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

Viscoelastic modeling of highly hydrated laminin layers at homogeneous and nanostructured surfaces: quantification of protein layer properties using QCM-D and SPR

The adsorption of proteins at material surfaces is important in applications such as biomaterials, drug delivery, and diagnostics. The interaction of cells with artificial surfaces is mediated through adsorbed proteins, where the type of protein, amount, orientation, and conformation are of consequence for the cell response. Laminin, an important cell adhesive protein that is central in developmental biology, is studied by a combination of quartz crystal microbalance with dissipation (QCM-D) and surface plasmon resonance (SPR) to characterize the adsorption of laminin on surfaces of different surface chemistries. The combination of these two techniques allows for the determination of the thickness and effective density of the protein layer as well as the adsorbed mass and viscoelastic properties. We also evaluate the capacity of QCM-D to be used as a quantitative technique on a nanostructured surface, where protein is adsorbed specifically in a nanopattern exploiting PLL-g-PEG as a protein-resistant background. We show that laminin forms a highly hydrated protein layer with different characteristics depending on the underlying substrate. Using a combination of QCM-D and atomic force microscopy (AFM) data from nanostructured surfaces, we model laminin and antibody binding to nanometer-scale patches. A higher amount of laminin was found to adsorb in a thicker layer of a lower effective density in nanopatches compared to equivalent homogeneous surfaces. These results suggest that modeling of QCM-D data of soft viscoelastic layers arranged in nanopatterns may be applied where an independent measure of the "dry" mass is known.

Submicron poly(L-lactic acid) pillars affect fibroblast adhesion and proliferation

Controlling cell adhesion and proliferation on synthetic polymers is key to tissue engineering scaffold development. It is accepted that surface topography influences cell response but the mechanisms behind this remain unclear. In this work, cell response is assessed to topographies larger than focal complexes (FXs) but smaller than focal adhesions (FAs). Poly(L-lactic acid) was patterned with 400- and 700-nm pillars via replication molding. Human fibroblast adhesion and proliferation were assessed. The development of focal contacts and actin microfilaments were evaluated via immunofluorescence. Cell interactions with surface topography were observed via scanning electron microscopy. Initial fibroblast adhesion (<1 day) increased with texture as 400 nm > 700 nm > smooth, but proliferation (>1 day) decreased with texture. Increased FX formation was observed on textured surfaces. However, FAs were narrower on textured surfaces compared with smooth materials and confined to interpillar regions. SEM showed that fibroblasts deformed the 400-nm pillars. It is hypothesized that surface texture mediated FX formation and increased cell adhesion, possibly via increased material surface area. Texture geometry limited maturation of FXs to FAs, decreasing proliferation. We conclude that surface texture can alter cell adhesion and proliferation and propose geometric constraint as a mechanism for this process.

Colloidal lithography and current fabrication techniques producing in-plane nanotopography for biological applications

Substrate topography plays a vital role in cell and tissue structure and function in situ, where nanometric features, for example, the detail on single collagen fibrils, influence cell behaviour and resultant tissue formation. In vitro investigations demonstrate that nanotopography can be used to control cell reactions to a material surface, indicating its potential application in tissue engineering and implant fabrication. Developments in the catalyst, optical, medical and electronics industries have resulted in the production of nanopatterned surfaces using a variety of methods. The general protocols for nanomanufacturing require high resolution and low cost for fabricating devices. With respect to biological investigations, nanotopographies should occur across a large surface area (ensuring repeatability of experiments and patterning of implant surfaces), be reproducible (allowing for consistency in experiments), and preferably, accessible (limiting the requirement for specialist equipment). Colloidal lithography techniques fit these criteria, where nanoparticles can be utilized in combination with a functionalized substrate to produce in-plane nanotopographies. Subsequent lithographic processing of colloidal substrates utilizing, for example, reactive ion etching allows the production of modified colloidal-derived nanotopographies. In addition to two-dimensional in-plane nanofabrication, functionalized structures can be dip coated in colloidal sols, imparting nanotopographical cues to cells within a three-dimensional environment.

