• <tr id="yyy80"></tr>
  • <sup id="yyy80"></sup>
  • <tfoot id="yyy80"><noscript id="yyy80"></noscript></tfoot>
  • 99热精品在线国产_美女午夜性视频免费_国产精品国产高清国产av_av欧美777_自拍偷自拍亚洲精品老妇_亚洲熟女精品中文字幕_www日本黄色视频网_国产精品野战在线观看 ?

    Preparation and Surface Modification of High-Density Chitosan/Functionalized Multi-walled Carbon Nanotubes Hollow Fibers

    2015-08-07 10:54:14SHAOMeiling邵梅玲DUPan杜盼YANGQing楊慶HSIAOBenjamin
    關(guān)鍵詞:整數(shù)教科書例題

    SHAO Mei-ling(邵梅玲),DU Pan(杜盼),YANG Qing(楊慶),HSIAO Benjamin S

    College of Material Science and Engineering,Donghua University,Shanghai201620,China

    Preparation and Surface Modification of High-Density Chitosan/Functionalized Multi-walled Carbon Nanotubes Hollow Fibers

    SHAO Mei-ling(邵梅玲),DU Pan(杜盼),YANG Qing(楊慶)*,HSIAO Benjamin S

    College of Material Science and Engineering,Donghua University,Shanghai201620,China

    Functionalized multi-walled carbon nanotubes(f-MWNTs)were prepared with chitosan via controlled surface deposition and crosslinking process and scanning electron m icroscopy (SEM),F(xiàn)ourier translation infrared spectroscopy(FT-IR)and X-ray diffraction(XRD)are used to character properties.A novel high-density chitosan(HCS)was dissolved in f-MWNTs dispersed dilute acetic acid with a maximal concentration of 5.8%.The hollow fibers can be made by extruding the solution into a dilute alkali solution through a wet-spinning process and the tensile properties of thematerialswere evaluated by universal tester.The surface property of fibers,pretreated by Helium(He)and the following grafted with gelatin was evaluated with X-ray photoelectron spectroscopy(XPS).As the hollow fibers were intended for neural tissue engineering,its suitability was evaluated in vitro using rat Schwann cells(RSC96)as model cells.The cells attachment,proliferation and morphology,were studied by variousm icroscopic techniques.Based on the results,the gelatin grafted HCS/f-MWNTs hollow fibers could be used as a potential cell carrier in neural tissue engineering.

    chitosan;multi-walled carbon nanotubes(MWNTs); hollow fibers;wet-spinning;cold plasma treatment;biocompatibility

    Introduction

    In recent years,the treatment for injury-induced nerve defect typically relays on donor tissues from the patient,and it leads to the issue of function loss at the donor sites,formation of potential painful neuromas and structural differences between donor and recipientnerves[1-2].Consequently,the development of artificial matrices that can support cell attachment,proliferation and differentiation,as well as deliver bioactive factors and/or host cells has attracted a great deal of attention[3-4].At present,chitin and chitosan have become protagonist in the field of nerve regeneration thanks to the relevant biochem ical significance,and in particular itaccelerates macrophage m igration and nerve cells proliferation,and promotes granulation and vascularization[5].Besides,the solubility of chitosan with high density is quite high(nearly 3 times as ordinary chitosan)for the regular spatial structure,which will endow fiber production with good mechanical strength ow ing to the dense structure.

    Carbon nanotubes(CNTs)have also attracted a great deal of attention for biological applications both at molecular and cellular levels due to their novel properties,such as superior strength,electrical conductivity and availability of chemical functionalization[6].Mattson et al.[7]reported the feasibility of using CNTs as a substrate for neuronal grow th and it had well elaborated neuritis and branching on multi-walled carbon nanotubes(MWNTs).In this work,chemically functionalized MWNTs(f-MWNTs)were dispersed in high-density chitosan (HCS)to obtain high strength hollow fibers.

    Gelatin is a partial derivative of collagen,which is the major component of skin,bone,cartilage and connective tissues[8].It is commonly used in tissue engineering because of its biodegradability,biocompatibility and easy availability.In this paper,gelatin is used formodification of the hollow fibers' surface property to strengthen the interaction between fibers and cells.Among the various surface modification approaches available for chitosan,plasma treatment seems to be most prom ising.So cold plasma pretreatment is carried out to induce gelatin grafting and rat Schwann cells(RSC96)are used to assess its efficacy in promoting neuron attachment and proliferation in vitro.

    1 Experimental

    1.1 M aterials

    HCS(bulk density≥0.8 g/mL)in our experiments was supplied by Golden-Shell Biochemical Co.,Ltd.,China with the deacetylation degree of 90%,and the viscosity-average molecular weight measured by Ubbelohde viscometer(NCY-4,China)is 6.81×105.MWNTs were obtained from Shenzhen Nanotech PortCo.Ltd.,China.Acetic acid,nitric acid,sulphuric acid,ethanol and sodium hydroxide(NaOH)are all purchased from National Pharmaceutical Group Chemical Reagent Co.,Ltd. China.Gelatin for surface grafting was obtained from Shanghai Fankelbio Science&Technology Co.,Ltd.,China.All of the cell-related reagentswere bought from Gibco(Invitrogen,USA).

    1.2 Preparation of f-MWNTs

    The purified and oxidized pretreatmentof raw MWNTswas performed in hot reflux condenser by heating concentrated sulphuric acid and nitrating acid mixtures(3∶1 by volume)at 110℃for12 h.Then themixturewas extracted through a0.22 μm polytetrafluoroethylene filter membrane.Follow ing that,the residue was washed by deionized water to neutrality after extraction and then dried in vacuum oven at 80℃.Then 100 mg HCS was dissolved in 100 m L dilute acetic acid solution (pH=2),and 100 mg pretreated MWNTs were added in the solution and ultrasonic treated for 2 h in a sonicating bath followed by magnetic stirring for 1 h.The weak aqua ammonia was dropped into the HCS/MWNTs dispersion to make pH of the system up to 10 and HCS would deposit on the surface of MWNTs.After adding 0.02 g glutaraldehyde(6%water solution)into themixture,itwas heated to 60℃for 1.5 h for deposited HCS cross linking reaction and unreacted HCS was removed by dilute acetic acid solution.Then f-MWNTs was obtained by collecting with centrifugation and drying to constant weight at50℃in a vacuum oven.

