M. Basiaga

Biomechanical Analysis of Lumbar Spine Stabilization by Means of Transpedicular Stabilizer

The fundamental purpose of research was determination of biomechanical characteristic of lumbar spine–transpedicular stabilizer system made of stainless steel (Cr-Ni-Mo) and Ti6Al4V alloy. To define biomechanical characteristic of the system finite element method was applied. Geometric models of part spine L3-L4 and stabilizer, was discretised by means of SOLID 95 element. Appropriate boundary conditions imitating phenomena in real system with appropriate accuracy were established. The aim of biomechanical analysis was calculation of displacements and stresses in the vertebras and the stabilizer in a function of the applied loading: 700 N–1600 N. The results of the numerical analysis can be applied to determine a construction features of the stabilizer, and to select mechanical properties of metallic biomaterial. The defined displacements for vertebras L3-L4 show that the proposed type of stabilizer enables correct course of treatment.

Technological capabilities of surface layers formation on implant made of Ti-6Al-4V ELI alloy

PURPOSE The aim of the presented research was to find a combination of surface modification methods of implants made of the Ti-6Al-4V ELI alloy, that lead to formation of effective barrier for metallic ions that may infiltrate into solution. METHODS To this end, the following tests were carried out: roughness measurement, the voltamperometric tests (potentiodynamic and potentiostatic), and the ion infiltration test. RESULTS The electropolishing process resulted in the lowering of surface roughness in comparison with mechanical treatment of the surface layer. The anodization process and steam sterilization increased corrosion resistance regardless of the mechanical treatment or electropolishing. The crevice corrosion tests revealed that independent of the modification method applied, the Ti-6Al-4V ELI alloy has excellent crevice corrosion resistance. The smallest quantity of ions infiltrated to the solution was observed for surface modification consisting in the mechanical treatment and anodization with the potential of 97 V. CONCLUSIONS Electric parameters deter- mined during studies were the basis for effectiveness estimation of particular surface treatment methods. The research has shown that the anodization process significantly influences the pitting corrosion resistance of the Ti-6Al-4V ELI alloy independent of the previous surface treatment methods (mechanical and electrochemical). The surface layer after such modification is a protective barrier for metallic ions infiltrated to solution and protects titanium alloy against corrosive environment influence.

EIS Study of SiO2 Oxide Film on 316L Stainless Steel for Cardiac Implants

The correct relationship between implant and tissue environment provides a properly prepared surface of a medical device. The combination of advantages of metal implants with the required biocompatibility is achieved through various methods of surface treatment such as: electrochemical polishing, chemical passivation, preparation of oxide coatings obtained with the sol-gel method. The relatively short history of use of silica layers in biomedical applications transfers into a small amount of literature relating to the electrochemical properties of these layers. Therefore, the authors proposed in the work forming a silica layer of the established technological parameters on surface of the 316L stainless steel. In order to determine the usefulness of this technology electrochemical impedance spectroscopy studies were performed. Furthermore, corrosion resistance tests by means of the potentiodynamic method were also carried out. The obtained results were the basis for optimization of technological conditions for deposition of silica layers on the 316L steel surface.

Electrochemical Impedance Spectroscopy and Corrosion Resistance of SiO2 Coated CpTi and Ti-6Al-7Nb Alloy

One of the ways to increase the hemocompatibility of surface of titanium and its alloys is to apply sol-gel method to form oxide films based on such elements as Ti or Si. However, the literature suggests existence of group of undefined phenomena associated with oxide layer formation on surfaces of metallic biomaterals in the presence of silicon. Therefore, the study involves development of conditions suitable for production of surface layers that have phisycal and chemical properties adequate for application in cardiovascular system. To assess the usefulness of proposed modifications, the Authors carried out electrochemical tests involving potentiodynamic and impedance measurements. The tests were performed in artificial serum in temperature T = 37±1°C in order to simulate real-life conditions. The obtained results show diverse properties of SiO2 layer that depend on process parameters of its formation.

Biomechanical Behaviour of Surgical Drills in Simulated Conditions of Drilling in a Bone

The main aim of this work is a biomechanical analysis of a surgical drill-femur system under conditions simulating the bone drilling process, using a finite-element method. The geometrical model of the surgical drill was prepared for different point angle values of the drill tip (2κ 1 = 90 o and 2κ 2 = 120 o ) and different diameters (d 1 = 9.0 mm, d 2 = 4.5 mm, d 3 = 3.2 mm and d 4 = 1.0 mm). The analysis included two variants of the drilling process: Variant I included drilling a single layer of the cortical tissue of a femur, while Variant II included the simulation of another step of the drilling process - drilling in the opposite area of cortical tissue. Calculations were made for two types of drill material. The biomechanical analysis may form the basis for improving the geometry of surgical tool tips and optimising a selection of the mechanical properties of the material used to manufacture them.

Evaluation of physicochemical properties of SiO2-coated stainless steel after sterilization.

