Novel Nanoporous Superabsorbent Hydrogel Based on Poly(acrylic acid) Grafted onto Salep: Synthesis and Swelling Behavior

A novel pH-responsive hydrogel system based on Prunus armeniaca gum and acrylic acid: Preparation and evaluation as a potential candidate for controlled drug delivery

pH-responsive hydrogels have become effective and attractive materials for the controlled release of drugs at pre-determined destinations. In the present study, a novel hydrogel system based on Prunus armeniaca gum (PAG) and acrylic acid (AA) was prepared by a free radical mechanism using N, N-methylene bisacrylamide (MBA) as cross-linker and potassium persulfate (KPS) as initiator. A series of hydrogels varying PAG, AA, and MBA concentration was developed to determine the impact of these components. Formulated hydrogels were characterized for pH-responsive swelling, drug release, gel content, and porosity. Structural analysis was performed by FTIR, XRD, and SEM analysis. TGA study was applied to assess thermal stability. Oral acute toxicity and in vivo drug release were performed in rabbits. Hydrogels exhibited pH-dependent swelling and drug release. Swelling, drug loading and release, and porosity increased by increasing PAG and AA concentration while decreased by increasing MBA. The gel content of formulations was increased by increasing all three components. FTIR studies confirmed the development of copolymeric networks and the loading of drug. XRD studies revealed that hydrogels were amorphous, and the crystalline drug was changed into an amorphous form during loading. TGA results indicated that hydrogels were stable up to 600 °C. Acute oral toxicity results confirm that hydrogels were nontoxic up to a dose of 2 g/kg body weight in rabbits. The pharmacokinetic evaluation revealed that hydrogels prolonged the availability of the drug and the peak plasma concentration of the drug was obtained in 6 h as compared to the oral solution of the drug. Tramadol hydrochloride (THC) was used as a model drug. Hence, pH-responsive swelling and release, nontoxic nature and improved pharmacokinetics support that PAG-based hydrogels may be considered as potential controlled-release polymeric carriers.

Highly efficient poly(acrylic acid-co-aniline) grafted itaconic acid hydrogel: Application in water retention and adsorption of rhodamine B dye for a sustainable environment

The present study used a free radical co-polymerization approach to synthesize a smart hydrogel of itaconic acid grafted poly(acrylic acid-co-aniline) (ItA-g-poly(AA-co-ANi)). ItA-g-poly(AA-co-ANi) hydrogel was characterized by Fourier transform infrared spectroscopy (FT-IR), Raman, X-ray diffraction (XRD), thermogravimetric analysis (TGA), field emission scanning electron microscope (FE-SEM), and X-ray photoelectron spectroscopy (XPS) analysis. Rhodamine B (RhB) dye was removed from an aqueous medium using ItA-g-poly(AA-co-ANi) hydrogel. To determine the maximum adsorption, the effect of parameters such as initial dye concentration, contact time, pH, and adsorbent dose were examined. The ItA-g-poly(AA-co-ANi) hydrogel had a high swelling percentage of 1755.3%. The high water penetration of ItA-g-poly(AA-co-ANi) hydrogel with a high swelling rate exposed the internal adsorption sites for RhB dye adsorption. The adsorption performance of ItA-g-poly(AA-co-ANi) hydrogel was explained by the pseudo-first-order and Freundlich adsorption isotherm models. Moreover, after four adsorption-desorption cycles, the ItA-g-poly(AA-co-ANi) hydrogel maintained an adsorption efficiency of 85.2%. The high water retention ability of ItA-g-poly(AA-co-ANi) hydrogel improved the moisture maintenance limit of soil for irrigation up to 23 days. As a result, ItA-g-poly(AA-co-ANi) hydrogel can be used in the elimination of toxic dyes as well as in irrigation systems.

