Natural Porous Structures Research Articles

Photothermal Fish Gelatin-Graphene Microneedle Patches for Chronic Wound Treatment.

Microneedles are demonstrated as an effective strategy for chronic wound treatment. Great endeavors are devoted to developing microneedles with natural compositions and potent functions to promote therapeutic effects for wound healing. Herein, a novel graphene oxide-integrated methacrylated fish gelatin (GO-FGelMA) microneedle patch encapsulated with bacitracin and vascular endothelial growth factor (VEGF) is developed for chronic wound management. As the natural components and porous structures of FGelMA, the fabricated microneedle patches display satisfactory biocompatibility and drug-loading ability. Owing to the integration of graphene oxide, the microneedle patches can realize promoted drug release via near-infrared (NIR) irradiation. Besides, the encapsulated bacitracin and VEGF endow the microneedle patches with the ability to inhibit bacterial growth and promote angiogenesis. It is demonstrated that the GO-FGelMA microneedle patches with efficient drug release exert a positive influence on the wound healing process through reduced inflammation, enhanced wound closure, and improved tissue regeneration. Thus, it is believed that the proposed drugs-loaded GO-FGelMA microneedle patches will hold great potential in future chronic wound treatment.

Fluid Unidirectional Transport Induced by Structure and Ambient Elements across Porous Materials: From Principles to Applications.

Spontaneous or nonspontaneous unidirectional fluid transport across multidimension can occur under specific structural designs and ambient elements for porous materials. While existing reviews have extensively summarized unidirectional fluid transport on surfaces, there is an absence of literature summarizing fluid's unidirectional transport across porous materials. This review introduces wetting phenomena observed on natural biological surfaces or porous structures. Subsequently, it offers an overview of diverse principles and potential applications in this field, emphasizing various physical and chemical structural designs (surface energy, capillary size, topographic curvature) and ambient elements (underwater, under oil, pressure, and solar energy). Applications encompass moisture-wicking fabric, sensors, skincare, fog collection, oil-water separation, electrochemistry, liquid-based gating, and solar evaporators. Additionally, significant principles and formulas from various studies are compelled to offer readers valuable references. Simultaneously, potential advantages and challenges are critically assessed in these applications and the perspectives are presented.

Zwitterionic Hydrogel Coating with Antisediment Properties for Marine Antifouling Applications.

Biofouling is a serious issue affecting the marine industry because the attached micro- and macrocontaminants can increase fuel consumption and damage ship hulls. A hydrophilic hydrogel-based coating is considered a promising antifouling material because it is environmentally friendly and the dense hydration layer can protect the substrate from microbial attachment. However, sediment adsorption can be an issue for hydrogel-based coatings. Their natural soft and porous structures can trap sediment from the marine environment and weaken the antifouling capability. There is still little research on the antisediment properties of hydrogels, and none of them deal with this problem. Here, we report on optimizing zwitterionic hydrogel-based coatings to improve their antisediment properties and achieve comparable performance to commercial biocidal coatings, which are the gold standard in the antifouling coating area. After 1 week of sediment contamination and 2 weeks of diatom coculturing, this optimized zwitterionic hydrogel coating maintained its antifouling properties with a few diatoms on the surface. Its large-scale samples also achieved antifouling performance similar to that of biocidal coatings in the Atlantic Ocean for 1.5 months. More importantly, our research provides a universal strategy to improve the antisediment properties of soft hydrogel-based coatings. For the first time, we report that the introduction of interfacial electrostatic interactions enhanced the antisediment properties of hydrogels.

Multiple Cubes Growth Algorithms for Simple Representative Elementary Volume Determination on 3D Binary Images

Porosity analysis is fundamental for understanding various material properties and transport phenomena in scientific and engineering disciplines. This study delves into the challenging task of determining the representative elementary volume (REV) in porous media, crucial for accurate analyses. Two novel algorithms, Center-Corner Cubes Growing (3CG) and Random Cubes Growing (RCG), were proposed and tested on synthetic body-centered cubic (BCC) sphere packing and natural porous structures of Berea sandstone and Indiana limestone, obtained using µCT. First algorithm (3CG) operates by analyzing porosity within cubes growing from each of the eight corners and a central region of a 3D binarized stack. In contrast, the Random Cube Growing (RCG) algorithm randomly selects seed points within the 3D stack and grows cubic regions around them. Both algorithms systematically compute porosity for various cube sizes, determining the average porosity and standard deviation for each extent. These visual analytics tools contribute to identifying the specific size ranges where porosity curves converge and stabilize, indicating potential REV within the material. While 3CG simplifies the approach by focusing on a limited number of curves, RCG provides a broader view, capturing diverse porosity patterns. The absence of consistent local minima in certain cases indicates high porosity heterogeneity and the impossibility of achieving REV in certain sample sizes.

