Alginate System Research Articles

Removal of Cadmium from Aqueous Solutions by Saccharomyces cerevisiae-Alginate System.

The aim of this study was to determine the Cd2+ removal capacity of a biosorbent system formed by Saccharomyces cerevisiae in calcium alginate beads. The adsorption of Cd2+ by a S. cerevisiae–alginate system was tested either by batch or fixed-bed column experiments. The S. cerevisiae–alginate system was characterized using dynamic light scattering (DLS, zeta potential), size, hardness, scanning electron microscopy (SEM), and Fourier-transform infrared spectroscopy. Beads of the S. cerevisiae–alginate system showed a spherical–elliptical morphology, diameter of 1.62 ± 0.02 mm, 96% moisture, negative surface charge (−29.3 ± 2.57 mV), and texture stability during storage at 4 °C for 20 days. In batch conditions, the system adsorbed 4.3 µg of Cd2+/g of yeast–alginate beads, using a Cd2+ initial concentration of 5 mg/L. Adsorption capacity increased to 15.4 µg/g in a fixed-bed column system, removing 83% of total Cd2+. In conclusion, the yeast–alginate system is an efficient option for the removal of cadmium at low concentrations in drinking water.

Preparation of Liquid Oral Mucoadhesive Gastro-retentive System of Nimodipine.

Nimodipine is a calcium channel blocker frequently used in critical care settings. It is mainly absorbed in the upper gastrointestinal tract. Accordingly, the development of gastroretentive formulation will be beneficial. The benefit would be maximized for critical care patients if the developed system was in liquid form to facilitate the administration through nasogastric tubing. Development of gastro-retentive liquid oral controlled release formulation of nimodipine through in situ gellation. Nimodipine dissolution was improved by solid dispersion (SD) using poloxamer 407. Sodium alginate solutions (1, 1.5 and 2%w/v) were loaded with the optimized SD microparticles. Carboxymethylcellulose was added to modulate the release and to augment mucoadhesion power. All in situ gelling alginate solutions were characterized regarding viscosity, gelling capacity and drug release. SD microparticles showed considerable improvement in nimodipine dissolution. All alginate systems were pourable. Increasing alginate concentration increased the gelling capacity and reduced drug release rate. The addition of carboxymethylcellulose produced greater control over drug release rate. X-ray radiography showed successful stomach-retention over 8 hours in rabbits, which correlates with the controlled release pattern of the developed systems. The study provides the formulator with a range of gastroretentive controlled release formulations of nimodipine while maintaining the convenience of administration through nasogastric tubing with the potential for enhanced bioavailability.

Alginate as a support ligand for enhanced colloidal liquid aphron immobilization of proteins and drug delivery.

Research within the field of colloidal liquid aphrons (CLAs) for enzyme immobilization has often used ionic surfactants for the retention of enzymes. Although these charged interactions allow for enhanced immobilization, they can often lead to denaturation of enzyme activity, and even release of the protein. Sodium alginate has been used in drug delivery applications due to its low toxicity and charged interactions that allow for encapsulation. Hence, alginate systems can be used as an alternative to ionic surfactants in CLA immobilization. This paper presents, for the first time, the use of sodium alginate as potential ligand for enhanced CLA immobilization. The use of five model proteins; lysozyme, bovine serum albumin, ovalbumin, insulin, and α-chymotrypsin, of various pIs and hydrophobicities, showed the relevance of electrostatic interactions in promoting binding with sodium alginate when the pH < pI, with 100% immobilization attributed to alginate incorporated CLAs over general nonionic formulations. Furthermore, above their pI, >80% protein recovery was observed, with activity and conformation comparable to their native counterparts. Finally, the use of proteolysis showed that as the degree of ionic bonding increased between the protein and sodium alginate, the degree of protease resistance decreased due to conformational changes experienced during binding.

