Influence of protein nativity on the stability of bovine serum albumin coated microbubbles.

Protein-coated microbubbles have become one of the emerging platforms in biomedical research as theranostic agents. In recent years, microbubbles have been extensively used as ultrasound contrast agents and carriers of molecular cargoes, pertaining to which several studies have focused on tuning the properties of these bubbles to achieve a higher degree of biocompatibility and extended stability. Synthesis of microbubbles has so far been traditionally carried out with pre-heated proteins like bovine serum albumin (BSA) as shell coatings, owing to the ease in making BSA crosslinked structures through disulfide bridge formation. We, however, have performed experiments to demonstrate that air core microbubbles formed with native BSA are more stable compared with those formed using denatured BSA. The experimental observations have been supported with analytical modeling and computational studies, which offer insights into the effect of BSA conformation in stabilizing the microbubbles shells and prolonging their lifetimes.

Influence of Substrate Surface Properties on Spin Dewetting, Texture, and Phase Transitions of 5CB Liquid-Crystal Thin Films.

We report how the texture and stability of a nematic liquid-crystal (LC) thin film of 5CB vary as a function of UV-ozone (UVO) exposure of the underlying poly(methyl methacrylate) (PMMA) substrate. UVO exposure of the PMMA substrate not only increases its surface energy, making it more wettable, but also results in the generation of oxygen-containing polar functional groups on the PMMA surface due to photolysis of ester. While the stability of the 5CB films is expectedly enhanced on UVO-exposed PMMA substrates against thermally induced dewetting, the texture of the film also changes as a function of the UV exposure time (tE). We show that the films continue to exhibit the nematic Schlieren texture for tE ≤ 20 min, although the disclination point density (|m|) gradually reduces with an increase in tE. However, the texture changes completely to a spherulite or fanlike texture in tE ≥ 20 min due to enhanced anchoring of the 5CB molecules on the substrates. In addition, enhanced wettability and stronger anchoring by the UVO-exposed PMMA substrates also suppress the tendency of spin dewetting of the 5CB films due to spontaneous rupture of the dispensed solution layer during spin coating, particularly when the solute concentration (Cn) is very low. The latter observation allows possible creation of thinner LC films, which are otherwise difficult to form by spin coating due to enhanced cohesive interactions between the anisotropic LC molecules. Finally, we show that in continuous films, the nematic-to-isotropic (N → I) and I → N phase transitions with gradual heating and cooling remain completely reversible, irrespective of the texture of the film and wettability of the substrate.

Phase transition and dewetting of a 5CB liquid crystal thin film on a topographically patterned substrate.

We report thermally induced nematic to isotropic (N-I) phase transition as well as dewetting of 5CB Liquid Crystal (LC) thin films coated on flat and topographically patterned substrates with grating geometry of different line width (l P) and periodicity (λ P). On a flat substrate, the nematic to isotropic (N-I) phase transition, which takes place within a temperature range between 31.1 °C and 34.4 °C is fully reversible, with re-appearance of identical Schlieren texture when the sample is cooled down during isotropic to nematic (I-N) transition. Upon further heating beyond N-I transition and annealing at T ≈ 65 °C, the film undergoes nucleated dewetting with formation and growth of holes, which eventually merge to form isolated droplets. The morphology of the dewetted structures remains unaltered when the film is cooled to room temperature from this stage, though the features undergo phase transition to the nematic state. In contrast on a topographically patterned substrate, the phase transition cycle is associated with a change of the texture of the film during cooling to the nematic stage. Interestingly the molecules exhibit homeotropic anchoring when λ P ≈ 1.5 µm and planar anchoring when λ P large (≈10 µm). When heated further to T ≈ 65 °C, the film dewets on topographically patterned substrates resulting in a collection of droplets, which are aligned to the substrate patterns when λ P is large (≈10 µm). In contrast the dewetted droplets are random and not correlated to the patterns when λ P is lower (≈1.5 µm).

Transition from Spin Dewetting to continuous film in spin coating of Liquid Crystal 5CB.

Spin dewetting refers to spontaneous rupture of the dispensed solution layer during spin coating, resulting in isolated but periodic, regular sized domains of the solute and is pre-dominant when the solute concentration (C n ) is very low. In this article we report how the morphology of liquid crystal (LC) 5CB thin films coated on flat and patterned PMMA substrate transform from spin dewetted droplets to continuous films with increase in C n . We further show that within the spin dewetted regime, with gradual increase in the solute concentration, periodicity of the isotropic droplets (λ D ) as well as their mean diameter (d D ), gradually decreases, till the film becomes continuous at a critical concentration (C n *). Interestingly, the trend that λ D reduces with increase in C n is exact opposite to what is observed in thermal/solvent vapor induced dewetting of a thin film. The spin dewetted droplets exhibit transient Radial texture, in contrast to Schlieren texture observed in elongated threads and continuous films of 5CB, which remains in the Nematic phase at room temperature. Finally we show that by casting the film on a grating patterned substrate it becomes possible to align the spin dewetted droplets along the contours substrate patterns.

A Case of Good's Syndrome Presenting with Pulmonary Tuberculosis.

Adult onset immunodeficiency associated with thymoma is a rare condition. The combination of hypogammaglobulinemia, reduced number of peripheral B and CD4+ T cells, along with thymoma constitutes Good's syndrome (GS). This immunodeficiency condition is often complicated with opportunistic infection with organisms, like bacteria (Haemophilus influenzae, Streptococcus pneumonia etc), viruses (Cytomegalovirus, Herpes simplex etc), fungi and protozoa. We present an unusual case of Good's syndrome with pulmonary tuberculosis (PTB). A 40-year-old man presented with sputum-positive PTB and was started on anti-tuberculosis treatment. Subsequently, he developed symptoms and findings consistent with thymoma and other components of Good's syndrome. Although patients of Good's syndrome are susceptible to various opportunistic infections, infection with Mycobacterium tuberculosis is uncommon. Evidence of recurrent infections or some opportunistic infection in a thymoma patient should trigger a suspicion of Good's syndrome.