Liwei Ma

Lanzhou University, Kao-lan-hsien, Gansu Sheng, China

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Publications (11)31.22 Total impact

  • Liwei Ma · Mingzhu Liu · Xiang Shi
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    ABSTRACT: A simple method was developed to prepare the microcapsules and microparticles as drug carriers. The drug-loaded microcapsules and microparticles were prepared by self-assembly of carboxymethyl chitosan (CMCTS) and carboxymethyl chitosan-graft-poly(N,N-diethylacrylamide) (CMCTS-g-PDEA) in aqueous media under mild conditions. The preparation method did not involve any organic solvent and surfactant, and it could offer good control over the morphology and the size of self-assemblies. Through adjusting the grafting percentage, nanosized drug-delivery systems with different shapes, that is, microcapsules and microparticles, could be obtained. The grafting reaction was confirmed by comparing the FTIR spectra of CMCTS and the grafted copolymer, and the morphologies of the drug-delivery systems were observed by dynamic light scattering and transmission electron micrograph. Preliminary characterization of the biocompatibility of these microgels was done by the cytotoxicity assays using the L02 human hepatic natural cell as probes. The in vitro bovine serum albumin (BSA) release behavior indicated that drug release rate and encapsulation efficiency depended upon pH value and nanoparticle structure. The release of BSA could be effectively sustained from both drug-loaded microgels, which passed the qualitative cytotoxicity test and have no apparent cytotoxicity for the CMCTS-g-PDEA microgel self-assembly. © 2011 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 2012.
    No preview · Article · Feb 2012 · Journal of Biomedical Materials Research Part B Applied Biomaterials
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    ABSTRACT: The poly(N,N-diethylacrylamide-co-(2-dimethylamino)ethyl methacrylate) (poly(DEA-co-DMAEMA)) macromonomers with three different chain lengths were prepared by telomerization of DEA and DMAEMA monomers with different ratios of the chain transfer agent, 2-mercaptoethanol. The number-average weight of three macromonomers determined by gel permeation chromatography of the terminal hydroxyl groups was 8355, 10,516 and 15,953, respectively. The comb-type grafted poly(DEA-co-DMAEMA) hydrogels having the different lengths of the grafted chains were synthesized in the presence of crosslinker. Equilibrium and dynamic swelling/deswelling properties of the prepared hydrogels responding to temperature and pH were investigated. Compared to normal-type hydrogel, the comb-type grafted hydrogels exhibited excellent variational values in response to an alternation of the temperature and pH. Moreover, the grafted hydrogels showed quite fast reswelling and deswelling behaviors in response to simultaneous dual temperature and pH stimuli. This is because that the introduction of side chains with freely mobile ends in the comb-type grafted hydrogels made the mobility of the networks increased. The responsive rates of the grafted hydrogels were also controlled by modifying the length of the grafted chains. The dual thermo- and pH-sensitive comb-type grafted poly(DEA-co-DMAEMA) hydrogels in this study may find various potential applications.
    No preview · Article · Aug 2010 · Sensors and Actuators B Chemical
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    ABSTRACT: In this study, a novel semi-interpenetrating polymer network (semi-IPN) hydrogel of poly(diallyldimethylammonium chloride)/poly(N,N-diethylacrylamide) (PDADMAC/PDEA) was prepared using ammonium persulfate as an initiator and N,N,N′,N′-tetramethylethylenediamide as an accelerator at room temperature. The influence of this additive on the property of resulting PDEA hydrogels was investigated and characterized. The interior morphology by scanning electron microscopy (SEM) revealed that PDADMAC introduced PDEA hydrogels have large and interconnected porous network structures. Differential scanning calorimetry (DSC) studies showed the difference in the state of the water between PDEA and semi-IPN hydrogels. The incorporating of PDADMAC significantly improved the equilibrium swelling ratio of modified hydrogels when comparing with a normal PDEA hydrogel. The semi-IPN hydrogels exhibited improved thermosensitive characteristics, such as faster deswelling and swelling rates and great oscillating deswelling–swelling behavior, and the level of improvement depended on the PDADMAC content. The swelling dynamic transport of the hydrogels was analyzed based on the Fickian equation.
