Preparation and properties of monodispersed rifampicin-loaded poly(lactide-co-glycolide) microspheres

Monodispersed rifampicin (RFP)-loaded poly(lactide-co-glycolide) (PLGA) microspheres were prepared by a solvent evaporation method. In order to control the sizes of the microspheres, a membrane emulsification technique using Shirasu porous glass (SPG) membranes was applied. RFP/PLGA microspheres with the average diameters of 1.3, 2.2, 5.2, and 9.0 microm were obtained. They were relatively monodisperse and the values of the coefficient of variation (CV) for the size distributions of the microspheres were in the range between 7.0 and 16.0%. The loading efficiency of RFP was in the range between 50.3 and 67.4% independent of the microsphere size. The release ratio of RFP from RFP/PLGA microspheres was measured in pH 7.4 PBS at 37 degrees C. From RFP/PLGA microspheres with average diameters of 1.3 and 2.2 microm, almost 60% of RFP loaded in the microspheres was released in the initial day and the release was terminated almost within 10 days. On the other hand, from those with average diameters of 5.2, and 9.0 microm, the release of RFP was observed even 20 days after the release started.     

Efficient intracellular delivery of rifampicin to alveolar macrophages using rifampicin-loaded PLGA microspheres: effects of molecular weight and composition of PLGA on release of rifampicin

Monodispersed PLGA microspheres containing rifampicin (RFP) have been prepared by solvent evaporation method using a Shirasu porous glass (SPG) membrane. The microspheres were spherical and their average diameter was about 2 microm. The loading efficiency of rifampicin was dependent on the molecular weight of PLGA. The higher loading efficiency was obtained by the usage of PLGA with the lower molecular weight, which may be caused by the interaction of the amino groups of rifampicin with the terminal carboxyl groups of PLGA. PLGA with the monomer compositions of 50/50 and 75/25, of lactic acid/glycolic acid, were used in this study. From rifampicin-loaded PLGA microspheres formulated using PLGA with the molecular weight of 20,000, rifampicin was released with almost constant rate for 20 days after the lag phase was observed for the initial 7 days at pH 7.4. On the other hand, from rifampicin-loaded PLGA microspheres formulated using PLGA with the molecular weight of 5000 or 10,000, almost 90% of rifampicin-loaded in the microspheres was released in the initial 10 days. Highly effective delivery of rifampicin to alveolar macrophages was observed by the usage of rifampicin-loaded PLGA microspheres. Almost 19 times higher concentration of rifampicin was found to be incorporated in alveolar macrophages when rifampicin-loaded PLGA microspheres were added to the cell culture medium than when rifampicin solution was added.     

Effect of polyethylene glycol on preparation of rifampicin-loaded PLGA microspheres with membrane emulsification technique

Monodisperse poly(lactide-co-glycolide) (PLGA) microspheres containing rifampicin (RFP), anti-tubercle drug, as hydrophobic model drug were prepared by solvent evaporation method with a membrane emulsification technique using Shirasu Porous Glass (SPG) membranes. Five kinds of rifampicin-loaded PLGA (RFP/PLGA) microspheres with different sizes were prepared by changing pore size of the membranes. Effect of polyethylene glycol (PEG) added to polyvinyl alcohol (PVA) solution (continuous phase) upon the monodispersity of microspheres was studied. PEG was used as a stabilizer for microspheres dispersing in PVA solution. The most suitable molecular weight of PEG as a stabilizer was 20,000. RFP/PLGA microspheres prepared with PEG20000 were apparently more uniform than those prepared without PEG. The yield of RFP/PLGA microspheres was 100%. The initial burst observed in the release of RFP from RFP/PLGA microspheres was suppressed by the addition of PEG.     

