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2011壳聚糖MPC的表面改性研究

2011壳聚糖MPC的表面改性研究
2011壳聚糖MPC的表面改性研究

Colloids and Surfaces B:Biointerfaces 85 (2011) 48–55

Contents lists available at ScienceDirect

Colloids and Surfaces B:

Biointerfaces

j o u r n a l h o m e p a g e :w w w.e l s e v i e r.c o m /l o c a t e /c o l s u r f

b

Fabrication and hemocompatibility of cell outer membrane mimetic surfaces on chitosan by layer by layer assembly with polyanion bearing phosphorylcholine groups

Ming Gong a ,Yan-Bing Wang a ,Ming Li a ,Bi-Huang Hu b ,Yong-Kuan Gong a ,?

a

Key Laboratory of Synthetic and Natural Functional Molecule Chemistry of Ministry of Education,College of Chemistry and Materials Science,Northwest University,Xi’an,Shaanxi 710069,PR China b

College of Oceanography,Hainan University,Haikou,Hainan 570228,PR China

a r t i c l e i n f o Article history:

Available online 5 November 2010Keywords:

Hemocompatible surface Layer by layer assembly Phosphorylcholine Chitosan

Electrostatic interaction

a b s t r a c t

Three random copolymers poly(2-methacryloyloxyethyl phosphorylcholine-co -methacrylic acid)(PMAs)were synthesized by free radical polymerization of 2-methacryloyloxyethyl phosphorylcholine (MPC)and methacrylic acid (MA)with different monomer ratios under monomer-starved conditions.The syn-thesized PMA polyanions were assembled on chitosan (CS)?lm surfaces via electrostatic https://www.wendangku.net/doc/4a18080807.html,ing layer by layer (LbL)assembly with PMA polyanion and chitosan polycation,PMA/CS multilayer thin ?lms with phosphorylcholine groups on the outer surfaces were fabricated.The modi?ed surfaces were characterized by dynamic contact angle (DCA),X-ray photoelectron spectroscopy (XPS)and atomic force microscopy (AFM).Hemocompatibility of the surfaces was estimated by protein adsorption and platelet adhesion measurements.The results indicated that cell outer membrane mimetic structures were formed on the modi?ed surfaces with PMA as the outermost layer,and the hemocompatibility of the modi?ed surfaces was signi?cantly improved.This facile method of fabricating cell outer membrane mimetic sur-faces may have potential applications in the ?elds of hemocompatible coatings,drug delivery,and tissue engineering.

? 2010 Elsevier B.V. All rights reserved.

1.Introduction

Chitosan (CS)is a polycationic biopolymer obtained by the alka-line deacetylation of chitin,one of the most abundant natural polysaccharides from crustacean shells.With numerous desirable properties such as biodegradability,antibacterial,and non-toxicity to human tissues [1–3],chitosan has emerged as a promising biomedical material with potential applications as a scaffold in tissue engineering [3,4],as a hemodialysis membrane [2,5]and as a coating for coronary stents [6].However,as a stand-alone membrane or coating,chitosan is susceptible to biofouling and thrombus formation,limiting its use in hemodialysis and endovas-cular devices.

To prepare hemocompatible surfaces,phosphorylcholine (PC)functional groups were attached to chitosan surfaces by several methods,including bonding to surface amino groups through Michael addition of 2-methacryloyloxyethyl phosphorylcholine (MPC)[7–9],reaction with 2-chloro-1,3,2-dioxaphosphospholane (COP)[10,11],and grafting of phosphorylcholine dichloride [12].

?Corresponding author.Tel.:+862988302109.E-mail address:gongyk@https://www.wendangku.net/doc/4a18080807.html, (Y.-K.Gong).

Furthermore,modi?cation of chitosan through amino groups by reductive amination of phosphorylcholine-glyceraldehyde (PC-CHO)[13]or conjugation with zwitterionic PC through the Atherton–Todd reaction [14]afforded water soluble PC function-alized chitosans.As anticipated,PC-modi?ed chitosan surfaces showed improved hemocompatibility in blood clotting and platelet adhesion assays,attributed to the cell outer membrane mimetic structures formed on the surfaces [15–17].

In this communication we propose another approach to pre-pare hemocompatible surfaces by attaching phosphorylcholine (PC)groups to chitosan through layer-by-layer (LbL)assembly using a polyanion containing phosphorylcholine (PC)groups by electrostatic adsorption [18,19].LbL assembly involves consec-utive adsorption of polyanions and polycations by alternately depositing polyanions and polycations to fabricate multilayer thin ?lms/surfaces [19,20].The LbL deposition technique has been employed to build biocompatible surfaces [21–23].

Combining the advantages of LbL technique such as simplicity and easy thickness control with the effectiveness of cell outer mem-brane mimetic structure approaches,we report a facile method for the preparation of hemocompatible surfaces by modifying chitosan surface with cell outer membrane mimetic structure using LbL assembly of poly(2-methacryloyloxyethyl phosphorylcholine-co -

0927-7765/$–see front matter ? 2010 Elsevier B.V. All rights reserved.doi:10.1016/j.colsurfb.2010.10.049

M.Gong et al./Colloids and Surfaces B:Biointerfaces 85 (2011) 48–5549

methacrylic acid)(PMA)and chitosan.The structure and stability of these surfaces were investigated by X-ray photoelectron spec-troscopy (XPS),dynamic contact angle (DCA)and atomic force microscopy (AFM).The hemocompatibility of the surfaces was eval-uated by platelet adhesion and protein adsorption experiments.2.Materials and methods 2.1.Materials

Chitosan with a degree of deacetylation of 94%(average molecular weight of 330,000Da)was purchased from Xi’an Wolsen Biotechnology Company.2-Methacryloyloxyethyl phos-phorylcholine (MPC)was synthesized according to the method reported by Ishihara et al.[24].Methacrylic acid (MA)was pur-chased from Aldrich Chemical Co.and used as received.The initiator

2,2 -azoisobutyronitrile (AIBN,from Shanghai Chemical Co.)was recrystallized from methanol.Bovine serum albumin (BSA)and bovine plasma ?brinogen (Fg)were purchased from Sigma–Aldrich.Platelet-rich plasma (PRP)was prepared using fresh blood provided by a healthy donor according to a previously reported method [12].2.2.Synthesis of poly(2-methacryloyloxyethyl phosphorylcholine-co-methacrylic acid)(PMA)

