High glycolic poly (DL lactic co glycolic acid) nanoparticles for controlled release of meropenem

Nanospheres of low molecular weight poly lactic co glycolic acid (PLGA) with high glycolic acid content (10:90) and polylactic acid (PLA) are synthesized and loaded with meropenem, a broad spectrum antibiotic. The loading efficiency of the drug is 82 and 70% in PLGA 10:90 and PLA respectively. The rate of drug release is higher with PLGA 10:90 (3.2 μg/s) than with PLA (2.4 μg/s). Eighty and 60% of the encapsulated drug is released from the two polymers in 30 days respectively. Initial burst followed by sustained drug release is observed which is mathematically explained using a biphasic model. The drug release from the former polymer leads to two times lower E. coli growth than the release from the latter. The nanoparticles are biocompatible with no significant effect on the viability of 3T3 cells. This study indicates that PLGA 10:90 can be used for the delivery of antibiotics for interim period, especially for post orthopaedic surgeries.     

Use of poly(ortho esters) for the controlled release of 5-fluorouracyl and a LHRH analogue

The controlled release of 5-fluorouracyl (5FU) and a luteinizing hormone releasing hormone analogue (LHRH) from a crosslinked bioerodible poly (ortho ester) was studied. Unlike our previous results with levonorgestrel which was released by a predominant surface erosion process, the much more water-soluble 5FU and LHRH analogue are released predominantly by diffusion. However, rate of diffusion is strongly influenced by rate of polymer hydrolysis. Because the LHRH analogue has two reactive hydroxyl groups, some are chemically bound to the crosslinked matrix via ortho ester linkages. Analysis of a model polymer matrix indicates that 95% of the LHRH analogue is released in its original form and 5% is released as the propionate ester.     

Antimicrobial efficacy of a new antibiotic-loaded poly(hydroxybutyric-co-hydroxyvaleric acid) controlled release system

OBJECTIVE: Failure of orthopaedic devices, mainly femoral hip replacements, due to infection is of increasing medical importance. There is a need for improved antibiotic delivery systems in the treatment of orthopaedic infections and here we have evaluated polyhydroxyalkanoate formulations for their suitability as a constant delivery system for gentamicin. METHODS: Gentamicin was incorporated in poly(hydroxybutyric-co-hydroxyvalerate) (PHBV) with 8% or 12% hydroxyvalerate (HV) content at 2:1 or 5:1 (weight to weight) ratio. In conjunction with an elution study, a scanning electron microscopy and a porosity study were carried out to explore physical characteristics of the complexes before and after the leaching effect. The antibacterial effectiveness of the complexes was analysed in a bacterial adhesion assay using clinical isolates of Staphylococcus haemolyticus and Staphylococcus aureus. In addition, the polymers were exposed to pooled human blood to test their biocompatibility in both static and dynamic environments. RESULTS: We have shown that increasing the HV content from 8% to 12% leads to a faster release of the integrated antibiotic. An increase in antibiotic content enhanced the homogeneity while decreasing the permeability of the complexes and reducing the release rate. A significant reduction in the number of the adherent S. aureus and gentamicin-resistant S. haemolyticus within a 48 h exposure to our formulations confirmed the effectiveness of the PHBV/gentamicin complexes. Finally, these formulations did not alter the haemodynamics of the pooled blood samples after an extended period of time. CONCLUSION: Taken together, the PHBV/gentamicin formulations may prove to be effective preventive therapeutic modalities in implant-related Staphylococcus infections.     

