Porous Microbeads Research Articles

Exfoliated MoS2 nanosheets immobilized in porous microbeads as recoverable photocatalysts.

Molybdenum disulfide (MoS2) is a highly effective visible light photocatalyst when used as well-exfoliated 2D nanosheets. The ability to make effective use of these properties is significantly compromised by the challenge of preventing nanosheet aggregation or restacking in fluid suspensions. We report a strategy for immobilizing chemically exfoliated MoS2 as single- and few-layer nanosheets in porous crosslinked polymers prepared as microbeads. The polymeric support prevents aggregation of the nanosheets while allowing access to the nanomaterial for model organic compounds present in the surrounding fluid. Exposure to visible light results in high degradation yields (>99%) of these organic species in aqueous media, and the MoS2 nanosheets maintain their photocatalytic efficacy through multiple cycles of use. The recoverability of the porous beads and the persistent photocatalytic activity of the polymer-supported MoS2 offer the potential of realizing an effective, environmentally sustainable platform for photocatalytic degradation of dissolved solutes.

Synthesis and characterization of silver nanoparticle-decorated coal gasification fine slag porous microbeads and their application in antistatic polypropylene composites

A conductive powder of coal gasification fine slag porous microbeads (CMs) coated with silver (Ag) nanoparticles was synthesized by a simplified electroless plating method. CMs were coated with uniform and dense Ag nanoparticles ([email protected]) to form a conductive structure consisting of internal conductive channels and a surface coating layer. The powder volume resistivity of [email protected] reached 1.47 Ω·cm. Subsequently, [email protected] were mixed with polypropylene (PP) to prepare an [email protected]@PP composite with a volume resistivity of 3.35 × 105 Ω·cm, a tensile strength of 26.06 MPa, and an elongation at break of 43.09%. Due to the high specific surface area (65.41 m2/g), small particle size (8.13 μm), and low density (1.51 g/cm3) of [email protected], the [email protected]@PP composite had better volume resistivity and mechanical properties than the PP composite filling with commercial silver-plated glass beads. The findings of this research could provide a theoretical foundation for future applications of [email protected]

Intraparticle Macromolecular Migration Alters the Structure and Function of Proteins Reversibly Immobilized on Porous Microbeads

AbstractWhile migration of reversibly immobilized proteins across the volume of supports is investigated in conditions where an external force is applied or under fluid flow conditions, their passive migration upon sample storage and its effect on the protein functionality remain unexplored. Understanding such intraparticle macromolecular migration is essential to develop protein functionalized biomaterials with a longer life span. This work investigates the spatiotemporal migration of His‐tagged immobilized fluorescent proteins inside porous agarose microbeads under different storage conditions. A tool that assesses the intraparticle protein migration across the surface of the porous supports is developed. Differences in migration patterns between different proteins suggest that binding dynamics between proteins and their supports play a key role in their migration. The effect of macromolecular migration on the functional and structural properties of bound proteins and enzymes is also explored. Therefore, single‐particle measurements to understand how the migration process affects the functionality of immobilized enzymes are performed. Evaluating protein migration and understanding the reason behind such phenomena allows gaining control over immobilization processes and design immobilization chemistries that either prevent or promote intraparticle macromolecular diffusion upon storage, depending on the desired final application.

Solid-Phase Assembly of Multienzyme Systems into Artificial Cellulosomes.

We herein describe a bioinspired solid-phase assembly of a multienzyme system scaffolded on an artificial cellulosome. An alcohol dehydrogenase and an ω-transaminase were fused to cohesin and dockerin domains to drive their sequential and ordered coimmobilization on agarose porous microbeads. The resulting immobilized scaffolded enzymatic cellulosome was characterized through quartz crystal microbalance with dissipation and confocal laser scanning microscopy to demonstrate that both enzymes interact with each other and physically colocalize within the microbeads. Finally, the assembled multifunctional heterogeneous biocatalyst was tested for the one-pot conversion of alcohols into amines. By using the physically colocalized enzymatic system confined into porous microbeads, the yield of the corresponding amine was 1.3 and 10 times higher than the spatially segregated immobilized system and the free enzymes, respectively. This work establishes the basis of a new concept to organize multienzyme systems at the nanoscale within solid and porous immobilization carriers.

