Elastic Sponges Research Articles

Low-/Negative-Pressure Hydrocephalus: To Understand the Formation Mechanism from the Perspective of Clinicians.

Low-/negative-pressure hydrocephalus (LPH/NePH) is uncommon in clinical practice, and doctors are unfamiliar with it. LPH/NePH is frequently caused by other central nervous system diseases, and patients are frequently misdiagnosed with other types of hydrocephalus, resulting in delayed treatment. LPH/NePH therapy evolved to therapeutic measures based on "external ventricular drainage below atmospheric pressure" as the number of patients with LPH/NePH described in the literature has increased. However, the mechanism of LPH/NePH formation is unknown. Thus, understanding the process of LPH/NePH development is the most important step in improving diagnosis and treatment capability. Based on case reports of LPH/NePH, we reviewed theories of transcortical pressure difference, excessive cerebral venous drainage, brain viscoelastic changes, and porous elastic sponges.

Wet-Stable Lamellar Wood Sponge with High Elasticity and Fatigue Resistance Enabled by Chemical Cross-Linking.

The excessive consumption of fossil-based plastics and the associated environmental concerns motivate the increasing exploitation of sustainable biomass-based materials for advanced applications. Natural wood-derived lamellar wood sponges via a top-down approach have recently attracted significant attention; however, the insufficient compressive fatigue resistance and lack of structural stability in water limit their wide applications. Here, we report a facile chemical cross-linking strategy to tackle these challenges, by which the cellulose fibrils in the lamellas are covalently bridged to enhance their connectivity. The cross-linked wood sponges demonstrate high compressibility up to 70% strain and exceptional compressive fatigue resistance (∼5% plastic deformation after 10,000 cycles at 50% strain). The interfibrillar cross-linking inhibits the swelling of cellulose fibrils and preserves the arch-shaped lamellas of the sponge in water, endowing the wood sponge with excellent wet stability. Such highly elastic and wet-stable lamellar wood sponges offer a sustainable alternative to synthetic polymer-based sponges used in diverse applications.

Polypyrrole@CNT@PU Conductive Sponge-Based Triboelectric Nanogenerators for Human Motion Monitoring and Self-Powered Ammonia Sensing.

Elastic sponges are ideal materials for triboelectric nanogenerators (TENGs) to harvest irregular and random mechanical energy from the environment. However, the conductive design of the elastic materials in TENGs often limits its applications. In this work, we have demonstrated that an elastic conductive sponge can be used as the triboelectric layer and electrode for TENGs. Such an elastic conductive sponge is prepared by a simple way of adsorbing multiwalled carbon nanotubes and monomers of pyrrole to grow conductive polypyrroles on the surface of an elastic polyurethane (PU) sponge. Due to the porous structure of the PU sponge and the conductive multiwalled carbon nanotubes (MWCNTs), PPy on the surface of PU could provide a large contact area to improve the output performance of TENGs, and the conductive sponge-based TENG could generate an output of open-circuit voltage of 110 V or a short-circuit current of 12 μA, respectively. The good flexibility of the conductive PU sponge makes the TENG harvest the kinetic energy of disordered motion with different amplitudes, allowing for human motion monitoring. Furthermore, the porous structure of PU and the synergistic effects of PPy and MWCNTs enable the conductive sponge to sense NH3 as a self-powered NH3 sensor. This work offers a simple way to construct a flexible TENG system for random mechanical energy harvesting, human motion monitoring, and self-powered NH3 sensing.

Surface fabrication of silica aerogels from inorganic precursor achieving elastic and superhydrophobic sponges for oil-water separation

