Neal K. Vail

Materials for biomedical applications

Abstract This paper discusses the physical and mechanical characterization of a calcium phosphate ceramic material system developed for biomedical applications in the repair of skeletal defects. The rapid prototyping process selective laser sintering (SLS) is the preferred forming process to produce complex porous ceramic matrices suitable for biomedical applications. The effects of SLS processing conditions on the properties of fabricated objects are quantified. The effects of post-processing conditions on the properties of SLS-fabricated objects are also quantified. SLS-fabricated implants are shown to perform well in vivo exhibiting excellent biocompatibility as well as showing considerable osseous integration and remodeling of the ceramic implant material.

Selective laser sintering of alumina with polymer binders

The selective laser sintering (SLS) process is used to prepare test bars from Al2O3/polymer binder powders. Finds that binder‐coated A12O3 particles formed bars that were approximately twice as strong as could be formed from mixtures of alumina and polymer binder at the same binder level and processing conditions. In mixed systems, bar strengths increased nearly in proportion to increases in polymer binder content over the 20‐40 per cent volume binder range. Parts made in any particular laser scanning mode showed optimum values for strength and density as the laser energy density was systematically increased from 2‐8cal/cm2. Suggests that optima result from the counteracting influences of energy density on binder fusion and thermal degradation. The optimum energy density is mode or geometry sensitive and shifts to lower values as the laser scanning vector is reduced. Concludes that this behaviour is probably the result of the lower heat losses. Equivalently better utilization of laser energy is associated with the shorter scan vectors. Some of the SLS fabricated bars were infiltrated with colloidal alumina, fired to remove the binder, and sintered at 1,600°C to achieve alumina bars with 50 per cent relative densities, interconnected porosity, and strengths between 2 and 8MPa.

Competitive FRET-aptamer-based detection of methylphosphonic acid, a common nerve agent metabolite

Competitive fluorescence resonance energy transfer (FRET)-aptamer-based assay formats are described for one-step detection of methylphosphonic acid (MPA; a metabolite of several organophosphorus (OP) nerve agents). AminoMPA was attached to tosyl-magnetic beads and used for DNA aptamer selection from which one dominant aptamer sequence emerged. Two different FRET approaches were attempted. In one approach, the complementary DNA sequence was used as a template for labeling the aptamer with Alexa Fluor 546 (AF 546)-14-dUTP by asymmetric PCR. Following 3-dimensional (3-D), molecular modeling of the aptamer-MPA complex, a series of three fluoresceinated aptamers labeled at positions 50, 51, and 52 in the putative optimal binding pocket were synthesized. In both FRET formats, aminoMPA was linked to Black Hole Quencher (BHQ-1 or BHQ-2)-succinimides and allowed to bind the fluorescein or AF 546-labeled MPA aptamer. Following gel filtration to purify the labeled MPA aptamer-BHQ-aminoMPA FRET complexes, the complexes were competed against various concentrations of unlabeled MPA, MPA derivatives, and unrelated compounds in titration and cross-reactivity studies. Both approaches yielded low microgram per milliliter detection limits for MPA with generally low levels of cross-reactivity for unrelated compounds. However, the data suggest a pattern of traits that may effect the direction (lights on or off) and intensity of the FRET.