海藻酸钠-聚丙烯酰胺固定氧化亚铁硫杆菌技术的研究

以海藻酸钠(SA)、聚丙烯酰胺(HPAM)为复合载体,加入聚乙二醇(PEG)为致孔剂,对氧化亚铁硫杆菌进行固定化研究。实验考察了SA、HPAM、PEG的浓度对SA-HPAM凝胶微球的机械强度及固定化细胞的氧化活性的影响,确定了三种材料的最佳浓度:SA为2.5%,HPAM为0.4%,PEG为2%,此条件下固定化细胞对Fe~(2+)的最大氧化速率可达2.853g·(L·h)~(-1),24h后Fe~(2+)的氧化率在98%以上,固定化细胞目前重复使用了15次,并在3℃冰箱中存放两个月后,依然具有很好的氧化活性,表明SAHPAM固定化的氧化亚铁硫杆菌具有较好的稳定性。     

Mechanistic study on hydration and drug release behavior of sodium alginate compacts

The influence of sodium alginate viscosity on the dynamics of matrix hydration, solvent front movement, swelling, erosion, and drug release from alginate matrix tablets were examined. The solvent front showed preferential penetration from the radial direction even though matrix swelling showed axial predominance. This study proposed alternative views for the anisotropic behavior of hydrating alginate compacts, namely, formation of gel barrier with different permeability characteristics, tension at the gel-core interface and preferential radial erosion, in addition to an in-depth examination on the contribution of stress relaxation of hydrated polymer as well as core expansion. Alginate matrices demonstrated pH-dependent hydration, swelling and erosion behavior, resulting in pH-dependent drug release mechanisms. Dissolution profiles for alginate matrices of different viscosities were similar in acid but differed upon increase of pH. This was due to the influence of alginate viscosity grade on liquid uptake, erosion and pronounced swelling at near neutral pH.     

Evaluation of In Vitro Enzymatic Degradation of Various Thiomers and Cross-Linked Thiomers

ABSTRACT

The aim of this study was to examine the biodegradability of thiomers and cross-linked thiomers in comparison with unmodified polymers. Disulfide-cross-linked conjugates were prepared by air oxidation at room temperature. Thiomers were investigated by viscosity measurements and spectrophotometric assays. The influence of different factors on the hydrolysis rate, such as the degree of modification of thiomers, structure of the conjugates, pH value of the reaction medium, and the impact of the process of cross-linking were evaluated. Due to the modification, thiolated chitosans degraded 12.9–24.7% less than unmodified chitosan in the framework of viscosity measurements. In addition, the hydrolysis degree of thiolated alginates and modified carboxymethylcelluloses was 25.6–32.4% and 18.4–27.0% lower, respectively, in comparison to the corresponding unmodified polymers. Conjugates with higher coupling rate of thiol groups were degraded even more slowly. Moreover, the cross-linking process via disulfide bonds additionally reduced the rate of thiomer degradation. The range of degradation rates achieved in vitro could be modified by alterations of the contents of thiol and disulfide groups, as well as by suitable design of the polymer structure and ligands used.

These results represent helpful basic information for the development of mucoadhesive drug delivery systems, implantable delivery systems and tissue engineering constructs.     

Chitosan-Alginate Multilayer Beads for Gastric Passage and Controlled Intestinal Release of Protein

