An inverted microcontact printing method on topographically structured polystyrene chips for arrayed micro-3-D culturing of single cells

Microwell array chip-based single-cell analysis

Single-cell profiling is key to uncover the cellular heterogeneity and drives deep understanding of cell fate. In recent years, microfluidics has become an ideal tool for single-cell profiling owing to its benefits of high throughput and automation. Among various microfluidic platforms, microwell has the advantages of simple operation and easy integration with in situ analysis ability, making it an ideal technique for single-cell studies. Herein, recent advances of single-cell analysis based on microwell array chips are summarized. We first introduce the design and preparation of different microwell chips. Then microwell-based cell capture and lysis strategies are discussed. We finally focus on advanced microwell-based analysis of single-cell proteins, nucleic acids, and metabolites. The challenges and opportunities for the development of microwell-based single-cell analysis are also presented.

Biomimetic Approaches in Clinical Endodontics

In the last few decades, biomimetic concepts have been widely adopted in various biomedical fields, including clinical dentistry. Endodontics is an important sub-branch of dentistry which deals with the different conditions of pulp to prevent tooth loss. Traditionally, common procedures, namely pulp capping, root canal treatment, apexification, and apexigonesis, have been considered for the treatment of different pulp conditions using selected materials. However, clinically to regenerate dental pulp, tissue engineering has been advocated as a feasible approach. Currently, new trends are emerging in terms of regenerative endodontics which have led to the replacement of diseased and non-vital teeth into the functional and healthy dentine-pulp complex. Root- canal therapy is the standard management option when dental pulp is damaged irreversibly. This treatment modality involves soft-tissue removal and then filling that gap through the obturation technique with a synthetic material. The formation of tubular dentine and pulp-like tissue formation occurs when stem cells are transplanted into the root canal with an appropriate scaffold material. To sum up tissue engineering approach includes three components: (1) scaffold, (2) differentiation, growth, and factors, and (3) the recruitment of stem cells within the pulp or from the periapical region. The aim of this paper is to thoroughly review and discuss various pulp-regenerative approaches and materials used in regenerative endodontics which may highlight the current trends and future research prospects in this particular area.

Bio-Activated PEEK: Promising Platforms for Improving Osteogenesis through Modulating Macrophage Polarization

The attention on orthopedic biomaterials has shifted from their direct osteogenic properties to their osteoimmunomodulation, especially the modulation of macrophage polarization. Presently, advanced technologies endow polyetheretherketone (PEEK) with good osteoimmunomodulation by modifying PEEK surface characteristics or incorporating bioactive substances with regulating macrophage polarization. Recent studies have demonstrated that the fabrication of a hydrophilic surface and the incorporation of bioactive substances into PEEK (e.g., zinc, calcium, and phosphate) are good strategies to promote osteogenesis by enhancing the polarization of M2 macrophages. Furthermore, the modification by other osteoimmunomodulatory composites (e.g., lncRNA-MM2P, IL-4, IL-10, and chitosan) and their controlled and desired release may make PEEK an optimal bio-activated implant for regulating and balancing the osteogenic system and immune system. The purpose of this review is to comprehensively evaluate the potential of bio-activated PEEK in polarizing macrophages into M2 phenotype to improve osteogenesis. For this objective, we retrieved and discussed different kinds of bio-activated PEEK regarding improving osteogenesis through modulating macrophage polarization. Meanwhile, the relevant challenges and outlook were presented. We hope that this review can shed light on the development of bio-activated PEEK with more favorable osteoimmunomodulation.

Hematopoietic progenitors polarize in contact with bone marrow stromal cells in response to SDF1

The fate of hematopoietic stem and progenitor cells (HSPCs) is regulated by their interaction with stromal cells in the bone marrow. However, the cellular mechanisms regulating HSPC interaction with these cells and their potential impact on HSPC polarity are still poorly understood. Here we evaluated the impact of cell–cell contacts with osteoblasts or endothelial cells on the polarity of HSPC. We found that an HSPC can form a discrete contact site that leads to the extensive polarization of its cytoskeleton architecture. Notably, the centrosome was located in proximity to the contact site. The capacity of HSPCs to polarize in contact with stromal cells of the bone marrow appeared to be specific, as it was not observed in primary lymphoid or myeloid cells or in HSPCs in contact with skin fibroblasts. The receptors ICAM, VCAM, and SDF1 were identified in the polarizing contact. Only SDF1 was independently capable of inducing the polarization of the centrosome–microtubule network.

