Low Molecular Weight Chitosan Research Articles

Constitutive chitosanase from Bacillus thuringiensis B-387 and its potential for preparation of antimicrobial chitooligomers.

The article proves the ability of the entomopathogenic strain B. thuringiensis var. dendrolimus B-387 to high the constitutive production (3-12.5 U/mL) of extracellular chitosanase, that was found for the first time. The enzyme was purified in 94-fold by ultrafiltration, affinity sorption and cation-exchange chromatography and characterized biochemically. The molecular mass of the chitosanase determined using SDS-PAGE is 40kDa. Temperature and pH-optima of the enzyme are 55°C and pH 6.5, respectively; the chitosanase was stable under 50-60°C and pH 4-10.5. Purified chitosanase most rapidly (Vmax ~ 43µM/mL × min, KM ~ 0.22mg/mL, kcat ~ 4.79 × 104s-1) hydrolyzed soluble chitosan of the deacetylation degree (DD) 85% by endo-mode, and did not degrade colloidal chitin, CM-cellulose and some other glucans. The main reaction products of the chitosan enzymolysis included chitobiose, chitotriose and chitotetraose. In addition to small chitooligosaccharides (CHOs), the studied chitosanase also generated low-molecular weight chitosan (LMWC) with average Mw in range 14-46kDa and recovery 14-35%, depending on the enzyme/substrate ratio and incubation temperature. In some cases, the chitosan (DD 85 and 50%) oligomers prepared using crude chitosanase from B. thuringiensis B-387 indicated higher antifungal and antibacterial activities in vitro in comparison with the initial polysaccharides. The data obtained indicate the good prospect of chitosanase B-387 for the production of bioactive CHOs.

Co-delivery of celastrol and lutein with pH sensitive nano micelles for treating acute kidney injury

To treat acute kidney injury with high efficiency and low toxicity, a novel nanoplatform was developed to remove excess reactive oxygen species (ROS). Lutein (LU) and celastrol (Cel) were loaded into low molecular weight chitosan (CS) to prepare Cel@LU-CA-CS nanomicelles. Renal tubular epithelial (HK−2) cell uptake experiments showed that the drugs could be internalized in renal tubular via the megalin receptor. In this study, the amide bond formed by the reaction of citraconic anhydride (CA) with an amino group of CS could be destroyed under acidic conditions.Therefore, the drugs were released in HK-2 cells due to the acidic environment of the lysosome. In vitro studies showed that the nanomicelles could reduce toxicity in non-target organs and enhance therapeutic efficacy in acute kidney injury (AKI). In addition, Cel@LU-CA-CS micelles had alleviated kidney oxidative stress disorder and stabilized the mitochondrial membrane potential quickly. Next, in vivo studies proved that Cel@LU-CA-CS micelles could inhibit the activation of the NF-κB p65 and p38 MAPK inflammatory signaling pathways. Therefore, the micelles further reduced the overexpression of related inflammatory factors. In conclusion, Cel@LU-CA-CS nanomicelles could treat AKI with high efficiency and low toxicity, and inhibit renal fibrosis.

Betalains nanodispersions: Effects on betalains stability and on rheological properties of Greek yogurt

Red beetroot (Beta vulgaris L.) is a great source of betalains. The main betalains are the betacyanins, responsible for the purple color, and betaxanthins, which present a brownish color. These pigments can present antioxidant activity and are very unstable under certain conditions, such as temperature, extreme ranges of pH, and exposure to light. The aim of this work was to obtain beetroot extract (BE) via ultrasound and transform it into nanoparticles by using polyethylene glycol (PBE) and polyethylene glycol with low molecular weight chitosan (PCBE) as dispersants. The stability of the main betalains in the nanodispersions and the effects of the nanodispersions on the color and rheological properties of commercial Greek yogurt were evaluated. Compared to pristine BE, PCBE nanoparticles presented increased stability for the main betalains in acidic conditions (pH 3.0 and 5.0) of 56% and 22%, respectively. Both PBE and PCBE showed enhanced relative thermal stability compared to pristine BE. Furthermore, PCBE improved commercial Greek yogurt's rheological properties and color parameters. PCBE nanodispersions can be successfully applied as a color additive to commercial Greek yogurt.

