Control of release characteristics in pH‐sensitive poly(vinyl alcohol)/poly(acrylic acid) microcapsules containing chemically treated alumina core

The pH‐sensitive poly(vinyl alcohol)/poly(acrylic acid) hydrogel microcapsules containing vitamin B₁₂‐loaded Al₂O₃ core were prepared with a three‐step emulsion polymerization. Al₂O₃ was chemically treated with HCl or NaOH solutions at room temperature for 24 h to modify the binding properties with vitamin B₁₂. The colon‐targeted release characteristics of vitamin B₁₂ from the microcapsules were evaluated at different pHs. These microcapsules showed the faster and larger release of vitamin B₁₂ due to the high swelling of microcapsule shell as the pH was changed into more basic condition. However, these microcapsules showed the slower and less release of vitamin B₁₂ as the acid value of Al₂O₃ increased due to the strong binding interaction between Al₂O₃ core and vitamin B₁₂ even though the initial loading of vitamin B₁₂ was higher. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Sustained release behavior of pH‐responsive poly(vinyl alcohol)/poly(acrylic acid) hydrogels containing activated carbon fibers

The composites of pH‐responsive poly(vinyl alcohol)/poly(acrylic acid) hydrogel and activated carbon fibers (ACFs) were prepared as sustained drug release system with excellent mechanical properties. The mechanical properties of hydrogels were improved greatly by addition of ACFs. The thinner ACFs were more effective in increasing the mechanical properties of composite hydrogels. The cumulative amount of release and the release period were dependent on the surface area and the pore volume of ACFs. The drug release was maximized at basic condition due to the pH‐sensitive hydrogel matrices and the initial bust phenomenon was alleviated by incorporating ACFs in the hydrogels. The drug release was sustained about four times longer and the mechanical property was increased about 2.6 times higher because ACFs worked as drug reservoir and reinforcement. Cytotoxicity evaluation confirmed the biocompatible characteristics of the ACFs‐containing hydrogels. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Dual-responsive release behavior of pH-sensitive PVA/PAAc hydrogels containing temperature-sensitive PVA/PNIPAAm microcapsules

Both temperature and pH responsive drug delivery system was prepared by combining temperature-sensitive poly(vinyl alcohol) (PVA)/poly(N-isopropylacrylamide) (PNIPAAm) microcapsules and pH-sensitive PVA/poly(acrylic acid) (PAAc) hydrogels. The release of drug from the composite hydrogels increased as the pH increased due to the repulsion among the carboxylate anions in the PVA/PAAc hydrogels. The release of drug from the composite hydrogels also increased as the temperature decreased due to the higher hydrophilicity generated below the lower critical solution temperature of PNIPAAm. The compression moduli of composite hydrogels increased with increasing the content of PVA/PNIPAAm microcapsules. The biocompatibility of composite hydrogels was confirmed by the cytotoxicity test.     

Preparation of poly(vinyl alcohol)/poly(acrylic acid)/TiO2/carbon nanotube composite nanofibers and their photobleaching properties

The composite nanofibers of poly(vinyl alcohol) (PVA)/poly(acrylic acid) (PAAc)/titanium(IV) oxide (TiO₂) were prepared by electrospinning for a novel photocatalytic treatment of waste water. To improve the photoelectronic properties of PVA/PAAc/TiO₂ composite nanofibers, carbon nanotubes (CNTs) were used as an additive. The TiO₂ and CNTs were immobilized in the PVA/PAAc hydrogels as electrospun nanofibers for an easier recovery after the wastewater treatment. The improved efficiency of pollutant dye removal was observed at pH 10 due to the pH-sensitive swelling behavior of the PVA/PAAc/TiO₂/CNTs composite nanofibers. The photocatalytic activity of TiO₂ was improved noticeably by applying electric field to the CNTs-embedded composite nanofibers.     

Preparation of pH‐sensitive poly(vinyl alcohol‐g‐methacrylic acid) and poly(vinyl alcohol‐g‐acrylic acid) hydrogels by gamma ray irradiation and their insulin release behavior

A series of pH‐responsive hydrogels were studied as potential drug carriers for the protection of insulin from the acidic environment of the stomach before releasing in the small intestine. Hydrogels based on poly(vinyl alcohol) networks grafted with acrylic acid or methacrylic acid were prepared by a two‐step process. Poly(vinyl alcohol) hydrogels were prepared by gamma ray irradiation (50 kGy) and then followed by grafting either acrylic acid or methacrylic acid onto these poly(vinyl alcohol) hydrogels with subsequent irradiation (5–20 kGy). These graft hydrogels showed pH‐sensitive swelling behavior and were used as carriers for the controlled release of insulin. The in vitro release of insulin was observed for the insulin‐loaded hydrogels in a simulated intestinal fluid (pH 6.8) but not in a simulated gastric fluid (pH 1.2). The release behavior of insulin in vivo in a rat model confirmed the effectiveness of the oral delivery of insulin to control the level of glucose. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 91: 636–643, 2004     

