Effect of drying methods on retention of moist sucralfate gel properties

The aim of this work was to find a drying procedure for moist sucralfate gel capable of producing dried sucralfate gel that retains the original gel properties of bioadhesion, rheology, and micromeritics. Spray-drying and microwave-drying procedures were employed. Mannitol was used as a gel-protective substance during the drying processes. The spray drying of moist sucralfate gel gave rise to a powder whose water suspensions showed significantly reduced viscosity. The bioadhesion of spray-dried sucralfate gel was strongly reduced by drying. When mannitol was used as a gel protector, the spray-dried sucralfate in part maintained the original bioadhesion of moist sucralfate gel. The preparation of a dried sucralfate gel retaining the bioadhesion characteristics, avoiding the use of mannitol, was made possible using the microwavedrying procedure. The microwave-dried product possesses a granular morphology suitable for direct compression because it is a free flowing and strongly coherent granular powder.     

Photon transmission study on swelling of kappa-carrageenan gels prepared in various concentrations

κ-Carrageenan gels prepared with various carrageenan concentrations in pure water were completely dried and then swelled in pure water. Photon transmission measurements were performed using a UV-Vis (UVV) spectrometer during the swelling of κ-carrageenan gels. Transmitted photon intensity, I_tr, increased exponentially as swelling time is increased for all gel samples. The behaviour of I_tr was interpreted by Monte-Carlo Simulation. The increase in I_tr was quantified by employing Li-Tanaka equation, from which time constants τ₁ and collective diffusion coefficients, D_o were determined for the gels in various carrageenan concentrations. Gravimetric and volumetric measurements were also carried out during swelling of gels. It is observed that gel with high carrageenan content possess more double helices and more lattice dislocations and swell slower than gels with low carrageenan content which may contain less double helices and less lattice imperfections. Increase in I_tr was interpreted by the homogeneous distribution of double helices in the carrageenan gel system.     

预热处理金针菇蛋白对猪肉肌原纤维蛋白凝胶特性的影响

本文研究预热处理（preheat treatment,PT）金针菇蛋白（Flammulina filiformis protein,FFP）对肌原纤维蛋白（myofibrillar protein,MP）凝胶特性的影响。试验将FFP在65、75、85和95℃下分别预热处理30、60、90和120min,以蛋白溶解度、总巯基含量和表面疏水性为指标,确定FFP预热处理的最佳温度与时间;将预热处理的FFP（PT-FFP）与MP以不同的比例（0:10、1:9、2:8、3:7、4:6,M/M）混合制备复合凝胶（总蛋白质量浓度均为40mg/mL）,以凝胶强度、持水性、流变学特性与微观结构为指标,考察PT-FFP对MP凝胶特性的影响。结果表明,75℃预热处理60min,FFP的溶解度与表面疏水性最高,总巯基含量最低,故确定该预热处理条件为最佳;将该条件下制备的PT-FFP以不同比例与MP混合制备凝胶,结果发现PT-FFP比FFP更有利于复合凝胶的凝胶强度和持水性的提高（P<0.05）,特别是当PT-FFP与MP混合比例为1:9时,复合凝胶的凝胶强度和持水性达到最高值121.38g和85.25%;流变学结果也表明,PT-FFP能够提高复合凝胶的弹性模量Gʹ和损耗模量G″;电镜观察可以看出PT-FFP与MP复合的凝胶具有更强的连续性,结构更为致密。总之,经过75℃预热处理60min后的FFP和MP以1:9混合时能够改善肌原纤维蛋白凝胶特性和流变学特性。     

