Using electroactive substrates to pattern the attachment of two different cell populations

Real-time monitoring of voltage-responsive biomolecular binding onto electro-switchable surfaces

Voltage-responsive biosensors capable of monitoring real-time adsorption behavior of biological analytes onto electroactive surfaces offer attractive strategies for disease detection, separations, and other adsorption-dependent analytical techniques. Adsorption of biological analytes onto electrically switchable surfaces can be modelled using neutravidin and biotin. Here, we report self-assembled monolayers formed from voltage-switchable biotinylated molecules on gold surfaces with tunable sensitivity to neutravidin in response to applied voltages. By using electrochemical quartz crystal microbalance (EQCM), we demonstrated real-time switchable behavior of these bio-surfaces and investigate the range of sensitivity by varying the potential of the same surfaces from -400 mV to open circuit potential (+155 mV) to +300 mV. We compared the tunability of the mixed surfaces to bare Au surfaces, voltage inert surfaces, and switchable biotinylated surfaces. Our results indicate that quartz crystal microbalance allows real-time changes in analyte binding behavior, which enabled observing the evolution of neutravidin sensitivity as the applied voltage was shifted. EQCM could in principle be used in kinetic studies or to optimize voltage-switchable surfaces in adsorption-based diagnostics.

Microelectrode Arrays, Electrocatalysis, and the Need for Proper Characterization

Indirect electrochemical methods are a powerful tool for synthetic chemistry because they allow for the optimization of chemical selectivity in a reaction while maintaining the advantages of electrochemistry in terms of sustainability. Recently, we have found that such methods provide a handle for not only the synthesis of complex molecules, but also the construction of complex, addressable molecular surfaces. In this effort, the indirect electrochemical methods enable the placement or synthesis of molecules by any electrode or set of electrodes in a microelectrode array. The success of these surface-based reactions are typically evaluated with the use of fluorescence labelling studies. However, these fluorescence-based evaluations can be misleading. While they are excellent for determining that a reaction has occurred in a site-selective fashion on an array, they do not provide information on whether that reaction is the one desired or how well it worked. We describe here how the use of a "safety-catch" linker strategy allows for a more accurate assessment of reaction quality on an array, and then use that capability to illustrate how the use of transition metal mediated cross-coupling reactions on an array prevent unwanted background reactions that can occur on a polymer-coated electrode surface. The method enables a unique level of quality control for array-based transformations.

Machine learning-enabled constrained multi-objective design of architected materials

Architected materials that consist of multiple subelements arranged in particular orders can demonstrate a much broader range of properties than their constituent materials. However, the rational design of these materials generally relies on experts' prior knowledge and requires painstaking effort. Here, we present a data-efficient method for the high-dimensional multi-property optimization of 3D-printed architected materials utilizing a machine learning (ML) cycle consisting of the finite element method (FEM) and 3D neural networks. Specifically, we apply our method to orthopedic implant design. Compared to uniform designs, our experience-free method designs microscale heterogeneous architectures with a biocompatible elastic modulus and higher strength. Furthermore, inspired by the knowledge learned from the neural networks, we develop machine-human synergy, adapting the ML-designed architecture to fix a macroscale, irregularly shaped animal bone defect. Such adaptation exhibits 20% higher experimental load-bearing capacity than the uniform design. Thus, our method provides a data-efficient paradigm for the fast and intelligent design of architected materials with tailored mechanical, physical, and chemical properties.

Photoaffinity labeling and bioorthogonal ligation: Two critical tools for designing "Fish Hooks" to scout for target proteins

Small molecules remain an important category of therapeutic agents. Their binding to different proteins can lead to both desired and undesired biological effects. Identification of the proteins that a drug binds to has become an important step in drug development because it can lead to safer and more effective drugs. Parent bioactive molecules can be converted to appropriate probes that allow for visualization and identification of their target proteins. Typically, these probes are designed and synthesized utilizing some or all of five major tools; a photoactivatable group, a reporter tag, a linker, an affinity tag, and a bioorthogonal handle. This review covers two of the most challenging tools, photoactivation and bioorthogonal ligation. We provide a historical and theoretical background along with synthetic routes to prepare them. In addition, the review provides comparative analyses of the available tools that can assist decision making when designing such probes. A survey of most recent literature reports is included as well to identify recent trends in the field.