Effect of molecular weight of chitosan on the physicochemical, morphological, and biological properties of polyplex nanoparticles intended for gene delivery

The use of viral vectors in gene therapy has many disadvantages that have been widely described. The development of new nonviral vectors using safe polymers such as chitosan provides a viable alternative. Chitosan molecular weight and nitrogen/phosphorus (N/P) ratio are key factors that determine the shape, size, and surface charge of polyplex nanoparticles (NPs) assembled by complex coacervation for gene therapy; and at the same time, their transfection efficiency is affected by these characteristics, besides the cell line used for transfection. However, there are some inconsistencies in previous reports about the effect of chitosan molecular weight on all these parameters. Enhanced Green Fluorescent Protein plasmid (pEGFP-N1) and two molecular weight (MW) chitosan (20.6 and 57.5 kDa) with a high degree of deacetylation (≥85%) were used to design and assembly nanoparticles by complex coacervation with N/P ratios of 43 and 8. NPs were characterized determining morphology by Scanning Electron Microscopy (SEM), size by Dynamic Light Scattering (DLS) and zeta-potential by Laser-Doppler velocimetry (LDV). Also, biological functionality was assessed by in vitro transfection assays. NPs assembled using the lowest MW chitosan (20.6NPs) and N/P ratio = 8 had spherical shape, smaller mean size and polydispersity index (119 ± 20 nm; 0.257, respectively), and lower zeta-potential (17.65 ± 1.21 mV). Moreover, no significant difference was observed in size, polydispersity index and zeta-potential after 30 days of storage, in contrast with NPs assembled using the 57.5 kDa chitosan (57.5NPs). In vitro transfection assays using two cervical cancer cell lines (HeLa and SiHa) showed that 20.6NPs leaded to a higher expression of Green Fluorescent Protein (GFP) in contrast to 57.5NPs for both cell lines, and expression in HeLa cells was higher than in SiHa cell line. It was confirmed that transfection efficiency depends on all these physical parameters given by MW of chitosan, cell physiology, and the addition of fetal bovine serum in the transfection formulation. These results indicate that low MW chitosan and a low N/P ratio are more suitable to design chitosan-based nonviral vectors for gene therapy, given that physicochemical and biological properties, so as the stability of these NPs are better that those formulated with chitosan of higher MW.

Eco-Friendly Hybrid PLLA/Chitosan/Trichoderma asperellum Nanomaterials as Biocontrol Dressings against Esca Disease in Grapevines.

Fungi constitute the largest number of plant pathogens and are responsible for a range of serious plant diseases. Phaeomoniella chlamydospora (P. chlamydospora) and Phaeoacremonium aleophilum (P. aleophilum) are the main fungal pathogens causing esca disease in grapevines. On the other hand, there are beneficial microorganisms such as Trichoderma spp., which are able to control the growth of many phytopathogens. In the present study, innovative, eco-friendly hybrid nanomaterials were created by electrospinning PLLA, followed by the formation of a film of chitosan/Trichoderma asperellum (T. asperellum) spores on the fibers. The polymer carrier used in this study plays an active role in ensuring the viability of the biological agent during storage and, when placed in contact with moisture, ensures the agent’s normal development. Oligochitosan, as well as low molecular weight and high molecular weight chitosan, were used. The effects of chitosan molecular weight on the dynamic viscosity of chitosan solutions, film formation, mechanical properties, spore incorporation and growth were studied. The morphology of the prepared nanomaterials, and the presence of a film based on the formation of chitosan/T. asperellum spores on the PLLA fibers, were examined using scanning electron microscopy (SEM). The surface chemical compositions of the fibrous materials were studied using attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR). The mechanical properties of the obtained materials were also tested. The microbiological screening that was performed revealed that the eco-friendly hybrid nanomaterials incorporated with the beneficial microorganism, T. asperellum, to hamper the growth of the pathogenic P. chlamydospora and P. aleophilum fungi. The suppression rate depended on the viscosity of the chitosan solution used for the film formation. The use of oligochitosan resulted in the most effective infection of the material with T. asperellum spores. The environmentally friendly hybrid nanomaterials obtained in this study—in which the bioagent was embedded—are promising bioactive dressings for protecting grapevines against esca disease.

