A rapid and efficient micromotor-based bacteria killing strategy is described. The new antibacterial approach couples the attractive antibacterial properties of chitosan with the efficient ...water-powered propulsion of magnesium (Mg) micromotors. These Janus micromotors consist of Mg microparticles coated with the biodegradable and biocompatible polymers poly(lactic-co-glycolic acid) (PLGA), alginate (Alg) and chitosan (Chi), with the latter responsible for the antibacterial properties of the micromotor. The distinct speed and efficiency advantages of the new micromotor-based environmentally friendly antibacterial approach have been demonstrated in various control experiments by treating drinking water contaminated with model Escherichia coli (E. coli) bacteria. The new dynamic antibacterial strategy offers dramatic improvements in the antibacterial efficiency, compared to static chitosan-coated microparticles (e.g., 27-fold enhancement), with a 96% killing efficiency within 10 min. Potential real-life applications of these chitosan-based micromotors for environmental remediation have been demonstrated by the efficient treatment of seawater and fresh water samples contaminated with unknown bacteria. Coupling the efficient water-driven propulsion of such biodegradable and biocompatible micromotors with the antibacterial properties of chitosan holds great considerable promise for advanced antimicrobial water treatment operation.
Low molecular weight chitosan has a stronger effect on phospholipid membrane models which represent mammalian (DPPC) and bacterial (DPPG) membranes.
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•The model explaining interaction ...between chitosan and DMPA is also valid for DPPC and DPPG monolayers.•Low molecular weight chitosans interact more strongly with DPPC and DPPG monolayers.•Penetration into the hydrophobic chains was confirmed with PM-IRRAS and SFG data.•Chitosan-rich and lipid-rich condensed domains are formed with chitosan incorporation.•Rh for LMWChi is smaller than for Chi which explains its easier access to hydrophobic tails.
The interaction between chitosans and Langmuir monolayers mimicking cell membranes has been explained with an empirical scheme based on electrostatic and hydrophobic forces, but so far this has been tested only for dimyristoyl phosphatidic acid (DMPA). In this paper, we show that the mode of action in such a scheme is also valid for dipalmitoyl phosphatidyl choline (DPPC) and dipalmitoyl phosphatidyl glycerol (DPPG), whose monolayers were expanded and their compressibility modulus decreased by interacting with chitosans. In general, the effects were stronger for the negatively charged DPPG in comparison to DPPC, and for the low molecular weight chitosan (LMWChi) which was better able to penetrate into the hydrophobic chains than the high molecular weight chitosan (Chi). Penetration into the hydrophobic chains was confirmed with polarization-modulated infrared reflection absorption spectroscopy (PM-IRRAS) and sum frequency generation (SFG) spectroscopy. A slight reduction in conformational order of the lipid chains induced by the chitosans was quantitatively estimated by measuring the ratio between the intensities of the methyl (r+) and methylene (d+) peaks in the SFG spectra for DPPG. The ratio decreased from 35.6 for the closely packed DPPG monolayer to 7.0 and 6.6 for monolayers containing Chi and LMWChi, respectively. Since in both cases there was a significant phospholipid monolayer expansion, the incorporation of chitosans led to chitosan-rich and lipid-rich condensed domains, which mantained conformational order for their hydrophobic tails. The stronger effects from LMWChi are ascribed to an easier access to the hydrophobic tails, as corroborated by measuring aggregation in solution with dynamic light scattering, where the hydrodynamic radius for LMWChi was close to half of that for Chi. Taken together, the results presented here confirm that the same mode of action applies to different phospholipids that are important constituents of mammalian (DPPC) and bacterial (DPPG) cell membranes.
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High molecular weight Chi modulates the orientation of SF groups (Try and Try).Chi and SF LbL films were successfully used as template for phytase immobilization.The matrix ...improved the performance of phytic acid biosensing.
In this paper, we show that chitosan may induce conformation changes in silk fibroin (SF) in layer-by-layer (LbL) films, which were used as matrix for immobilization of the enzyme phytase to detect phytic acid. Three chitosan (CH) samples possessing distinct molecular weights were used to build CH/SF LbL films, and a larger change in conformation from random coils to β-sheets for SF was observed for high molecular weight chitosan (CHH). The CHH/SF LbL films deposited onto interdigitated gold electrodes were coated with a layer of phytase, with which phytic acid could be detected down to 10⿿9M using impedance spectroscopy as the principle of detection and treating the data with a multidimensional projection technique. This high sensitivity may be ascribed to the suitability of the CHH/SF matrix, thus indicating that the molecular-level interactions between chitosan and SF may be exploited in other biosensors and biodevices.
