Co-reporter:Dongdong Zhou, Shaoyong Huang, Jingru Sun, Xinchao Bian, Gao Li, and Xuesi Chen
Macromolecules June 27, 2017 Volume 50(Issue 12) pp:4707-4707
Publication Date(Web):June 5, 2017
DOI:10.1021/acs.macromol.7b00855
The crystallization behaviors and microstructures of poly(l-2-hydroxyl-3-methylbutanoic acid)/poly(l-lactide) blends [P(L-2H3MB)/PLLA] were investigated by OM, DSC, SAXS, in situ temperature-dependent WAXD, and in situ synchrotron WAXS. The blends exhibited a homogeneous state at 250 °C. In the cooling process, P(L-2H3MB), with higher melting temperature, crystallized first at 166.7 °C and drove the formation of the phase separation and microstructure. And the amorphous P(L-2H3MB) and PLLA were excluded into the interlamellar and interfibrillar regions of the former P(L-2H3MB) crystallites. For P(L-2H3MB)/PLLA (5/5), the amorphous P(L-2H3MB) in the interfibrillar regions continued to form crystallites sequentially at 134.6 °C, which clearly confirmed the fractional crystallization of P(L-2H3MB). In our knowledge, this unique fractional crystallization has not been reported yet, of the component in miscible blend, which crystallized first under little confinement. This work provided a new viewpoint and understanding of the relationship between fractional crystallization and microstructures in crystalline/crystalline blends.
Co-reporter:Kaixuan Ren;Bin Li;Qinghua Xu;Chunsheng Xiao;Chaoliang He;Xuesi Chen
Polymer Chemistry (2010-Present) 2017 vol. 8(Issue 45) pp:7017-7024
Publication Date(Web):2017/11/21
DOI:10.1039/C7PY01597F
In the present work, a horseradish peroxidase (HRP)-catalyzed hydrogel based on a double-end tyramine conjugated linear poly(ethylene glycol) (TA-PEG-TA) polymer is developed. The TA-PEG-TA is designed to act as not only a substrate of HRP, but also a macromonomer. We find that, the linear structure is sufficient to form robust hydrogels, and therefore it greatly simplifies the polymer architecture applicable to HRP-catalyzed hydrogels, which are always based on graft or branched polymers. The gelation time and strength of the TA-PEG-TA hydrogels can be well tuned by varying the concentrations of the polymer and HRP as well as the molar ratios of H2O2 to TA groups. The gelation mechanism is clarified by exploring the HRP-catalyzed reaction of a single-end tyramine conjugated poly(ethylene glycol) monomethyl ether (mPEG-TA). The multiple active hydrogen atoms (in the hydroxyl group and the o-position) of phenol moieties can be oxidized by H2O2via HRP catalysis, which should be responsible for the generation of mPEG-TA oligomers and the gelation of TA-PEG-TA. This study provides a new strategy for the design of injectable enzymatically crosslinked hydrogels.
Co-reporter:Kaixuan Ren;Bin Li;Qinghua Xu;Chunsheng Xiao;Chaoliang He;Xuesi Chen
Polymer Chemistry (2010-Present) 2017 vol. 8(Issue 45) pp:7017-7024
Publication Date(Web):2017/11/21
DOI:10.1039/C7PY01597F
In the present work, a horseradish peroxidase (HRP)-catalyzed hydrogel based on a double-end tyramine conjugated linear poly(ethylene glycol) (TA-PEG-TA) polymer is developed. The TA-PEG-TA is designed to act as not only a substrate of HRP, but also a macromonomer. We find that, the linear structure is sufficient to form robust hydrogels, and therefore it greatly simplifies the polymer architecture applicable to HRP-catalyzed hydrogels, which are always based on graft or branched polymers. The gelation time and strength of the TA-PEG-TA hydrogels can be well tuned by varying the concentrations of the polymer and HRP as well as the molar ratios of H2O2 to TA groups. The gelation mechanism is clarified by exploring the HRP-catalyzed reaction of a single-end tyramine conjugated poly(ethylene glycol) monomethyl ether (mPEG-TA). The multiple active hydrogen atoms (in the hydroxyl group and the o-position) of phenol moieties can be oxidized by H2O2via HRP catalysis, which should be responsible for the generation of mPEG-TA oligomers and the gelation of TA-PEG-TA. This study provides a new strategy for the design of injectable enzymatically crosslinked hydrogels.
