Bioinspired Fibers Research Articles

Orientation-Induced Effects of Water Harvesting on Humps-on-Strings of Bioinspired Fibers.

Smart water-collecting functions are naturally endowed on biological surfaces with unique wettable microstructures, e.g., beetle back with “alternate hydrophobic, hydrophilic micro-regions”, and spider silk with wet-rebuilt “spindle-knot, joint” structures. Enlightened by the creature features, design of bio-inspired surfaces becomes the active issue in need of human beings for fresh water resource. Recently, as observed from spider web in nature, the net of spider silk is usually set in different situations and slopes in air, thus spider silks can be placed in all kinds of orientations as capturing water. Here, we show the styles and orientations of hump-on-string to control the ability of water collection as bioinspired silks are fabricated successfully. As different strings, sizes (height, length, pitch) of humps can become the controlling on volumes of extreme water drops. It is related to the different solid/liquid contact regions resulting in the as-modulated wet adhesion due to orientations of humps-on-strings. The conversion of high-low adhesion can be achieved to rely on orientations for the effect of capturing water drops. These studies offer an insight into enhancement of water collection efficiency and are helpful to design smart materials for controlled water drop capture and release via conversions of high-low adhesion.

A bioinspired study on the interlaminar shear resistance of helicoidal fiber structures

Helicoidal fibril structures are identified in many natural animals and plants. This research uses an integrated experimental and modeling approach to study the interlaminar shear resistance of bioinspired helicoidal fiber structures. First, helicoidal fiber-reinforced polymeric composites were created using 3D printed fiber cores and polymeric matrices, including plain, ring and helix reinforced helicoidal specimens. Then, monotonic torsional tests were performed to characterize the composite failure under interlaminar shear stresses, and fractographic characterization was conducted to elucidate corresponding fracture mechanisms in each specimen type. Finally, finite element modeling was performed to explore the critical factors on the interlaminar shear resistance of helicoidal fiber structures. The results showed that fiber-matrix modulus ratios and pitch angles of helix reinforcements played important roles on the interlaminar shear resistance of helicoidal fiber structures.

Controlling of water collection ability by an elasticity-regulated bioinspired fiber.

A special artificial spider silk is presented which is fabricated by using both an elastic polymer and a fiber, and the water collection behavior is investigated. Through exerting tension in varying degree, the length of the three-phase contact line (TCL) and the area of spindle knot can be regulated readily, which makes a great contribution to the improvement of collecting efficiency and water-hanging ability. The water-hanging ability can be predicted at a given stretching ratio according to the given expression of the TCL. As a result, liquid capture or release of distinct measure can be achieved via exerting tension. This research is helpful to design smart materials for developing applications in fogwater collection, dehumidification, high-efficiency humidity control, and controllable adhesion.

Modulus–density negative correlation for CNT-reinforced polymer nanocomposites: Modeling and experiments

Mechanical and weight properties of polymer nanocomposites (PNCs) are measured and modeled at the interlaminar region, predicting the density and elastic modulus of individual carbon nanotubes (CNTs). A simple model of the CNTs density and elastic modulus within the PNC, accounting for fundamental material properties, geometry, and interactions, is developed, capable of predicting CNT contributions in the PNCs. Furthermore, the model is validated with experimental results that demonstrate enhancement of the elastic modulus, while reducing density in the presence of aligned CNTs. By establishing an inverse relation of density and elastic modulus (negative correlation), it is demonstrated the potential of increasing mechanical properties while reducing weight. Therefore, by introducing controlled nanoporosity through suitable CNT distributions within the interlayer of multi-lamina structures, it is possible to simultaneously control effective weight reduction and enhanced modulus, toward bio-inspired carbon fiber reinforced polymer composites.

A bio-inspired flexible fiber array with an open radial geometry for highly efficient liquid transfer

Highly efficient liquid transfer is realized using an open radial glass fibers array bio-inspired by the dandelion pappus. The highly adhesive property and the elastic nature of the fiber, together with the large open angle between the fibers, endow the open radial fibers array the ability to encapsulate huge amount of water.

The optimal shape of elastomer mushroom-like fibers for high and robust adhesion.

