Study on mechanism of chitosan degradation with hydrodynamic cavitation

Degradation of hydroxypropyl methylcellulose (HPMC) by acoustic and hydrodynamic cavitation

The present study aims to investigate the degradation of HPMC on a laboratory scale by acoustic and hydrodynamic cavitation. The effects of temperature and the addition of an external oxidizing agent on the effectiveness of HPMC degradation were systematically investigated by SEC/MALS-RI, FTIR and 1H NMR. The results of the experiments without cavitation show that an external oxidizing agent alone reduces the weight-average molar mass at 60 °C in 30 min for 45.1 % (from 335 to 184 kg mol-1). However, the weight-average molar mass of HPMC decreased significantly more in the cavitation treatment, for 98.8 % (from 335 to 4 kg mol-1) in 30 min at optimal operating conditions of hydrodynamic cavitation (i.e. addition of external oxidant and 60 °C) with a concomitant narrowing of the molar mass distribution, as shown by the dispersity value, which decreased from 2.24 to 1.31. Compared to acoustic cavitation, hydrodynamic cavitation also proved to be more energy efficient. The FTIR spectra of the cavitated HPMC samples without the addition of H2O2 show negligible oxidation of the hydroxyl groups and the glycosidic bonds, confirming that mechanical effects predominate in HPMC degradation in these cases. In contrast, when H2O2 was added, FTIR and 1H NMR show typical signals for cellulose oxidation products, especially when the experiments were performed at 60 °C, confirming that chemical as well as mechanical effects are responsible for the extensive HPMC degradation in these cases. Since treatment methods that lead to lower molar masses and narrower molar mass distributions of the polymers are lacking or require longer treatment times (e.g. 24 h), mechanochemical treatment methods such as cavitation have great potential, as they enable faster polymer degradation (in our case 30 min) through a combination of mechanical and/or chemical degradation mechanisms.

Drug Loading in Chitosan-Based Nanoparticles

Chitosan nanoparticles (CSNPs) are promising vehicles for targeted and controlled drug release. Recognized for their biodegradability, biocompatibility, low toxicity, and ease of production, CSNPs represent an effective approach to drug delivery. Encapsulating drugs within nanoparticles (NPs) provides numerous benefits compared to free drugs, such as increased bioavailability, minimized toxic side effects, improved delivery, and the incorporation of additional features like controlled release, imaging agents, targeted delivery, and combination therapies with multiple drugs. Keys parameters in nanomedicines are drug loading content and drug loading efficiency. Most current NP systems struggle with low drug loading, presenting a significant challenge to the field. This review summarizes recent research on developing CSNPs with high drug loading capacity, focusing on various synthesis strategies. It examines CSNP systems using different materials and drugs, providing details on their synthesis methods, drug loadings, encapsulation efficiencies, release profiles, stability, and applications in drug delivery. Additionally, the review discusses factors affecting drug loading, providing valuable guidelines for future CSNPs' development.

Combination of a STING Agonist and Photothermal Therapy Using Chitosan Hydrogels for Cancer Immunotherapy

Cyclic dinucleotides (CDNs) are a promising class of immune agonists that trigger the stimulator of interferon genes (STING) to activate both innate and acquired immunity. However, the efficacy of CDNs is limited by drug delivery barriers. Therefore, we developed a combined immunotherapy strategy based on injectable reactive oxygen species (ROS)-responsive hydrogels, which sustainably release 5,6-dimethylxanthenone-4-acetic acid (DMXAA) as known as a STING agonist and indocyanine green (ICG) by utilizing a high level of ROS in the tumor microenvironment (TME). The STING agonist combined with photothermal therapy (PTT) can improve the biological efficacy of DMXAA, transform the immunosuppressive TME into an immunogenic and tumoricidal microenvironment, and completely kill tumor cells. In addition, this bioreactive gel can effectively leverage local ROS to facilitate the release of immunotherapy drugs, thereby enhancing the efficacy of combination therapy, improving the TME, inhibiting tumor growth, inducing memory immunity, and protecting against tumor rechallenge.

