Chitosan is a cationic polysaccharide derived from chitin, the second most abundant natural polymer on Earth after cellulose and the structural backbone of crustacean exoskeletons. Chemically, chitosan consists of repeating units of D-glucosamine and N-acetyl-D-glucosamine linked by beta-(1,4) glycosidic bonds, and its native amine groups become protonated at physiological pH. This positive charge allows the polymer to interact electrostatically with negatively charged cell membranes, modulating cell adhesion, migration and proliferation. Because of these properties, chitosan has long attracted interest as a wound-dressing material that can promote tissue regeneration, stimulate fibroblast activity, accelerate hemostasis and suppress microbial infection. The single most important quality parameter is the degree of deacetylation, the proportion of deacetylated glucosamine units in the chain; a chitin sample with more than 50 percent deacetylation is generally classified as chitosan, and higher values typically improve solubility, antimicrobial performance and biological interactions.

The catch has always been how to make it. Conventional extraction subjects shrimp shell powder to concentrated sodium hydroxide at high temperatures for hours, an energy-intensive process that risks degrading the polymer backbone and inflating production costs. Alternative technologies each carry their own burdens: ultrasound can accelerate extraction but may cleave polymer chains and reduce molecular weight, enzyme-assisted routes offer selectivity at the price of costly catalysts and long processing times, and deep eutectic solvents reduce harsh chemical use but complicate solvent recovery at industrial scale. Microwave-assisted extraction promises shorter reaction times, lower electricity consumption, simpler equipment and easier scalability, because microwave radiation heats the reaction mixture directly and uniformly through dipole rotation and ionic conduction rather than through slow conduction and convection.

The research team, working with shrimp shell waste from Indonesian processing of Litopenaeus vannamei, ground and sieved the dried shells to 74 to 150 micrometers and then optimized each of the three extraction stages under microwave irradiation. Demineralization with hydrochloric acid proved to be governed mainly by acid concentration rather than microwave power: at 0.5 M HCl more than 72 percent of the calcium remained, while both 1 M and 2 M HCl achieved complete calcium removal across 400, 500 and 600 watts within just five minutes. Deproteinization with sodium hydroxide followed a similar pattern, with protein removal rising from 99.18 percent at 2 percent NaOH to a full 100 percent at 10 percent NaOH, regardless of the power level applied.

Deacetylation, the step that transforms chitin into chitosan, responded strongly to both alkali concentration and microwave power. At a fixed 600 watts, increasing NaOH from 40 to 80 weight percent pushed the degree of deacetylation toward 80 percent even in five-minute treatments, and extending the reaction to ten minutes at 600 watts and 80 percent NaOH lifted the value to nearly 85 percent. FTIR spectroscopy, using the ratio of absorbance bands at 1320 and 1420 inverse centimeters, confirmed a degree of deacetylation of 85 percent for microwave-synthesized chitosan versus 80 percent for the conventionally produced material. More striking was the yield: microwave processing converted 10 percent of the starting shell mass into final chitosan, compared with only 1.6 percent for the conventional route, a six-fold improvement in material efficiency.

Structural characterization reinforced the case for the microwave route. X-ray diffraction showed that both products were semi-crystalline, but the conventionally synthesized sample exhibited a broadened and weakened peak near 2 theta of 10 degrees, indicating loss of crystallinity, whereas the microwave product retained a well-defined crystalline peak, suggesting that rapid volumetric heating minimizes disruption of the polymer backbone. Scanning electron microscopy revealed characteristic lamellar flake morphologies with smooth surfaces and dense packing for both materials, consistent with a high density of free amino groups. At the molecular level, the researchers explain the difference through kinetics: hydroxide ions attack the electrophilic carbonyl carbon of chitin’s acetamide groups, cleaving the C–N bond and releasing acetate, and microwave-driven dipolar heating accelerates this nucleophilic attack throughout the crystalline core instead of forcing slow diffusion from a hot surface inward.

The biological evaluation focused on RAW 264.7 murine macrophage-like cells, key players in the inflammatory phase of wound repair. In MTT cytotoxicity assays, microwave-derived chitosan at concentrations from 0.1 to 10 milligrams per milliliter did not significantly reduce cell viability over 24 or 48 hours of incubation, demonstrating excellent cytocompatibility. In scratch assays, monolayers cultured on the chitosan-coated substrates showed progressive wound closure beginning around 12 hours, with the cell-free gap nearly completely closed after 48 hours. The authors attribute this activity in part to positively charged calcium ions released from the biopolymer, which may enhance cell proliferation, and to the hydrophilic character of the chitosan surface. They caution, however, that macrophage results represent only one facet of a process that also depends on fibroblasts, keratinocytes, endothelial cells and extracellular matrix remodeling, and that fibroblast and keratinocyte models plus in vivo studies are needed to confirm therapeutic efficacy.

