A viscoelastic deadly fluid in carnivorous pitcher plants

Background : The carnivorous plants of the genus Nepenthes, widely distributed in the Asian tropics, rely mostly on nutrients derived from arthropods trapped in their pitcher-shaped leaves and digested by their enzymatic fluid. The genus exhibits a great diversity of prey and pitcher forms and its mechanism of trapping has long intrigued scientists. The slippery inner surfaces of the pitchers, which can be waxy or highly wettable, have so far been considered as the key trapping devices. However, the occurrence of species lacking such epidermal specializations but still effective at trapping insects suggests the possible implication of other mechanisms. Methodology/Principal Findings : Using a combination of insect bioassays, high-speed video and rheological measurements, we show that the digestive fluid of Nepenthes rafflesiana is highly viscoelastic and that this physical property is crucial for the retention of insects in its traps. Trapping efficiency is shown to remain strong even when the fluid is highly diluted by water, as long as the elastic relaxation time of the fluid is higher than the typical time scale of insect movements. Conclusions/Significance : This finding challenges the common classification of Nepenthes pitchers as simple passive traps and is of great adaptive significance for these tropical plants, which are often submitted to high rainfalls and variations in fluid concentration. The viscoelastic trap constitutes a cryptic but potentially widespread adaptation of Nepenthes species and could be a homologous trait shared through common ancestry with the sundew (Drosera) flypaper plants. Such large production of a highly viscoelastic biopolymer fluid in permanent pools is nevertheless unique in the plant kingdom and suggests novel applications for pest control

Comparative investigation of NbN and Nb–Si–N films: experiment and theory

NbN and Nb–Si–N films have been deposited by magnetron sputtering of the Nb and Si targets on silicon wafers at various powers supplied to the Nb target. The films have been investigated by an atomic force microscope, X-ray diffraction, X-ray photoelectron spectroscopy, nanoindentaion and microindentation. The NbN films were nanostructured, and the Nb–Si–N films represented an aggregation of δ-NbNx nanocrystallites embedded into the amorphous CSi₃N₄ matrix (nc-δ-NbNx/a-CSi₃N₄). The annealing of the films in vacuum showed that their intensive oxidation occurred at annealing temperature higher than 600 °C. To explain the experimental results on the Nb–Si–N films, first-principles molecular dynamics simulations of the NbN(001)/CSi₃N₄ heterostructures have been carried out.NbN і Nb–Si–N плівки осаджували на кремнієві пластини методом магнетронного розпилення мішеней Nb і Si при різних потужностях розряду на мішені із Nb. Плівки були досліджені за допомогою атомно-силового мікроскопа, дифракції рентгенівських променів, рентгенівської фотоелектронної спектроскопії, нано- і мікроіндентування. NbN плівки були наноструктуровані, тоді як Nb–Si–N плівки являли агрегацію δ-NbNx нанокристалітів, вкраплених в аморфну CSi₃N₄ матрицю (nc-δ-NbNx/ a-CSi₃N₄). Відпал плівок у вакуумі показав, що їх інтенсивне окислення відбувається при температурі вищій, ніж 600 °C. Для пояснення експериментальних результатів по Nb–Si–N плівках проведено моделювання NbN (001)/CSi₃N₄ гетероструктури із перших принципів в рамках молекулярної динаміки.NbN и Nb–Si–N пленки осаждали на кремниевые пластины методом магнетронного распыления мишеней Nb и Si при различных мощностях разряда на мишени с Nb. Пленки были исследованы с помощью атомно-силового микроскопа, дифракции рентгеновских лучей, рентгеновской фотоэлектронной спектроскопии, нано- и микроиндентирования. NbN пленки были наноструктурированные, тогда как Nb–Si–N пленки представляли агрегацию δ-NbNx нанокристаллитов, вкрапленных в аморфную CSi₃N₄ матрицу (nc-δ-NbNx/a-CSi₃N₄). Отжиг пленок в вакууме показал, что их интенсивное окисление происходит при температуре выше, чем 600 °C. Для объяснения экспериментальных результатов по Nb–Si–N пленках проведено моделирование NbN (001)/CSi₃N₄ гетероструктуры из первых принципов в рамках молекулярной динамики.This work was partially supported by STCU Contract No. 5539. The authors are grateful to Dr. Timofejeva, I. I. and Dr. Dub, S. N. for XRD investigations and nanoindentation of the films. The authors are grateful to the directorate of the Summery Institute at Jackson State University for financial support and the possibility to perform large-scale calculations

Adhesion between oppositely-charged polyelectrolytes

The adhesion between a grafted polyelectrolyte layer (brush) and a gel of an oppositely charged polyelectrolyte has been measured as a function of applied pressure, and the interface has been traced using neutron reflectometry. The interface (in aqueous medium at pH 6) between the (polycationic) brush and the (polyanionic) gel has a limited pressure-dependence, with a small amount of deformation of the interface at the brush-gel contact. Brushes with a dry thickness of up to 13 nm exhibit weak adhesion (measured using a mechanical force tester) with an adhesive failure when the gel is detached. Thicker brushes result in the gel exhibiting cohesive failure. Reversing the geometry, whereby a polycationic brush is replaced with a polyanion and the polyanionic gel is replaced with a polycation reveals that the pH-dependence of the adhesion is moderately symmetric about pH 6, but that the maximum force required to separate the polycation gel from the polyanion brush over the range of pH is greater than that for the polycation brush and polyanion gel. The polyanion used is poly(methacrylic acid) (PMAA) and polycations of poly[2-(diethyl amino)ethyl methacrylate] (PDEAEMA) and poly[2-(dimethyl amino)ethyl methacrylate] (PDMAEMA) were used

Influence of packing density and surface roughness of vertically-aligned carbon nanotubes on adhesive properties of gecko-inspired mimetics.

