Biological Template Research Articles

Biotemplated facile synthesis of three‐dimensional micro/nanoporous tin oxide: improving the flammable and mechanical properties of flexible PVC

In this study, a flame retardant [Pollen-type SnO2 (P-SnO2)] with a micro/nanoporous structure was synthesised by the simple immersion–calcination method using pollen as a biological template. When applied into flexible polyvinyl chloride (PVC), PVC composite adding P-SnO2 (PVC/P-SnO2) exhibited much better mechanical property than that adding commercial SnO2 (PVC/[C-type SnO2 (C-SnO2)] for the results that the tensile strength and impact toughness are increased by 11.3 and 37.9%, respectively. Moreover, PVC/P-SnO2 has always the same flame retardancy and smoke suppression abilities compared with PVC/C-SnO2. It provides a method using biotemplate for preparing metal oxide flame retardants with both great flame retardant and toughening properties.

Molecularly Imprinted Materials for Selective Biological Recognition.

Molecular imprinting is an approach of generating imprinting cavities in polymer structures that are compatible with the target molecules. The cavities have memory for shape and chemical recognition, similar to the recognition mechanism of antigen-antibody in organisms. Their structures are also called biomimetic receptors or synthetic receptors. Owing to the excellent selectivity and unique structural predictability of molecularly imprinted materials (MIMs), practical MIMs have become a rapidly evolving research area providing key factors for understanding separation, recognition, and regenerative properties toward biological small molecules to biomacromolecules, even cell and microorganism. In this review, the characteristics, morphologies, and applicability of currently popular carrier materials for molecular imprinting, especially the fundamental role of hydrogels, porous materials, hierarchical nanoparticles, and 2D materials in the separation and recognition of biological templates are discussed. Moreover, through a series of case studies, emphasis is given on introducing imprinting strategies for biological templates with different molecular scales. In particular, the differences and connections between small molecular imprinting (bulk imprinting, "dummy" template imprinting, etc.), large molecular imprinting (surface imprinting, interfacial imprinting, etc.), and cell imprinting strategies are demonstrated in detail. Finally, future research directions are provided.

Flexible Self-Cleaning Broadband Antireflective Film Inspired by the Transparent Cicada Wings.

Cicada wings, covered with arranged nanostructures, were widely studied owing to their high transparency and low reflection. However, limited by technologies, their exquisite surface structures and multifunctional features were not inherited and applied by most artificial materials adequately. Here, the excellent optical properties of the cicada wing were investigated in detail experimentally and theoretically. Besides, a flexible self-cleaning broadband antireflective film inspired by the cicada wing has been successfully fabricated by a well-designed biological template method and sol-gel process. The cicada wing ( Megapomponia intermedia) was selected as the original template directly, and a SiO2 negative replica was obtained by a sol-gel process. Then, chemical corrosion was used to remove the original template, retaining the pure negative replica. Subsequently, the polymethyl methacrylate (PMMA) positive replica could be rebuilt after another sol-gel process. Compared with a flat PMMA film, the average reflectivity of the structured PMMA film over the visible region was reduced from 10 to 2%. Besides, the bio-inspired film with a thickness of 0.18 mm exhibited satisfactory comprehensive performances with low reflectance (≤2%) in most of the visible region, as well as superhydrophobic property and perfect flexibility. Our results offered a quick and simple method to rebuild the nanostructured functional materials, promoting the practical applications of the bionic nanostructured materials. Meanwhile, the modified biomimetic fabrication method provides a solution for rebuilding exquisite biological materials and designing multifunctional surfaces. Moreover, the multifunctional antireflective film with wider universality will exhibit an enormous potential application value in optical communications, photoelectric devices, flexible display screens, and antidazzle glasses.