Abstract

Chitosan-alginate beads loaded with a model protein, bovine serum albumin (BSA) were investigated to explore the temporary protection of protein against acidic and enzymatic degradation during gastric passage. Optimum conditions were established for preparation of homogenous, spherical, and smooth chitosan-alginate beads loaded with BSA. Multilayer beads were prepared by additional treatment with either chitosan or alginate or both. The presence of chitosan in the coagulation bath during bead preparation resulted in increased entrapment of BSA. During incubation in simulated gastric fluid (SGF pH 1.2), the beads showed swelling and started to float but did not show any sign of erosion. Inclusion of pepsin in the gastric fluid did not show a further effect on the properties of the beads. Release studies were done in simulated gastric fluid (SGF pH 1.2) and subsequently in simulated intestinal fluid (SIF pH 7.5) to mimic the physiological gastrointestinal conditions. After transfer to intestinal fluid, the beads were found to erode, burst, and release the protein. Microscopic and macroscopic observations confirmed that the release of protein was brought about by the burst of beads. Chitosan-reinforced calcium-alginate beads showed delay in the release of BSA. The multilayer beads disintegrated very slowly. The enzymes pepsin and pancreatin did not change the characteristics of BSA-loaded chitosan-alginate beads. Single layer chitosan-alginate beads released 80–90% of the model protein within 12 h while multilayer beads released only 40–50% in the same period of time. The release from chitosan-alginate beads and multilayer beads in SIF was further delayed without prior incubation in SGF. It is concluded that alginate beads reinforced with chitosan offer an excellent perspective for controlled gastrointestinal passage of protein drugs.     

Formation and characterization of pDNA-loaded alginate microspheres for oral administration in mice

Alginate, a natural polysaccharide, was explored in this study as an oral delivery vehicle of a mammalian expression vector into the murine intestinal mucosa. Alginate microspheres were produced through water-in-oil (W/O) emulsification method. Average diameter sizes of microspheres were 46.88 μm±3.07 μm with significant size reduction upon utilization of 1.0% Span80. Plasmid DNA (pDNA) carrying green fluorescent protein reporter gene (GFP), pVAX-GFP, was encapsulated within microspheres at efficiencies of 72.9 to 74.4%, carrying maximum load of 6 μg pDNA. Alginate microspheres demonstrated shrinkage in pH 1.2 and swelling in pH 9.0 with pDNA release about twice the amount released in acidic environment. Oral delivery of pVAX-GFP loaded-microspheres, at 50 μg, 100 μg and 150 μg dose, was performed on BALB/c mice. Tissue biodistribution, investigated through flow cytometric analysis, demonstrated GFP positive intestinal cells (<1.0%) with 1.3-fold higher levels for the 100 μg dose; therefore suggesting feasibility of the approach for oral gene delivery and vaccination.     

Uptake of Zn2+ from dilute aqueous solutions using protonated dry alginate beads

The uptake of zinc ions from dilute aqueous solutions was studied at 25°C using protonated dry alginate beads (PDAB) of around 1 mm in diameter. The Zn²⁺ uptake increases with the pH of the Zn bearing solution, reaching a value of around 90 mg of Zn per gram of beads (dry weight) at pH 4·5. For an initial Zn concentration as low as 10 mg L^?1, the removal reached was complete.

The mechanism of Zn uptake was found to be ion exchange between zinc ions and protons form the functional groups of the beads, which followed a pseudo-second order kinetic behaviour. In equilibrium condition the experimental data followed the Langmuir adsorption model.

The maximum uptake reached were around 145 and 165 mg g^?1 at pH values of 3·5 and 4·5, respectively, which is higher than most of the sorbents used for zinc removal. EPMA-EDX analysis shows that the functional groups of the PDAB were homogeneously distributed during preparation of beads, and that zinc ions were able to reach functional groups in the entire structure of the beads without a concentration gradient across the beads.

On a étudié le changement d′ions de le Zinc depuis des solutions aqueuses diluées à 25°C en utilisant des sphères protonadas sèches d′alginatos (PDAB) d′autour de 1 mm de diamètre. Le changement de Zn²⁺ augmente avec le pH de la solution, en atteignant une valeur d′autour de 90 mg de Zn par gramme de sphères (un poids sec) à un pH 4.5. Pour un concetración initial de Zn plus bas que 10 mg L^?1, le changement à court d'argent a été complet. Le mécanisme de changement de Zn est été par un échange ionique entre des ions de zinc et protones provenants depuis les groupes fonctionnels des sphères, qui a un comportement cinétique du pseudo-deuxième ordre. Dans des conditions d′équilibre, les données expérimentales suivent un modèle d′adsorpcin de Langmuir. Le changement maximal à court d′argent a été de 145 et 165 mg g^?1 aux valeurs de pH de 3.5 et 4.5, respectivement, où elles ont été plus hautes que les sorbentes utilisés pour le changement de Zn. Des analyses par EPMA-EDX ont montré que les groupes fonctionnels du PDAB ont été distribués de façon homogène durant la préparation des sphères, et que les ions de zinc ont été capables d′atteindre les groupes fonctionnels dans toute la structure des sphères sans une pente de concentration à travers des sphères.     

