Microscale Mechanism of Age Dependent Wetting Properties of Prickly Pear Cacti (Opuntia)

Optimizing anisotropic transport on bioinspired sawtooth surfaces

Species ranging from butterflies and other insects, to cactuses and lotus plants have evolved to use geometrically patterned surfaces to influence the transport of water droplets. While this phenomenon is well known, an ideal geometry has yet to be discovered. To determine the impact of surface geometry on droplet transport, we have studied the contact angle and droplet motion across anisotropically wetting patterned surfaces. The surface geometries tested were sawtooth patterns with angles (8.62-26.70°) and lengths (0.56-1.67 μm). The droplet contact angles were measured on 45° angled surfaces to simulate the droplet in motion. Velocities were measured using a high-speed camera shooting at 500 frames per second and the tailing edges of the droplets were hand tracked over 18 frames. It was found that travel along the sawtooth ridges is significantly faster than travel against the ridges for geometries with shallow angles. The optimal geometry was determined to be α = 8.62° and b = 1.67 μm and was replicated using nanoimprint lithography using materials with different surface energies. When replicated with acrylate resins and PDMS, the contact angles remained high, regardless of wettability, but we find that the overall velocity and velocity hysteresis depends on the hydrophobicity. More hydrophobic surfaces have overall higher hysteresis. The ability to tune imprinted surfaces to achieve ideal wetting characteristics using geometry will lead to interesting anisotropic material design.

Cladodes of Opuntia ficus-indica (L.) Mill. Possess Important Beneficial Properties Dependent on Their Different Stages of Maturity

Opuntia ficus-indica (L.) Mill. belongs to the Cactaceae family and the genus Opuntia; it is a succulent plant that adapts to extreme climatic conditions. The aerial part of the plant consists of the cladodes, morphological changes of branches that appear green, are covered with thorns, and are essential to reduce excessive perspiration of water. The composition of cladodes is very varied, and the main constituents are water, fibers, polysaccharides, proteins, fatty acids, vitamins, sterols, minerals, and polyphenols. Polyphenols are responsible for many beneficial activities for human health, such as antioxidant, anti-inflammatory, anticancer, and nutritional properties. The purpose of this manuscript was to compare the properties of cladodes belonging to the same plant but with different stages of maturity. Relative extracts were tested both in vitro and on a cell line and antioxidant and anti-apoptotic properties were found. The antioxidant activity was tested by the Oxygen Radical Absorbance Capacity (ORAC) test, the 1,1-diphenyl-2-picrylhydrazil (DPPH) test, and the measurement of cellular accumulation of reactive oxygen species (ROS). Anti-apoptotic activity was evaluated by the annexin/PI assay and measurement of caspases 9 and 3 expression. The results obtained showed that the extracts considered possess antioxidant and anti-apoptotic properties. However, the different stages of maturity of cladodes are essential for the performance of both functions. In addition, important variations were made in the dissolution of the extracts that brought greater safety in their use. In conclusion, this manuscript provides further information on cladodes of Opuntia ficus-indica, which can be used as adjuvants in many human pathologies.

Antioxidant Activity and Seasonal Variations in the Composition of Insoluble Fiber from the Cladodes of Opuntia ficus-indica (L.) Miller: Development of New Extraction Procedures to Improve Fiber Yield

Opuntia ficus-indica (L.) Miller is a plant belonging to the Cactaceae family adapted to live in environments characterized by long periods of drought and arid or desert climates. This plant is characterized by an aerial part composed of structures transformed by branches, called "cladodes", which are essential to reduce excessive perspiration of water and appear covered with thorns. The composition of the cladodes includes water, polysaccharides, fiber, proteins, vitamins, fatty acids, sterols, polyphenols, and minerals. The main purposes of this scientific work are (a) to compare the insoluble fiber (IF) extracted from the cladodes of O. ficus-indica belonging to the same plant but collected in different seasonal periods (winter and summer) and develop new extraction protocols that are able to improve the yield obtained and (b) evaluate the antioxidant potential of the fiber and study possible variations as a result of the extraction protocol chosen. The first objective was achieved (1) by measuring the amount of IF extracted from cladodes harvested in winter and summer (CW and CS, respectively) and (2) by modifying three variables involved in the fiber extraction protocol. To achieve the second objective, the following experiments were carried out: (1) measurement of the antioxidant potential of IF in CW and CS; (2) measurement of cellular reactive oxygen species; (3) measurement of the activity of some antioxidant enzymes; and (4) comparison of the polyphenol content in CW and CS. In conclusion, the results obtained showed that the IF extraction process can be improved, achieving a uniform yield regardless of seasonality; the antioxidant effect may vary depending on the extraction protocol.