Some challenges exist in oil-water separation materials, including complex synthesis, high preparation costs, and weak recovery. Herein, the elastic and superhydrophobic silica aerogels/polyurethane sponges (SA/PUS) were prepared by fabricating silica aerogels (SA) on the skeleton of the cheap polyurethane sponges (PUS), through a simple dipping and sol-gel method under ambient pressure drying procedure. Importantly, boosted by the inorganic silicon precursors, the dense and rough coating by the functionalized SA on the surface was realized under environmentally friendly modification and adhesive-free, which contributed to the superhydrophobicity of the SA/PUS. The splendid thermal stability allowed the SA/PUS to maintain a hydrophobic property at high temperatures (over the flash point of the oil in this work). The excellent adsorption performance was confirmed on both oil/water mixture (11 times own weight) and oil-in-water emulsion (separation efficiency up to 98.78%). Moreover, the elastic SA/PUS could recover from large-scale deformations owing to the combination with the PUS with a three-dimensional skeleton, which improved the mechanical strength and overcome the limitation of the brittle SA. The recovery efficiency of the adsorbed oil from oil/water mixture was 92.70% and nearly no decline in reusing by simple mechanical squeezing. Such excellent performance was also demonstrated in oil-in-water emulsion. Advantages (superhydrophobic and lipophilic, elastic, and thermal stability, etc.) of the SA/PUS, which were prepared by simple synthesis, bring application potential for treating automobile maintenance sewages and expanded applications, including separation and recovery of oil from oily wastewater circularly and uptake of high-value-added hydrophobic molecules in biomass or other processes.

B-line Elastography Measurement of Lung Parenchymal Elasticity.

This paper proposes a method to determine the elasticity of the lung parenchyma from the B-line Doppler signal observed using continuous shear wave elastography, which uses a small vibrator placed on the tissue surface to propagate continuous shear waves with a vibration frequency of approximately 100 Hz. Since the B-line is generated by multiple reflections in fluid-storing alveoli near the lung surface, the ultrasonic multiple-reflection signal from the B-line is affected by the Doppler shift due to shear waves propagating in the lung parenchyma. When multiple B-lines are observed, the propagation velocity can be estimated by measuring the difference in propagation time between the B-lines. Therefore, continuous shear wave elastography can be used to determine the elasticity of the lung parenchyma by measuring the phase difference of shear wave between the B-lines. In this study, three elastic sponges (soft, medium, and hard) with embedded glass beads were used to simulate fluid-storing alveoli. Shear wave velocity measured using the proposed method was compared with that calculated using Young's modulus obtained from compression measurement. Using the proposed method, the measured shear wave velocities (mean ± S.D.) were 3.78 ± 0.23, 4.24 ± 0.12, and 5.06 ± 0.05 m/s for soft, medium, and hard sponges, respectively, which deviated by a maximum of 5.37% from the values calculated using the measured Young's moduli. The shear wave velocities of the sponge phantom were in a velocity range similar to the mean shear wave velocities of healthy and diseased lungs reported by magnetic resonance elastography (3.25 and 4.54 m/s, respectively). B-line elastography may enable emergency diagnoses of acute lung disease using portable ultrasonic echo devices.

A green strategy to recycle the waste PP melt-blown materials: From 2D to 3D construction

The demand for polypropylene (PP) melt-blown materials has dramatically increased due to the COVID-19 pandemic. It has caused serious environmental problems because of the lack of effective treatment for the waste PP melt-blown materials. In this study, we propose a green and sustainable recycling method to create PP sponges from waste PP melt-blown material for oil spill cleaning by freeze-drying and thermal treatment techniques. The recycling method is simple and without secondary pollution to the environment. The developed recycling method successfully transforms 2D laminar dispersed PP microfibers into elastic sponges with a 3D porous structure, providing the material with good mechanical properties and promotes its potential application in the field of oil spill cleaning. The morphology structure, thermal properties, mechanical properties, and oil absorption properties are tested and characterized. The PP sponges with a three-dimensional porous network structure show an exceedingly low density of >0.014 g/cm3, a high porosity of <98.77 %, and a high water contact angle range of 130.4–139.9°. Moreover, the PP sponges own a good absorption capacity of <47.61 g/g for different oil and solvents. In particular, the compressive modulus of the PP sponges is 33.59–201.21 kPa, which is higher than that of most other fiber-based porous materials, indicating that the PP sponges have better durability under the same force. The excellent comprehensive performance of the PP sponges demonstrates the method developed in this study has large application potential in the field of the recycle of waste PP melt-blown materials.