缓释成骨生长肽聚乳酸-聚羟乙酸共聚物微球的制备及其体外释放实验

背景:既往动物实验证实,局部或全身应用成骨生长肽,能够促进骨折愈合。但存在着半衰期短及口服生物利用率低等缺点,限制了其在临床上的应用。目的:用可吸收性生物材料包裹成骨生长肽于微球中,观察成骨生长肽在体外释放的过程及其结构变化,为控制释放系统选取合适的载体材料。设计:分组观察对比实验。单位:西安交通大学生命科学院实验室。材料:成骨生长肽由西安蓝晶生物科技公司按照Fmoc系统合成。质谱分析其纯化后纯度超过98%,Mr1523650符合理论Mr1523750),其序列分析符合理论序列。聚乳酸-聚羟乙酸共聚物(PLGA)(50∶50,Mr30000;75∶25Mr80000)由山东医疗器械研究所提供。方法:应用两种不同Mr的PLGA,用复乳溶剂挥发法包裹成骨生长肽,制备成骨生长肽PLGA微球。利用扫描电镜观察微球的表面结构及形态。应用激光粒度计数仪测量微球的粒径分布。高效液相色谱法检测成骨生长肽的包裹率、缓释时间及制备过程对多肽的结构稳定性的影响。结果:①成功制备了较均匀的圆形成骨生长肽微球。PLGA50∶50微球的平均粒径为(19.6±4.5)μm,包裹率为(83.9±4.2)%,载药率为(83.9±4.2)%;PLGA75:25微球的平均粒径为(35.8±3.6)μm,包裹率为(65.6±6.8)%,载药率为(65.6±6.8)%。②高效液相色谱法结果显示,成骨生长肽在制备过程没有发生化学结构改变及凝集,与制备前的结构一致。两种微球均有突释现象,但成骨生长肽-PLGA75∶25微球突释较重,成骨生长肽-PLGA50∶50微球能够缓释成骨生长肽56d,且累计缓释效果良好,成骨生长肽-PLGA75∶25缓释70d。成骨生长肽-PLGA50∶50微球35d的成骨生长肽累计缓释率低于成骨生长肽-PLGA75∶25,差异有显著性意义(P<0.05)。结论:与成骨生长肽-PLGA75∶25缓释微球相比,成骨生长肽-PLGA50∶50缓释微球具有较好的控制释放效果,且缓释时间能够满足骨折或骨缺损愈合局部应用需要。     

In vitro and in vivo release of levonorgestrel from poly(ortho esters): II. Crosslinked polymers

The in vitro and in vivo release of levonorgestrel from crosslinked poly(ortho ester) cylindrical devices containing 30 wt.% drug and 7.1 wt.% Mg(OH)₂ was studied. For reasons not entirely understood, hydrolysis rates of crosslinked poly(ortho ester) are faster than hydrolysis of linear polymers. The in vitro release rate of levonorgestrel was about 10 μg/day for 160 days at which point the experiment was discontinued. The in vivo levonorgestrel release rate in rabbits from identical devices was about 20 μg/day. In the in vitro studies polymer erosion leads drug release but in vivo release of levonorgestrel is fast enough so that concomitant polymer erosion and drug release take place. SEM examination of devices explanted from rabbits are consistent with a surface erosion process.     

New segmented copolymers containing poly(epsilon-caprolactone) and etheramide segments for the controlled release of bioactive compounds.

Segmented poly(ether-ester-amide)s (PEEAs) derived from poly(epsilon-caprolactone) oligomers, sebacoyl chloride, hydrophilic diamide-diamines based on short sequences of ethylenoxy groups and containing amino acids, were used to produce matrix systems intended for the delivery of metronidazole in the periodontal pocket. PEEAs are soluble in chloroform and insoluble in water and show M(n) values in the range 8.5-18.6 kDa. The melting temperatures (53-59 degrees C) are close to that of poly(epsilon-caprolactone) (PCL) with a similar M(n). The water absorption of PEEAs is improved if compared with that of pure PCL and depends on both the length of oxyethylene sequences and the amino acid number, as well as on copolymer composition. Loaded-films containing 20% (w/w) of metronidazole were prepared by compression-molding. The release rate was diffusive in the first stage, whereas also other mechanisms, probably polymer degradation, contributed to the slower second phase. The rate of medium penetration within the film depended on PEEA hydrophilicity and crystallinity and was the main determinant governing the drug release rate. The opportunity to control effectively drug release rates by modulating the composition, and in turn the properties, of PEEAs is an attracting feature for their use in a number of drug delivery systems.     

Development of a new dissolution test method for an oral controlled release preparation, the PVA swelling controlled release system (SCRS).