Fibroblast behavior on gels of type I, III, and IV human placental collagens

Various collagens were extracted and purified from human placenta after partial pepsin digestion. We prepared type III + I (57:43), enriched type I, type III, and type IV collagens on an industrial level, and studied their biological properties with MRC5 fibroblast cells. Using the process of contraction of a hydrated collagen lattice described by Bell, we found tha the contraction rate was dependent on collagen type composition. The contraction was faster and more pronounced with pepsinized type I collagen than with pepsinized type III + I (57:43) collagen; the lowest rate was obtained with the pepsinized type III collagen. Using a new technique of collagen cross-linking, a gel was made with type IV collagen. This cross-linking procedure, based on partial oxidation of sugar residues and hydroxylysine by periodic acid, followed by neutralization, resulted in an increased number of natural cross-link bridges between oxidized and nonoxidized collagen molecules, without internal toxic residues. The fibroblasts were unable to contract type IV/IVox collagen gels. The type IV/IVox collagen gel was transparent and its amorphous ultrastructure lacked any visible striated fibrils. Fibroblast cells exhibited atypical behavior in these type IV/IVox collagen gels as evidenced by optical and electron microscopy. The penetration of fibroblasts could be measured. Fibroblasts penetrated faster in type IV/IVox collagen gels than in untreated type III + I collagen gels. The lowest rate of penetration was obtained with cross-linked type III + I gels. Fibroblast proliferation was similar on untreated or cross-linked type III + I collagen gels and slightly increased on type IV/IVox collagen gels, suggesting that this cross-linking procedure was not toxic.     

Immobilization of a lipoxygenase in silica gels for application in aqueous media

The encapsulation of soybean lipoxygenase-1 (LOX-1) in silica gels and its application in an aqueous medium, were studied. The main silica precursor was tetramethoxysilane (TMOS) but the introduction of hydrophobic SiCH₃ groups brought with methyltrimethoxysilane (MTMS) was evaluated. Other sol–gel synthesis parameters investigated comprised partial or complete drying by evaporation and CO₂ supercritical drying. The influence on LOX-1 activity of the various chemicals with which the enzyme was in contact during encapsulation (acetone, methanol, polyvinyl alcohol), as well as the temperature and pH, were examined. The activity of free and encapsulated LOX-1 was assayed on the oxygenation reaction of linoleic acid by dioxygen from air dissolved in aqueous medium, in a UV–vis spectrophotometer. With free LOX-1, the reaction advancement could be followed in continuous in the spectrophotometer. With the gels, in a first approach, the conversion was simply determined after 15 min reaction after filtration of the liquid, to discriminate between active and inactive gels. For the most interesting gels, the kinetics were then assessed by continuous recording in the UV spectrophotometer, after placing a small piece of gel (≈15 mg) directly in the cell. The best gels had an activity ≈30% of free LOX. The present studies, supplemented by characterization of the gels texture and structure, respectively by nitrogen adsorption and ²⁹Si MAS NMR, showed that drying a gel before use in aqueous media was detrimental to the activity. This effect is due to a contraction of the gel network which occurs when a dry aerogel sample is dipped in water after drying. Hence gels containing LOX-1 enzyme must not be dried but kept in water impregnated state, for optimum use.     

Buffering effect of a prophylactic gel on dental plaque in institutionalised elderly

Objectives: The effect of multiple daily applications of a prophylactic gel, with buffering substances, on plaque acidogenicity in elderly institutionalised individuals was evaluated. Background: Many elderly suffer from reduced salivary flow, poor oral hygiene and increased levels of cariogenic bacteria and are considered to be at an increased risk for coronal and root caries. Reinforcing the buffering capacity of dental plaque by the addition of substances such as bicarbonate and phosphates may decrease their caries activity. Materials and methods: Fourteen elderly, with subjective dry mouth, were treated for 16‐day‐periods at random with: (i) Profylin fluoride gel with buffering components; (ii) Profylin fluoride gel without buffering components and (iii) rinsing with water. Applications were made four times a day and each period was followed by a 2‐week wash‐out period. The plaque pH was registered after a carbohydrate challenge and the following were recorded before and after each test period: stimulated salivary secretion rate, buffer capacity, number Colony Farming Units (CFU) mutans streptococci, lactobacilli and a sample of Candida albicans on oral mucosa. Results: Eleven participants (mean age 76.6 years) fulfilled the study. Changes in plaque pH measurements, when calculated as area under the curve (AUC_6.2 and AUC_5.7) values (pH × min), before and after each of the three treatments, showed no significant differences. A tendency to a higher plaque acidogenicity and amount of cariogenic microorganisms was found after the gel treatments. C. albicans was found in low levels. Conclusion: Frequent applications of the gel did not result in an improved neutralising effect in the elderly. This may be caused by a combination of several factors, such as the level of oral dryness of the individuals and low solubility, release and retention of the gel substances in plaque. Instead, an increased plaque acidogenicity was noted.     

