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

Shrink-film configurable multiscale wrinkles for functional alignment of human embryonic stem cells and their cardiac derivatives

A biomimetic substrate for cell-culture is fabricated by plasma treatment of a prestressed thermoplastic shrink film to create tunable multiscaled alignment "wrinkles". Using this substrate, the functional alignment of human embryonic stem cell derived cardiomyocytes is demonstrated.

Inducing functional radial glia-like progenitors from cortical astrocyte cultures using micropatterned PMMA

Radial glia cells (RGC) are multipotent progenitors that generate neurons and glia during CNS development, and which also served as substrate for neuronal migration. After a lesion, reactive glia are the main contributor to CNS regenerative blockage, although some reactive astrocytes are also able to de-differentiate in situ into radial glia-like cells (RGLC), providing beneficial effects in terms of CNS recovery. Thus, the identification of substrate properties that potentiate the ability of astrocytes to transform into RGLC in response to a lesion might help in the development of implantable devices that improve endogenous CNS regeneration. Here we demonstrate that functional RGLC can be induced from in vitro matured astrocytes by using a precisely-sized micropatterned PMMA grooved scaffold, without added soluble or substrate adsorbed biochemical factors. RGLC were extremely organized and aligned on 2 μm line patterned PMMA and, like their embryonic counterparts, express nestin, the neuron-glial progenitor marker Pax6, and also proliferate, generate different intermediate progenitors and support and direct axonal growth and neuronal migration. Our results suggest that the introduction of line patterns in the size range of the RGC processes in implantable scaffolds might mimic the topography of the embryonic neural stem cell niche, driving endogenous astrocytes into an RGLC phenotype, and thus favoring the regenerative response in situ.

Control of cell nucleus shapes via micropillar patterns

We herein report a material technique to control the shapes of cell nuclei by the design of the microtopography of substrates to which the cells adhere. Poly(D,L-lactide-co-glycolide) (PLGA) micropillars or micropits of a series of height or depth were fabricated, and some surprising self deformation of the nuclei of bone marrow stromal cells (BMSCs) was found in the case of micropillars with a sufficient height. Despite severe nucleus deformation, BMSCs kept the ability of proliferation and differentiation. We further demonstrated that the shapes of cell nuclei could be regulated by the appropriate micropillar patterns. Besides circular and elliptoid shapes, some unusual nucleus shapes of BMSCs have been achieved, such as square, cross, dumbbell, and asymmetric sphere-protrusion.

Topographic modulation of the orientation and shape of cell nuclei and their influence on the measured elastic modulus of epithelial cells

The influence of nucleus shape and orientation on the elastic modulus of epithelial cells was investigated with atomic force microscopy. The shape and orientation were controlled by presenting the epithelial cells with anisotropic parallel ridges and grooves of varying pitch at the cell substratum. As the cells oriented to the underlying topography, the volume of the nucleus increased as the pitch of the topography increased from 400 nm to 2000 nm. The increase in nucleus volume was reflected by an increase in the measured elastic modulus of the topographically aligned cells. Significant alterations in the shape of the nucleus, by intimate contact with the topographic ridge and grooves of the underlying cell, were also observed via confocal microscopy, indicating that the nucleus may also act as a direct mechanosensor of substratum topography.

Quantitative analysis of the combined effect of substrate rigidity and topographic guidance on cell morphology

Live cells are exquisitely sensitive to both the substratum rigidity and texture. To explore cell responses to both these types of inputs in a precisely controlled fashion, we analyzed the responses of Chinese hamster ovary (CHO) cells to nanotopographically defined substrata of different rigidities, ranging from 1.8 MPa to 1.1 GPa. Parallel arrays of nanogrooves (800-nm width, 800-nm space, and 800-nm depth) on polyurethane (PU)-based material surfaces were fabricated by UV-assisted capillary force lithography (CFL) over an area of 5 mm × 3 mm. We observed dramatic morphological responses of CHO cells, evident in their elongation and polarization along the nanogrooves direction. The cells were progressively more spread and elongated as the substratum rigidity increased, in an integrin β1 dependent manner. However, the degree of orientation was independent of substratum rigidity, suggesting that the cell shape is primarily determined by the topographical cues.

Chondrogenic potential of electrospun nanofibres for cartilage tissue engineering

Articular cartilage has a heterogeneous structure, comprising elongated cells at the articulating surface and rounded cells elsewhere. This feature poses a complex challenge when fabricating 3D tissue engineering scaffolds able to mimic the native extracellular matrix (ECM) of cartilage for tissue repair and regeneration. Nanofibre scaffolds can provide an ECM-like structure, but are mechanically weak and typically have subcellular pore geometries. In this study, the use of poly(L,D-lactide) (PLDLA) nanofibre coatings on PLDLA microfibres or films (nanofibre composites) to influence bovine chondrocyte behaviour was investigated. It was demonstrated that electrospun nanofibres facilitated the adhesion of chondrocytes and helped to maintain smaller projected cell areas and a rounded cell phenotype, when compared to PLDLA films or microfibres. Random nanofibre composites were associated with the smallest and most rounded cells and aligned nanofibre composites also demonstrated a similar tendency. Quantitative PCR revealed that nanofibres promoted the expression of chondrogenic markers, such as collagen type IIaI and aggrecan, while maintaining low levels of collagen IaI. It was also found, by water contact angle measurement, that nanofibres were significantly more hydrophobic than cast films. The lower wettability of polymeric nanofibres favoured the maintenance of rounded chondrocyte morphology. To our knowledge this is the first study to confirm the positive influence on preserving chondrogenic phenotype and gene expression at the interface of true nano-microfibrous composites by using individual microfibres coated with aligned nanofibres. Such composites can potentially be fabricated into mechanically durable 3D scaffolds with better cell infiltration throughout the scaffolds.

