Assessing the degradation profiles of a thermoresponsive polyvinyl alcohol (PVA)-based hydrogel for biomedical applications

Primary challenges associated with the design and success of polymeric biomedical devices are generally related to the control of the biomaterial in terms of degradability characteristics, sufficient processability characteristics, and required mechanical strength that may be altered during sterilization or manufacturing procedures. Polyvinyl alcohol-based thermoresponsive biomaterials provide a distinct advantage for biomedical applications as their physiochemical properties can be easily modified according to their desired use. In this work, we evaluated the thermal degradation characteristics of a polyvinyl alcohol (PVA)/polyethylene glycol (PEG)/polyvinylpyrrolidone (PVP) hydrogel that undergoes a steam sterilization autoclave cycle at 121°C to induce fluid-like behavior. FTIR was used to characterize the evolution of the area of the carbonyl region between 1800 and 1525 cm⁻¹. The carbonyl area increased at temperatures beyond 121°C which were used to accelerate the onset of degradation during both thermal oxidation and pyrolysis. The change in the carbonyl region was shown to correlate with respect to both temperature and time of exposure. The carbonyl region increased significantly in the presence of oxygen at temperatures above 150°C. Despite showing signs of thermal degradation at temperatures exceeding 150°C, our biomaterial was shown to be stable at 121°C during thermal degradation testing. Furthermore, bulk property analysis showed the hydrogel's mechanical and swelling properties were preserved even after being subject to multiple autoclave cycles beyond what would be experienced during a sterilization or clinical procedure.     

Properties of poly(vinyl alcohol)-graft-polyacrylamide copolymers depending on the graft length. 3. Benzene solubilization by solutions of the copolymer

The peculiarities of poly(vinyl alcohol)-graft-polyacrylamide copolymers (PVA-g-PAA), which are characterized by the equal average number (N=9), but various molecular weight (or length) of graft chains, in comparison with individual PAA and PVA, were investigated in aqueous medium. Sharp rise in benzene solubilization in PVA-g-PAA solutions at M_PAA higher than 4.3·10⁵ has been established. It was shown that such effect is stipulated by the destruction of intramolecular polymer-polymer complex in the copolymer and increasing the benzene binding to separate PVA-g-PAA groups by means of hydrogen bonds. The changes in the PVA-g-PAA solubilizing ability as the function of temperature were also investigated. The obtained results are discussed from the point of view of conformational transitions of intramolecular polymer-polymer complexes (intraPPC), which exist in copolymers, in dependence on the length of graft chains.     

Anti-atherosclerotic activity of Betulinic acid loaded polyvinyl alcohol/methylacrylate grafted Lignin polymer in high fat diet induced atherosclerosis model rats

Betulinic acid is one such natural pentacyclic triterpenoid compound, holding various pharmacological properties but its poor bioavailability is the only limitation. One of the biological macromolecules such as Lignin is a plant-derived aromatic, eco-friendly and low-cost polymer that certainly self-assembles into nano-sized colloids. Therefore, onto the current investigation, we increased the bioavailability of betulinic acid by coating on to a nanopolymer prepared with poly vinyl alcohol, lignins and methyl acrylate. Betulinic acid loaded polyvinyl alcohol/ethylacrylate grafted Lignin polymer (PVA/Lig-g-MA) nanoformulation was characterized using FTIR, XRD, SEM and TEM analysis and also the drug entrapment, in vitro drug releasing capacity was done to examine the efficiency of the nanoformulation of a drug. The MTT assay was evaluated the cytotoxicity of synthesized nanoformulation against normal endothelial cells HUVEC and HAPEC to confirm the side effects of the drug. The anti-atherosclerotic property of the nanoformulation was ascertained in both in vitro condition (with HUVEC and HPAEC) and in vivo studies (with Wistar rats). As a result, the characterization studies and in vitro studies clearly confirmed the Betulinic acid loaded PVA/Lig-g-MA nanoformulation is an ideal nanopolymer and it doesn’t cause any cytotoxic effect in normal endothelial cells. It also decreased the lipopolysaccharides induced inflammation through the down-regulation of NFκB and MAP/JNK signaling molecule expressions. Following in vivo results confirmed the synthesized nanoformulation effectively decreased the hyperchlostremia, inflammation and vasoconstriction, which induced over high fat diet. The results of histopathological analysis of cardiac tissues also confirmed the cardioprotective role of synthesized nanoformulation. Overall, both the in vitro and in vivo studies authentically proven the Betulinic acid loaded PVA/Lig-g-MA nanoformulation would be a potent cost effective anti-atherosclerotic nanodrug.     