Regulation of implant surface cell adhesion: characterization and quantification of S-phase primary osteoblast adhesions on biomimetic nanoscale substrates

Integration of an orthopedic prosthesis for bone repair must be associated with osseointegration and implant fixation, an ideal that can be approached via topographical modification of the implant/bone interface. It is thought that osteoblasts use cellular extensions to gather spatial information of the topographical surroundings prior to adhesion formation and cellular flattening. Focal adhesions (FAs) are dynamic structures associated with the actin cytoskeleton that form adhesion plaques of clustered integrin receptors that function in coupling the cell cytoskeleton to the extracellular matrix (ECM). FAs contain structural and signalling molecules crucial to cell adhesion and survival. To investigate the effects of ordered nanotopographies on osteoblast adhesion formation, primary human osteoblasts (HOBs) were cultured on experimental substrates possessing a defined array of nanoscale pits. Nickel shims of controlled nanopit dimension and configuration were fabricated by electron beam lithography and transferred to polycarbonate (PC) discs via injection molding. Nanopits measuring 120 nm diameter and 100 nm in depth with 300 nm center-center spacing were fabricated in three unique geometric conformations: square, hexagonal, and near-square (300 nm spaced pits in square pattern, but with +/-50 nm disorder). Immunofluorescent labeling of vinculin allowed HOB adhesion complexes to be visualized and quantified by image software. Perhipheral adhesions as well as those within the perinuclear region were observed, and adhesion length and number were seen to vary on nanopit substrates relative to smooth PC. S-phase cells on experimental substrates were identified with bromodeoxyuridine (BrdU) immunofluorescent detection, allowing adhesion quantification to be conducted on a uniform flattened population of cells within the S-phase of the cell cycle. Findings of this study demonstrate the disruptive effects of ordered nanopits on adhesion formation and the role the conformation of nanofeatures plays in modulating these effects. Highly ordered arrays of nanopits resulted in decreased adhesion formation and a reduction in adhesion length, while introducing a degree of controlled disorder present in near-square arrays, was shown to increase focal adhesion formation and size. HOBs were also shown to be affected morphologicaly by the presence and conformation of nanopits. Ordered arrays affected cellular spreading, and induced an elongated cellular phenotype, indicative of increased motility, while near-square nanopit symmetries induced HOB spreading. It is postulated that nanopits affect osteoblast-substrate adhesion by directly or indirectly affecting adhesion complex formation, a phenomenon dependent on nanopit dimension and conformation.

The interaction of human bone marrow cells with nanotopographical features in three dimensional constructs

Until now, nanotopography has been considered in 2D construct designs. This has been due to fabrication limitations with traditional lithographic processes relying on the ability to focus radiation that will expose a radiation sensitive resist (e.g. photolithography and electron beam lithography). More recently, alternative methods that offer rapid and cheap nanofabrication have been developed; such methods include polymer demixing and colloidal lithography. Polymer demixing in 2D has relied on spin casting of polymer blends-such as polystyrene and polybromostyrene in a solvent such as toluene. As the solvent evaporates, the polymers phase separate and form nanoislands. In this study, the polymer blend solution has been blown through fine tubes and allowed to demix, thus providing 3D constructs for cell biology. The ability to fabricate in tubes may be useful in many applications, for example stents, conduits, and bone repair (when considering structures such as Haversian tubes and Volkmann's canals). As proof of concept, human osteoprogenitor cells have been used to test the cell response to the nanopatterned tubes. The results show that nanofeatures of size X, diameter Y, and spacing Z decrease cell spreading, reduce cytoskeletal organization, and increase endocytotic activity within the cells.

Continuing differentiation of human mesenchymal stem cells and induced chondrogenic and osteogenic lineages in electrospun PLGA nanofiber scaffold

