Implant-related infections are a serious complication in prosthetic surgery, substantially jeopardizing implant fixation. As porous coatings for improved osseointegration typically present an increased surface roughness, their resulting large surface area (sometimes increasing with over 700% compared to an ideal plane) renders the implant extremely susceptible to bacterial colonization and subsequent biofilm formation. Therefore, there is particular interest in orthopaedic implantology to engineer surfaces that combine both the ability to improve osseointegration and at the same time reduce the infection risk. As part of this orthopaedic coating development, the interest of in vitro studies on the interaction between implant surfaces and bacteria/biofilms is growing. In this study, the in vitro staphylococcal adhesion and biofilm formation on newly developed porous pure Ti coatings with 50% porosity and pore sizes up to 50 μm is compared to various dense and porous Ti or Ti-6Al-4V reference surfaces. Multiple linear regression analysis indicates that surface roughness and hydrophobicity are the main determinants for bacterial adherence. Accordingly, the novel coatings display a significant reduction of up to five times less bacterial surface colonization when compared to a commercial state-of-the-art vacuum plasma sprayed coating. However, the results also show that a further expansion of the porosity with over 15% and/or the pore size up to 150 μm is correlated to a significant increase in the roughness parameters resulting in an ascent of bacterial attachment. Chemically modifying the Ti surface in order to improve its hydrophilicity, while preserving the average roughness, is found to strongly decrease bacteria quantities, indicating the importance of surface functionalization to reduce the infection risk of porous coatings.

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 α–β 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.

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Porous titanium coatings on dense Ti6Al4V substrates were made by electrophoretic deposition (EPD) of titanium particle stabilized Pickering emulsions. The samples were consecutively dried and microwave sintered in helium to prevent oxidation. The obtained coatings have a thickness ranging from 50 to 250 μm with open spherical macropores in the 20 to 200 μm range.

Bulk titanium foams were prepared by emulsion templating during slip casting. The emulsion template was stabilized using partially hydrophobized titanium particles while the continuous phase consisted of a titanium hydride powder suspension. Sintering was performed in inert atmosphere. The use of titanium hydride resulted in lower sintering temperatures and denser, stronger struts. Both homogeneous foams with high compressive strength and structures with a gradient in pore size were obtained.

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 °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 µm. 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.