Mussel-inspired resilient hydrogels with strong skin adhesion and high-sensitivity for wearable device.

Stretchable and self-adhesive conductive hydrogels hold significant importance across a wide spectrum of applications, including human-machine interfaces, wearable devices, and soft robotics. However, integrating multiple properties, such as high stretchability, strong interfacial adhesion, self-healing capability, and sensitivity, into a single material poses significant technical challenges. Herein, we present a multifunctional conductive hydrogel based on poly(acrylic acid) (PAA), dopamine-functionalized pectin (PT-DA), polydopamine-coated reduction graphene oxide (rGO-PDA), and Fe3+ as an ionic cross-linker. This hydrogel exhibits a combination of high stretchability (2000%), rapid self-healing (~ 94% recovery in 5 s), and robust self-adhesion to various substrates. Notably, the hydrogel demonstrates a remarkable skin adhesion strength of 85 kPa, surpassing previous skin adhesive hydrogels. Furthermore, incorporating rGO within the hydrogel network creates electric pathways, ensuring excellent conductivity (0.56 S m-1). Consequently, these conductive hydrogels exhibit strain-sensing properties with a significant increase in gauge factor (GF) of 14.6, covering an extensive detection range of ~ 1000%, fast response (198 ms) and exceptional cycle stability. These multifunctional hydrogels can be seamlessly integrated into motion detection sensors capable of distinguishing between various strong or subtle movements of the human body.

3D Printable Self-Adhesive and Self-Healing Ionotronic Hydrogels for Wearable Healthcare Devices.

Ionotronic hydrogels have attracted significant attention in emerging fields such as wearable devices, flexible electronics, and energy devices. To date, the design of multifunctional ionotronic hydrogels with strong interfacial adhesion, rapid self-healing, three-dimensional (3D) printing processability, and high conductivity are key requirements for future wearable devices. Herein, we report the rational design and facile synthesis of 3D printable, self-adhesive, self-healing, and conductive ionotronic hydrogels based on the synergistic dual reversible interactions of poly(vinyl alcohol), borax, pectin, and tannic acid. Multifunctional ionotronic hydrogels exhibit strong adhesion to various substrates with different roughness and chemical components, including porcine skin, glass, nitrile gloves, and plastics (normal adhesion strength of 55 kPa on the skin). In addition, the ionotronic hydrogels exhibit intrinsic ionic conductivity imparting strain-sensing properties with a gauge factor of 2.5 up to a wide detection range of approximately 2000%, as well as improved self-healing behavior. Based on these multifunctional properties, we further demonstrate the use of ionotronic hydrogels in the 3D printing process for implementing complex patterns as wearable strain sensors for human motion detection. This study is expected to provide a new avenue for the design of multifunctional ionotronic hydrogels, enabling their potential applications in wearable healthcare devices.

Bifunctional Amphiphilic Nanospikes with Antifogging and Antibiofouling Properties.

Over the past few decades, extensive research efforts have been devoted to developing surfaces with unique functionalities, such as controlled wettability, antibiofouling, antifogging, and anti-icing behavior, for applications in a wide range of fields, including biomedical devices, optical instruments, microfluidics, and energy conservation and harvesting. However, many of the previously reported approaches have limitations with regard to eco-friendliness, multifunctionality, long-term stability and efficacy, and cost effectiveness. Herein, we propose a scalable bifunctional surface that simultaneously exhibits excellent antifogging and antibiofouling properties based on the synergistic integration of an eco-friendly and bio-friendly polyethylene glycol (PEG) hydrogel, oleamide (OA), and nanoscale architectures in a single flexible platform. We demonstrate that the PEG-OA-nanostructure hybrid exhibits excellent antifogging performance owing to its enhanced water absorption and spreading properties. We further show that the triple hybrid exhibits notable biofilm resistance without the use of toxic biocides or chemicals by integrating the "fouling-resistant" mechanism of the PEG hydrogel, the "fouling-release" mechanism of OA, and the "foulant-killing" mechanism of the nanostructures.

Efficiency of air-dried and freeze-dried alginate/xanthan beads in batch, recirculating and column adsorption processes.

