Topographic compensation: guidance and directed locomotion of fibroblasts on grooved micromachined substrata in the absence of microtubules

The influence of physical and spatial substrate characteristics on endothelial cells

Cardiovascular diseases are a main cause of death worldwide, leading to a growing demand for medical devices to treat this patient group. Central to the engineering of such devices is a good understanding of the biology and physics of cell-surface interactions. In existing blood-contacting devices, such as vascular grafts, the interaction between blood, cells, and material is one of the main limiting factors for their long-term durability. An improved understanding of the material's chemical- and physical properties as well as its structure all play a role in how endothelial cells interact with the material surface. This review provides an overview of how different surface structures influence endothelial cell responses and what is currently known about the underlying mechanisms that guide this behavior. The structures reviewed include decellularized matrices, electrospun fibers, pillars, pits, and grated surfaces.

Microtubule-Actomyosin Mechanical Cooperation during Contact Guidance Sensing

Cancer cell migration through and away from tumors is driven in part by migration along aligned extracellular matrix, a process known as contact guidance (CG). To concurrently study the influence of architectural and mechanical regulators of CG sensing, we developed a set of CG platforms. Using flat and nanotextured substrates with variable architectures and stiffness, we show that CG sensing is regulated by substrate stiffness and define a mechanical role for microtubules and actomyosin-microtubule interactions during CG sensing. Furthermore, we show that Arp2/3-dependent lamellipodia dynamics can compete with aligned protrusions to diminish the CG response and define Arp2/3- and Formins-dependent actin architectures that regulate microtu-bule-dependent protrusions, which promote the CG response. Thus, our work represents a comprehen-sive examination of the physical mechanisms influ-encing CG sensing.

Aligned extracellular matrix architectures in tumors direct migration of invasive cancer cells. Tabdanov et al. show that the mechanical properties of aligned extracellular matrix environments influence invasive cell behavior and define a mechanical role for microtubules and actomyosin-microtubule interactions during sensing of contact guidance cues that arise from aligned extracellular matrix.

The role of nonmuscle myosin 2A and 2B in the regulation of mesenchymal cell contact guidance

Contact guidance refers to the ability of cells to sense the geometrical features of the microenvironment and respond by changing their shape and adopting the appropriate orientation. Inhibition and ablation of nonmuscle myosin 2 (NM2) paralogues have demonstrated their importance for contact guidance. However, the specific roles of the NM2 paralogues have not been systematically studied. In this work we use micropatterned substrates to examine the roles of NM2A and NM2B and to elucidate the relationship of the microenvironment, actomyosin, and microtubules in contact guidance. We show that contact guidance is preserved following loss of NM2B and that expression of NM2A alone is sufficient to establish an appropriate orientation of the cells. Loss of NM2B and overexpression of NM2A result in a prominent cell polarization that is found to be linked to the increased alignment of microtubules with the actomyosin scaffold. Suppression of actomyosin with blebbistatin reduces cell polarity on a flat surface, but not on a surface with contact guidance cues. This indicates that the lost microtubule-actomyosin interactions are compensated for by microtubule-microenvironment interactions, which are sufficient to establish cell polarity through contact guidance.

Abrogated Cell Contact Guidance on Amino-Functionalized Microgrooves

Topographical and chemical features of biomaterial surfaces affect the cell physiology at the interface and are promising tools for the improvement of implants. The dominance of the surface topography on cell behavior is often accentuated. Striated surfaces induce an alignment of cells and their intracellular adhesion-mediated components. Recently, it could be demonstrated that a chemical modification via plasma polymerized allylamine was not only able to boost osteoblast cell adhesion and spreading but also override the cell alignment on stochastically machined titanium. In order to discern what kind of chemical surface modifications let the cell forget the underlying surface structure, we used an approach on geometric microgrooves produced by deep reactive ion etching (DRIE). In this study, we systematically investigated the surface modification by (i) methyl-, carboxyl-, and amino functionalization created via plasma polymerization processes, (ii) coating with the extracellular matrix protein collagen-I or immobilization of the integrin adhesion peptide sequence Arg-Gly-Asp (RGD), and (iii) treatment with an atmospheric pressure plasma jet operating with argon/oxygen gas (Ar/O₂). Interestingly, only the amino functionalization, which presented positive charges at the surface, was able to chemically disguise the microgrooves and therefore to interrupt the microtopography induced contact guidance of the osteoblastic cells MG-63. However, the RGD peptide coating revealed enhanced cell spreading as well, with fine, actin-containing protrusions. The Ar/O₂-functionalization demonstrated the best topography handling, e.g. cells closely attached even to features such as the sidewalls of the groove steps. In the end, the amino functionalization is unique in abrogating the cell contact guidance.