A spheres-in-sphere structure for improving protein-loading poly (lactide-co-glycolide) microspheres

In present study, protein loaded poly (lactide-co-glycolide)/chitosan microspheres (PLGA/CS MSs) with spheres-in-sphere structure were prepared in order to weaken the burst release of protein from PLGA microspheres (PLGA MSs) and to buffer acidic micro-milieu. The PLGA MSs and PLGA/CS MSs were characterized in terms of their size distribution, morphology, drug-loading rate, zeta potential and physical-chemical properties. The incubation experiments of PLGA MSs and PLGA/CS MSs were manipulated in PBS solution at pH 7.4, 37 °C to monitor the release of BSA and the vehicles degradation. The release kinetic of BSA was illuminated mainly based on the degradation processes of the matrices. External CS crusts were proved to strikingly improve the release kinetic of the model protein by reducing initial burst release and extending continuous release while acting as a diffusion barrier. Moreover, using PLGA/CS MSs could avoid the decrease of pH value resulted from the acidic products of PLGA MSs because of the effective buffer action of the basic groups in CS. The results demonstrated that the spheres-in-sphere structure is an effective way to control the initial burst release of protein and to overcome the acidic problem of protein-loading PLGA MSs.     

Factors affecting the loading efficiency of water-soluble drugs in PLGA microspheres

Poly(lactide-co-glycolide), PLGA, microspheres containing blue dextran as a hydrophilic model drug were prepared by a solvent evaporation method from w/o/w emulsions using a micro homogenizer. Effects of surfactant concentration in oil phase, stirring time period and stirring rate in the preparation procedure of primary emulsion (w/o) upon drug-loading efficiency were evaluated. Stirring rate during preparation of primary emulsion and surfactant concentration in oil phase affected drug-loading efficiency and the particle size of primary emulsion. Microspheres having the higher drug-loading efficiency were obtained when size differences between the primary emulsions and the secondary ones were large. That is, when the diameter of the primary emulsion is much smaller than that of the secondary emulsion, PLGA microspheres with high-loading efficiency of blue dextran were obtained.     

Long-term controlled release of dual drugs from MBG/PLGA composite microspheres

In this study, a long-term controlled drug release system was designed based on mesoporous bioactive glass coated with poly(lactide-co-glycolide) (MBG/PLGA). In this system ibuprofen (Ibu) and egg white protein were used as the model drugs. Firstly, Ibu was loaded into MBG and MBG/PLGA microspheres were formed after MBG/PLGA. Then the egg white protein was adsorbed outside of the MBG/PLGA because of the interaction between the hydroxyapatite and the protein. The drug release tests indicate that Ibu and egg white protein can release from the long-term controlled dual drugs system at the same time. Notably, the release time of Ibu can reach 18 days, and the release time of egg white protein can reach to 6 days due to the role of PLGA. The release rate of Ibu is 49 % of loading rate (46 %), while the release rate of egg white protein is 47 % of adsorption value (184 μg/mg), indicating that the dual drug release system is highly potential in the practical bone repair application.     

A dual microsphere based on PLGA and chitosan for delivering the oligopeptide derived from BMP-2

In this paper, we document the process and findings of preparing dual poly (lactide-co-glycolide)/chitosan microspheres (PLGA/CS MSs) for osteoinductive oligopeptide derived from BMP-2 (abbreviated as Peptide-24). Through adjusting the amount of Peptide-24, three kinds of PLGA/CS MSs were successfully constructed in twice encapsulations. We studied the morphology, size distribution and loading efficiency of the PLGA/CS MSs. We also focused on the pH change of the environment and the molecular weight of the matrix during the degradation process of PLGA/CS MSs. More specifically, the release of Peptide-24 from three kinds of PLGA/CS MSs was monitored in PBS at 37 °C and pH 7.4. The structural stability of the released Peptide-24 was detected by Far-UV circular dichroism and MALDI-TOF-MS analysis. The mean sizes of the three kinds of PLGA/CS MSs are 47.5, 63.0 and 89.1 μm; and their drug-loading rates are 2.61, 3.21 and 2.21%, respectively. Comparing with Chitosan microspheres (abbreviated as CS MSs), the PLGA/CS MSs have excellent release curves with zero-order kinetics and controllable model. The incubation solution of PLGA/CS MSs avoided producing acid environment as poly (lactide-co-glycolide) microspheres (PLGA MSs) did, which was explained by analyzing the molecular weight of the matrix. The released oligopeptide kept its original structure and relative molecular weight throughout the procedures of encapsulation, storage and release. This indicates its structure stability. Thus, we conclude that dual PLGA/CS MSs is a promising vehicle that is suitable for the delivery of bioactive factors.     