The random copolymer PMA was synthesized by free-radical copolymerization of MPC and MA.The two monomers with molar proportions of 30,50and 70%MPC were dissolved in a solvent mix-ture of isopropanol (iPA)and tetrahydrofuran (THF)(35:5)(v/v),respectively.After addition of 1wt%AIBN in THF to the monomer solution over 3–4h using a “monomer-starved”method [25]under N 2protection and with agitation at 80?C,the reaction mixture was re?uxed and stirred for 20h to complete the polymerization reaction.The resulting polymer products were puri?ed by dialysis against deionized water (6000-MW-cutoff)for 48h at 25?C.After freeze-drying,the PMA samples were labeled as PMA30,PMA50,and PMA70according to their MPC monomer molar percentage in the feed of 30,50and 70%,respectively.The actual percent-ages of MPC unit in PMA30,PMA50and PMA70determined by 1H NMR were 28%,54%and 77%,respectively.MALDI TOF mass spectra showed m /z peaks at 7100–7400,suggesting that the aver-age molecular weights of PMAs were greater than 7000Da.The synthesis scheme is shown in Fig.1.

2.3.Surface modi?cation of chitosan ?lm

Chitosan (CS)?lm was prepared according to our previous work [12].Brie?y,a 0.5wt%solution of CS was prepared by dissolving CS in 1%(v/v)aqueous acetic acid.After ?ltration,a clean glass cover slip was immersed upright into the solution to attach the CS.The cover slip was gently removed from the solution,and the adhered CS coating was dried in vacuo at 40?C for 24h.Finally the CS ?lm was thoroughly rinsed with de-ionized water and dried at 30?C under vacuum.

Solutions of PMA (1.0mg/mL in 0.14M aqueous NaCl)and CS (1.0mg/mL in 0.10M acetic acid containing 0.14M NaCl)were prepared separately.PMA coated monolayer ?lms were prepared by the following procedure.CS ?lms were immersed in the PMA solution for 15min at room temperature,followed by rinsing with 0.14M NaCl solution and deionized water to remove weakly adhered PMA [26].Multilayer build-up was accomplished by sequentially dipping the CS substrate into the two solutions (alter-nating between CS and PMA),followed by adsorbing for 15min and washing with 0.14M NaCl solution.After rinsing thoroughly with deionized water and freeze drying,a cell outer membrane mimetic surface (PMA as the outermost layer)was ?nally obtained.2.4.Characterization of the modi?ed surfaces

2.4.1.Dynamic contact angle measurement

The hydrophilicity and hydrophobicity of the modi?ed sur-faces were characterized by a highly sensitive dynamic contact angle technique with a DCAT 21tensiometer from Dataphysics Instruments.Dynamic contact angles,including advancing (?adv )and receding (?rec )angles,can provide information on the surface hydrophilicity/hydrophobicity and group reorientation [27,28].The technique,which is based on the Wilhelmy plate method,requires samples presenting identical front and back surfaces.These were obtained by coating square ?lms on both sides with polyelectrolyte CS or PMA as the outermost layer.In each case,a minimum of three specimens was analyzed to ensure reproducibil-ity.Deionized water (Millipore system,18M )was used as probe liquid.The water surface tension was determined before and after the analysis of each surface.A dry specimen was attached to the electrobalance via a clip and the stage carrying a beaker of water was automatically raised and lowered (10mm/min)to allow water to contact the specimen.A dwell time of 60s was allowed between

H 2C

C H 2C C

C C CH 3

CH 3

O O

H 2

C C

H 2C C

C C CH 3CH 3O

O

m n

O

OH

O

OH

O P O

O

O O P O

O

O N CH 3H 3C CH 3

N CH 3

H 3C CH 3

Fig.1.Synthesis scheme of poly(MPC-co -MA)random copolymer (PMA).

50M.Gong et al./Colloids and Surfaces B:Biointerfaces85 (2011) 48–55

sample immersion and withdrawal.Analysis of the resulting force versus distance curves(loops)yields the advancing and receding angles(?adv and?rec).

2.4.2.X-ray photoelectron spectroscopy measurements

The elemental composition of the modi?ed surfaces was deter-mined by X-ray photoelectron spectroscopy(XPS).The XPS spectra were recorded with an Axis Ultra,Kratos instrument(UK)using monochromatic Al K?radiation(150W,15KV,1486.6ev).The vac-uum in the spectrometer was kept at10?9Torr.All spectra were collected at an electron take-off angle of70?from the surface.Bind-ing energies were calibrated relative to the C1S peak(284.8ev)from hydrocarbons adsorbed on the surface of the samples.

2.4.

3.Atomic force microscopy(AFM)measurements

The topography of the surfaces was observed using an atomic force microscope(SPA-400,Seiko Instruments Inc.).The AFM images were recorded in tapping mode in air using a silicon can-tilever at ambient temperature.

2.4.4.Stability in PBS

The modi?ed chitosan?lms were immersed in PBS buffer solu-tion(pH7.4).After being immersed for10,40,and60days,the samples were rinsed with deionized water and freeze-dried.The surface stability was veri?ed mainly by dynamic contact angles. Surface chemical composition was also determined by XPS for sev-eral surfaces.

2.4.5.Stability in air

The multilayer modi?ed chitosan?lms were stored in room con-ditions for2months.The dynamic contact angles before and after storage were compared to show stability in air.

2.4.6.Protein adsorption

In vitro single protein adsorption experiments were performed in phosphate-buffered saline(PBS,pH=7.4).The sample surfaces were?rst equilibrated with the PBS solution for2h,and then immersed in a solution of bovine serum albumin(BSA)(4.5mg/mL) or?brinogen(Fg)(0.3mg/mL)at37?C.The adsorption system was kept in a humidi?ed water jacketed incubator equilibrated with5% CO2in air for2h.After being rinsed with PBS three times,the sam-ples were transferred to a beaker?lled with2mL of PBS solution containing1wt%of sodium dodecyl sulfate(SDS).The adsorbed protein was completely desorbed by sonication for20min.The bicinchoninic acid(BCA)method was used to determine the con-centration of protein in the SDS solution[29,30],and this was used to calculate the amount of protein on the sample surface.At least three replicate samples were analyzed to ensure reproducibility of the measurements.