Towards a bionic IoT: Environmental monitoring using smartphone interrogated plant sensors

The utilisation of plants directly as quantifiable natural sensors is proposed. A case study measuring surface wettability of Aucuba japonica, or Japanese Laurel, plants using a novel smartphone field interrogator is demonstrated. This plant has been naturalised globally from Asia. Top-down contact angle measurements map wettability on-site and characterise a range of properties impacting plant health, such as aging, solar and UV exposure, and pollution. Leaves at an early age or in the shadow of trees are found to be hydrophobic with contact angle θ ~ 99°, while more mature leaves under sunlight are hydrophilic with θ ~ 79°. Direct UVA irradiation at λ = 365 nm is shown to accelerate aging, changing contact angle of one leaf from slightly hydrophobic at θ ~ 91° to be hydrophilic with θ ~ 87° after 30 min. Leaves growing beside a road with heavy traffic are observed to be substantially hydrophilic, as low as θ ~ 47°, arising from increased wettability with particulate accumulation on the leaf surface. Away from the road, the contact angle increases as high as θ ~ 96°. The results demonstrate that contact angle measurements using a portable diagnostic IoT edge device can be taken into the field for environmental detection, pollution assessment and more. Using an Internet connected smartphone combined with a plant sensor allows multiple measurements at multiple locations together in real-time, potentially enabling tracking of parameter change anywhere where plants are present or introduced. This hybrid integration of widely distributed living organic systems with the Internet marks the beginning of a new bionic Internet-of-things (b-IoT).

Banana Leaf Surface’s Janus Wettability Transition from the Wenzel State to Cassie–Baxter State and the Underlying Mechanism

Janus wettability plays an important role in certain special occasions. In this study, field emission scanning electron microscopy (FESEM) was used to observe the surface microstructure of banana leaves, the static wettability of the banana leaf surface was tested, and the dynamic response of water droplets falling at different heights and hitting on the adaxial and abaxial sides was studied. The study found that the nanopillars on the adaxial and abaxial sides of the banana leaf were different in shape. The nanopillars on the adaxial side were cone-shaped with large gaps, showing hydrophilicity (Wenzel state), and the heads of the nanopillars on the abaxial side were smooth and spherical with small gaps, showing weak hydrophobicity (Cassie–Baxter state). Banana leaves show Janus wettability, and the banana leaf surface has high adhesion properties. During the dynamic impact test, the adaxial and abaxial sides of the banana leaves showed different dynamic responses, and the wettability of the adaxial side of the banana leaves was always stronger than the abaxial side. Based on the structural parameters of nanopillars on the surface of the banana leaf and the classical wetting theory model, an ideal geometric model around a single nanopillar on both sides of the banana leaf was established. The results show that the established model has high accuracy and can reflect the experimental results effectively. When the apparent contact angle was 76.17°, and the intrinsic contact angle was 81.17° on the adaxial side of the banana leaf, steady hydrophilicity was shown. The abaxial side was similar. The underlying mechanism of Janus wettability on the banana leaf surface was elucidated. This study provides an important reference for the preparation of Janus wettability bionic surfaces and the efficient and high-quality management of banana orchards.

Controlled Mass Rearing of Cochineal Insect (Hemiptera: Dactylopiidae) Using Two Laboratory-Scale Production Systems in Peru

The carmine cochineal (Dactylopius coccus Costa) has high economic value as it is a natural source of carminic acid, an organic chromophore used in a wide range of sectors including pharmaceutics, food, and cosmetics. High demand is fuelling the search for innovative production techniques in order to move away from dependence on the prickly pear, which carries a number of limitations. The aim of this study was to establish cochineal colonies and breed and mass-produce the insects using two laboratory-scale production systems. The first system (STC-01) comprised a prismatic acrylic box with three compartments; synthetic matrices were placed vertically inside the box to provide support and a source of nutrients for the cochineal, and the system was lit artificially during fixed daylight periods. The second system (STC-02) comprised an automated micro-tunnel allowing the insects to move towards the sunlight, containing synthetic matrices arranged horizontally. There was a significant difference in yield between the two systems in a cochineal total life cycle of 120 d (80-90 d harvest period in both cases), with STC-01 being superior and producing a maximum yield of 4.86 ± 0.68 g fresh weight per day per square metre compared with 3.20 ± 0.14 g fresh weight per day per square metre production yield in STC-02. We conclude that cochineal production under controlled artificial conditions is feasible and sustainable, removing the need for natural and biological support and overcoming the environmental limitations posed by traditional production methods.