    1.3 Preparation of HCS/f-MWNTs hollow fibers via wet spinning

    The preparation of spinning solution was carried out as follows.A certain amount of f-MWNTs was ultrasonic welldispersed in 2%dilute acetic acid solution,and then dried HCS power was added and stirred rapidly.The concentration of HCS was unchanged(maintained at 5.8%)in the solution and the content of f-MWNTs were 0.1%,0.3%,0.5%and 0.7%(relative to the mass of HCS)respectively.The m ixture gradually turned into a homogeneous solution after stirring for 3 h.In this work,the wet spinning line used to produce the hollow fibers was our laboratory homemade instrument. Solutions were spun at room temperature with extrusion rate of 300m L/h and coagulated in coagulation baths(3%NaOH and 3%ethanol water mixture).The collected hollow fibers were washed in deionized water for about 24 h to remove residual solvent and dried at room temperature for 12 h.

    1.4 Plasma pretreatment and surfacemodification

    The hollow fibers were put into a vacuum chamber of the cold plasma processor;then evacuated the chamber until the atmospheric pressure dropped down to 2-3 Pa and the reactant He gas was charged into for 10 m in to remove residual air. Next,He was fed into constantly to maintain the working pressure at20 Pawith the discharge power of20-100W.After treated for 30-150 s,some of the pretreated samples were soaked into gelatin solution(10%)overnight to allow the graft reaction completed.Follow ing by washed with deionized water and cleaned ultrasonically for 3 times to remove absorbed gelatin,the products were immersed into deionized water overnight at 40℃to remove the unreacted gelatin thoroughly and then died at room temperature.

    1.5 Cell culture on the hollow fibers

    The samples were immersed in 75%(v/v)ethanol aqueous for 1 h followed by ultraviolet radiation for 1 h to sterilize and five parts with the same quality of every sample were selected to participate in the experiment to calculate the error bar.Then all the samples were pre-cultured in RCS96 culture medium that containing 90%Dulbecco's modified eagle'smedium(DMEM)solution,9%bovine serum albumin (BSA)and 1%Penicillin-Streptomycin for 24 h.Next,cell suspensionswith specific density were seeded on each sample in a 24-well plate and themedium was changed every third day.The density of cells for assessing attachmentand proliferation were2. 5×106cells/well and 1×104cells/well respectively.The cell/ sample constructswere incubated under sterile conditions at37℃in a humidified incubator of 5%CO2.

    1.6 M easurements

    The morphology of the samples and cell grow th on the fiberswere examined by scanning electron m icroscopy(SEM) (JSM-5600LV,Japan).For SEM analysis,the fibers were frozen in liquid nitrogen,fractured immediately,and vacuumdried.The cell/sample constructs immobilized with 4% paraformaldehyde and subjected to sequential dehydration for 15 min each with ethanol series(60%,70%,80%,90%and 100%),then dried at room temperature.Surface properties of the f-MWNTswere tested using the automatic target recognition (ATR)attachment of Fourier translation infrared spectroscopy (FT-IR,Nicolet8700,USA)under spectral range of650-4 000 cm-1at a resolution of 4 cm-1.The crystalline structure of the sampleswas examined using X-ray diffraction(XRD)(D/max- 2550 PC,Japan).The tensile properties of the fibers were measured by a universal testing machine(20 kN WDW3020,China).The sample was fixed in the clamp with a loading velocity of10mm/min and five parts of every samplewere tested to take the average.The surface elements and contents of fibers after modification were characterized with the X-ray photoelectron spectroscopy(XPS)(ESCALAB 200R,UK).

    1.7 Cell attachment and proliferation on hollow fibers

    Cell adhesion evaluation on the hollow fiberswasmeasured by the follow ing method in this paper:the cell/sample constructs after 2,8 and 24 h of incubation were washed with DMEM for 3 times to remove the cells thathad not adsorbed on the surface,then 0.5 m L Tryspin-ethylene diamine tetraacetic acid(EDTA)and 0.5 m L cell-culturemedium were added into every constructand fluttered lightly to help cells slough-off from the construct.The number of cells in the suspension was counted by using Cell Counter(Moxi Z,USA).The adhesion rate on the surface of cell-culture plate is regarded as100%,so the cell adhesion rate(R)was calculated as follows:R/%=where N is the cell number of attached on samples'1surface;N0is the number of blank plate.CCK-8(cell counting kit-8)is a kind of cell viability assay reagent with higher sensitivity and better reproducibility;and the cytotoxicity of fibers was measured by the common method:cell/sample constructs after1,3,5,7,9 and 11 d of culturewerewashed for 3 times with DMEM to remove dead cells,then incubated at 37℃for 2.5 h with the addition of 500μL CCK-8 reagent in medium solution(10%(v/v)).The cell activity can be obtained from the optical density(OD)of the solutionmeasured by Multifunctionalmicroplate reader(DG5031,USA).

    2 Results and Discussion

    Figure 1 is the representative SEM micrographs of MWNTs taken with large enough magnification before and after treatment.We can view directly that most of the tube bodies spread out with significant improvement of agglomeration that close to single dispersion and tangle also is eased after surface deposition and crosslinking process(from Fig.1(b)).In addition,during the process of pre-oxidation,amorphous carbon and some short tubes are removed by the role of concentrated acid,so the treatment also endows the tubes with uniform thickness,and it shows a little thicker than the raw tubes for the deposition of HCS coating around the tubes.

    From photos of dispersivity(Fig.1(c)),we can clearly see that the dispersion of f-MWNTs ismuch better than the raw one and this superiority already appears after ultrasonication for half an hour.Even though the MWNTs dispersed as well as f-MWNTs after 2 h,it agglomerates together again after 12 h.

    Fig.1 Themicromorphologies of MWNTs(a)before and(b)after surface functional treatment and(c)the dispersivity contrast in water

    2.2 Chem ical and crystalline structures of f-MWNTs

    Typical FT-IR spectra of MWNTs before and after being treated with acid mixture for 2 h and then deposited with HCS are shown in Fig.2(A),in which two new peaks around 1 425.1 and 1 027.0 cm-1appear.The peak at1 425.1 cm-1is normally assigned to the stretching vibration of C—O and bending vibration of O—H in COOH[9-10];the peak at 1027 cm-1that caused by stretching vibration of symmetrical C—O—C is also the characteristic peak of HCS.Meanwhile,after treatment peaks at around 3 327.1,2 923.1 and 2 363.0 cm-1are all weakened which ow ing to the attenuation of van der Waals forceswith strong acid.Moreover,the peak ataround 1 631.0 cm-1,which can be assigned to the stretching mode of—C=C—groups[11-12],shows a little shift to lower frequency with treatment,which also suggests some structural change in the tubes.

