Material model measurements and predictions for a random pore poly(epsilon-caprolactone) scaffold.

We investigated material models for a polymeric scaffold used for bone. The material was made by co-extruding poly(epsilon-caprolactone) (PCL), a biodegradable polyester, and poly(ethylene oxide) (PEO). The water soluble PEO was removed resulting in a porous scaffold. The stress-strain curve in compression was fit with a phenomenological model in hyperbolic form. This material model will be useful for designers for quasi-static analysis as it provides a simple form that can easily be used in finite element models. The ASTM D-1621 standard recommends using a secant modulus based on 10% strain. The resulting modulus has a smaller scatter in its value compared with the coefficients of the hyperbolic model, and it is therefore easier to compare differences in material processing and ensure quality of the scaffold. A prediction of the small-strain elastic modulus was constructed from images of the microstructure. Each pixel of the micrographs was represented with a brick finite element and assigned the Young's modulus of bulk PCL or a value of 0 for a pore. A compressive strain was imposed on the model and the resulting stresses were calculated. The elastic constants of the scaffold were then computed with Hooke's law for a linear-elastic isotropic material. The model was able to predict the small-strain elastic modulus measured in the experiments to within one standard deviation. Thus, by knowing the microstructure of the scaffold, its bulk properties can be predicted from the material properties of the constituents.

Microstructure determination of AOT + phenol organogels utilizing small-angle X-ray scattering and atomic force microscopy.

Dry reverse micelles of the anionic twin-tailed surfactant bis(2-ethylhexyl) sulfosuccinate (AOT) dissolved in nonpolar solvents spontaneously form an organogel when p-chlorophenol is added in a 1:1 AOT:phenol molar ratio. The solvents used were benzene, toluene, m-xylene, 2,2,4-trimethylpentane (isooctane), decane, dodecane, tetradecane, hexadecane, and 2,6,10,14-tetramethylpentadecane (TMPD). The proposed microstructure of the gel is based on strands of stacked phenols linked to AOT through hydrogen bonding. Small-angle X-ray scattering (SAXS) spectra of the organogels suggest a characteristic length scale for these phenol-AOT strands that is independent of concentration but dependent on the chemical nature of the nonpolar solvent used. Correlation lengths determined from the SAXS spectra indicate that the strands self-assemble into fibers. Direct visualization of the gel in its native state is accomplished by using tapping mode atomic force microscopy (AFM). It is shown that these organogels consist of fiber bundle assemblies. The SAXS and AFM data reinforce the theory of a molecular architecture consisting of three length scales-AOT/phenolic strands (ca. 2 nm in diameter) that self-assemble into fibers (ca. 10 nm in diameter), which then aggregate into fiber bundles (ca. 20-100 nm in diameter) and form the organogel.

Late relapse of pulmonary blastomycosis after adequate treatment with amphotericin B. Case report.

A 53-year-old man experienced relapse of pulmonary blastomycosis 9 years after having been treated successfully with amphotericin B and responded satisfactorily to retreatment. Relapse of blastomycosis after adequate treatment with amphotericin B is apparently uncommon. However, published reports include relatively few patients who have had long-term follow-up.

Allergic bronchopulmonary aspergillosis: an increasing clinical problem.

Allergic bronchopulmonary aspergillosis is being recognized with increasing frequency in the United States. The characteristics of the disease are recurrent pyrexia, cough, wheezing, sputum plugs containing aspergilli, fleeting pulmonary infiltrates, eosinophilia, dual skin reactions (immediate and late), and antibodies to the fungus in the blood. The pathogenetic mechanism is believed to involve type I and type III hypersensitivity reactions. Adrenal corticosteroids are effective in treating this condition.

Reactivation of pulmonary tuberculosis due to trauma.

A 53-year-old man developed pulmonary tuberculosis, presumably reactivation, with ten days of sustaining multiple fractured ribs. Tuberculous bronchopneumonia developed in the right lung adjacent to the site of injury and spread to the contralateral lung. Sputum smears were positive for acid-fast bacilli three weeks after trauma. Theories for the reactivation of pulmonary tuberculosis secondary to trauma are reviewed.