Human Fetal Osteoblast Response on Poly(Methyl Methacrylate)/Polystyrene Demixed Thin Film Blends: Surface Chemistry Vs Topography Effects

Recent advances in materials sciences have allowed for the development and fabrication of biomaterials that are capable of providing requisite cues to instigate cells to respond in a predictable fashion. We have developed a series of poly(methyl methacrylate)/polystyrene (PMMA/PS) polymer demixed thin films with nanotopographies ranging from nanoislands to nanopits to study the response of human fetal osteoblast cells (hFOBs). When PMMA was in excess in the blend composition, a nanoisland topography dominated, whereas a nanopit topography dominated when PS was in excess. PMMA was found to segregate to the top of the nanoisland morphology with PS preferring the substrate interface. To further ascertain the effects of surface chemistry vs topography, we plasma treated the polymer demixed films using an atmospheric pressure dielectric barrier discharge reactor to alter the surface chemistry. Our results have shown that hFOBs did not have an increased short-term cellular response on pristine polymer demixed surfaces. However, increasing the hydrophilicty/wettability of the surfaces by oxygen functionalization causes an increase in the cellular response. These results indicate that topography alone is not sufficient to induce a positive cellular response, but the underlying surface chemistry is also important in regulating cell function.

Novel grooved substrata stimulate macrophage fusion, CCL2 and MMP-9 secretion

Rough surface topographies on implants attract macrophages but the influence of topography on macrophage fusion to produce multinucleated giant cells (MGC) and foreign body giant cells (FBGC) is unclear. Two rough novel grooved substrata, G1 and G2, fabricated by anisotropic etching of Silicon <110> crystals without the use of photolithographic patterning, and a control smooth surface (Pol) were produced and replicated in epoxy. The surfaces were compared for their effects on RAW264.7 macrophage morphology, gene expression, cyto/chemokine secretion, and fusion for one and five days. Macrophages on grooved surfaces exhibited an elongated morphology similar to M2 macrophages and increased cell alignment with surface directionality, roughness and cell culture time. Up-regulated expression of macrophage chemoattractants at gene and protein level was observed on both grooved surfaces relative to Pol. Grooved surfaces showed time-dependent increase in soluble mediators involved in cell fusion, CCL2 and MMP-9, and an increased proportion of multinucleated cells at Day 5. Collectively, this study demonstrated that a rough surface with surface directionality produced changes in macrophage shape and macrophage attractant chemokines and soluble mediators involved in cell fusion. These in vitro results suggest a possible explanation for the observed accumulation of macrophages and MGCs on rough surfaced implants in vivo. © 2016 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 104A: 2243-2254, 2016.

Linear fibroblast alignment on sinusoidal wave micropatterns

Micrometer and nanometer grooved surfaces have been determined to influence cellular orientation, morphology, and migration through contact guidance. Cells typically elongate along the direction of an underlying groove and often migrate with guidance provided by constraints of the pattern. This phenomenon has been studied primarily using linear grooves, post, or well patterns. We investigated the behavior of mouse embryonic fibroblasts on non-linear, sinusoidal wave grooves created via electron beam lithography on a polymethyl methacrylate (PMMA) substrate that was spin-coated onto a positively charged glass surface. Three different wave patterns, with varying wavelengths and amplitudes, and two different line patterns were created. Cell orientation and adhesion was examined after 4, 24, and 48 h after cell seeding. Attachment strength was studied via subjecting cells on substrates to centrifugal force following a 24-h incubation period. For all wave patterns studied, it was noted that cells did not reside within the groove, rather they were observed to cross over each groove, residing both inside and outside of each wave pattern, aligning linearly along the long axis of the pattern. For the linear patterns, we observed that cells tended to reside within the grooves, consistent with previous observations. The ability to add texture to a surface to manipulate cell adhesion strength and growth with only localized attachment, maintaining free space in curvilinear microtopography underlying the cell, may be a useful addition for tissue engineering and the fabrication of novel biomedical devices.

Migration of periodontal ligament fibroblasts on nanometric topographical patterns: influence of filopodia and focal adhesions on contact guidance

Considered to be the "holy grail" of dentistry, regeneration of the periodontal ligament in humans remains a major clinical problem. Removal of bacterial biofilms is commonly achieved using EDTA gels or lasers. One side effect of these treatment regimens is the etching of nanotopographies on the surface of the tooth. However, the response of periodontal ligament fibroblasts to such features has received very little attention. Using laser interference lithography, we fabricated precisely defined topographies with continuous or discontinuous nanogrooves to assess the adhesion, spreading and migration of PDL fibroblasts. PDL fibroblasts adhered to and spread on all tested surfaces, with initial spreading and focal adhesion formation slower on discontinuous nanogrooves. Cells had a significantly smaller planar area on both continuous and discontinuous nanogrooves in comparison with cells on non-patterned controls. At 24 h post seeding, cells on both types of nanogrooves were highly elongated parallel to the groove long axis. Time-lapse video microscopy revealed that PDL fibroblast movement was guided on both types of grooves, but migration velocity was not significantly different from cells cultured on non-patterned controls. Analysis of filopodia formation using time-lapse video microscopy and labeling of vinculin and F-actin revealed that on nanogrooves, filopodia were highly aligned at both ends of the cell, but with increasing time filopodia and membrane protrusions developed at the side of the cell perpendicular to the cell long axis. We conclude that periodontal ligament fibroblasts are sensitive to nanotopographical depths of 85-100 µm, which could be utilized in regeneration of the periodontal ligament.

