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1.
Tsuji H  Tezuka Y 《Biomacromolecules》2004,5(4):1181-1186
The spherulite growth of stereocomplex crystallites in the blend from low-molecular-weight poly(L-lactide) [i.e., poly(L-lactic acid) (PLLA)] and poly(D-lactide) [i.e., poly(D-lactic acid) (PDLA)] from the melt, together with that of the homocrystallites in pure PLLA and PDLA films, was investigated using polarization optical miscroscopy. The spherulite growth of stereocomplex crystallites occurred at a wider temperature range (相似文献   

2.
Stereocomplexes between poly(D-lactide) (PDLA) and poly(L-lactide) (PLLA) have been extensively studied, including, in recent years, several reports on the stereocomplexation of PDLA with small molecules such as peptides. Here, the possible complexation between PDLA and luteinizing hormone releasing hormone (LHRH), a l-configured decapeptide, is considered for which several observations were made: (1) in calorimetry an additional endothermic peak appears at a lower temperature than the melting temperature of pure PDLA; (2) in Raman analyses a band splitting of the C=O stretching mode (not present in pure PDLA) shows up; (3) in X-ray diffraction, however, no change is observed after mixing the two species, indicating no crystal structure modification (and the absence of any stereocomplex crystal structure). The calorimetric double melting peak is merely explained by the presence of two distinct morphological forms of PDLA, whereas the spectroscopic band splitting can be due to simple differences of crystallinity. From these observations it is concluded that the LHRH modifies the crystallization of PDLA without, however, the formation of a stereocomplex.  相似文献   

3.
Duan Y  Liu J  Sato H  Zhang J  Tsuji H  Ozaki Y  Yan S 《Biomacromolecules》2006,7(10):2728-2735
The molecular weight dependence of poly(L-lactide)/poly(D-lactide) (PLLA/PDLA) stereocomplex behavior at the air-water interface was studied by surface pressure-area (pi-A) isotherms and atomic force microscopy (AFM). It was found that the compression-induced sterecomplexation of a PDLA/PLLA equimolar blend with high molecular weight (M(w) = 1 x 10(6) and 9.8 x 10(5), respectively) could occur at the air-water interface. This result is in marked contrast with the stereocomplexation of PDLA/PLLA blends in the bulk from the melt or in solutions, where the homocrystallites of either PLLA or PDLA rather than stereocomplex crystallites will be formed preferentially when the molecular weights of both polymers are higher than 1 x 10(5). Unexpectedly, the Langmuir-Blodgett behavior of the PDLA/PLLA blend with lower molecular weight (M(w) = 4 x 10(3) and 3.2 x 10(3), respectively), which should be favored in the stereocomplex, was distinct from that of other higher molecular weight blends. AFM images clearly disclosed for the first time the morphological changes of the equimolar blends of PLLA and PDLA at the air-water interface induced by increasing the surface pressure of the monolayer. Of particular note, the bilayer mechanism for the plateau in the isotherm was directly verified by the AFM height images.  相似文献   

4.
Fiber morphology and crystalline structure of poly[(R)-3-hydroxybutyrate] (P(3HB)) and stereocomplexed poly(lactide) (PLA) nanofibers were investigated by using scanning and transmission electron microscopies and X-ray and electron diffractions. In the P(3HB) nanofibers spun from less than 1 wt% 1,1,1,3,3,3-hexafluoro-2-propanol (HFIP) solution, planar zigzag conformation (beta-form) as well as 2(1) helix conformation (alpha-form) structure was formed. Based on the electron diffraction measurement of single P(3HB) nanofiber, it was revealed that the molecular chains of P(3HB) align parallel to the fiber direction. From the enzymatic degradation test of P(3HB) nanofiber, it was shown that beta-form molecular chains are degraded more preferentially than alpha-form chains. Stereocomplexed PLA nanofibers were electrospun from 1 wt% poly(l-lactide)/poly(d-lactide) (PLLA/PDLA) solution in HFIP, which contains equal amounts of PLLA and PDLA. While as-spun stereocomplexed PLA nanofiber was amorphous, PLA nanofiber annealed at 100 degrees C contained only racemic crystal. It was supposed that the crystallization behavior of stereocomplexed PLA in the nanofiber is affected by the electrospinning process, which forcibly exerts the strain onto the polymer chains.  相似文献   

