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PubMed1986

Alginate dental impression materials: chemistry, structure, and properties.

The setting behavior of calcium alginate impression materials was investigated by monitoring the viscosity, calcium ion activity, and shear modulus during the reaction. Structural information was also obtained from the dependence of viscosity and compressive modulus on the calcium concentration in model systems. The gelation time is primarily controlled by the concentration of Na4P2O7 in solution acting as a retarder, while the level and particle size of the alginate and CaSO4 X 2H2O also affect the kinetics through the dissolution rates and concentration effects. The Ca2+ crosslinks bridging the alginate chains in the network appear to be labile. Although this process of bond interchange and that of continued polymerization during deformation may be contributory mechanisms to permanent set, bond rupture appears to be the primary mechanism. Bond rupture can be reduced by increasing the alginate content in the system which also raises the tear energy. Both the permanent set and tear energy are affected by the filler particle morphology.

Alginates↗
PubMed2003

How to build an adapted and bioactive cell microenvironment? A chemical interaction study of the structure of Ca-alginate matrices and their repercussion on confined cells.

Alginates are increasingly being used as medical materials (matrices for tissue regeneration, surgical sponges, hemostatic bandages, microbial and cell encapsulation, artificial bacterial biofilms, etc.). The constitution of alginate gel networks is a complex phenomenon. A great number of different kinds of polysaccharidic frameworks can come to existence depending on the conditions used for their attainment. For instance, the degree of heterogeneity and porosity of Ca-alginate beads rely on this molecular organization. The formation of structural irregularities (superficial crust, cavities, shafts, dense or light gel frameworks, ordered or chaotic domains, etc.) within the alginate gel beads are inherent to this skeletal design. Several specific staining molecules (e.g. calcon carboxylic acid, murexide, methylene blue) that are negatively or positively charged interact with the gel network. These molecules allowed us to reveal a great variety of chemical interactions shown by the pattern coloration of the internal structure of the gel. The results observed are very different for the several matrices analyzed, which could explain to a great extent the singular behavior that cells confined in these kind of matrices exhibit.

Alginates↗
PubMed2005

Neocartilage from human mesenchymal stem cells in alginate: implied timing of transplantation.

Previous reports have demonstrated the suitability of alginate microencapsulation for chondrogenesis of human mesenchymal stem cells (MSCs) in vitro. This study examined the MSCs-alginate constructs that were transplanted beneath the dorsal skin of nude mice for 8 weeks after a variety of in vitro culture periods. The in vitro culture had great effects on gross morphology and histological characteristics of transplants. The integrity of alginate of transplants increased as the in vitro culture period increased. Transplants were characterized by an opaque and yellowish color, fair burnish, a firm to elastic texture, but without any evidence of calcification spots. Histological findings agreed with the clinical determination of hyaline cartilage, characterized by isolated cells with basophilic ground substance positive in Safranin-O staining and collagen type II immunohistochemistry. Transplants with exposure to TGF-beta1 for more than 2 weeks before transplantation, lost burnish, were flexible in texture, and had an increased formation of calcification spots. Accordingly, 1-week exposure to TGF-beta1 in vitro before transplantation is appropriate for neocartilage formation of human MSCs in alginate. These findings suggested that regeneration using cell therapy or tissue engineering should assist in ascertaining the optimal timing of transplantation.

Alginates↗
PubMed2005

Endoluminal hydrogel films made of alginate and polyethylene glycol: physical characteristics and drug-eluting properties.

Drug-eluting stents signify a major achievement in reducing the incidence of coronary restenosis after percutaneous transluminal coronary angioplasty. However, where drug-eluting stents have been unsuccessful, endoluminal gel-paving strategies offer renewed optimism, mainly in a variety of vascular procedures requiring catheter-based sustained, localized delivery of therapeutic drugs, and biological factors. Despite promising results in animals, endoluminal paving has met with very limited clinical success because of the technical difficulties and stringent safety demands. The current study presents an alternative to gel paving using 40-mum-thick biodegradable polymeric films for deployment onto the artery wall during balloon angioplasty and stenting. The films are made from a durable yet compliant network of alginate and polyethylene glycol (PEG), and are securely held affixed to the vessel wall by the expanded stent struts. The alginate-based films are characterized by measuring their strength, elasticity, degree of swelling, degradability in water and saline, and drug release properties. The combination of alginate and PEG afforded the films sufficient strength and compliance for endoluminal deployment using an in vitro organ culture system. In characterizing the film degradability, it was discovered that the ionic concentration of the buffered saline was the main determinant in regulating the degradation kinetics and the release kinetics of the drug molecule Paclitaxel. These results suggest that the use of alginate-based, PEG-containing polymeric films for endoluminal coverage offers an alternative solution to conventional drug-eluting stents, with the added advantage of uniform endoluminal coverage of the treated segment and homogeneous endoluminal application of the active substance.

