Osteoblast response to zirconia surfaces with different topographies.

Zirconia-3 mol% yttria ceramics were prepared with as-sintered, abraded, polished, and porous surfaces in order to explore the attachment, proliferation and differentiation of osteoblast-like cells. After modification, all surfaces were heated to 600°C to extinguish traces of organic contamination. All surfaces supported cell attachment, proliferation and differentiation but the surfaces with grain boundary grooves or abraded grooves provided conditions for enhanced initial cell attachment. Nevertheless, overall cell proliferation and total DNA were highest on the polished surface. Zirconia sintered at a lower temperature (1300°C vs. 1450°C) had open porosity and presented reduced proliferation as assessed by alamarBlue™ assay, possibly because the openness of the pores prevented cells developing a local microenvironment. All cells retained the typical polygonal morphology of osteoblast-like cells with variations attributable to the underlying surface notably alignment along the grooves of the abraded surface.

Self-assembly of montmorillonite platelets during drying.

This work is prompted by the quest for nanocomposites in which ordered, layered reinforcement preforms similar in structure to the arrangements seen in nacre are achieved without complex automated layer-by-layer assembly. Lamellar structures were obtained in montmorillonite films simply by slow drying without the use of additives. Clay alignment was found in films derived from suspensions of less than 0.9 vol%, ranging over a pH range of 2-11, at low drying rates and with both the natural ionic strength of the clay suspension and adjusted ionic strength. The greatest degree of order was found at the unadjusted pH and ionic strength. This method offers a potentially simple way of preparing clay preforms for polymer-clay nanocomposites at a drying rate at or below 23 nm s(-1).

Measurement of diffuse reflectance from combinatorial samples.

Using a luminescence spectrometer as a platform, a system of fibre-optic probes was created that allows full colour characterisation, fluorescence and phosphorescence spectra to be recorded in diffuse reflectance and in transmission from thick or thin film arrays of combinatorial samples of diameter down to 2 mm and from liquids. An integrating sphere is not required and the method is more versatile than the instrument's fibre-optic plate reader which has conjoined fibre bundles set at a fixed angle. Incident and detected light is routed via separate optical fibre bundles which remain stationary above or below a two-axis table. The validation and calibration are described. A library of 25 members was scanned for both diffuse reflectance (colour) and fluorescence in less than an hour. The method thus combines techniques that conventionally rely on different instruments and makes them amenable for high throughput libraries.

Mechanical strength of extrusion freeformed calcium phosphate filaments.

Hydroxyapatite-tricalcium phosphate mixtures of various compositions were extruded by a solid free-forming process to form lattice structures to serve as hard tissue scaffolds. The unwelded filaments, sintered at temperatures from 1100 to 1300 degrees C, had radii from 115 to 135 microm and were tested in three point flexural loading using a purpose-built fixture. Flexural strength ranged from 20 to 100 MPa depending on composition and sintering temperature. Weibull moduli up to 13 were obtained. Compositions with 50% or more tri-calcium phosphate did not develop strengths much above 40 MPa and the strength of most compositions fell when the sintering temperature exceeded 1250 degrees C. Multiple layer lattice structures were created and tested in compression.

In vitro evaluation of samarium (III) oxide as a bone substituting material.

The biocompatibility of natural samarium (III) oxide, which has previously been used for treatment in bone-related diseases was determined as a first step in its evaluation as a bone implant material. Assessment for 28 days using osteoblast-like cells revealed no indications of cytotoxicity. The cells adhered and proliferated on the surface. Furthermore, the differentiation and mineralization were observed, indicating a normal biological response of the cells on the samarium (III) oxide surface. The in vitro, short term biocompatibility assessment of this oxide has indicated its biosafety with no damaging toxic effects on the cells and biofunctionality; with an appropriate cell response for a bone-contacting material. Hence, samarium (III) oxide deserves recognition in the field of biomaterials for its excellent in vitro performance and demonstrates that the class of potential bioceramics may be larger than previously thought. (c) 2010 Wiley Periodicals, Inc. J Biomed Mater Res, 2010.

Dissolution characteristics of extrusion freeformed hydroxyapatite-tricalcium phosphate scaffolds.

The dissolution behaviour of calcium phosphate filaments made by extrusion freeforming for hard tissue scaffolds was measured. The solubility of filaments with different HA/beta-TCP ratios sintered at temperatures from 1,100 to 1,300 degrees C was measured under simulated physiological conditions (tris buffer solution: tris(hydroxyl) methyl-aminomethane-HCl), pH 7.4, 37 degrees C). Calcium and phosphate concentrations were measured separately by inductively coupled plasma (ICP) atomic emission spectroscopy. Surface morphologies and composition before and after immersion were analyzed by SEM and EDS. The results clearly show that as the beta-TCP content increased, the dissolution increased. Higher sintering temperatures, with consequent closure of surface pores, resulted in lower dissolution. Examination of the surface suggested dissolution on preferred sites by pitting.

