Modell zur Analyse des knöchernen Anwachsverhaltens auf bioaktiv beschichteten Implantatoberflächen

Model to analyse the bone on‐growth on bioactive coated implant surfaces Especially on the field of bone regeneration, transient and permanent implants are an important method of therapy in the Orthopaedic Surgery. In this context, bioactive surfaces on metallic implants provide an improved contact to the surrounding bone. The goal of our study was to establish an in‐vitro test system to evaluate the on‐growth of bone‐derived cells on different surface coatings. Therefore, we invented a special kind of clamps made of commercially‐pure (c‐p) titanium and blasted with hydroxyapatite particles followed by electrochemically coating with calcium phosphate (BONIT®‐HA, BONIT®). Definite pieces of human cancellous bone were attached to these clamps, inserted onto tissue culture plates and cultivated in DMEM for ten days. Finally, the contact area between human cancellous bone and the implant surface was analyzed and the spreading of osteoblast‐like cells evaluated by scanning electron microscopy (SEM). A well‐spread morphology of bone cells was observed on the implant surfaces coated with calcium phosphate (CaP). In comparison the clamps without CaP coatings showed only a marginal growth of bone cells on the clamp surface. The presented newly in‐vitro test setup using titanium clamps coated with bioactive layers attached to human cancellous bone represents a well‐functioning model for qualitative evaluation of bone on‐growth.     

Methoden zur mechanischen Charakterisierung von modifizierten Implantatoberflächen in der Orthopädischen Chirurgie

Methods for the mechanical characterisation of modified implant surfaces in orthopaedic surgery Nowadays, on average approximately 10 % of all hip and knee endoprostheses have to be exchanged within the first 10 years. Implant revision is often necessary following aseptic or septic loosening. Hence, today implants for orthopaedic surgery are increasingly being coated for better osseointegration. Coatings have to be biocompatible and meet high mechanical requirements, whereby the adhesive strength and the abrasive wear resistance of the coatings take on a key role. This study presents different methods to asses these parameters experimentally using two innovative coatings (TiN, TiO2‐Cu) exemplary. The adhesive bonding strength of the coatings was investigated using different standardised methods, such as the arbour bending test, scratch test and the standard adhesive test. Wear resistance was determined after 1.5 million cycles in a special testing machine. The investigations showed for both coatings, TiN and TiO2‐Cu, good adhesive strength and wear resistance. The adhesive strength and wear resistance of bio‐active, wear reducing or anti‐allergenic surface coatings can be determined reliably using the above‐mentioned methods.     

Zur Plausibilität der Methode der Zugdreiecke

On the Plausibility of the Method of Tensile Triangles (MTT) The shape optimization of components, developed in Forschungszentrum Karlsruhe after the design rules of nature [1] has during the last 15 years very well spread and proven itself in industry, especially in automotive engineering. The limits for using the CAO‐method (Computer Aided Optimization) are more or less of economical nature. In this paper the plausibility for a new pure graphical method is shown, which works without any FEM or optimization software.     

CA3O – Eine neue Methode der Klebeschichtoptimierung nach dem Vorbild der Natur

CA³O – A New Method of Adhesive Optimization Modeled on Nature For millions of years, nature has optimized its constructions such that a maximum degree of material utilization is reached with a minimum expenditure. These optimizations of living tissue are by no means completed. Constantly, natural constructions are adapted to newly generated loads. To learn from nature therefore means to transfer the optimization knowledge from natural constructions to technical components. Reproduction of exact biologic processes mostly does not lead to the goal. Instead, it is crucial to search for the directives of growth. The CAO method (computer‐aided optimization) [1] is a very successful method of component optimization that mimics the growth of trees based on a simple rule and, thus, optimizes technical components. The growth rule is summarized by an axiom: The axiom of constant stress [1]. The CAO method represents the starting point of the new method of adhesive optimization. The method of optimizing adhesive layers and the underlying growth rules shall be described below.adhesive layer, assembly component, optimization, axiom of constant stress, bionics     

Quantitative Bewertung von Werkstoffinhomogenitäten auf der Basis der Bruchmechanik

Today it is impossible to quantitatively judge defects of welded joints, because a definite connection between defect and failurestress does not exist. Based on fracture mechanics a theoretical connection is produced between the portion of defects in a welded joint and the failurestress of such a welded component (plate or pipe). It Proved right that the failure-stress is dependent upon both the ratio K_c/σ* (K_c = fracture toughness; σ* = flow stress) and the component-size, whereas the allowable portion of defects rise with increasing K_c/σ* However, the allowable portion of defects decrease with increasing component-size.     

