Z. Paszenda

Numerical analysis of three-layer vessel stent made from Cr-Ni-Mo steel and tantalum

The main aim of the work was determination of biomechanical characteristics of a three-layer vascular stent made of stainless steel and tantalum Ta. Furthermore, the numerical analysis of the same stent form made exclusively of the stainless steel was carried out. The result of the numerical analysis was determination of the relation between reduced stresses and strains present in the individual regions of the stent, in function of the expansion diameter (d = 1,0 3,5 mm). The analysis of the obtained results showed the diverse distribution of stresses and strains in the individual regions of the stent. The results of the numerical analysis are valuable information for appropriate design of the stent form, its geometrical features and for selection of mechanical properties of the applied metallic biomaterials. The strains obtained from the numerical analysis showed that only deformable surface layer reduce the surface reactivity in blood environment. [Received 15 October 2006; Accepted 14 January 2007]

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.

Biomechanical Behaviour of Double Threaded Screw in Tibia Fixation

The aim of the work was assessment of stability of tibia fixation realized with the use of double threaded screw. Biomechanical analysis of the tibia – double threaded screw system was carried our for the implant made of two biomaterials used in bone surgery – Cr-Ni-Mo stainless steel and Ti-6Al-4V alloy. Finite element method was applied to calculate displacements, strains and stresses. The obtained results allowed to work out biomechanical characteristics of the analyzed system. These characteristics can be a basis for selection of degree of strain hardening of the applied metallic biomaterial and optimization of the screw’s geometry.

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.

Application Problems of Implants Used in Interventional Cardiology

The paper discusses application issues of using the metal implants for treatment of the cardiovascular diseases. The analysis of the biophysical conditions of the heart-coronary vessels system has been used to distinguish the tissue environment properties which should be compatible with properties of the metal biomaterial and stent surface. The need to determine the correct quality and service properties of the coronary stents has been indicated, which refer first of all to their design form, physical and chemical properties of the metal biomaterial and its surface. Based on that the Author of the work has proposed his own methodology for forming and controlling the service properties of the stents. It takes into account the required relationships between structure, and mechanical properties of the stent biomaterial, and the physical and chemical properties of its surface - adjusted to the specific features of the cardiovascular system.

Kinematic Analysis of Complex Therapeutic Movements of the Upper Limb

The paper presents the results of kinematic analysis of therapeutic movements of the upper limb, according to PNF method recommendations. Real trajectories of upper limb movements were recorded using the photogrammetric method. The measuring site consisted of a set of 8 digital cameras, two computer workstations, a set of markers, calibrating dice and light sources. On the basis of the recorded images and calculations performed with the use of specialized software, model trajectories of the analyzed movements and values of relative angular translocations and angular velocity in individual joints of the limb were defined.

Application of Motion Analysis Systems in the Designing of a Rehabilitation Device

The paper presents the results of kinematic analysis of the prototype of rehabilitation device for human upper limb. The aim of these measurements was to assess possibility to execute PNF movements in upper limb joints and correctness of functioning of control algorithms responsible for reproducing of assigned movements The measuring site consisted of a set of 4 digital cameras, computer workstation, a set of markers, calibrating dice and light sources. Measurements were carried out for simple and complex movements. First a man forced a motion sequence, and then the device had to repeat it. Measurements revealed necessity of changes in constructions due to unacceptable positioning inaccuracy. Exemplary results before and after these changes are presented in the paper.