A novel pH‐sensitive and freeze‐thawed carboxymethyl chitosan/poly(vinyl alcohol) blended hydrogel for protein delivery

BACKGROUND: Blended hydrogels are widely applied in medical fields. They can provide many advantages, such as biocompatibility and biodegradability. Many materials and methods are used to obtain blended hydrogels. In this work, carboxymethyl chitosan (CMCS) and poly(vinyl alcohol) (PVA) blended hydrogels were prepared using the freezing and thawing technique. The properties of the hydrogels prepared, i.e. gel fraction, swelling and pH‐responsive behaviors, were investigated. RESULTS: The gel fraction increased with increasing time of freezing and thawing as determined through gravimetric analysis. It was also found that the equilibrium degree of swelling improved obviously due to the addition of CMCS compared to pure PVA hydrogel. The blended hydrogel with composition CMCS/PVA 80/20 (by weight) possessed the highest swelling ratio. The results of the influence of pH values on the swelling behavior showed that minimum swelling ratios of the hydrogels occurred near the isoelectric point of CMCS. Protein release studies were performed under various pH conditions: the release was much slower under acid than under basic conditions. The release showed a burst in the first 15 h and then steadily increased. CONCLUSION: The addition of CMCS can improve the physical properties of pure PVA hydrogels and provide pH sensitivity. It is concluded that PVA hydrogels containing CMCS could be potentially applied as oral delivery systems for protein drugs. Copyright © 2009 Society of Chemical Industry     

A novel cationic waterborne polyurethane coating modified by chitosan biguanide hydrochloride with application potential in medical catheters

This study reported the synthesis and properties of a new cationic waterborne polyurethane coating. In this work, a chitosan derivative, chitosan biguanide hydrochloride (CSGH), was synthesized, which was used as a blocking agent and cross-linking agent to participate in the copolymerization of waterborne polyurethane (WPU) and a bioactive ingredient to enhance the biocompatibility of the coating. FTIR results demonstrated the reaction of CSGH with WPU. Moreover, the particle size distribution of the emulsion and SEM results showed that CSGH and WPU were well integrated. Benefiting from the formation of the cross-linking network, the thermodynamic properties of the coating were significantly improved. Furthermore, due to adding 3 wt% CSGH, the water contact angle of the coating surface decreased from 97.01° to 69.30°, indicating that the coating surface changed from hydrophobic to hydrophilic. And a specific resistance to Staphylococcus aureus and Escherichia coli was exhibited without cytotoxicity, the resistance rates could reach 85% and 91% respectively. It is highlighted that this WPU-CSGH coating has great application potential in the field of medical interventional catheters.     

PCL–PEG–PCL triblock copolydiol-based waterborne polyurethane. I. Effects of the soft-segment composition on the structure and physical properties

This article examines the effects of the soft-segment composition on the structure and physical properties of waterborne polyurethane (WBPU) based on polycaprolactone–poly(ethylene glycol)–polycaprolactone (PCL–PEG–PCL) triblock copolydiol as the soft segment. The molecular weight of PEG in the soft-segment composition and soft-segment content (SSC) are varied in this study. The water-vapor permeability (WVP) for the WBPU-coated nylon fabric is also studied. The results showed that the glass transition temperatures (T_g's) of the soft segment decreased and its temperature range (ΔT_g's) narrowed with increase of SSC up to 63 wt % and decrease of the PEG molecular weight. The dynamic mechanical analysis results showed that the α-peak height of the soft segment increased with SSC when the SSC was less than 63 wt %. However, when SSC was more than 63 wt %, the α-peak height became smaller with increasing SSC due to the crystallization of the soft segment. At the same SSC, the number of spherulites was reduced and the spherulites become larger with decrease of the PEG molecular weight. As for the mechanical properties of the WBPU cast film, the breaking stress decreased and the breaking elongation increased with increasing SSC or decreasing PEG molecular weight. For the WBPU-coated nylon fabrics, either higher SSC or higher PEG molecular weight improves the WVP. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 65:883–892, 1997     

