Feed Weight Ratio Research Articles

Preparation and characterization novel polymer-coated magnetic nanoparticles as carriers for doxorubicin

The poly(lactide-co-glycolide)-coated magnetic nanoparticles (PLGA MNPs) were prepared as carriers of doxorubicin (PLGA-DOX MNPs) through water-in-oil-in-water (W/O/W) emulsification method. The characteristics of PLGA-DOX MNPs were measured by using transmission electron microscopy (TEM) and vibrating-sampling magnetometry (VSM). It was found that the synthesized nanoparticles were spherical in shape with an average size of 100±20 nm, low aggregation and good magnetic responsivity. Meanwhile, the drug content and encapsulation efficiency of nanoparticles can be achieved by varying the feed weight ratios of PLGA and DOX particles. These PLGA-DOX MNPs also demonstrated sustained release of DOX at 37°C in buffer solution. Besides, influence of drug-loaded nanoparticles on in vitro cytotoxicity was determined by MTT assay, while cellular apoptosis was detected by Annexin V-FITC apoptosis detection kit. The results showed that PLGA-DOX MNPs retained significant antitumor activities. Therefore, PLGA-DOX MNPs might be considered a promising drug delivery system for cancer chemotherapy.

Nanoparticle carriers based on copolymers of poly(l-aspartic acid co-l-lactide)-1,2-dipalmitoyl-sn-glycero-3-phosphoethanolamine for drug delivery

A novel poly(l-aspartic) derivative (PAL-DPPE) containing polylactide and 1,2-dipalmitoyl-sn-glycero-3-phosphoethanolamine (DPPE) segments has been successfully synthesized. The chemical structures of the copolymers were confirmed by Fourier-transform infrared spectroscopy (FTIR), NMR (1H NMR, 13C NMR, 31P NMR), and thermogravimetric analysis (TGA). Fluorescence spectroscopy, dynamic light scattering (DLS), and transmission electron microscopy (TEM) confirmed the formation of micelles of the PAL-DPPE copolymers. In order to estimate the feasibility as novel drug carriers, an anti-tumor model drug doxorubicin (DOX) was incorporated into polymeric micelles by double emulsion and nanoprecipitation method. The DOX-loaded micelle size, size distribution, and encapsulation efficiency (EE) were influenced by the feed weight ratio of the copolymer to DOX. In addition, in vitro release experiments of the DOX-loaded PAL-DPPE micelles exhibited that faster release in pH 5.0 than their release in pH 7.4 buffer. The poly(l-aspartic) derivative copolymer was proved to be an available carrier for the preparation of micelles for anti-tumor drug delivery.

Graphene nanosheets-polypyrrole hybrid material as a highly active catalyst support for formic acid electro-oxidation

A novel electrode material based on graphene oxide (GO)-polypyrrole (PPy) composites was synthesized by in situ chemical oxidation polymerization. Palladium nanoparticles (NPs) with a diameter of 4.0 nm were loaded on the reduced graphene oxide(RGO)-PPy composites by a microwave-assisted polyol process. Microstructure analysis showed that a layer of coated PPy film with monodisperse Pd NPs is present on the RGO surface. The Pd/RGO-PPy catalysts exhibit excellent catalytic activity and stability for formic acid electro-oxidation when the weight feed ratio of GO to pyrrole monomer is 2:1. The superior performance of Pd/RGO-PPy catalysts may arise from utilization of heterogeneous nucleation sites for NPs and the greatly increased electronic conductivity of the supports.

Microencapsulation of a cooling agent by interfacial polymerization: Influence of the parameters of encapsulation on poly(urethane–urea) microparticles characteristics

A series of polyurea–urethane microparticles containing xylitol were synthesized by interfacial polymerization from reaction between diphenyl methylene diisocyanate (MDI) and xylitol. This research was conducted to clarify the influence of different parameters on the encapsulation process, i.e. during the emulsion formation step and during the shell formation using contact angle measurement, Fourier-transform infrared spectroscopy, differential scanning calorimetry and thermogravimetric analyses. By carefully analyzing the influencing factors stirring rate and feeding weight ratio of core/shell monomers, the optimum synthetic conditions were found out. The results show that core/shell weight ratio influences not only the shell formation mechanism but also the mean diameter, microcapsule morphology, the encapsulation yield and the xylitol content. Thus, the choice of a core/shell weight ratio of 77.0–23.0 is the most suitable to obtain high encapsulation yield and xylitol loading content.

