Salt and cosolvent effects on ionic drug loading into microspheres using an O/W method

Developing a synergistic rate-retarding polymeric implant for controlling monoclonal antibody delivery in minimally invasive glaucoma surgery

Monoclonal antibodies (mAbs) have garnered substantial attention within the field of ophthalmology and can be used to suppress scar formation after minimally invasive glaucoma surgeries. Here, by controlling mAb passive diffusion, we developed a polymeric, rate-controlling membrane reservoir loaded with poly(lactic-co-glycolic acid) microspheres to deliver mAb for several weeks. Different parameters were tested to ensure that the microspheres achieved a good quality characteristic, and our results showed that 1 %W/V emulsifier with 5 %W/V NaCl achieved mAb-loaded microspheres with the highest stability, encapsulation efficiency and minimal burst release. Then, we fabricated and compared 10 types of microporous films based on polylactic acid (PLA), polycaprolactone (PCL), and polyethylene glycol (PEG). Our results revealed distinct pore characteristics and degradation patterns in different films due to varying polymer properties, and all the polymeric film formulations showed good biocompatibility in both human trabecular meshwork cells and human conjunctival fibroblasts. Finally, the optimized microspheres were loaded into the reservoir-type polymeric implant assembled by microporous membranes with different surface coating modifications. The implant formulation, which was fabricated by 60 PCL: 40 PEG (3 %W/V) polymer with 0.1 %W/V poly(lactic-co-glycolic acid) barrier, exerted the best drug release profile that can sustained release mAb (83.6 %) for 4 weeks.

Microstructure Formation and Characterization of Long-Acting Injectable Microspheres: The Gateway to Fully Controlled Drug Release Pattern

Long-acting injectable microspheres have been on the market for more than three decades, but if calculated on the brand name, only 12 products have been approved by the FDA due to numerous challenges in achieving a fully controllable drug release pattern. Recently, more and more researches on the critical factors that determine the release kinetics of microspheres shifted from evaluating the typical physicochemical properties to exploring the microstructure. The microstructure of microspheres mainly includes the spatial distribution and the dispersed state of drug, PLGA and pores, which has been considered as one of the most important characteristics of microspheres, especially when comparative characterization of the microstructure (Q3) has been recommended by the FDA for the bioequivalence assessment. This review extracted the main variables affecting the microstructure formation from microsphere formulation compositions and preparation processes and highlighted the latest advances in microstructure characterization techniques. The further understanding of the microsphere microstructure has significant reference value for the development of long-acting injectable microspheres, particularly for the development of the generic microspheres.

Synthesis and Characterization of PCL-Idebenone Nanoparticles for Potential Nose-to-Brain Delivery

The present work is focused on the preparation of an optimal model of poly-ε-caprolactone nanoparticles as potential carriers for nasal administration of idebenone. A solvent/evaporation technique was used for nanoparticle preparation. Poly-ε-caprolactone with different molecular weights (14,000 and 80,000 g/mol) was used. Polysorbate 20 and Poloxamer 407, alone and in combination, were used as emulsifiers at different concentrations to obtain a stable formulation. The nanoparticles were characterized using dynamic light scattering, SEM, TEM, and FTIR. The resulting structures were spherical in shape and their size distribution depended on the type of emulsifier. The average particle size ranged from 188 to 628 nm. The effect of molecular weight and type of emulsifier was established. Optimal models of appropriate size for nasal administration were selected for inclusion of idebenone. Three models of idebenone-loaded nanoparticles were developed and the effect of molecular weight on the encapsulation efficiency was investigated. Increased encapsulation efficiency was found when poly-ε-caprolactone with lower molecular weight was used. The molecular weight also affected the drug release from the nanostructures. Dissolution study data were fitted into various kinetic models and the Korsmeyer-Peppas model was found to be indicative of the release mechanism of idebenone.