Protein Expression of STRO-1 Cells in Response to Different Topographic Features

Human skeletal stem cells (STRO-1 positive) display distinct responses to different topographical features. On a flat surface, skeletal cells spread, and in vitro, they typically display a polarized, fibroblast-like morphology. However, on microgrooved surfaces, these cells prefer to stretch along the grooves forming a similar morphology to in vivo, bipolarized fibroblasts. In contrast, on nanopits, these cells display a polygonal and osteoblastic phenotype. We have examined mechanotransduction events of STRO-1 positive in response to fibroblastic, microgrooved and osteogenic, controlled disorder nanopit, topographies using proteomics after 3 days in culture. Protein expression profiles were analyzed by difference gel electrophoresis to identify proteins that showed modulation of expression in response to different topographic features to assess early decision events in these cells on these discrete topographies. After only 72 hours in culture, STRO-1 positive displayed differential regulations of families of proteins involved in cell migration and proliferation. The current study indicated that osteogenic decision specific events had already occurred. Runx2 was localized in nuclei of the skeletal stem cells on the osteogenic nanopits; however, few signaling pathway changes were observed. This study demonstrated that micro- and nanotopographies activated skeletal stem cells at different times and with distinct mechanotransduction profiles.

Biomimetic microtopography to enhance osteogenesis in vitro

Biomimicry is being used in the next generation of biomaterials. Tuning material surface features such as chemistry, stiffness and topography allow the control of cell adhesion, proliferation, growth and differentiation. Here, microtopographical features with nanoscale depths, similar in scale to osteoclast resorption pits, were used to promote in vitro bone formation in basal medium. Primary human osteoblasts were used to represent an orthopaedically relevant cell type and analysis of adhesions, cytoskeleton, osteospecific proteins (phospho-Runx2 and osteopontin) and mineralisation (alizarin red) was performed. The results further demonstrate the potential for biomimicry in material design and show that the osteoblast response can be tuned from changes in feature size.

Micropatterned methacrylate polymers direct spiral ganglion neurite and Schwann cell growth

Significant advances in the functional outcomes achieved with cochlear implantation will likely require tissue-engineering approaches to improve the neural prosthesis interface. One strategy is to direct spiral ganglion neuron (SGN) axon growth in a highly organized fashion to approximate or contact stimulating electrodes. Here we assessed the ability of micropatterns induced by photopolymerization in methacrylate (MA) polymer systems to direct cultured neonatal rat SGN neurite growth and alignment of SG Schwann cells (SGSCs). SGN survival and neurite length were comparable among various polymer compositions. Remarkably, there was no significant difference in SGN survival or neurite length between laminin and non-laminin coated MA polymer substrates, suggesting high biocompatibility with SG tissue. Micropatterning with photopolymerization generated microchannels with a ridge periodicity of 50 μm and channel depths of 0.6-1.0 μm. SGN neurites grew within the grooves of the microchannels. These topographies strongly induced alignment of dissociated SGN neurites and SGSCs to parallel the pattern. By contrast, fibroblasts failed to align with the micropattern suggesting cell specific responses to topographical cues. SGN neurites extending from explants turned to parallel the pattern as they encountered the microchannels. The extent of turning was significantly correlated with angle at which the neurite initially encountered the pattern. These results indicate that SGN neurites respond to microtopographical features and that these features can be used to direct neurite growth in a highly organized fashion.

Heterotypic cell-cell interaction on micropatterned surfaces

PURPOSE

The aim of this paper was to study the influence of chemical and topographical signals on cell behavior and to obtain a heterotypic cell-cell interaction on microstructured domains.

METHODS

The polysaccharide hyaluronic acid (Hyal) was photoimmobilized on glass surfaces in order to obtain a pattern with squares and rectangles of different dimensions and chemistry. The microstructured surfaces were characterized by scanning electron microscopy (SEM) and atomic force microscopy (AFM). The behavior of human coronary artery endothelial cells (HCAEC) and human tumoral dermal fibroblasts (C54) was investigated on these micropatterned surfaces by adhesion studies. Moreover heterotypic interaction among C54 and HCAEC adherent on patterned surfaces was evaluated by time-lapse video microscopy

RESULTS

Surface analysis revealed the presence of a pattern consisting of alternating glass and Hyal microstructures whose dimensions decreased from the center to the edge of the sample. Neither HCAEC nor C54 adhered to the immobilized Hyal but both adapted their shape to the different sizes of the glass squares and rectangles. The number of adherent cells depended on the dimensions of both the glass domains and the nuclei of the cells. Co-cultured C54 on HCAEC patterned surfaces showed a heterotypic cell-cell interaction in the same chemical and topographic domain.