双酚A环氧树脂改性水性聚氨酯的合成及性能研究

以环氧树脂(EP)、异佛尔酮二异氰酸酯(IPDI)、聚酯二元醇和二羟甲基丙酸(DMPA)等为原料,合成了一系列不同EP含量的水性聚氨酯(WPU)分散体,讨论了EP、亲水基团含量对EP改性WPU分散体的储存稳定性、胶膜力学性能等影响。结果表明:当u(EP)≤3%、w(羧基)=1.6%时,EP改性WPU分散体及其胶膜的综合性能良好;利用WPU中残留的-NCO与EP中羟基反应,使EP被包覆在PU链段中,乳化后EP可稳定存在于WPU中,并且具储存稳定性、耐水性、耐溶剂性及力学性能等俱佳。     

PCL–PEG–PCL triblock ester–ether copolydiol-based waterborne polyurethane. II. Effect of NCO/OH mole ratio and DMPA content on the physical properties

This article was focused on the effects of the NCO/OH molar ratio and 2,2-bis(hydroxyl methyl) propionic acid (DMPA) content during prepolymerization on the physical properties of synthesized waterborne polyurethane (WBPU) by using the polycaprolactone–poly(ethyl glycol)–polycaprolactone triblock copolydiol (PCL–PEG–PCL) as the soft segment. The results showed that the particle size of the WBPUs' dispersion decreased with a decreasing NCO/OH molar ratio or increasing DMPA content. Regarding thermal and mechanical properties, the WBPUs had a higher T_g's and lower T_m's and a higher breaking stress and a lower breaking strain of film with the NCO/OH molar ratio or DMPA content increase. The increasing NCO/OH molar ratio was advantageous to the water vapor permeability (WVP)-breaking stress balance, but the effect of the DMPA content on the WVP was not significant. The WBPU with PCL–PEG–PCL as the soft segment had a smaller particle size in dispersion and a better WVP-breaking stress balance than those of WBPU with the blending PCL and PEG as the soft segment. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 67:1301–1311, 1998     

Durability of wood flour‐plastic composites exposed to accelerated freeze–thaw cycling. II. High density polyethylene matrix

This study examined the durability of extruded HDPE/wood‐flour composites exposed to 15 accelerated cycles of water submersion, freezing, and thawing, according to ASTM standard D6662. The durability of both maple and pine composites was assessed by testing the flexural properties and density. Mercury intrusion porosimetry and scanning electron microscopy were also used to evaluate the interfacial adhesion between the matrix and wood flour before and after exposure to accelerated freeze–thaw cycling. Freeze–thaw actions had no apparent effect on the density of the composites after exposure, regardless of the wood species. However, these actions led to moisture uptake, which decreased the interfacial adhesion and increased the pore size and quantity in the composites, which resulted in a significant loss in flexural properties. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 100: 35–39, 2006     

Study of cryostructuration of polymer systems. XV. Freeze–Thaw‐induced formation of cryoprecipitate matter from low‐concentrated aqueous solutions of poly(vinyl alcohol)

Freeze–thaw treatment of low‐concentrated (<C*) aqueous solutions of poly(vinyl alcohol) (PVA) results in the formation of a cryoprecipitate fraction. It is shown that the efficiency of such a process (the yield of PVA cryoprecipitation) depends on the initial polymer concentration in the solution to be frozen and the conditions of a cryogenic influence. The key factor is defrostation dynamics: The slower the thawing rate, the higher the cryoprecipitation yield. The iodine‐staining method is employed for the quantitative analysis of PVA concentrations in the solutions under study and the necessity of the use of reduced (0–2°C) temperatures throughout such a PVA quantification is demonstrated. Observation of the kinetics of the freeze–thaw‐induced formation of cryoprecipitate matter reveals the extreme character of the temperature dependence of the efficacy of PVA macromolecule aggregation, the extreme point being situated in the vicinity of −2°C. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 1978–1986, 1999     

A simulation study on gas-to-liquid (natural gas to Fischer–Tropsch synthetic fuel) process optimization

