Optimization of preparative conditions for poly-DL-lactide- polyethylene glycol microspheres with entrapped Vibrio cholera antigens

Ultrasound-Propelled Janus Rod-Shaped Micromotors for Site-Specific Sonodynamic Thrombolysis

Antithrombosis therapy is confronted with short half-lives of thrombolytic agents, limited therapeutic effects, and bleeding complications. Drug delivery systems of thrombolytic agents face challenges in effective penetration into thrombi, which are characterized by well-organized fibrin filled with abundant activated platelets. Herein, Janus rod (JR)-shaped micromotors are constructed by side-by-side electrospinning and cryosection, possessing advantages in controlling the Janus structure and aspect ratio of microrods. Silicon phthalocyanine (Pc) and CaO₂ nanoparticles (NPs) are loaded into the separate sides of JRs, and Arg-Gly-Asp (RGD) peptides are grafted on the surface to obtain Pc/Ca@r-JRs for the sonodynamic therapy (SDT) of thrombosis without using any thrombolytic agents. Decomposition of CaO₂ NPs ejects O₂ bubbles from one side of JRs, and ultrasonication of O₂ bubbles produces the cavitation effect, both generating mechanical force to drive the thrombus penetration. The integration of ultrasonication-propelled motion and RGD mediation effectively increases the targeting capabilities of r-JRs to activated platelets. In addition to mechanical thrombolysis, ultrasonication of the released Pc produces ¹O₂ to destruct fibrin networks of clots. In vitro thrombolysis of whole blood clots shows that ultrasonication of Pc/Ca@r-JRs has a significantly higher thrombolysis rate (73.6%) than those without propelled motion or RGD-mediated clot targeting. In a lower limb thrombosis model, intravenous administration of Pc/Ca@r-JRs indicates 3.4-fold higher accumulations at the clot site than those of JRs, and ultrasonication-propelled motion further increases thrombus retention 2.1 times. Treatment with Pc/Ca@r-JRs and ultrasonication fully removes thrombi and significantly prolongs tail bleeding time. Thus, this study has achieved precise and prompt thrombolysis through selective targeting to clots, efficient penetration into dense networks of thrombi, and SDT-executed thrombolysis.

Cefquinome-loaded microsphere formulations against Klebsiella pneumonia infection during experimental infections

The aim of this study was to prepare cefquinome-loaded polylactic acid microspheres and to evaluate their in vitro and in vivo characteristics and pharmacodynamics for the therapy of pneumonia in a rat model. Microspheres were prepared using a 0.7 mm two-fluid nozzle spray drier in one step resulting in spherical and smooth microspheres of uniform size (9.8 ± 3.6 μm). The encapsulation efficiency and drug loading of cefquinome were 91.6 ± 2.6% and 18.7 ± 1.2%, respectively. In vitro release of cefquinome from the microspheres was sustained for 36 h. Cefquinome-loaded polylactic acid microspheres as a drug delivery system was successful for clearing experimental Klebsiella pneumonia lung infections. A decrease in inflammatory cells and an inhibition of inflammatory cytokines TNF-α, IL-1β and IL-8 after microspheres treatment was found. Changes in cytokine levels and types are secondary manifestations of drug bactericidal effects. Rats were considered to be microbiologically cured because the bacterial load was less than 100 CFU/g. These results also indicated that the spray-drying method of loading therapeutic drug into polylactic acid microspheres is a straightforward and safe method for lung-targeting therapy in animals.

An implantable depot capable of in situ generation of micelles to achieve controlled and targeted tumor chemotherapy

Camptothecin (CPT)-containing promicelle polymers (PM_CPT) based on 4-armed poly(ethylene glycol) (PEG) were developed previously to self-assemble into folate-targeted and glutathione (GSH)-sensitive micelles (M_CPT). To address severe systemic toxicity and lack of tumor specificity implicated in the intravenous administration of M_CPT, a micelle-generating depot has been developed by blend electrospinning of PEG-poly(lactide) (PELA) copolymers, PM_CPT and polyethylene oxide (PEO). Upon implantation of the depot onto a tumor, PM_CPT are sustainably released to self-assemble into M_CPT on the tumor site. The release of PM_CPT is adjusted by varying PEO/PELA ratios and reaches in the range of 23-92% after 30 days of incubation. By making use of the aggregation-induced emission (AIE) features of tetraphenylethylene (TPE) derivatives, the release process of TPE-containing promicelle polymers (PM_TPE) from the depot and the spontaneous formation of micelles (M_TPE) have been monitored from the self-assembly-induced fluorescence light-up both in vitro and in vivo. Compared with intravenous injection of M_CPT, the micelle-generating depot has significantly enhanced micelle accumulation in the tumor for an extended period of time and resulted in stronger tumor inhibitory efficacy, reduced systemic toxicity and more effective inhibition of tumor metastasis, demonstrating great potential for targeted cancer therapy with sustained efficacy.

STATEMENT OF SIGNIFICANCE

The promicelle polymer-co-electrospun fibers are developed to form a micelle-generating depot after implantation onto the tumor. The promicelle polymers are continuously released and simultaneously self-assemble into folate-targeted and glutathione-sensitive micelles, ensuring sustained micelle delivery for more than 30 days. The process of micelle formation in the tumor tissue is visualized in vivo for the first time based on the mechanism of aggregation-induced emission. This in situ micelle formation also prevents premature drug release and rapid clearance from the bloodstream. In addition, these fibers deliver anti-cancer agents directly within tumor cells via dual selectivity (i.e. spatially selective accumulation in tumor tissues via implantation and selective internalization into tumor cells via folate receptor-mediated endocytosis) and on-demand drug release in response to cytosol GSH. They exhibit superior tumor inhibitory efficacy with minimal systemic toxicity, and prevent from malignant metastasis of cancer cells.

