Silk Hydrogels Armored with Silver-Laced Titanium Nanofibers Fight Bacteria and Support Cells

Researchers at the University of Kashmir have engineered a silk fibroin hydrogel decorated with titanium dioxide nanofibers that encapsulate silver nanoparticles, creating a multifunctional biomaterial that kills bacteria on contact while remaining friendly to living cells. The work, published in Polymer Bulletin, combines three well-established fabrication techniques—sol-gel electrospinning, surfactant-triggered gelation, and ultrasonic coating—into a single pipeline for producing wound-healing scaffolds with unusually balanced properties. The team, led by Faheem A. Sheikh of the Nanostructured and Biomimetic Lab, reports that the resulting nanocomposite hydrogels form clear bacterial killing zones against both Escherichia coli and Staphylococcus aureus while supporting the growth of mouse embryonic fibroblast cells in standard viability assays.

Silk fibroin, the structural protein extracted from the cocoons of the silkworm Bombyx mori, has long been prized in biomaterials science for its biocompatibility, controllable biodegradability, and remarkably low immunogenicity. Surgeons and tissue engineers have used it in sutures, films, sponges, and hydrogels, and a growing body of literature documents its usefulness in wound dressings and bone regeneration scaffolds. Yet silk fibroin hydrogels on their own suffer from two persistent weaknesses: they lack intrinsic antibacterial activity, leaving implanted or dressings-based scaffolds vulnerable to infection, and their mechanical strength can be insufficient for demanding structural applications. The Kashmir group set out to address both shortcomings simultaneously without compromising the protein’s natural compatibility with human tissue.

The first stage of the fabrication process focused on the nanofibers themselves. Using sol-gel electrospinning, the researchers produced titanium dioxide nanofibers with silver nanoparticles embedded within them. Electrospinning draws a precursor solution through an electrified needle, whipping it into fibers with diameters in the nanometer range as the solvent evaporates; a subsequent sol-gel conversion and calcination step transforms the polymer-ceramic composite into pure titanium dioxide fibers. Silver was incorporated into the precursor so that the antimicrobial metal became an integral part of the fiber structure rather than a surface decoration that might wash away. This combination matters because titanium dioxide contributes its own antibacterial and photocatalytic behavior, while silver nanoparticles release silver ions that disrupt bacterial membranes, proteins, and DNA—a dual mechanism that has been extensively documented against both Gram-positive and Gram-negative organisms.

Turning liquid silk fibroin into a solid hydrogel quickly and controllably is a challenge in its own right, and here the team exploited a surfactant-based trick. Sodium dodecyl sulfate, or SDS, was added to the fibroin solution to trigger the transition from soluble random coils to the beta-sheet-rich network that gives silk its gel structure. The researchers found a strikingly concentration-dependent effect: at 0.1 molar SDS, gelation was fastest, completing in just twenty to thirty minutes. Above that threshold, however, the trend reversed. At concentrations between 0.12 and 0.5 molar, gelation times increased progressively, which the authors attribute to micellar repulsion—above a critical concentration, SDS molecules assemble into micelles whose charged surfaces interfere with the protein aggregation needed for gel formation. The finding gives future scaffold designers a precise dial for tuning how quickly a silk hydrogel sets, which is critical when the material must conform to a wound bed or be cast into a mold before solidifying.

With the hydrogel formed, the silver-loaded titanium dioxide nanofibers were deposited onto its surface using ultrasonication. The high-frequency vibrations drive the fibers into intimate contact with the soft, porous gel surface, anchoring them without harsh chemical adhesives that could compromise biocompatibility. Scanning electron microscopy revealed that the hydrogel retained its desired porous morphology both before and after the coating step, an essential feature because interconnected pores allow nutrient diffusion, waste removal, and cell infiltration in tissue engineering applications. The porosity of a scaffold is one of the most important determinants of how well cells populate it, and the team’s microscopy confirmed that the decoration process did not clog or collapse this architecture.

Structural confirmation came from X-ray diffraction and Fourier-transform infrared spectroscopy. The XRD patterns verified the crystalline phases of both the titanium dioxide and the embedded silver, while FT-IR confirmed the characteristic beta-sheet signatures of the silk fibroin matrix and showed no adverse chemical interactions between the components. Mechanical testing added a welcome bonus: incorporating the Ag-TiO2 nanofibers significantly improved the compressive strength of the hydrogel, indicating enhanced structural stability. For a material intended to line or fill a wound, resisting deformation under load can mean the difference between a dressing that protects tissue and one that disintegrates during handling or movement.

