Biocompatible Micropatterning of Two Different Cell Types

Micro-patterned cell populations as advanced pharmaceutical drugs with precise functional control

Human cells are both advanced pharmaceutical drugs and 'drug deliverers'. However, functional control prior to or after cell implantation remains challenging. Micro-patterning cells through geometrically defined adhesion sites allows controlling morphogenesis, polarity, cellular mechanics, proliferation, migration, differentiation, stemness, cell-cell interactions, collective cell behavior, and likely immuno-modulatory properties. Consequently, generating micro-patterned therapeutic cells is a promising idea that has not yet been realized and few if any steps have been undertaken in this direction. This review highlights potential therapeutic applications, summarizes comprehensively the many cell functions that have been successfully controlled through micro-patterning, details the established micro-pattern designs, introduces the available fabrication technologies to the non-specialized reader, and suggests a quality evaluation score. Such a broad review is not yet available but would facilitate the manufacturing of therapeutically patterned cell populations using micro-patterned cell-instructive biomaterials for improved functional control as drug delivery systems in the context of cells as pharmaceutical products.

Gravitational sedimentation-based approach for ultra-simple and flexible cell patterning coculture on microfluidic device

Combining patterning coculture technique with microfluidics enables the reconstruction of complex in-vivo system to facilitate in-vitro studies on cell-cell and cell-environment interactions. However, simple and versatile approaches for patterning coculture of cells on microfluidic platforms remain lacking. In this study, a novel gravitational sedimentation-based approach is presented to achieve ultra-simple and flexible cell patterning coculture on a microfluidic platform, where multiple cell types can be patterned simultaneously to form a well-organized cell coculture. In contrast to other approaches, the proposed approach allows the rapid patterning of multiple cell types in microfluidic channels without the use of sheath flow and a prepatterned functional surface. This feature greatly simplifies the experimental setup, operation, and chip fabrication. Moreover, cell patterning can be adjusted by simply modifying the cell-loading tubing direction, thereby enabling great flexibility for the construction of different cell patterns without complicating the chip design and flow control. A series of physical and biological experiments are conducted to validate the proposed approach. This research paves a new way for building physiologically realistic in-vitro coculture models on microfluidic platforms for various applications, such as cell-cell interaction and drug screening.

Engineering an aligned endothelial monolayer on a topologically modified nanofibrous platform with a micropatterned structure produced by femtosecond laser ablation

Laser ablated nanofibers with micropattern regulated adhesion and orientation of HUVEC and also contributed to generate an aligned endothelial monolayer.

A novel chitosan hydrogel membrane by an improved electrophoretic deposition and its characteristics in vitro and in vivo

Here, we report a novel chitosan hydrogel membrane (CHM) created by an improved electrophoretic deposition. Unlike a traditional CHM by electrophoretic deposition, the CHM was formed on a nanoporous film as a barrier using a homemade device at a high DC voltage (60 V_DC). The CHM maximum recovery of 81.7% could be achieved after 1h of electrophoretic deposition. The transparent CHM with an elongation of 42.46% and swelling index of 538.86% was a mixture of type I and type II crystal structures. SEM revealed that the CHM had an irregular net structure. The CHM was sufficient for L-929 mouse fibroblast cell adhesion and growth. To demonstrate immunocompatibility with host tissues, H&E and TGF-β₁ were observed and the expressions of TNF-α and NF-κB were measured up to 3weeks post-implantation. Although these scaffolds demonstrated an initial pro-inflammatory response, the amount of inflammatory cells and the expressions of TGF-β₁ returned to baseline control values at 3weeks. The expressions of TNF-α and NF-κB had no significant difference between the experimental and control groups. Animal experiments showed that the CHM did not incite serious inflammatory reactions. Thus, the CHM is a promising medical biomaterial candidate for loading appropriate cells for use as artificial skin or in transplantation.

