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PubMed1994

Addition of a bacterial alginate lyase to purulent CF sputum in vitro can result in the disruption of alginate and modification of sputum viscoelasticity.

Alginate is a large molecular weight exopolysaccharide present in the purulent airway secretions of cystic fibrosis (CF) patients. This polymer, produced by some of the opportunistic pathogens associated with the recurrent lung infections characteristic of CF, has been suggested to effect an increase in the viscoelastic properties of purulent CF airway secretions. We have investigated the use of an enzyme targeted at this exopolysaccharide, an alginate lyase obtained from a bacterial source, to disrupt its polymeric nature and effect a change in the rheological properties of CF sputum in vitro. Expectorated sputum samples obtained from hospitalized CF patients were found to contain 80-200 micrograms alginate per ml sputum with no measurable endogenous alginate lyase activity. Treatment with exogenous alginate lyase prepared from a mucoid strain of Pseudomonas aeruginosa resulted in the disruption of alginate and a decrease in sputum viscoelasticity in a small percentage of the samples tested. Similar treatment of these samples with recombinant human deoxyribonuclease I to cleave DNA present in purulent sputum and the use of alginate extracted from sputum as an alginate lyase assay substrate suggested that the inability of the exogenous alginate lyase to disrupt sputum alginate was not due to substrate inaccessibility or an unresponsive substrate. Concentrations of Ca2+ and Zn2+ in alginate lyase-resistant sputum samples, determined by metal ion analysis, were found to inhibit enzyme activity in studies using seaweed alginate as a substrate. High concentrations of Ca2+ and Zn2+ in sputum samples initially resistant to lyase activity could be reduced significantly in some samples by dialysis and these same samples acquired sensitivity to the lyase. Other sputum samples did not show reduced concentrations of Ca2+ and Zn2+ following dialysis and these samples remained lyase-insensitive. Together, these results suggest that bacterial alginate present within purulent CF sputum may be quite stable, that endogenous alginate lyase activities appear to be limited and that the in vitro addition of exogenous alginate lyase can lead to the disruption of alginate and a change in the viscoelastic properties of some purulent CF sputum samples.

Alginates↗

PubMed2003

Biocompatibility of alginates for grafting: impact of alginate molecular weight.

Optimising microencapsulation technology towards the effective clinical transplantation has created the need for highly biocompatible alginates. Therefore, in this study the biocompatibility of different beads prepared from alginates with varying average molecular weight was examined. In some experiments the beads were covered with a multilayer membrane surrounded by an alginate layer. First of all, we found that beads made of a lower weight average alginate elicted a much stronger fibrotic response compared to beads made of a higher weight average alginate (LV-alginate > MV-alginate). The results were confirmed by the observation that the extent of tissue fibrosis was significantly increased in multilayer capsules made of an alginate with a lower weight average (core and surface LV-alginate, Mw 0.7-1 * 10(6) g/mol, viscosity of a 0.1% solution 1-2.5 mPa s(-1)) compared to multilayer capsules made of an alginate with a higher weight average (core and surface MV-alginate; Mw 1.2-1.3 * 10(6) g/mol, viscosity of a 0.1% solution 5-7 mPa s(-1)). It should be stressed, that the pro-fibrotic effect of the LV-alginate alginate in the core was only partially reversed by a MV-alginate on the surface of the multilayer capsules. On the basis of the raised data, it can be assumed that the molecular weight average of the alginates have an decisive effect on the biocompatibility. Therefore, it seems to be recommendable to reduce the low molecular weight fractions of the alginate during the purification process to improve the biocompatibility.

Alginates↗

PubMed1993

Identification of algF in the alginate biosynthetic gene cluster of Pseudomonas aeruginosa which is required for alginate acetylation.

