Evaluation of BSA protein release from hollow hydroxyapatite microspheres into PEG hydrogel

Implants that simultaneously function as an osteoconductive matrix and as a device for local drug or growth factor delivery could provide an attractive system for bone regeneration. In our previous work, we prepared hollow hydroxyapatite (abbreviated HA) microspheres with a high surface area and mesoporous shell wall and studied the release of a model protein, bovine serum albumin (BSA), from the microspheres into phosphate-buffered saline (PBS). The present work is an extension of our previous work to study the release of BSA from similar HA microspheres into a biocompatible hydrogel, poly(ethylene glycol) (PEG). BSA-loaded HA microspheres were placed in a PEG solution which was rapidly gelled using ultraviolet radiation. The BSA release rate into the PEG hydrogel, measured using a spectrophotometric method, was slower than into PBS, and it was dependent on the initial BSA loading and on the microstructure of the microsphere shell wall. A total of 35–40% of the BSA initially loaded into the microspheres was released into PEG over ~ 14 days. The results indicate that these hollow HA microspheres have promising potential as an osteoconductive device for local drug or growth factor delivery in bone regeneration and in the treatment of bone diseases.     

Hollow hydroxyapatite microspheres as a device for controlled delivery of proteins

Hollow hydroxyapatite (HA) microspheres were prepared by reacting solid microspheres of Li₂O–CaO–B₂O₃ glass (106–150 μm) in K₂HPO₄ solution, and evaluated as a controlled delivery device for a model protein, bovine serum albumin (BSA). Reaction of the glass microspheres for 2 days in 0.02 M K₂HPO₄ solution (pH = 9) at 37°C resulted in the formation of biocompatible HA microspheres with a hollow core diameter equal to 0.6 the external diameter, high surface area (~100 m²/g), and a mesoporous shell wall (pore size ≈13 nm). After loading with a solution of BSA in phosphate-buffered saline (PBS) (5 mg BSA/ml), the release kinetics of BSA from the HA microspheres into a PBS medium were measured using a micro bicinchoninic acid (BCA) protein assay. Release of BSA initially increased linearly with time, but almost ceased after 24–48 h. Modification of the BSA release kinetics was achieved by modifying the microstructure of the as-prepared HA microspheres using a controlled heat treatment (1–24 h at 600–900°C). Sustained release of BSA was achieved over 7–14 days from HA microspheres heated for 5 h at 600°C. The amount of BSA released at a given time was dependent on the concentration of BSA initially loaded into the HA microspheres. These hollow HA microspheres could provide a novel inorganic device for controlled local delivery of proteins and drugs.     

Preparation Methods of Biodegradable Microspheres on Bovine Serum Albumin Loading Efficiency and Release Profiles

The solvent evaporation and multiple phase methods for preparing poly-(d, l) lactide microspheres of bovine serum albumin (BSA) were compared. The effects of poly (vinyl alcohol) concentration and external aqueous phase temperature on the loading efficient of BSA microspheres prepared by multiple phase emulsion method were evaluated as well. The BSA loading efficient of microspheres by multiple phase emulsion method was much higher than that by solvent evaporation method. The high aqueous solubility of BSA contributes to the low loading efficieny in the solvent evaporation method, suggesting that this method is inappropriate for proteins with high water solubility. The loading efficieny of microspheres, whcih were prepared by multiple phase emulsion method, increased with PVA concentration but decreased with external aqueous phase temperature. The burst phenomenon of release profiles of microspheres was influenced by poly (vinyl alcohol) concentrations and the external aqueous phase temperature. Considering the duration sustained release, 0.5% w/v of poly (vinyl alcohol) is most appropriate among the concentrations tested for preparing BSA microspheres by multiple phase emulsion method.     