Insulin amyloid fibrils-templated rational self-assembly of vine-tree-like PtRh nanocatalysts for efficient methanol electrooxidation

Shape-controlled synthesis of platinum-based alloy nanocatalysts with well-designed size and structure is essential for developing highly efficient catalysts. Here, a biomolecule-based strategy for the synthesis of vine-tree-like PtRh nanowires (VT-PtRhNWs) using insulin amyloid fibrils (INSAFs) as sacrificial templates is presented. In this structure, the inner PtRh nanowires behave as the rigid ‘tree’ and the outer PtRh nanoparticles interconnects to form a spiral chain-like structure as the flexible ‘vine’. Owning to the limitation effect of biological template, both of nanoparticles and nanowires present a very small size of less than 2 nm, and thus leading to a large electrochemical active surface area of 79.20 m2/g. As a result, the as-prepared VT-PtRhNWs exhibit a much higher catalytic activity toward methanol oxidation compared with the commercial Pt/C catalyst, and also an improved CO tolerance, indicating a great potential as excellent electrocatalysts for fuel cells.

Nanoindentation Properties and Finite Element Analysis of the Rostrum of Cyrtotrachelus buqueti Guer (Coleoptera: Curculionidae).

This work focuses on the application of nanoindentation measurements and the finite element method for analyzing the mechanical properties of the rostrum of the outstanding driller Cyrtotrachelus buqueti Guer. Nanoindentation tests were carried out to measure the Young's modulus and hardness of the rostrum, with the results for the "dry" samples being 13.886 ± 0.75 and 0.368 ± 0.0445 GPa, respectively. The values for the "fresh" samples showed no clear difference from those of the "dry" ones. Moreover, field observation was conducted to determine the motion behaviors of the rostrum on the weevil. Micro-computed tomography technology was employed to obtain structural information about the rostrum, using 9 µm slices. A real three-dimensional model of the rostrum was created using the MIMICS application. Finally, the mechanical properties of the rostrum were determined by finite element analysis. It was concluded that the rostrum provides an ideal biological template for the design of biocomposite materials and lightweight tube-shaped structures. The properties determined in this study can potentially be applied in different fields, such as in the design of automotive hybrid transmission shafts, helicopter tail drive shafts, robotic arms, and other sandwich structures in aerospace engineering.

Engineered nanostructured virus/ZnO hybrid materials with dedicated functional properties

Bioinspired mineralization for the production of new functional materials offers mild reaction conditions suitable for integrating biological templates and build hierarchically organized hybrid nanostructures with defined properties. In this respect, the tobacco mosaic virus (TMV) stands out due to its unique structural dimensions. Here, the authors present a novel mineralization pathway for the synthesis of virus-based zinc oxide (ZnO) hybrids with multifunctional properties. Wild-type TMV, two TMV mutants (E50Q and TMV-Cys) and amino-functionalized self-assembled monolayers (NH2-SAMs), as a reference, were used as templates. This mineralization approach allows control of the particle size of the inorganic phase. Further, the virus contributes additionally to the texturing of zinc oxide. Field-effect transistors (FETs) built from the hybrid films, obtained at close to ambient conditions, showed reproducible results at optimized conditions and without posttreatment. This significantly reduced the threshold voltage of the E50Q/zinc oxide FET compared to that of the NH2-SAMs/zinc oxide FET points to the impact of the organic template on FET performance. Nacre-like virus-based zinc oxide multilayers and corresponding monolithic references were prepared. The mechanical properties, namely, Young’s modulus, hardness and fracture toughness, were determined and an improvement in the mechanical performance by genetic modification was observed.

Bio-template synthesis of Mo-doped polymer carbon nitride for photocatalytic hydrogen evolution

Herein, a novel strategy is established to synthesize Mo-doped graphitic carbon nitride (g-C3N4) with excellent photocatalytic activity through a green approach of biological template. The addition of biotemplates provides a microenvironment for the formation of hydrogen bonds in which the flower-like g-C3N4 is formed by self-assembly between precursors, which not only increases the specific surface area of the material but also exposes more catalytic activity edge. Benefiting from the non-localized of Mo(VI) 4d orbital, Mo-doped g-C3N4 constructs a suitable band structure and a built-in electric field that promotes electron delocalization, which improves the absorption range of visible light and separation efficiency of photo-generated electron-hole pairs. Subsequently, a possible chelation-hydrogen bond coordination mechanism was proposed based on the characterization results of X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), electron paramagnetic resonance (EPR) and 15N solid-state NMR (15N NMR). As a result, the π-conjugated system of g-C3N4 was extended by forming a chelate centered on Mo(VI). Photocatalytic hydrogen evolution (PHE) showed that the optimal hydrogen evolution rate of Mo-doped g-C3N4 was as high as 2008.9 umol/g·h, which was 9.6 times than that of bulk g-C3N4.