Carrier type affects anammox community assembly, species interactions and nitrogen conversion

The impacts of carrier type on anammox community assembly, species interactions and nitrogen conversion were studied in this work. It was found that in addition to shared species with higher abundance, different carrier types recruited rare species by imposing selection pressure. Results from co-occurrence networks revealed that carrier type strongly influenced interactions between keystone species inhabiting within anammox biofilm through potentially inducing niche differences. Overall, elastic cubic sponges would lead to closer cooperation between different populations, whereas plastic hollow cylinders would trigger fiercer competition. Meanwhile, the results based on metagenomics sequencing showed carrier type significantly affected nitrogen conversion related genes abundances, and higher reads number was detected on the elastic cubic sponges. The information obtained in this work could provide some valuable information for the selection and optimization of carrier type in the anammox process.

Fabrication of Mechanically Robust and Highly Elastic Epoxy Sponges via Surface Embedding of Nanoparticles for Long-Term Oil/Water Separation

Nanoparticles have been extensively utilized to improve the mechanical robustness, compressibility, wettability, and oil/water separation properties of polymeric sponges due to their advantages of significant effects, ease of operation, and cost-effectiveness. In this work, small quantities of SiO2, TiO2, and La2O3 nanoparticles were embedded in the surface of the epoxy/polyether amine (PEA) sponge skeleton by the mold transfer approach to improve the mechanical stability, compressibility, and oil/water separation efficiency of epoxy/PEA sponges. Embedding a small number of SiO2 and TiO2 nanoparticles improved the compressibility apparently, while the mechanical stability was weakened, ascribed to the aggregation of SiO2 and TiO2 nanoparticles at the skeleton surface. Continuously increasing the embedding content caused a rapid reduction in compressibility. In contrast, embedding La2O3 nanoparticles in epoxy/PEA ensured that the sponges returned to their original size after 100 cycles of compressive test under 80% strain (high compressibility) and maintained the network under a maximum compressive strength of 15.75 MPa after 15 cycles, indicating outstanding mechanical stability. Continuously increasing the embedding content of La2O3 generated negligible effects on the mechanical stability, while the elasticity dropped slightly. Embedding a small amount of La2O3 nanoparticles changed the curing reaction heat of epoxy/PEA and resulted in the formation of nanolayer structures, which offset the applied pressure and deformation. Embedding La2O3 nanoparticles increased the surface roughness, resulting in high hydrophilicity and underwater superoleophobicity, thereby delivering high oil/water separation properties. The reported method might therefore open a new avenue for the fabrication of highly elastic and mechanically robust oil/water separation polymer sponges.

Highly Elastic and Fatigue-Resistant Graphene-Wrapped Lamellar Wood Sponges for High-Performance Piezoresistive Sensors

Three-dimensional (3D) conductive aerogels with structural robustness and mechanical resilience are highly attractive for sensitive and stable pressure sensing. However, the fabrication of such 3D aerogels often relies on complicated bottom-up assembly processes that involve costly raw materials or intensive energy consumption or directly coating synthetic polymer sponges (e.g., polyurethane) with conductive materials, which may pose environmental concerns for their disposal. Herein, a simple and sustainable strategy is proposed to fabricate a reduced graphene oxide-coated wood sponge (RGO@WS) with a lamellar structure for high-performance piezoresistive sensors. The introduced RGO nanosheets endow the RGO@WS not only with high conductivity but also with high elasticity and excellent fatigue resistance. These features make it an ideal piezoresistive sensor with a high sensitivity of 0.32 kPa–1 (superior to most polymeric sponge-based sensors), high working stability over 10 000 cycles, and excellent sensing reproducibility at ultralow temperatures. Thanks to its prominent sensing performance, the RGO@WS-based sensor can serve as a wearable device for detecting human motions and physiological signals and allows for spatially resolved pressure mapping via integrating the sensors into a large-area sensing array. The developed highly elastic and fatigue-resistant RGO@WS represents a promising and sustainable alternative to the synthetic polymer-based piezoresistive sensors.