Intrinsic factor and vitamin B12 complex‐loaded poly[lactic‐co‐(glycolic acid)] microspheres: preparation,characterization and drug release

BACKGROUND: Vitamin B12 is an essential vitamin required by all mammals. Absorption of vitamin B12 is facilitated by binding of intrinsic factor–vitamin B₁₂ complex to specific receptors in the ileum. In humans a deficiency of this vitamin or a lack of intrinsic factor leads to pernicious anaemia. The major objective of the present study was to prepare intrinsic factor–vitamin B12 complex‐loaded poly[lactic‐co‐(glycolic acid)] (PLGA)‐based microparticles and to investigate their release kinetics. RESULTS: PLGA copolymer was synthesized by the ring‐opening polymerization method and characterized using gel permeation chromatography, Fourier transform infrared spectroscopy and ¹H NMR. The glass transition temperature measurement showed a single T_g at 40 °C. The intrinsic factor–vitamin B12 complex‐loaded PLGA microspheres were prepared by a water‐in‐oil‐in‐water double emulsion solvent extraction/evaporation technique. An environmental scanning electron microscopy investigation demonstrated that the PLGA particles had a mean particle diameter of 38 µm. Interestingly, different drug release patterns (bi‐ and triphasic ones) were observed for vitamin B12‐loaded and intrinsic factor–vitamin B12 complex‐loaded microspheres. In contrast to the rapid release of vitamin B12 by itself, in vitro release tests showed that intrinsic factor and vitamin B12 in the complex were released from PLGA microspheres in a sustained manner over 15 days. CONCLUSION: PLGA microspheres can be an effective carrier for the intrinsic factor–vitamin B12 complex. Copyright © 2007 Society of Chemical Industry     

Uniform hollow-structured poly(vinyl amine) hydrogel microparticles with controlled mesh property and enhanced cell adhesion

This study introduces a useful approach for fabrication of hollow-structured hydrogel microparticles and for encapsulation of biomacromolecules in the hollow core of the particles. Monodisperse hollow-structured poly(vinyl amine) hydrogel particles were fabricated without using templates that combines the dispersion polymerization and the sequential hydrolysis/crosslinking. The hydrogel shell showed pH-dependent mesh sizes; ∼2 nm at a normal condition (pH 3–12) and ∼11 nm at an expanded condition (pH 2). By taking advantage of pH-responsive mesh property, we demonstrated that dextran macromolecules, whose hydrodynamic radius is between the mesh sizes of the normal and expanded pH conditions, could be encapsulated and stored inside of the shell. Moreover, our hydrogel particles showed strong adhesion to human cells. Some of them were even engulfed by the cell membrane and drawn into the cell even with no aid of site-specific moieties. From these results, it is expected that the hydrogel hollow microcapsules synthesized in this study could be used for delivery of macromolecules into the cells.     

Synthesis and Characterization Superabsorbent Polymers Made of Starch,Acrylic Acid,Acrylamide, Poly(Vinyl Alcohol), 2-Hydroxyethyl Methacrylate, 2-Acrylamido-2-methylpropane Sulfonic Acid

Three polymers with excellent absorption properties were synthesized by graft polymerization: soluble starch-g-poly(acrylic acid-co-2-hydroxyethyl methacrylate), poly(vinyl alcohol)/potato starch-g-poly(acrylic acid-co-acrylamide), poly(vinyl alcohol)/potato starch-g-poly(acrylic acid-co-acrylamide-co-2-acrylamido-2-methylpropane sulfonic acid). Ammonium persulfate and potassium persulfate were used as initiators, while N,N′-methylenebisacrylamide was used as the crosslinking agent. The molecular structure of potato and soluble starch grafted by synthetic polymers was characterized by means of Fourier Transform Infrared Spectroscopy (FTIR). The morphology of the resulting materials was studied using a scanning electron microscope (SEM). Thermal stability was tested by thermogravimetric measurements. The absorption properties of the obtained biopolymers were tested in deionized water, sodium chroma solutions of various concentrations and in buffer solutions of various pH.     