We have systematically studied the macroscopic adhesive properties of vertically aligned nanotube arrays with various packing density and roughness. Using a tensile setup in shear and normal adhesion, we find that there exists a maximum packing density for nanotube arrays to have adhesive properties. Too highly packed tubes do not offer intertube space for tube bending and side-wall contact to surfaces, thus exhibiting no adhesive properties. Likewise, we also show that the surface roughness of the arrays strongly influences the adhesion properties and the reusability of the tubes. Increasing the surface roughness of the array strengthens the adhesion in the normal direction, but weakens it in the shear direction. Altogether, these results allow progress toward mimicking the gecko's vertical mobility.The authors acknowledge funding from the EC project Technotubes.This is the accepted manuscript. The final version is available at http://pubs.acs.org/doi/abs/10.1021/am507822b

Strong attachment as an adaptation of flightless weevils on windy oceanic islands

Enhanced attachment ability is common in plants on islands to avoid potential fatal passive dispersal. However, whether island insects also have increased attachment ability remains unclear. Here we measured the attachment of a flightless weevil, Pachyrhynchus sarcitis kotoensis, from tropical islands, and compared it with documented arthropods from the mainland. We examined the morphology and material gradient of its attachment devices to identify the specific adaptive modifications for attachment. We find that the weevil has much stronger attachment force and higher safety factor than previously studied arthropods, regardless of body size and substrate roughness. This probably results from the specific flexible bases of the adhesive setae on the third footpad of the legs. This softer material on the setal base has not been reported hitherto and we suggest that it acts as a flexible hinge to form intimate contact to substrate more effectively. By contrast, no morphological difference in tarsomeres and setae between the weevil and other beetles is observed. Our results show the remarkably strong attachment of an island insect and highlights the potential adaptive benefits of strong attachment in windy island environment. The unique soft bases of the adhesive hairs may inspire the development of strong biomimetic adhesives

Holding on or falling off: The attachment mechanism of epiphytic Anthurium obtusum changes with substrate roughness

Premise For vascular epiphytes, secure attachment to their hosts is vital for survival. Yet studies detailing the adhesion mechanism of epiphytes to their substrate are scarce. Examination of the root hair-substrate interface is essential to understand the attachment mechanism of epiphytes to their substrate. This study also investigated how substrate microroughness relates to the root-substrate attachment strength and the underlying mechanism(s). Methods Seeds of Anthurium obtusum were germinated, and seedlings were transferred onto substrates made of epoxy resin with different defined roughness. After 2 months of growth, roots that adhered to the resin tiles were subjected to anchorage tests, and root hair morphology at different roughness levels was analyzed using light and cryo scanning electron microscopy. Results The highest maximum peeling force was recorded on the smooth surface (glass replica, 0 µm). Maximum peeling force was significantly higher on fine roughness (0, 0.3, 12 µm) than on coarse (162 µm). Root hair morphology varied according to the roughness of the substrate. On smoother surfaces, root hairs were flattened to achieve large surface contact with the substrate. Attachment was mainly by adhesion with the presence of a glue-like substance. On coarser surfaces, root hairs were tubular and conformed to spaces between the asperities on the surface. Attachment was mainly via mechanical interlocking of root hairs and substrate. Conclusions This study demonstrates for the first time that the attachment mechanism of epiphytes varies depending on substrate microtopography, which is important for understanding epiphyte attachment on natural substrates varying in roughness

Getting a Grip on the Adhesion Mechanism of Epiphytic Orchids – Evidence From Histology and Cryo-Scanning Electron Microscopy

Plants and animals evolve different attachment structures and strategies for reversible or permanent adhesion to different substrate types. For vascular epiphytes, having the ability to permanently attach to their host plants is essential for establishment and survival. Unlike mistletoe roots, roots of vascular epiphytes do not penetrate the host tissues but instead achieve attachment by growing in close contact to the surface of the substrate. However, the fundamental understanding of the attachment functions of epiphytic roots remains scarce, where majority of studies focused on the general root morphology, their functional properties and the descriptions of associated microbial endophytes. To date, research on attachment strategies in plants is almost entirely limited to climbers. Therefore, this study aims to fill the knowledge gap and elucidate the attachment functions of roots of epiphytic orchids. With the use of histology and high-resolution cryo-scanning electron microscopy (cryo-SEM) technique with freeze fracturing, the intimate root-bark substrate interface of epiphytic orchid Epidendrum nocturnum Jacq was investigated. Results showed a flattened underside of the root upon contact with the substrate surface, and the velamen layer appeared to behave like a soft foam, closely following the contours of the substrate. Root hairs emerged from the outermost velamen layer and entered into the crevices in the substrate, whenever possible