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The preparation of dense, high-strength calcium phosphate-zirconia (CaP-ZrO2) composed bioceramics is realized via versatile pressureless sintering by adding silica nanoparticles. Two different weight ratios of HAp:ZrO2, 9:1 and 1:1, are used with varying silica contents from 5 to 20 wt%. After sintering at 1200 °C, the phase composition, microstructure, porosity, biaxial bending strength, and fracture toughness as well as SBF in vitro bioactivity are characterized. We show that the addition of silica altered the crystal phase composition, inhibiting the formation of non-favourable cubic ZrO2. Furthermore, SiO2 addition leads to an increase of the biaxial bending strength, and the fracture toughness of CaP-ZrO2-containing materials. With the addition of 20 wt% silica we find the highest characteristic strength (268 MPa) and toughness (2.3 ± 0.1 MPam(0.5)) at

Size-controlled fluorescence silica nanoparticles (NPs) are widely used for nanotoxicological studies, and diagnostic and targeted therapies. Such particles can be easily visualized and localized within cell environments and their interactions with cellular components can be monitored. We developed an amino acid-catalyzed seed regrowth technique (ACSRT) to synthesize spherical rhodamine-doped silica NPs with tunable sizes, low polydispersity index as well as high labeling efficiency and enhanced fluorescence photostability. Via ACSRT, fluorescent silica NPs can be obtained by introducing the fluorophore in seed formation step, while a precise control over particle size can be achieved by simply adjusting the concentration of reactants in the regrowth step. Unlike the conventional methods, the proposed ACSRT permits the synthesis of fluorescent silica NPs in a water-based system, without the use of any surfactants and co-surfactants. By this approach, additional linkers for covalent coupling of the fluorophore to silica matrix can be omitted, while a remarkable doping efficiency is achieved. The suitability of these particles for biomedical application is demonstrated by in vitro tests with normal and malignant bone cells. We show that the particles can be easily and unambiguously visualized by a conventional fluorescence microscope, localized, and distinguished within intracellular components. In addition, it is presented that the cellular uptake and cytotoxic profile of silica NPs are strongly correlated to the particle size, concentration, and cell line. The results of in vitro experiments demonstrate that tunable fluorescent silica NPs synthesized with ACSRT can be potentially used for toxicological assessments and nanomedical studies.

The production of hierarchical nanopatterns (using a top-down microfabrication approach combined with a subsequent bottom-up self-assembly process) will be an important tool in many research areas. We report the fabrication of silica nanoparticle arrays on lithographically pre-patterned substrates suitable for applications in the field of nanobiotechnology. Two different approaches to reach this goal are presented and discussed: in the first approach, we use capillary forces to self-assemble silica nanoparticles on a wettability contrast pattern by controlled drying and evaporation. This allows the efficient patterning of a variety of nanoparticle systems and—under certain conditions—leads to the formation of novel branched structures of colloidal lines, that might help to elucidate the formation process of these nanoparticle arrays. The second approach uses a recently developed chemical patterning method that allows for the selective immobilization of functionalized sub-100 nm particles at distinct locations on the surface. In addition, it is shown how these nanocolloidal micro-arrays offer the potential to increase the sensitivity of existing biosensing devices. The well-defined surface chemistry (of particle and substrate) and the increased surface area at the microspots, where the nanoparticles self-assemble, make this patterning method an interesting candidate for micro-array biosensing.

We have investigated the influence of pH and ionic strength on the conformation of porcine gastric mucin (PGM) in bulk aqueous solution, its adsorption behavior onto poly(dimethylsiloxane) (PDMS) surfaces, and its lubricating behavior upon the self-mated sliding contact of a PDMS tribopair by means of circular dichroism (CD) spectroscopy, optical waveguide lightmode spectroscopy (OWLS), and pin-on-disk tribometry, respectively. In a low-concentration regime (1 mg/mL), where the formation of a mucus-gel is generally excluded, PGM is still observed to exhibit effective aqueous lubricating properties under specific conditions of acidic pH and low ionic strength. This behavior was closely correlated with specific conformations in the bulk solution as well as specific adsorption behavior at the water/PDMS interface. The lubrication mechanism of the self-mated sliding contact of PDMS by means of surface modification with PGM is discussed in terms of isoviscous-elastic/soft-elastohydrodynamic lubrication (soft-EHL).

The adsorption of lysozyme and bovine serum albumin on silica and AlOOH-coated silica particles-representing negatively and positively charged oxide surfaces-was investigated. The protein-treated uncoated and completely AlOOH-coated silica particles were characterized by zeta potential analysis and UV/VIS spectroscopy. It was found that at pH 7 a protein oppositely charged to the oxide surface adsorbs in significantly higher amounts. In contrast, proteins of the same charge did not or only in very low amounts adsorbed on an oxide surface. As both oxide surfaces were measured to be very hydrophilic it can be concluded that electrostatic interactions dominate the adsorption process at the investigated experimental conditions. The pH regions where the proteins interact via attractive and repulsive coulomb interaction with the particular oxide surfaces were calculated and outlined.