2.4.7.Platelet adhesion

The platelet adhesion test was performed under static con-ditions[31,32].The sample surfaces were?rst equilibrated by immersion in PBS for2h,then20?L of fresh PRP was applied at the center of the samples,followed by incubation at37?C in a humidi-?ed water jacketed incubator equilibrated with5%CO2in air for2h. The samples were then rinsed with phosphate buffer solution(PBS, pH7.4)three times to remove the weakly adherent platelets.The remaining adherent platelets were?xed in2.5wt%glutaraldehyde for1h.The?xed samples were then rinsed with PBS and deion-ized water several times.After freeze-drying at?50?C,the samples were observed with a scanning electron microscope(Quanta200, Philips-FEI,Netherlands)and the images were

recorded.Fig.2.Contact angles of CS and PMA adsorbed CS(CS–PMA)surfaces.Bars represent SD(n=3).

3.Results and discussion

3.1.Fabrication of PMA modi?ed surfaces

The partial N-acylation of the CS and hydrogen bonding between the polysaccharide chains increased the surface hydrophobicity of the CS?lms.When hydrophilic PMA polyanion was immobilized on the CS polycation surface by electrostatic adsorption,a decrease in contact angle should be observed.As shown in Fig.2,both the advancing and receding contact angles of PMA modi?ed surfaces decreased signi?cantly.?adv decreased by at least37%from84.5?on CS to48?,49?and53?on the PMA30,PMA50and PMA70modi?ed monolayer surfaces,respectively,and?rec decreased by at least41% from12?on CS to4?,5?and7?on the PMA30,PMA50and PMA70 surfaces,respectively.These large changes in the contact angles indicate that the fabrication of the CS–PMA monolayer surfaces was successful.

This conclusion is further supported by the surface elemen-tal composition data listed in Table1from XPS survey spectra.A phosphorus concentration of2.7%on the CS–PMA30surface sug-gests that a3–5nm PMA30layer was adsorbed on the CS surface. When the CS–PMA30surface was covered by a layer of positively charged CS by LbL deposition,the surface phosphorus concen-tration decreased signi?cantly to1.4%,suggesting that a3–5nm CS layer was deposited(CS–PMA30–CS).The layer thickness was estimated by comparing the bulk atomic concentration with the measured one and assuming a maximum detection depth of9nm at a take off angle of70?for polymers[33].No silicon signal was detected in the XPS survey spectra,suggesting that the?lms coated on the glass substrate were thicker than10nm.

The high resolution XPS spectra shown in Fig.3gave additional information on the surface modi?cations.First,the new signals for P2p at133eV and–N+(CH3)3at402.8eV showed the presence of PC groups on the CS–PMA30surface.Second,the decreased peak areas of P2p and–N+(CH3)3on the CS–PMA30–CS sample con?rmed the deposition of CS on the CS–PMA surface.Third,the large–NH2 signal on the CS–PMA surface suggested that the PMA coated layer was less than8nm in thickness,while the–N+(CH3)3signal of the CS–PMA–CS surface indicated that the outer CS layer was less than

Table1

Surface elemental composition of CS and the LbL modi?ed?lms measured by XPS survey scan.

Surface Atomic concentration(%)

C O N P P/C

CS57.729.313.000

CS–PMA3062.530.1 4.7 2.7 4.3 CS–PMA30–CS61.631.1 5.9 1.4 2.3

M.Gong et al./Colloids and Surfaces B:Biointerfaces85 (2011) 48–55

51

Fig.3.High resolution C1s,N1s,O1s and P2p XPS spectra of the CS,CS–PMA,and CS–PMA–CS surfaces. 9nm.Fourth,the degree of deacetylation of the chitosan of94%

was con?rmed by the–NCOCH3peak area of6%in the N1s high

resolution spectrum of the CS surface.

Multilayers of CS/PMA were also fabricated by LbL deposition.

Fig.4indicates that the deposition of PMA30on CS surfaces as the

outermost layer(odd numbers)resulted in a sharp decrease of the

dynamic contact angles,while for CS as the outermost layer(even

numbers)the contact angles increased.The variation of the contact

angle with layer number showed clear alternation of the outermost

layer between PMA30and CS.The remarkable decrease of contact

angles on the deposition of PMA(polyanion bearing PC groups)

as the outermost layer indicates an increase in the hydrophilicity

of the CS membrane.Based on both the contact angle and surface

elemental composition data,we conclude that all of the monolayer

and multilayer modi?ed CS surfaces with PMA as the outermost

layer formed cell outer membrane mimetic structures,in which

the zwitterionic PC groups were oriented to the surface/interface

of the polymer layer.

3.2.Stability of PMA modi?ed surfaces

The stability of CS–PMA monolayer surfaces in PBS solution

was investigated for up to60days.As shown in Fig.5,?adv of

the

Fig.4.Dynamic contact angle change with the number of coated layers of PMA30 and CS.Even numbers represent membranes with CS as the outermost layer, whereas odd numbers represent membranes with PMA30as the outermost layer. Bars represent SD(n=3).CS–PMA30surface was stable in PBS solution for40days at room temperature.We know that self assembled monolayers formed by electrostatic interaction are very thin.XPS data(Table1)sug-gest a thickness of3–5nm.A small loss or dissolution of PMA polymer from the CS surface would change the surface contact angles dramatically.As shown in Fig.5,?adv of the CS–PMA50and CS–PMA70surfaces increased dramatically in40days.Further-more,slow hydrolysis or degradation of the CS substrate in PBS solution is also suggested by the contact angle data.Therefore,the stable contact angles of the CS–PMA30surface indicate that the electrostatically assembled cell outer membrane mimetic structure was stable.