Hierarchical Patterning of Cells with a Microeraser and Electrospun Nanofibers

For tissue engineering applications, it is important to develop fabrication strategies for building models with controlled cell distributions in defined structures. Here, a simple, flexible approach (named the μ-eraser strategy) is developed to construct multicell micropatterns. This approach involves pressing a poly(dimethylsiloxane) stamp to erase cells growing on substrates, and seeding other types of cells. The pressing/seeding process can be conducted in any designed pattern at desired time point. In a proof of concept, multicell micropatterns of human lung adenocarcinoma epithelial A549 cells, murine fibroblast (FB) cells and murine osteoblast (OB) cells are achieved on Petri dishes and electrospun sheets. Besides forming multicell micropatterns, the cell orientation can be regulated by microstripes and alignment of nanofibers. On Petri dishes and random fiber sheets, FB and OB cells align along microstripes, while A549 cells do not. However, when growing on aligned fiber sheets, no matter whether solo-cultured or co-cultured, all cells in micropatterns orient along the fibers. Based on this technique, a platform is built up to investigate rates of cell migration and interinvasion under solo-culture and co-culture systems. It is believed that this μ-eraser strategy has promise for biological, pharmaceutical, and biomedical applications.

Engineering Dynamic Biointerfaces

Recent advances in dynamic biointerfaces enable spatiotemporal control over cell position and migration after attachment using substrates that employ chemical, optical, thermal, or electrical triggers. This review focuses on flexible and accessible methods for the fabrication of cellular arrays or co cultures for fundamental studies of cell biology or regenerative medicine.

Breast Cancer/Stromal Cells Coculture on Polyelectrolyte Films Emulates Tumor Stages and miRNA Profiles of Clinical Samples

In this study, we demonstrate a method for controlling breast cancer cells adhesion on polyelectrolyte multilayer (PEM) films without the aid of adhesive proteins/ligands to study the role of tumor and stromal cell interaction on cancer biology. Numerous studies have explored engineering coculture of tumor and stromal cells predominantly using transwell coculture of stromal cells cultured onto coverslips that were subsequently added to tumor cell cultures. However, these systems imposed an artificial boundary that precluded cell-cell interactions. To our knowledge, this is the first demonstration of patterned coculture of tumor cells and stromal cells that captures the temporal changes in the miRNA signature as the breast tumor develops through various stages. In our study we used synthetic polymers, namely poly(diallyldimethylammonium chloride) (PDAC) and sulfonated poly(styrene) (SPS), as the polycation and polyanion, respectively, to build PEMs. Breast cancer cells attached and spread preferentially on SPS surfaces while stromal cells attached to both SPS and PDAC surfaces. SPS patterns were formed on PEM surfaces, by either capillary force lithography (CFL) of SPS onto PDAC surfaces or vice versa, to obtain patterns of breast cancer cells and patterned cocultures of breast cancer and stromal cells. In this study, we utilized cancer cells derived from two different tumor stages and two different stromal cells to effectively model a heterogeneous tumor microenvironment and emulate various tumor stages. The coculture model mimics the proliferative index (Ki67 expression) and tumor aggressiveness (HER-2 expression) akin to those observed in clinical tumor samples. We also demonstrated that our patterned coculture model captures the temporal changes in the miRNA-21 and miRNA-34 signature as the breast tumor develops through various stages. The engineered coculture platform lays groundwork toward precision medicine wherein patient-derived tumor cells can be incorporated within our in vitro models to identify potential pathways and drug treatment regimens for individual patients.

Biomaterials in co-culture systems: towards optimizing tissue integration and cell signaling within scaffolds

Most natural tissues consist of multi-cellular systems made up of two or more cell types. However, some of these tissues may not regenerate themselves following tissue injury or disease without some form of intervention, such as from the use of tissue engineered constructs. Recent studies have increasingly used co-cultures in tissue engineering applications as these systems better model the natural tissues, both physically and biologically. This review aims to identify the challenges of using co-culture systems and to highlight different approaches with respect to the use of biomaterials in the use of such systems. The application of co-culture systems to stimulate a desired biological response and examples of studies within particular tissue engineering disciplines are summarized. A description of different analytical co-culture systems is also discussed and the role of biomaterials in the future of co-culture research are elaborated on. Understanding the complex cell-cell and cell-biomaterial interactions involved in co-culture systems will ultimately lead the field towards biomaterial concepts and designs with specific biochemical, electrical, and mechanical characteristics that are tailored towards the needs of distinct co-culture systems.