Protein adsorption at interfaces is a common phenomenon that is considered both advantageous and a problem in many fields, including medicine, biotechnology, environmental science, food processing and analysis. As protein–material interaction is largely a function of the material surface chemistry, a wealth of current research is aimed at functionalizing surfaces to control the overall material properties and, therefore, achieving a highly specific, controllable and predictable protein interaction behaviour at interfaces. In this chapter, some recent developments in material surface modification and the characterization of interactions of proteins and metal oxide particles at the liquid/solid interface are presented. Discussion is mainly focused on the interaction of alumina colloids, which provide an ideal substrate for surface functionalization and a suitable model for studying protein/material interface processes as a function of different surface chemistries. Additionally, alumina represents a technically relevant material widely employed in biomedical, biotechnological and environmental applications, including biosensing, protein separation and purification and biocatalysis. Some fundamental concepts regarding protein–surface interactions and surface functionalization are given along with some examples and models for investigating and deciphering the adsorption of single or self-assembled proteins such as viruses at liquid/solid interfaces. Understanding such issues will give guidance to design novel, advanced functional materials for different applications.

An important challenge in the field of dental and orthopedic implantology is the preparation of implant coatings with bioactive functions that feature a high mechanical stability and at the same time mimic structural and compositional properties of native bone for a better bone ingrowth. This study investigates the influence of magnesium addition to zirconia-calcium phosphate coatings. The mixed coatings were prepared with varying additions of either magnesium oxide or magnesium fluoride to yttria-stabilized zirconia and hydroxyapatite. The coatings were deposited on zirconia discs and screw implants by wet powder spraying. Microstructure studies confirm a porous coating with similar roughness and firm adhesion not hampered by the coating composition. The coating morphology, mechanical flexural strength and calcium dissolution showed a magnesium content-dependent effect. Moreover, the in vitro results obtained with human osteoblasts reveal an improved biological performance caused by the presence of Mg2+ions. The magnesium-containing coatings exhibited better cell proliferation and differentiation in comparison to pure zirconia-calcium phosphate coatings. In conclusion, these results demonstrate that magnesium addition increases the bioactivity potential of zirconia-calcium phosphate coatings and is thus a highly suitable candidate for bone implant coatings.

Mechanical performance of three oxide/oxide ceramic matrix composites (CMCs) based on Nextel 610 fibers and SiOC, alumina, and mullite/SiOC matrices respectively, is evaluated herein. Tensile strength and stiffness of all materials decreased at 1000 °C and 1200 °C, probably because of degradation of fiber properties beyond 1000 °C. Microstructural changes in the composites during exposure at 1000 °C and 1200 °C for 50 h reduce their flexural strength, fracture toughness and work of fracture. A literature review regarding mechanical properties of several oxide/oxide CMCs revealed lower influence of fiber properties on composite strength compared with elastic modulus. The tested composites exhibit comparable stiffness and strength but higher fracture toughness compared with average values determined from a literature review. Considering CMCs with different compositions, we observed an interesting linear trend between strength and fracture toughness. The validity of the linear relationship between fracture strength and flexural toughness for CMCs is discussed.

Subsequent supercritical CO2-assisted deposition and foaming process followed by in situ synthesis was used to fabricate functional polylactide (PLA) and polylactide–poly(ɛ-caprolactone) (PLA–PCL) bone scaffolds. Deposition of zinc bis(2-thenoyltrifluoroacetonate) as a ZnO precursor onto biopolyester substrates (30 MPa; 110 °C) was followed by fast depressurization to create cellular structure. Contact time was optimized regarding the deposition yield (2 h), while PCL content in PLA was varied (1–10 wt %). Scaffolds impregnated with the precursor were treated with hydrazine alcoholic solution to obtain biopolyester–ZnO composites. Precursor synthesis and deposition onto the scaffolds was confirmed by Fourier-transform infrared. Processed scaffolds had micron-sized pores (d50 ∼ 20 μm). High open porosity (69–77%) and compressive strength values (2.8–8.3 MPa) corresponded to those reported for trabecular bone. PLA blending with PCL positively affected precursor deposition, crystallization rate, and compressive strength of the scaffolds. It also improved PLA surface roughness and wettability which are relevant for cell adhesion. ZnO improved compressive strength of the PLA scaffolds without significant effect on thermal stability. Analysis of structural, thermal, and mechanical properties of biopolyester–ZnO scaffolds testified a great potential of the obtained platforms as bone scaffolds. Proposed processing route is straightforward and ecofriendly, fast, easy to control, and suitable for processing of thermosensitive polymers. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017, 134, 45824.

In this study a bioinspired approach to induce self-mineralization of bone-like material on alumina surfaces is presented. The mineralizing enzyme alkaline phosphatase (ALP) is covalently immobilized by a carbodiimide-mediated chemoligation method. The enzymatic activity of immobilized ALP and its mineralization capability are investigated under acellular conditions as well as in the presence of human bone cells. Analytical, biochemical and immunohistochemical characterization show that ALP is efficiently immobilized, retains its activity and can trigger calcium phosphate mineralization on alumina at acellular conditions. In vitro cell tests demonstrate that ALP-functionalized alumina clearly boosts and enhances bone cell mineralization. Our results underpin the great potential of ALP-functionalized alumina for the development of bioactive surfaces for applications such as orthopaedic and dental implants, enabling a fast and firm implant osseointegration.

Nanodiamonds are a class of carbon-based nanoparticles that are rapidly gaining attention, particularly for biomedical applications, i.e., as drug carriers, for bioimaging, or as implant coatings. Nanodiamonds have generally been considered biocompatible with a broad variety of eukaryotic cells. We show that, depending on their surface composition, nanodiamonds kill Gram-positive and -negative bacteria rapidly and efficiently. We investigated six different types of nanodiamonds exhibiting diverse oxygen-containing surface groups that were created using standard pretreatment methods for forming nanodiamond dispersions. Our experiments suggest that the antibacterial activity of nanodiamond is linked to the presence of partially oxidized and negatively charged surfaces, specifically those containing acid anhydride groups. Furthermore, proteins were found to control the bactericidal properties of nanodiamonds by covering these surface groups, which explains the previously reported biocompatibility of nanodiamonds. Our findings describe the discovery of an exciting property of partially oxidized nanodiamonds as a potent antibacterial agent.