Making a meal out of bugs

Making a meal out of bugs

Effect of Different Molecular Weights of Chitosan on Formulation and Evaluation of Allopurinol-Loaded Nanoparticles for Kidney Targeting and in Management of Hyperuricemic Nephrolithiasis.

Present research study was conducted to formulate kidney-targeted allopurinol (AO)-loaded chitosan nanoparticles (ANPs) for management of hyperuricemic related nephrolithiasis. Different molecular weights of chitosan were used for fabricating ANP formulation by adopting modified ionotropic gelation method. The prepared batches were than evaluated for particle size analysis, entrapment efficiency, transmission electron microscopy, X-ray diffraction, Differential Scanning Calorimetry, in vitro release and in vivo animal study. The in vivo study depicted that post 2 h of administration of different formulations and pure drug; ANPs prepared from low molecular weight chitosan showed maximum concentration of AO in kidney signifying successful kidney targeting of drug (25.92 fold) whereas no or very less amount of AO was seen in other animal groups. Effectiveness (p < 0.01) of formulation in management of hyperuricemia-associated nephrolithiasis was also evaluated via estimation of urine pH and serum and urine uric acid levels of mice. Further histological study was also performed on kidney samples which again affirmed these results. Present investigation demonstrated that ANPs prepared from low MW chitosan depicted maximum kidney-targeting ability that might be due to its specific uptake by the kidneys as well as its higher solubility than other two polymers, which results in enhanced release rate from the formulation and also offers an efficient strategy for the management of hyperuricemic nephrolithiasis.

Synergistic effect of discrete ultrasonic and H2O2 on physicochemical properties of chitosan

Synergistic degradation of chitosan by discrete ultrasonic and H2O2 was investigated. The effects of ultrasonic time, ultrasonic power, chitosan concentration, and H2O2 concentration were evaluated. The results revealed that ultrasonic power, H2O2 concentration and ultrasonic time were positively correlated with degradation rate, while chitosan concentration was negative. The results of degradation kinetics revealed that the synergistic degradation process was consistent with the first-order reaction. Changes of characterization of chitosan were analyzed by FTIR, 13C NMR, XRD, SEM, and AFM analysis. The results indicated that the synergistic degradation did not destroy the pyranose ring. The crystal structure of degraded chitosan was destroyed, and the molecular conformation changed significantly. The antioxidant activity of the original and degraded chitosan was determined by DPPH and reducing power assays. The degraded chitosan had higher antioxidant activity. All results showed that the synergistic degradation of discrete ultrasound and H2O2 was a feasible method for large-scale low molecular weight chitosan production.

Resolving the Mutually Exclusive Immune Responses of Chitosan with Nanomechanics and Immunological Assays.