Nanofibers have recently gained substantial interest for potential applications in tissue engineering. The objective of this study was to determine whether electrospun nanofibers accommodate the viability, growth, and differentiation of human mesenchymal stem cells (hMSCs) as well as their osteogenic (hMSC-Ob) and chondrogenic (hMSC-Ch) derivatives. Poly(d,l-lactide-co-glycolide) (PLGA) beads with a PLA:PGA ratio of 85:15 were electrospun into non-woven fibers with an average diameter of 760+/-210 nm. The average Young's modulus of electrospun PLGA nanofibers was 42+/-26 kPa, per nanoindentation with atomic force microscopy (AFM). Human MSCs were seeded 1-4 weeks at a density of 2 x 10(6)cells/mL in PLGA nanofiber sheets. After 2 week culture on PLGA nanofiber scaffold, hMSCs remained as precursors upon immunoblotting with hKL12 antibody. SEM taken up to 7 days after cell seeding revealed that hMSCs, hMSC-Ob and hMSC-Ch apparently attached to PLGA nanofibers. The overwhelming majority of hMSCs was viable and proliferating in PLGA nanofiber scaffolds up to the tested 14 days, as assayed live/dead tests, DNA assay and BrdU. In a separate experiment, hMSCs seeded in PLGA nanofiber scaffolds were differentiated into chodrogenic and osteogenic cells. Histological assays revealed that hMSCs continuously differentiated into chondrogenic cells and osteogenic cells after 2 week incubation in PLGA nanofibers. Taken together, these data represent an original investigation of continuous differentiation of hMSCs into chondrogenic and osteogenic cells in PLGA nanofiber scaffold. Consistent with previous work, these findings also suggest that nanofibers may serve as accommodative milieu for not only hMSCs, but also as a 3D carrier vehicle for lineage specific cells.

Synthesis and cellular biocompatibility of two kinds of HAP with different nanocrystal morphology

Two kinds of hydroxyapatite (HA) with different nanocrystal morphology were obtained via a simple aqueous precipitation method under different reactants molar ratios. Under Ca/P molar ratio of 1.67/1, rod-like crystal was produced, while under Ca/P molar ratio of 1.80/1, spherical crystal was produced. The spherical crystal was 40-60 nm in diameter, while the rod-like crystal was 40-55 nm in diameter and 79-100 nm in length. The influence of HA nanocrystal morphology on osteoblasts growth was assayed by MTT method and SEM. The results indicated that there was a significantly higher absorbency value on the surface of HA with spherical crystal in MTT assay than the latter. In the process of SEM observation, it is found that osteoblasts spread out a large quantity of nano-filopodias on spherical crystal surface, thus exhibiting much more active cell morphology. In conclusion, HA with spherical nanocrystal showed more favorable properties than that with rod-like one for osteoblasts.

Magnetically-Guided Self-Assembly of Fibrin Matrices with Ordered Nano-Scale Structure for Tissue Engineering

The development of effective biological scaffold materials for tissue engineering and regenerative medicine applications hinges on the ability to present precise environmental cues to specific cell populations to guide their position and function. Natural extracellular matrices have an ordered nano-scale structure that can modulate cell behaviors critical for developmental control, including directional cell motility. Here we describe a method for fabricating fibrin gels with defined architecture on the nanometer scale in which magnetic forces are used to position thrombin-coated magnetic micro-beads in a defined 2-dimensional array and thereby guide the self-assembly of fibrin fibrils through catalytic cleavage of soluble fibrinogen substrate. Time-lapse and confocal microscopy confirmed that fibrin fibrils nucleate near the surface of the thrombin-coated beads and extend out in a radial direction to form these gels. When controlled magnetic fields were used to position the beads in hexagonal arrays, the fibrin nano-fibrils that polymerized from the beads oriented preferentially along the bead--bead axes in a geodesic (minimal path) pattern. These biocompatible scaffolds supported adhesion and spreading of human microvascular endothelial cells, which exhibited co-alignment of internal actin stress fibers with underlying fibrin nano-fibrils within some membrane extensions at the cell periphery. This magnetically-guided, biologically-inspired microfabrication system is unique in that large scaffolds may be formed with little starting material, and thus it may be useful for in vivo tissue engineering applications in the future.

UV-embossed microchannel in biocompatible polymeric film: Application to control of cell shape and orientation of muscle cells

This article shows that ultra violet (UV) micro-embossing can be successfully used for fabricating biocompatible micropatterned films with microchannels separated by high aspect ratio microwalls. Eight series of micropatterns were investigated; the width of the microwall was either 10 or 25 microm and that of the microchannel either 40, 80, 120, or 160 microm. The material investigated was principally polyurethane diacrylate. The UV-embossed micropattern was extracted with methanol, converting the micropatterns from cytotoxic to biocompatible. The typical UV embossing method was modified by using a marginally adhesive polyester substrate, which facilitates demolding but is removable before methanol extraction to avoid fragmentation of the embossed micropatterns. The effect of the micropatterns on A7r5 smooth muscle cells and C2C12 skeletal muscle cells was investigated. The dimensions of both channel and wall have significant effects on the elongation of both muscle cells. In the narrower 40-microm channel, the C2C12 cells merged together to form myofibers. These results indicate that UV-embossed micropatterns may present a useful scaffold for in vitro cell shape and orientation control needed in vascular and muscle tissue engineering.

