Synthesis of Poly(allyl glycidyl ether)-Derived Polyampholytes and Their Application to the Cryopreservation of Living Cells.

Through the postpolymerization modification of poly(allyl glycidyl ether) (PAGE), a functionalizable polyether with a poly(ethylene oxide) backbone, we engineered a new class of highly tunable polyampholyte materials. These polyampholytes can be synthesized to have several useful properties, including low cytotoxicity and pH-responsive coacervate formation. In this study, we used PAGE-based polyampholytes (PAGE-PAs) for the cryopreservation of mammalian cell suspensions. Typically, dimethyl sulfoxide (DMSO) is the cryoprotectant used for preserving mammalian cells, but DMSO suffers from key drawbacks including toxicity and difficult post-thaw removal that motivates the development of new materials and methods. Toxicity and post-thaw survival were dependent on PAGE-PA composition with the highest immediate post-thaw survival for normal human dermal fibroblasts occurring for the least toxic PAGE-PA at a cation/anion ratio of 35:65. With low toxicity, the PAGE-PA concentration could be increased in order to increase immediate post-thaw survival of the immortalized mouse embryonic fibroblasts (NIH/3T3). While immediate post-thaw viability was achieved using only the PAGE-PAs, long-term cell survival was low, highlighting the challenges involved with the design of cryoprotective polyampholytes. An environment utilizing both PAGE-PAs and DMSO in a cryoprotective solution offered promising post-thaw viabilities exceeding 70%, with long-term metabolic activities comparable to unfrozen cells.

Mechanism of Polymer-Mediated Cryopreservation Using Poly(methyl glycidyl sulfoxide).

Under the right conditions, some biological systems can maintain high viability after being frozen and thawed, but many others (e.g., organs and many mammalian cells) cannot. To increase the rates of post-thaw viability and widen the library of living cells and tissues that can be stored frozen, an improved understanding of the mode of action of polymeric cryoprotectants is required. Here, we present a polymeric cryoprotectant, poly(methyl glycidyl sulfoxide) (PMGS), that achieved higher post-thaw viability for fibroblast cells than its small-molecule analogue dimethyl sulfoxide. By limiting the amount of water that freezes and facilitating cellular dehydration after ice nucleation, PMGS mitigates the mechanical and osmotic stresses that the freezing of water imparts on cells and facilitates higher-temperature vitrification of the remaining unfrozen volume. The development of PMGS advances a fundamental physical understanding of polymer-mediated cryopreservation, which enables new material design for long-term preservation of complex cellular networks and tissue.

The natural statistics of blur.

Blur from defocus can be both useful and detrimental for visual perception: It can be useful as a source of depth information and detrimental because it degrades image quality. We examined these aspects of blur by measuring the natural statistics of defocus blur across the visual field. Participants wore an eye-and-scene tracker that measured gaze direction, pupil diameter, and scene distances as they performed everyday tasks. We found that blur magnitude increases with increasing eccentricity. There is a vertical gradient in the distances that generate defocus blur: Blur below the fovea is generally due to scene points nearer than fixation; blur above the fovea is mostly due to points farther than fixation. There is no systematic horizontal gradient. Large blurs are generally caused by points farther rather than nearer than fixation. Consistent with the statistics, participants in a perceptual experiment perceived vertical blur gradients as slanted top-back whereas horizontal gradients were perceived equally as left-back and right-back. The tendency for people to see sharp as near and blurred as far is also consistent with the observed statistics. We calculated how many observations will be perceived as unsharp and found that perceptible blur is rare. Finally, we found that eye shape in ground-dwelling animals conforms to that required to put likely distances in best focus.

Agreement is poor among current criteria used to define response to cardiac resynchronization therapy.

