Josef Sepitka

PDMS substrate stiffness affects the morphology and growth profiles of cancerous prostate and melanoma cells.

A deep understanding of the interaction between cancerous cells and surfaces is particularly important for the design of lab-on-chip devices involving the use of polydimethylsiloxane (PDMS). In our studies, the effect of PDMS substrate stiffness on mechanical properties of cancerous cells was investigated in conditions where the PDMS substrate is not covered with any of extracellular matrix proteins. Two human prostate cancer (Du145 and PC-3) and two melanoma (WM115 and WM266-4) cell lines were cultured on two groups of PDMS substrates that were characterized by distinct stiffness, i.e. 0.75 ± 0.06 MPa and 2.92 ± 0.12 MPa. The results showed the strong effect on cellular behavior and morphology. The detailed analysis of chemical and physical properties of substrates revealed that cellular behavior occurs only due to substrate elasticity.

The effect of nitrogen ion implantation on the surface properties of Ti6Al4V alloy coated by a carbon nanolayer

The ion beam assisted deposition (IBAD) method was chosen for preparing a carbon thin film with a mixing area on a substrate of Ti6Al4V titanium alloy. Nitrogen ions with energy 90 keV were used. These form a broad ion beam mixing area at the interface between the carbon film and the substrate. We investigated the chemical composition by the glow discharge optical emission spectroscopy (GD-OES) method and the phases by the X-ray diffraction (XRD) method. The measured concentration profiles indicate the mixing of the carbon film into the substrate, which may have an effect on increasing the adhesion of the deposited film. The nanohardness and the coefficient of friction were measured. We found that the modified samples had a markedly lower coefficient of friction even after damage to the carbon film, and they also had higher nanohardness than the unmodified samples. The increased nanohardness is attributed to the newly created phases that arose with ion implantation of nitrogen ions.

Influence of diamond and graphite bonds on mechanical properties of DLC thin films

Mechanical properties of diamond-like carbon thin films with various ratios of sp3/sp2 bonds were studied. The films were prepared in argon atmosphere (0.25 Pa) by laser deposition method for laser energy densities from 4 Jcm−2 to 14 Jcm−2. The sp2 and sp3 bonds were calculated by X-ray photoelectron spectroscopy. Films contained sp3 bonds up to 70 %. Surface properties as roughness and atomic force microscopy topology were measured. Hardness (and reduced Youngs modulus) were determined by nanoindentation and reached of 30 GPa (203 GPa). Films adhesion was studied using scratch test and was up to 12 N for biomedical alloy (titanium substrates – Ti-6Al-4V). Relations among deposition conditions and measured properties are presented.

Elastic Properties of Human Osteon and Osteonal Lamella Computed by a Bidirectional Micromechanical Model and Validated by Nanoindentation

Knowledge of the anisotropic elastic properties of osteon and osteonal lamellae provides a better understanding of various pathophysiological conditions, such as aging, osteoporosis, osteoarthritis, and other degenerative diseases. For this reason, it is important to investigate and understand the elasticity of cortical bone. We created a bidirectional micromechanical model based on inverse homogenization for predicting the elastic properties of osteon and osteonal lamellae of cortical bone. The shape, the dimensions, and the curvature of osteon and osteonal lamellae are described by appropriately chosen curvilinear coordinate systems, so that the model operates close to the real morphology of these bone components. The model was used to calculate nine orthotropic elastic constants of osteonal lamellae. The input values have the elastic properties of a single osteon. We also expressed the dependence of the elastic properties of the lamellae on the angle of orientation. To validate the model, we performed nanoindentation tests on several osteonal lamellae. We compared the experimental results with the calculated results, and there was good agreement between them. The inverted model was used to calculate the elastic properties of a single osteon, where the input values are the elastic constants of osteonal lamellae. These calculations reveal that the model can be used in both directions of homogenization, i.e., direct homogenization and also inverse homogenization. The model described here can provide either the unknown elastic properties of a single lamella from the known elastic properties at the level of a single osteon, or the unknown elastic properties of a single osteon from the known elastic properties at the level of a single lamella.

