Volume 10 (2010): Issue 4 (December 2010)

The contact of a biomaterial with the biological environment in in vitro and in vivo tests leads to the production of a particular ecosystem in which the active roles perform both, the material surface and the extracellular matrix protein forming a biofilm. Proteins affect cell and bacteria adhesion processes, biological activity of cells and activation of inflammatory response.

The knowledge of the reaction mechanisms active on the surface of the material and the contacting tissues enables definite modification of the material surface layer eliminating their disadvantages, giving new, desired properties, affecting the biology of cells. Testing the biocompatibility of titanium materials emphasises their reactivity with proteins and cells and the possibility of modifying the biological reactivity of the surface by changing its properties by biochemical and surface engineering methods. This article presents results of previous studies on this problem.

Silver particles having fine or ultrafine sizes are one of the fastest growing research interests with wide applications. Here we report the preparation method of silver modified paints which revealed antimicrobial activity against gram-negative bacteria Escherichia coli, gram-positive Staphylococcus aureus, yeast Saccharomyces cerevisiae and pathogenic fungi belonging to Candida family. In this work, we choose heptane and cyclohexane, as the oil phase for preparation nanometer sized metallic particles. We have also studied the effect of different silver precursors - silver nitrate, silver citrate and different surfactants: anionic AOT, non-ionic Triton X100, Span 80 and Tween 85 for stabilization of obtained silver colloids. UV-VIS spectrum contained a strong plasmon band near 410 nm, which confirmed silver ions reduction to Ag○ in microemulsion system or aqueous phases. Prepared samples contained from 500 to 2000 ppm of silver. The diameter size of silver nanoparticles was in the range from 16 nm to 82 nm and were stable for 3 months without precipitation.

The main objective of here presented research is to develop the titanium (Ti) alloy base composite materials possessing better biocompatibility, longer lifetime and bioactivity behaviour for load-bearing implants, e.g. hip joint and knee joint endoprosthesis. The development of such materials is performed through: modeling the material behaviour in biological environment in long time and developing of new procedures for such evaluation; obtaining of a Ti alloy with designed porosity; developing of an oxidation technology resulting in high corrosion resistance and bioactivity; developing of technologies for hydroxyapatite (HA) deposition aimed at composite bioactive coatings; developing of technologies of precipitation of the biodegradable core material placed within the pores.

The examinations of degradation of Ti implants are carried out in order to recognize the sources of both early allergies and inflammation, and of long term degradation. The theoretical assessment of corrosion is made assuming three processes: electrochemical dissolution through imperfections of the anodic oxide layer, diffusion of metallic ions through the oxide layer, and dissolution of oxides themselves.

In order to increase the biocompatibility, the toxic elements, aluminium (Al) and vanadium (V) are eliminated. The experiments have shown that titanium - zirconium - niobium (Ti-Zr-Nb) alloy may be a such a material which can also be prepared by both powder metallurgy (P/M) technique and selective laser melting. The porous (scaffold) Ti-Zr-Nb alloy is now obtained by powder metallurgy, classical and with space holders used before melting and decomposed, or remained during melting and removed by subsequent water dissolution. The oxidation of porous materials is performed either by electrochemical technique in special electrolytes or by chemical and/or hydrothermal method in order to obtain the optimal oxide layer well adjacent to an interface, preventing the base metal against corrosion and bioactive because of its nanotubular structure, permitting injection of some species into the pores. The Ca, O and N ion implantation or deposition of zirconia sublayers may be used to increase the biocompatibility, bioactivity and corrosion resistance. The HA coating obtained by either electrophoretic, biomimetic or by sol-gel deposition should result in gradient structure similar to bone structure, possessing high adhesion strength. The core material of the porous material should result in a biodegradable material, allowing slower dissolution followed by stepwise growth of bone tissue and angiogenesis, preventing local inflammation processes, sustaining the mechanical strength close to that of non-porous material.

The relationship between microstructure and mechanical properties of structural materials is still relevant problem in the theory of materials science and mechanical engineering. The question is how the macro-mechanical parameters can be derived from the microscale mechanisms taking into account local structural heterogeneities. Another question is how to make quantitative descriptions of the strength and toughness properties of welded joints made of non-matching weld metal. These problems are the objects of welding and mechanical investigation and they are related to estimation of weldability. The results of this study concern the evaluation stress state at interface of the under- and overmatched weld joints. After formulating a simplified model of under- and overmatched weld joints an analysis was made of stress at interface for the cases of perpendicular and non - perpendicular orientation of the zones (soft - layer and hard - layer) relative to the load action direction under tension.

