Guidance and activation of murine macrophages by nanometric scale topography

Subcellular topological effect of particle monolayers on cell shapes and functions

We studied topological effects of subcellular roughness displayed by a closely packed particle monolayer on adhesion and growth of endothelial cells. Poly(styrene-co-acrylamide) (SA) particles were prepared by soap-free emulsion copolymerization. Particle monolayers were prepared by Langmuir-Blodgett deposition using particles, which were 527 (SA053) and 1270 nm (SA127) in diameter. After 24-h incubation, cells tightly adhered on a tissue culture polystyrene dish and randomly spread. On the other hand, cells attached on particle monolayers were stretched into a narrow stalk-like shape. Lamellipodia spread from the leading edge of cells attached on SA053 monolayer to the top of the particles and gradually gathered to form clusters. This shows that cell-cell adhesion became stronger than cell-substrate interaction. Cells attached to SA127 monolayer extended to the reverse side of a particle monolayer and engulfed particles. They remained immobile without migration 24h after incubation. This shows that the inhibition of extensions on SA127 monolayer could inhibit cell migration and cell proliferation. Cell growth on the particle monolayers was suppressed compared with a flat TCPS dish. The number of cells on SA053 gradually increased, whereas that on SA127 decreased with time. When the cell seeding density was increased to 200,000 cells cm(-2), some adherent cells gradually became into contact with adjacent cells. F-actin condensations were formed at the frame of adherent cells and the thin filaments grew from the edges to connect each other with time. For the cell culture on SA053 monolayer, elongated cells showed a little alignment. Cells showed not arrangement of actin stress fibers but F-actin condensation at the contact regions with neighboring cells. Interestingly, the formed cell monolayer could be readily peeled from the particle monolayer. These results indicate that endothelial cells could recognize the surface roughness displayed by particle monolayers and the response was dependent on the pitch of particle monolayers.

Surface-textured PEG-based hydrogels with adjustable elasticity: Synthesis and characterization

Poly(ethylene glycol)-dimethacrylate (PEGDMA)-based hydrogels with adjustable shear modulus within the range of 10kPa to 1MPa and precisely predefinable surface textures on a micro-scale were made. It was observed that the volume of all hydrogels after preparation almost exactly matched the volume of the precursor solution and that there were only slight volume changes upon equilibration in excess solvent. This characteristic swelling behavior enables the preparation of textures on the hydrogel's surface with precisely predefinable dimensions. The behavior can be modeled with the Flory-Huggins theory assuming a concentration-dependent polymer-solvent interaction parameter. Additionally, activation of the hydrogels by electrophilic oxirane groups creates reactive sites that will enable the later grafting of the hydrogel's surface with various specific nucleophiles, e.g. biomolecules. Thus, these hydrogels are particularly suitable as biomaterials for systematic investigations of cellular response to surface topography and elasticity of the substrate, both in vivo and in vitro.

Human foetal osteoblastic cell response to polymer-demixed nanotopographic interfaces

Nanoscale cell-substratum interactions are of significant interest in various biomedical applications. We investigated human foetal osteoblastic cell response to randomly distributed nanoisland topography with varying heights (11, 38 and 85 nm) produced by a polystyrene (PS)/polybromostyrene polymer-demixing technique. Cells displayed island-conforming lamellipodia spreading, and filopodia projections appeared to play a role in sensing the nanotopography. Cells cultured on 11 nm high islands displayed significantly enhanced cell spreading and larger cell dimensions than cells on larger nanoislands or flat PS control, on which cells often displayed a stellate shape. Development of signal transmitting structures such as focal adhesive vinculin protein and cytoskeletal actin stress fibres was more pronounced, as was their colocalization, in cells cultured on smaller nanoisland surfaces. Cell adhesion and proliferation were greater with decreasing island height. Alkaline phosphatase (AP) activity, an early stage marker of bone cell differentiation, also exhibited nanotopography dependence, i.e. higher AP activity on 11 nm islands compared with that on larger islands or flat PS. Therefore, randomly distributed island topography with varying nanoscale heights not only affect adhesion-related cell behaviour but also bone cell phenotype. Our results suggest that modulation of nanoscale topography may be exploited to control cell function at cell-biomaterial interfaces.

Does the nanometre scale topography of titanium influence protein adsorption and cell proliferation?

To investigate the influence of titanium films with nanometre scale topography on protein adsorption and cell growth, three different model titanium films were utilized in the present study. The chemical compositions, surface topographies and wettability were investigated by using X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM) and water contact angle measurement, respectively. The films share the same surface chemistry but exhibit different topographies on a nanometre scale. Thus, they act as model systems for biological studies regarding surface topography effects. The films were obtained by varying the deposition rate and the film thickness, respectively. These films displayed nanometre scale surface roughness (root mean square roughness, R(rms)) from 2 to 21 nm over areas of 50 microm x 50 microm, with different grain sizes at their surfaces. Albumin and fibrinogen adsorption on these model titanium films were performed in this study. Bicinchoninic acid assay was employed to determine the amount of adsorbed protein on titanium film surfaces. No statistically significant differences, however, were observed for either albumin or fibrinogen adsorption between the different groups of titanium films. No statistically significant influence of surface roughness on osteoblast proliferation and cell viability was detected in the present study.

Cell orientation by a microgrooved substrate can be predicted by automatic control theory

Cells have the ability to measure and respond to extracellular signals like chemical molecules and topographical surface features by changing their orientation. Here, we examined the orientation of cultured human melanocytes exposed to grooved topographies. To predict the cells' orientation response, we describe the cell behavior with an automatic controller model. The predicted dependence of the cell response to height and spatial frequency of the grooves is obtained by considering the symmetry of the system (cell + substrate). One basic result is that the automatic controller responds to the square of the product of groove height and spatial frequency or to the aspect ratio for symmetric grooves. This theoretical prediction was verified by the experiments, in which melanocytes were exposed to microfabricated poly(dimethylsiloxane) substrates having parallel rectangular grooves of heights (h) between 25 and 200 nm and spatial frequencies (L) between 100 and 500 mm(-1). In addition, the model of the cellular automatic controller is extended to include the case of different guiding signals acting simultaneously.