Bio-based hydrogels prepared by cross-linking of microbial poly(gamma-glutamic acid) with various saccharides

Novel bio-based hydrogels were prepared by cross-linking of microbial poly(gamma-glutamic acid) (PGA) with saccharides such as glucose, maltotriose, and cyclodextrin (CD) in the presence of water-soluble carbodiimide in dimethyl sulfoxide (DMSO) by one-pot synthesis at 25 degrees C for 24 h. The degradation of the gels in alkaline solution (pH 9) at 37 degrees C was also investigated. The PGA gels cross-linked with various neutral saccharides were obtained in relatively high recovery yields by use of a base like 4,4-(dimethylamino)pyridine. The PGA gel cross-linked by glucose showed the highest water absorption of 3000 g/g. The PGA gels cross-linked by CDs showed higher water absorption than those cross-linked by the corresponding linear saccharides. It was revealed that the water absorption of the PGA gel was affected by the cross-linker content and also the structure of cross-linkers as they had an effect on the cross-linking density of the PGA gel. The PGA gels were hydrolyzed under alkaline condition (pH 9) at 37 degrees C. The degradation rate was higher when the cross-linker content of the gel was lower.     

A correlation between mechanical and electrical properties of the synthetic hydrogel chosen as an experimental model of cytoskeleton

The correlation between the electrochemical (Donnan) potential and volume swelling was studied for synthetic polyelectrolyte hydrogels considered as models of cytoskeleton gel-forming biopolymers. Hydrogels involving polyacrylic and polymethacrylic acids with varying network density were synthesized by a radical polymerization in aqueous solution. Electrical charge was introduced into the gel network by partial neutralization of monomer acids with several alkali and alkali earth (hydr)oxides. The electrochemical (Donnan) potential of synthetic gels was determined using conventional microelectrode tools for cell potential determination. It was demonstrated that the negative electrical potential of many anionic gels with various charges and network densities decreased with the decrease of equilibrium swelling, i.e., with the decrease in water content in the gel. It was shown that a drastic phase transition in the gel structure from a swollen to a compressed state induced by K⁺/Ca²⁺ exchange is accompanied by an analogous decrease in the absolute Donnan potential of the gels. A kinetic study demonstrated that the gel volume changed ahead of its electrical potential. This suggests that the volume phase transition in gel is the main cause of the electrical response. A similarity between the swelling/compression transition in synthetic gels and the volume changes in the cytoskeleton in the vicinity of the cell membrane was demonstrated. Based on the universal analogy between the properties of synthetic and natural polymer gels, a possible involvement of swelling of the gel-like cytoskeleton structures in electrical regulation in the cell was postulated.     

Stomatal response to drying soil in relation to changes in the xylem sap composition of Helianthus annuus. I. The concentration of cations, anions, amino acids in, and pH of, the xylem sap

Sunflower plants (Helianthus annuus L.) were subjected to soil drying with their shoots either kept fully turgid using a Passioura-type pressure chamber or allowed to decrease in water potential. Whether the shoots were kept turgid or not, leaf conductance decreased below a certain soil water content. During the soil drying, xylem sap samples were taken from individual intact and transpiring plants. Xylem sap concentrations of nitrate and phosphate decreased with soil water content, whereas the concentrations of the other anions (SO₄² and Cl^?) remained unaltered. Calcium concentrations also decreased. Potassium, magnesium, manganese and sodium concentrations stayed constant during soil drying. In contrast, the pH, the buffering capacity at a pH below 5 and the cation/anion ratio increased after soil water content was lowered below a certain threshold. Amino acid concentration of the xylem sap increased with decreasing soil water content. The effect of changes in ion concentrations in the xylem sap on leaf conductance is discussed.     