Microscale mechanism of microstructure, micromorphology and Janus wettability of the banana leaf surface

As a result of natural selection, the adaxial and abaxial sides of banana leaves show different wetting states and anisotropy. Janus wettability between the adaxial and abaxial sides of the banana leaf surface is revealed for the first time in this work. This has relevance for the preparation of bionic materials and an important role in the efficient and high-quality production management of pesticide spraying in banana orchards. The main purpose of this research is to analyze and study the microscale mechanism and coupling relationship between the Janus wettability of banana leaf surface and the microstructure and micromorphology. We adopt advanced modern instrument analysis technology, such as contact angle (CA) measurements, field emission scanning electron microscopy (FESEM), X-ray spectrometric analysis (EDS), and Fourier transform infrared spectroscopy (FTIR), and performed tests on the adaxial and abaxial sides of banana leaves to investigate the cause of Janus wettability. The results show that banana leaves exhibit different degrees of anisotropy, mainly due to the surface micromorphology. Banana leaves exhibit a hydrophilic Wenzel state on the adaxial side and a weakly hydrophobic Cassie-Baxter state on the abaxial side. We focused on studying the coupling effect and found that the main coupling element impacting the Janus wettability of the banana leaf surface is the nanopillars microstructure, and the secondary coupling element is the content of hydrophilic functional groups on the surface. This work may lead to the design and fabrication of Janus wetting surfaces by mimicking the nanopillar structure on banana leaf surfaces and help explore the potential application of efficient and high-quality pesticide spraying in banana orchards.

Understanding trait diversity associated with crassulacean acid metabolism (CAM)

Crassulacean acid metabolism (CAM) is a specialized mode of photosynthesis that exploits a temporal CO₂ pump with nocturnal CO₂ uptake and concentration to reduce photorespiration, improve water-use efficiency (WUE), and optimize the adaptability of plants to climates with seasonal or intermittent water limitations. CAM plants display a plastic continuum in the extent to which species engage in net nocturnal CO₂ uptake that ranges from 0 to 100%. CAM plants also display diverse enzyme and organic acid and carbohydrate storage systems, which likely reflect the multiple, independent evolutionary origins of CAM. CAM is often accompanied by a diverse set of anatomical traits, such as tissue succulence and water-storage and water-capture strategies to attenuate drought. Other co-adaptive traits, such as thick cuticles, epicuticular wax, low stomatal density, high stomatal responsiveness, and shallow rectifier-like roots limit water loss under conditions of water deficit. Recommendations for future research efforts to better explore and understand the diversity of traits associated with CAM and CAM Biodesign efforts are presented.

Hydraulic Strategy of Cactus Root-Stem Junction for Effective Water Transport

Cactus roots function as a hydraulic safety valve by conducting available water quickly and preventing water loss under drought condition. In particular, the root-stem (R-S) junction is responsible for effective water transport by direct coupling of the water absorptive thin roots and the moisture-filled bulky stem. In this study, the morphological features of the R-S junction were observed by using X-ray micro-imaging technique. Their structural and functional characteristics were also elucidated according to a hydrodynamic viewpoint. With regard to the axial water transport through xylem, the R-S junction prevents water leakage by embolizing large-scale vessels with relatively high hydraulic conductivity. In addition, the axial theoretical hydraulic conductivity of xylem vessels from the roots to the stem drastically increases to facilitate water absorption and prevent water loss. The cortex cell layer of a cactus is thinner than that of other plant species. In the viewpoint of radial conductivity, this property can be the hydraulic strategy of the cactus R-S junction to transport water quickly from the root surface into the xylem. These results suggest that the R-S junction functions as a hydraulic safety valve that can maximize water uptake in axial and radial directions at limited rainfall. This junction can also prevent the stem from leaking water under drought condition.

Recent advances in the study and design of parahydrophobic surfaces: From natural examples to synthetic approaches

Parahydrophobic surfaces are an interesting class of materials that combines both high contact angles and very strong adhesion with wetting fluids, most commonly water. This unique set of properties makes parahydrophobic surfaces attractive for a variety of applications, including water harvesting and collection, guided fluid transport, and membrane development, amongst many others. Taking inspiration from natural surfaces that display this same behavior such as rose petals and gecko feet, synthetic approaches aim to incorporate the nano- and micro-scale topography as well as the low surface energy chemistry found on these interfaces. Here, we discuss the chemical and physical factors that contribute to parahydrophobic behavior and provide a comprehensive overview on the current technologies and procedures used towards constructing surfaces that mimic this behavior already observed in nature. This includes etching processes, colloidal assemblies, deposition methods, and in situ growth of surface features. Furthermore, issues such as ease of scale-up, efficiency of technical procedures, and other current challenges associated with these methods will be discussed to provide insight as to the future directions for this growing area of research.