Modeling the Mechanical Microenvironment of Coiled Cerebral Aneurysms.

Successful occlusion of cerebral aneurysms using coil embolization is contingent upon stable thrombus formation, and the quality of the thrombus depends upon the biomechanical environment. The goal of this study was to investigate how coil embolization alters the mechanical micro-environment within the aneurysm dome. Inertialess particles were injected in three-dimensional, computational simulations of flow inside patient aneurysms using patient-specific boundary conditions. Coil embolization was simulated as a homogenous porous medium of known permeability and inertial constant. Lagrangian particle tracking was used to calculate the residence time and shear stress history for particles in the flow before and after treatment. The percentage of particles entering the aneurysm dome correlated with the neck surface area before and after treatment (pretreatment: R2 = 0.831, P < 0.001; post-treatment: R2 = 0.638, P < 0.001). There was an inverse relationship between the change in particles entering the dome and coil packing density (R2 = 0.600, P < 0.001). Following treatment, the particles with the longest residence times tended to remain within the dome even longer while accumulating lower shear stress. A significant correlation was observed between the treatment effect on residence time and the ratio of the neck surface area to porosity (R2 = 0.390, P = 0.007). The results of this study suggest that coil embolization triggers clot formation within the aneurysm dome via a low shear stress-mediated pathway. This hypothesis links independently observed findings from several benchtop and clinical studies, furthering our understanding of this treatment strategy.

Recombinant expression and purification of a functional bacterial metallo-chaperone PbrD-fusion construct as a potential biosorbent for Pb(II).

PbrD is a lead (II) binding protein encoded by the pbr lead resistance operon found exclusively in Cupriavidus metallidurans CH34. Its ability to sequester Pb(II) shows potential for it to be developed as a biosorbent for Pb in the bioremediation of contaminated wastewaters. In this study the pbrD gene from C. metallidurans CH34 was transformed and overexpressed in Escherichia coli BL21 (DE3) using the pET32 Xa/Lic vector. Optimal expression of recombinant (r)PbrD (∼50 kDa) was achieved post-induction with IPTG within inclusion bodies (IBs). Inclusion bodies were solubilised by denaturation and purified by Ni-NTA affinity chromatography. The purified denatured protein containing the N-terminal Trx•Tag™, His•Tag® and S®Tag™ was refolded in vitro via dialysis to a biologically functional form. Circular dichroism spectra of refolded rPbrD-fusion protein indicated a high degree of turns, ß-sheets and 310 helices content and tryptophan fluorescence showed a structural conformational change in the presence of Pb(II). Refolded rPbrD-fusion protein bound 99.7% of Pb(II) when mixed with lead nitrate in ten-fold increasing concentrations. Adsorption isotherms including Langmuir, Freundlich, Temkin and Dubinin-Radushkevich models were applied to determine the biosorption mechanism. A biologically functional rPbrD-fusion protein has potential application in the development of a biosorbent for remediation of Pb(II) from wastewater.