    Fig.2 FT-IR spectra(A)and WAXD patterns(B)of raw and modified MWNTs

    The crystallinity of MWNTs characterized by XRD is shown in Fig.2(B).It can be clearly seen there is a visible diffraction peak at around 18°which can represent the existence of HCS on the pattern of f-MWNTs.Based on the above conclusions,the result of this functional experiment agrees with our opinion that the HCS deposits on the MWNTs successfully.

    2.3 Cross section morphologies of hollow fibers

    Seen from the SEM cross section photos of hollow fibers in Fig.3,there are significant differences with increasing of f-MWNTs.The white highlights in these photos represent the existence of f-MWNTs,and we can get the follow ing conclusions.When the content of f-MWNTs increases to 0. 5%,it can be evenly distributed in the HCSmatrix thatendows the section with dense structures(from Fig.3(c))and the image also can further illustrate that the MWNTs after modification can disperse uniform ly in the solution;while if the content continues to increase to 0.7%,the excess f-MWNTs aggregates together that make the section rough and uneven (from Fig.3(d)).To sum up the above analysis,the adequate addition of f-MWNTs can offer perfect section morphology for hollow fibers.

    Fig.3 SEM cross section photographs of hollow fibers with different contents of f-MWNTs:(a)0.0%,(b)0.3%,(c)0.5%,and(d)0.7%

    2.4 M echanical properties of hollow fibers

    從認知難度上看,循環(huán)小數(shù)、有限小數(shù)和分數(shù)形式的數(shù)的理解要比整數(shù)困難,但是RJ版教科書中以整數(shù)形式考查有理數(shù)的例題數(shù)目要多于分數(shù)和小數(shù),對形式不易理解的數(shù)的舉例少于易理解的數(shù),甚至未涉及循環(huán)小數(shù)的例題,這易導(dǎo)致學(xué)生對難點掌握不牢固.CM教科書中以分數(shù)、有限小數(shù)形式考查有理數(shù)的例題數(shù)量要大于整數(shù),相比RJ版教科書更遵循學(xué)生的認知難度.

    Themechanical properties of hollow fibers with different contents of f-MWNTs are shown in Fig.4 and it shows that the addition of f-MWNTs can improve fibers'mechanical properties effectively.After comparative analysis,we can easily obtain that the hollow fiberswith 0.5%f-MWNTs exhibit the optimal tensile property with themaximum tensile strength and elasticity modulus of 9.33 MPa and 2.34 GPa,respectively(as shown in Fig.4(b)).It can be closely related to the dense structures as mentioned in the previous analysis.For one thing,in the solution flow field,f-MWNTs with excellent length/diameter ratio and flexibility orient along the fibers'axial direction,so the axial tensile force can be increased;for another,the addition of f-MWNTs with high crystallinity can enhance the intermolecular force thus affecting the movement of long segments,which leads to the reduced deformation of the macromolecules,and consequently there is the grow th of strength and modulus whereas elongation at break reduces slightly.When the amount of addition reaches 0.7%,the mechanical parameters reducemainly for the increase of internal defects in hollow fibers caused by excess particle agglomeration.To sum up,the results of mechanical analysis are nearly consistentwith themorphology analysiswhich follows thatmicrostructure is a direct factor to affect the mechanical properties.Thus,the hollow fibers with 0.5%f-MWNTs (HCS/f-MWNTs hollow fibers)will be chosen to carry out the follow ing experiments.

    Fig.4 Stress-strain curves of the hollow fiberswith different contents of f-MWNTs(a)and the changes of tensile strength and elasticity moduluswith content(b)

    2.5 Surface elemental analysis of the modified hollow fibers

    Plasma treatment which is an efficient method with simplicity of operation has been w idely used in improving the surface properties of materials for a long time.In this paper,cold plasma technology was applied for the modification of hollow fibers to endure the surface with reactive property.In previous experiments,we found that the surface properties after plasma treatmentwas closely linked to the processing time and discharge power[13-14].From several exploratory experiments,we may draw a conclusion that,the HCS/f-MWNTs hollow fibers samples treated at 60 W maintained for 120 s displayed the optimal hydrophilicity which means the surface with active properties,so this value of the parameter will be chosen for surface grafting.

    In this paper,XPS technology was carried out to characterize the changes of chem ical composition and combination of the surface before and after modification.The survey scan spectra that can be used to identify the elements existing on the surface of fibers are shown in Fig.5(A).The figure shows that there are C1s,N1s and O1s peaks at approximate 285,420 and 530 eV respectively on the surface of all fibers[15].The reinforcement of O1s peak on the fibers after He-plasma pretreated can testify that the increase in oxygen content of the surface and the obviousenhanced N1s peak on the gelatin-grafted fibers can also illustrate that gelatin has been introduced onto the surface successfully.In Fig.5,B.E. represents electron binding energy.

    Figures 5(B)-(D)show the spectrogram of C1s after peak separation and fitting which can determ ine the elemental combination of themodified fibers.The peaks located at284.2,286.0 and 288.4 eV correspond to C—C,C= O and C= N,respectively[16-17].After carefully analyzing the research result,the integral peak areas of C= O and C= N bonds increased obviously after modification.This is a strong indication that there are more polar groups bonded on the surface aftermodification,such as carboxyl groups(—COOH)and amide bonds(—CO—NH—).

    The percentage and ratio of elements of the samples based on XPSquantitative analysis are shown in Table1.The data can reflect the visual change of the carbon-containing function groups.After plasma pretreatment,the O/C ratio is significantly increased,from 42.01%to 65.71%.This can be associated with the formation of new oxygen-containing groups. During the pretreatment process,He-plasma acted on samples' surface and energy was transm itted by metastable chemical group with a relatively high energy,and then the samples were exposed to air to incorporate oxygen and resulted in the oxygen content significantly increasing(from 29.07%to 38.28%).In the follow ing grafting reaction,the active groups from gelatin reacted with the above-mentioned new groups to introduce a large amount of nitrogen(from 1.73%to 7.54%)to realize the grafting reaction.By data analysis,after modification the ratio of C—C drops from 61.03%down to 45.79%with the increase of both C= O(from 27.31%to 34.79)and C=N bonds(from 11.67%to 19.42%).The results indicate that during the treatment process,the C—C bond breaks down to form C= O and C= N bonds or other polar groups.