Shape-Preserved Transformation of Biological Cells into Synthetic Hydrogel Microparticles.

The synthesis of materials that can mimic the mechanical, and ultimately functional, properties of biological cells can broadly impact the development of biomimetic materials, as well as engineered tissues and therapeutics. Yet, it is challenging to synthesize, for example, microparticles that share both the anisotropic shapes and the elastic properties of living cells. Here, a cell-directed route to replicate cellular structures into synthetic hydrogels such as polyethylene glycol (PEG) is described. First, the internal and external surfaces of chemically fixed cells are replicated in a conformal layer of silica using a sol-gel process. The template is subsequently removed to render shape-preserved, mesoporous silica replicas. Infiltration and cross-linking of PEG precursors and dissolution of the silica result in a soft hydrogel replica of the cellular template as demonstrated using erythrocytes, HeLa, and neuronal cultured cells. The elastic modulus can be tuned over an order of magnitude (≈10-100 kPa) though with a high degree of variability. Furthermore, synthesis without removing the biotemplate results in stimuli-responsive particles that swell/deswell in response to environmental cues. Overall, this work provides a foundation to develop soft particles with nearly limitless architectural complexity derived from dynamic biological templates.

Relevant aspects of the biosynthesis of porous aluminas using glycosides and carbohydrates as biological templates

This research paper comparison of the use of biological templates obtained from steviol glycosides and glucose (monosaccharide) directed toward the synthesis of metal oxides. The results obtained shown the synthesis of aluminum oxides in an aqueous medium, using different green porogenic agents. The influences of the aging period and its impact on the alumina's porosity and phase transition were evaluated. The FTIR studies provided evidence of the surface modification of the aluminum oxide by carboxylate groups generated in the hydrolysis of diterpenic glycosides. The application of prolonged aging periods favored the production of η-alumina vs γ-alumina in the synthesis in which Stevia rebaudiana was used. The materials were characterized, using XRD, TGA, N2 physical adsorption, FE-SEM, NMR, FTIR and TPD-NH3. The TGA profiles indicate appreciable differences as to the yields achieved between samples prepared with the two biological templates (alumina–stevia up to 62%, alumina–glucose yields of 30%). The acidity obtained for the different aluminas synthesized by the use of biological templates showed a trend toward: glucose>stevia>sol–gel method/stevia, in the range of 0.994–0.485mmol/g.

Highly adjustable 3D nano-architectures and chemistries via assembled 1D biological templates.

Porous metal nanofoams have made significant contributions to a diverse set of technologies from separation and filtration to aerospace. Nonetheless, finer control over nano and microscale features must be gained to reach the full potential of these materials in energy storage, catalytic, and sensing applications. As biologics naturally occur and assemble into nano and micro architectures, templating on assembled biological materials enables nanoscale architectural control without the limited chemical scope or specialized equipment inherent to alternative synthetic techniques. Here, we rationally assemble 1D biological templates into scalable, 3D structures to fabricate metal nanofoams with a variety of genetically programmable architectures and material chemistries. We demonstrate that nanofoam architecture can be modulated by manipulating viral assembly, specifically by editing the viral surface coat protein, as well as altering templating density. These architectures were retained over a broad range of compositions including monometallic and bi-metallic combinations of noble and transition metals of copper, nickel, cobalt, and gold. Phosphorous and boron incorporation was also explored. In addition to increasing the surface area over a factor of 50, as compared to the nanofoam's geometric footprint, this process also resulted in a decreased average crystal size and altered phase composition as compared to non-templated controls. Finally, templated hydrogels were deposited on the centimeter scale into an array of substrates as well as free standing foams, demonstrating the scalability and flexibility of this synthetic method towards device integration. As such, we anticipate that this method will provide a platform to better study the synergistic and de-coupled effects between nano-structure and composition for a variety of applications including energy storage, catalysis, and sensing.