To probe mechanism, the team performed molecular docking of chitosan malate against AKT1, a protein kinase central to the PI3K/AKT signaling pathway that drives cell proliferation, migration and angiogenesis during tissue repair. Chitosan malate showed a predicted binding affinity of minus 9.6 kilocalories per mole toward AKT1, stronger than the known AKT activator SC79 at minus 7.9, with predicted contacts at residues Thr81, Thr82 and Arg273 in the PH domain and near the kinase domain interface. The researchers stress that these are exploratory computational estimates: the study did not measure AKT1 expression or phosphorylation, so any involvement of the pathway in the observed wound-closure behavior remains a hypothesis requiring experimental validation.

The economic case may prove equally consequential. By integrating equipment power ratings over operating times, the team calculated that microwave-assisted synthesis consumed up to 94.6 percent less energy than conventional heating. A techno-economic analysis anchored to Indonesian market conditions yielded a positive net present value of approximately USD 10.73 million, an annual profitability investment of 18.62 percent, and a benefit-cost ratio of 17.72, comfortably above the feasibility threshold of unity. Sensitivity analyses varying the product selling price by plus or minus 15 percent showed that the project remained profitable even in the worst scenario, with NPV near USD 9 million and a benefit-cost ratio of 15. Taken together, the results position microwave extraction as a commercially viable, energy-efficient pathway for turning one of the seafood industry’s largest waste streams into a biomedical raw material, though the authors note that pilot-scale validation, molecular-weight characterization, in vivo testing and continuous reactor design remain the next hurdles before clinical and industrial adoption.

Subject of Research: Microwave-assisted synthesis of high-quality chitosan from shrimp shell biowaste for wound-healing applications

Article Title: Comparative study of microwave-assisted and conventional methods for the synthesis of high-quality chitosan from shrimp shell biowaste to manipulate cell growth and functions: Supported molecular docking analysis

Article References: Rahmatunnisa, C., Budi, C. S., Ilhami, F. B., Puspitarini, S., Melanie, M., Hapidin, D. A., Kuo, D.-H., Zeleke, M. A., Kurnia, I., Hastuti, L. P., Rahmah, D. M., & Gultom, N. S. (2026). Comparative study of microwave-assisted and conventional methods for the synthesis of high-quality chitosan from shrimp shell biowaste to manipulate cell growth and functions: Supported molecular docking analysis. Case Studies in Chemical and Environmental Engineering, 14, Article 101481. https://doi.org/10.1016/j.cscee.2026.101481

Image Credits: AI Generated

DOI: 10.1016/j.cscee.2026.101481

Keywords: chitosan, shrimp shell waste, microwave-assisted extraction, chitin deacetylation, wound healing, biomaterials, molecular docking, AKT1, techno-economic analysis, biocompatibility, energy efficiency, marine biowaste

At the heart of this novel hydrogel lies ε-poly-L-lysine, a natural antimicrobial peptide recognized for its broad-spectrum bactericidal properties. By embedding ε-PLL within a biocompatible matrix of sodium alginate and gelatin, the researchers engineered a material that not only physically covers wounds but actively combats infections caused by common and dangerous pathogens such as Escherichia coli and Staphylococcus aureus. This is a critical advancement given the rising toll of chronic wound infections, which often culminate in antibiotic-resistant strains and delayed tissue regeneration.

The physical characteristics of PSG15 demonstrate remarkable suitability for clinical deployment. Its injectability ensures precise, minimally invasive application even in irregular wound topographies. Meanwhile, the hydrogel’s self-adhesive nature promotes effective retention at the injury site, mitigating frequent dressing changes and associated discomfort. Moreover, its mechanical robustness ensures resilience under physiological stresses without compromising flexibility. These features collectively underscore PSG15’s potential to improve patient compliance and therapeutic outcomes in wound care settings.

Experimental evaluations reveal PSG15’s impressive antibacterial efficacy, achieving bacterial load reductions exceeding 89% for E. coli and over 92% for S. aureus. Such potent antimicrobial effects are indispensable for halting infection progression and preventing biofilm formation, a notorious barrier to healing. Importantly, this localized bactericidal action circumvents systemic antibiotic exposure, reducing adverse effects and mitigating the emergence of resistant microorganisms—a growing global health concern.