Recent Advances in Additive Manufacturing and 3D Bioprinting for Organs-On-A-Chip and Microphysiological Systems

The re-creation of physiological cellular microenvironments that truly resemble complex in vivo architectures is the key aspect in the development of advanced in vitro organotypic tissue constructs. Among others, organ-on-a-chip technology has been increasingly used in recent years to create improved models for organs and tissues in human health and disease, because of its ability to provide spatio-temporal control over soluble cues, biophysical signals and biomechanical forces necessary to maintain proper organotypic functions. While media supply and waste removal are controlled by microfluidic channel by a network the formation of tissue-like architectures in designated micro-structured hydrogel compartments is commonly achieved by cellular self-assembly and intrinsic biological reorganization mechanisms. The recent combination of organ-on-a-chip technology with three-dimensional (3D) bioprinting and additive manufacturing techniques allows for an unprecedented control over tissue structures with the ability to also generate anisotropic constructs as often seen in in vivo tissue architectures. This review highlights progress made in bioprinting applications for organ-on-a-chip technology, and discusses synergies and limitations between organ-on-a-chip technology and 3D bioprinting in the creation of next generation biomimetic in vitro tissue models.

Glycoprotein- and Lectin-Based Approaches for Detection of Pathogens

Infectious diseases alone are estimated to result in approximately 40% of the 50 million total annual deaths globally. The importance of basic research in the control of emerging and re-emerging diseases cannot be overemphasized. However, new nanotechnology-based methodologies exploiting unique surface-located glycoproteins or their patterns can be exploited to detect pathogens at the point of use or on-site with high specificity and sensitivity. These technologies will, therefore, affect our ability in the future to more accurately assess risk. The critical challenge is making these new methodologies cost-effective, as well as simple to use, for the diagnostics industry and public healthcare providers. Miniaturization of biochemical assays in lab-on-a-chip devices has emerged as a promising tool. Miniaturization has the potential to shape modern biotechnology and how point-of-care testing of infectious diseases will be performed by developing smart microdevices that require minute amounts of sample and reagents and are cost-effective, robust, and sensitive and specific. The current review provides a short overview of some of the futuristic approaches using simple molecular interactions between glycoproteins and glycoprotein-binding molecules for the efficient and rapid detection of various pathogens at the point of use, advancing the emerging field of glyconanodiagnostics.

Spatiotemporally Controlled Photoresponsive Hydrogels: Design and Predictive Modeling from Processing through Application

Photoresponsive hydrogels (PRHs) are soft materials whose mechanical and chemical properties can be tuned spatially and temporally with relative ease. Both photo-crosslinkable and photodegradable hydrogels find utility in a range of biomedical applications that require tissue-like properties or programmable responses. Progress in engineering with PRHs is facilitated by the development of theoretical tools that enable optimization of their photochemistry, polymer matrices, nanofillers, and architecture. This review brings together models and design principles that enable key applications of PRHs in tissue engineering, drug delivery, and soft robotics, and highlights ongoing challenges in both modeling and application.

Surface Modification with Control over Ligand Density for the Study of Multivalent Biological Systems

In the study of multivalent interactions at interfaces, as occur for example at cell membranes, the density of the ligands or receptors displayed at the interface plays a pivotal role, affecting both the overall binding affinities and the valencies involved in the interactions. In order to control the ligand density at the interface, several approaches have been developed, and they concern the functionalization of a wide range of materials. Here, different methods employed in the modification of surfaces with controlled densities of ligands are being reviewed. Examples of such methods encompass the formation of self-assembled monolayers (SAMs), supported lipid bilayers (SLBs) and polymeric layers on surfaces. Particular emphasis is given to the methods employed in the study of different types of multivalent biological interactions occurring at the functionalized surfaces and their working principles.

Micropatterned hydrogels and cell alignment enhance the odontogenic potential of stem cells from apical papilla in-vitro

INTRODUCTION

An understanding of the extracellular matrix characteristics which stimulate and guide stem cell differentiation in the dental pulp is fundamental for the development of enhanced dental regenerative therapies. Our objectives, in this study, were to determine whether stem cells from the apical papilla (SCAP) responded to substrate stiffness, whether hydrogels providing micropatterned topographical cues stimulate SCAP self-alignment, and whether the resulting alignment could influence their differentiation towards an odontogenic lineage in-vitro.

