Gum-Based Magnetic Hydrogel Shows pH-Controlled Naproxen Release in Lab Tests

Researchers in India have engineered a gum acacia-based nanocomposite hydrogel that releases the anti-inflammatory drug naproxen sodium in a strongly pH-dependent manner, releasing more than 82 percent of its cargo under alkaline laboratory conditions while suppressing release under acidic ones. The work, published as an open-access article in the Springer journal Discover Surfaces on 7 May 2026, describes the structural characterization of the material and the kinetics of drug release from two formulations: a plain gum acacia-grafted poly(N,N-dimethylacrylamide) hydrogel and a version loaded with 50 milligrams of cobalt ferrite nanoparticles.

The motivation behind the study is a familiar pharmaceutical problem. Naproxen is a widely used nonsteroidal anti-inflammatory drug that works by inhibiting cyclooxygenase enzymes, but it is associated with gastrointestinal side effects and suffers from poor water solubility, which forces higher doses and worsens those adverse effects. The authors propose that a smart hydrogel carrier could mimic the passage of the drug through the stomach and ensure its slow release in the intestine, potentially alleviating the gastrointestinal burden. Their system is built from gum acacia, also known as gum arabic, a high-molecular-weight polysaccharide exudate from Acacia species, grafted with the synthetic monomer N,N-dimethylacrylamide and reinforced with cobalt ferrite nanoparticles.

Synthesis followed a free radical graft copolymerization route. Gum acacia powder was dissolved in triple-distilled water, cobalt ferrite nanoparticles dispersed by ultrasonication were added, and the crosslinker N,N’-methylene bis-acrylamide and initiator ammonium persulfate were introduced at 60 degrees Celsius to drive the reaction. Upon thermal activation, ammonium persulfate generates sulfate radical anions that abstract hydrogen atoms from the hydroxyl groups on the polysaccharide backbone, creating macroradicals onto which the vinyl monomer adds and grows. The bifunctional crosslinker bridges adjacent chains into a three-dimensional network. Homopolymer byproducts were removed by acetone extraction, and the dried products were milled into a powder for characterization and drug studies.

The cobalt ferrite nanoparticles themselves were made by chemical co-precipitation, mixing cobalt and iron nitrate solutions at 80 degrees Celsius, raising the pH to roughly 10.5 to 11 with sodium hydroxide, and calcining the washed precipitate at 500 degrees Celsius for five hours. Powder X-ray diffraction confirmed the inverse cubic spinel structure of the nanoparticles, with characteristic reflections matching reference patterns, and the Scherrer equation yielded an average crystallite size of 15.7 nanometers. The characteristic cobalt ferrite peak appeared prominently in the diffraction pattern of the 50-milligram nanocomposite, confirming incorporation of the nanoparticles into the polymer matrix.

Several spectroscopic and imaging techniques corroborated the successful construction of the material. Fourier transform infrared spectra of the plain hydrogel showed a new peak at 1504 wavenumbers assigned to C-N stretching in the amide group of the grafted monomer, alongside the disappearance of the vinyl C=C peaks of the free monomer, evidence that polymerization occurred on the gum acacia backbone. Notably, the characteristic metal-oxide peak of cobalt ferrite near 586 wavenumbers was not observed in the nanocomposite spectrum, which the authors interpret as the nanoparticle surface being harmonized, or coated, by the polymer. Field emission scanning electron microscopy showed that the rough, uneven surface of the natural gum became flat and even after grafting, with nanoparticles dispersed across the hydrogel surface.

Surface and thermal measurements further distinguished the two formulations. Nitrogen adsorption analysis showed that loading cobalt ferrite improved all measured surface properties of the nanocomposite relative to the plain hydrogel, including BET surface area, total pore volume and BJH pore parameters. Thermogravimetric analysis revealed that both hydrogels were more thermally stable than gum acacia alone, and the nanocomposite was more stable than the plain hydrogel, providing additional evidence of grafting and nanoparticle loading. The authors also note that the compact appearance of dried hydrogel samples in electron microscopy does not contradict the mesoporosity measured by BET analysis, because the two techniques probe different length scales of the material structure.