CONCLUSIONS

A heterotypic cell-cell interaction occurred in the same chemical and topographic micro-domains but in narrow areas only. Moreover, the number of cells adhering to the glass domains and cell morphology depended on the dimensions of both adhesive areas and cell nuclei.

Engineering of a microfluidic cell culture platform embedded with nanoscale features

Cells residing in a microenvironment interact with the extracellular matrix (ECM) and neighboring cells. The ECM built from biomacromolecules often includes nanotopography. Through the ECM, interstitial flows facilitate transport of nutrients and play an important role in tissue maintenance and pathobiology. To create a microenvironment that can incorporate both nanotopography and flow for studies of cell-matrix interactions, we fabricated microfluidic channels endowed with nanopatterns suitable for dynamic culture. Using polymer thin film technology, we developed a versatile stitching technique to generate a large area of nanopatterned surface and a simple microtransfer assembly technique to assemble polydimethylsiloxane-based microfluidics. The cellular study showed that both nanotopography and fluid shear stress played a significant role in adhesion, spreading, and migration of human mesenchymal stem cells. The orientation and deformation of cytoskeleton and nuclei were regulated through the interplay of these two cues. The nanostructured microfluidic platform provides a useful tool to promote the fundamental understanding of cell-matrix interactions and may be used to regulate the fate of stem cells.

High-throughput screening of microscale pitted substrate topographies for enhanced nonviral transfection efficiency in primary human fibroblasts

Optimization of nonviral gene delivery typically focuses on the design of particulate carriers that are endowed with desirable membrane targeting, internalization, and endosomal escape properties. Topographical control of cell transfectability, however, remains a largely unexplored parameter. Emerging literature has highlighted the influence of cell-topography interactions on modulation of many cell phenotypes, including protein expression and cytoskeletal behaviors implicated in endocytosis. Using high-throughput screening of primary human dermal fibroblasts cultured on a combinatorial library of microscale topographies, we have demonstrated an improvement in nonviral transfection efficiency for cells cultured on dense micropit patterns compared to smooth substrates, as verified with flow cytometry. A 25% increase in GFP(+) cells was observed independent of proliferation rate, accompanied by SEM and confocal microscopy characterization to help explain the phenomenon qualitatively. This finding encourages researchers to investigate substrate topography as a new design consideration for the optimization of nonviral transfection systems.

Microcontact printing of fibronectin on a biodegradable polymeric surface for skeletal muscle cell orientation

BACKGROUND AND OBJECTIVES

Micropatterning and microfabrication techniques have been widely used to control cell adhesion and proliferation along a preferential direction according to contact guidance theory. One of these techniques is microcontact printing, a soft lithographic technique based on the transfer of a "molecular ink" from an elastomeric stamp to a surface. This method allows the useful attachment of biomolecules in a few seconds on a variety of surfaces with sub-micrometer resolution and control, without modifying the biomolecule properties. The aim of this study is to develop an easy and versatile technique for in vitro production of arrays of skeletal muscle myofibers using microcontact printing technique on biodegradable substrata.

METHODS

Microcontact printing of fibronectin stripes (10, 25, 50 μm in width) was performed onto biodegradable L-lactide/trimethylene carbonate copolymer (PLLA-TMC) films. C2C12, a murine myoblast cell line, was used for the production of parallel myofibers.

RESULTS

This approach proved to be simple, reliable and effective in obtaining a stable pattern of fibronectin on the PLLA-TMC surface as observed by fluorescence microscopy. C2C12 cells were well aligned along the pattern 24 hours after seeding, especially on fibronectin stripes 10 and 25 μm in width. Seven days after confluence cells fused and formed aligned multinucleated cells expressing a-actinin.

CONCLUSIONS

Fibronectin patterning seems to be a useful method to induce cell alignment and to improve myotube formation. Further studies will be focused on the possibility of applying external stimuli to these structures to obtain healthy myotubes and to induce myofiber development.

Selective axonal growth of embryonic hippocampal neurons according to topographic features of various sizes and shapes

Purpose

Understanding how surface features influence the establishment and outgrowth of the axon of developing neurons at the single cell level may aid in designing implantable scaffolds for the regeneration of damaged nerves. Past studies have shown that micropatterned ridge-groove structures not only instigate axon polarization, alignment, and extension, but are also preferred over smooth surfaces and even neurotrophic ligands.

Methods

Here, we performed axonal-outgrowth competition assays using a proprietary four-quadrant topography grid to determine the capacity of various micropatterned topographies to act as stimuli sequestering axon extension. Each topography in the grid consisted of an array of microscale (approximately 2 μm) or submicroscale (approximately 300 nm) holes or lines with variable dimensions. Individual rat embryonic hippocampal cells were positioned either between two juxtaposing topographies or at the borders of individual topographies juxtaposing unpatterned smooth surface, cultured for 24 hours, and analyzed with respect to axonal selection using conventional imaging techniques.

