Dual-Degradable Biohybrid Microgels by Direct Cross-Linking of Chitosan and Dextran Using Azide-Alkyne Cycloaddition

Recent developments in chitosan based microgels and their hybrids

Chitosan based microgels have gained great attention because of their chemical stability, biocompatibility, easy functionalization and potential uses in numerous fields. Production, properties, characterization and applications of chitosan based microgels have been systematically reviewed in this article. Some of these systems exhibit responsive behavior towards external stimuli like pH, light, temperature, glucose, etc. in terms of swelling/deswelling in an aqueous medium depending upon the functionalities present in the network which makes them a potential candidate for various applications in the fields of biomedicine, agriculture, catalysis, sensing and nanotechnology. Current research development and critical overview in this field accompanying by future possibilities is presented. The discussion is concluded with recommended possible future works for further progress in this field.

pH-controlled breakup of fractal aggregates, microgels and gels formed by self-assembled amphiphilic triblock copolymers

The degradation of (micro)gels and fractal aggregates based on self-assembled amphiphilic triblock copolymers has been investigated in water by confocal microscopy and light scattering respectively. The triblock copolymer consisted of a central hydrophilic poly(acrylic acid) (pAA) block and two hydrophobic end blocks that contained an equal amount of randomly distributed n-butyl acrylate (nBA) and AA units. These latter units helped at tempering the hydrophobic end blocks resulting in the control and the fine tuning of the dynamics of the self-assembled triblock through the pH. Starting from a pH where the dynamics is frozen, the rate of breakup of the macroscopic gels, microgels and of fractal aggregates was measured after increasing the pH to different values. The mechanism of the breakup was found to be independent of the pH, but its rate increased exponentially with increasing pH. The degradation proceeded through the release of the polymers from the bulk into the surrounding aqueous phase.

Enhanced anticancer activity of piperine: Structural optimization and chitosan-based microgels with boosted drug delivery

As a plant-derived drug, piperine possesses therapeutic efficacy for many diseases, but its inherent low solubility and bioavailability have greatly limited its clinical use. Herein, we extracted piperine from black pepper, optimized the structure of piperine to prepare various derivatives, and then explored the anticancer activity of these derivatives. Piperine and its derivatives have high anticancer selectivity against 4T1 cells, exhibiting obvious anticancer properties even at a low concentration of 100 μg/mL. Furthermore, the physicochemical properties of piperine and its derivatives were investigated using density functional theory, demonstrating their considerable biological activity. Moreover, the chitosan-based microgels were prepared to encapsulate the hydrophobic piperine derivative with a high loading efficiency of 81.7 % to overcome the low water solubility of the piperine derivative. It is worth noting that excessive glutathione in tumor cells triggers the degradation of microgels and realizes controllable drug release of up to 72.3 %. Due to its excellent properties, chitosan-based microgels loaded with the piperine derivative can obtain good anticancer behavior of approximately 13.14 % cell viability against 4T1 cells. Therefore, the chitosan-based microgels overcome the low water solubility of the piperine derivative through encapsulation and thus further augment their delivery efficiency and cell internalization capability to realize excellent anticancer activity. This work demonstrates the enhanced anticancer efficacy of the hydrophobic plant-derived drug by means of structural optimization of piperine and chitosan-based microgels with boosted drug delivery.

Smart chitosan-based microgels for enhanced photothermal-assisted antibacterial activity

During recent years, antibiotic-resistant bacteria have rapidly emerged owing to the irrational use of antibiotics, rendering a global problem. Currently, few studies introduce customized antibacterial nanoplatforms to overcome antibiotic-resistance according to specific characteristic of bacteria, rather than abuse of antibiotic. Herein, with regard to personalized antibacterial nanoplatform, we design a novel antibiotic delivery nanocarrier composed of polyaniline-grafted-chitosan, presenting pH-responsive, conductive, photothermal, and biodegradable properties. After treatment with divalent anion (SO42-), the negatively charged nanocarriers are obtained for improving the loading efficacy of cationic vancomycin. Meanwhile, the controlled vancomycin release is achieved by lysozyme-triggered degradation of the nanocarrier. With the assistance of photothermal effect, the photothermal-assisted antibacterial effect of the nanocarriers have been effectively enhanced rather than that of a single antibacterial effect of vancomycin. Owing to the low heat resistance of Escherichia coli, photothermal effect can break the antibiotic-resistant bacteria membrane to render the convenient antibiotic entry, leading to the improved antibacterial efficacy. Therefore, the customization of a photothermal-assisted antibacterial on account of the characteristic of specific bacteria can definitely expand our arsenal for enhancing the antibacterial effect against antibiotic-resistant bacteria.

