Development of Multifunctional Biocompatible Coatings

The increased life expectancy in combination with a population that is more active or prone to medical problems such as obesity and diabetes raise the demand for orthopaedic implants. Although medical technology already has written a lot of success stories, implant failure still occurs. The resulting revision surgeries do not only cause pain for the patients but they also form a financial and social burden on our society. Most failures can be accredited to implant loosening and infections. Therefore, current implant technology focuses on enhancing the long term implant fixation and reducing the incidence of infections. To improve osseointegration, macroporous Ti coatings are of special interest in this work. The macroporous structure can provide a mechanical anchorage by bone ingrowth and at the same time improve the loading capacity for antibacterial drugs or bone growth stimulating agents. Furthermore, by applying a bioactive glass coating, the inert Ti surface can be modified to create a strong chemical bond between the implant and surrounding tissue, while, the osteoinductive behavior of the glass enhances faster bone regeneration. In this doctoral research, macroporous Ti coatings on Ti or Ti6Al4V substrates are established by electrophoretic codeposition of various grades of ethanol based TiH2 stabilised emulsions and TiH2 suspensions, followed by dehydrogenation and subsequent high vacuum sintering. Depending on the powder particle size, the emulsion droplet size and processing parameters, macroporous Ti coatings with varying thickness and morphology can be obtained. In addition, the use of hydrides allows to lower the sintering temperature below the aß transition temperature of the Ti6Al4V substrate (Taß: 995°C), hence preserving the original microstructure of the substrate and its beneficial mechanical properties. Coatings with a tensile adhesion strength which was up to 50% higher than the state-of-the-art vacuum plasma sprayed Ti coatings can be obtained. For further chemical modification, a four component (SiO2-CaO-Na2O-P2O5) bioactive glass is synthesised following the melting process. This glass is applied on dense Ti or Ti6Al4V substrates and on the macroporous Ti coatings by dip coating or electrophoretic deposition and subsequent vacuum or microwave sintering at 800°C. This results in a crystalline top coating which fills up the open surface pores and has a good mechanical strength. In vitro staphylococcal biofilm formation is examined on several Ti-based implant materials trying to make a correlation between biofilm formation and the physical features of the implants i.e. roughness, porosity, pore size… Although the lower surface roughness of the macroporous Ti coatings obtained by electrophoretic deposition, no distinctive reduction in the biofilm formation compared to state-of-the-art vacuum plasma sprayed Ti coatings can be observed. At the same time, the in vitro biocompatibility studies show that the macroporous Ti coatings have a better cell adhesion and proliferation of HOC and HEC as well as a better specific labeling of the cytoskeleton and focal adhesion proteins and a lower inflammation potential compared to the state-of-the-art vacuum plasma sprayed Ti coatings. A 4 weeks in vivo experiment, focusing on the early peri-implant bone formation in a rabbit model, proves that the pore morphology of the macroporous Ti coatings allows bone in-growth of trabecular bone over a distance of 200 µm, confirming the ability of mechanical fixation. The osteostimulatory effect of bioactive glass is demonstrated by an enhanced bone formation compared to pure Ti implant.nrpages: 200status: publishe

Novel high-resolution micro-CT based surface roughness measurement protocol for complex porous structures

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Novel micro-ct based characterization tool for surface roughness measurements of porous structures

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Ti coatings with macropores for improved implant fixation obtained by electrophoretic deposition of TiH2 stabilized emulsions

Current implant technology focuses on enhancing the fixation between implant and surrounding tissue in order to reduce the risk of implant loosening and subsequent failing. Modifying the implant's surfaces with a macroporous metallic coating can provide a mechanical anchorage by bone ingrowth and at the same time improves the loading capacity for antibacterial drugs or bone growth stimulating agents. In this work, pure Ti coatings with spherical macropores are applied on dense Ti6Al4V substrates by electrophoretic deposition of TiH2 stabilized emulsions, followed by drying, dehydrogenation, and subsequent vacuum sintering at 850?degrees C. The obtained Ti coatings exhibit a porous network with an open porosity varying from 50 to 65% and a mean spherical pore size changeable from 50 to 80?mu m. The morphology of the coating is easily adapted by changing the powder particle size, the emulsion droplet size, and the deposition parameters. Since the coatings are produced in the frame of optimizing implant technology, a good adhesion between the substrate and the coating is a crucial prerequisite. Measurements show that the obtained tensile adhesion strength is >29?MPa.status: publishe