    Fig.5 XPS survey scan spectra and C1s spectra of the hollow fibers before and after treatment:(A)survey scan spectra of three samples;(B)C1s of the untreated samples;(C)C1s of the He-plasma pretreated samples;(D)C1s of the gelatin-grafted samples

    Table 1 Quantitative elementary analysis of the untreated,He-plasma pretreated,and gelatin-grafted samplesmeasured by XPS

    2.6 Attachment and proliferation of RSC96 on hollow fibers

    The results of cell attachmentand proliferation on fibers are shown in Fig.6.As indicated in Fig.6(a),RSC96 cells can be well attached on all the fibers after about 8 h and the rates of four fibers'change tendency with culture time are almost consistent.So we can come to the conclusions that a small amount of f-MWNTs in fibers with the rate of 77.44%that equal to HCS fibers(78.29%)after 24 h has no influence on cell adhesion;the rate of fibers after plasma pretreatment also accounts for 96.30%which mainly benefits from the improved hydrophilicity;as an important aspect,it shows that fibers after gelatin grafted with adhesion rate up to 75.10%have the best cell affinity than other fibers in the first2 h and this advantage has beenmaintained to the last(up to 101.86%).

    The activity and proliferation of cellon different fibers after culturing for different days are shown in Fig.6(b)and the higher OD value representsmore live cells.As revealed in this figure,the tendency of cell proliferation on HCS/f-MWNTs fibers can nearly keep in step with the HCS fibers;after pretreated with plasma and especially grafted with gelatin,compared with others the viability of cell is improvedsignificantly,and obvious cells grow ths on the modified fibers are still observed after cultivation over one week.Reports by a few researchers demonstrated that gelatin enhanced the attachment and proliferation of cells[18-19].Gelatin has the same structure with extracellularmatrix.For the protein of cell wall,hydrophilic amino acids existed in outer region because of a repulsion caused by a protein and hydrophobic component at the inner region[20].So it can create amore favorable environment for cells and the cytocompatibility of the fibers is substantially improved by the bioactivity of the gelatin layer.

    Fig.6 Grow th of RSC96 on different fibers:(a)adhesion rate in different time on hollow fibers before and aftermodification; (b)cell proliferation results obtained by the CCK-8 test

    2.7 Cellmorphology on nano-fibersmats

    The representative SEM micrographs of RSC96 cells cultured for5 d on the fibers are shown in Fig.7.It can be seen that the cell grow th on the composite hollow fibers with f-MWNTs is in the same way with HCS fibers(shown in Figs.7 (a)and(b)),meaning that the addition of f-MWNTs has no effect on cell grow th.In addition,after pretreatment the numbers of cells on fibers(Fig.7(c))are obviouslymore than the untreated samples and it provides an evidence for the stronger cell-fibers interaction with amore hydrophilic surface. In comparison,the gelatin grafted fibers culture has a more intense than other samples,even a part or portion that overlaps (Fig.7(d)).It justmeans that cells canmultiply rapidly on the fibers,so it indicates that gelatin grafting is beneficial for cell grow th with the provision of some factors by gelatin layerwhich can enhance cells cytoactivity and cytoproliferation throughout the culture period.

    Fig.7 SEM micrographs of RSC96 cells cultured for 5 d on the different fibers:(a)HCS hollow fibers,(b)HCS/f-MWNTs fibers,(c)plasma pretreated HCS/f-MWNTs fibers,and(d)gelatin grafted HCS/f-MWNTs fibers

    3 Conclusions

    The dispersivity and compatibility with HCS of f-MWNTs thatobtained via a controlled surface deposition and crosslinking process had been improved a lot;the hollow fibers with the f-MWNTs content up to 0.5%relative to HCS exhibited the optimal tensile property with the maximum tensile strength and elasticity modulus of 9.33 MPa and 2.34 GPa,respectively. The fiber was then immersed into gelatin solution for grafting after pretreatment.XPS results showed that some oxygen elementwas introduced on the surface of the pretreated samples for subsequently exposing to air(atomic fraction rising from 29.07%to 38.28%);in the follow ing grafting reaction,the active groups from gelatin reacted with the new groups to introduced a large amountof nitrogen(from 1.73%to 7.54%) and the C—C bond broke down to form C= O and C= N bonds or other polar groups to realize the grafting reaction. From biological characterization such as cell attachment,cell morphology and proliferation,these results demonstrated the follow ing two aspects.First,the addition of a small amount of f-MWNTs in fiberswith the celladhesion rate of77.44%which equalled HCS fibers(78.29%)after 24 h had no effect on cell behavior;second,cells seeded in fibers grafted with gelatin had higher adhesion rate and cells could proliferate faster in the same timewhich proved that the superior ability of fibers after surface modification with gelatin could well support RSC96 grow th and proliferation.

    [1]Richardson P M.Peripheral Nerve Regeneration:an Overview[M].New York:Academic Press,2009:557-560.

    [2]Chen Y S,Liu C J,Cheng C Y,et al.Effect of Bilobalide on Peripheral Nerve Regeneration[J].Biomaterials,2004,25(3): 509-514.

    [3]Nair L S,Laurencin C T.Biodegradable Polymers as Biomaterials[J].Progress in Polymer Science,2007,32(8/9): 762-798.

    [4]Whang K,Goldstick T K,Healy K E.A Biodegradable Polymer Scaffold for Delivery of Osteotropic Factors[J].Biomaterials,2000,21(24):2545-2551.

    [5]Jayakumar R,Prabaharan M,Sudheesh Kumar P T,et al.Biomaterials Based on Chitin and Chitosan in Wound Dressing Applications[J].Biotechnology Advances,2011,29(3):322-337.

    [6]Hu H,Ni Y C,Montana V,et al.Chem ically Functionalized Carbon Nanotubes as Substrates for Neuronal Grow th[J].Nano Letters,2004,4(3):507-511.

    [7]Mattson M P,Haddon R C,Rao A M.Molecular Functionalization of Carbon Nanotubes and Use as Substrates for Neuronal Grow th[J].Journal of Molecular Neuroscience,2000,14(3):175-182.