Direct synthesis of ultralong platinum nanowires with prominent electrocatalytic performance using lanreotide biotemplate

Due to the dependence on the morphology, size and composition of Pt-based nanomaterials on their catalytic properties, rational design can improve the utilization efficiency and catalytic performance of Pt. As inspired by this, the ultralong Pt nanowires (ULPtNWs) with a diameter of 25 nm were prepared by a mild, green and direct peptide mediated biological template method. Impressively, ULPtNWs with a large electrochemical active surface area (57.2 m2 g−1) were obtained, exhibiting that the peak current density for the methanol oxidation was approximately three-fold better than commercial Pt/C catalyst owing to the high aspect ratio (1.6 × 103 or more). Additionally, the excellent poison resistance of the product was demonstrated, which can be attributed to the high (111) plane. These enhancements indicate that ULPtNWs as a promising catalyst have broad application prospects in the field of direct methanol fuel cells or other electrocatalysis.

Hierarchically structured Mg–Al mixed metal oxides templated from pine sawdust: fabrication, Congo red adsorption and antibacterial properties

ABSTRACTBiomorphic Mg–Al layered double hydroxides (LDHs) templated from pine sawdust as precursors, hierarchically structured Mg–Al mixed metal oxides (MMOs) with well-developed porosity were prepared through biological template method and hydrothermal process. As-synthesized composites were characterized by scanning electron microscopy, transmission electron microscopy, X-ray diffraction and nitrogen adsorption measurements. Adsorption conditions including different Congo red concentration, contact time, pH and temperature were investigated. Antibacterial ability and mechanism against Escherichia coli and Staphylococcus aureus were analyzed. MMOs exhibited higher adsorption and stronger antibacterial ability as compared with biomorphic LDHs. The concept provides new insight into design and preparation efficient adsorption and antibacterial materials.

Enhanced acetone sensing properties of hollow SnO2 fibers using poplar catkins as a bio-template

Porous hollow SnO2 fibers with an average crystallite size of 6.1 ± 0.5 nm were synthesized by a facile solvothermal method using poplar catkins as a biological template. The synthesized hollow SnO2 fibers were characterized by X-ray photoelectron spectroscopy, powder X-ray diffraction, transmission electron microscopy, nitrogen adsorption/desorption measurements, and high-resolution scanning electron microscopy. Results showed that the products presented a high specific surface area of 110.1 m2/g and maintained mesoporous structures with a narrow pore size concentrated at 4.9 nm. The results of gas sensing tests showed that the response of SnO2 fibers was about 1016.4 and 7.0 to 100 ppm and 1 ppm acetone at 100 °C, respectively, indicating that the products exhibited excellent gas sensing performance towards acetone.