Hofmeister Effects Shine in Nanoscience

Hofmeister effects play a crucial role in nanoscience by affecting the physicochemical and biochemical processes. Thus far, numerous wonderful applications from various aspects of nanoscience have been developed based on the mechanism of Hofmeister effects, such as hydrogel/aerogel engineering, battery design, nanosynthesis, nanomotors, ion sensors, supramolecular chemistry, colloid and interface science, nanomedicine, and transport behaviors, etc. In this review, for the first time, the progress of applying Hofmeister effects is systematically introduced and summarized in nanoscience. It is aimed to provide a comprehensive guideline for future researchers to design more useful Hofmeister effects-based nanosystems.

Design and Development of Levodopa Loaded Polymeric Nanoparticles for Intranasal Delivery

Intranasal delivery is an alternative administration route to deliver levodopa (L-Dopa) to the brain. This drug delivery route offers high drug permeability across the nasal epithelium and rapid absorption into the central nervous system (CNS) while bypassing first-pass metabolism. In this study, we developed a library of polymeric nanocarrier systems for L-Dopa utilising poly(lactic-co-glycolic acid) (PLGA) and chitosan. A total of three PLGA nanoparticles formulations (P1, P2 and P3) were prepared using a modified water-in-oil-in-water (W/O/W) solvent evaporation technique, while four formulations of chitosan nanoparticles (C1, C2, C3 and C4) were prepared by ionic gelation method with sodium tripolyphosphate (TPP) as a cross-linking agent. Upon characterising nanocarriers developed, it was discovered that C2 demonstrated the best results with regard to droplet size (553 ± 52 nm), polydispersity index (0.522), zeta potential (+46.2 ± 2.3 mV), and encapsulation efficiency (82.38% ± 1.63). Transmission electron microscopy (TEM) and scanning electron microscopy (SEM) further corroborated the particle size analysis highlighting that C2 displayed uniform particle size with spherical morphology. Additionally, X-ray diffraction analysis (XRD) revealed that C2 was in an amorphous state while Fourier transform infrared (FTIR) analysis showed that there were no chemical interactions that might change the chemical structure of L-Dopa within the polymeric nanoparticle matrix. Lastly, an in-vivo intranasal study in male Wistar rats showed that the absorption of L-Dopa when formulated as chitosan nanoparticles was significantly enhanced (p < 0.05) by approximately two-fold compared to unmodified L-Dopa. Therefore, this work illustrates that formulating L-Dopa into chitosan nanoparticles for intranasal delivery is a potentially viable formulation strategy to improve the bioavailability of the drug for the treatment of Parkinson’s disease.

An Assessment of Occasional Bio-Inequivalence for BCS1 and BCS3 Drugs: What are the Underlying Reasons?

Despite having adequate solubility properties, bioequivalence (BE) studies performed on immediate release formulations containing BCS1/3 drugs occasionally fail. By systematically evaluating a set of 17 soluble drugs where unexpected BE failures have been reported and comparing to a set of 29 drugs where no such reports have been documented, a broad assessment of the risk factors leading to BE failure was performed. BE failures for BCS1/3 drugs were predominantly related to changes in C_max rather than AUC. C_max changes were typically modest, with minimal clinical significance for most drugs. Overall, drugs with a sharp plasma peak were identified as a key factor in BE failure risk. A new pharmacokinetic term (t½C_max) is proposed to identify drugs at higher risk due to their peak plasma profile shape. In addition, the analysis revealed that weak acids, and drugs with particularly high gastric solubility are potentially more vulnerable to BE failure, particularly when these features are combined with a sharp C_max peak. BCS3 drugs, which are often characterised as being more vulnerable to BE failure due to their potential for permeation and transit to be altered, particularly by excipient change, were not in general at greater risk of BE failures. These findings will help to inform how biowaivers may be optimally applied in the future.