Electrospinning of chitosan/poly(vinyl alcohol)/acrylic acid aqueous solutions

Chitosan bicomponent fibers were prepared via the electrospinning of chitosan/poly(vinyl alcohol)/acrylic acid aqueous solutions with different concentrations. With a 4% acrylic acid aqueous solution, when the chitosan/poly(vinyl alcohol) mass ratios were lower than 80/20, electrospinning nanofibers could be obtained. With a 90% acrylic acid aqueous solution, when the chitosan/poly(vinyl alcohol) mass ratios were less than 95/5, good nanofibers could be electrospun. The average diameter of the nanofibers gradually decreased, and its distribution became narrower as the poly(vinyl alcohol) concentration increased. Chitosan/poly(vinyl alcohol)/acrylic acid aqueous solutions could be electrospun at various concentrations by the adjustment of the chitosan and poly(vinyl alcohol) concentrations. The effects of the viscosity and conductivity of the blend solution on the morphologies of the fiber mats were also investigated. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 5692–5697, 2006     

聚乙烯醇/聚丙烯酸/腐植酸钠高吸水性树脂的制备及溶胀行为

以N,N＇-亚甲基双丙烯酰胺为交联剂、过硫酸铵为引发剂,采用水溶液聚合法合成了聚乙烯醇/聚丙烯酸/腐植酸钠多功能高吸水性树脂。研究了聚乙烯醇和腐植酸钠含量对树脂吸水倍率的影响,同时考察了树脂的吸水速率、溶液pH值对吸水倍率的影响及反复溶胀性能。结果表明,在体系中引入廉价的腐植酸钠,能够显著提高树脂的吸水能力。在腐植酸钠含量为10wt%时,树脂具有最高的吸水倍率,其吸蒸馏水和0.9wt%NaCl溶液分别达到1020g/g和80g/g。     

Characteristics of poly(vinyl pyrrolidone)/poly(acrylic acid) interpolymer complex prepared by template polymerization of acrylic acid: Effect of reaction solvent and molecular weight of template

Poly(vinyl pyrrolidone) (PVP)/poly(acrylic acid) (PAA) interpolymer complexes were prepared, in ethanol or dimethylformamide (DMF), by template polymerization of acrylic acid in the presence of PVP (MW: 42.5 or 1100 K) used as the template. FTIR analysis showed that the complexes were formed through hydrogen bonding between the carboxyl groups of the PAA and the carbonyl groups of the PVP. The glass‐transition temperature (T_g) of the complex, prepared in ethanol, was higher than that of the component polymers, whereas the T_g of the complex, prepared in DMF, was located between that of the component polymers. The dissolution rate of the complex was affected by the molecular weight of the PVP and the reaction solvent. The release rate of ketoprofen from the complexes showed a pH dependency, and was slower at a lower pH. The ketoprofen release rate from the complex was controlled mainly by the dissolution rate of the complex above the pK_a of PAA (4.75) and by the diffusion rate below the pK_a. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 94: 2390–2394, 2004     

The tough microcapsules of acrylic acid–styrene–isoprene–styrene quadrablock copolymer shell via Pickering emulsion technique

Pickering emulsion technique has been demonstrated a simple method to fabricate the microcapsules. However, the resulted microcapsules are often fragile. This limits their applications. Here, we report that the microcapsules with the nanostructured shell of poly(acrylic acid‐b‐styrene‐b‐isoprene‐b‐styrene) (ASIS), which is of high toughness and elasticity, could be fabricated via Pickering emulsions using ASIS nanoparticles as stabilizing particles. The surfactant‐free ASIS latex (with theoretical molecular weight for each block: 1.5k–15k–55k–10k) was synthesized by reversible additional fragmentation transfer (RAFT) emulsion polymerization using amphiphilic macro‐RAFT agent [poly(acrylic acid)₂₀‐b‐polystyrene₅ trithiocarbonate] as both reactive surfactant and polymerization mediator. It was found that the ASIS nanoparticles were able to self‐assemble on oil/water interface to stabilize Pickering emulsion of hexadecane in the pH range from 8 to 12. The droplet diameter was finely tuned from 17 to 5 µm by increasing the ASIS particle levels from 0.13 to 12 wt % based on the mass of the ASIS aqueous dispersions. With toluene as a coalescing aid, the capsules with a coherent and nonporous shell were obtained with the dispersed phase volume percentage as high as 50%. The toluene treated capsules were so mechanically strong to survive the utrasonic treatment. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46700.     