Spatial Regulation of Thrombopoiesis in the Bone Marrow

Blood platelets play key roles in hemostasis and thrombosis and are the second most abundant cell type in the circulation. Due to their short life span of only a few days, anuclear platelets are continuously replenished and thus provide a classic system to study hematopoiesis. In mammals, platelets are produced by megakaryocytes (MKs) that are predominantly residing in the bone marrow (BM). MKs originate from hematopoietic stem cells and are thought to migrate from an endosteal niche towards the vascular sinusoids during their maturation. Unfortunately, previous studies on megakaryopoiesis were often limited by 2D imaging and cutting artefacts when analyzing bone sections, potentially resulting in underestimation of MK-to-vessel contacts and MK volumes. We studied megakaryopoiesis by visualizing MKs in their 3D environment. To this end, murine bones were simultaneously stained for MKs and endothelial cells, fixed, chemically cleared and imaged by Light Sheet Fluorescence Microscopy (LSFM). Thus, we achieved 3D-reconstructions of the complete and intact bone with subcellular resolution. Through imaging of MKs in the intact BM, we show that MKs can be found within the entire BM, without a bias towards bone-distant regions. We developed and compared different image processing pipelines and simulation scenarios for precise identification of MKs in 3D light-sheet fluorescence microscopy of uncut murine bones. By combining in vivo two-photon microscopy and in situ LSFM with computational simulations, we reveal surprisingly slow MK migration, limited intervascular space, and a vessel-biased MK pool. To complement limited imaging approaches computational simulations represent an important, well-controllable tool. Typically, simulation studies use artificial meshes as templates to minimize the computational effort or due to the lack of experimental data. Unfortunately, such simplified artificial templates for MKs and the vasculature can bias simulations and lead to misinterpretations as we show here. Using the segmented cell and vessel objects of true 3D images can overcome those limitations providing a simulation framework that has the prerequisites to maximally reflect the physiological situation. Thus, imaging and simulations go hand in hand when the respective 3D cell and vessel objects perfectly serve as biological templates for advanced simulations. We demonstrate reliable whole-bone analysis in silico, and found that MKs influence neutrophil and HSC migration as biomechanical restrainers modulating cell mobility and extravasation. These data challenge the current thrombopoiesis model of MK migration and support a modified model, where MKs at sinusoids are replenished by sinusoidal precursors rather than cells from a distant periostic niche (1). Furthermore, we identify MKs as biomechanical restraints for bone marrow cell mobilization. As MKs themselves do not need to migrate to reach the vessel, therapies to increase MK numbers might be sufficient to raise platelet counts.(1) Stegner D, van Eeuwijk JMM, Angay O, Gorelashvili MG, Semeniak D, Pinnecker J, Schmithausen P, Meyer I, Friedrich M, Dütting S, Brede C, Beilhack A, Schulze H, Nieswandt B, Heinze KG. Thrombopoiesis is spatially regulated by the bone marrow vasculature, Nat Commun. 2017 8(1):127. DisclosuresNo relevant conflicts of interest to declare.

Peptide‐Templated Synthesis of TiO2 Nanofibers with Tunable Photocatalytic Activity

Nanofabrication based on biological templates has attracted considerable interest because of its applications in materials science and biomedicine. Herein, a facile method is reported for the synthesis of well-defined TiO2 nanofibers by using a simple N-(9-fluorenylmethoxycarbonyl)-protected phenylalanine-phenylalanine-aspartic acid tripeptide (Fmoc-Phe-Phe-Asp-OH, Fmoc-FFD) as the template. Compared with other synthetic methods of inorganic nanomaterials, these self-assembling peptides could control the structure and the catalytic activity of the synthesized nanomaterials produced under mild synthetic conditions. The as-synthesized peptide-TiO2 hybrid nanofibers and the calcined TiO2 nanofibers were characterized by using transmission electron microscopy (TEM), scanning electron microscopy (SEM), circular dichroism (CD) spectroscopy, and X-ray diffraction (XRD). The results show that well-defined TiO2 nanofibers could form when the pH of the peptide solution was 5-7, whereas nanoparticles formed when the pH was 8. Moreover, the peptide-templated TiO2 nanofibers showed improved photocatalytic activity for the degradation of methyl orange (MO). Finally, the photocatalytic activity of the TiO2 could be controlled by adjusting the pH of the peptide solution during the synthetic process.

Bio-templated fabrication of MnO nanoparticles in SiOC matrix with lithium storage properties

Silicon oxycarbide (SiOC) materials are considered as a promising high capacity anode for next-generation Li-ion batteries. However, the rapid capacity fading and poor cycling stability often occur in the SiOC materials with high Si content. In this work, an effective and facile strategy is reported to construct nanocomposites of MnO/SiOC, in which SiOC acts as buffer agent and conductive matrix, while MnO contributes to the major reversible capability. Microalgae (Chlorella) serves as both biological template and carbon source to synthesize SiOC microspheres with the assistance of supercritical CO2 fluid, then rice-like MnO nanoparticles are tightly embedded in the SiOC matrix through the heavy metal ion bio-sorption behavior of Chlorella. As anode materials for Li-ion batteries, the C/MnO/SiOC composites exhibit high reversible capacity of 770 mAh g−1 after 200 cycles at a current density of 100 mA g−1 with excellent cycling stability and great rate capability. This work provides a novel strategy to fabricate SiOC-based high capacity anode materials for advanced Li-ion batteries.

