外文翻譯--基于生物材料的殼聚糖海藻酸鈉的表面電荷和機(jī)械特性的研究（英文）

1、Characterization of surface charge and mechanical properties of chitosan/alginate based biomaterialsDevendra Verma ?, Malav S. Desai, Namrata Kulkarni, Noshir LangranaDepartment of Biomedical Engineering, Rutgers, The St

2、ate University of New Jersey, 599 Taylor Road, Piscataway, NJ 08854, USAa b s t r a c t a r t i c l e i n f oArticle history:Received 24 September 2010Received in revised form 17 July 2011Accepted 10 August 2011Available

3、 online 17 August 2011Keywords:Polyelectrolyte complexSurface chargeAFMChitosanAlginateThis study aims to examine mechanical properties and surface charge characteristics of chitosan/alginate-basedfilms for biomedical ap

4、plications. By varying the concentrations of chitosan and alginate, we have developed filmswith varying surface charge densities and mechanical characteristics. The surface charge densities of these filmswere determinedb

5、y applying an analyticalmodel on force curves derivedfrom an atomic force microscope (AFM).The average surface charge densities of films containing 60% chitosan and 80% chitosan were found tobe?0.46 mC/m2 and?0.32 mC/m2,

6、 respectively. The surface chargedensity of 90% chitosancontainingfilms wasfound tobe neutral. Theelasticmoduliand thewatercontent were found to be decreasing with increasing chitosanconcentration. The films with 60%, 80

7、% and 90% chitosan gained 93.5±6.6%, 217.1±22.1% and 396.8±67.5%of their initial weight, respectively. Their elastic moduli were found to be 2.6±0.14 MPa, 1.9±0.27 MPa and0.93±0.12 MPa, resp

8、ectively. The trend observed in the mechanical response of these films has been attributed tothe combined effect of the concentration of polyelectrolyte complexes (PEC) and the amount of water absorbed.The Fourier transf

9、orm infrared spectroscopy experiments indicate the presence of higher alginate on the surface ofthe films compared to the bulk in all films. The presence of higher alginate on surface is consistent with negativesurface c

10、harge densities of these films, determined from AFM experiments.© 2011 Elsevier B.V. All rights reserved.1. IntroductionBiomaterials are synthetic or biological in origin and are expected toperform the biological fu

11、nctions of the tissue they replace. In someapplications such as bone grafts, they can interact with surroundingtissues and form a strong bond [1–3]. In others such as vascular graftsand anti-adhesion barriers, they shoul

12、d behave inertly and avoid anycellular adhesions [4–6]. All implanted biomaterials may potentiallyevoke a host-tissue response and this response can be attributed tocomplex interactions from a vast array of material prop

13、erties, such asmechanical properties, surface chemistry, bulk chemistry, topography,shape, and degradation rate, to name a few. All of these ultimatelyinvolve surface interactions [7,8].In addition to aforementioned fact

14、ors, surface charge has also beenobserved to have significant effects on cellular behaviors such asinflammatory response, colony formation, orientation, adhesions andproliferation. Hunt et al. investigated the influence

15、of surface charge onthe stimulation of the inflammatory response [9]. The surface charge ofpoly(ether)urethanes was gradually increased by varying substitution ofnegatively charged sulfonate groups. The results indicate

16、a significantinfluence on early phase acute inflammatory response. Surface chargedensity has also been found to influence vascular ingrowth withinfibrous meshes coated with positively and negatively charged molecules[10]

17、. Negatively charged meshes promoted significantly higher vesselingrowth. The surface charge density has also been reported to affectcolony formation by osteoblast and orientation of neuroblastoma cells[11,12].When polym

18、ers having oppositely charged groups, such aschitosan and alginate, are mixed under aqueous condition, theyspontaneously combine to form polyelectrolyte complexes (PEC).PECs primarily consist of at least two oppositely c

19、harged polymers[13]. The driving force for the formation of polyelectrolyte complex isthe entropy and strong electrostatic attraction between the oppositelycharged polymers. Chitosan can serve as a non-protein matrix for

20、three-dimensional tissue growth. Potentially, it could provide thebiological primer for cell–tissue proliferation and reconstruction [14].However, chitosan has very low mechanical integrity and degradesvery rapidly. Many

21、 studies have been conducted on designing andfabricating chitosan-based hybrid systems [15–17], by chemicallymodifying the amino and/or hydroxyl groups in order to achieveimproved mechanical properties as well as an impr

22、oved biologicalperformance [18–20]. Alginate is regarded as an anionic polyelectro-lyte. Both chitosan and alginate have been shown in animal studies tobe biocompatible, biodegradable and biofunctional [21–24]. Polyelec-

23、trolyte complex biomaterials, especially polysaccharide based, haveMaterials Science and Engineering C 31 (2011) 1741–1747? Corresponding author. Tel.: +1 732 445 4500; fax: +1 732 445 3753.E-mail address: devendra@rci.r

24、utgers.edu (D. Verma).0928-4931/$ – see front matter © 2011 Elsevier B.V. All rights reserved.doi:10.1016/j.msec.2011.08.005Contents lists available at SciVerse ScienceDirectMaterials Science and Engineering Cjourna

25、l homepage: www.elsevier.com/locate/msecretracting and approaching curves were recorded. Force curves ateach point were the average of 1000 retracting and approachingcurves. FV data sets were collected in NaCl solution a