The high stability of the CS–PMA30surface was mainly due to the strong electrostatic interaction between the positively charged chitosan and negatively charged PMA.It is clear that the more charges the polyions bear,the stronger the interaction between the oppositely charged polyelectrolytes.On the other hand,the zwit-terionic PC group does not enhance the attachment of PMA to CS, but weakens the interaction by“dragging”PMA molecules into the water phase.Since PMA30has both the largest amount of negative charges and the smallest amount of hydrophilic PC groups among the three PMA polymers,it forms the most stable assembly on CS (CS–PMA30)with a cell outer membrane mimetic structure.Con-sidering that complete prevention of protein adsorption requires at least25%of the PC moiety in the polyanion[21],PMA with

a

Fig.5.Advancing contact angle changes of CS–PMA monolayer surfaces with time immersed in PBS solution.Bars represent SD(n=3).

52M.Gong et al./Colloids and Surfaces B:Biointerfaces

85 (2011) 48–55

Fig.6.Contact angle change of the CS/PMA multilayer surfaces measured before (

,

advancing,,receding)and after storage (,

advancing,,receding)for2months

in air.The layer numbers4,5and6represent?lm compositions of CS–(PMA30–CS)2, CS–(PMA30–CS)2–PMA30and CS–(PMA30–CS)3,respectively.Bars represent SD (n=3).

lower PC ratio is not recommended for fabricating a high quality hemocompatible surface.

3.3.Stability of CS–PMA surfaces in air

The stability of CS/PMA30multilayers in air was also investi-gated by contact angle measurements.Fig.6shows the contact angles of the CS–(PMA30–CS)2,CS–(PMA30–CS)2–PMA30and CS–(PMA30–CS)3surfaces.?adv of the5-layer surface with PMA30 as the outermost layer increased about9?in2months,indicating an increase of hydrophobicity during storage in room conditions, whereas?adv of the4and6layer surfaces with CS as the outermost layers decreased by6?during storage.The clear changes in?adv suggest an instability of the multilayer surfaces caused by inter-penetration between adjacent layers[20].Since the hydrophilic surface has high energy in the dry state,the PC groups on the sur-face showed a natural tendency to migrate to the inside of the coating layer[34],resulting in a large increase in?adv.When CS was deposited as the outermost layer,inter-penetration between adjacent layers was mainly an entropy driven process and was equi-librated by the increased surface energy of the hydrophilic groups on the surface.This may explain why the increase in?adv of the hydrophilic(PMA)surface was greater than the decrease in?adv of the hydrophobic(CS)surface during storage.3.4.Surface morphology

CS and CS/PMA30multilayer modi?ed surfaces were inves-tigated by atomic force microscopy(AFM).Representative 1.0?m×1.0?m micrographs taken in air are shown in Figs.7and8. Compared with the CS surface,the PMA30coated monolayer surface(CS–PMA30)showed numerous100nm sized irregular domains with heights of4–8nm(Fig.7).The raised domains on the CS surface are additional strong evidence of the CS–PMA30 monolayer.

The successful fabrication of CS/PMA30multilayer surfaces is supported by the AFM3D images as shown in Fig.8.The sur-face roughness and size of domains increased with increasing layer number.During the LbL deposition,oppositely charged poly-electrolytes formed complexes by electrostatic interaction which reorganized further into islands.The gradual growth of the islands was suggested by additional LbL deposition of polyelectrolytes onto islands[35,36].

3.5.Protein adsorption

The interaction of proteins at the surface is a key factor for the biocompatibility of medical devices.Reducing the amount of nonspeci?c protein adsorption may be the most effective way to improve the performance of biomedical materials[37].Reduc-tion of protein adsorption may effectively reduce activation of the immune system.In this work,the sample surfaces were exposed to two common proteins(Fg and BSA)to investigate the effects of surface modi?cation on protein adsorption.

The adsorbed amounts of BSA and Fg on CS,CS–PMA30and the CS/PMA30multilayer surfaces are shown in Fig.9,and can be sum-marized as follows.First,for all of the modi?ed surfaces,protein adsorption was clearly suppressed compared with the unmodi-?ed CS.Second,resistance to protein adsorption increased roughly with increasing number of layers deposited on CS substrate.Third, when PMA30was the outermost layer of the modi?ed surface (odd layer number),the Fg adsorbed amount was less than on the surface bearing one more outermost CS layer(odd layer num-ber+1).These results appear reasonable when both the surface layer structure and the contact angles are considered.When the CS substrate(0layer)was coated with PMA monolayer(CS–PMA, 1layer),a cell outer membrane mimetic surface was formed with reduced contact angle and with protein resistant properties. When the CS–PMA surface was covered by one additional CS layer forming CS–PMA–CS(2layer)surface,the characteristics of

cell Fig.7.AFM height images in air of surfaces(a)CS and(b)CS–PMA30for a scanning area of1?m×1?m.

M.Gong et al./Colloids and Surfaces B:Biointerfaces 85 (2011) 48–55

53

Fig.8.AFM 3D images of the LbL modi?ed surfaces.(a)CS–PMA30;(b)CS–(PMA30–CS)1–PMA30;(c)CS–(PMA30–CS)2–PMA30;(d)CS–(PMA30–CS)4–PMA30.

outer membrane mimetic surface were decreased as shown by the increased ?adv ,resulting in increased adsorption of Fg.How-ever,Fg adsorption on the 3-layered surface was further decreased compared to that on the 1layer surface and the increase on the 4layer surface was insigni?cant.We conclude that Fg adsorption was suppressed by both the cell outer membrane mimetic struc-ture and increasing multilayer number.On the other hand,BSA adsorption did not show the same variations as Fg with surface structure,but decreased monotonically with increasing deposited layer number and showed the lowest adsorption after 3layer depo-sition.

3.6.Platelet adhesion

It is well known that when a material contacts blood,proteins instantaneously adsorb onto the surface and deform.

Subsequently,

Fig.9.Protein adsorption on the surfaces modi?ed with different numbers of PMA/CS layers.Bars represent SD (n =3).

platelets adhere,are activated,and aggregate.The adhesion and aggregation of platelets play a signi?cant role in thrombus for-mation [38].Therefore,the extent of platelet adhesion and the morphology of the adhered platelets are considered to be early indi-cators of the thrombogenicity of biomaterials in contact with blood [39,40].