β-Cyclodextrin-poly (β-Amino Ester) Nanoparticles Are a Generalizable Strategy for High Loading and Sustained Release of HDAC Inhibitors

Therapeutic development of histone deacetylase inhibitors (HDACi) has been hampered by a number of barriers to drug delivery, including poor solubility and inadequate tissue penetration. Nanoparticle encapsulation could be one approach to improve the delivery of HDACi to target tissues; however, effective and generalizable loading of HDACi within nanoparticle systems remains a long-term challenge. We hypothesized that the common terminally ionizable moiety on many HDACi molecules could be capitalized upon for loading in polymeric nanoparticles. Here, we describe the simple, efficient formulation of a novel library of β-cyclodextrin-poly (β-amino ester) networks (CDN) to achieve this goal. We observed that network architecture was a critical determinant of CDN encapsulation of candidate molecules, with a more hydrophobic core enabling effective self-assembly and a PEGylated surface enabling high loading (up to ∼30% w/w), effective self-assembly of the nanoparticle, and slow release of drug into aqueous media (up to 24 days) for the model HDACi panobinostat. We next constructed a library of CDNs to encapsulate various small, hydrophobic, terminally ionizable molecules (panobinostat, quisinostat, dacinostat, givinostat, bortezomib, camptothecin, nile red, and cytarabine), which yielded important insights into the structural requirements for effective drug loading and CDN self-assembly. Optimized CDN nanoparticles were taken up by GL261 cells in culture and a released panobinostat was confirmed to be bioactive. Panobinostat-loaded CDNs were next administered by convection-enhanced delivery (CED) to mice bearing intracranial GL261 tumors. These studies confirm that CDN encapsulation enables a higher deliverable dose of drug to effectively slow tumor growth. Matrix-assisted laser desorption/ionization (MALDI) analysis on tissue sections confirms higher exposure of tumor to drug, which likely accounts for the therapeutic effects. Taken in sum, these studies present a novel nanocarrier platform for encapsulation of HDACi via both ionic and hydrophobic interactions, which is an important step toward better treatment of disease via HDACi therapy.

Polylactide/Polyvinylalcohol-Based Porous Bioscaffold Loaded with Gentamicin for Wound Dressing Applications

This study explores the feasibility of modifying the surface liquid spraying method to prepare porous bioscaffolds intended for wound dressing applications. For this purpose, gentamicin sulfate was loaded into polylactide-polyvinyl alcohol bioscaffolds as a highly soluble (hygroscopic) model drug for in vitro release study. Moreover, the influence of inorganic salts including NaCl (10 g/L) and KMnO4 (0.4 mg/L), and post-thermal treatment (T) (80 °C for 2 min) on the properties of the bioscaffolds were studied. The bioscaffolds were characterized by scanning electron microscopy, Fourier Transform infrared spectroscopy, and differential scanning calorimetry. In addition, other properties including porosity, swelling degree, water vapor transmission rate, entrapment efficiency, and the release of gentamicin sulfate were investigated. Results showed that high concentrations of NaCl (10 g/L) in the aqueous phase led to an increase of around 68% in the initial burst release due to the increase in porosity. In fact, porosity increased from 68.1 ± 1.2 to 94.1 ± 1.5. Moreover, the thermal treatment of the Polylactide-polyvinyl alcohol/NaCl (PLA-PVA/NaCl) bioscaffolds above glass transition temperature (Tg) reduced the initial burst release by approximately 11% and prolonged the release of the drug. These results suggest that thermal treatment of polymer above Tg can be an efficient approach for a sustained release.

Liquid jet breakup: A new method for the preparation of poly lactic-co-glycolic acid microspheres

The purpose of this study was to apply the phenomenon of liquid jet breakup to the preparation of sustained-release microspheres. The mechanisms of liquid jet breakup in different jet states were investigated and the single factor method was used to study the effect of each process parameter on the particle size and size distribution of microspheres. Meantime, the prepared microspheres were characterized by morphology, drug loading, encapsulation efficiency and in vitro release. The results indicated that the process of liquid jet breakup could have 5 different states. The laminar flow state dominated when the Reynolds number (Re) was low, and the prepared microspheres had larger particle sizes. When the Re was high, the turbulent state was dominant and the microspheres had smaller particle sizes. And during the transition state from the laminar flow to the turbulence, the microspheres had a wide particle size distribution. Different process parameters could affect the particle size and distribution of microspheres by changing the Re, surface tension coefficient and viscosity. The microspheres prepared by liquid jet breakup were smooth and round with the drug loading of 35% and the encapsulation efficiency of 88%. In addition, when the polymeric carrier materials were different, the microspheres could have various drug release models such as sustained release with a lag phase, sustained release with no lag phase, pulsed release and so on, which could be applied widespread in the future.