The effect of sodium alginate on nutrient digestion and metabolic responses during both in vitro and in vivo digestion process

The purpose of this study was to investigate the contribution of long-term and short-term consumption of sodium alginate on the nutrient digestion and metabolic regulation of rats and to explore their actions on energy intake and glycemic regulation. Results were obtained from both in vitro and animal experiments. Two feeding methods were used to raise rats in two groups to study the influence of consumption of sodium alginate on food intake, gastrointestinal chyme, blood glucose and related hormones, body weight, apparent protein digestibility (APD) and changes in the digestive tract. Our findings showed that the calcium carbonate-containing sodium alginate system formed a gel in stomach conditions, and the formation of gel lowered dextrin and whey protein isolate (WPI) hydrolysis rate in vitro. The short-term results showed that a clear gel mass was observed in the rats’ stomach which could potentially affect distension of the stomach and prolong the gastric emptying time, leading to reduced food intake of the rats in the short time (4 h). By studying the long-term feeding containing sodium alginate in the diet, it was found that the addition of sodium alginate reduced food intake, body weight and APD, the peak value of blood glucose was 10.8 mmol/L, which was about 77% of the peak blood glucose level in the control group, indicating the impaired nutrient digestibility, and the maximal rate at which glucose was entering the blood was reduced. However, the length of the small intestine increased in order to obtain sufficient nutrients for normal growth and metabolism. The results of this research suggested that sodium alginate could potentially be effective in the treatment of metabolic syndrome and obesity in humans.

Thermal degradation of calcium and sodium alginate: A greener synthesis towards calcium oxide micro/nanoparticles

Processes for nanoparticle synthesis often use toxic solvents under aggressive conditions. A greener alternative is the burning of self-organized alginate systems. We followed the influence of the CaCl2 concentrations during gelation of sodium alginate and the heating rate on the synthesis of nanoparticles by the combustion method using TGA as a reactor vessel. Samples were collected after each main process of mass loss and characterized using the Scanning Electron Microscopy, Infrared Spectroscopy, and X-ray Diffraction. Samples treated at 50 °C·min−1 presented porous structures at temperatures more than 500 °C lower than the treatments at 10 °C·min−1. All calcium alginate samples presented changing from a predominantly amorphous to crystalline structures such as Ca(OH)2, CaCO3 in the calcite phase and CaO as a function of the temperature, while sodium alginate produced mainly Na2CO3, NaOH and NaO. We observed two main correlations: 1) between the porosity and the heating rate, and 2) between the formation of crystalline structure in intermediate temperatures and the CaCl2 concentration in the gelation step.

Development and characterization of a photocurable alginate bioink for three-dimensional bioprinting.

Alginate is a biocompatible material suitable for biomedical applications, which can be processed under mild conditions on irradiation. This paper investigates the preparation and the rheological behavior of different pre-polymerized and polymerized alginate methacrylate systems for three-dimensional photopolymerization bioprinting. The effect of the functionalization time on the mechanical, morphological, swelling, and degradation characteristics of cross-linked alginate hydrogel is also discussed. Alginate was chemically-modified with methacrylate groups and different reaction times considered. Photocurable alginate systems were prepared by dissolving functionalized alginate with 0.5- 1.5% w/v photoinitiator solutions and cross-linked by ultraviolet light (8 mW/cm2 for 8 minutes).

Functional and structural effects of hydrocolloids on Ca(II)-alginate beads containing bioactive compounds extracted from beetroot

In the present research, valuable bioactives such as betacyanin and polyphenols of beetroot leaf and stem (a food waste) were extracted and encapsulated in Ca(II)-alginate beads, using sucrose, arabic and guar gums, and low and high methoxyl pectins as excipients. A complete SAXS evaluation from the molecular to the supramolecular changes (1–100 nm) produced by excipients and extracts on the microstructure of the hydrogel network was performed. Thus, combining structural-functional information allows for the design of Ca(II)-alginate systems based not only on functional aspects. Here we demonstrate that the presence of hydrocolloids affected the alginate dimers size and density, the rods size and compactness as well as their interconnectivity. Nevertheless, these modifications can be overlied by the presence of an extract, which leads to alginate coordination prior to gelation, strongly affecting the resulting microstructure. Among the used hydrocolloids, only guar gum achieves the two proposed criteria: increasing functional properties and generating stable microstructural modulations.