Multifaceted functions displayed by both pro- and anti-inflammatory properties of chitosan hinder its effective development as an immunomodulatory agent. Herein, the contributions of the bending stiffness of chitosan with regard to its immune regulatory properties toward inflammation are investigated. The anti-inflammatory properties of chitosan molecular weight (MW) with a shorter (≈1kDa) or longer (≈15kDa) than the persistent length (LP ) are compared using immunological assays and nanomechanics-based experiments on the surface forces apparatus (SFA). Interestingly, 1kDa chitosan significantly enhances the generation of anti-inflammatory regulatory T cells (Tregs) through the Dectin-1-dependent pattern recognition receptor (PRR) on antigen-presenting cells. SFA analyses also show a similar trend of interaction forces between chitosan and diverse PRRs depending on their MW. The results obtained in the immunological and nanomechanical experiments are consistent and imply that the binding features of PRRs vary depending on the MW of chitosan, which may alter immune activity. In accordance, in vivo administration of only 1kDa represses inflammatory responses and suppresses the progression of experimental colitis. This study elucidates a previously unexplored bending stiffness-dependent immune regulatory property of chitosan and suggests the applicability of low MW (rod-like) chitosan as a pharmaceutical ingredient to treat diverse inflammatory disorders.

Enhancing the antibacterial effect of chitosan to combat orthopaedic implant-associated infections

The development of antibacterial resistance imposes the development of novel materials to relieve the burden of infection. Chitosan, a material of natural and sustainable origin, possesses ideal characteristics to translate into a novel biomaterial with antibacterial properties, as it already has these properties and it allows easy and scalable chemical modification to enhance its activity. The aim of the present work was that of producing low molecular weight chitosans that have higher solubility and can remain protonated at physiological pH, thus enhancing the antimicrobial action. This was achieved by reacting acid hydrolysed low molecular weight chitosan with 2-bromoethyleneamine hydrobromide or Fmoc-Lys(Fmoc)-OH to elicit N-(2-ethylamino)-chitosan and N-2(2,6-diaminohexanamide)-chitosan polymers. The latter derivative, CS3H Lys, that was synthesised for the first time, showed superior efficacy against Staphylococcus aureus, supporting further studies for its inclusion in implant coating materials to tackle the burden of orthopaedic implant-associated infections.

Quantitative functionalization of chitosan using green and efficient azetidinium-amine reactions

Despite significant advances in the field, quantitative post-polymer modification of chitosan, specifically attaching diverse hydrophobic moieties with experimentally predefined (via the ratio of reagents) degree of functionalization remain extremely challenging. In this context, we report our studies towards the use of green and efficient azetidinium-amine reactions to prepare a library of modified chitosan with a predefined degree of functionalization, with excellent conversion (>90%), atom economy and very low E-factor (<0.1). Initially six different azetidinium functionalized coupler molecules, which contains azetidinium functionality attached with other defined target functionality (ranging from hydrophobic to hydrophilic) are synthesized. In the next stage the azetidinium functionalized coupler molecules are reacted with chitosan (both low molecular weight and high molecular weight chitosans are used) in presence of 1,4-diazabicyclo[2.2.2]octane(DABCO, as base) using water as solvent and the other functional moiety are attached with the chitosan backbones. The degree of functionalization was calculated using 1H NMR and excellent match (80–100%) was noted between calculated degree of functionalization and feed ratio of the reagents used (experimentally defined ratio).

Improvement of chitosan water solubility by fumaric acid modification

Chitosan is a natural biopolymer with widespread availability. Its absorption, biodegradability, and biocompatibility make it ideal for extensive application. However, the high molecular weight and the high degree of polymerization limit its water solubility at neutral pH. Water solubility can be improved through the transformation in chitosan properties. We aimed to enhance the physicochemical properties through the modification of low, medium, and high molecular weight chitosan by using fumaric acid. With increasing molecular weight of native chitosan, the modified chitosan showed a decrease in water solubility and thermal properties. According to the pH dependence study, the modified products showed higher water solubility than native chitosan in a wide pH range. Fourier transform infrared (FTIR) spectroscopy results proved the effectiveness of modification by fumaric acid. The enhanced water solubility of modified chitosan can maximize its application to the food, biomedical, and cosmetic industry.

Addition time plays a major role in the inhibitory effect of chitosan on the production of Pseudomonas aeruginosa virulence factors.

