A new type of three-dimensional scaffold with inverted colloidal crystal geometry for the investigation of topological effects in cell cultures is introduced in this publication. The scaffolds are made by infiltration of the hexagonal crystal lattice of polystyrene spheres with sol-gel formulation and subsequent annealing. It possesses a relatively high degree of order among existing cell scaffolds and affords tight control over the scaffold porosity and tissue organization. The prepared scaffolds can be a convenient system for the investigation of cell-cell and cell-matrix interactions. Their biocompatibility is demonstrated for human hepatocellular carcinoma HEP G2 and human bone marrow HS-5 cell cultures. A preliminary effect of the scaffold topology on cell proliferation is observed. HEP G2 hepatocytes form a large number of 10-15 cell colonies on scaffolds made from 75-microm spheres, while their number diminishes for scaffolds from 10- and 160-microm spheres. Under similar conditions, HS-5 forms smaller colonies consisting of three to four cells in 90-microm cavities.
Chemical vapors originating from the explosive charge within landmines and unexploded ordnance (UXO) form a chemical "signature" unique to these devices. The fact that canines can detect this signature was a primary motivation for the Defense Advanced Research Projects Agency's (DARPA) Dog's Nose Program. One goal of this program was to develop electronic chemical sensors that mimic the canine's ability to detect landmines. The sensor described here, developed under this program, utilizes novel fluorescent polymers to detect landmine signature vapors in air at ultratrace concentration levels (parts-per-trillion or less). Thin films of the polymers are highly emissive but undergo a dramatic reduction in emission intensity when molecules of target analytes bind to the polymer. Binding of a single explosive molecule can quench the fluorescence from hundreds of polymer repeat units, resulting in an amplification of the quenching response. The polymer structure contains receptor sites designed to interact specifically with nitroaromatic explosives, enhancing the selectivity of the polymers for target analytes. A man-portable sensor prototype, similar in size and configuration to metal detectors currently used for mine detection, has demonstrated performance comparable to that of canines during field tests monitored by DARPA at Fort Leonard Wood, MO.
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