Mucoid strains of Pseudomonas aeruginosa produce a high-molecular-weight exopolysaccharide called alginate that is modified by the addition of O-acetyl groups. To better understand the acetylation process, a gene involved in alginate acetylation called algF was identified in this study. We hypothesized that a gene involved in alginate acetylation would be located within the alginate biosynthetic gene cluster at 34 min on the P. aeruginosa chromosome. To isolate algF mutants, a procedure for localized mutagenesis was developed to introduce random chemical mutations into the P. aeruginosa alginate biosynthetic operon on the chromosome. For this, a DNA fragment containing the alginate biosynthetic operon and adjacent argF gene in a gene replacement cosmid vector was utilized. The plasmid was packaged in vivo into lambda phage particles, mutagenized in vitro with hydroxylamine, transduced into Escherichia coli, and mobilized to an argF auxotroph of P. aeruginosa FRD. Arg+ recombinants coinherited the mutagenized alginate gene cluster and were screened for defects in alginate acetylation by testing for increased sensitivity to an alginate lyase produced by Klebsiella aerogenes. Alginates from recombinants which showed increased sensitivity to alginate lyase were tested for acetylation by a colorimetric assay and infrared spectroscopy. Two algF mutants that produced alginates reduced more than sixfold in acetyl groups were obtained. The acetylation defect was complemented in trans by a 3.8-kb XbaI-BamHI fragment from the alginate gene cluster when placed in the correct orientation under a trc promoter. By a merodiploid analysis, the algF gene was further mapped to a region directly upstream of algA by examining the polar effect of Tn501 insertions. By gene replacement, DNA with a Tn501 insertion directly upstream of algA was recombined with the chromosome of mucoid strain FRD1. The resulting strain, FRD1003, was nonmucoid because of the polar effect of the transposon on the downstream algA gene. By providing algA in trans under the tac promoter, FRD1003 produced nonacetylated alginate, indicating that the transposon was within or just upstream of algF. These results demonstrated that algF, a gene involved in alginate acetylation, is located directly upstream of algA.

Acetylation↗

PubMed1997

Effect of the alginate composition on the biocompatibility of alginate-polylysine microcapsules.

Alginate-polylysine (PLL) capsules are commonly applied for immunoprotection of endocrine tissues. Alginate is composed of mannuronic acid (M) and guluronic acid (G). Different types of alginate have different ratios of G to M, but little is known of the influence of these differences on biocompatibility. Therefore, we have investigated in vivo the effect of the G-content of the alginate on the biocompatibility of the capsules. Capsules prepared of commercially available alginates with either a high or an intermediate G-content were implanted in the peritoneal cavity of rats and retrieved one month later for histological evaluation. The fibrotic reaction was more severe against high-G alginate capsules than to intermediate-G alginate capsules. The majority of the high-G capsules proved to be overgrown and adherent to the abdominal organs whereas with intermediate-G alginate most capsules were found freely floating in the peritoneal cavity and free of any adhesion of cells. This was not caused by the alginate as such but rather by inadequate binding of high-G alginate to PLL since in the absence of PLL, i.e. with beads instead of capsules, no fibrotic reaction was observed. As high-G alginates have beneficial effects for islet encapsulation, efforts should be made to apply polycations which more effectively interact with high-G alginate than PLL.

Alginates↗

PubMed1996

Identification of algI and algJ in the Pseudomonas aeruginosa alginate biosynthetic gene cluster which are required for alginate O acetylation.

Mucoid strains of Pseudomonas aeruginosa overproduce alginate, a linear exopolysaccharide Of D-mannuronate and variable amounts of L-guluronate. The mannuronate residues undergo modification by C-5 epimerization to form the L-guluronates and by the addition of acetyl groups at the 0-2 and 0-3 positions. Through genetic analysis, we previously identified algF, located upstream of algA in the 18-kb alginate biosynthetic operon, as a gene required for alginate acetylation. Here, we show the sequence of a 3.7-kb fragment containing the open reading frames termed algI, algJ, and algF. An algI::Tn5O1 mutant, which was defective in algIJFA because of the polar nature of the transposon insertion, produced alginate when algA was provided in trans. This indicated that the algIJF gene products were not required for polymer biosynthesis. To examine the potential role of these genes in alginate modification, mutants were constructed by gene replacement in which each gene (algI, algJ, or algF) was replaced by a polar gentamicin resistance cassette. Proton nuclear magnetic resonance spectroscopy showed that polymers produced by strains deficient in algIJF still contained a mixture of D-mannuronate and L-guluronate, indicating that C-5 epimerization was not affected. Alginate acetylation was evaluated by a colorimetric assay and Fourier transform-infrared spectroscopy, and this analysis showed that strains deficient in algIJF produced nonacetylated alginate. Plasmids that supplied the downstream gene products affected by the polar mutations were introduced into each mutant. The strain defective only in algF expression produced an alginate that was not acetylated, confirming previous results. Strains missing only algJ or algI also produced nonacetylated alginates. Providing the respective missing gene (algI, algJ, or algF) in trans restored alginate acetylation. Mutants defective in algI or algJ, obtained by chemical and transposon mutagenesis, were also defective in their ability to acetylate alginate. Therefore, algI and algJ represent newly identified genes that, in addition to algF, are required for alginate acetylation.