Alginates↗
PubMed2005

Biological properties of photocrosslinked alginate microcapsules.

An alternative form of gene therapy using recombinant cell lines delivering therapeutic products encapsulated in alginate hydrogel has proven effective in treating many murine models. The lack of long-term capsule stability has led to a new strategy to reinforce the microcapsules with a photopolymerized interpenetrating covalent network of N-vinylpyrrolidone (NVP) and sodium acrylate. Here the properties for potential application in gene therapy are reported. In assessing potential toxicity of the unpolymerized residues, HPLC showed that even after 1 week of washing, no toxic monomers could be detected. Their ability to sustain cell growth was monitored with growth of the encapsulated cells in vitro and in vivo. Although the initial photopolymerization caused significant cell damage, the cells were able to recover normal growth rates thereafter. After implanting into mice, the NVP-modified capsules showed a high level of biocompatibility as measured by hematological and biochemical functional tests. There was also no difference in the amount and type of plasma proteins adsorbing to the NVP-modified and the classical alginate capsules, thus indicating their similar biological compatibility. Both in vitro and in vivo tests confirmed that the NVP-modified capsules were more resistant to osmotic stress than the alginate microcapsules. Furthermore, when applied to the treatment of a murine model of human cancer by delivering encapsulated cells secreting angiostatin, the NVP-modified microcapsules suppressed tumor growth as successfully as the regular alginate microcapsules. In conclusion, the covalently modified microcapsules have shown a high level of biocompatibility, safety, increase in stability, and clinical efficacy for use as immunoisolation devices in gene therapy.

Alginates↗
PubMed2005

Novel alginate-poly(L-histidine) microcapsules as drug carriers: in vitro protein release and short term stability.

Spherical, smooth-surfaced and mechanically stable alginate-poly(L-histidine) (PLHis) microcapsules with narrow particle size distributions were prepared by incubating calcium alginate beads in aqueous solutions of PLHis. The in vitro release characteristics, drug loading and encapsulation efficiency of the microcapsules were investigated using bovine erythrocytes hemoglobin (Hb) as a model drug. The results showed that the concentration of Ca(2+) ions had a considerable effect on the drug loading, encapsulation efficiency and in vitro release behavior of the microcapsules. When the concentration of CaCl(2) in the PLHis solution was increased from 0 to 3.0% (w/v), the drug loading and encapsulation efficiency decreased significantly from 38.0 to 4.3% and from 92.9 to 8.0%, respectively, while the total cumulative release of Hb from microcapsules in phosphate buffered saline solution (PBS, pH 6.8) decreased from 96.2 to 72.8% in 24 h. No significant protein release was observed during 70 h of incubation in hydrochloric acid solution (pH 1.2). However, under neutral conditions (PBS, pH 6.8), the Hb was completely and stably released within 24-70 h. An explosion test showed that the stability of alginate-PLHis microcapsules depended strongly on the concentration of PLHis and the calcium ions in solution. [Diagram: see text] Microscopy photo of Hb-loaded alginate-PLHis microcapsules.

Alginates↗
PubMed2006

Elastic, superporous hydrogel hybrids of polyacrylamide and sodium alginate.

A novel approach was developed to prepare a superporous hydrogel with superior mechanical and elastic properties. According to this method, a synthetic monomer was polymerized and crosslinked in the presence of a water-soluble alginate polymer. Later in the process, the alginate part of the synthesized hydrogel was treated with metal cations, which resulted in a hydrogel hybrid with an interpenetrating network structure. In this article, a hydrogel hybrid of acrylamide and alginate is highlighted because of its unique swelling and mechanical properties. This hydrogel hybrid shows resilience and a rubbery property in its fully water-swollen state, which not previously been reported. To help understand the underlying mechanism responsible for such unique properties with hydrogel hybrids, the ionotropic gelation of the alginate polymer was also studied in more detail.