    [8]Chen J,Su C L.Surface Modification of Electrospun PLLA Nanofibers by Plasma Treatment and Cationized Gelatin Immobilization for Cartilage Tissue Engineering[J].Acta Biomaterialia,2011,7(1):234-243.

    [9]Mawhinney D B,Naumenko V,Kuznetsova A,et al.Infrared Spectral Evidence for the Etching of Carbon Nanotubes:Ozone Oxidation at 298 K[J].Journal of the American Chemical Society,2000,122(10):2383-2384.

    [10]Bahr JL,Tour JM.Covalent Chem istry of Single-Wall Carbon Nanotubes[J].Journal of Materials Chemistry,2002,12(7): 1952-1958.

    [11]Zhang JF,Zou H X,Qing Q,et al.Effect of Chemical Oxidation on the Structure of Single-Walled Carbon Nanotubes[J].Journal of Physical Chemistry B,2003,107(16):3712-3718.

    [12]Chiang Y,Lin W H,Chang Y C.The Influence of Treatment Duration on Multi-walled Carbon Nanotubes Functionalized by H2SO4/HNO3Oxidation[J].Applied Surface Science,2011,257(6):2401-2410.

    [13]Shi T N,Shao M L,Zhang H R,et al.Surface Modification of Porous Poly(tetrafluoro-ethylene)Film via Cold Plasma Treatment[J].Applied Surface Science,2011,258(4):1474-1479.

    [14]Shao M L,Chen L,Yang Q.Preparation and Surface Modification of Electrospun Aligned Poly(butylene carbonate)Nanofibers[J].Journal of Applied Polymer Science,2013,130(1):411-418.

    [15]Kull K R,Steen M L,F(xiàn)isher E R.Surface Modification with Nitrogen-Containing Plasmas to Produce Hydrophilic,Low-Fouling Membranes[J].Journal of Membrane Science,2005,246(2):203-215.

    [16]Kim E S,Yu Q S,Deng B L.Plasma Surface Modification of Nanofiltration(NF)Thin-Film Composite(TFC)Membranes to Improve Anti Organic Fouling[J].Applied Surface Science,2011,257(23):9863-9871.

    [17]Ni H C,Lin Z Y,Hsu S H,et al.The Use of Air Plasma in Surface Modification of Peripheral Nerve Conduits[J].Acta Biomaterialia,2010,6(6):2066-2076.

    [18]Ghasem iM L,Prabhakaran M P,Morshed M,et al.Electrospun Poly(ε-caprolactone)/Gelatin Nanofibrous Scaffolds for Nerve Tissue Engineering[J].Biomaterials,2008,29(34):4532-4539.

    [19]Kwon O,M yung S,Lee C,et al.Comparison of the Surface Characteristics of Polypropylene Films Treated by Ar and M ixed Gas(Ar/O2)Atmospheric Pressure Plasma[J].Journal of Colloid and Interface Science,2006,295(2):409-416.

    [20]Martino S,D'Angelo F,Armentano I,et al.Stem Cell-Biomaterial Interactions for Regenerative Medicine[J]. Biotechnology Advances,2012,30(1):338-351.

    TQ342+.8

    A

    1672-5220(2015)04-0602-07

    date:2014-03-26

    s:State Key Laboratory for Modification of Chem ical Fibers and Polymer Materials,China(No.LZ0902);Shanghai Science and Technical Comm ittee,China(No.12DZ194030)