Acetylation↗

PubMedDate not supplied

Small-angle X-ray scattering and rheological characterization of alginate gels. 3. Alginic acid gels.

Alginic acid gels were studied by small-angle X-ray scattering and rheology to elucidate the influence of alginate chemical composition and molecular weight on the gel elasticity and molecular structure. The alginic acid gels were prepared by homogeneous pH reduction throughout the sample. Three alginates with different chemical composition and sequence, and two to three different molecular weights of each sample were examined. Three alginate samples with fractions of guluronic acid residues of 0.39 (LoG), 0.50 (InG), and 0.68 (HiG), covering the range of commercially available alginates, were employed. The excess scattering intensity I of the alginic acid gels was about 1 order of magnitude larger and exhibited a stronger curvature toward low q compared to ionically cross-linked alginate. The I(q) were decomposed into two components by assuming that the alginic acid gel is composed of aggregated multiple junctions and single chains. Time-resolved experiments showed a large increase in the average size of aggregates and their weight fraction within the first 2 h after onset of gelling, which also coincides with the most pronounced rheological changes. At equilibrium, little or no effect of molecular weight was observed, whereas at comparable molecular weights, an increased scattering intensity with increasing content of guluronic acid residues was recorded, probably because of a larger apparent molecular mass of domains. The results suggest a quasi-ordered junction zone is formed in the initial stage, followed by subsequent assembling of such zones, forming domains in the order of 50 A. The average length of the initial junction zones, being governed by the relative fraction of stabilizing G-blocks and destabilizing alternating (MG) blocks, determines the density of the final random aggregates. Hence, high-G alginates give alginic acid gels of a higher aggregate density compared to domains composed of loosely packed shorter junction zones in InG or LoG system.

Alginates↗

PubMed2003

Visualization of alginate-poly-L-lysine-alginate microcapsules by confocal laser scanning microscopy.

Confocal laser scanning microscopy (CLSM) was used to study the distribution of polymers and cross-linking ions in alginate-poly-L-lysine (PLL) -alginate microcapsules made by fluorescent-labeled polymers. CLSM studies of Ca-alginate gel beads made in the presence and absence of non-gelling sodium ions revealed a more inhomogeneous distribution of alginate in beads formed in the absence of non-gelling ions. In the formation of alginate-PLL capsules, the polymer gradients in the preformed gel core were destabilized by the presence of non-gelling ions in the washing step and in the PLL solution. Ca-alginate gels preserved the inhomogeneous structure by exposure to ion-free solution in contrast to exposure to non-gelling ions (Na(+)). By exchanging Ca(2+) with Ba(2+) (10 mM), extremely inhomogeneous gel beads were formed that preserved their structure during the washing and exposure to PLL in saline. PLL was shown to bind at the very surface of the alginate core, forming a shell-like membrane. The thickness of the PLL-layer increased about 100% after 2 weeks of storage, but no further increase was seen after 2 years of storage. The coating alginate was shown to overlap the PLL layer. No difference in binding could be observed among coating alginates of different composition. This paper shows an easy and novel method to study the distribution of alginate and PLL in intact microcapsules. As the labeling procedures are easy to perform, the method can also be used for a variety of other polymers in other microencapsulation systems.

Alginates↗

PubMed2003

The roles of oxygen and alginate-lyase in determining the molecular weight of alginate produced by Azotobacter vinelandii.

An Azotobacter vinelandii mutant lacking alginate-lyase (SML2) and the wild type (ATCC 9046) were used to discriminate between the roles of the polymerase complex and alginate-lyase in the synthesis of alginate in cultures conducted under controlled dissolved oxygen tension (DOT). To avoid the presence of pre-synthesized alginates, all cultures were inoculated with washed cells. For cultures carried out at 3% DOT using the mutant, a well defined family of alginates of high mean molecular weight (MMW) were obtained (985 kDa). Under 1% and 5% DOT, the mutant produced unique families of alginates with lower MMW (150 and 388 kDa). A similar behavior was observed using the wild type: a production of well defined families of alginates of high MMW at 3% DOT (1,250 kDa) and lower MMW at 1% and 5% DOT (370 and 350 kDa). At the end of the ATCC 9046 fermentations, alginate was depolymerized by the action of lyases. Overall, the evidence indicated that polymerization of alginate is carried out by producing families of polysaccharide in a narrow MMW range, and that it is highly dependent on DOT. The role of alginate-lyase (present in the wild type) is restricted to a post-polymerization step.