In vitro dissolution tests of novel controlled release tablets, the poly(vinyl alcohol) (PVA) swelling controlled release system (SCRS), were performed by various methods under different conditions in the sinking state in water. The in vitro release profiles of various tests were almost the same and faster than the in vivo absorption profiles calculated from the plasma drug concentrations of humans. A novel dissolution test method was developed considering the gastrointestinal tract (GI) conditions. PVA particles were used as the filler in a flow-through cell. PVA particles swelled with water were put in the flow-through cell and the tablet was buried in PVA. The test medium was dropped from the top of the cell, and the dissolution medium that dripped from the bottom of the cell was collected and assayed. The in vitro dissolution profile determined by this method was similar to the in vivo absorption profile against other in vitro methods in the sinking state in water. Furthermore, a good correlation between in vitro and in vivo for the two different release rate preparations was obtained using a flow pattern imitating the GI transition.     

A controlled release system for proteins based on poly(ether ester) block-copolymers: polymer network characterization.

The properties of a series of multiblock copolymers, based on hydrophilic poly(ethylene glycol) (PEG) and hydrophobic poly(butylene terephthalate) (PBT) blocks were investigated with respect to their application as a matrix for controlled release of proteins. The degree of swelling, Q, of the copolymers increased with increasing PEG content and with increasing molecular weight of the PEG segment. Within the composition range tested, Q varied from 1.26 for polymers with PEG segments of 600 g/mol and a PBT content of 60 weight.% up to 3.64 for polymers with PEG segments of 4000 g/mol and a PEG/PBT weight ratio of 80:20. Equilibrium stress (compression)-strain measurements were performed in order to estimate mesh sizes. The mesh size of the copolymers ranged from 38 to 93 A, which was experimentally confirmed by diffusion of vitamin B(12) (hydrodynamic diameter d(h)=16.6 A), lysozyme (d(h)=41 A) and bovine serum albumin (d(h)=72 A). The in vitro degradation of PEG/PBT copolymers with a PEG block length of 1000 g/mol and PEG/PBT weight ratios of 70:30, 60:40 and 40:60 was studied. Matrices with increasing PEG contents exhibited a faster weight loss in phosphate-buffered saline (pH 7.4) at 37 degrees C. Over a degradation period of 54 days, M(n) decreased by about 35-45%, while the composition of the matrices, determined by NMR, remained almost constant.     

Low-density poly( -lactide-co-glycolide) foams for prolonged release of isoniazid

Incorporation of the antitubercular drug isoniazid, INH, into low density poly( -lactide-co-glycolide), PLGA, foams of high interstitial void volume prior to high pressure extrusion is shown to prolong the in vitro release of INH. In vitro studies indicate that the duration of INH release can be significantly increased, the early burst dramatically reduced, and variation in replicate samples reduced. Control of the specific gravity and interstitial void volume of the foam is achieved by lyophilization of frozen polymer solutions of specified concentration. The morphology of foams prepared by lyophilization of glacial acetic acid solutions of the polymers produces leaflet or platelet structures. Matrices were prepared by (1) extruding INH impregnated foams previously compacted and ground to 125–180 microns, (2) directly extruding impregnated foams without prior compaction and grinding, and (3) extruding mechanically mixed micronized INH and ground PLGA which had not been prepared as foam. INH release kinetics, analyzed in terms of the Roseman-Higuchi model, confirms that release is diffusion controlled. Diffusion constants for the three methods are 1.2( ±0.1) × 10⁻⁴, 2.1(±0.3) × 10⁻⁴, and 3.2(± 1.6) × 10⁻⁴ cm²/day.     