Cation effects on swelling of kappa-carrageenan: a photon transmission study

Swelling behavior of kappa-carrageenan gels in water and KCl solutions was investigated by photon transmission experiments following the preparation of gels in the presence and absence of externally added K+ ion as a gel promoting agent. Transmitted photon intensity, Itr, increased continuously during swelling depending on the carrageenan and ion content in the gel. This increase in Itr was modeled using the Li-Tanaka equation. Both the experimental work and the model showed that the swelling of low carrageenan and ion content gels took less time than that of high ion content gels. It is confirmed that double helices in a swollen gel move much faster in pure water than in KCl solution during swelling processes. Swelling time constants, tau1, and collective diffusion coefficients, Do, were measured for the gels swollen in water and KCl solutions.     

Influence of agar on in vitro cultures: I. Physicochemical properties of agar and agar gelled media

Summary The success of in vitro culture is related to several factors. Beside factors associated with the plant material or the medium composition, the physicochemical characteristics of gelled media can play an important role. In this paper, the latter aspect has been considered and the nature of agar powders has been investigated. Moreover, the process of gel formation for three different media and the availability of water and minerals for the corresponding gels have been studied. Analysis of agar powders showed that they can contain different amounts of impurities and the dialysis of these powders suggested that the impurities might be available to the tissues. Thermal analysis on the hygroscopic properties of the agar brands suggest the importance of these data to obtain comparable and reproducible gelled media. The study on the process of formation of gelled media indicates that there is a critical temperature T_ss which can be used to control the gel processing. In fact, at this temperature, agar powders in water transform into a sol status through a rapid shift of electrical conductivity. Water potential of the medium, water loss from gels over the culture period, and the ease of releasing liquid from gels under pressure were shown to be different for different agar brands. A different availability of water and minerals in Murashige and Skoog medium was deduced from the gels prepared with three agar brands (Oxoid, Merck, and Roth).     

Methacrylated glycol chitosan as a photopolymerizable biomaterial

Glycol chitosan is a derivative of chitosan that is soluble at neutral pH and possesses potentially useful biological properties. With the goal of obtaining biocompatible hydrogels for use as tissue engineering scaffolds or drug delivery depots, glycol chitosan was converted to a photopolymerizable prepolymer through graft methacrylation using glycidyl methacrylate in aqueous media at pH 9. N-Methacrylation was verified by both (1)H NMR and (13)C NMR. The degree of N-methacrylation, measured via (1)H NMR, was easily varied from 1.5% to approximately 25% by varying the molar ratio of glycidyl methacrylate to glycol chitosan and the reaction time. Using a chondrocyte cell line, the N-methacrylated glycol chitosan was found to be noncytotoxic up to a concentration of 1 mg/mL. The prepolymer was cross-linked in solution using UV light and Irgacure 2959 photoinitiator under various conditions to yield gels of low sol content ( approximately 5%), high equilibrium water content (85-95%), and thicknesses of up to 6 mm. Cross-polarization magic-angle spinning (13)C solid state NMR verified the complete conversion of the double bonds in the gel. Chondrocytes seeded directly onto the gel surface, populated the entirety of the gel and remained viable for up to one week. The hydrogels degraded slowly in vitro in the presence of lysozyme at a rate that increased as the cross-link density of the gels decreased.     