    No preview · Article · May 2010 · The Chemical Engineering Journal
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    ABSTRACT: A strategy to prepare dual-stimuli sensitive poly(N,N-diethylacrylamide-co-acrylic acid) composite hydrogels has been demonstrated. Multi-walled carbon nanotubes (MWCNTs) functionalized with vinyl groups were copolymerized with N,N-diethylacrylamide (DEA), acrylic acid (AA) and N,N′-methylenebisacrylamide (NNMBA) to obtain the composites (NCG). As expected, the compression properties of the NCG were greatly improved without noticeably reducing the response rates to temperature changes. Field emission scanning electron microscopy showed that the surface of the NCG was denser, which affords the NCG better compression properties, while there was obvious MWCNTs aggregation on the surface of the hybrid gel sample by physical mixing of the MWCNTs (HYG).
    No preview · Article · May 2010 · Reactive and Functional Polymers
  • Lu Wang · Mingzhu Liu · Chunmei Gao · Liwei Ma · Dapeng Cui
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    ABSTRACT: In this work, a series of hydrogels were prepared by copolymerization of (2-dimethylamino) ethyl methacrylate (DMAEMA) and 3-acrylamidephenylboronic acid (AAPBA). The structure of the resultant hydrogels was studied by Fourier transform infrared (FTIR) spectroscopy and scanning electron microscopy (SEM). The experimental results from swelling studies revealed that the hydrogels displayed definite glucose sensitivity under physiological conditions, as well as sharp changes in the mesh size of their network as a function of the pH and temperature of the swelling media. Bovine serum albumin (BSA) was selected as a model compound when examining protein release from hydrogels. The results suggested that the temperature, pH and glucose concentration of buffer solutions greatly influenced release profiles.
    No preview · Article · Mar 2010 · Reactive and Functional Polymers
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    ABSTRACT: In this work, the carboxymethyl chitosan (CMCTS) grafted poly(N-vinylpyrrolidone) (PVP) copolymers were synthesized. The hydrogel beads containing VB2 were prepared from the copolymers by an ionic crosslinked. The experimental results shown that VB2 drug release rate from those beads decreased with the increasing grafting percentage, crosslinker concentration and pH value of the medium. Besides, the beads have the better control ability for releasing of model drug than CMCTS does.
    No preview · Article · Dec 2009 · Advanced Engineering Materials
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    ABSTRACT: Fast responsive temperature- and pH-sensitive hydrogels of poly(N,N-diethylacrylamide-co-acrylic acid) (P(DEA-co-AA)) have been synthesized successfully by a two-step procedure, in which the initial polymerization was conducted at constant temperature for 15 min, followed by further polymerization at −30°C for 12 hr. Swelling studies showed that hydrogels thus prepared had almost the same temperature and pH sensitivity compared with the conventional ones (polymerized at 24°C for 12 hr). However, hydrogels thus prepared had faster swelling/deswelling rates in distilled water than the conventional ones, and their deswelling rates in low pH buffer solutions were also faster than the conventional ones. These improved properties were attributed to the porous network structure, which was confirmed by the results of scanning electron microscopy. Copyright © 2009 John Wiley & Sons, Ltd.
    Full-text · Article · Dec 2009 · Polymers for Advanced Technologies
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    ABSTRACT: A simple method has been developed to prepare smart P(N,N-diethylacrylamide-co-methacrylic acid) (P(DEA-co-MAA)) microspheres that consist of well-defined temperature-sensitive cores and pH sensitive shells. The microgels have been prepared by surfactant-free emulsion polymerization using water as the solvent. The core-shell hydrogel microspheres have been characterized by Fourier transform infrared (FTIR) spectroscopy, UV spectrometry, dynamic light scattering (DLS) and transmission electron micrograph (TEM). Preliminary characterization of the biocompatibility of hydrogel microspheres has been done by the cytotoxicity assays using the HeLa human breast cancer cell line as probes. The in vitro drug release indicates that drug release rate, encapsulation efficiency (EE) and release kinetics depend upon the pH value and copolymer composition. According to this study, the hydrogel microspheres based on P(DEA-co-MAA) could serve as suitable candidate for drug site-specific carrier in intestine.