Preparation Methods of Biodegradable Microspheres on Bovine Serum Albumin Loading Efficiency and Release Profiles

The solvent evaporation and multiple phase methods for preparing poly-(d, l) lactide microspheres of bovine serum albumin (BSA) were compared. The effects of poly (vinyl alcohol) concentration and external aqueous phase temperature on the loading efficient of BSA microspheres prepared by multiple phase emulsion method were evaluated as well. The BSA loading efficient of microspheres by multiple phase emulsion method was much higher than that by solvent evaporation method. The high aqueous solubility of BSA contributes to the low loading efficieny in the solvent evaporation method, suggesting that this method is inappropriate for proteins with high water solubility. The loading efficieny of microspheres, whcih were prepared by multiple phase emulsion method, increased with PVA concentration but decreased with external aqueous phase temperature. The burst phenomenon of release profiles of microspheres was influenced by poly (vinyl alcohol) concentrations and the external aqueous phase temperature. Considering the duration sustained release, 0.5% w/v of poly (vinyl alcohol) is most appropriate among the concentrations tested for preparing BSA microspheres by multiple phase emulsion method.     

Controlled dual release of hydrophobic and hydrophilic drugs from electrospun poly(l-lactic acid) fiber mats loaded with chitosan microspheres

This work is to develop novel electrospun poly(l-lactic acid) (PLLA) fiber mats for controllable delivery of hydrophobic and hydrophilic drugs. For this aim, bovine serum albumin (BSA, used as a hydrophilic model drug) was firstly enveloped into chitosan microspheres by spray drying. Benzoin (used as a hydrophobic model drug) was directly dissolved in PLLA solution and then the chitosan microspheres were suspended into the PLLA solution, which was used to prepare PLLA fiber mats by electrospinning. Polyvinylpyrrolidone (PVP) was added into the PLLA solution to tune the drug release behaviors. The results showed that the chitosan microspheres were uniformly distributed in the fibers. BSA had a short-term release while benzoin had a long-term and sustained release in all the dual drug delivery systems, and the release of both hydrophobic and hydrophilic drugs could be adjusted by changing the ratio of PVP/PLLA.     

Controlled release of BSA by microsphere-incorporated PLGA scaffolds under cyclic loading

Localized delivery of bioactive molecules from porous biodegradable scaffolds is very important in advanced tissue engineering strategies, and it is necessary to study the delivery under dynamic loading which mimics the in vivo biomechanical environments. In this study, bovine serum albumin (BSA), a model of bioactive proteins, was incorporated into porous poly(l-lactide-co-glycolide) (PLGA) scaffolds by seeding BSA-loaded microspheres onto the scaffold pore wall, where the microspheres of poly(ethylene glycol)-b-poly(l-lactide) (PELA) were prepared by double emulsion technique. The in vitro release behavior of BSA from the scaffold under dynamic cyclic loading was studied in comparison with that under a static condition as well as from PELA microspheres. It was observed that the microsphere-incorporated scaffold prolonged BSA release with respect to the microspheres. The cyclic loading accelerated the release of BSA from the scaffold and the cumulative release on day 10 reached 85% of the totally encapsulated BSA. The delivery under a dynamic condition would be an initial study of in vivo localized delivery of growth factors.     

A pH-sensitive nanocomposite microsphere based on chitosan and montmorillonite with in vitro reduction of the burst release effect

Objective: The aim of this study was to prepare pH-sensitive ofloxacin (OFL)/montmorillonite (MMT)/chitosan (CTS) nanocomposite microspheres that improve the burst release effect of the drug by the solution intercalation technique and emulsification cross-linking techniques. Methods: First, OFL/MMT hybrids were prepared through the solution intercalation technique. Then, OFL/MMT-intercalated OFL/MMT/CTS nanocomposite microspheres were obtained through emulsification cross-linking technology. The intercalated nanocomposite was confirmed by Fourier-transform infrared spectroscopy and X-ray diffraction. Finally, in vitro release of OFL from the microspheres was performed in simulated gastric fluids and simulated intestinal fluids. The effect of MMT content on drug encapsulation efficiency and the drug release of the nanocomposite microspheres were investigated. Results: The results showed that the release rate of OFL from the nanocomposite microspheres at pH 7.4 was higher than that at pH 1.2. Compared with pure CTS microspheres, the incorporation of certain amount of MMT in the nanocomposite microspheres can enhance the drug encapsulation efficiency and reduce the burst release. Conclusion: A sustained release particulate system can be obtained by incorporating MMT into the nanocomposite microspheres and can improve the burst release effect of the drug.     