Adsorption of a cationic dye molecule on polystyrene microspheres in colloids: effect of surface charge and composition probed by second harmonic generation

Nonlinear optical probe, second harmonic generation (SHG), of the adsorption of the dye molecule malachite green (MG), in cationic form at pH < or = 5, on polystyrene microspheres in aqueous solution is used to study the effect of surface charge and composition on molecular adsorption. Three types of polystyrene microspheres with different surface composition are investigated: (1) a sulfate terminated, anionic surface, (2) a neutral surface without any functional group termination, and (3) an amine terminated, cationic surface. The cationic dye was found to adsorb at all three surfaces, regardless of surface charge. The adsorption free energies, DeltaG's, measured for the three surfaces are -12.67, -12.39, and -10.46 kcal/mol, respectively, with the trend as expected from the charge interactions. The adsorption density on the anionic surface, where attractive charge-charge interaction dominates, is determined by the surface negative charge density. The adsorption densities on the neutral and cationic surfaces are on the other hand higher, perhaps as a result of a balance between minimizing repulsive charge interaction and maximizing attractive molecule-substrate and intermolecular interactions. The relative strength of the SH intensity per molecule, in combination of a model calculation, reveals that the C(2) axis of the MG molecule is nearly perpendicular to the surface on the anionic surface and tilts away from the surface norm when the surface is neutral and further away when cationic. Changing the pH of the solution may alter the surface charge and subsequently affect the adsorption configuration and SH intensity.     

生物降解聚酯包埋利福平缓释微球的制备及释放行为

以生物可降解乙交酯和丙交酯的无规共聚物(PLGA)为载体,将抗结核病药利福平溶解于PLGA的有机溶液中,采用通常乳化-溶剂挥发方法制备了药物缓释微球.研究了影响微球制备的工艺条件.用电子显微镜观察了微球及降解后的表面形态,测定了微球粒径及载药量,评价了载药微球的体外释放行为.结果表明,以质量分数为1%的明胶为稳定剂,制备的微球形态完整,粒径范围为10～30μm,微球中利福平的平均质量分数为24.3%.体外释药时间可以通过高分子的降解速率来调控,本实验的释药时间可以在42～84d之间调控,药物缓释达到了理想的零级动力学释放.因此,利福平PLGA微球具有显著的长效、恒量药物缓释作用.     

Enhanced gentamicin loading and release of PLGA and PLHMGA microspheres by varying the formulation parameters

The purpose of this study was to develop a suitable formulation for gentamicin sulfate (GS) that gives a sustained release of the drug. Therefore this drug was loaded into poly(D,L-lactide-co-glycolide) (PLGA) and poly(lactic-co-hydroxymethyl glycolic acid) (PLHMGA) microspheres. The effects of various formulation parameters (ethanol, surfactant, osmotic value of the external phase, polymer type and concentration) on particle characteristics (size, loading and release) were investigated. The GS loaded microspheres were prepared using a double emulsion evaporation technique. The results demonstrate that neither ethanol nor surfactants had beneficial effects on the drug loading efficiency (around 4-10%). However, an increase in buffer concentration (and thus osmotic pressure) of the external phase resulted in a substantial increase of GS-loading (from 10 to 28%). Further, an increase of concentration of PLGA in DCM from 10% to 15/20% caused a 4-time increase of the drug loading. The best formulation identified in this study had a loading efficiency of around 70% resulting in PLGA microspheres with a 6% (w/w) loading. The particles showed a burst release of the drug depending on their porosity, followed by a phase of 35 days where hardly any release occurred. The drug was then slowly released for around 25 days likely due to degradation of the microspheres. The drug loading efficiency of GS in PLHMGA was not significantly different from PLGA microspheres (64%). The release of GS from PLHMGA microspheres was faster than that of PLGA because the degradation rate of PLHMGA is more rapid than PLGA. This study shows that prolonged release of gentamicin can be obtained by loading this drug into microspheres made of biodegradable aliphatic polyesters.     