Methocel-Lipid Hybrid Nanocarrier for Efficient Oral Insulin Delivery

Even with the use of double-emulsion technique for preparation, the hydrophobic nature of solid lipid nanoparticles (SLNs) limits their encapsulation efficiency (EE%) for peptides such as insulin. In this study, we hypothesize that inclusion of Methocel into SLN to form Methocel-lipid hybrid nanocarriers (MLNs) will significantly enhance insulin EE% without compromising the various characteristics of SLN favorable for oral drug delivery. Our data show that incorporation of 2% wt/wt of Methocel A15C had doubled insulin EE% (around 40%) versus conventional SLN prepared using standard double emulsion technique. MLN significantly protected the entrapped insulin against chymotrypsin degradation at gastrointestinal pH. Using intestinal epithelial cells Caco2 as a model, it was shown that MLN could be extensively taken up by Caco2 cells while demonstrating low cytotoxicity. The results indicate that MLN have preserved the key advantages of SLN (biocompatibility, low cytotoxicity, good drug protection, and good interaction with cells) while overcoming their key limitation for efficient peptide entrapment. Based on this, MLN may serve as a promising nanocarrier for oral delivery of peptides.

Polymeric nanoparticles and microparticles for the delivery of peptides, biologics, and soluble therapeutics

Biologically derived therapeutics, or biologics, are the most rapidly growing segment of the pharmaceutical marketplace. However, there are still unmet needs in improving the delivery of biologics. Injectable polymeric nanoparticles and microparticles capable of releasing proteins and peptides over time periods as long as weeks or months have been a major focus in the effort to decrease the frequency of administration. These particle systems fit broadly into two categories: those composed of hydrophilic and those composed of hydrophobic polymeric scaffolds. Here we review the factors that contribute to the slow and controlled release from each class of particle, as well as the effects of synthesis parameters and product design on the loading, encapsulation efficiency, biologic integrity, and release profile. Generally, hydrophilic scaffolds are ideal for large proteins while hydrophobic scaffolds are more appropriate for smaller biologics without secondary structure. Here we also introduce a Flash NanoPrecipitation method that has been adopted for encapsulating biologics in nanoparticles (40-200nm) at high loadings (50-75wt.%) and high encapsulation efficiencies. The hydrophilic gel interior and hydrophobic shell provide an opportunity to combine the best of both classes of injectable polymeric depots.

Spatial distribution and antitumor activities after intratumoral injection of fragmented fibers with loaded hydroxycamptothecin

There was only a small percentage of drug delivered to tumors after systemic administration, and solid tumors also have many barriers to prevent drug penetration within tumors. In the current study, intratumoral injection of drug-loaded fiber fragments was proposed to overcome these barriers, allowing drug accumulation at the target site to realize the therapeutic efficacy. Fragmented fibers with hydroxycamptothecin (HCPT) loaded were constructed by cryocutting of aligned electrospun fibers, and the fiber lengths of 5 (FF-5), 20 (FF-20), and 50μm (FF-50) could be easily controlled by adjusting the slice thickness. Fragmented fibers were homogeneously dispersed into 2% sodium alginate solution, and could be smoothly injected through 26G1/2 syringe needles. FF-5, FF-20 and FF-50 fiber fragments indicated similar release profiles except a lower burst release from FF-50. In vitro viability tests showed that FF-5 and FF-20 fiber fragments caused higher cytotoxicity and apoptosis rates than FF-50. After intratumoral injection into murine H22 subcutaneous tumors, fragmented fibers with longer lengths indicated a higher accumulation into tumors and a better retention at the injection site, but showed less apparent diffusion within tumor tissues. In addition to the elimination of invasive surgery, HCPT-loaded fiber fragments showed superior in vivo antitumor activities and fewer side effects than intratumoral implantation of drug-loaded fiber mats. Compared with FF-5 and FF-50, FF-20 fiber fragments indicated optimal spatial distribution of HCPT within tumors and achieved the most significant effects on the animal survival, tumor growth inhibition and tumor cell apoptosis induction. It is suggested that the intratumoral injection of drug-loaded fiber fragments provided an efficient strategy to improve patient compliance, allow the retention of fragmented fibers and spatial distribution of drugs within tumor tissues to achieve a low systemic toxicity and an optimal therapeutic efficacy.

Therapeutic angiogenesis in ischemic muscles after local injection of fragmented fibers with loaded traditional Chinese medicine

Therapeutic angiogenesis remains the most effective method to re-establish a proper blood flow in ischemic tissues. There is a great clinical need to identify an injectable format to achieve a well accumulation following local administration and a sustained delivery of biological factors at the ischemic sites. In the current study, fragmented nanofibers with loaded traditional Chinese medicines, astragaloside IV (AT), the main active ingredient of astragalus, and ferulic acid (FA), the main ingredient of angelica, were proposed to promote the microvessel formation after intramuscular injection into ischemic hindlimbs. Fragmented fibers with average lengths of 5 (FF-5), 20 (FF-20) and 80 μm (FF-80) were constructed by the cryocutting of aligned electrospun fibers. Their dispersion in sodium alginate solution (0.2%) indicated good injectability. After injection into the quadriceps muscles of the hindlimbs, FF-20 and FF-80 fiber fragments showed higher tissue retentions than FF-5, and around 90% of the injected doses were determined after 7 days. On a hindlimb ischemia model established by ligating the femoral arteries, intramuscular injection of the mixtures of FA-loaded and AT-loaded FF-20 fiber fragments substantially reduced the muscle degeneration with minimal fibrosis formation, significantly enhanced the neovessel formation and hindlimb perfusion in the ischemic tissues, and efficiently promoted the limb salvage with few limb losses. Along with the easy manipulation and lower invasiveness for in vivo administration, fragmented fibers should become potential drug carriers for disease treatment, wound recovery and tissue repair after local injection.