Results

Topography was found to influence axon formation and extension relative to smooth surface, and the distance of neurons relative to topography was found to impact whether the topography could serve as an effective cue. Neurons were also found to prefer submicroscale over microscale features and holes over lines for a given feature size.

Conclusion

The results suggest that implementing physical cues of various shapes and sizes on nerve guidance conduits and other advanced biomaterial scaffolds could help stimulate axon regeneration.

Microtopographical regulation of adult bone marrow progenitor cells chondrogenic and osteogenic gene and protein expressions

Microtopographic features affect diverse cell behaviors. Adult bone marrow progenitor cells (AMPCs) constitute a multipotent heterogeneous population. We hypothesized that microtopographies could direct AMPCs lineage-specific differentiation. AMPCs isolated from Sprague-Dawley rats were CD45 depleted, expanded, and plated at 10(5) cells/cm2 on epoxy-microfabricated: (1) 60-microm-deep grooves with 95-microm pitch (D60P95), (2) 55-microm-wide and 10-microm-deep squares (W55D10), (3) 30-microm-deep grooves with 45-microm pitch (D30P45), (4) 17-microm-wide and 10-microm-deep pillars (W17D10), and (5) smooth control. AMPCs were cultured using expansion, chondrogenesis, or osteogenesis supporting media. Cell cultures were examined by scanning electron microscopy, qRT-PCR, and immunostaining at 2, 9, 16, and 23 days after plating. Expressions of osteogenesis-related genes, such as Runx-2, alkaline phosphatase, osteopontin, osteocalcin, and parathyroid hormone-related protein receptor (PTHr), and chondrogenesis-associated genes, such as Sox-9, type II collagen, and aggrecan, were determined. In expansion medium, W55D10 induced a transient increase of Sox9 expression. Compared with smooth surfaces, type II collagen mRNA and protein expressions in chondrogenic medium were significantly upregulated on W55D10 by day 23. In contrast, osteocalcin and PTHr expressions were significantly increased on D30P45 in osteogenic medium. We have demonstrated that W55D10 and D30P45 enhanced AMPCs chondrogenic and osteogenic terminal differentiation with appropriate culture conditions.

Emerging links between surface nanotechnology and endocytosis: impact on nonviral gene delivery

Significant effort continues to be exerted toward the improvement of transfection mediated by nonviral vectors. These endeavors are often focused on the design of particulate carriers with properties that encourage efficient accumulation at the membrane surface, particle uptake, and endosomal escape. Despite its demonstrated importance in successful nonviral transfection, relatively little investigation has been done to understand the pressures driving internalized vectors into favorable nondegradative endocytic pathways. Improvements in transfection efficiency have been noted for complexes delivered with a substrate-mediated approach, but the reasons behind such enhancements remain unclear. The phenotypic changes exhibited by cells interacting with nano- and micro-featured substrates offer hints that may explain these effects. This review describes nanoscale particulate and substrate parameters that influence both the uptake of nonviral gene carriers and the endocytic phenotype of interacting cells, and explores the molecular links that may mediate these interactions. Substrate-mediated control of endocytosis represents an exciting new design parameter that will guide the creation of efficient transgene carriers.

Alterations in gene expression of human vascular endothelial cells associated with nanotopographic cues

Human cells in vivo are exposed to a topographically rich, 3-dimenisional environment which provides extracellular cues initiating a cascade of biochemical signals resulting in changes in cell behavior. One primary focus of our group is the development of biomimetic substrates with anisotropic nanoscale topography to elucidate the mechanisms by which physical surface cues are translated into biochemical signals. To investigate changes in gene expression as a result of nanotopographic cues, Human Umbilical Vein Endothelial Cells (HUVECs) were cultured on chemically identical flat and 400 nm pitch nanogrooved surfaces. After 12 h, RNA was harvested for an Affymetrix HG U133 Plus 2.0 gene array. Of over 47,000 possible gene probes, 3171 had at least a two-fold difference in expression between the control flat and 400 nm pitch. The gene ontology groups with the most significant increase in expression are involved in protein modification and maintenance, similar to cells upregulating chaperone and protein synthesis genes in response to physical stresses. The most significant decreases in expression were observed with cell cycle proteins, including cyclins and checkpoint proteins. Extracellular matrix proteins, including integrins, collagens, and laminins, are almost uniformly downregulated on the 400 nm pitch surfaces compared to control. The downregulation of one of these genes, integrin beta 1, was confirmed via quantitative PCR. Together, these gene array data, in addition to our studies of cell behavior on nanoscale surfaces, contribute to our understanding of the signaling pathways modulated by topographical surface cues.

Topography, cell response, and nerve regeneration

In the body, cells encounter a complex milieu of signals, including topographical cues, in the form of the physical features of their surrounding environment. Imposed topography can affect cells on surfaces by promoting adhesion, spreading, alignment, morphological changes, and changes in gene expression. Neural response to topography is complex, and it depends on the dimensions and shapes of physical features. Looking toward repair of nerve injuries, strategies are being explored to engineer guidance conduits with precise surface topographies. How neurons and other cell types sense and interpret topography remains to be fully elucidated. Studies reviewed here include those of topography on cellular organization and function as well as potential cellular mechanisms of response.