Co-reporter:Dongdong Zhou, Jun Shao, Jingru Sun, Xinchao Bian, Sheng Xiang, Gao Li, Xuesi Chen
Polymer 2017 Volume 123(Volume 123) pp:
Publication Date(Web):11 August 2017
DOI:10.1016/j.polymer.2017.07.005
•Linear and 4-arm PEG-PLLA and PEG-PDLA block copolymers with different molecular weights were synthesized.•Only PLA SC and PEG crystallites were observed in both linear and 4-arm blends prepared via solution-casting method.•The crystal structures of PLA SC and PEG did not alter.•The molecular weights and chain architectures greatly influenced the formation of PLA SC and PEG crystallites.Poly(lactide) stereocomplex (PLA SC) and poly(ethylene glycol) (PEG) crystallites were obtained in MPEG-b-PLLA/MPEG-b-PDLA (linear blend, 1/1) and 4PEG-b-PLLA/4PEG-b-PDLA (4-arm blend, 1/1) by solution-casting method. The molecular weights of PLLA and PDLA (Mn, PLA) were similar in all the linear and 4-arm blends. Only PLA SC and PEG crystallites were observed, and PLA homocrystallites were absent in all blends. The different Mn, PLA and chain architectures did not alter the crystalline structures of PLA SC and PEG, but greatly influenced their melting temperatures and crystallinities. As the average Mn, PLA per arm of linear and 4-arm blends were similar, the melting temperatures and crystallinities of PLA SC and PEG in 4-arm blends were always lower than those of linear blends, which could be ascribed to the huge steric hindrance of 4-arm structures. This investigation on PEG-b-PLLA/PEG-b-PDLA blends with various structures could provide basic data for the applications of PLA stereocomplex.Download high-res image (175KB)Download full-size image
Co-reporter:Bin Sun;Yanlong Liu;Bao Zhang;Xinchao Bian;Xuesi Chen
Journal of Applied Polymer Science 2016 Volume 133( Issue 1) pp:
Publication Date(Web):
DOI:10.1002/app.42857
ABSTRACT
The enhancement of mechanical properties were achieved by solution blending of poly(d-lactide) (PDLA) and 5-arm poly(l-lactide) (5-arm PLLA). Differential scanning calorimetry (DSC) and wide-angle X-ray diffraction (WAXD) results indicated almost complete stereocomplex could be obtained when 5-arm PLLA exceeded 30wt %. Tensile test results showed that the addition of 5-arm PLLA in linear PDLA gave dramatically improvement both on tensile strength and elongation at break, which generally could not be increased simultaneously. Furthermore, this work transformed PDLA from brittle polymer into tough and flexible materials. The mechanism was proposed based on the TEM results: the stereocomplex crystallites formed during solvent evaporation on the blends were small enough (100–200 nm), which played the role of physical crosslinking points and increased the interaction strength between PDLA and 5-arm PLLA molecules, giving the blends high tensile strength and elongation at break. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016, 132, 42857.
Co-reporter:Kaixuan Ren, Haitao Cui, Qinghua Xu, Chaoliang He, Gao Li, and Xuesi Chen
Biomacromolecules 2016 Volume 17(Issue 12) pp:
Publication Date(Web):October 24, 2016
DOI:10.1021/acs.biomac.6b00884
Bone-marrow-derived mesenchymal stem cells (BMSCs) possess vast potential for tissue engineering and regenerative medicine. In this study, an injectable hydrogel comprising poly(l-glutamic acid)-graft-tyramine (PLG-g-TA) with tunable microenvironment was developed via enzyme-catalyzed cross-linking and used as an artificial extracellular matrix (ECM) to explore the behaviors of BMSCs during three-dimensional (3D) culture. It was found that the mechanical property, porous structure as well as degradation process of the hydrogels could be tuned by changing the copolymer concentration. The PLG-g-TA hydrogels showed good cytocompatibility in vitro. After being subcutaneously injected into the back of rats, the hydrogels degraded gradually within 8 weeks and exhibited good biocompatibility in vivo. BMSCs were then encapsulated in the polypeptide-based hydrogels with different copolymer concentration to investigate the influence of 3D matrix microenvironment on stem cell behaviors. It is intriguing to note that the BMSCs within the 2% hydrogel showed a well-spread morphology after 24 h and a higher proliferation rate during 7 days of culture, in contrast to a rounded morphology and lower proliferation rate of BMSCs in the 4% hydrogel. Furthermore, the hydrogels with different microenvironment also regulated the matrix biosynthesis and the gene expression of BMSCs. After incubation in the 2% hydrogel for 4 weeks, the BMSCs produced more type II collagen and expressed higher amounts of chondrogenic markers, compared to the cells in the 4% hydrogel. Therefore, the PLG-g-TA hydrogels with tunable microenvironment may serve as an efficient 3D platform for guiding the lineage specification of BMSCs.