Preparation of dextran–poly(lactide)–1,2-dipalmitoyl-sn-glycero-3-phosphoethanolamine copolymer and its micellar characteristics

A novel amphiphilic copolymer based on dextran, poly(lactide) (PLA) and 1,2-dipalmitoyl-sn-glycero-3-phosphoethanolamine (DPPE) was synthesized and characterized by FT-IR, 1H NMR, 13C NMR and 31P NMR spectra. Their molecular weights were determined by gel permeation chromatography (GPC). The molecular weights range from 30 000 g mol −1 to 37 000 g mol −1 with a feed weight ratio of 20:1–50:1 (DPPE/activated dextran–PLA). Its micellar characteristics were investigated using fluorescence technique, transmission electron microscopy (TEM) and dynamic light scattering (DLS). It was found that dextran–PLA–DPPE copolymer could form spherical micelles. The micelle diameters ranged from 85 to 120 nm with a feed weight ratio of 20:1–50:1 (DPPE/activated dextran–PLA) in the absence of surfactant.

Tailoring the efficacy of nimodipine drug delivery using nanocarriers based on A 2B miktoarm star polymers

We report a nanocarrier based on A 2B type miktoarm polymers (A = polyethylene glycol (PEG); B = polycaprolactone (PCL)) for nimodipine (NIM), a hydrophobic drug with very poor aqueous solubility that is commonly prescribed for the prevention and treatment of delayed ischemic neurological disorders. The A 2B star polymers were constructed on a core with orthogonal functionalities that facilitated the performance of “click” chemistry followed by ring-opening polymerization. These star polymers assemble into spherical micelles into which NIM can be easily loaded by the co-solvent evaporation method. The micelles obtained from the star polymer PEG775 2–PCL5800 showed NIM encapsulation efficiency of up to 78 wt% at a feed weight ratio of 5.0%. The loading efficiency of the micelles was dependent on the length of the PCL arm in the A 2B miktoarm polymers. Aqueous solubility of NIM was increased by ∼200 fold via micellar encapsulation. The in vitro release of NIM from the micelles was found to occur at a much slower rate than from its solution. Lipopolysaccharide induced nitric oxide production in N9 microglia cells was reduced in the presence of micelle-encapsulated NIM, as well as in the presence of micelles alone. The treatment of microglia with micelle-encapsulated NIM reduced the release of TNF-α, a pro-inflammatory cytokine. These results suggest that NIM-loaded miktoarm micelles could be useful in the treatment of neuroinflammation.

Synthesis, characterization and cytotoxicity of photo-crosslinked maleic chitosan–polyethylene glycol diacrylate hybrid hydrogels

Synthetic hydrogels are important biomaterials for many biomedical applications and hydrogels produced via photo-gelation have shown particular promise. In this paper, we describe a new family of biodegradable hybrid hydrogels fabricated in aqueous solution via long wavelength UV photo-crosslinking using maleic chitosan and polyethylene glycol diacrylate (PEGDA) as precursors. The maleic chitosan precursor was prepared by a simple one-step chemical modification of chitosan, with high yields, and characterized by Fourier transform infrared spectroscopy, (1)H NMR and (13)C NMR. Maleic chitosan and PEGDA precursors at a wide range of weight feed ratios were mixed in aqueous solution and directly photo-crosslinked for 10 min under a long wavelength UV light (365 nm) using 4-(2-hydroxyethoxy) phenyl-(2-hydroxy-2-propyl) ketone (Irgacure 2959) as photoinitiator. It was observed that as the weight feed ratio of maleic chitosan to PEGDA decreased the pore sizes of the hydrogel samples decreased, thereby increasing the densities of the hydrogel networks and producing a lower swelling ratio and a higher compressive modulus. The molecular weight of PEGDA had a similar effect. Preliminary cell cytotoxicity tests of both the maleic chitosan precursor and maleic chitosan/PEGDA hydrogels, based on the MTT assay and live-dead assay, respectively, showed that these new chitosan-based biodegradable biomaterials were relatively non-toxic to bovine aortic endothelial cells at low dosages.