Pseudomonas aeruginosa is a gram-negative bacterium capable of forming persistent biofilms that are extremely difficult to eradicate. The species is most infamously known due to complications in cystic fibrosis patients. The high mortality of cystic fibrosis is caused by P. aeruginosa biofilms occurring in pathologically overly mucous lungs, which are the major cause facilitating the organ failure. Due to Pseudomonas biofilm-associated infections, remarkably high doses of antibiotics must be administered, eventually contributing to the development of antibiotic resistance. Nowadays, multidrug resistant P. aeruginosa is one of the most terrible threats in medicine, and the search for novel antimicrobial drugs is of the utmost importance. We have studied the effect of low molecular weight chitosan (LMWCH) on various stages of P. aeruginosa ATCC 10145 biofilm formation and eradication, as well as on production of othervirulence factors. LMWCH is a well-known naturally occurring agent with a vast antimicrobial spectrum, which has already found application in various fields of medicine and industry. LMWCH at a concentration of 40mg/L was able to completely prevent biofilm formation. At a concentration of 60mg/L, this agent was capable to eradicate already formed biofilm in most studied times of addition (2-12h of cultivation). LMWCH (50mg/L) was also able to suppress pyocyanin production when added 2 and 4h after cultivation. The treatment resulted in reduced formation of cell clusters. LMWCH was proved to be an effective antibiofilm agent worth further clinical research with the potential to become a novel drug for the treatment of P. aeruginosa infections.

Mupirocin-Loaded Chitosan Microspheres Embedded in Piper betle Extract Containing Collagen Scaffold Accelerate Wound Healing Activity.

This study reports the formulation of mupirocin-loaded chitosan microspheres embedded in Piper betle extract containing collagen scaffold as combinational drug delivery for improved wound healing. Selection of chitosan type (molecular weight and degree of deacetylation) was carried out based on their antibacterial efficacy. The low molecular weight chitosan was selected owing to the highest antibacterial action against gram-positive as well as gram-negative bacteria. Low molecular weight chitosan-microspheres showed spherical shape with largely smooth surface morphology, 11.81% of mupirocin loading, and its controlled release profile. The XRD, DSC thermograms, and FT-IR spectral analysis revealed the mupirocin loaded in molecularly dispersed or in amorphous form, and having no chemical interactions with the chitosan matrix, respectively. The in vivo study indicates potential effect of the mupirocin, Piper betle, and chitosan in the collagen scaffold in the wound healing efficiency with approximately 90% wound healing observed at the end of 15 days of study for combinational drug-loaded chitosan microspheres-collagen scaffold-treated group. The histopathology examination further revealed tissue lined by stratified squamous epithelium, collagen deposition, fibroblastic proliferation, and absence of inflammation indicating relatively efficient wound healing once treated with combinational drug-loaded chitosan microspheres containing scaffold.

Encapsulation of roselle anthocyanins in blank alginate beads by adsorption and control of anthocyanin release in beverage by coatings with different molecular weight chitosan

In this study, the encapsulation of roselle anthocyanins was improved by immersing blank alginate beads in concentrated anthocyanin extracts. When increasing the alginate concentration (1–3%) and the anthocyanin concentration in the soaking solution (0.1–1.0 g/L), the phenolics, flavonoids, and anthocyanins gradually adsorbed to the matrix over time and peaked at 84–108 hr, leading to higher antioxidant activities. Before added to an acidic beverage, 3% alginate hydrogels soaked in solution of 1.0 g/L after 84 hr were coated using two types of chitosan with low and medium molecular weight. The results showed that low-molecular weight chitosan was superior to medium-molecular weight chitosan in limiting the diffusion of anthocyanins into beverage. The release rates of anthocyanins into beverage were in descending order: control > medium-molecular weight chitosan > low-molecular weight chitosan, as illustrated by the time required for anthocyanins to reach an equilibrium state being 1, 150, and more than 400 hr, respectively. Novelty impact statement Blank alginate gels were soaked in the concentrated roselle solution for anthocyanin adsorption. The antioxidant contents and activities increased at higher alginate and anthocyanin concentrations in the soaking solution and peaked at 84–104 hr. Low-molecular weight chitosan coating reduced the rate of anthocyanin release from beads into acidic beverages.

