23 research outputs found

    Designed Microbial Biosynthesis of Hierarchical Bone-Mimetic Biocomposites in 3D-Printed Soft Bioreactors

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    The creation of 3D biomimetic composite structures has important applications in tissue engineering, lightweight structures, drug delivery, and sensing. Previous approaches in fabricating 3D biomimetic composites have relied on blending or assembling chemically synthesized molecules or structures, making it challenging to achieve precise control of the size, geometry, and internal structure of the biomimetic composites. Here, we present a new approach for the creation of 3D bone-mimetic biocomposites with precisely controlled shape, hierarchical structure, and functionalities. Our approach is based on the integration of programmable microbial biosynthesis with 3D printing of gas-permeable and customizable bioreactors. The organic and inorganic components are bacterial cellulose and calcium hydroxyapatite via a mineral precursor, which are generated by Komagataeibacter xylinus and Bacillus simplex P6A, respectively, in 3D-printed silicone bioreactors in consecutive culturing cycles. This study is of high significance to biocomposites, biofabrication, and tissue engineering as it paves the way for the synergistic integration of microbial biosynthesis and additive manufacturing

    Multiresponsive Star-Graft Quarterpolymer Monolayers

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    Multifunctional star-graft quarterpolymers PS<sub><i>n</i></sub>[P2VP-<i>b</i>-(PAA-<i>g</i>-PNIPAM)]<sub><i>n</i></sub> with two different arm types, shorter PS arms and longer P2VP-<i>b</i>-PAA block copolymer arms with grafted PNIPAM chains, were studied in terms of their ability to form micellar structures at the air/water and air/solid interfaces. Because of the pH-dependent ionization of P2VP and PAA blocks, as well as thermoresponsiveness of PNIPAM chains, these multifunctional stars have multiple responsive properties to pH, temperature, and ionic strength. We observed that the molecular surface area of the stars is the largest at basic pH, when the PAA blocks are strongly charged and extended, and PNIPAM chains are spread at the interface. At acidic conditions, the molecular surface area is the smallest because the P2VP blocks submerge into the water subphase and the PAA blocks are contracted and form hydrogen bonding with grafted PNIPAM chains. The molecular surface area of the stars at the air/water interface gradually increases at elevated temperature. We suggest that the transition across lower critical solution temperature (LCST) results in the emerging of PNIPAM chains from the water subphase to the interface due to the hydrophilic to hydrophobic transition. Moreover, at higher surface pressure, the stars tend to form intermolecular micellar aggregates above LCST. The graft density of PNIPAM chains as well as the arm number was also found to have strong effects on the thermo- and pH-response. Overall, this study demonstrates that the star block copolymer conformation and aggregation are strongly dependent on the intramolecular interactions between different blocks and spatial distribution of the arms, which can be controlled by the external conditions, including pH, temperature, ionic strength, and surface pressure

    Star Polymer Unimicelles on Graphene Oxide Flakes

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    We report the interfacial assembly of amphiphilic heteroarm star copolymers (PS<sub><i>n</i></sub>P2VP<sub><i>n</i></sub> and PS<sub><i>n</i></sub>(P2VP-<i>b</i>-P<i>t</i>BA)<sub><i>n</i></sub> (<i>n</i> = 28 arms)) on graphene oxide flakes at the air–water interface. Adsorption, spreading, and ordering of star polymer micelles on the surface of the basal plane and edge of monolayer graphene oxide sheets were investigated on a Langmuir trough. This interface-mediated assembly resulted in micelle-decorated graphene oxide sheets with uniform spacing and organized morphology. We found that the surface activity of solvated graphene oxide sheets enables star polymer surfactants to subsequently adsorb on the presuspended graphene oxide sheets, thereby producing a bilayer complex. The positively charged heterocyclic pyridine-containing star polymers exhibited strong affinity onto the basal plane and edge of graphene oxide, leading to a well-organized and long-range ordered discrete micelle assembly. The preferred binding can be related to the increased conformational entropy due to the reduction of interarm repulsion. The extent of coverage was tuned by controlling assembly parameters such as concentration and solvent polarity. The polymer micelles on the basal plane remained incompressible under lateral compression in contrast to ones on the water surface due to strongly repulsive confined arms on the polar surface of graphene oxide and a preventive barrier in the form of the sheet edges. The densely packed biphasic tile-like morphology was evident, suggesting the high interfacial stability and mechanically stiff nature of graphene oxide sheets decorated with star polymer micelles. This noncovalent assembly represents a facile route for the control and fabrication of graphene oxide-inclusive ultrathin hybrid films applicable for layered nanocomposites

    Exogenous γ-Aminobutyric Acid Improves the Structure and Function of Photosystem II in Muskmelon Seedlings Exposed to Salinity-Alkalinity Stress