Development of Porous Epoxy Micro-Beads Using Ammonium Bicarbonate through a Single Epoxy Droplet in Corn Oil.

This paper explored the effects of ammonium bicarbonate and different ratios of epoxy to polyamide on the formation of porous epoxy micro-beads through a single epoxy droplet. A single drop of a mixture, consisting of epoxy, polyamide, and ammonium bicarbonate, was dropped into heated corn oil at a temperature of 100 °C. An epoxy droplet was formed due to the immiscibility of the epoxy mixture and corn oil. The ammonium bicarbonate within this droplet underwent a decomposition reaction, while the epoxy and polyamide underwent a curing reaction, to form porous epoxy micro-beads. The result showed that the higher ammonium bicarbonate content in the porous, epoxy micro-beads increased the decomposition rate up to 11.52 × 10−3 cm3/s. In addition, a higher total volume of gas was generated when a higher ammonium bicarbonate content was decomposed. This led to the formation of porous epoxy micro-beads with a smaller particle size, lower specific gravity, and better thermal stability. At an epoxy to polyamide ratio of 10:6, many smaller micro-beads, with particle sizes ranging from 201 to 400 μm, were obtained at an ammonium bicarbonate content of 10 phr. Moreover, the porous epoxy micro-beads with open pores were shown to have a low specific gravity of about 0.93 and high thermal stability at a high ammonium bicarbonate content. Based on the findings, it was concluded that porous epoxy micro-beads were successfully produced using a single epoxy droplet in heated corn oil, where their shape and particle size depended on the content of ammonium bicarbonate and the ratio of epoxy to polyamide used.

Synthesis and characterization of composite conductive powders prepared by Sb-SnO2-coated coal gasification fine slag porous microbeads

In the present paper, the synthesis of composite conductive powders of coal gasification fine slag porous microbeads (CMs) coated with antimony-doped tin oxide (Sb-SnO2) by chemical deposition was reported. It was found that CMs were coated with well-crystallized and uniform antimony-doped tin oxide nanoparticles (ATCM), and the volume resistivity of ATCM powders reached 2.60 × 103 Ω·cm with an average particle size of 18.3 μm. The effects of calcination temperature and time on the resistivity of ATCM were studied. It was found that the effects of calcination conditions on volume resistivity could be attributed to a coaction of the changes in the valence state and concentration of Sb, the crystal integrity of Sb-SnO2 and the agglomeration degree on the surface. For doping, the extension of calcination time could improve the number of carriers, while the calcination temperature affected the resistivity of ATCM due to surface segregation.

Experimental demonstration of negative refraction with 3D locally resonant acoustic metafluids

Negative refraction of acoustic waves is demonstrated through underwater experiments conducted at ultrasonic frequencies on a 3D locally resonant acoustic metafluid made of soft porous silicone-rubber micro-beads suspended in a yield-stress fluid. By measuring the refracted angle of the acoustic beam transmitted through this metafluid shaped as a prism, we determine the acoustic index to water according to Snell’s law. These experimental data are then compared with an excellent agreement to calculations performed in the framework of Multiple Scattering Theory showing that the emergence of negative refraction depends on the volume fraction Phi of the resonant micro-beads. For diluted metafluid (Phi =3%), only positive refraction occurs whereas negative refraction is demonstrated over a broad frequency band with concentrated metafluid (Phi =17%).

An enhanced fluorescence detection of a nitroaromatic compound using bacteria embedded in porous poly lactic-co-glycolic acid microbeads.