Acrylic Resins↗
PubMed1992

NMR studies of erythrocytes immobilized in agarose and alginate gels.

31P and 13C NMR were used to study the energy metabolism in perfused, human erythrocytes. The erythrocytes were immobilized in agarose threads, Ca- or Ba-alginate beads, and Ba-alginate-coated agarose threads. Erythrocytes were easily washed out from the agarose threads, but not from alginate-containing gels. Various small molecules, such as hypophosphite, dimethyl methylphosphonate, and methylphosphonate, were taken up from the perfusion medium in a normal manner. In addition, the 2,3-bisphosphoglycerate (2,3-DPG) chemical shifts were sensitive to the oxygen partial pressure suggesting that O2 molecules were diffusing through the gel and modifying the binding of 2,3-DPG to hemoglobin. A combination of inosine and pyruvate stimulated the synthesis of 2,3-DPG, but only if inorganic phosphate was present in the perfusion medium. Inosine only resulted in a dramatic rise in the intracellular sugarphosphate concentrations. Furthermore, [2-13C]glucose was converted to [2-13C]lactate by immobilized cells at a rate which was comparable to that in a control suspension. In summary, immobilization in Ba-alginate-coated agarose threads was an efficient way of trapping human erythrocytes for whole cell NMR investigations.

Alginates↗
PubMed2000

Chondrocyte extracellular matrix synthesis and turnover are influenced by static compression in a new alginate disk culture system.

The goal of this study was to examine the effects of mechanical compression on chondrocyte biosynthesis of extracellular matrix (ECM) components during culture in a new alginate disk culture system. Specifically, we have examined chondrocyte biosynthesis rates, and the structure of aggrecan core protein species present in the cell-associated matrix (CM), in the further removed matrix (FRM) and in the surrounding culture medium. In this alginate disk culture system, chondrocytes can be subjected to mechanical deformations similar to those experienced in vivo. Our results show that over an 8-week culture period, chondrocytes synthesize a functional ECM and can respond to mechanical forces similarly to chondrocytes maintained in native cartilage. In the alginate disk system, static compression was shown to decrease and dynamic compression to increase synthesis of aggrecan of bovine chondrocytes. Western blot analysis of the core proteins of aggrecan molecules identified a number of different species that were present in different relative amounts in the CM, FRM, and medium. Over 21 days of culture, the predominant form of aggrecan found in the ECM was a full-length link-stabilized species. In addition, our data show that the application of 40 h of static compression caused an increase in the proportion of newly synthesized aggrecan molecules released into the medium. However, this was not accompanied by a significant change in the size and composition of aggrecan and aggrecan fragments in the different compartments, suggesting that mechanical compression did not alter the catabolic pathways. Together, these data show that chondrocyte function is maintained in an alginate disk culture system and that this culture system is a useful model to examine chondrocyte ECM assembly and some aspects of catabolism normally found in vivo.

Aggrecans↗
PubMed1997

Differentiation of mesenchymal limb bud cells to chondrocytes in alginate beads.

Many in vitro models of embryonic material used for the cultivation of chondrocytes yield mixed cultures consisting of chondrocytes and fibroblast-like cells. For the optimization of cartilage cell cultures, alginate, a semisolid medium, was employed to obtain pure chondrocyte cultures. Isolated mesenchymal cells from 12-day-old mouse limb buds were grown in alginate for up to 4 weeks. A sub-population of the cells differentiated to chondrocytes and exhibited a stable phenotype until the end of the culture period. After 3 to 4 days a cartilage-specific matrix started to develop. Fibroblast-like cells from this mixed culture did not survive; they became necrotic. When alginate was later on dissolved by chelating agents, only chondrocytes were isolated. During dissolution of alginate and centrifugation, chondrocytes did not lose their contact with their new matrix present on their surfaces. Cultivation of these chondrocytes or chondrones in mass culture yields a pure chondrocyte population. Immunoelectron microscopic investigations revealed collagen type II, fibronectin, decorin and chondroitin sulfate-proteoglycans in the chondrocyte capsules and in mass culture.

Alginates↗
PubMed1999

Abnormal collagen assembly, though normal phenotype, in alginate bead cultures of chick embryo chondrocytes.

