Substrate topography and shape of motile cells

Bioactivation of 3D Cell-Imprinted Polydimethylsiloxane Surfaces by Bone Protein Nanocoating for Bone Tissue Engineering

Physical and chemical parameters that mimic the physiological niche of the human body have an influence on stem cell fate by creating directional signals to cells. Micro/nano cell-patterned polydimethylsiloxane (PDMS) substrates, due to their ability to mimic the physiological niche, have been widely used in surface modification. Integration of other factors such as the biochemical coating on the surface can achieve more similar microenvironmental conditions and promote stem cell differentiation to the target cell line. Herein, we investigated the effect of physical topography, chemical functionalization by acid bone lysate (ABL) nanocoating, and the combined functionalization of the bone proteins' nanocoated surface and the topographically modified surface. We prepared four distinguishing surfaces: plain PDMS, physically modified PDMS by 3D cell topography patterning, chemically modified PDMS with bone protein nanocoating, and chemically modified nano 3D cell-imprinted PDMS by bone proteins (ABL). Characterization of extracted ABL was carried out by Bradford staining and sodium dodecyl sulfate polyacrylamide gel electrophoresis analysis, followed by the MTT assay for evaluation of cell viability on ABL-coated PDMS. Moreover, field emission scanning electron microscopy and profilometry were used for the determination of optimal coating thickness, and the appropriate coating concentration was identified and used in the study. The binding and retention of ABL to PDMS were confirmed by Fourier transform infrared spectroscopy and bicinchoninic acid assay. Sessile drop static water contact angle measurements on substrates showed that the combined chemical functionalization and nano 3D cell-imprinting on the PDMS surface improved surface wettability by 66% compared to plain PDMS. The results of ALP measurement, alizarin red S staining, immunofluorescence staining, and real-time PCR showed that the nano 3D cell-imprinted PDMS surface functionalized by extracted bone proteins, ABL, is able to guide the fate of adipose derived stem cellss toward osteogenic differentiation. Eventually, chemical modification of the cell-imprinted PDMS substrate by bone protein extraction not only improved the cell adhesion and proliferation but also contributed to the topographical effect itself and caused a significant synergistic influence on the process of osteogenic differentiation.

Cell-Imprinted Substrates Modulate Differentiation, Redifferentiation, and Transdifferentiation

Differentiation of stem cells into mature cells through the use of physical approaches is of great interest. Here, we prepared smart nanoenvironments by cell-imprinted substrates based on chondrocytes, tenocytes, and semifibroblasts as templates and demonstrated their potential for differentiation, redifferentiation, and transdifferentiation. Analysis of shape and upregulation/downregulation of specific genes of stem cells, which were seeded on these cell-imprinted substrates, confirmed that imprinted substrates have the capability to induce specific shapes and molecular characteristics of the cell types that were used as templates for cell-imprinting. Interestingly, immunofluorescent staining of a specific protein in chondrocytes (i.e., collagen type II) confirmed that adipose-derived stem cells, semifibroblasts, and tenocytes can acquire the chondrocyte phenotype after a 14 day culture on chondrocyte-imprinted substrates. In summary, we propose that common polystyrene tissue culture plates can be replaced by this imprinting technique as an effective and promising way to regulate any cell phenotype in vitro with significant potential applications in regenerative medicine and cell-based therapies.

Neurite bridging across micropatterned grooves

After injury, regenerating axons must navigate complex, three-dimensional (3D) microenvironments. Topographic guidance of neurite outgrowth has been demonstrated in vitro with culture substrates that contain micropatterned features on the nanometer-micron scale. In this study we report the ability of microfabricated biomaterials to support neurite extension across micropatterned grooves with feature sizes on the order of tens of microns, sizes relevant to the design of biomaterials and tissue engineering scaffolds. Neonatal rat dorsal root ganglion (DRG) neurons were cultured on grooved substrates of poly(dimethyl siloxane) coated with poly-L-lysine and laminin. Here we describe an unusual capability of a subpopulation of DRG neurons to extend neurites that spanned across the grooves, with no underlying solid support. Multiple parameters influenced the formation of bridging neurites, with the highest numbers of bridges observed under the following experimental conditions: cell density of 125,000 cells per sample, groove depth of 50 microm, groove width of 30 microm, and plateau width of 200 microm. Bridges were formed as neurites extended from a neuron in a groove, contacted adjacent plateaus, pulled the neuron up to become suspended over the groove, and the soma translocated to the plateau. These studies are of interest to understanding cytoskeletal dynamics and designing biomaterials for 3D axon guidance.