Over the last decade, significant effort has been put into mimicking the ability of the gecko lizard to strongly and reversibly cling to surfaces, by using synthetic structures. Among these structures, mushroom-like elastomer fiber arrays have demonstrated promising performance on smooth surfaces matching the adhesive strengths obtained with the natural gecko foot-pads. It is possible to improve the already impressive adhesive performance of mushroom-like fibers provided that the underlying adhesion mechanism is understood. Here, the adhesion mechanism of bio-inspired mushroom-like fibers is investigated by implementing the Dugdale–Barenblatt cohesive zone model into finite elements simulations. It is found that the magnitude of pull-off stress depends on the edge angle θ and the ratio of the tip radius to the stalk radius β of the mushroom-like fiber. Pull-off stress is also found to depend on a dimensionless parameter χ, the ratio of the fiber radius to a length-scale related to the dominance of adhesive stress. As an estimate, the optimal parameters are found to be β = 1.1 and θ = 45°. Further, the location of crack initiation is found to depend on χ for given β and θ. An analytical model for pull-off stress, which depends on the location of crack initiation as well as on θ and β, is proposed and found to agree with the simulation results. Results obtained in this work provide a geometrical guideline for designing robust bio-inspired dry fibrillar adhesives.

Bioinspired wet-assembly fibers: from nanofragments to microhumps on string in mist

A bioinspired wet-assembly microhump fiber (BWMF) is successfully fabricated by employing the water coalescence-induced self-assembly of nanofragments attached on the fibers. The sizes and distances of the humps on the BWMF are easily controlled by regulating coalescence time and relative humidity. Furthermore, the strong water collecting ability of the BWMF is demonstrated. This finding is significant for fabricating smart materials with homo- or heterostructures at micro- and nano-levels that can be extended into realms such as microreactors, sensors, and fog harvesting.

Biophotonics: Bio‐Inspired Band‐Gap Tunable Elastic Optical Multilayer Fibers (Adv. Mater. 15/2013)

The back cover illustrates band-gap tunable bioinspired photonic fibers created by Peter Vukusic, Mathias Kolle, and co-workers on page 2239 that incorporate the structural key elements responsible for a tropical fruit's bright coloration. In the foreground a rendering of a gradually strained, colorchanging fiber is winding around another real fiber. The background features the cells in the fruit's skin.

Photo-controlled water gathering on bio-inspired fibers

We report photo-controlled water gathering on bio-inspired fibers. We have designed a bio-inspired fiber using azobenzene (Azo) polymer materials, with roughness and a curvature similar to the spindle-knots of wetted spider silk. We demonstrate that the cooperation between roughness and curvature and the photo-responsive wettability play a key role in water gathering after Vis or UV irradiation, which regulate effectively the separation of water droplets away from the spindle-knots or the coalescence towards the spindle-knots, respectively. This study offers an insight into the design of novel gradient surfaces that may drive tiny droplets to move in as-desired directions, which could potentially be extended to the realms of fluid-control in micro-scale engines, sub-micron masks, heat transfer, water-collecting devices and systems.

Preparation and heat-insulating property of the bio-inspired ZrO2 fibers based on the silk template

Natural silk fibers were used as the template to prepare biomorphic ZrO2 fibers. Silk fibers were first immersed into a Zr(NO3)4 solution and then sintered in air at high temperatures to produce the final ZrO2 fibers. Their microstructures, phases, synthesis process, infrared absorption spectra and thermal conductivity were analyzed. The results show that these synthesized fibers retained the morphologies of silk faithfully. These ZrO2 fibers also obtained the ability of absorbing infrared from the silk, so that they possessed better heat-insulating property than the traditional ZrO2 fibers.

Water Collection Behavior and Hanging Ability of Bioinspired Fiber

Since the water-collecting ability of the wetted cribellate spider capture silk is the result of a unique fiber structure, bioinspired fibers have been researched significantly so as to expose a new water-acquiring route in fogging-collection projects. However, the design of the geometry of bioinspired fiber is related to the ability of hanging drops, which has not been investigated in depth so far. Here, we fabricate bioinspired fibers to investigate the water collection behavior and the influence of geometry (i.e., periodicity of spindle knot) on the hanging-drop ability. We especially discuss water collection related to the periodicity of geometry on the bioinspired fiber. We reveal the length of the three phase contact line (TCL) at threshold conditions in conjunction with the maximal volume of a hanging drop at different modes. The study demonstrates that the geometrical structure of bioinspired fiber induces much stronger water hanging ability than that of uniform fiber, attributed to such special geometry that offers effectively an increasing TCL length or limits the contact length to be shorted. In addition, the geometry also improves the fog-collection efficiency by controlling tiny water drops to be collected in the large water drops at a given location.

