Focused ion beam (FIB) microscopy is used to form an image similar to that formed in a conventional scanning electron microscope (SEM), but with greatly enhanced grain contrast due to the use of a primary ion beam as opposed to a beam of primary electrons as found in the SEM. In addition, by increasing the current of the positively charged gallium ion beam, it can be used as a precision, essentially stress‐free milling machine on a scale of tens of nanometres to several hundred microns. In this paper, the application of FIB microscopy to the study of crack profiles is reported. Samples of a Grade 448 (X‐65) pipeline steel were cyclically loaded in a dilute simulated groundwater solution of near neutral pH. Cracks that initiated on these samples were imaged in plan view and were locally cross‐sectioned using a high‐current focused gallium ion beam at different locations along the cracks. Samples were then tilted in situ to permit imaging of the crack profile, the grain structures around the crack tip and accurate measurement of the crack depth using the same ion beam at lower currents. The transgranular crack path and other microstructural features associated with crack development were clearly illustrated, and crack aspect ratio (depth/length) could be obtained. The capability of the FIB for enhanced imaging of grain structures, combined with its precision‐sectioning capability, make it a novel new tool for the study of cracks.
Infection is a major complication when using biomaterials such as polyurethane in the clinical setting. The purpose of this study was to develop a novel infection resistant polyurethane biomaterial using textile dyeing technology. This procedure results in incorporation of the antibiotic into the polymer, resulting in a slow, sustained release of antibiotic from the material over time, without the use of exogenous binder agents. Polycarbonate based urethanes were synthesized that contained either a non-ionic (bdPU) or anionic (cPU) chain extender within the polymer backbone and cast into films. The fluoroquinolone antibiotic ciprofloxacin (Cipro) was applied to bdPU and cPU using textile dyeing technology, with Cipro uptake determined by absorbance reduction of the "dyebath." These dyed bdPU/cPU samples were then evaluated for prolonged Cipro release and antimicrobial activity by means of spectrophotometric and zone of inhibition assays, respectively. Cipro release and antimicrobial activity by dyed cPU segments that were aggressively washed persisted over 9 days, compared with dyed bdPU and dipped cPU control segments that lasted < 24 hours. Dyed cPU segments, which remained in a static wash solution, maintained antimicrobial activity for 11 days (length of study), whereas controls again lost antimicrobial activity within 24 hours. Thus, application of Cipro to the cPU polymer by means of dyeing technology results in a slow sustained release of antibiotic with persistent bacteriocidal properties over extended periods of time.
It is difficult to study effectively microstructural damage in metal matrix composites (MMCs) due to artefacts arising from traditional metallographic sample preparation techniques. The sectioning and imaging capabilities of the focused ion beam (FIB) microscope provide an excellent method for studying damage accumulation in MMCs. The capabilities of the FIB system have been used to carry out a study of damage evolution in a powder-processed/hot-extruded Al2080/SiCp MMC. Microvoid damage is found to be preserved accurately during FIB sectioning, allowing measurements of the fraction of decohered particles and the void area fraction. These microscopic damage measurements are correlated with the macroscopic damage parameter, D, as determined by density measurements. Using transmission electron microscopy, the evolution of dislocation structures at the SiC-matrix interfaces has been examined. A previously unreported decohesion mechanism has been observed.
SummaryIn a continuing effort to create an agent which has both thrombolytic and antithrombotic properties, streptokinase (SK) was covalently bound to the potent antithrombin agent recombinant hirudin (rHir). Linkage of SK to 125I-rHir was accomplished via heterobifunctional crosslinkers in an average molar ratio of 1:1. The 125I-rHir-SK complex was purified from starting components by anion exchange and gel filtration chromatography. The major band containing covalently bound 125I-rHir had a molecular weight of 53 kDa as determined by SDS-PAGE and autoradiography. Biologic activity of each component was then assayed utilizing the chromogenic substrate for each compound. Complex bound 125I-rHir exhibited a 1.2 fold decrease in thrombin inhibition when compared to concentrations of, 25I-rHir greater than 3.13 nM. Complex bound i25I-SK, replacing the 125I label on rHir, displayed a 7.9-fold loss in plasminogen activation when compared to l25I-SK. These chromogenic assay results were not adversely altered in the presence of the converse compound’s substrate. The 125I-SK-rHir complex (examined at various concentrations) also demonstrated a 0. 17- to 17-fold greater affinity for thrombin immobilized onto Sepha- rose beads as compared to 125I-SK. These findings indicate the rHir-SK complex maintained both thrombolytic and antithrombin properties while also obtaining affinity for immobilized thrombin.
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