Water-borne synthesis of multi-responsive and biodegradable chitosan-crosslinked microgels: Towards self-assembled films with adaptable properties

The present study aims in the synthesis of new biodegradable stimuli-responsive microgels with controllable microstructure and with the ability to form cohesive films. Such self-assembled films by water evaporation at ambient conditions without any chemicals but just physical entanglements between soft colloid shell, present adaptable mechanical, adhesive and mechano-electrical properties. For that, oligo(ethylene glycol)-based stimuli-responsive microgels have been synthesized using biodegradable chitosan-methacrylates (Chi-MAs) with different degree of substitution (DS) as unique cross-linking agents by precipitation polymerization in water, for the first time. In all the cases, the microgels present thermo-responsiveness with hysteresis between heating and cooling cycles. However, this behavior is tuned and controlled using different types and amounts of Chi-MAs. In addition, the type of Chi-MA used can control microgels' microstructure as well as their enzymatic biodegradation. In addition, spontaneous cohesive films formation from colloidal aqueous dispersion with sol-gel transition is demonstrated. The films present tunable mechanical and adhesive properties through microgels' microstructure and enhanced mechano-electrical properties triggered by simple finger pressure (10-15 N). As self-supported films are able to encapsulate different types of active molecules, this study paves the way for suitable self-assembled microgel films for skincare applications as transdermal delivery systems.

Radiofluorination of an Anionic, Azide-Functionalized Teroligomer by Copper-Catalyzed Azide-Alkyne Cycloaddition

This study describes the synthesis, radiofluorination and purification of an anionic amphiphilic teroligomer developed as a stabilizer for siRNA-loaded calcium phosphate nanoparticles (CaP-NPs). As the stabilizing amphiphile accumulates on nanoparticle surfaces, the fluorine-18-labeled polymer should enable to track the distribution of the CaP-NPs in brain tumors by positron emission tomography after application by convection-enhanced delivery. At first, an unmodified teroligomer was synthesized with a number average molecular weight of 4550 ± 20 Da by free radical polymerization of a defined composition of methoxy-PEG-monomethacrylate, tetradecyl acrylate and maleic anhydride. Subsequent derivatization of anhydrides with azido-TEG-amine provided an azido-functionalized polymer precursor (o14PEGMA-N₃) for radiofluorination. The ¹⁸F-labeling was accomplished through the copper-catalyzed cycloaddition of o14PEGMA-N₃ with diethylene glycol-alkyne-substituted heteroaromatic prosthetic group [¹⁸F]2, which was synthesized with a radiochemical yield (RCY) of about 38% within 60 min using a radiosynthesis module. The ¹⁸F-labeled polymer [¹⁸F]fluoro-o14PEGMA was obtained after a short reaction time of 2-3 min by using CuSO₄/sodium ascorbate at 90 °C. Purification was performed by solid-phase extraction on an anion-exchange cartridge followed by size-exclusion chromatography to obtain [¹⁸F]fluoro-o14PEGMA with a high radiochemical purity and an RCY of about 15%.

Facile fabrication of a broad-spectrum starch/poly(α-l-lysine) hydrogel adsorbent with thermal/pH-sensitive IPN structure through simultaneous dual-click strategy

A thermal/pH-sensitive interpenetrating network (IPN) hydrogel was prepared facilely from starch and poly(α-l-lysine) through amino-anhydride and azide-alkyne double-click reactions in one pot. The synthesized polymers and hydrogels were systematically characterized using different analytical techniques such as Fourier transform infrared spectroscopy (FTIR), nuclear magnetic resonance (NMR), scanning electron microscope (SEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and rheometer. The preparation conditions of the IPN hydrogel were optimized via one-factor experiments. Experimental results indicated the IPN hydrogel possessed pH and temperature sensitivity. Effect of different parameters (pH, contact time, adsorbent dosage, initial concentration, ionic strength, and temperature) on adsorption behavior were investigated in monocomponent system with cationic methylene blue (MB) and anionic Eosin Y (EY) as model pollutants. The results indicated that the adsorption process of the IPN hydrogel for MB and EY followed pseudo-second-order kinetics. The adsorption data for MB and EY fitted well with the Langmuir isotherm model, indicating monolayer chemisorption. The good adsorption performance was due to various active functional groups (-COOH, -OH, -NH₂, etc.) in the IPN hydrogel. The strategy described here opens up a new way for preparing IPN hydrogel. The as-prepared hydrogel exhibits potential application and bright prospects as an adsorbent in wastewater treatment.