The collagens produced by chick embryo chondrocytes cultured in alginate beads were investigated both biochemically and ultrastructurally. The cartilage phenotype is maintained for at least 14 days, as indicated by the production of the cartilage-specific collagens II, IX, and XI and the absence of collagen I. There were differences in the distributions of collagens among the three different compartments analyzed (cells and their associated matrix, further-removed matrix (released by alginate solubilization), and culture medium), with large amounts of collagen IX (mainly in proteoglycan form) in the culture medium. Inhibition of lysyl oxidase activity by beta-aminopropionitrile led to an overall decrease in collagen production. In contrast to the biochemical observations, collagen ultrastructure in the extracellular matrix of alginate cultures was not in the form of the expected 64-nm banded fibrils, but rather in the form of segment-long-spacing-like crystallites. This abnormal structure is likely to be a result of alginate disrupting normal assembly. We conclude that, in this system, the native fibrillar structure of the collagenous matrix is not essential for the maintenance of the differentiated phenotype of chondrocytes.

Alginates↗
PubMed2002

Crystal structure of AlgQ2, a macromolecule (alginate)-binding protein of Sphingomonas sp. A1 at 2.0A resolution.

Sphingomonas sp. A1 possesses a high molecular mass (average 25,700 Da) alginate uptake system mediated by a novel pit-dependent ABC transporter. The X-ray crystallographic structure of AlgQ2 (57,200 Da), an alginate-binding protein in the system, was determined by the multiple isomorphous replacement method and refined at 2.0 A resolution with a final R-factor of 18.3% for 15 to 2.0 A resolution data. The refined structure of AlgQ2 was comprised of 492 amino acid residues, 172 water molecules, and one calcium ion. AlgQ2 was composed of two globular domains with a deep cleft between them, which is expected to be the alginate-binding site. The overall structure is basically similar to that of maltose/maltodextrin-binding protein, except for the presence of an N2-subdomain. The entire calcium ion-binding site is similar to the site in the EF-hand motif, but comprises a ten residue loop. This calcium ion-binding site is about 40 A away from the alginate-binding site.

Alginates↗
PubMed2000

Overexpression in Escherichia coli, purification, and characterization of Sphingomonas sp. A1 alginate lyases.

A bacterium Sphingomonas sp. A1 produces three kinds of alginate lyases [A1-I (66 kDa), A1-II (25 kDa), and A1-III (40 kDa)] from a single precursor, through posttranslational processing. Overexpression systems for these alginate lyases were constructed in Escherichia coli cells by controlling of the lyase genes under T7 promoter and terminator. Expression levels of A1-I, A1-II, and A1-III in E. coli cells were 3.50, 3.04, and 2.13 kU/liter of culture, respectively, and were over 10-fold higher than those in Sphingomonas sp. A1 cells. Purified A1-I, A1-II, and A1-III from E. coli cells were monomeric enzymes with molecular masses of 63, 25, and 40 kDa, respectively. The depolymerization pattern of alginate with A1-I and A1-II indicated that both enzymes cleaved the glycosidic bond of the polymer endolytically and by beta-elimination reaction. A1-II preferred polyguluronate rather than polymannuronate and released tri- and tetrasaccharides, which have unsaturated uronyl residues at the nonreducing terminal, from alginate as the major final products. A1-I acted equally on both homopolymers and produced di- and trisaccharides as the final products.

Alginates↗
PubMed1994

Production of purified alginates suitable for use in immunoisolated transplantation.

Alginate is used as a matrix for immunoisolation of cells and tissues in vivo. We have demonstrated previously that commercial alginates contain various fractions of mitogenic impurities and that they can be removed by free flow electrophoresis. The use of purified material is a necessity in order to reveal the parameters that control biocompatibility of the implanted material (such as stability, size, surface charge and curvature, etc.). In this study, we present a protocol for the chemical purification of alginates on a large-scale. Beads made from alginates purified by this multi-step chemical extraction procedure did not induce a significant foreign body reaction when implanted for 3 weeks either intraperitoneally or beneath the kidney capsule of Lewis or non-diabetic BB/Gi rats.

Alginates↗
PubMed1990

Growth of poliovirus using alginate entrapped-anchorage dependent Vero cells.