Novel Materials for Urban Farming

Scarcity of natural resources, shifting demographics, climate change, and increasing waste are four major challenges in the quest to feed the exploding world population. These challenges serve as the impetus to harness novel technologies to improve agriculture, productivity, and sustainability. Urban farming has several advantages over conventional farming: higher productivity, improved sustainability, and the ability to provide fresh food all year round. Novel materials are key to accelerating the evolution of urban farming - with their ability to facilitate controlled release of nutrients and pesticides, improved seed health, substrates with better water retention capability, more efficient recycling of agricultural waste, and precise plant health monitoring. Materials science enables environmental sustainability and higher harvest yields in urban farms. Here, Singapore is used as an example of a land-scarce city where urban farming may be the solution for future food production. Potential research directions and challenges in urban farming are highlighted, and how material optimization and innovation drive the development of urban farming to meet national and global food demands is briefly discussed. This review serves as a guide for researchers and a reference for stakeholders of urban farms, policy makers, and other interested parties.

Development and Evaluation of pH-Responsive Pluronic F 127 Co-Poly- (Acrylic Acid) Biodegradable Nanogels for Topical Delivery of Terbinafine HCL

Research aimed to develop and evaluate biodegradable, pH-responsive chemically cross-linked Pluronic F127 co-poly- (acrylic acid) nanogels for dermal delivery of Terbinafine HCL (TBH) to increase its permeability and as a new approach to treat skin fungal infections. TBH-loaded nanogels were successfully synthesized from acrylic acid (AA) and Pluronic F127 by free-radical copolymerization technique using N,N′-methylene bisacrylamide (MBA) as crosslinker and ammonium persulphate (APS) as initiator. Prepared nanogels exhibited 93.51% drug entrapment efficiency (DEE), 45 nm particle size, pH-dependent swelling and release behavior. Nanogels were characterized using different physicochemical techniques. The ex-vivo skin retention studies through rat skin showed about 42.34% drug retention from nanogels while 1% Lamisil cream (marketed product) showed about 26.56% drug retention. Moreover, skin irritation studies showed that nanogels were not irritating. Nanogels showed improved in-vitro antifungal activity against Candida albicans compared to commercial product. In-vivo studies on rats infected with Candida albicans confirmed superiority of nanogels over 1% Lamisil for eradication of fungal infection. This confirms that TBH loaded in Pluronic F127 co-poly-(acrylic acid) nanogels provided greater targetibility and cure rates of poorly soluble TBH in animal model and hence nanogels could be a potential carrier for effective topical delivery of TBH for skin fungal infection treatment.

Interdroplet Interactions and Rheology of Concentrated Nanoemulsions for Templating Porous Polymers

In the current study, we investigate the colloidal behavior of nanoemulsions over a wide range of oil volume fractions (φ) from dilute to concentrated regime. The dilute system contains 25% silicone oil dispersed in the aqueous phase consisting of poly(ethylene glycol)-diacrylate (PEGDA) and sodium dodecyl sulfate (SDS), which is concentrated through evaporation of water at two different rates at ambient temperature. The rheological studies show that the liquid-like nanoemulsions transform into viscoelastic gels at a volume fraction of ∼30%. The plateau storage modulus of the nanoemulsions increases in the semidilute systems (φ below 45%) and then decreases steadily with increasing φ up to 60%. Dependency of the modulus on the evaporation rate can be observed in the rheological results. According to the rheological results and the overall pairwise interactions estimated between droplets, we propose two regimes of colloidal interactions. In the semidilute regime, the attractive gelation occurs due to considerable short-range attractive depletion induced by the PEGDA oligomer and SDS micelles. In the concentrated regime, the gel weakens by increasing φ mainly due to the structural stabilization barrier from a high concentration of micelles. The PEGDA in the continuous phase of the nanoemulsions can be crosslinked through photopolymerization, resulting in nanoporous PEGDA hydrogels upon removal of oil droplets. We study the water uptake of the nanoporous hydrogels prepared from the nanoemulsion templates at φ = 60%. The hydrogel obtained from the nanoemulsion with fast evaporation rate shows higher water uptake than that obtained from the slowly concentrated nanoemulsion. The tunable viscoelastic behavior of concentrated nanoemulsions as well as the resulting nanoporous hydrogels offers a new platform to design the soft materials for a wide range of applications.