Co-reporter:Sheng Xiang;Shao Jun 李杲;Xin-chao Bian 边新超
Chinese Journal of Polymer Science 2016 Volume 34( Issue 1) pp:69-76
Publication Date(Web):2016 January
DOI:10.1007/s10118-016-1727-2
In this study, a series of monodispersed poly(L-lactide) (PLLA) were synthesized by the ring-opening polymerization with Schiff base aluminum catalyst, and the effects of the number-average molecular weight (Mn) on the crystallization and melting behaviors of PLLA were investigated by differential scanning calorimetry (DSC) and wide-angle X-ray diffraction (WAXD). The total crystallization rate of PLLA was Mn-dependent, which reached the maximum value for PLLA with Mn of 18.6 kg/mol. In addition, when Mn of PLLA was 18.6 kg/mol, the melting enthalpy (ΔHm) showed a maximum value (87.1 J/g), which was the highest reported value till now. The critical temperature for change of crystal formation from δ- to α-form crystals increased in the isothermal crystallization process with Mn increasing. In the reheating procedure, high-Mn PLLA demonstrated a small exothermal peak prior to the dominant melting peak, corresponding to crystal transition from δ- to α-form, but low-Mn PLLA didn’t show the peak of crystal transition. These different crystallization and melting behaviors were attributed to the different chain mobility of PLLA with different Mn.
Co-reporter:Jun Shao, Sheng Xiang, Xinchao Bian, Jingru Sun, Gao Li, and Xuesi Chen
Industrial & Engineering Chemistry Research 2015 Volume 54(Issue 7) pp:2246
Publication Date(Web):February 6, 2015
DOI:10.1021/ie504484b
The linear PLLA/PDLA blends were prepared by solution mixing method, and the melting behavior and structure evolution of neat PLLA and PLLA/PDLA specimens were investigated in this study. Results indicated that PLA stereocomplex crystallites (sc) preferentially formed in all blends, and the crystal structure of PLA sc and homochiral crystallites (hc) did not vary as molecular weights. The melting temperature of PLA neat specimens (Thm) increased monotonously with molecular weights. However, significantly different from the neat samples, the melting temperature of PLA sc (Tsc) increased at first, then decreased as the molecular weight of polymers increased from 4 to 100 kg/mol. When the molecular weights of PLLA and PDLA ranged from 23 to 50 kg/mol, multimelting behaviors observed at 230 °C in the blends. After annealing at a fix temperature (Tsc – 10 °C), the highest Tsc was observed at 249.9 °C in L32/D31 specimen, which was the highest report value until now. The WAXD and SAXS results attested that not crystal structure, but the variation of the thickness of lamellar crystal was the exterior reason, and the higher optical purity of PLLA and PDLA would be the inherent cause which resulted in the superior thermal properties. This investigation provides more potential for the application of PLA sc materials at higher temperature environments.
Co-reporter:Dongdong Zhou, Jun Shao, Gao Li, Jingru Sun, Xinchao Bian, Xuesi Chen
Polymer 2015 Volume 62() pp:70-76
Publication Date(Web):7 April 2015
DOI:10.1016/j.polymer.2015.02.019
•PEG/PLLA block copolymers with different architectures were synthesized.•The different architectures did not alter the crystal structures of PEG and PLLA.•The effect of architectures was markedly on the crystallization behavior of PEG and PLLA.•A mode of the confined environment of PEG in the PEG/PLLA block copolymers with different architectures was suggested.PEG/PLLA block copolymers bearing various number of arms were synthesized. The molecular weights of PLLA in the block polymers were determined by 1H NMR and GPC. For 1-arm, 2-arm, 4-arm PEG/PLLA block copolymers, DSC and WAXD results indicated that the different architectures and compositions of the block copolymers didn't alter the structures of PEG and PLLA crystallites, but markedly affected the crystallinities and melting temperatures of PEG and PLLA. The critical Mn, PLLA of each arm decreased with the number of arms increasing (Mn, MPEG5-PLLA > Mn, 2PEG10-PLLA > Mn, 4PEG20-PLLA), when the PEG crystallites were not detected. As Mn, PLLA of each arm was similar in the copolymers, Tm, PEG and XPEG decreased gradually with the number of arms increasing, and the similar regularities also displayed for PLLA. The crystallization behavior and the variation architectures of PEG/PLLA copolymers can provide primary data to the applications in the drug delivery and industry parts.
