Comparison of the abrasion resistance of the selected biomaterials for friction components in orthopedic endoprostheses

Rosnące z każdym rokiem zapotrzebowanie na endoprotezy stawów ortopedycznych przy jednoczesnym dążeniu do zwiększenia ich trwałości i wyeliminowania negatywnych skutków ubocznych produktów zużycia, które mogą wywoływać proces zapalny w tkankach determinuje potrzebę poszukiwania nowych biomateriałów bądź metody modyfikacji ich powierzchni. Nadrzędnym celem prowadzonych przez nas badań było oszacowanie intensywności zużycia ściernego biomateriałów obecnie stosowanych na pary trące w endoprotezach ortopedycznych oraz nowego stopu tytanu Ti13Nb13Zr w aspekcie zastosowania go na elementy trące endoprotez. Do badań użyto czterech biomateriałów metalicznych: stopu Ti13Nb13Zr, stali nierdzewnej 316 LVM, stopu CoCrMo oraz stopu Ti6Al4V. Materiałem przeciwpróbki był polietylen o ultrawysokiej masie cząsteczkowej (PE-UHMW). Oceny odporności na zużycie ścierne badanych biomateriałów dokonano na podstawie wyznaczania wartości współczynnika tarcia dla konkretnej pary trącej, zmierzenia profili chropowatości powierzchni oraz obserwacji mikroskopowych (LM).The demand for orthopaedic joint prosthesis is growing each year. Simultaneously striving to increase their durability and eliminate negative effects of wear products that can cause inflammation in the tissues determines the need to search for new biomaterials or methods for the modification their surfaces. The overall objective of our research was to estimate the intensity of abrasive wear in currently used biomaterials on the friction pairs in orthopaedic endoprosthesis and the intensity of abrasive wear of a new titanium alloy (Ti13Nb13Zr) in the aspect of its practical use on the friction pairs in orthopaedic prostheses. For the research purposes, the following four metallic biomaterials were used: Ti13Nb13Zr alloy, 316 LVM stainless steel, CoCrMo alloy, and Ti6Al4V alloy. The counter samples in each of the friction pairs were made from ultra-high molecular weight polyethylene (PE-UHMW). It is important to tribological tests on the samples of friction pairs and then on the elements of endoprostheses. Evaluation of the abrasive wear resistance of the tested biomaterials was based on the determination of the friction coefficient for the particular friction pair and the measurement of the profiles of the surface roughness and optical microscopy observations by means of a light microscopy (LM). The analysis of the research results shows that the Ti13Nb13Zr alloy has relatively good tribological properties and allows for obtaining a low frictional resistance in the friction pair with PE-UHMW. Furthermore, considering the favourable mechanical properties of the tested Ti13Nb13Zr alloy and its high biocompatibility with the human body, it seems to be the very perspective biomaterial for use for the longterm implants. The desire to improve its durability in the researched biotribological system leads to searching for methods for the modification its surface

Analiza wpływu rozkładu naprężeń na profil zużycia w smarowanym styku ślizgowym UHMW-PE ze stopem tytanu Ti-13Nb-13Zr

Metal – polymer sliding contacts are a typical combination in industry and medicine. For decades such a set of materials has been the primary choice in human joints endoprosthetic technology. In this paper tribological issues of are presented from a research on the potential for practical use of Ti-13Nb-13Zr/UHMW-PE couple for orthopedic endoprosthesis. In tests on simplified models it is critically important to carefully select geometry of contact, load and velocity magnitudes and profiles to the later interpretation of results. In case of organic polymers interacting with metallic components the problem is even more prominent, than in the case of all metal systems because of great differences in the modulus of elasticity between the specimens in contact. High local loading can cause excessive heat generation and accelerated loss in polymer’s strength induced by thermal plastification. The process may not be manifested in the course of the experiment in any way detectable and might compromise the accuracy of wear measurement. In the case of the presented research an analysis has been performed to evaluate the observed wear profile of UHMW-PE with respect to non-uniform distribution of contact stress. A simulation was run with the use of FEM to evaluate the contact conditions between the titanium alloy and UHMW-PE specimens and the results were confronted with the wear profiles. Interesting similarities were discovered yielding useful information on the fundamentals of the wear in and for future research on similar systems.Skojarzenia ślizgowe metalowo-polimerowe są często spotykane w zastosowaniach przemysłowych i medycznych. Od długiego czasu są najczęściej wybierane w technice protez ortopedycznych. W artykule przedstawiono wybrane problemy tribologiczne spotykane w skojarzeniach stopu tytanu Ti-13Nb-13Zr oraz polietylenu UHMW-PE. W przypadku badań na modelach uproszczonych bardzo ważną kwestią jest właściwy dobór geometrii styku, wartości obciążenia i prędkości ślizgania oraz przebiegu zmian tych parametrów wymuszenia. Późniejsza interpretacja wyników i ich przydatność do zastosowań praktycznych jest ściśle związana z tak rozumianym przygotowaniem doświadczenia. W przypadku skojarzeń materiałów polimerowych z metalowymi ważnym czynnikiem wpływającym na skutki tarcia jest różnica w wartościach modułów sprężystości tych dwóch grup materiałów. Duże lokalne obciążenia mogą np. prowadzić do miejscowego przegrzewania powierzchni polimeru i plastyfikacji, co może zmniejszyć wartość uzyskanych wyników. W pracy przedstawiono analizę profilu zużycia próbek UHMW-PE w zależności od rozkładu nacisków powierzchniowych. Zastosowano symulacje z wykorzystaniem MES w celu analizy czynników wpływających na warunki kontaktu próbek ze stopu tytanu i polietylenu UHMW. Uzyskane wyniki symulacji znajdują potwierdzenie w zarejestrowanych doświadczalnie profilach zużycia próbek polimerowych. Zaobserwowano zależność rozkładu nacisków od warunków podparcia i naprężeń montażowych działających na próbkę