Engineered sub-micron particles are being used in many technical applications, leading to an increasing introduction into the aquatic environment. Only a few studies have dealt with the biodegradability of non-functionalized organic particles. In fact the knowledge of organically surface functionalized colloids is nearly non-existent. We have investigated the biodegradability of organically surface functionalized silica (SiO2) particles bearing technically relevant groups such as amino-, carboxyl-, benzyl-, sulfonate-, chloro-, and phosphatoethyl-derivatized alkyls. Essential physicochemical properties including zeta potential, isoelectric point, morphology, surface area, porosity, surface density, and elemental composition of the particles were investigated, followed by biodegradability testing using the Closed Bottle Test (OECD 301D). None of the particles met the biodegradability threshold value of 60%. Only a slight biodegradation was revealed for SiO2-Benzyl (13.7±6.7%) and for SiO2-3-Chlorpropane (10.8±1.5%). For the other particles biodegradability was below the normal background fluctuation of 5%. The results were different of those obtained from structurally similar chemicals not being functionalized on the particle surface and from general rules of structure-biodegradation prediction of organic molecules. Therefore, our results suggest that the attachment of the organic groups heavily reduces their biodegradability, increases their residence time and possibility for adverse effects to environmental species.

Ca3ZrSi2O9 (baghdadite) has become a major research focus within the biomaterial community due to its remarkable in-vitro and in-vivo bioactivity. Although baghdadite seems to exhibit interesting biological properties, as yet there has been no data published concerning its mechanical properties. This lack of knowledge hinders targeting this novel bioactive material towards potential applications. In this study we prepare dense Ca3ZrSi2O9 bulk ceramics for the first time, allowing the evaluation of its mechanical properties including hardness, bending strength, Young׳s modulus, and fracture toughness. The preparation of baghdadite has been accomplished by a direct solid-state synthesis in combination with conventional sintering at 1350-1450°C for 3h. Our results show that samples sintered at 1400°C exhibit the best mechanical properties, resulting in a bending strength, fracture toughness, and hardness of 98±16MPa, 1.3±0.1MPam(0.5), and 7.9±0.2GPa. With a comparable mechanical strength to hydroxyapatite, but with an increased fracture toughness by 30% and hardness by 13% baghdadite is highly suitable for potential applications in non-load bearing areas (e.g. coatings or filler materials).

Akermanite (Ca 2 MgSi 2 O 7 ) ceramics have been successfully prepared by a novel approach, consisting of the heat treatment of silicone resins embedding MgO and CaO precursors, in the form of micro- and nano-sized particles, that act as reactive fillers. Phase purity was promoted by the use of nano-sized particles or by secondary additives, such as sodium borate. The use of hydroxyapatite as additional filler allowed the fabrication of monoliths with good specific mechanical properties, although with a complex phase assemblage. Sodium borate, besides favoring the crystallization of the desired silicate, promoted a substantial and homogeneous foaming of polymer/filler mixtures, leading to akermanite foams possessing good compressive strength.

Membrane clogging and biofilm formation are the most serious problems during water filtration. Silver nanoparticle (Agnano) coatings on filtration membranes can prevent bacterial adhesion and the initiation of biofilm formation. In this study, Agnano are immobilized via direct reduction on porous zirconia capillary membranes to generate a nanocomposite material combining the advantages of ceramics being chemically, thermally and mechanically stable with nanosilver, an efficient broadband bactericide for water decontamination. The filtration of bacterial suspensions of the fecal contaminant Escherichia coli reveals highly efficient bacterial retention capacities of the capillaries of 8 log reduction values, fulfilling the requirements on safe drinking water according to the U.S. Environmental Protection Agency. Maximum bacterial loading capacities of the capillary membranes are determined to be 3 × 109 bacterial cells/750 mm2 capillary surface until back flushing is recommendable. The immobilized Agnano remain accessible and exhibit strong bactericidal properties by killing retained bacteria up to maximum bacterial loads of 6 × 108 bacterial cells/750 mm2 capillary surface and the regenerated membranes regain filtration efficiencies of 95–100%. Silver release is moderate as only 0.8% of the initial silver loading is leached during a three-day filtration experiment leading to average silver contaminant levels of 100 μg/L., Highlights • Silver nanoparticle-doped zirconia capillary membrane for water filtration purposes • Characterization of the silver loading capacity of the capillary membrane • Excellent bacteria filtration performances of log reduction values of 8 • Efficient killing of 6 × 108 filtrated bacteria/750 mm2 capillary surface • Back flushing enables the regeneration of the membrane by removing dead bacteria.

We present a mild one-pot freeze gelation process for fabricating near-net, complex-shaped hydroxyapatite scaffolds and to directly incorporate active proteins during scaffold processing. In particular, the direct protein incorporation enables a simultaneous adjustment and control of scaffold microstructure, porosity, resorbability and enhancement of initial mechanical and handling stability. Two proteins, serum albumin and lysozyme, are selected and their effect on scaffold stability and microstructure investigated by biaxial strength tests, electron microscopy, and mercury intrusion porosimetry. The resulting hydroxyapatite/protein composites feature adjustable porosities from 50% to 70% and a mechanical strength ranging from 2 to 6 MPa comparable to that of human spongiosa without any sintering step. Scaffold degradation behaviour and protein release are assessed by in vitro studies. A preliminary in vivo assessment of scaffold biocompatibility and resorption behaviour in adult domestic pigs is discussed. After implantation, composites were resorbed up to 50% after only 4 weeks and up to 65% after 8 weeks. In addition, 14% new bone formation after 4 weeks and 37% after 8 weeks were detected. All these investigations demonstrate the outstanding suitability of the one-pot-process to create, in a customisable and reliable way, biocompatible scaffolds with sufficient mechanical strength for handling and surgical insertion, and for potential use as biodegradable bone substitutes and versatile platform for local drug delivery.

