Implantable strain sensor to monitor fracture healing with standard radiography.

Current orthopaedic clinical methods do not provide an objective measure of fracture healing or weight bearing for lower extremity fractures. The following report describes a novel approach involving in-situ strain sensors to objectively measure fracture healing. The sensor uses a cantilevered indicator pin that responds to plate bending and an internal scale to demonstrate changes in the pin position on plain film radiographs. The long lever arm amplifies pin movement compared to interfragmentary motion, and the scale enables more accurate measurement of position changes. Testing with a human cadaver comminuted metaphyseal tibia fracture specimen demonstrated over 2.25 mm of reproducible sensor displacement on radiographs with as little as 100 N of axial compressive loading. Finite element simulations determined that pin displacement decreases as the fracture callus stiffens and that pin motion is linearly related to the strain in the callus. These results indicate that an implanted strain sensor is an effective tool to help assess bone healing after internal fixation and could provide an objective clinical measure for return to weight bearing.

Inorganic sensing using organofunctional sol-gel materials.

This Account describes recent work in the development and applications of sol-gel sensors for concentrated strong acids and bases and metal ions. The use of sol-gel films doped with organic indicators for the optical sensing of concentrated strong acids (HCl, 1-10 M) and bases (NaOH, 1-10 M) has been explored, and the development of dual optical sensor approaches for ternary systems (HCl-salt-H 2O and NaOH-alcohol-H 2O) to give acid and salt, as well as base and alcohol, concentrations is discussed. The preparation of transparent, ligand-grafted sol-gel monoliths is also described, and their use in the analysis of both metal cations (Cu (2+)) and metal anions [Cr(VI)] is presented. A new model using both metal ion diffusion and immobilization by the ligands in such monoliths has been developed to give metal concentrations using the optical monolith sensors. In addition to optical sensing, a method utilizing ligand-grafted sol-gel films for analyte preconcentration in the electrochemical determination of Cr(VI) has been explored and is discussed.

Optical determination of Cr(VI) using regenerable, functionalized sol-gel monoliths.

Transparent, pyridine-functionalized sol-gel monoliths have been formed and their use in Cr(VI) sensing applications is demonstrated. The monoliths were immersed in acidic Cr(VI)-containing solutions, and the Cr(VI) uptake was monitored using UV-vis and atomic absorption spectroscopies. At concentrations at the ppm level, the monoliths exhibit a yellow color change characteristic of Cr(VI) uptake, and this can be measured by monitoring the absorption change at about 350 nm using UV-vis spectroscopy. Concentrations at the ppb level are below the limit of detection using this wavelength of 350 nm for measurement. However, by adding a diphenylcarbazide solution to monoliths that have been previously immersed in ppb-level Cr(VI) solutions, a distinct color change takes place within the gels that can be measured at about 540 nm using UV-vis spectroscopy. Concentrations as low as 10 ppb Cr(VI) can be measured using this method. The monoliths can then be regenerated for subsequent sensing cycles by thorough washing with 6.0M HCl. The factors affecting monolith uptake of Cr(VI) have been explored. In addition, the gels have been characterized using X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), and Brunauer-Emmett-Teller (BET) measurements.

Quantitative analysis of trace chromium in blood samples. Combination of the advanced oxidation process with catalytic adsorptive stripping voltammetry.

A new method for pretreating blood samples for trace Cr analysis is described. The advanced oxidation process (AOP with H2O2 and 5.5-W UV irradiation for 60 min) is used to remove biological/organic species for subsequent analysis. Prior to the AOP pretreatment, acid (HNO3) is used at pH 3.0 to inhibit the enzyme catalase in the blood samples. Catalytic adsorptive stripping voltammetry at a bismuth film electrode gives a Cr concentration of 6.0 +/- 0.3 ppb in the blood samples. This concentration was confirmed by dry-ashing the blood samples and subsequent analysis by atomic absorption spectroscopy. This current method may be used to monitor chromium, a trace metal in humans, and the efficacy and safety of chromium supplements as adjuvant therapy for diabetes.

Electrochemical deposition of sol-gel films for enhanced chromium(VI) determination in aqueous solutions.

A pyridine-functionalized sol-gel film has been formed by electrodeposition at a glassy carbon electrode surface. When this protonated film is exposed to a Cr(VI) solution, the Cr(VI) anions are preconcentrated at the electrode surface. Using square wave voltammetry, the Cr(VI) species are reduced to Cr(III), and a peak current corresponding to this reduction is generated at 0.17V. The peak currents can be correlated with the Cr(VI) concentration. The functionalized sol-gel films demonstrated an enhanced sensitivity for Cr(VI) in aqueous solutions, providing a limit of detection at the low ppb level. Interference studies also displayed the high selectivity of the films for Cr(VI), and the system was able to tolerate a large excess of Cr(III) with no adverse affects. The reported electrodeposition method of film formation uses commercially available reagents and yields films quickly and reproducibly. The growth of these sol-gel films was monitored using an electrochemical quartz crystal microbalance (EQCM), and they were characterized by X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM). The reported work shows the promise of such an electrode for use in Cr(VI) sensing applications.

Palladium and the electrochemical quartz crystal microbalance: a new method for the in situ analysis of the precious metal in aqueous solutions.