Alginates↗

PubMed1996

Alginate polycation microcapsules. I. Interaction between alginate and polycation.

The interactions between alginate and polycations have been studied by using different labelling techniques. Binding of poly-L-lysine (PLL) to alginate in the gel state is mainly governed by the amount of dissociable negative charges on the bead surface. PLL was found to bind more rapidly to gel beads made from alginate with a high content of mannuronic acid. The binding was enhanced by increasing the alginate concentration on the surface by making inhomogeneous beads. When the capsules were stored in the presence of cations with high affinity for alginate (Ca2+, Sr2+), PLL was washed off. Less PLL is bound to strontium alginate than to calcium alginate beads. Two mechanisms appear to be responsible for the binding of sodium alginate to alginate PLL capsules (coating): (i) an electrostatic interaction between the soluble coating material and excess positive charges on PLL on the surface; (ii) the formation of a calcium alginate gel on the surface owing to leaching of calcium ions from the core. The stability and efficiency of the coating as a function of molecular size and sequential structure of the coating polymer have also been investigated.

Alginates↗

PubMedDate not supplied

Calcium alginate microparticles for oral administration: I: Effect of sodium alginate type on drug release and drug entrapment efficiency.

The natural polymers alginate and chitosan were used for the preparation of controlled release nicardipine HCl gel microparticles. The effect of the mannuronic/guluronic acid content and the alginate viscosity on the prolonged action of the microparticles, which were prepared with different types of alginates, were investigated. The mean particle sizes and the swelling ratios of the microparticles were also determined. The in vitro release studies were carried out with a flow-through cell apparatus in different media (pH 1.2, 2.5, 4.5, 7 and 7.5 buffer solutions). The release of nicardipine was extended with the alginate gel microparticles prepared with guluronic acid rich alginate. After the determination of the most appropriate alginate type, the effect of alginate-chitosan complex formation was studied on the release pattern of drug incorporated. It was observed that the alginate-chitosan complex formation reduced the erosion of the alginate-chitosan matrix at pH 7-7.5. The release of drug from the chitosan-alginate gel microparticles took place by both diffusion through the swollen matrix and relaxation of the polymer at pH 1.2-4.5.

Alginates↗

PubMed2002

Alginate production by an Azotobacter vinelandii mutant unable to produce alginate lyase.

Alginate is an industrially relevant linear copolymer composed of beta-1,4-linked D-mannuronic acid and its C-5 epimer L-guluronic acid. The rheological and gel-forming properties of alginates depend on the molecular weight and the relative content of the two monomers. Alginate produced by Azotobacter vinelandii was shown to be degraded towards the end of the culture, an undesirable situation in terms of potential alginate applications. A gene ( algL) encoding the alginate lyase activity AlgL is present within the alginate biosynthetic gene cluster of A. vinelandii. We constructed strain SML2, an A. vinelandii strain carrying a non-polar mutation within algL. No alginate lyase activity was detected in SML2. Under 3% dissolved oxygen tension, higher values of maximum mean molecular weight alginate were obtained (1240 kDa) with strain SML2, compared to those from the parental strain ATCC 9046 (680 kDa). These data indicate that AlgL activity causes the drop in the molecular weight of alginate produced by A. vinelandii.

Alginates↗

PubMedDate not supplied

Control of molecular weight cut-off for immunoisolation by multilayering glycol chitosan-alginate polyion complex on alginate-based microcapsules.

Glycol chitosan is a positively charged polysaccharide which is water-soluble at pH 7.4, and is able to form a polyion complex (PIC) with anionic polymers, such as alginate. The authors attempt to develop a novel type of alginate-based microcapsule using this glycol chitosan for a islets-encapsulated bioartificial pancreas. The number of layers composed of glycol chitosan-alginate (GC-Alg) PIC were optimized, in order to cut off immunoglobulin transport and to protect encapsulated islets from the host immune reaction, and the transport characteristics were evaluated of glucose, bovine serum albumin (BSA) and gamma-globulin. To add mechanical stability to the microcapsule, calcium ions, which crosslinked the alginate polymers close to the interface between core Ca-alginate and multilayered membrane, were partially substituted with barium ions after the formation of multilayered Ca-alginate gel beads. The partition coefficients of BSA and gamma-globulin were decreased with the increasing number of layers. The immunoisolation was achieved against gamma-globulin with four layers of the GC-Alg PIC membrane, while BSA could permeate the membrane. The four-layered Ba-alginate gel bead had a good permeability for glucose, giving a diffusion coefficient corresponding to 80% of that in pure water. Insulin secretion from the islets in the four-layered Ba-alginate microcapsule was satisfactorily observed with the fractional stimulation ratio of 2.17. This result indicates that the encapsulated islets maintained their viability even after encapsulation. It was, thus, shown that the Ba-alginate microcapsule with four layers of the GC-Alg PIC membrane is promising as the microencapsulation material for a bioartificial pancreas.

