Encapsulation Of Poly Research Articles

Maintaining bioactivity of NGF for controlled release from PLGA using PEG

The goal of this work was to investigate methods to retain bioactivity of nerve growth factor (NGF) after encapsulation in poly(lactic-co-glycolic acid) (PLGA) discs for controlled release. Poly(ethylene glycol) (PEG) was chosen as a porogen not only to control the release rate of NGF but also because it has been used to help maintain bioactivity of molecules in organic solvents. NGF and PEG were encapsulated in PLGA via standard dissolution-evaporation techniques with methylene chloride as the solvent. Morita et al. (Pharm Res 2000; 17:1367-1373) indicated that colyophilization of PEG and bioactive factors before exposure to organic solvents increased the retention of bioactivity. Therefore, various PEG:NGF mass ratios were colyophilized before encapsulation within PLGA to examine retained activity of NGF. When PEG was not colyophilized before encapsulation, NGF activity was lost during the fabrication process. In contrast, colyophilization of PEG and NGF supported retention of NGF activity during the entire fabrication process. The amount of PEG encapsulated was the dominating factor in the rate of NGF release regardless of the fabrication method. These results demonstrate the usefulness of PEG in both acting as a porogen to modulate release and aiding in the retention of activity of NGF. This process may be extended to other methods to enhance activity of growth factors after exposure to organic solvents.

Preparation of Poly (n-butyl acrylates) Encapsulated Carbon Black via Ultrasonic Irradiation Initiating Emulsion Polymerization

The encapsulation of poly (n-butyl acrylates) (PBA) onto carbon black (CB) surface via ultrasonic irradiation initiating emulsion polymerization was investigated. The results showed that the route performed at ambient temperature can efficiently prepare PBA encapsulated CB as proved by the aggregation of PBA encapsulated CB in the precipitator of PBA. The surface properties of CB coated with PBA were analyzed by FT-IR and XPS. The content of PBA encapsulated on the CB surface reaches 11.87% determined by TGA. Compared with the conventional chemical modification of CB, it was found that the particle size of CB obtained by the present approach can be controlled, and dynamic light scattering results quantified that CB particles with narrower size distribution and smaller size were obtained. The PBA encapsulated CB can be dispersed uniformly in the polymer matrix.

Chondrogenic Differentiation of Human Embryonic Stem Cell–Derived Cells in Arginine-Glycine-Aspartate–Modified Hydrogels

Human embryonic stem cells (hESCs) have the potential to self-renew and generate multiple cell types, producing critical building blocks for tissue engineering and regenerative medicine applications. Here, we describe the efficient derivation and chondrogenic differentiation of mesenchymal-like cells from hESCs. These cells exhibit mesenchymal stem cell (MSC) surface markers, including CD29, CD44, CD105, and platelet-derived growth factor receptor-alpha. Under appropriate growth conditions, the hESC-derived cells proliferated without phenotypic changes and maintained MSC surface markers. The chondrogenic capacity of the cells was studied in pellet culture and after encapsulation in poly(ethylene glycol)-diacrylate (PEGDA) hydrogels with exogenous extracellular proteins or arginineglycine- aspartate (RGD)-modified PEGDA hydrogels. The hESC-derived cells exhibited growth factor- dependent matrix production in pellet culture but did not produce tissue characteristic of cartilage morphology. In PEGDA hydrogels containing exogenous hyaluronic acid or type I collagen, no significant cell growth or matrix production was observed. In contrast, when these cells were encapsulated in RGDmodified poly(ethylene glycol)hydrogels, neocartilage with basophilic extracellular matrix deposition was observed within 3 weeks of culture, producing cartilage-specific gene up-regulation and extracellular matrix production. Our results indicate that precursor cells characteristic of a MSC population can be cultured from differentiating hESCs through embryoid bodies, thus holding great promise for a potentially unlimited source of cells for cartilage tissue engineering.