Obligatory anchorage dependant Vero cells were successfully grown in gelatinous-like macrocarriers made of calcium alginate. Entrapped single cells were immobilized within the polymerized alginate matrix divide to form large spherical clumps of cells. A cell density of 17 x 10(6) cells/ml of alginate with over 95% viability was obtained after 14 days in spinner flasks. When subjected to poliovirus type I infection, spherical masses of Vero cells progressively showed extensive cytopathic effect but remained entrapped in the alginate matrix of the macrocarriers. Virus was released into a cellular debris free-like supernatant and reached a peak titer of 10(8.0) TCID50/ml after 72 hours.

Alginates↗
PubMed2005

[Traumatic tympanic membrane perforactions. Local application of an alginate matrix loaded with epidermal growth factor in an animal model].

BACKGROUND: The aim of this study was to evaluate the effects of an alginate matrix releasing epidermal growth factor on healing after acute tympanic membrane perforation in rats. METHOD: A total of 20 male rats were divided into two groups. In each animal, a randomly chosen tympanic membrane was perforated by heat. A piece of alginate matrix (control group) or alginate matrix loaded with 0.25 microg epidermal growth factor (EGF group) was then placed on the perforation. The rat ears were examined after days 3, 6, 9, and 14 and every week thereafter for a total of 11 weeks. Each matrix was removed on day 9. To examine the status of the tympanic membranes on day 14, one randomly chosen membrane from each group was histopathologically examined. RESULTS: By day 6, complete closure of the tympanic membrane perforation was achieved in 56% of the EGF group, whereas it was achieved in only 10% in the control group. By day 14, all tympanic membrane perforations were closed in both groups. There were no complications and no significant differences in the histopathologic parameters between the EGF group and the control group. CONCLUSION: An alginate matrix seems to be a useful EGF-delivery system to the tympanic membrane.

Administration, Topical↗
PubMed2003

Phase separation in calcium alginate gels.

Alginates are polysaccharides consisting of beta-D-mannuronate and alpha-L-guluronate units. In the presence of bivalent cations like calcium the guluronate blocks form physically cross-linked gels. The gelation properties of alginates play an important role in the stability of extracellular polymer substances and in the food industry. When stock solutions of Ca2+ ions and alginate are mixed, the gelation starts before the Ca2+ ions are evenly distributed, which leads to non-uniform gels. In this contribution, Ca alginate gels were prepared by in situ gelation using glucono-delta-lactone and CaCO3. In this way, uniform gels could be prepared directly in the measuring cell. Below a critical concentration, highly viscous solutions were obtained, which were below the critical point of gel formation. In these solutions at low rotational speeds a Schlieren peak arose, which became smaller and steeper with increasing time until a new meniscus could be detected. This behaviour is in contrast to the peak broadening due to diffusion after a synthetic boundary was formed. Evaluation of the data leads to negative diffusion coefficients. It has been shown by others that the mutual diffusion coefficient must be negative in the spinodal region. This phenomena is known as uphill diffusion and leads to phase separation of a binary system. The formation of the gel phase in this case is therefore discussed as uphill diffusion.

Alginates↗
PubMed2003

Cross-linking properties of alginate gels determined by using advanced NMR imaging and Cu(2+) as contrast agent.

The entrapment of enzymes, drugs, cells or tissue fragments in alginates cross-linked with Ca(2+) or Ba(2+) has great potential in basic research, biotechnology and medicine. The swelling properties and, in turn, the mechanical stability are key factors in designing an optimally cross-linked hydrogel matrix. These parameters depend critically on the cross-linking process and seemingly minor modifications in manufacture have a large impact. Thus, sensitive and non-invasive tools are required to determine the spatial homogeneity and efficacy of the cross-linking process. Here, we show for alginate microcapsules (between 400 microm and 600 microm in diameter) that advanced (1)H NMR imaging, along with paramagnetic Cu(2+) as contrast agent, can be used to validate the cross-linking process. Two- and three-dimensional images and maps of the spin-lattice relaxation time T(1) of Ba(2+) cross-linked microcapsules exposed to external Cu(2+) yielded qualitative as well as quantitative information about the accumulation of Cu(2+) within and removal from microcapsules upon washing with Cu(2+) free saline solution. The use of Cu(2+) (having a slightly higher affinity constant to alginate than Ba(2+)) for gelling gave a complementary insight into the spatial homogeneity of the cross-linking process together with information about the mechanical stability of the microcapsules. The potential of this technique was demonstrated for alginates extracted from two different algal sources and cross-linked either externally by the conventional air-jet dropping method or internally by the "crystal gun" method.

Alginates↗