Alginates↗

PubMed1999

Transplantation of alginate microcapsules: generation of antibodies against alginates and encapsulated porcine islet-like cell clusters.

BACKGROUND: Microencapsulation of islets of Langherhans in alginate poly-L-lysine capsules provides an effective protection against cell-mediated immune destruction, and ideally should allow the transplantation of islets in the absence of immunosuppression. It has previously been suggested that alginate rich in mannuronic acid (high M) is more immunogenic than alginate rich in guluronic acid (high G). The ability of these alginates to induce an antibody response in the recipient or act as an adjuvant to antibody responses against antigens leaked from the capsule was investigated in the present study. METHODS: Empty capsules made from these different types of alginate were transplanted intraperitoneally to Wistar rats or Balb/c mice. In addition, some animals were also injected with bovine serum albumin to assess the ability of the alginates to act as an adjuvant to this antigen. Antibody responses to intraperitoneally transplanted free and microencapsulated fetal porcine islet like cell clusters (ICC) were also evaluated, in animals treated with or without cyclosporine. RESULTS: Antibodies against high M-alginate capsules were detected in the sera of mice transplanted with this capsule type. However, this response was not seen after the transplantation of high G capsules. When Wistar rats were used as recipients, no antibody responses were detected against any type of alginate capsules. Neither type of capsule acted as an adjuvant. Antibodies against ICC were present, in rats transplanted with both nonencapsulated and encapsulated ICCs. Administration of cyclosporine could abolish this production of antibodies against ICC. CONCLUSIONS: High G-alginate capsules are less immunogenic than high M capsules. Because encapsulation did not protect against the generation of antibodies against ICC, it can be assumed that antigen leakage from the capsules occurs, as no evidence was found for capsules breaking in vivo.

Adjuvants, Immunologic↗

PubMed1996

Alginate synthesis in Pseudomonas aeruginosa: the role of AlgL (alginate lyase) and AlgX.

Previous studies localized an alginate lyase gene (algL) within the alginate biosynthetic gene cluster at 34 min on the Pseudomonas aeruginosa chromosome. Insertion of a Tn501 polar transposon in a gene (algX) directly upstream of algL in mucoid P. aeruginosa FRD1 inactivated expression of algX, algL, and other downstream genes, including algA. This strain is phenotypically nonmucoid; however, alginate production could be restored by complementation in trans with a plasmid carrying all of the genes inactivated by the insertion, including algL and algX. Alginate production was also recovered when a merodiploid that generated a complete alginate gene cluster on the chromosome was constructed. However, alginate production by merodiploids formed in the algX::Tn501 mutant using an alginate cluster with an algL deletion was not restored to wild-type levels unless algL was provided on a plasmid in trans. In addition, complementation studies of Tn501 mutants using plasmids containing specific deletions in either algL or algX revealed that both genes were required to restore the mucoid phenotype. Escherichia coli strains which expressed algX produced a unique protein of approximately 53 kDa, consistent with the gene product predicted from the DNA sequencing data. These studies demonstrate that AlgX, whose biochemical function remains to be defined, and AlgL, which has alginate lyase activity, are both involved in alginate production by P. aeruginosa.

Alginates↗

PubMed1999

Self-setting barrier membrane for guided tissue regeneration method: initial evaluation of alginate membrane made with sodium alginate and calcium chloride aqueous solutions.

Alginate membrane was proposed as a self-setting barrier membrane that can be used for guided tissue regeneration (GTR). The alginate membrane can be prepared and placed at the bone defect during the surgical procedure. The procedure consists of two simple steps. First, the bone defect is filled with sodium alginate (Na-Alg) aqueous solution. Then calcium chloride aqueous solution is dropped on the surface of the Na-Alg aqueous solution. An alginate membrane is formed on the bone defect, keeping the inside of the bone defect filled with unreacted Na-Alg aqueous solution. In this investigation, a preliminary animal study was conducted for an initial evaluation as to whether or not the alginate membrane can be used as a barrier membrane for the GTR method. Bone defects were made in the tibiae of 15-week-old rats. The alginate membrane was made on the surface of existing bone by filling the defect with Na-Alg aqueous solution and then dropping calcium chloride aqueous solution onto the surface of the Na-Alg solution. Four weeks after surgery, the bone defect was found to be reconstructed with new bone when the defect had been covered with alginate membrane whereas the bone defect was filled only with connective tissue when it had been kept open. We concluded, therefore, that this alginate membrane may be a useful barrier membrane when the GTR method is employed.