A new method for the quantitative determination of palladium(II) by the electrochemical quartz crystal microbalance (EQCM) technique has been developed. Using a bare carbon-coated quartz crystal, Pd(II) ions are directly deposited from aqueous solution as palladium metal onto the crystal surface, and the Pd(II) concentration is determined with a detection limit of 0.0156 mM, or 1.66 ppm. No complexing agent or preconcentration of palladium is required for the analysis. The palladium is stripped from the crystal through its electrochemical oxidation, regenerating the crystal for subsequent multi-cycle palladium analyses. A conventional gold-coated quartz crystal was incapable of carrying out the same measurements. The EQCM technique presented is simple, sensitive, and reproducible for the detection of this widely used precious metal.

Conversion of Chromium(III) Propionate to Chromate/dichromate(VI) by the Advanced Oxidation Process. Pretreatment of a Biomimetic Complex for Metal Analysis.

The use of H(2)O(2) and UV irradiation to remove organic ligands in a chromium(III) complex for the subsequent chromium analysis is reported. The Advanced Oxidation Process (AOP) using a 5.5-W UV lamp, H(2)O(2) and Fe(2+)/Fe(3+) as catalyst (photo Fenton process) was found to give complete and quantitative Cr(III) → Cr(VI) conversion and removal of ligands in chromium(III) propionate [Cr(3)O(O(2)CCH(2)CH(3))(6)(H(2)O)(3)]NO(3), a biomimetic chromium species, as subsequent chromium analyses by the 1,5-diphenylcarbazide method and atomic absorption revealed. The current process eliminates the need for mineralization and/or dissolution of the matrix in order to remove the organic ligand, the traditional pretreatments of a sample for metal analysis. Studies to optimize the conditions for the oxidation processes, including the use of Fe(2+)/Fe(3+) catalyst, length of UV irradiation, H(2)O(2) concentration, pH, power of UV lamp, and reactor size, are reported.

Studies of the oxidation of palladium complexes by the advanced oxidation process Pretreatment of model catalysts for precious metal analysis.

The advanced oxidation process (AOP) for the pretreatment of model palladium catalysts has been studied. Most standard metal analysis techniques are for metal ions free of organic ligands. Spent palladium catalysts contain organic ligands that need to be removed prior to analysis. AOP uses a combination of hydrogen peroxide and UV light to generate radicals that decompose such ligands, freeing up metals for further analysis. Palladium acetate Pd(OAc)(2), palladium acetylacetonate Pd(acac)(2), and tris(dibenzylideneacetone)dipalladium (Pd(2)(dba)(3)) were chosen as model precious metal catalysts for investigation. AOP was found to decompose ligands in Pd(OAc)(2), Pd(acac)(2) and give accurate Pd(II) quantification, while ligand decomposition and oxidation of Pd(0) to Pd(II) were demonstrated in treatments involving Pd(2)(dba)(3). The effects of solubility of the palladium complexes, continuous addition of H(2)O(2) during AOP treatments, sample pH, concentration of H(2)O(2), and length of UV irradiation are reported.

Conversion of chromium(III) propionate to chromium(VI) by the Advanced Oxidation Process Pretreatment of a biomimetic complex for metal analysis.

The use of H(2)O(2) and UV irradiation to remove organic ligands in a chromium(III) complex for the subsequent chromium analysis is reported. The Advanced Oxidation Process (AOP) using a 5.5-W UV lamp, H(2)O(2) and Fe(2+)/Fe(3+) as catalyst (photo Fenton process) was found to give complete and quantitative Cr(III)-->Cr(VI) conversion and removal of ligands in chromium(III) propionate [Cr(3)O(O(2)CCH(2)CH(3))(6)(H(2)O)(3)]NO(3), a biomimetic chromium species, as subsequent chromium analyses by the 1,5-diphenylcarbazide method and atomic absorption revealed. The current process eliminates the need for mineralization and/or dissolution of the matrix in order to remove the organic ligand, the traditional pretreatments of a sample for metal analysis. Studies to optimize the conditions for the oxidation processes, including the use of Fe(2+)/Fe(3+) catalyst, length of UV irradiation, H(2)O(2) concentration, pH, power of UV lamp, and reactor size, are reported.

Predicting second gas-solid virial coefficients using calculated molecular properties on various carbon surfaces.

Gas-solid chromatography was used to obtain values of the second gas-solid virial coefficient, B2s, in the temperature range from 343 to 493 K for seven adsorbate gases: methane, ethane, propane, chloromethane, chlorodifluoromethane, dimethyl ether, and sulfur hexafluoride. Carboxen-1000, a 1200 m2/g carbon molecular sieve (Supelco Inc.), was used as the adsorbent. These data were combined with earlier work to make a combined data set of 36 different adsorbate gases variously interacting with from one to four different carbon surfaces. All B2s values were extrapolated to 403 K to create a set of 65 different gas-solid B2s values at a fixed temperature. The B2s value for a given gas-solid system can be converted to a chromatographic retention time at any desired flow rate and can be converted to the amount of gas adsorbed at any pressure in the low-coverage, Henry's law region. Beginning with a theoretical equation for the second gas-solid virial coefficient, various quantitative structure retention relations (QSRR) were developed and used to correlate the B2s values for different gas adsorbates with different carbon surfaces. Two calculated adsorbate molecular parameters (molar refractivity and connectivity index), when combined with two adsorbent parameters (surface area and a surface energy contribution to the gas-solid interaction), provided an effective correlation (r2 = 0.952) of the 65 different B2s values. The two surface parameters provided a simple yet useful representation of the structure and energy of the carbon surfaces and thus our correlations considered variation in both the adsorbate gas and the adsorbent solid.