Effects of Micro-Arc Oxidation Process Parameters on Characteristics of Calcium-Phosphate Containing Oxide Layers on the Selective Laser Melted Ti13Zr13Nb Alloy

Titania-based films on selective laser melted Ti13Zr13Nb have been formed by micro-arc oxidation (MAO) at different process parameters (voltage, current, processing time) in order to evaluate the impact of MAO process parameters in calcium and phosphate (Ca + P) containing electrolyte on surface characteristic, early-stage bioactivity, nanomechanical properties, and adhesion between the oxide coatings and substrate. The surface topography, surface roughness, pore diameter, elemental composition, crystal structure, surface wettability, and the early stage-bioactivity in Hank’s solution were evaluated for all coatings. Hardness, maximum indent depth, Young’s modulus, and Ecoating/Esubstrate, H/E, H3/E2 ratios were determined in the case of nanomechanical evaluation while the MAO coating adhesion properties were estimated by the scratch test. The study indicated that the most important parameter of MAO process influencing the coating characteristic is voltage. Due to the good ratio of structural and nanomechanical properties of the coatings, the optimal conditions of MAO process were found at 300 V during 15 min, at 32 mA or 50 mA of current, which resulted in the predictable structure, high Ca/P ratio, high hydrophilicity, the highest demonstrated early-stage bioactivity, better nanomechanical properties, the elastic modulus and hardness well close to the values characteristic for bones, as compared to specimens treated at a lower voltage (200 V) and uncoated substrate, as well as a higher critical load of adhesion and total delamination

Deposition of phosphate coatings on titanium within scaffold structure

Purpose. Existing knowledge about the appearance, thickness, and chemical composition of 37 phosphate coatings on titanium inside porous structures is insufficient. Such knowledge is 38 important for the design and fabrication of porous implants. 39 Methods. Metallic scaffolds were fabricated by selective laser melting of 316L stainless steel 40 powder. Phosphate coatings were deposited on Ti sensors placed either outside the scaffolds 41 or in the holes in the scaffolds. The electrochemically-assisted cathodic deposition of 42 phosphate coatings was performed under galvanostatic conditions in an electrolyte containing 43 the calcium and phosphate ions. The phosphate deposits were microscopically investigated; 44 this included the performance of mass weight measurements and chemical analyses of the content of Ca2+ and PO4 2‒ 45 ions after the dissolution of deposits. 46 Results. The thicknesses of the calcium phosphate coatings were about 140 and 200 nm for 47 isolated titanium sensors and 170 and 300 nm for titanium sensors placed inside pores. 48 Deposition of calcium phosphate occurred inside the pores up to 150 mm below the scaffold 49 surface. The deposits were rich in Ca, with a Ca/P ratio ranging between 2 and 2.5. 50 Conclusions. Calcium phosphate coatings can be successfully deposited on a Ti surface 51 inside a model scaffold. An increase in cathodic current results in an increase in coating 52 thickness. Any decrease in the cathodic current inside the porous structure is slight. The 53 calcium phosphate inside the pores has a much higher Ca/P ratio than that of stoichiometric 54 HAp, likely due to a gradual increase in Ca fraction with distance from the surface

3D Printing of Metallic Implants

The fabrication of various elements, solid and open porous structures of stainless steel and Ti alloy is described. The process was started with the design of 3D models in CAD/CAMnbsp system. The 3D models were transformed into *.stl files and then the manufacturing process of the real structures by means of the selective laser melting with the SLM Realizer 100 3D printer was made. The paper shows the porous specimens made for possible application in medicine and the prosthetic bridges. The appropriate mechanical strength is the important property of porous structures for medical application and for curved prosthetic bridges it is necessary to take into account the thermal stresses, which appear during their SLM/DMLS manufacturing process