Effects of artificial micro- and nano-structured surfaces on cell behaviour

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  • Ann Anat 191 (2009) 126135

    Effects of articial micro- and nano-structured

    E. Martneza,, E. Eng

    aNanobioengineering Group, Instit08028 Barcelona, SpainbBio/Non-Bio Interactions for RegJosep Samitier 1-5, 08028 BarcelocBiomaterials, Biomechanics and T

    atalunUnive

    ccept

    KEYWORDS Summary

    and parameters measured. This paper intends to compile and review the relevant

    In recent years, the interest in basic knowledgeon cellsubstrate interaction has grown increas-ingly as it has now been recognized to play a key

    ARTICLE IN PRESS

    Corresponding author.

    role in the differences observed in cell behaviour

    0940-9602/$ - see front matter & 2008 Elsevier GmbH. All rights reserved.doi:10.1016/j.aanat.2008.05.006

    E-mail address: emartinez@pcb.ub.es (E. Martnez).existing information on the behaviour of cells on micro- and nano-structuredarticial substrates and analyze possible general behavioural trends.& 2008 Elsevier GmbH. All rights reserved.

    IntroductionMicrostructure;Topography;Cell behaviour;Cell morphology;Cell orientation

    Substrate topography, independently of substrate chemistry, has been reported tohave signicant effects on cell behaviour. Based on the use of fabrication techniquesdeveloped by the silicon microtechnology industry, numerous studies can now befound in the literature analyzing cell behaviour as to various micro- and nano-features such as lines, wells, holes and more. Most of these works have been found torelate the micro- and nano-sized topographical features with cell orientation,migration, morphology and proliferation. In recent papers, even the inuence ofsubstrate nanotopography on cell gene expression and differentiation has beenpointed out. However, despite the large number of papers published on this topic,signicant general trends in cell behaviour are difcult to establish due todifferences in cell type, substrate material, feature aspect-ratio, feature geometryUniversitat Polite`cnica de CdDepartment of Electronics,

    Received 1 February 2008; al behaviour

    elb,c, J.A. Planellb,c, J. Samitiera,d

    ute for Bioengineering of Catalonia (IBEC), Josep Samitier 1-5,

    enerative Medicine Group, Institut de Bioenginyeria de Catalunya (IBEC),na, Spainissue Engineering Group, Department of Materials Science and Metallurgy,ya, Avda. Diagonal 647, 08028 Barcelona, Spainrsity of Barcelona, c/ Mart i Franque`s 1, 08028 Barcelona, Spain

    ed 24 May 2008surfaces on celwww.elsevier.de/aanat

  • matching the physical topology of the ECM.Additionally, broblasts and kidney epithelial cells

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    Effects of articial micro- and nano-structured surfaces on cell behaviour 127when comparing in vitro and in vivo culturing(Flemming et al., 1999). This thus represents acrucial factor in the elds of tissue engineering,drug development and regenerative medicine.Cells in their natural environment are surrounded

    by nanostructures, when contacting with othercells (membranes have nano-size features) or withthe extra-cellular matrix (ECM), formed by biomo-lecules congured in different geometrical ar-rangements (nanopores, nanobers, nanocrystals).Cell behaviour is determined via intrinsic cellsignals, but also via extrinsic cell signals comingfrom the cellcell contact and the cellECMcomponents. These signals may be chemical(growth factors such as cytokines) or mechanical(tensile forces caused by the cell interacting withmicro- or nano-structured surfaces). For example,mechanical stress has been found to affect thestrength of the integrincytoskeleton links and theintegrin receptor distribution and conformation,thus activating intracellular pathways active in celldevelopment and behaviour (Chen et al., 1997;Clark, 1995).The ability of the substratum to inuence cell

    orientation, migration and cytoskeletal organiza-tion was rst noted by Harrison in 1911 when hegrew cells on a spider web and the cells followedthe bers of the web in a phenomenon calledstereotropism or physical guidance (Harrison,1911). Later, in 1964, it was rst proposed thatcells react to the topography or their environment(Curtis and Varde, 1964). Since then, and thanks tothe various micro- and nano-fabrication techniquesdeveloped in the silicon microelectronics industry(Chen and Pepin, 2001), numerous studies haveshown that many cell types react strongly tomicrotopography (Hasirci and Kenar, 2006; Flem-ming et al., 1999; Curtis et al., 2006). Changes incell adhesion (Matsuzaka et al., 2003; Recknoret al., 2004), alignment (Clark et al., 1987, 1990;Recknor et al., 2004), morphology (cytoskeletalorganization) (Wojciak-Stothard et al., 1995; Flem-ming et al., 1999), proliferation (Keselowsky et al.,2007), vitality (Chen et al., 1997) and geneexpression and differentiation (Bruinink and Win-termantel, 2001; Watt et al., 1988) have beenreported.Recently, it has also been shown that nanotopo-