Colorectal cancer targeted Irinotecan-Assam Bora rice starch based microspheres: a mechanistic,pharmacokinetic and biochemical investigation

The purpose of this investigation was to evaluate the colon-targeted Irinotecan Hydrochloride (ITC-HCl) loaded microspheres by pharmacokinetic and biochemical studies. The microspheres were prepared by double emulsion solvent evaporation method with natural polymer Assam Bora rice starch. The microspheres were characterized for their micromeritics properties, incorporation efficiency, in vitro and in vivo drug release studies. The release study confirmed the insignificant release of ITC-HCl in physiological condition of stomach and small intestine and major drug release in the caecal content. In vivo release study of the optimized microsphere was compared with immediate release (IR) ITC-HCl. ITC-HCl was distributed predominantly in the upper GI tract from the IR, whereas ITC-HCl was distributed primarily to the lower part of GI tract from the microspheres formulation. Enhanced levels of liver enzymes were found in animals given IR ITC-HCl as well as augmented levels of serum albumin, creatinine, leucocytopenia and thrombocytopenia was also observed. In summary, Assam Bora rice starch microspheres exhibit slow and extended release of ITC-HCl over longer periods of time with reduced systemic side-effects.     

BSA-PLGA微球的优化制备及特性

目的:优化BSA-PLGA微球制备工艺,并对其包封率、形态、体外释放药物及微球包裹前后BSA的稳定性进行评价。方法:以PLGA为载体,采用复乳溶剂挥发法制备BSA-PLGA微球。Micro BCA法测定微球的包封率和载药量,扫描电子显微镜观察微球的形态,激光粒度仪测定粒度及分布,聚丙烯酰胺凝胶电泳(SDS-PAGE)研究微球包裹前后BSA分子结构的完整性,同时考察体外释药性能。结果:根据优化工艺制备的微球外观圆整,平均粒径(2275.8±256.9)nm,包封率(82.59±2.92)%,载药量(13.76±0.49)×10-2%,包裹前后BSA结构稳定,体外释放28天以上,释放曲线符合Higuchi方程。结论:本研究获得了较优化的BSA-PLGA微球制备工艺,所制备的微球具有较高的包封率和明显的缓释效果。     

Dynamics of controlled release of heparin from swellable crosslinked starch microspheres

The microspheres of crosslinked starch have been prepared and characterized by IR spectral analysis and SEM technique. The prepared microspheres were loaded with an anticoagulant drug ‘heparin’ and the kinetics of in-vitro release of heparin was investigated spectrophotometrically at physiological pH (7.4) and body temperature (37 °C). The influence of percent loading of heparin, chemical architecture of the microspheres and pH of the release medium were examined on the release profiles of the drug. The chemical stability of heparin was tested in phosphate buffer saline (pH 7.4) and the release was also studied in various simulated biological fluids.     

Alginate microsphere-collagen composite hydrogel for ocular drug delivery and implantation

A composite collagen hydrogel containing protein encapsulated alginate microspheres was developed for ocular applications. Bovine serum albumin (BSA) served as a drug model. The composite hydrogel retained optical clarity and mechanical robustness of control hydrogels without microspheres. A sustained release of BSA was achieved during an 11-day period in neutral phosphate buffer. The composite hydrogel supported human corneal epithelial cell growth and had adequate mechanical strength and excellent optical clarity for possible use as therapeutic lens for drug delivery and/or use as corneal substitute for transplantation into patients who have corneal diseases.     