A role for L-alpha-lysophosphatidylinositol and GPR55 in the modulation of migration, orientation and polarization of human breast cancer cells

BACKGROUND AND PURPOSE

Increased circulating levels of L-alpha-lysophosphatidylinositol (LPI) are associated with cancer and LPI is a potent, ligand for the G-protein-coupled receptor GPR55. Here we have assessed the modulation of breast cancer cell migration, orientation and polarization by LPI and GPR55.

EXPERIMENTAL APPROACH

Quantitative RT-PCR was used to measure GPR55 expression in breast cancer cell lines. Cell migration and invasion were measured using a Boyden chamber chemotaxis assay and Cultrex invasion assay, respectively. Cell polarization and orientation in response to the microenvironment were measured using slides containing nanometric grooves.

KEY RESULTS

GPR55 expression was detected in the highly metastatic MDA-MB-231 breast cancer cell line. In these cells, LPI stimulated binding of [(35)S]GTPgammaS to cell membranes (pEC(50) 6.47 +/- 0.45) and significantly enhanced cell chemotaxis towards serum. MCF-7 cells expressed low levels of GPR55 and did not migrate or invade towards serum factors. When GPR55 was over-expressed in MCF-7 cells, serum induced a robust migratory and invasive response, which was further enhanced by LPI and prevented by siRNA to GPR55. The physical microenvironment has been identified as a key factor in determining breast tumour cell metastatic fate. LPI endowed MDA-MB-231 cells with the capacity to detect shallow (40 nm deep) grooved slides and induced marked cancer cell polarization on both flat and grooved surfaces.

CONCLUSIONS AND IMPLICATIONS

LPI and GPR55 play a role in the modulation of migration, orientation and polarization of breast cancer cells in response to the tumour microenvironment.

Hippocampal neurons respond uniquely to topographies of various sizes and shapes

A number of studies have investigated the behavior of neurons on microfabricated topography for the purpose of developing interfaces for use in neural engineering applications. However, there have been few studies simultaneously exploring the effects of topographies having various feature sizes and shapes on axon growth and polarization in the first 24 h. Accordingly, here we investigated the effects of arrays of lines (ridge grooves) and holes of microscale (approximately 2 microm) and nanoscale (approximately 300 nm) dimensions, patterned in quartz (SiO2), on the (1) adhesion, (2) axon establishment (polarization), (3) axon length, (4) axon alignment and (5) cell morphology of rat embryonic hippocampal neurons, to study the response of the neurons to feature dimension and geometry. Neurons were analyzed using optical and scanning electron microscopy. The topographies were found to have a negligible effect on cell attachment but to cause a marked increase in axon polarization, occurring more frequently on sub-microscale features than on microscale features. Neurons were observed to form longer axons on lines than on holes and smooth surfaces; axons were either aligned parallel or perpendicular to the line features. An analysis of cell morphology indicated that the surface features impacted the morphologies of the soma, axon and growth cone. The results suggest that incorporating microscale and sub-microscale topographies on biomaterial surfaces may enhance the biomaterials' ability to modulate nerve development and regeneration.

Effects of a surface topography composite with puerariae radix on human STRO-1-positive stem cells

Human skeletal stem cells (STRO-1 positive/STRO-1+) respond to different topographical features in various ways. On a flat surface these cells spread and tend to develop a fibroblast-like morphology. On a microgrooved surface enriched skeletal stem cell populations prefer to stretch along the grooves, which affects their cellular structure and differentiation, a phenomenon known as contact guidance. Growth factors, hormones and chemicals can also stimulate cell differentiation. A traditional Chinese medicine, puerariae radix, has previously been observed to stimulate bone formation. The active ingredients have been identified as isoflavones with estrogen-like bioactivity. This study combined the effects of microgrooved topology and hormone-like isoflavones in the biodegradable polymer polycaprolactone (PCL). Human osteogenic cells (STRO-1+) were cultured on flat PCL, grooved PCL and puerariae powder-impregnated grooved PCL for 5 weeks. Coomassie staining indicated that cell growth and survival was similar on flat PCL, grooved PCL and grooved PCL impregnated with 1 wt.% or 2 wt.% puerariae powder. Grooved PCL impregnated with 2 wt.% puerariae powder was observed to have an influence on protein expression, as observed by positive osteocalcin staining. Protein expression profiles were analyzed by difference gel electrophoresis to identify proteins that showed modulation of expression in response to these different environments. Overall, our results suggest that puerariae powder has an additive effect, along with microgrooved topographical stimulation, to promote changes in the STRO-1+ proteome that affect cell phenotype.