Time-resolved microwell cell-pairing array reveals multiple T cell activation profiles

The differences in behaviour between individual cells in a large population are often important, yet are masked in bulk analyses where only average parameters are measured. One unresolved question in the field of immunology is the extent to which important immunological phenomena such as immunodominance to cancer antigens correlates with the average activity of a population of antigen-specific T lymphocytes, or with the activity of individual "outlier" cells. Despite progress in single cell technologies, few platforms are available that can deliver time-resolved, functional analysis at single cell resolution, for these investigations. We have developed an accessible high-throughput platform to measure single T cell signalling in real time following time-controlled stimulation by live antigen presenting cells. The cell-trap array consists of thousands of individual microwells cast in an agarose block, which is biocompatible and permeable to nutrients. Single T cells are isolated in wells via passive sedimentation and size exclusion, achieving up to 90% occupancy. The device enables simultaneous activation of thousands of single CD8⁺ cells. Stimulation with soluble reagents (ionomycin, anti-CD3 antibodies) or antigen presenting cells leads to changes in intracellular calcium concentrations which were measured using calcium-chelating fluorophore dyes. The platform was used to demonstrate a range of activation profiles among individual cells of a cloned, antigen specific CD8⁺ T cell hybridoma in response to both nonspecific stimuli and specific, physiologically relevant antigen stimulation. The presence of two different activation profiles was demonstrated, together with rare outlier behaviour among cells that are essentially clonal.

Facile Fabrication of Thin-Bottom Round-Well Plates Using the Deformation of PDMS Molds and Their Application for Single-Cell PCR

Recently, microdevices made of resins have been strongly supporting cell analysis in a range of fields, from fundamental life science research to medical applications. Many microdevices are fabricated by molding resin to a mold made precisely from rigid materials. However, because dimensional errors in the mold are also accurately printed to the products, the accuracy of the product is limited to less than the accuracy of the rigid mold. Therefore, we hypothesized that if dimensional errors could be self-corrected by elastic molds, microdevices could be facilely fabricated with precision beyond that of molds. In this paper, we report a novel processing strategy in which an elastic mold made of polymethylsiloxane (PDMS) deforms to compensate for the dimensional error on the products. By heat-press molding a polycarbonate plate using a mold that has 384 PDMS convexes with a large dimensional error of height of ± 15.6 µm in standard deviation, a 384-round-well plate with a bottom thickness 13.3 ± 2.3 µm (n = 384) was easily fabricated. Finally, single-cell observation and polymerase chain reactions (PCRs) demonstrated the application of the products made by elastic PDMS molds. Therefore, this processing method is a promising strategy for facile, low-cost, and higher precision microfabrication.

A digital microfluidic system with 3D microstructures for single-cell culture

Despite the precise controllability of droplet samples in digital microfluidic (DMF) systems, their capability in isolating single cells for long-time culture is still limited: typically, only a few cells can be captured on an electrode. Although fabricating small-sized hydrophilic micropatches on an electrode aids single-cell capture, the actuation voltage for droplet transportation has to be significantly raised, resulting in a shorter lifetime for the DMF chip and a larger risk of damaging the cells. In this work, a DMF system with 3D microstructures engineered on-chip is proposed to form semi-closed micro-wells for efficient single-cell isolation and long-time culture. Our optimum results showed that approximately 20% of the micro-wells over a 30 × 30 array were occupied by isolated single cells. In addition, low-evaporation-temperature oil and surfactant aided the system in achieving a low droplet actuation voltage of 36V, which was 4 times lower than the typical 150 V, minimizing the potential damage to the cells in the droplets and to the DMF chip. To exemplify the technological advances, drug sensitivity tests were run in our DMF system to investigate the cell response of breast cancer cells (MDA-MB-231) and breast normal cells (MCF-10A) to a widely used chemotherapeutic drug, Cisplatin (Cis). The results on-chip were consistent with those screened in conventional 96-well plates. This novel, simple and robust single-cell trapping method has great potential in biological research at the single cell level.

Quasi-3D morphology and modulation of focal adhesions of human adult stem cells through combinatorial concave elastomeric surfaces with varied stiffness

In vivo cell niches are complex architectures that provide a wide range of biochemical and mechanical stimuli to control cell behavior and fate. With the aim to provide in vitro microenvironments mimicking physiological niches, microstructured substrates have been exploited to support cell adhesion and to control cell shape as well as three dimensional morphology. At variance with previous methods, we propose a simple and rapid protein subtractive soft lithographic method to obtain microstructured polydimethylsiloxane substrates for studying stem cell adhesion and growth. The shape of adult renal stem cells and nuclei is found to depend predominantly on micropatterning of elastomeric surfaces and only weakly on the substrate mechanical properties. Differently, focal adhesions in their shape and density but not in their alignment mainly depend on the elastomer stiffness almost regardless of microscale topography. Local surface topography with concave microgeometry enhancing adhesion drives stem cells in a quasi-three dimensional configuration where stiffness might significantly steer mechanosensing as highlighted by focal adhesion properties.

Asymmetric multifunctional 3D cell microenvironments by capillary force assembly

The fabrication and characterization of advanced 3D cell culture microenvironments that enable systematic structure–property relationship studies are reported.

Topographical patterning: characteristics of current processing techniques, controllable effects on material properties and co-cultured cell fate, updated applications in tissue engineering, and improvement strategies

Topographical patterning has recently attracted lots of attention in regulating cell fate, understanding the mechanism of cell–microenvironment interactions, and solving the great issues of regenerative medicine.