    *Correspondence should be addressed to YANG Qing,E-mail:yangqing@dhu.edu.cn

    猜你喜歡
    整數(shù)教科書例題
    《備急千金要方》:中醫(yī)急診教科書
    由一道簡單例題所引發(fā)的思考
    由一道簡單例題所引發(fā)的思考
    一類整數(shù)遞推數(shù)列的周期性
    向量中一道例題的推廣及應(yīng)用
    藏起來的教科書
    對一道教科書習(xí)題的再探索
    問渠哪得清如許 為有源頭活水來
    被藏起來的教科書
    聚焦不等式(組)的“整數(shù)解”
    久久精品国产自在天天线| 美女xxoo啪啪120秒动态图| 黑人高潮一二区| 免费观看人在逋| 成年女人永久免费观看视频| 欧美人与善性xxx| 国产成人aa在线观看| 最近在线观看免费完整版| 少妇熟女欧美另类| 亚洲精品久久国产高清桃花| 综合色丁香网| 国内少妇人妻偷人精品xxx网站| 国产av在哪里看| 99国产极品粉嫩在线观看| 搡老岳熟女国产| www.色视频.com| 欧美精品国产亚洲| 亚洲无线在线观看| 色哟哟·www| 久久久久久伊人网av| 在线免费观看的www视频| 亚洲国产欧洲综合997久久,| 亚洲一级一片aⅴ在线观看| 变态另类丝袜制服| 少妇裸体淫交视频免费看高清| 欧美性感艳星| 欧美成人一区二区免费高清观看| 国产精品精品国产色婷婷| 精品免费久久久久久久清纯| 日本一二三区视频观看| 久久午夜亚洲精品久久| 美女 人体艺术 gogo| 国产亚洲欧美98| 精品一区二区三区视频在线| 久久久久九九精品影院| 在线免费十八禁| 性色avwww在线观看| 最近的中文字幕免费完整| 亚洲人与动物交配视频| 午夜福利成人在线免费观看| 一本精品99久久精品77| 国产伦一二天堂av在线观看| 欧美区成人在线视频| 大香蕉久久网| 全区人妻精品视频| 精品不卡国产一区二区三区| 一级黄色大片毛片| 桃色一区二区三区在线观看| 免费看光身美女| 亚洲av免费在线观看| 在线天堂最新版资源| 欧美成人精品欧美一级黄| 精品一区二区免费观看| 国产老妇女一区| 看片在线看免费视频| 国产精品伦人一区二区| 91久久精品国产一区二区成人| 亚洲国产欧美人成| 国产亚洲精品久久久久久毛片| 国产 一区 欧美 日韩| a级毛片免费高清观看在线播放| 国产精品一区二区性色av| 日韩国内少妇激情av| 久久久精品大字幕| 日本熟妇午夜| 久久精品久久久久久噜噜老黄 | 国产伦精品一区二区三区视频9| 亚洲国产欧美人成| 麻豆精品久久久久久蜜桃| 成人综合一区亚洲| 三级国产精品欧美在线观看| 亚洲内射少妇av| 禁无遮挡网站| 免费观看精品视频网站| 国产女主播在线喷水免费视频网站 | 日韩欧美精品v在线| 欧美色欧美亚洲另类二区| 黄色一级大片看看| а√天堂www在线а√下载| 亚洲av中文av极速乱| 日本撒尿小便嘘嘘汇集6| 寂寞人妻少妇视频99o| 午夜精品在线福利| 欧美性猛交黑人性爽| 蜜臀久久99精品久久宅男| 亚洲中文日韩欧美视频| 又粗又爽又猛毛片免费看| 久久亚洲国产成人精品v| 日日摸夜夜添夜夜添av毛片| 亚洲精品日韩av片在线观看| 欧美激情在线99| 国产69精品久久久久777片| 久久久欧美国产精品| 在线观看av片永久免费下载| 乱人视频在线观看| 国产91av在线免费观看| 亚洲电影在线观看av| 国产精品国产三级国产av玫瑰| 久久久久九九精品影院| 亚洲欧美日韩高清在线视频| 日韩精品青青久久久久久| 菩萨蛮人人尽说江南好唐韦庄 | 国产女主播在线喷水免费视频网站 | 日本撒尿小便嘘嘘汇集6| 久久久欧美国产精品| 男人舔奶头视频| 久久久精品94久久精品| 欧美3d第一页| 岛国在线免费视频观看| 一级黄片播放器| 五月伊人婷婷丁香| 国产成人a区在线观看| 久久久久国内视频| АⅤ资源中文在线天堂| 国产极品精品免费视频能看的| 99国产精品一区二区蜜桃av| 欧美高清性xxxxhd video| 欧美不卡视频在线免费观看| 免费电影在线观看免费观看| 国产真实乱freesex| 国产探花在线观看一区二区| av中文乱码字幕在线| 国产精品爽爽va在线观看网站| 国产中年淑女户外野战色| 看黄色毛片网站| 日韩av不卡免费在线播放| 亚洲熟妇中文字幕五十中出| 三级毛片av免费| 18+在线观看网站| 人人妻,人人澡人人爽秒播| 亚洲最大成人av| 日本撒尿小便嘘嘘汇集6| 特级一级黄色大片| 九九久久精品国产亚洲av麻豆| 久久天躁狠狠躁夜夜2o2o| 日本在线视频免费播放| 麻豆久久精品国产亚洲av| 国产黄a三级三级三级人| 亚洲成人久久爱视频| 看黄色毛片网站| 国产午夜精品久久久久久一区二区三区 | 亚洲七黄色美女视频| 亚洲人成网站在线播| 国产高清不卡午夜福利| 99在线人妻在线中文字幕| 成人性生交大片免费视频hd| 国产精品99久久久久久久久| 久久久成人免费电影| 日韩高清综合在线| a级一级毛片免费在线观看| 日产精品乱码卡一卡2卡三| 俄罗斯特黄特色一大片| 尤物成人国产欧美一区二区三区| 日韩欧美 国产精品| 久久久精品94久久精品| 国产91av在线免费观看| 12—13女人毛片做爰片一| 91久久精品国产一区二区三区| 最近的中文字幕免费完整| 国产精品不卡视频一区二区| 国产高清激情床上av| 中国美女看黄片| 国产色爽女视频免费观看| 12—13女人毛片做爰片一| 嫩草影院精品99| 一级av片app| 亚洲av五月六月丁香网| 欧美精品国产亚洲| 国产精品久久久久久久久免| 亚洲国产高清在线一区二区三| 床上黄色一级片| 久久人人爽人人片av| 久久精品国产亚洲av涩爱 | 毛片一级片免费看久久久久| 夜夜夜夜夜久久久久| 精品少妇黑人巨大在线播放 | 最好的美女福利视频网| 六月丁香七月| 亚洲无线观看免费| 亚洲av免费在线观看| 国产精品一二三区在线看| 熟妇人妻久久中文字幕3abv| 亚洲精品在线观看二区| 少妇被粗大猛烈的视频| 搡女人真爽免费视频火全软件 | 观看美女的网站| 