Electrophoretic study of the degradation properties of poly(L-lactide) microcapsules

The degree of degradation of poly(L-lactide) microcapsules was measured as a function of the time elapsed in solutions of different pH values. To determine how the distribution of poly(L-lactide) molecules in the microcapsule membrane changes during degradation, poly(L-lactide) microcapsules, at various stages of the degradation process in various solutions, were sampled and redispersed in pH 7.6 buffer solutions of different ionic strengths and their zeta potentials determined. In the early stages of the process, the zeta potential became more negative as time elapsed. Analysis of the ionic strength dependence of the surface potential on the basis of a simple model shows that hydrolytic scission of ester bonds in the polymer chains takes place preferentially at the microcapsule membrane surface creating negative charges localized at the membrane/solution interface. In the later stages of the degradation process, the zeta potential again became less negative. This suggests that liberation of degraded segments takes place in the later stages.     

Transfer of protons from bulk solution to the surface of poly(L-lactide) microcapsules

Excessive proton transfer from bulk solution to the surface of poly(L-lactide) microcapsules was observed. In acidic solutions of pH less than 3.0, the zeta potential of the microcapsules became slightly positive, although poly(L-lactide) has only carbonyl groups and alcoholic hydroxyl groups which can be charged. In an NMR study, the signal of the water protons shifted towards a higher applied field with increasing interaction of water with the poly(L-lactide) microcapsule surface when the microcapsules were dispersed at low concentrations (up to 4 x 10(-3) per cent). In solutions of pH 3.2-7.6, the observed values of the zeta potential were in good accordance with theoretical values calculated assuming that the charged groups distribute uniformly in the microcapsule wall. In this pH range, the average density of charged groups in the wall was estimated to be 0.04 M. The average volume occupied by one polymer unit (one poly(L-lactide) molecule) in the microcapsule membrane was estimated to be (35 A)3, suggesting a rather tight polymer network in the poly(L-lactide) microcapsule membrane.     

Interaction of poly(L-lysine-alt-terephthalic acid) microcapsules with fibrinogen

Interaction of poly(L-lysine-alt-terephthalic acid) microcapsules with fibrinogen was investigated by measuring the degree of microcapsule disintegration, fibrinogen adsorption to microcapsules, and the zeta potential of microcapsules as a function of fibrinogen concentration in phosphate buffer solutions of pH 7.4 at different ionic strengths. A minimum concentration was found to exist for fibrinogen to cause disintegration of the microcapsules at any ionic strength, and at this fibrinogen concentration the fibrinogen adsorption levelled off and the zeta potential exhibited an abrupt change. Increases in the ionic strength of the medium and the surface hydrophobicity of microcapsules produced an increase in the degree of microcapsule disintegration by fibrinogen. These findings were interpreted as showing that the interaction of the microcapsules with the protein is not of an ionic nature but of a hydrophobic nature.     

Effects of Plasma Proteins on Degradation Properties of Poly(L-lactide) Microcapsules

The degradation rate of poly(L-lactide) microcapsules in an aqueous medium was accelerated by the addition of albumin, -globulins, and fibrinogen. These proteins form adsorption layers on the surface of poly(L-lactide) microcapsules. At the interface between the microcapsules and the adsorbed protein layers, the value of the electric potential is expected to increase in magnitude, i.e., become highly negative compared with that at the interface between the microcapsules and the bulk buffer solution containing no plasma protein. This potential increase causes an increase in H⁺ concentration at that interface, which may result in an acceleration of the hydrolytic degradation rate of poly(L-lactide) microcapsules. Also, the presence of plasma proteins can increase the solubility of poly(L-lactide), causing the poly(L-lactide) molecules to exist in an expanded form. This effect may also accelerate the degradation of poly(L-lactide) microcapsules.     