Effect of cyclodextrins on α-chymotrypsin stability and loading in PLGA microspheres upon S/O/W encapsulation

The potential of cyclodextrins to stabilize α-chymotrypsin upon encapsulation in Poly(lactic-co-glycolic) acid (PLGA) microspheres using a solid-in-oil-in-water (s/o/w) technique was investigated. Two cyclodextrins, hydroxyl-propyl-β-cyclodextrin (HPβCD) and methyl-β-cyclodextrin (MβCD), one insoluble and the other soluble in methylene chloride, were used. The results demonstrate that HPβCD failed to stabilize α-chymotrypsin upon encapsulation. Specifically, 19% of the protein was aggregated and the specific activity of the enzyme was reduced to ca. 50% of that prior to encapsulation. In contrast, MβCD significantly decreased the formation of aggregates to 3% and the retained specific activity of the enzyme was approximately 90%. The co-lyophilization of α-chymotrypsin with MβCD prior to encapsulation was a requisite to preserve the protein stability in microspheres. Furthermore, MβCD prevented the loss of protein during the preparation of microspheres and the encapsulation efficiency was improved to 90%. Release experiments showed the use of MβCD modified the release profile: the burst release decreased from 54% (in the absence of the excipient) to 36%. The results suggest that MβCD might be a suitable excipient to improve protein stability in s/o/w encapsulation procedures.

Formation of Nanoparticles of a Hydrophilic Drug Using Supercritical Carbon Dioxide and Microencapsulation for Sustained Release

The objective of this work was to develop sustained release formulation for hydrophilic drugs with minimal burst effects. For this purpose, nanoparticles of a hydrophilic drug were produced using supercritical CO2, which were then encapsulated into polymer microparticles using an anhydrous method, followed by studying their sustained in-vitro drug release. A hydrophilic drug, dexamethasone phosphate, was dissolved in methanol and injected in supercritical CO2 with ultrasonic field for enhanced molecular mixing (SAS-EM technique). Supercritical CO2 rapidly extracts methanol leading to instantaneous precipitation of drug nanoparticles of 150 nm. These nanoparticles, on encapsulation in poly(lactideco-glycolide) polymer using anhydrous s/o/o/o technique, resulted in the well-dispersed encapsulation of drug nanoparticles in polymer microspheres of ~70 µm. Their invitro drug release showed sustained release of dexamethasone phosphate over a period of 700 hours with almost no initial burst release.

Effect of the Covalent Modification with Poly(ethylene glycol) on α-Chymotrypsin Stability upon Encapsulation in Poly(lactic-co-glycolic) Microspheres

The effectiveness of the covalent modification of α-chymotrypsin with methoxy poly(ethylene glycol) (PEG) to afford its stabilization during encapsulation in poly(lactic-co-glycolic) acid (PLGA) microspheres by a solid-in-oil-in-water method was investigated. α-Chymotrypsin was chemically modified with PEG (Mw = 5000) using molar ratios of PEG-to-chymotrypsin ranging from 0.4 to 96. Various conjugates were obtained and the amount of PEG modification was determined by capillary electrophoresis. In this investigation, only those conjugates with PEG/chymotrypsin molar ratios between approximately 1 and 8 were considered because higher levels of modification caused protein instability even before encapsulation. The stability and functionality of the chymotrypsin formulations were investigated before encapsulation by measuring enzyme kinetics, thermal stability, and tertiary structure intactness, and after the initial lyophilization process by determining the secondary structure content. These stability parameters were related to select ones after encapsulation in PLGA microspheres (specifically, the amount of insoluble aggregates, residual enzyme activity, and magnitude of protein structural perturbations). The results show that the more stable the protein conformation before encapsulation was, the higher was the retention of the specific activity after encapsulation. In contrast, no relationship was found between the protein stability before encapsulation and the magnitude of encapsulation-induced protein aggregation. Even the lowest level of modification (PEG-to-chymotrypsin molar ratio of 0.7) drastically reduced the amount of insoluble aggregates from 18% for the nonmodified protein to 4%. The results demonstrate that PEG modification was able to largely prevent chymotrypsin aggregation and activity loss upon solid-in-oil-in-water encapsulation in PLGA microspheres. It is demonstrated that it is essential to optimize the degree of protein modification to ascertain protein stability upon encapsulation. © 2004 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 94:327–340, 2005