女人被狂操c到高潮| 免费看光身美女| 在线观看一区二区三区| 午夜亚洲福利在线播放| 国产美女午夜福利| 中文字幕av在线有码专区| 欧美又色又爽又黄视频| 天美传媒精品一区二区| 欧美3d第一页| 熟妇人妻久久中文字幕3abv| 日日啪夜夜撸| 麻豆国产97在线/欧美| 一区二区三区免费毛片| 日本一本二区三区精品| 伦理电影大哥的女人| 日韩欧美精品v在线| 听说在线观看完整版免费高清| 秋霞在线观看毛片| 人妻丰满熟妇av一区二区三区| 欧美最新免费一区二区三区| 热99在线观看视频| 嫩草影院精品99| 99热这里只有是精品在线观看| 99热这里只有精品一区| 国产精品不卡视频一区二区| 波多野结衣高清作品| 国产视频内射| 老熟妇仑乱视频hdxx| 一区二区三区四区激情视频 | 永久网站在线| 91久久精品国产一区二区成人| 美女被艹到高潮喷水动态| 美女免费视频网站| 一进一出抽搐动态| 亚洲中文字幕日韩| 日日摸夜夜添夜夜爱| 国产伦精品一区二区三区四那| 黄片wwwwww| 亚洲国产色片| 欧美日韩综合久久久久久| 精品久久国产蜜桃| 亚洲图色成人| 日韩精品青青久久久久久| 欧美xxxx黑人xx丫x性爽| 精品久久久久久久人妻蜜臀av| 国产伦精品一区二区三区视频9| 99热6这里只有精品| 亚洲专区国产一区二区| 搡老妇女老女人老熟妇| 亚洲中文日韩欧美视频| 色吧在线观看| 成年av动漫网址| 在线观看av片永久免费下载| 精品久久久久久久末码| 久久久久免费精品人妻一区二区| 免费av毛片视频| 国产69精品久久久久777片| 永久网站在线| 插阴视频在线观看视频| 国产探花极品一区二区| 九色成人免费人妻av| 一卡2卡三卡四卡精品乱码亚洲| 悠悠久久av| 18禁在线无遮挡免费观看视频 | 久久6这里有精品| 成人精品一区二区免费| 国产私拍福利视频在线观看| 成人亚洲精品av一区二区| 97碰自拍视频| 插阴视频在线观看视频| 亚洲经典国产精华液单| 搡老妇女老女人老熟妇| 91狼人影院| 日本精品一区二区三区蜜桃| 国产乱人偷精品视频| 2021天堂中文幕一二区在线观| 日本一二三区视频观看| 国产探花极品一区二区| 久久综合国产亚洲精品| 麻豆一二三区av精品| 高清日韩中文字幕在线| 亚洲久久久久久中文字幕| av中文乱码字幕在线| 1024手机看黄色片| 亚洲人成网站在线播放欧美日韩| 日韩av在线大香蕉| 国产亚洲精品av在线| 亚洲av成人av| 久久久a久久爽久久v久久| 少妇人妻一区二区三区视频| 国产黄色视频一区二区在线观看 | 日韩,欧美,国产一区二区三区 | 性色avwww在线观看| 中文字幕免费在线视频6| 精品人妻偷拍中文字幕| av女优亚洲男人天堂| 欧美区成人在线视频| 日韩欧美免费精品| 国产亚洲精品综合一区在线观看| 成人特级av手机在线观看| 男女那种视频在线观看| 菩萨蛮人人尽说江南好唐韦庄 | 日日摸夜夜添夜夜爱| 91在线观看av| a级毛片a级免费在线| 国产在线精品亚洲第一网站| 久久久成人免费电影| 国产精品久久久久久久久免| 少妇人妻一区二区三区视频| 又爽又黄无遮挡网站| 久久久久久九九精品二区国产| 免费观看的影片在线观看| 黄色一级大片看看| 女人十人毛片免费观看3o分钟| 午夜免费男女啪啪视频观看 | 两性午夜刺激爽爽歪歪视频在线观看| 深爱激情五月婷婷| 国产午夜精品论理片| 国产精品日韩av在线免费观看| 老师上课跳d突然被开到最大视频| 国产 一区精品| 国产黄色视频一区二区在线观看 | 三级男女做爰猛烈吃奶摸视频| 亚洲七黄色美女视频| 搡老熟女国产l中国老女人| 亚洲内射少妇av| 十八禁国产超污无遮挡网站| 久久久久久伊人网av| 99热这里只有精品一区| 国产 一区精品| 欧美色欧美亚洲另类二区| 久久热精品热| 日韩亚洲欧美综合| 1000部很黄的大片| 成人av在线播放网站| 永久网站在线| 在现免费观看毛片| 国产精品一区二区性色av| 一本久久中文字幕| 欧美三级亚洲精品| 亚洲精品国产av成人精品 | 久久久色成人| 亚洲欧美精品自产自拍| 春色校园在线视频观看| 精品一区二区三区视频在线观看免费| 给我免费播放毛片高清在线观看| 欧美日韩一区二区视频在线观看视频在线 | 国产欧美日韩精品亚洲av| 午夜久久久久精精品| 99久久精品热视频| 天堂影院成人在线观看| 久久久久久久久大av| 国内久久婷婷六月综合欲色啪| 男人舔女人下体高潮全视频| 中出人妻视频一区二区| 黄片wwwwww| 特大巨黑吊av在线直播| 男女下面进入的视频免费午夜| 干丝袜人妻中文字幕| 波多野结衣高清无吗| 成人av在线播放网站| 国产女主播在线喷水免费视频网站 | 黄色一级大片看看| 久久韩国三级中文字幕| 欧美不卡视频在线免费观看| 美女内射精品一级片tv| 国产精品无大码| 午夜激情欧美在线| 自拍偷自拍亚洲精品老妇| 国产日本99.免费观看| 亚洲激情五月婷婷啪啪| 中文字幕精品亚洲无线码一区| 国产高潮美女av| 久久久国产成人免费| 国产极品精品免费视频能看的| 最近手机中文字幕大全| 精品一区二区三区视频在线观看免费| 久久久国产成人免费| 免费在线观看影片大全网站| 国产麻豆成人av免费视频| 国产高潮美女av| 国产人妻一区二区三区在| av在线蜜桃| 男人和女人高潮做爰伦理| av.