5.
A porous scaffold as a cell-compatible material was designed and prepared using a phospholipid copolymer composed of 2-methacryloyloxyethyl phosphorylcholine (MPC), n-butyl methacrylate, and enantiomeric macromonomers, the poly(L-lactic acid) (PLLA) macromonomer, and poly(D-lactic acid) (PDLA) macromonomer. On the basis of the wide-angle X-ray diffraction and differential scanning calorimetry measurements, the formation of a stereocomplex between the PLLA and PDLA segments of the copolymer was observed on the porous scaffold. The porous structure was prepared by a sodium chloride leaching technique, and the pore was linked to the scaffold. The pore size was confirmed by scanning electron microscopy and found to be ca. 200 microm. These observations suggest that the porous scaffold makes it possible to produce cell-compatible materials, which may involve the following advantages for tissue engineering: (i) cell compatibility using phospholipid copolymer, (ii) adequate cell adhesion by poly(lactic acid), and (iii) complete disappearance of scaffold by dissociation of stereocomplex. The cell experiment using the porous scaffold will be the next subject and reported in a forthcoming paper.  相似文献   

6.
Poly(D-lactic acid) (PDLA) and poly(L-lactic acid) (PLLA) macromonomers were synthesized for preparation of a novel cytocompatible polymer. The cytocompatible polymer was composed of 2-methacryloyloxyethyl phosphorylcholine (MPC), n-butyl methacrylate (BMA), and the enantiomeric PLLA (or PDLA) macromonomer. The degree of polymerization of the lactic acid in the PLLA and PDLA segments was designed to be ca. 20. The copolymer-coated surface was analyzed with static contact angle by water. From the result, the PLLA (or PDLA) segment and MPC unit were located on the coated surface, and the monomer unit in the copolymer was reconstructed by contacting water. Fibroblast cell culture was performed to evaluate cell adhesion on the coated surface, and the cell morphology was observed. The number of cell adhesion is correlated with the PL(D)LA content, and the cell morphology is correlated with the MPC unit content. The porous scaffold was prepared by the formation of a stereocomplex between the PLLA and PDLA, and the cell adhesion and following cell intrusion was then evaluated. The fibroblast cells adhered on the surface and intruded into the scaffold through the connecting pores after 24 h. The cell morphology became round shape from spreading with the decreasing PLLA (or PDLA) content in the copolymer. It is considered that the change in the cell morphology would be induced by the MPC unit as cytocompatible unit. These findings suggest that the porous scaffold makes it possible to have cytocompatibility and to produce three-dimensional tissue regeneration.  相似文献   

7.
Eight-arm poly(ethylene glycol)-poly(L-lactide), PEG-(PLLA)(8), and poly(ethylene glycol)-poly(D-lactide), PEG-(PDLA)(8), star block copolymers were synthesized by ring-opening polymerization of either L-lactide or D-lactide at room temperature in the presence of a single-site ethylzinc complex and 8-arm PEG (M(n) = 21.8 x 10(3) or 43.5 x 10(3)) as a catalyst and initiator, respectively. High lactide conversions (>95%) and well-defined copolymers with PLLA or PDLA blocks of the desired molecular weights were obtained. Star block copolymers were water-soluble when the number of lactyl units per poly(lactide) (PLA) block did not exceed 14 and 17 for PEG21800-(PLA)(8) and PEG43500-(PLA)(8), respectively. PEG-(PLA)(8) stereocomplexed hydrogels were prepared by mixing aqueous solutions with equimolar amounts of PEG-(PLLA)(8) and PEG-(PDLA)(8) in a polymer concentration range of 5-25 w/v % for PEG21800-(PLA)(8) star block copolymers and of 6-8 w/v % for PEG43500-(PLA)(8) star block copolymers. The gelation is driven by stereocomplexation of the PLLA and PDLA blocks, as confirmed by wide-angle X-ray scattering experiments. The stereocomplexed hydrogels were stable in a range from 10 to 70 degrees C, depending on their aqueous concentration and the PLA block length. Stereocomplexed hydrogels at 10 w/v % polymer concentration showed larger hydrophilic and hydrophobic domains as compared to 10 w/v % single enantiomer solutions, as determined by cryo-TEM. Correspondingly, dynamic light scattering showed that 1 w/v % solutions containing both PEG-(PLLA)(8) and PEG-(PDLA)(8) have larger "micelles" as compared to 1 w/v % single enantiomer solutions. With increasing polymer concentration and PLLA and PDLA block length, the storage modulus of the stereocomplexed hydrogels increases and the gelation time decreases. Stereocomplexed hydrogels with high storage moduli (up to 14 kPa) could be obtained at 37 degrees C in PBS. These stereocomplexed hydrogels are promising for use in biomedical applications, including drug delivery and tissue engineering, because they are biodegradable and the in-situ formation allows for easy immobilization of drugs and cells.  相似文献   