Interactions between nonpolar surfaces coated with the nonionic surfactant hexaoxyethylene dodecyl ether C12E6 and the origin of surface charges at the air/water interface

The interactions between nonpolar surfaces coated with the nonionic surfactant hexaoxyethylene dodecyl ether C12E6 were investigated using two techniques and three different types of surfaces. As nonpolar surfaces, the air/water interface, silanated negatively charged glass, and thiolated uncharged gold surfaces were chosen. The interactions between the air/water interfaces were measured with a thin film pressure balance in terms of disjoining pressure as a function of film thickness. The interactions between the solid/liquid interfaces were determined using a bimorph surface force apparatus. The influence of the nature of the surface on the interaction forces was investigated at surfactant concentrations below and above the cmc. The adsorption of the nonionic surfactant on the uncharged thiolated surface does not, as expected, lead to any buildup of a surface charge. On the other hand, adsorption of C12E6 on the charged silanated glass and the charged air/water interface results in a lowering of the surface charge density. The reduction of the surface charge density on the silanated glass surfaces is rationalized by changes in the dielectric permittivity around the charged silanol groups. The reason for the surface charge observed at the air/water interface as well as its decrease with increasing surfactant concentration is discussed and a new mechanism for generation of OH- ions at this particular interface is proposed.     

Preparation,characterization and in vitro anticoagulation of emodin-eluting controlled biodegradable stent coatings

In this study, emodin-eluting poly(lactide-co-glycolide) (PLGA) coating stents and emodin-loaded PLGA films were prepared to explore the potential application of emodin-eluting stent for treating cardiovascular disease. Fourier transform infrared spectra (FTIR) showed all characteristic adsorption peaks of emodin in emodin-loaded PLGA film in comparison to pure emodin. The balloon expansion experiment and surface morphology observation suggested that the integrated emodin-eluting coatings were successfully obtained on the stainless steel surfaces and the coatings had the ability to withstand the strains imparted during balloon experiment. The drug release profile revealed the nearly linear release curve without obvious burst release for different doses of emodin-eluting stents. As compared with stainless steel and PLGA, in vitro platelet adhesion and APTT (activated partial thromboplastin time) tests revealed better blood compatibility of emodin-eluting stent. In conclusion, the results of the present study showed that the emodin-eluting stent has a potential application for treating cardiovascular disease.     

The effect of adsorbed carboxymethyl cellulose on the cotton fibre adsorption capacity for surfactant

The research reported in this paper demonstrates that the capacity of cotton fibres to adsorb cationic surfactants as well as the rate of the adsorption process can be increased by adsorbing carboxymethyl cellulose (CMC) onto the fibre surfaces; in addition, the adsorption can be restricted to the fibre surface. CMC was deposited by means of adsorption from an aqueous solution. The adsorption of N-cetylpyridinium chloride (CPC) from an aqueous solution onto the CMC-modified fibres was measured using UV-spectrometric determination of the surfactant concentration in the solution. Adsorption onto the cotton fibres was studied in a weakly basic environment (pH 8.5) where cotton fibres are negatively charged and the CPC ion is positively charged. Modification of the fibres by adsorption of CMC introduces new carboxyl groups onto the fibre surfaces, thereby increasing the adsorption capacity of the fibres for CPC. The initial rate of adsorption of CPC increased proportionally with the amount of charge; however, this rate slowed down at high degrees of coverage on fibres with a high charge. The adsorption of cationic surfactant to the anionic surface groups was stoichiometric, with no indication of multilayer or admicelle formation. It was evident that the acidic group content of the fibres was the primary factor determining cationic surfactant adsorption to these fibres.     