Development of micropatterned cell-sensing surfaces

Microfabricated surfaces have been widely utilized for defining adhesion of single cells or groups of cells of various kinds. Beyond simple control of cell attachment, it is often important to monitor the molecules released by cells. Co-immobilizing miniature sensors alongside cells enables more sensitive detection of secreted factors and may allow for such detection to happen within the context of local microenvironment. Methods for interfacing cells and sensors are central to the notion of local in situ detection of cell function. This chapter describes the use of hydrogel photolithography for integrating cells and sensing elements on culture surfaces. Two types of micropatterned sensing surfaces are described: (1) arrays of microwells for single cell capture that contain antibodies against secreted proteins and (2) entrapment of enzymes inside hydrogel microstructures for local detection of cell metabolism. In both cases, poly(ethylene glycol) hydrogel lithography was employed to control cell attachment, in the second approach hydrogel structures also carried enzymes and functioned as sensors. The development of robust cell/sensor interfaces has implications for diagnostics, tissue engineering, and drug screening.

Rapid Prototyping of Heterotypic Cell-Cell Contacts

Disparities in cellular behaviour between cultures of a single cell type and heterogeneous co-cultures require constructing spatially-defined arrays of multiple cell types. Such arrays are critical for investigating cellular properties as they exist in vivo. Current methods rely upon covalent surface modification or external physical micromanipulation to control cellular organization on a limited range of substrates. Here, we report a direct approach for creating co-cultures of different cell types by microcontact printing a photosensitive cell resist. The cell-resistant polymer converts to cell adhesive 0 with light exposure, thus the initial copolymer pattern dictates the position of both cell types. This strategy enables straightforward preparation of tailored heterotypic cell-cell contacts on materials ranging from polymers to metallic substrates.

Geometric control of cell migration

Morphological polarization involving changes in cell shape and redistribution of cellular signaling machinery, initiate the migration of mammalian cells. Golgi complex typically localizes in front of the nucleus, and this frontwards polarization has been proposed to be involved in directional migration. However, the sequence of events remains unresolved. Does Golgi polarization precede directional migration or vice-versa? We address this question by constraining cells to specific areas and shapes then tracking their motile behavior and the spatio-temporal distribution of Golgi apparatus upon release. Results show that while the position of the Golgi complex depends on the cell geometry, the subcellular localization of the Golgi complex does not define the cell's leading edge. Cells constrained within elongated geometries exhibit polarized extension of lamellipodia and upon release, migrate preferentially along the long axis of the cell. Minimally constrained cells released from larger areas however, exhibit retarded migration regardless of lamellipodia protrusion activity.

The pivotal role of vascularization in tissue engineering

Vascularization is one of the great challenges that tissue engineering faces in order to achieve sizeable tissue and organ substitutes that contain living cells. There are instances, such as skin replacement, in which a tissue-engineered substitute does not absolutely need a preexisting vascularization. However, tissue or organ substitutes in which any dimension, such as thickness, exceeds 400 μm need to be vascularized to ensure cellular survival. Consistent with the wide spectrum of approaches to tissue engineering itself, which vary from acellular synthetic biomaterials to purely biological living constructs, approaches to tissue-engineered vascularization cover numerous techniques. Those techniques range from micropatterns engineered in biomaterials to microvascular networks created by endothelial cells. In this review, we strive to provide a critical overview of the elements that must be considered in the pursuit of this goal and the major approaches that are investigated in hopes of achieving it.