8.
Monodisperse stereocomplex nanogels were obtained through the self-assembly of an equimolar mixture of dextran-graft-poly(L-lactide) (Dex-g-PLLA) and dextran-graft-poly(D-lactide) (Dex-g-PDLA) amphiphilic copolymers with well-defined composition in a dilute aqueous solution. The stereocomplex nanogel possessed partially crystallized cores of hydrophobic polylactide (PLA) and the hydrophilic dextran skeleton by intra- and/or intermolecular self-assembly between PLLA and PDLA chains. The stereocomplex nanogels exhibited significantly lower critical aggregation concentration (CAC) value as well as stronger thermodynamic stability compared with those of the corresponding L- or D-isomer nanogels. The mean diameter of the stereocomplex nanogels was 70 nm with narrow size distribution, implying they were well-defined and presumably nanogels. Furthermore, stereocomplex nanogel exhibited strong kinetic stability. The tunable degradation properties of Dex-g-PLA nanogels were achieved by varying the number of grafted PLA chains as well as applying stereocomplexation. This study demonstrates the advantage of stereocomplexation in the design of biodegradable nanogels with enhanced stability.  相似文献   

9.
Homocrystallized and amorphous enantiomeric blend films were prepared from the melt of high molecular weight poly(L-lactide) (PLLA) and poly(D-lactide) (PDLA) (1:1) by crystallization and quenching, respectively. A phosphate-buffered solution was used to investigate effects of homocrystallinity via in vitro hydrolysis as well as crystallization process during the hydrolysis, which was performed for a period of 24 months at 37 degrees C and pH 7.4. Results derived from gravimetry, gel permeation chromatography, and tensile testing showed that hydrolyzability was higher for the homocrystallized film than for the amorphous film. Thus, probable mechanisms are proposed for the enhanced hydrolysis of the homocrystallized blend film compared with that of the amorphous blend film. The hydrolysis rate constant (k) values of the homocrystallized and amorphous films estimated from the changes in number-average molecular weight (M(n)) were 5.00 x 10(-3) and 3.32 x 10(-3) day(-1), respectively. Moreover, hydrolyzability of equimolar enantiomeric poly(lactic acid) blends can be altered in the k range of 0.73 x 10(-3) and 5.00 x 10(-3) day(-1) by varying their crystalline species, crystallinity, or molecular weights.  相似文献   

10.
The present paper reports, for the first time, the successful fabrication of layered double hydroxide (Mg-Al LDH)-reinforced polycaprolactone (PCL) nanofibers by electrospinning. Either the LDH in carbonate form or an LDH organically modified with 12-hydroxydodecanoic acid (LDH-HA) were incorporated into PCL and electrospun using a voltage of 20 KV. The LDH-HA was prepared by an ionic exchange reaction from pristine LDH and encapsulated into PCL from acetone solutions at 15 wt %. The morphological analysis showed pure PCL fibers with an average diameter of 600 +/- 50 nm, and this dimension was maintained in the fibers with LDH, with the inorganic component residing outside the fibers and not exfoliated. At variance, the fibers with the LDH-HA showed a significantly lower average diameter in the range of 350 +/- 50 nm, indicating the improved electrospinnability of PCL. Moreover, the inorganic lamellae were exfoliated, as shown by X-rays and residing inside the nanofibers as demonstrated by energy dispersive X-ray spectroscopy analysis. The structural parameters, such as degradation temperature and crystallinity, were investigated for all the samples and correlated with the electrospinning process.  相似文献   