Elastic, super-hydrophobic and biodegradable chitosan sponges fabricated for oil/water separation

Due to easy availability and biodegradability, chitosan (CS)-based porous adsorbents have attracted significant interest in oil-spill and organic solvent removal. Herein, a multi-network CS-based sponge was fabricated via ion and hydrogen bond cross-linking using lemon, followed by covalent cross-linking via heptanal, in-situ loading of Fe3O4-polydopamine (PDA) particles and polylactic acid (PLA) coating. The as-fabricated sponge was systematically characterized by Fourier transform-infrared spectrometry (FT-IR), X-ray diffraction (XRD), vibrating sample magnetometer (VSM), X-ray photoelectron spectroscopy (XPS), scanning electron microscope (SEM), transmission electron microscope (TEM), static water contact angles (WCA) and so on. The as-fabricated CS-based sponge exhibits excellent elasticity, which could be compressed to large strains (80%) at a relatively high stress (0.685 MPa). The WCA of the targeted sponge can reach to 152.2 ± 1.2º after multiple surface functionalization. In addition, the degradation rate of the as-fabricated sponge can still reach 45.01 ± 1.11% within 15 days. Particularly, the sponge could selectively adsorb oil/organic solvent with up to 50 times of its own weight, and effectively separate the surfactant-stabilized oil-in-water emulsion with a flux of 8753 ± 423.56 L m−2 h−1. Last but not least, the sponge can be driven and recycled magnetically. In conclusion, this promising multifunctional sponge can be applied as a new absorbent for oil-water separation.

Superhydrophobic and elastic 3D conductive sponge made from electrospun nanofibers and reduced graphene oxide for sweatproof wearable tactile pressure sensor

Herein, we report an innovative method to produce three-dimensional (3D), elastic, and conductive nanofibrous sponges with high sensitivity, great mechanical properties, and sweatproof feature for wearable tactile pressure sensor. The 3D sponges were prepared by assembling the shortened polyacrylonitrile/polyimide (PAN/PI) electrospun nanofibers and reduced graphene oxide (rGO) nanosheets. In specific, the PAN/PI nanofibers and graphene oxide (GO) nanosheets were mixed in aqueous circumstance first and then freeze dried to form a 3D porous sponge. Subsequently, the sponge was thermally treated at 100 °C and 210 °C successively to reduce the GO nanosheets to conductive rGO nanosheets. Thereafter, the polydimethylsiloxane (PDMS) treatment was carried out to provide the sponge with elasticity/robustness and hydrophobicity. Upon varying the amount of rGO, three types of sponges were fabricated to study their mechanical and electrical properties. The obtained 3D conductive sponge with the most rGO amount (3-rGO/NF) possessed light weight (11.50 mg/cm3) and high porosity (99.23%). The mechanical strength and current change ratio during the cyclic compression process were investigated, and the results were closely correlated with the amount of rGO existed in the sponge. The 3-rGO/NF had the largest current change ratio when compressed, leading to the highest sensitivity even at a relatively small compressive strain. It is important to note that the prepared 3D conductive sponges were sensitive, bendable, and sweatproof, which would be particularly suitable for making wearable tactile pressure sensors.

Highly elastic conductive sponges by joule heat-driven selective polymer reinforcement at reduced graphene oxide junctions

Polymer reinforcement of reduced graphene oxide (rGO) sponges is widely employed to enhance mechanical strength and elasticity. However, the surplus polymer decreases electrical conductivity by passivating the conductive surface of rGO flakes. Here we firstly report the selective polydimethylsiloxane (PDMS) reinforcement at the flake junction of rGO sponge by the Joule heating process utilizing the high electrical contact resistance. The preferential Joule heating of the junction is theoretically simulated by finite element modeling and experimentally confirmed by micro-thermal infrared imaging. The local temperature increase results in the further reduction of rGO and preferential PDMS curing at the flake junction only. The PDMS/rGO mass ratio was carefully optimized at 3.96. The electrical conductivity (0.087 S m−1 at 0% strain) is more than an order of magnitude higher than that (0.00251 S m−1) of the conventional oven-heated sponge with a similar PDMS/rGO mass ratio. The mechanical strength is equivalent (210.3 kPa at 70% strain), in spite of the preferential polymer coating at the rGO flake junction only, with excellent elasticity. The Joule heating method is an excellent curing strategy to selectively reinforce flake junctions for conductive elastic rGO-polymer sponges.