Green Chemistry Principles for Nano- and Micro-Sized Hydrogel Synthesis

The growing demand for drug carriers and green-technology-based tissue engineering materials has enabled the fabrication of different types of micro- and nano-assemblies. Hydrogels are a type of material that have been extensively investigated in recent decades. Their physical and chemical properties, such as hydrophilicity, resemblance to living systems, swelling ability and modifiability, make them suitable to be exploited for many pharmaceutical and bioengineering applications. This review deals with a brief account of green-manufactured hydrogels, their characteristics, preparations, importance in the field of green biomedical technology and their future perspectives. Only hydrogels based on biopolymers, and primarily on polysaccharides, are considered. Particular attention is given to the processes of extracting such biopolymers from natural sources and the various emerging problems for their processing, such as solubility. Hydrogels are catalogued according to the main biopolymer on which they are based and, for each type, the chemical reactions and the processes that enable their assembly are identified. The economic and environmental sustainability of these processes are commented on. The possibility of large-scale processing in the production of the investigated hydrogels are framed in the context of an economy aimed at waste reduction and resource recycling.

Cellulose-based functional hydrogels derived from bamboo for product design

Hydrogels have outstanding research and application prospects in the field of product design. Among them, the design and preparation of cellulose-based functional hydrogels derived from bamboo have attracted increasing research interest. Cellulose-based hydrogels not only have the skeleton function of hydrogels, but also retain excellent specificity, smart structural design, precise molecular recognition ability, and superior biocompatibility. Cellulose-based hydrogels show important application prospects in various fields, such as environmental protection, biomedicine, and energy. What's more, they are potentially viable for application in food packaging and plant agriculture, such as fertilizers release and crop production. Recently, researchers have extracted cellulose from bamboo and generated a variety of cellulose-based functional hydrogels with excellent properties by various cross-linking methods. In addition, a variety of multifunctional hybrid cellulose-based hydrogels have been constructed by introducing functional components or combining them with other functional materials, thus expanding the breadth and depth of their applications. Herein, we elaborate on advances in the field of cellulose-based hydrogels and highlight their applications in food packaging and plant agriculture. Meanwhile, the existing problems and prospects are summarized. The review provides a reference for the further development of cellulose-based hydrogels.

Facile synthesis of chitosan-based nanogels through photo-crosslinking for doxorubicin delivery

Chitosan-based nanogels are effective carriers for drug delivery due to their biocompatibility and biodegradability. However, the chemically cross-linked nanogels usually require complicated procedures or tough conditions. Herein, we report a simple approach to generate chitosan-based nanogels by photo-crosslinking of poor solvent-induced nanoaggregates without requiring any emulsifying agent, catalyst, or external crosslinker. O-nitrobenzyl alcohol-modified carboxymethyl chitosan was synthesized and self-crosslinked into the nanogels in a mixed solution of ethanol and water under 365 nm light irradiation due to UV-induced primary amine and o-nitrobenzyl alcohol cyclization. The nanogels (CMC-NBA NPs) and lactobionic acid-decorated nanogels (LACMC-NBA NPs) displayed a uniform diameter (~200 nm) and excellent stability under physiological conditions. Notably, the nanogels exhibited a high loading content (~28 %) due to π-π stacking and electrostatic interactions between doxorubicin (DOX) and the carriers. These DOX-loaded nanogels showed rapid drug release under slightly acidic conditions. The cell and animal experiments confirmed that LACMC-NBA NPs increased cellular uptake, improved cytotoxicity in tumor cells, and enhanced growth inhibition in vivo than CMC-NBA NPs. Thus, these photo-crosslinked nanogels possess great potential for DOX delivery.