11.
We report on the preparation and characterization of core-shell structure of bovine serum albumin (BSA) blended poly(vinyl alcohol) (PVA) composite nanofibers by using electrospinning process. The core-shell structure nanofibers have been electrospun from the homogeneous solution of BSA (as shell) and PVA (as core). The morphology, chemical compositions, structure and thermal properties of the resultant products were characterized by scanning electron microscopy (SEM), energy dispersive X-ray spectrometer (EDX), high-resolution transmission electron microscopy (HR-TEM), Fourier transform infrared (FT-IR) spectroscopy, differential scanning calorimetry, thermogravimetric analysis (TGA) and X-ray photoelectron spectroscopy (XPS) techniques. The blending ratio of PVA and BSA, molecular weight of BSA and the applied voltage of electrospinning process were observed to be the key influence factors on the formation of core-shell nanofibers structure. Based on the experimental findings, we proposed a possible physical mechanism for the formation of core-shell nanofibers structure of PVA blended BSA composite.  相似文献   

12.
R-lactide, a pivotal monomer for the production of poly (D-lactic acid) (PDLA) or stereocomplex poly (lactic acid) (PLA) was synthesized from alkyl (R)-lactate through a lipase-catalyzed reaction without racemization. From among several types of lipase, only lipase B from Candida antarctica (Novozym 435; CAL-B) was effective in the reaction that synthesized (R,R)-lactide. Enantiopure (R,R)-lactide, which consisted of over 99% enantiomeric excess, was synthesized from methyl (R)-lactate through CAL-B catalysis. Removal of the methanol by-product was critical to obtain a high level of lactide conversion. The (R,R)-lactide yield was 56% in a reaction containing 100 mg of Novozym 435, 10 mM methyl (R)-lactate and 1500 mg of molecular sieve 5 A in methyl tert-butyl ether (MTBE). The important monomer (R,R)-lactide that is required for the production of the widely recognized bio-plastic PDLA and the PLA stereocomplex can be obtained using this novel synthetic method.  相似文献   

13.
Electrospinning is a versatile process used to prepare micro- and nano- sized fibers from various polymers dissolved in volatile solvents. In this report, cellulose and cellulose-heparin composite fibers are prepared from nonvolatile room temperature ionic liquid (RTIL) solvents by electrospinning. RTILs are extracted from the biopolymer fiber after the fiber formation using a cosolvent. Micron to nanometer sized, branched fibers were obtained from 10% (w/w) concentration of polysaccharide biopolymer in RTIL solution with an applied voltage of 15-20 kV. Cellulose-heparin composite fibers showed anticoagulant activity, demonstrating that the bioactivity of heparin remained unaffected even on exposure to a high voltage involved in electrospinning.  相似文献   

14.
Poly(L-lactide) [i.e., poly(L-lactic acid) (PLLA)] was hydrolyzed in the melt in high-temperature and high-pressure water at the temperature range of 180-350 degrees C for a period of 30 min, and formation, racemization, and decomposition of lactic acids and molecular weight change of PLLA were investigated. The highest maximum yield of l-lactic acid, ca. 90%, was attained at 250 degrees C in the hydrolysis periods of 10-20 min. Too-high hydrolysis temperatures such as 350 degrees C induce the dramatic racemization and decomposition of formed lactic acids, resulting in decreased maximum yield of L-lactic acid. The hydrolysis of PLLA proceeds homogeneously and randomly via a bulk erosion mechanism. The molecular weight of PLLA decreased exponentially without formation of low-molecular-weight specific peaks originating from crystalline residues. The activation energy for the hydrolysis (deltaE(h)) of PLLA in the melt (180-250 degrees C) was 12.2 kcal x mol(-1), which is lower than 20.0 kcal x mol(-1) for PLLA and 19.9 kcal x mol(-1) for poly(dl-lactide) [i.e., poly(DL-lactic acid)] as a solid in the temperature range below the glass-transition temperature (21-45 degrees C). This study reveals that hydrolysis of PLLA in the melt is an effective and simple method to obtain l-lactic acid and to prepare PLLA having different molecular weights without containing the specific low-molecular-weight chains, because of the removal of the effect caused by crystalline residues.  相似文献   