Elastic Cu@PPy sponge for hybrid device with energy conversion and storage

Elastic and electrical conductive sponges are attracting materials for energy storage and energy harvest devices. In this study, we have demonstrated that a flexible and durable Cu doped PDMS sponge (Cu) can be adopted as electrodes for triboelectric nanogenerators (TENG) and flexible supercapacitors (SC). The Cu sponge loading with polypyrrole (PPy) was newly applied as single-electrode TENG for the first time. The outputs of the TENG were tuned by varying the PPy content or by combining with PDMS sponge. Due to the feasibility of changing the PPy content in the Cu@PPy sponges, this study offers a facile way to enhance the performance of TENG from the material itself with a tunable manner. Moreover, this study potentiates a better understanding of the triboelectricity produced by the TENG from the view of materials. The Cu@PPy sponges were further utilized as electrodes for all solid-state symmetrical SCs, in which the Cu sponge and PPy showed a synergistic effect on promoting the stability and performance of the SC. The SC exhibits lightweight, good capacitance, high flexibility, excellent mechanical and long-term stability, which is suitable for wearable energy storage devices. For the application of the TENG and the SC, a self-powered hybrid device was assembled, which provides a prospect for integrated devices. As a summary, we reported a new metal sponge based TENG and self-powered hybrid device, which demonstrated our study provides new opportunities for elastic multifunctional power sources and potential applications in wearable electronics.

Elastic three-dimensional graphene sponge fabricated by the liquid crystals of controlled large graphene oxide sheets

Three-dimensional graphene (3DG) sponge has attracted increasing attention because it combines the unique properties of cellular materials and the excellent performance of graphene. Preparation of 3DG sponge depends mainly on the self-assembly of graphene oxide sheets. In the case of using uniform large graphene oxide and ultralarge graphene oxide sheets, the nematic liquid crystals (LCs) phases are formed at low concentration. After chemical reduction, the LCs of GO solution are converted to 3DG sponges with a high degree of orientation, offering a new methodology to regulate the controlled large GO sheets. The orientation of GO solution can be inherited by 3DG sponge, making the sponge to have a large-scale ordered network structure. The 3D elastic graphene sponges have low density and good elasticity, promising for the applications in strain sensing, shock damping, and energy cushioning. Our work explores a novel strategy for organizing the ordered alignment of controlled large GO sheets and exploring the relationship between the microstructures and mechanical properties of 3DG sponge.

Single-Particle Tracking To Probe the Local Environment in Ice-Templated Crosslinked Colloidal Assemblies

We use single-particle tracking to investigate colloidal dynamics in hybrid assemblies comprising colloids enmeshed in a crosslinked polymer network. These assemblies are prepared using ice templating and are macroporous monolithic structures. We investigate microstructure-property relations in assemblies that appear chemically identical but show qualitatively different mechanical response. Specifically, we contrast elastic assemblies that can recover from large compressive deformations with plastic assemblies that fail on being compressed. Particle tracking provides insights into the microstructural differences that underlie the different mechanical response of elastic and plastic assemblies. Since colloidal motions in these assemblies are sluggish, particle tracking is especially sensitive to imaging artifacts such as stage drift. We demonstrate that the use of wavelet transforms applied to trajectories of probe particles from fluorescence microscopy eliminates stage drift, allowing a spatial resolution of about 2 nm. In elastic and plastic scaffolds, probe particles are surrounded by other particles-thus, their motion is caged. We present mean square displacement and van Hove distributions for particle motions and demonstrate that plastic assemblies are characterized by significantly larger spatial heterogeneity when compared with the elastic sponges. In elastic assemblies, particle diffusivities are peaked around a mean value, whereas in plastic assemblies, there is a wide distribution of diffusivities with no clear peak. Both elastic and plastic assemblies show a frequency independent solid modulus from particle tracking microrheology. Here too, there is a much wider distribution of modulus values for plastic scaffolds as compared to elastic, in contrast to bulk rheological measurements where both assemblies exhibit a similar response. We interpret our results in terms of the spatial distribution of crosslinks in the polymer mesh in the colloidal assemblies.