Potential distribution across a plasma protein-coated poly(L-lactide) microcapsule surface

A model is presented for the potential distribution across a protein-coated microcapsule membrane. The adsorbed protein layer is assumed to be divided into three sub-layers. The outer sub-layer is rich in positive fixed charges and the medium sub-layer in negative fixed charges, while the inner sub-layer may be either charged or uncharged. Also, the microcapsule membrane is negatively charged. The ionic partition coefficients into the inner sub-layer are less than unity, while those into the other sub-layers are unity. This model explains well the accelerated degradation of poly(L-lactide) microcapsules with an adsorbed protein layer onto their surface (Makino et al., 1987 c).     

Effect of self-association on rate of penicillin G degradation in concentrated aqueous solutions.

The apparent rate of degradation of penicillin G potassium micellar solutions of 500,000 units/ml, a concentration commonly encountered in vials reconstituted for storage in the refrigerator, was investigated and compared to that of nonmicellar solutions of 8000 units/ml at 25 degrees, ionic strength of 1.1 M, and pH range from 5.0 to 9.5. In the micellar solutions the apparent rate of the H+-catalyzed degradation was increased twofold but that of water- and OH minus-catalyzed hydrolysis was decreased two- to three-fold. Consequently, the pH-rate profile of the micellar solutions was shifted to higher pH values and the pH of minimum degradation was found to be at 7.0 compared to 6.5 for the nonmicellar solution of the same ionic strength. Compared at their respective pH-rate profile minima, micellar penicillin G is 2.5 times as stable as the nonmicellar solution under the conditions of constant pH and ionic strength.     

盐酸青藤碱水溶液的降解动力学研究

目的:研究盐酸青藤碱水溶液的降解动力学特征。方法:应用比色法确定盐酸青藤碱在不同pH值、不同离子强度、不同介电常数水溶液中经80℃恒温加速试验所得的降解动力学参数。结果:经过线性拟合对比分析,盐酸青藤碱水溶液的降解反应级数为n=1。降解速率常数(k)值随pH值的上升而增高,在pH<3的低pH值区域降解十分缓慢;而进入pH3.9～5的区域趋于稳定,出现一个较低的平台;当pH>5时,k值随pH值的上升而迅速增高。盐酸青藤碱水溶液随离子强度的增加,降解速率增加;溶液的介电常数增加,其降解速率也增加。结论:盐酸青藤碱水溶液的降解属于近似1级动力学过程,降解速率受溶液pH影响显著;降解速率与溶液离子强度成正相关,与溶液介电常数亦成正相关。     

离子凝胶法制备壳聚糖纳米粒的影响因素研究

目的 探讨离子凝胶法制备壳聚糖纳米粒(CS-NPs)的影响因素.方法 用碱降解法制备高脱乙酰度的壳聚糖(CS),并以之为材料,采用离子凝胶法制备CS-NPs,以微粒的平均粒径、分散度和Zeta电位为指标,考察CS及三聚磷酸钠(TPP)的质量浓度、CS/TPP质量比、CS溶液pH值和CS溶液温度对制备CS-NPs的影响....     

An experimental investigation of the stability of ethylcellulose latex: correlation between zeta potential and sedimentation.

This paper aims at explaining the experimental observations of the stability and redispersibility of an aqueous ethylcellulose latex through the electrokinetic characterization of the particles. The surface charge and the electrical double layer thickness play an essential role in the stability of the system, hence the need for a full characterization of the polymeric particles. The effect of both pH and ionic strength of the dispersion medium were investigated. It was found that at acid pH values the latex displays "delayed" or "hindered" sedimentation: in such conditions, the electrophoretic mobility and zeta potential are rather low, indicating a small electrokinetic charge on the particles. At alkaline pH, when the dissociation of ionizable surface groups must be complete, the zeta potential is high and negative. The electrostatic repulsion between polymer particles is responsible for the low sedimentation volume and poor redispersibility of the latex. The effect of NaCl and CaCl(2) concentration on both the zeta potential and stability of the latexes was also investigated: it was found that CaCl(2) has the greatest influence, yielding flocculated, easily re-dispersible systems when its concentration in the dispersion medium is high enough. There qualitative observations were ascertained by means of calculations of the potential energy of interaction between particles. In the case of NaCl solutions, a high and relatively wide potential energy barrier was predicted, that may prevent the particle aggregation. Above 5mM NaCl a shallow minimum in the potential energy curves must lead to the formation of aggregates. Similar results were found with CaCl(2) solutions, although in this case the secondary minima are deeper and appear at lower concentrations.     