Single-injection vaccines: Progress, challenges, and opportunities

Currently, vaccination is the most efficient and cost-effective medical treatment for infectious diseases; however, each year 10 million infants remain underimmunized due to current vaccination schedules that require multiple doses to be administered across months or years. These dosing regimens are especially challenging in the developing world where limited healthcare access poses a major logistical barrier to immunization. Over the past four decades, researchers have attempted to overcome this issue by developing single-administration vaccines based on controlled-release antigen delivery systems. These systems can be administered once, but release antigen over an extended period of time to elicit both primary and secondary immune responses resulting in antigen-specific immunological memory. Unfortunately, unlike controlled release systems for drugs, single-administration vaccines have yet to be commercialized due to poor antigen stability and difficulty in obtaining unconventional release kinetics. This review discusses the current state of single-administration vaccination, challenges delaying the development of these vaccines, and potential strategies for overcoming these challenges.

Modulating the release of drugs from alginate matrices with the addition of gelatin microbeads

Injectable drug-loaded matrices and controlled release technology offer numerous advantages over conventional dosages. Cross-linkable alginate hydrogels have been proposed for in vivo injection, but their large initial burst release of encapsulated drugs represents a limitation for the transition to the clinical phase. To reduce this effect, a new drug delivery system was prepared by combining uncross-linked, drug-loaded gelatin microbeads with cross-linkable alginate solution. Gelatin microbeads ranging from 5 to 50 µm were obtained depending on gelatin concentration, stirring rate, and emulsifying time. The release behavior of drug-loaded gelatin microbeads encapsulated within cross-linked alginate gel was characterized both at room temperature and 37°C and compared with the release from gelatin microbeads and cross-linked alginate gel alone. Gelatin microbeads reduced the initial burst release of fluorescein from cross-linked alginate matrix, with a corresponding decrease in the release efficiency. Burst release in the first 2 h was reduced from 30% to about 5%, while cumulative release at 37°C declined from about 95% to 50% after 7 days. This system represents a promising approach for the development of novel and versatile injectable drug delivery systems.

Synergistic promotion of blood vessel regeneration by astragaloside IV and ferulic acid from electrospun fibrous mats

The promotion of blood vessel initiation and growth plays an important role in the realization of therapeutic vascularization and regeneration of functional tissues. Astragalus membranaceus and angelica sinensis are commonly used traditional Chinese medicines for enriching the blood. In the current study astragaloside IV (AT, the main active ingredient of astragalus) and ferulic acid (FA, the main ingredient of angelica) were loaded into electrospun fibrous scaffolds to provide abundant and sustained biological factors required to initiate vascularization and bring it to maturity. The cell viability after AT and FA treatment was dose-dependent with an optimal concentration of around 50 μg/mL, and the most significant synergistic effect was demonstrated for the combined treatment with AT and FA with the ratio of 7/3 on both primary endothelial and smooth muscle cells. The in vitro release study showed that the amount of AT and FA release could be regulated by their loading amount and ratios in electrospun fibers. The localized and sustained codelivery of AT and FA indicated significantly high cell viability and secretion of extracellular matrices for both endothelial and smooth muscle cells, and induced significantly high densities of vascular structures after subcutaneous implantation. The most significant angiogenesis promotion with few inflammatory reactions was demonstrated for electrospun fibers containing AT and FA with the ratio of 7/3. It was suggested that the integration of the synergistic effect of Chinese medicine into electrospun fibrous scaffolds should provide clinical relevance for therapeutic vascularization, full vascularization in engineered tissues, and regeneration of blood vessel substitutes.

Biodegradable paclitaxel-loaded microparticles prepared from novel block copolymers: influence of polymer composition on drug encapsulation and release

This study covers the preparation of microspheres for the controlled and targeted release of paclitaxel, using novel degradable polymers as carrier materials. Paclitaxel-loaded microspheres were prepared by oil-in-water single-emulsion solvent extraction/evaporation technique by using a series of polyurethanes and a block copolymer; the physicochemical properties of these polymers were modulated by changing nature and composition of their structural units. The obtained microparticles showed a regular morphology and properties (diameter: 1-100 µm; resuspension index: 18.8-100%; encapsulation efficiency: 26.6-97.2%) depending on polymer hydrophilicity and emulsifier used. In vitro release curves showed in all cases almost zero-order kinetics after an initial low burst effect (from 1 to 8.4%), which is required to minimize the drug side effects. This work also proposes a novel strategy to combine a controlled and a targeted release through the functionalization of the polymer matrix with peptide sequences. An RGD-functionalized polyurethane was used to successfully prepare paclitaxel-loaded microparticles. Studies on the preparation of polymer microspheres are reported.

Promoted antitumor activities of acid-labile electrospun fibers loaded with hydroxycamptothecin via intratumoral implantation

The acidosis of tumor microenvironments is one of the universal phenomena of solid tumors, and the increased acidity may be in fact essential intermediates in the progression of tumor growth and several lethal phenotypic traits of tumors, such as invasion and metastasis. Acid-labile polymers PBELA with incorporating acetal groups into biodegradable backbone of poly(d,l-lactide)-poly(ethylene glycol) (PELA) were utilized to load hydroxycamptothecin (HCPT) into electrospun fibers for intratumoral chemotherapy. Compared with that under a simulated physiological condition of pH 7.4, the incubation of PBELA fibers in acidic media resulted in larger mass loss and molecular weight reduction of fiber matrices and enhanced HCPT release from fibers. In vitro cytotoxicity assay of HCPT-loaded PBELA fibers indicated 6-fold higher inhibitory activity against HepG2 cells after incubation in pH 6.8 media than that of pH 7.4, while there was no significant difference for free HCPT and HCPT-loaded PELA fibers. The tumor growth, tumor cell apoptosis, and animal survival rate after intratumoral implantation of HCPT-loaded PBELA fibers indicated a superior in vivo antitumor activity and fewer side effects than other treatment. Therefore, acid-labile electrospun fibers may be promising implants for localized therapy of inoperable tumors and for prevention of post-surgical tumor recurrence.