Effect of chitosan on the mechanical properties and acid resistance of metakaolin-blast furnance slag-based geopolymers

Adding organics in the process of geopolymer synthesis can combine the functional groups of organics with the three-dimensional structure of geopolymer, thus changing the properties of geopolymer such as compressive strength, flexural strength, and acid resistance. In this work, excellent mechanical properties and acid resistance of metakaolin-blast furnance slag (Mk-BFS)-based geopolymer were synthesized by the incorporation of chitosan. The formation of sodium-alumino-silicate-hydrate (N-A-S-H) gel and calium-alumino-silicate-hydrate (C-A-S-H) gel in geopolymerization were characterized by ²⁹Si nuclear magnetic resonance (NMR). At 5% of chitosan, the compressive strength of Mk-BFS-based geopolymer could reach to 33.7 MPa. The results could be ascribed to that chitosan reacts with geopolymer to generate new C-O-Si structure meanwhile adhesion produced by the combination of positively charged cations and negatively charged ions makes the structure of geopolymer denser. After 7 days of sulfuric acid immersion, the reduction of compressive strength is less than 3 MPa, demonstrating its great acid resistance. The acid resistance of Mk-BFS-based geopolymer could attribute to that the free amino groups in chitosan preferentially react with acid solution and weakened the erosion of sulfuric acid. This study optimizes the compressive strength and acid resistance of geopolymer by adding appropriate amount of chitosan.

Effect of additives on degradation of poly vinyl alcohol (PVA) using ultrasound and microwave irradiation

The degradation of polyvinyl alcohol (PVA) has been investigated using ultrasonic (US) as well as microwave (MW) irradiation techniques with the approach of process intensification based on different additives, such as Titanium Dioxide (TiO2), Sodium Lauryl Sulphate (SLS), Zinc Oxide (ZnO) and air. The effects of sonication time, initial polymer concentration, and temperature on the extent of reduction in viscosity have been thoroughly investigated using US as well as MW irradiation approaches. Basically, the degradation process has been optimized by utilizing two different ultrasonic reactors in a combined approach of ultrasonic horn and bath. The maximum extent of degradation of PVA was found to be 69.33% using MW irradiation with a required energy of 0.321 g/JL, and 62.47% using US horn with a required energy of 0.054 g/JL when operated at 0.1 g/L of TiO2 catalyst. The combination of US horn and US bath results in same degradation as 0.1 g/L of TiO2 catalyst with US horn. It has also been observed that the maximum degradation of PVA was obtained with a minimum treatment time of 3 min using MW irradiation, whereas the US horn required 40 min. Moreover, a lower extent of PVA degradation was obtained when additives were used, such as surfactants (SLS) and air. As a result, it can be inferred that the MW-assisted approach in the presence of process-intensifying additives/catalysts is the best approach for the degradation of PVA with a minimum energy consumption.

Degradation of pefloxacin by hybrid hydrodynamic cavitation with H2O2 and O3

The degradation of toxic chemicals, antibiotics and other residues in organic wastewater has attracted much attention. Among various degradation technologies, hydrodynamic cavitation (HC) reactors have the advantage of being simple to operate. Through the combination of HC and other oxidants, the removal efficiency and energy efficiency of organic matter can be greatly improved, and the consumption of chemicals and the processing costs can be reduced. In this work, HC technology combined with oxidants was used to degrade pefloxacin (PEF), and the effect of different operating conditions on PEF degradation was investigated. The results indicated that the removal efficiency of PEF treated with HC alone was 84.9% under the optimal HC conditions of pH 3.3 and 120 min, which is much higher than that (35.5%) of pH 5.3. When co-treating the PEF solution with HC and H₂O₂ at 0.3 MPa and pH 5.3, the optimal molar ratio of PEF to H₂O₂ was 1:5, the highest PEF removal efficiency was 69.7%, and the synergy index (SI) was 4.4. When combining HC with O₃, the PEF removal efficiency gradually elevated with increasing ozone addition. When the addition amount of ozone was 0.675 g/h, the removal efficiency of PEF was the highest, which was 91.5% after treatment of 20 min. The intermediate products in the reaction process were analyzed based on UV-Vis spectroscopy and LC-MS, and the mechanism and reaction pathways of PEF were proposed.