Gene expression profiling on global cDNA arrays gives hints concerning potential signal transduction pathways involved in cardiac fibrosis of renal failure

Cardiac remodelling with interstitial fibrosis in renal failure, which so far is only poorly understood on the molecular level, was investigated in the rat model by a global gene expression profiling analysis. Sprague–Dawley rats were subjected to subtotal nephrectomy (SNX) or sham operation (sham) and followed for 2 and 12 weeks, respectively. Heart-specific gene expression profiling, with RZPD Rat Unigene-1 cDNA arrays containing about 27 000 gene and EST sequences revealed substantial changes in gene expression in SNX compared to sham animals. Motor protein genes, growth and differentiation markers, and extracellular matrix genes were upregulated in SNX rats. Obviously, not only genes involved in cardiomyocyte hypertrophy, but also genes involved in the expansion of non-vascular interstitial tissue are activated very early in animals with renal failure. Together with earlier findings in the SNX model, the present data suggest the hypothesis that the local renin–angiotensin system (RAS) may be activated by at least two pathways: (a) via second messengers and Gproteins (short-term signalling); and (b) via motor proteins, actins and integrins (longterm signalling). The study documents that complex hybridization analysis yields reproducible and promising results of patterns of gene activation pointing to signalling pathways involved in cardiac remodelling in renal failure. The complete array data are available via http://www.rzpd.de/cgi-bin/services/exp/viewExpressionData.pl.cgi

Different sensitivity of human endothelial cells, smooth muscle cells and fibroblasts to topography in the nano-micro range

Cell adhesion, orientation and migration are influenced by surface topographies in the micrometer and nanometer range. In this work, we demonstrate the stimulation by topographical signals of human fibroblast cells (FCs), endothelial cells (ECs) and smooth muscle cells (SMCs). We systematically quantified the contact guidance alignment and directed migration of FCs, ECs and SMCs adhering to grooved substrates with lateral dimensions of 2-10microm and depths of 50-200nm. We found a common quantitative response characteristic of all three cell types: contact guidance significantly increased when the cells were cultured on substrates with smaller lateral dimensions or deeper grooves. Despite their general behavior, the three cell types exhibited a cell-type specific sensitivity to the groove patterns. The minimum groove depth to induce an orientation response and change cell shape was 50nm for FCs and about two times deeper for ECs and SMCs. The degree of alignment and directed migration of the FCs along the grooves was significantly stronger than for the ECs and SMCs. We demonstrate that ECs and SMCs can be stimulated by topographical signals but are less sensitive than FCs.

Directional change produced by perpendicularly-oriented microgrooves is microtubule-dependent for fibroblasts and epithelium

Anisotropic substrata such as micromachined grooves can control cell shape, orientation, and the direction of cell movement, a phenomena termed topographic guidance. Although many types of cells exhibit topographic guidance, little is known regarding cell responses to conflicting topographic cues. We employed a substratum with intersecting grooves in order to present fibroblasts and epithelial cells with conflicting topographic cues. Using time-lapse and confocal microscopy, we examined cell behavior at groove intersections. Migrating fibroblasts and epithelial cells typically extended a cell process into the intersection ahead of the cell body. After travelling along the "X" groove to enter the intersection, the leading lamellipodia of the cell body encountered the perpendicular "Y" groove, and spread latterly along the "Y" groove. The formation of lateral lamellipodia resulted in cells forming "T" or "L" morphologies, which were characterized by the formation of phosphotyrosine-rich focal adhesions at the leading edges. The "Y" groove did not prove an absolute barrier to cell migration, particularly for epithelial cells. Analysis of cytoskeletal distribution revealed that F-actin bundles did not adapt closely to the groove patterns, but typically did align to either the "X" or "Y" grooves. In contrast microtubules (MT) adapted closely to the walls. Inhibition of microtubule nucleation attenuated fibroblast and epithelial cell orientation within the intersection of the perpendicular grooves. We conclude that MT may be the prime determinant of fibroblast and epithelial cell conformation to conflicting topographies.

