Alexandra Wittmar

Preparation of a silicate-containing hydroxyapatite-based coating by magnetron sputtering: structure and osteoblast-like MG63 cells in vitro study

Silicate-containing hydroxyapatite-based coatings with different structure and calcium/phosphate ratios were prepared by radio-frequency magnetron sputtering on silicon and titanium substrates, respectively. Scanning electron microscopy, X-ray diffraction and IR spectroscopy were used to investigate the effect of the substrate bias on the properties of the silicate-containing hydroxyapatite-based coatings. The deposition rate, composition, and microstructure of the deposited coatings were all controlled by changing the bias voltage from grounded (0 V) to −50 and −100 V. The biocompatibility was assessed by cell culture with human osteoblast-like cells (MG-63 cell line), showing a good biocompatibility and cell growth on the substrates.

Nano-hydroxyapatite-coated metal-ceramic composite of iron-tricalcium phosphate: Improving the surface wettability, adhesion and proliferation of mesenchymal stem cells in vitro

Thin radio-frequency magnetron sputter deposited nano-hydroxyapatite (HA) films were prepared on the surface of a Fe-tricalcium phosphate (Fe-TCP) bioceramic composite, which was obtained using a conventional powder injection moulding technique. The obtained nano-hydroxyapatite coated Fe-TCP biocomposites (nano-HA-Fe-TCP) were studied with respect to their chemical and phase composition, surface morphology, water contact angle, surface free energy and hysteresis. The deposition process resulted in a homogeneous, single-phase HA coating. The ability of the surface to support adhesion and the proliferation of human mesenchymal stem cells (hMSCs) was studied using biological short-term tests in vitro. The surface of the uncoated Fe-TCP bioceramic composite showed an initial cell attachment after 24h of seeding, but adhesion, proliferation and growth did not persist during 14 days of culture. However, the HA-Fe-TCP surfaces allowed cell adhesion, and proliferation during 14 days. The deposition of the nano-HA films on the Fe-TCP surface resulted in higher surface energy, improved hydrophilicity and biocompatibility compared with the surface of the uncoated Fe-TCP. Furthermore, it is suggested that an increase in the polar component of the surface energy was responsible for the enhanced cell adhesion and proliferation in the case of the nano-HA-Fe-TCP biocomposites.

Routes towards catalytically active TiO2 doped porous cellulose

Cellulose–TiO2 nanocomposites have been successfully prepared by non-solvent induced phase separation, either from cellulose solutions in ionic liquids or from cellulose acetate solutions in classical organic solvents followed by deacetylation (“regeneration”). Commercially available titania nanoparticles from gas phase synthesis processes have been used and processed as dispersions in the respective polymer solution. The used TiO2 nanoparticles have been characterized by means of transmission electron microscopy (TEM) and X-ray diffraction (XRD), and their dispersions in ionic liquids and organic solvents have been evaluated by dynamic light scattering (DLS) and advanced rheology. The intermediate polymer solutions used in the phase separation process have been studied by advanced rheology. The resulting nanocomposites have been characterized by means of scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FT-IR). Special attention has been given to the complex relationship between the characteristics of the phase separation process and the porous structure of the formed nanocomposites. Two catalytic tests, based on the photocatalytic degradation of model organic dyes under UV irradiation, have been used for the characterization of the TiO2 doped nanocomposites. The proof-of-concept experiments demonstrated the feasibility of photocatalyst immobilization in porous cellulose via phase separation of nanoparticle dispersions in polymer solutions, as indicated by UV-activated dye degradation in aqueous solution.

Two step and one step preparation of porous nanocomposite cellulose membranes doped with TiO2

Cellulose–TiO2 nanocomposites have been successfully prepared by non-solvent induced phase separation from cellulose acetate solutions in classical organic solvents followed by deacetylation (“regeneration”). The cellulose deacetylation has been performed either sequentially, i.e. after the completion of the phase separation process, or simultaneously, i.e. during the phase separation process. Commercially available titania nanoparticles from gas phase synthesis processes have been used and processed as a dispersion in the respective polymer solutions. The resulting nanocomposites have been characterized by means of scanning electron microscopy (SEM) and Fourier transform infrared (FT-IR) spectroscopy. Special attention has been given to the complex relation between the conditions of the deacetylation process, the structure of the resulting TiO2 doped cellulose membranes and their corresponding catalytic activities. Two catalytic activity tests, based on the photocatalytic degradation of model organic dyes under UV irradiation, have been used for the functional characterization of the TiO2 doped nanocomposites. The performed experiments demonstrated the successful photocatalyst immobilization in porous cellulose acetate together with good catalytic activity of this nanocomposite intermediate. By simply varying the conditions of the cellulose deacetylation, nanocomposite cellulose membranes with different structures and properties have been obtained. However after the regeneration of cellulose a partial decrease of the catalytic activity was observed.

Stable zinc oxide nanoparticle dispersions in ionic liquids

The influence of the hydrophilicity and length of the cation alkyl chain in imidazolium-based ionic liquids on the dispersability of ZnO nanoparticles by ultrasound treatment was studied by dynamic light scattering and advanced rheology. ZnO nanopowder synthesized by chemical vapor synthesis was used in parallel with one commercially available material. Before preparation of the dispersion, the nanoparticles characteristics were determined by transmission electron microscopy, X-ray diffraction, nitrogen adsorption with BET analysis, and FT-IR spectroscopy. Hydrophilic ionic liquids dispersed all studied nanopowders better and in the series of hydrophilic ionic liquids, an improvement of the dispersion quality with increasing length of the alkyl chain of the cation was observed. Especially, for ionic liquids with short alkyl chain, additional factors like nanoparticle concentration in the dispersion and the period of the ultrasonic treatment had significant influence on the dispersion quality. Additionally, nanopowder characteristics (crystallite shape and size as well as the agglomeration level) influenced the dispersion quality. The results indicate that the studied ionic liquids are promising candidates for absorber media at the end of the gas phase synthesis reactor allowing the direct preparation of non-agglomerated nanoparticle dispersions without supplementary addition of dispersants and stabilizers.

Correlation between surface properties and wettability of multi-scale structured biocompatible surfaces

The influence of surface properties of radio-frequency (RF) magnetron deposited hydroxyapatite (HA) and Si-containing HA coatings on wettability was studied. The composition and morphology of the coatings fabricated on titanium (Ti) were characterized using atomic force microscopy (AFM) and X-ray diffraction (XRD). The surface wettability was studied using contact angle analysis. Different geometric parameters of acid-etched (AE) and pulse electron beam (PEB)-treated Ti substrates and silicate content in the HA films resulted in the different morphology of the coatings at micro- and nano- length scales. Water contact angles for the HA coated Ti samples were evaluated as a combined effect of micro roughness of the substrate and nano-roughness of the HA films resulting in higher water contact angles compared with acid-etched (AE) or pulse electron beam (PEB) treated Ti substrates.