Cryostructuring of Polymeric Systems. 52. Properties, Microstructure and an Example of a Potential Biomedical Use of the Wide-Pore Alginate Cryostructurates.

Wide-pore cryostructurates were prepared via freezing sodium alginate aqueous solutions with subsequent ice sublimation from the frozen samples, followed by their incubation in the ethanol solutions of calcium chloride or sulfuric acid, rinsing, and final drying. Such sequence of operations resulted in the calcium alginate or alginic acid sponges, respectively. The swelling degree of the walls of macropores in such matrices decreased with increasing polymer concentration in the initial solution. The dependence of the degree of swelling on the cryogenic processing temperature had a bell-like character with a maximum for the samples formed at −20 °C. According to 1H NMR spectroscopy, the content of mobile (non-frozen) water in the frozen water-sodium alginate systems also depended on the initial polymer concentration and freezing temperature. The cryostructurates obtained did not lose their integrity in water, saline, in an acidic medium at pH 2 for at least three weeks. Under alkaline conditions at pH 12 the first signs of dissolution of the Ca-alginate sponge arose only after a week of incubation. Microbiological testing of the model depot form of the antibiotics entrapped in the Ca-alginate cryostructurate demonstrated the efficiency of this system as the antibacterial material.

Thiol-Ene Alginate Hydrogels as Versatile Bioinks for Bioprinting.

Bioprinting is a powerful technique that allows precise and controlled 3D deposition of biomaterials in a predesigned, customizable, and reproducible manner. Cell-laden hydrogel (“bioink”) bioprinting is especially advantageous for tissue engineering applications as multiple cells and biomaterial compositions can be selectively dispensed to create spatially well-defined architectures. Despite this promise, few hydrogel systems are easily available and suitable as bioinks, with even fewer systems allowing for molecular design of mechanical and biological properties. In this study, we report the development of a norbornene functionalized alginate system as a cell-laden bioink for extrusion-based bioprinting, with a rapid UV-induced thiol–ene cross-linking mechanism that avoids acrylate kinetic chain formation. The mechanical and swelling properties of the hydrogels are tunable by varying the concentration, length, and structure of dithiol PEG cross-linkers and can be further modified by postprinting secondary cross-linking with divalent ions such as calcium. The low concentrations of alginate needed (<2 wt %), coupled with their rapid in situ gelation, allow both the maintenance of high cell viability and the ability to fabricate large multilayer or multibioink constructs with identical bioprinting conditions. The modularity of this bioink platform design enables not only the rational design of materials properties but also the gel’s biofunctionality (as shown via RGD attachment) for the expected tissue-engineering application. This modularity enables the creation of multizonal and multicellular constructs utilizing a chemically similar bioink platform. Such tailorable bioink platforms will enable increased complexity in 3D bioprinted constructs.

Structuring new alginate network aimed for delivery of dandelion (Taraxacum officinale L.) polyphenols using ionic gelation and new filler materials

Alginate hydrogels are often used for immobilization of plant-derived bioactive compounds by fast and simple ionic gelation technique. However, the structure of alginate gel network is very porous and mostly result with high-diffusion rates of encapsulated compound, what limits its application as delivery vehicle. In order to prevent losses of bioactives and prepare efficient encapsulation systems, the aim of this study was to evaluate a potential of new natural fillers, cocoa powder (CP) and carob (C) for structuring alginate network aimed for encapsulation of aqueous dandelion (Taraxacum officinale L.) leaf extract using ionic gelation. Whey protein isolates served as a standard filler. The influence of different concentrations of gelling medium (2% and 3% calcium chloride) on encapsulation properties of alginate systems was also evaluated.Calcium concentration affected morphological properties (more acceptable when using 3% CaCl2), while textural properties and encapsulation efficiency of polyphenols and retained antioxidant capacity were more influenced by selected delivery materials. Alginate-whey protein isolates beads were scored with the highest loading capacity of polyphenols (>93%), while newly formulated binary mixtures (alginate-cocoa powder and alginate-carob) also enabled highly efficient entrapment of polyphenols (>88%). The slowest release of polyphenols in simulated gastrointestinal fluids were obtained when alginate was combined with CP and C, where system alginate-cocoa powder prepared with lower concentration of calcium chloride (2% CaCl2) enabled the most extended release of total polyphenols and hydroxycinnamic acids. Obtained results strongly justified implementation of new plant-derived functional fillers (cocoa powder and carob) for encapsulation purposes and opened new directions for designing of binary carrier's.