Microfluidic alignment of collagen fibers for in vitro cell culture

Three dimensional gels of aligned collagen fibers were patterned in vitro using microfluidic channels. Collagen fiber orientation plays an important role in cell signaling for many tissues in vivo, but alignment has been difficult to realize in vitro. For microfluidic collagen fiber alignment, collagen solution was allowed to polymerize inside polydimethyl siloxane (PDMS) channels ranging from 10-400 microm in width. Collagen fiber orientation increased with smaller channel width, averaging 12+/-6 degrees from parallel for channels between 10 and 100 microm in width. In these channels 20-40% of the fibers were within 5 degrees of the channel axis. Bovine aortic endothelial cells expressing GFP-tubulin were cultured on aligned collagen substrate and found to stretch in the direction of the fibers. The use of artificially aligned collagen gels could be applied to the study of cell movement, signaling, growth, and differentiation.

The effect of combined cyclic mechanical stretching and microgrooved surface topography on the behavior of fibroblasts

Under the influence of mechanical stress, cultured fibroblasts have a tendency to orient themselves perpendicular to the stress direction. Similar cell alignment can be induced by guiding cells along topographical clues, like microgrooves. The aim of this study was to evaluate cell behavior on microgrooved substrates, exposed to cyclic stretching. We hypothesized that cellular shape is mainly determined by topographical clues. On basis of earlier studies, a 10-microm wide square groove, and a 40-microm wide V-shaped groove pattern were used. Smooth substrates served as controls. Onto all substrates fibroblasts were cultured and 1-Hz cyclic stretching was applied (0, 4, or 8%) for 3-24 h. Cells were prepared for scanning electron microscopy, immunostaining of filamentous actin, alignment measurements, and PCR (collagen-I, fibronectin, alpha1- and beta1-integrins). Results showed that cells aligned on all grooved surfaces, and fluorescence microscopy showed similar orientation of intracellular actin filaments. After 3 h of stretch, cellular orientation started to commence, and after 24 h the cells had aligned themselves almost entirely. Image analysis showed better orientation with increasing groove depth. Statistical testing proved that the parameters groove type, groove orientation, and time all were significant, but the variation of stretch force was not. Substrates with microgrooves perpendicular to the stretch direction elicit a better cell alignment. The expression of beta1-integrin and collagen-I was higher in the stretched samples. In conclusion, we can maintain our hypothesis, as microgrooved topography was most effective in applying strains relative to the long axis of the cell, and only secondary effects of stretch force were present.

Topographic guidance of endothelial cells on silicone surfaces with micro- to nanogrooves: Orientation of actin filaments and focal adhesions

To mimic the uniformly elongated endothelium in natural linear vessels, bovine aortic endothelial cells (BAECs) are cultured on micro- to nanogrooved, model poly(dimethylsiloxane) (PDMS) substrates preadsorbed with about 300 ng/cm(2) of fibronectin. BAEC alignment, elongation, and projected area were investigated for channel depths of 200 nm, 500 nm, 1 microm, and 5 microm, as well as smooth surfaces. Except for the 5 microm case, the ridge and channel widths were held nearly constant about 3.5 microm. With increasing channel depth, the percentage of aligned BAECs increased by factors of 2, 2, 1.8, and 1.7 for 1, 4, 24, and 48 h. Maximum alignment, about 90%, was observed for 1 microm deep channels at 1 h. The alignment of BAECs on grooved PDMS was maintained at least until cells reached near confluence. F-actin and vinculin at focal adhesions also aligned with channel direction. Analysis of confocal microscopy images showed that focal adhesions localized at corners and along the sidewalls of 1-microm deep channels. In contrast, focal adhesions could not form on the bottom of the 5-microm deep channels. Cell proliferation was similar on grooved and smooth substrates. In summary, PDMS substrates engraved with micro- and nanochannels provide a powerful method for investigating the interplay between topography and cell/cytoskeletal alignment.

Nanopattern-induced changes in morphology and motility of smooth muscle cells

Cells are known to be surrounded by nanoscale topography in their natural extracellular environment. The cell behavior, including morphology, proliferation, and motility of bovine pulmonary artery smooth muscle cells (SMC) were studied on poly(methyl methacrylate) (PMMA) and poly(dimethylsiloxane) (PDMS) surfaces comprising nanopatterned gratings with 350 nm linewidth, 700 nm pitch, and 350 nm depth. More than 90% of the cells aligned to the gratings, and were significantly elongated compared to the SMC cultured on non-patterned surfaces. The nuclei were also elongated and aligned. Proliferation of the cells was significantly reduced on the nanopatterned surfaces. The polarization of microtubule organizing centers (MTOC), which are associated with cell migration, of SMC cultured on nanopatterned surfaces showed a preference towards the axis of cell alignment in an in vitro wound healing assay. In contrast, the MTOC of SMC on non-patterned surfaces preferentially polarized towards the wound edge. It is proposed that this nanoimprinting technology will provide a valuable platform for studies in cell-substrate interactions and for development of medical devices with nanoscale features.

The recognition of adsorbed and denatured proteins of different topographies by β2 integrins and effects on leukocyte adhesion and activation

Leukocyte beta2 integrins Mac-1 and p150,95 are promiscuous cell-surface receptors that recognise and mediate cell adhesion to a variety of adsorbed and denatured proteins. We used albumin as a model protein to study whether leukocyte adhesion and activation depended on the nm-scale topography of a protein adlayer. Albumin adsorbed from the native conformation gave rise to different adlayer topographies and different amounts of adsorbed protein on hydrophobic and relatively hydrophilic polystyrene and silanised silicon-wafer surfaces, whereas adsorption of pre-denatured Alb resulted in similar adlayer topographies and similar amounts of adsorbed protein on these surfaces. All three distinct protein-adlayer topographies supported adhesion of in vitro differentiated, macrophage-like U937 and THP-1 cells, but did not support adhesion of their promonocytic precursors. Human monocytes freshly isolated from peripheral blood did not adhere to adsorbed albumin, not even in the presence of monocyte chemoattractant protein-1 and macrophage inflammatory protein-1alpha chemokines. Adhesion of the macrophage-like cells to albumin in any of the three topographies was inhibited by antibodies against beta2 integrins, but not by antibodies against beta1 integrins, and did not induce secretion of the proinflammatory cytokine tumour necrosis factor-alpha.

