In this study we examine the potential for using brushite (dicalcium phosphate dihydrate) as a coating for orthopedic implants. It was found that brushite is transformed into a more stable calcium phosphate (hydroxyapatite), regardless of the aqueous transforming media utilized. The transformation was carried out at room temperature in deionized water, deionized water with added calcium ions, and modified Hank's type solution without calcium and magnesium ions, modified Hank's type solution with calcium and magnesium ions, and modified Hank's type solution with added calcium ions. In several of the transformation systems it was noted that brushite provided an increased amount of calcium ions to the transforming media through solubility. The process was monitored using X-ray diffraction, X-ray photoelectron spectroscopy, and dissolution studies. Scanning electron microscopy and energy dispersive spectroscopy were also utilized for characterization. The brushite coatings can be easily achieved electrolytically on conducting substrates. The process is non line of sight, simple, and inexpensive; and when using an electrolyte that can sustain currents of approximately 100 mA/cm2, the necessary coating can be completed in about 3 min.

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Polymer-bonded explosives (PBX) fulfil the need for insensitive munitions. However, the environmental impacts of PBX are unclear, even though it is likely that PBX residues from low-order detonations and unexploded ordnance are deposited on military training ranges. The release of high explosives from the polymer matrix into the environment has not been studied in detail, although as polymers degrade slowly in the environment we anticipate high explosives to be released into the environment. In this study, PBXN-109 (nominally 64% RDX) samples were exposed to variable UK climatic conditions reproduced in the laboratory to determine the effects of temperature, UV irradiation and rainfall on the release of RDX from the polymer binder. The most extreme conditions for spring, summer and winter in the UK were artificially reproduced. We found that up to 0.03% of RDX was consistently released from PBXN-109. The rate of RDX release was highest in samples exposed to the summer simulation, which had the lowest rainfall, but the highest temperatures and longest UV exposure. This was confirmed by additional experiments simulating an extreme summer month with consistently high temperatures and long periods of sunlight. These results probably reflect the combination of polymer swelling and degradation when samples are exposed to higher temperatures and prolonged UV irradiation.

In bony defects of the cranium, bone healing may be complicated by prolapse of surrounding tissue into the defect. This tissue acts as a potential obstruction to the migration of osteogenic cells, resulting in impaired bone formation. It has been shown in previous studies that when a membrane composed of resorbable polymers (LactoSorb) is placed over a cranial bone defect, it inhibits connective tissue from entering the wound and improves the rate and quality of the bony regenerate. This study is an extension of this work and specifically evaluated the effects of differing calcium-based surface coatings on membrane-covered cranial defects in the rabbit model. In non-critical size, full-thickness defects of the mature rabbit calvarium, four differently treated LactoSorb membranes were evaluated in each animal model over a 1-year postoperative period. The surface coatings (three treated, one untreated) consisted of a base-powdered material of calcium sodium phosphate (Osteostim, EBI, NJ), which were applied by different methods (pressed, brushed, one-sided versus two-sided). Evaluation consisted of cross-sectional histologic assessment of the cranial detects determining the quantitative bony fill and the presence of residual polymer material and calcium sodium phosphate. This study produced the following findings: (1) cranial defect regeneration occurs faster with calcium-coated membranes and is complete by 3 months; (2) no difference could be seen between the different methods of calcium sodium phosphate coating; (3) the calcium sodium phosphate coatings did not inhibit resorption of the biodegradable membranes for those systems that had coatings on one side; however, systems completely covered showed delayed resorption; and (4) the calcium sodium phosphate coatings did not produce any inflammatory reactions. These findings suggest that, in addition to inhibiting connective tissue from entering the wound site, the calcium coatings on resorbable devices may have beneficial effects in selected clinical conditions, especially in conditions where faster bone regeneration is necessary.

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The conformations of trialkylphosphates (alkyl = propyl, butyl, pentyl and hexyl) in various diluents were studied by molecular dynamics simulations. The population density of various conformers of trialkylphosphate in different diluents such as water and n-dodecane was determined. The Helmholtz energy change accompanied by the transition between various conformations was computed. The aggregation behavior of tributylphosphate in water and water-dodecane medium was studied.