Mechanisms of Gadographene-Mediated Proton Spin Relaxation

Gd(III) associated with carbon nanomaterials relaxes water proton spins at an effectiveness that approaches or exceeds the theoretical limit for a single bound water molecule. These Gd(III)-labeled materials represent a potential breakthrough in sensitivity for Gd(III)-based contrast agents used for magnetic resonance imaging (MRI). However, their mechanism of action remains unclear. A gadographene library encompassing GdCl3, two different Gd(III)-complexes, graphene oxide (GO), and graphene suspended by two different surfactants and subjected to varying degrees of sonication was prepared and characterized for their relaxometric properties. Gadographene was found to perform comparably to other Gd(III)-carbon nanomaterials; its longitudinal (r1) and transverse (r2) relaxivity is modulated between 12-85 mM-1s-1 and 24-115 mM-1s-1, respectively, depending on the Gd(III)-carbon backbone combination. The unusually large relaxivity and its variance can be understood under the modified Florence model incorporating the Lipari-Szabo approach. Changes in hydration number (q), water residence time (τM), molecular tumbling rate (τR), and local motion (τfast) sufficiently explain most of the measured relaxivities. Furthermore, results implicated the coupling between graphene and Gd(III) as a minor contributor to proton spin relaxation.

Fibrinogen Level as a Surrogate for the Outcome of Thrombolytic Therapy Using Tissue Plasminogen Activator for Acute Lower Extremity Intravascular Thrombosis

Purpose:

Monitoring of fibrinogen level is used to predict bleeding during lower extremity tissue plasminogen activator (tPA) infusions for peripheral arterial or venous thrombolysis. This practice is not fully addressed in the literature.

Materials and Methods:

We retrospectively reviewed fibrinogen levels and studied bleeding rate from charts of patients who underwent lower extremity tPA infusions at a single hospital from January 2010 to May 2012.

Results:

The rate of thrombolytic success did not correlate with fibrinogen level ( P = .53). The rate of major bleeding was significantly higher for patients with a fibrinogen level at or below 150 mg/dL ( P = .01). Patients whose tPA infusion was terminated within 46 hours had significantly lower rates of major bleeding ( P = .01) and thrombolytic failure ( P < .01). Periprocedural systolic blood pressure above 160 mm Hg was a risk factor for major bleeding ( P = .02). There was no association between concomitant aspirin use ( P = .90, .51) or hourly tPA dose ( P = .71, .62) and thrombolytic success or major bleeding, respectively.

Conclusion:

Fibrinogen level ≤150 mg/dL is associated with increased risk of major bleeding during tPA infusions. We suggest serial fibrinogen measurement as a viable method to monitor bleeding risk during lower extremity tPA infusions.

Impact of synthesis methods on the transport of single walled carbon nanotubes in the aquatic environment

In this study, a systematic approach has been followed to investigate the fate and transport of single walled carbon nanotubes (SWCNTs) from synthesis to environmentally relevant conditions. Three widely used SWCNT synthesis methods have been investigated in this study including high pressure carbon monoxide (HiPco), SWeNT CoMoCat, and electric arc discharge technique (EA). This study relates the transport of three SWCNTs (HiPco-D, SG65-D, and P2-D) with different synthesis methods and residual catalyst content revealing their influence on the subsequent fate of the nanotubes. To minimize nanotube bundling and aggregation, the SWCNTs were dispersed using the biocompatible triblock copolymer Pluronic, which allowed the comparison in the transport trends among these SWCNTs. After purification, the residual metal catalyst between the SWCNTs follows the trend: HiPco-D > SG65-D > P2-D. The electrophoretic mobility (EPM) and hydrodynamic diameter of SWCNTs remained insensitive to SWCNT type, pH, and presence of natural organic matter (NOM); but were affected by ionic strength (IS) and ion valence (K(+), Ca(2+)). In monovalent ions, the hydrodynamic diameter of SWCNTs was not influenced by IS, whereas larger aggregation was observed for HiPco-D with IS than P2-D and SG65-D in the presence of Ca(2+). Transport of HiPco-D in the porous media was significantly higher than SG65-D followed by P2-D. Release of HiPco-D from porous media was higher than SG65-D followed by P2-D, though negligible amount of all types of SWCNTs (<5%) was released. Both transport and release patterns follow a similar trend to what was observed for residual metal catalysts in SWCNTs. Addition of NOM increased the transport of all SWCNTs primarily due to electrosteric repulsion. HiPco-D was notably more acidic than SG65-D followed by P2-D, which is similar to the transport trend. Overall, it was observed that the synthesis methods resulted in distinctive breakthrough trends, which were correlated to metal content. These findings will facilitate the safe design of environmental friendly SWCNTs by minimizing mobility in aquatic environments.