Thermal conductivity analysis of natural fiber-derived porous thermal insulation materials

Natural fibers, derived from plants such as wood, hemp, straw and cotton, have been explored for the fabrication of porous structures for thermal insulation applications due to their widespread availability, sustainability, and cost-effectiveness. Understanding the fundamental heat transfer mechanisms within natural fiber-derived porous structures is crucial for both optimized geometric design and real-world insulation applications. Herein, we developed a theoretical framework considering geometric parameters, including pore size, fiber diameter and porosity (i.e., density), to examine the contribution of various heat transfer modes (i.e., conduction, convection, and radiation) on the effective thermal conductivity of porous structures derived from natural fibers. Our results indicate that thermal radiation is largely responsible for the rapid increase in effective thermal conductivity of the natural fiber-derived porous insulations in low-density regions (< 50 kg/m3) and that natural convection rarely occurs within these materials. The insulation materials derived from natural fibers with diameters in the micron range (5–50 μm) can achieve their minimum thermal conductivity at an optimal density of 50–90 kg/m³. Effective strategies to lower the effective thermal conductivity of natural fiber-derived porous materials include increasing porosity to curtail solid conduction, incorporating nanoscale pores by using nanosize fibers to diminish gaseous thermal conductivity. This research offers valuable insights into the heat transfer mechanisms in natural fiber-derived materials and should guide the structural design and optimization process toward developing super-thermal insulation materials derived from natural fibers.

Preparation of carbon dots from carbonized corncobs by electrochemical oxidation and their application in Na-batteries

AbstractCarbon dots (CDs) have attracted increasing attention due to their high specific surface area, good dispersion, abundant surface functional groups, low biotoxicity and photoluminescence. However, their preparation on a large-scale is still a great challenge because of the high cost and environmental problems, and this seriously limits their practical applications. Carbonized corncobs were used as the starting material for the preparation of the CDs by electrochemical oxidation. Their natural porous structures with well-developed channels allow the electrode to be filled with electrolyte, and the electrochemical oxidation takes place both on the inside and outside surfaces of the corncob, achieving a CD output of 79.8 mg h−1 per gram of electrode material at 1 A. The CDs were combined with graphene oxide (GO) to produce CD/rGO composite aerogels by a hydrothermal method. After heat treatment at 600 °C, the materials obtained were used as the anode in a sodium ion battery, which had a capacity of 263.3 mAh g−1 after 1 000 cycles at 1 A g−1. This work suggests a new way to prepare CDs and possibly expand their range of application.

Impact of Temperature and Etching Methods on Surface Roughness, Topography, and Composition of Glass Micromodels

Fluid flow in porous media is affected by surface characteristics such as roughness and topography. In this work, to simulate the surface of natural porous structures in transparent interconnected media like micromodels, various degrees of roughness have been artificially created on flat glass substrates via different methods of laser ablation, cream etching, combination of laser ablation and cream etching, and hydrofluoric acid (HF) etching. The obtained surfaces by each method were characterized in detail via field emission scanning electron microscopy (FESEM), atomic force microscopy (AFM), energy-dispersive X-ray spectroscopy (EDX/EDS), and surface profilometry. The impact of high temperature, as often used during the thermal bonding step in micromodel fabrication, on the surface roughness and topography was also investigated. The results show that laser ablation leads to a homogenous distribution of roughness with an average value of 21.7 μm, not affected by temperature during the bonding step. In contrast, the chemical reaction of HF with the glass surface leads to a vast range of roughness values from 8.4 to 31.3 μm, with a heterogeneous distribution, varying with the exposure time. Applying etching cream on a laser-engraved surface reduces the previously created sharp hillocks as a result of a weak chemical reaction with the surface, resulting in a low roughness value of 5.5 μm. No significant changes were observed in the chemical composition of surfaces etched by the abovementioned methods, even in cases where a chemical reaction occurred on the surface, attributed to the water solubility of the reaction products. The novel findings of this study can be used for better controlling the surface characteristics in the fabrication of transparent porous structures to mimic the natural porous media and study the role of surface roughness and topography on fluid flow behavior.