Alignment of Osteoblast-Like Cells and Cell-Produced Collagen Matrix Induced by Nanogrooves

Alignment of bone cells and collagen matrix is closely related to the anisotropic mechanical properties of bone. Intact scaffolds that promote osteoblast differentiation and mineralization in the preferred direction offer promise in the generation of biomimetic bone tissue. In this study, we examined the alignment of osteoblast-like cells and collagen fibers guided by nanogrooves. Nanoscale groove-ridge patterns (approximately 300 nm in periodicity, 60-70 nm in depth) on the surface of polystyrene (PS) were made by polarized Nd:YAG laser irradiation, at a wavelength of 266 nm. The influence of such "nanoscale features" on the orientation and alignment of cells and their mineralized collagen matrix was investigated, using rabbit mesenchymal stem cell (MSC)-derived osteoblast-like cells. The cells and actin stress fibers were aligned and elongated along the direction of the nanogrooves. In addition, the alignment of collagen matrix was also influenced by underlying nanogrooves. The results suggested that nanoscale fibrous cues in the longitudinal direction might contribute to the aligned formation of bone tissue. This may provide an effective approach for constructing biomimetic bone tissue.

In vivo cytokine secretion and NF-kappaB activation around titanium and copper implants

The early biological response at titanium (Ti), copper (Cu)-coated Ti and sham sites was evaluated in an in vivo rat model. Material surface chemical and topographical properties were characterized using Auger electron spectroscopy, energy dispersive X-ray spectroscopy and interferometry, respectively. The number of leukocytes, cell types and cell viability (release of lactate dehydrogenase) were determined in the implant-interface exudate. The contents of activated nuclear transcription factor NF-kappaB, interleukin-6 (IL-6) and interleukin-10 (IL-10) were determined by enzyme linked immunosorbent assay. An increase in the number of leukocytes, in particular, polymorphonuclear leukocytes, was observed between 12 and 48 h around Cu. A marked decrease of exudate cell viability was found around Cu after 48 h. The total amounts of activated NF-kappaB after 12 h was highest in Ti exudates whereas after 48 h the highest amount of NF-kappaB was detected around Cu. The levels of cytokine IL-6 were consistently high around Cu at both time periods. No differences in IL-10 contents were detected, irrespective of material/sham and time. The results show that materials with different toxicity grades (titanium with low and copper with high toxicity) exhibit early differences in the activation of NF-kappaB, extracellular expression and secretion of mediators, causing major differences in inflammatory cell accumulation and death in vivo.

Significance of synthetic nanostructures in dictating cellular response

Cell-substratum interaction is influenced by topographical in addition to chemical cues. The majority of patterning studies on cellular response have been conducted on micropatterned surfaces. Cells clearly respond to the topography of substrates in the micron range in terms of adhesion, proliferation, migration, and gene expression. However, cells in their natural environment also interact with extracellular matrix components in the nanometer scale. This review will cover recent studies that show mammalian cells responding to nanoscale features on a synthetic surface. An important and exciting direction of research in nanomedicine would be to gain a better understanding of the interaction between cells and nanostructures. This will facilitate the creation of the next generation of biomaterials with well-defined nanotopography that can elicit the desired cellular and tissue response.

Biological length scale topography enhances cell-substratum adhesion of human corneal epithelial cells

The basement membrane possesses a rich 3-dimensional nanoscale topography that provides a physical stimulus, which may modulate cell-substratum adhesion. We have investigated the strength of cell-substratum adhesion on nanoscale topographic features of a similar scale to that of the native basement membrane. SV40 human corneal epithelial cells were challenged by well-defined fluid shear, and cell detachment was monitored. We created silicon substrata with uniform grooves and ridges having pitch dimensions of 400-4000 nm using X-ray lithography. F-actin labeling of cells that had been incubated for 24 hours revealed that the percentage of aligned and elongated cells on the patterned surfaces was the same regardless of pitch dimension. In contrast, at the highest fluid shear, a biphasic trend in cell adhesion was observed with cells being most adherent to the smaller features. The 400 nm pitch had the highest percentage of adherent cells at the end of the adhesion assay. The effect of substratum topography was lost for the largest features evaluated, the 4000 nm pitch. Qualitative and quantitative analyses of the cells during and after flow indicated that the aligned and elongated cells on the 400 nm pitch were more tightly adhered compared to aligned cells on the larger patterns. Selected experiments with primary cultured human corneal epithelial cells produced similar results to the SV40 human corneal epithelial cells. These findings have relevance to interpretation of cell-biomaterial interactions in tissue engineering and prosthetic design.

Changes in fibroblast morphology in response to nano-columns produced by colloidal lithography

In designing new biomaterials, specific chemical and topographical cues will be important in guiding cell response. Filopodia are actin-driven structures produced by cells and speculated to be involved in cell sensing of the three-dimensional environment. This report quantifies filopodia response to cylindrical nano-columns (100 nm diameter, 160 nm high) produced by colloidal lithography. Also observed were actin cytoskeleton morphology by fluorescence microscopy and filopodia morphology by electron microscopy (scanning and transmission). The results showed that the fibroblasts used produced more filopodia per microm of cell perimeter and that filopodia could often be seen to interact with the cells' nano-environment. By understanding as to which features evoke spatial reactions in cells, it may be possible to design better biomaterials.

Investigating filopodia sensing using arrays of defined nano-pits down to 35 nm diameter in size

In order for cells to react to topography, they must be able to sense shape. When considering nano-topography, these shapes are much smaller than the cell, but still strong responses to nano-topography have been seen. Filopodia, or microspikes, presented by cells at their leading edges are thought to be involved in gathering of special information. In order to investigate this, and to develop an understanding of what size of feature can be sensed by cells, morphological observation (electron and fluorescent microscopy) of fibroblasts reacting to nano-pits with 35, 75 and 120 nm diameters has been used in this study. The nano-pits are especially interesting because unlike many of the nanofeatures cited in the literature, they have no height for the cells to react to. The results showed that cell filopodia, and retraction fibres, interacted with all pit sizes, although direct interaction was hard to image on the 35 nm pits. This suggests that cells are extremely sensitive to their nanoevironment and that should be taken in to consideration when designing next-generation tissue engineering materials. We suggest that this may occur through nanocontact guidance as filopodia are moved over the pits.