Biological cell template synthesis of nitrogen-doped porous hollow carbon spheres/MnO2 composites for high-performance asymmetric supercapacitors

Nitrogen-doped porous hollow carbon spheres were fabricated via hydrothermal pre-carbonization and pyrolysis carbonization using yeast cell templates. After that, the MnO2 nanowires were deposited by the in-situ hydrothermal reaction. By controlling the reaction concentration, various MnO2 nanostructures with different morphologies and electrochemical properties were obtained. The as-prepared sample exhibited an ultrahigh specific capacitance of 255 F g-1 at a current density 1 A g-1 in 1 M Na2SO4 electrolyte. The MnO2/HCS-30 material was used as the positive electrode, and the HCS was used as the negative electrode to assemble the asymmetric supercapacitor. The maximum energy density operating at the 2.0 V voltage window is 41.4 Wh kg−1 at a power density of 500 W kg−1 and still maintains 23.0 Wh kg−1 at a power density of 7901 W kg−1. Moreover, it displayed excellent cycle stability, retained approximately 93.9% of the capacitance after 5000 cycles. This work innovatively combines biomass and energy, provides an environmentally benign strategy and new insights for the preparation of electrode materials.

Study on mechanical and electrical properties of cellulose nanofibrils/graphene-modified natural rubber

Abstract To improve the mechanical and electrical properties of natural rubber (NR), we used cellulose nanofibrils (CNF) as biotemplates, dispersing conductive graphene composites at 10% and 7.5% and coated graphenes (GNS) between natural rubber molecules on the CNF surface by solution blending. The conductive CNF-GNS/NR nanocomposite material was prepared by dispersing and overlapping CNF and GNS in NR to form a three-dimensional multi-layered network structure composite. The product was characterized by scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), tensile testing, and conductivity testing. Results show that the combination of GNS and CNF did not clearly change the GNS chain, did not destroy the GNS structure, and maintained GNS conductivity. When 10% GNS was added, the draw ratio of the CNF-GNS/NR composite was 208%, 56% higher than that of pure NR. The tensile strength increased by 340% compared with pure NR and was 79% higher than that of CNS without CNF. The percolation threshold of CNF-GNS/NR was between 5 and 7.5 phr, lower than the 7.5–10 phr permeation threshold of GNS-NR. When 7.5% GNS was added, the conductivity of CNF-GNS/NR was 3.80 × 10−2 S/m. Compared to the conductivity of 1.25 × 10−6 S/m GNS-NR, the improvement was approximately 4 orders of magnitude. The percolation threshold of CNF-GNS/NR composites was significantly lower than that of composites without CNF. Thus, the addition of CNF can reduce the percolation threshold of composites. Using CNF as a biological template to construct a multi-level three-dimensional conductive network in NR can improve the conductive properties of NR composites substantially.