Co-reporter:Kaixuan Ren, Chaoliang He, Chunsheng Xiao, Gao Li, Xuesi Chen
Biomaterials 2015 51() pp: 238-249
Publication Date(Web):
DOI:10.1016/j.biomaterials.2015.02.026
Co-reporter:Jun Shao;Yan-long Liu;Sheng Xiang;Xin-chao Bian
Chinese Journal of Polymer Science 2015 Volume 33( Issue 12) pp:1713-1720
Publication Date(Web):2015 December
DOI:10.1007/s10118-015-1715-y
In this study, the poly(L-lactide)/poly(D-lactide) (PLLA/PDLA) blends with different optical purities of PLLA and various molecular weights of PDLA are prepared by solution mixing, and the stereocomplex formation and phase separation behaviors of these blends are investigated. Results reveal that optical purity and molecular weight do not vary the crystal structure of PLA stereocomplex (sc) and homochiral crystallites (hc). As the optical purity increasing in the blends, the melting temperature of sc (Tsc) and the content of sc (ΔHsc) increased, while the melting temperature of hc (Thm) hardly changes, although the content of hc (ΔHhm) decreased gradually. The Tsc and ΔHsc are also enhanced as the molecular weight of PDLA reduces, and the ΔHhm reduces rapidly even though the Thm does not vary apparently. With lower optical purities of PLLA and higher molecular weights of PDLA, three types of crystals form in the blends, i.e., PLA sc, PLLA hc and PDLA hc. As molecular weight decreases and optical purity enhances, the crystal phase decreases to two (sc and PDLA hc), and one (sc) finally. This investigation indicates that the phase separation behavior between PLLA and PDLA in the PLLA/PDLA blends not only depends on molecular weights, but also relies on the optical purities of polymers.
Co-reporter:Kaixuan Ren, Chaoliang He, Yilong Cheng, Gao Li and Xuesi Chen
Polymer Chemistry 2014 vol. 5(Issue 17) pp:5069-5076
Publication Date(Web):07 May 2014
DOI:10.1039/C4PY00420E
Enzymatically crosslinked injectable hydrogels based on poly(L-glutamic acid) grafted with tyramine and poly(ethylene glycol) (denoted as PLG-g-TA/PEG) were developed under physiological conditions in the presence of horseradish peroxidase (HRP) and hydrogen peroxide (H2O2). Their gelation time, mechanical properties, swelling behaviors and porous structure were evaluated. The hydrogels were rapidly formed in the presence of low concentrations of HRP and H2O2. The storage modulus of the hydrogels could be well controlled and increased by increasing the concentrations of HRP and H2O2. The average pore-size of the hydrogels varied from 20 to 120 μm, depending on the H2O2 concentration. In addition, the encapsulated L929 fibroblast cells in the PLG-g-TA/PEG hydrogels exhibited high viability. After subcutaneous injection of the PLG-g-TA/PEG solutions containing HRP and H2O2 into the back of rats, the hydrogels were rapidly formed in situ. The hydrogels were found to persist for up to 10 weeks in vivo, and histological analysis indicated that the hydrogels exhibited acceptable biocompatibility. These results suggested that the biocompatible, injectable enzyme-mediated PLG-g-TA/PEG hydrogels are promising for biomedical applications including tissue engineering scaffolds and drug delivery carriers.
Co-reporter:Jun Shao;Zhaohui Tang;Jingru Sun;Xuesi Chen
Journal of Polymer Science Part B: Polymer Physics 2014 Volume 52( Issue 23) pp:
Publication Date(Web):
DOI:10.1002/polb.23597
Abstract
Linear and four-armed poly(l-lactide)-block-poly(d-lactide) (PLLA-b-PDLA) block copolymers are synthesized by ring-opening polymerization of d-lactide on the end hydroxyl of linear and four-armed PLLA prepolymers. DSC results indicate that the melting temperature and melting enthalpies of poly (lactide) stereocomplex in the copolymers are obviously lower than corresponding linear and four-armed PLLA/PDLA blends. Compared with the four-armed PLLA-b-PDLA copolymer, the similar linear PLLA-b-PDLA shows higher melting temperature (212.3 °C) and larger melting enthalpy (70.6 J g−1). After these copolymers blend with additional neat PLAs, DSC, and WAXD results show that the stereocomplex formation between free PLA molecular chain and enantiomeric PLA block is the major stereocomplex formation. In the linear copolymer/linear PLA blends, the stereocomplex crystallites (sc) as well as homochiral crystallites (hc) form in the copolymer/PLA cast films. However, in the four-armed copolymer/linear PLA blends, both sc and hc develop in the four-armed PLLA-b-PDLA/PDLA specimen, which means that the stereocomplexation mainly forms between free PDLA molecule and the inside PLLA block, and the outside PDLA block could form some microcrystallites. Although the melting enthalpies of stereocomplexes in the blends are smaller than that of neat copolymers, only two-thirds of the molecular chains participate in the stereocomplex formation, and the crystallization efficiency strengthens. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2014, 52, 1560–1567
Co-reporter:Bao Zhang, Xinchao Bian, Sheng Xiang, Gao Li, Xuesi Chen
Polymer Degradation and Stability (February 2017) Volume 136() pp:58-70
Publication Date(Web):February 2017
DOI:10.1016/j.polymdegradstab.2016.11.022
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