Bioinspired spindle-knotted fibers with a strong water-collecting ability from a humid environment

We fabricate a bioinspired spindle-knotted fiber (BSF) via an improved method of Rayleigh instability break-up droplets. The BSF is composed of multi-level spindle-knots that can generate continuous gradients of surface energy and different Laplace pressures. We investigate the water collecting ability of BSF under humid environments and observe how the spindle-knots collect water from the environmental humidity by means of cooperative driving forces resulting from individual spindle-knots. We reveal that the multi-level spindle-knots of BSF may play a role in water collection compared with uniform fibers without any spindle-knots. We demonstrate that the size effect of a spindle-knot is related to the capillary adhesion of hanging-drops, thus BSF has a much higher water collection efficiency in humid environments than normal uniform fibers. The mechanism is elucidated further to open a model of high efficiency materials for water collection.

Bioinspired Fibers: Large‐Scale Fabrication of Bioinspired Fibers for Directional Water Collection (Small 24/2011)

Bioinspired Fibers: Large‐Scale Fabrication of Bioinspired Fibers for Directional Water Collection (Small 24/2011)

Bioinspired Fibers: Controlling Water Capture of Bioinspired Fibers with Hump Structures (Adv. Mater. 46/2011)

Bioinspired Fibers: Controlling Water Capture of Bioinspired Fibers with Hump Structures (Adv. Mater. 46/2011)

Large‐Scale Fabrication of Bioinspired Fibers for Directional Water Collection

Spider-silk inspired functional fibers with periodic spindle-knots and the ability to collect water in a directional manner are fabricated on a large scale using a fluid coating method. The fabrication process is investigated in detail, considering factors like the fiber-drawing velocity, solution viscosity, and surface tension. These bioinspired fibers are inexpensive and durable, which makes it possible to collect water from fog in a similar manner to a spider's web.

Controlling Water Capture of Bioinspired Fibers with Hump Structures

Geometrically engineered thin fibers that feature introduced hump structures similar to wetted spider capture silk greatly improve the adhesive ability to drops than uniform ones, which is attributed to an unusual three-phase contact line that extends axially along the fibers. The hump structures improve the stability of the contact line through a combination of "slope" and "curvature" effects, which creates sufficient capillary adhesion to pin drops.

Bioinspired Fibers Follow the Track of Natural Spider Silk

The mechanical behavior and microstructure of bioinspired fibers spun from solutions of recombinant spidroin-like proteins were extensively characterized, and compared with those of natural spider silk fibers. It is confirmed that high performance bioinspired fibers indistinguishable from natural spider silk up to large strains can be produced through genetic engineering and conventional spinning technologies. It is also found that fibers spun from spidroin-like proteins that contain different motifs of sequence exhibit variations in their microstructure in terms of crystallinity and chain alignment, but these differences are not reflected in distinct tensile properties. This similarity in terms of their mechanical behavior indicates that bioinspired fibers are largely independent of their exact sequence of recombinant proteins and, in particular, of their proline content. Finally, it is shown that the largest differences between natural and bioinspired fibers are found at very large deformations, marking the ultimate challenge in the synthesis of silk-like fibers.

Polymeric fibers with tunable properties: Lessons from spider silk

Making artificial fibers inspired in spider silks is considered as one of the milestones in the field of biomimetics. The interest is usually justified by the outstanding tensile properties of natural fibers, but it is usually overlooked that spider silk is endowed with a number of related properties – supercontraction, recovery and the existence of a ground state – that impart the material with additional desirable features, such as the possibility of tuning its mechanical behaviour. In this work we present a review on the experimental analysis and significance of these properties, stressing the contributions of our research group to the field. It is also demonstrated how the knowledge gained in the basic study of the natural material has been essential for the improvement of the properties exhibited by artificially processed bio-inspired silk fibers.

Similarities and Differences in the Supramolecular Organization of Silkworm and Spider Silk

The characterization of silkworm and spider silk from nanometer to micrometer scale by atomic force microscopy reveals similar design principles despite the distance of their spinning organisms in evolutionary terms. Nanoglobules are the basic microstructural blocks in both materials, but this common microstructural design is tuned to fulfill the biological function of each silk. Spider silk nanoglobules are isotropic, and its size varies during stretching. Silkworm silk nanoglobules are anisotropic and loosely aligned with the fiber axis. The combination of our results with previous data on the structure of silks at a molecular level allows a model of the supramolecular organization of both silkworm and spider silk to be proposed. The detailed characterization of the microstructure of natural silks should contribute to the development and production of a new family of bioinspired fibers.