The Evolution of Polystyrene as a Cell Culture Material

Polystyrene (PS) has brought in vitro cell culture from its humble beginnings to the modern era, propelling dozens of research fields along the way. This review discusses the development of the material, fabrication, and treatment approaches to create the culture material. However, native PS surfaces poorly facilitate cell adhesion and growth in vitro. To overcome this, liquid surface deposition, energetic plasma activation, and emerging functionalization methods transform the surface chemistry. This review seeks to highlight the many potential applications of the first widely accepted polymer growth surface. Although the majority of in vitro research occurs on two-dimensional surfaces, the importance of three-dimensional (3D) culture models cannot be overlooked. The methods to transition PS to specialized 3D culture surfaces are also reviewed. Specifically, casting, electrospinning, 3D printing, and microcarrier approaches to shift PS to a 3D culture surface are highlighted. The breadth of applications of the material makes it impossible to highlight every use, but the aim remains to demonstrate the versatility and potential as both a general and custom cell culture surface. The review concludes with emerging scaffolding approaches and, based on the findings, presents our insights on the future steps for PS as a tissue culture platform.

3D Microcontact Printing for Combined Chemical and Topographical Patterning on Porous Cell Culture Membrane

Micrometer-scale biochemical or topographical patterning is commonly used to guide the cell attachment and growth, but the ability to combine these patterns into an integrated surface with defined chemical and geometrical characteristics still remains a technical challenge. Here, we present a technical solution for simultaneous construction of 3D morphologies, in the form of channels, on porous membranes along with precise transfer of extracellular matrix proteins into the channels to create patterns with geometrically restricting features. By combining the advantages of microthermoforming and microcontact printing, this technique offers a unique patterning process that provides spatiotemporal control over morphological and chemical feature in a single step. By use of our 3D-microcontact printing (3DμCP), determined microstructures like channels with different depths and widths even with more complex patterns can be fabricated. Collagen, fibronectin, and laminin were successfully transferred inside the predesigned geometries, and the validity of the process was confirmed by antibody staining. Cells cultivated on 3DμCP patterned polycarbonate membrane have shown selective adhesion and growth. This technique offers a novel tool for creating freeform combinatorial patterning on the thermoformable surface.

Effect of Poly-L-lysine Coating on Retinoic Acid-Loaded PLGA Microspheres in the Differentiation of Carcinoma Stem Cells into Neural Cells

In this study, PLGA microspheres were prepared using a water-in-oil-in-water emulsion/solvent evaporation technique. Some microspheres were coated with poly-L-lysine (an extracellular matrix (ECM) component), and then pluripotent P19 embryonic carcinoma cells were seeded on them. P19 cells attached onto the PLGA microspheres; subsequently, by adding retinoic acid (RA) to cell culture medium as a neurogenic inducer (RA was released from the microspheres), the cells differentiated into neural cells. Size and morphology of PLGA microspheres was characterized by scanning electron microscopy (SEM). Neurogenic differentiation was studied by immunofluorescent staining, real-time polymerase chain reaction (RT-PCR), and light microscopy. Histological assay showed that more cells attached onto microspheres coated with poly-L-lysine than the uncoated group. Immunofluoresent staining and RT-PCR analysis for β-Tubulin, Nestin and Pax6 genes indicated differentiation of P19 cells into neural cells on both coated and uncoated microspheres. It was found that a high surface area of microspheres improves cell attachment and expansion, which was significantly increased in those coated with poly-L-lysine. Finally, these results highlight the versatility of these sample scaffolds as a model system for nerve tissue engineering.

Mask-free fabrication of a versatile microwell chip for multidimensional cellular analysis and drug screening

Cells are frequently studied because they are basic structural, functional, and biological units of living organisms. Extracting features from cellular behaviors can facilitate decision making in medical diagnoses and represents an important aspect in the development of biomedical engineering. Previous studies have just focused on either the individual cell or cell clusters separately, which leads to a great lack of information. Microwell technologies could address the challenges of in vitro cellular studies, from individual cell studies to 3D functional assays, by providing more information from smaller sample volumes and enabling the incorporation of low-cost high-throughput assays in the drug discovery process. To this end, the present study describes an easy-to-use method for fabricating a versatile microwell chip that utilizes a digital micro-mirror device printing system, and the chip can be employed in multidimensional cellular analysis, ranging from the single cell to the 3D spheroid level. The microwell manufacturing process, using a digital mask in place of a conventional physical mask, is based on shadowed light and is full of flexibility. Three different dimensions (single cell (1D), cell monolayer (2D) and cell spheroid (3D)) of one cell type can be formed using a microwell array and the analyses of biological characteristics are achieved separately. Single cells and cell clusters can be controlled via customized geometries of microfabricated selectively adhesive poly(ethylene glycol) diacrylate (PEGDA) wells. The effects of shape on cellular growth and hybrid tissue layers were investigated by peeling off the microwells. Furthermore, 3D multicellular spheroids were successfully established in a controllable and high-throughput format. Preclinical drug screening was investigated and distinct differences were observed in the tolerance response to drug testing between the 2D and 3D conditions. The study results further demonstrate that the high-density microwell chip is an easy-to-use multidimensional cellular analysis and rapid drug screening technique, and it could be easily adapted for a wide range of biological research applications.

