Experimental and Computational Study of a Liquid Crystalline Dimesogen Exhibiting Nematic, Twist-Bend Nematic, Intercalated Smectic, and Soft Crystalline Mesophases

Liquid crystalline dimers and dimesogens have attracted significant attention due to their tendency to exhibit twist-bend modulated nematic (NTB) phases. While the features that give rise to NTB phase formation are now somewhat understood, a comparable structure-property relationship governing the formation of layered (smectic) phases from the NTB phase is absent. In this present work, we find that by selecting mesogenic units with differing polarities and aspect ratios and selecting an appropriately bent central spacer we obtain a material that exhibits both NTB and intercalated smectic phases. The higher temperature smectic phase is assigned as SmCA based on its optical textures and X-ray scattering patterns. A detailed study of the lower temperature smectic ''X'' phase by optical microscopy and SAXS/WAXS demonstrates this phase to be smectic, with an in-plane orthorhombic or monoclinic packing and long (>100 nm) out of plane correlation lengths. This phase, which has been observed in a handful of materials to date, is a soft-crystal phase with an anticlinic layer organisation. We suggest that mismatching the polarities, conjugation and aspect ratios of mesogenic units is a useful method for generating smectic forming dimesogens.

In vitro photoacoustic visualization of myocardial ablation lesions

BACKGROUND

Radiofrequency (RF) ablation to treat atrial arrhythmia is limited by the inability to reliably assess lesion durability and transmurality.

OBJECTIVE

The purpose of this study was to determine the feasibility of photoacoustic characterization of myocardial ablation lesions in vitro. In this study, we investigated the feasibility of combined ultrasound (US) and spectroscopic photoacoustic imaging to visualize RF ablation lesions in three dimensions (3D) based on unique differences in the optical absorption spectra between normal and ablated myocardial tissue.

METHODS

Tissue samples were excised from the ventricles of fresh porcine hearts. Lesions were generated using an RF catheter ablation system using 20 to 30 W of power applied for 40 to 60 seconds. Ablated samples were imaged in the near-infrared regime (740-780 nm) using a combined PA/US imaging system. Measured PA spectra were correlated to the absorption spectra of deoxyhemoglobin and ablated tissue to produce a tissue characterization map (TCM) identifying 3D lesion location and extent. Tissue samples were stained and photographed for gross pathology. TCM and gross pathology images were coregistered to assess TCM accuracy.

RESULTS

TCM reliably characterized ablated and non-ablated tissue up to depths of 3 mm. TCM also assessed lesion position and extent with submillimeter accuracy in multiple dimensions. Segmented TCMs achieved >69% agreement with gross pathology.

CONCLUSION

The study results suggest that spectroscopic photoacoustic imaging has the potential to accurately assess RF ablation lesion size and position with submillimeter precision and may be well suited to guide transcatheter RF atrial ablation in clinical practice.

Genetic and non-genetic factors affecting the visual outcome of ocular Behcet's disease

OBJECTIVE

To examine the prognostic factors for visual outcome in Korean BD patients with uveitis.

METHODS

Seventy-seven Korean BD patients with uveitis were enrolled. HLA-B and HLA-A genotypes were determined by PCR-based method. Visual acuity was measured by Snellen chart. Vision loss was graded into visual impairment (VI) defined as VA<20/40 for more than 6 months, loss of useful vision (LUV) as VA < 20/200, and near total blindness (NTB) as VA of light perception or worse.

RESULTS

VI was associated with a longer duration of uveitis, posterior uveitis, and cataract, LUV with male gender, a longer duration of uveitis, posterior uveitis, and cataract, and NTB with a longer duration of uveitis, cataract, and glaucoma. HLA-B*51 and HLA-A*26:01 did not show any association with VI, LUV, or NTB. However, HLA-B*51 carriers had earlier onset of uveitis and HLA-A*26:01 was strongly associated with posterior uveitis. In patients with posterior uveitis, VI was associated with a longer duration of uveitis and cataract, LUV with a longer duration, and NTB with HLA-B*51.

CONCLUSION

Longer duration of uveitis, posterior uveitis, male gender, cataract, and glaucoma were found to be associated with poor visual outcome in BD-related uveitis. HLA-B*51 was associated with NTB in patients with posterior uveitis. HLA-A*26:01 showed no association with VI, LUV, or NTB, however, was strongly associated with posterior uveitis.

Simultaneous solid phase extraction and derivatization of aliphatic primary amines prior to separation and UV-absorbance detection

To overcome the problem of poor sensitivity of capillary electrophoresis-UV absorbance for the detection of aliphatic amines, a solid phase extraction and derivatization scheme was developed. This work demonstrates successful coupling of amines to a chromophore immobilized on a solid phase and subsequent cleavage and analysis. Although the analysis of many types of amines is relevant for myriad applications, this paper focuses on the derivatization and separation of amines with environmental relevance. This work aims to provide the foundations for future developments of an integrated sample preparation microreactor capable of performing simultaneous derivatization, preconcentration, and sample cleanup for sensitive analysis of primary amines.