Enhanced neurite alignment on micro-patterned poly-L-lactic acid films

The ability of the damaged central nervous system and peripheral nervous system to properly recover hinges on the regenerative mechanisms and functional reconnection to appropriate targets. Successful pathfinding of axons is controlled by a complex interplay of diffusible or substrate-bound biochemical and electrical cues. Physical guidance has also been shown to occur in vivo and in vitro, either via cell-cell or cell-extracellular matrix mediated contact. In the current study, we probe the role of contact guidance in facilitating neural regeneration and pathfinding. Using soft lithographic techniques, we have created thin films of poly-L-lactic acid polymer (PLLA) possessing periodic features approaching the nanometer regime. Rat PC-12 cells and chick sympathetic neurons were subsequently cultured onto these substrates and parameters, such as neurite emergence and orientation angle, neurite length, and neuronal architecture are characterized. Our results reveal that both PC-12 and chick sympathetic neurites can be effectively guided by unidirectional grooves as small as 100 nm in height and 1 microm in width. Moreover, sympathetic cells produced neurites that were longer on patterned substrata than on controls. The development of novel degradable micro/nanopatterned substrates for cell study will permit more in-depth analysis of contact mediated guidance mechanisms in addition to having applications in neural and tissue engineering.

The geometric pattern of a pillared substrate influences the cell-process distribution and shapes of fibroblasts

Fibroblasts alter their shape, direction of movement, cytoskeleton arrangement, and focal contact when placed upon square array pillars. We prepared pillars of 1 microm diameter, separated by 3 microm, and having 1, 5, and 10 microm heights using substrates displaying identical surface chemistry. When cells seeded initially onto the tops of the pillars, fibroblasts subsequently were immobilized in situ by several pillars that visibly protruded through, but did not pierce, the cell bodies. The cytoplasma then migrated outward with long straight lamella along the interval of the pillars and formed several discrete attachment zones at their side walls - the value of their form index (FI) was as high as 35 - which altered the cellular shape entirely. Most of the cells interacted with the pillar substrate by spreading preferentially in a particular direction, but some of them had the ability to undergo coincident two-direction (x and y) migration; right-angle turn orientations led to the growth of dramatic cellular morphologies. Interestingly, this fibroblast's behavior variation was gradually in proportion to the pillar height of substrate. Our results confirm that cellular migration and cellular shape are both strongly affected by the geometry of the growth microenvironment.

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.

Microfabricated discontinuous-edge surface topographies influence osteoblast adhesion, migration, cytoskeletal organization, and proliferation and enhance matrix and mineral deposition in vitro

The fabrication of surfaces that stimulate increased adhesion, migration, and differentiated function of osteoblasts has been viewed as being desirable for many orthopedic applications. Previous studies have shown that microfabricated pits and grooves alter adhesion, spreading, matrix secretion, and production of mineral by rat calvarial osteoblasts (RCOs). The mechanisms underlying these effects are unknown, although microenvironment and cell alignment are considered to play a role. The aim of this work was to investigate the behavior of RCOs on microfabricated discontinuous-edge surfaces (DESs), which could provide an alternative means to control both the microenvironment and cellular alignment. Two types of discontinuous-type structures were employed, gap-cornered boxes and micron scale pillars. DES gap-cornered boxes and the pillars influenced the arrangement of F-actin, microtubules, and vinculin. Osteoblasts were guided in their direction of migration on both types of substrata. Both box DESs and pillars altered the staining intensity and localization pattern of phosphotyrosine and src-activated FAK localization. Cell multilayering, matrix deposition, and mineralization were enhanced on both discontinuous topographies when compared with smooth controls. This study shows that DESs alter adhesion, migration, and proliferative responses from osteoblasts at early time points (<1 week) and promote multilayering, matrix deposition, and mineral deposition at later times (2-6 weeks). Such topographical patterns could potentially be employed as effective surface features on bone-contacting implants or in membrane-based periodontal applications.

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.

Co-culture of hepatocytes and fibroblasts by micropatterned immobilization of beta-galactose derivatives

Photosensitive poly(allylamine) containing beta-galactose moieties in the side chain (LPAN(3)) was prepared by the reaction of poly(allylamine) with lactobionic acid and azidobenzoic acid. To create micropatterned surfaces, a LPAN(3)-coated poly(methyl methacrylate) (PMMA) substrate was irradiated with an ultraviolet lamp under a photomask. The presence of a LPAN(3) layer on the substrate was confirmed using an electron spectroscopy for chemical analysis. Micropatterned cell culture was carried out by seeding hepatocytes and/or fibroblasts on the substrate. As a result, hepatocytes and fibroblasts adhered only to the LPAN(3) and PMMA lane, respectively. Co-culture on the stripe patterned substrate was carried out by the first cell seeding of hepatocytes and subsequently by the second cell seeding of fibroblasts. The co-cultured cells produced extracellular matrix such as fibronectin, suggesting a biological function.