Multiple release of polyplexes of plasmids VEGF and bFGF from electrospun fibrous scaffolds towards regeneration of mature blood vessels

Key challenges associated with the outcomes of vascular grafting (for example, to fully vascularize engineered tissues and promptly regenerate blood vessel substitutes) remain unsolved. The local availability of angiogenic growth factors is highly desirable for tissue regeneration, and plasmid loading in scaffolds represents a powerful alternative for local production of tissue-inductive factors. No attempt has been made so far to clarify the efficacy of electrospun fibers with the loading of multiple plasmids to promote tissue regeneration. In the present study, core-sheath electrospun fibers with the encapsulation of polyplexes of basic fibroblast growth factor-encoding plasmid (pbFGF) and vascular endothelial growth factor-encoding plasmid (pVEGF) were evaluated to promote the generation of mature blood vessels. In vitro release indicated a sustained release of pDNA for ∼4 weeks with as low as ∼10% initial burst release, and the release patterns from the single and twofold plasmid-loaded systems coincided. In vitro investigations on human umbilical vein endothelial cells showed that the sustained release of pDNA from fibrous mats promoted cell attachment and viability, cell transfection and protein expression, and extracellular secretion of collagen IV and laminin. The acceleration of angiogenesis was assessed in vivo after subcutaneous implantation of fibrous scaffolds, and the explants were evaluated after 1, 2 and 4 weeks' treatment by histological and immunohistochemical staining. Compared with pDNA polyplex infiltrated fibrous mats, the pDNA polyplex encapsulated fibers alleviated the inflammation reaction and enhanced the generation of microvessels. Although there was no significant difference in the total number of microvessels, the density of mature vessels was significantly enhanced by the combined treatment with both pbFGF and pVEGF compared with those incorporating individual pDNA. The integration of the core-sheath structure, DNA condensation and multiple delivery strategies provided a potential platform for scaffold fabrication to regenerate functional tissues.

Galactose decorated acid-labile nanoparticles encapsulating quantum dots for enhanced cellular uptake and subcellular localization

PURPOSE

Biodegradable polymers containing acid-labile segments and galactose grafts were formulated into nanoparticles in current study, and enhanced cellular uptake and subcellular distribution were clarified.

METHODS

Quantum dots (QDs) was utilized as an imaging agent and a model of bioactive substances, and entrapped into nanoparticles of around 200 nm through a nanoprecipitation process.

RESULTS

The acid-labile characteristics of QDs-loaded nanoparticles were approved by the hemolysis capability, the degradation behaviors of matrix polymers, and the fluorescence decay of entrapped QDs after incubation into buffer solutions of different pH values. The galactose grafts increased the acid-lability, due to the hydrophilic moieties on the acid-labile segments, and enhanced uptake efficiency of over 50 % was found after 4 h incubation with HepG2 cells, due to the galactose-receptor mediated endocytosis. The acid-lability led to an efficient endosomal escape of QDs-loaded nanoparticles into cytoplasm.

CONCLUSIONS

The integration of acid-lability, targeting effect, and full biodegradable backbone into nanoparticle matrices constitutes a promising platform for intracellular delivery of bioactive substances for disease diagnosis, imaging and treatment.

Effects of poly(lactic-co-glycolic acid) on preparation and characteristics of plasmid DNA-loaded solid lipid nanoparticles

Poly(lactic-co-glycolic acid) (PLGA) was used as a polymeric emulsifier to encapsulate plasmid DNA into hydrogenated castor oil (HCO)-solid lipid nanoparticles (SLN) by w/o/w double emulsion and solvent evaporation techniques. The effects of PLGA on the preparation, characteristics and transfection efficiency of DNA-loaded SLN were studied. The results showed that PLGA was essential to form the primary w/o emulsion and the stability of the emulsion was enhanced with the increase of PLGA content. DNA-loaded SLN were spherical with smooth surfaces. The SLN had a negative charge in weak acid and alkaline environment but acquired a positive charge in acidic pH and the cationisation capacity of the SLN increased with the increase of PLGA/HCO ratio. Agarose gel electrophoresis demonstrated that the majority of the DNA maintained its structural integrity after preparation and being extracted or released from DNA-loaded SLN. When PLGA/HCO ratio increased from 5 to 15%, the encapsulation efficiency, loading capacity and transfection efficiency of the nanoparticles increased significantly, whereas the changes of particle size and polydispersity index were insignificant. Cytotoxicity study in cell culture demonstrated that the SLN was not toxic.