Buffer controlled release of indomethacin from ethylcellulose microcapsules

The rate of release of indomethacin from ethylcellulose microcapsules prepared by coacervation was studied using internal buffer, dibasic sodium phosphate (DSP), to increase the solubility of the core. The dissolution rate of the drug was determined in phosphate buffer solutions of varying pH and concentration. The role of the stagnant diffusion layer at the microcapsule surface was also evaluated by changing the mixing in the dissolution test. Indomethacin release was accelerated considerably with increasing amounts of DSP in the core. DSP increases the pH inside the microcapsules, thus enhancing the release of the acidic drug. Increasing bulk solution pH increased the release rate of indomethacin, the enhancing effect being more pronounced with buffered microcapsules. Neither increasing phosphate concentration of the bulk solution nor increasing mixing of the microcapsules influenced the rate of release of indomethacin from unbuffered capsules. With buffered capsules the increase in phosphate concentration of bulk solution prevented leaching out of internal phosphate increasing the release rate of indomethacin. The release of indomethacin also accelerated slightly with increasing mixing.     

Superior cell delivery features of poly(ethylene glycol) incorporated alginate, chitosan, and poly-L-lysine microcapsules

Microencapsulation is an emerging technology in the development of bioartificial organs for drug, protein, and delivery systems. One of the advancements in establishing an appropriate membrane material for live cell and tissue encapsulation is the incorporation of poly(ethylene glycol) (PEG) to the widely studied alginate microcapsules. The current study investigates the properties of integrating PEG to microcapsules coated with poly-L-lysine (PLL) and chitosan as well as a novel microcapsule membrane which combines both PLL and chitosan. Results show that microcapsules containing PEG can support cell viability and protein secretion. The addition of PEG to PLL and chitosan-coated microcapsules improves the stability of microcapsules when exposed to a hypotonic solution. We also compared the novel microcapsule with two other previously used microcapsules including alginate-chitosan-PEG and alginate-PLL-PEG-alginate. Results show that all three membranes are capable of providing immunoprotection to the cells and have the potential for long-term storage at -80 degrees C. The novel membrane containing PEG, chitosan, and PLL, however, revealed the highest cell viability and mechanical strength when exposed to external rotational force, but it was unable to sustain osmotic pressure. The study revealed the potential of using PEG-incorporated alginate, chitosan, and PLL microcapsules for encapsulating live cells producing proteins and hormones for therapy.     

Degradation kinetics of mometasone furoate in aqueous systems

Mometasone furoate (MF) is a synthetic glucocorticoid. There is little information available on the stability of MF and no degradation products have been unequivocally identified. Thus, the primary objective of this study was to characterize the degradation of MF, qualitatively and quantitatively. Stability of MF decreased with increasing pH (>4) and decreasing ionic strength in aqueous media. The chemical stability of MF in aqueous systems was significantly dependent on pH. MF appeared to be stable at pH < 4 but degraded to four products at higher pH. The degradation of MF in aqueous solutions follows pseudo-first-order kinetics and involved a series of parallel and consecutive reactions. The turnover of MF and its products appears to be catalyzed by the hydroxide ion. The pH dependence of these reactions should be considered, when formulating or extemporaneously compounding MF formulations. An optimal pH of stability was below pH 4. The changes in pH, however, do not appear to be the only factor of importance, since an increase in ionic strength and buffer concentration displayed a stabilizing effect on this glucocorticoid in the buffers tested. Trace metal ions are unlikely to be involved in degradation of MF in aqueous solution.     