Fig.10shows the adhesion of platelets to CS,CS–PMA30and the CS/PMA30multilayer https://www.wendangku.net/doc/4a18080807.html,pared with the CS surface,the numbers of platelets adhered to the CS–PMA30and the CS/PMA30multilayer surfaces were signi?cantly reduced,demonstrating the effectiveness of the cell outer membrane mimetic surface in sup-pressing platelet adhesion,activation and aggregation.Platelet adhesion on the modi?ed surfaces did not show ?uctuation with surface structure change.

It is well documented that Fg is the key plasma protein mediat-ing platelet adhesion under static conditions [41,42].The adsorbed amount of Fg is an important factor in?uencing platelet adhe-sion.The results from Figs.9and 10suggest that when Fg adsorption from single protein in buffer decreased to less than 0.6?g /cm 2platelet adhesion was effectively suppressed on the modi?ed surfaces.This threshold value of Fg adsorption appears much higher than the value that has been shown to cause sig-ni?cant platelet adhesion on poly(dimethylsiloxane)surfaces [43].This difference may be due to the conformational difference of the adsorbed Fg [44].Our data indicate that the PMA30coated sur-faces reduced Fg adsorption,and more importantly that they did not change the protein conformation as much as other materials may have.

In summary,the data from contact angle,XPS,AFM,protein adsorption and platelet adhesion experiments provided strong evi-dence for the successful fabrication of cell outer membrane mimetic surfaces/interfaces with indications of excellent hemocompatibil-ity.In addition the cell outer membrane mimetic surfaces fabricated

54M.Gong et al./Colloids and Surfaces B:Biointerfaces

85 (2011) 48–55

Fig.10.Scanning electron micrographs of platelet adhesion on:(a)CS;(b)CS–PMA30;(c)CS–PMA30–CS;(d)CS–(PMA30–CS)1–PMA30;(e)CS–(PMA30–CS)2;(f)CS–(PMA30–CS)2–PMA30.

by electrostatic interaction were stable for up to 40days.It seems,however,that development of a more stable biomimetic sur-face/interface for speci?c applications is still a challenge.4.Conclusions

A facile method of fabricating cell outer membrane mimetic surfaces was developed based on electrostatic assembly of poly-electrolytes bearing phosphorylcholine groups on an oppositely charged polymer surface.Water contact angles,XPS surface elemental analysis,and AFM morphology data con?rmed the suc-cessful fabrication of these cell outer membrane mimetic surfaces.Protein adsorption and platelet adhesion investigations suggested that the hemocompatibility of the modi?ed surfaces were signif-icantly improved.More speci?cally,Fg adsorption showed clear surface structure dependence,while BSA adsorption was sup-pressed mainly by the thickness or number of layers deposited.Platelet adhesion was effectively suppressed on the cell outer membrane mimetic surface when the adsorbed amount of Fg,as determined in single protein experiments,was less than the thresh-old value of 0.6?g /cm 2.Acknowledgements

This work was supported by the National Natural Science Foun-dation of China (No.20774073,No.20974087)and a open fund from Key Laboratory of Synthetic and Natural Functional Molecule Chemistry of Ministry of Education (No.KF09008).References

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磁性壳聚糖微球的制备及其应用_杨晋青

现代食品科技 Modern Food Science and Technology 2008, Vol.24, No.10 1079 磁性壳聚糖微球的制备及其应用 杨晋青,叶盛权,郭祀远 (华南理工大学轻工与食品学院,广东广州 510640) 摘要:由新型的高分子材料制成的磁性壳聚糖微球具有很多优良的应用特性。本文着重综述磁性壳聚糖微球的制备方法和性能表征, 介绍其在生物医学,食品工程和废水处理方面的应用进展, 并展望其研究和开发的光明前景。 关键词:磁性壳聚糖微球;改性;医学;食品工程;废水处理 中图分类号:TQ333.99;文献标识码:A ;文章篇号:1673-9078(2008)10-1079-04 Review of Preparation and Application of Magnetic Chitosan Microspheres YANG Jin-qing, YE Sheng-quan, GUO Si-yuan (College of Light Industry & Food Sciences, South China University of Technology, Guangzhou 510640) Abstract: Magnetic chitosan microspheres made from novel polymer materials showed outstanding applied characteristics. In this paper, the preparation and characterization of magnetic chitosan microspheres were reviewed. The applications of magnetic chitosan microspheres in biomedical, food engineering and wastewater treatment were also introduced and their bright futures were prospected for further research and development. Key words: magnetic chitosan microspheres; modification; medicine; food engineering; wastewater treatment 新型的高分子微球材料因其具有很多优良特性为而被广为应用。如粒径小、表面积大、吸附性强,可通过共聚、表面改性赋予其多种功能性基团(如-OH 、-COOH 、-CHO 、-NH2、-SH 等),进而可结合各种物质,使高分子微球具有多种功能。对于磁性高分子微球,由于其具有磁响应性,在外加磁场的作用下可以很方便地分离、回收。因此,在许多领域有广阔的开发前景[1,2]。 壳聚糖(CTS)是自然界存在的唯一碱性多糖,可由蟹、虾壳中的甲壳素经脱乙酰化反应而制得。其资源丰富,安全无毒,具有独特的分子结构和易于化学修饰、生物可相容性和可再生性等功能。它的胺基极易形成四级胺正离子,有弱碱性阴离子交换作用。壳聚糖在酸性溶液中会溶解,稳定性差[3,4]。将壳聚糖进行交联制成磁性壳聚糖(MCS )微球[5,6],不但可提高其稳定性及机械强度,而且使其易与介质分离,利于广泛应用于医学、食品、化工等领域[7]。本文通过对磁性壳聚糖微球的制备方法和性能表征方法及其在生物医药,食品工程和废水处理方面应用的综述,介绍磁性 收稿日期:2008-04-27 基金项目:高等学校博士学科点专项科研基金资助项目(20050561014) 作者简介:杨晋青(1983-),硕士研究生,研究方向:糖类分离提纯新方法新技术 通讯作者:郭祀远,教授 壳聚糖微球有关领域的研究进展情况,并展望其发展 的前景。 1 磁性壳聚糖微球的制备及表征 1.1 乳化交联法 常用的磁性壳聚糖微球制备方法有乳化交联法[8]。将磁性Fe 3O 4粒子加到一定浓度的壳聚糖溶液中,经均质分散,再在适当的温度,pH 和搅拌条件下逐滴加入含有乳化剂的水相中,产生乳液,在常压下自由挥发或用真空抽提使溶剂挥发,通过洗涤、过滤和干燥等过程即可制得磁性壳聚糖微球[9,10]。 1.2 包埋法 1.2.1 磁性高分子微球的制备 运用机械搅拌、超声分散等方法将磁性粒子分散于高分子溶液中,通过雾化、絮凝、沉积、蒸发等过程得到内部包有磁性粒子的高分子微球,常用的包埋材料有壳聚糖、纤维素、尼龙、磷脂、聚酰胺、聚丙烯酰胺等。徐慧显利用葡聚糖制备了具有较好的单分散性磁性葡聚糖微球[11],董聿生采用反相悬浮包埋技术合成了多分散性的磁性葡聚糖微球[12]。 1.2.2 改性磁性壳聚糖微球的制备 以(NH 4)2Fe(SO 4)2·6H 2O 、NH 4Fe(SO 4)2·12H 2O 和壳聚糖为原料,经羟丙基化、胺基化,采用一步包埋法制备了一种新型的多胺基化磁性壳聚糖微球[13]。此方 DOI:10.13982/j.mfst.1673-9078.2008.10.005