Novel PLGA Microspheres for Sustained Delivery of Antisense Oligonucleotide

Novel poly(lactide-co-glycolide acid)(PLGA) microspheres were developed for sustained delivery of antisense oligonucleotide(ASO). First, a new cationic agent, polyethylenimine(PEI) conjugated to linoleic acid(LA)(PEI-LA) was synthesized by reacting PEI(M_w=800) with linoleoyl chloride. Then, PEI-LA was combined with LOR-2501 to form electrostatic complexes at moderate nitrogen-to-phosphate(N/P) molar ratios which were then encapsulated into poly(lactide-co-glycolide) microspheres by a multiple emulsion-solvent evaporation technique. With an increase in ASO/PEI-LA concentration from 5% to 10%, encapsulation efficiency of ASO in the microspheres reduced from 72.14% to 57.62%, and the particle size of microspheres increased from 28.58 μm to 34.76 μm. In vitro studies show that the release profile of ASO from microspheres prepared at 7.5% ASO-PEI-LA lasted for 14 d. The novel microspheres have a potential use as a sustained release vehicle for ASO.     

以PHBV-PLGA为载体的硫酸庆大霉素缓释微球

以生物可降解聚羟基丁酸酯和羟基戊酸酯的共聚物(PHBV)、乙交酯和丙交酯的无规共聚物(PLGA)两种高分子作为壁材,采用复乳溶剂挥发法,制备了包裹硫酸庆大霉素(GS)的载药微球。在扫描电镜下观察到所得微球表面呈多孔状,为球形或椭圆形,粒径在20~80μm。分析结果表明,包封率在60%以上,在体外16~20 d内药物全部释放,90 d微球体外降解50%左右。     

Electrochemical surface plasmon resonance investigation of dodecyl sulfate adsorption to electroactive self-assembled monolayers via ion-pairing interactions

The redox-induced assembly of amphiphilic molecules and macromolecules at electrode surfaces is a potentially attractive means of electrochemically modulating the organization of materials and nanostructures on solid substrates via ion-pairing interactions or charge-transfer complexation. In this regard, we have investigated the potential-induced adsorption and aggregation of dodecyl sulfate, a common anionic surfactant, at a ferrocenylundecanethiolate (FcC11SAu) self-assembled monolayer (SAM)/aqueous solution interface by electrochemical surface plasmon resonance (ESPR) spectroscopy. The surfactant anions adsorb onto the electroactive SAM by specific ion-pairing interactions with the oxidized ferricinium species. The ferricinium charge density (QFc+) obtained by cyclic voltammetry and surface coverage measured by SPR indicate that the dodecyl sulfate forms an interdigitated monolayer, where half of the surfactant molecules have their sulfate headgroups paired to the surface and half have their headgroups exposed to the aqueous solution. The surface coverage of dodecyl sulfate was found to depend on both the ferricinium surface concentration and the surfactant aggregation state in solution. A maximum coverage of dodecyl sulfate on the ferricinium surface is obtained below the critical micelle concentration (cmc), in contrast to dodecyl sulfate adsorption to SAM surfaces of static positive charge. This marked difference in adsorption behavior is attributed to the dynamic generation of ferricinium by potential cycling and the specific nature of the ion-pairing interactions versus pure electrostatic ones. The results presented point to a new way of organizing molecules via electrical stimulus.     

Biodegradable PLGA microspheres as a sustained release system for a new luteinizing hormone-releasing hormone (LHRH) antagonist