Encapsulating acetaminophen into poly(L-lactide) microcapsules by solvent-evaporation technique in an O/W emulsion

Microencapsulation of acetaminophen in poly(L-lactide) was studied using the oil-in-water emulsification solvent-evaporation technique. Methylene chloride was used as the dispersed medium and water as the dispersing medium. The thermogravimetric analysis and differential scanning calorimetry data indicated that the acetaminophen was encapsulated and uniformly distributed in the poly(L-lactide) microcapsules. The addition of either gelatin or polyvinyl alcohol as the protective colloid to the emulsion was found to have a significant impact on the resulting microcapsules. Increasing the concentration of either protective colloid in the dispersing medium increased the recovery and the release rate of acetaminophen, but reduced the particle size and loading efficiency of the microcapsules. Scanning electron micrographs manifested that all the microcapsules attained a nearly round shape. While gelatin imparted a smooth topography to the surface of the microcapsules, PVA made the surface of the microcapsules bumpy and humped.     

Electrostatic interaction of microcapsules with guinea-pig polymorphonuclear leucocytes

Electrostatic interaction of microcapsules with guinea-pig polymorphonuclear leucocytes was investigated at different ionic strengths of the medium through measurements of the degree of phagocytosis by the cells of microcapsules. At any ionic strength, the interaction exhibited a maximum when the surface potential of microcapsules was equal to that of the leucocytes to make phagocytosis of microcapsules by the cells minimum. The experimental findings were analyzed by a novel model for the electrostatic interaction between ion-penetrable membranes. In this analysis, it was assumed that the leucocytes have an area (or areas) which permits cations to partition much more into the membrane than anions on their surface to reduce the electric potential of the area.     

Stability of Gonadorelin and Triptorelin in Aqueous Solution

The influence of pH, temperature, various buffer species at different concentrations, and ionic strength on the stability of gonadorelin and triptorelin in aqueous solution has been studied using stability-indicating high-performance liquid chromatographic methods. The degradation behavior of both peptides is similar. The maximum stability of both peptides was shown to be at an approximate pH of 5.0. Acetate has the most favorable effect on stability, while phosphate causes higher degradation. Varying the concentration of acetate buffer does not affect the degradation behavior of the peptides. A higher phosphate concentration in buffer solutions causes higher degradation, however. The ionic strength of buffer solutions has no significant influence on stability. Solutions of gonadorelin and triptorelin, respectively, buffered with acetate (0.1 M, pH 5.0) with 3% (w/v) mannitol as an additive show a predicted t _90% of 9.0 years and 7.7 years at 20°C, respectively.     

Solution stability of ciclosidomine

The stability of N-cyclohexanecarbonyl-3-(4-morpholino)-sydnone imine hydrochloride (ciclosidomine) in solution was studied as a function of pH, temperature, ionic strength, and buffer species. The rate of hydrolysis in the absence of light was found to be apparent first order in drug and general acid- and base-catalyzed reactions. The pH rate profile at an ionic strength of 0.1 M at 60 degrees C had a minimum value near pH 6. Change in ionic strength in the range of 0.05 to 0.2 M did not affect the rate of degradation at pH 7 (carbonate buffer) or pH 2 (phosphate buffer) at 60 degrees C. Similar degradation rates were noticed in air or nitrogen in the dark at pH 3, 5, and 6. However, degradation in light was very rapid in either case at pH 3, 5, and 6, and, therefore, the protection of solutions from light was required during all studies. The time for 10% loss of drug in solution at pH 6 in dilute phosphate or citrate buffer at an ionic strength of 0.154 M was projected to be 9 months at 20 degrees C and 2.6 months at 30 degrees C.     

Triazolines. XXI: Preformulation degradation kinetics and chemical stability of a novel triazoline anticonvulsant.