聚乙烯醇(PVA)/壳聚糖(CS)合金膜的醇-水渗透汽化分离性能研究

在表征了PVA/CS共混体系相容性的基础上,本文报导MeOH-H_2O,EtOH-H_2O和i-PrOH-H_2O体系在PVA,CS及其合金膜中的渗透汽化行为。讨论了温度、料液浓度、合金膜的组成对分离性质的影响。从膜的分子和聚集态结构出发对相关的渗透行为进行了解释。对于PVA、CS及其合金膜来说,膜内自由体积大小看来是影响分离性能的主要因素,小分子在膜中的渗透性质主要是由扩散控制的。     

Study of cryostructurization of polymer systems VII. Structure formation under freezing of poly(vinyl alcohol) aqueous solutions

Rheological properties of the cryogels produced by freezing of concentrated aqueous solutions of poly(vinyl alcohol) have been studied. These properties were shown to depend on the polymer concentration in the initial solution, on PVA molecular weight, cryostructurization duration and temperature. Electron microscopy demonstrates the heterogeneous porous structure of these cryogels and the dependence of the observed pattern on the conditions of formation of the studied objects.     

Study on ketalization reaction of poly(vinyl alcohol) by ketones. VIII. kinetic study on acetalization and ketalization reactions of poly(vinyl alcohol)

The kninetics of acid-catalyzed acetalization and ketalization of poly(vinyl alcohol) (PVA) were systematically studied in completely homogeneous media with carefully selected solvents. Thus the acetalization reaction was run in water with six aldehydes [R₁CHO (R₁ = H, CH₃, C₂H₅, n-C₃H₇, i-C₃H₇, ClCH₂)], whereas the ketalization in dimethylslfoxide with 11 ketones [R₂CH₃CO (R₂ = CH₃, C₂H₅, n-C₃H₇, i-C₃H₇, n-C₄H₉, i-C₄H₉, tert-C₄H₉, C₆H₅CH₂, C₆H₅CH₂CH₂), cyclopentanone, and cyclohexanone]. The latter was difficult to proceed in aqueous media. Both reactions were reversible and bimolecular and, despite the use of different solvents, gave similar heats of reaction (7.5 kcal/mol) and activation energies (ca. 15 kcal/mol) except for the case of formaldehyde and chloroacetaldehyde; however the equilibrium constants at 25°C showed that the acetalization is thermodynamically much more favored than the ketalization (ca. 5000 vs. 0.01–0.9), probably because of steric hindrance of the ketone substrate. The rate constants of hydrolysis (reverse reactions) for the poly(vinyl acetal) and poly(vinyl ketal) followed the Hammett-Taft equation to give a single p* (=3.60) that is very close to that for the hydrolysis of diethyl acetal and ketal. From these and other data, it was concluded that the polymer hydrolysis, as well as PVA acetalization and ketalization, are all electrophilic reaction where the formation of hemiacetal or hemiketal is the rate-determining step. © 1996 John Wiley & Sons, Inc.     

Use of isopropyl alcohol as a solvent in Ti(O-i-Pr)4-catalyzed Knöevenagel reactions

Knöevenagel reactions of aldehydes and ketones with malononitrile, isopropyl cyanoacetate and diisopropyl malonate catalyzed by Ti(O-i-Pr)₄ proceeded smoothly in i-PrOH to give the corresponding reaction products in good to high yield. 3-Substituted coumarins were prepared by the present method.     