Biological and biophysical principles in extracorporal bone tissue engineering

Advances in the field of bone tissue engineering have encouraged physicians to introduce these techniques into clinical practice. Bone tissue engineering is the construction, repair or replacement of damaged or missing bone in humans or animals. Engineering of bone can take place within the animal body or extracorporal in a bioreactor for later grafting into the body. Appropriate cell types and non-living substrata are minimal requirements for an extracorporal tissue engineering approach. This review discusses the biological and biophysical background of in vitro bone tissue engineering. Biochemical and biophysical stimuli of cell growth and differentiation are regarded as potent tools to improve bone formation in vitro. The paper focuses on basic principles in extracorporal engineering of bone-like tissues, intended to be implanted in animal experiments and clinical studies. Particular attention is given in this part to the contributions of cell and material science to the development of bone-like tissues. Several approaches are at the level of clinical applicability and it can be expected that widespread use of engineered bone constructs will change the surgeon's work in the near future.

Attempted endocytosis of nano-environment produced by colloidal lithography by human fibroblasts

Control of the cells' nanoenvironment is likely to be important in the future of cell and tissue engineering. Microtopography has been shown to provide cues to cells that elicit a large range of cell responses, including control of adhesion, morphology, apoptosis and gene regulations. Now, researchers are focusing on nanotopography as techniques such as colloidal and electron beam lithography and polymer demixing have become available. In this study, human fibroblast response to nanocolumns (160-nm high, 100-nm diameter, 230-nm centre-centre spacing) produced by colloidal lithography are considered. Using electron microscopy and immunofluorescence to image the cytoskeleton, clathrin and dynamin, it was observed that the cells try to endocytose the nanocolumns. It also appeared that a small population of the cells changed to unusual morphologies with macrophage-like processes and highly disrupted cytoskeleton. These observations could have implications for nanomaterials science in areas such as cell transfection and drug delivery.

The effects of collagen type I topography on myoblasts in vitro

Cells respond to a variety of cues from their environment, which can include chemical, mechanical, and topographical signals. The differentiation of myoblasts requires a combination of signals. Myoblast fusion is strongly influenced by the chemical nature of the surrounding matrix and can be affected by mechanical stimulation. Studies also have shown that a large variety of cell types also are influenced by details of surface topography of a substrate as small as 44 nm. Cells grown on a collagen-coated surface differentiate more readily than those grown in the absence of the extracellular matrix protein. It is not known whether the effects of myoblast interaction with collagen are due solely to chemical interactions or if myoblasts also respond to the topography of collagen type I fibers. To determine the importance of collagen-generated topographical signals on myoblast development, cells were cultured and differentiated in vitro on surfaces that had been coated with either soluble collagen type I or fibrous collagen type I. Both surfaces present the same chemical interactions, but the additional topographical signals lead to differences in cell morphology, adhesion, spreading rates and, proliferation. Cells on the fibrous form of collagen are more stellate, form more adhesion plaques, spread faster, and proliferate at a faster, rate than cells on a surface of soluble collagen. Our data indicate that topographical signals play a role in early muscle development, but that other or additional signaling pathways regulate differentiation.

The effect of surface chemistry and nanotopography of titanium nitride (TiN) films on primary hippocampal neurones

The cell-substrate interaction of primary hippocampal neurones with thin films of TiN was studied in vitro. TiN films of different surface chemistries and topographies were deposited by pulsed DC reactive magnetron sputtering and closed field unbalanced magnetron sputter ion plating by Teer Coatings Ltd., Hartlebury, UK to result in TiN films with similar surface chemistries but different topographical features. TiN films were characterised using X-ray diffraction, X-ray photoelectron spectroscopy and atomic force microscopy. The neuron-substrate interaction was examined using environmental scanning electron microscopy (FEG-ESEM) for morphological information. Bromodeoxyuridine and TUNEL assays were used to identify proliferating neurones as well as apoptotic neurones. Fluorescent staining for MAP-2 was used to label neuronal network formation. Primary hippocampal neurones were found to attach and spread to all of the TiN film chemistries and topographies investigated. Neuronal network morphology appeared to be more preferential on the nitrogen rich TiN films and also with reduced nanotopographical features.

The effect of surface chemistry and nanotopography of titanium nitride (TiN) films on 3T3-L1 fibroblasts

The cell-material interaction of 3T3-L1 fibroblasts with TiN films was studied in vitro. TiN films were deposited onto glass substrates to thicknesses of 0.2 and 1.0 microm by pulsed dc reactive magnetron sputtering. For comparison TiN films were deposited by closed field unbalanced magnetron sputter ion plating by Teer Coatings Ltd. (Hartlebury, UK) to result in TiN films with similar surface chemistries but having increased topographical features. TiN films were characterized using X-ray diffraction, X-ray photoelectron spectroscopy, and atomic force microscopy. The cell-material interaction was examined morphologically by monitoring fibroblast attachment and growth and comparing to a control substrate. At early time points increased numbers of 3T3-L1 fibroblasts were found to preferentially attach to TiN films with an increase in the percentage of surface interstitial nitrogen and also with decreased topographical features. At later time points the presence of nanotopography appeared to play a greater role than the effects of surface chemistry and resulted in increased numbers of attached 3T3-L1 fibroblasts. The results show that by changing the deposition route and parameters to produce TiN films, the resultant films can be used to investigate the cellular response to surfaces of differing chemistry and topography.

Nanoscale features influence epithelial cell morphology and cytokine production

Available, easy and fast fabrication methods of nanostructured surfaces, and the knowledge that cells in vivo interacts with nanometer-sized structures/objects, led us to study the impact of nanotopography on cell morphology and cytokine production. Uroepithelial cells were seeded on three different substrate types: two with defined nanometer topographies and a flat control, all three having identical surface chemistry. The nanostructured substrates contained hemispherical pillars or step edges, the latter in the form of parallel grooves and ridges. Qualitative and quantitative analysis of cell morphology and cytokine production were studied. Both quantities were significantly different between cells cultured on hemispherically structured surfaces compared to flat control surfaces. Cells cultured on hemispherically structured surfaces showed a decrease in IL-6 and IL-8 production and were less spread, less round and more stellate (larger dispersion). Only cell morphology differed between cells cultured on grooved surfaces and flat control surfaces. These findings suggest that epithelial cell morphology and cytokine production are dependent on the underlying nanotopography.