Numerical weldability analysis is a new powerful research and development tool which is useful for metallurgistics technologist and design engineers. Saying strictly the numerical analysis of weldability comprises thermodynamic, thermomechanical and microstructural modelling of the welding process. The fracture resistance of welded joints is mainly characterised by normalised parameters: SU₁ = K_Ith / K_IC for cold cracking or in the exploitation condition by or SU₂ = Δ/Δ_C or J/J_C, SU₁ ≠ SU₂. Conclusions from the theoretical analysis form a basis to an assessment measure of the stress state parameter S_p as a physical measure of the deformation and effort of the mismatched weld joints. There also was made characteristic of the effect on the inclination of the layer (W) on the form of fracture. Finally, some aspects of estimation of the K_C and K_IC values for the layer (W) with the SINTAP programme overview are presented.

Due to the increasing number of cases of hypersensitivity caused by direct contact with metals, as well as the increasing demand for implants in humans all ages numerous studies on the effects of the impact of implant components are being carried out. The paper presents the phenomenon of etiology of allergy in general terms and in relation to the biomaterials used in medicine. There have been characterized in terms of impact on the body, metallic biomaterials, such as: stainless steels, cobalt based alloys, titanium and its alloys, shape memory alloys and other materials for medical applications (ceramics, plastics, carbon and composite materials), with respect to their reaction in contact with human tissue. The article presents the research included in the MPh of the author, performed on stainless steel.

The study presents some strength parameters of structural materials, including steel grades 13HMF, P91 and P92, currently used in professional power engineering to produce pipelines, boiler super-heaters, steam tanks, steam pressure tanks and pipelines designed to operate at the temperature range up to 650° C. The author presented results of material stress tests performed by him for pipelines in as-delivered state as well as after 40 000 hours of operation. The tests were made using Mathar strain gauge method. Hardness test results for areas subjected to strain gauge tests and structural changes of tested samples are also presented. Stress test results indicate stress increase for operated material as well as for grain size growth compared to as-delivered material. It is caused by operating load (both thermal and mechanical) of the pipeline material.

The article presents the investigation results of titanium alloy Ti6Al4V surface layer after laser melting process. The process of laser melting was performed using Nd-YAG laser. The evaluation of structure of the alloy as well as hardness and chemical composition was performed. It was shown that laser melting changes the structure and properties of titanium alloy Ti6Al4V and process parameters as scanning speed affects the thickness of zones in top layer of the material. Due to the laser melting process more wear resistive surface can be obtained that increases the wear and corrosion resistance of orthopeadic prosthesis.

A method is presented for the comparative testing of wear resistance of ceramic coatings made from materials potentially feasible in tribo - medical applications, mainly orthopaedic implants made from ceramics coated metals for low cost, long life and low wear particle emission into the body. The method was devised as the main tool for use in research and is comprised of flat on flat and ball on flat surface (sliding) tests. Seven ceramic coatings were chosen as potentially feasible for the application area known to perform well in low viscosity fluid lubrication condition. The materials used in coatings were diamond like carbon (DLC), diamond like carbon with tungsten additive (DLC-W), titanium nitride (TiN), titanium carbide (TiC), silicon carbide (SiC), chromium nitride (CrN), carbon nitride (CNx). The coatings tested were deposited in vacuum to a stainless steel substrate with the use of several methods, each suited to the coating material; The methods were the following: cathode arc evaporation (ARC), magnetron sputtering (MAG), plasma assisted chemical vapour deposition (PACVD), impulse reactive magnetron sputtering (IRMS) and a combined method ARC-MAG-RF-PACVD (radio frequency assisted - RF); A multiple role PT-3 tribometer was used for flat on flat surface tests (ring shaped surface) and a reciprocating linear motion TPZ-1 tribometer for ball on flat surface tests and a CSEM REVETEST® Scratch Tester to perform standard scratch test in air on coatings. A set of results was obtained illustrating the limiting load for each coating (the load inflicting rapid destruction of the coating) and the endurance under light loading conditions. As lubricating agents distilled water and saline water solution were used. Test results examples are presented and discussed as an illustration of the method's usability for the target application area.

The article presents the results of diagnostic examination of P265GH boiler steel plate. During blanking, cutting and cold forming of elements from this plate, their spontaneous plastic deformation and warping took place, indicating an unfavourable internal stress state of a considerable magnitude occurring in the steel plate. In order to identify the causes of this situation, examinations were carried out, which included a microstructure assessment and a Vickers hardness test. In view of the absence of clear differentiation, in terms of both structure and hardness, in different steel plate areas, diagnostic examination was performed by the Barkhausen magnetic method, which included the determination of the principal direction of residual stresses and the determination of their anisotropy based on the measurement of the effective value of Barkhausen noise. As their result, a significant anisotropy of residual stresses was revealed on the steel plate surface. Moreover, the adverse phenomenon of perpendicularity of the principal directions of stresses was found to occur on the opposite plate surfaces, being the direct cause of warping of elements cut out from the plate