Combined Poly(Lactide-Co-Glycolide) Microspheres Containing Diphtheria Toxoid for a Single-shot Immunization

To develop a single-shot vaccine containing diphtheria toxoid (DT) with a sufficient immune response, poly(lactide-co-glycolide) (PLGA) microspheres were prepared by water-in-oil-in-water double emulsification and solvent extraction techniques using low or high-molecular-weight PLGA (LMW-MS or HMW-MS). Stearic acid (SA) was introduced to HMW-MS (HMW/SA-MS) as a release modulator. Mean particle sizes (dvs, μm) varied between the prepared microspheres, with LMW-MS, HMW-MS, and HMW/SA-MS having the sizes of 29.83, 110.59, and 69.5 μm, respectively; however, the protein entrapment and loading efficiency did not vary, with values of 15.2-16.8 μg/mg and 61-75%, respectively. LMW-MS showed slower initial release (~ 2 weeks) but faster and higher release of antigen during weeks 3~7 than did HMW-MS. HMW/SA-MS showed rapid initial release followed by a continuous release over an extended period of time (~ 12 weeks). Mixed PLGA microspheres (MIX-MS), a combination of HMW/SA-MS and LMW-MS (1:1), demonstrated a sufficient initial antigen release and a subsequent boost release in a pulsatile manner. Serum antibody levels were measured by ELISA after DT immunization of Balb/c mice, and showed a greater response to MIX-MS than to alum-adsorbed DT (control). A lethal toxin challenge test with MIX-MS (a DT dose of 18 Lf) using Balb/c mice revealed complete protection, indicating a good candidate delivery system for a single-shot immunization.

Nanoparticle-Encapsulated Curcumin Inhibits Diabetic Neuropathic Pain Involving the P2Y12 Receptor in the Dorsal Root Ganglia

Diabetic peripheral neuropathy results in diabetic neuropathic pain (DNP). Satellite glial cells (SGCs) enwrap the neuronal soma in the dorsal root ganglia (DRG). The purinergic 2 (P2) Y12 receptor is expressed on SGCs in the DRG. SGC activation plays an important role in the pathogenesis of DNP. Curcumin has anti-inflammatory and antioxidant properties. Because curcumin has poor metabolic stability in vivo and low bioavailability, nanoparticle-encapsulated curcumin was used to improve its targeting and bioavailability. In the present study, our aim was to investigate the effects of nanoparticle-encapsulated curcumin on DNP mediated by the P2Y12 receptor on SGCs in the rat DRG. Diabetic peripheral neuropathy increased the expression levels of the P2Y12 receptor on SGCs in the DRG and enhanced mechanical and thermal hyperalgesia in rats with diabetes mellitus (DM). Up-regulation of the P2Y12 receptor in SGCs in the DRG increased the production of pro-inflammatory cytokines. Up-regulation of interleukin-1β (IL-1β) and connexin43 (Cx43) resulted in mechanical and thermal hyperalgesia in rats with DM. The nanoparticle-encapsulated curcumin decreased up-regulated IL-1β and Cx43 expression and reduced levels of phosphorylated-Akt (p-Akt) in the DRG of rats with DM. The up-regulation of P2Y12 on SGCs and the up-regulation of the IL-1β and Cx43 in the DRG indicated the activation of SGCs in the DRG. The nano-curcumin treatment inhibited the activation of SGCs accompanied by its anti-inflammatory effect to decrease the up-regulated CGRP expression in the DRG neurons. Therefore, the nanoparticle-encapsulated curcumin treatment decreased the up-regulation of the P2Y12 receptor on SGCs in the DRG and decreased mechanical and thermal hyperalgesia in rats with DM.