High crosslinked sodium carboxyl methylstarch-g-poly (acrylic acid-co-acrylamide) resin for heavy metal adsorption: its characteristics and mechanisms

A lower expansive heavy metal adsorbent, high crosslinked sodium carboxyl methylstarch-g-poly (acrylic acid-co-acrylamide) resin (HCAA), has been prepared by enhancing the crosslinking degree of the traditional water-absorbing polymer under the graft copolymerization reaction. Further heavy metal adsorption experiments, morphology analysis, and structure characteristic observations indicate that HCAA resin has an excellent heavy metal adsorption properties for Cr³⁺, Cu²⁺, Ni²⁺, and Zn²⁺ of 80.08, 158.07, 155.71, and 137.15 mg/g, respectively. The nanoholes in network structures of HCAA resin expanding in solution provide an effective diffusion and exchange channels for heavy metal ions and Na⁺. The adsorption process of HCAA containing -COONa is attributed to ion exchange process, and its essence is to form the coordination bond with heavy metals. The adsorption capacity differences of -COO^- have been explained by using the coordination chemistry theory. In addition, the adsorption selectivity of an expansive adsorbent containing -COONa are heavy metals > H₂O >> Na⁺. Our research puts forward an insight that increasing the crosslinker content on the basis of the traditional super absorbent resin can obtain a lower expansive adsorbent to heavy metal pollutants.

Sprayed in-situ synthesis of polyvinyl alcohol/chitosan loaded silver nanocomposite hydrogel for improved antibacterial effects

To overcome the practical limitations of hydrogel preparations, applications and strength-based problems, the present study utilizes the use of sprayers for preparing polyvinyl alcohol/chitosan (PVA/CH) hydrogels. The particle size, morphology, stability, release studies and antibacterial activity of silver nanoparticles (AgNPs) had been studied. The particle size of AgNPs was found to be in the range of 4.59-10 nm (75 °C) with a polydispersity index (PDI) of 0.84. The morphological images exhibited inter-connecting porous structure with pore size in submicron's (<1 µm). Major infra-red spectral peaks of PVA (2946.67 cm-1; stretching of CH, 1142.72 cm-1; CO stretching) and CH (3287.49 cm-1; OH stretching, 2917.48 cm-1; CH stretching) maintain their place in PVA/CH and PVA/CH/Ag hydrogels. In addition, X-ray diffraction (XRD) pattern showed peaks with 2θ values at 38.08°, 44.29° and 64.50° corresponding to the crystal planes of (1 1 1), (2 0 0) and (2 2 0), respectively, allocated to face-centered cubic crystalline structure of AgNPs. The drug release and antibacterial studies showed a maximum release of 91.83% from hydrogels and a concentration dependent zone of inhibition (ZOI) for >24 h, respectively. Thus, the newly developed sprayed hydrogels could turn out to be a suitable dressing material for wound healing applications.

Novel low-cost carboxymethyl cellulose microspheres with excellent fertilizer absorbency and release behavior for saline-alkali soil

Saline-alkali soil and fertilizer loss severely restrict agriculture on the Songnen Plain in China. To resolve this problem, carboxymethyl cellulose immobilized slow-release fertilizer microspheres (CFM) with homogeneity pore structure, high porosity, biodegradable biological macromolecules and excellent fertilizer absorbency were synthesized by the combination of inverse emulsion polymerization and microfluidic method. By optimizing the synthesis conditions, the water absorption of CFM reached 8725 g g^-1 in deionized water. The absorbency behaviors of CFM were highly sensitive to pH, ionic strength, and ionic species. In 5 g L^-1 urea solution, the adsorption capacity of CFM was 3342.84 g g^-1. The CFM showed excellent urea retention at 80 °C for 5 h and sustained release performance in soil. Besides, degradation rate of CFM was closed to 98.2% in Aspergillus niger at the third day. CFM had the advantages of high pH sensitivity, salt resistance, and good fertilizer absorbency and retention. Therefore, it will be prospecting fertilizer sustained release agent in agriculture.

Graphene oxide nanocomposite hydrogel based on poly(acrylic acid) grafted onto salep: an adsorbent for the removal of noxious dyes from water

In this study, a graphene oxide nanocomposite hydrogel (GONH) based on poly(acrylic acid) grafted onto a natural salep polysaccharide was synthesized and investigated as an adsorbent for the removal of cationic dye from aqueous solution.