Preparation of Gold Nanoparticle/Graphene Composites with Controlled Weight Contents and Their Application in Biosensors

Positively charged gold nanoparticles (GNPs) with diameters of 2−6 nm were self-assembled onto the surfaces of 1-pyrene butyric acid functionalized graphene (PFG) sheets simply by mixing their aqueous dispersions. The amount of GNPs assembled on PFG sheets can be easily modulated by controlling the feeding weight ratio of both components. Furthermore, it was found that PFG sheets had a high loading capability of GNPs, and the maximum value was determined to be about 300 times the PFG’s own weight. Glassy carbon (GC) electrodes modified with the composite of GNPs and PFG (GNP−PFG composite) showed strong electrocatalytic activity and high electrochemical stability. A uric acid electrochemical sensor based on the composite modified electrode exhibited rapid response and high sensitivity.

Nanoparticles formed from PNIPAM- g-PEO copolymers in the presence of indomethacin

Biocompatible double-hydrophilic PNIPAM- g-PEO copolymers containing 0.3–3.2 mol% PEO grafts were synthesized and utilized to prepare indomethacin (IMC)-loaded core–shell nanoparticles by dialysis and nanoprecipitation methods. IMC loading was conducted at room temperature using the organic solvents ethanol and DMF, which induced phase separation in the copolymers aqueous solutions due to the cononsolvency of PNIPAM. In ethanol–water solutions, the cononsolvency-induced phase separation of the copolymers promoted effective drug incorporation into the formed micellar structures. In DMF–water system, the formation of the nanoparticles did not correspond to the cononsolvent region of PNIPAM- g-PEO. In this case, hydrophobic interactions between PNIPAM and IMC allowed the copolymer self-association and drug loading. Irrespective of the solvents or preparation methods applied, the drug loading content (DLC) depended on the drug-to-copolymer feed weight ratio. DLC was relatively low at the 0.5:1 ratio but it significantly increased at the ratios of 0.75:1 and 1:1 (DLC∼90%). The particle size was strongly affected by the different mechanisms of nanoparticles formation. The nanoprecipitation from ethanol produced significantly smaller particles (<150 nm) with narrow size distribution than the dialysis from DMF. The velocity of indomethacin release from the nanoparticles was influenced by the amount of encapsulated drug, the process being faster at lower DLC.

Amphiphilic biodegradable poly(ε-caprolactone)-poly(ethylene glycol)-poly(ε-caprolactone) triblock copolymers: synthesis, characterization and their use as drug carriers for folic acid

Amphiphilic biodegradable poly(e-caprolactone)-poly(ethylene glycol)-poly (e-caprolactone) (PCEC) triblock copolymers have been successfully synthesized by the ring-opening polymerization of e-caprolactone (e-CL) employing SnOct as catalyst and double-hydroxyl capped PEG (DHPEG) as macro-initiator. The triblock structure and copolymer composition were conformed by FT-IR, 1H-NMR, and GPC. Using a membrane dialysis method, PCEC micelles were prepared with a core–shell type. The critical micelle concentration (CMC) of PCEC triblock copolymers was determined by fluorescence technique using pyrene as probe, and CMC values decreased with the increase of PCL chain length. From the observation of transmission electron microscopy (TEM), the morphology of polymer micelles was spherical in shape. Micelles size measured by dynamic light scattering (DLS) exhibited a narrow size distribution. Folic acid (FA) was then used as a model drug to incorporate into PCEC micelles. The diameter, drug loading, and drug release rate of PCEC micelles were influenced by the feed weight ratio of FA and copolymer, and polymer composition. In addition, in vitro release experiments of the drug-loaded PCEC micelles exhibited sustained release behavior without any burst effects and the release behavior was also affected by the pH of release media.