15.
Periodontal diseases can lead to soft tissue defects. Tissue engineering can provide functional replacements for damaged tissues. Recently, electrospun nanofibers have attracted great interest for tissue engineering and drug delivery applications. This has been revealed that statins exhibit positive impacts on the proliferation and regeneration of periodontal tissues. Electrospun simvastatin loaded poly (lactic-co-glycolic acid) (SIM-PLGA-NF) were prepared using electrospinning technique. Optimal conditions for preparation of SIM-PLGA-NF (PLGA concentration of 30 wt%, voltage of 15 kV, and flow rate of 1.5 ml h−1) were identified using a 23 factorial design. The optimized SIM-PLGA-NFs (diameter of 640.2 ± 32.5 nm and simvastatin entrapment efficacy of 99.6 ± 1.5%) were surface modified with 1% w/v hyaluronic acid solution (1%HA- SIM-PLGA-NF) to improve their compatibility with fibroblasts and potential application as a periodontal tissue engineering scaffold. HA-SIM-PLGA NFs were analyzed using SEM, FTIR, and XRD. 1%HA-SIM-PLGA-NF had uniform, bead-free and interwoven morphology, which is similar to the extracellular matrix. The mechanical performance of SIM-PLGA-NFs and release profile of simvastatin from these nanofibers have been also greatly improved after coating with HA. In vitro cellular tests showed that the proliferation, adhesion, and differentiation of fibroblast cells positively enhanced on the surface of 1%HA- SIM-PLGA-NF. These results demonstrate the potential application of 1%HA-SIM-PLGA-NFs as a scaffold for periodontal tissue engineering.  相似文献   

16.
In this study, silk sericin nanofibers from sericin hope-silkworm, whose cocoons consist almost exclusively of sericin were successfully prepared by electrospinning method. Scanning electron microscopy (SEM) was used to observe the morphology of the fibers. The effect of spinning conditions, including the concentration of sericin cocoon solution, acceleration voltage, spinning distance and flow rate on the fiber morphologies and the size distribution of sericin nanofibers were examined. The structure and physical properties were also observed by Fourier transform infrared (FT-IR), differential scanning calorimetry (DSC) and thermogravimetric analysis (TG). The optimum conditions for producing finely thinner fibrous sericin nanofibers without beads were the concentration of sericin solution above 6-8 wt%, acceleration voltage ranging from 25 to 32 kV, spinning distance above 9 cm, and flow rate above 0.06 cm min(-1). The mean diameter of as spun sericin fibers varied from 114 to 430 nm at the different spinning conditions. In the as-spun fibers, silk sericin was present in a random coil conformation, while after methanol treatment, the molecular structure of silk sericin was transformed into a β-sheet containing structure. Sericin hope nanofiber demonstrated thermal degradation at lower temperature than the sericin hope cocoon, which probably due to the randomly coiled rich structure of the sericin hope nanofiber.  相似文献   