Effects of nanoparticle-encapsulated curcumin on HIV-gp120-associated neuropathic pain induced by the P2X3 receptor in dorsal root ganglia

HIV-1 envelope glycoprotein (Glycoprotein 120, gp120) can directly stimulate primary sensory afferent neurons and cause chronic neuropathic pain. The P2X₃ receptor in the dorsal root ganglia (DRG) is associated with the transmission of neuropathic pain. Curcumin isolated from the herb Curcuma rhizome has anti-inflammatory and anti-tumor effects. The water solubility, targeting and bioavailability of curcumin can be improved by nanoparticle encapsulation. In this study, we sought to explore the effects of nanoparticle-encapsulated curcumin (nano curcumin) on HIV-gp120-induced neuropathic pain mediated by the P2X₃ receptor in DRG neurons. The results showed that mechanical and thermal hyperalgesia in rats treated with gp120 were increased compared to those in the control group. The expression levels of P2X₃ mRNA and protein in rats treated with gp120 were higher than those in the control group. Nano curcumin treatment decreased mechanical hyperalgesia and thermal hyperalgesia and upregulated the expression levels of P2X₃ mRNA and protein in rats treated with gp120. Nano curcumin treatment also reduced the ERK1/2 phosphorylation levels in gp120-treated rat DRG. In addition, P2X₃ agonist α,β-methylene ATP (α,β-meATP)-induced currents in DRG neurons cultured with gp120 significantly decreased after co-treatment with nano curcumin. Therefore, nano curcumin treatment may inhibit P2X₃ activation, decrease the sensitizing DRG primary afferents and relieve mechanical hyperalgesia and thermal hyperalgesia in gp120-treated rats.

Ultradeformable liposome loaded with zinc phthalocyanine and [Ru(NH.NHq)(tpy)NO]3+ for photodynamic therapy by topical application

Ultradeformable liposomes (UDLs) as a drug delivery system (DDS), prepared from the unsaturated phospholipid, dioleylphosphocholine (DOPC), and containing the non-ionic surfactant Tween 20 as edge activator, have been explored as topical vehicles for zinc phthalocyanine (ZnPc) and the nitrosyl ruthenium complex [Ru(NH.NHq)(tpy)NO]³⁺ (RuNO) as a photosensitizers for co-generation of ¹O₂ and NO as reactive species, respectively. However, in order to ensure that ZnPc was present in the UDLs in its monomeric form - essential for maximal ZnPc photophysical properties - it was necessary to replace 40wt% of the DOPC with the saturated phospholipid, dimyristoylphosphocholine (DMPC). The resultant ZnPc and complex [Ru(NH.NHq)(tpy)NO]³⁺ containing UDLs were stable for at least a month when stored at 4°C, six times more elastic/deformable than conventional liposome (c-Ls), i.e. liposome prepared using the same weight ratio of lipids but in the absence of Tween 20, and to significantly enhance the in vitro permeation of ZnPc across fresh pig ear skin. The UDLs DDS incorporating ZnPc and [Ru(NH.NHq)(tpy)NO]³⁺ were toxic (by the MTT assay) towards B16-F10 melanoma cells when irradiated with visible light at 670nm, the maximum absorption of ZnPc, and at a dose of 3.18J/cm², but not when applied in the absence of light as expected. Based on these results it is proposed that the novel topical UDLs formulation developed is a suitable delivery vehicle for photodynamic therapy.

PLGA particle production for water-soluble drug encapsulation: degradation and release behaviour

Particles for subcutaneous depot use encapsulating a model water-soluble drug have been produced from poly(lactic-glycolic acid) (PLGA) using a membrane emulsification-solvent evaporation technique. The release behaviour, mainly the change in size and inner morphology are reported. During release, the particles initially swelled in size, then reduced. A diffusion based model, taking in to account the change in particle size, is presented. Surface erosion is evident from the particle size and image evidence, and the diffusion model provides a fit to the data even during the surface erosion period, suggesting that the model drug diffuses before the particle degrades.