METHODS

Experiments utilized gelatin methacryloyl (GelMA) hydrogels of increasing concentrations (5, 10 and 15%). We determined their compressive modulus via unconfined compression and analyzed cell spreading via F-actin/DAPI immunostaining. GelMA hydrogels were micropatterned using photolithography, in order to generate microgrooves and ridges of 60 and 120μm, onto which SCAP were seeded and analyzed for self-alignment via fluorescence microscopy. Lastly, we analyzed the odontogenic differentiation of SCAP using alkaline phosphatase protein expression (ANOVA/Tukey α=0.05).

RESULTS

SCAP appeared to proliferate better on stiffer hydrogels. Both 60 and 120μm micropatterned hydrogels guided the self-alignment of SCAP with no significant difference between them. Similarly, both 60 and 120μm micropattern aligned cells promoted higher odontogenic differentiation than non-patterned controls.

SIGNIFICANCE

In summary, both substrate mechanics and geometry have a statistically significant influence on SCAP response, and may assist in the odontogenic differentiation of dental stem cells. These results may point toward the fabrication of cell-guiding scaffolds for regenerative endodontics, and may provide cues regarding the development of the pulp-dentin interface during tooth formation.

Generating Multiscale Gold Nanostructures on Glass without Sidewall Deposits Using Minimal Dry Etching Steps

The advent of recent technologies in the nanoscience arena requires new and improved methods for the fabrication of multiscale features ( e.g., from micro- to nanometer scales). Specifically, biological applications generally demand the use of transparent substrates to allow for the optical monitoring of processes of interest in cells and other biological materials. Whereas wet etching methods commonly fail to produce essential nanometer scale features, plasma-based dry etching can produce features down to tens of nanometers. However, dry etching methods routinely require extreme conditions and extra steps to obtain features without residual materials such as sidewall deposits (veils). This work presents the development of a gold etching process with gases that are commonly used to etch glass. Our method can etch gold films using reactive ion etching (RIE) at room temperature and mild pressure in a trifluoromethane (CHF₃)/oxygen (O₂) environment, producing features down to 50 nm. Aspect ratios of 2 are obtainable in one single step and without sidewall veils by controlling the oxygen present during the RIE process. This method generates surfaces completely flat and ready for the deposition of other materials. The gold features that were produced by this method exhibited high conductivity when carbon nanotubes were deposited on top of patterned features (gold nanoelectrodes), hence demonstrating an electrically functional gold after the dry etching process. The production of gold nanofeatures on glass substrates would serve as biocompatible, highly conductive, and chemically stable materials in biological/biomedical applications.

Biomimetic Dextran-Based Hydrogel Layers for Cell Micropatterning over Large Areas Using the FluidFM BOT Technology

Micropatterning of living single cells and cell clusters over millimeter-centimeter scale areas is of high demand in the development of cell-based biosensors. Micropatterning methodologies require both a suitable biomimetic support and a printing technology. In this work, we present the micropatterning of living mammalian cells on carboxymethyl dextran (CMD) hydrogel layers using the FluidFM BOT technology. In contrast to the ultrathin (few nanometers thick in the dry state) CMD films generally used in label-free biosensor applications, we developed CMD layers with thicknesses of several tens of nanometers in order to provide support for the controlled adhesion of living cells. The fabrication method and detailed characterization of the CMD layers are also described. The antifouling ability of the CMD surfaces is demonstrated by in situ optical waveguide lightmode spectroscopy measurements using serum modeling proteins with different electrostatic properties and molecular weights. Cell micropatterning on the CMD surface was obtained by printing cell adhesion mediating cRGDfK peptide molecules (cyclo(Arg-Gly-Asp-d-Phe-Lys)) directly from aqueous solution using microchanneled cantilevers with subsequent incubation of the printed surfaces in the living cell culture. Uniquely, we present cell patterns with different geometries (spot, line, and grid arrays) covering both micrometer and millimeter-centimeter scale areas. The adhered patterns were analyzed by phase contrast microscopy and the adhesion process on the patterns was real-time monitored by digital holographic microscopy, enabling to quantify the survival and migration of cells on the printed cRGDfK arrays.