Development of Hollow Microspheres as Floating Controlled-Release Systems for Cardiovascular Drugs: Preparation and Release Characteristics

Hollow microspheres of cellulose acetate loaded with four cardiovascular drugs (nifedipine [NFD], nicardapine hydrochloride [NCD], verapamil hydrochloride [VRP], and dipyridamole [DIP]) were prepared by a novel solvent diffusion-evaporation method. The oil-in-water emulsion prepared in an aqueous solution of 0.05% poly(vinyl alcohol) medium with ethyl acetate, a water-soluble and less toxic solvent, was used as the dispersing solvent. The yield of the microspheres was up to 80%. The microspheres had smooth surfaces, with free-flowing and good-packing properties. Scanning electron microscopy (SEM) confirmed their hollow structures, with sizes in the range 489–350 μm. The microspheres tended to float over the gastric media for more than 12 h. The drug loaded in hollow microspheres was in an amorphous state, as confirmed by differential scanning microscopy (DSC). The release of the drugs was controlled for more than 8 h. The release kinetics followed different transport mechanisms depending on the nature of the drug molecules.     

Development of hollow microspheres as floating controlled-release systems for cardiovascular drugs: preparation and release characteristics

Hollow microspheres of cellulose acetate loaded with four cardiovascular drugs (nifedipine [NFD], nicardapine hydrochloride [NCD], verapamil hydrochloride [VRP], and dipyridamole [DIP]) were prepared by a novel solvent diffusion-evaporation method. The oil-in-water emulsion prepared in an aqueous solution of 0.05% poly(vinyl alcohol) medium with ethyl acetate, a water-soluble and less toxic solvent, was used as the dispersing solvent. The yield of the microspheres was up to 80%. The microspheres had smooth surfaces, with free-flowing and good-packing properties. Scanning electron microscopy (SEM) confirmed their hollow structures, with sizes in the range 489-350 μm. The microspheres tended to float over the gastric media for more than 12 h. The drug loaded in hollow microspheres was in an amorphous state, as confirmed by differential scanning microscopy (DSC). The release of the drugs was controlled for more than 8 h. The release kinetics followed different transport mechanisms depending on the nature of the drug molecules.     

聚氨酯/淀粉复合微球的制备及药物释放性能研究

采用预聚-扩链-中和-分散法合成聚氨酯(PU)水溶液,将PU与淀粉(ST)溶液按照不同质量比进行复合,采用凝聚相分离法制备PU/ST复合微球;用傅立叶变换红外光谱(FTIR)、扫描电子显微镜(SEM)对微球进行表征,并以盐酸四环素为模型药物制备载药复合微球,初步研究了载药PU/ST复合微球的药物释放性能.结果表明,微球...     

Evaluation of PLGA microspheres as delivery system for antitumor agent-camptothecin

Camptothecin (CPT) and its analogues are a new class of anticancer agents that have been identified over the past several years. Camptothecin exists in two forms depending on the pH: An active lactone form at pH below 5 and an inactive carboxylate form at basic or physiological neutral pH. Poly(lactide-co-glycolide) (PLGA) microspheres have been considered good delivery vehicles for CPT because of acidic microenvironment formed through PLGA degradation. The objective of this study is to investigate antitumor activity of CPT after it is encapsulated in PLGA microspheres. In this study, PLGA microspheres containing various CPT loadings were prepared and characterized. Cytotoxicity of these microspheres to B16 melanoma cells was then evaluated, and uptake of microspheres by B16 cells was also studied. Analysis of drug stability revealed that CPT is released from the microspheres in its active lactone form over the entire release duration. It was also found that there was no interaction between CPT and PLGA matrix within microspheres through Differential Scanning Calorimetry (DSC) and Fourien Transform Infrared Spectroscopy (FT-IR) and hign performance liquid chromatography (HPLC) studies. Cytotoxicity assay showed that CPT encapsulated in PLGA microspheres still retained its antitumor potency. Uptake study revealed quick uptake of the microspheres by B16 cells, which was desirable. It was concluded that PLGA microspheres were suitable delivery vehicles to stabilize and deliver CPT for the treatment of cancer.     