Endothelization and adherence of leucocytes to nanostructured surfaces

We analyse the leucocyte and endothelial cell response to polybromostyrene-polystyrene (PS/PBrS) and the poly-n-butylmethacrylate-polystyrene (PnBMA/PS) systems, both in flat form or nanostructured surfaces consisting of nanohills with increasing hill height (13-95nm). Experiments were carried out first with blood leucocytes alone, endothelial cells (of three different types) alone, and finally, using blood cells and endothelized nanosurfaces. Blocking monoclonal antibodies specific for CD11, CD29, CD31, CD54, CD166 were used to analyse whether and to what extent adhesion molecules could be involved in the adherence of both blood leucocytes and endothelial cells to different nanosurfaces. Expression of CD29 (beta-1 integrin), CD54 (ICAM-1) and CD166 (ALCAM) on blood leucocytes was dependent on the hill height, being most prominent with 13nm (PS/PBrS) and 45nm hill (PnBMA/PS) nanosurfaces. Adherence of a human microvascular endothelial cell line and umbilical primary endothelial cells was also related to hill height, being most prominent with 13nm hill height. An indirect correlation was observed between the extent of endothelization and the degree of leucocyte adherence. In cases of low to medium extent of endothelization, the adherence of monocytes and granulocytes was mediated by the expression of CD166, CD29 and CD11a (alpha-L integrin), CD29, CD31 (PECAM-1), respectively. Scanning electron microscopy studies showed the predominant emission of pseudopodia at the holes of the surfaces and the focal contacts with the nanosurfaces. Our studies emphasize the relevance of testing functional properties in co-culture experiments in the development and optimization of nanosurfaces for biomedical application.

Influence of systematically varied nanoscale topography on the morphology of epithelial cells

With the knowledge that cells can react to lithographically manufactured nanometer-sized surface objects, our interest concerned whether cells would respond to surface structures of systematically increasing size. Our approach to answer this question was to fabricate surfaces with the same surface chemistry and similar surface roughness but increasing size of structural features. To fabricate large areas of patterned surfaces, required for cell culture studies, we used colloidal lithography utilizing colloidal particles as a template for surface nanostructuring. The fabricated surfaces contained hemispherical nanopillars with diameters ranging from 60 to 170 nm. Changes in cell morphology of a pancreatic epithelial cell line (AR4-2J) were studied by evaluating cell area and cell shape. The latter was studied by applying the cell shape classification method using three shape descriptors. The pancreatic cells responded in a systematic way to the surface nanostructures. The cells spread more and became more nonround when cultured on surfaces with increasing size of the topographic features. Index Terms-Biological cells, image analysis, nanotechnology, shape measurement, surfaces.

Epithelial contact guidance on well-defined micro- and nanostructured substrates

The human corneal basement membrane has a rich felt-like surface topography with feature dimensions between 20 nm and 200 nm. On the basis of these findings, we designed lithographically defined substrates to investigate whether nanotopography is a relevant stimulus for human corneal epithelial cells. We found that cells elongated and aligned along patterns of grooves and ridges with feature dimensions as small as 70 nm, whereas on smooth substrates, cells were mostly round. The percentage of aligned cells was constant on substrate tomographies with lateral dimensions ranging from the nano- to the micronscale, and increased with groove depth. The presence of serum in the culture medium resulted in a larger percentage of cells aligning along the topographic patterns than when no serum was added to the basal medium. When present, actin microfilaments and focal adhesions were aligned along the substrate topographies. The width of the focal adhesions was determined by the width of the ridges in the underlying substrate. This work documents that biologic length-scale topographic features that model features encountered in the native basement membrane can profoundly affect epithelial cell behavior.

Nucleus alignment and cell signaling in fibroblasts: response to a micro-grooved topography

Cellular response to scaffold materials is of great importance in cellular and tissue engineering, and it is perhaps the initial cell contact with the scaffold that determines development of new tissue. Material surface morphology has strong effects on cell cytoskeleton and morphology, and it is thought that cells may react to the topography of collagen and surrounding cells during tissue embryology. A poorly understood area is, however, gene-level responses to topography. Thus, this paper used microarray to probe for consistent gene changes in response to lithographically produced topography (12.5 x 2-microm grooves) with time. The results showed many initial gene changes and also down-regulation of gene response with time. Cell and nucleus morphology were also considered, with nuclear deformation linked to cell signaling.

Titanium surface topography alters cell shape and modulates bone morphogenetic protein 2 expression in the J774A.1 macrophage cell line

Macrophage cytokine expression significantly affects wound healing. Macrophage secretion of transforming growth factor beta 1 (TGFbeta1) and bone morphogenetic proteins (BMP) may affect osteogenesis at endosseous implant surfaces. The aim of this investigation was to determine the effect of commercially pure titanium (cpTi) substrate topography on adherent macrophage osteogenic and osteoinductive cytokine expression. J774A.1 murine macrophage cell adhesion was examined by scanning electron microscopy, 0-72 h following plating onto polished, machined, and grit-blasted cpTi surfaces. TGFbeta1 and BMP-2 gene expression by adherent macrophages was determined by the reverse transcription polymerase chain reaction. Macrophage adhesion increased with time on all surfaces and spreading increased with increasing surface roughness (polished < machined < grit-blasted). BMP-2 expression was not evident for cells adherent to polished cpTi at 24 h. In contrast, BMP-2 expression occurred at 24 h in cells adherent to machined and grit-blasted cpTi. BMP-2 expression was evident on all surfaces at 72 h and was greatest in grit-blasted titanium adherent cells. Increasing concentrations of cytochalasin B (0-50 microM) inhibited macrophage spreading and reduced BMP-2 mRNA expression, suggesting a relationship between cell shape and BMP-2 expression. This was further characterized using anti-beta1 and anti-beta3 integrin antibodies. The anti-beta1 integrin antibodies inhibited adherent macrophage BMP-2 mRNA expression. Anti-beta3 integrin antibody treatment only modestly reduced BMP-2 mRNA expression. Endosseous implant surface topography induced changes in macrophage shape that were associated with changes in BMP-2 expression in J774A.1 mouse macrophage cell line. This first demonstration of BMP-2 expression by cpTi adherent macrophages suggests that the macrophage may contribute surface-specific osteoinductive signals during bone formation at implanted alloplastic surfaces.