Scaffold topography alters intracellular calcium dynamics in cultured cardiomyocyte networks

Structural and functional changes ensue in cardiac cell networks when cells are guided by three-dimensional scaffold topography. We report enhanced synchronous pacemaking activity in association with slow diastolic rise in intracellular Ca2+concentration ([Ca2+]i) in cell networks grown on microgrooved scaffolds. Topography-driven changes in cardiac electromechanics were characterized by the frequency dependence of [Ca2+]iin syncytial structures formed of ventricular myocytes cultured on microgrooved elastic scaffolds (G). Cells were electrically paced at 0.5–5 Hz, and [Ca2+]iwas determined using microscale ratiometric (fura 2) fluorescence. Compared with flat (F) controls, the G networks exhibited elevated diastolic [Ca2+]iat higher frequencies, increased systolic [Ca2+]iacross the entire frequency range, and steeper restitution of Ca2+transient half-width ( n = 15 and 7 for G and F, respectively, P < 0.02). Significant differences in the frequency response of force-related parameters were also found, e.g., overall larger total area under the Ca2+transients and faster adaptation of relaxation time to pacing rate ( P < 0.02). Altered [Ca2+]idynamics were paralleled by higher occurrence of spontaneous Ca2+release and increased sarcoplasmic reticulum load ( P < 0.02), indirectly assessed by caffeine-triggered release. Electromechanical instabilities, i.e., Ca2+and voltage alternans, were more often observed in G samples. Taken together, these findings 1) represent some of the first functional electromechanical data for this in vitro system and 2) demonstrate direct influence of the microstructure on cardiac function and susceptibility to arrhythmias via Ca2+-dependent mechanisms. Overall, our results substantiate the idea of guiding cellular phenotype by cellular microenvironment, e.g., scaffold design in the context of tissue engineering.

Nanotopographical guidance of C6 glioma cell alignment and oriented growth

The surface properties of the extracellular matrix play vital roles in cellular behavior such as adhesion, spreading, migration, proliferation and differentiation. While cell attachment and adhesion onto surfaces are mainly mediated by surface molecular interaction, cell morphology and orientation are significantly affected by the topographical cues of the substrate. We reported here the alignment of C6 glioma cells on polystyrene (PS) substrate containing periodic nanotopography. The ridge/groove type structures (210 nm in periodicity, and 30-40 nm in depth) were generated on polystyrene surface using Nd:YAG polarized laser radiation at 266 nm. The cultured cells were shown to align strictly along the direction of the ridges/grooves. And there were distinctive features such as elongated morphology and asymmetrical cell surface extensions, revealed by confocal laser scanning microscopy (CLSM), atomic force microscopy (AFM), and scanning electron microscopy (SEM). The results indicated that ordered and continuous nanostructures on substrates can pattern cell, and guide cell alignment and oriented growth along definite directions. The possible mechanism and significance of these observations were also discussed.

Effects of multigrooved surfaces on fibroblast behavior

Microgrooves have been investigated as substrates for the control of cell alignment. However, they are relatively too narrow and shallow for controlling the orientation of extracellular matrices (ECM) such as collagen. Multigrooves, a combination of microgrooves and macrogrooves, are expected to be able to control the orientation of both cells and ECM. This study investigated a method for fabricating multigrooves and evaluated fibroblast behavior on these novel surfaces. Multigrooved patterns were fabricated on a gold-alloy metal die, in which 90-degree V-shaped microgrooves with a 2-microm pitch were cut on trapezoidal macrogrooves. The macrogrooves had a 50- microm ridge width, a 50-microm wall width, a 50-microm bottom width, and a 25-microm depth. The grooves were made by an ultraprecision micromachine using a single crystal diamond. This metal die served as a template for making surface replicas from polystyrene. Microgrooved and smooth polystyrene replicas also were prepared as comparative substrates. Mouse fibroblast L929 cells were cultured in each type of replica substrate for 7 to 21 days. After these periods, the cells were fixed with 2.5% glutaraldehyde, treated with conventional methods, and, finally, observed by SEM. Confocal laser scanning microscopy was performed to investigate ECM formation. The multigrooved metal die exhibited the desired sharp configuration without defects. The dimensional values of the multigrooves on the polystyrene replicas were almost the same as the designed values. The fibroblasts on the multigrooved and microgrooved substrates were aligned parallel to the surface grooves after 7 days of incubation. In contrast to the microgrooved and flat surfaces, a dense extracellular matrix was produced along the multigrooves after 21 days of incubation. These results suggest that multigrooves can control the orientation of ECM as well as cells and thus enhance the production of ECM.

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.