The detection of explosive nitroaromatic compounds has caused worldwide concern for human safety. In this study, we introduce a fluorescent biosensor based on porous biocompatible microspheres loaded with a bioreporter for the detection of nitroaromatic compounds. Poly(lactic-co-glycolic acid) microbeads were designed as biosensors embedded with the bacterial bioreporters. The genetically engineered bacterial bioreporter can express a green fluorescent protein in response to nitroaromatic compounds (e.g., trinitrotoluene and dinitrotoluene). The modified surface structure in microbeads provides a large surface area, as well as easy penetration, and increases the number of attached bioreporters for enhanced fluorescent signals of biosensors. Moreover, the addition of the M13 bacteriophage in open porous microbeads significantly amplified the fluorescence signal for detection by the π-π interaction between peptides in the M13 bacteriophage and nitroaromatic compounds. The modification of the surface morphology, as well as the genetically engineered M13 phage, significantly amplifies the fluorescence signal, which makes the detection of explosives easier, and has great potential for the stand-off remote sensing of TNT buried in the field.

Design of the Enzyme-Carrier Interface to Overcome the O2 and NADH Mass Transfer Limitations of an Immobilized Flavin Oxidase.

Understanding how the immobilization of enzymes on solid carriers affects their performance is paramount for the design of highly efficient heterogeneous biocatalysts. An efficient supply of substrates onto the solid phase is one of the main challenges to maximize the activity of the immobilized enzymes. Herein, we apply advanced single-particle analysis to decipher the optimal design of an immobilized NADH oxidase (NOX) whose activity depends both on O2 and NADH concentrations. Carrier physicochemical properties and its functionality along with the enzyme distribution across the carrier were implemented as design variables to study the effects of the intraparticle concentration of substrates (O2 and NADH) on the activity. Intraparticle O2-sensing analysis revealed the superior performance of the enzyme immobilized at the outer surface in terms of effective supply of O2. Furthermore, the co-immobilization of NADH and NOX within the tuned surface of porous microbeads increases the effective concentration of NADH in the surroundings of the enzyme. As a result, the optimal spatial organization of NOX and its confinement with NADH allow a 100% recovery of the activity of the soluble enzyme upon the immobilization process. By engineering these variables, we increase the NADH oxidation activity of the heterogeneous biocatalyst by up to 650% compared to NOX immobilized under suboptimal conditions. In conclusion, this work highlights the rational design and engineering of the enzyme-carrier interface to maximize the efficiency of heterogeneous biocatalysts.

Core–Sheath Wet Electrospinning of Nanoporous Polycaprolactone Microtubes to Mimic Fenestrated Capillaries

Back Cover: In article number 2000180, George Z. Tan and Yingge Zhou present a novel core–sheath wet electrospinning approach to fabricate nanoporous polycaprolactone microtubes as potential functional capillaries for tissue engineering. The solution viscosity and humidity significantly influence the morphology of electrospun polymers, leading to various products including porous microbeads, helical microfibers, and microtubes. The nanoporous microtubes have similar size and morphology to human fenestrated capillary vessels.

Core–Sheath Wet Electrospinning of Nanoporous Polycaprolactone Microtubes to Mimic Fenestrated Capillaries

AbstractFormation of capillary vessel structures in scaffolds is critical for engineering various tissues and organs. Various biofabrication techniques are developed in recent years to create scaffolds integrated with perfusion channels. However, rapid fabrication of artificial capillary vessels (<10 µm) still remains challenging. In this study, a novel electrospinning approach is developed to fabricate nanoporous polycaprolactone microtubes as potential functional capillaries. The results show that ambient environment parameters and solution properties affect the pore formation and tube morphology. Porous microbeads, helical fibers, and microtubes were fabricated under different processing conditions. The optimal tubular structure is obtained with consistent viscosities between the core and the sheath solutions. The biomimetic nanoporous microtubes hold great potential for vascularization in tissue engineering.

Fracture characterization of novel bioceramic microbeads filled polymer composite

