). Referring to the physical model, the two-scale model of LVAD developed in the previous works in the authors’ finite element code is composed of a macro-model of blood chamber and a micro-model of wall: TiN, Au and Bionate II. The numerical analysis of stress and strain states confirmed the possibility of fracture based on localization of zones of the biggest values of triaxiality factor. The introduction of Au interlayer between TiN and polymer improved the toughness of the connection, and increased the compressive residual stress in the coating what resulted in reduction of stress and strain close to the boundary between substrate and coating. However, the proper design of multilayer wall of the medical device requires the introduction of the real stress and strain states in the deposited coatings. The characteristics of TiN nano-coating such as residual stress, material model and fracture model were determined in the previously completed studies such as experimental and numercial nanoindentation tests, profilometry studies and in situ SEM’s micro-tension tests. The experimental in situ SEM’s micro-shear test was performed in the present paper and the corresponding numerical model of the test was also developed, and then, interpreted. The critical strains taken from experiment and considered as the effective strains in the model of test are the values which are the function of triaxiality factors for the tested samples. The developed in the authors’ FE code model of multilayer wall of VAD enriched with critical strain determined in the present paper enables prediction of fracture.

PL

Polska lewa komora wspomagania pracy serca (LVAD – RELIGA_EXT) zostanie wykonana z termoplastycznego poliwęglano-uretanu (Bionate II) z naniesionymi atrombogennymi powłokami: złota (Au) i azotku tytanu (TiN). W odniesieniu do modelu fizycznego, dwuskalowy model komory LVAD opracowany we wcześniejszych pracach w autorskim kodzie elementów skończonch jest złożony z modelu makro czaszy krwistej i z mikro-modelu ściany: TiN, Au i Bionate II. Analiza numeryczna stanów naprężenia i odkształcenia potwierdziła prawdopodobieństwo pękania poprzez zlokalizowanie stref o największej wartości współczynnika naprężenia trójosiowego. Wprowadzenie międzywarstwy złota pomiędzy TiN i polimer poprawiło wytrzymałość tego połączenia i powiększyło ściskające naprężenie własne w powłoce, co doprowadziło do redukcji naprężenia i odkształcenia blisko granicy pomiędzy podłożem i powłoką. Jednakże, właściwy projekt wielowarstwowej ściany urządzenia medycznego wymaga wprowadzenia rzeczywistych stanów naprężeń i odkształceń w naniesionych powłokach. Charakterystyki powłok TiN takie jak naprężenie własne, model materiału i model pękania zostały określone we wcześniej wykonanych badaniach takich jak doświadczalne i numeryczne testy nanoindentacji, badania profilometryczne, i testy mikrorozciągania prowadzone pod elektronowym mikroskopem skaningowym. W niniejszej pracy przeprowadzono doświadczalny test mikrościnania pod skaningowym mikroskopem elektronowym, opracowano model numeryczny tego testu, a następnie go zinterpretowano. Odkształcenia krytyczne otrzymane z doświadczenia i określone w modelu testu jako intensywność odkształcenia są wartościami będącymi funkcją współczynników naprężeń trójosiowych dla badanych próbek. Opracowany w kodzie własnym model elementów skończonych wielowarstwowej ściany komory VAD wzbogacony o określone w niniejszej pracy odkształcenia krytyczne umożliwia przewidywanie pękania.

3

Failure Strain and Strain-Stress Analysis in Titanium Nitride Coatings Deposited on Religa Heart Ext Ventricular Assist Device

Kopernik M.

Archives of Metallurgy and Materials

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2015

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Vol. 60, iss. 1

121--129

EN

The Polish ventricular assist device is made of Bionate II with deposited TiN biocompatible nano-coating. The two scale finite element model is composed of a macro-model of blood chamber and a micro-model of the TiN/Bionate II. The numerical analysis of stress and strain states confirmed the possibility of fracture. Therefore, the identification of a fracture parameter considered as a failure strain is the purpose of the present work. The tensile test in a micro chamber of the SEM was performed to calibrate the fracture parameter of the material system TiN/Bionate II. The failure strain is a function of a temperature, a thickness of coating and parameters of surface's profile. The failure strain was calculated at the stage of the test, in which the initiation of fracture occurred. The finite element micro-model includes the surface roughness and the failure strain under tension condition for two thicknesses of coatings which will be deposited on the medical device.