Nanotopographical control of stem cell differentiation

Stem cells have the capacity to differentiate into various lineages, and the ability to reliably direct stem cell fate determination would have tremendous potential for basic research and clinical therapy. Nanotopography provides a useful tool for guiding differentiation, as the features are more durable than surface chemistry and can be modified in size and shape to suit the desired application. In this paper, nanotopography is examined as a means to guide differentiation, and its application is described in the context of different subsets of stem cells, with a particular focus on skeletal (mesenchymal) stem cells. To address the mechanistic basis underlying the topographical effects on stem cells, the likely contributions of indirect (biochemical signal-mediated) and direct (force-mediated) mechanotransduction are discussed. Data from proteomic research is also outlined in relation to topography-mediated fate determination, as this approach provides insight into the global molecular changes at the level of the functional effectors.

Novel Modeling Approach to Generate a Polymeric Nanofiber Scaffold for Salivary Gland Cells

BACKGROUND: Electrospun nanofibers have been utilized in many biomedical applications as biomimetics of extracellular matrix proteins that promote self-organization of cells into 3D tissue constructs. As progress towards an artificial salivary gland tissue construct, we prepared nanofiber scaffolds using PLGA, a biodegradable and biocompatible material. METHOD OF APPROACH: We used electrospinning to prepare nanofiber scaffolds using PLGA with both DMF and HFIP as solvents. Using a design of experiment (DOE) approach, system and process parameters were optimized concurrently and their effects on the diameter of the resulting fibers were computed into a single model. A transfer function was used to reproducibly produce nanofibers of a defined diameter, which was confirmed by SEM. The mouse salivary gland epithelial cell line, SIMS, was seeded on the nanofiber scaffolds, and morphology, cell proliferation, and viability were assayed. RESULTS: Varying two or more parameters simultaneously yielded trends diverging from the linear response predicted by previous studies. Comparison of two solvents revealed that the diameter of PLGA nanofibers generated using HFIP is less sensitive to changes in the system and process parameters than are fibers generated using DMF. Inclusion of NaCl reduced morphological inconsistencies and minimized process variability. The resulting nanofiber scaffolds supported attachment, survival and cell proliferation of a mouse salivary gland epithelial cell line. In comparison with glass and flat PLGA films, the nanofibers promoted self-organization of the salivary gland cells into 3D cell clusters, or aggregates. CONCLUSIONS: These data indicate that nanofiber scaffolds promote salivary gland cell organization, and suggest that a nanofiber scaffold could provide a platform for engineering of an artificial salivary gland tissue construct. This study additionally provides a method for efficient production of nanofiber scaffolds for general application in tissue engineering.

Modulation of alignment and differentiation of skeletal myoblasts by submicron ridges/grooves surface structure

Alignment and fusion of myoblasts into parallel arrays of multinucleated myotubes are critical in skeletal muscle tissue engineering. It is well known that contact guidance by grooves/ridges structures induces myoblasts to align and to migrate along the anisotropic direction. In this study, two series of grooved substrata with different widths (450 and 900 nm) and different depths (100, 350, and 550 nm) were studied on their effects on myoblast adhesion, proliferation, and differentiation into myotubes. We found that C2C12 cells were aligned and elongated along the direction of grooves. Groove depth was more influential on cellular morphology, proliferation, and differentiation than groove width. While cell proliferation was retarded on the grooved surfaces especially on the substrate with 900/550 nm (width/depth), differentiation was also enhanced on the patterned surfaces compared to the flat control. Our results demonstrated the potential of grooved substrata with submicron scale in skeletal muscle tissue engineering.

Use of force spectroscopy to investigate the adhesion of living adherent cells

The use of force spectroscopy to study the adhesion of living fibroblasts to their culture substrate was investigated. Both primary fibroblasts (PEMF) and a continuous cell line (3T3) were studied on quartz surfaces. Using a fibronectin-coated AFM cantilever, it was possible to detach a large proportion of the 3T3 cells from the quartz surfaces. Their adhesion to the quartz surface and the effects of topography on this adhesion could be quantified. Three parameters characteristic of the adhesion were measured: the maximum force of detachment, the work of adhesion, and the distance of detachment. Few PEMF cells were detached under the same experimental conditions. The potential and limitations of this method in measuring cell/surface interactions for adherent cells are discussed.

Biodegradable microgrooved polymeric surfaces obtained by photolithography for skeletal muscle cell orientation and myotube development

During tissue formation, skeletal muscle precursor cells fuse together to form multinucleated myotubes. To understand this mechanism, in vitro systems promoting cell alignment need to be developed; for this purpose, micrometer-scale features obtained on substrate surfaces by photolithography can be used to control and affect cell behaviour. This work was aimed at investigating how differently microgrooved polymeric surfaces can affect myoblast alignment, fusion and myotube formation in vitro. Microgrooved polymeric films were obtained by solvent casting of a biodegradable poly-l-lactide/trimethylene carbonate copolymer (PLLA-TMC) onto microgrooved silicon wafers with different groove widths (5, 10, 25, 50, 100microm) and depths (0.5, 1, 2.5, 5microm), obtained by a standard photolithographic technique. The surface topography of wafers and films was evaluated by scanning electron microscopy. Cell assays were performed using C2C12 cells and myotube formation was analysed by immunofluorescence assays. Cell alignment and circularity were also evaluated using ImageJ software. The obtained results confirm the ability of microgrooved surfaces to influence myotube formation and alignment; in addition, they represent a novel further improvement to the comprehension of best features to be used. The most encouraging results were observed in the case of microstructured PLLA-TMC films with grooves of 2.5 and 1microm depth, presenting, in particular, a groove width of 50 and 25microm.