The biomaterial poly(l-lactic acid) (PLLA) is commonly used for bone fixation devices and dental surgeries; however its natural osseointegrating ability is generally poor, which can lead to dislocation and partial fractures. Recently, calcium phosphate bioceramics have been incorporated into PLLA in order to redress this issue and improve the osseointegrating ability of the material. This study incorporated calcium phosphate microbeads in PLLA at various concentrations and measured their effect on the critical stress intensity factor, KIC and critical energy release rate at crack initiation, Gin, as well as the unusual fracture mechanic they induced. The inclusion of microbeads into the polymer matrix reduced the materials’ fracture toughness, from a KIC of 34 ± 7 Pa m−1/2 for blank PLLA, to 18 ± 1 Pa m−1/2 for the strongest bead containing group; and from a Gin of 1030 ± 150 J m−2 for blank PLLA to 200 ± 18 J m−2 for the same microbead containing group. Importantly however, the microbead containing groups fractured by a different mechanism, which was identified by observing fracture surface morphologies, electron probe microanalysis and finite element analysis. It was seen that polymer intruded into the porous microbeads, and resulted in regions of increased stiffness in the polymer matrix around each bead. This prevented void formation at the polymer/microbead interface, but it allowed the strain energy density to increase rapidly under load in microbead containing groups. This energy concentration in turn caused fractures to occur sooner, and resulted in the brittle fracture surfaces seen around microbeads. The identification of this fracture mechanism is important to understand, as it suggests a way to greatly improve the fracture toughness of the material, reducing the difference in stiffness of the two components. This fracture mechanism may also be useful in explaining other observed fracture events containing two materials of greatly varying stiffness.

Deciphering the Effect of Microbead Size Distribution on the Kinetics of Heterogeneous Biocatalysts through Single-Particle Analysis Based on Fluorescence Microscopy

Understanding the functionality of immobilized enzymes with spatiotemporal resolution and under operando conditions is an unmet need in applied biocatalysis, as well as priceless information to guide the optimization of heterogeneous biocatalysts for industrial purposes. Unfortunately, enzyme immobilization still relies on trial-and-error approximations that prevail over rational designs. Hence, a modern fabrication process to achieve efficient and robust heterogeneous biocatalysts demands comprehensive characterization techniques to track and understand the immobilization process at the protein–material interface. Recently, our group has developed a new generation of self-sufficient heterogeneous biocatalysts based on alcohol dehydrogenases co-immobilized with nicotinamide cofactors on agarose porous microbeads. Harnessing the autofluorescence of NAD+(P)H and using time-lapse fluorescence microscopy, enzyme activity toward the redox cofactors can be monitored inside the beads. To analyze these data, herein we present an image analytical tool to quantify the apparent Michaelis–Menten parameters of alcohol dehydrogenases co-immobilized with NAD(P)+/H at the single-particle level. Using this tool, we found a strong negative correlation between the apparent catalytic performance of the immobilized enzymes and the bead radius when using exogenous bulky substrates in reduction reactions. Therefore, applying image analytics routines to microscopy studies, we can directly unravel the functional heterogeneity of different heterogeneous biocatalyst samples tested under different reaction conditions.

Electrospun hydrogen manganese oxide nanofibers as effective adsorbents for Li+ recovery from seawater

Highly porous hydrogen manganese oxide (HMO) nanofibers were fabricated by combining electrospinning, calcination, and ion exchanges, and their lithium (Li) recovery performance was systematically compared to other adsorbent types (i.e., nanoparticles and porous microbeads with equivalent properties). In seawater, the HMO nanofibers exhibited an excellent Li+ adsorption capacity (18.8mg/g) with greater Li+ selectivity over other adsorbents. These might be attributed to the high number of macropores in the nanofiber, which facilitated the inward diffusion of Li+ and enhanced the accessibility of activated sites. Moreover, the Li+ recovery efficiency of the nanofibers remained approximately 95% after 20 recovery cycles.

Biodegradable and Porous Poly(lactic-co-glycolic acid) Microbeads for In vitro Evaluation of Negatively Charged Fluorescent Bacteria

In this study, porous microbeads synthesized by water-oil-water [water/oil/water (W1/O/W2)] double-emulsion solvent evaporation method exhibited immense potential as biocarriers for the attachment of bacteria. Poly(lactic-co-glycolic acid) (PLGA) was selected as a biodegradable, biocompatible material for fabricating porous microbeads. Ammonium bicarbonate and polyvinyl alcohol concentrations played a significant role in the modification of the microbead size. The microbead surface structure was modified by partial hydrolysis using sodium hydroxide to generate open pores on the surface and a more hydrophilic surface than PLGA itself. To examine the inner morphology of the microbeads, confocal laser scanning microscopy was employed in combination with rhodamine B during the fabrication of porous microbeads. Finally, the attachment of fluorescent bacteria to these porous microbeads was analyzed in terms of affinity between bacteria and porous PLGA microbeads. The affinity of microbeads to negatively charged bacteria was observed as a function of the charges of the PLGA microbead surfaces, indicating that surface-modified PLGA porous microbeads decorated with positively charged chitosan exhibit an enhanced affinity to negatively charged bacteria.