硫酸软骨素酶ABC-聚乳酸-聚乙醇酸共聚物缓释微球的制备及其体外性质

背景:硫酸软骨素酶ABC能够分解脊髓损伤局部持续产生的硫酸软骨素蛋白多糖,从而促进轴突的生长,但该酶性质不稳定,需要多次局部用药.目的:制备硫酸软骨素酶ABC-聚乳酸-聚乙醇酸共聚物缓释微球,观察其体外释药特性.设计、时间及地点:重复测量设计,于2006-03/2007-01在中国科学院成都有机所和四川大学华西医学中心药理实验室完成.材料:聚乳酸-聚乙醇酸共聚物、硫酸软骨素酶ABC、CH2Cl2、硫酸软骨素B.方法:复乳法制备硫酸软骨素酶ABC缓释微球,并以生理盐水为体外释药介质.主要观察指标:扫描电镜下观察硫酸软骨素酶ABC缓释微球的形态.应用Malvern激光粒度分布测试仪测定其粒径分布并自动计算微球的平均粒径和径距.采用酶解分光光度测定硫酸软骨素酶ABC含量,并计算载药量与包封率.于0.5,1,1.5,2,3,4,6,8,10,12,14,16,18,21 d取样,绘制体外释药曲线.结果:硫酸软骨素酶ABC缓释微球形态均匀.其平均粒径5.538 ì m,径距1.479,呈正态分布.平均载药量(15.554±0.90)×10 3%,甲均包封率(53.88±1,45)%,硫酸软骨素酶ABC微球在3周内的体外累积释药分数为O.851 4,释药平稳,其最佳体外释药拟合方程为Weibull方程:Inln(1/1-Y)=0.739 61nX-1.617,R2=0.993 3.结论:所制备的硫酸软骨素酶ABC微球形态均匀.粒径分布窄,再分散性好,3周内能维持有效的药物浓度.     

Amphiphilic poly(caprolactone-b-N-hydroxyethyl acrylamide) micelles for controlled drug delivery

To increase the bioavailability and water solubility of hydrophobic medicine, an amphiphilic block copolymer, polycaprolactone-block-polyhydroxyethyl acrylamide (PCL-b-PHEAA), was synthesized. The copolymer can self-assemble into micelles by dialysis. The micelles were characterized by the Tyndall effect, static drop method, fluorescence spectrometry, dynamic light scattering, scanning electron microscopy and transmission electron microscopy. Ibuprofen was encapsulated inside the micelles by dialysis as a model medicine. The results show that the amphiphilic copolymer forms a uniform micelle system, with spherical micelles dispersed well in solution which have a low critical micelle concentration. In addition, the system shows good amphipathic behavior. Average particle size of a micelle is 104 nm, which increases a lot after drug loading and standing for half a month. In the first few hours, the cumulative release of the drug increases gradually; the rate of increase in the first ten hours is faster, then reaching a plateau which tends to be flat finally. It is similar under two different pH conditions. This biocompatible, biodegradable amphiphilic block copolymer has potential applications in the biomedical field.

To increase the bioavailability and water solubility of hydrophobic medicine, an amphiphilic block copolymer, polycaprolactone-block-polyhydroxyethyl acrylamide (PCL-b-PHEAA), was synthesized.     

Incorporation and controlled release of a hydrophilic antibiotic using poly(lactide-co-glycolide)-based electrospun nanofibrous scaffolds.

The successful incorporation and sustained release of a hydrophilic antibiotic drug (Mefoxin, cefoxitin sodium) from electrospun poly(lactide-co-glycolide) (PLGA)-based nanofibrous scaffolds without the loss of structure and bioactivity was demonstrated. The morphology and density of the electrospun scaffold was found to be dependent on the drug concentration, which could be attributed to the effect of ionic salt on the electrospinning process. The drug release behavior from the electrospun scaffolds and its antimicrobial effects on Staphylococcus aureus cultures were also investigated. In all tested scaffolds, the maximum dosage of drug was released after 1 h of incubation in water at 37 degrees C. The usage of the amphiphilic block copolymer (PEG-b-PLA) reduced the cumulative amount of the released drug at earlier time points and prolonged the drug release rate at longer times (up to a 1-week period). The antibiotic drug released from these electrospun scaffolds was effective in their ability to inhibit Staphylococcus aureus growth (>90%). The combination of mechanical barriers based on non-woven nanofibrous biodegradable scaffolds and their capability for local delivery of antibiotics increases their desired utility in biomedical applications, particularly in the prevention of post-surgical adhesions and infections.     