This study analyses the effects of heat treatments in oxidative atmosphere on the mechanical and microstructural properties of a fiber-reinforced weak interface composite (UMOX™) which is composed of a mullite-SiOC matrix and Nextel™ 610 fibers with fugitive coatings. Composites of different porosity grades, depending on the polymer infiltration and pyrolysis cycle, are exposed to 1000 and 1200 °C for 50 h. The exposure provokes the formation of silica, which leads to matrix densification and the formation of silica bridges at the fiber–matrix interface, resulting in an increased interfacial bonding strength. Consequently, the fracture toughness and the flexural strength are significantly reduced. The study confirms that SiOC-based materials are suitable for an application at high temperatures in oxygen-rich atmospheres up to 1000 °C. It is, however, important to consider the microstructural changes and thereby induced decrease of the overall mechanical performance during a high-temperature use.

The tensile and creep performance of two Nextel® 610 (N610) reinforced polymer derived ceramic composites (UMOX™, OXIPOL) is studied up to 1200 °C. Independent of the fiber orientation (±45° or 0°/90°) all samples exhibit a segment where the strain rate was constant. The creep performance in ±45° is matrix dominated and shows a more pronounced primary creep regime, due to changes within the matrix. The following creep regime with a constant strain rate might be attributed to viscous flow of the SiOC within the matrix based on activation energy (283 kJ/mol) and stress exponent (0.6). In 0°/90° orientation the creep and tensile performance is independent of oxidation, but directly influenced by grain structure of the fiber. The coarser and non-uniform microstructure of the fibers in UMOX™ decreases the stationary creep rates and changes the diffusional creep mechanism. The possibility to modify the microstructure of the fiber during the manufacturing process might be used to adjust e.g. the strength and creep stability of these materials related to the desired applications.

We show that different ratios of bovine serum albumin (BSA) and lysozyme (LSZ) can be achieved in a mixed protein adsorption layer by tailoring the amounts of carboxyl (-COOH) and aluminum hydroxyl (AlOH) groups on colloidal alumina particles (d50 ≈ 180 nm). The particles are surface-functionalized with -COOH groups, and the resultant surface chemistry, including the remaining AlOH groups, is characterized and quantified using elemental analysis, ζ potential measurements, acid-base titration, IR spectroscopy, electron microscopy, nitrogen adsorption, and dynamic light scattering. BSA and LSZ are subsequently added to the particle suspensions, and protein adsorption is monitored by in situ ζ potential measurements while being quantified by UV spectroscopy and gel electrophoresis. A comparison of single-component and sequential protein adsorption reveals that BSA and LSZ have specific adsorption sites: BSA adsorbs primarily via AlOH groups, whereas LSZ adsorbs only via -COOH groups (1-2 -COOH groups on the particle surface is enough to bind one LSZ molecule). Tailoring such groups on the particle surface allows control of the composition of a mixed BSA and LSZ adsorption layer. The results provide further insight into how particle surface chemistry affects the composition of protein adsorption layers on colloidal particles and is valuable for the design of such particles for biotechnological and biomedical applications.

This paper discusses the potential of using porous ceramic lining as insulating material in combustion chambers with respect to their sound absorbent ability to suppress thermoacoustic instabilities. For this purpose a combustion chamber test rig was developed and different types of ceramic linings were tested. The examined range of power was between 40 and 250 kW and the air-propane equivalence ratio was between 1.2 and 2.0. The overall sound pressure level and frequency domain of a lean premixed swirl stabilized and piloted burner are presented. The resonance frequencies and sound pressure levels are obtained and compared for the different combustion chamber linings. The results show a significant decrease in overall sound pressure level by up to 23.5 dB for sound absorbent lining in comparison to the common sound reflecting combustion chamber lining. In summary, sound absorbent ceramic combustion chamber lining can contribute to improve the stability of lean premixed gas turbines.Copyright © 2013 by ASME

Materials that interact in a controlled manner with viruses attract increasing interest in biotechnology, medicine, and environmental technology. Here, we show that virus–material interactions can be guided by intrinsic material surface chemistries, introduced by tailored surface functionalizations. For this purpose, colloidal alumina particles are surface functionalized with amino, carboxyl, phosphate, chloropropyl, and sulfonate groups in different surface concentrations and characterized in terms of elemental composition, electrokinetic, hydrophobic properties, and morphology. The interaction of the functionalized particles with hepatitis A virus and phages MS2 and PhiX174 is assessed by virus titer reduction after incubation with particles, activity of viruses conjugated to particles, and imaged by electron microscopy. Type and surface density of particle functional groups control the virus titer reduction between 0 and 99.999% (5 log values). For instance, high sulfonate surface concentrations (4.7 groups/nm 2 ) inhibit attractive virus–material interactions and lead to complete virus recovery. Low sulfonate surface concentrations (1.2 groups/nm 2 ), native alumina, and chloropropyl-functionalized particles induce strong virus-particle adsorption. The virus conformation and capsid amino acid composition further influence the virus–material interaction. Fundamental interrelations between material properties, virus properties, and the complex virus–material interaction are discussed and a versatile pool of surface functionalization strategies controlling virus–material interactions is presented.