Enhancement of Topical Delivery from Biodegradable Nanoparticles

To determine whether and how encapsulation of lipophilic compounds in polymeric nanoparticles is able to improve topical delivery to the skin. The penetration of octyl methoxycinnamate (OMC; Parsol MCX), a highly lipophilic sunscreen, into and across porcine ear skin in vitro was investigated, subsequent to encapsulation in poly(epsilon-caprolactone) nanoparticles, using tape-stripping. Confocal laser scanning microscopy (CLSM) was used to visualize the distribution of nanoparticles, charged with Nile red (NR), a lipophilic and fluorescent dye. Quantification of OMC in the skin using tape-stripping demonstrated that nanoparticulate encapsulation produced a 3.4-fold increase in the level of OMC within the stratum corneum (SC), although the use of nanoparticles did not appear to increase skin permeation (it was not possible to detect OMC in the receiver compartment after 6 h). The confocal images showed that the fluorescence profile observed in the skin after application of NR-containing nanoparticles was clearly different from that seen following application of NR dissolved in propylene glycol. Two hours postapplication of NR-containing nanoparticles, fluorescence was perceptible at greater depths (up to 60 microm) within the skin. i) Nanoparticulate encapsulation of OMC increased its "availability" with the SC. ii) The altered distribution of NR when delivered via nanoparticles was due, at least in part, to its altered thermodynamic activity (relative to that in propylene glycol) and, as a result, an increase in its partition coefficient into the SC.

Stabilization of α-chymotrypsin at the CH 2Cl 2/water interface and upon water-in-oil-in-water encapsulation in PLGA microspheres

Protein inactivation and aggregation are serious drawbacks in the encapsulation of proteins in bioerodible polymers by water-in-oil-in-water (w/o/w) encapsulation. The model protein α-chymotrypsin was employed to investigate whether its stabilization towards the major stress factors in the w/o/w encapsulation procedure would allow for the encapsulation and release of non-aggregated and active protein. Due to the formation of amorphous aggregates α-chymotrypsin is an excellent sensor to probe unfolding events. Furthermore, its enzymatic activity is highly sensitive towards the presence of organic solvents. α-Chymotrypsin in aqueous solution showed substantial aggregation and activity loss when it was homogenized with CH 2Cl 2 due to adsorption to the interface. Its w/o/w encapsulation in poly(lactic-co-glycolic)acid (PLGA) microspheres caused formation of 35% non-covalent aggregates and reduced the specific activity by 14%. Screening for efficient excipients revealed that co-dissolving the protein with maltose and polyethylene glycol (PEG, M w 5000) in the first aqueous phase reduced interface-induced protein aggregation and inactivation. Employing these excipients during encapsulation led to a reduction in α-chymotrypsin inactivation (10%) and aggregation (12%). Optimizing the effect of PEG by also dissolving the excipient in the organic phase prior to encapsulation further decreased the amount of non-covalent aggregates to 7% and loss in activity to 5%. The data obtained demonstrate that the w/o emulsification step is the main stress-factor in the w/o/w encapsulation procedure but subsequent encapsulation steps also cause some protein aggregation.

Synthesis and optical properties of cds semiconductor nanocrystallites encapsulated in a poly (ethylene oxide) matrix

In this paper, CdS nanocrystallites are prepared by encapsulation in poly (ethylene oxide) polymer (PEO). It is found that PEO could provide a confined environment for particle neucleation and crystallite growth of CdS nanocrystallites. The absorption onset of the CdS nanocrystallites shifts to shorter wavelength with decreasing the amounts of Cd 2+ in PEO, indicating the particle size could be controlled under the change of the Cd 2+/PEO relative concentration. Their corresponding photoluminescence peaks are all located at about 630 nm, which origins from the sulfur vacancies, but the intensities increase with increasing the molar ratio of Cd 2+/PEO. When CdS nanocrystallites are modified by excessive S 2−, the emissions from band gap are observed and the peak positions show coherent shift with the absorption onsets. Such a blue-shift of the emissions could be explained by size quantization effects.

