Electron beam patterning of fibronectin nanodots that support focal adhesion formation

Engineered cocultures of iPSC-derived atrial cardiomyocytes and atrial fibroblasts for modeling atrial fibrillation

Atrial fibrillation (AF) is the most common sustained cardiac arrhythmia treatable with antiarrhythmic drugs; however, patient responses remain highly variable. Human induced pluripotent stem cell-derived atrial cardiomyocytes (iPSC-aCMs) are useful for discovering precision therapeutics, but current platforms yield phenotypically immature cells and are not easily scalable for high-throughput screening. Here, primary adult atrial, but not ventricular, fibroblasts induced greater functional iPSC-aCM maturation, partly through connexin-40 and ephrin-B1 signaling. We developed a protein patterning process within multiwell plates to engineer patterned iPSC-aCM and atrial fibroblast coculture (PC) that significantly enhanced iPSC-aCM structural, electrical, contractile, and metabolic maturation for 6+ weeks compared to conventional mono-/coculture. PC displayed greater sensitivity for detecting drug efficacy than monoculture and enabled the modeling and pharmacological or gene editing treatment of an AF-like electrophysiological phenotype due to a mutated sodium channel. Overall, PC is useful for elucidating cell signaling in the atria, drug screening, and modeling AF.

DNA-POINT: DNA Patterning of Optical Imprint for Nanomaterials Topography

Engineering well-defined scale-spanning structures through transfer of diverse biomolecules and materials to a surface is of tremendous interest in life sciences research yet remains profoundly challenging. Here, we report a novel method, termed as DNA patterning of optical imprint for nanomaterials topography (DNA-POINT), for rapid photopatterning of large area, geometrically complex surfaces via light-responsive DNA. Our method employs top-down multiphoton-driven patterning of azobenzene-modified DNA strands, offering precise position control of molecules and nanoparticles along the axial plane and a template for bottom-up self-assembly of multiple layers of different chemical composition along the vertical plane. We demonstrate the surface patterning of plasmonic gold nanoparticles, fluorophore-labeled oligonucleotides, and multiple layers consisting of molecule-nanoparticle hybrid patterns into preconceived shapes without compromising on the functionality of the biomolecules. Furthermore, we exhibit scanning mode operation of DNA-POINT, thereby paving the way for maskless and cleanroom-free fast fabrication of biochips for high-throughput diagnostics and biosensing applications.

Combinatorial nanodot stripe assay to systematically study cell haptotaxis

Haptotaxis is critical to cell guidance and development and has been studied in vitro using either gradients or stripe assays that present a binary choice between full and zero coverage of a protein cue. However, stripes offer only a choice between extremes, while for gradients, cell receptor saturation, migration history, and directional persistence confound the interpretation of cellular responses. Here, we introduce nanodot stripe assays (NSAs) formed by adjacent stripes of nanodot arrays with different surface coverage. Twenty-one pairwise combinations were designed using 0, 1, 3, 10, 30, 44 and 100% stripes and were patterned with 200 × 200, 400 × 400 or 800 × 800 nm² nanodots. We studied the migration choices of C2C12 myoblasts that express neogenin on NSAs (and three-step gradients) of netrin-1. The reference surface between the nanodots was backfilled with a mixture of polyethylene glycol and poly-d-lysine to minimize nonspecific cell response. Unexpectedly, cell response was independent of nanodot size. Relative to a 0% stripe, cells increasingly chose the high-density stripe with up to ~90% of cells on stripes with 10% coverage and higher. Cell preference for higher vs. lower netrin-1 coverage was observed only for coverage ratios >2.3, with cell preference plateauing at ~80% for ratios ≥4. The combinatorial NSA enables quantitative studies of cell haptotaxis over the full range of surface coverages and ratios and provides a means to elucidate haptotactic mechanisms.