Novel blend microspheres of poly(vinyl alcohol) and succinyl chitosan for controlled release of nifedipine

Water-soluble succinyl chitosan (SCS) was synthesized by reacting succinic anhydride with –OH and –NH₂ reactive groups of chitosan (CS). The blend hydrogel microspheres were prepared from SCS with poly(vinyl alcohol) (PVA) by water-in-oil (w/o) emulsion cross-linking using glutaraldehyde (GA) as the cross-linking agent. Nifedipine (NFD), an antihypertensive drug having a plasma half-life of 2 h, was encapsulated giving encapsulation efficiency up to 92 % and its release was extended up to 12 h. Scanning electron microscopy (SEM) confirmed the spherical nature and smooth surfaces of the microspheres, while Fourier transform infrared spectroscopy (FTIR) confirmed succinylation of CS and chemical stability of NFD in the matrix. Thermogravimetry (TGA) and differential scanning calorimetry (DSC) characterized the SCS and the blend hydrogel microspheres. X-ray diffraction (XRD) and DSC were also used to study the crystalline or amorphous nature of NFD. Swelling and in vitro release experiments performed in pH 1.2 and 7.4 buffer media showed a dependence of blend composition, extent of cross-linking and pH of the media. The mechanism of drug release as analyzed by an empirical equation, suggested non-Fickian trends.     

Synthesis and characterization of pH‐ and salt‐responsive hydrogels based on etherificated sodium alginate

Hydrogels composed of etherificated sodium alginate (ESA), sodium acrylic acid (NaAA), and poly (vinyl alcohol) (PVA) were synthesized by aqueous solution polymerization. The effects of reaction variables such as terminal pH, ions, and ionic strength on hydrogel swelling ratio (SR) were determined and compared. SR was influenced strongly by pH and ionic strength. SR increased with increasing pH but tended to decrease with PVA content. At a given ionic strength, SR of ESA/NaAA/PVA hydrogel was dependent on the valence of anion; SR was higher in multivalent anion salt solution than in monovalent anion salt solution, i.e., SR_K2SO4 > SR_KCl and SR_Na2SO4 > SR_NaCl. The swelling kinetic of the hydrogels showed Fickian kinetic diffusion in acidic media and non‐Fickian behavior in alkaline media. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Swelling behavior of poly(sodium acrylate)/kaoline superabsorbent composite

Using partly neutralized acrylic acid as monomer, kaoline ultrafine powder as filler and N,N′‐(dimethyl)acrylamide as crosslink agent, poly(sodium acrylate)/kaoline superabsorbent composite was synthesized by aqueous solution polymerization method. Using the superabsorbent composite as collagen, a hydrogel was prepared. The influence of the neutralization degree of superabsorbent collagen, the compositions, the concentration, and the pH value of exterior solution on the swelling behavior of the hydrogel was investigated. It was found that the swelling capability of the hydrogel depended on the groups on the collagen. The swelling capability of the hydrogel relied on the ionic intensity, molecular polarity, molecular volume, as well as the concentration of exterior solution. When the pH value of exterior solution was equal to seven, the hydrogel has a maximum swelling value of 800 times. POLYM. ENG. SCI. 46:324–328, 2006. © 2006 Society of Plastics Engineers     

Using Green Process for the Synthesis of Poly(Vinyl Alcohol)/α-Al2O3-Thiamine Nanocomposite: Thermal,Mechanical, Contact Angle,and Morphological Studies

Hydrophilic surface of α-Al₂O₃ nanoparticles was treated with thiamine as a green modifier for better compatibility with poly(vinyl alcohol) matrix. In this regard, poly(vinyl alcohol)/α-Al₂O₃-vitamin B₁ nanocomposites with different ratios of modified α-Al₂O₃ (3, 5, and 7?wt%) were prepared through ultrasonic irradiation and their properties were compared with the pure poly(vinyl alcohol). Many techniques were used to study the properties of poly(vinyl alcohol)/α-Al₂O₃-vitamin B₁ nanocomposites. Morphology images of poly(vinyl alcohol)/α-Al₂O₃-vitamin B₁ nanocomposites showed the good dispersion of the α-Al₂O₃ nanoparticles in poly(vinyl alcohol) matrix in nanometer-scale. The results demonstrated that poly(vinyl alcohol)/α-Al₂O₃-vitamin B₁ nanocomposites give better thermal stability, strain, and E-modulus than the pure poly(vinyl alcohol.     