Core-sheath structured fibers with pDNA polyplex loadings for the optimal release profile and transfection efficiency as potential tissue engineering scaffolds

Emulsion electrospinning was initially applied to prepare core-sheath structured fibers with a core loading of pDNA or pDNA polyplexes inside a fiber sheath of poly(DL-lactide)-poly(ethylene glycol) (PELA). The inclusion of poly(ethylene imine) (PEI) and poly(ethylene glycol) (PEG) were expected to modulate the release profiles and achieve a balance between cytotoxicity and transfection efficiency. The core-sheath fibers enhance the structural integrity and maintain the biological activity of pDNA during the electrospinning process, incubation in release buffer and enzyme digestion. The addition of hydrophilic PEI into the fiber matrix accelerates pDNA release, while the encapsulation of pDNA polyplexes within the fibers led to no further release after an initial burst. However, sustained release of pDNA polyplexes has been achieved through PEG incorporation, and the effective release lifetime can be controlled between 6 and 25 days, dependent on the amount loaded and the molecular weight of PEG. Higher N/P ratios of PEI to DNA result in lower cell attachment, while cell viability is dependent on the effective concentration of pDNA polyplexes released from the fibers. While no apparent transfection is detected for pDNA-loaded PELA fibers, PEG incorporation into fibers containing pDNA polyplexes leads to over an order of magnitude increase in the transfection efficiency. pDNA polyplex-loaded fibers containing 10% PEG show the best performance in balancing transfection efficiency and cell viability. It is suggested that electrospun core-sheath fibers integrated with DNA condensation techniques provide the potential to produce inductive tissue engineering scaffolds able to manipulate the desired signals at effective levels within the local tissue microenvironment.

Preparation and in vitro characterization of vascular endothelial growth factor (VEGF)-loaded poly(D,L-lactic-co-glycolic acid) microspheres using a double emulsion/solvent evaporation technique

Biodegradable Poly(lactic-co-glycolic acid; PLGA), microspheres encapsulating the angiogenic protein recombinant human vascular endothelial growth factor (rhVEGF) were formed to achieve VEGF release in a sustained manner. These microspheres are a promising delivery system which can be used for therapeutic angiogenesis. The PLGA microspheres incorporating two different initial loading amounts of rhVEGF have been prepared by a modified water-in-oil-in-water (w/o/w) double emulsion/solvent evaporation technique. The microspheres have been characterized by particle size distribution, environmental scanning electron microscopy (ESEM), light microscopy, encapsulation efficiency and their degradation was studied in vitro. The rhVEGF released from microspheres was quantified by the competitive enzyme-linked immunosorbent assay (ELISA) and human umbilical vein endothelial cell (HUVEC) proliferation assay was used to assess biological activity of the released VEGF. The microspheres were spherical with diameters of 10-60 µm and the encapsulation efficiency was between 46% and 60%. The release kinetics of rhVEGF was studied for two different amounts: 5 µg VEGF (V5) and 50 µg VEGF (V50) per 500 mg starting polymer. The total protein (VEGF:BSA) release increased up to 4 weeks for two rhVEGF concentrations. The ELISA results showed that the burst release for V5 and V50 microspheres were 4 and 27 ng/mL, respectively. For V5, the microspheres showed an initial burst release, followed by a higher steady-state release until 14 days. VEGF release increased up to 2 weeks for V50 microsphere. HUVEC proliferation assay showed that endothelial cells responded to bioactive VEGF by proliferating and migrating.

Polyethylenglycol-co-poly-D,L-lactide copolymer based microspheres: preparation, characterization and delivery of a model protein

PURPOSE

To prepare and characterize polyethylenglycol-co-poly-D,L-lactide (PEG-D,L-PLA) multiblock copolymer microspheres containing ovalbumin. Microsphere batches made of Poly-D,L-lactide (PLA) homopolymers were prepared in order to evaluate how the presence of PEG segments into PEG-D,L-PLA copolymer could affect the behaviour of microspheres as carrier of protein drugs.

METHODS

The PEG-D,L-PLA and PLA microspheres, loaded with the model protein ovalbumin, were prepared using double emulsion solvent evaporation method. The effect of PEG segments in the microparticles matrix, on the morphology, size distribution, encapsulation efficiency and release behaviour was studied.

RESULTS

According to the results, PEG-D,L-PLA microspheres were more hydrophilic than PLA microparticles and with lower glass transition temperature. The surface of PEG-D,L-PLA microspheres was not as smooth as that of PLA microparticles, the mean diameter of PEG-D,L-PLA microparticles was bigger than that of PLA microspheres. Protein release from the microspheres was affected by the morphological structure of PEG-D,L-PLA microspheres and properties of PEG-D,L-PLA copolymer. This study suggests that PEG-D,L-PLA multiblock copolymer may be used as carrier in protein delivery systems for different purposes.

Response Surface Methodology to Obtain β-Estradiol Biodegradable Microspheres for Long-Term Therapy of Osteoporosis

The purpose of this work was to evaluate the main and interaction effects of formulation factors on the drug encapsulation efficiency of beta-estradiol biodegradable microspheres by applying response surface methodology. A secondary purpose was to obtain an optimized formula for long-term therapy of osteoporosis. A three factor, three level Box-Behnken experimental design was used to get 15 experimental runs. The independent variables were drug/polymer ratio (X1), dispersing agent concentration (X2), and deaggregating agent concentration (X3). The dependent variables were percentage encapsulation efficiency (Y1), cumulative percent drug released (Y2), and percentage yield of the microspheres (Y3). The formulations were prepared by emulsion solvent evaporation technique using ethyl acetate as organic solvent. The optimized formulation was maximized for encapsulation efficiency and further characterized for the particle size distribution, scanning electron microscopy (SEM), X-ray diffraction (XRD), and Fourier transform infrared (FT-IR). The mathematical relationship obtained between X1, X2, X3, and Y1 was: Y1 = -129.85 + 29.35X1 + 129.99X2 + 64.82X3 - 3.2X1X2 - 0.29X1X3 - 35.83X2X3 - 2.05X(2)(1) - 13.23X(2)(2) - 5.92X(2)(3) (R2 = 0.99) The equation showed that X1, X2, and X3 affect Y1 positively but interaction between any two of these factors affects Y1 negatively. The most significant interaction was between X2 and X3. The finding indicated that controlled releases beta-estradiol biodegradable microspheres with high encapsulation efficiency and low pulsatile release can be prepared and the quantitative response surface methodology applied helped in understanding the effects and the interaction effects between the three factors applied.