Differentiation of Normal and Cancer Cell Adhesion on Custom Designed Protein Nanopatterns

Cell adhesion to the extracellular matrix is deregulated in metastasis. However, traditional surfaces used to study cell adhesion do not faithfully mimic the in vivo microenvironment. Electron beam lithography (EBL) is able to generate customized protein nanopatterns. Here, we used an EBL-based green lithography approach to fabricate homogeneous and gradient, single (fibronectin, K-casein) and double (fibronectin, laminin) active component protein nanopatterns with micrometer scale spacing to investigate differences in adhesion of breast cancer cells (BCC) and normal mammary epithelial cells (NMEC). Our results showed that as expected, in contrast to NMEC, BCC were plastic: they tolerated nonadhesion promoting regions, adapted to flow and exploited gradients better. In addition, the number of focal adhesions but not their area appeared to be the dominant parameter for regulation of cell adhesion. Our findings also demonstrated that custom designed protein nanopatterns, which can properly mimic the in vivo microenvironment, enable realistic distinction of normal and cancerous cell adhesion.

Trehalose glycopolymer resists allow direct writing of protein patterns by electron-beam lithography

Direct-write patterning of multiple proteins on surfaces is of tremendous interest for a myriad of applications. Precise arrangement of different proteins at increasingly smaller dimensions is a fundamental challenge to apply the materials in tissue engineering, diagnostics, proteomics and biosensors. Herein, we present a new resist that protects proteins during electron-beam exposure and its application in direct-write patterning of multiple proteins. Polymers with pendant trehalose units are shown to effectively crosslink to surfaces as negative resists, while at the same time providing stabilization to proteins during the vacuum and electron-beam irradiation steps. In this manner, arbitrary patterns of several different classes of proteins such as enzymes, growth factors and immunoglobulins are realized. Utilizing the high-precision alignment capability of electron-beam lithography, surfaces with complex patterns of multiple proteins are successfully generated at the micrometre and nanometre scale without requiring cleanroom conditions.

Investigation of size-dependent cell adhesion on nanostructured interfaces

BACKGROUND

Cells explore the surfaces of materials through membrane-bound receptors, such as the integrins, and use them to interact with extracellular matrix molecules adsorbed on the substrate surfaces, resulting in the formation of focal adhesions. With recent advances in nanotechnology, biosensors and bioelectronics are being fabricated with ever decreasing feature sizes. The performances of these devices depend on how cells interact with nanostructures on the device surfaces. However, the behavior of cells on nanostructures is not yet fully understood. Here we present a systematic study of cell-nanostructure interaction using polymeric nanopillars with various diameters.

RESULTS

We first checked the viability of cells grown on nanopillars with diameters ranging from 200 nm to 700 nm. It was observed that when cells were cultured on the nanopillars, the apoptosis rate slightly increased as the size of the nanopillar decreased. We then calculated the average size of the focal adhesions and the cell-spreading area for focal adhesions using confocal microscopy. The size of focal adhesions formed on the nanopillars was found to decrease as the size of the nanopillars decreased, resembling the formations of nascent focal complexes. However, when the size of nanopillars decreased to 200 nm, the size of the focal adhesions increased. Further study revealed that cells interacted very strongly with the nanopillars with a diameter of 200 nm and exerted sufficient forces to bend the nanopillars together, resulting in the formation of larger focal adhesions.

CONCLUSIONS

We have developed a simple approach to systematically study cell-substrate interactions on physically well-defined substrates using size-tunable polymeric nanopillars. From this study, we conclude that cells can survive on nanostructures with a slight increase in apoptosis rate and that cells interact very strongly with smaller nanostructures. In contrast to previous observations on flat substrates that cells interacted weakly with softer substrates, we observed strong cell-substrate interactions on the softer nanopillars with smaller diameters. Our results indicate that in addition to substrate rigidity, nanostructure dimensions are additional important physical parameters that can be used to regulate behaviour of cells.

Development of functional biomaterials with micro- and nanoscale technologies for tissue engineering and drug delivery applications

Micro- and nanotechnologies have emerged as potentially effective fabrication tools for addressing the challenges faced in tissue engineering and drug delivery. The ability to control and manipulate polymeric biomaterials at the micron and nanometre scale with these fabrication techniques has allowed for the creation of controlled cellular environments, engineering of functional tissues and development of better drug delivery systems. In tissue engineering, micro- and nanotechnologies have enabled the recapitulation of the micro- and nanoscale detail of the cell's environment through controlling the surface chemistry and topography of materials, generating 3D cellular scaffolds and regulating cell-cell interactions. Furthermore, these technologies have led to advances in high-throughput screening (HTS), enabling rapid and efficient discovery of a library of materials and screening of drugs that induce cell-specific responses. In drug delivery, controlling the size and geometry of drug carriers with micro- and nanotechnologies have allowed for the modulation of parametres such as bioavailability, pharmacodynamics and cell-specific targeting. In this review, we introduce recent developments in micro- and nanoscale engineering of polymeric biomaterials, with an emphasis on lithographic techniques, and present an overview of their applications in tissue engineering, HTS and drug delivery.

