Omega-3 Fatty Acids Locked Into Smart Chitosan Nanofibers Unleash Antibacterial Power Only Where Wounds Need It

Omega-3 fatty acids have long been celebrated for their anti-inflammatory and antimicrobial properties, but their Achilles heel has always been the same: they oxidize rapidly when exposed to light, oxygen, or heat, losing their therapeutic potency before they can do much good. Now, a team of biomedical engineers at the University of Memphis, working with collaborators at the University of Tennessee Health Science Center, has developed a clever solution that locks these fragile molecules onto a wound dressing and releases them only when infection strikes. The research, published in Frontiers in Medical Engineering, describes how docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA) — the two most biologically active long-chain omega-3 polyunsaturated fatty acids — were covalently grafted onto electrospun chitosan membranes through cleavable ester bonds, creating a smart material that stays silent in healthy tissue but springs into action in the hostile chemistry of an infected wound.

The problem the researchers set out to solve is one that has plagued every attempt to harness omega-3 fatty acids for topical therapy. These molecules carry multiple carbon-carbon double bonds that are exquisitely vulnerable to oxidative degradation, producing lipid peroxides and free radicals that destroy their bioactivity. Conventional approaches have relied on encapsulation — wrapping the fatty acids in liposomes, microcapsules, or nanoparticles stabilized with antioxidants — but these systems still suffer from burst release, where a large fraction of the payload dumps out immediately upon contact with fluid, potentially reaching toxic concentrations while leaving little behind for sustained therapy. Covalent attachment, by contrast, eliminates the burst problem entirely: the fatty acids cannot leach out until the chemical bonds holding them are deliberately broken.

The Memphis team’s approach hinges on a transesterification reaction that swaps the ester linkages in omega-3 triglycerides for new ester bonds directly connecting the fatty acid chains to hydroxyl groups on the chitosan polymer backbone. Chitosan, a polysaccharide derived from crustacean shells, was chosen because it carries both amine and hydroxyl functional groups that can participate in such chemistry, and because electrospun chitosan nanofibers already excel as wound healing templates — they mimic the architecture of the extracellular matrix, absorb moisture, remain breathable, and support cell attachment and proliferation. The researchers dissolved 86% deacetylated chitosan in a mixture of trifluoroacetic acid and dichloromethane, electrospun it at 26 kilovolts into randomly oriented nanofibers roughly 100 nanometers in diameter, and collected them into membranes approximately 700 micrometers thick.

After neutralizing residual acid with triethylamine, the membranes were immersed in pyridine containing commercial omega-3 triglyceride oil and left to react for 24 hours at room temperature. Fourier-transform infrared spectroscopy confirmed the chemistry had worked: new peaks appeared at 1740 inverse centimeters, corresponding to the carbonyl stretch of ester bonds, alongside a broad alkyl signature around 2900 inverse centimeters attributable to the grafted fatty acid chains. Water contact angle measurements revealed the membranes had become markedly hydrophobic, with a contact angle of 127 degrees — a dramatic shift from the hydrophilic character of unmodified chitosan that reflects the dense layer of fatty acid chains now coating the fiber surfaces.

Quantifying exactly how much omega-3 had been loaded onto the membranes revealed a fascinating structural asymmetry. High-performance liquid chromatography of deacylated membrane samples showed approximately 25 micrograms per square centimeter of DHA and 13 micrograms per square centimeter of EPA. But when the team compared surface-sensitive X-ray photoelectron spectroscopy, which probes only the outermost 3 to 5 nanometers, with bulk acid-base titration that measures the entire fiber volume, they found a stark discrepancy. XPS indicated that nearly 97% of available surface hydroxyl groups were substituted with fatty acids, while titration showed only about 6.75% substitution across the bulk material. The explanation lies in geometry: DHA and EPA are bulky molecules — DHA alone occupies roughly 355 cubic angstroms — while the crystalline spacing between aligned chitosan units is only about 5.2 angstroms. Covalent conjugation therefore forces the fatty acid chains to extend outward from the fiber surface, creating a dense hydrophobic canopy roughly 1.3 to 2.6 nanometers thick that dominates the XPS sampling depth while leaving the fiber interior largely unmodified. This core-shell architecture, the researchers note, is not a flaw but a feature: it concentrates the therapeutic payload precisely where it will contact bacteria and tissue.

The real magic emerged in the release experiments. Over five days of elution testing, the conjugated membranes released essentially nothing in neutral phosphate-buffered saline at pH 7.4 — no measurable lipid leaching whatsoever. But when the pH dropped to 4.5 in acetate-buffered saline, or when Pseudomonas lipase enzyme was added to the neutral buffer, the ester bonds began hydrolyzing and the fatty acids poured out. DHA showed a particularly favorable profile, releasing an average of 20 micrograms per day in both acidic and enzyme-containing conditions, with sustained delivery over the full five-day period and complete release achieved by day four. EPA release was more sporadic and limited, totaling roughly 20% of the initial loading. The differential behavior likely reflects differences in how the two fatty acids pack within the surface canopy and how readily their ester bonds access water and enzyme active sites.