The synthesis of porous hydroxyapatite scaffolds is essential for biomedical applications such as bone tissue engineering and replacement. One way to induce macroporosity, which is needed to support bone in-growth, is to use protein additives as foaming agents. Another reason to use protein additives is the potential to introduce a specific biofunctionality to the synthesized scaffolds. In this work, we study the rheological properties of a hydroxyapatite suspension system with additions of the proteins bovine serum albumin (BSA), lysozyme (LSZ) and fibrinogen (FIB). Both the rheology of the bulk phase as well as the interfacial shear rheology are studied. The bulk rheological data provides important information on the setting behavior of the thixotropic suspension, which we find to be faster with the addition of FIB and LSZ and much slower with BSA. Foam bubble stabilization mechanisms can be rationalized via interfacial shear rheology and we show that it depends on the growth of interfacial films at the suspension/air interface. These interfacial films support the stabilization of bubbles within the ceramic matrix and thereby introduce macropores. Due to the weak interaction of the protein molecules with the hydroxyapatite particles of the suspension, we find that BSA forms the most stable interfacial films, followed by FIB. LSZ strongly interacts with the hydroxyapatite particles and thus only forms thin films with very low elastic moduli. In summary, our study provides fundamental rheological insights which are essential for tailoring hydroxyapatite/protein suspensions in order to synthesize scaffolds with controlled porosities.

Understanding the interrelation between surface chemistry of colloidal particles and surface adsorption of biomolecules is a crucial prerequisite for the design of materials for biotechnological and nanomedical applications. Here, we elucidate how tailoring the surface chemistry of colloidal alumina particles (d50 = 180 nm) with amino (-NH2), carboxylate (-COOH), phosphate (-PO3H2) or sulfonate (-SO3H) groups affects adsorption and orientation of the model peptide glutathione disulfide (GSSG). GSSG adsorbed on native, -NH2-functionalized, and -SO3H-functionalized alumina but not on -COOH- and -PO3H2-functionalized particles. When adsorption occurred, the process was rapid (≤5 min), reversible by application of salts, and followed a Langmuir adsorption isotherm dependent on the particle surface functionalization and ζ potential. The orientation of particle bound GSSG was assessed by the release of glutathione after reducing the GSSG disulfide bond and by ζ potential measurements. GSSG is likely to bind via the carboxylate groups of one of its two glutathionyl (GS) moieties onto native and -NH2-modified alumina, whereas GSSG is suggested to bind to -SO3H-modified alumina via the primary amino groups of both GS moieties. Thus, GSSG adsorption and orientation can be tailored by varying the molecular composition of the particle surface, demonstrating a step toward guiding interactions of biomolecules with colloidal particles.

In this study, we demonstrate the control of protein adsorption by tailoring the sulfonate group density on the surface of colloidal alumina particles. The colloidal alumina (d(50)=179±8nm) is first accurately functionalized with sulfonate groups (SO(3)H) in densities ranging from 0 to 4.7SO(3)H nm(-2). The zeta potential, hydrophilic/hydrophobic properties, particle size, morphology, surface area and elemental composition of the functionalized particles are assessed. The adsorption of three model proteins, bovine serum albumin (BSA), lysozyme (LSZ) and trypsin (TRY), is then investigated at pH 6.9±0.3 and an ionic strength of 3mM. Solution depletion and zeta potential experiments show that BSA, LSZ and TRY adsorption is strongly affected by the SO(3)H surface density rather than by the net zeta potential of the particles. A direct correlation between the SO(3)H surface density, the intrinsic protein amino acid composition and protein adsorption is observed. Thus a continuous adjustment of the protein adsorption amount can be achieved between almost no coverage and a theoretical monolayer by varying the density of SO(3)H groups on the particle surface. These findings enable a deeper understanding of protein-particle interactions and, moreover, support the design and engineering of materials for specific biotechnology, environmental technology or nanomedicine applications.

In this study, we present porous ceramics combining the antibacterial effect of copper with an integrated copper removal adsorbent. After preparing and characterizing the antibacterial copper-doped microbeads and monoliths (CuBs and CuMs), their antibacterial efficiency is probed against different nonpathogenic and pathogenic bacteria (Bacillus subtilis, Escherichia coli, Staphylococcus aureus, and Pseudomonas aeruginosa). An antibacterial efficiency of 100% is reached within 15 min to 3 h for all tested strains under static conditions. Dynamic tests with B. subtilis and E. coli showed high antibacterial efficiency up to 99.93% even at continuous flux. To avoid any adverse effects on the environment, continuous removal of released copper-ions is accomplished with porous, high surface area monolithic adsorbents (MAds). MAds are prepared similarly to the CuMs but without adding copper during the manufacturing process. MAds reduce the amount of copper released from the CuMs ≥ 99% during the first 15 min, ≥90% up to 2 h, and after 22 h of continuous filtration up to 56% of the released copper is removed.

