The development of the dorsal mesentery in human embryos and fetuses.

The vertebrate intestine has a continuous dorsal mesentery between pharynx and anus that facilitates intestinal mobility. Based on width and fate the dorsal mesentery can be subdivided into that of the caudal foregut, midgut, and hindgut. The dorsal mesentery of stomach and duodenum is wide and topographically complex due to strong and asymmetric growth of the stomach. The associated formation of the lesser sac partitions the dorsal mesentery into the right-sided "caval fold" that serves as conduit for the inferior caval vein and the left-sided mesogastrium. The thin dorsal mesentery of the midgut originates between the base of the superior and inferior mesenteric arteries, and follows the transient increase in intestinal growth that results in small-intestinal looping, intestinal herniation and, subsequently, return. The following fixation of a large portion of the abdominal dorsal mesentery to the dorsal peritoneal wall by adhesion and fusion is only seen in primates and is often incomplete. Adhesion and fusion of mesothelial surfaces in the lesser pelvis results in the formation of the "mesorectum". Whether Toldt's and Denonvilliers' "fasciae of fusion" identify the location of the original mesothelial surfaces or, alternatively, represent the effects of postnatal wear and tear due to intestinal motility and intra-abdominal pressure changes, remains to be shown. "Malrotations" are characterized by growth defects of the intestinal loops with an ischemic origin and a narrow mesenteric root due to insufficient adhesion and fusion.

Changing Practice Patterns and Long-term Outcomes of Endothelial Versus Penetrating Keratoplasty: A Prospective Dutch Registry Study.

PURPOSE: To compare graft survival, best-corrected visual acuity (BCVA), endothelial cell density (ECD), and refraction following penetrating keratoplasty (PK) vs endothelial keratoplasty (EK) for Fuchs endothelial dystrophy (FED) and pseudophakic bullous keratopathy (PBK). DESIGN: Nonrandomized treatment comparison with national registry data. METHODS: All consecutive patients undergoing first keratoplasty for FED and PBK between 1998 and 2014 were analyzed, with a maximum follow-up of 5 years (mean ± SD follow-up 39 ± 20 months, range 0-60 months). Graft survival was analyzed using Kaplan-Meier survival curves and Cox regression analysis. BCVA, ECD, and refractive error were compared using linear mixed models. Main outcome measures were graft survival, BCVA, refraction, and ECD. RESULTS: A total of 5115 keratoplasties (PK = 2390; EK = 2725) were identified. Two-year graft survival following EK was lower compared with PK (94.5% vs 96.3%, HR = 1.56, P = .001). Five-year survival was comparable for EK and PK (93.4% vs 89.7%, HR = 0.89, P = .261). EK graft survival improved significantly over time while remaining stable for PK. One-year BCVA was better following EK vs PK (0.34 vs 0.47 logMAR, P < .001). Astigmatism was lower 1 year after EK vs PK (-1.69 vs -3.52 D, P < .001). One-year ECD was lower after EK vs PK (1472 vs 1859 cells/mm2, P < .001). At 3 years, ECD did not differ between EK and PK. CONCLUSIONS: Long-term graft survival after EK and PK is high and comparable despite lower short-term survival for EK. EK graft survival improved over time, suggesting a learning curve. EK results in better BCVA, lower astigmatism, and similar long-term ECD compared with PK for FED and PBK.

Coupled nanomechanical motions: metal-ion-effected, pH-modulated, simultaneous extension/contraction motions of double-domain helical/linear molecular strands.

A new class of shape-enforced synthetic polyheterocyclic molecular strands, containing both a helical and a linear domain, has been designed and synthesized. On reaction with Pb(II), under the effect of cation binding to the coordination subunits, the helical section unfolds into a linear shape in the complex and the linear domain folds into a helical ligand wrapped around the bound cations. Such double-domain ligand strands are thus able to undergo a combined unfolding-folding interconversion on binding and release of metal cations. These changes can be modulated through coupling to a competing ligand that reversibly binds and releases metal cations, when respectively unprotonated and protonated, on effecting alternate pH changes. The resulting process thus performs nanomechanical extension/contraction molecular motions of a linear motor type, which is fueled by acid-base neutralization.

Dynamers: polyacylhydrazone reversible covalent polymers, component exchange, and constitutional diversity.

Component exchange in reversible polymers allows the generation of dynamic constitutional diversity. The polycondensation of dihydrazides with dialdehydes generates polyacylhydrazones, to which the acylhydrazone functionality formed confers both hydrogen-bonding and reversibility features through the amide and imine groups, respectively. Polyacylhydrazones are thus dynamic polyamides. They are able to reversibly exchange either one or both of their repeating monomer units in the presence of different monomers, thus presenting constitutional dynamic diversity. The polymers subjected to monomer exchange/interchange may be brought to exhibit physical properties vastly different from those of the original polymer. The principle may be extended to other important classes of polymers, giving access, for instance, to dynamic polyureas or polycarbamates. These reversible polymers are therefore able to incorporate, decorporate, or reshuffle their constituting monomers, namely in response to environmental physical or chemical factors, an adaptability feature central to constitutional dynamic chemistry.