Influence of process parameters on microcapsules loaded with n-hexadecane prepared by in situ polymerization

A series of melamine–formaldehyde microcapsules containing n-hexadecane were synthesized by in situ polymerization from partial etherified melamine–formaldehyde resins. This research was conducted to clarify the influence of different parameters on the encapsulation process, i.e. during the emulsion formation step and during the shell formation using surface tension measurement, Fourier-transform infrared spectroscopy and differential scanning calorimetry. By carefully analyzing the influencing factors including phase volume ratio, types of surfactants and content, stirring rate and time, pH, reaction time, feeding weight ratio of core/shell pre-polymer, the optimum synthetic conditions were found out. The results indicated that a binary mixture of Tween-20 and Brij-35 was found suitable emulsifier at low pH. Furthermore, formaldehyde/melamine (F/M) mole ratio influenced not only the shell formation mechanism but also the particle size distribution, microcapsule morphology and resin conversion rate.

Microencapsulation of styrene with melamine-formaldehyde resin

Melamine-formaldehyde (MF) resin-walled microcapsules containing styrene were prepared by in situ polymerization in an oil-in-water emulsion. In response to the characteristics of styrene (i.e., high volatility, non-polarity, low molecular weight, and low viscosity), the synthesis method was improved by optimizing the reaction conditions accordingly. It was found that utilization of macromolecular emulsifier of lower molecular weight, moderate dispersion rate, and higher feeding weight ratio of core/shell monomers is critical for the fast formation of capsules’ wall. The highest loading of styrene in the resultant microcapsules can be about 60%, and mean diameter of the capsules fell in the range of 20∼71 μm, which can be adjusted by changing processing parameters. It is believed that the present work provides a feasible approach to encapsulate monomers for manufacturing polyester based self-healing composites.

New Preparation of Structurally Symmetric, Biodegradable Poly(L‐lactide) Disulfides and PLLA–Stabilized, Photoluminescent CdSe Quantum Dots

New, biodegradable poly(L-lactide) disulfides, PLLA-SS-PLLA, were first prepared through the DMAP-catalyzed ring-opening polymerization of L-lactide with a dihydroxyethyl disulfide initiator, and were further catalytically reduced into thiol-end-functionalized poly(L-lactide)s, HO-PLLA-SH, with a tributyl phosphine catalyst (PBu3). Employing the HO-PLLA-SH as the ligand, new core-shell CdSe/PLLA quantum dots (QDs) were continuously prepared via a facile ligand-exchanging process with the CdSe/TOPO QD precursor. The chemical structures, morphologies and solvent solubility of these prepared CdSe/PLLA QDs were investigated by NMR spectroscopy, FTIR spectroscopy, XRD, TEM and excitation under either room light or UV radiation at 365 nm, demonstrating the successful ligand replacement and the new formation of core-shell CdSe/PLLA QDs (diameter:4.0 +/- 0.3 nm). Finally, UV and FL results indicate the two factors of the HO-PLLA-SH ligand molecular weight and the ligand/QD precursor feeding weight ratio were important for preparing stable and highly photoluminescent CdSe/PLLA QDs.

Microwave-Assisted Single-Step Synthesis of Poly(L-lactic acid)-poly(ethylene glycol) Copolymers

Microwave-assisted synthesis of poly(L-lactic acid)-poly(ethylene glycol) copolymers(PLEG) by single-step polycondensation of L-lactic acid and poly(ethylene glycol) has been studied. The synthetic conditions, including catalysts, reaction time, pressure and feed weight ratios (mLA/mPEG)on the molecular weights, yields and appearance of the copolymershave been discussed. PLEG copolymers with a weight-average molecular weight of 11000 g/mol can be obtained when L-lactic acid and PEG800 mixture is irradiated for about 60 min under a reduced pressure of around 40 mmHg using SnCl2·2H2O as catalyst. The higher feed weight ratios of mLA/mPEG lead to copolymers with higher molecular weight. The products are characterized by 1H-NMR, GPC and DSC. It is found that the resultant polymers have a relatively narrow polydispersity index (PDI), which is lower than 1.3. The higher glass transition and melting temperatures of the copolymers can be obtained when the content of PEG is lower. Microwave irradiation accelerates the copolymerization rate of L-lactic acid and PEG compared with the conventional heating.