17.
The emerging fields of tissue engineering and biomaterials have begun to provide potential treatment options for liver failure. The goal of the present study is to investigate the ability of a poly L-lactic acid (PLLA) nanofiber scaffold to support and enhance hepatic differentiation of human bone marrow-derived mesenchymal stem cells (hMSCs). A scaffold composed of poly L-lactic acid and collagen was fabricated by the electrospinning technique. After characterizing isolated hMSCs, they were seeded onto PLLA nanofiber scaffolds and induced to differentiate into a hepatocyte lineage. The mRNA levels and protein expression of several important hepatic genes were determined using RT-PCR, immunocytochemistry and ELISA. Flow cytometry revealed that the isolated bone marrow-derived stem cells were positive for hMSC-specific markers CD73, CD44, CD105 and CD166 and negative for hematopoietic markers CD34 and CD45. The differentiation of these stem cells into adipocytes and osteoblasts demonstrated their multipotency. Scanning electron microscopy showed adherence of cells in the nanofiber scaffold during differentiation towards hepatocytes. Our results showed that expression levels of liver-specific markers such as albumin, α-fetoprotein, and cytokeratins 8 and 18 were higher in differentiated cells on the nanofibers than when cultured on plates. Importantly, liver functioning serum proteins, albumin and α-1 antitrypsin were secreted into the culture medium at higher levels by the differentiated cells on the nanofibers than on the plates, demonstrating that our nanofibrous scaffolds promoted and enhanced hepatic differentiation under our culture conditions. Our results show that the engineered PLLA nanofibrous scaffold is a conducive matrix for the differentiation of MSCs into functional hepatocyte-like cells. This represents the first step for the use of this nanofibrous scaffold for culture and differentiation of stem cells that may be employed for tissue engineering and cell-based therapy applications.  相似文献   

18.
Electrospinning is a versatile method to fabricate nanofibers of a range of polymeric and composite materials suitable as scaffolds for tissue engineering applications. In this study, we report the fabrication and characterization of polyaniline-carbon nanotube/poly(N-isopropyl acrylamide-co-methacrylic acid) (PANI-CNT/PNIPAm-co-MAA) composite nanofibers and PNIPAm-co-MAA nanofibers suitable as a three-dimensional (3D) conducting smart tissue scaffold using electrospinning. The chemical structure of the resulting nanofibers was characterized with FTIR and (1)H NMR spectroscopy. The surface morphology and average diameter of the nanofibers were observed by SEM. Cellular response of the nanofibers was studied with mice L929 fibroblasts. Cell viability was checked on 7th day of cell culture by double staining the cells with calcein-AM and PI dye. PANI-CNT/PNIPAm-co-MAA composite nanofibers were shown the highest cell growth and cell viability as compared to PNIPAm-co-MAA nanofibers. Cell viability in the composite nanofibers was obtained in order of 98% that indicates the composite nanofibers provide a better environment as a 3D scaffold for the cell proliferation and attachment suitable for tissue engineering applications.  相似文献   

19.
Y Li  F Chen  J Nie  D Yang 《Carbohydrate polymers》2012,90(4):1445-1451
The core-shell structure nanofibers of poly(lactic acid)/chitosan with different weight ratios were successfully electrospun from homogeneous solution. The preparation process was more simple and effective than double-needle electrospinning. The nanofibers were obtained with chitosan in shell while poly(lactic acid) in core attributing to phase separation, which were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD) and energy dispersive spectrometer (EDS). The electrospun nanofibrous membrane was evaluated in vitro by using mouse fibroblasts (L929) as reference cell lines. Cell culture results indicated that these materials were good in promoting cell growth and attachment, thus they could be used for tissue engineering and wound healing dressing.  相似文献   

20.
The electrospinning technique is a method used to produce nano and microfibers using the influence of electrostatic forces. Porous three dimensional networks of continuous and interconnected fibers as scaffolds were obtained from a poly (lactic acid) solution. The concentration of the polymeric solution, 12.5% m/w, as well as the conditions of voltage (V=11kV) and tip-metallic collector distance (H=13cm) were established to develop these scaffolds through the electrospinning process. The characteristics of the scaffolds, such as fiber diameter, sintering and the biomimetics of the characteristics of a native extra cellular matrix were verified by Scanning Electron Microscopy (SEM). The orientation induced in the material as a consequence of the electrospinning forces was studied by Differential Scanning Calorimetry (DSC) and X-Ray Diffraction (XRD).The same techniques were used to study the hydrolytic degradation of samples in a ringer solution (pH=7-7.4 at 37oC) for 12 weeks and showed evidences of superficial degradation on the microfibers. The suitability of these scaffolds for tissue engineering was studied through the primary cell culture of chondrocytes, by observing adhesion and cellular proliferation developed during 14 days of assay.  相似文献   

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