凋落物对土壤酸化的缓冲及其对根系生长的影响

凋落物层是森林生态系统中一个十分活跃的界面,一方面环境因素影响凋落物的积累和分解,另一方面凋落物的动态反过来又影响到系统内的水热收支平衡、土壤的理化特性以至森林生产力。值得注意的是,在高度工业化的现代社会,大气污染作为一种新生的环境因子不同程度地作用于森林生态系统,凋落物层则是大气污染物(如酸雨)作用于森林土壤亚系     

Preparative isoelectric focusing in immobilized pH gradients. II. A case report

The preparative aspects of isoelectric focusing (IEF) in immobilized pH gradients (IPG) have been investigated as a function of the following parameters: environmental ionic strength (I), gel geometry and shape of pH gradient. As model proteins, hemoglobin (Hb) A and a minor, glycosylated component (HbA1c), with a delta pI = 0.04 pH units, have been selected. The load capacity increases almost linearly, as a function of progressively higher I values, from 0.5 X up to 2 X molarity of buffering Immobiline (pK 7.0) to abruptly reach a plateau at 3 X concentration of buffering ion. The load capacity also increases almost linearly as a function of gel thickness from 1 to 5 mm, without apparently levelling off. When decreasing the pH interval from 1 pH unit (pH 6.8-7.8) to 1/2 pH unit (pH 7.05-7.55) the amount of protein loaded in the HbA zone could be increased by 40%. In 5 mm thick gels, at 2 X pK 7.0 Immobiline concentration, over a 1/2 pH unit span, up to 350 mg HbA (in a 12.5 X 11 cm gel) could be loaded in a single zone, the load limit of the system being around 45 mg protein/ml gel volume.     

Water holding capacity and microstructure of gellan gels

This project studied the water holding capacity of gellan gels as affected by gel composition and microstructure. When not subjected to external forces such as centrifugal force, gellan gel properties including water holding capacity and texture properties were stable at room temperatures. The water losses from gellan gels after four months storage at 4°C were only 1–2%, independent of calcium concentrations. The freeze–thaw stability of gellan gels was poor. Water holding capacity of gellan gels, when subjected to centrifugal forces, was dependent on calcium concentrations, and was related to the texture properties. Two discrete pore-size distributions in gel matrix on the order of 0.1 and 1 μ were observed with scanning electronic microscopy. Large pores were formed with thick strings while the small ones were formed by a thin web structure. Defects in the large pore structure were observed at high calcium concentrations. The small pores may be responsible for the water holding capacity during storage, while large pore structures provide the strength of gels.     

Hyaluronate-alginate gel as a novel biomaterial: mechanical properties and formation mechanism

With the aim of producing a biomaterial for surgical applications, the alginate-hyaluronate association has been investigated to combine the gel-forming properties of alginate with the healing properties of hyaluronate. Gels were prepared by diffusion of calcium into alginate-hyaluronate mixtures, with an alginate content of 20 mg/mL. The hyaluronate source was shown to have significant effect on the aspect and the properties of the gels. The gels have viscoelastic behaviour and the transient measurements carried out in creep mode could be interpreted through a Kelvin-Voigt generalised model: experimental data led to the steady state hardness and a characteristic viscosity of the gel. Gels prepared from Na rooster comb hyaluronate with weight ratio up to 0.50 have satisfactory mechanical properties, and fully stable gels are obtained after a few days; on the contrary, use of lower molecular weight hyaluronate led to loose gels for hyaluronate contents over 0.25. Gel formation was investigated by measurements of the exchange fluxes between the calcium chloride solution and the forming gel, which allowed thorough investigations of the occuring diffusion phenomena of water, calcium ion and hyaluronate. Strong interactions of water with hyaluronate reduce significantly the rate of weight loss from the gel beads and allows higher water content in steady-state gels. Calcium content in the gel samples could be correlated to the actual alginate concentration, whatever the nature and the weight ratio of hyaluronate.     