Effects of formulation factors on encapsulation efficiency and release behaviourin vitroof huperzine A-PLGA microspheres

To develop a long-acting injectable huperzine A-PLGA microsphere for the chronic therapy of Alzheimer's disease, the microsphere was prepared by using an o/w emulsion solvent extraction evaporation method based on a series of formulation design of the emulsion. The dialysis method was used for release analysis. The encapsulation efficiency and release amount of the microspheres were determined by a UV/VIS spectrophotometer. The morphology of the microspheres was observed by scanning electron microscopy. The distribution of the drug within microspheres was observed by a confocal laser scanning microscope. The results indicated that the PLGA 15,000 microspheres possessed a smooth and round appearance with average particle size of 50 microm or so. The encapsulation percentages of microspheres prepared from PLGA 15,000, 20,000 and 30,000 were 62.75%, 27.52% and 16.63%, respectively. The drug release percentage during the first day decreased from 22.52% of PLGA 30,000 microspheres to 3.97% of PLGA 15,000 microspheres, the complete release could be prolonged to 3 weeks. The initial burst release of microspheres with higher molecular weight PLGA could be explained by the inhomogeneous distribution of drug within microspheres. The encapsulation efficiency of the microspheres improved as the polymer concentration increased in the oil phase and PVA concentration decreased in the aqueous phase. The burst release could be controlled by reducing the polymer concentration. Evaporation temperature had a large effect on the drug release profiles. It had better be controlled under 30 degrees C. Within a certain range of particle size, encapsulation efficiency decreased and drug release rate increased with the reducing of the particle size.

Enhancing drug incorporation into tetracycline-loaded chitosan microspheres for periodontal therapy

PURPOSE

To identify optimal formulation parameters for enhancing the incorporation of tetracycline hydrochloride into chitosan microspheres for periodontal therapy.

METHODS

Tetracycline-loaded chitosan microspheres were prepared by ionotropic gelation. Various formulation parameters (salt form of drug, aqueous phase pH, anion structure, inorganic salts and electrolytes, preparation method) were investigated for their influence on drug incorporation efficiency. Microspheres were assessed in terms of drug entrapment and content, microsphere recovery, particle size and morphology.

RESULTS

Although drug incorporation efficiency was increased marginally, the use of a dihydrate form of the drug was not considered feasible due to the lowered microsphere recovery and higher costs. A decrease in the aqueous pH from 9 to 6 enhanced drug incorporation efficiency without an adverse effect on microsphere morphology. The use of inorganic salts/electrolytes and other approaches of microsphere preparation did not significantly enhance drug incorporation efficiency and these approaches also adversely affected microsphere morphology. The ionotropic preparation method in terms of the drug loading technique significantly affected drug incorporation efficiencies.

CONCLUSIONS

This study has shown that formulation variables can be exploited in order to enhance the incorporation of a water soluble drug into chitosan microspheres using the ionotropic gelation technique. Based on a comparison of all results obtained with the different approaches, the modification of the aqueous phase to pH 6 was identified as the most feasible approach.

Effect of poly(lactide-co-glycolide) molecular weight on the release of dexamethasone sodium phosphate from microparticles

The objective of this study was to investigate the effect of poly(lactide-co-glycolide) (PLGA) molecular weight (Resomer RG 502H, RG 503H, and RG 504H) on the release behavior of dexamethasone sodium phosphate-loaded microparticles. The microparticles were prepared by three modifications of the solvent evaporation method (O/W-cosolvent, O/W-dispersion, and W/O/W-methods). The encapsulation efficiency of microparticles prepared by the cosolvent- and W/O/W-methods increased from approximately 50% to >90% upon addition of NaCl to the external aqueous phase, while the dispersion method resulted in lower encapsulation efficiencies. The release of dexamethasone sodium phosphate from PLGA microparticles (>50 microm) was biphasic. The initial burst release correlated well with the porosity of the microparticles, both of which increased with increasing polymer molecular weight (RG 504H > 503H > 502H). The burst was also dependent on the method of preparation and was in the order of dispersion method > WOW method > consolvent method. In contrast to the higher molecular weight PLGA microparticles, the release from RG 502H microparticles prepared by cosolvent method was not affected by volume of organic solvent (1.5-3.0 ml) and drug loading (4-13%). An initial burst of approximately 10% followed by a 5-week sustained release phase was obtained. Microparticles with a size <50 microm released in a triphasic manner; an initial burst was followed by a slow release phase and then by a second burst.