26、t 0.1 mM saltconcentration and 7.4 pH, which was maintained using NaOH.In the force curves, the x-axis corresponds to the height betweencantilever and the sample surface, and the y-axis corresponds to thedeflection of th

27、e cantilever. The curve was divided into three regions(Fig. 2). Region C corresponded to the initial movement of thecantilever, where there was no interaction between the surface andthe tip. As the tip approaches closer

28、to the surface, the long rangeelectrostatic interactions caused the deflection of the tip (Region B).Since the surface charges are neutralized by the adsorption ofcounter-ions in aqueous conditions, the forces in AFM mea

29、surementwere basically the electrostatic interactions between the counter-ionsof the AFM tip and the sample surface. As the cantilever moved furtherdown, eventually the tip made contact with the sample surface andcompres

30、sion of sample by the tip gave rise to further deflection of thetip (Region A).2.6. Determination of surface charge densitySince the electrostatic forces result from the interactions betweenthe double layers of the AFM t

31、ip and the sample surface, these forcescan be modeled using Poisson–Boltzmann equation. The Poisson–Boltzmann equation for a double layer is described as:d2ψdx2 = κ2βe sinh βeψ ð Þ ð1Þwhere ψ is the s

32、urface potential, e is the elementary charge, β=1/(kT) is the inverse thermal energy, and k?1 is the Debye lengthdefined as k2=2βe2n/(εε0), whereby n is the number concentrationof the monovalent salt in the bulk and εε0

33、is the dielectric permittivityof water. The Poisson–Boltzman equation can be solved either byconsidering constant charge (CC) or constant potential (CP) boundaryconditions [34,35].Another approach is to derive surface ch

34、arge density with ananalytical equation [31]. Butt derived the electric double layer forcebetween a spherical tip and planar sample in an electrolyte solutionbased on an expression for the pressure between two charged pl

35、anesin an electrolyte [36]. The force, F was described as:FR = 4πλσtipσsample εε0 e?z=λ ð2Þwhere, R was the tip radius, l was the Debye screening length, σtip andσsample were the tip and the sample charge densi

36、ties respectively, andz was the tip–sample separation. This derivation required severalassumptions, including small surface potentials, tip–sample separa-tions larger than the Debye length, and tip radii larger than thes

37、eparation, R?z. Despite these approximations, this expressionsuccessfully described experimental measurements in terms of theforce dependence on tip–sample separation, tip radius, electrolyteconcentration, and pH. It has

38、 been widely applied to electrostaticinteractions between Si3N4 and Silica probe tips, and inorganicsurfaces as well as lipid membranes [37].The radius, R, was that of the silicon bead tip given as 2.5 μm andthe force, F

39、, was calculated using the Hooke's Law (F=k.x) andthe values for the deflection and the spring constant (k=0.18 N/m) ofthe calibrated tip. σtip was the surface charge of the silicon beadknown to be ?7.1×10?3 C/m

40、2, z was the movement of the tip alongthe z-axis, εε0 and λ were taken as 7.08335×10?10 and 9.1×10?8 mrespectively.Since chitosan and alginate contained oppositely charged func-tional groups, mixing them at dif

41、ferent proportions changes thesurface charge characteristics of the films. Atomic force microscopy(AFM) was utilized to determine the surface charge densities. Forcesbetween chitosan/alginate films and silica bead were m

42、easureddirectly with AFM in aqueous conditions at pH 7.4 and 0.1 mM ionicstrength. Ionic strength was maintained by adding NaCl. Silica bead isnegatively charged under aqueous conditions. The forces betweensilica bead an

43、d films were determined from the cantilever deflection.The data in region C was used to normalize the curve with respect tothe deflection-axis (Fig. 3), while that from B contained the deflectiondata from the surface cha

44、rge and that from A contained the data fromindentation of the surface. The average deflection in the linear part inregion C was determined and used to normalize the force curves asshown in Fig. 3A. Next, a linear fit was

45、 performed for the deflectionvalues and these values were compared with the actual data points.The linear region was identified based on the deviation of the actualdata from the calculated data. This point was taken as t

46、he contactpoint between silica bead and film surface. This linear region waseliminated upon identification (Fig. 3C) and the curve was normalizedto the z-axis (Fig. 3D). An analytical equation (Eq. (2)) was used to fitth

47、e data to determine the surface charge density. All these steps wereperformed using a MATLAB program.2.7. Determination of elastic modulus from force curvesElastic modulus can be determined from Region A of force curves.

48、On an infinitely stiff sample, the deflection of the cantilever isidentical to the movement of the piezo in z direction; however, on asoft sample, indentation leads to smaller deflection. Indentation onthe soft sample ca

49、n be determined by subtracting cantileverdeflection from that on a hard sample. Since Hooke's Law connectsthe deflection of the cantilever and the applied loading force via theforce constant k of the cantilever, the

50、loading force can be writtenasF=kd. Elastic modulus was determined by plotting indentation vs.loading force and modeling with the Hertz Model. In the case of aninfinitely hard sphere of radius R (AFM tip) touching a soft

51、 planarsurface the Hertz model gives the following relation between theloading force F and the indentation, δ:FSphere = 43E1?ν2ffiffiffi R p δ3= 2 ð3Þwhere E is the Young's modulus and ν is the Poisson rati

52、o of the softmaterial.Fig. 2. Schematic of tip movement along z-axis vs. Deflection curve obtained from AFMtests. (A) Linear region from tip indentation and deflection on material surface;(B) Non-linear region from tip d