Biology on a chip: microfabrication for studying the behavior of cultured cells

The ability to culture cells in vitro has revolutionized hypothesis testing in basic cell and molecular biology research and has become a standard methodology in drug screening and toxicology assays. However, the traditional cell culture methodology--consisting essentially of the immersion of a large population of cells in a homogeneous fluid medium--has become increasingly limiting, both from a fundamental point of view (cells in vivo are surrounded by complex spatiotemporal microenvironments) and from a practical perspective (scaling up the number of fluid handling steps and cell manipulations for high-throughput studies in vitro is prohibitively expensive). Microfabrication technologies have enabled researchers to design, with micrometer control, the biochemical composition and topology of the substrate, the medium composition, as well as the type of neighboring cells surrounding the microenvironment of the cell. In addition, microtechnology is conceptually well suited for the development of fast, low-cost in vitro systems that allow for high-throughput culturing and analysis of cells under large numbers of conditions. Here we review a variety of applications of microfabrication in cell culture studies, with an emphasis on the biology of various cell types.

Effects of multigrooved surfaces on osteoblast-like cellsin vitro: Scanning electron microscopic observation and mRNA expression of osteopontin and osteocalcin

This study evaluated the behavior of osteoblast-like cells on multigrooved surfaces consisting of a combination of microgrooves and macrogrooves. A polystyrene substrate was fabricated with multigrooves with 90-degree, V-shaped microgrooves with a 2-microm pitch cut on trapezoidal macrogrooves, which had a 50-microm ridge width, a 50-microm wall width, a 50-microm bottom width, and 25-microm depth. Smooth polystyrene substrates were also prepared as controls. Rat bone marrow cells were cultured as osteoblast-like cells on the substrates for morphological evaluation using a scanning electron microscope, and for biochemical evaluation using the quantitative reverse transcriptase-polymerase chain reaction technique for osteopontin and osteocalcin mRNA expression. After 8 days of incubation, the osteoblast-like cells were aligned parallel to the surface grooves on the multigrooved substrates. After 16 days of incubation, a dense mineralized extracellular matrix (ECM) was produced along the multigrooves. The ECM on the multigrooved surface appeared oriented more in the direction of the grooves than on the smooth surface, and trapezoid-shaped macrogrooves of the ECM were cast upside down. Although there were not significant differences, the osteopontin and osteocalcin mRNA expressions of the osteoblast-like cells on the multigrooved surfaces tended to be higher than on smooth surfaces. These results suggest that multigrooves could be used to control the orientation of mineralized ECM as well as of cells, and also to enhance the production of mineralized ECM.

Diverse chemotactic responses of Dictyostelium discoideum amoebae in the developing (temporal) and stationary (spatial) concentration gradients of folic acid, cAMP, Ca(2+) and Mg(2+)

The responses of Dictyostelium discoideum amoebae to developing (temporal) and stationary (spatial) gradients of folic acid, cAMP, Ca(2+), and Mg(2+) were studied using the methods of computer-aided image analysis. The results presented demonstrate that the new type of experimental chambers used for the observation of single cells moving within the investigated gradients of chemoattractants permit time lapse recording of single amoebae and determination of the trajectories of moving cells. It was found that, besides folic acid and cAMP (natural chemoattractants for Dictyostelium discoideum amoebae), also extracellular Ca(2+) and Mg(2+) are potent inducers of these cells' chemotaxis, and the amoebae of D. discoideum can respond to various chemoattractants differently. In the positively developing gradients of folic acid, cAMP, Ca(2+), and Mg(2+) oriented locomotion of amoebae directed towards the higher concentration of the tested chemoattractants was observed. However, in the negatively developing (temporal) and stationary linear (spatial) gradients, the univocal chemotaxis of amoebae was recorded only in the case of the Mg(2+) concentration gradient. This demonstrates that amoebae can respond to both developing and stationary gradients, depending upon the nature of the chemoattractant. We also investigated the effects of chosen inhibitors of signalling pathways upon chemotaxis of D. discoideum amoebae in the positively developing (temporal) gradients of tested chemoattractants. Verapamil was found to abolish the chemotaxis of amoebae only in the Ca(2+) gradients. Pertussis toxin suppressed the chemotactic response of cells in the gradients of folic acid and cAMP but did not prevent chemotaxis in those of Ca(2+) and Mg(2+), while quinacrine inhibited chemotaxis in the gradients of folic acid, cAMP, and Ca(2+) but only slightly affected chemotaxis in the Mg(2+) gradient. None of the tested inhibitors causes inhibition of cell random movement, when applied in isotropic solution. Also EDTA and EGTA up to 50 mM concentration did not inhibit locomotion of amoebae in control isotropic solutions.

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.

Soft tissue and epithelial models

The applicability of a biomaterial for the manufacturing of oral implants is determined by its physicochemical and geometric surface properties. Research, therefore, is concerned with the cellular reactions that occur when an implant material comes into contact with body tissues. For permucosal oral implants, this involves both the reaction of bone and gingival cells. In vitro cell culturing--including the use of various analytical techniques like light microscopy, scanning and transmission electron microscopy, confocal laser scanning microscopy, and digital image analysis--is a good tool whereby investigators can obtain more insight into the relevant components of implant-tissue adhesion. In the current overview, the role of cell models in oral implant research is discussed, specifically with reference to responses of epithelial cells and fibroblasts.