Effect of surfactant HLB and different formulation variables on the properties of poly-D,L-lactide microspheres of naltrexone prepared by double emulsion technique

The aim of this work was to investigate the role of HLB of emulsifier as well as volume of the internal aqueous phase (W(1)) and presence of salt in the external aqueous phase (W(2)) on the morphology, size and encapsulation efficiency of poly(D,L-lactide) microspheres containing naltrexone HCl. PLA microparticles containing naltrexone HCl, an effective opiate antagonist, were prepared by a water-in-oil-in-water emulsification-solvent evaporation procedure. One of the five different emulsifiers: span 80, span 20, tween 85, tween 80 and tween 20, with HLB values from 4-17 were added to W(1). Presence of emulsifier in W(1) resulted in smaller particles with a more dense and uniform internal structure. Incorporation of span 80 (HLB 4.3, suitable for W/O emulsions) yield the highest encapsulation efficiency. Increasing the HLB value to 8 or 11 (span 20 or tween 85) decreased the efficiency of naltrexone HCl-loading. HLB values higher than 15 (tween 80 or tween 20) increased encapsulation efficiency unexpectedly, which could be attributed to migration of these emulsifiers to the O/W(2) interface and modifying the surface properties of microparticles. Increasing the internal water phase volume from 0.2-1.8 ml resulted in larger particle size with poor encapsulation efficiency. Addition of 10% w/w NaCl to the W(2) changed the surface morphology of microspheres from a porous form to a smooth surface. It was shown that, by selecting the appropriate HLB value of emulsifier in W(1), addition of salt to W(2) and controlling the volume of W(1), one can control the encapsulation efficiency, size and morphology of microspheres.

Effects of formulation factors on encapsulation efficiency and release behaviourin vitroof huperzine A-PLGA microspheres

To develop a long-acting injectable huperzine A-PLGA microsphere for the chronic therapy of Alzheimer's disease, the microsphere was prepared by using o/w emulsion solvent extraction evaporation method based on a series of formulation design of the emulsion. The dialysis method was used for release analysis. The encapsulation efficiency and release amount of the microspheres were determined by UV/VIS spectrophotometry. The morphology of the microspheres was observed by scanning electron microscopy. The distribution of the drug within microspheres was observed by a confocal laser scanning microscope. The results indicated that the PLGA 15 000 microspheres possessed a smooth and round appearance with average particle size of 50 microm or so. The encapsulation percentages of microspheres prepared from PLGA 15 000, 20 000 and 30 000 were 62.75, 27.52 and 16.63%, respectively. The drug release percentage during the first day decreased from 22.52% of PLGA 30 000 microspheres to 3.97% of PLGA 15 000 microspheres, the complete release could be prolonged to 3 weeks. The initial burst release of microspheres with higher molecular weight PLGA could be explained by the inhomogeneous distribution of drug within microspheres. The encapsulation efficiency of the microspheres improved as the polymer concentration increase in oil phase and PVA concentration decreased in aqueous phase. The burst release could be controlled by reducing the polymer concentration. Evaporation temperature had a large effect on the drug release profiles. It had better be controlled under 30 degrees C. Within a certain range of particle size, encapsulation efficiency decreased and drug release rate increased with the reducing of the particle size.

New drug salt formation in biodegradable microspheres

PURPOSE

To investigate the effects of inorganic salts in the external phase of an oil-in-water (O/W) emulsion method during microsphere preparation.

METHODS

An O/W emulsion method was used to prepare poly(D,L-lactic acid) microspheres containing quinidine sulfate. Different inorganic salts were used in the external phase during microsphere preparation. Microsphere drug loading was determined by UV and the drug salt anions inside the microspheres were determined by ion chromatography.

RESULTS

New drug salts were formed during encapsulation in the microspheres when salts with non-common anions to the drug salt were used. Drug loading increased when NaClO4 or NaSCN were used. The fraction of drug as the new salt in microspheres increased non-linearly with the salt concentration in the external phase, however, the fraction of drug as the new encapsulated salt was linearly related to drug loading. Drug loading decreased and new salt fraction increased with increasing organic solvent volume or with decreasing cosolvent polarity.