Structure of the IgG-binding ligand of the T-gel

We examine the ligand requirements for the divinylsulphone (DVS) based T-gel to bind immunoglobulins. The original gel consisted of 2-mercaptoethanol coupled to a DVS activated support, with both the thioether and sulphone sulphurs thought necessary for protein binding. No differences in the capacity for human IgG were observed for a highly activated gel coupled with mercaptoethanol, or when the same activated gel was incubated at high pH to hydrolyse the majority of its reactive groups before the remainder were coupled with the thiol, indicating that the thioether S may be replaced with a hydroxyl O. Increasing the time of the DVS-activation results in gels with higher concentrations of immobilised sulphone but lower concentrations of active groups. The IgG capacities of the mercaptoethanol coupled gels were found to increase with the time of the activation reaction, which may be exploited to produce high capacity gels while minimising the concentration of DVS. Reducing the vinyl of the DVS-activated gel with borohydride was found to decrease the amount of protein binding, with residual binding being attributed to the presence of hydrolysed or cross-linked sulphones in the gel. Reacting the activated gels with amines decreased the capacity for IgG still further, suggesting that not only are these ligands unable to bind IgG, they also prevent its interacting with neighbouring sulphones, perhaps due to the small amount of positive charge they carry.     

Effect of physico-chemical properties of polyacrylamide gel media on the growth of Escherichia coli colonies]

We studied the growth of Escherichia coli LE-392 colonies on polyacrylamide gels (PAAG) depending on the physico-chemical properties of the latter, i.e. polymer concentration in the gel, swelling degree, bound water content (fm), spin-lattice relaxation and spin-spin relaxation times of water molecule protons, and modulus of elasticity (G0). S- or R-type colonies formed depending on gel properties; the diametral growth rate of S colonies was 3 times less compared with that on the control agar medium (Tryptose broth). The procedure is proposed for preparation of PAAG which rules out syneresis. Functional relations between the polymer concentrations in uniformly swelling gels and concentrations of copolymers in the reaction mixture, fm and G0 were revealed. The fm and G0 parameters can be used for controlling the quality of PAAG.     

Influence of network structure on the degradation of photo-cross-linked PLA-b-PEG-b-PLA hydrogels

Triblock copolymers of functionalized poly(lactic acid)-b-poly(ethylene glycol)-b-poly(lactic acid) (PLA-b-PEG-b-PLA) have been widely investigated as precursors for fabricating resorbable polymeric drug delivery vehicles and tissue engineering scaffolds. Previous studies show degradation and erosion behavior of PLA-b-PEG-b-PLA hydrogels to rely on macromer chemistry as well as structural characteristics of the cross-linked networks. In this research, the degradation kinetics of diacrylated PLA-b-PEG-b-PLA copolymers as soluble macromers and cross-linked gels are directly compared as a function of macromer concentration, buffer pH, and ionic strength. The pseudo first-order rate constants for degradation of soluble macromers increase with water concentration and show a minimum at intermediate pH values, but are insensitive to ionic strength. The degradation rate constants for covalently cross-linked gels display a greater sensitivity to local water concentration and a minimum at lower pH values than corresponding soluble macromers. In addition, ionic strength significantly affects the rate of gel degradation due to the direct correlation between the degree of network ionization and gel water content.     

施肥和增水对弃耕草地土壤酸中和容量的影响

大气氮沉降增加是草地土壤酸化的主要原因。土壤酸缓冲性能作为评估土壤酸化的重要指标,对氮输入的响应受到降水与其他限制养分含量的影响。本研究以我国北方温带弃耕草地氮、磷、水添加试验13年后的土壤为对象,利用二次多项式模型拟合酸滴定曲线,计算了土壤酸缓冲容量(ABC)以及以pH 5.0和4.0为参比的土壤酸中和容量(ANC)。结果表明: 不增水处理下,单独加氮和同时添加氮磷均显著降低土壤pH,降低以pH 5.0和4.0为参比时的酸中和容量(ANC_pH5.0和ANC_pH4.0);单独加磷对土壤pH、ANC_pH5.0和ANC_pH4.0均无显著影响。增水处理下,加氮及加氮磷显著降低土壤pH、ANC_pH5.0和ANC_pH4.0;加磷显著降低土壤pH,但增加了ANC_pH4.0,而对ANC_pH5.0无显著影响。与不增水处理相比,增水处理对土壤pH、酸中和容量均具有显著的正效应。对于初始pH值不同的土壤,采用土壤酸中和容量比酸缓冲容量能更好地指示土壤抗酸化能力。