Eine Methode zur Ermittlung der anwendungsspezifischen Leistungsgrenze trockenlaufender Friktionspaarungen

Forschung im Ingenieurwesen - Eine immer grenzwertigere Auslegung trockenlaufender Friktionssysteme sowie die Steigerung der bauraum- und massenspezifischen Leistungsdichte führen zu permanent...     

Einfluss der chemischen Umgebung auf Morphologie und Struktur von Magnesiumhydroxid auf Magnesiumoberflächen

Influence of the Chemical Environment on the Morphology and Structure of Magnesium Hydroxide formed on Magnesium Surfaces Successful application of magnesium in metal construction is promoted by available methods for surface protection and, if needed, an electrical isolating layer between magnesium and other construction metals of composite materials [1]. Suitable materials for surface protection are polymer coatings, e. g. polymer paints. These coatings require a sufficiently corrosions resistant ground, which up to now normally is a environmentally dangerous, chromium‐containing conversion layer. In case of destruction of a conversion layer, caustic magnesium hydroxide is formed and responsible for a promoted delamination of various commercial polymer paints. Thus, development of a new magnesium – polymer – systems is of great interest. One probably successful possibility is a defined chemical attachment of molecular adhesion promoters to the magnesium conversion layers. These adhesion promoters should include a magnesium hydroxide specific group for a strong chemical attachment to magnesium conversion layer, which is hydrolytically stable in water, and additionally a second adhesive group at the other end of a hydrophobic spacer to ensure the attachment of a polymer. Direct attachment of these molecular adhesion promoters onto magnesium metal is not promising as all known magnesium organic compounds are hydrolytically instable [2]. As the hydroxide conversion coating is a substantial part of a magnesium‐polymer‐composite, the properties of the magnesium hydroxide layer have to be investigated and optimized depending on preparation conditions. In order to characterize the magnesium hydroxide conversion layer we use IR‐spectroscopy, quartz microbalance and Scanning Probe Microscopy. IR‐spectroscopic investigations show the presence of water in hydroxide conversion coatings formed at pH = 7–10. Conversion coatings prepared at pH > 12 are spectroscopically free of water. Taking into account the isoelectric point and the reactions resulting from a pH change, a model for the formation of the hydroxide layer is presented. This model explains the formation of a water free hydroxide layer at pH levels above 12 and the formation of water containing hydroxide layers below pH 12. The topography of the conversion layers is investigated by Scanning Probe Microscopy. If the conversion layer is formed in a solution with low pH a rough structure is built up compared to conversion layers, which are formed in solutions with high pH. These differences can be explained by taking into account the solubility of magnesium hydroxide and the change of OH⁻‐concentration in the solution due to different pH.     

Niedrigemittierende Außenoberflächen bei Wärmedämmverbundsystemen – ein Studie zur Vermeidung von Algenwuchs

Algae growth on the outside surface of thermal insulating composite systems (TICS) occurs because of long‐lasting wetting. The present techniques for its avoidance are without long‐term effect. Especially, dew and frost are an essential reason for its occurrence because of the highly thermal insulation of the TICSs. In the following report, it will be investigated by an algorithm on the basis of a worst case scenario for outside condensation whether outside condensation on TICSs can be counteracted by a low‐emissivity outside surface as it is well‐proven on highly insulating window glazing. The calculations showed that outside condensation on TICSs with heat transfer coefficients (U) values from 0.1 to 0.2 W/(m² K) cannot be avoided theoretically by thermal emissivity values ε in the range of 0.05 till 0.1. However, because the most critical scenario conditions for outside condensation are very stringent and, in addition, the calculations have shown that outside condensation is only possible for relative outdoor humidity rH_o ≥ 95%, it can be deduced that the occurrence of outside condensation will be very improbably in praxis for TICSs with U values from 0.1 to 0.2 W/(m² K) and ε values from 0.05 to 0.1. A weathering and soiling resistant surface with ε ≤ 0.1 can be realized by aluminum which may be additionally passivated by a titanium dioxide coating. Because of the hydrophilic property, this coating shows also self‐cleaning effect and quickly drying of the surface after rain. The latter may counteract algae growth, too.     