Modulation of lumen formation by microgeometrical bioactive cues and migration mode of actin machinery

How endothelial cells (ECs) express the particular filopodial or lamellipodial form of the actin machinery is critical to understanding EC functions such as angiogenesis and sprouting. It is not known how these mechanisms coordinately promote lumen formation of ECs. Here, adhesion molecules (RGD peptides) and inductor molecules (BMP-2 mimetic peptides) are micropatterned onto polymer surfaces by a photolithographic technique to induce filopodial and lamellipodial migration modes. Firstly, the effects of peptide microgeometrical distribution on EC adhesion, orientation and morphogenesis are evaluated. Large micropatterns (100 μm) promote EC orientation without lumen formation, whereas small micropatterns (10-50 μm) elicit a collective cell organization and induce EC lumen formation, in the case of RGD peptides. Secondly, the correlation between EC actin machinery expression and EC self-assembly into lumen formation is addressed. Only the filopodial migration mode (mimicked by RGD) but not lamellipodial migration mode (mimicked by BMP-2) promotes EC lumen formation. This work gives a new concept for the design of biomaterials for tissue engineering and may provide new insight for angiogenesis inhibition on tumors.

Micropatterning different cell types with microarray amplification of natural directional persistence

In vivo, different cell types assemble in specific patterns to form functional tissues. Reproducing this process in vitro by designing scaffold materials to direct cells precisely to the right locations at the right time is important for the next generation of biomaterials. Here, using microarray amplification of natural directional persistence (MANDIP), simultaneous assembly of fibroblasts and endothelial cells is demonstrated by directing their long-range migration. Amplification of the directional persistence occurs through morphology-induced polarity and the asymmetric positioning of individual microsized adhesive islands that restrict lamellipodia attachment, and thus migration, to one preset direction. Quantitative analysis of cell migration on different MANDIP designs yields insight to the relative importance of the asymmetric island shapes and their arrangement. The approach enables spatial patterning of different cell types with micrometer-scale precision over large areas for investigation of cell-cell interactions within complex tissue architectures.

Survival and structural evaluations of three-dimensional tissues fabricated by the hierarchical cell manipulation technique

Mouse L929 fibroblasts and normal human dermal fibroblasts (NHDFs) were constructed into three-dimensional (3-D) multilayered tissues by directly coating them with nano-films consisting of fibronectin (FN) and gelatin (G) onto the surface of the cell layer using layer-by-layer assembly. The one-, two- and five-layered (1L, 2L and 5L) tissues were cultured for 1 month in order to evaluate their long-term survival and structural changes. L929 cells in the 3-D tissues showed excessive proliferation throughout the culture period, regardless of the starting layer number. The cross-sectional images stained with hematoxylin and eosin revealed heterogeneous and random increases in the thickness of their layered structures, probably due to the immortalized property of L929 fibroblasts. On the other hand, NHDFs, which are primary cells, showed high stability in their amount of DNA in the multilayered structures, and their thicknesses were completely maintained even after 1 month of incubation. To evaluate the living cell density in each layer of 5L tissues during the culture period, 5L NHDFs were fluorescently labeled with LIVE/DEAD reagent and analyzed by confocal laser scanning microscopy. Although the upper layers did not show any dead cells, the bottom layers showed pieces of dead cell nuclei depending on culture time. However, the living cell densities in all layers were almost the same, even after 1 month of culture, suggesting that the 5L structures were completely filled with living cells. These findings from the multilayered tissue constructs will provide important information not only for the construction of 3-D engineered tissues in tissue engineering but also on 3-D cell culture in biological science generally.

Precise control of cell adhesion by combination of surface chemistry and soft lithography

The adhesion of cells on an extracellular matrix (ECM) (in vivo) or the surfaces of materials (in vitro) is a prerequisite for most cells to survive. The rapid growth of nano/microfabrication and biomaterial technologies has provided new materials with excellent surfaces with specific, desirable biological interactions with their surroundings. On one hand, the chemical and physical properties of material surfaces exert an extensive influence on cell adhesion, proliferation, migration, and differentiation. On the other hand, material surfaces are useful for fundamental cell biology research and tissue engineering. In this Review, an overview will be given of the chemical and physical properties of newly developed material surfaces and their biological effects, as well as soft lithographic techniques and their applications in cell biology research. Recent advances in the manipulation of cell adhesion by the combination of surface chemistry and soft lithography will also be highlighted.