PL

Polska komora wspomagania pracy serca jest wykonana z Bionate II z naniesioną biokompatybilną powłoką TiN. Dwu-skalowy model elementów skończonych składa się z modelu makro czaszy krwistej i z modelu mikro dla TiN/Bionate II. Numeryczna analiza stanów naprężeń i odkształceń potwierdza prawdopodobieństwo pękania. Zatem, identyfikacja parametru pękania rozpatrywanego jako odkształcenie uszkodzenia jest celem niniejszej pracy. Próba rozciągania w komorze SEM została przeprowadzona, aby skalibrować parametr pękania dla układu materiałowego TiN/Bionate II. Odkształcenie uszkodzenia jest funkcją temperatury, grubości powłoki i parametrów profilu powierzchni. Odkształcenie uszkodzenia zostało obliczone w tym etapie testu, w którym pojawiła się inicjacja pęknięcia. Mikro model elementów skończonych zawiera chropowatość powierzchni i odkształcenie uszkodzenia w warunkach rozciągania dla dwóch grubości powłok, które będą nanoszone w tym urządzeniu medycznym.

4

Numerical modeling of substrate effect on determination of elastic and plastic properties of TiN nanocoating in nanoindentation test

Kopernik M., Milenin A.

Archives of Civil and Mechanical Engineering

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2014

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Vol. 14, no. 2

269--277

EN

The wall of a ventricular assist device is composed of a titanium nitride (TiN) nanocoating deposited on a biopolymer. Because of difficulties of the precise measurement of the force–displacement data for the soft substrate of polymer and for the very thin hard nanocoating of TiN in the nanoindentation test, it is assumed that the correctness of the results measured for these coatings deposited on steel is better. The sensitivity of results of nanoindentation test reached for different substrates with respect to properties of TiN influences the accuracy of the determination of mechanical properties in inverse analysis. In this work it is proved that the use of the steel instead of the biopolymer as a substrate for the measurement of the properties of the TiN increases the accuracy of determination of the plastic properties of the coating TiN in the nanoindentation test without significant reduction the accuracy of the determination of the elastic properties.

5

The new multiscale finite element model of multilayer ventricular assist device

Kopernik M., Milenin A.

Computer Methods in Materials Science

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2012

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Vol. 12, No. 1

20-36

EN

Ventricular assist device is an artificial organ, which is used to treat heart diseases. In the world, as well as in Poland, efforts are made towards the development of such a device that is biocompatible, durable, low energy consuming, allows monitoring and does not introduce changes to the blood morphology. The review paper discusses the types of ventricular assist devices (VADs), including VADs proposed in Poland. The particular emphasis is put on the numerical modelling and computer aided design of such an artificial organ. The walls of the ventricular assist device are covered with a nanocoating of TiN using modern techniques (Pulsed Laser Deposition) to improve the biocompatibility. The nanocoating modifies the surface properties of the device. Mechanical properties of nanocoating are determined in experimental nanotests and using imaging techniques of nanostructures. However, these tests give average values of properties and this information is not sufficient for advanced designof ventricular assist devices. To eliminate this constraint, the multiscale modelling is applied. Developed solution, which is based on application and combination of methods such as finite element method, multiscale approach and inverse analysis, is presented in the review paper. These methods are helpful in prediction the location of failure zones in the material of the ventricular assist device and then to analyze the local behaviour of nanocoating. Furthermore, it is possible to identify the parameters of the rheological model of nanocoating and introduce the residual stresses into models.

PL

Komora wspomagania pracy serca jest sztucznym narządem, który jest wykorzystywany do leczenia chorób serca. Na świecie, jak i w Polsce, czynione są wysiłki zmierzające do opracowania takiego urządzenia, które jest biokompatybilne, trwałe, zużywa mało energii, pozwala na monitorowanie i nie wprowadza zamian w morfologii krwi. Niniejszy artykuł omawia rodzaje komór wspomagania pracy serca, łącznie z komorą wspomagania zaproponowaną w Polsce. Szczególnie nacisk jest położony na modelowanie numeryczne i komputerowe wspomaganie projektowania takiego sztucznego narządu. Ściany komory wspomagania pracy serca są pokryte nanopowłoką TiN za pomocą nowoczesnych technik (ablacja laserowa) w celu poprawy biokompatybilności. Nanopowłoką modyfikuje własności powierzchniowe takiego urządzenia. Własności mechaniczne nanopowłoki są określane w doświadczalnych nanotestach i za pomocą technik obrazowania nanostruktur. Jednakże, te testy podają średnie wartości własności i taka informacja nie jest wystarczająca dla zaawansowanego projektowania komory wspomagania pracy serca. Aby wyeliminować to ograniczenie, zastosowano modelowanie wieloskalowe. Opracowane rozwiązanie, które jest oparte na zastosowaniu i kombinacji metod takich jak: metoda elementów skończonych, podejście wieloskalowe i analiza odwrotna, zostało przedstawione w artykule. Te metody są pomocne przy przewidywaniu lokalizacji stref uszkodzenia w materiale komory wspomagania pracy serca i potem, aby analizować lokalne zachowanie nanopowłoki. Ponadto, jest możliwa identyfikacja parametrów modelu Teologicznego nanopowłoki i wprowadzenie naprężeń własnych do modeli.