Characterization of dynamic adsorption regimes in synthetic and natural porous structures using lattice Boltzmann simulations

This paper presents the first systematic study on the characterization of dynamic adsorption regimes of gas in porous media using the ratio of inter- to intraparticle diffusion coefficients. The effect of the ratio between the two diffusion coefficients on the adsorption dynamics was investigated in combination with the adsorbent particles size and the disorder parameter, which numerically describes pore space heterogeneity, by mathematical modelling using the lattice Boltzmann simulations for fluid flow and the convective-diffusive transport of an adsorbate dissolved in a fluid. To characterize the dynamic adsorption regimes, for the first time, a relationship between the surface and total adsorption amount was used. The obtained results during simulations in two-dimensional synthetic porous structures showed that the size of the adsorbent particle strongly affects the surface and the total adsorption dynamics. An increase in the particle size promotes an increase in the rate of surface adsorption. Depending on the ratio of inter- to intraparticle diffusion coefficients, increasing particle size promotes either an acceleration or slowdown of the total adsorption dynamics. The results revealed in two-dimensional structures were verified by simulations in three-dimensional digital models of natural sandstones, which were obtained using X-ray computed tomography.

Growth of oriented orthotropic structures with reaction/diffusion

Lattice structures can present advantageous mechanical properties while remaining remarkably lightweight. Precise lattice design can however be tricky to set up with classical 3D modeling methods as it involves very fine details. Interestingly, natural porous structures can present such lattice-like or membrane-like features which motivates to seek for more bio-inspired approaches to microstructure design. In this paper, we present a novel method to grow lattice-like and membrane-like structures within an arbitrary shape and aligned along an oriented field. Our method relies on the use of a dedicated anisotropic reaction–diffusion system guided by an orthotropic diffusion tensor field. Assuming for instance the diffusion tensor to be related to the stress analysis of a given shape allows to generate emerging stripes patterns aligned along each one of the principal stress directions independently. A globally coherent mechanical model conforming to the initial shape boundary and infilled with oriented microstructures can therefore be synthesized. Further, we demonstrate the capability of this approach to handle other types of oriented fields such as obtained through optimization of material directions in scenarios with multiple load cases. Our approach relies on spatially and temporally local operations allowing for efficient parallelization. This permits user-interaction and automated adaptation of the design, even for fine meshes over large volumes. For instance, a designer can locally erase or “draw” over the structure and let it regrow and adapt as well as enforce regions to be deliberately full or empty. The proposed approach yields smooth and conformal oriented anisotropic geometrical patterns. This is related to recent effort in the structural optimization community on the topic of optimized oriented infills and microstructure de-homogenization. One of the resulting designs is validated by means of a full scale general non-linear analysis showcasing the advantageous properties of oriented microstructures for stability and robustness to buckling.

Novel porous structures with non-cubic symmetry: Synthesis, elastic anisotropy, and fatigue life behavior

Natural porous structures are often anisotropic in their elastic properties, i.e., they have directional variations that are related to their topology and geometry. This paper presents the synthesis and simulation framework of novel families of non-cubic porous structures based on implicit modeling of cosine surfaces in the three-dimensional Euclidean space. The synthesis was performed using Field-Driven Design (FDD). An in-depth study of the elastic properties and simulated fatigue compression–compression behavior of a selection of five structures from the orthotropic anisotropy family is presented as case studies exposing the stretching-dominated mechanisms. The apparent properties characterized include Young’s modulus , Poisson’s ratio , shear modulus , bulk modulus , and relative density . A systematic approach to the characterization of average apparent properties was performed according to the schemes of Voigt, Reuss, and Hill. We show the anisotropic variation of the cosine surface–based porous structures using the Universal Elastic Anisotropy Index (AU) and compare it with six well-known triply periodic minimal surface (TPMS) structures by analyzing the stiffness tensor to validate and discuss which individual property (stiffness, rigidity, compressibility) has a higher impact on the final anisotropy value. We also provide a formal curvature analysis, based on the notions of mean and Gaussian curvatures to evidence the ridge-shaped surface in the structures. The proposed porous structures showed advantages when compared to cubic TPMS structures. From the data processing of the five analyzed porous structures, two synthesized structures have AU = 0.394 and 0.478, which are lower values than the structures based on Neovius and Schwarz’s Primitive surfaces with AU = 0.529 and 0.604. In addition, simulation results of cyclic compressive fatigue loading indicate that the fatigue resistance properties of the non-cubic porous structures are higher than the TPMS structures.