Perfusable branching microvessel bed for vascularization of engineered tissues

Vascularization is critical for the survival of engineered tissues in vitro and in vivo. In vivo, angiogenesis involves endothelial cell proliferation and sprouting followed by connection of extended cellular processes and subsequent lumen propagation through vacuole fusion. We mimicked this process in engineering an organized capillary network anchored by an artery and a vein. The network was generated by inducing directed capillary sprouting from vascular explants on micropatterned substrates containing thymosin β4-hydrogel. The capillary outgrowths connected between the parent explants by day 21, a process that was accelerated to 14 d by application of soluble VEGF and hepatocyte growth factor. Confocal microscopy and transmission electron microscopy indicated the presence of tubules with lumens formed by endothelial cells expressing CD31, VE-cadherin, and von Willebrand factor. Cardiac tissues engineered around the resulting vasculature exhibited improved functional properties, cell striations, and cell-cell junctions compared with tissues without prevascularization. This approach uniquely allows easy removal of the vasculature from the microfabricated substrate and easy seeding of the tissue specific cell types in the parenchymal space.

Geometrical microfeature cues for directing tubulogenesis of endothelial cells

Angiogenesis, the formation of new blood vessels by sprouting from pre-existing ones, is critical for the establishment and maintenance of complex tissues. Angiogenesis is usually triggered by soluble growth factors such as VEGF. However, geometrical cues also play an important role in this process. Here we report the induction of angiogenesis solely by SVVYGLR peptide micropatterning on polymer surfaces. SVVYGLR peptide stripes were micropatterned onto polymer surfaces by photolithography to study their effects on endothelial cell (EC) behavior. Our results showed that the EC behaviors (cell spreading, orientation and migration) were significantly more guided and regulated on narrower SVVYGLR micropatterns (10 and 50 µm) than on larger stripes (100 µm). Also, EC morphogenesis into tube formation was switched on onto the smaller patterns. We illustrated that the central lumen of tubular structures can be formed by only one-to-four cells due to geometrical constraints on the micropatterns which mediated cell-substrate adhesion and generated a correct maturation of adherens junctions. In addition, sprouting of ECs and vascular networks were also induced by geometrical cues on surfaces micropatterned with SVVYGLR peptides. These micropatterned surfaces provide opportunities for mimicking angiogenesis by peptide modification instead of exogenous growth factors. The organization of ECs into tubular structures and the induction of sprouting angiogenesis are important towards the fabrication of vascularized tissues, and this work has great potential applications in tissue engineering and tissue regeneration.

Review paper: Critical Issues in Tissue Engineering: Biomaterials, Cell Sources, Angiogenesis, and Drug Delivery Systems

Tissue engineering is a newly emerging biomedical technology, which aids and increases the repair and regeneration of deficient and injured tissues. It employs the principles from the fields of materials science, cell biology, transplantation, and engineering in an effort to treat or replace damaged tissues. Tissue engineering and development of complex tissues or organs, such as heart, muscle, kidney, liver, and lung, are still a distant milestone in twenty-first century. Generally, there are four main challenges in tissue engineering which need optimization. These include biomaterials, cell sources, vascularization of engineered tissues, and design of drug delivery systems. Biomaterials and cell sources should be specific for the engineering of each tissue or organ. On the other hand, angiogenesis is required not only for the treatment of a variety of ischemic conditions, but it is also a critical component of virtually all tissue-engineering strategies. Therefore, controlling the dose, location, and duration of releasing angiogenic factors via polymeric delivery systems, in order to ultimately better mimic the stem cell niche through scaffolds, will dictate the utility of a variety of biomaterials in tissue regeneration. This review focuses on the use of polymeric vehicles that are made of synthetic and/or natural biomaterials as scaffolds for three-dimensional cell cultures and for locally delivering the inductive growth factors in various formats to provide a method of controlled, localized delivery for the desired time frame and for vascularized tissue-engineering therapies.