Shape changes during the drying of droplets of suspensions.

During drying of droplets of suspensions, several flow regimes contribute to the radial flow of powder to the periphery to leave a pile-up of powder at the rim. It is shown that the shape of the droplet residues can be controlled both by restricting evaporation and by combining high and low boiling point solvents which modify particle flows and produce a range of droplet residues varying from a concave "doughnut" shape, sometimes with a central hole, to a convex dome shape. Addition of formamide to aqueous suspensions is shown to affect powder deposition by setting up a Marangoni flow rather than by reducing evaporation at the periphery. The results find direct application in thick-film combinatorial printing of ceramics to form small disks by droplet drying.

Functional ceramic materials database: an online resource for materials research.

We present work on the creation of a ceramic materials database which contains data gleaned from literature data sets as well as new data obtained from combinatorial experiments on the London University Search Instrument. At the time of this writing, the database contains data related to two main groups of materials, mainly in the perovskite family. Permittivity measurements of electroceramic materials are the first area of interest, while ion diffusion measurements of oxygen ion conductors are the second. The nature of the database design does not restrict the type of measurements which can be stored; as the available data increase, the database may become a generic, publicly available ceramic materials resource.

Protocols for printing thick film ceramic libraries using the London University Search Instrument (LUSI).

Thick film combinatorial libraries can be prepared by mixing ceramic suspensions using stepper-driven syringes to control ink-jet-printing nozzles, but a more tolerant and efficient method has been devised using a simplification of the same equipment. By simplifying the printing sequence and using direct deposition from the stepper syringes, the time committed to a repetitive sequence of priming and cleaning the ink-jet printer nozzles is reduced. Polytetrafluoroethylene (PTFE) open ended tubes and commercial pipette tips are used as the printing nozzles. Calibration and corrections for the method are described. This method opens up the possibility for making ceramic libraries more rapidly with much simpler and less expensive equipment.

Scandia--a potential biomaterial?

Biocompatibility is a pre-requisite for all biomaterials used for medical application. During the last two decades significant advances have been made in the development of novel materials and selection and use of these materials has been directly dependent upon their biocompatibility. Several materials containing calcium or titanium cations demonstrate biocompatibility and are routinely used in various forms within the human body. Due to its position in the periodic table, scandium in the form of its oxide scandia (Sc(2)O(3)) was studied as the first stage of a wider exploration of the biocompatibility of ceramics. A commercial human osteoblast-like cell line (HOS TE 85) was used to study the biocompatibility of both sintered and abraded scandia surfaces. Scanning electron microscopy was used to examine cell adhesion, the MTT assay was used to measure cell metabolic function and the alamarBlue for the assessment of proliferation. Although the results are only preliminary findings, qualitative observations showed that both sintered and abraded surfaces favoured cell adhesion to the same extent. Quantitatively, a significant increase in cell proliferation was observed on Sc(2)O(3) compared to Thermanox, tissue culture control. Furthermore, Sc(2)O(3) has been shown to be non-toxic, able to be maintain cell viability and support cell growth and proliferation.

Porous hydroxyapatite ceramics for tissue engineering.

We have determined the biocompatibility of high porosity (92%) sintered hydroxyapatite (HA) foams prepared using a novel ceramic foaming system. The ability of human osteoblast-like cells to grow within the HA foam was investigated in vitro using human osteosarcoma cells seeded directly on the ceramic surfaces to determine the bioactivity. Scanning electron microscopy showed evidence of attachment of numerous cells to the surface. Significant proliferation was observed and the pattern was comparable to that of the tissue culture control, Thermanox TM . There was an increase in cell proliferation and retention of phenotype for the period studied. This hydroxyapaptite foam which has the advantage of being easily fashioned by surgeons, shows potential as a bone substitute scaffold for tissue engineering and future development for clinical application.

Novel MMC microstructure with tailored distribution of the reinforcing phase.

Saffil short fibre agglomerates with diameters of 0.4 mm to 1 mm have been prepared using a tumbling technique. These were packed and infiltrated with molten 6061 Al alloy to make a metal matrix composite (MMC) with a novel microstructure in which the composite spheres are randomly distributed in the fibre-free aluminium matrix. In parallel, a commercial preform made of identical Saffil alumina short fibres and having the same fibre volume faction was used to prepare a conventional MMC by the same technique. Microstructural observation indicates that, within the composite spheres, the local volume fraction of fibre decreases from the outer layer to the centre region. The energy absorption during fracture was estimated by using a three point loading test on notched samples and was compared with that for conventional MMCs. Preliminary results suggest that this novel MMC possesses higher energy absorption capability and hence better damage tolerance. The fracture surfaces were examined by scanning electron microscopy in order to inform these experimental results.