Ultrasonically controlled release of ciprofloxacin from self-assembled coatings on poly(2-hydroxyethyl methacrylate) hydrogels for Pseudomonas aeruginosa biofilm prevention

Indwelling prostheses and subcutaneous delivery devices are now routinely and indispensably employed in medical practice. However, these same devices often provide a highly suitable surface for bacterial adhesion and colonization, resulting in the formation of complex, differentiated, and structured communities known as biofilms. The University of Washington Engineered Biomaterials group has developed a novel drug delivery polymer matrix consisting of a poly(2-hydroxyethyl methacrylate) hydrogel coated with ordered methylene chains that form an ultrasound-responsive coating. This system was able to retain the drug ciprofloxacin inside the polymer in the absence of ultrasound but showed significant drug release when low-intensity ultrasound was applied. To assess the potential of this controlled drug delivery system for the targeting of infectious biofilms, we monitored the accumulation of Pseudomonas aeruginosa biofilms grown on hydrogels with and without ciprofloxacin and with and without exposure to ultrasound (a 43-kHz ultrasonic bath for 20 min daily) in an in vitro flow cell study. Biofilm accumulation from confocal images was quantified and statistically compared by using COMSTAT biofilm analysis software. Biofilm accumulation on ciprofloxacin-loaded hydrogels with ultrasound-induced drug delivery was significantly reduced compared to the accumulation of biofilms grown in control experiments. The results of these studies may ultimately facilitate the future development of medical devices sensitive to external ultrasonic impulses and capable of treating or preventing biofilm growth via "on-demand" drug release.     

Bioadhesive poly(methyl methacrylate) microdevices for controlled drug delivery.

Oral delivery is the preferred route of drug administration. However, the breakdown of molecules and low levels of absorption in the gastrointestinal system render the oral delivery of proteins and peptides ineffective. Bioadhesive delivery devices can be used to circumvent these problems by protecting the drug from gastrointestinal denaturation, localizing and prolonging a drug at a specific target site, and maintaining direct contact with the intestinal cells, thereby increasing the drug concentration gradient. Microfabrication technology may offer some potential advantages over conventional delivery technologies. The benefits of microfabrication include the ability to tailor the size, shape, reservoir volume, and surface characteristics of the drug delivery vehicle. In this study, bioadhesive properties were introduced to microfabricated poly(methyl methacrylate) (PMMA) microdevices by attachment of lectins, a group of proteins capable of specifically targeting cells in the gastrointestinal tract. In this process, the PMMA microdevices were chemically modified by aminolysis to yield amine-terminated surfaces. Avidin molecules were covalently bound to the surface of the particles using a hydroxysuccinimide catalyzed carbodiimide reagent and then incubated in an aqueous solution of biotinylated lectin. The lectin-modified microdevices were examined in vitro in terms of their bioadhesive characteristics.     

Methods for improving drug release from poly(methyl)methacrylate bone cement

Poly(methylmethacrylate) (PMMA) is a widely used material with both dental and orthopaedic applications. The acrylic cement is produced by the combination of polymethylacrylate beads with methylmethacrylate monomer. After polymerisation, a heterogeneous and porous matrix is formed which can be used to deliver therapeutic agents. In this work, the release of antibiotic, growth hormone and serum albumin is demonstrated. The mechanism is similar for all agents; a rapid release followed by a slow continuous release. The quantity of drug released depends upon the formulation of both the PMMA and the drug. The polymer-to-monomer ratio can greatly affect the ratio of drug release; increased polymer-to-monomer ratio leads to increased release of antibiotic. Optimum release is achieved if a crystalline formulation of the drug is used rather than a fine powder. Experimental methods to improve the drug release performance of bone cements are presented.     

Polyacetal and poly(ortho ester)-poly(ethylene glycol) graft copolymer thermogels: preparation, hydrolysis and FITC-BSA release studies.