Amphibious polymer-functionalized CdTe quantum dots: Synthesis, thermo-responsive self-assembly, and photoluminescent properties

A straightforward strategy is presented to functionalize aqueous-phase synthesized CdTe quantum dots (QDs) with thermo-sensitive poly(2-(dimethylamino)ethyl methacrylate) (PDMAEMA) via direct surface-initiated oxyanionic vinyl polymerization. The polymer grafting quantity can be facilely controlled in a wide range up to 95.2wt% by adjusting the weight feed ratio of monomer to pristine QDs. The polymer-grafted QDs still retain good fluorescence properties in solution, solid polymer matrix, and on surfaces of silica (SiO2) sphere. The resulting QD@PDMAEMAs show excellent solubility both in water and organic solvents (e.g., chloroform, dichloromethane, dioxane, ethyl acetate, acetone, methanol, and N, N-dimethylformamide). We have called them amphibious QDs. The thermo-sensitive PDMAEMAs make QDs accessible to self-assemble reversibly by adjusting temperature when the grafted polymer content is over a certain value. The self-assembly process and resulting structure were demonstrated by TEM, variable temperature dynamic light scattering (DLS) and UV-vis spectrometer. Because PDMAEMA is a kind of positive polyelectrolyte, QD@PDMAEMAs were used as building blocks in the layer-by-layer self-assembly process on the surface of SiO2 spheres, affording fluorescent SiO2 spheres.

Prolonged antidiabetic effect of zinc-crystallized insulin loaded glycol chitosan nanoparticles in type 1 diabetic rats

New basal insulin formulation was designed and their structural characteristics were investigated in vitro and biological activities in type 1 diabetic rats. Zinc-crystallized insulin was physically loaded into hydrophobically modified glycol chitosan (HGC) nanoparticles by a dialysis method. The series of insulin-HGC formulations were prepared with different feed weight ratio of insulin to HGC from 0.5:1 to 4:1. The loading contents of insulin and size distribution of insulin-HGCs were characterized, and blood glucose responses were investigated in streptozotocin-induced diabetic rats after single subcutaneous injection of regular insulin and insulin-HGCs. The highest loading efficiency and content were obtained in insulin-HGC when a 1:1 feed weight ratio of insulin to HGC was employed. The hydrodynamic diameter of insulin-HGC nanoparticles were in the range of 200 to 500 nm with narrow size distribution. Insulin-HGC effectively sustained insulin release up to 40% within 12 hours followed by a slower controlled release. Insulin-HGC showed an extended blood glucose lowering effect up to 24 h and provided normal blood glucose levels after oral glucose (1.5 g/kg) load at 24 hours post-injection while regular insulin showed severe hypoglycemia. The prolonged time action profiles and low variability of insulin-HGC formulation resulted in improved blood glucose control in diabetic rats and fulfilled a pattern desirable of a basal insulin.

Poly(aniline‐co‐o‐anisidine)/Sulfonated Carbon Nanotubes Composites Prepared by Surface Adsorption Method

Poly(aniline‐co‐o‐anisidine) (P(An‐co‐o‐As))/sulfonated multiwalled carbon nanotubes (s‐MWNTs) composites were prepared by adsorption of P(An‐co‐o‐As) on MWNTs surface in a N,N‐dimethyl acetamide (DMAc) solution. This research demonstrated that it was possible to sulfonate MWNTs and use a copolymer as a substitute for polyaniline (PANI) to synthesize MWNTs/conducting polymer composites easily by a one‐step mixing of solutions. The thickness of the P(An‐co‐o‐As) adsorption layer could be controlled effectively by adjusting the weight feed ratio of the two components. The resulting composites were characterized using transmission electron microscopy, thermogravimetric analysis, elemental analysis, and Fourier transform infrared spectroscopy. The electrical conductivity of the composites was unusually higher than that of pure MWNTs. Furthermore, the resultant product was compared with the P(An‐co‐o‐As)/MWNTs composite obtained via the in‐situ polymerization process. All the results demonstrated a facile route to the synthesis of P(An‐co‐o‐As)/MWNTs composites, possessing good electrical conductivity and outstanding thermal stability in the high temperature range from 450°C to 600°C.