Encapsulation of PROLI/NO in biodegradable microparticles

Biodegradable hydrophilic polymers poly-lactic-co-glycolic acid (PLGA) and polyethylene oxide-co-lactic acid (PELA) were used to encapsulate a small hydrophilic prodrug (PROLI/NO) as a strategy to deliver nitric oxide (NO) by inhalation. The microparticles were prepared using double emulsion and solvent evaporation, followed by freeze-drying. The NO release kinetics were characterized by three parameters: the maximum concentration of NO per unit weight of microparticles, C(max) (nM mg(-1)); the window of time for which the concentration exceeded 50% of C(max), W(50) (min); and the initial rate of release, R(i) (nM mg(-1) min(-1)). PLGA-based microparticles did not encapsulate PROLI/NO. PELA-based microparticles demonstrated an entrapment efficiency rate of 43%, a mass median diameter of 2.3 micro m, and NO release in a physiological buffer characterized by C(max) = 123, W(50) = 4.11, and R(i) = 78.7. Addition of gelatin as a hydrophilic binding moiety in the first emulsion allowed PLGA-based microparticles to encapsulate PROLI/NO; however, the mass median diameter was too large for inhalation (23.5 micro m). It is concluded that the hydrophilic polyethylene glycol-moiety in PELA allows for efficient encapsulation of PROLI/NO, and PELA-based microparticles might be a strategy to generate a stable inhalable form of NO.

Biodegradable Microparticulates of Beta-Estradiol: Preparation and In Vitro Characterization

Beta-estradiol has been recommended for the long-term therapy of osteoporosis and its oral formulations are subjected to intensive first pass metabolism. The present investigation was aimed at preparing and characterizing biodegradable microparticles of beta-estradiol with polymers such as PLA, PLGA 85/15, PLGA 75/25, and their mixtures. The microparticles were prepared by solvent evaporation method using methylene chloride as a solvent and polyvinyl alcohol as a surfactant. The drug-polymer ratios were 1:3, 1:5, and 1:7. The prepared microparticles (twelve formulations) were tested for encapsulation efficiency and in vitro drug release in 50% methyl alcohol/phosphate buffer pH 7.4. The results showed that the encapsulation efficiency varied from 81 to 100% and the formulation fabricated from PLGA 85/15 (1:3) showed less burst and consistent long time release. This formulation when further characterized displayed irregular spherical shape with an average particle size of 72 microm. The crystallinity of the drug was reduced when investigated using X-ray diffractometry. No chemical interaction between the drug and the polymer was observed as evidenced by FT-IR analysis. The results indicated that beta-estradiol biodegradable microparticles with PLGA 85/15 (1:3) could be a suitable approach for long term therapy of osteoporosis.

Microbubbles in ultrasound-triggered drug and gene delivery

Ultrasound contrast agents, in the form of gas-filled microbubbles, are becoming popular in perfusion monitoring; they are employed as molecular imaging agents. Microbubbles are manufactured from biocompatible materials, they can be injected intravenously, and some are approved for clinical use. Microbubbles can be destroyed by ultrasound irradiation. This destruction phenomenon can be applied to targeted drug delivery and enhancement of drug action. The ultrasonic field can be focused at the target tissues and organs; thus, selectivity of the treatment can be improved, reducing undesirable side effects. Microbubbles enhance ultrasound energy deposition in the tissues and serve as cavitation nuclei, increasing intracellular drug delivery. DNA delivery and successful tissue transfection are observed in the areas of the body where ultrasound is applied after intravascular administration of microbubbles and plasmid DNA. Accelerated blood clot dissolution in the areas of insonation by cooperative action of thrombolytic agents and microbubbles is demonstrated in several clinical trials.

Anti-tumor effects of anti-VEGF siRNA encapsulated with PLGA microspheres in mice

The suppression of gene expression of vascular endothelial growth factor (VEGF) which regulates tumor angiogenesis in vivo and is an important factor in tumor growth represents a novel approach to cancer treatment. Although small interfering RNA (siRNA) has rapidly become a major tool in gene therapy and is a key inhibitory factor of gene expression, its effect is temporary. The present study investigates the preparation of long-term sustained release poly (dl-lactic/glycolic acid) (PLGA) microspheres encapsulating anti-VEGF siRNA with a carrier (arginine or branched polyethylenimine) using the w/o/w in-water drying method and their anti-tumor activities. The ratio (%) of encapsulated siRNA increased when arginine or PEI was added to the inner water phase during preparation. The release of siRNA from microspheres in phosphate buffer (pH 7.4) was sustained for over one month. The anti-tumor effects of microspheres in vivo were evaluated in mice bearing S-180 tumors. An intra-tumor injection of microspheres with encapsulated siRNA obviously suppressed tumor growth. These results indicate that the microspheres of anti-VEGF siRNA with a transfection agent (carrier) have achieved a higher and sustained suppressive effect on VEGF gene expression and should be a practically useful preparation.

Preparation and characterization of fenofibrate-loaded PLA-PEG microspheres

A series of biodegradable block copolymer of poly(lactide)(PLA)/poly(ethylene glycol) (PEG) were prepared by Ring-Opening polymerization of D, L-lactide, using stannous octoate as a catalyst. By nanoprecipitation method, the PLA-PEG can be made into microspheres containing fenofibrate, which is a kind of important cholesterol-lowering drugs. The purpose of this study is to investigate the effect of the copolymer composition on the size, the entrapment and the release behavior of the fenofibrate loaded microspheres. The microspheres can be achieved with small size below 100 nm, better encapsulation efficiencies of more than 55.3% and slower release rates. The release of fenofibrate from microsphere would reach the balance first, when the microsphere prepared by high proportion of hydrophilic PEG block. And the release property of fenofibrate/PLA-PEG microsphere was better than Lipanthyl (a commercial capsule of fenofibrate). It was observed that the composition of PLA-PEG copolymer played a major role in encapsulation efficiency of microspheres and release rates.