Alginate Microparticle Arrays as Self-Polishing Bio-Fouling Release Coatings.

Biofouling is a severe problem of any water borne structure. Since the ban of tin-organic compounds and expected bans of other poisonous chemical formulations in the near future, replacement of these compounds are sought. This study investigates antibiofouling properties of micro- and nanostructured alginate layer films. Alginate is a natural product from brown algae and was in this study electro-sprayed and crosslinked with divalent calcium and copper ions to produce homogeneous micro- and nanoparticles. These calcium- and copper-alginate particles were assembled into micro- and nanostructured layer films and the antifouling properties of these low elastic modulus, hydrophilic, biodegradable system were evaluated with the microalgae chlorella. Comparison with pristine glass slides, smooth copper- and calcium alginate bulk films was performed. The comparison shows less biofouling for smooth bulk films compared to micro-nanostructured alginate, while all alginate systems are less bio-fouled on long timescales compared to pristine glass.

The Influence of Humidity and Soil Texture on the Degradation Process of Selected Herbicides Immobilized in Alginate Matrix in Soil under Laboratory Conditions

The inflence of humidity and soil type on the degradation process of clomazone, metazachlor and pendimethalin immobilized in the alginate matrix were studied under laboratory condi tions, and herbicidal degradation parameters obtained for alginate systems and commercial formulations (Command 480 EC, Metazachlor 500 SC and Panida 330 SC) were compared. Two soils with different organic content were used in the experiment: loamy sand (S1) and sand (S2). The effect of soil humidity on the rate of herbicide degradation was assessed for soil S1 at 15% and 60% of maximum water holding capacity. Herbicides residues were analyzed using GC/MS method. The experimental data were fited to the mathematical model based on the fist-order reaction kinetics. There was no signifiant effect of soil type on the degradation rate of herbicides immobilized in the alginate matrix. For all alginate systems analyzed process was faster with an increased soil moisture. Formulation is a signifiant factor affecting the degradation process of herbicides in soil.

Formation, reactivity and aging of amorphous ferric oxides in the presence of model and membrane bioreactor derived organics

Iron salts are routinely dosed in wastewater treatment as a means of achieving effluent phosphorous concentration goals. The iron oxides that result from addition of iron salts partake in various reactions, including reductive dissolution and phosphate adsorption. The reactivity of these oxides is controlled by the conditions of formation and the processes, such as aggregation, that lead to a reduction in accessible surface sites following formation. The presence of organic compounds is expected to significantly impact these processes in a number of ways. In this study, amorphous ferric oxide (AFO) reactivity and aging was investigated following the addition of ferric iron (Fe(III)) to three solution systems: two synthetic buffered systems, either containing no organic or containing alginate, and a supernatant system containing soluble microbial products (SMPs) sourced from a membrane bioreactor (MBR). Reactivity of the Fe(III) phases in these systems at various times (1–60 min) following Fe(III) addition was quantified by determining the rate constants for ascorbate-mediated reductive dissolution over short (5 min) and long (60 min) dissolution periods and for a range (0.5–10 mM) of ascorbate concentrations. AFO particle size was monitored using dynamic light scattering during the aging and dissolution periods. In the presence of alginate, AFO particles appeared to be stabilized against aggregation. However, aging in the alginate system was remarkably similar to the inorganic system where aging is associated with aggregation. An aging mechanism involving restructuring within the alginate-AFO assemblage was proposed. In the presence of SMPs, a greater diversity of Fe(III) phases was evident with both a small labile pool of organically complexed Fe(III) and a polydisperse population of stabilized AFO particles present. The prevalence of low molecular weight organic molecules facilitated stabilization of the Fe(III) oxyhydroxides formed but subsequent aging observed in the alginate system did not occur. The reactivity of the Fe(III) in the supernatant system was maintained with little loss in reactivity over at least 24 h. The capacity of SMPs to maintain high reactivity of AFO has important implications in a reactor where Fe(III) phases encounter alternating redox conditions due to sludge recirculation, creating a cycle of reductive dissolution, oxidation and precipitation.