Optimal Design of an Hourglass in-Fiber Air Fabry-Perot Microcavity-Towards Spectral Characteristics and Strain Sensing Technology

An hourglass in-fiber air microcavity Fabry-Perot interferometer is proposed in this paper, and its second reflecting surface of in-fiber microcavity is designed to be a concave reflector with the best curvature radius in order to improve the spectral characteristics. Experimental results proved that the extinction ratio of Fabry-Perot interferometer with cavity length of 60 μm and concave reflector radius of 60 μm is higher than for a rectangular Fabry-Perot interferometer with cavity length of 60 μm (14 dB: 11 dB). Theory and numerical simulation results show that the strain sensitivity of sensor can be improved by reducing the microcavity wall thickness and microcavity diameter, and when the in-fiber microcavity length is 40 μm, the microcavity wall thickness is 10 μm, the microcavity diameter is 20 μm, and the curvature radius of reflective surface II is 50 μm, the interference fringe contrast of is greater than 0.97, an Axial-pull sensitivity of 20.46 nm/N and resolution of 1 mN can be achieved in the range of 0–1 N axial tension. The results show that the performance of hourglass in-fiber microcavity interferometer is far superior to that of the traditional Fabry-Perot interferometer.

Bioelectrical impedimetric sensor for single cell analysis based on nanoroughened quartz substrate; suitable for cancer therapeutic purposes

Single cells analysis has been interested in recent decade. Apart from scientific benefits to achieve new biological phenomena in cell study, many diagnostic and therapeutic protocols in non-communicable diseases were introduced by single cell analysis. Moreover, non-invasive methods to maintain the investigated cell for time dependent monitoring has been widely studied because of its importance in some crucial cases such as drug resistance in cancer. Bioelectrical monitoring is one of such methods Although the procedures reported based on electrical probing might not induce cell disruption, indirect connection between recording electrodes and cell membrane (mostly in microfluidic approaches) reduced the quality of response and limited the precision of the results. Here, a bioelectronic sensor for monitoring the effect of anticancer drugs on single breast cancer cells was fabricated based on nano-roughened gold electrodes on a quartz substrate applied direct contacts to cell membrane. Whole of the surface except a microcircle surrounded the sensing region was passivated by overbaked photoresist layer. Cells were dropped on the sensor without the assistance of any micropipette or microfluidic systems and just individual regions for attachment of one cell has been opened on the sensing region arrays. MCF-7 cancer cells were time tracked under the effect of Paclitaxel and Mebendazole anti-tubulin drugs in low and high doses. Inducing non regulated depolymerization and polymerization in tubulin structures of the single cancer cells were monitored by the electrical signals recorded before and after drug treatment. Electrical responses of single cells to their incubation with drugs completely reflected their vitality and biological states which were confirmed by confocal imaging. This is one of the first investigation on bioelectrical monitoring of single cell's resistance to anticancer drugs.

High-definition micropatterning method for hard, stiff and brittle polymers

Polystyrene (PS) is the most commonly used material in cell culture devices, such as Petri dishes, culture flasks and well plates. Micropatterning of cell culture substrates can significantly affect cell-material interactions leading to an increasing interest in the fabrication of topographically micro-structured PS surfaces. However, the high stiffness combined with brittleness of PS (elastic modulus 3-3.5GPa) makes high-quality patterning into PS difficult when standard hard molds, e.g. silicon and nickel, are used as templates. A new and robust scheme for easy processing of large-area high-density micro-patterning into PS film is established using nanoimprinting lithography and standard hot embossing techniques. Including an extra step through an intermediate PDMS mold alone does not result in faithful replication of the large area, high-density micropattern into PS. Here, we developed an approach using an additional intermediate mold out of OrmoStamp, which allows for high-quality and large-area micro-patterning into PS. OrmoStamp was originally developed for UV nanoimprint applications; this work demonstrates for the first time that OrmoStamp is a highly adequate material for micro-patterning of PS through hot embossing. Our proposed processing method achieves high-quality replication of micropatterns in PS, incorporating features with high aspect ratio (4:1, height:width), high density, and over a large pattern area. The proposed scheme can easily be adapted for other large-area and high-density micropatterns of PS, as well as other stiff and brittle polymers.

Multiphoton photochemical crosslinking-based fabrication of protein micropatterns with controllable mechanical properties for single cell traction force measurements

Engineering 3D microstructures with predetermined properties is critical for stem cell niche studies. We have developed a multiphoton femtosecond laser-based 3D printing platform, which generates complex protein microstructures in minutes. Here, we used the platform to test a series of fabrication and reagent parameters in precisely controlling the mechanical properties of protein micropillars. Atomic force microscopy was utilized to measure the reduced elastic modulus of the micropillars, and transmission electron microscopy was used to visualize the porosity of the structures. The reduced elastic modulus of the micropillars associated positively and linearly with the scanning power. On the other hand, the porosity and pore size of the micropillars associated inversely and linearly with the scanning power and reagent concentrations. While keeping the elastic modulus constant, the stiffness of the micropillars was controlled by varying their height. Subsequently, the single cell traction forces of rabbit chondrocytes, human dermal fibroblasts, human mesenchymal stem cells, and bovine nucleus pulposus cells (bNPCs) were successfully measured by culturing the cells on micropillar arrays of different stiffness. Our results showed that the traction forces of all groups showed positive relationship with stiffness, and that the chondrocytes and bNPCs generated the highest and lowest traction forces, respectively.