Transistors for Chemical Monitoring of Living Cells

We review here the chemical sensors for pH, glucose, lactate, and neurotransmitters, such as acetylcholine or glutamate, made of organic thin-film transistors (OTFTs), including organic electrochemical transistors (OECTs) and electrolyte-gated OFETs (EGOFETs), for the monitoring of cell activity. First, the various chemicals that are produced by living cells and are susceptible to be sensed in-situ in a cell culture medium are reviewed. Then, we discuss the various materials used to make the substrate onto which cells can be grown, as well as the materials used for making the transistors. The main part of this review discusses the up-to-date transistor architectures that have been described for cell monitoring to date.

A Perspective on Bio-Mediated Material Structuring

Bioinspiration, biomorphy, biomimicry, biomimetics, bionics, and biotemplating are terms used to describe the fabrication of materials or, more generally, systems to solve technological problems by abstracting, emulating, using, or transferring structures from biological paradigms. Herein, a brief overview of how the different terminologies are being typically applied is provided. It is proposed that there is a rich field of research that can be expanded by utilizing various novel approaches for the guidance of living organisms for "bio-mediated" material structuring purposes. As examples of contact-based or contact-free guidance, such as substrate patterning, the application of light, magnetic fields, or chemical gradients, potentially interesting methods of creating hierarchically structured monolithic engineering materials, using live patterned biomass, biofilms, or extracellular substances as scaffolds, are presented. The potential advantages of such materials are discussed, and examples of live self-patterning of materials are given.

Manipulating cell fate: dynamic control of cell behaviors on functional platforms

We review the recent advances and new horizons in the dynamic control of cell behaviors on functional platforms and their applications.

A microfabricated 96-well wound-healing assay

This article presents a microfabricated 96-well wound-healing assay enabling high-throughput measurement of cellular migration capabilities. Within each well, the middle area is the wound region, made of microfabricated gold surface with self-assembled PEG repellent for cell seeding. After the formation of a cellular confluent monolayer around the wound region, collagen solution was applied to form three-dimensional matrix to cover the PEG surface, initiating the wound-healing process. By interpreting the numbers of migrated cells into the wound regions as a function of specific stimuli with different concentrations, EC50 (half-maximal effective concentration) was obtained. Using H1299 as a model, values of EC50 were quantified as 8% and 160 ng/ml for fetal bovine serum and CXCL12, respectively. In addition, the values of EC50 were demonstrated not to be affected by variations in compositions of extracellular matrix and geometries of wounds, which can thus be regarded as an intrinsic marker. Furthermore, the migration capabilities of a second cell type (HeLa) were characterized by the developed wound-healing assay, producing EC50 of 2% when fetal bovine serum was used as the stimuli. These results validated the proposed high-throughput wound-healing assay, which may function as an enabling tool in studying cellular capabilities of migration and invasion. © 2017 International Society for Advancement of Cytometry.

Collective cell migration: a physics perspective

Cells have traditionally been viewed either as independently moving entities or as somewhat static parts of tissues. However, it is now clear that in many cases, multiple cells coordinate their motions and move as collective entities. Well-studied examples comprise development events, as well as physiological and pathological situations. Different ex vivo model systems have also been investigated. Several recent advances have taken place at the interface between biology and physics, and have benefitted from progress in imaging and microscopy, from the use of microfabrication techniques, as well as from the introduction of quantitative tools and models. We review these interesting developments in quantitative cell biology that also provide rich examples of collective out-of-equilibrium motion.

Cell Microarray Technologies for High-Throughput Cell-Based Biosensors

Due to the recent demand for high-throughput cellular assays, a lot of efforts have been made on miniaturization of cell-based biosensors by preparing cell microarrays. Various microfabrication technologies have been used to generate cell microarrays, where cells of different phenotypes are immobilized either on a flat substrate (positional array) or on particles (solution or suspension array) to achieve multiplexed and high-throughput cell-based biosensing. After introducing the fabrication methods for preparation of the positional and suspension cell microarrays, this review discusses the applications of the cell microarray including toxicology, drug discovery and detection of toxic agents.

