Adhesion in humid conditions is a fundamental challenge to both natural and synthetic adhesives. Yet, glue from most spider species becomes stickier as humidity increases. We find the adhesion of spider glue, from five diverse spider species, maximizes at very different humidities that matches their foraging habitats. By using high-speed imaging and spreading power law, we find that the glue viscosity varies over 5 orders of magnitude with humidity for each species, yet the viscosity at maximal adhesion for each species is nearly identical, 10(5)-10(6) cP. Many natural systems take advantage of viscosity to improve functional response, but spider glue's humidity responsiveness is a novel adaptation that makes the glue stickiest in each species' preferred habitat. This tuning is achieved by a combination of proteins and hygroscopic organic salts that determines water uptake in the glue. We therefore anticipate that manipulation of polymer-salts interaction to control viscosity can provide a simple mechanism to design humidity responsive smart adhesives.

← Background Patients treated with peritoneal dialysis (PD) have increased intra-abdominal pressure and a high prevalence of abdominal wall complications. ← Objective The purpose of this study was to determine the incidence of hernias and peritoneal leaks in our PD patients and to investigate their potential risk factors. ← Patients We studied 142 unselected patients treated with PD during the past 5 years, including those that were already on PD and those that started PD during this period. Mean age was 54 years and mean follow-up on PD was 39 months. 72 patients had been treated with only continuous ambulatory PD (CAPD), 8 with automated PD (APD), and 62 with both modalities. ← Results 53 patients (37%) developed hernia and/or leak. A total of 39 hernias and 63 leaks were registered. The overall rates were 0.08 hernias/patient/year and 0.13 leaks/patient/year, 17 patients had both abdominal complications. Hernia was most frequently located in the umbilical region, and the most frequent site of leakage was the pericatheter area. Both complications appeared more frequently during the CAPD period (87% of hernias, 81% of leaks). The rate of hernias was higher in patients treated only with CAPD than in those that used only cyclers [0.08 vs 0.01 hernias/patient/year, not significant (NS)]. No patient treated only with APD had peritoneal leak; 25% (18/72) of patients treated with CAPD developed this complication ( p = 0.18, NS). Dialysate exchange volumes ranged from 2000 to 2800 mL. 25 (66%) patients required surgical repair of the hernia, with recurrence in 7 patients (28%). 27 (84%) patients with leaks were initially treated with transitory temporary transfer to hemodialysis, low volume APD, or intermittent PD for 4 weeks. The leak recurred in half of the cases and surgical repair was necessary in 12 cases. The development of hernia and/or leak did not correlate with gender, diabetes, duration of follow-up, type of PD, history of abdominal surgery, or with the largest peritoneal exchange volume used. Polycystic kidney disease was the only factor associated with higher rate of hernias ( p = 0.005), whereas increased age ( p = 0.04) and higher body mass index ( p = 0.03) were significantly associated with the appearance of leaks. ← Conclusion Abdominal hernias and peritoneal leaks are very frequent in the PD population. Advanced age, polycystic kidney disease, and high body mass index are independent risk factors for their development. Automated PD with low daytime fill volume should be considered in all patients at risk for hernias and/or leaks.

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Orb webs produced by araneoid spiders depend upon aggregate glue-coated capture threads to retain their prey. Moths are challenging prey for most spiders because their scales detach and contaminate the glue droplets, significantly decreasing adhesion. Cyrtarachne are moth-specialist orb-weaving spiders whose capture threads adhere well to moths. We compare the adhesive properties and chemistry of Cyrtarachne aggregate glue to other orb-weaving spiders to test hypotheses about their structure, chemistry and performance that could explain the strength of Cyrtarachne glue. We show that the unusually large glue droplets on Cyrtarachne capture threads make them approximately 8 times more adhesive on glass substrate than capture threads from typical orb-weaving species, but Cyrtarachne adhesion is similar to that of other species after normalization by glue volume. Glue viscosity reversibly changes over 1000-fold in response to atmospheric humidity, and the adhesive strength of many species of orb spiders is maximized at a viscosity of approximately 105–106 cst where the contributions of spreading and bulk cohesion are optimized. By contrast, viscosity of Cyrtarachne aggregate glue droplets is approximately 1000 times lower at maximum adhesive humidity, likely facilitating rapid spreading across moth scales. Water uptake by glue droplets is controlled, in part, by hygroscopic low molecular weight compounds. NMR showed evidence that Cyrtarachne glue contains a variety of unknown low molecular weight compounds. These compounds may help explain how Cyrtarachne produces such exceptionally large and low viscosity glue droplets, and also why these glue droplets rapidly lose water volume after brief ageing or exposure to even slightly dry (e.g. < 80% RH) conditions, permanently reducing their adhesion. We hypothesize that the combination of large glue droplet size and low viscosity helps Cyrtarachne glue to penetrate the gaps between moth scales.