Chitosan molecular weights affect anthracnose incidence and elicitation of defence-related enzymes in avocado (Persea americana) cultivar ‘Fuerte’

Anthracnose decay is one of the major causes of postharvest losses of avocados (Persea americana), during marketing. Currently, Prochloraz® fungicide is used to control anthracnose at postharvest stage which poses threat to consumer safety. Therefore, this study evaluated the effects of high and low molecular weight chitosan on the control of avocado anthracnose and fruit defence mechanism. In curative inoculation, avocados ‘(Fuerte’) were inoculated via the wounds with C. gloeosporioides spore suspension (20 μL, 1 × 106 spores mL−1). Thereafter coated with different concentrations (0.5%, 1% and 1.5%) of low (LMWC) and high molecular weight (HMWC) chitosan and fruits were held at 25 °C for 5 days. The % anthracnose incidence in avocado fruits was recorded on day 5. During preventative inoculation, wounded fruits were dipped in different concentrations of LMWC or HMWC solutions, and subsequently inoculated with C. gloeosporioides suspension. Preventatively inoculated fruits were stored for 28 days at 6.5 °C, 85% RH and thereafter for 5 days at 25 °C and 75% RH to simulated market shelf condition. The % anthracnose incidence was recorded on day 5. Fruit treated with Prochloraz® and water were included as controls for both curative and preventative infected fruits. Promising chitosan coatings with the lowest anthracnose incidence and the controls were investigated for skin epicatechin content, defence-related genes; phenylalanine ammonia lyase (PAL), lipoxygenase (LOX), fatty acid elongase (avael) and desaturase (avfad 12–3), chalcone synthase (CHS) and flavonol synthase (FLS) using RT- qPCR method. The zeta potential of selected chitosan coatings was done following standard procedures. Percentage of anthracnose incidence were lowest in 1.5% LMWC (18%, 3 mm) compared to Prochloraz® (23%, 5 mm) and the untreated fruit (90%, 24 mm). The 1.5% LMWC had the highest up-regulation of PAL, avfael, avfad 12–3, CHS, FLS genes and down-regulation of LOX gene with concomitant increase in epicatechin content (340 mg kg−1) relative to other chitosan treatments, untreated and Prochloraz® treated fruits. The superior positive zeta potential of LMWC 1.5% coating corroborates its effectiveness in controlling avocado anthracnose than HMWC 1.5%. It is possible that the interaction between the positively charged chitosan amino group (-NH3+) and the negatively charged microbial cell membrane is responsible for the enhanced antifungal activity. In late season naturally infected fruits dipped in 1.5% LMWC, anthracnose incidence dropped to 28% while Prochloraz® treated fruits showed anthracnose incidence of 82% on day 8 at the market shelf. LMWC 1.5% can replace the currently used Prochloraz®.

The Use of Chitosan and Starch-Based Flocculants for Filter Backwash Water Treatment

Inorganic aluminum or iron salts supported with synthetic polymers are commonly used to eradicate colloidal particles from water in coagulation and flocculation processes. Nevertheless, these agents have several disadvantages, such as large volumes of sludge produced or environmental toxicity. Recently biodegradable polymers have been suggested as eco-friendly flocculants for water treatment. This study aimed to investigate the possibilities of using starch and chitosan and their oxidized derivatives as flocculants for filter backwash water treatment. Dialdehyde starch (DST) and dialdehyde chitosan (DCT) were synthesized by periodate oxidization of natural starch from corn and low molecular weight chitosan. The obtained materials have been characterized with scanning electron microscopy (SEM), ATR-FTIR spectroscopy, and thermogravimetric analysis (TGA). Furthermore, we studied the flocculation properties of polysaccharide flocculants in a series of jar tests. The effectiveness of chitosan and starched-based flocculants was compared to synthetic polymers commonly used to treat iron ions-rich filter backwash water. The environmental aspects of these chemicals, particularly the biodegradability of post-flocculation residues, were also addressed. It was found that oxidized starch and chitosan derivatives can be used as ecological flocculating materials to treat potable water or sludge.