Thermosensitive Microgels Containing AIEgens: Enhanced Luminescence and Distinctive Photochromism for Dynamic Anticounterfeiting

The proposal of the aggregation-induced emission (AIE) effect shines a light on the practical application of luminescent materials. The AIE-active luminescence microgels (TPEC MGs) with photo-induced color-changing behavior were developed by integrating positively charged AIE luminogens (AIEgens) into the anionic network of microgels, where AIEgens of TPEC were obtained from the quaternization reaction between tetra-(4-pyridylphenyl)ethylene (TPE-4Py) and 7-(6-bromohexyloxy)-coumarin. The aqueous suspensions of TPEC MGs exhibit a significant AIE effect following the enhancement of quantum yield. In addition, further increase in fluorescence intensity and blueshift occur at elevated temperatures due to the collapse of microgels. The distinctive photochromic behavior of TPEC MGs was observed, which presents as the transition from orange-yellow to blue-green color under UV irradiation, which is different from TPEC in good organic solvents. The phenomenon of color changing can be ascribed to the competition between photodimerization of the coumarin part and photocyclization of TPE-4Py in TPEC. The photochromic TPEC MG aqueous suspensions can be conducted as aqueous microgel inks for information display, encryption, and dynamic anticounterfeiting.

Multi-Bit Biomemristic Behavior for Neutral Polysaccharide Dextran Blended with Chitosan

Natural biomaterials applicable for biomemristors have drawn prominent attention and are of benefit to sustainability, biodegradability, biocompatibility, and metabolism. In this work, multi-bit biomemristors based on the neutral polysaccharide dextran were built using the spin-casting method, which was also employed to explore the effect of dextran on the ternary biomemristic behaviors of dextran–chitosan nanocomposites. The doping of 50 wt% dextran onto the bio-nanocomposite optimized the ratio of biomemristance in high-, intermediate-, and low-resistance states (10⁵:10⁴:1). The interaction between dextran and chitosan (hydrogen-bond network) was verified by Fourier transform infrared (FTIR) and Raman spectroscopy analysis; through this interaction, protons derived from the self-dissociation of water may migrate under the electric field, and so proton conduction may be the reason for the ternary biomemristic behaviors. Observations from X-ray diffraction (XRD), thermogravimetric analysis (TGA), and differential scanning calorimetry (DSC) analysis displayed that the 50 wt% dextran/50 wt% chitosan nanocomposite had the greatest amorphous ratio as well as the highest decomposition and peak transition temperatures in comparison with the other three dextran–chitosan nanocomposites. This work lays the foundation for neutral biomaterials applied to green ultra-high-density data-storage systems.

Charge-reversible and biodegradable chitosan-based microgels for lysozyme-triggered release of vancomycin

INTRODUCTION

High-dose drug administration for the conventional treatment of inflammatory bowel disease induces cumulative toxicity and serious side effects. Currently, few reports have introduced smart carriers for intestinal inflammation targeting toward the treatment of inflammatory bowel disease.

OBJECTIVES

For the unique lysozyme secretory microenvironment of the inflamed intestine, vancomycin-loaded chitosan-polyaniline microgels (CH-PANI MGs) were constructed for lysozyme-triggered VM release.

METHODS

Aniline was first grafted to chitosan to form polymers that were crosslinked by glutaraldehyde to achieve CH-PANI MGs using the inverse (water-in-oil) miniemulsion method. Interestingly, CH-PANI MGs exhibit polyampholyte behaviour and display charge-reversible behaviour (positive to negative charges) after treatment with a NaCl solution.

RESULTS

The formed negatively charged N-CH-PANI MG aqueous solution is employed to load cationic vancomycin with a satisfactory loading efficiency of 91.3%, which is significantly higher than that of chitosan-based MGs. Moreover, N-CH-PANI MGs present lysozyme-triggered biodegradation and controllable vancomycin release upon the cleavage of glycosidic linkages of chitosan. In the simulated inflammatory intestinal microenvironment, vancomycin is rapidly released, and the cumulative release reaches approximately 76.9%. Remarkably, N-CH-PANI@VM MGs not only exhibit high resistance to harsh gastric acidity but also prevent the premature leakage of vancomycin in the healthy gastrointestinal tract. Encouragingly, the N-CH-PANI@VM MGs show obvious antibacterial activity against Staphylococcus aureus at a relatively low concentration of 20 μg/mL.

CONCLUSION

Compared to other pH-responsive carriers used to treat inflammatory bowel disease, the key advantage of lysozyme-responsive MGs is that they further specifically identify healthy and inflammatory intestines, achieving efficient inflammatory bowel disease treatment with few side effects. With this excellent performance, the developed smart MGs might be employed as a potential oral delivery system for inflammatory bowel disease treatment.