Methods for Fabrication of Nanoscale Topography for Tissue Engineering Scaffolds

Observations of how controlling the microenvironment of cell cultures can lead to changes in a variety of parameters has lead investigators to begin studying how the nano-environment of a culture can affects cells. Cells have many structures at the nanoscale such as filipodia and cytoskeletal and membrane proteins that interact with the environment surrounding them. By using techniques that can control the nano-environment presented to a cell, investigators are beginning to be able to mimic the nanoscale topographical features presented to cells by extracellular matrix proteins such as collagen, which has precise and repeating nano-topography. The belief is that these nanoscale surface features are important to creating more natural cell growth and function. A number of techniques are currently being used to create nanoscale topographies for cell scaffolding. These techniques fall into two main categories: techniques that create ordered topographies and those that create unordered topographies. Electron Beam lithography and photo-lithography are two standard techniques for creating ordered features. Polymer demixing, phase separation, colloidal lithography and chemical etching are most typically used for creating unordered surface patterns. This review will give an overview of these techniques and cite observations from experiments carried out using them.

Osteoprogenitor response to semi-ordered and random nanotopographies

In bone tissue engineering, it is desirable to use materials to control the differentiation of mesenchymal stem cell populations in order to gain direct bone apposition to implant materials. It has been known for a number of years that microtopography can alter cell adhesion, proliferation and gene expression. More recently, the literature reveals that nanotopography is also of importance. Here, the reaction of primary human osteoprogenitor cell populations to nanotopographies down to 10 nm in size is considered. The topographies were originally produced by colloidal lithography and polymer demixing on silicon and then embossed (through an intermediate nickel shim) into polymethylmethacrylate. The biological testing considered cell morphology (image analysis of cell spreading and scanning electron microscopy), cell cytoskleton and adhesion formation (fluorescent staining of actin, tubulin, vimentin and vinculin) and then subsequent cell growth and differentiation (fluorescent staining of osteocalcin and osteopontin). The results demonstrated that the nanotopographies stimulated the osteoprogenitor cell differentiation towards an osteoblastic phenotype.

Topographically induced direct cell mechanotransduction

This review is designed to introduce the cytoskeleton and then discuss how mechanical forces may be transduced to the cell nucleus. In addition to this, it also tries to explain current thinking as to how the nucleus turns these mechanical cues into gene changes and is especially interested in mechanotransduction arising from topographically induced morphological changes, specifically nanotopography. Thus, this review also describes cell responses to topography.

Use of nanotopography to study mechanotransduction in fibroblasts--methods and perspectives

The environment around a cell during in vitro culture is unlikely to mimic those in vivo. Preliminary experiments with nanotopography have shown that nanoscale features can strongly influence cell morphology, adhesion, proliferation and gene regulation, but the mechanisms mediating this cell response remain unclear. In this perspective article, we attempt to illustrate that a possible mechanism is direct transmittal of forces encountered by cells during spreading to the nucleus via the cytoskeleton. We further try to illustrate that this 'self-induced' mechanotransduction may alter gene expression by changing interphase chromosome positioning. Whilst the observations described here to show how we think nanotopography can be developed as a tool to look at mechanotransduction are preliminary, we feel they indicate that topography may give cell biologists a non-invasive tool with which to investigate in vitro cellular mechanisms.

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

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

Cell response to nano-islands produced by polymer demixing: a brief review

This review looks at the present literature available regarding cell response to nano-islands produced by nanotopography. Polymer demixing is a chemical method of fabricating large areas of nanotopography quickly and cheaply, making it ideal for cell testing and thus allowing it to be one of the first well-researched methods in cell engineering. The review shows that cells respond strongly to the islands (cell types observed include endothelial cells, fibroblasts, osteoblasts, leucocytes and platelets). Such changes include differences in adhesion, growth, gene expression and morphology.