Study on Fabrication of Antibacterial Low Molecular Weight Nanochitosan Using Sodium Tripolyphosphate and Hydrogen Peroxide

In the study, chitosan was decomposed into low molecular weight chitosan by using different H2O2 concentrations for chain termination, and then chitosan was prepared with different concentrations of tripolyphosphate cations (TPP). We have obtained the following result: the formation of chitosan depends on the concentration of TPP; TPP at low or high concentrations does not react with chitosan to form small chitosan molecules. Properly structured chitosan is only obtained when the mass ratio of chitosan/TPP is 6 : 3. At this rate, when the mass ratio of chitosan/TPP is approximately 6 : 3, there the formed nanochitosan particles have good antibacterial ability against strains of E. coli, M. catarrhalis, and S. aureus. In this work, initially, a successful preparation of a suspension between nasal spray and small chitosan suspension was found at manufacturing ratios: 5 ml nasal spray and 5 ml manufactured chitosan suspension at concentrations of 1 mg/ml, 3 mg/ml, and 5 mg/ml. It proves that the chain termination process by using H2O2 and the creation cross-linking when adding TPP are successful to a certain extent.

Evaluation of Antibacterial and Antifungal Properties of Low Molecular Weight Chitosan Extracted from Hermetia illucens Relative to Crab Chitosan.

This study shows the research on the depolymerisation of insect and crab chitosans using novel enzymes. Enzyme preparations containing recombinant chitinase Chi 418 from Trichoderma harzianum, chitinase Chi 403, and chitosanase Chi 402 from Myceliophthora thermophila, all belonging to the family GH18 of glycosyl hydrolases, were used to depolymerise a biopolymer, resulting in a range of chitosans with average molecular weights (Mw) of 6–21 kDa. The depolymerised chitosans obtained from crustaceans and insects were studied, and their antibacterial and antifungal properties were evaluated. The results proved the significance of the chitosan’s origin, showing the potential of Hermetia illucens as a new source of low molecular weight chitosan with an improved biological activity.

One-step preparation of hydrogel based on different molecular weights of chitosan with citric acid.

Chitosan-based hydrogels have been prepared previously by a two-step protocol in which chitosan was first dissolved in dilute acetic acid and then crosslinked by glutaraldehyde or genipin. This was a time-consuming method, which had the disadvantages of high costs and biological safety problems. Scanning electron microscopy (SEM) results verified the successful preparation of hydrogels based on high, medium, and low molecular-weight chitosan (HCS, MCS, and LCS), respectively. The hydrogels prepared with HCS, MCS, and LCS were formed through the accumulation of different-sized crystals. The framework density of the hydrogel was enhanced by an increase in the chitosan molecular weight and exhibited a crack pore pattern composed of flake particles. Medium molecular-weight chitosan-based hydrogel exhibited the highest specific surface area and total pore volume, with values of 3.81 m2 g-1 and 0.0109 cm3 g-1 , respectively. The water absorption rate of the chitosan based hydrogels was influenced by its molecular weights at the sequence of LCS > HCS > MCS, while the maximum compression stress was affected at the sequence of HCS > MCS > LCS. The network structure was enhanced with an increase in the chitosan molecular weight and reached maximum stress levels of 4.50, 1.50 and 0.75 MPa for HCS-, MCS-, and LCS-based hydrogels, respectively. Citric acid was shown to be an effective dissolving and crosslinking agent in the preparation of MCS- and HCS-based hydrogels. The physiochemical properties of the hydrogels were enhanced as the molecular weight of the chitosan increased. © 2021 Society of Chemical Industry.