改性沥青的研究进展

改性沥青的研究进展 黄 彬,马丽萍,许文娟 (昆明理工大学环境科学与工程学院,昆明650093) 摘要 为了得到性能更优良的改性沥青,越来越多的材料被用作改性沥青改性剂,同时新的评价标准和方法及其他领域的新化学分析方法也被用来更完整准确地评价改性沥青的性能。总结了国内外改性沥青的研究现状及进展,从改性机理、性能影响因素及评价方法等方面来介绍各种改性沥青的概况,并概述了改性沥青的发展方向。 关键词 改性沥青 改性剂 机理 发展Rsearch Development of Modif ied Asphalt HUAN G Bin ,MA Liping ,XU Wenjuan (Faculty of Environmental Science and Engineering ,Kunming University of Science and Technology ,Kunming 650093) Abstract More materials ,as modifier ,are used to improve the properties of modified asphalt.Besides ,the new evaluation standards and methods ,new chemical analysis methods are used to evaluate the properties more com 2pletely and accurately.The situation and development of modified asphalt research at home and abroad are summa 2rized.From the aspcts of modification mechanism ,influencing factors and evaluation methods ,various modified as 2phalts are introduced ,and the development trend of modified asphalt technology is illustrated in the paper. K ey w ords modified asphalt ,modifier ,mechanism ,development  黄彬:女,1986年生,硕士研究生,主要研究方向为固体废物资源化 E 2mail :binbin_huang @https://www.wendangku.net/doc/4a18080807.html, 马丽萍:女,1966年生,教 授,主要研究方向为工业废气污染控制、固废综合开发利用 E 2mail :lipingma22@https://www.wendangku.net/doc/4a18080807.html, 0 前言 普通道路沥青由于自身的组成和结构决定了其感温性能差,弹性和抗老化性能差,高温易流淌,低温易脆裂。而且在过去的10年中,车轴负荷增加、车流量增加、气候条件恶劣,难以满足高级公路的使用要求,必须对其改性以改善使用性能。在沥青或沥青混合料中加入天然或合成的有机或无机材料,熔融或分散在沥青中与沥青发生反应或裹覆在沥青集料表面,可以改善或提高沥青路面性能。 1 改性沥青的分类 在沥青的改性材料中,高分子聚合物是应用最广泛、研究最集中的一种。其他改性材料还有两大类:矿物质填料和添加剂。矿物质填料,如硅藻土、石灰、水泥、炭黑、硫磺、木质素、石棉和炭棉等,对沥青进行物理改性,可提高沥青抗磨耗性、内聚力和耐候性。添加剂,包括抗氧化剂和抗剥落剂,如有机酸皂、胺型或酚型抗氧化剂或阴、阳离子型或非离子型表面活性剂,可提高沥青粘附性、耐老化或抗氧化能力。聚合物改性沥青(PMA 、PMB ),按照改性剂的不同一般可分为3类:①热塑性橡胶类,即热塑性弹性体,主要是嵌段共聚物,如SBS 、SIS 、SE/BS ,是目前世界上最为普遍使用的道路沥青改性剂,并以SBS 最多;②橡胶类,如NR 、SBR 、CR 、BR 、IR 、EP 2DM 、IIR 、SIR 及SR 等,以胶乳形式使用,其中SBR 应用最为广泛;③树脂类,如EVA 、PE 、PVC 、PP 及PS 。 2 各种改性沥青及其发展现状 通过SCI 和EI 分别检索近15年来改性沥青在交通、建筑、材料、能源及环境等学科方面研究的文献情况,检索结果如图1、图2及表1、表2所示。根据表1、表2数据和图1、图2情况可以看出,近几年国内外对改性沥青的研究越来越多,尤其以SBS 和胶粉最为突出,出现了多种新型改性剂。下面 将分别介绍各种改性沥青及其发展现状。 图1 SCI 检索统计表 Fig.1 SCI search results 2.1 矿物质材料改性沥青 矿物质材料作改性剂的研究较少,主要为硅藻土、纳米 碳酸钙、矿渣粉、白炭黑等,可与基质沥青形成均匀、稳定的 共混体系以改善沥青性能[1] 。