Microstructural and surface modifications and hydroxyapatite coating of Ti-6Al-4V triply periodic minimal surface lattices fabricated by selective laser melting

Ti-6Al-4V Gyroid triply periodic minimal surface (TPMS) lattices were manufactured by selective laser melting (SLM). The as-built Ti-6Al-4V lattices exhibit an out-of-equilibrium microstructure with very fine α' martensitic laths. When subjected to the heat treatment of 1050°C for 4h followed by furnace cooling, the lattices show a homogenous and equilibrium lamellar α+β microstructure with less dislocation and crystallographic defects compared with the as-built α' martensite. The as-built lattices present very rough strut surfaces bonded with plenty of partially melted metal particles. The sand blasting nearly removed all the bonded metal particles, but created many tiny cracks. The HCl etching eliminated these tiny cracks, and subsequent NaOH etching resulted in many small and shallow micro-pits and develops a sodium titanate hydrogel layer on the surfaces of the lattices. When soaked in simulated body fluid (SBF), the Ti-6Al-4V TPMS lattices were covered with a compact and homogeneous biomimetic hydroxyapatite (HA) layer. This work proposes a new method for making Ti-6Al-4V TPMS lattices with a homogenous and equilibrium microstructure and biomimetic HA coating, which show both tough and bioactive characteristics and can be promising materials usable as bone substitutes.

Dynamically Tunable Cell Culture Platforms for Tissue Engineering and Mechanobiology

Human tissues are sophisticated ensembles of many distinct cell types embedded in the complex, but well-defined, structures of the extracellular matrix (ECM). Dynamic biochemical, physicochemical, and mechano-structural changes in the ECM define and regulate tissue-specific cell behaviors. To recapitulate this complex environment in vitro, dynamic polymer-based biomaterials have emerged as powerful tools to probe and direct active changes in cell function. The rapid evolution of polymerization chemistries, structural modulation, and processing technologies, as well as the incorporation of stimuli-responsiveness, now permit synthetic microenvironments to capture much of the dynamic complexity of native tissue. These platforms are comprised not only of natural polymers chemically and molecularly similar to ECM, but those fully synthetic in origin. Here, we review recent in vitro efforts to mimic the dynamic microenvironment comprising native tissue ECM from the viewpoint of material design. We also discuss how these dynamic polymer-based biomaterials are being used in fundamental cell mechanobiology studies, as well as towards efforts in tissue engineering and regenerative medicine.

Fibronectin in Layer-by-Layer Assembled Films Switches Tumor Cells between 2D and 3D Morphology

Tumor cells showing a 3D morphology and in coculture with endothelial cells are a valuable in vitro model for studying cell-cell interactions and for the development of pharmaceuticals. Here, we found that HepG2 cells, unlike endothelial cells, show differences in adhesion to fibronectin alone, or in combination with poly(allylamine hydrochloride). This response allowed us to engineer micropatterned heterotypic cultures of the two cell types using microfluidics to pattern cell adhesion. The resulting cocultures exhibit spatially encoded and physiologically relevant cell function. Further, we found that the protrusive, migratory and 3D morphological responses of HepG2 are synergistically modulated by the constituents of the hybrid extracellular matrix. Treating the hybrid material with the cross-linking enzyme transglutaminase inhibited 3D morphogenesis of tumor cells. Our results extend previous work on the role of fibronectin in layer-by-layer assembled films, and demonstrate that cell-specific differences in adhesion to fibronectin can be used to engineer tumor cell cocultures.