BACKGROUND: Numerous criteria believed to define a positive response to cardiac resynchronization therapy have been used in the literature. No study has investigated agreement among these response criteria. We hypothesized that the agreement among the various response criteria would be poor. METHODS AND RESULTS: A literature search was conducted with the keywords "cardiac resynchronization" and "response." The 50 publications with the most citations were reviewed. After the exclusion of editorials and reviews, 17 different primary response criteria were identified from 26 relevant articles. The agreement among 15 of these 17 response criteria was assessed in 426 patients from the Predictors of Response to Cardiac Resynchronization Therapy (PROSPECT) study with Cohen's kappa-coefficient (2 response criteria were not calculable from PROSPECT data). The overall response rate ranged from 32% to 91% for the 15 response criteria. Ninety-nine percent of patients showed a positive response according to at least 1 of the 15 criteria, whereas 94% were classified as a nonresponder by at least 1 criterion. kappa-Values were calculated for all 105 possible comparisons among the 15 response criteria and classified into standard ranges: Poor agreement (kappa< or =0.4), moderate agreement (0.4 or =0.75). Seventy-five percent of the comparisons showed poor agreement, 21% showed moderate agreement, and only 4% showed strong agreement. CONCLUSIONS: The 26 most-cited publications on predicting response to cardiac resynchronization therapy define response using 17 different criteria. Agreement between different methods to define response to cardiac resynchronization therapy is poor 75% of the time and strong only 4% of the time, which severely limits the ability to generalize results over multiple studies.

Stereopsis is adaptive for the natural environment.

Humans and many animals have forward-facing eyes providing different views of the environment. Precise depth estimates can be derived from the resulting binocular disparities, but determining which parts of the two retinal images correspond to one another is computationally challenging. To aid the computation, the visual system focuses the search on a small range of disparities. We asked whether the disparities encountered in the natural environment match that range. We did this by simultaneously measuring binocular eye position and three-dimensional scene geometry during natural tasks. The natural distribution of disparities is indeed matched to the smaller range of correspondence search. Furthermore, the distribution explains the perception of some ambiguous stereograms. Finally, disparity preferences of macaque cortical neurons are consistent with the natural distribution.

Why do animal eyes have pupils of different shapes?

There is a striking correlation between terrestrial species' pupil shape and ecological niche (that is, foraging mode and time of day they are active). Species with vertically elongated pupils are very likely to be ambush predators and active day and night. Species with horizontally elongated pupils are very likely to be prey and to have laterally placed eyes. Vertically elongated pupils create astigmatic depth of field such that images of vertical contours nearer or farther than the distance to which the eye is focused are sharp, whereas images of horizontal contours at different distances are blurred. This is advantageous for ambush predators to use stereopsis to estimate distances of vertical contours and defocus blur to estimate distances of horizontal contours. Horizontally elongated pupils create sharp images of horizontal contours ahead and behind, creating a horizontally panoramic view that facilitates detection of predators from various directions and forward locomotion across uneven terrain.

Variability in tissue Doppler echocardiographic measures of dyssynchrony is reduced with use of a larger region of interest.

BACKGROUND: Doppler tissue imaging (DTI)-based dyssynchrony parameters failed to predict response to cardiac resynchronization therapy (CRT) in the multicenter Predictors of Response to Cardiac Resynchronization Therapy (PROSPECT) trial. Large variability during the interpretation of DTI data was one of several factors thought to contribute to this failure. In this study, the authors hypothesized that using larger regions of interest (ROIs) to generate velocity curves from Doppler tissue images would significantly reduce the variability of DTI dyssynchrony parameters. METHODS: The variability of 3 ROI sizes (6 x 6, 18 x 6, and 30 x 6 mm) was compared in 30 patients undergoing CRT. Variability due to manual ROI placement was determined for each ROI size by placing 3 ROIs in each myocardial segment, 6mm apart from one another. Thus, 3 velocity curves were generated for each segment and each ROI size. Four published dyssynchrony parameters were calculated from all permutations of the 3 ROI positions per segment. A mean modified coefficient of variation was calculated for each parameter and ROI size. RESULTS: The 6 x 6 mm ROI had a mean coefficient of variation of 27%. The 18 x 6 and 30 x 6 mm ROIs had significantly lower coefficients of variation (17% and 14%, respectively) than the 6 x 6 mm ROI (P < .01 for both). The 30 x 6 mm ROI also reduced the diagnostic inconsistency of dyssynchrony parameters by 44% (P = .024) compared with the 6 x 6 mm ROI. CONCLUSION: Using a 30 x 6 mm ROI instead of a 6 x 6 mm ROI to quantify tissue Doppler dyssynchrony reduces variability by 47% and diagnostic inconsistency by 44%. The authors recommend using a 30 x 6 mm ROI in future trials to minimize variability.