Nano and micro mechanical properties of uncross-linked and cross-linked chitosan films

The aim of this study is to determine the nano and micro mechanical properties for uncross-linked and cross-linked chitosan films. Specifically, we looked at nanoindentation hardness, microhardness, and elastic modulus. It is important to study the nano and microscale mechanical properties of chitosan since chitosan has been widely used for biomedical applications. Using the solvent-cast method, the chitosan films were prepared at room temperature on the cleaned glass plates. The chitosan solution was prepared by dissolving chitosan in acetic acid 1% (v/v). Tripolyphosphate (TPP) was used to create the cross-links between amine groups in chitosan and phosphate groups in TPP. In this study, atomic force microscopy was used to measure the nanoindentation hardness and surface topography of the uncross-linked and cross-linked chitosan films. Elastic modulus was then calculated from the nanoindentation results. The effective elastic modulus was determined by microhardness with some modifications to previous theories. The microhardness of the chitosan films were measured using Vicker's hardness meter under three different loads. Our results show that the microhardness and elastic modulus for cross-linked chitosan films are higher than the uncross-linked films. However, the cross-linked chitosan films show increased brittleness when compared to uncross-linked films. By increasing the load magnitude, the microhardness increases for both uncross-linked and cross-linked chitosan films.

Endothelial cell micropatterning: methods, effects, and applications

The effects of flow on endothelial cells (ECs) have been widely examined for the ability of fluid shear stress to alter cell morphology and function; however, the effects of EC morphology without flow have only recently been observed. An increase in lithographic techniques in cell culture spurred a corresponding increase in research aiming to confine cell morphology. These studies lead to a better understanding of how morphology and cytoskeletal configuration affect the structure and function of the cells. This review examines EC micropatterning research by exploring both the many alternative methods used to alter EC morphology and the resulting changes in cellular shape and phenotype. Micropatterning induced changes in EC proliferation, apoptosis, cytoskeletal organization, mechanical properties, and cell functionality. Finally, the ways these cellular manipulation techniques have been applied to biomedical engineering research, including angiogenesis, cell migration, and tissue engineering, are discussed.

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.

Multi-membrane chitosan hydrogels as chondrocytic cell bioreactors

We investigated the bioactivity of new chitosan-based multi-membrane hydrogel (MMH) architectures towards chondrocyte-like cells. The microstructure of the hydrogels constituting the membranes precludes any living cell penetration, whereas their lower scale architecture allows the protein diffusion. The biological behavior of chondrocytes implanted within the MMH inter-membrane spaces was studied for 45 days in culture. Chondrocytes formed cell aggregates and proliferated without loosing their chondrogenic phenotype as illustrated by collagen II and aggrecan expressions at the mRNA and protein levels. Cells produced neo-formed alcyan blue matrix proteins filling MMH interspaces. The HiF-2α/SOX9 pattern of expression suggested that the elevated chondrocytic phenotype in MMH could be related to a better hypoxic local environment than in classical culture conditions. Pro-inflammatory markers were not expressed during the period of culture. The low level of nitric oxide accumulation within the inter-membrane spaces and in the incubation medium implied that chitosan consumed nitrites produced by entrapped chondrocytes, in relation with the decrease of its molecular weight of 50%. Our data suggest that MMH structures may be considered as complex chondrocytic cell bioreactors; "active decoys of biological media", potentially promising for various biomedical applications like the inter-vertebral disk replacement.

Vascularization is the key challenge in tissue engineering

The main limitation in engineering in vitro tissues is the lack of a sufficient blood vessel system - the vascularization. In vivo almost all tissues are supplied by these endothelial cell coated tubular networks. Current strategies to create vascularized tissues are discussed in this review. The first strategy is based on the endothelial cells and their ability to form new vessels known as neoangiogenesis. Herein prevascularization techniques are compared to approaches in which biomolecules, such as growth factors, cytokines, peptides and proteins as well as cells are applied to generate new vessels. The second strategy is focused on scaffold-based techniques. Naturally-derived scaffolds, which contain vessels, are distinguished from synthetically manufactured matrices. Advantages and pitfalls of the approaches to create vascularized tissues in vitro are outlined and feasible future strategies are discussed.