Graft copolymers comprised of a polyacetal backbone with pendant poly(ethylene glycol) side-chains were prepared using a condensation reaction between a divinyl ethers, a diol and Fmoc-protected serinol, followed by deprotecting the amine and reacting the polyacetal with pendant amino groups with PEG-alpha-methoxy-omega-succimidylcarbonate. A series of materials having lower critical solution temperature (LCST) between 25 and 60 degrees C has been prepared. Since LCST is determined by the hydrophilic-hydrophobic balance, and this in turn is determined by the molecular weight of the polyacetal backbone, the molecular weight of the grafted PEG and the amount grafted, materials having a desired LCST could be readily prepared. Incorporating FITC-BSA at 1 wt.% into the thermogel resulted in sustained release over about 100 days at pH 7.4 and 40 days at pH 5.5 without a burst and by reasonably linear kinetics. Incorporating FITC-BSA at 5 wt.% into the thermogel significantly increased delivery time at pH 5.5 and decreased the difference in delivery rates between pH 5.5 and pH 7.4. FITC-BSA is released by a predominantly erosion-controlled process and FITC-BSA depletion coincides closely with total gel dissolution. More rapidly eroding thermogels were prepared by replacing the polyacetal backbone with a poly(ortho ester) backbone. Such gels completely dissolved between 3 and 6 days. It is hoped that intermediate erosion rates can be achieved by preparing backbones containing both acetal and ortho ester linkages. Such materials have been prepared and shown to have LCST values in the desired range, but no erosion, or drug release studies have as yet been completed.     

Drug release characteristics of multi-reservoir type microspheres with poly(dl-lactide-co-glycolide) and poly(dl-lactide).

For the multi-reservoir type microspheres composed of poly(dl-lactide-co-glycolide) (PLGA) and poly(dl-lactide) (PLA), the influence of the drug-holding layer and the non-drug-holding layer on drug release profiles was studied. The microspheres with the blend of PLGA and PLA were prepared by the W/O type emulsion-solvent evaporation technique, and cisplatin was used as a model drug. The degree of water uptake and the erosion of each polymer were evaluated to clarify the mechanism of drug release for multi-reservoir type microspheres. The blending of PLA and PLGA provided two types of microspheres in terms of the drug distribution in a microsphere, depending on the ratio of the blend: the microspheres with the drug-holding layer covered by the non-drug layer and the microspheres with the drug on the outer region. The drug release in the early period was governed by the pattern of drug distribution. The drug release rate at a steady state was governed by the erosion of the drug-holding layer. The results of present study indicate that drug release from multi-reservoir type microspheres involves the following process: (a) rapid release of the drug near the surface of microspheres, (b) formation of micropores in the non-drug-holding layer by hydration and erosion, (c) degradation of the drug-holding layer, and (d) diffusion of the drug through micropores.     

Microspheres based on inulin for the controlled release of serine protease inhibitors: preparation, characterization and in vitro release.

The pharmacological activity of serine protease inhibitors, potential drugs for the treatment of thrombosis, is often linked to the presence of amidine functions. With the aim of developing a suitable formulation for these compounds, inulin and inulin acetate associated or not with 1,12-dodecanedicarboxylic acid, were chosen to prepare microspheres. Using a coacervation method, these biocompatible polymers led to microspheres of about 0.5-5 microm. The encapsulation of a water-soluble model drug (E,E)-bis(amidinobenzylidene)cycloheptanone [(E,E)-BABCH] in these microspheres was studied. In this investigation, factorial designs were used to determine the joint influence of several variables (drug mass, speed and time of formulation stirring, centrifugation time) for an optimum encapsulation efficiency. Results revealed that encapsulation efficiency reached 65% whatever the nature of the biopolymer, by using a stirring time of 30 min, a high stirring speed and a centrifugation time of 15 min. (E,E)-BABCH release from microspheres was examined in an in vitro model. The profiles were characterized by three phases strongly dependent on the microspheres and the diacid association displayed a crucial role. With inulin and inulin acetate, the initial phase was a rapid 'drug burst'. Within the first 5 min, 58-62% of the drug were delivered. Microspheres of inulin acetate associated with 1,12-dodecanedicarboxylic acid, showed a slower release with only 32% of the drug delivered after 15 min. After a slow diffusion phase (33 h), an increasing rate until complete drug release was observed for 2.5 days.