Exploration on Aqueous Lubrication of Polymeric Microgels between Titanium Alloy Contacts

Since titanium alloys have been widely used as joint replacement biomaterials, their superficial lubrication has evolved to be a critical factor for normal use. For this purpose, one kind of typical microgel, poly(NIPAAm-co-AA), was synthesized by emulsifier-free emulsion polymerization and used as an aqueous lubricating additive between titanium alloy contacts. The results show that the as-synthesized microgels reduced the coefficient of friction by 46% and the wear volume by 45%, compared with pure water. Meanwhile, due to their thermosensitive property, the microgels were employed as smart additives to modulate the interfacial friction, which was attributed to the transition of the hydrated state and the elastic deformation of microgel particles. To further dissect the lubrication mechanism, it was found that the lubricating property of microgels was substantially associated with the formation of a hydrated layer surrounding microgels, microbearing effect, interfacial adsorption, and the colloidal stability. Looking beyond, as one kind of soft colloidal lubricant, the microgels may play an important role in the biomedical metal lubrication.

pH-Sensitive Dextran-Based Micelles from Copper-Free Click Reaction for Antitumor Drug Delivery

There remains a need to develop new strategies to fabricate dextran-based biocompatible drug delivery systems for safe and effective chemotherapy. Herein, a copper-free azide-propiolate ester click reaction was introduced for dextran modification to fabricate a pH-sensitive dextran-based drug delivery system. A pH-sensitive dextran-based micelle system, self-assembled from amphiphilic dextran-graft-poly(2-(diisopropylamino)ethyl methacrylate-co-2-(2',3',5'-triiodobenzoyl)ethyl methacrylate) or dextran-g-P(DPA-co-TIBMA), is reported for effective chemotherapy. The amphiphilic dextran-g-P(DPA-co-TIBMA) was prepared via reversible addition-fragmentation chain-transfer (RAFT) polymerization and copper-free azide-propiolate ester click reaction. Doxorubicin (DOX)-loaded dextran-g-P(DPA-co-TIBMA) micelles were prepared through self-assembly of DOX and dextran-g-P(DPA-co-TIBMA) in aqueous solution, and had a mean diameter of 154 nm and a drug loading content of 9.7 wt %. The release of DOX from DOX-loaded dextran-g-P(PDPA-co-TIBMA) micelles was slow at pH 7.4, but was greatly accelerated under acidic conditions (pH 6 and 5). Confocal laser scanning microscopy and flow cytometry experiments showed that the dextran-g-P(DPA-co-TIBMA) micelles could effectively deliver and release DOX in human breast cancer cell line (MCF-7 cells). MTT assay showed that dextran-g-P(DPA-co-TIBMA) exhibited excellent biocompatibility while DOX-loaded dextran-g-P(DPA-co-TIBMA) micelles have good antitumor efficacy in vitro. The in vivo therapeutic studies indicated that the DOX-loaded dextran-g-P(PDPA-co-TIBMA) micelles could effectively reduce the growth of tumor with little body weight reduction.

Multistage Extraction of Star Anise and Black Pepper Derivatives for Antibacterial, Antioxidant, and Anticancer Activity

Recently, natural resources have attracted considerable interest for their applications in food security and human health problems. Traditional natural spices, such as star anise and black pepper, played important roles in the pharmaceutical and food industries due to their strong pharmacological activity, antioxidant potential and rare complications. In order to achieve biomasses from the natural product with multiple bioactivities, we developed the multistage extraction method to extract and separate various bioactive compounds from these natural plants. Our work demonstrated that various bioactive-rich extractives were achieved using steam distilled- or oxidative-extraction methods with high extraction yields and purity. Furthermore, the extractives in each step can be used not only as bioactive compounds, but also as a resource to further prepare different derivatives during the next extractive step, providing biomass-saving to a great extent. The extractives obtained with high yields and purities (>82%) were identified by ¹H NMR, ¹³C NMR, FTIR, UV-vis, fluorescence spectroscopy, and high-performance liquid chromatography (HPLC). Moreover, these biomasses display potent antibacterial activities against some types of microorganisms such as S.aureus, S.pyogenes, E.coli, and S.typhi with a lowest MIC of 400 μg/ml for the development of antibacterial agents, significant antioxidant activity as the natural antioxidant for enhancing food shelf-life, and excellent anticancer activity that induces significant cancer cell apoptosis. This work showed the different multistage extracts from natural products, which enable them to be applied in the fields of the pharmaceutical industry and the food industry.

Magnetic AgNPs/Fe3O4@chitosan/PVA nanocatalyst for fast one-pot green synthesis of propargylamine and triazole derivatives

A new green magnetic nanocatalyst was introduced for one-pot fast synthesis of propargylamine and triazole derivatives.