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    <div><p>Gamma-aminobutyric acid (GABA) is important in plant responses to environmental stresses. We wished to clarify the role of GABA in maintenance of photosynthesis in muskmelon seedlings (<i>Cucumis melo</i> L., cv. Yipintianxia) during saline-alkaline stress. To this end, we assessed the effect of GABA on the structure and function of the photosynthetic apparatus in muskmelon seedlings grown under saline-alkaline stress. These stresses in combination reduced net photosynthetic rate, gas-exchange, and inhibited photosystem II (PSII) electron transport as measured by the JIP-test. They also reduced the activity of chloroplast ATPases and disrupted the internal lamellar system of the thylakoids. Exogenous GABA alleviated the stress-induced reduction of net photosynthesis, the activity of chloroplast ATPases, and overcame some of the damaging effects of stress on the chloroplast structure. Based on interpretation of the JIP-test, we conclude that exogenous GABA alleviated stress-related damage on the acceptor side of PSII. It also restored energy distribution, the reaction center status, and enhanced the ability of PSII to repair reaction centers in stressed seedlings. GABA may play a crucial role in protecting the chloroplast structure and function of PSII against the deleterious effects of salinity-alkalinity stress.</p></div

    Linear and Star Poly(ionic liquid) Assemblies: Surface Monolayers and Multilayers

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    The surface morphology and organization of poly­(ionic liquid)­s (PILs), poly­[1-(4-vinylbenzyl)-3-butylimidazolium bis­(trifluoromethylsulfonyl)­imide] are explored in conjunction with their molecular architecture, adsorption conditions, and postassembly treatments. The formation of stable PIL Langmuir and Langmuir–Blodgett (LB) monolayers at the air–water and air–solid interfaces is demonstrated. The hydrophobic bis­(trifluoromethylsulfonyl)­imide (Tf<sub>2</sub>N<sup>–</sup>) is shown to be a critical agent governing the assembly morphology, as observed in the reversible condensation of LB monolayers into dense nanodroplets. The PIL is then incorporated as an unconventional polyelectrolyte component in the layer-by-layer (LbL) films of hydrophobic character. We demonstrate that the interplay of capillary forces, macromolecular mobility, and structural relaxation of the polymer chains influence the dewetting mechanisms in the PIL multilayers, thereby enabling access to a diverse set of highly textured, porous, and interconnected network morphologies for PIL LbL films that would otherwise be absent in conventional LbL films. Their compartmentalized internal structure is relevant to molecular separation membranes, ultrathin hydrophobic coatings, targeted cargo delivery, and highly conductive films

    Two performance indices in muskmelon seedlings.

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    <p>A. Performance index on an absorption basis (PI<sub>ABS</sub>). B. Proton motor force on an absorption basis (DF<sub>ABS</sub>). Control, plants grown in medium only; CG, medium with leaf spraying with GABA; S, nutrient medium with complex neutral and alkali salt; SG, medium with both complex neutral and alkali salt and leaf spraying with GABA. Data represent the mean ± SE of three independent experiments (<i>n</i> = 3). Different letters indicate significant differences between treatments (<i>p</i> < 0.05).</p

    Energy distributions during photosynthesis in muskmelon seedlings.

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    <p>A. Quantum yield for electron transport (φE<sub>o</sub>). B. The probability that the energy of an absorbed photon is dissipated as heat (φD<sub>o</sub>). C. Maximum quantum yield for primary photochemistry (φP<sub>o</sub>). Control, plants grown in medium only; CG, medium with leaf spraying with GABA; S, nutrient medium with complex neutral and alkali salt; SG, medium with both complex neutral and alkali salt and leaf spraying with GABA. Data represent the mean ± SE of three independent experiments (n = 3). Different letters indicate significant differences between treatments (<i>p</i> < 0.05).</p

    JIP-test parameters on the donor side of PSII in muskmelon seedlings.

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    <p>A. Ratio of the K phase to the J phase (Wk value). B. The fraction of oxygen evolving complex. Control, plants grown in medium only; CG, medium with leaf spraying with GABA; S, nutrient medium with complex neutral and alkali salt; SG, medium with both complex neutral and alkali salt and leaf spraying with GABA. Data represent the mean ± SE of three independent experiments (n = 3). Different letters indicate significant differences between treatments (<i>p</i> < 0.05).</p

    Photomicrographs of chloroplasts isolated from muskmelon seedlings.

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    <p>Control, plants grown in medium only; CG, medium with leaf spraying with GABA; S, nutrient medium with complex neutral and alkali salt; SG, medium with both complex neutral and alkali salt and leaf spraying with GABA. SL, stroma lamellae; GL, grana lamellae; SG, starch grains; P, plastoglobuli. Scale bars for chloroplasts and thylakoids are 0.2μm and 0.1μm, respectively.</p

    Activity of ATPases in chloroplasts isolated from muskmelon seedlings.

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    <p>Activity of: A. H<sup>+</sup>-ATPase, B. Mg<sup>2+</sup>-ATPase, C. Ca<sup>2+</sup>-ATPase. Control, plants grown in medium only; CG, medium with leaf spraying with GABA; S, nutrient medium with complex neutral and alkali salt; SG, medium with both complex neutral and alkali salt and leaf spraying with GABA. Data represent the mean ± SE of three independent experiments (n = 3). Different letters indicate significant differences between treatments (<i>p</i> < 0.05).</p
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