The effects of the surface topography of micromachined titanium substrata on cell behavior in vitro and in vivo

Surface properties, including topography and chemistry, are of prime importance in establishing the response of tissues to biomaterials. Microfabrication techniques have enabled the production of precisely controlled surface topographies that have been used as substrata for cells in culture and on devices implanted in vivo. This article reviews aspects of cell behavior involved in tissue response to implants with an emphasis on the effects of topography. Microfabricated grooved surfaces produce orientation and directed locomotion of epithelial cells in vitro and can inhibit epithelial downgrowth on implants. The effects depend on the groove dimensions and they are modified by epithelial cell-cell interactions. Fibroblasts similarly exhibit contact guidance on grooved surfaces, but fibroblast shape in vitro differs markedly from that found in vivo. Surface topography is important in establishing tissue organization adjacent to implants, with smooth surfaces generally being associated with fibrous tissue encapsulation. Grooved topographies appear to have promise in reducing encapsulation in the short term, but additional studies employing three-dimensional reconstruction and diverse topographies are needed to understand better the process of connective-tissue organization adjacent to implants. Microfabricated surfaces can increase the frequency of mineralized bone-like tissue nodules adjacent to subcutaneously implanted surfaces in rats. Orientation of these nodules with grooves occurs both in culture and on implants. Detailed comparisons of cell behavior on micromachined substrata in vitro and in vivo are difficult because of the number and complexity of factors, such as population density and micromotion, that can differ between these conditions.

Electrical, chemical, and topological addressing of mammalian cells with microfabricated systems

This communication describes our work in electrical, topological, and chemical micromodification of surfaces to modulate cellular form and function. We have addressed the surface physico-chemico-mechano properties of cell culture substrates that play a role in modulating cellular behavior. Single factorial model systems have been built using techniques adapted from microlithography. The tools and techniques of microfabrication, if harnessed and used correctly, can be enabling in elucidating the underlying principles and fundamental forces driving the cell-substrate interface. Additionally, the long-term practical applications of microfabrication in medicine and biomaterial/tissue engineering lie in enabling "communication" with living cells/tissues at the cellular and subcellular levels.

Orientation of ECM protein deposition, fibroblast cytoskeleton, and attachment complex components on silicone microgrooved surfaces

The microfilaments and vinculin-containing attachment complexes of rat dermal fibroblasts (RDF) incubated on microtextured surfaces were investigated with confocal laser scanning microscopy (CLSM) and digital image analysis (DIA). In addition, depositions of bovine and endogenous fibronectin and vitronectin were studied. Smooth and microtextured silicone substrata were produced that possessed parallel surface grooves with a groove and ridge width of 2.0, 5.0, and 10.0 microns. The groove depth was approximately 0.5 micron. CLSM and DIA make it possible to visualize and analyze intracellular and extracellular proteins and the underlying surface simultaneously. It was observed that the microfilaments and vinculin aggregates of the RDFs on the 2.0 microns grooved substrata were oriented along the surface grooves after 1, 3, 5, and 7 days of incubation while these proteins were significantly less oriented on the 5.0 and 10.0 microns grooved surfaces. Vinculin was located mainly on the surface ridges on all textured surfaces. In contrast, bovine and endogenous fibronectin and vitronectin were oriented along the surface grooves on all textured surfaces. These proteins did not seem to be hindered by the surface grooves since many groove-spanning filaments were found on all the microgrooved surfaces. In conclusion, it can be said that microtextured surfaces influence the orientation of intracellular and extracellular proteins. Although results corroborate three earlier published hypotheses, they do not justify a specific choice of any one of these hypotheses.

Sensitivity of fibroblasts and their cytoskeletons to substratum topographies: topographic guidance and topographic compensation by micromachined grooves of different dimensions