The Influence of Surfactant on PLGA Microsphere Glass Transition and Water Sorption: Remodeling the Surface Morphology to Attenuate the Burst Release

PURPOSE

The stability of protein unloaded and loaded poly(lactic-co-glycolic acid) (PLGA) microspheres fabricated with surfactant was challenged through exposure to environmental conditions of different relative humidity.

METHODS

Polyvinyl alcohol (PVA) or Triton X-100 was added to the primary emulsion of the double-emulsion solvent evaporation technique. After storage at ambient humidity and 75% relative humidity, the mechanical stability of the polymer was tested to reveal PLGA chain mobility using differential scanning calorimetry. Subsequent surface modifications were examined by atomic force microscopy (AFM), and protein release profiles were collected.

RESULTS

Residual amounts of PVA and particularly Triton X-100 raised the hydrophilicity of the microspheres. When exposed to ambient humidity or 75% relative humidity, PVA and Triton X-100 had, respectively, an antiplasticizing and a plasticizing effect upon PLGA, and both led to physical aging. The high-resolution AFM imaging of microspheres containing model protein and Triton X-100 showed that the depth of the surface pores was reduced when exposed to 75% relative humidity, and the initial burst release subsequently decreased.

CONCLUSION

These studies suggested that the mechanical stability of PLGA was influenced by the addition of surfactants, which, depending on the formulation, led to surface pore remodeling under high humidity, reducing the initial burst release while maintaining the spherical integrity of the microsphere.

Microencapsulation by solvent extraction/evaporation: reviewing the state of the art of microsphere preparation process technology

The therapeutic benefit of microencapsulated drugs and vaccines brought forth the need to prepare such particles in larger quantities and in sufficient quality suitable for clinical trials and commercialisation. Very commonly, microencapsulation processes are based on the principle of so-called "solvent extraction/evaporation". While initial lab-scale experiments are frequently performed in simple beaker/stirrer setups, clinical trials and market introduction require more sophisticated technologies, allowing for economic, robust, well-controllable and aseptic production of microspheres. To this aim, various technologies have been examined for microsphere preparation, among them are static mixing, extrusion through needles, membranes and microfabricated microchannel devices, dripping using electrostatic forces and ultrasonic jet excitation. This article reviews the current state of the art in solvent extraction/evaporation-based microencapsulation technologies. Its focus is on process-related aspects, as described in the scientific and patent literature. Our findings will be outlined according to the four major substeps of microsphere preparation by solvent extraction/evaporation, namely, (i) incorporation of the bioactive compound, (ii) formation of the microdroplets, (iii) solvent removal and (iv) harvesting and drying the particles. Both, well-established and more advanced technologies will be reviewed.

Normal phase high performance liquid chromatography for determination of paclitaxel incorporated in a lipophilic polymer matrix

A normal phase (NP) high performance liquid chromatography (HPLC) method was developed for analysis of paclitaxel incorporated in poly(sebacic-co-ricinoleic acid), a lipophilic polymer matrix utilized for preparation of an injectable formulation for the localized delivery of paclitaxel. Thin layer chromatography experiments revealed that separation of paclitaxel from the polymer is dependent on the eluting strength (solvent strength) of the mobile phase. The HPLC system consists of a Purospher STRAR Si analytical HPLC column (5 microm, 250mm x 4mm, Merck), and 1-2.5% (v/v) methanol in dichloromethane as the mobile phase. Detection was by UV absorbance at 240 and 254 nm. The effect of the mobile phase composition on paclitaxel retention, peak shape and column efficiency, and the influence of the sample loading on the shape of the paclitaxel peak were studied. The mobile phases used for the chromatography consisted of 1.5% (v/v) methanol in dichloromethane. Paclitaxel was determined in the formulation and in the samples from degradation studies using UV detection at a wavelength of 254 nm. UV detection at 240 nm has advantages for following polymer matrix degradation products due to higher detector response at this wavelength. The utility of the proposed NP HPLC approach was demonstrated by assessment of intra- and inter-batch content uniformity, and by the determination of paclitaxel content after 7 and 60 days exposure of the paclitaxel-loaded polymer matrix to in vitro and in vivo degradation.

Development of novel 5-FU-loaded poly(methylidene malonate 2.1.2)-based microspheres for the treatment of brain cancers

In order to treat malignant brain tumors by local delivery of antineoplastic agents, the feasibility of 5-fluorouracil (5-FU)-sustained release biodegradable microspheres with a novel material, poly(methylidene malonate 2.1.2), was investigated using an emulsion/extraction method. This polymer was expected to present a slow degradation rate, thus leading to a long term local delivery system. Microparticles were successfully obtained and characterized in terms of drug loading, size, morphology and release profile. The size of the particles was between 40 and 50 microm, which was compatible with a stereotactic injection through a needle. Sufficient drug loadings were obtained (i.e. compatible with the preparation of therapeutic 5-FU doses in a minimal volume of injection), and perfectly spherical microspheres were observed. The respective influences of the polymer molecular weight, the polymer concentration, and the emulsion time on the release profiles were studied using a 2(3) factorial design. In the same objective, the solvent extraction time was extended while keeping all the previous parameters fixed at their optimal values. The in vitro study of these different parameters allowed a reduction of the initial burst release, with a percentage of 5-FU released after 24 h that was lowered from 90 to 65%, and the achievement of a long term drug delivery system, since the release was still ongoing after 43 days. Moreover, the microparticles could be gamma-sterilized (25 kGy) without modification of the release kinetics. Thus, the requested specifications to perform animal experiments were attained.