Alginate (Alg) beads are low-cost adsorbents used for wastewater remediation. In this work, alginate (Alg) and alginate/xanthan (Alg/XG) blend beads were synthesized by gelation method into calcium chloride and freeze-dried to improve the porosity. Their adsorption efficiency was tested for methylene blue (MB) dye in batch, recirculating and column adsorption systems. The blend beads were characterized using by SEM, FTIR-ATR and X-ray microcomputer tomography (Micro-CT) analyzes. Freeze-dried Alg and Alg/XG beads presented porosity of 46 ± 5% and 77 ± 3%, respectively. Adsorption isotherms of MB on freeze-dried Alg/XG beads indicated better adsorption capacity in comparison to the air-dried ones. Adsorption kinetics and breakthrough curves based on recirculating and vertical column adsorption processes of MB on freeze dried Alg/XG and air-dried Alg/XG beads indicated higher efficiency for the vertical column system packed with freeze dried Alg/XG beads. The removal efficiency of 91% MB by the freeze-dried Alg/XG beads in vertical column remained even after four consecutive adsorption-desorption cycles, disclosing these beads as potential systems for the wastewater treatment.

Magnetic hydrogels for levodopa release and cell stimulation triggered by external magnetic field.

Magnetic responsive hydrogels composed of alginate (Alg) and xanthan gum (XG), crosslinked with Ca2+ ions, were modified by in situ magnetic nanoparticles (MNP) formation. In comparison to magnetic Alg hydrogels, magnetic Alg-XG hydrogels presented superior mechanical and swelling properties, due to the high charge density and molecular weight of XG. The loading efficiency of levodopa (LD), an important antiparkinson drug, in the Alg-XG/MNP hydrogels was the highest (64%), followed by Alg/MNP (56%), Alg-XG (53%) and Alg (28%). A static external magnetic field (EMF) of 0.4 T stimulated the release of LD from Alg-XG/MNP hydrogels achieving 64 ±â€¯6% of the initial loading after 30 h. The viability, proliferation and expression of dopaminergic markers of human neuroblastoma SH-SY5Y cell on the LD loaded magnetic hydrogels were successful, particularly under EMF, which stimulated the release of LD. Overall, the results of this study provided the rational design of magnetic hydrogels for the delivery of drugs, which combined with external magnetic stimulus, might improve cell proliferation and specific differentiation.

Microbicidal gentamicin-alginate hydrogels.

Sodium alginate (Alg) reacted with antibiotic gentamicin sulfate (GS) in an aqueous-phase condition mediated by carbodiimide chemistry, in the molar ratios Alg: GS of (1:0.5), (1:1) and (1:2). The Alg-GS conjugated derivatives were characterized by elemental analysis for nitrogen content, Fourier transform infrared spectroscopy in the attenuated total reflection mode (FTIR-ATR), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), thermogravimetric analyses (TGA) and water sorption measurements. XPS and FTIR-ATR analyses clearly indicated that GS molecules covalently attached to the backbone of the alginate chains by amide bond formation. The highest amount of GS bound to Alg (43.5 ±â€¯0.4 wt%) and the highest swelling ratio (4962 ±â€¯661%) were observed for the Alg-GS (1:2) sample. Bioluminescence assays with Pseudomonas aeruginosa PAO1/lecA:lux and colony forming counting of Staphylococcus aureus and Escherichia coli upon contact with all Alg-GS conjugates revealed microbicidal activity; however, Alg-GS (1:2) was the most efficient, due to the highest GS content.

Sustainable hydroxypropyl methylcellulose/xyloglucan/gentamicin films with antimicrobial properties.

Hydroxypropyl methylcellulose (HPMC) and xyloglucan (XG) crosslinked with citric acid over a range of HPMC/XG weight ratios formed sustainable blend films characterized by Fourier transform infrared spectroscopy, thermogravimetric analysis, scanning electron microscopy, tensile tests, circular dichroism and determination of inhibitory activity against Staphylococcus aureus and Escherichia coli. Both in solution and in the crosslinked films, HPMC chains lost the original ordered conformation upon interacting with XG, giving rise to an entropic gain. The highest values of tensile strength (25MPa) and Young's modulus (689MPa) occurred for the 50:50 HPMC/XG blend films. In vitro loading of gentamicin sulfate (GS) in the films amounted to 0.18±0.05 -0.37±0.05g of GS per g polymer. At pH 7.4 and 37°C, the GS release kinetics from the films fitted with the Korsmeyer-Peppas model revealed a non-Fickian release mechanism with diffusional coefficient n∼0.7. The cross-linked films of HPMC, XG and their blends loaded with GS showed outstanding antibacterial activity against Staphylococcus aureus and Escherichia coli, disclosing their potential for novel biomedical applications.