Patterning of Fibroblast and Matrix Anisotropy within 3D Confinement is Driven by the Cytoskeleton

Effects of 3D confinement on cellular growth and matrix assembly are important in tissue engineering, developmental biology, and regenerative medicine. Polydimethylsiloxane wells with varying anisotropy are microfabicated using soft-lithography. Microcontact printing of bovine serum albumin is used to block cell adhesion to surfaces between wells. The orientations of fibroblast stress fibers, microtubules, and fibronectin fibrils are examined 1 day after cell seeding using laser scanning confocal microscopy, and anisotropy is quantified using a custom autocorrelation analysis. Actin, microtubules, and fibronectin exhibit higher anisotropy coefficients for cells grown in rectangular wells with aspect ratios of 1:4 and 1:8, as compared to those in wells with lower aspect ratios or in square wells. The effects of disabling individual cytoskeletal components on fibroblast responses to anisotropy are then tested by applying actin or microtubule polymerization inhibitors, Rho kinase inhibitor, or by siRNA-mediated knockdown of AXL or cofilin-1. Latrunculin A decreases cytoskeletal and matrix anisotropy, nocodazole ablates both, and Y27632 mutes cellular polarity while decreasing matrix anisotropy. AXL siRNA knockdown has little effect, as does siRNA knockdown of cofilin-1. These data identify several specific cytoskeletal strategies as targets for the manipulation of anisotropy in 3D tissue constructs.

High Content Imaging (HCI) on Miniaturized Three-Dimensional (3D) Cell Cultures

High content imaging (HCI) is a multiplexed cell staining assay developed for better understanding of complex biological functions and mechanisms of drug action, and it has become an important tool for toxicity and efficacy screening of drug candidates. Conventional HCI assays have been carried out on two-dimensional (2D) cell monolayer cultures, which in turn limit predictability of drug toxicity/efficacy in vivo; thus, there has been an urgent need to perform HCI assays on three-dimensional (3D) cell cultures. Although 3D cell cultures better mimic in vivo microenvironments of human tissues and provide an in-depth understanding of the morphological and functional features of tissues, they are also limited by having relatively low throughput and thus are not amenable to high-throughput screening (HTS). One attempt of making 3D cell culture amenable for HTS is to utilize miniaturized cell culture platforms. This review aims to highlight miniaturized 3D cell culture platforms compatible with current HCI technology.

Cell Sheet-Based Tissue Engineering for Organizing Anisotropic Tissue Constructs Produced Using Microfabricated Thermoresponsive Substrates

In some native tissues, appropriate microstructures, including orientation of the cell/extracellular matrix, provide specific mechanical and biological functions. For example, skeletal muscle is made of oriented myofibers that is responsible for the mechanical function. Native artery and myocardial tissues are organized three-dimensionally by stacking sheet-like tissues of aligned cells. Therefore, to construct any kind of complex tissue, the microstructures of cells such as myotubes, smooth muscle cells, and cardiomyocytes also need to be organized three-dimensionally just as in the native tissues of the body. Cell sheet-based tissue engineering allows the production of scaffold-free engineered tissues through a layer-by-layer construction technique. Recently, using microfabricated thermoresponsive substrates, aligned cells are being harvested as single continuous cell sheets. The cell sheets act as anisotropic tissue units to build three-dimensional tissue constructs with the appropriate anisotropy. This cell sheet-based technology is straightforward and has the potential to engineer a wide variety of complex tissues. In addition, due to the scaffold-free cell-dense environment, the physical and biological cell-cell interactions of these cell sheet constructs exhibit unique cell behaviors. These advantages will provide important clues to enable the production of well-organized tissues that closely mimic the structure and function of native tissues, required for the future of tissue engineering.

Design of surface modifications for nanoscale sensor applications

Nanoscale biosensors provide the possibility to miniaturize optic, acoustic and electric sensors to the dimensions of biomolecules. This enables approaching single-molecule detection and new sensing modalities that probe molecular conformation. Nanoscale sensors are predominantly surface-based and label-free to exploit inherent advantages of physical phenomena allowing high sensitivity without distortive labeling. There are three main criteria to be optimized in the design of surface-based and label-free biosensors: (i) the biomolecules of interest must bind with high affinity and selectively to the sensitive area; (ii) the biomolecules must be efficiently transported from the bulk solution to the sensor; and (iii) the transducer concept must be sufficiently sensitive to detect low coverage of captured biomolecules within reasonable time scales. The majority of literature on nanoscale biosensors deals with the third criterion while implicitly assuming that solutions developed for macroscale biosensors to the first two, equally important, criteria are applicable also to nanoscale sensors. We focus on providing an introduction to and perspectives on the advanced concepts for surface functionalization of biosensors with nanosized sensor elements that have been developed over the past decades (criterion (iii)). We review in detail how patterning of molecular films designed to control interactions of biomolecules with nanoscale biosensor surfaces creates new possibilities as well as new challenges.

Patterning of individual Staphylococcus aureus bacteria onto photogenerated polymeric surface structures

This manuscript describes the fabrication of bacterial surface arrays by using photolithographic techniques having in addition some particularly interesting features.