Removal of heavy metal ions from aqueous solutions by filtration with a novel complexing membrane containing poly(ethyleneimine) in a poly(vinyl alcohol) matrix

A novel complexing membrane was used for the removal of heavy metal ions such as Pb(II), Cd(II) and Cu(II) from aqueous solutions. The membrane consists in a semi-interpenetrating polymer network of crosslinked poly(vinyl alcohol) as the matrix and poly(ethyleneimine) as the complexing polymer. The absorption reactions followed pseudo-first-order kinetics with similar rate constants for the three cations. A model is proposed for the absorption–desorption process in order to rationalize the data obtained for the retention ratio and the retention efficiency ratio. The corresponding equilibrium constants were determined for the three metal ions, showing that the affinity order of the membrane is Pb > Cu > Cd. This sequence is consistent with the order of maximum uptake of the ions per gram of membrane: 0.59, 0.47 and 0.33 mmol g⁻¹, respectively. On the other hand, the uptake order is different on a mass basis: 123, 30 and 37 mg g⁻¹, respectively. Regeneration of the membrane and metal recovery were studied with HCl and HNO₃ at different concentrations. Filtration of solutions of each metal ion showed large elimination ratios (96–99.5%) with a retention sequence Cd > Cu > Pb. The membrane remained efficient until complete saturation of its sites. Moreover, Cu retention is larger than expected, indicating possible additional chelation by the PVA matrix. Better retention ratios were observed when the concentration of the feed solution was kept constant. Filtration of a mixture of the three cations (all at 100 ppm concentration) resulted in the same retention sequence, but the elimination ratios were smaller and Pb was eventually displaced by Cu and Cd that were present in larger molar concentrations.     

Modification and characterization of semi-crystalline poly(vinyl alcohol) with interpenetrating poly(acrylic acid) by UV radiation method for alkaline solid polymer electrolytes membrane

Semi-crystalline poly(vinyl alcohol) was modified by UV radiation with acrylic acid monomer to get interpenetrating poly(acrylic acid) modified poly(vinyl alcohol), PVAAA, membrane. The stability of various PVAAA membranes in water, 2 M CH₃OH, 2 M H₂SO₄, and 40 wt% KOH aqueous media were evaluated. It was found that the stability of PVAAA membrane is stable in 40 wt% KOH solution. The PVAAA membranes were characterized by differential scanning calorimetry, X-ray diffraction, and thermogravimetry analysis. These results show that (1) the crystallinity in PVAAA decreased with increasing the content of poly(acrylic acid) in the PVAAA membranes. (2) The melting point of the PVAAA membrane is reduced with increasing the content of poly(acrylic acid) in the membrane. (3) Three stages of thermal degradation were found for pure PVA. Compared to pure PVA, the temperature of thermal degradation increased for the PVAAA membrane. The various PVAAA membranes were immersed in KOH solution to form polymer electrolyte membranes, PVAAA-KOH, and their performances for alkaline solid polymer electrolyte were conducted. At room temperature, the ionic conductivity increased from 0.044 to 0.312 S/cm. The result was due to the formation of interpenetrating polymer chain of poly(acrylic acid) in the PVAAA membrane and resulting in the increase of charge carriers in the PVA polymer matrix. Compared to the data reported for different membranes by other studies, our PVAAA membrane are highly ionic conducting alkaline solid polymer electrolytes membranes.     

RAFT synthesis of a water‐soluble triblock copolymer of poly(styrenesulfonate)‐b‐poly(ethylene glycol)‐b‐poly(styrenesulfonate) using a macromolecular chain transfer agent in aqueous solution