    No preview · Article · Oct 2009 · International Journal of Pharmaceutics
  • Jun Chen · Mingzhu Liu · Hongliang Liu · Liwei Ma
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    ABSTRACT: In this study, poly(N,N-diethylacrylamide-co-N-hydroxymethyl acrylamide) (poly(DEA-co-NHMAA)) hydrogels were synthesized by changing the initial DEA/NHMAA mole ratio, N,N'-methylenebisacrylamide and total monomer concentration. The thermosensitive and mechanical performances were optimized by altering the above parameters. The hydrogels were characterized by using Fourier transform infrared (FTIR) spectroscope and scanning electron microscope (SEM). In comparison with the PDEA hydrogel, the equilibrium swelling ratio (ESR) and lower critical solution temperature (LCST) of the hydrogels increased with the increase of NHMAA content in the feed. The swelling kinetics was also studied. The release behaviors of the model drug, aminophylline, are found dependent on hydrogel composition and environmental temperature, which suggests that these materials have potential application as intelligent drug carriers.
    No preview · Article · Aug 2009 · Materials Science and Engineering C
  • Hongliang Liu · Mingzhu Liu · Liwei Ma · Jun Chen
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    ABSTRACT: Poly(N,N-diethylacrylamide) with a terminal hydroxyl end group (PDEA-OH) was synthesized by radical telomerization of N,N-diethylacrylamide (DEA) monomer using 2-hydroxyethanethiol as a chain transfer agent. Macromonomer of thermo-sensitive PDEA was synthesized by condensation reaction of PDEA-OH with acryloyl chloride. The macromonomer was characterized by FTIR and 1H NMR, and the molecular weight was determined by GPC. Thermo- and pH-sensitive comb-type grafted poly(N,N-diethylacrylamide-co-acrylic acid) (PDEA-co-AA) hydrogels (GHs) were successfully prepared by grafting PDEA chains with freely mobile ends onto the backbone of a cross-linked (PDEA-co-AA) network. The results showed that the deswelling behavior of the hydrogels was dependent on the test temperature. At 45 °C (beneath the VPTT of the hydrogels), both the normal-type hydrogels (NHs) and comb-type grafted P(DEA-co-AA) hydrogels had lower deswelling rates. While at 60 °C (far beyond the VPTT of the hydrogels), the deswelling rates of the GHs were faster than that of the NHs. Furthermore, pulsatile stimuli-responsive studies indicated that the GHs had excellent thermo-reversibility and were superior to the NHs in the magnitude of their swelling ratios to temperature changes. However, the reversibility to pH changes was poor for both the NHs and the GHs.
    No preview · Article · Jul 2009 · European Polymer Journal
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    ABSTRACT: Novel drug-loaded hydrogel beads for intestine-targeted controlled release were developed by using pH- and temperature-sensitive carboxymethyl chitosan-graft-poly(N,N-diethylacrylamide) (CMCTS-g-PDEA) hydrogel as carriers and vitamin B2 (VB2) as a model drug. The hydrogel beads were prepared based on Ca2+ ionic crosslinking in acidic solution and formed dual crosslinked network structure. The structure of hydrogel and morphology of drug-loaded beads were characterized by Fourier transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC), and scanning electron microscopy (SEM). The study about swelling characteristics of hydrogel beads indicated that the beads had obvious pH- and temperature-sensitivity. In vitro release studies of drug-loaded beads were carried out in pH 1.2 HCl buffer solution and pH 7.4 phosphate buffer solution at 37°C, respectively. The results indicated that the dual crosslinked method could effectively control the drug release rate under gastrointestinal tract (GIT) conditions, which was superior to traditional single crosslinked beads. In addition, the effects of grafting percentage, pH value, and temperature on the release behavior of the VB2 were investigated. The drug release mechanism of CMCTS-g-PDEA drug-loaded beads was analyzed by Peppa's potential equation. According to this study, the dual crosslinked hydrogel beads based on CMCTS-g-PDEA could serve as suitable candidate for drug site-specific carrier in intestine. Copyright © 2009 John Wiley & Sons, Ltd.
    No preview · Article · Jan 2009 · Polymers for Advanced Technologies