W/O/W double emulsion technique using ethyl acetate as organic solvent: effects of its diffusion rate on the characteristics of microparticles

Monomethoxypoly(ethylene glycol)-b-poly(DL-lactide) copolymer (PELA) microparticles loading lysozyme were prepared through a modified W/O/W double emulsion-solvent diffusion method using ethyl acetate (EA) as organic solvent. The modified process was divided into five steps: (1) primary emulsification (W1/O), (2) re-emulsification (W1/O/W2), (3) pre-solidification, (4) solidification and (5) purification. The pre-solidification step was carried out in the modified process to control the diffusion rate of EA from oil phase into outer aqueous phase, in order to prevent the wall polymer from precipitation, which usually occurred when the diffusion rate was too fast. The adequately rapid solidification of microparticle caused by controlled fast diffusion of EA and the use of amphiphilic copolymer PELA as wall material, facilitated a high protein entrapment (always above 94%) and full preservation of bioactivity of entrapped lysozyme. It was found that the volume of the outer aqueous phase in the re-emulsification step and the shear stress in the pre-solidification step had a significant effect on the diffusion rate of EA from the droplets into outer aqueous solution, and thereby on the characteristics of the resultant microparticles. With the volume or the shear stress increasing, the removal rate of EA increased, resulting in rapid solidification of the microparticles. This result led to a lower burst effect and a slower lysozyme release from the microparticles. This study suggests that the modified W/O/W double emulsion-solvent diffusion method with EA as organic solvent is a prospective technique to prepare biodegradable microparticles containing water-soluble sensitive agents.

Biodegradable poly(epsilon-caprolactone)-poly(ethylene glycol) block copolymers: characterization and their use as drug carriers for a controlled delivery system

Poly(epsilon-caprolactone)-poly(ethylene glycol) (PECL) copolymers were synthesized from polyethylene glycol (PEG) and epsilon-caprolactone (epsilon-CL) using stannous octoate as catalyst at 160 degrees C by bulk polymerization. The effect of the molecular weight of PEG and the copolymer ratio on the properties of the copolymers was investigated by (1)H-NMR, IR, DSC and GPC. PCL and PECL microspheres containing human serum albumin were elaborated by solvent extraction method based on the formation of double w/o/w emulsion. Microspheres were characterized in terms of morphology, size, loading efficiency, and the efficiency of microspheres formation. The results show that the microspheres prepared from PECL-10 and PECL-15 copolymers achieved the highest loading efficiency (about 50%) among all copolymers. These results indicate that the properties of copolymers could be tailored by adjusting polymer composition. It is suggested that these matrix polymers may be optimized as carriers in the protein (antigen) delivery system for different purposes.

The preparation and characterization of monomethoxypoly(ethylene glycol)-b-poly-DL-lactide microcapsules containing bovine hemoglobin

Methoxypoly(ethylene glycol)-b-poly-DL-lactide (PELA) microcapsules containing bovine hemoglobin (bHb) were prepared by a W/O/W double emulsion-solvent diffusion process. bHb solution was used as the internal aqueous phase, PELA/organic solvent as the oil phase, and polyvinyl alcohol (PVA) solution as the external aqueous phase. This W/O/W double emulsion was added into a large volume of water (solidification solution) to allow organic solvent to diffuse into water. The optimum preparative condition for PELA microcapsules loaded with bovine hemoglobin was investigated. It was found that homogenization rate, type of organic solvent, and volume of the solidification solution influenced the activity of bovine hemoglobin encapsulated. When the homogenization rate was lower than 9000 rpm and ethyl acetate was used as the organic solvent, there was no significant influence on the activity of hemoglobin. High homogenization rate as 12 000 rpm decreased the P50 and Hill coefficient. Increasing the volume of solidification solution had an effect of improving the activity of microencapsulated hemoglobin. The composition of the PELA had the most important influence on the success of encapsulation. Microcapsules fabricated by PELA with MPEG2k block (molecular weight of MPEG block: 2000) achieved a high entrapment efficiency of 90%, better than PL A homopolymer and PELA with MPEG5k blocks. Hemoglobin microcapsules with native loading oxygen activity (P50 = 26.0 mmHg, Hill coefficient = 2.4), mean size of about 10 microm, and high entrapment efficiency (ca. 93%) were obtained at the optimum condition.

Poly-D,L-lactide-co-poly(ethylene glycol) microspheres as potential vaccine delivery systems

Adjuvants aimed at increasing the immunogenicity of recombinant antigens remain a focus in vaccine development. Worldwide, there is currently considerable care for the development of biodegradable microspheres as controlled release of vaccines, since the major disadvantage of several currently available vaccines is the need for repeated administration. Microspheres prepared from the biodegradable and biocompatible polymers, the polylactide (PLA) or polylactide-co-glycolide (PLGA), have been shown to be effective adjuvants for a number of antigens. This review mainly focuses on polylactide-co-poly(ethylene glycol) (PELA) microspheres adjuvant as vaccine delivery systems by summarizing our and other research groups' investigation on properties of the microspheres formulation encapsulating several kinds of antigens. The results indicate that compared with the commonly used PLA and PLGA, PELA showed several potentials in vaccine delivery systems, which may be due to the block copolymer have its capability to provide a biomaterial having a broad range of amphiphilic structure. PELA microspheres can control the rate of release of entrapped antigens and therefore, offer potential for the development of single-dose vaccines. The PELA microspheres have shown great potential as a next generation adjuvant to replace or complement existing aluminum salts for vaccine potential. The review mainly aims to promote the investigation of PELA microspheres adjuvant for antigens for worldwide researcher.