在线天堂| 毛片女人毛片| 麻豆久久精品国产亚洲av| 精品欧美国产一区二区三| 亚洲电影在线观看av| 国内精品宾馆在线| 国内精品美女久久久久久| 老司机影院成人| 1000部很黄的大片| 午夜激情欧美在线| 色在线成人网| 一卡2卡三卡四卡精品乱码亚洲| 男人舔女人下体高潮全视频| 亚洲av不卡在线观看| 男人舔女人下体高潮全视频| 久久久久精品国产欧美久久久| 日日撸夜夜添| 大又大粗又爽又黄少妇毛片口| 五月玫瑰六月丁香| 真人做人爱边吃奶动态| 嫩草影院精品99| 国产伦一二天堂av在线观看| 亚洲aⅴ乱码一区二区在线播放| 国产白丝娇喘喷水9色精品| 亚洲五月天丁香| 波野结衣二区三区在线| 亚洲va在线va天堂va国产| 熟女电影av网| 男人和女人高潮做爰伦理| 日韩欧美 国产精品| 狂野欧美白嫩少妇大欣赏| 婷婷精品国产亚洲av在线| 免费在线观看成人毛片| 五月伊人婷婷丁香| 欧美国产日韩亚洲一区| 精品乱码久久久久久99久播| 美女被艹到高潮喷水动态| 综合色av麻豆| 亚洲欧美成人精品一区二区| 波多野结衣高清作品| 又爽又黄a免费视频| 精品日产1卡2卡| 亚洲精品一卡2卡三卡4卡5卡| 国产黄a三级三级三级人| 人妻久久中文字幕网| 大型黄色视频在线免费观看| videossex国产| 国产黄片美女视频| 免费不卡的大黄色大毛片视频在线观看 | 搡女人真爽免费视频火全软件 | 九九在线视频观看精品| 在现免费观看毛片| 波多野结衣高清无吗| 久久久国产成人精品二区| 国产一区二区在线观看日韩| 老女人水多毛片| 国产精品人妻久久久影院| 青春草视频在线免费观看| 国产精品三级大全| 日韩成人伦理影院| 亚洲七黄色美女视频| 波野结衣二区三区在线| 1024手机看黄色片| 亚洲真实伦在线观看| 亚洲欧美成人精品一区二区| 欧美zozozo另类| av天堂中文字幕网| 国产精品嫩草影院av在线观看| 国产女主播在线喷水免费视频网站 | 小说图片视频综合网站| 在线免费十八禁| 男女啪啪激烈高潮av片| 欧美成人精品欧美一级黄| 精品一区二区免费观看| 亚洲丝袜综合中文字幕| 99九九线精品视频在线观看视频| 国产白丝娇喘喷水9色精品| 亚洲精品国产av成人精品 | 亚洲欧美精品综合久久99| avwww免费| 中文字幕免费在线视频6| 久久中文看片网| 国产免费一级a男人的天堂| 能在线免费观看的黄片| 亚洲美女黄片视频| 内地一区二区视频在线| 五月玫瑰六月丁香| 搡老熟女国产l中国老女人| 丝袜美腿在线中文| 国产一级毛片七仙女欲春2| 精品人妻熟女av久视频| 亚洲成人中文字幕在线播放| 精品久久久久久久久久久久久| 长腿黑丝高跟| 久久久久久久久久成人| 日韩高清综合在线| 97碰自拍视频| 蜜桃久久精品国产亚洲av| 深夜精品福利| 欧美高清成人免费视频www| 岛国在线免费视频观看| 永久网站在线| 国产69精品久久久久777片| 草草在线视频免费看| 99热这里只有是精品50| 亚洲精品国产成人久久av| 国内精品一区二区在线观看| 亚洲精品国产av成人精品 | 精品久久久久久成人av| 亚洲av成人av| 日韩国内少妇激情av| 日韩高清综合在线| 波多野结衣高清无吗| 一卡2卡三卡四卡精品乱码亚洲| 在线免费观看的www视频| 国产激情偷乱视频一区二区| 欧美zozozo另类| 国产极品精品免费视频能看的| 在线看三级毛片| 男女做爰动态图高潮gif福利片| 亚洲在线观看片| 中文字幕熟女人妻在线| 国产白丝娇喘喷水9色精品| 1024手机看黄色片| 美女大奶头视频| 久久人妻av系列| 欧美一区二区国产精品久久精品| 日韩,欧美,国产一区二区三区 | 亚洲婷婷狠狠爱综合网| 在线观看av片永久免费下载| 如何舔出高潮| 欧美精品国产亚洲| 不卡视频在线观看欧美| 午夜精品在线福利| 亚洲国产精品sss在线观看| 观看免费一级毛片| 美女xxoo啪啪120秒动态图| 国产高清不卡午夜福利| 少妇熟女欧美另类| 久久这里只有精品中国| 可以在线观看毛片的网站| 一个人免费在线观看电影| 小说图片视频综合网站| 99热全是精品| 久久精品国产清高在天天线| 亚洲国产日韩欧美精品在线观看| 成人无遮挡网站| 日本免费一区二区三区高清不卡| 中文字幕免费在线视频6| 99在线人妻在线中文字幕| 日本熟妇午夜| 精品一区二区三区视频在线| www日本黄色视频网| 成人综合一区亚洲| 国产高清有码在线观看视频| 不卡一级毛片| 亚洲欧美精品综合久久99| 亚洲熟妇中文字幕五十中出| 日韩,欧美,国产一区二区三区 | 最后的刺客免费高清国语| 亚洲精品亚洲一区二区| 亚洲图色成人| 一级毛片电影观看 | 国产精品久久久久久精品电影| 成人精品一区二区免费| 精品久久久久久久末码| 人人妻,人人澡人人爽秒播| 国产在视频线在精品| a级毛片免费高清观看在线播放| 亚洲经典国产精华液单| 热99re8久久精品国产| 日韩制服骚丝袜av| 午夜日韩欧美国产| 精品久久久久久久末码| 99国产极品粉嫩在线观看| 国产在视频线在精品| 国产精品精品国产色婷婷| 亚洲中文字幕日韩| 国产单亲对白刺激| 国产成年人精品一区二区| 日韩成人伦理影院| 免费观看的影片在线观看| 国产 一区精品| 大又大粗又爽又黄少妇毛片口| 欧美激情在线99| 日韩人妻高清精品专区| 在线播放国产精品三级| 欧美性猛交╳xxx乱大交人| 欧美日韩一区二区视频在线观看视频在线 | 亚洲精品久久国产高清桃花| 2021天堂中文幕一二区在线观| 又黄又爽又刺激的免费视频.| 露出奶头的视频| 亚洲中文字幕日韩| 老司机午夜福利在线观看视频| 亚洲18禁久久av| 伊人久久精品亚洲午夜| 国产精品一区www在线观看| 九九久久精品国产亚洲av麻豆| 国产亚洲精品综合一区在线观看| 亚洲欧美清纯卡通| 国产一区二区三区av在线 | 老熟妇仑乱视频hdxx| 亚洲不卡免费看| a级毛片免费高清观看在线播放| 小说图片视频综合网站| 女人被狂操c到高潮| 哪里可以看免费的av片| 黄色日韩在线| 麻豆av噜噜一区二区三区| 日韩三级伦理在线观看| 又黄又爽又免费观看的视频| 狂野欧美白嫩少妇大欣赏| 免费电影在线观看免费观看| 国产精品乱码一区二三区的特点| 麻豆国产av国片精品| 少妇丰满av| 91在线观看av| 好男人在线观看高清免费视频| 精品国产三级普通话版| 亚洲中文日韩欧美视频| 男人的好看免费观看在线视频| 亚洲欧美日韩无卡精品| 婷婷亚洲欧美| a级毛色黄片| 国产成年人精品一区二区| 老熟妇乱子伦视频在线观看| 久久久久性生活片| 免费不卡的大黄色大毛片视频在线观看 | 亚洲内射少妇av| 免费av不卡在线播放| 麻豆精品久久久久久蜜桃| 欧美精品国产亚洲| .国产精品久久| 欧美中文日本在线观看视频| 床上黄色一级片| 欧美绝顶高潮抽搐喷水| 亚洲五月天丁香| 一进一出抽搐gif免费好疼| 中文字幕熟女人妻在线| 一本精品99久久精品77| 麻豆国产97在线/欧美| 欧美激情国产日韩精品一区| 99久久无色码亚洲精品果冻| 国产高潮美女av|