We present an interesting processing route for obtaining alumina/mullite-based ceramics with controlled porosity and airflow resistance leading to promising microstructures for application as sound absorbers. The use of ceramic materials aims for potential applications where high temperatures or corrosive atmospheres are predominant, e.g., in combustion chambers of gas turbines. For the production of the porous ceramics we combined freeze gelation and sacrificial templating processes to produce near-net-shaped parts with low shrinkage (

The development of β′-SiAlON from silicone resins, mixed with oxide nanoparticles, has already been shown to be particularly complex due to the phase separation of the oxycarbide ceramic residue of the polymers and to the formation of oxygen rich intermediate phases. This paper focuses on the fabrication of SiAlON–SiC composites, in which the phase separation is exploited in yielding part of SiC together with a reactive mixture of silica and carbon, to be combined with a relatively low amount of alumina nanoparticles and additional carbon, from carbon black or phenolic resin. SiC particles were bound by a polymer derived β′-SiAlON phase after treatment at 1500°C (3 h) in nitrogen; although featuring a significant amount of residual porosity (>44%), the developed ceramic composites have remarkable mechanical properties (biaxial bending strength exceeding 70 MPa), especially when containing Y2O3 doping (3 wt-%).

The influence of partially crystalline polymeric diols on the morphology and mechanical properties of a cationically polymerized cycloaliphatic epoxy resin is described and significantly enhanced material properties were observed. In particular, poly(e-caprolactone) (PCL) could be integrated covalently into the epoxy network leading to a toughened material with higher tensile strength and elongation at break combined with less brittleness and enhanced flexibility in the completely transparent thermosetting epoxy polymer. The PCL containing polymers were compared with polycarbonate containing epoxy polymers as rigid polyol phase. Scanning electron microscopy of samples broken below and above the glass transition temperature of PCL as well as above the melting point of PCL showed different fracture behavior of the elastified samples and an ordered morphology of the PCL in the epoxy matrix was observed. A distinct morphology known well from thermoplastic block-copolymers is formed in the prepared thermosetting polymers.

In order to understand fundamental interactions at the interface between immobilized enzymes and ceramic supports, the authors compare the adsorption features of chymotrypsin on SiO2 and TiO2 colloidal particles by means of a combination of adsorption experiments and molecular dynamics simulations. While the dependency of the adsorption amount on pH is consistent with the trend predicted the Derjaguin-Landau-Verwey-Overbeek theory, other effects can only be rationalized if the atomic-scale details of the water-mediated protein-surface interactions are considered. On both surfaces, a clear driving force for the formation of a double monolayer at the saturation coverage is found. Although nearly equal free energies of adsorption are estimated on the two materials via a Langmuir adsorption analysis, about 50% more proteins per unit of surface can be accommodated on TiO2 than on SiO2. This is probably due to the lower surface diffusion mobility of the adsorbed protein in the latter case. Surface anchoring is realized by a combination of direct ionic interactions between charged proteins and surface sites (more pronounced for SiO2) and distinct structuring of the surface hydration layers in which the contact residues are embedded (more pronounced for TiO2). Finally, normalization of the data with respect to particle surface areas accessible to the proteins, rather than determined by means of the Brunauer-Emmett-Teller nitrogen adsorption isotherm, is crucial for a correct interpretation of the results.

The current opinion on the toxicity of nanomaterials converges on a size-dependent phenomenon showing increasing toxicity with decreasing particle sizes. We demonstrate that SiO2 particles have no or only a mild effect on the viability of five bacterial strains, independently from the particle size. A two-hour exposure to 20 mg L(-1) of 15, 50 and 500 nm sized SiO2 particles neither alters bacterial adenosine triphosphate (ATP) levels nor reduces the number of colony forming units (CFU). Additionally, we tested the effect of Al2O3-coated LUDOX-CL (ACS 20) with a primary particle size of 20 nm. In contrast, these particles caused a significant reduction of ATP levels and CFU. Fluorescence microscopy revealed that ACS 20 induced a pronounced agglomeration of the bacteria, which led to underestimated counts in regard of CFU. Bactericide effects as indicated by decreased ATP levels can be explained by bactericide additives that are present in the ACS 20 suspension.

In the light of in vitro nanotoxicological studies fluorescence labeling has become standard for particle localization within the cell environment. However, fluorescent labeling is also known to significantly alter the particle surface chemistry and therefore potentially affect the outcome of cell studies. Hence, fluorescent labeling is ideally carried out without changing, for example, the isoelectric point. A simple and straightforward method for obtaining fluorescently labeled spherical metal oxide particles with well-defined isoelectric points and a narrow size distribution is presented in this study. Spherical amorphous silica (SiO 2 , 161 nm diameter) particles were used as the substrate material and were coated with silica, alumina (Al 2 O 3 ), titania (TiO 2 ), or zirconia (ZrO 2 ) using sol–gel chemistry. Fluorescent labeling was achieved by directly embedding rhodamine 6G dye in the coating matrix without affecting the isoelectric point of the metal oxide coatings. The coating quality was confirmed by high resolution transmission electron microscopy, energy filtered transmission electron microscopy and electrochemical characterization. The coatings were proven to be stable for at least 240 h under different pH conditions. The well-defined fluorescent particles can be directly used for biomedical investigations, e.g. elucidation of particle–cell interactions in vitro.

In this study, we present an ionotropic gelation route for obtaining porous alumina/silica microbeads (MBs) with tailorable morphology, specific surface area (SBET), and pore size, which can directly be sintered into porous, monolithic adsorbents (MAds). After sintering, SBETs from 20 m2/g up to 70 m2/g with open porosities up to 90% could be achieved depending on the silica nanoparticle addition. Due to the significantly increased SBET, a more than 100-fold faster uptake of model dye molecules was obtained. Pore sizes ranged between 13 and 184 nm with adjustable mono- and bimodal size distributions. Depending on silica content and sintering temperature, the MBs were also found to be chemically stable in technologically relevant solvents such as water, acetone, acetonitrile, hydrochloric acid, and methanol for at least 1 week except for sodium hydroxide. By adjusting the processing parameters, spherical, fibrous or irregular microbead morphologies could be obtained. The same route was also successfully applied for obtaining calcium phosphate, titania, and zirconia microbeads. The presented straight-forward ionotropic gelation route is basically applicable to any other ceramic material and therefore extremely versatile. The obtained MBs and MAds can be further adapted to any type of environmental or biotechnological purification process by additional functionalization steps.