Poly(ethylene glycol) as stabilizer and emulsifying agent: a novel stabilization approach preventing aggregation and inactivation of proteins upon encapsulation in bioerodible polyester microspheres

Protein aggregation and inactivation are major problems associated with the encapsulation of pharmaceutical proteins in biodegradable microspheres. The objectives of this study were to identify the causes of aggregation and inactivation of two model enzymes upon solid-in-oil-in-water (s/o/w) encapsulation in poly(lactic-co-glycolic) acid (PLGA) microspheres in order to rationally develop approaches assuring their stability. S/o/w encapsulation of γ-chymotrypsin in PLGA microspheres caused aggregation of ca. 30% and halved its specific activity. Co-lyophilization with poly(ethylene glycol) (PEG) substantially reduced the loss in enzyme activity but 8% of the protein still aggregated during encapsulation. Model studies performed under conditions relevant to the encapsulation procedure allowed pinpointing the cause of γ-chymotrypsin instability, which was mainly the formation of the oil-in-water emulsion. To prevent aggregation in this encapsulation step, the most commonly used emulsifying agent polyvinyl alcohol (PVA) was replaced by PEG because it is known to reduce protein aggregation at interfaces. The use of PEG as the emulsifying agent in the aqueous and organic phase prevented γ-chymotrypsin inactivation and aggregation during encapsulation. The stabilization approach also worked for the model protein horseradish peroxidase and thus is of a general nature.

Feeding liquid, non-ionic surfactant and cyclodextrin affect the properties of insulin-loaded poly(lactide-co-glycolide) microspheres prepared by spray-drying

The potential of spray-drying technique for the encapsulation in poly(lactide-co-glycolide) (PLGA) microspheres of bovine insulin, a poorly stable peptide, has been investigated. Insulin-loaded microspheres were prepared by spray-drying different feeding liquids containing insulin and PLGA, that is a S/O dispersion, a W/O emulsion or an acetic acid solution. In the case of the emulsion, insulin was also co-encapsulated with either non-ionic surfactants such as polysorbate 20 and poloxamer 188, or complexing agents such as HPβCD. In the microspheres prepared from the acetic acid solution of insulin and PLGA, HPβCD was tested. Microspheres containing surfactants were aggregated, whereas good quality particles displaying a mean diameter in the range 12.1–27.9 μm were produced in the other cases. Insulin was efficiently loaded inside microspheres except for S/O formulation (only 22% of total insulin content was entrapped). The impact of the microencapsulation process on insulin chemical and conformational stability was assessed by HPLC, circular dichroism and turbidimetry studies. Under the adopted manufacture conditions, insulin was encapsulated in the native state and its chemical and conformational stability was preserved along the fabrication process. The formulations containing only insulin displayed low burst effects (6–11%), whereas the addition of surfactants resulted in much higher burst effects (49–54%) and faster release rate. The co-encapsulation of HPβCD slowed down the overall release rate and, in the case of microspheres prepared from the emulsion, allowed a constant insulin release up to 45 days. The study of insulin stability along the release phase showed that insulin was released in the intact form and un-released insulin was stable inside all the microsphere formulations. We conclude that insulin can be effectively encapsulated in PLGA microspheres by the spray-drying technique. Additives with complexing properties such as HPβCD have demonstrated a potential in optimizing the release rate of insulin when used in microspheres prepared from W/O emulsions.

Poly(acrylonitrile) encapsulated graphite as anode materials for lithium ion batteries

Novel surface modification approach for graphite anode of lithium ion batteries was developed in this study. Poly(acrylonitrile) was in situ encapsulated on the surface of natural graphite (N-graphite) particles via radiation-initiated polymerization. The graphite obtained shows a large improvement in electrochemical performance such as initial Coulombic efficiency and cycleability compared with the original N-graphite. The structural stability of graphite surface is enhanced due to the fact that encapsulated poly(acrylonitrile) can depress the co-intercalation of solvated lithium ion.