Triblock copolymers of poly(styrenesulfonate)‐b‐poly(ethylene glycol)‐b‐poly(styrenesulfonate) with narrow molecular weight distribution (M_w/M_n = 1.28–1.40) and well‐defined structure have been synthesized in aqueous solution at 70 °C via reversible addition‐fragmentation chain transfer polymerization. Poly(ethylene glycol) (PEG) capped with 4‐cyanopentanoic acid dithiobenzoate end groups was used as the macro chain transfer agent (PEG macro‐CTA) for sole monomer sodium 4‐styrenesulfonate. The reaction was controllable and displayed living polymerization characteristics and the triblock copolymer had designed molecular weight. The reaction rate depended strongly on the CTA and initiator concentration ratio [CTA]₀/[ACPA]₀: an increase in [CTA]₀/[ACPA]₀ from 1.0 to 5.0 slowed down the polymerization rate and improved the molecular weight distribution with a prolonged induction time. The polymerization proceeded, following first‐order kinetics when [CTA]₀/[ACPA]₀ = 2.5 and 5.0. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 3698–3706, 2007     

Sorption and filtration of Hg(II) ions from aqueous solutions with a membrane containing poly(ethyleneimine) as a complexing polymer

The performances of a PVA/PEI complexing membrane for the removal of Hg(II) from aqueous solutions were investigated by performing sorption and filtration experiments. This membrane, that was previously shown to ensure efficient sorption of the heavy metal ions Pb(II), Cd(II) and Cu(II) at pH 5, presented a higher affinity for Hg(II) at pH 2.5. The sorption equilibrium was satisfactorily represented by the Langmuir model. In view of possible application to the treatment of industrial wastewaters, the effects of parameters such as pH, temperature, water hardness, and the presence of complexing chloride anions were investigated. The effect of increasing temperature was not straightforward: the complexation equilibrium constant decreased, but the mass of mercury sorbed increased, probably due to the higher mobility of the polymer chains that made internal sites available for complexing mercury. The maximum retention capacity of the membrane was 311 mg Hg g⁻¹. Also, operating at large calcium or chloride concentrations was not detrimental to the membrane performances. For regeneration of the membrane, a 0.05 M solution of EDTA is recommended on the basis of limited performance loss. When used in the filtration mode, the elimination ratio of Hg(II) was close to 99%.     

Synthesis of graft copolymer from copolymerization of styrene‐terminated poly(ethylene oxide) macromonomer and styrene with CpTiCl3/methylaluminoxane catalyst

Copolymerization of styrene (St) and St‐terminated poly(ethylene oxide) macromonomer (SEOM) with CpTiCl₃/methylaluminoxane (MAO) catalyst in toluene was investigated. The copolymerization of St and SEOM proceeded easily to give a graft copolymer consisting of syndiotactic polystyrene as the main chain and hydrophilic poly(ethylene oxide) as the side chain. A number of side chains in the graft copolymer could be controlled by the amount of SEOM in the feed. The reactivity of SEOM was determined from copolymerization of St and SEOM with the CpTiCl₃/MAO catalyst, and the reactivity of SEOM depended on the molecular weight of SEOM. The thermal properties of the graft copolymer such as the melting temperature were influenced by the introduction of SEOM. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 2904–2910, 2004     

Copolymerization of poly(vinyl alcohol)‐graft‐poly(1,4‐dioxan‐2‐one) with designed molecular structure by a solid‐state polymerization method

Poly(vinyl alcohol)‐graft‐poly(1,4‐dioxan‐2‐one) (PVA‐g‐PPDO) with designed molecular structure was synthesized by a solid‐state polymerization. The solid‐state copolymerization was preceded by a graft copolymerization of PDO initiated with PVA as a multifunctional initiator, and Sn (Oct)₂ as a coininitiator/catalyst in a homogeneous molten state. The polymerization temperature was then decreased and the copolymerization was carried out in a solid state. The products prepared by solid‐state polymerization were characterized by ¹H NMR and DSC, and were compared with those synthesized in the homogeneous molten state. The degree of polymerization (D_p), degree of substitution (D_s), yield and the average molecular weight of the graft copolymer with different molecular structure were calculated from the ¹H NMR spectra. The results show that the crystallization process during the solid‐state polymerization may suppress the undesirable inter‐ or intramolecular side reactions, then resulting in a controlled molecular structure of PVA‐g‐PPDO. The results of DSC measurement show that the molecular structures determine the thermal behavior of the PVA‐g‐PPDO. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 3083–3091, 2006     