Alginates↗

PubMed1998

Culture of chondrocytes in alginate gel: variations in conditions of gelation influence the structure of the alginate gel, and the arrangement and morphology of proliferating chondrocytes.

Sodium alginate, which gels in the presence of calcium ions, is commonly used for culture of anchorage-independent cells, such as chondrocytes. Normally, the gel appears microscopically homogeneous but, depending on the conditions of gelation, it may contain a varying number of small channels that extend inward from the surface. We have examined the influence of these channels on the morphology of cultured chondrocytes entrapped in alginate beads. Growth-plate or articular chondrocytes cultured in alginate normally proliferate and form rounded cell clusters but, in alginate beads containing numerous channels, many chondrocytes become aligned and form columns similar to those in the growth plate in vivo. As the pattern of cellular growth and morphology in alginate is profoundly influenced by the presence of channels in the gel, further studies were conducted to determine what specific conditions of gelation affect their formation. The channels are especially numerous when both the alginate and the gelling solutions lack sodium ions or other monovalent cations. The channels are cavities in the gel formed by particulate blocking of the rapid diffusion of calcium ions from the gelling solution into the boundary of the calcium alginate solution, and hence they extend inward from cells at the surface of the alginate gel. An understanding of the conditions under which these channels develop makes it possible either to avoid their formation or, alternatively, to enhance the number of channels in order to encourage proliferating cells to grow in radial columns, rather than in a less organized pattern characteristic of most culture systems.

Alginates↗

PubMed1998

Microcapsules of alginate-chitosan--I. A quantitative study of the interaction between alginate and chitosan.

The binding of chitosan to alginate beads was studied quantitatively by using radioactive labelled fractions of chitosan. The alginate-chitosan capsules were made either by dropping a solution of sodium alginate into a solution containing chitosan or by incubating calcium alginate beads in a solution of chitosan. The first procedure yielded a binding of 0.015 microg chitosan per mm2 of capsule surface, while the latter procedure yielded over 2 microg mm(-2). The maximum obtained weight ratio of chitosan to alginate in a microcapsule after 24 h was 0.40. The binding of chitosan was markedly increased by reducing the number average molecular weight of chitosan below 20000 Da and by increasing the porosity of the alginate gel. The porosity was increased by producing homogeneous gels, and by adding calcium chloride to the chitosan solution during the membrane forming stage. The effect of calcium ions on the porosity of the gel was studied by experiments involving release of blue dextran from calcium alginate beads. The binding of chitosan was also found to increase with decreasing fraction of N-acetylations, FA, on chitosan in the range of FA = 0.3 to FA = 0, and with increasing pH in the range from pH 4 to 6. Capsules with a diameter of 500 microm had a higher weight ratio of chitosan to alginate after 24 h of binding than the capsules with the larger diameter of 1500 microm.

Acetylation↗

PubMed1999

Compressive and shear properties of alginate gel: effects of sodium ions and alginate concentration.

The equilibrium and viscoelastic properties of alginate gel crosslinked with Ca2+ were determined as a function of alginate concentration and duration of exposure to physiologic concentrations of NaCl. Compressive and shear stress relaxation tests and oscillatory shear tests were performed to measure the material properties at two time periods after storage in NaCl compared to no NaCl exposure. The effect of concentration was determined by testing 1-3% alginate gel in a bath of physiological NaCl and CaCl2. After 15 h of exposure to NaCl, the compressive, equilibrium shear, and dynamic shear moduli decreased by 63, 84, and 90% of control values, respectively. The material properties exhibited no further changes after 7 days of exposure to NaCl. The loss angle and amplitude of the relaxation function in the shear also decreased, indicating less viscous behaviors in both dynamic and transient configurations. All moduli, but not the loss angle, significantly increased with increasing alginate concentration. The observed decrease in compressive and shear stiffness for alginate gel after exposure to Na+ was significant and indicated that physiological conditions will soften the gel over a time period of up to 7 days after gelation. The alginate gel retains significant solid-like behaviors, however, as measured by a loss angle of approximately 3 degrees. This study provides the first available data for material properties of alginate gel tested in physiological saline.

Alginates↗