A rapid co-culture stamping device for studying intercellular communication

Regulation of tissue development and repair depends on communication between neighbouring cells. Recent advances in cell micro-contact printing and microfluidics have facilitated the in-vitro study of homotypic and heterotypic cell-cell interaction. Nonetheless, these techniques are still complicated to perform and as a result, are seldom used by biologists. We report here development of a temporarily sealed microfluidic stamping device which utilizes a novel valve design for patterning two adherent cell lines with well-defined interlacing configurations to study cell-cell interactions. We demonstrate post-stamping cell viability of >95%, the stamping of multiple adherent cell types, and the ability to control the seeded cell density. We also show viability, proliferation and migration of cultured cells, enabling analysis of co-culture boundary conditions on cell fate. We also developed an in-vitro model of endothelial and cardiac stem cell interactions, which are thought to regulate coronary repair after myocardial injury. The stamp is fabricated using microfabrication techniques, is operated with a lab pipettor and uses very low reagent volumes of 20 μl with cell injection efficiency of >70%. This easy-to-use device provides a general strategy for micro-patterning of multiple cell types and will be important for studying cell-cell interactions in a multitude of applications.

Electrically Responsive Surfaces: Experimental and Theoretical Investigations

Stimuli-responsive surfaces have sparked considerable interest in recent years, especially in view of their biomimetic nature and widespread biomedical applications. Significant efforts are continuously being directed at developing functional surfaces exhibiting specific property changes triggered by variations in electrical potential, temperature, pH and concentration, irradiation with light, or exposure to a magnetic field. In this respect, electrical stimulus offers several attractive features, including a high level of spatial and temporal controllability, rapid and reverse inducement, and noninvasiveness. In this Account, we discuss how surfaces can be designed and methodologies developed to produce electrically switchable systems, based on research by our groups. We aim to provide fundamental mechanistic and structural features of these dynamic systems, while highlighting their capabilities and potential applications. We begin by briefly describing the current state-of-the-art in integrating electroactive species on surfaces to control the immobilization of diverse biological entities. This premise leads us to portray our electrically switchable surfaces, capable of controlling nonspecific and specific biological interactions by exploiting molecular motions of surface-bound electroswitchable molecules. We demonstrate that our self-assembled monolayer-based electrically switchable surfaces can modulate the interactions of surfaces with proteins, mammalian and bacterial cells. We emphasize how these systems are ubiquitous in both switching biomolecular interactions in highly complex biological conditions while still offering antifouling properties. We also introduce how novel characterization techniques, such as surface sensitive vibrational sum-frequency generation (SFG) spectroscopy, can be used for probing the electrically switchable molecular surfaces in situ. SFG spectroscopy is a technique that not only allowed determining the structural orientation of the surface-tethered molecules under electroinduced switching, but also provided an in-depth characterization of the system reversibility. Furthermore, the unique support from molecular dynamics (MD) simulations is highlighted. MD simulations with polarizable force fields (FFs), which could give proper description of the charge polarization caused by electrical stimulus, have helped not only back many of the experimental observations, but also to rationalize the mechanism of switching behavior. More importantly, this polarizable FF-based approach can efficiently be extended to light or pH stimulated surfaces when integrated with reactive FF methods. The interplay between experimental and theoretical studies has led to a higher level of understanding of the switchable surfaces, and to a more precise interpretation and rationalization of the observed data. The perspectives on the challenges and opportunities for future progress on stimuli-responsive surfaces are also presented.

Introduction to Microelectrode Arrays, the Site-Selective Functionalization of Electrode Surfaces, and the Real-Time Detection of Binding Events

Microelectrode arrays have great potential as analytical tools because currents can be independently measured at each electrode in the array. In principle, these currents can be monitored in order to follow in real time the binding events that occur between the members of a molecular library and a biological target. To capitalize on this potential, the surface of the array must be selectively functionalized so that each unique member of the molecular library is associated with a unique individually addressable electrode or set of electrodes in the array. To this end, this instructional review summarizes methods for coating the arrays with porous polymers that allow for the attachment of molecules to the surface of the array, selectively conducting reactions at individual electrodes in the array, characterizing molecules that are placed on the arrays, and running the analytical experiments needed to monitor in real time binding events between molecules on the array and a biological target.

Facile preparation of a photoactivatable surface on a 96-well plate: a versatile and multiplex cell migration assay platform

A novel photoactivatable 96-well plate based on photocleavable PEG and poly-d-lysine serves as a useful high-throughput cell migration assay platform.

Dynamic stiffness of polyelectrolyte multilayer films based on disulfide bonds for in situ control of cell adhesion

Dynamic stiffness of (poly-l-lysine/hyaluronan-SH) films was developed for in situ control of cell adhesion by using reversible disulfide linkages.