Delivery of Doxorubicin Using Double-Layered Core-Shell Nanocarrier Based on Magnetic Fe3O4 Core and Salep Shells

Herein, we developed a magnetic drug delivery system based on magnetic Fe₃O₄ nanoparticles with double shells of modified salep polysaccharide for the delivery of doxorubicin (Dox). The drug-loaded nanocarrier was synthesized in an easy way, and large amounts of drug molecules were loaded into the nanocarrier. The drug-loaded nanocarrier showed excellent pH responsibility in vitro, and large amounts of Dox were released at lower pH (60% release), whereas the nanocarrier was stable at neutral pH. The hemolysis assay results showed that the nanocarrier has negligible hemolytic effects on human red blood cells and showed good biocompatibility. Moreover, the result of coagulation assays showed that the nanocarrier was not active in any coagulation pathways. Cytotoxicity assays of nanocarrier and drug-loaded nanocarrier toward HeLa cells demonstrated that the nanocarrier has negligible toxicity, whereas the drug-loaded nanocarrier kills more than 90% of cells during 48 h. The flow cytometry analysis also showed that the uptake of drug-loaded nanocarrier into the cancerous cells is time-dependent and higher concentrations of drug internalized into the cells at longer incubation time. On the basis of the results, we suggest that the present nanocarrier can be applicable for in vivo drug delivery as an easy-made and cheap nanocarrier.

Cellulose-Based Absorbent Production from Bacterial Cellulose and Acrylic Acid: Synthesis and Performance

Cellulose-based superabsorbent was synthesized by bacterial cellulose (BC) grafting acrylic acid (AA) in the presence of N,N′-methylenebisacrylamide (NMBA) as a crosslinker and ammonium persulfate (APS) as an initiator. The influence of different factors on composite synthesis, including the weight ratio of the monomer to BC, initiator content, crosslinker content, AA neutralization degree, reaction temperature, and reaction time on the water absorbency of the composite, were systematically learned. Under the optimized conditions, the maximum water absorbency of the composite was 322 ± 23 g/g distilled water. However, the water absorbency was much less for the different salt solutions and the absorption capacity of the composite decreased as the concentration of the salt solutions increased. The pH value had a significant influence on water absorption performance, and with the increase of temperature, the water retention rate of the composite decreased. Additionally, the structure of this composite was characterized with nuclear magnetic resonance (NMR), Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), and thermogravimetric analysis (TGA). The results of NMR and FT-IR provided evidence that the composite was synthesized by BC and AA, and the microstructure showed that it had good performance for water absorption. In addition, the composite possessed suitable thermal stability, and that it could be used in a few high-temperature environments. Overall, this composite is promising for application in water absorption.

Elastic, crosslinked poly(acrylic acid) filaments: nanocellulose reinforcement and graphene lubrication

Hybrid monofilaments of poly(acrylic acid) (PAA) and 1,6-hexanediol diglycidyl ether (16DGE), compounded with nanofibrillated cellulose (NFC) and graphene, were thermally crosslinked and subsequently spun from aqueous solution.

Multiresponsive hydrogels based on xylan-type hemicelluloses and photoisomerized azobenzene copolymer as drug delivery carrier

Stimulus-responsive hydrogels, which can undergo significant physicochemical changes in response to various physical or chemical stimuli, have drawn wide attention in many fields. In this study, novel photoresponsive hydrogels prepared by free radical copolymerization of xylan-type hemicellulose methacrylate with 4-[(4-acryloyloxyphenyl)azo]benzoic acid (AOPAB) were investigated, which showed multiresponsive behaviors to pH, water/ethanol alternating solutions, and light. The swelling ratios of the prepared hydrogels in distilled water decreased from 9.8 to 2.2 g/g with AOPAB content increase from 2% to 16%. The hydrogel displayed rapid swelling and deswelling performance in water and ethanol alternating solutions. Additionally, under UV irradiation the trans-conformation of azobenzene in the hydrogel would generally convert into the cis-conformation and resulted in the hydrophilic/hydrophobic balance variation of the hydrogel. Therefore, the hydrogel loaded with vitamin B12 (VB12) showed a higher drug cumulative release rate under UV irradiation than that without UV irradiation.