The effect of pH, temperature, and two buffer species (citric acid-phosphate and bicarbonate-carbonate) on the stability of 1-(4-chlorophenyl)-5-(4-pyridyl)-delta 2-1,2,3-triazoline (ADD17014; 1), a novel triazoline anticonvulsant, was determined by HPLC. One of the main degradation products of 1 at pH 7.0 was isolated by TLC and identified as the aziridine derivative by MS. Investigations were carried out over a range of pH (2.2-10.7) and buffer concentration [ionic strength (mu), 0.25-4.18] at 23 degrees C. The degradation followed buffer-catalyzed, pseudo-first-order kinetics and was accelerated by a decrease in pH and an increase in temperature. The activation energy for the degradation in citric acid-phosphate buffer (pH 7.0 and constant ionic strength mu at 0.54) was 12.5 kcal/mol. General acid catalysis was observed at pH 7.0 in citric acid-phosphate buffer. The salt effect on the degradation obeyed the modified Debye-Hückel equation well; however, the observed charge product (ZAZB) value (2.69) deviated highly from the theoretical value (1.0), perhaps because of the high mu values (0.25-4.18) of the solutions used. The stability data will be useful in preformulation studies in the development of a stable, oral dosage form of 1.     

Understanding and Modulating Opalescence and Viscosity in a Monoclonal Antibody Formulation

Opalescence and high viscosities can pose challenges for high concentration formulation of antibodies. Both phenomena result from protein–protein intermolecular interactions that can be modulated with solution ionic strength. We studied a therapeutic monoclonal antibody (mAb) that exhibits high viscosity in solutions at low ionic strength (～20 cP at 90 mg/mL and 23°C) and significant opalescence at isotonic ionic strength (approximately 100 nephelometric turbidity units at 90 mg/mL and 23°C). The intermolecular interactions responsible for these effects were characterized using membrane osmometry, static light scattering, and zeta potential measurements. The net protein–protein interactions were repulsive at low ionic strength (～4 mM) and attractive at isotonic ionic strengths. The high viscosities are attributed to electroviscous forces at low ionic strength and the significant opalescence at isotonic ionic strength is correlated with attractive antibody interactions. Furthermore, there appears to be a connection to critical phenomena and it is suggested that the extent of opalescence is dependent on the proximity to the critical point. We demonstrate that by balancing the repulsive and attractive forces via intermediate ionic strengths and by increasing the mAb concentration above the apparent critical concentration both opalescence and viscosity can be simultaneously minimized. © 2009 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 99:82–93, 2010     

Application of high-frequency rheology measurements for analyzing protein-protein interactions in high protein concentration solutions using a model monoclonal antibody (IgG2)

The purpose of this work was to explore the utilization of high-frequency rheology analysis for assessing protein-protein interactions in high protein concentration solutions. Rheology analysis of a model monoclonal immunoglobulin G2 solutions was conducted on indigenously developed ultrasonic shear rheometer at frequency of 10 MHz. Solutions at pH 9.0 behaved as most viscous and viscoelastic whereas those at pH 4.0 and 5.4 exhibited lower viscosity and viscoelasticity, respectively. Intrinsic viscosity, hydrophobicity, and conformational analysis could not account for the rheological behavior of IgG2 solutions. Zeta potential and light scattering measurements showed the significance of electroviscous and specific protein-protein interactions in governing rheology of IgG2 solutions. Specific protein-protein interactions resulted in formation of reversible higher order species of monomer. Solution storage modulus (G'), and not loss modulus or complex viscosity, was the more reliable parameter for predicting protein-protein interactions. Predictions about the nature of protein-protein interactions made on the basis of solution G' were found to be consistent with observed effect of pH and ionic strength on zeta potential and scattered intensity of IgG2 solutions. Results demonstrated the potential of high-frequency storage modulus measurements for understanding behavior of proteins in solutions and predicting the nature of protein-protein interactions.     

4种氟喹诺酮液体制剂降解析因试验

模拟4种喹诺酮输液剂及滴眼剂在不同pH和离子强度的条件下,考察了光、pH以及离子强度分别对诺氟沙星(NFX)、氧氟沙星(OFX)、环丙沙星(CPX)、洛美沙星(LEMX)降解程度的影响,应用2³析因试验方法,经F检验确证:NFX,OFX,CPX,LEMX离子强度影响均不显著,光影响均极显著;pH对NFX和LEMX影响不显著,对OFX和CPX影响极显著;OFX和CPX由光及pH二因素交互作用影响极显著,NFX和LEMX由光及pH二因素交互作用影响不显著。