J. Szewczenko

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.

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.

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.

Electrochemical properties of ti-6al-4v ELI alloy after anodization

Techniques of surface modification are very important in forming final physicochemical properties and biocompability of titanium alloys. Quality of surface layer is determined by metallic ions infiltrating to body fluid and tissue environment. Performing anodization process as a final technological treatment we could minimalizing that effect. A prior mechanical treatment which could be performed in different ways, we can influence final properties. Different variants of mechanical treatment connected with anodization process require insightful quantitative evaluation. Especially surface final physicochemical properties are need to be checked in order to assess the effectiveness of metallic ions infiltration blocking on the reservoir layer, what is strongly bounded with the initiation and development of implant corrosion process. The aim of the work were the research on ways and conditions and surface treatment of Ti-6Al-4V ELI alloy for physicochemical properties to implantation applications.

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.

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.

Effect of surface pretreatment on corrosion resistance of anodically oxidized ti6al7nb alloy

Results presented in the paper are an attempt of defining the influence of selected preliminary treatments of surface on the final biocompatibility of anodized Ti6Al7Nb alloy. The anodization process was preceded by combination of different surface modification treatments including grinding, vibration machining, mechanical polishing, sandblasting and electropolishing. Steam sterilization was the final surface modification treatment. Range of research included: surface roughness tests, crevice and pitting corrosion investigations in Ringers solution, determination of concentration of metallic elements which penetrated to the solution after 28 days exposition and microscopic observations of the specimens surface. The results of research have shown significant influence of preliminary methods of surface preparing which precede anodization. Preliminary preparing of the surface to anodization, as a multistage process, can not be understood solely as a single treatment which directly preceded anodization process. In fact, all the earlier treatments of surface modification before anodization have influence on corrosion resistance.

Corrosion resistance of PLGA-coated biomaterials

The aim of the study was to determine the influence of PLGA bioresorbable polymer coating on corrosion resistance of metal biomaterial. Polymer coating deposited by immersion method was applied. Corrosion resistance of metal biomaterials (stainless steel, Ti6Al4V, Ti6Al7Nb) coated with PLGA polymer, after 90 days exposure to Ringers solution was tested. The amount of metal ions released to the solution was also investigated (inductively coupled plasma-atomic emission spectrometry (ICP-AES) method). The surface of the samples was observed using atomic force microscopy (AFM) and scanning electron microscopy (SEM). Degradation of PLGA was monitored with the use of the 1H NMR spectroscopy and GPC (Gel Permeation Chromatography). The studies were carried out for non-sterilized (NS) and sterilized (S) samples. Application of the polymer coating causes a reduction of release of metal ions to the solution. Depending on metal substrate different course of destruction of polymer layer was observed. After 90 days of incubation in Ringers solution polymer layer was highly degraded, however, the composition of copolymer (ratio of the comonomeric units in the chain) remained unchanged during the whole process, which suggests even degradation. The polymer layer reduced degradation kinetics of the metal substrate. Moreover, degradation process did not change surface morphology of metal substrate and did not disturb its integrity. The results obtained indicate that the applied polymer layer improves corrosion resistance of the alloys being investigated. Thus, the developed implants with bioresorbable coatings could be advantageous for medical applications.

Influence of Ultrasound Bone Union Stimulation on Corrosion Resistance of Titanium Alloys

The influence of bone union activation realized with the use of the low-intensity pulsed ultrasound (LIPUS) on degradation of titanium alloys was presented in the work. Ti6Al4V ELI and Ti6Al7Nb alloy samples of modified surface layer were used in the study. The preliminary surface treatments were: grinding, vibration machining, mechanical polishing, sandblasting and electrochemical polishing. The final procedures of the surface modification were anodization and steam sterilization. The scope of the work included the study of pitting corrosion resistance and concentration of metal ions released to the Ringer’s solution. The study was performed for the undeformed and deformed samples subjected to the influence of ultrasound. The reference samples were the samples kept in the solution and not having the impact of ultrasound. On the basis of the study it was found that the conditions for bone union stimulation by low intensity pulsed ultrasound do not initiate pitting corrosion of the titanium alloy samples, although they increase the mass of ions released from the surface to the solution.