Recent advances in hydrodynamic cavitation-based pretreatments of lignocellulosic biomass for valorization

Recently, the hydrodynamic cavitation (HC)-based pretreatment has shown high effectiveness in laboratories and even in industrial productions for conversion of lignocellulosic biomass (LCB) into value-added products. The pretreatment capability derives from the extraordinary conditions of pressures at ∼500 bar, local hotspots with ∼5000 K, and oxidation (hydroxyl radicals) created by HC at room conditions. To promote this emerging technology, the present review summarizes the recent advances in the HC-based pretreatment of LCB. The principle of HC including the sonochemical effect and hydrodynamic cavitation reactor is introduced. The effectiveness of HC on the delignification of LCB as well as subsequent fermentation, paper production, and other applications is evaluated. Several key operational factors (i.e., reaction environment, duration, and feedstock characteristics) in HC pretreatments are discussed. The enhancement mechanism of HC including physical and chemical effects is analyzed. Finally, the perspectives on future research on the HC-based pretreatment technology are highlighted.

The hydroxyl radical yields prediction of cavitation bubble clouds during hydrodynamic cavitation process for chitosan degradation

In order to measure the influence of chemical effects in the process of hydrodynamic cavitation (HC) degradation of chitosan, a prediction model for the hydroxyl radical (·OH) yields of cavitation...

Insight on Solution Plasma in Aqueous Solution and Their Application in Modification of Chitin and Chitosan

Sustainability and environmental concerns have persuaded researchers to explore renewable materials, such as nature-derived polysaccharides, and add value by changing chemical structures with the aim to possess specific properties, like biological properties. Meanwhile, finding methods and strategies that can lower hazardous chemicals, simplify production steps, reduce time consumption, and acquire high-purified products is an important task that requires attention. To break through these issues, electrical discharging in aqueous solutions at atmospheric pressure and room temperature, referred to as the "solution plasma process", has been introduced as a novel process for modification of nature-derived polysaccharides like chitin and chitosan. This review reveals insight into the electrical discharge in aqueous solutions and scientific progress on their application in a modification of chitin and chitosan, including degradation and deacetylation. The influencing parameters in the plasma process are intensively explained in order to provide a guideline for the modification of not only chitin and chitosan but also other nature-derived polysaccharides, aiming to address economic aspects and environmental concerns.

Degradation Behavior of Polymers Used as Coating Materials for Drug Delivery-A Basic Review

The purpose of the work was to emphasize the main differences and similarities in the degradation mechanisms in the case of polymeric coatings compared with the bulk ones. Combined with the current background, this work reviews the properties of commonly utilized degradable polymers in drug delivery, the factors affecting degradation mechanism, testing methods while offering a retrospective on the evolution of the controlled release of biodegradable polymeric coatings. A literature survey on stability and degradation of different polymeric coatings, which were thoroughly evaluated by different techniques, e.g., polymer mass loss measurements, surface, structural and chemical analysis, was completed. Moreover, we analyzed some shortcomings of the degradation behavior of biopolymers in form of coatings and briefly proposed some solving directions to the main existing problems (e.g., improving measuring techniques resolution, elucidation of complete mathematical analysis of the different degradation mechanisms). Deep studies are still necessary on the dynamic changes which occur to biodegradable polymeric coatings which can help to envisage the future performance of synthesized films designed to be used as medical devices with application in drug delivery.

Analysis of the Influencing Factors of the Hydroxyl Radical Yield in a Hydrodynamic Cavitation Bubble of a Chitosan Solution Based on a Numerical Simulation

In this paper, the hydroxyl radical yield of a cavitation bubble and its influencing factors in the process of chitosan degradation with hydrodynamic cavitation in a single-hole orifice plate was investigated by a numerical simulation method. The hydroxyl radical yield of the cavitation bubble was calculated and analyzed by the Gilmore equation as the dynamic equation combined with the mass transfer equation, heat transfer equation, energy balance equation, and the principle of Gibbs free energy minimization. The influence of geometric parameters of the orifice plate and operating parameters on the formation of hydroxyl radicals was investigated. The results showed that the hydroxyl radicals produced at the moment of cavitation bubble collapse increased with the increase of the initial radius (R ₀), upstream inlet pressure (P ₁), downstream recovery pressure (P ₂), downstream pipe diameter (d _p), and the ratio of the orifice diameter to the pipe diameter (β). The simulation results provide a certain basis for the regulation of hydrodynamic cavitation degradation of chitosan.