Controlling major cellular processes of human mesenchymal stem cells using microwell structures

Directing stem cells towards a desired location and function by utilizing the structural cues of biomaterials is a promising approach for inducing effective tissue regeneration. Here, the cellular response of human adipose-derived mesenchymal stem cells (hADSCs) to structural signals from microstructured substrates comprising arrays of square-shaped or round-shaped microwells is explored as a transitional model between 2D and 3D systems. Microwells with a side length/diameter of 50 μm show advantages over 10 μm and 25 μm microwells for accommodating hADSCs within single microwells rather than in the inter-microwell area. The cell morphologies are three-dimensionally modulated by the microwell structure due to differences in focal adhesion and consequent alterations of the cytoskeleton. In contrast to the substrate with 50 μm round-shaped microwells, the substrate with 50 μm square-shaped microwells promotes the proliferation and osteogenic differentiation potential of hADSCs but reduces the cell migration velocity and distance. Such microwell shape-dependent modulatory effects are highly associated with Rho/ROCK signaling. Following ROCK inhibition, the differences in migration, proliferation, and osteogenesis between cells on different substrates are diminished. These results highlight the possibility to control stem cell functions through the use of structured microwells combined with the manipulation of Rho/ROCK signaling.

3D printed microfluidic devices with integrated versatile and reusable electrodes

We report two 3D printed devices that can be used for electrochemical detection. In both cases, the electrode is housed in commercially available, polymer-based fittings so that the various electrode materials (platinum, platinum black, carbon, gold, silver) can be easily added to a threaded receiving port printed on the device; this enables a module-like approach to the experimental design, where the electrodes are removable and can be easily repolished for reuse after exposure to biological samples. The first printed device represents a microfluidic platform with a 500 × 500 μm channel and a threaded receiving port to allow integration of either polyetheretherketone (PEEK) nut-encased glassy carbon or platinum black (Pt-black) electrodes for dopamine and nitric oxide (NO) detection, respectively. The embedded 1 mm glassy carbon electrode had a limit of detection (LOD) of 500 nM for dopamine and a linear response (R(2) = 0.99) for concentrations between 25-500 μM. When the glassy carbon electrode was coated with 0.05% Nafion, significant exclusion of nitrite was observed when compared to signal obtained from equimolar injections of dopamine. When using flow injection analysis with a Pt/Pt-black electrode and standards derived from NO gas, a linear correlation (R(2) = 0.99) over a wide range of concentrations (7.6-190 μM) was obtained, with the LOD for NO being 1 μM. The second application showcases a 3D printed fluidic device that allows collection of the biologically relevant analyte adenosine triphosphate (ATP) while simultaneously measuring the release stimulus (reduced oxygen concentration). The hypoxic sample (4.8 ± 0.5 ppm oxygen) released 2.4 ± 0.4 times more ATP than the normoxic sample (8.4 ± 0.6 ppm oxygen). Importantly, the results reported here verify the reproducible and transferable nature of using 3D printing as a fabrication technique, as devices and electrodes were moved between labs multiple times during completion of the study.

Miniaturized pre-clinical cancer models as research and diagnostic tools

Cancer is one of the most common causes of death worldwide. Consequently, important resources are directed towards bettering treatments and outcomes. Cancer is difficult to treat due to its heterogeneity, plasticity and frequent drug resistance. New treatment strategies should strive for personalized approaches. These should target neoplastic and/or activated microenvironmental heterogeneity and plasticity without triggering resistance and spare host cells. In this review, the putative use of increasingly physiologically relevant microfabricated cell-culturing systems intended for drug development is discussed. There are two main reasons for the use of miniaturized systems. First, scaling down model size allows for high control of microenvironmental cues enabling more predictive outcomes. Second, miniaturization reduces reagent consumption, thus facilitating combinatorial approaches with little effort and enables the application of scarce materials, such as patient-derived samples. This review aims to give an overview of the state-of-the-art of such systems while predicting their application in cancer drug development.

Exchangeable colloidal AFM probes for the quantification of irreversible and long-term interactions

An original method is presented to study single-colloid interaction with a substrate in liquid environment. Colloids, either in solution or adsorbed on a surface, are fixed by suction against the aperture of a microchanneled atomic force microscopy cantilever. Their adhesion to the substrate is measured, followed by their release via a short overpressure surge. Such colloid exchange procedure allows for 1), the quick variation of differently functionalized colloids within the same experiment; 2), the investigation of long-term interactions by leaving the colloids on a surface for a defined time before detaching them; and 3), the inspection of irreversible interactions. After validation of the method by reproducing literature results obtained with traditional colloidal atomic force microscopy, the serial use of colloids with different surface functionalization was shown on a micropatterned surface. Finally, concanavalin A-coated colloids were allowed to adsorb on human embryonic kidney cells and then detached one by one. The adhesion between cells and colloids was up to 60 nN, whereas individual cells adhered with 20 nN to the glass substrate. A cellular elastic modulus of 0.8 kPa was determined using the attached colloid as indenter.

