Biomedical subjects

Julian R G Evans

Publications and source records attributed to Julian R G Evans.

5 recordsLinked to original sources

PubMed2006

Segregation in multicomponent ceramic colloids during drying of droplets.

Studies of drying of colloidal droplets focus on unary particle systems. We report here the drying of binary and ternary powder suspensions. When multicomponent ceramic suspensions are deposited in the form of small drops (5 microl), particle segregation can occur on drying so that the upper surface of the powder residue does not match that of the bulk composition. We show that the segregation effect and the shape of the droplet residues are both related to the participation of particles in two types of flow during drying; radial flow toward the rim where the three-phase boundary becomes locked by a pile up of particles and secondly, recirculation flows in the remaining liquid driven by Marangoni stresses. Methods to control both shape and segregation are described. The phenomenon described is general and independent of the method of preparing the drops but the motivation is to obtain uniform drop shape and composition in thick film ceramic libraries in combinatorial ink-jet printing.

Journal Article↗

PubMed2006

Fine ceramic lattices prepared by extrusion freeforming.

Fine ceramic lattices with spatial resolution <100 microm and having precise dimensions and intricate hierarchical structure are fabricated by extrusion freeforming, a rapid prototyping technique, which allows overall shape and structure to be controlled by computer. The procedure can be used for any fine ceramic powder and can therefore find applications as diverse as microwave and terahertz metamaterials (artificial crystals), hard tissue scaffolds, microfluidic devices, and metal matrix composite preforms. The examples presented here are calcium phosphate lattices with three structure levels: submicron pores, which enhance cell-surface interactions, pores of tens of microns to encourage bone ingrowth, and corridors (hundreds of microns) for vascularization. With controlled pore structures on these scales, the lattices are expected to provide customized biological, mechanical, and geometrical requirements.

Biocompatible Materials↗

PubMedDate not supplied

A drop-on-demand ink-jet printer for combinatorial libraries and functionally graded ceramics.

A printer has been designed and built for the preparation of combinatorial libraries of ceramics and for solid freeforming of functionally graded ceramics with three-dimensionally programmable spatial variation in composition. Several ceramic suspensions (as inks) can be subjected to micromixing behind the nozzle and printed at precise positions. Both mixing and positioning are computer-controlled. The machine consists of an XY table to control the geometry, a set of electromagnetic valves that manage the mixing, a combined electromagnetic valve and sapphire nozzle that form the print head, and a computer that controls the whole system. The mixing valves can eject as little as 1 mg/s ink into the mixing chamber. The printer has been controlled, run, calibrated and tested; the composition and geometry of printed mixtures can be controlled precisely. This method for the controlled mixing of powders facilitates the advance of combinatorial methods within the materials sciences.

Journal Article↗

PubMedDate not supplied

Device for preparing combinatorial libraries in powder metallurgy.

This paper describes a powder-metering, -mixing, and -dispensing mechanism that can be used as a method for producing large numbers of samples for metallurgical evaluation or electrical or mechanical testing from multicomponent metal and cermet powder systems. It is designed to make use of the same commercial powders that are used in powder metallurgy and, therefore, to produce samples that are faithful to the microstructure of finished products. The particle assemblies produced by the device could be consolidated by die pressing, isostatic pressing, laser sintering, or direct melting. The powder metering valve provides both on/off and flow rate control of dry powders in open capillaries using acoustic vibration. The valve is simple and involves no relative movement, avoiding seizure with fine powders. An orchestra of such valves can be arranged on a building platform to prepare multicomponent combinatorial libraries. As with many combinatorial devices, identification and evaluation of sources of mixing error as a function of sample size is mandatory. Such an analysis is presented.

Journal Article↗

PubMedDate not supplied

London University Search Instrument: a combinatorial robot for high-throughput methods in ceramic science.

This paper describes the design, construction, and operation of the London University Search Instrument (LUSI) which was recently commissioned to create and test combinatorial libraries of ceramic compositions. The instrument uses commercially available powders, milled as necessary to create thick-film libraries by ink-jet printing. Multicomponent mixtures are prepared by well plate reformatting of ceramic inks. The library tiles are robotically loaded into a flatbed furnace and, when fired, transferred to a 2-axis high-resolution measurement table fitted with a hot plate where measurements of, for example, optical or electrical properties can be made. Data are transferred to a dedicated high-performance computer. The possibilities for remote interrogation and search steering are discussed.

Aluminum Oxide↗