These trigger mechanisms are not arbitrary — they map directly onto the biology of wound infection. Healthy intact skin maintains a slightly acidic pH of approximately 4.7, while infected and chronic wounds typically shift toward alkalinity and harbor elevated levels of bacterial lipases, extracellular enzymes that specifically cleave ester linkages. By exploiting both low pH and bacterial enzyme activity as release triggers, the membrane effectively uses the presence of infection itself as the signal to deploy its therapeutic payload. Scanning electron microscopy added another dimension to the story: after five weeks of exposure to acidic buffer, the nanofiber architecture underwent significant structural breakdown, driven by the combination of chitosan’s inherent solubility at low pH and the localized release of fatty acids. In neutral buffer with lipase, the fibers remained relatively intact. The researchers argue this degradation profile is clinically advantageous — the membrane holds together during the active treatment phase and then dissolves once its biological function is complete, eliminating the need for painful dressing changes that disrupt healing.

Biocompatibility testing using L929 mouse fibroblasts in transwell co-cultures showed the membranes maintained over 90% cell viability, well above the 70% threshold that ISO 10993-5 considers indicative of cytocompatibility. Live/dead fluorescence staining confirmed the majority of cells remained viable, and the membranes supported cellular migration — a critical property for a wound dressing intended to facilitate tissue repair. This is particularly notable given that other studies have shown high concentrations of unencapsulated omega-3 fatty acids can induce cytotoxicity and hemolysis in gelatin and carboxymethyl cellulose hydrogels; the slow, controlled release from the covalently conjugated membranes appears to keep local concentrations within a safe therapeutic window.

The antimicrobial results were equally striking, if selectively so. Against methicillin-resistant Staphylococcus aureus — one of the two most prevalent wound pathogens and a notorious source of antibiotic-resistant infections — the membranes inhibited planktonic growth by approximately 75% and suppressed biofilm formation on the culture plate by around 50%, while also reducing biofilm growth on the membrane surface itself by roughly 50% compared to gauze controls. These effects were achieved without any conventional antibiotics, against a bacterial load of 100,000 colony-forming units, a concentration far higher than what would typically be found in clean or contaminated wounds. Scanning electron micrographs showed dramatically fewer MRSA cells adhered to the omega-3-conjugated membrane surface compared to gauze. Against Pseudomonas aeruginosa, however, the membranes were less effective, inhibiting only about 15% of biofilm formation with no statistically significant difference from controls. The researchers attribute this selectivity to the outer membrane of Gram-negative bacteria, whose lipopolysaccharide layer restricts diffusion of hydrophobic compounds — a barrier that Gram-positive MRSA lacks.

The implications extend beyond wound care alone. The transesterification conjugation strategy is modular and could, in principle, be adapted to graft other cleavable-bond therapeutics onto chitosan or similar biopolymer scaffolds for stimuli-responsive delivery in diverse biomedical contexts. The researchers acknowledge important limitations that must be addressed before clinical translation: the degradation studies relied on qualitative electron microscopy rather than quantitative mass-loss tracking, the biological evaluations used a single fibroblast cell line and only two microbial strains, and the baseline loading measurements may have underestimated the true DHA content because the high-temperature deacylation process required for quantification likely degraded a fraction of the heat-sensitive fatty acids. Future work will need to explore the precise molecular mechanisms of microbial inhibition, test the membranes in combination with co-administered clinical antimicrobials, and validate performance in preclinical in vivo wound models that capture the complex, multi-species biofilms and dynamic enzymatic environments of real infections. But the core concept — a dressing that stays inert until infection activates it — represents a compelling new paradigm in the ongoing battle against chronic and antibiotic-resistant wound infections.

Subject of Research: Stimuli-responsive covalent conjugation of omega-3 fatty acids DHA and EPA onto electrospun chitosan membranes for controlled release in infected wound healing

Article Title: Stimuli-responsive release of covalently attached Omega-3 fatty acids from electrospun chitosan membranes

Article References: Yeasmin, R., Abuhussein, E., Tubbs, A. R., Lee, M., Fujiwara, T., Bumgardner, J. D., Cho, H., & Jennings, J. A. (2026). Stimuli-responsive release of covalently attached Omega-3 fatty acids from electrospun chitosan membranes. Frontiers in Medical Engineering, 4, Article 1897565. https://doi.org/10.3389/fmede.2026.1897565

Image Credits: AI Generated

DOI: 10.3389/fmede.2026.1897565

Keywords: omega-3 fatty acids, chitosan, electrospinning, wound dressing, stimuli-responsive drug delivery, DHA, EPA, MRSA, biofilm, ester bonds, antimicrobial biomaterials, wound healing