A simulation study on gas-to-liquid (natural gas to Fischer–Tropsch synthetic fuel) process was carried out in order to find optimum reaction conditions for maximum production of synthetic fuel. Optimum operating condition for GTL (gas-to-liquid) process was determined by changing reaction variable such as temperature. During the simulation, overall synthetic process was assumed to proceed under steady-state conditions. It was also assumed that physical properties of reaction medium were governed by RKS (Redlich–Kwong–Soave) equation. ATR (auto-thermal reforming) in synthesis gas production unit and slurry phase reaction over Co-based catalyst in FTS (Fischer–Tropsch synthesis) unit were considered as reaction models for GTL process. The effect of reaction temperature on CO conversion and C₅–C₂₀ hydrocarbon yield in FTS unit was mainly examined. Simulation and experimental results showed that optimum reaction temperature in FTS unit was 255 °C. Simulation results were also compared to experimental results to confirm the reliability of simulation model. Simulation results were reasonably well matched with experimental results.     

Flow through diffusion cell method: A novel approach to study in vitro enzymatic degradation of a starch‐based ternary semi‐interpenetrating network for gastrointestinal drug delivery

A ter‐polymeric semi‐IPN has been synthesized by aqueous polymerization of methacrylamide in the presence of polyethylene glycol (PEG) and natural polysaccharides starch, and its enzymatic degradation has been studied in the phosphate buffer medium of pH 6.8 at the physiological temperature 37°C. With the increase in content of enzyme in the external solution and starch in the hydrogel, the degradation is enhanced while the extent of degradation is lowered with the increase in the amount of PEG in the hydrogel. The initial water content also affects the degradability of the polymer matrix. The degradation follows Michaelis–Menten kinetics and K_M was found to be 3.92 × 10^?5 mol dm^?3. The hydrogel exhibits different degradation behavior when studied by “traditional degradation method” (TDM) and “flow through diffusion cell” (FTDC) method. The degradability is suppressed in FTDC method because of the absorption of amylase molecules onto filler particles. Finally the nature and size of the filler particles also affects the degradation behavior of hydrogels. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 2975–2984, 2006     

Au/TS‐1 catalyst for propene epoxidation with H2/O2: A novel strategy to enhance stability by tuning charging sequence

For propene epoxidation with H₂ and O₂, the catalytic performance of Au/TS‐1 catalyst is extremely sensitive to preparation parameters of deposition‐precipitation (DP) method. In this work, effect of charging sequence in DP process on catalyst structure and catalytic performance of Au/TS‐1 catalyst is first investigated. For different charging sequences, the compositions of Au complexes (e.g., [AuCl(OH)₃]^?) and pore property of TS‐1 (i.e., with or without H₂O prefilling micropores) could affect the transfer of Au complexes into the micropores, resulting in different Au locations and thus significantly different catalytic performance. Notably, when TS‐1 is first filled with H₂O and then mixed with Au complexes, the reduced Au/TS‐1 catalyst could expose Au nanoparticles on the external surface of TS‐1 and show high stability. The results provide direct evidence showing that micropore blocking is the deactivation mechanism. Based on the results, a simple strategy to design highly stable Au/Ti‐based catalysts is developed. © 2016 American Institute of Chemical Engineers AIChE J, 62: 3963–3972, 2016     

A novel route to α,ω-telechelic poly(-caprolactone) diols, precursors of biodegradable polyurethanes, using catalysis by decamolybdate anion

A new convenient route for the synthesis of poly(-caprolactone) (PCL) with α,ω-telechelic diols' end-groups is presented. Synthesis of α,ω-telechelic PCL diols (HOPCLOH) was achieved by ring-opening polymerization (ROP) of -caprolactone (CL) catalyzed with ammonium decamolybdate (NH₄)₈[Mo₁₀O₃₄] and using diethylene glycol (DEG) as initiator. Obtained HOPCLOH was characterized by ¹H and ¹³C NMR, FT-IR, GPC and MALDI-TOF. Comparative studies demonstrate that ammonium decamolybdate (NH₄)₈[Mo₁₀O₃₄] is better catalyst than Sn-octanoate (SnOct₂) toward CL polymerization in presence of DEG, under the conditions tested. A biodegradable poly(ester-urethane-urea) derivative was efficiently prepared from synthesized HOPCLOH. Obtained polymer shows minor differences with respect to the properties recorded for a poly(ester-urethane-urea) obtained from commercial HOPCLOH.