Neurite outgrowth at the biomimetic interface

Understanding the cues that guide axons and how we can optimize these cues to achieve directed neuronal growth is imperative for neural tissue engineering. Cells in the local environment influence neurons with a rich combination of cues. This study deconstructs the complex mixture of guidance cues by working at the biomimetic interface--isolating the topographical information presented by cells and determining its capacity to guide neurons. We generated replica materials presenting topographies of oriented astrocytes (ACs), endothelial cells (ECs), and Schwann cells (SCs) as well as computer-aided design materials inspired by the contours of these cells (bioinspired-CAD). These materials presented distinct topographies and anisotropies and in all cases were sufficient to guide neurons. Dorsal root ganglia (DRG) cells and neurites demonstrated the most directed response on bioinspired-CAD materials which presented anisotropic features with 90 degrees edges. DRG alignment was strongest on SC bioinspired-CAD materials followed by AC bioinspired-CAD materials, with more uniform orientation to EC bioinspired-CAD materials. Alignment on replicas was strongest on SC replica materials followed by AC and EC replicas. These results suggest that the topographies of anisotropic tissue structures are sufficient for neuronal guidance. This work is discussed in the context of feature dimensions, morphology, and guidepost hypotheses.

Correlation of cell adhesive behaviors on superhydrophobic, superhydrophilic, and micropatterned superhydrophobic/superhydrophilic surfaces to their surface chemistry

A micropatterned superhydrophobic/superhydrophilic surface was successfully fabricated by plasma CVD and VUV irradiation. Physicochemical properties of the superhydrophobic, superhydrophilic, and superhydrophobic/superhydrophilic surfaces were investigated. The roughness structures on the superhydrophilic surface remained intact compared to those of the superhydrophobic surface. The micropatterned superhydrophobic/superhydrophilic surface was used as a scaffold of cell culture. On the micropatterned surface, the cells attached to the superhydrophilic regions in a highly selective manner, forming circular microarrays of the cells corresponding to the pattern. On the micropatterned surface with pattern distances of 200 microm between superhydrophilic regions, the cells adhered on the superhydrophilic regions and partly extended to the neighboring cells. In contrast, when the pattern distances between the superhydrophilic regions were more than 400 microm, the cells did not extend to the neighboring cells. Cell adhesion behaviors on superhydrophobic and superhydrophilic surfaces were also examined. The cells adhered and proliferated on both superhydrophobic and superhydrophilic surfaces. However, on the superhydrophobic surface, constant contact to facilitate cell division and proliferation was required. On the other hand, the cells easily adhered and proliferated on the superhydrophilic surface immediately after seeding. These differences in cell adhesion behavior induced site-selective cell adhesion on the superhydrophilic regions. Furthermore, protein adsorption behavior that plays an important role in cell adhesion on flat hydrophobic and hydrophilic surface was also examined. The amounts of the protein adsorption on the flat hydrophilic surface were much greater than those on the flat hydrophobic surface.

Topographically induced self-deformation of the nuclei of cells: dependence on cell type and proposed mechanisms

Osteosarcoma-derived cell lines (SaOs-2, MG63) have recently been shown to deform their nucleus considerably in response to surface topography. Such a deformation had not been described previously. Here we present results on additional cell lines, including cancerous (OHS4, U2OS), immortalized (F/STRO-1(+)A and FHSO6) and healthy cells (HOP). The cancerous cells were found to deform extensively, the immortalized cells showed small deformations, whereas the healthy cells showed deformation only at short incubation times. These results suggest a strong link between the malignant transformation of cells and the state of the cytoskeletal network. We propose mechanisms to explain the deformation in which the cytoskeleton either pushes down on the nucleus during spreading or pulls it down upon adhesion to the pillars.

Low oxygen tension and synthetic nanogratings improve the uniformity and stemness of human mesenchymal stem cell layer

A free-standing, robust cell sheet comprising aligned human mesenchymal stem cells (hMSCs) offers many interesting opportunities for tissue reconstruction. As a first step toward this goal, a confluent, uniform hMSC layer with a high degree of alignment and stemness maintenance needs to be created. Hypothesizing that topographical cue and a physiologically relevant low-oxygen condition could promote the formation of such an hMSC layer, we studied the culture of hMSCs on synthetic nanogratings (350 nm width and 700 nm pitch) and either under 2 or 20% O(2). Culturing hMSCs on the nanogratings highly aligned the cells, but it tended to create patchy layers and accentuate the hMSC differentiation. The 2% O(2) improved the alignment and uniformity of hMSCs, and reduced their differentiation. Over a 14-day culture period, hMSCs in 2% O(2) showed uniform connexon distribution, secreted abundant extracellular matrix (ECM) proteins, and displayed a high progenicity. After 21-day culture on nanogratings, hMSCs exposed to 2% O(2) maintained a higher viability and differentiation capacity. This study established that a 2% O(2) culture condition could restrict the differentiation of hMSCs cultured on nanopatterns, thereby setting the foundation to fabricate a uniformly aligned hMSC sheet for different regenerative medicine applications.