A sustained release poly(DL-lactide-co-glycolide) (PLGA) microsphere delivery system to treat prostate cancer for a luteinizing hormone-releasing hormone (LHRH) antagonists, LXT-101 was prepared and evaluated in the paper. LXT-101 microspheres were prepared from PLGA by three methods: (1) double-emulsion solvent extraction/evaporation technique, (2) single-emulsion solvent extraction/evaporation technique, and (3) S/O/O (solid-in-oil-in-oil) method. The microspheres were investigated on drug loading, particle size, surface morphology and in vitro release profiles. An accelerated release approach was also established in order to expedite the evaluation periods. The in vivo evaluation of the microspheres was made by monitoring testosterone levels after subcutaneous administration to rats. The LXT-101 PLGA microspheres showed smooth and round surfaces according to a scanning electron microscopic investigation, and average particle size of ca. 30 mum according to laser diffractometry. The drug encapsulation efficiency of microspheres was influenced by LA/GA ratio of PLGA, salt concentrations, solvent mixture and preparation methods. Moreover, LA/GA ratio of PLGA, different preparation methods and different peptide stabilizers affected in vitro release of drugs. In vivo study, the testosterone levels were suppressed to castration up to 42 d as for the 7.5 mg/kg dose. And in vivo performance of LXT-101 microspheres was dose-dependent. The weights of rat sexual organs decreased and histopathological appearance of testes had little changes after 4-month microspheres therapy. This also testified that LXT-101 sustained release microspheres could exert the efficacy to suppress the testosterone level to castration with little toxicity. In conclusion, the PLGA microspheres could be a well sustained release system for LXT-101.     

表面等离子体子共振技术实时研究蛋白质在修饰表面的静电吸附行为

研究蛋白质在固相表面的静电吸附特性,进而控制蛋白质在修饰表面的静电吸附尤为重要,表面等离子体子共振可以检测金属表面吸附物质厚度和折射率的变化^[1]。这种技术已在研究生物分子相互作用^[2]和考察自组装单层的形成^[3]及蛋白质在固体表面吸附行为^[9-11]等方面得到广泛的应用。对蛋白质在固体表面吸附行为的研究多为考察不同的蛋白质在不同的修饰表面的吸附行为。然而,对蛋白质在修饰表面静电吸附的本质影响因素的研究却少有报道^[4]。本文使用表面等离子体子共振技术实时研究了蛋白质在甲羧基化葡聚糖修饰表面的静电吸附与溶液pH值及离子强度的依赖关系。     

作为细胞微载体的明胶基缓释微球的制备

用改良的乳化冷凝法制备载牛血清蛋白(BSA)的大粒径明胶微球. 结果表明, 明胶水溶液的质量分数为25%、水相与油相体积比3∶20、搅拌速度300 r/min、交联剂用0.1 mL质量分数为25%的戊二醛、 表面活性剂用0.1 g span-80为制备平均直径约250 μm明胶微球的理想条件. 所制备微球的后处理方法不同, 则明胶微球的表面形貌也不同, 细胞粘附率不同. 空白明胶微球在体外可以完全降解, 载BSA的明胶微球对BSA具有良好的缓释性, 释放时间可长达30 d. 显微镜观察成纤维细胞在明胶微载体上生长良好.     

The effect of formulation variables on the characteristics of insulin-loaded poly(lactic-co-glycolic acid) microspheres prepared by a single phase oil in oil solvent evaporation method

Biodegradable polymeric microspheres are ideal vehicles for controlled delivery applications of drugs, peptides and proteins. Amongst them, poly(lactic-co-glycolic acid) (PLGA) has generated enormous interest due to their favorable properties and also has been approved by FDA for drug delivery. Insulin-loaded PLGA microparticles were prepared by our developed single phase oil in oil (o/o) emulsion solvent evaporation technique. Insulin, a model protein, was successfully loaded into microparticles by changing experimental variables such as polymer molecular weight, polymer concentration, surfactant concentration and stirring speed in order to optimize process variables on drug encapsulation efficiency, release rates, size and size distribution. A 2⁴ full factorial design was employed to evaluate systematically the combined effect of variables on responses. Scanning electron microscope (SEM) confirmed spherical shapes, smooth surface morphology and microsphere structure without aggregation. FTIR and DSC results showed drug–polymer interaction. The encapsulation efficiency of insulin was mainly influenced by surfactant concentration. Moreover, polymer concentration and polymer molecular weight affected burst release of drug and size characteristics of microspheres, respectively. It was concluded that using PLGA with higher molecular weight, high surfactant and polymer concentrations led to a more appropriate encapsulation efficiency of insulin with low burst effect and desirable release pattern.