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► Low molecular weight chitosans have stronger effects on membrane models. ► DMPA was used as membrane model for its negative charge. ► Results could be rationalized in terms of ...electrostatic and hydrophobic interactions. ► Lower molecular weight chitosans more effective if activity depends on membrane.
The influence from the chitosan molecular weight on its interaction with cell membrane models has been studied. A low molecular weight chitosan (LMWChi) adsorbed from the subphase expanded the surface pressure–area and surface potential–area isotherms of dimyristoyl phosphatidic acid (DMPA) monolayers and decreased the compressional modulus. The expansion in the monolayers and the decrease in the compressional modulus were larger for LMWChi than for a high molecular weight chitosan (Chi). The polymeric nature is still essential for the interaction though, which was demonstrated by measuring negligible changes in the mechanical properties of the DMPA monolayer when the subphase contained glucosamine and acetyl-glucosamine. The results were rationalized in a model through which chitosan interacted with the membrane via electrostatic and hydrophobic interactions, with the smaller chains of LMWChi having less steric hindrance to be accommodated in the membrane. In summary, the activity based on membrane interactions depends on the distribution of molar mass, with lower molecular weight chitosan more likely to have stronger effects.
Herein, a simple, low-cost and fast approach was proposed to produce fluorescent fibers from the electrospinning of poly (vinyl alcohol)/water-soluble graphene quantum dots (GQDs). Initially, the ...preparation of GQDs was explored via an easy bottom-up method based on the incomplete carbonization of citric acid under different times (30, 45 and 60 min). Next, fluorescent fibrous mats were prepared from the electrospinning of PVA solutions with different contents of GQDs. These materials were further characterized via several techniques, including High-Resolution Transmission Electronic Microscopy (HRTEM), UV–vis and fluorescence spectroscopies, Thermogravimetric Analysis (TGA) and Differential Scanning Calorimetry (DSC). The GQDs presented a strong blue photoluminescence under UV light exposure. Among the investigated carbonization times, 45 min led to GQDs with the highest fluorescence intensity (regardless the pH) and fluorescence quantum yield (10.5%). HRTEM analysis showed that this carbonization time led to GQDs with uniform and homogeneous dimensions, with an average diameter of 2.5 ± 0.2 nm. After electrospinning, HRTEM revealed a homogeneous distribution of GQDs into the polymeric ultrathin fibers, while increasing the GQDs content in the PVA matrix led to a clear increase in the fluorescence intensity. Interestingly, as the GQDs content increased, a slight red-shift was observed for the maximum of emission, which may be related to light re-adsorption or even as result of Föster Resonance Energy Transfer. This set of results widens the perspectives of application of this low-cost substrate in many fields, via a simple approach using a water-soluble polymer and a naturally occurring component from citrus fruits.
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•Graphene quantum dots with well-controlled size were prepared via an approach based on the carbonization of citric acid.•A green and fast method was proposed for the production of electrospun fluorescent fibers from PVA and graphene quantum dots.•Increasing the GQDs content in the PVA matrix led to a clear increase in the fluorescence intensity.
•O-acyl chitosans have stronger effects than parent chitosan on membrane models.•Hydrogen bonding with phospholipids appears not to be crucial for activity.•Results confirm the importance of ...hydrophobic interactions.•Hydrophobic derivatives should be more effective if activity depends on the membrane.
One of the major challenges in establishing the mechanisms responsible for the chitosan action in biomedical applications lies in the determination of the molecular-level interactions with the cell membrane. In this study, we probed hydrophobic interactions and H-bonding in experiments with O,O′-diacetylchitosan (DACT) and O,O′-dipropionylchitosan (DPPCT) incorporated into monolayers of distinct phospholipids, the zwitterionic dipalmitoyl phosphatidyl choline (DPPC), and the negatively charged dipalmitoyl phosphatidyl glycerol (DPPG) and dimyristoyl phosphatidic acid (DMPA). The importance of hydrophobic interactions was confirmed with the larger effects observed for DACT and DPPCT than for parent chitosan (Chi), particularly for the more hydrophobic DPPCT. Such larger effects were noted in surface pressure isotherms and elasticity of the monolayers. Since H-bonding is hampered for the chitosan derivatives, which have part of their hydroxyl groups shielded by O-acylation, these effects indicate that H-bonding does not play an important role in the chitosan–membrane interactions. Using polarization-modulated infrared reflection absorption (PM-IRRAS) spectroscopy, we found that the chitosan derivatives were incorporated into the hydrophobic chain of the phospholipids, even at high surface pressures comparable to those in a real cell membrane. Taken together, these results indicate that the chitosan derivatives containing hydrophobic moieties would probably be more efficient than parent chitosan as antimicrobial agents, where interaction with the cell membrane is crucial.
