Room temperature atom transfer radical polymerizations of N-isopropylacrylamide (NIPAM) carried out in 2-propanol (i-PrOH) and tert-butyl alcohol (t-BuOH) resulted in PNIPAMs with polydispersities between 1.1 and 1.2 and degrees of polymerization of up to 300. Methyl 2-chloropropionate (MCP), copper(I) chloride, and tris[2-(dimethylamino)ethyl]amine (Me6TREN) were used as initiator, catalyst, and ligand in a 1:1:1 ratio. Conversions were as high as 91 and 79%, respectively, without the need for excess catalyst as was required in previous studies. Aqueous solutions of these narrow-disperse PNIPAMs showed a strong decrease of the phase transition temperature with increasing molecular weight, as measured by turbidimetry and differential scanning calorimetry. In low molecular weight samples, containing significant oligomeric fractions, the slightly hydrophobic methyl propionate end group becomes significant and further decreases the onset temperature of the phase transition.

Temperature- and pH-sensitive random copolymers of N-isopropylacrylamide (NIPAAm) and propylacrylic acid (PAA) were prepared using the reversible addition fragmentation chain transfer (RAFT) polymerization method. The lower critical solution temperatures (LCSTs) (or phase separation temperatures) of the NIPAAm-co-PAA copolymer solutions were measured by the cloud-point method. At slightly acidic conditions, the LCST decreased with increase in PAA content, which suggests that the hydrophobic propyl group of PAA has a greater influence on the LCST than the polar carboxylic acid group at those conditions. An increase of pH led to a significant increase in LCST of the copolymers due to the ionization of the -COOH group. The LCSTs were studied as a function of copolymer composition over the pH range from 5.0 to 7.0. Because the pK(a) of the polymers can be tuned to fall close to neutral pH, these polymer compositions can be designed to have phase transitions triggered near physiological pH or at slightly acidic pH values that fall within acidic gradients found in biology. The NIPAAm-co-PAA copolymers thus display tunable properties that could make them useful in a variety of molecular switching and drug delivery applications where responses to small pH changes are relevant.

Abstract. Despite the existence of automatic segmentation techniques, trained graders still rely on manual segmentation to provide retinal layers and features from clinical optical coherence tomography (OCT) images for accurate measurements. To bridge the gap between this time-consuming need of manual segmentation and currently available automatic segmentation techniques, this paper proposes a user-guided segmentation method to perform the segmentation of retinal layers and features in OCT images. With this method, by interactively navigating three-dimensional (3-D) OCT images, the user first manually defines user-defined (or sketched) lines at regions where the retinal layers appear very irregular for which the automatic segmentation method often fails to provide satisfactory results. The algorithm is then guided by these sketched lines to trace the entire 3-D retinal layer and anatomical features by the use of novel layer and edge detectors that are based on robust likelihood estimation. The layer and edge boundaries are finally obtained to achieve segmentation. Segmentation of retinal layers in mouse and human OCT images demonstrates the reliability and efficiency of the proposed user-guided segmentation method.

Amphiphilic copolymers with thermosensitive and pH-sensitive properties were prepared by grafting methoxy poly(ethylene glycol) (MPEG) of different molecular weights onto alternating copolymers of maleic anhydride with styrene and 4-tert-butylstyrene. Aqueous solutions of these graft copolymers exhibit lower critical solution temperatures (LCST). These LCST's are highly sensitive to changes in pH and salinity and to the presence of hydrophobic and hydrogen-bonding additives. The phase transitions are attributed to the cooperative effects of both hydrophobic interactions and intra/ intermolecular hydrogen-bonding interactions.

During developmental stages, biomechanical stimuli on cardiac cells modulate genetic programs, and deviations from normal stimuli can lead to cardiac defects. Therefore, it is important to characterize normal cardiac biomechanical stimuli during early developmental stages. Using the chicken embryo model of cardiac development, we focused on characterizing biomechanical stimuli on the Hamburger–Hamilton (HH) 18 chick cardiac outflow tract (OFT), the distal portion of the heart from which a large portion of defects observed in humans originate. To characterize biomechanical stimuli in the OFT, we used a combination of in vivo optical coherence tomography (OCT) imaging, physiological measurements and computational fluid dynamics (CFD) modeling. We found that, at HH18, the proximal portion of the OFT wall undergoes larger circumferential strains than its distal portion, while the distal portion of the OFT wall undergoes larger wall stresses. Maximal wall shear stresses were generally found on the surface of endocardial cushions, which are protrusions of extracellular matrix onto the OFT lumen that later during development give rise to cardiac septa and valves. The non-uniform spatial and temporal distributions of stresses and strains in the OFT walls provide biomechanical cues to cardiac cells that likely aid in the extensive differential growth and remodeling patterns observed during normal development.

The measurement of blood-plasma absolute velocity distributions with high spatial and temporal resolution in vivo is important for the investigation of embryonic heart at its early stage of development. We introduce a novel method to measure absolute blood flow velocity based on high speed spectral domain optical coherence tomography (OCT) and apply it to measure velocities across the heart outflow tract (OFT) of a chicken embryo (stage HH18). First, we use the OCT system to acquire 4D 
[(x,y,z) + t] images of the OFT in vivo. Second, we reconstruct the 4D microstructural images and obtain the orientation of the OFT at its maximum expansion, from which the centerline of the OFT is calculated based on the OFT boundary segmentation. Assuming flow is parallel to the vessel orientation, the obtained centerline indicates the flow direction. Finally, the absolute flow velocity is evaluated based on the direction given by the centerline and the axial velocity obtained from Doppler OCT. Using this method, we compare flow velocity profiles at various positions along the chicken embryo OFT.

Three novel metal-cluster based coordination polymers (MCCPs)

Energetic materials (explosives, propellants, and pyrotechnics) are used extensively for both civilian and military applications and the development of such materials, particularly in the case of energetic salts, is subject to continuous research efforts all over the world. This Review concerns recent advances in the syntheses, properties, and potential applications of ionic salts based on tetrazole N-oxide. Most of these salts exhibit excellent characteristics and can be classified as a new family of highly energetic materials with increased density and performance, alongside decreased mechanical sensitivity. Additionally, novel tetrazole N-oxide salts are proposed based on a diverse array of functional groups and ions pairs, which may be promising candidates for new energetic materials.