Swelling behavior guided the choice of the optimal formulation. Loading cobalt ferrite from 10 to 50 milligrams progressively enhanced the swelling capacity of the hydrogels, apparently by creating porosity and hydrophilicity, while a higher loading of 60 milligrams retarded swelling, an effect attributed to nanoparticle agglomeration that reduced porosity and homogeneity. The 50-milligram formulation, designated GADMA CF-50, showed the highest swelling ratio at 13.85 grams per gram and roughly double the BET surface area of the plain hydrogel, and it was therefore selected, together with the unloaded GADMA CF-0 control, for the drug loading and release experiments.

Naproxen sodium was loaded into the dried hydrogels by the swelling-diffusion method, in which one gram of hydrogel was immersed in 100 milliliters of a 1000 milligram per liter drug solution and stirred for 24 hours so that the swelling network took up the drug by diffusion. Analysis of the remaining solution by ultraviolet-visible spectrophotometry at the drug’s maximum absorbance wavelength of 230 nanometers gave loading efficiencies of 82.90 percent for the plain hydrogel and 84.12 percent for the nanocomposite. Release experiments were then run in triplicate at 37 degrees Celsius in three media: an acidic potassium hydrogen phthalate buffer at pH 4.0, phosphate-buffered saline at pH 7.4, and an alkaline borate buffer at pH 9.2, chosen to represent stomach conditions, normal physiological pH and an exploratory alkaline environment, respectively.

The release results traced a clear pH gradient. In the acidic medium, only 14.55 percent of the drug was released from the plain hydrogel and 17.57 percent from the nanocomposite. At physiological pH 7.4, those figures rose to 68.30 and 72.63 percent, and at pH 9.2 the release climbed to 82.39 and 84.83 percent, respectively. The authors explain this pattern through electrostatics: the point of zero charge of the nanocomposite was measured at pH 3.7, so above that value the hydrogel surface carries a negative charge, as does the ionized drug, producing repulsion that expands the polymer network, increases swelling and drives drug diffusion. Under acidic conditions the drug becomes protonated, interactions with the carrier tighten, the network contracts and release is suppressed. Release increased with time from 2 to 12 hours and then reached equilibrium.

Kinetic modeling of the release data showed that the Korsmeyer-Peppas model, with regression coefficients closest to one, best described the release from both hydrogels, pointing to diffusion as the dominant pathway. The diffusional exponent values fell between 0.45 and 0.89 in nearly all cases, indicating non-Fickian, anomalous diffusion in which Fickian drug diffusion and viscoelastic relaxation of the polymer chains proceed at comparable rates, a profile the authors associate with gradual release without a sudden burst. The single exception was the nanocomposite at pH 9.2, where the exponent of 0.44430 indicated Fickian diffusion. The authors caution that comprehensive cytotoxicity evaluation, including MTT assays and hemocompatibility testing, is planned as part of a subsequent biological validation study, and they note that the magnetic character of cobalt ferrite could offer potential for magnetically guided targeted delivery in future in vivo investigations.

Subject of Research: pH-responsive gum acacia-grafted poly(N,N-dimethylacrylamide)/CoFe2O4 nanocomposite hydrogels for naproxen sodium loading and release

Article Title: Structural characterization and drug release kinetics of naproxen sodium loaded gum acacia grafted poly N N dimethylacrylamide CoFe2O4 nanocomposite hydrogels

Article References: Dave, P. N., Chopda, L. V., & Bamaniya, S. M. (2026). Structural characterization and drug release kinetics of naproxen sodium loaded gum acacia grafted poly N N dimethylacrylamide CoFe2O4 nanocomposite hydrogels. Discover Surfaces, 1(1), Article 2. https://doi.org/10.1007/s44507-026-00001-x

Image Credits: AI Generated

DOI: 10.1007/s44507-026-00001-x

Keywords: hydrogel, naproxen sodium, gum acacia, cobalt ferrite nanoparticles, drug delivery, drug release kinetics, Korsmeyer-Peppas model, pH-responsive, graft copolymerization, nanocomposite, BET surface area, sustained release