Nanoindentation of intervertebral disc tissues localised by SHG imaging

J. Šepitka*, J. Lukeš, L. Staněk, E. Filová, Z. Burdı́ková and J. Řeznı́ček Department of Mechanics, Biomechanics and Mechatronics, Faculty of Mechanical Engineering, Czech Technical University in Prague, Technicka 4, Prague 16607, Czech Republic; General Faculty Hospital, Institute of pathology, Charles University, Prague, Czech Republic; Institute of Experimental Medicine of the Academy of Sciences of the Czech Republic, Prague, Czech Republic; Department of Biomathematics, Institute of Physiology, Academy of Sciences of the Czech Republic, Prague, Czech Republic

Micromechanical Properties of Biocompatible Materials for Bone Tissue Engineering Produced by Direct 3D Printing

Bone implants in form of artificial scaffolds manufactured from poly-lactic acid (PLA) represent an attractive alternative to traditional surgical treatments of defective bones (i.e. autografts and allografts). In this work factors influencing biocompatibility and primary stability of implants manufactured from PLA using direct 3D printing were assessed using nanoindentation. For this reason bulk sample of the PLA material and a printed object were subjected to nanomechanical measurement. Quasi-static nanoindentation was employed to identify elastic modulus and hardness distribution on surface and within volume of the samples. Moreover mechanical properties along scanning direction and interlayer characteristics were also assessed. Gradients in mechanical properties have been identified within volume of the material, within the printing layers and at contact between individual layers.

Inspection of Post Impact Fatigue Damage in Carbon Fibre Composite Using Modulus Mapping Technique

This study is focused on inspection of damage extent induced into C/PPS composite material by fatigue and impact loading. Initial damage to specimens was induced by drop-weight out-of-plane impact damage. Several levels of damage states (intact specimen, fatigued and impacted specimen, ruptured specimen) were inspected using modulus mapping (MM) technique. Quantification of the damage level was based on comparison of results from MM obtained in distinct locations on the specimens. Regions of interest were selected in order to determine magnitude of damage after impact and to assess remaining loading capabilities of the material. For this purpose, material maps provided information about location where matrix had been inflicted by the damage. Results show that impact loading has no measurable influence on mechanical properties of the matrix. However, gradient in mechanical properties was detected in the vicinity of crack. Results were validated using quasi-static nanoindentation and constant strain rate continuous measurement that showed depth profile of mechanical properties.

Compression tests of a living cell: a contact detection problem

Alterations in the mechanical properties of cells are associated with cellular diversification and diseases. Assessment of mechanical properties of living cells was mostly associated with atomic force microscopy (AFM) technique. However, the contact conditions of AFM tip with cell’s membrane are very complex (Vichare et al. 2012). Advantageously, very well-defined geometry of flat-end probe used for nanoindentation can simplify the contact problem into compression of an inflated spherical membrane by two rigid parallel planes (Arfsten et al. 2008;Nadler 2010). From our previous experiments, we used the following cell because of their long viability and good adhesion: COS-1 cells (ATCC code: CRL-1650) were derived from African green monkey kidney; the cells grow attached to the base (adherent) and have the morphology of fibroblasts (ATCC, VA, USA). The aims of this study are as follows: (1) determination of the contact between flat punch tip and single cell and (2) to identify membrane bursting critical load.

Mechanical and Tribological Properties of Carbon Thin Film with Tungsten Interlayer Prepared by Ion Beam Assisted Deposition

Mechanical and tribological properties of the thin carbon film with tungsten interlayer were investigated. The carbon film (130 nm) and the tungsten interlayer (20 nm) were prepared by ion beam assisted deposition (IBAD) method. Both layers were electron beam evaporated and were simultaneously irradiated by the beam of argon (Ar) or nitrogen (N) ions with energy of 700 eV. Mechanical properties of the thin carbon film with tungsten interlayer were investigated by the nanoindentation method. Concerning tribological properties the coefficient of friction was investigated by means of pin on disc tribometer. Phase composition was investigated by X-ray diffraction method (XRD), and bonding characterization of carbon thin film was characterized by Raman spectroscopy.

Structural Characterization and Mechanical Properties of a Titanium Nitride-Based Nanolayer Prepared by Nitrogen Ion Implantation on a Titanium Alloy

A functionalized surface nanolayer less than 200 nm in thickness was prepared by nitrogen ion implantation at fluences of 2·1017, 4·1017, and 6·1017 cm-2 and at an accelerating voltage of 90 kV on the Ti6Al4V alloy. The evolution of the surface mechanical properties and the structural mechanism of the hardening were investigated. X-ray diffraction showed a great number of αTi+N interstitial nitrogen atoms and finely dispersed TiN precipitates in the modified surface nanolayer. The functionalized surface nanolayer on the sample with applied fluence of 2·1017 cm-2 had a predominant amount of αTi+N of about 45 wt% with minority TiN compound up to 20 wt%. The TiN content increased dramatically with increasing fluence of the implanted nitrogen. Nanoindentation investigations found that the indentation hardness improved up to 408% and that the reduced elastic modulus was increased up to 140%. The main hardening mechanism varied with the nitrogen concentration. Nitrogen ion implantation at low fluence of 2·1017 cm-2 led to a functionalized surface nanolayer in which the hardening was mainly caused by the microstrain due to the large amount of interstitially located nitrogen. Applied fluences of 4·1017 and 6·1017 cm-2 increased the content of TiN compounds, which became the predominant hardening mechanism.