CONCLUSIONS

Introducing salts containing non-common anions to the drug salt employed in the external phase of O/W emulsion microsphere method leads to new salt formation. The extent of new drug salt formation is affected by salt levels added, cosolvent type and polymer concentration.

Development of new reverse micellar microencapsulation technique to load water-soluble drug into PLGA microspheres

The objective of this study was to develop a new reverse micelle-based microencapsulation technique to load tetracycline hydrochloride into PLGA microspheres. To do so, a reverse micellar system was formulated to dissolve tetracycline hydrochloride and water in ethyl formate with the aid of cetyltrimethylammonium bromide. The resultant micellar solution was used to dissolve 0.3 to 0.75 g of PLGA, and microspheres were prepared following a modified solvent quenching technique. As a control experiment, the drug was encapsulated into PLGA microspheres via a conventional methylene chloride-based emulsion procedure. The microspheres were then characterized with regard to drug loading efficiency, their size distribution and morphology. The reverse micellar procedure led to the formation of free-flowing, spherical microspheres with the size mode of 88 microm. When PLGA microspheres were prepared following the conventional methylene chloride-based procedure, most of tetracycline hydrochloride leached to the aqueous external phase: A maximal loading efficiency observed our experimental conditions was below 5%. Their surfaces had numerous pores, while their internal architecture was honey-combed. In sharp contrast, the new reverse micellar encapsulation technique permitted the attainment of a maximal loading efficiency of 63.19 +/- 0.64%. Also, the microspheres had smooth and pore-free surfaces, and hollow cavities were absent from their internal matrices. The results of this study demonstrated that PLGA microspheres could be successfully prepared following the new reverse micellar encapsulation technique.

Solubility of guaifenesin in the presence of common pharmaceutical additives

The aqueous solubility of guaifenesin, a highly water-soluble drug, in the presence of salts, sugars, and cosolvents was determined at 25 degrees C and 40 degrees C. The solubility of drug at both temperatures was reduced with increasing concentrations of salts and sugars. The extent of reduction in drug solubility was dependent on the type of salts and sugars used. The salting-out coefficient of additives was calculated by plotting log-linear solubility profiles of the drug against the concentrations of the additives. The solubility of guaifenesin, a neutral compound, was found to be higher at lower pH values, which could be due to hydrogen-bonding effects. At 25 degrees C, glycerin, PEG 300, and propylene glycol increased the solubility of drug at low solvent concentrations while the solubility was reduced at high concentrations. At 40 degrees C, the solubility of drug was reduced at all concentrations of cosolvents. The thermodynamic events accompanying the solubility process were discussed to explain the solubility phenomena observed in the presence of additives. The reduced aqueous solubility of guaifenesin in the presence of additives greatly improved the entrapment of drug into controlled-release wax microspheres.

Water absorbency by wool fibers: Hofmeister effect

Wool is a complex material, composed of cuticle and epicuticle cells, surrounded by a cell membrane complex. Wool fibers absorb moisture from air, and, once immersed in water, they take up considerable amounts of liquid. The water absorbency parameter can be determined from weight gain, according to a standard method, and used to quantify this phenomenon. In this paper we report a study on the water absorbency (or retention) of untreated wool fibers in the presence of aqueous 1 M salt solutions at 29 degrees C and a relative humidity of either 33% or 56%. The effect of anions was determined by selecting a wide range of different sodium salts, while the effect of cations was checked through some chlorides and nitrates. Our results show a significant specific ion and ion pair "Hofmeister" effects, that change the amount of water absorbed by the fibers. To understand this phenomenon, the water absorbency parameter (A(w)) is compared to different physicochemical parameters such as the lyotropic number, free energy of hydration of ions, molar surface tension increment, polarizability, refractive index increment, and molar refractivity. The data indicate that this Hofmeister phenomenon is controlled by dispersion forces that depend on the polarizability of ionic species, their adsorption frequencies, the solvent, and the substrate. These dispersion forces dominate the behavior in concentrated solutions. They are in accord with new developing theories of solutions and molecular interactions in colloidal systems that account for Hofmeister effects.