Durability of the coating was assessed by immersing the decorated hydrogels in phosphate-buffered saline, a standard physiological mimic. Post-immersion electron microscopy showed that the ultrasonically deposited nanofibers remained firmly attached to the hydrogel surface, demonstrating that the coating can withstand the aqueous, ion-rich conditions it would encounter in the body. This adhesion is not a trivial detail; many nanoparticle-laden biomaterials lose their active layers through leaching, which both diminishes antibacterial protection over time and raises concerns about where the released particles ultimately travel.

The antibacterial performance of the finished scaffolds was quantified using zone-of-inhibition assays, in which the material is placed on a lawn of bacteria and the surrounding cleared area is measured. The nanofiber-coated hydrogels produced killing zones of 15.491 plus or minus 0.46 millimeters against E. coli and 12.706 plus or minus 0.47 millimeters against S. aureus. Both organisms are clinically significant: E. coli is a common Gram-negative cause of wound and urinary infections, while S. aureus, including its antibiotic-resistant strains, is a leading culprit in surgical site and chronic wound infections. The somewhat larger zone against the Gram-negative organism suggests effective silver ion diffusion from the fiber surface, and the results position the scaffold as a candidate for infection-prone wound environments where conventional antibiotics struggle against biofilms.

Crucially, antimicrobial potency did not come at the cost of cytotoxicity. The team evaluated biocompatibility using the MTT assay with mouse embryonic fibroblast cells, a colorimetric test in which metabolically active cells convert a yellow tetrazolium compound into a purple formazan product, providing a readout of viability and proliferation. The nanocomposite hydrogels proved biocompatible, and the coating nanofibers showed no counterproductive effect on cell growth. This balance—lethal to bacteria, hospitable to mammalian cells—is the central design goal of infection-resistant biomaterials, and it is one that many silver-based systems fail to strike, since free silver at high concentrations can damage healthy tissue and provoke inflammatory responses.

The authors suggest that the multifunctional silk-based hydrogel holds particular promise for tissue engineering, and the broader context supports that optimism. Chronic wounds afflict millions of patients worldwide, and infected or poorly vascularized wound beds are a major barrier to healing, driving demand for dressings that combine moisture retention, mechanical protection, infection control, and cellular support in one material. By tuning SDS concentration to control gelation speed, embedding silver within electrospun titanium dioxide fibers for durable antimicrobial action, and using ultrasonication to bond those fibers to a porous silk scaffold, the Kashmir team has assembled a modular recipe in which each step can be independently optimized. The work, supported by the University of Kashmir and published as volume 83, article 649 of Polymer Bulletin, adds to a rapidly expanding toolkit of silk fibroin nanocomposites and points toward preclinical testing in wound models as the logical next step for a material that kills bacteria, holds its shape, and lets cells thrive.

Subject of Research: Silk fibroin hydrogels decorated with silver nanoparticle-encapsulating titanium dioxide nanofibers for antimicrobial and cell-supportive tissue engineering applications

Article Title: Silk fibroin hydrogels decorated with titanium dioxide nanofibers encasing silver nanoparticles for antimicrobial action and cell-supportive properties: Using gelation, electrospinning, and ultrasonication

Article References: Hamid, I., Khan, R. S., Kabli, S. A., Rather, A. H., Khanday, F. A., Abdal-Hay, A., & Sheikh, F. A. (2026). Silk fibroin hydrogels decorated with titanium dioxide nanofibers encasing silver nanoparticles for antimicrobial action and cell-supportive properties: Using gelation, electrospinning, and ultrasonication. Polymer Bulletin, 83(12), Article 649. https://doi.org/10.1007/s00289-026-06703-z

Image Credits: AI Generated

DOI: 10.1007/s00289-026-06703-z

Keywords: silk fibroin, hydrogels, titanium dioxide nanofibers, silver nanoparticles, antimicrobial biomaterials, electrospinning, ultrasonication, wound healing, tissue engineering, biocompatibility, sodium dodecyl sulfate, gelation