The study of most of the literature devoted to the use of coronary stents indicates that their efficiency is determined by the physicochemical properties of the implant surface. Therefore, the authors of this study suggested conditions for the formation of SiO2 layers obtained with the use of sol-gel methodology showing physicochemical properties adequate to the specific conditions of the cardio-vascular system. Previous experience of authors helped them much to optimize the coating of 316LVM steel surface with SiO2. The values of parameters that determine the usefulness of the coating in medical applications have been determined. In order to identify the phenomena taking place at the boundary of phases and to evaluate the usefulness of the proposed surface modification, taking into consideration the medical sterilization (steam or ethylene oxide (EO)), the potentiodynamic, impedance, adhesion, surface morphology and biological assessment characterizations were performed. Regardless of the usage of the sterilizing agent (steam, EO) the study showed the reduction of critical force causing layers delamination. The research results of corrosion resistance study also confirmed a slight decrease of SiO2 barrier properties of the samples after sterilization in contact with the artificial plasma. SiO2 layers after the sterilization process did not show significant features of cytotoxicity and had no negative influence on blood cell counts, which confirmed the results of quantitative and qualitative studies.

The effects of a SiO2 coating on the corrosion parameters cpTi and Ti-6Al-7Nb alloy

The aim of this paper was to evaluate the usefulness of the sol-gel method application, to modificate the surface of the Ti6Al7Nb alloy and the cpTi titanium (Grade 4) with SiO2 oxide, applied on the vascular implants to improve their hemocompatibility. Mechanical treatment was followed by film deposition on surface of the titanium samples. An appropriate selection of the process parameters was verified in the studies of corrosion, using potentiodynamic and impedance method. A test was conducted in the solution simulating blood vessels environment, in simulated body fluid at t = 37.0 ± 1 °C and pH = 7.0 ± 0.2. Results showed varied electrochemical properties of the SiO2 film, depending on its deposition parameters. Correlations between corrosion resistance and layer adhesion to the substrate were observed, depending on annealing temperature.

Numerical Analysis of Spine Stabilizers on Lumbar Part of Spine

The numerical analysis of spine stabilizers was carried out in the work. The aim of the work was determination of more favourable stabilization variant. Moreover, this analysis is the basis to determine an optimal geometry of the stabilizer as well as to select mechanical properties of metallic biomaterial. The work presents the results of biomechanical analysis of lumbar spine stabilization by plate and transpedicular stabilizer. The finite element method was applied for biomechanical characteristic of implants made of stainless steel Cr-Ni-Mo and Ti-6Al-4V alloy. Geometrical models of part of spine L3-L4 and the stabilizer were discretized by SOLID95 element. Appropriate boundary conditions imitating phenomena in real system with appropriate accuracy were established. The result of numerical analysis was calculation of displacements and reduced stresses in particular elements of system in a function of the applied loading: 700 - 1600 N. The displacements calculated for part L3-L4 show that the proposed type of stabilizer enables the correct treatment process. The obtained numerical results should be verified in ”in vitro” tests.

Evaluation of physicochemical properties of surface modified Ti6Al4V and Ti6Al7Nb alloys used for orthopedic implants.

The paper presents the results of selected functional properties of TiO2 layers deposited by ALD method on the surface of Ti6Al4V and Ti6Al7Nb alloys intended for implants in bone surgery. TiO2 layer was applied at the constant temperature of the ALD process at T=200°C at a variable number of cycles, which resulted in a different layer thickness. Different process cycles of 500, 1250, and 2500 were analyzed. The application of experimental methods (AFM, SEM, wettability, potentiodynamic test, EIS, scratch test, nanohardness and layer thickness) enabled to select the optimal number of cycles, and thus the thickness of the TiO2 layer of the most favorable functional properties. The obtained results clearly showed that regardless of the type of titanium substrate, the TiO2 layer applied in a 2500cycle ALD process has the best physicochemical and electrochemical properties. These properties have major impact on biocompatibility, and therefore the quality of the final product. The information obtained can be useful for manufacturers of medical devices involved in the production of implants used in reconstructive surgery of skeletal system.

Corrosion Resistance of Ti6Al7Nb Alloy after Various Surface Modifications

The influence of surface pretreatment prior to the anode oxidation of Ti6Al7Nb alloy samples on corrosion resistance was presented in the work. The preliminary surface treatments were: grinding, vibration machining, sandblasting and electrochemical polishing. Anodic oxidation process was carried out at different voltages. The final procedure of the surface modification was steam sterilization. The scope of the work included: corrosion resistance study (pitting and crevice) of both non-sterilized and sterilized samples, and samples after 28 days exposure to the Ringer’s solution, concentration evaluation of metal ions releasing from the sterilized surface as well as observations of surface topography. The research revealed a significant influence of surface pretreatment of Ti6Al7Nb alloy, prior to the anode oxidation and steam sterilization, on corrosion resistance.