6

Two-scale finite element model of multilayer blood chamber of POLVAD_EXT

Kopernik M., Milenin A.

Archives of Civil and Mechanical Engineering

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2012

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Vol. 12, no. 2

178--185

EN

The latest construction of heart prosthesis - Polish ventricular assist device (POLVAD_EXT) is made of polymer and biocompatible TiN nanocoating. The two-scale model of the POLVAD_EXT is based on the finite element method. The theory of nonlinear elasticity and elasto-plasticity is applied in computations. The model in microscale includes: model of residual stress in TiN nanocoating, working loading of the POLVAD_EXT and profile of surface of deposited TiN nanocoating. The analysis of the stress–strain state is performed in two scales for the blood chamber of the POLVAD_EXT. The verification of the calculated macroresults is prepared by applying Authors' FEM code and experimental digital image correlation data. The computed distributions of stresses and strains in macro- and microscales are helpful to determine the regions of blood chamber of the POLVAD_EXT considered as the failure-source areas.

7

Numerical modelling and verification of Polish ventricular assist device

Milenin A., Kopernik M., Jurkojć D., Gawlikowski M., Rusin T., Darłak M., Kustosz R.

Acta of Bioengineering and Biomechanics

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2012

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Vol. 14, no. 3

49-57

EN

The developed multiscale model of blood chamber of POLVAD (Polish ventricular assist device) was introduced. The tension test for polymer and digital image correlation (DIC) were performed for verification of the strains and displacements obtained in the numerical model of POLVAD_EXT. The numerical simulations were carried out in conditions given in the experiment to compare the results obtained on external surfaces of blood chamber of the POLVAD_EXT. The examined polymer applied in the POLVADs is sensitive to changes of temperature and this observation is considered in all prepared numerical models. The comparison of experimental and numerical results shows acceptable coincidence. There are some heterogeneous distributions of strains in experiment with respect to analysis of computed parameters. The comparison of two versions of blood chambers (POLVAD and POLVAD_EXT) in numerical analysis shows that POLVAD_EXT construction is better with respect to analysis of strain and stress. The maximum values of computed parameters are located in the regions between connectors on the internal surfaces of blood chambers of POLVAD.

8

Microscale analysis of strain-stress state for TiN nanocoating of POLVAD and POLVAD_EXT

Milenin A., Kopernik M.

Acta of Bioengineering and Biomechanics

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2011

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Vol. 13, no. 4

11-19

EN

The main purpose of the research was to develop the micromodel of biocompatible titanium nitride nanocoating deposited on polymer by pulsed laser deposition method in blood chambers of Polish ventricular assist devices: POLVAD and POLVAD_EXT. The analysis of the parameters of micromodel crucial for the phenomenon of loss of cohesion occurring between coating and substrate was carried out as well. The micromodel takes into account residual stress, material model of nanocoating, stress resulting from blood pressure in chamber, the thickness of coating and wave parameters of nanocoating (wavelength and antinode). The investigation shows that thickness and residual stress are the most influential parameters. The phenomenon of the loss of cohesion will be observed more frequently for thicker coatings with higher residual stresses.

9

Comparative analysis of ventricular assist devices (POLVAD and POLVAD_EXT) based on multiscale FEM model

Milenin A., Kopernik M.

Acta of Bioengineering and Biomechanics

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2011

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Vol. 13, no. 2

13-23

EN

The prosthesis - pulsatory ventricular assist device (VAD) - is made of polyurethane (PU) and biocompatible TiN deposited by pulsed laser deposition (PLD) method. The paper discusses the numerical modelling and computer-aided design of such an artificial organ. Two types of VADs: POLVAD and POLVAD_EXT are investigated. The main tasks and assumptions of the computer program developed are presented. The multiscale model of VAD based on finite element method (FEM) is introduced and the analysis of the stress-strain state in macroscale for the blood chamber in both versions of VAD is shown, as well as the verification of the results calculated by applying ABAQUS, a commercial FEM code. The FEM code developed is based on a new approach to the simulation of multilayer materials obtained by using PLD method. The model in microscale includes two components, i.e., model of initial stresses (residual stress) caused by the deposition process and simulation of active loadings observed in the blood chamber of POLVAD and POLVAD_EXT. The computed distributions of stresses and strains in macro- and microscales are helpful in defining precisely the regions of blood chamber, which can be defined as the failure-source areas.