Self-template bagasse-based porous carbons for high performance supercapacitors

Developing the unique structure of biomass as a template is beneficial for promoting the commercial application of template-based hierarchical porous carbon materials. Herein, self-template bagasse-based porous carbons with high capacitance performance are successfully synthesized though low-temperature carbonization to fix the original vascular bundle structure of the bagasse and high-temperature activated carbonization to obtain hierarchical porous structures in the tube wall. As electrode materials for supercapacitors, the as-fabricated self-template porous carbons display a high specific surface of 1351.7 m2 g−1, abundant oxygen functional groups of 17.33%, an ultrahigh specific capacitance of 418.5 F g−1 at 0.5 A g−1 and a good rate performance of 63.1% at a current density ranging from 0.5 to 10 A g−1, which is mainly attributed to both natural and synthetic hierarchical porous structures in the obtained samples. Moreover, the self-template bagasse-based porous carbon devices also possess a remarkable energy density of 14.5 Wh kg−1 at 125 W kg−1 and good cycling stability of up to 98.9% after 10,000 cycles at 2 A g−1. The design strategy described in this work offers a method to further simplify the template synthesis steps, while improving the performance, of biomass-based hierarchical porous carbons. Therefore, these materials can be developed as high capacitance electrodes for energy storage applications.

Facile electrodeposition of Mn3O4 nanoparticles on wood-derived porous carbon for high-performance asymmetric supercapacitor

In this study, we report a facile method of anchoring Mn3O4 nanoparticles on the surface of wood-derived porous carbon via electrodeposition to enhance the specific capacitance and cycling performance of electrodes for supercapacitors. Owing to the synergistic effect of the natural tubular porous structures of wood-derived porous carbon and the high theoretical specific capacitance of Mn3O4, wood-derived porous carbon-Mn3O4 composites (WPC-Mn3O4) deliver a high specific capacitance (315 F g−1 at the current density of 1 A g−1) and an outstanding cycling stability (91% of maximum capacitance after 10,000 cycles at 10 A g−1) in 1 M Na2SO4 electrolyte. Furthermore, the WPC-Mn3O4 and activated carbon (AC) assembled asymmetric supercapacitor (ASC) WPC-Mn3O4//AC delivers a high energy density of 34.85 Wh kg−1 at 700.0 W kg−1, demonstrating a high applicability in practical energy storage devices. The resultant WPC-Mn3O4 composites with excellent electrochemical properties are expected to be used as a potential cathode material for the development of high-performance supercapacitors.

Controlling the Porosity and Biocidal Properties of the Chitosan-Hyaluronate Matrix Hydrogel Nanocomposites by the Addition of 2D Ti3C2Tx MXene.

A recent discovery of the unique biological properties of two-dimensional transition metal carbides (MXenes) resulted in intensive research on their application in various biotechnological areas, including polymeric nanocomposite systems. However, the true potential of MXene as an additive to bioactive natural porous composite structures has yet to be fully explored. Here, we report that the addition of 2D Ti3C2Tx MXene by reducing the porosity of the chitosan-hyaluronate matrix nanocomposite structures, stabilized by vitamin C, maintains their desired antibacterial properties. This was confirmed by micro computed tomography (micro-CT) visualization which enables insight into the porous structure of nanocomposites. It was also found that given large porosity of the nanocomposite a small amount of MXene (1–5 wt.%) was effective against gram-negative Escherichia coli, gram-positive Staphylococcus aureus, and Bacillus sp. bacteria in a hydrogel system. Such an approach unequivocally advances the future design approaches of modern wound healing dressing materials with the addition of MXenes.

Synthetic and Marine-Derived Porous Scaffolds for Bone Tissue Engineering.

Bone is a vascularized and connective tissue. The cortical bone is the main part responsible for the support and protection of the remaining systems and organs of the body. The trabecular spongy bone serves as the storage of ions and bone marrow. As a dynamic tissue, bone is in a constant remodelling process to adapt to the mechanical demands and to repair small lesions that may occur. Nevertheless, due to the increased incidence of bone disorders, the need for bone grafts has been growing over the past decades and the development of an ideal bone graft with optimal properties remains a clinical challenge. This review addresses the bone properties (morphology, composition, and their repair and regeneration capacity) and puts the focus on the potential strategies for developing bone repair and regeneration materials. It describes the requirements for designing a suitable scaffold material, types of materials (polymers, ceramics, and composites), and techniques to obtain the porous structures (additive manufacturing techniques like robocasting or derived from marine skeletons) for bone tissue engineering applications. Overall, the main objective of this review is to gather the knowledge on the materials and methods used for the production of scaffolds for bone tissue engineering and to highlight the potential of natural porous structures such as marine skeletons as promising alternative bone graft substitute materials without any further mineralogical changes, or after partial or total transformation into calcium phosphate.