Encapsulation of lactase in Ca(II)-alginate beads: Effect of stabilizers and drying methods

The purpose of the present work was to analyze the effect of trehalose, arabic and guar gums on the preservation of β-galactosidase activity in freeze-dried and vacuum dried Ca(II)-alginate beads. Freezing process was also studied as a first step of freeze-drying. Trehalose was critical for β-galactosidase conservation, and guar gum as a second excipient showed the highest conservation effect (close to 95%). Systems with Tg values ~40°C which were stables at ambient temperature were obtained, being trehalose the main responsible of the formation of an amorphous matrix. Vacuum dried beads showed smaller size (with Feret's diameter below 1.08±0.09mm), higher circularity (reaching 0.78±0.06) and large cracks in their surface than freeze-dried beads, which were more spongy and voluminous. Ice crystallization of the beads revealed that the crystallization of Ca(II)-alginate system follows the Avrami kinetics of nucleation and growth. Particularly, Ca(II)-alginate showed an Avrami index of 2.03±0.07, which means that crystal growing is bidimensional. Neither the addition of trehalose nor gums affected the dimension of the ice growing or its rate. These results open an opportunity in the development of new lactic products able to be consumed by lactose intolerance people.

Diatomite Modified Immobilized Delftia sp. for the Bio-Abiotic Removal of Antibiotics Amoxicillin in the Aqueous System

Diatomite modified sodium alginate (Si/SA) immobilized Delftia sp. A2(2011) (STT01) was applied to degrade amoxicillin. The immobilized pellets provided a direct and visual probe for the degradation process due to their intrinsic bright colour. The results demonstrated that 100% of amoxicillin and 68.5% of CODcr removal were achieved after 72 h, comparing with the cases of sodium alginate (SA) system (81.2%, 46.9%) and the free cells system (60.5%, 35.5%). The degradation kinetics was in good agreement with Michaelis-Menten equation. The maximum rate (Vm) and Michaelis constant (Km) were calculated as 9.09 mg L-1 h-1 and 228 mg L-1, respectively. The results further revealed that diatomite not only acted as immobilization support to improve the mechanical strength and lifetime of the pellets but also as absorbent to promote the treatment efficiency. Therefore, both enzymatic catalysis and chemisorption were responsible for the removal of amoxicillin.

Delivery of therapeutics to posterior eye segment: cell-encapsulating systems.

Delivery of therapeutics to posterior eye segment: cell-encapsulating systems.

Delivery vehicle effects on bone regeneration and heterotopic ossification induced by high dose BMP-2.

Alginate hydrogel-based BMP-2 delivery has induced better spatiotemporal bone regeneration in animals, compared to clinically used collagen sponge, at lower BMP-2 doses. Lack of clear dose-response relationships for BMP-2 vis-à-vis bone regeneration has contributed to the use of higher doses clinically. We investigated the potential of the alginate system, with comparatively favorable BMP-2 release-kinetics, to reduce heterotopic ossification and promote bone regeneration, when used with a high BMP-2 dose. While defect mineralization improved with alginate hydrogel, the initial high-release phase and likely early tissue exposure to BMP-2 appeared sufficient to induce heterotopic ossification. The characterization presented here should provide the framework for future evaluations of strategies to optimize bone formation and minimize adverse effects of high dose BMP-2 therapy.