壳聚糖改性工艺的研究

壳聚糖改性工艺的研究 壳聚糖[是自然界中唯一大量存在的高分子碱性氨基多糖,与合成高分子材料相比,具有来源广泛、价格低廉、性质稳定、无刺激、无致敏、无致突变、良好的生物相容性和生物可降解性、低免疫原性以及生物活性等优点,已被广泛应用于工业、农业、生物工程、医药、食品、日化、污水处理、纺织印染等领域。壳聚糖不溶于普通溶剂,使其应用受到了一定限制,因此,对壳聚糖进行化学改性,提高其溶解性,并赋予其一些其他功能,扩大其应用领域成为了一个研究热点。 20116壳聚糖的结构和性质 1. 1壳聚糖的结构特性 壳聚糖具有复杂的双螺旋结构,其功能基团有氨基葡萄糖单元上的6位伯经基、3位仲羟基和2位氨基或一些N位乙酰氨基以及糖酐键,其结构式如图1所示。 1. 2.壳聚糖的一般理化性质 壳聚糖是生物界中惟一的一种碱性多糖,它是白色、无定型、半透明、略有珍珠光泽的固体,因原料和制备方法不同,其相对分子质量也从数十万至数百万不等。 1. 3壳聚糖的溶解性质 壳聚糖可溶于稀的盐酸、硝酸、醋酸等无机酸和大多数有机酸但不溶于稀硫酸和稀磷酸。影响壳聚糖溶解的主要因素有脱乙酰度、壳聚糖的相对分子质量、酸的种类等。 2壳聚糖的改性研究 由于壳聚糖自身性能的局限性,科研工作者对其进行了改性研究,通过控制反应条件在壳聚糖上引人其他基团来改变其理化性质[6]。本文将介绍壳聚糖改性的研究进展及应用,并对目前的一些改性方法进行了较全面的总结。 2. 1化学改性 壳聚糖分子上有许多经基和氨基,可通过对其进行分子设计实现可控化学修饰,从而改善壳聚糖本身性能的一些不足。根据壳聚糖的化学性质,可以从酰化、酯化、烷基化等几个方面对其进行化学改性。 2.1.1酸化改性 壳聚糖可与多种有机酸的衍生物如酸酐,酰卤等反应,可引人不同相对分子质量的脂肪族或芳香族的酰基进行改性。酰化反应既可在轻基上反应(O位酰化)生成酯,也可在氨基上反应(N位酞化)生成酰胺。酰化化改性后的产物的溶解度有所改善,它具有良好的生物相容性,是一种潜在的医用生物高分子材料。如脂肪族酰化化产物可作为生物相 容性材料,N一甲酰化产物可增强人造纤维的物理性能。

壳聚糖的应用研究进展(综述性论文)

绿色原料——壳聚糖的应用研究进展 09化学1班 XXX 指导老师:沈友教授 (惠州学院化学工程系,广东,惠州,516007) 摘要:本文综述了绿色原料壳聚糖的应用研究进展,着重介绍了壳聚糖在食品,水处理,生物药用,造纸业等方面的应用。 关键词:壳聚糖应用食品水处理 前言 原料在化学品的合成中非常重要,其可以成为影响一个化学品的制造、加工与使用的最大因素之一。如果一个化学品的原料对环境有负面的影响,则该化学品也很可能对环境具有净的负面影响。要实现绿色化学,在选择原料时应尽量使用对人体和环境无害的材料,避免使用枯竭或稀有的材料,尽量采用回收再生的原材料,采用易于提取、可循环利用的原材料,使用环境可降解的原材料。 自然界的有机物,数量最大的是纤维素,其次是蛋白质,排在第三位的是甲壳素,估计每年生物合成甲壳素100 亿t。甲壳素N-脱乙酰基的产物壳聚糖就是一种重要的绿色原料。 壳聚糖化学名称为聚葡萄糖胺(1-4)-2-氨基-B-D葡萄糖,壳聚糖的外观为白色或淡黄色半透明状固体, 略有珍珠光泽, 可溶于大多数稀酸如盐酸、醋酸、苯甲酸等溶液, 且溶于酸后,分子中氨基可与质子相结合, 而使自身带正电荷。自1859年,法国人Rouget首先得到壳聚糖后,这种天然高分子的生物官能性和相容性、血液相容性、安全性、微生物降解性等优良性能被各行各业广泛关注,在医药、食品、化工、化妆品、水处理、金属提取及回收、生化和生物医学工程等诸多领域的应用研究取得了重大进展。壳聚糖无毒无害,具有良好的保湿性、润湿性,能防止静电; 化学稳定性良好, 但吸湿性较强, 遇水易分解。对壳聚糖进行化学改性, 得到的壳聚糖衍生物在许多物化性质方面都得到改善,其应用也更加受到关注。本文着重介绍了壳聚糖在食品,医药,水处理方面的应用进展。

壳聚糖改性与在水处理方面的应用

《文献检索与科技论文写作》作业 壳聚糖的改性在水处理中的应用进展 年级: 学院: 专业:高分子材料 学生: 学号: 指导教师: 提纲

0 引言 壳聚糖是性能优异、应用广泛且具有开发价值的天然高分子絮凝剂。虽然在应用中有一些不足,但可以通过物理或化学改性来提高其性能,拓展其应用围。本文主要介绍壳聚糖改性后在水处理中的应用进展。 1 壳聚糖的改性在饮用水处理中的应用 从对氟离子的吸附及对浊度的降低介绍改性壳聚糖的应用效果; 2 壳聚糖的改性在工业废水中的应用 2.1 印染废水 从对偶氮染料的吸附及对阳离子染料的吸附介绍改性壳聚糖的应用; 2.2 重金属离子 2+、Th4+的吸附及对Cr(VI)的吸附,主要从对铜离子、对镍离子的吸附;对UO 2 来介绍改性壳聚糖的应用; 2.3 造纸废水 主要介绍接枝改性壳聚糖和壳聚糖微球对造纸废水的处理效果; 3 壳聚糖的改性在城市污水和海水中的应用 主要介绍改性壳聚糖对SS、浊度、BOD5及COD等的处理效果; 4 结语与展望 介绍目前的改性研究情况及未来研究的方向。 5 参考文献