Investigation on plasma immersion ion implantation treated medical implants

In this work the biocompatibility of osteosynsthesis plates treated with plasma immersion ion implantation (PIII) was tested using a rat model. Small rods (Ø 0.9 mm, and length 10 mm) prepared from different materials-pure Ti, anodised Ti, and two NiTi alloys (SE 508, and SM 495)-were implanted with oxygen by PIII to form a rutile surface layer and subsequently inserted into rat femurs, together with a control group of untreated samples. The results of the biomechanical tests correlate with the histological results, and show that plasma immersion ion implantation leads to an increase of biocompatibility and osseointegration of titanium and NiTi, albeit no improvement of the (bad) biocompatibility of the anodised Ti. Despite the layer thickness of up to 0.5 microm a strong influence of the base material is still present.

Nanoscale modifications of PET polymer surfaces via oxygen-plasma discharge yield minimal changes in attachment and growth of mammalian epithelial and mesenchymal cells in vitro

Surface topography is believed to be a factor affecting cellular morphology, proliferation, and differentiation. The effect of surface roughness in the micron to supramicron range has been investigated previously. In the current study, the influence of nanoscale surface roughness was examined in terms of its effects on morphology, cytoskeleton expression, proliferation, differentiation, and apoptosis of three model cell types. Polyethylene terephthalate (PET) disks were etched using oxygen plasma to produce uniform and decidedly nanoscale levels of surface roughness. Three distinct types of cell lines-mouse 3T3-L1 preadipocytes, human JEG-3 choriocarcinoma cells, and human MCF-7 breast adenocarcinoma cells-were cultured on the plasma-treated disks. Untreated PET disks were used as a control. Cytoskeletal proteins (F-actin and cytokeratin) exhibited similar patterns of expression. Cell morphology also was similar on both surfaces. Cell growth kinetics for the three types of cells and hormone secretion from the JEG-3 cells were not significantly different from that of the controls (p > 0.05). However, the differentiation of preadipocyte 3T3-L1 cells into lipid-laden fat cells was modestly affected by nanoscale surface topography. In addition, 15-deoxy-Delta(12,14)-prostaglandin J(2) (15dPGJ(2))-induced apoptosis of the JEG-3 and MCF-7 cells revealed differences between the two surfaces. Plasma-treated surfaces showed more differentiated and apoptotic cells, respectively, compared to the controls. These results indicate that nanoscale roughness contributes in only moderate ways to cellular adhesion, proliferation, and differentiation in the cell lines tested.

Adsorption characteristics of human plasma fibronectin in relationship to cell adhesion

Adsorption of human plasma fibronectin (FN) on nonsulfonated and sulfonated polymer surfaces was studied, by using a polyclonal antiserum to FN and the ELISA method. ELISA signal was recorded as a function of FN concentration in solutions. The concentration dependence of FN binding shows the saturation effect in the range 5-10 microg/mL. ELISA data are discussed in the terms of a self-assembled monolayer and different conformations of the FN molecule. The early adhesion of L1210 cells to polymer surfaces after prior adsorption of FN on these surfaces was studied under static conditions. In the case of FN adsorbed on sulfonated surfaces, the relative number of adhering cells increased with the increase of the interfacial surface tension (i.e., the cell adhesion depends on the surface density of sulfonic groups). However, in the case of FN adsorbed on nonsulfonated surfaces, the relative number of adhering cells was low and independent on the interfacial surface tension. The alpha(5)beta(1)-integrin blocking by a monoclonal antibody resulted in a strong inhibition of the cell adhesion to FN adsorbed on sulfonated polymer surfaces. This indicates that cell adhesion to FN adsorbed on these surfaces is mostly mediated by the alpha(5)beta(1)-integrin. In contrast, in the case of FN adsorbed on nonsulfonated surfaces the cell adhesion was not inhibited by the alpha(5)beta(1)-integrin blocking.

Topographical control of human neutrophil motility on micropatterned materials with various surface chemistry

Controlling cell responses to an implantable material is essential to tissue engineering. Because the surface is in direct contact with cells, both chemical and topographical properties of a material surface can play a crucial role. In this study, parallel ridges/grooves were micropatterned on glass surfaces using photosensitive polyimide to create transparent substrates. The migratory behavior of live human neutrophils on the patterned surfaces was observed using a light microscope with transmitted light source. The width (2 microm) and length (400 microm) of the ridges were kept constant. The height (5 or 3 microm) and the repeat spacing (6-14 microm) of the ridges were systematically changed to investigate the effect of microgeometry on neutrophil migration. In addition, the effect of surface chemistry on neutrophil migration was studied by deposition of a thin layer of "inert", biocompatible metal such as Au-Pd alloy and titanium on patterned substrates. More than 95% of neutrophils moved in the direction of the long axis of ridges/grooves regardless of the topographical geometry and chemistry, consistent with a phenomenon termed "contact guidance". Therefore, cell migration was characterized using a one-dimensional persistent random walk. The rate of cell movement was strongly dependent on the topographical microgeometry of the ridges. The random motility coefficient mu, 9.8 x 10(-9) cm2/s, was the greatest at a ridge height of 5 microm and spacing of 10 microm, about 10 times faster than on smooth glass surface. The Au-Pd coating did not change neutrophil migratory behavior on patterned surfaces, whereas titanium decreased cell motility substantially. The results of this study suggest that optimization of both surface chemistry and topography may be important when designing biomaterials for tissue engineering. In addition, parallel ridges/grooves can be used to control the direction and rate of cell migration on the surface.