Controlling neurite outgrowth with patterned substrates

In vivo, neurons form neurites, one of which develops into the axon while others become dendrites. While this neuritogenesis process is well programmed in vivo, there are limited methods to control the number and location of neurite extension in vitro. Here we report a method to control neuritogenesis by confining neurons in specific regions using cell resistant poly(oligoethyleneglycol methacrylate-co-methacrylic acid (OEGMA-co-MA)) or poly(ethyleneglycol-block-lactic acid) PEG-PLA. Line patterned substrates reduce multiple extension of neurites and stimulate bi-directional neurite budding for PC12 and cortical neurons. PC12 cells on 20 and 30 μm line patterns extended one neurite in each direction along the line pattern while cortical neuron on 20 and 30 μm line patterns extended one or two neurites in each direction along the line pattern. Statistical analysis of neurite lengths revealed that PC12 cells and cortical neurons on line patterns extend longer neurites. The ability to guide formation of neurites on patterned substrates is useful for generating neural networks and promoting neurite elongation.

Opcm Transducer and a Novel Standing-Surface-Acoustic-Wave Sensor

Standing surface acoustic wave (SSAW) technology combined with microtechnology opens up new areas for the development of advanced microparticle and cell separating microfluidic system. A novel SSAW sensor made of the orthotropic piezoelectric composite material (OPCM) is proposed and described. A SSAW field with target wavelength can be generated by this technology and with this new sensor. The wavelength of SSAW generated by this sensor can vary the range from several to a few hundred micrometers. The acoustic radiation force (ARF) generated by the SSAW field can be used to manipulate different dimensional particles.

Engineering systems for the generation of patterned co-cultures for controlling cell-cell interactions

BACKGROUND

Inside the body, cells lie in direct contact or in close proximity to other cell types in a tightly controlled architecture that often regulates the resulting tissue function. Therefore, tissue engineering constructs that aim to reproduce the architecture and the geometry of tissues will benefit from methods of controlling cell-cell interactions with microscale resolution.

SCOPE OF THE REVIEW

We discuss the use of microfabrication technologies for generating patterned co-cultures. In addition, we categorize patterned co-culture systems by cell type and discuss the implications of regulating cell-cell interactions in the resulting biological function of the tissues.

MAJOR CONCLUSIONS

Patterned co-cultures are a useful tool for fabricating tissue engineered constructs and for studying cell-cell interactions in vitro, because they can be used to control the degree of homotypic and heterotypic cell-cell contact. In addition, this approach can be manipulated to elucidate important factors involved in cell-matrix interactions.

GENERAL SIGNIFICANCE

Patterned co-culture strategies hold significant potential to develop biomimetic structures for tissue engineering. It is expected that they would create opportunities to develop artificial tissues in the future. This article is part of a Special Issue entitled Nanotechnologies - Emerging Applications in Biomedicine.

Merging photolithography and robotic protein printing to create cellular microarrays

Photolithographic patterning of proteins on surfaces has been used extensively in the past to define cell adhesion domains with micrometer-scale resolution. However, photolithographic patterning is not amenable to depositing several different proteins on the same surface. We propose to merge photolithography with robotic printing of proteins in order to create arrays of protein spots (∼300-500 μm diameters) with encoded micrometer-scale cell adhesive domains. This method for biointerface design can employ standard positive tone resist lithography to create temporary stencils for printing of protein arrays. Alternatively, nonfouling poly(ethylene glycol) hydrogels can be micropatterned on top of protein spots. In both cases, cells become adherent on the underlying protein domains, but on-the-spot distribution of cells is defined by the photolithographic pattern. The ability to define multiple cell-substrate and cell-cell interaction scenarios on the same surface is applicable to high-throughput screening of the microenvironment components required for cellular differentiation, for example, for guiding stem cells toward the desired tissue type.