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壳聚糖及其结构特点

第一章 绪 论 1.1 壳聚糖及其结构特点 壳聚糖(Chitosan)是甲壳素(Chitin)脱乙酰基后的产物,是甲壳素最基本、最重要的衍生物。甲壳素又名甲壳质、几丁质,化学名为(1,4)—2—乙酰胺—2—脱氧—β—D—葡聚糖,主要存在于虾、蟹、蛹及昆虫等动物外壳以及菌类、藻类植物的细胞壁中。节肢类动物的干外壳约含20~50%甲壳素。自然界中甲壳素有三种结构:α、β、γ,其中最为常见、普通的是α型。地球上每年甲壳素的生物合成量为数十亿吨,是产量仅次于纤维素的天然高分子化合物。下图1-1是甲壳素和壳聚糖的结构: 图1-1 甲壳素、壳聚糖分子的结构示意图 Fig.1-1 The configuration schematic of chitin and chitosan 纯净的甲壳素和壳聚糖均为白色片状或粉状固体,比重0.3,常温下能稳定存在。甲壳素分子之间存在强烈的氢键作用,使得甲壳素形成高度的结晶结构,因而甲壳素分子高度难溶。甲壳素不溶于水及绝大多数有机溶剂,也不溶于稀酸、稀浓碱,只溶于浓酸和某些溶剂。壳聚糖分子的活性基团为氨基而不是乙酰基,因而化学性质和溶解性较甲壳素有所改善,可溶于稀酸、甲酸、乙酸,但也不溶于水和绝大多数有机溶剂。由于氨基和羟基比较活泼,壳聚糖的化学性质较甲壳素活泼,可以发生多种化学反应,比如烷基化、酰基化反应等等。 1.2 壳聚糖及其衍生物产品的应用 壳聚糖及其衍生物由于其可再生性、生物相容性以及结构中的多种活性基团,具有多种优良的性质,已经广泛应用于化妆品、食品、医药、农业、环保等多个行业中。 1.2.1 在环保中的应用 壳聚糖及其衍生物能够通过分子中的氨基和羟基与多种金属离子形成稳定的整合物且可帮助微粒凝聚,故广泛用作化工、轻工纺织等废水处理中的吸附剂和絮凝剂。壳聚糖作为吸附剂和絮凝剂,能够有效地捕集溶液中的重金属离子和 有机物,并可以抑制细菌生长,使污水变清,特别是对于汞、铬、铜、铅、钴、3n n 甲壳素壳聚糖

082.磁性壳聚糖微球在水处理中应用的研究进展

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纤维改性沥青混合料研究进展

龙源期刊网 https://www.wendangku.net/doc/4a18080807.html, 纤维改性沥青混合料研究进展 作者:刘哲 来源:《中国科技纵横》2015年第24期 【摘要】通过对纤维改性沥青混合料研究历史及现状的调研,总结了纤维改性沥青混合 料的主要影响因素以及纤维改性沥青混合料的作用机理;阐述了纤维种类、长度、添加量以及界面粘结对沥青混合料性能的影响情况,不同因素的变化会影响沥青混合料的不同性能;总结了纤维在沥青混合料中的吸附、稳定、桥接以及加筋作用。 【关键词】纤维改性沥青混合料作用机理 1 概述 纤维作为一种新型的增强材料,被广泛的用作复合材料增强体,应用于航空航天、电子机械等尖端领域[1-3],由于纤维具有高模量、高强度、高长径比以及较强的吸附能力,在道路沥青及沥青混合料中也多有应用。多年来,国内外对纤维改善沥青及其混合料性能进行了大量研究,并根据实际需求,开发出了一系列适用于道路沥青改性的路用纤维,主要包括木质素纤维、矿物纤维、聚合物纤维以及新兴的玄武岩纤维等。本文主要针对道路纤维在沥青混合料中的应用进行调研,分析了纤维对混合料性能影响的主要作用机理及影响因素,对其未来发展进行了展望。 2纤维改性沥青混合料的主要影响因素 2.1 纤维种类及性能 按处理方式划分,纤维可分为天然纤维和化学合成纤维,不同种类的纤维具有不同的性能,包括强度、模量、吸持沥青量、长径比以及表面形貌等等,而这些因素都会对沥青混合料性能产生影响。李智慧[4]等考察了聚丙烯腈纤维、聚酯纤维以及木质素纤维等三类不同的增 强体对沥青混合料性能的影响,同时分析了三类纤维的常规技术性能,建立了纤维性能与外掺纤维沥青混合料路用性能之间的关系。结果表明,掺加聚丙烯腈纤维和聚酯纤维的沥青混合料性能相当,而木质素纤维混合料性能稍差;纤维的种类还影响着其对沥青混合料的主要作用机理。对外掺纤维沥青混合料路用性能影响程度最大的纤维性质因素是抗拉强度与极限拉伸应变,其次是熔融温度,吸持沥青量也有一定程度影响,纤维直径影响最小,在纤维形状特征因素中纤维长度的影响程度大于纤维直径与长径比。T.Serkan[5]采用聚酯纤维对石油沥青进行改性处理,石油沥青混合料的马歇尔稳定度增加而流值降低,同时抗车辙及抗疲劳性能增加,表明聚酯纤维有效提高了石油沥青混合料的路用性能;F.M.Nejad等[6]使用碳纤维增强沥青混凝土,结果显示,碳纤维的加入有效提升了沥青混凝土的强度和抗老化性能。此外,有不少学者采用不同种类的纤维对沥青混合料进行混杂改性,取得了良好的效果[7-8]。

改性壳聚糖的研究进展

改性壳聚糖的研究进展 1壳聚糖的理化性质 壳聚糖(chitosan,(1,4)-2-氨基-2-脱氧-β-D-葡聚糖)是甲壳素(chitin,(1,4)-2-乙酰氨基-2-脱氧-β-D-葡聚糖)部分脱乙酰化的产物。甲壳素广泛存在于蟹、虾以及藻类、真菌等低等动植物中,含量极其丰富,自然界每年产量约在100亿吨,是仅次于纤维素的第二大多糖。它是由葡萄糖结构单元组成的直链多糖,此多糖中含有数千个乙酰己糖胺残基,因此在分子间形成很强的氢键,导致其不溶于水和普通有机溶剂,这就大大限制了其应用范围。 将甲壳素在碱性条件下加热,脱去N-乙酰基后可生成壳聚糖。人们常将N-脱乙酰度和粘度(平均相对分子质量)作为衡量壳聚糖性能的两项指标。N-脱乙酰度是判定壳聚糖溶解性的依据,脱乙酰度越高,分子链上的游离氨基就越多,在酸中的溶解性就越好;而壳聚糖相对分子质量越大,分子之间的缠绕程度就越大,溶解度就越小。壳聚糖是自然界中唯一的一种碱性多糖,它一般是白色无定型、半透明、略有珍珠光泽的固体。壳聚糖可溶于大多数稀酸,如盐酸、醋酸、苯甲酸溶液,且溶于酸后分子中氨基可与质子结合,使自身带上正电荷。甲壳素及壳聚糖的结构式如图1所示:

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