中空羟基磷灰石微球作为rhBMP-2缓释载体的研究

利用锂钙硼玻璃在磷酸盐溶液中的原位转化反应制备表面多孔且中空的羟基磷灰石(HA)微球, 将重组人骨形态发生蛋白2(rhBMP-2)装载到微球中, 研究了微球中rhBMP-2的体外缓释行为, 并采用体外细胞培养技术, 将载有rhBMP-2的微球和大鼠骨髓间充质干细胞(MSCs)一起培养, 测定细胞的碱性磷酸酶(ALP)活性, 并与单纯rhBMP-2的作用进行比较. 结果显示, 微球中所装载的rhBMP-2具有明显的缓释效应, 体外释放周期达到1000h以上, 该微球缓释系统具有一定的生物活性, 其作用效果优于单纯使用rhBMP-2.     

Preparation and Characterization of Coacervate Microcapsules for the Delivery of Antimicrobial Oyster Peptides

Oyster peptides-loaded alginate/chitosan/starch microcapsules were prepared using external gelation method and internal emulsion gelation method. The solution of oyster peptides complexes was encapsulated into the microcapsules, which endowed the microcapsules with intestine passive targeting properties. The swelling behavior, encapsulation efficiency, and release behavior of oyster peptides from the microcapsules at different pH values were investigated. The microcapsules exhibited sustained release of the peptides in intestinal medium, and the release rate could be regulated by the pH value: in simulated gastric fluid, the release rate was greatly decreased, and in simulated body fluid and intestinal fluid, the microcapsules exhibited a sustained release in 24 h with different release rates. The microspheres were characterized by Fourier transform infrared. The results suggested that the alginate/chitosan/starch microcapsules could be a suitable copolymeric carrier system for intestinal protein or peptides delivery in the intestine.     

Preparation and characterization of coacervate microcapsules for the delivery of antimicrobial oyster peptides

Oyster peptides-loaded alginate/chitosan/starch microcapsules were prepared using external gelation method and internal emulsion gelation method. The solution of oyster peptides complexes was encapsulated into the microcapsules, which endowed the microcapsules with intestine passive targeting properties. The swelling behavior, encapsulation efficiency, and release behavior of oyster peptides from the microcapsules at different pH values were investigated. The microcapsules exhibited sustained release of the peptides in intestinal medium, and the release rate could be regulated by the pH value: in simulated gastric fluid, the release rate was greatly decreased, and in simulated body fluid and intestinal fluid, the microcapsules exhibited a sustained release in 24 h with different release rates. The microspheres were characterized by Fourier transform infrared. The results suggested that the alginate/chitosan/starch microcapsules could be a suitable copolymeric carrier system for intestinal protein or peptides delivery in the intestine.     

Formulation and characterization of formaldehyde cross-linked degradable starch microspheres containing terbutaline sulfate

Preparation of starch microspheres using epichlorohydrin is a time consuming method and requires around 18 hr for cross-linking reaction. To reduce reaction time, terbutaline sulfate (TBS) loaded degradable starch microspheres (DSM) were prepared using formaldehyde as the cross-linking agent. All microspheres were spherical in shape and had a porous, rough surface with a mean particle size of 18-24 microm. Whatever the cross-linking time, it was seen that the release of the TBS was not complete during the release experiments. The influence of enzyme on the degradation of microspheres was moderate. Following intravenous administration, initial uptake of microspheres by the lung was higher than those of other organs.     

可缓释药物的明胶/磷酸钙骨水泥复合组织工程支架材料

采用向孔隙中灌注含聚乳酸聚乙醇酸共聚物（PLGA）载药微球的明胶溶液的方法制备了具有药物缓释功能的明胶/磷酸钙骨水泥复合组织工程支架。用扫描电子显微镜观察了微球和支架的形貌特征,用万能材料试验机测定了支架材料的抗压强度,用紫外-可见分光光度计分析了复合支架的释药率。结果表明,灌注明胶对多孔磷酸钙骨水泥支架起到显著的增强作用,抗压强度达2.42 MPa。复合支架携载硫酸庆大霉素, 具有良好的药物缓释功能,缓释时间可达30天以上,使支架在修复骨缺损的同时能消除炎症反应,成为一种集骨修复和治疗于一体的新型组织工程支架材料,具有良好的应用前景。