Co-lyophilization of bovine serum albumin (BSA) with poly(ethylene glycol) improves efficiency of BSA encapsulation and stability in polyester microspheres by a solid-in-oil-in-oil technique

The effect of the co-lyophilization of bovine serum albumin (BSA) with poly(ethylene glycol) (PEG) on the BSA encapsulation efficiency and formation of soluble BSA aggregates upon solid-in-oil-in-oil (s/o/o) encapsulation in poly(lactic-co-glycolic) acid (PLGA) microspheres was investigated. Suspension of the lyophilized BSA-PEG formulations in methylene chloride produced small protein powder particles of less than 1 μm diam. and this afforded high encapsulation efficiencies of typically ≥90% ameliorating one of the problems in s/o/o encapsulation. Formation of soluble BSA aggregates upon s/o/o encapsulation followed by 24 h in vitro release was between 5% and 22%, much lower than values of 59% reported for BSA without stabilizing excipients. Therefore, PEG also afforded BSA stabilization during s/o/o encapsulation. Sustained release occurred over ca. 2 months and was complete.

Extraction of metal cations by polyterephthalamide microcapsules containing a poly(acrylic acid) gel

Polyterephthalamide microcapsules containing a poly(acrylic acid) gel as a macromolecular ligand (PAA-CAPS) were prepared using an original two step polymerization process in a water-in-oil inverse emulsion system. A polyamide microcapsule containing acrylic acid, initiator and cross-linking agent, is formed by interfacial polycondensation of terephthaloyl dichloride with hexamethylenediamine. In situ radical polymerization of the microcapsule core acrylic acid is initiated to obtain encapsulated poly(acrylic acid) gel. Reference polyamide microcapsules, i.e. without ligand (CAPS), were also synthesized. The mean diameter of synthesized microcapsules was 210 #181;m, and the microcapsule wall thickness was evaluated by SEM and TEM observations of microcapsule cross-section cuts. The microcapsule water content was determined by thermogravimetric experiments. The extractabilities of Cu(II), Ni(II), Co(II) and Zn(II) into PAA-CAPS were examined. The stripping of the various cations can be promoted in diluted hydrochloric acid solutions.

Laminated TaS2/Polymer Nanocomposites through Encapsulative Precipitation of Exfoliated Layers

Several TaS2/polymer nanocomposites prepared through the encapsulative precipitation method are described. Namely, the encapsulation of poly(ethylene oxide) (PEO), polyethylene imine (PEI), and poly(vinylpyrrolidinone) (PVP) into TaS2 was examined in detail, and the nanocomposites were characterized by a wide variety of techniques. The nanocomposites disperse in water and are easily cast into free-standing films. The flexible metallic TaS2/polymer nanocomposite films display bulk superconductivity. In addition, in this work the exfoliation properties of LixTaS2 were systematically explored, and it was found that material prepared from controlled lithiation with 0.2 equiv of LiBH4 exfoliates well in water and has high affinity for various polymers. The likely conformation of PEO molecules sandwiched between the TaS2 slabs was explored with analysis of the X-ray diffraction patterns of a highly oriented Lix(PEO)yTaS2 nanocomposite films. The one-dimensional electron density maps, obtained for Lix(PEO)yTaS2,...

Study of the mechanism of insulin encapsulation in poly(isobutylcyanoacrylate) nanocapsules obtained by interfacial polymerization.