Eine neue Methode zur Festigkeits- und Zähigkeitsbestimmung von dünnen Schichten

A New Method of Determining Strength and Fracture Toughness of Thin Films A method is presented for measuring strength and fracture toughness of thin films. The basic idea of this method is to use a compact steel specimen as a substrate, which is deeply precracked by means of fatigue loading prior to the coating process. Under bend loading of this composite crack opening occurs accompanied by straining the free-standing thin film which bridges the crack. Film rupture firstly occurs at the front face of the specimen followed by crack growth on both sides. The film properties can be derived by eliminating the substrate effect through determining the difference between the two load-displacement curves corresponding to the intact and the damaged film, respectively. The strength of the film can be calculated from the load difference at film rupture at the front face of the composite. The fracture toughness is evaluated from load and compliance change during successive crack growth on both sides of the specimen. First results on PACVD TiN-films are presented and compared with available bulk data, thus demonstrating the applicability of the proposed method.     

Eine effiziente Methode zur Ermittlung des Schädigungsbereiches bei Wöhleruntersuchungen

An Efficient Method for the Estimation of the “French Damage Area” By a statistically planned and evaluated variant of French's method, the French damage line may be transformed into a quantitatively describable “damage area”. For this purpose a considerable amount of tests has to be applied (app. 400 specimens). A new evaluation of statistically planned investigations of Panagopoulos [23] showed two remarkable results:

• 100% probability of fracture is nearly related to 100% probability of damage
• the arcsin √-transformation is a well fitting model describing the distribution of damage.

A new efficient method for the estimation of the damage area based on this observations was derived and described. The damage area is discussed regarding two level and multi-level tests.     

Eine auf der Systemanalyse von Reibungs- und Verschleißvorgängen aufbauende Methodik zur Auswahl von tribotechnischen Werkstoffen

A method for the selection of tribotechnical materials based on a system analysis of friction and wear processes . The tribological behaviour of materials cannot be specified by their physical, chemical and mechanical properties only. Besides these ?system-independant”? properties ?system-dependant”? data are important. This is demonstrated by applying the methods of systems analysis to friction and wear processes. Based on systems thicking a method for the selection of tribotechnical materials is outlined.     

The two‐shearfield test – A suitable method for the empirical shear capacity design of masonry / Der Zweifeld‐Schubversuch – Eine praxistaugliche Methode zur versuchsgestützten Bemessung der Schubtragfähigkeit von Bestandsmauerwerk

The investigations [1] demonstrate that the two‐shearfield test is a suitable method for the determination of the shear capacity of masonry. The testing equipment is mounted directly on the wall in order to retain realistic boundary conditions like stiffness, load and prior damage. The behaviour factor q and the capacity curves of certain masonry walls can be directly obtained from the experimental results and realistic material behaviour in earthquake design can be represented. In particular, existing masonry can be assessed realistically with methods like the response spectrum, the push‐over and the capacity spectrum by using the two‐shearfield test.     

Stabilität antielektrostatischer Beschichtungen auf der Basis von Polyethylendioxithiophenen

Stability of antielectrostatic coatings on basis of polyethylenedioxythiophene Antielectrostatic properties of products manufactured from polymer materials are of great relevance for applications. It has been demonstrated for the engineering polymer polyamide 6 and the high temperature resistant polymer polyethersulphone that by coating them with polyethylenedioxythiophene an electrical conductivity can be achieved which is sufficient for antielectrostatic applications. Due to chemical ageing of the electrical conducting polymer the surface resistance of the coated specimen increases. The change of the electrical resistance with time was measured for various temperatures, layer thicknesses, and resin formulations. The ageing can be described by an Arrhenius behaviour. By this relationship an estimation of the change in resistance under different conditions of application is feasible.     

Komplexe zur Herstellung niederenergetischer Oberflächen

Low Surface Energie from Waterborne Nano‐Dispersions of Polymer Complexes Waterborne nano‐dispersions with a supra‐molecular ordering were prepared by using a commercially available polyelectrolyte and a fluorinated surfactant. From this complex, thin coatings on chemically very different surfaces can be prepared at room temperature without using organic solvents. The resulting coatings are smooth, optically invisible and have low surface energies. Critical surface tensions according to Zisman [16] were determined to be in the range from 5.7 to 13.1 mN/m and dispersive surface energies according to the Girifalco‐Good‐Fowkes‐Young equation [17, 18] are in the range from 10.2 to 10.7 mN/m. The low surface energies observed for fluorinated polyelectrolyte surfactant complexes as well as their liquid crystalline‐like structures are caused by the strong segregation tendency of fluorinated and ionic moieties [27].