Evaluation of calcium alginate beads for Ce, La and Nd preconcentration from groundwater prior to ICP OES analysis.

Analytical methods for the determination of rare earth elements (REE) in natural waters by plasma spectrochemical techniques often require sample preparation procedures for analytes preconcentration as well as for removing matrix constituents, that may interfere on the analytical measurements. In the present work, calcium alginate (CA) beads were used for the first time aiming at Ce, La and Nd preconcentration from groundwater samples for further determination by inductively coupled plasma optical emission spectrometry (ICP OES). Test samples were analyzed in batch mode by transferring a 40mL test portion (pH=5±0.2) into a 50mL polyethylene flask containing 125mg CA beads. After 15min contact, the analytes were quantitatively extracted from the loaded CA beads with 2.0mL of 1.0molL-1 HCl solution for further determination by ICP OES, using Ce (II) 456.236, La (II) 379.478 and Nd (II) 430.358nm emission lines. The proposed approach is a reliable alternative for REE single-stage preconcentration from aqueous samples, as it provided accurate results based on the addition and recovery analysis of groundwater. The results obtained by the proposed method were also compared with those from reference method based on inductively coupled plasma mass spectrometry (ICP-MS) and no significant differences were observed after applying the Student's t-test at 95% confidence level.

Alginate/magnetite hybrid beads for magnetically stimulated release of dopamine.

Hybrid beads composed of magnetite nanoparticles (MNP) and alginate (Alg) were synthesized and coded as Alg-MNP. They were incubated in dopamine (DOPA) solution (5 g/L), at pH 7.4 and 8 °C, during 12 h, promoting the DOPA loaded magnetic beads, coded as Alg-MNP/DOPA. The release of DOPA was further evaluated in the absence and the presence of external magnetic field (EMF) of 0.4 T. The products Alg-MNP and Alg-MNP/DOPA were characterized by scanning electron microscopy with energy dispersive spectroscopy (SEM-EDS), Fourier transform infrared vibrational spectroscopy (FTIR), UV spectrophotometry, thermogravimetric analyses (TGA), inductively coupled plasma atomic emission spectroscopy (ICP-AES) analyses and superconducting quantum interference device (SQUID) magnetometer. The magnetic and chemical properties of Alg-MNP beads were not affected by DOPA loading. The incorporation of DOPA into the beads depended on the pH and on the negative charge density. At pH 7.4 38% of DOPA were loaded into Alg-MNP beads, whereas at pH 2 or using neat Alg beads (lower charge density than Alg-MNP) the loading efficiency decreased to one third or less. In the absence of EMF, 24% of the loaded DOPA was released from Alg-MNP at pH 7.4 over a period of 26 h. The released amount increased to 33% under the stimulus of EMF. A model was proposed to explain the loading efficiency of charged drugs, as DOPA, into hybrid beads and the role played by EMF on delivery systems, where drug and matrix are oppositely charged. The results suggest that the alginate combined with magnetite nanoparticles is a promising system for release of DOPA in the presence of EMF.

Modification of agarose: 6-aminoagarose mediated syntheses of fluorogenic pyridine carboxylic acid amides.

A facile 6-aminoagarose (AA) mediated synthesis of new fluorogenic amides of agarose with nicotinic (AA-NA) and picolinic acids (AA-PA) employing carbodiimide chemistry have been described. 6-Amino agarose (AA) was synthesized in a facile Mitsunobu-inspired microwave mediated method involving the reaction of agarose with phthalimide in presence of diisopropyl azodicarboxylate and triphenylphosphene (DIAD/TPP) followed by hydrazinolysis. All compounds were characterized by GPC, UV spectrophotometry, fluorescence spectroscopy, FT-IR, (1)H and (13)C NMR spectra. The fluorescence emissions (λmax 430 and 412 nm) of 1 × 10(-3)M solutions of AA-NA and AA-PA in water were significantly higher (ca. 82% and ca. 90%) than those of the molar equivalents (0.2mg) of NA and PA present in the 1 × 10(-3)M solutions of the amides, respectively. These fluorogenic pyridine carboxylic acid amides of agarose may find applications as sensors in biomedical and pharmaceutical industries.

Galactans of Gracilaria pudumadamensis (Gracilariales, Rhodophyta) of Indian waters.