Electrically-driven modulation of surface-grafted RGD peptides for manipulation of cell adhesion

Reported herein is a switchable surface that relies on electrically-induced conformational changes within surface-grafted arginine–glycine–aspartate (RGD) oligopeptides as the means of modulating cell adhesion.

Reported herein is a switchable surface that relies on electrically-induced conformational changes within surface-grafted arginine–glycine–aspartate (RGD) oligopeptides as the means of modulating cell adhesion.

In situ modification of cell-culture scaffolds by photocatalytic decomposition of organosilane monolayers

We demonstrate a novel application of TiO2 photocatalysis for modifying the cell affinity of a scaffold surface in a cell-culture environment. An as-deposited octadecyltrichlorosilane self-assembled monolayer (OTS SAM) on TiO2 was found to be hydrophobic and stably adsorbed serum albumins that blocked subsequent adsorption of other proteins and cells. Upon irradiation of ultraviolet (UV) light, OTS molecules were decomposed and became permissive to the adhesion of PC12 cells via adsorption of an extracellular matrix protein, collagen. Optimal UV dose was 200 J cm(-2) for OTS SAM on TiO2. The amount of collagen adsorption decreased when excessive UV light was irradiated, most likely due to the surface being too hydrophilic to support its adsorption. This UV-induced modification required TiO2 to be present under the SAM and hence is a result of TiO2 photocatalysis. The UV irradiation for surface modification can be performed before cell plating or during cell culture. We also demonstrate that poly(ethylene glycol) SAM can also be patterned with this method, indicating that it is applicable to both hydrophobic and hydrophilic SAMs. This method provides a unique tool for fabricating cell microarrays and studying dynamical properties of living cells.

Cell patterning with a heptagon acoustic tweezer--application in neurite guidance

Accurate control over positioning of cells is a highly desirable feature in tissue engineering applications since it allows, for example, population of substrates in a controlled fashion, rather than relying on random seeding. Current methods to achieve a differential distribution of cells mostly use passive patterning methods to change chemical, mechanical or topographic properties of surfaces, making areas differentially permissive to the adhesion of cells. However, these methods have no ad hoc control over the actual deposition of cells. Direct patterning methods like bioprinting offer good control over cell position, but require sophisticated instrumentation and are often cost- and time-intensive. Here, we present a novel electronically controlled method of generating dynamic cell patterns by acoustic trapping of cells at a user-determined position, with a heptagonal acoustic tweezer device. We demonstrate the capability of the device to create complex patterns of cells using the device's ability to re-position acoustic traps by using a phase shift in the acoustic wave, and by switching the configuration of active piezoelectric transducers. Furthermore, we show that by arranging Schwann cells from neonatal rats in a linear pattern we are able to create Bands of Büngner-like structures on a non-structured surface and demonstrate that these features are able to guide neurite outgrowth from neonatal rat dorsal root ganglia.

Integrated micro/nanoengineered functional biomaterials for cell mechanics and mechanobiology: a materials perspective

The rapid development of micro/nanoengineered functional biomaterials in the last two decades has empowered materials scientists and bioengineers to precisely control different aspects of the in vitro cell microenvironment. Following a philosophy of reductionism, many studies using synthetic functional biomaterials have revealed instructive roles of individual extracellular biophysical and biochemical cues in regulating cellular behaviors. Development of integrated micro/nanoengineered functional biomaterials to study complex and emergent biological phenomena has also thrived rapidly in recent years, revealing adaptive and integrated cellular behaviors closely relevant to human physiological and pathological conditions. Working at the interface between materials science and engineering, biology, and medicine, we are now at the beginning of a great exploration using micro/nanoengineered functional biomaterials for both fundamental biology study and clinical and biomedical applications such as regenerative medicine and drug screening. In this review, an overview of state of the art micro/nanoengineered functional biomaterials that can control precisely individual aspects of cell-microenvironment interactions is presented and they are highlighted them as well-controlled platforms for mechanistic studies of mechano-sensitive and -responsive cellular behaviors and integrative biology research. The recent exciting trend where micro/nanoengineered biomaterials are integrated into miniaturized biological and biomimetic systems for dynamic multiparametric microenvironmental control of emergent and integrated cellular behaviors is also discussed. The impact of integrated micro/nanoengineered functional biomaterials for future in vitro studies of regenerative medicine, cell biology, as well as human development and disease models are discussed.