Pressure Sensors: Highly Sensitive Pressure Sensor Based on Bioinspired Porous Structure for Real‐Time Tactile Sensing (Adv. Electron. Mater. 12/2016)

S. Kang et al. report a flexible and highly sensitive pressure sensor developed using a highly deformable dielectric layer inspired by natural porous structures in article number 1600356. This sensor exhibits an outstanding sensitivity, fast response, and high stability. It is successfully integrated into an array and applied to fabricate a real-time tactile sensing platform.

Highly Sensitive Pressure Sensor Based on Bioinspired Porous Structure for Real‐Time Tactile Sensing

A flexible pressure sensor with high performances is one of the promising candidates for achieving electronic skins (E‐skin) related to various applications such as wearable devices, health monitoring systems, and artificial robot arms. The sensitive response for external mechanical stimulation is fundamentally required to develop the E‐skin which imitates the function of human skin. The performance of capacitive pressure sensors can be improved using morphologies and structures occurring in nature. In this work, highly sensitive capacitive pressure sensors based on a porous structure of polydimethylsiloxane (PDMS) thin film, inspired on the natural multilayered porous structures seen in mushrooms, diatoms, and spongia offilinalis, have been developed and evaluated. A bioinspired porous dielectric layer is used, resulting in high‐performance pressure sensors with high sensitivity (0.63 kPa−1), high stability over 10 000 cycles, fast response and relaxation times, and extremely low‐pressure detection of 2.42 Pa. Additionally, the resulting pressure sensors are demonstrated to fabricate multipixel arrays, thus achieving successful real‐time tactile sensing of various touch shapes. The developed high‐performance flexible pressure sensors may open new opportunities for innovative applications in advanced human‐machine interface systems, robotic sensory systems, and various wearable health monitoring devices.

Synthesis and characterization of 3D MnO2/carbon microtube bundle for supercapacitor electrodes

A simple and scalable method was developed to fabricate MnO2/carbon composites that contained carbon microtube bundles (CMB) produced from sawdust and 3D nanostructured MnO2 by anodic electrodeposition. The 3D-MnO2/CMB composites exhibited excellent electrochemical performance because of the synergistic effect between the natural tubular porous structures of charred materials from sawdust. The high conductivity of these composites provided sufficient space for the MnO2 deposition and the high theoretical specific capacitance of MnO2. The composites had a high specific capacitance of 617.6F/g at the current density of 1A/g based on the mass of MnO2 and outstanding cycle performance. Thus, this hybrid is a potential competitive candidate for developing supercapacitors.

Oxygen transmission of modified natural rubber, poly (lactic acid) and chitosan porous structures for wound dressing

Oxygen transmission of modified natural rubber, poly (lactic acid) and chitosan porous structures for wound dressing

Water Resistance and Mechanical Properties of Modified Porous Carbon Materials Made from Rice Hull

Recently, new porous carbon materials have been developed utilizing the natural porousstructures of some plant matters. The carbon materials are manufactured by mixing with a phenol resin, pressure forming, drying, and then carbonizing at 900°C. The authors have been studied the carbon material made from the defatted rice bran (RB carbon). However, the RB carbon includes some deliquescent components, and therefore has large hygroscopic expansion and large reduction of the mechanical strengths under wet and aquatic conditions. The low water resistance is associated with the inorganic components of P and K in the rice bran. In contrast, the rice hull does not contain such inorganic components. In this study, the authors proposed the production of the water-resistant rice-hull silica carbon (RHS carbon) from the rice hull and the correcting methods of the low water resistance for the RB carbon. The RHS carbon has low hygroscopic expansion and no reduction of the compressive strengths under aquatic conditions.

Heterogeneous porous media as multiscale structures for maximum flow access

Natural porous structures are heterogeneous with multiple scales that are distributed nonuniformly. Few large pores (fissures, channels, and cracks) are accompanied by numerous finer channels. Can this type of flow architecture be attributed to a principle of maximization of global flow access? Features similar to those of multiscale porous structures are exhibited by tree-shaped flow structures. Trees have been deduced from the maximization of flow access between a point and a volume, a point and an area, and a point and a curve (e.g., circle). In this paper we invoke the same principle and consider fundamentally the question of how to bathe with minimal flow resistance a microchannel structure that globally behaves as a porous medium. We develop completely multiscale configurations that guide the flow from one side of the porous structure to the other (line to line and plane to plane) and show analytically the advantages of tree structures over the usual stacks of parallel microchannels. The “porous medium” that has tree-shaped labyrinths is heterogeneous, with multiple scales that are distributed nonuniformly. These features justify comparisons with the design of natural porous structures.