Electric Field Assisted Microfluidic Platform for Generation of Tailorable Porous Microbeads as Cell Carriers for Tissue Engineering

Adv. Funct. Mater. 2018, 28, 1800874 The initially published version of the manuscript unfortunately contains an error in the second sentence of the abstract of the html version. The correct sentence should read as in the pdf version, which is as follows: “…Here, a novel and highly efficient method is presented for preparation of porous microbeads of tailorable dimensions (in the range ≈300–1500 μm) and with a uniform and fully interconnected internal porous texture…” We apologize for any inconvenience or misunderstanding that this error may have caused.

Energy Harvesting: Electric Field Assisted Microfluidic Platform for Generation of Tailorable Porous Microbeads as Cell Carriers for Tissue Engineering

Energy Harvesting: Electric Field Assisted Microfluidic Platform for Generation of Tailorable Porous Microbeads as Cell Carriers for Tissue Engineering

One‐Step Fabrication of Uniform Biodegradable Microbeads with Unimodal and Bimodal Porous Structures Using Spontaneous Microphase Separation

AbstractUniform poly(l‐lactic acid) (PLLA) microbeads with unimodal or bimodal porous structures are fabricated using a simple fluidic device based on a single oil‐in‐water emulsion method, where an alkane (octane, undecane, tridecane, and pentadecane) serves as the porogen. During the solvent evaporation, the alkanes spontaneously undergo a microphase separation, resulting in a highly porous structure. The size and size distribution of the pores in the PLLA microbeads can be easily controlled by changing the alkane type and concentration. When the undecane, tridecane, and pentadecane are used as the porogen at 6 wt%, the PLLA microbeads have the bimodal porous structure with a large hollow pore in the center and many small pores. In vitro and in vivo studies reveal that those PLLA microbeads with the bimodal porous structure readily facilitate the penetration and proliferation of cells and host tissues compared with the other PLLA microbeads. These results indicate that the superior properties of PLLA porous microbeads with a bimodal porous structure are suitable for diverse biomedical applications such as tissue engineering, cell delivery, and plastic surgery.

Energy Harvesting: Electric Field Assisted Microfluidic Platform for Generation of Tailorable Porous Microbeads as Cell Carriers for Tissue Engineering (Adv. Funct. Mater. 20/2018)

Energy Harvesting: Electric Field Assisted Microfluidic Platform for Generation of Tailorable Porous Microbeads as Cell Carriers for Tissue Engineering (Adv. Funct. Mater. 20/2018)

Electric Field Assisted Microfluidic Platform for Generation of Tailorable Porous Microbeads as Cell Carriers for Tissue Engineering

AbstractInjection of cell‐laden scaffolds in the form of mesoscopic particles directly to the site of treatment is one of the most promising approaches to tissue regeneration. Here, a novel and highly efficient method is presented for preparation of porous microbeads of tailorable dimensions (in the range ≈300–1500 mm) and with a uniform and fully interconnected internal porous texture. The method starts with generation of a monodisperse oil‐in‐water emulsion inside a flow‐focusing microfluidic device. This emulsion is later broken‐up, with the use of electric field, into mesoscopic double droplets, that in turn serve as a template for the porous microbeads. By tuning the amplitude and frequency of the electric pulses, the template droplets and the resulting porous bead scaffolds are precisely produced. Furthermore, a model of pulsed electrodripping is proposed that predicts the size of the template droplets as a function of the applied voltage. To prove the potential of the porous microbeads as cell carries, they are tested with human mesenchymal stem cells and hepatic cells, with their viability and degree of microbead colonization being monitored. Finally, the presented porous microbeads are benchmarked against conventional microparticles with nonhomogenous internal texture, revealing their superior performance.