Laser inactivation protein patterning of cell culture microenvironments

Protein micropatterned substrates have emerged as important tools for studying how cells interact with their environment, as well as allowing useful experimental control over, for example, cell shape and cell position on a surface. Here we present a new approach for protein micropatterning in which a focused laser is used to locally inactivate proteins on a protein-coated substrate. By translating the laser relative to the substrate, protein patterns of essentially arbitrary shape can be produced. This approach has a number of useful features. To begin, it is a maskless writing approach. Thus new patterns can be designed and implemented quickly. Laser inactivation can also be performed on a number of different substrate materials, ranging from glass to polydimethylsiloxane. Further, the inactivation is dose dependent, thus complex gradients and other non-uniform distributions of proteins can be produced. Because the focus of the laser can be changed quickly, laser-based patterning can also be applied to substrates with complex topographies or enclosed surfaces--as long as an optical path is available. To demonstrate this capability, protein patterns were made on the inside of small quartz capillary tubes. Patterned substrates produced using laser inactivation constrain cell shape in predictable ways, and we show that these substrates are compatible with a number of different eukaryotic cell lines.

Investigation of the growth of focal adhesions using protein nanoarrays fabricated by nanocontact printing using size tunable polymeric nanopillars

Here we describe a simple approach to create various sizes of protein nanoarrays for the investigation of cell adhesion. Using a combination of nanosphere lithography, oxygen plasma treatment, deep etching and nanomolding processes, well-ordered polymeric nanopillar arrays have been fabricated with diameters in the range of 50-600 nm. These nanopillar arrays were used as stamps for nanocontact printing to create fibronectin nanoarrays, which were used to study the size dependent formation of focal adhesion. It was found that cells can adhere and spread on fibronectin nanoarrays with a fibronectin pattern as small as 50 nm. It was also found that the average size of focal adhesion decreased as the size of the fibronectin pattern was reduced.

Biomimetic nanopatterns as enabling tools for analysis and control of live cells

It is becoming increasingly evident that cell biology research can be considerably advanced through the use of bioengineered tools enabled by nanoscale technologies. Recent advances in nanopatterning techniques pave the way for engineering biomaterial surfaces that control cellular interactions from the nano- to the microscale, allowing more precise quantitative experimentation capturing multi-scale aspects of complex tissue physiology in vitro. The spatially and temporally controlled display of extracellular signaling cues on nanopatterned surfaces (e. g., cues in the form of chemical ligands, controlled stiffness, texture, etc.) that can now be achieved on biologically relevant length scales is particularly attractive enabling experimental platform for investigating fundamental mechanisms of adhesion-mediated cell signaling. Here, we present an overview of bio-nanopatterning methods, with the particular focus on the recent advances on the use of nanofabrication techniques as enabling tools for studying the effects of cell adhesion and signaling on cell function. We also highlight the impact of nanoscale engineering in controlling cell-material interfaces, which can have profound implications for future development of tissue engineering and regenerative medicine.

Modulation of cell adhesion complexes by surface protein patterns

Cell adhesion is an important process in several biological phenomena. To investigate the formation and organization of focal adhesions, we developed a patterning approach based on electron beam lithography. Nanodots (radius <1230 nm) and nanorings (inner radius <320 nm) of fibronectin (FN) were patterned on a K-Casein background. Intracellular vinculin immunofluorescence mirrored the FN nanopatterns. Atomic force microscopy showed that FN nanodots and nanorings organize the immediate cytoskeleton into straight fibrils and diverging fibril bundles, respectively. Our results suggest that a minimum of approximately 40 FN molecules is required for a cell to form a focal adhesion.