Influence of Drying Conditions on Physical Properties of Alginate Films

The effect of drying conditions of the film-forming solution on thickness, moisture content, water vapor permeability, and tensile properties of alginate films were investigated. A long period of constant rate was observed in all conditions and the model proposed by Wang and Singh was able to adjust the drying data. As expected, there was a clear effect of temperature on drying kinetics; that is, increasing the drying temperature decreased the drying time. Considerable glycerol losses were observed when alginate gel was oven dried at temperatures above 40°C. Compared to other drying conditions, films oven dried at 60°C were thinner, had lower moisture content, and were less flexible.     

A computational analysis of the impact of mass transport and shear on three-dimensional stem cell cultures in perfused micro-bioreactors

In this study, Computational Fluid Dynamics(CFD) is used to investigate and compare the impact of bioreactor parameters(such as its geometry, medium flow-rate, scaffold configuration) on the local transport phenomena and, hence, their impact on human mesenchymal stem cell(hM SC) expansion. The geometric characteristics of the TissueFlex174;(Zyoxel Limited, Oxford, UK) microbioreactor were considered to set up a virtual bioreactor containing alginate(in both slab and bead configuration) scaffolds. The bioreactor and scaffolds were seeded with cells that were modelled as glucose consuming entities. The widely used glucose medium, Dulbecco's Modified Eagle Medium(DMEM), supplied at two inlet flow rates of 25 and 100 μl·h~(-1), was modelled as the fluid phase inside the bioreactors. The investigation, based on applying dimensional analysis to this problem, as well as on detailed three-dimensional transient CFD results, revealed that the default bioreactor design and boundary conditions led to internal and external glucose transport, as well as shear stresses, that are conducive to h MSC growth and expansion. Furthermore, results indicated that the ‘top-inout' design(as opposed to its symmetric counterpart) led to higher shear stress for the same media inlet rate(25 μl·h~(-1)), a feature that can be easily exploited to induce shear-dependent differentiation. These findings further confirm the suitability of CFD as a robust design tool.     

超顺磁性海藻酸钠的制备及其结构研究

采用氧化法制备巨藻型及海带型超顺磁性海藻酸钠,通过X-衍射、扫描电镜、古埃磁天平分析;结果表明,氧化法生成的磁性离子体达到纳米级（44．656～66．99nm）,在海藻酸钠中分布比较均匀,巨藻型海藻酸钠制备的磁性海藻酸钠磁化率比海带型海藻酸钠的高1～2倍。     

Controlling lipid digestion by encapsulation of protein-stabilized lipid droplets within alginate–chitosan complex coacervates

The control of lipid digestibility within the human gastrointestinal tract is important for the development of many functional food and pharmaceutical products. This article describes the preparation, characterization, and in vitro digestibility of lipid droplets encapsulated within hydrogel beads. Protein-stabilized lipid droplets were first coated with an alginate layer, and then they were trapped within chitosan/calcium alginate coacervates. The filled hydrogel beads were formed using two methods: “direct method” – add a suspension of alginate-coated lipid droplets to a calcium/chitosan solution; “indirect method” – add chitosan solution to a suspension of alginate-coated lipid droplets and calcium. The in vitro digestibility of the encapsulated lipid droplets was then monitored using a pH-stat method to simulate the small intestine. For both methods, the filled hydrogel beads were relatively stable to aggregation/dissociation from pH 1 to 6, but underwent extensive aggregation and sedimentation at higher pH values. Relatively small hydrogel beads (d < 50 μm) caused a moderate delay in the rate of lipid digestion, while large hydrogel beads (d > 100 μm) could delay the digestion rate appreciably. This study has important implications for designing delivery systems that control lipid digestion by encapsulating lipid droplets within hydrogel beads.