Synthesis of copolymeric acrylamide/potassium acrylate hydrogels blended with poly(vinyl alcohol): Effect of crosslinking and the amount of poly(vinyl alcohol) on swelling behavior

A novel series of copolymeric acrylamide/potassium acrylate superabsorbents, blended with poly(vinyl alcohol), have been synthesized by using N, N′‐methylenebisacrylamide as a crosslinker and potassium persulphate (K₂S₂O₈) as an initiator. Swelling behavior of these hydrogels in water was investigated; and on the basis of swelling properties, the diffusional behavior of water into these hydrogel systems was analyzed. It was observed that with the increase of amount of poly(vinyl alcohol) or crosslinking, the swelling of the hydrogels decreased. The hydrogel synthesized by addition of 5% poly(vinyl alcohol) and 0.25% crosslinking showed maximum swelling of 54445%. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 1927–1931, 2005     

Controlled release of proteins from poly(L-lactic acid) coated polyisobutylcyanoacrylate microcapsules

Poly(L -lactic acid)-coated polyisobutylcyanoacrylate microcapsules containing protein molecules were prepared by a single-step procedure based on either a double-emulsion-solvent evaporation method or a spray-drying method. First, an aqueous protein solution was emulsified in an organic phase of methylene chloride containing a wall-forming monomer (isobutylcyanoacrylate), various kinds of poly(L -lactic acid), and a surfactant. An immediate polymerization process of isobutylcyanoacrylate takes place at the W/O interface upon contact with hydroxide ion in the aqueous phase, leading to the formation of a polyisobutylcyanoacrylate wall around the aqueous droplets. This W/O emulsion was reemulsified in an aqueous solution to promote the solvent removal and, consequently, the precipitation of poly(L -lactic acid) onto polyisobutylcyanoacrylate microcapsules or was spraydried to directly deposit the poly(L -lactic acid) on the wall. Three proteins, bovine serum albumin, horseradish peroxidase, and tetanus toxoid, were encapsulated in these poly(L -lactic acid)-coated polyisobutylcyanoacrylate microcapsules, and then their release profiles were examined in vitro as a function of molecular weight of poly(L -lactic acid) and its copolymers with glycolic acid. These formulations exhibited a low “burst” effect at initial incubation stages and released the proteins for extended periods of time. Subcutaneous injections of the tetanus toxoid-loaded microparticles into rats showed that the time course of immunization (antibody titer) can be controlled by the type of polymer matrices used. © 1994 John Wiley & Sons, Inc.     

Preparation of fast pH‐responsive ferric carboxymethylcellulose/poly(vinyl alcohol) double‐network microparticles

BACKGROUND: Carboxymethylcellulose (CMC) and poly(vinyl alcohol) (PVA) are biocompatible, and their complex hydrogel shows pH responsiveness. Thus, they are chosen as starting materials to prepare physically dual‐crosslinked Fe‐CMC/PVA microparticles with improved properties. RESULTS: Fe‐CMC/PVA double‐network microparticles were obtained via a facile process under mild conditions. Sodium carboxymethylcellulose was crosslinked with ferric ions to form particles that contained aqueous PVA solution in an emulsion system. The hydrogel particles were then subjected to a freezing–thawing cycle to achieve further crosslinking; the size of the particles formed was in the range 0.2–1.2 µm. The microparticles were capable of maintaining the stability of proteins such as hemoglobin in an acidic environment and exhibited pH‐responsive release behavior. CONCLUSION: The pH responsivity of the Fe‐CMC/PVA physical double‐network microparticles is fast, which is helpful for effectively protecting a loaded bioactive substance. Thus, they may be potential candidates for pH‐sensitive applications. Copyright © 2008 Society of Chemical Industry     

Swelling and drug release profile of poly(2‐ethyl‐2‐oxazoline)‐based hydrogels prepared by gamma radiation‐induced copolymerization

Poly(2‐ethyl‐2‐oxazoline) and acrylic acid were copolymerized in different compositions using γ‐rays‐induced polymerization and cross‐linking to obtain a series of pH‐sensitive hydrogels. The preparation parameters that may affect the copolymerization process such as the feed solution composition and irradiation dose were optimized. Swelling characteristics of the obtained polymeric hydrogels were evaluated. The results show the significant effects of the hydrogel composition, soaking time, and pH on the swelling equilibrium. The diffusion parameters obtained at pH 1 and 7 show the possibility of using the prepared hydrogels in the field of colon‐specific drug delivery systems. Ibuprofen as a model drug was loaded into (poly(2‐ethyl‐2‐oxazoline)/acrylic acid) copolymer hydrogel to investigate their drug release behavior at different pH values. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011