Preparation and characterization of microencapsulated polythiol

Microcapsules containing curing agent for epoxy were successfully prepared by in situ polymerization with poly(melamine–formaldehyde) (PMF) as the shell material and high-activity polythiol (pentaerythritol tetrakis (3-mercaptopropionate), PETMP) as the core substance. Having been encapsulated, the core material PETMP had the same activity as its raw version. The synthesis approach was so improved that the consumption of polythiol was reduced to a low level. By carefully analyzing the influencing factors including catalyst concentration, reaction time, reaction temperature, feeding weight ratio of core/shell monomers, dispersion rate and emulsifier content, the optimum synthetic conditions were found out. The results indicated that not only core content and size of the microcapsules but also thickness and strength of the shell wall can be readily adjusted by the proposed technical route. The relatively thin shell wall (∼0.2μm) assured sufficient core content even if the microcapsules were very small (1–10μm). The polythiol-loaded microcapsules proved to be qualified for acting as the mate of epoxy in making two-part microencapsulated healing agent of self-healing composites.

Solubilization of hydrophobic drugs by methoxy poly(ethylene glycol)‐block‐polycaprolactone diblock copolymer micelles: Theoretical and experimental data and correlations

The solubilization of five model hydrophobic drugs by a series of micelle-forming, water-soluble methoxy poly(ethylene glycol)-block-polycaprolactone diblock copolymers (MePEG-b-PCL) with varying methoxy poly(ethylene glycol) (MePEG) and polycaprolactone (PCL) block lengths was investigated. Variation of the feed weight ratio of MePEG to caprolactone resulted in the synthesis of copolymers with predictable block lengths. The micelle diameter and pyrene partition coefficient (Kv) were directly related to the PCL block length whereas the critical micelle concentrations (CMC) were inversely related to the PCL block length. The aqueous solubilities of the model hydrophobic drugs, indomethacin, curcumin, plumbagin, paclitaxel, and etoposide were increased by encapsulation within the micelles. Drug solubilization was directly related to the compatibility between the solubilizate and PCL as determined by the Flory-Huggins interaction parameter (chisp). Furthermore, the concentration of solubilized drug was also directly related to the PCL block length.

Synthesis and characterization of organo‐attapulgite/polyaniline‐dodecylbenzenesulfonic acid based on emulsion polymerization method

AbstractOrgano‐attapulgite (OAT) was obtained by pretreating attapulgite (AT) with hexadecyltrimethyl ammonium bromide (HDTMABr) and dodecylbenzenesulfonic acid doped polyaniline (PAn‐DBSA) (OAT/PAn‐DBSA) was synthesized by emulsion polymerization at different OAT weight ratios. The perhaps polymerization procedure was supposed. The chemical structure and electronic absorption of the composites was confirmed by FTIR and UV–Vis spectroscopy, respectively. According to the X‐ray diffraction (XRD) results, it can be concluded that HDTMABr and PAn‐DBSA was just adsorbed on the surface of AT during the cation‐exchange process and OAT respectively without destroying the crystalline structure of AT or OAT. The composites showed a higher thermal stability than pure PAn‐DBSA by introduction of OAT into this polymerization system by using TGA analysis. Morphologies of the samples were confirmed by TEM and it showed that OAT was dispersed well in organic solvent after AT was pretreated with HDTMABr. The morphologies of OAT/PAn‐DBSA also supported the perhaps formation procedure we hypothesized. The electrical conductivity of the composite decreased with increasing the feed weight ratios of OAT in this polymerization system. POLYM. COMPOS., 2008 © 2007 Society of Plastics Engineers