Substrate microtopography can enhance cell adhesive and migratory responsiveness to matrix ligand density

The regulation of cell motility by ligand density on substrates with variable microtopography is not well understood. In this report, we studied the adhesion and motility behavior of HepG2 cells on microtextured poly(glycolic-co-lactic)acid (PGLA) copolymer substrates, whose surface bioactivity was differentially modified through the adsorption of 0-5.5 ng/cm(2) collagen. Microtextured PGLA substrates were fabricated as thin films with a uniform surface distribution of micropores of median size of 3.1 +/- 1.5 microm and three-dimensional root mean squared roughness of 0.253 microm. Even in the absence of collagen, cells on microtextured substrates responded to substrate topography by exhibiting a 200% increase in adhesion strength compared with untextured controls and ventral localization of the intracellular adhesion protein vinculin. Further enhancement in adhesion strength (420% over untextured, untreated substrates) was demonstrated with bioactivated, microtextured surfaces, indicating that cell adhesion responses to topography and surface ligand density were cooperative. Our motility studies of cells on untextured substrates adsorbed with different levels of collagen demonstrated that a classical biphasic relationship between the cell population averaged migration rate, mu, and the collagen ligand density was preserved. However, comparison of cell motility responses between untextured and microtextured substrates indicates that the motility versus ligand density curve shifted, such that equivalent levels of cell motility were achieved at lower ligand density on microtextured surfaces. Furthermore, the maximum mu values achieved on the microtextured substrates exceeded those on untextured substrates by twofold. Taken together, we show that the magnitude of subcellular scale microtexture of a polymer substrate can sensitize the cell motility responsiveness to substrate ligand concentration; we suggest that the underlying mechanisms involve alteration in the degree of cell-substrate adhesivity as well as changes in the nature of ligand-induced cell activation processes.

The culture of chick embryo mesoderm cells in hydrated collagen gels

Chick embryo mesoderm cells are various stages of differentiation were cultured in three-dimensional matrices of hydrated collagen. The tissues used were: stage 5 mesoderm from regions adjacent to the primitive streak; stage 12 mesoderm, comprising somitic, unsegmented (segmental plate) and lateral plate mesoderm; and stage 18 sclerotome. Explants were examined by phase contrast microscopy, including time-lapse, and scanning and transmission electron microscopy. The cells showed an increased ability to adhere to, and move in, the collagen gel with advancing stage. Of the stage 12 tissues, the unsegmented mesoderm was initially the slowest to grow out of the explant. Sclerotome cells showed by far the greatest ability to move within the gel. Where the collagen fibrils were randomly oriented, the cell morphology was polypodial and advancing lamellipodia showed clear undulations at their leading edges. A distinction was drawn between these undulations and the classical major ruffles which are seen in two-dimensional culture to uplift and pass back along the cell surface. The latter were not seen in the collagen matrix and were presumably suppressed by the three-dimensional culture configuration while the leading edge undulations were not. Ultrastructural examination showed that the cells possessed patches of amorphous material on their surface, which was sometimes interposed between the plasma membrane and collagen fibrils. Addition of hyaluronic acid (2 mg/ml) had an effect only the segmented mesoderm, where outgrowth was enhanced. Although the addition of plasma fibronectin (50 micrograms/ml) to the cultures did not affect any of the tissues, the removal of this substance, by antifibronectin antiserum or by the use of fibronectin depleted serum, inhibited outgrowth in most cases. The only tissue not reproducibly inhibited in this way was sclerotome. Alignment of the collagen fibres by the explants was observed, accompanied by an elongation of the outgrowing cells which, in bipolar form, preferentially moved up and down the aligned tracts. Scanning electron microscopy suggested that cell processes attached to, and presumably exerted tension on, bundles of fibrils thereby pulling them into line. Cell-to-cell contact was not accompanied by contact paralysis as judged by time-lapse micrography.

Contact relations and guidance of primordial germ cells on their migratory route in embryos of Xenopus laevis

This paper describes the relationship between primordial germ cells (p.g.cs) and the substrate over which they migrate in early embryos of the anuran amphibian Xenopus laevis. P.g.cs migrate from the embryonic gut to the dorsal body wall along the dorsal mesentery at the earliest swimming stage. Our earlier papers have described the way in which p.g.cs move in vitro. In this work we have studied the shape and cytoarchitecture of both p.g.cs and the coelomic epithelial cells (c.e.cs) over which they migrate. We have concentrated on three aspects of the morphology of these cells: first the shapes of the c.e.cs and the way that they affect the shapes of the p.g.cs; secondly the presence of adhesion plaques between the two types of cell; and thirdly the arrangement of cytoskeleton elements. The results show that c.e.cs in the dorsal mesentery are orientated cranio-caudally while those on the dorsal body wall and at the junction with the mesentery are arranged transversely, at 90 degrees to the cranio-caudal plane. P.g.cs are found in both elongated and rounded state. Where elongated, they are always in the same plane as the c.e.cs with which they are associated. The implications of this are discussed. Adhesion plaques between p.g.cs and c.e.cs are shown both by disaggregation studies and transmission electron microscope studies. Plaques are associated with the well defined microfilamentous cytoskeleton of c.e.cs, but only with a sparse array of filaments in p.g.cs. The only parts of p.g.cs where filaments are regularly found are their filopodia, which are generally seen on elongated p.g.cs in longitudinal section. We suggest on the basis of this work that p.g.cs have a dispersed cytoskeleton except during filopod extension, that they move by forming direct adhesion plaques with c.e.cs, and that c.e.cs provide a firm orientated support and possible guide to p.g.c. movement.