Fibroblasts alter their shape, orientation, and direction of movement to align with the direction of micromachined grooves, exhibiting a phenomenon termed topographic guidance. In this study we examined the ability of the microtubule and actin microfilament bundle systems, either in combination with or independently from each other, to affect alignment of human gingival fibroblasts on sets of micromachined grooves of different dimensions. To assess specifically the role of microtubules and actin microfilament bundles, we examined cell alignment, over time, in the presence or absence of specific inhibitors of microtubules (colcemid) and actin microfilament bundles (cytochalasin B). Using time-lapse videomicroscopy, computer-assisted morphometry and confocal microscopy of the cytoskeleton we found that the dimensions of the grooves influenced the kinetics of cell alignment irrespective of whether cytoskeletons were intact or disturbed. Either an intact microtubule or an intact actin microfilament-bundle system could produce cell alignment with an appropriate substratum. Cells with intact microtubules aligned to smaller topographic features than cells deficient in microtubules. Moreover, cells deficient in microtubules required significantly more time to become aligned. An unexpected finding was that very narrow 0.5-microm-wide and 0.5-microm-deep grooves aligned cells deficient in actin microfilament bundles (cytochalasin B-treated) better than untreated control cells but failed to align cells deficient in microtubules yet containing microfilament bundles (colcemid treated). Thus, the microtubule system appeared to be the principal but not sole cytoskeletal substratum-response mechanism affecting topographic guidance of human gingival fibroblasts. This study also demonstrated that micromachined substrata can be useful in dissecting the role of microtubules and actin microfilament bundles in cell behaviors such as contact guidance and cell migration without the use of drugs such as cytochalasin and colcemid.

Controlling cell interactions by micropatterning in co-cultures: hepatocytes and 3T3 fibroblasts

The repair or replacement of damaged tissues using in vitro strategies has focused on manipulation of the cell environment by modulation of cell-extracellular matrix interactions, cell-cell interactions, or soluble stimuli. Many of these environmental influences are easily controlled using macroscopic techniques; however, in co-culture systems with two or more cell types, cell-cell interactions have been difficult to manipulate precisely using similar methods. Although microfabrication has been widely utilized for the spatial control of cells in culture, these methods have never been adapted to the simultaneous co-cultivation of more than one cell type. We have developed a versatile technique for micropatterning of two different cell types based on existing strategies for surface modification with aminosilanes linked to biomolecules and the manipulation of serum content of cell culture media. This co-culture technique allowed manipulation of the initial cellular microenvironment without variation of cell number. Specifically, we were able to control the level of homotypic interaction in cultures of a single cell type and the degree of heterotypic contact in co-cultures over a wide range. This methodology has potential applications in tissue engineering, implant biology, and developmental biology, both in the arena of basic science and optimization of function for technological applications.

The use of micromachined surfaces to investigate the cell behavioural factors essential to osseointegration

OBJECTIVE

Although currently available implants can be used to achieve osseointegration under well-defined conditions, a greater understanding of cell behaviour is required to improve the designs and embark on actual tissue engineering.

MATERIALS AND METHODS

We employed micromachined substrata to investigate some of the main behavioural responses of osteoblasts from rat fetal calvaria to surface topography. In particular, confocal laser scanning microscopy (CLSM), differential interference contrast microscopy, time-lapse cinemicrography, immunofluorescence, digital radiography and image analysis were used to investigate cell adhesion, cell shape and cytoskeleton distribution, tissue organization, cell differentiation, and microenvironment.

RESULTS AND CONCLUSIONS

A grooved surface permitted the attachment of more cells than a smooth one. Cell shape and cytoskeleton were strikingly influenced as early as 20 min after cell attachment, when the cytoskeleton begins to align with the topography. Some grooved surfaces appeared to promote osteogenesis in vitro as assessed by the production of bone-like nodules. Moreover, these nodules align with the topography in vitro, and preliminary results indicate that bone-like tissue also aligns with grooves when such surfaces are implanted in vivo.

Effects of electroporation on the tubulin cytoskeleton and directed migration of corneal fibroblasts cultured within collagen matrices

Electroporation provides a useful method for loading fibroblasts with fluorescent probes for the cytoskeleton, but the possible deleterious effects of this loading technique on cell motility are unknown. We have used conventional and confocal microscopy of living cells and immunohistochemistry to examine the migration and cytoskeleton of chick embryo corneal fibroblasts electroporated while cultured within collagen gels. Fibroblasts cultured in collagen (1 mg/ml) are successfully electroloaded (0.5-1.0 kVcm-1/960 microF in DMEM/F12/20 mM Hepes, pH 7.2) with dextran (4-150 kDa) and immunoglobulin, but subsequently display uncoordinated pseudopodia and hence are unable to migrate effectively in any one direction. The lack of directed movement is due to depolymerization of microtubules and/or a perinuclear collapse of vimentin filaments, seemingly caused by millimolar levels of Ca2+ ions derived from culture medium following electroporation. Fibroblasts loaded in a buffer which resembles intracellular fluid (< or = 10 microM Ca2+) maintain their cytoskeleton and continue to migrate, when returned to culture medium within 10 min. Using this novel approach, we have loaded fibroblasts migrating through extracellular matrix (ECM) with rhodamine phalloidin and monitored the behavior of the labeled actin cortex by confocal microscopy. During migration phalloidin-actin accumulates near the base of pseudopodia and at the rear of the cell where it is subsequently left behind. We conclude that electroporation is a valuable technique for loading fibroblasts to study migration within ECM, provided that the conditions used support stability of the tubulin cytoskeleton.