    graphy can also have strong effects on a range ofcell types. Some articles have reported a decreasein cell attachment and focal adhesion complexes innanostructures (Dalby et al., 2004a; Curtis et al.,2004), while cell morphology, proliferation andspreading (checked by cytoskeleton development)are also decreased in these nano-structured sur-faces (Gallagher et al., 2002; Dalby et al., 2004b;seeded onto nanobers have fewer stress bers andsmaller focal adhesions than those seeded on glasscoverslips (Schindler et al., 2005).Despite the accepted idea that the role of

    substrates is more than that of merely providingmechanical support but that they actually act asintelligent surfaces capable of providing chemicaland topographical signals to guide cell adhesion,spreading, morphology, proliferation and, even-tually, cell differentiation (Wilkinson et al., 2002;Curtis et al., 2006), there is a clear lack ofsystematic studies and just a very few reviewssummarizing these effects (Flemming et al., 1999).The purpose of this paper is, then, to review thetechniques used to fabricate articial surfaces withmicro- and nano-topographies and the results foundin the literature about the effects of these micro-and nano-features on cell behaviour.

    Fabrication of substrates with micro- andnano-topographies

    The denition of micro- and nano-structures onthe substrates relies on lithographic methods.Usually, a computer-designed pattern is exposedby means of light, electrons, ions or imprinted.The lithography is carried out on a special lightor electron-sensitive material or imprinted intoa special deformable polymer, which is thenused in subsequent pattern transfer processesas a mask, or, alternatively, used for cell culturingas it is.The most standard lithography technique is UV

    lithography, which uses photocurable resists sensi-tive to the UV radiation. A transparent polymer, orAndersson et al., 2003). The nanostructures havealso been reported to largely alter gene expression(Andersson et al., 2003) and, in some instances,promote or direct cell differentiation (Dalby et al.,2006, 2007; Popat et al., 2007).Mimicking the random structure of the ECM by

    nano-fabrication techniques has provided valuableinformation on cell behaviour. The use of multi-walled carbon nanobers (100 nm diameter)produced by chemical vapour deposition has re-vealed that osteoblasts seeded on them proliferatemuch better than those grown on at glass surfaces(Elias et al., 2002). Likewise, alkaline phosphataseactivity, an indicator of osteoblastic bone forma-tion, was also increased on these substrates. Thisindicates that specialized cellular functions may beenhanced when cells grow on a substrate closely

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    E. Martnez et al.128a metal-coated glass slide, with the desiredfeatures can be used as a mask through which thephotoresist can be irradiated. The photoresist isthen developed and the structures transferred tothe substrate. This patterned resist layer can thenact as a mask for the substrate etching, either bywet etching processes or by dry etching techniques(Madou, 1997; Thompson et al., 1995). The resolu-tion of this method is about 2 mm.More recent lithographic methods, based on

    particle beam, have led to the fabrication ofnano-sized topographical features. The focusedion beam lithography technique uses an energeticion beam (Ga ions for example) that is acceleratedand focused on the sample, thus producing colli-sions with the atoms of the surface and resulting inthe etching of these atoms (Langford, 2002). Theion beam can be controlled to scan the sample inthe shape of the desired patterns with a maximumlateral resolution of about 20 nm. This is a directwriting process that does not require masks.Electron beam lithographic processes consistof using an electron beam to scan the samplesurface, which has been coated with an electron-sensitive polymer (Marrian and Tennant, 2003). Thepolymer is affected by the beam and acts as anetching mask after development. This procedure,then, requires masks and etching procedures, but ithas an excellent lateral resolution of less than10 nm.Very recently, fast parallel replication techni-

    ques, such as nano-imprint lithography (Chou et al.,1995), have made it possible to overcome thedifculties of particle beam techniques (too slowand too expensive), thus allowing the applicationof nano-structured polymeric materials to cellculture (Mills et al., 2005). Materials, such asthermoplastic polymers (polymethylmethacrylate)or UV curable materials (acrylates, epoxies, etc.),can be micro/nanostructured by using these tech-niques, which require the use of a mould with thepattern to be transferred to the polymer. Themould is placed in contact with the polymer surfaceand both are heated and pressed. When thetemperature surpasses the glass transition tem-perature of the polymer (Tg), the polymer startsowing and the applied pressure forces it to ll thegaps in the mould. The system is nally cooled, andthe mould and the replica can be separated.Imprinting is a quick and easy fabrication methodin which a single mould can be used to produceseveral replicas.Other techniques for the fabrication of micro-

    and nano-structured substrates suitable for cellculture include laser deposition and etching, softlithography and colloidal lithography.Effects of micro- and nano-topographicalstructures on cell orientation andadhesion