Plasma lithography--thin-film patterning of polymeric biomaterials by RF plasma polymerization I: Surface preparation and analysis

Plasma lithography, combining plasma deposition with photolithography, is described as a versatile method to manufacture all-polymeric substrates with thin-film patterns for applications in biomedical engineering. Patterns of a hydrophobic fluorocarbon plasma polymer with feature sizes between 5 and 100 microm were deposited on a base substrate in a lift-off process: an intermediate tetraglyme plasma polymer layer provides non-fouling properties to the base substrate. Careful analysis of critical process parameters identified the narrow window of process conditions that led to the formation of functional surface patterns. High pattern fidelity, aspect ratios, and resolution of the patterns are demonstrated by atomic force microscopy. Electron spectroscopy for chemical analysis (ESCA) and secondary ion mass spectroscopy (SIMS) were used to characterize the surfaces, showing good retention of the original chemical structure of the pattern components throughout the process. SIMS imaging was used for specific chemical imaging of the components. Potential applications for the patterned polymer films, e.g., for studying cell behavior in vitro in dependence of shape and size of adhering cells, are discussed.

Soft lithography in biology and biochemistry

Soft lithography, a set of techniques for microfabrication, is based on printing and molding using elastomeric stamps with the patterns of interest in basrelief. As a technique for fabricating microstructures for biological applications, soft lithography overcomes many of the shortcomings of photolithography. In particular, soft lithography offers the ability to control the molecular structure of surfaces and to pattern the complex molecules relevant to biology, to fabricate channel structures appropriate for microfluidics, and to pattern and manipulate cells. For the relatively large feature sizes used in biology (> or = 50 microns), production of prototype patterns and structures is convenient, inexpensive, and rapid. Self-assembled monolayers of alkanethiolates on gold are particularly easy to pattern by soft lithography, and they provide exquisite control over surface biochemistry.

Substratum nanotopography and the adhesion of biological cells. Are symmetry or regularity of nanotopography important?

Animal cells live in environments where many of the features that surround them are on the nanoscale, for example detail on collagen molecules. Do cells react to objects of this size and if so, what features of the molecules are they responding to? Here we show, by fabricating nanometric features in silica and by casting reverse features in polycaprolactone and culturing vertebrate cells in culture upon them, that cells react in their adhesion to the features. With cliffs, adhesion is enhanced at the cliff edge, while pits or pillars in ordered arrays diminish adhesion. The results implicate ordered topography and possibly symmetry effects in the adhesion of cells. Parallel results were obtained in the adhesion of carboxylate-surfaced 2-microm-diameter particles to these surfaces. These results are in agreement with recent predictions from non-biological nanometric systems.

Modulation of epithelial tissue and cell migration by microgrooves

We used a polystyrene substratum to study the response of migrating epithelium to 1- or 5-microm depth microgrooves with groove/ridge widths of 1, 2, 5, or 10 microm. The migration of a tissue sheet was enhanced along the microgrooves, while migration across the microgrooves was inhibited. Changing the depth of the microgrooves had a greater effect on migration than alteration of the groove/ridge width. The migration of epithelial cells from a confluent monolayer culture followed a similar pattern to that of intact epithelial tissue. Cellular extensions generally followed the microgroove direction by tracking along the top of the ridges or following the ridge walls, as revealed by scanning electron microscopy. Actin filaments within the basal cell layer of the tissue were aligned with the microgrooves, unlike filaments in the superficial layers that did not appear to be affected by the presence of underlying microgrooves. The basal cell layer of the tissue conformed to the contours of the microgroove following migration. However, the ultrastructure of the tissue above the ridges resembled that of tissue on a flat surface. We concluded that surface microgrooves have the potential to direct the migration of immediately adjacent epithelial tissue, the effect of which is to guide epithelial tissue on the surface of implanted biomaterials.

Biocompatible hydrogel supports the growth of respiratory epithelial cells: possibilities in tracheal tissue engineering

Extensive tracheal defect reconstruction is a major challenge in plastic and reconstructive surgery. The lack of an epithelial lining on the luminal surfaces of tracheal prostheses is among the major causes of their failure. Chitosan-gelatin hydrogels were synthesized for the development of biocompatible, growth-supportive substrata for respiratory epithelial cells. We employed J774 macrophages to test the immunocompatibility of this gel. The hydrogel did not exert a cytotoxic effect on macrophages, as confirmed by tetrazolium reduction and neutral red uptake assay. Flow cytometric analysis of macrophages cultured on the hydrogel showed a comparable expression of activation markers CD11b/CD18, CD45, and CD14 to the control. Semiquantitative RT-PCR results showed an absence of upregulation of interleukin-6 (IL-6) and TNF-alpha in these macrophages with respect to the controls. Primary human respiratory epithelial cells cultured on the hydrogel showed proper attachment, normal morphology, and growth. A small proportion of cells on the hydrogel showed synchronously beating cilia. RT-PCR analysis showed that cells on the hydrogel expressed mucins 2 and 5 and cytokeratin 13, which are markers for secretory goblet and squamous cells, respectively. All these results demonstrate that the hydrogel supports the growth of a mixed population of differentiated epithelial cells. This hydrogel is suitable as a culture substratum for respiratory epithelial cells and could be used as a potential candidate for coating tracheal prostheses.

Tissue engineering: the biophysical background

Tissue engineering is the construction, repair or replacement of damaged or missing tissue in humans and other animals. This engineering may take place within the animal body or as tissue constructs to be made in a bioreactor for later grafting into the animal. The minimal set of materials for this are the appropriate types of cell. Usually, however, non-living substrata are used as well. These substrata may be nothing more than materials that bulk up any voids in the damaged tissue and provide the mechanical strength that has been lost when the tissue is damaged or removed. They may serve a similar pair of functions in the bioreactor. They can do much more in terms of pattern formation. The orientations and morphology of the cells, the arrangement of intercellular material as it is laid down and the relationships between different cell types in the repairing or construct tissue are all of importance, for these should resemble the correct normal tissue as closely as possible. Most of these requirements are ones involving pattern formation. This review discusses the various ways in which tissue pattern can be engineered chiefly from a biophysical standpoint. Unpatterned cells are effectively not tissue. This engineering includes the use of topography on the substrata, chemical patterning of adhesive and other cues for the cells, mechanical force application to cause cell orientation and appropriate synthetic responses and electrical fields. The review also discusses the methods used to impart the appropriate cues to and through the materials which are often biodegradable polymers. The article gives particular attention to regions of research and practice where the involvement of the physicist or biophysicist is of importance.