Imaging of Hydrogel Microsphere Structure and Foreign Body Response Based on Endogenous X-Ray Phase Contrast.

Transplantation of functional islets encapsulated in stable biomaterials has the potential to cure Type I diabetes. However, the success of these materials requires the ability to quantitatively evaluate their stability. Imaging techniques that enable monitoring of biomaterial performance are critical to further development in the field. X-ray phase-contrast (XPC) imaging is an emerging class of X-ray techniques that have shown significant promise for imaging biomaterial and soft tissue structures. In this study, XPC imaging techniques are shown to enable three dimensional (3D) imaging and evaluation of islet volume, alginate hydrogel structure, and local soft tissue features ex vivo. Rat islets were encapsulated in sterile ultrapurified alginate systems produced using a high-throughput microfluidic system. The encapsulated islets were implanted in omentum pouches created in a rodent model of type 1 diabetes. Microbeads were imaged with XPC imaging before implantation and as whole tissue samples after explantation from the animals. XPC microcomputed tomography (μCT) was performed with systems using tube-based and synchrotron X-ray sources. Islets could be identified within alginate beads and the islet volume was quantified in the synchrotron-based μCT volumes. Omental adipose tissue could be distinguished from inflammatory regions resulting from implanted beads in harvested samples with both XPC imaging techniques. Individual beads and the local encapsulation response were observed and quantified using quantitative measurements, which showed good agreement with histology. The 3D structure of the microbeads could be characterized with XPC imaging and failed beads could also be identified. These results point to the substantial potential of XPC imaging as a tool for imaging biomaterials in small animal models and deliver a critical step toward in vivo imaging.

A three-dimensional alginate system for in vitro culture of cumulus-denuded feline oocytes.

In the case of high valuable individuals with very precious genetic material, widening the genetic pool including gametes with poor morphological characteristics, as cumulus-denuded oocytes (CDOs), could be an option. To improve the in vitro culture of low-competence feline CDOs, an enriched three-dimensional (3D) system in association with competent cumulus-oocyte complexes (COCs) was developed. For this purpose, domestic cat CDOs were cultured with or without companion COCs in the 3D barium alginate microcapsules. The overall viability and the meiotic progression of feline CDOs cocultured with COCs or cultured separately in 3D or in 2D (traditional microdrops) system were compared. The 3D system was able to support viability and meiotic resumption of the feline oocytes, as well as the 2D microdrops. In 3D microcapsules, the presence of COCs resulted in a higher viability of CDOs (91.1%, p<.05), than that obtained without COCs or in 2D microdrops (71.2% and 67.3%, respectively), but the percentages of meiotic resumption were similar of those of CDOs cultured separately (55.4% vs. 40.4%, p>.05). It is notable that the presence of CDOs seemed to enhance the meiotic progression of the associated COCs. In conclusion, the 3D barium alginate microcapsules are a suitable system for feline oocytes in vitro culture, but more specific enriched conditions should be developed to improve the CDOs full competence in vitro.

Influence of electrostatic interactions on behavior of mixed rice glutelin and alginate systems: pH and ionic strength effects

The influence of pH (2–7) and ionic strength (0–200 mM NaCl) on the properties of hydrolyzed rice glutelin (HRG), alginate, and their mixtures in aqueous solutions was investigated using turbidity, ζ-potential, and microscopy measurements. Soluble or insoluble complexes could be formed between HRG and alginate by manipulating solution conditions such as HRG:alginate ratio, pH, and ionic strength. Relatively small complexes that were relatively stable to aggregation and sedimentation over a wide range of pH conditions could be formed using a 3:1 HRG to alginate mass ratio. The addition of salt (NaCl) to solutions containing HRG-alginate complexes weakened the electrostatic attraction between them, which led to release of the protein. As a result, the protein molecules tended to interact with other protein molecules (rather than polysaccharide molecules) leading to the formation of precipitates and sediments. The electrostatic complexes formed in this study may be a useful means of extending the utilization of rice proteins as functional ingredients in food and beverage products.