Porous titanium coatings through electrophoretic deposition of particle stabilized emulsions

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Porous titanium coatings through electrophoretic deposition of TiH2 suspensions

In the biomedical field, modification of titanium surfaces to improve the osteoinductive and antibacterial behavior is widely investigated. This functionalization can be further ameliorated by providing a porous coating with high loading capacity for bioactive materials and drug delivery carriers at the implant surface. In this work, a new powder metallurgical processing route used to deposit such porous pure titanium coatings on Ti based substrates is presented. The coatings were prepared by electrophoretic deposition (EPD) of TiH2 powder suspensions followed by dehydrogenation and sintering in vacuum. The use of hydrides allowed to lower the sintering temperature below that of the alpha-beta transition of the Ti6Al4V substrate. Measurement of the tensile bond strength confirmed a strong adhesion of the porous coating. Deposition of powders with different grain sizes resulted in porous titanium coatings with varying thickness, pore morphology, and surface roughness. The possibility to extend this coating technique to complex shaped implants is highlighted.status: publishe

Porous titanium coatings for improved implant fixation

A major challenge in implant technology nowadays is preventing premature loosening of the implants since this comprises the main reason for revision surgery. By tailoring the surface morphology and controlling the porosity and pore size of a porous coating on prosthetic devices, osteointegration can be promoted resulting in implant fixation by bone ingrowth. A new powder metallurgical processing route for the production of porous titanium coatings on metallic substrates was developed. By the electrophoretic deposition of a TiH2 powder suspension followed by sintering in vacuum, a pure Ti coating was applied on Ti-6Al-4V substrates. The use of TiH2 powders resulted in a higher sinterability compared to pure Ti systems. Hence the substrates original superior mechanical properties can be maintained. Pure Ti coatings with a porosity ranging from 37 to 52% have been produced. Adhesion testing of the coatings revealed a tensile bond strength that is higher than for state-of-the-art vacuum plasma sprayed coatings.CD-ROMstatus: publishe

Sol-gel based bioactive coatings inside open porous titanium structures

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Porous titanium coatings obtained by electrophoretic deposition (EPD) of pickering emulsions and microwave sintering

The multitude of published work reveals that the field of biomaterials is of great interest to the academic and industrial world.[1] The outlook of ameliorating the life of human beings has made this niche in the porous materials spectrum a favourite amongst researchers. In order for a porous material to qualify as a possibly successful biomaterial not only its structure needs to be controlled but its composition has to be regarded with even higher scrutiny. Even the smallest impurities are to be avoided since they might influence the tissue implant interaction. In this paper, emulsions stabilized with titanium particles are used to establish porous coatings on Ti6Al4V substrates. After coating the substrate with the emulsion by means of electrophoretic deposition (EPD), the liquid phases are removed by evaporation and the porous coatings are sintered in helium in a microwave furnace.status: publishe

Bioactive glass-ceramic coated titanium implants prepared by electrophoretic deposition

Surface modification of Ti alloys towards an improved osteoinductive behaviour is one of the major challenges in orthopaedic implant technology nowadays. One way to achieve this is by applying a bioactive coating which can increase the rate of osseointegration and chemical bonding of surrounding bone to the implant. In the present work, the production of a bioactive glass-ceramic coating on flat Ti alloys by electrophoretic deposition is demonstrated. The coatings are applied by cathodic deposition from non-aqueous suspensions followed by sintering in vacuum, avoiding uncontrolled oxidation of the Ti substrates. The use of non-aqueous suspensions both allowed to reduce the deposition time and yielded homogeneous coatings with a uniform thickness of 8 μm. Evaluation of the coating adhesion confirmed the good mechanical performance of the coatings with a tensile bond strength of 41.0 ± 11.1 MPa. Additionally, a feasibility study demonstrated the potential of electrophoretic deposition as a coating technique for commercial complex implants. © 2012 Elsevier B.V.status: publishe