In previous studies, insulin-loaded poly(alkylcyanoacrylate) nanocapsules were found to reduce the blood glucose level after oral administration to diabetic rats and dogs. The reduction of the glycemia induced by the nanocapsules was the same regardless of the insulin doses administered, but the effect appeared only after a delay of a few days. The purpose of this study was to investigate the mechanism of insulin encapsulation and the type of interactions that may exist between the polymer forming the nanocapsule wall and the insulin. The results of this study showed, based on the interfacial polymerization of isobutylcyanoacrylate, that the insulin molecule is not chemically modified during the nanoencapsulation process. In addition, no interaction between the poly(isobutylcyanoacrylate) and the insulin could be observed. The observed high encapsulation efficiency of intact insulin may be explained by the fact that the ethanol used in the preparation of the nanocapsules is responsible for the initiation of the interfacial polymerization of isobutylcyanoacrylate instead of the insulin. The zeta potential measurements suggest that insulin is located within the core of the nanocapsules. Thus the biological activity of the nanoencapsulated peptide and the high efficiency of insulin encapsulation achieved with this nanoencapsulation process cannot be explained by a specific interaction of the insulin with the polymer forming the nanocapsule's wall. It may be due, however, to the fact that the encapsulated insulin molecule is chemically intact and located within the oily core of the nanocapsules.

Controlled Lipidation and Encapsulation of Peptides as a Useful Approach to Mucosal Immunizations

To generate a useful strategy for mucosal immunization, we have developed an approach of lipidating a multiple Ag peptide (MAP) containing part of the V3 loop from HIV-1 gp120IIIB. In this work, we compare two delivery systems, lipidated MAP in PBS and encapsulation in poly(DL-lactide-co-glycolide) microparticles. Subcutaneous immunization, followed by intragastric administration of MAP peptide entrapped or not entrapped in microparticles, induced mucosal and systemic immune responses at local and distant sites, including mucosal IgA in saliva, vaginal secretions and feces, and IgG in blood. However, lipidated Ag delivered in microparticles induced higher levels of mucosal Abs, particularly of intestinal IgA, and generated CTL responses. In contrast, lipidated MAP delivered by nasal route microparticles was less effective in inducing CTL responses. These results demonstrate the feasibility of using a lipidated multimeric peptide for mucosal immunization to stimulate both systemic and mucosal immune systems, including the genital tract, irrespective of the route or method of delivery and without requiring the use of a carrier or an extraneous adjuvant.

Oral immunization with an anti–idiotypic antibody to the exoglycolipid antigen protects against experimental Chlamydia trachomatis infection

Chlamydia trachomatis is the leading cause worldwide of preventable infectious blindness (trachoma) and sexually transmitted disease, including nongonoccocal urethritis and pelvic inflammatory disease. To date, no effective vaccine against C. trachomatis infection has been identified. A monoclonal anti-idiotypic antibody (anti-Id) to the chlamydial exoglycolipid antigen (GLXA) was tested in a murine model of ocular chlamydial infection for its ability to induce systemic immunity, which reduces microbiologic and clinical disease. The anti-Id to GLXA, delivered either systemically in soluble form or orally after encapsulation in poly(lactide) microspheres, induced significant protective immunity against ocular challenge of mice with a human biovar of C. trachomatis. Protection was associated with induction of anti-GLXA antibody and anti-chlamydial neutralizing antibody.

Free and Liposome-Encapsulated Double-Stranded RNAs as Inducers of Interferon, Interleukin-6, and Cellular Toxicity

Poly(rI:rC) and Ampligen were entrapped in liposomes that were covalently coupled to Protein A, permitting binding to antibodies specific for the major histocompatibility complex-encoded H2K molecule of L929 cells, or to control antibodies. Free and encapsulated polynucleotides were compared for their capacity to stimulate secretion of interferon (IFN) and interleukin-6 (IL-6) and to induce cellular toxicity on L929 cells pretreated with IFN-alpha/beta. Free and encapsulated poly(rI:rC) or Ampligen (poly(rI:rC12-rU] induced similar levels of secretion of IFN over a broad dose range. The activity of the liposome-encapsulated polynucleotides was dependent on its binding to an antibody that permitted cell association and internalization; the same liposomes were inactive in the presence of control antibodies. IL-6 secretion was induced by double-stranded (ds) RNA in a dose-dependent manner, with a significantly greater effect seen for targeted, liposome-encapsulated material. The marked toxicity of targeted poly(rI:rC), as compared to free poly(rI:rC), was confirmed. Encapsulated Ampligen was less toxic than encapsulated Poly(rI:rC).