Fabrication of bionic reed leaf superhydrophobic surface by laser processing

In the natural evolution, animals and plants have evolved many unique structures and properties. For example, butterfly wings appear to be colorful due to grating structures. Lotus leaves have super-hydrophobic property because of micro/ nano-structures. Nepenthes pitcher plants show slippery wettability by reason of the lubricant infused surfaces. Therefore, more and more researchers are trying to prepare unique structures which are similar to the surface of biological templates by different methods. Taking superhydrophobic surfaces as an example, there are many methods having been adopted to achieve superhydrophobic surfaces, such as etching, template method, UV lithography, electrostatic spinning, and nano-imprint technique. In recent years, laser processing technique has the advantages of high precision and arbitrary design, which shows great advantages in bionic manufacturing. For example, various kinds of micro/nano composites or structures have been successfully prepared by laser direct writing, two/four-beam interference, etc. However, these methods rely mainly on complex or sophisticated instruments, which take long time to prepare large-area superhydrophobic surfaces. Reed leaves show anisotropic superhydrophilicity property because of grating structures, which has applications in droplet transmission without loss and directional collection. Herein, we demonstrated the fabrication of bionic reed leaf by laser treatment of structured polydimethylsiloxane (PDMS) surface. Laser treatment of PDMS with micro-grating structures can induce the micro-nano structures and improve the surface roughness. To investigate the change of surface chemical composition, we carried out X-ray photoelectron spectroscopy (XPS) of PDMS before and after the laser treatment. After the laser treatment, the carbon content was decreased from 43.6% to 33.1%. The decrease in carbon content indicates the emission of carbon material during laser treatment, which is caused by the carbonization of the methyl group on the surface of the PDMS. At the same time, the oxygen content increased from 27.8% to 33.6% and the silicon content increased from 28.3% to 33.3%. To compare the surface morphologies changes of PDMS before and after laser treatment, we observed the surface morphology by confocal laser scanning microscopy (CLSM) and scanning electron microscope (SEM). The initial PDMS grating is about 100 μm wide, ~130 μm high and the structure surface is smooth. After laser treatment, it changes to about 200 μm wide, ~110 μm high and becomes much rougher surface. The variation in the width and height is mainly because that the laser treatment causes PDMS surface material to carbonize into rough structures. In order to evaluate the wettability changes of samples, the static water contact angle and dynamic water sliding angle measurement was carried out on the flat PDMS, the structured PDMS, and the laser-treated structured PDMS, respectively. The contact angle along the parallel direction was ∼155°, which is larger than that along the vertical direction (~150°). The sliding angle along the parallel direction was approximately 3°, which was smaller than the SA along the vertical direction (12°). This method provides a new idea for preparation of superhydrophobic surfaces with bionic structures by laser technology. The method is simple, convenient, and low cost, which may become a general method for preparing superhydrophobic surface.

Sol-gel materials for electro-optical and optically active humidity-sensitive devices

One of the main research activities of the Sol-Gel Group@ICMM (GSG-ICMM) is devoted to smart photonic materials derived from the incorporation of optically active substances in glasses. Those smart materials allow the control of their optical properties by applying external stimuli (e.g., electric field). That is the case of gel-glass dispersed liquid crystals (GDLC), where a sol-gel derived matrix with large porosity and embedded with liquid crystal (LC), forms a thin film between transparent conductive substrates needed to apply the electric field. The dielectric anisotropy of the LC permits the reorientation of the encapsulated LC by means of electric fields, enabling the control of its light transmission properties, from opaque (scattering) to transparent states. A different route to obtain LC dispersion devices was designed, taking advantage of biological structures created by bacterial activity. In this case, biofilms of the bacterium Pseudomonas putida mt-2 were grown on transparent conductive substrates from microbiological culture media. The chemical composition and the tridimensional porous structure of the biofilm enabled its use as a biological template for a LC dispersion device, where the LC is embedded in the biofilm porosity. The electrical control of the light transmission properties of these devices was carried out by applying electric fields. This new and non-chemical strategy expanded the possibilities for creating smart photonic materials by using bacterial cell factories. In the same topic of materials for the smart control of light transmission, a new concept was stablished to obtain an optical thin film material that exhibits reversible humidity-responsive transmittance. This material consists on a porous structure, with embedded hygroscopic and deliquescent compounds, having light scattering properties that depend on the humidity of the air in contact with the material. With dry air the material displays an opaque state due to light scattering. When exposed to humid air, the material scavenges water from the air, filling up its porosity with water and becoming transparent to the incident light. Upon exposure to dry air, water is released from the thin film material, recovering its previous light scattering state. The developed thin films can change their transparency when exposed to air with different relative humidity (RH), adjusting the light throughput. Therefore, this material concept can be used to design new optical devices, having the advantage that they do not require LC, transparent conductive glass substrates or complex layer-by-layer architectures for operation as in conventional smart windows.