Simple and biocompatible micropatterning of multiple cell types on a polymer substrate by using ion implantation

A noncytotoxic procedure for the spatial organization of multiple cell types remains as a major challenge in tissue engineering. In this study, a simple and biocompatible micropatterning method of multiple cell types on a polymer surface is developed by using ion implantation. The cell-resistant Pluronic surface can be converted into a cell-adhesive one by ion implantation. In addition, cells show different behaviors on the ion-implanted Pluronic surface. Thus this process enables the micropatterning of two different cell types on a polymer substrate. The micropatterns of the Pluronic were formed on a polystyrene surface. Primary cells adhered to the spaces of the bare polystyrene regions separated by the implanted Pluronic patterns. Secondary cells then adhered onto the implanted Pluronic patterns, resulting in micropatterns of two different cells on the polystyrene surface.

Chitosan: an integrative biomaterial for lab-on-a-chip devices

Chitosan is a naturally derived polymer with applications in a variety of industrial and biomedical fields. Recently, it has emerged as a promising material for biological functionalization of microelectromechanical systems (bioMEMS). Due to its unique chemical properties and film forming ability, chitosan serves as a matrix for the assembly of biomolecules, cells, nanoparticles, and other substances. The addition of these components to bioMEMS devices enables them to perform functions such as specific biorecognition, enzymatic catalysis, and controlled drug release. The chitosan film can be integrated in the device by several methods compatible with standard microfabrication technology, including solution casting, spin casting, electrodeposition, and nanoimprinting. This article surveys the usage of chitosan in bioMEMS to date. We discuss the common methods for fabrication, modification, and characterization of chitosan films, and we review a number of demonstrated chitosan-based microdevices. We also highlight the advantages of chitosan over some other functionalization materials for micro-scale devices.

High-throughput methods to define complex stem cell niches

The potential of stem cells in clinics and as a diagnostic tool is still largely unmet, partially due to a lack of in vitro models that efficiently mimic the in vivo stem cell microenvironment-or niche-and thus would allow reproducible propagation of stem cells or their controlled differentiation in vitro. The current methodological challenges in studying and manipulating stem cells have spurred intense development and application of microfabrication and micropatterning technologies in stem cell biology. These approaches can be readily used to dissect the complex molecular interplay of stem cells and their niche and study single-cell behavior in high-throughput. Increased merging of microfabrication with advanced biomaterials technologies may ultimately result in functional artificial niches capable of recapitulating extrinsic stem cell regulation in vitro and on a single-cell level.

Surface actuation of smart nanoshutters

Patterned polymer brush surfaces have been fabricated using the molecular scratchcard lithography technique, where a functional top nanolayer (acting also as a resist) is selectively removed using a scanning probe tip to expose underlying atom-transfer radical polymerization (ATRP) initiator sites. The lateral spreading of grafted polymer brush patterns across the adjacent functional resist surface can be reversibly actuated via solvent exposure. Effectively, this methodology provides a means for hiding/unveiling functional surfaces on the nanoscale.

Development of three-dimensional biomimetic scaffold to study epithelial-mesenchymal interactions

Epithelial-mesenchymal interactions play a key role in the development of tissues such as tooth, lungs, and kidneys. To successfully engineer or repair such living tissues it is necessary to first understand the complex cell-cell and cell-matrix interactions underlying organogenesis. To mimic an in vivo setting it is necessary to assemble a three-dimensional matrix that would facilitate cell-cell interaction leading to proliferation and cellular differentiation. In this study, we have developed an in vitro three-dimensional multilayered coculture system using type I collagen and chitosan blends as matrices, to study epithelial-mesenchymal interactions that occur during tooth morphogenesis. Results from this study showed that the matrix composition influenced the migration, proliferation, and differentiation properties of the epithelial and mesenchymal cells. Specifically, the system supported the migration and differentiation of the HAT-7 epithelial cells and mesenchymal-derived dental pulp stem cells. Results from the in vivo implantation study of the coculture system in mice demonstrated a similar cellular migration and differentiation pattern that corroborates well with the in vitro model. Interestingly, the biopolymer matrix also permitted neovascularization in vivo.