Beyond bactericidal activity, PSG15 exhibits a remarkable ability to influence immune cell dynamics, particularly macrophage polarization. Wound healing critically depends on the balance between pro-inflammatory (M1) and anti-inflammatory, tissue-repair promoting (M2) macrophage phenotypes. In vivo studies in murine models showed that PSG15 treatment shifts this balance by elevating M2 marker expression (CD206) while suppressing M1 markers (CD80). This immunomodulatory effect attenuates inflammation, thereby expediting the transition to tissue regeneration phases essential for effective wound closure.

Complementing immune regulation, PSG15 exerts modulatory effects on the skin microbiota, preserving microbial diversity and preventing pathogenic overgrowth. This aspect is particularly novel, as dysbiosis of skin microbiota is increasingly recognized as a critical factor contributing to chronic wound pathology. By stabilizing the microbial community, PSG15 not only prevents reinfection but also supports homeostatic processes necessary for sustained tissue repair.

Histological analyses further elucidate the regenerative potential of PSG15. Compared with untreated wounds, PSG15-treated tissue displayed enhanced angiogenesis—a pivotal process that restores blood supply and oxygenation to regenerating tissues. The hydrogel also promoted more organized collagen fiber deposition, laying a robust extracellular matrix scaffold to restore skin integrity. These histopathological improvements translate into accelerated wound closure and reduced scar formation, addressing critical clinical goals.

The synthesis of PSG15 employs calcium chloride as a crosslinking agent, facilitating the formation of a stable, three-dimensional hydrogel network integrating ε-PLL within the sodium alginate/gelatin framework. This method enhances the hydrogel’s mechanical stability while ensuring controlled release of the antimicrobial peptide. The controlled release is essential to maintaining effective antibacterial concentrations at the wound site over extended periods, thereby maximizing therapeutic benefit without cytotoxicity.

Biocompatibility assays confirm that PSG15 exhibits minimal cytotoxic effects on mammalian cells, ensuring its suitability for in vivo application. Its injectable and self-adhesive properties further improve ease of use in clinical settings, enabling healthcare providers to deliver personalized and targeted therapies. The non-toxic nature of the hydrogel also opens the door to long-term applications, especially for chronic wounds where repeated treatments are often necessary.

Dr. Chaoji Huangfu, a lead researcher on the project, emphasized the hydrogel’s dual-action strategy as a significant advancement in wound therapeutics. By integrating antimicrobial efficacy with microbiota regulation and immune modulation, PSG15 addresses the multifactorial challenges of infected wounds in a holistic manner. This approach could redefine treatment paradigms, particularly in cases complicated by persistent infections and disrupted skin homeostasis.

The broader significance of PSG15 extends to global health challenges related to antibiotic resistance. As systemic antibiotic administration faces increasing limitations, local treatments like PSG15 that reduce systemic exposure while ensuring focused antibacterial action are critical for sustainable healthcare. In addition, by fostering wound microenvironment normalization and immune balance, PSG15 may reduce the incidence of chronic, non-healing wounds that impose heavy economic and social burdens worldwide.

Future investigations are poised to explore PSG15’s efficacy in chronic wound models, including diabetic ulcers and pressure sores, where complex pathophysiology often impedes healing. These studies will also delve deeper into the molecular mechanisms by which the hydrogel modulates macrophage polarization and microbiota dynamics. Understanding these pathways could facilitate further optimization and personalization of hydrogel formulations for diverse clinical scenarios.

In conclusion, the multifunctional ε-poly-L-lysine-loaded sodium-alginate/gelatin hydrogel PSG15 integrates potent antibacterial capacity, immune modulation, and microbiota stabilization within a biocompatible, injectable scaffold. Its demonstrated acceleration of infected wound healing and restoration of skin integrity in preclinical models positions it as a promising candidate for next-generation wound management solutions. This innovation represents a critical step forward in bridging infection control with tissue regeneration, promising safer and more effective therapies for patients worldwide.

Subject of Research: Not applicable

Article Title: A multifunctional injectable ε-poly-L-lysine-loaded sodium-alginate/gelatin hydrogel promotes the healing of infected wounds by regulating macrophage polarization and the skin microbiota

News Publication Date: 31-May-2025

Web References:

• https://doi.org/10.1093/burnst/tkaf037
• https://academic.oup.com/burnstrauma

References:

• DOI: 10.1093/burnst/tkaf037

Keywords
Hydrogels, Antimicrobial peptides, Wound healing, Macrophage polarization, Skin microbiota, Tissue regeneration, ε-poly-L-lysine, Sodium alginate, Gelatin, Injectable biomaterials, Antibiotic resistance, Angiogenesis