Multilayered heparin hydrogel microwells for cultivation of primary hepatocytes

The biomaterial scaffolds for regenerative medicine need to be rationally designed to achieve the desired cell fate and function. This paper describes the development of hydrogel microstructures for cultivation of primary hepatocytes. Four different micropatterned surfaces are tested: 1) poly(ethyelene glycol) (PEG) microwells patterned on glass, 2) heparin hydrogel microwells patterned on glass, 3) PEG microwells patterned on heparin hydrogel-coated substrates, and 4) heparin hydrogel microwells patterned on heparin hydrogel-coated substrates. The latter surfaces are constructed by a combination of micromolding and microcontact printing techniques to create microwells with both walls and floor composed of heparin hydrogel. Individual microwell dimensions are 200 μm diameter and 20 μm in height. In all cases, the floor of the microwells is modified with collagen I to promote cell adhesion. Cultivation of hepatocytes followed by analysis of hepatic markers (urea production, albumin synthesis, and E-cadherin expression) reveals that the all-heparin gel microwells are most conducive to hepatic phenotype maintenance. For example, ELISA analysis shows 2.3 to 13.1 times higher levels of albumin production in all-heparin gel wells compared with other micropatterned surfaces. Importantly, hepatic phenotype expression can be further enhanced by culturing fibroblasts on the heparin gel walls of the microwells. In the future, multicomponent all-heparin gel microstructures may be employed in designing hepatic niche for liver-specific differentiation of stem cells.

Accelerating drug discovery via organs-on-chips

Considerable advances have been made in the development of micro-physiological systems that seek to faithfully replicate the complexity and functionality of animal and human physiology in research laboratories. Sometimes referred to as "organs-on-chips", these systems provide key insights into physiological or pathological processes associated with health maintenance and disease control, and serve as powerful platforms for new drug development and toxicity screening. In this Focus article, we review the state-of-the-art designs and examples for developing multiple "organs-on-chips", and discuss the potential of this emerging technology to enhance our understanding of human physiology, and to transform and accelerate the drug discovery and preclinical testing process. This Focus article highlights some of the recent technological advances in this field, along with the challenges that must be addressed for these technologies to fully realize their potential.

Advances in high-throughput single-cell microtechnologies

Micro-scale biological tools that have allowed probing of individual cells--from the genetic, to proteomic, to phenotypic level--have revealed important contributions of single cells to direct normal and diseased body processes. In analyzing single cells, sample heterogeneity between and within specific cell types drives the need for high-throughput and quantitative measurement of cellular parameters. In recent years, high-throughput single-cell analysis platforms have revealed rare genetic subpopulations in growing tumors, begun to uncover the mechanisms of antibiotic resistance in bacteria, and described the cell-to-cell variations in stem cell differentiation and immune cell response to activation by pathogens. This review surveys these recent technologies, presenting their strengths and contributions to the field, and identifies needs still unmet toward the development of high-throughput single-cell analysis tools to benefit life science research and clinical diagnostics.

In situ metallization of patterned polymer brushes created by molecular transfer print and fill

A chemical pattern consisting of end-grafted polystyrene brushes (20 nm lines on a 40 nm pitch) on the native oxide of silicon wafers was defined by molecular transfer printing from assembled block co-polymer films. End-grafted hydroxyl-terminated poly(2-vinyl pyridine) brushes were selectively deposited in the interspatial regions. The poly(2-vinyl pyridine) regions selectively sequester acidic HAuCl4 from solution and form arrays of small Au nanoparticles upon exposure to oxygen plasma within the confines of the macromolecular brush layer. This print and fill process to pattern polymer brushes is a generalizable strategy to create functional chemical surface patterns.

Constructing robust and functional micropatterns on polystyrene surfaces by using deep UV irradiation

We report the preparation of different surface patterns based on the photo-cross-linking/degradation kinetics of polystyrene (PS) by using UV light. Upon exposure to UV light, PS can be initially cross-linked, whereas an excess of the exposure time or intensity provokes the degradation of the material. Typically photolithography employs either positive or negative photoresist layers that upon removal of either the exposed or the nonexposed areas transfer the pattern of the mask. Herein, we present a system that can be both negative and positive depending on several aspects, including the irradiation time, intensity, or presence of absorbing active species (photoinitiators) using a general setup. As a result of the optimization of the time of exposure and the use of an appropriate cover or the incorporation of an appropriate amount of photoinitiator (in this particular case IRG 651), different tailor-made surface patterns can be obtained. Moreover, changes of the chemical composition of the polystyrene using, for instance, block copolymers can lead to surface patterns with variable functional groups. In this study we describe the formation of surface patterns using polystyrene-block-poly(2,3,4,5,6-pentafluorostyrene) block copolymers. The introduction of fluorinated moieties clearly modifies the wettability of the films when compared with that of the same structures obtained with PS. As a consequence we present herein a patterning methodology that can simultaneously vary not only the morphology but also the surface chemical composition.