    A list of the most important results obtained oncell orientation and adhesion when using micro-and nano-structured surfaces of different materialsis presented in Table 1. It may be noted that a verywide range of cell types such as broblasts,osteoblast, nerve cells and mesenchymal stemcells respond profoundly to a groove substrate(Wojciak-Stothard et al., 1995; Wood, 1988; Meyleet al., 1995; Clark et al., 1990; Charest et al.,2004; Miller et al., 2001; Baac et al., 2004; Recknoret al., 2004). Cells seeded onto articially pro-duced micro- and nano-grooves aligned their shapeand elongated in the direction of the groove(Figure 1b) in almost all cases, although the degreeof morphology depends on cell type, on groovedepth and, to a lesser extent, on groove width(Clark et al., 1990; Dalby et al., 2003; Flemminget al., 1999; Teixeira et al., 2003, 2004). Indeed,for grooves of period greater than 20 mm, no celltype (except red blood cells) has been found thatresponds (Wilkinson et al., 2002). Cell alignment tothe long axis of the groove is accompanied byorganization of actin and other cytoskeletalelements in an orientation parallel to the grooves.Actin and microtubules align along walls and edges,the microtubules being the rst element to bealigned, followed by actin (Oakley and Brunette,1993). Orientation often increases with increasingdepth, but decreases with increasing groove width(Clark et al., 1990). It is remarkable, however, thatthe general trend of this parallel alignmenttendency is interrupted in the case of the experi-ments published by Teixeira et al. (2006). In thisstudy, epithelial cells switched from parallel toperpendicular alignment to the grooved sub-strate when features decreased in pitch size from4000 to 400 nm, also changing their focal adhesiondistribution.Although almost all sorts of cells have been found

    to align with respect to grooves, other topographi-cal features as wells, pits or pillars do not showsuch a clear cell alignment for all cell types(Gallagher et al., 2002; Fewster, 1994; Huntet al., 1995). However, studies of Curtiss groupseem to point out that cells can feel symmetriesin the topography (Figure 1a), especially if they arein the nanorange (Curtis et al., 2004).Regarding cell adhesion, there is not a common

    trend for the various cell types or micro/nanos-tructures assayed. To illustrate this fact, Table 1shows that cell adhesion has been reported to be

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    Table 1. Summary of the effects of micro- and nano-structured surfaces on cell orientation and adhesion

    Feature type Material Widtha/diameter

    Depth/height Pitch Cell type Effects on orientation and adhesion Reference

    Grooves Quartz 0.5, 5, 10,25mm

    0.5, 5 mm 1:1 Murine P388D1macrophage

    Orientation Wojciak-Stothardet al. (1995)

    Grooves Quartz 1, 4mm 1.1 mm 1:1 Mesenchymalstem cells

    Alignment better in the widestgrooves

    Wood, (1988)

    Grooves Silicon dioxide 0.5 mm 1mm 1:1 Fibroblasts Strong alignment Meyle et al. (1995a)Grooves Silicon dioxide 0.5 mm 1mm 1:1 Keratinocytes No alignment Meyle et al.

    (1995b)Grooves PMMA 2, 3, 6, 12mm 0.2, 0.5, 1.1,

    1.9 mm1:1 BHK cells Alignment increased with d. and

    decreased with w.Clark et al. (1990)

    Grooves Photo-responsivePMMA

    1mm 250nm 1:1 Humanastrocytes(HAs)

    Improved adhesion, strongalignment

    Baac et al. (2004)

    Grooves PS 110 mm 0.51.5 mm N/D Rat bone cells Large grooves: focal adhesions allover the surface.

    Matsuzaka, et al.(2003)

    Narrow grooves: only on the edgesGrooves Polyimide 4mm 5mm 34mm Osteoblasts Strong alignment, no changes in

    adhesionCharest et al.(2004)

    Grooves PDLA 10mm 3mm 20mm Schwann cells(nerve cells)

    Strong alignment Miller et al. (2001)

    Grooves PS 10mm 3mm 20mm Rat astrocytes Less adhesion, strong alignment Recknor et al.(2004)

    Grooves PS 201000 nm 5530 nm 1:1 Fibroblasts No alignment for depthso35 nm orwidthso100 nm

    Loesberg et al.(2007)

    Grooves Silicon 3302100 nm 600nm 4004000 nm Human cornealepithelial cells

    Perpendicular alignment for400800 nm pitch. Parallel for16004000 nm

    Teixeira et al.(2006)

    Steps PMMA 118 mm N/D N/D BHK Alignment at steps Clark et al. (1987)Wells PC 7, 25, 50mm 0.5, 1.5, 2.5 mm 1:1 Fibroblasts No orientation Hunt et al. (1995)Pits PCL 150 nm 80nm 300nm Fibroblasts Less focal contacts and vinculin

    patternGallagher et al.(2002)

    Pits PCL, PMMA 35, 75 and120 nm

    N/D 100, (200,300 nm

    Fibroblasts Reduced adhesion, orientation anddistinction of symmetries

    Dalby et al.(2004a), Curtis etal. (2001), Curtis etal. (2004)

    Random PLGA, PU, PCL 206, 370 nm N/D N/D Bladder smoothmuscle cells

    Enhanced adhesion Thapa et al. (2003)

    Abbreviation list: N/D: non-determined; PMMA: poly(methylmethacrylate); PDMS: poly-dimethyl siloxane; PC: polycarbonate; PS: polystyrene; PLLA: poly(L-lactide acid); PET:poly(ethylene terephthalate); PBrS: poly(4-bromostyre...

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