A rapid and efficient micromotor-based bacteria killing strategy is described. The new antibacterial approach couples the attractive antibacterial properties of chitosan with the efficient ...water-powered propulsion of magnesium (Mg) micromotors. These Janus micromotors consist of Mg microparticles coated with the biodegradable and biocompatible polymers poly(lactic-
co
-glycolic acid) (PLGA), alginate (Alg) and chitosan (Chi), with the latter responsible for the antibacterial properties of the micromotor. The distinct speed and efficiency advantages of the new micromotor-based environmentally friendly antibacterial approach have been demonstrated in various control experiments by treating drinking water contaminated with model
Escherichia coli
(
E. coli
) bacteria. The new dynamic antibacterial strategy offers dramatic improvements in the antibacterial efficiency, compared to static chitosan-coated microparticles (
e.g.
, 27-fold enhancement), with a 96% killing efficiency within 10 min. Potential real-life applications of these chitosan-based micromotors for environmental remediation have been demonstrated by the efficient treatment of seawater and fresh water samples contaminated with unknown bacteria. Coupling the efficient water-driven propulsion of such biodegradable and biocompatible micromotors with the antibacterial properties of chitosan holds great considerable promise for advanced antimicrobial water treatment operation.
A rapid and efficient micromotor-based bacteria killing strategy is described.
The chitin insoluble characteristics in aqueous media creates a barrier for biological applications. While the chitosan, the most used derivative from chitin, have been widely used for several ...applications, due to high solubility in slightly acidic aqueous solution. Reported herein is a new approach, consisting of ultrasound irradiation of beta-chitin, which can produce stable suspensions in water (pH= 7.0). With the aim of obtained the most stable beta-chitin suspensions, we played with beta-chitin concentration (0.4 g/L and 1.6 g/L), sonication time (ranged in the interval from 5 min. to 30 min.) and the irradiation amplitude (from 30 % to 50%). When beta-chitin is processed by ultrasound, in aqueous media, we observed the decrease of crystallinity (DRX) and the appearance of micro and nanofibers (MEV). Testing the stability of beta-chitin suspensions, was demonstrate that these suspensions can be stable since 5 min. until several days. Coupling the efficient process to produce stable suspensions in water with biodegradable and biocompatible characteristics of beta-chitin holds great considerable promise for advanced in biological applications.
Chitin occurs in biomass as two main polymorphs, named as β- and α-chitin, which differ on their arrangements on the solid state. The control of chitin physical-chemistry properties by adjustments in ...their extraction process is an important key to improve its applications and derivatization reactions. Thus, the influences of the extraction parameters process on the β and α-chitin characteristics were studied. Squid pens (Loligo sp.) and shrimp shells (Macrobrachium r.), were used as raw material for β-chitin and α-chitin extraction, respectively. The obtained chitin, regardless polymorphs, was subjected to grinding in a knives mill, sieved and classified in different fractions according to the particles size. The fractions were characterized according to the degree of N-acetylation (DA), viscosimetric molecular weight (Mv), crystallinity, morphology and thermal stability. According to the scanning electron microscopy β-chitin particles present a fiber-like characteristic while α-chitin exhibit a flake-like shape. The procedure of grinding affected the DA and Mv of α-chitin (63%<DA<82%; 1.6x106 g.mol-1<Mv<3.8x106 g.mol-1) and β-chitin (60%<DA<85%; 0.7x106 g.mol-1<Mv<1.7x106 g.mol-1), the decrease of both parameters, DA and Mv, being more important to smaller particles sizes. The main bands due to the characteristic functional groups of chitin were observed in all infrared spectra, however β-chitin fractions spectrum exhibited shifts and different resolution of bands depending on the particles dimensions, while fractions of α-chitin were identical. Such results suggest that mild procedures, such as grinding at low temperature (cryo-grinding), should be carried out to process chitin if one aims the preparation of high quality products.
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