Fabrication of hexagonally packed cell culture substrates using droplet formation in a T-shaped microfluidic junction

A method is here proposed to fabricate ordered hexagonally packed cell culture substrates with hexagonally arranged cell patterning areas. We generated photo-sensitive polymeric microdroplets in a T-shaped microfluidic junction by an immiscible liquid, and then solidified the collective self-assembled hexagonal droplet array to obtain the cell culture substrate, on which we took the grooves formed between the solidified droplets as the hexagonally arranged cell patterning areas. The most promising advantage of our method is that we can actively tune the droplet size by simply adopting different volumetric flow rates of the two immiscible fluids to form cell culture substrates with differently sized cell patterning areas. Besides, the examination results of the cell culture substrate's characteristics validate whether our method is capable of creating substrates with high spatial uniformity. To verify the cell patterning function of our cell culture substrates, we used the semi-adherent RAW cells to demonstrate the effectiveness of patterning of suspended/adherent cells before/after adhesion. Over 90% cell viability and cell patterning rate suggest that our method may be a promising approach for future applications of cell patterning on biochips.

Collagen-nanofiber hydrogel composites promote contact guidance of human lymphatic microvascular endothelial cells and directed capillary tube formation

Collagen and fibronectin matrices are known to stimulate migration of microvascular endothelial cells and the process of tubulogenesis, but the physical, chemical, and topographical cues for directed vessel formation have yet to be determined. In this study, growth, migration, elongation, and tube formation of human lymphatic microvascular endothelial cells (LECs) were investigated on electrospun poly(D,L-lactic-co-glycolic acid) (PLGA) and poly(L-lactic-co-D-lactic acid) (PLDL) nanofiber-coated substrates, and correlated with fiber density and diameter. Directed migration of LECs was observed in the presence of aligned nanofibers, whereas random fiber alignment slowed down migration and growth of LECs. Cell guidance was significantly enhanced in the presence of more hydrophobic PLDL polymer nanofibers compared to PLGA (10:90). Subsequent experiments with tube-forming assays reveal the ability of resorbable hydrophobic nanofibers >300 nm in diameter to promote cell guidance in collagen gels without direct cell-fiber contact, in contrast to the previously reported contact-guidance phenomena. Our results show that endothelial cell guidance is possible within nanofiber/collagen-gel constructs that mimic the native extracellular matrix in terms of size and orientation of fibrillar components.

A Review of Additive Manufacturing

Additive manufacturing processes take the information from a computer-aided design (CAD) file that is later converted to a stereolithography (STL) file. In this process, the drawing made in the CAD software is approximated by triangles and sliced containing the information of each layer that is going to be printed. There is a discussion of the relevant additive manufacturing processes and their applications. The aerospace industry employs them because of the possibility of manufacturing lighter structures to reduce weight. Additive manufacturing is transforming the practice of medicine and making work easier for architects. In 2004, the Society of Manufacturing Engineers did a classification of the various technologies and there are at least four additional significant technologies in 2012. Studies are reviewed which were about the strength of products made in additive manufacturing processes. However, there is still a lot of work and research to be accomplished before additive manufacturing technologies become standard in the manufacturing industry because not every commonly used manufacturing material can be handled. The accuracy needs improvement to eliminate the necessity of a finishing process. The continuous and increasing growth experienced since the early days and the successful results up to the present time allow for optimism that additive manufacturing has a significant place in the future of manufacturing.

Microfabricated biomaterials for engineering 3D tissues

Mimicking natural tissue structure is crucial for engineered tissues with intended applications ranging from regenerative medicine to biorobotics. Native tissues are highly organized at the microscale, thus making these natural characteristics an integral part of creating effective biomimetic tissue structures. There exists a growing appreciation that the incorporation of similar highly organized microscale structures in tissue engineering may yield a remedy for problems ranging from vascularization to cell function control/determination. In this review, we highlight the recent progress in the field of microscale tissue engineering and discuss the use of various biomaterials for generating engineered tissue structures with microscale features. In particular, we will discuss the use of microscale approaches to engineer the architecture of scaffolds, generate artificial vasculature, and control cellular orientation and differentiation. In addition, the emergence of microfabricated tissue units and the modular assembly to emulate hierarchical tissues will be discussed.

A novel method to fabricate thermoresponsive microstructures with improved cell attachment/detachment properties

A novel, simple, and rapid method to fabricate thermoresponsive micropatterned substrate for cell adhesion, growth, and thermally induced detachment was developed. Thermoresponsive polymer, poly(N-isopropylacrylamide) (PNIPAAm), was grafted onto the surface of polystyrene (PS) film with microstructure by plasma-induced graft polymerization technique. The thermoresponsive micropatterned films were characterized by attenuated total reflectance-Fourier transform infrared (ATR-FTIR) spectroscopy, hydrogen nuclear magnetic resonance ((1) H NMR) spectroscopy, X-ray photoelectron spectroscopy (XPS) and scanning electron microscope (SEM). These results indicated that the grafting ratio of PNIPAAm increased with increasing roughness of PS film. However, the microstructures on the substrate were not affected by grafted PNIPAAm. The optimal grafting conditions, such as plasma treatment time, monomer concentration, graft polymerization time, and graft medium were investigated. The thermoresponsive micropatterned films were investigated with the fibroblast cell (L929) adhesion, proliferation, and thermally induced detachment assay. The microstructure on the thermoresponsive micropatterned substrate facilitated cell adhesion above the lower critical solution temperature (LCST) of PNIPAAm and cell detachment below the LCST. Moreover, it can be used to regulate cell organization and tissue growth.