Surface modification of boron nitride via poly (dopamine) coating and preparation of acrylonitrile‐butadiene‐styrene copolymer/boron nitride composites with enhanced thermal conductivity

A biology‐inspired approach was utilized to functionalize hexagonal boron nitride (h‐BN), to enhance the interfacial interactions in acrylonitrile‐butadiene‐styrene copolymer/boron nitride (ABS/BN) composites. The poly (dopamine), poly (DOPA) layer, was formed on the surface of BN platelets via spontaneously oxidative self‐polymerization of DOPA in aqueous solution. The modified BN (named as mBN) coated with poly (DOPA) was mixed with ABS resin by melting. The strong interfacial interactions via π‐π stacking plus Van der Waals, both derived from by poly (DOPA), significantly promoted not only the homogeneous dispersion of h‐BN in the matrix, but also the effective interfacial stress transfer, leading to improve the impact strength of ABS/mBN even at slight mBN loadings. A high thermal conductivity of 0.501 W/(m·K) was obtained at 20 wt% mBN content, reaching 2.63 times of the value for pure ABS (0.176 W/(m·K)). Meanwhile, the ABS/mBN composites also exhibited an excellent electrical insulation property, which can be expected to be applied in the fields of thermal management and electrical enclosure.     

Diamine/Silane-Modified controlled pore glass: The covalent attachment reaction from aqueous solution and the mechanism of reaction of bound diamine with copper(II)

The reaction of N-2-aminoethyl-3-aminopropyltrimethyoxysilane (en-silane) with the surface of controlled pore glass (CPG) in aqueous solution was examined. The reaction appears to involve the rapid (ca. l min) formation of a covalently bound monolayer of en-silane at room temperature. Multilayers of bound polymeric en-silane can be obtained by reaction at elevated temperature. The latter reaction is slower, presumably because of the more stringent steric requirements of polymer formation in chain growth away from the CPG surface. For en-silane coverages ranging from 1.7 to 8.5 μ mol m^-2, the mechanism for the complexation of copper(II) by ethylenediamine (en) bound to a CPG surface by reaction of en-silane with CPG was also investigated by thermometric and potentiometric titrimetry. A two-step mechanism is proposed. The data indicate that the first step of the surface reaction involves formation of a Cu(en)₄ complex as opposed to the Cu(en) complex formed in the first step of the solution reaction. The second step results in a complex similar to the Cu(en)₂; species formed in solution.     

Hyperbranch‐polyethyleniminated functional polymers. I. Synthesis,characterization of novel ABA type of dumbbell‐like polyethyleniminated polyoxypropylenediamines,and their complexing properties with copper(II) ions in aqueous solution

Novel ABA‐type dumbbell‐like water‐soluble copolymers [D230(EI)₄, D400(EI)₄, and D400(EI)₈] were synthesized by introducing ethylenimine (EI) groups into both sides of polyoxypropylenediamines via a simple in situ ethylamination of polyoxypropylenediamine with 2‐chloroethylamine hydrochloride. The structures of the resultant polymers were identified by Fourier transform infrared spectroscopy and ¹H NMR. The percentages of primary, secondary, and tertiary amine present were determined by the potentiometric titration method after treatments with the appropriate chemicals of salicylaldehyde and acetic anhydride. The surface tension and solubilizing behavior of pyrene in the presence of these polymers in aqueous medium were also investigated, and the efficiency to reduce the surface tension and solubilizing behavior of pyrene depends on the attachments of EI to polymer backbone. The chelating properties of these polymers were examined quantitatively by ultraviolet–visible (UV–vis) spectroscopy in the presence of Cu²⁺ ions in aqueous solution, and continuous variation analysis revealed that the most stable complex is formed at the normality ratio of [N]/[Cu²⁺] = 3.0. UV–vis spectroscopy and transmission electron microscopy were used to evaluate the dumbbell‐like water‐soluble copolymer, D400(EI)₈, as a stabilizer for preparing colloidal noble metal nanoparticles (Au and Pt) in aqueous solution. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 1360–1370, 2003     

Formation of an η-allyl and a cyclic γ-hydroxyalkyl complex of molybdenum from reaction of MoH2(η-cyclopentadienyl)2 with homoallyl alcohol

The reaction of Cp₂MoH₂ (Cp=η⁵-C₅H₅) with homoallyl alcohol in the presence of a protonic acid afforded a cationic η³-crotyl molybdenum complex and a cyclic α-methyl-γ-hydroxypropyl molybdenum complex. This reaction proceeds via the stepwise formation of the cyclic complex, followed by formation of the η³-crotyl complex.     