Galactans from the Indian agarophyte Gracilaria pudumadamensis were extracted and characterized. The isolated native (GP(Native)) and alkali treated (GP(Alkali)) galactans were characterized by IR, 13C NMR, GC-MS and GPC. It was found that GP(Native) and GP(Alkali) were composed mainly of 3,6-anhydro L-galactose, 6-O-methylated D-galactose and galactose in various mole proportions (15.6:69.9:17.5 mole% for GP(Native) and 20.2:69.8:10.0 mole% for GP(Alkali)). The GP(Native) and GP(Alkali) exhibited low gel strengths (< 100 g/cm2) and high melting points (-76 degrees C), which may be due to the presence of high 6-O-Me-galactose contents. The latter, having low sulfate (2.1%), was by far the greatest 6-O-Me-galactose containing polysaccharide in a Gracilaria spp. reported in the literature. This methylated agar contained very low heavy metal ions estimated by inductively coupled plasma spectrophotometry (ICP). The results of this investigation would be useful in bioprospecting of agarophytes, especially those occurring in Indian waters and would be potentially useful in food, personal care and related domains.

A facile one-pot synthesis of a fluorescent agarose-O-naphthylacetyl adduct with slow release properties.

A microwave assisted facile synthesis of a fluorescent 6-O-naphthylacetyl agarose (NA-agarose) employing carbodiimide chemistry (dicyclohexylcarbodiimide/4-dimethylaminopyridine) has been described. NA-agarose was characterized by TGA, GPC, UV spectrophotometry, fluorescence spectroscopy, FT-IR, (1)H and (13)C NMR spectra, exhibiting that in NA-agarose the naphthylacetyl group was attached to the backbone of the agarose polymer. The hydrolysis of NA-agarose in heterogeneous aqueous phase showed that the 1-naphthyl acetic acid (NAA), a plant growth regulator, got released in a controlled manner, the release rate being dependent on the hydrophilicity of the polymer adduct as well as on pH and temperature. The fluorescence emission (λmax 332 nm) of NA-agarose (1×10(-3) M) in ethylene glycol was significantly higher (ca. 82%) than that of the molar equivalent of NAA content in the product i.e. 0.08 mg in 1×10(-3) M solution. The resulting polymer would be of potential utility as a sustained release plant growth regulator and sensory applications.

Functional modification of agarose: a facile synthesis of a fluorescent agarose-tryptophan based hydrogel.

Microwave assisted facile synthesis of a fluorescent agarose-l-tryptophan hydrogel material employing carbodiimide chemistry (dicyclohexylcarbodiimide/4-dimethylaminopyridine; DCC/DMAP) has been described. The product formed fluorescent hydrogel at 1-1.5% (w/v), exhibiting fluorescence emission in water (λmax 350 nm; 1x10(-4)M), which was significantly higher (ca. 65%) than that of tryptophan at the same concentration. Subsequently, the agarose ester was cross linked with the natural cross linker genipin to yield a blue hydrogel (G-Ag-TrpEst), confirming thereby the insertion of tryptophan moiety on to agarose backbone. Both the ester and cross linked hydrogels demonstrated gelling characteristics similar to agarose and were stable across a wide range of pH media (pHs 1.2, 7.0 and 12.5) under ambient conditions. These tryptophan containing fluorescent hydrogel materials may find applications in biomedical and pharmaceutical industries as potential radical scavengers and sensors.

Cellulose contents of some abundant Indian seaweed species.

Crude cellulose as well as alpha- and beta-celluloses were estimated in thirty-four seaweed species of fifteen orders of Chlorophyta, Phaeophyta and Rhodophyta of Indian waters. The greatest yields of crude cellulose and a-cellulose were obtained from Chaetomorpha aerea (approx. 20.0% and 18.5%, respectively), and of beta-cellulose (approx. 3.1%) from Caulerpa imbricata. The lowest crude cellulose, and alpha-and beta-contents were recorded for the calcareous red alga Liagora indica (approx. 0.90%, 0.70% and 0.10%, respectively). There was little variation in cellulose content among the brown algae, while wide variations in the yields were found in the green and red algae. The present work contributes to the repertoire of 67 Indian seaweed species studied to now for their cellulose contents in our laboratory. The combined studies highlight that Chaetomorpha aerea, Acrosiphonia orientalis, Caulerpa taxifolia, Sargassum tenerrimum, Hydroclathrus clathratus and Gelidiella acerosa possess relatively high (> 10%) cellulose contents, which could be of potential utility.