Micropatterned multicolor dynamically adhesive substrates to control cell adhesion and multicellular organization

We present a novel technique to examine cell-cell interactions and directed cell migration using micropatterned substrates of three distinct regions: an adhesive region, a nonadhesive region, and a dynamically adhesive region switched by addition of a soluble factor to the medium. Combining microcontact printing with avidin-biotin capture chemistry, we pattern nonadhesive regions of avidin that become adhesive through the capture of biotinylated fibronectin. Our strategy overcomes several limitations of current two-color dynamically adhesive substrates by incorporating a third, permanently nonadhesive region. Having three spatially and functionally distinct regions allows for the realization of more complex configurations of cellular cocultures as well as intricate interface geometries between two cell populations for diverse heterotypic cell-cell interaction studies. We can now achieve spatial control over the path and direction of migration in addition to temporal control of the onset of migration, enabling studies that better recapitulate coordinated multicellular migration and organization in vitro. We confirm that cellular behavior is unaltered on captured biotinylated fibronectin as compared to printed fibronectin by examining the cells' ability to spread, form adhesions, and migrate. We demonstrate the versatility of this approach in studies of migration and cellular cocultures, and further highlight its utility by probing Notch-Delta juxtacrine signaling at a patterned interface.

Dynamic photochemical lipid micropatterning for manipulation of nonadherent mammalian cells

Cell micropatterning methods with stimuli-responsive dynamic surfaces are getting a lot of attention in a wide variety of research fields, ranging from cell engineering to fundamental studies in cell biology. The surface of a slide coated with photo-cleavable poly(ethylene glycol) (PEG)-lipid can be used to spatiotemporally control cell immobilization and release by light irradiation. On the basis of this surface, it is easy to design simple methods for making a fine micropattern of any kind of cell. Furthermore, target cells can be selectively and rapidly released from this surface by light irradiation. In this review, we first describe how to obtain the photo-cleavable PEG-lipid from commercially available compounds through a facile four-step synthesis. Next, as a cell-patterning method, the protocols of coating substrates with the PEG-lipid, irradiating a pattern of light onto the coated substrate, and loading cells onto the irradiated surface are described. These protocols require no expensive equipment and potentially apply to any substrates that can adsorb serum albumin or chemically expose amine moieties on their surfaces. Finally, as an advanced method, cell release from the PEG-lipid surface in microfluidic devices is introduced. We also discuss the advantages and the possible applications of the present dynamic cell-patterning method.

Switchable substrates for analyzing and engineering cellular functions

Cellular activity is highly dependent on the extracellular environment, which is composed of surrounding cells and extracellular matrices. This focus review summarizes recent advances in chemically and physically engineered switchable substrates designed to control such cellular microenvironments by application of an external stimulus. Special attention is given to their molecular design, switching strategies, and representative examples for bioanalytical and biomedical applications.

A review of microfabrication and hydrogel engineering for micro-organs on chips

This review highlights recent trends towards the development of in vitro multicellular systems with definite architectures, or "organs on chips". First, the chemical composition and mechanical properties of the scaffold have to be consistent with the anatomical environment in vivo. In this perspective, the flourishing interest in hydrogels as cellular substrates has highlighted the main parameters directing cell differentiation that need to be recapitulated in artificial matrix. Another scaffold requirement is to act as a template to guide tissue morphogenesis. Therefore specific microfabrication techniques are required to spatially pattern the environment at microscale. 2D patterning is particularly efficient for organizing planar polarized cell types such as endothelial cells or neurons. However, most organs are characterized by specific sub units organized in three dimensions at the cellular level. The reproduction of such 3D patterns in vitro is necessary for cells to fully differentiate, assemble and coordinate to form a coherent micro-tissue. These physiological microstructures are often integrated in microfluidic devices whose controlled environments provide the cell culture with more life-like conditions than traditional cell culture methods. Such systems have a wide range of applications, for fundamental research, as tools to accelerate drug development and testing, and finally, for regenerative medicine.