The reactions of non-gem-hexanedioxytetrachlorocyclotriphosphazene with 2-(2-hydroxyethyl)thiophene,benzyl alcohol and 1,1,3,3-tetramethylguanidine. Spectroscopic studies of the derived products

Abstract

Reactions of non-gem-hexanedioxytetrachlorocyclotriphosphazene (1) with monofunctional nucleophilic reagents, 2-(2-hydroxyethyl)thiophene (2), benzyl alcohol (3) and 1,1,3,3-tetramethylguanidine (4) were investigated. The reactions, using an excess of NaH, in THF solutions, under refluxing conditions and with 1:2?mole ratios allow the synthesis of the following novel cyclotriphosphazene derivatives: 2,4-dichloro-2,4-(hexane-1,6-dioxy)-6,6-[2-(2-ethoxy)hiophene]-cyclotriphosphazatriene, N₃P₃Cl₂[O(CH₂)₆O-(C₆H₈OS)₂] (5); 2,4-(hexane-1,6-dioxy)-2,4,6,6-[2-(2-ethoxy) thiophene]-cyclotriphosphazatriene, N₃P₃[O(CH₂)₆O-(C₆H₈OS)₄] (6); 2,4-dichloro-2,4-(hexane-1,6-dioxy)-6,6-(methoxybenzene)-cyclotriphosphazatriene, N₃P₃Cl₂[O(CH₂)₆O-(C₆H₅CH₂O)₂] (7); 2,4-(hexane-1,6-dioxy)-2,4,6,6-(methoxybenzene)-cyclotriphosphazatriene, N₃P₃[O(CH₂)₆O-(C₆H₅CH₂O)₄] (8); and 2,4-dichloro-2,4-(hexane-1,6-dioxy)-6,6-(1,1,3,3-tetramethyguanidine)-cyclotriphosphazatriene, N₃P₃Cl₂[O(CH₂)₆O-HN-CN₂(CH₃)₄] (9). The structures of the synthesized compounds (5–9) have been characterized by elemental analysis, TLC-MS, ¹H, ¹³C and ³¹P {+¹H} and {?¹H} NMR spectral data.     

Stereoselective synthesis of (Z)-fluoroalkenes directed to peptide isosteres: copper mediated reaction of trialkylaluminum with 4,4-difluoro-5-hydroxyallylic alcohol derivatives

Copper mediated alkyl-transfer reaction of trialkylaluminum (R₃Al) with (E)-4,4-difluoro-5-hydroxyallylic alcohol derivative smoothly proceeded to give the corresponding 2-alkylated 4-fluoro-5-hydroxyhomoallylic alcohol derivative with completely Z and 2,5-syn selective manner. Regio- and stereoselective conversion of the C5-hydroxyl group of the fluoroolefin thus obtained to amino group could be achieved through one-pot mesylation and azidation reaction.     

Catalysis of the water gas shift reaction by cis -[Rh(CO)2(AMINE)2](PF6) complexes in an aqueous tetrabutylammonium hydrogensulfate solution

Rhodium(I) complexes, cis-[Rh(CO)₂(amine)₂](PF₆) (amine = 4-picoline, 3-picoline, 2-picoline, pyridine, 3,5-lutidine or 2,6-lutidine) dissolved in an aqueous solution of tetrabutylammonium hydrogensulfate (N(C₄H₉)₄HSO₄), catalyze the water-gas shift reaction (WGSR). The role of the coordinated amine on the catalytic activity was examined.