Nantotechniques and approaches in biotechnology

Nanotechnology has enabled the development of an amazing variety of methods for fabricating nanotopography and nanopatterned chemistry in recent years. Some of these techniques are directed towards producing single component particles, as well as multi-component assembly or self-assembly. Other methods are aimed at nanofeaturing and patterning surfaces that have a specific chemistry or topography. This article concentrates mainly on surface-directed nanobiotechnologies because they are nearer to commercial realisation, such as use in tissue engineering, control of biofouling and cell culture, than those directed at producing nanoparticles.

Attachment of astroglial cells to microfabricated pillar arrays of different geometries

We studied the attachment of astroglial cells on smooth silicon and arrays of silicon pillars and wells with various widths and separations. Standard semiconductor industry photolithographic techniques were used to fabricate pillar arrays and wells in single-crystal silicon. The resulting pillars varied in width from 0. 5 to 2.0 micrometer, had interpillar gaps of 1.0-5.0 micrometer, and were 1.0 micrometer in height. Arrays also contained 1.0-micromter-deep wells that were 0.5 micrometer in diameter and separated by 0.5-2.0 micrometer. Fluorescence, reflectance, and confocal light microscopies as well as scanning electron microscopy were used to quantify cell attachment, describe cell morphologies, and study the distribution of cytoskeletal proteins actin and vinculin on surfaces with pillars, wells, and smooth silicon. Seventy percent of LRM55 astroglial cells displayed a preference for pillars over smooth silicon, whereas only 40% preferred the wells to the smooth surfaces. Analysis of variance statistics performed on the data sets yielded values of p > approximately.5 for the comparison between pillar data sets and < approximately.0003 in the comparison between pillar and well data sets. Actin and vinculin distributions were highly polarized in cells found on pillar arrays. Scanning electron microscopy clearly demonstrated that cells made contact with the tops of the pillars and did not reach down into the spaces between pillars even when the interpillar gap was 5.0 microm. These experiments support the use of surface topography to direct the attachment, growth, and morphology of cells. These surfaces can be used to study fundamental cell properties such as cell attachment, proliferation, and gene expression. Such topography might also be used to modify implantable medical devices such as neural implants and lead to future developments in tissue engineering.

Effect of precise mechanical loading on fibroblast populated collagen lattices: morphological changes

The contraction of a collagen lattice by resident fibroblasts causes strains to be developed within that lattice. These strains can be increased or decreased by altering the aspect ratio (ratio of length/width/thickness) of the fibroblast populated collagen lattice, as the cross-sectional area resisting the strain is changed and by the application of an external load. The fibroblasts align themselves with the direction of the maximum principle strain; in effect, these cells are "hiding" from the perceived strain. The direction of the maximum principle strain can be predetermined by the use of a computational finite element analysis. Using the tensioning-Culture Force Monitor to apply pre-determined loading patterns of known repeatable magnitudes, as calculated by the finite element analysis, we have succeeded in aligning fibroblasts into a deliberate predicted orientation. This study has shown that the resident fibroblast population will respond to changes in strain resulting from the most subtle of mechanical loads. This may be an important mechanism in development and repair of connective tissue.

Effect of porosity and surface hydrophilicity on migration of epithelial tissue over synthetic polymer

The relative effects of porosity and surface chemistry on the migration of epithelial tissue over the surface of a polymer were determined in vitro. These studies compared nonporous polymers with those having 0.1-microm diameter track-etched pores and were conducted on polycarbonate and polyester. Epithelial tissue migration over the polymer surface was stimulated by the presence of these pores. The surface chemistries of the polymers were modified by deposition of various polymer films using radio frequency gas deposition, giving a range of surfaces that varied in air:water sessile contact angle (SCA) of between 26 and 100 degrees. Tissue migration on the nonporous surfaces was affected by the surface chemistry, being generally linear as a function of the SCA and higher on hydrophilic than on hydrophobic surfaces but reduced if the hydrophilic surface had a mobile chemistry. The effects of the 0.1-microm diameter pores and the surface hydrophilicity were additive with the maximal level of epithelial tissue migration occurring on a porous, hydrophilic polymer surface.

Nanoscale topography of the corneal epithelial basement membrane and Descemet's membrane of the human

PURPOSE

Quantitatively define and compare the nanoscale topography of the corneal epithelial basement membrane (anterior basement membrane) and Descemet's membrane (posterior basement membrane) of the human.

METHODS

Human corneas not suitable for transplantation were obtained from the Wisconsin Eye Bank. The corneas were placed in 2.5 mM EDTA for 2.5 h or 30 min. for removal of the epithelium or endothelium, respectively. After removal of the overlying cells, specimens were fixed in 2% glutaraldehyde and either examined in this state by atomic force microscopy only or dehydrated through an ethanol series and prepared for transmission electron microscopy (TEM), scanning electron microscopy (SEM), and atomic force microscopy (AFM).

RESULTS

The subepithelial and subendothelial basement membrane surfaces have a similar appearance that consists of an interwoven meshwork of fibers and pores. Topographic feature sizes were found to be in the nanometer size range with the epithelial basement membrane features larger and less densely packed than Descemet's membrane features. The topographic features are fractile in nature and increase surface area for cell contact.

CONCLUSION

With the use of the TEM, SEM, and AFM, a detailed description of the surface topography of corneal epithelial basement membrane and Descemet's membrane of the human cornea are provided. The significance of differences in corneal basement membrane topography may reflect differences in function of the overlying cells or may be related to differences in cell migration and turnover patterns between the epithelium and endothelium.

Reactions of cells to topography

Though contact guidance has been known since the very early days of cell culture very little quantitative examination of the reaction of cells to topography has been made. Exceptions to this subjective approach are given prominence below. Yet if we are to understand how cells react and if we are to be able to design ideal substrata for particular cells we need this information. Precision and quantitation are required both of the methods of examination of the cells but also in the definition of that topography. Recently it has become clear that the these reactions occur at the nanometric scale and have importance for use in cellular engineering and tissue repair. Topography appears to provide a set of very powerful signals for cells.