Colloidal oxide particles in biomedical or biotechnological applications immediately become coated with proteins of the biological medium, a process which is strongly influenced by the surface characteristics of the particles. Fundamental correlations between surface characteristics and the, so far mainly uncontrollable, protein adsorption are still not clear. In this study the surface of colloidal alumina particles ( d 50 = 179 ± 8 nm) was systematically adjusted with NH 2 , COOH, SO 3 H and PO 3 H 2 functional groups to investigate the influence on the adsorption of the three model proteins, bovine serum albumin (BSA), lysozyme (LSZ) and trypsin (TRY). The surface functionalization is characterized and discussed in detail with regard to the morphology, isoelectric point, zeta potential, hydrophilic/hydrophobic properties, functional group density and stability. Protein–particle interaction was then assessed by evaluating the amount of protein adsorbed and the zeta potentials of protein–particle conjugates. Protein adsorption was found to be influenced by the type of functional group as well as the expected electrostatic forces under the given experimental conditions. The level of protein adsorption might, hence, be specifically controlled by the type of surface functionalization. Possible adsorption modes of BSA, LSZ and TRY on the particles are suggested by considering the spatial surface potential distribution of the proteins calculated from the protein database file. The particles presented provide an excellent prerequisite for further investigation of fundamental particle–protein interactions and the design of functionally graded materials for biomedical and biotechnological applications, e.g. as drug carriers or for protein purification.

The effect of calcium phosphate-based microchannels on the growth and orientation of human osteoblast cells is investigated in this study. As substrates, hydroxyapatite-based microchannels with high contouring accuracy were fabricated by a novel micro-moulding technique. Microchannels obtained by this method featured widths ranging from 16.0 ± 0.7 to 76.6 ± 1.4 μm and depths from 7.9 ± 0.8 to 15.5 ± 1.3 μm. Surface and contour characterization was carried out using X-ray diffraction analysis, scanning electron microscopy imaging and 3D-confocal profilometry. Cell activity and alignment on microchannels with different widths were determined after 1 and 3 days by photometric spectroscopy and fluorescence microscopic imaging and statistically analysed by Tukey’s multiple comparison test. On days 1 and 3 for microchannels of width 16 and 30 μm, 70–80% of the osteoblasts oriented within an angular range of 0–15° relative to the microchannel direction. Interestingly, only 20% of the cells grew inside the microchannels for channel widths of 16 and 30 μm. Substrates with channel widths of 45, 65 and 76 μm allowed ∼40% of the cells to grow inside. The depth of the microchannel showed hardly any significant impact. All micropatterned surfaces provoked a good cell attachment, as flat and spread cell morphologies with lamellipodiae and filopodiae could already be observed after 1 day. The effect of the microchannels on osteoblast activity was determined using the colorimetric WST-1 assay. In addition, the cell differentiation was assessed by collagen type I staining. The cell activity obtained by WST-1 assay differed insignificantly for all micropatterned samples of various widths and depths. The assessment of collagen type I yielded the same amounts for all micropatterned samples after 1, 3 and 7 days. In summary, the microchannel width of HA-based patterns has a distinct effect on the directed growth of human osteoblast cells, allowing novel design strategies for surfaces such as dental implants.

In summary, we demonstrate that it is feasible to fabricate surfaces that feature antibacterial and abrasion-resistance properties at the same time by combining micropatterning with antibacterial enzymes and alumina nanoparticles. In particular, we have shown that antibacterial activity of lysozyme is maintained when the enzyme is adsorbed on alumina surfaces and that it can be efficiently protected by surface micropatterning even at abrasive and harsh chemical conditions. Therefore, antibacterial features may potentially be maintained over a long-time period. Furthermore, we show that natural antimicrobial enzymes, such as lysozyme, can be successfully employed to protect surfaces from bacterial colonization. Antimicrobial enzymes may present a valid alternative to the most commonly used but non-effective biocides in biofouling prevention.

Different micropatterning techniques were applied to elucidate the potential for cell proliferation studies on calcium phosphate surfaces. Sintered hydroxyapatite (HA) platelets were microstructured by three different techniques: Aerosol jet printing (M3 D® ), laser ablation and microcontact printing via polydimethylsiloxane (PDMS) stamps. The microstructures were designed as channels between 1000 and 3000 micron in length, 10 to 220 micron in width and 5 to 110 micron in height. An optical profilometer, a Scanning Electron Microscope (SEM) and X-ray diffraction were used to characterize the microstructures. Cell proliferation tests were carried out by incubating the microstructured ceramic samples in complete cell media for a maximum of seven days. Osteoblast-like cells (MG-63) were used for testing. Each sample was immersed in media in which the cells were already seeded. Imaging was performed by SEM and Fluorescence Microscopy. The cells proliferated on all three differently fabricated microstructures. Cell growth was observed in the microchannels as well as on the microchannel walls or spacers. In particular it turned out, that the microtopology can provoke the cells to elongate aligned to the direction of the microchannels. Non-directional growth was observed on non-structured areas. All three differently fabricated hydroxyapatite microstructuring methods seem to be attractive and promising techniques for use in bone cell growth studies. The applied fabrication techniques show many advantages for fundamental research in the field of cell interaction with ceramic microstructures and may exhibit possible methods of structuring implant surfaces.Copyright © 2008 by ASME