Nanotopographical modification: a regulator of cellular function through focal adhesions

As materials technology and the field of biomedical engineering advances, the role of cellular mechanisms, in particular adhesive interactions with implantable devices, becomes more relevant in both research and clinical practice. A key tenet of medical device design has evolved from the exquisite ability of biological systems to respond to topographical features or chemical stimuli, a process that has led to the development of next-generation biomaterials for a wide variety of clinical disorders. In vitro studies have identified nanoscale features as potent modulators of cellular behavior through the onset of focal adhesion formation. The focus of this review is on the recent developments concerning the role of nanoscale structures on integrin-mediated adhesion and cellular function with an emphasis on the generation of medical constructs with regenerative applications.

FROM THE CLINICAL EDITOR

In this review, recent developments related to the role of nanoscale structures on integrin-mediated adhesion and cellular function is discussed, with an emphasis on regenerative applications.

Quantitative analysis of osteoblast-like cells (MG63) morphology on nanogrooved substrata with various groove and ridge dimensions

Nanotextured silicon substrata with parallel ridges separated by grooves with equal width from 90 to 500 nm, were fabricated by electron beam lithography and dry etching techniques. Osteoblast-like cells, MG-63, were cultured on the sterilized nanopatterned substrata for 4 or 24 h, and then imaged by scanning electron microscopy. The influence of substrate topography on cell morphology was analyzed by image software. We found the initially cells spread faster on the nanopatterned surfaces than on the flat surface, suggesting that surface anisotropic feature facilitates initial cell extension along its direction. However, because of inhibition of cell lateral expansion across nanogrooved surfaces, the cells on the nanogrooved surface did not further expand laterally, and cell spreading area was less than that on the flat surface after 24 h of incubation. Cells elongated and aligned along the direction of grooves on all the nanopatterned substrata. Furthermore, fluorescence staining of cell nuclei indicated that the nuclei of the cells cultured on the nanopatterned surfaces also displayed a more elongated and aligned morphology along the direction of the grooves. Since cell shape and orientation influence cell functions and alignment of extracellular matrix secreted by cells, our results may provide the information regarding responses of osteoblasts to the nanostructure of collagen fibrils, and benefit bone tissue engineering and surface design of orthopedic implants.

Optimization by Response Surface Methodology of Confluent and Aligned Cellular Monolayers for Nerve Guidance

Anisotropic tissue structures provide guidance for navigating neurons in vitro and in vivo. Here we optimized the generation of comparable anisotropic monolayers of astrocytes, endothelial cells, and Schwann cells as a first step toward determining which properties of anisotropic cells are sufficient for nerve guidance. The statistical experimental design method Design of Experiments and the experimental analysis method Response Surface Methodology were applied to improve efficiency and utility. Factors investigated included dimensions of microcontact printed protein patterns, cell density, and culture duration. Protein patterning spacing had the strongest influence. When cells initially aligned at borders and proliferated to fill in spaces, space between stripes was most effective when it was comparable to cell size. Maximizing the area of adhesive molecule coverage was also important for confluence of these types of cells. When cells adhered and aligned over the width of a stripe and broadened to fill spaces, space width about half the cell width was most effective. These findings suggest that if the mechanism of alignment, alignment at borders or over the width of the stripe, is predetermined and the cell size determined, the optimal size of the micropatterning for aligned monolayers of other cell types can be predicted. This study also demonstrates the effective use of DOE and RSM to probe cellular responses to various and multiple factors toward determination of optimal conditions for a desired cellular response.

Narrow window in nanoscale dependent activation of endothelial cell growth and differentiation on TiO2 nanotube surfaces

Critical features of biomimetic materials used for vascular grafts and stents are surface structure and chemical features of the implant material supporting adhesion, proliferation, and differentiation of endothelial cells and smooth muscle cells, the major cell types of blood vessels. Recently, experimental evidence from several laboratories have indicated a strong stimulation of cellular activities on vertically aligned TiO(2) nanotube surfaces in comparison to amorphous TiO(2) surfaces. Conflicting reports exist, however, concerning the nanoscale dimension, and the role of the chemistry and crystallinity of the nanotubes in eliciting cell responses. Here we demonstrate that 15 nm nanotubes provide a substantially stronger stimulation of differentiation of mesenchymal cells to endothelial cells and smooth muscle cells than 70-100 nm nanotubes, while high rates of apoptosis were seen on 100 nm nanotubes. Also endothelial cell adhesion, proliferation, and motility were several-fold higher on 15 nm than on 100 nm nanotubes. Furthermore, our data indicate a clear dominance of the nanoscale geometry on endothelial cell behavior over surface chemistry and crystallinity of the TiO(2) nanotube surface. These findings indicate that fine-tuning of TiO(2) surfaces at nanoscale will be an essential parameter in optimizing endothelial cell and smooth muscle cell responses to vascular implants.