A two-step hydrophobic fabrication of melamine sponge for oil absorption and oil/water separation

Hydrophobic sponges have drawn great attention recently as potential absorption materials for oil spill cleanup and water/oil separation due to their excellent elasticity, absorptivity and selectivity. Herein, we demonstrate a facile and cost-effective method to fabricate hydrophobic sponges based on commercial melamine sponge via a two-step process, i.e., silica nanoparticle adsorption and silanization covering procedures. The hydrophobic modification was confirmed by ATR-FTIR and SEM characterization. The modified sponge shows hydrophobicity and oleophilicity and exhibited excellent absorption capacity for various oils and organic solvents (60–109 g/g). Interestingly, this modified sponge displays great endurability towards ultrasonication or at acid/alkali circumstance, and presents remarkable reusability after 12 cycles of absorption-squeezing process. In addition, a piece of modified sponge can be employed for continuous collecting of oil/solvent from water by using a simple collection device. These hydrophobic, elastic, and durable melamine sponges are very promising materials for practical oil absorption and oil/water separation.

Elastic Sponges: Hydrophilic Sponges for Leaf‐Inspired Continuous Pumping of Liquids (Adv. Sci. 6/2017)

In article number 1700028, Xuechang Zhou and co‐workers describe a leaf‐like pumping strategy by mimicking the transpiration process through leaves for autonomous and continuous liquid transport enabled by durable hydrophilic sponges. Highly‐defined flow patterns, chemical gradients, and “stop‐flow” manipulation of the flow were achieved by simply integrating the sponges to microfluidic devices.

Surface Chemistry: Superamphiphobic, Magnetic, and Elastic Silicone Sponges with Excellent Temperature Stability (Adv. Mater. Interfaces 23/2016)

Surface Chemistry: Superamphiphobic, Magnetic, and Elastic Silicone Sponges with Excellent Temperature Stability (Adv. Mater. Interfaces 23/2016)

The Template Determines Whether Chemically Identical Nanoparticle Scaffolds Show Elastic Recovery or Plastic Failure.

Subtle variations in the preparation of ice-templated nanoparticle assemblies yield monoliths that are chemically identical but exhibit qualitatively different mechanical behavior. We ice template aqueous dispersions to prepare macroporous monoliths largely comprising silica nanoparticles held together by a crosslinked polymer mesh. When the polymer is crosslinked in the presence of ice crystals, we obtain an elastic sponge that is capable of recovery after imposition of large compressive strains (up to 80%). If, however, the ice is lyophilized before the polymer is crosslinked, we obtain a plastic monolith that fails even for modest strains (less than 10%). The elastic sponge and the plastic monolith are chemically identical; they have the same organic content, the same ratio of polymer to crosslinker, and the same average crosslink density. Atomic force microscopy (AFM) was used to probe the local mechanical properties of the crosslinked polymer mesh. These measurements indicate that plastic monoliths dissipate significantly more energy and have a larger spatial variation in local mechanical response relative to the elastic sponges. We believe that this behavior might correlate with a wider spatial distribution of crosslinks in plastic scaffolds relative to elastic scaffolds.

Superamphiphobic, Magnetic, and Elastic Silicone Sponges with Excellent Temperature Stability

It is very challenging to create bioinspired superamphiphobic 3D porous materials that resist wetting of organic liquids with low surface tension. Here, preparation of superamphiphobic, magnetic, and elastic (SAME) silicone sponges is reported with excellent temperature stability. The SAME silicone sponges are prepared by hydrolytic condensation of methyltrimethoxysilane and dimethoxydimethylsilane in the presence of urea, n‐hexadecyltrimethyl ammonium bromide, and the Fe3O4@SiO2 nanoparticles, followed by surface modification with 1H,1H,2H,2H‐perfluorodecyltriethoxysilane (PFDTES) and tetraethoxysilane (TEOS). The SAME silicone sponges are characterized using a wide range of analytical techniques including scanning electron microscopy, X‐ray photoelectron spectroscopy, and thermal gravimetric analysis. It is found that the wettability of the SAME silicone sponges can be controllable simply by regulating their surface topography and surface chemical composition, in other words, the volume ratio of PFDTES and TEOS. The residual silanol groups on the pore surface of the silicone sponge act as the active sites for the hydrolytic condensation of PFDTES and TEOS. The SAME silicone sponges feature excellent superamphiphobicity for water and various organic liquids of low surface tension, fast magnetic responsiveness, high compressibility (90%), and stretchability (35%) as well as high stability in a wide range of temperature (−196–300 °C).