The design and fabrication of alumina microstructured surfaces that simultaneously present high mechanical and chemical features and do not suffer biofouling are here reported. An aerosol based patterning technique was employed to fabricate alumina microstructures directly on alumina surfaces with the aim to enhance wear and chemical resistance. Microstructured alumina surfaces were subsequently biofunctionalised with antibacterial biomolecules to inhibit bacterial adhesion. Lysozyme, an antibacterial enzyme commonly found in body secretions, was used as antibacterial agent and directly deposited onto microstructured alumina surfaces. Lysozyme-biofunctionalised microstructured alumina surfaces were tested at flow condition using abrasive particles and viable bacteria. The very preliminary results showed that alumina microstructures presented high resistance against mechanical abrasion and that bacterial biofilm formation could be suppressed. In particular alumina microstructures protected lysozyme molecules from desorption and loss of enzymatic activity. Such biofunctionalised microstructures present a promising system for fundamental research in the field of biomolecule adsorption on surfaces and maybe a feasible alternative e. g. to protect surfaces of water transport systems where abrasive particles and microorganisms are present.

For the first time the successful preparation of Sr doped baghdadite (Ca3-x Sr x ZrSi2O9 x = 0.1 and 0.75) is shown. Sr-doped as well as pure baghdadite are prepared via a versatile solid-state synthesis and conventional sintering at 1400 °C. XRD measurements and crystal structure refinements reveal that a substitution of Ca atoms with Sr and a high purity (>99%) is achieved. The physical, mechanical, and biological properties of these novel bioceramics are presented in relation to the dopant concentration. Incorporating Sr into the baghdadite crystal caused only minor changes to the grain size and the mechanical properties. The characteristic strength ranges from 145 to 168 MPa and a Weibull modulus of 4.9 to 9.2 is observed. Other mechanical properties like fracture toughness and hardness vary from 1.23 ± 0.07 MPam(0.5) to 1.31 ± 0.12 MPam(0.5) and 7.3 ± 0.6 GPa to 8.0 ± 0.7 GPa, respectively. The in vitro cellular response of human osteoblasts showed an increase in the cell proliferation and a significantly higher alkaline phosphatase (ALP) activity with an increase in the Sr content. From the improved biological properties and the suitable mechanical performance we conclude that this material is a highly promising candidate for bone replacement material and bioactive implant coatings.

Protein adsorption onto metal oxide surfaces is an essential aspect of the cascade of biological reactions taking place at all interfaces between implanted materials and the biological environment. The types and amounts of adsorbed proteins mediate subsequent adhesion, proliferation and differentiation of cells. Protein adsorption to surfaces of metal oxides and their kinetics are important in the formation and growth of seashells, one of the toughest natural ceramics, in modern bio-analytical devices as well as in bone and teeth implant technology. This paper describes results obtained in a feasibility study of how to use metal-oxide particles to obtain biosensors with a high turnover. The most important features of proteins are outlined describing them as purpose-built "polymers" from amino acids with specific conformations. Some key aspects of Metaloxide (MeO) surfaces in water and the influence of electrostatic and hydrophobic interaction on protein adsorption are reported. Results concerning the interaction between different proteins and MeO surfaces in water are discussed in detail. Examples of purely electrostatic interactions of proteins with MeO surfaces as well as the influence of hydrophobic interaction are elucidated. An outlook of the implications of the new insights on natural and synthetic materials will be given concerning bio-compatibility, bio-mineralization and self assembly of materials.

The amounts of negatively charged bovine serum albumin and positively charged lysozyme adsorbed on alumina, silica, titania, and zirconia particles (diameters 73 to 271 nm) in aqueous suspensions are measured. The adsorbed proteins change the zeta potentials and the isoelectric points (IEP) of the oxide particles. The added to adsorbed protein ratios at pH 7.5 are compared with the protein treated particle zeta potentials. It is found that the amounts of adsorbed proteins on the alumina, silica, and titania (but not on the zirconia) particle surfaces are highly correlated with the zeta potential. For the slightly less hydrophilic zirconia particles high amounts of protein adsorption are observed even under repulsive electrostatic conditions. One reason could be that the hydrophobic effect plays a more important role for zirconia than electrostatic interaction.

The self-assembly of nanosized colloidal particles on patterned substrates offers a convenient way of building nanostructures in an efficient way through a bottom-up approach. Combining such self-assembly methods with conventional top-down micro- and nanofabrication methods may lead to new devices with a structural hierarchy ranging from the nano/molecular to the macroscopic level. In this work, the self-assembly of functionalized nanosized silica particles on chemically structured substrates is studied. A newly developed chemical patterning method offering good control of the surface chemistry is used to selectively bind functionalized nanocolloids at distinct spots on the surface. Such nanocolloidal microarrays offer the potential to be used to increase the sensitivity of existing biosensing applications due to the well-defined surface chemistry (of particle and substrate) and the highly increased surface area at the microspots where the nanocolloidal particles self-assemble.

Bovine serum albumin and lysozyme mixtures of different mole fractions were adsorbed to colloidal alumina (116 nm) and titania particle (271 nm) suspensions of 2 vol % solid content for 16 h at pH 7.5. The total protein amount normalized to the powder surface area was 1000 ng/cm2. The zeta potential of the protein-treated suspensions was measured as a function of pH and the isoelectric point (IEP) obtained. A simple prediction model in two refinement steps was derived and evaluated for the obtained IEPs. The best model fit which takes into account moles of protein and surface fractions yielded an average prediction error of 7.5% and a maximum error of 16.7%.