Research and development of microenvironment's influence on stem cells from the apical papilla - construction of novel research microdevices: tooth-on-a-chip.

Stem cells are crucial in tissue engineering, and their microenvironment greatly influences their behavior. Among the various dental stem cell types, stem cells from the apical papilla (SCAPs) have shown great potential for regenerating the pulp-dentin complex. Microenvironmental cues that affect SCAPs include physical and biochemical factors. To research optimal pulp-dentin complex regeneration, researchers have developed several models of controlled biomimetic microenvironments, ranging from in vivo animal models to in vitro models, including two-dimensional cultures and three-dimensional devices. Among these models, the most powerful tool is a microfluidic microdevice, a tooth-on-a-chip with high spatial resolution of microstructures and precise microenvironment control. In this review, we start with the SCAP microenvironment in the regeneration of pulp-dentin complexes and discuss research models and studies related to the biological process.

Edge current and pairing order transition in chiral bacterial vortices.

Bacterial suspensions show turbulence-like spatiotemporal dynamics and vortices moving irregularly inside the suspensions. Understanding these ordered vortices is an ongoing challenge in active matter physics, and their application to the control of autonomous material transport will provide significant development in microfluidics. Despite the extensive studies, one of the key aspects of bacterial propulsion has remained elusive: The motion of bacteria is chiral, i.e., it breaks mirror symmetry. Therefore, the mechanism of control of macroscopic active turbulence by microscopic chirality is still poorly understood. Here, we report the selective stabilization of chiral rotational direction of bacterial vortices in achiral circular microwells sealed by an oil/water interface. The intrinsic chirality of bacterial swimming near the top and bottom interfaces generates chiral collective motions of bacteria at the lateral boundary of the microwell that are opposite in directions. These edge currents grow stronger as bacterial density increases, and, within different top and bottom interfaces, their competition leads to a global rotation of the bacterial suspension in a favored direction, breaking the mirror symmetry of the system. We further demonstrate that chiral edge current favors corotational configurations of interacting vortices, enhancing their ordering. The intrinsic chirality of bacteria is a key feature of the pairing order transition from active turbulence, and the geometric rule of pairing order transition may shed light on the strategy for designing chiral active matter.

Coupling Manipulation of Interfacial Chemistry and Coordination Structure in Vanadium Oxides Enables Rapid Magnesium Ion Diffusion Kinetics.

Rechargeable magnesium batteries (RMBs) are a highly promising energy storage system due to their high volumetric capacity and intrinsic safety. However, the practical development of RMBs is hindered by the sluggish Mg2+ diffusion kinetics, including at the cathode-electrolyte interface (CEI) and within the cathode bulk. Herein, we propose an efficient strategy to manipulate the interfacial chemistry and coordination structure in oligolayered V2O5 (L-V2O5) for achieving rapid Mg2+ diffusion kinetics. In terms of the interfacial chemistry, the specific exposed crystal planes in L-V2O5 possess strong electron donating ability, which helps to promote the degradation dynamics of C-F/C-S bonds in the electrolyte, thereby establishing the inorganic-organic interlocking CEI layer for rapid Mg2+ diffusion. In terms of the coordination structure, the straightened V-O structure in L-V2O5 provides efficient ions diffusion path for accelerating Mg2+ diffusion in the cathode. As a result, the L-V2O5 delivers a high reversible capacity (355.3 mA h g-1 at 0.1 A g-1) and an excellent rate capability (161 mAh g-1 at 1 A g-1). Impressively, the interdigital micro-RMBs is firstly assembled, exhibiting excellent flexibility and practicability. This work gives deeper insights into the interface and interior ions diffusion for developing high-kinetics RMBs.

Microraft arrays for serial-killer CD19 chimeric antigen receptor T cells and single cell isolation.

Chimeric antigen receptor T (CAR-T) cell immunotherapies have seen success in treating hematological malignancies in recent years; however, the results can be highly variable. Single cell heterogeneity plays a key role in the variable efficacy of CAR-T cell treatments yet is largely unexplored. A major challenge is to understand the killing behavior and phenotype of individual CAR-T cells, which are able to serially kill targets. Thus, a platform capable of measuring time-dependent CAR-T cell mediated killing and then isolating single cells for downstream assays would be invaluable in characterizing CAR-T cells. An automated microraft array platform was designed to track CD19 CAR-T cell killing of CD19+ target cells and CAR-T cell motility over time followed by CAR-T cell collection based on killing behavior. The platform demonstrated automated CAR-T cell counting with up to 98% specificity and 96% sensitivity, and single cells were isolated with 89% efficiency. On average, 2.3% of single CAR-T cells were shown to participate in serial-killing of target cells, killing a maximum of three target cells in a 6 h period. The cytotoxicity and motility of >7000 individual CAR-T cells was tracked across four microraft arrays. The automated microraft array platform measured temporal cell-mediated cytotoxicity, CAR-T cell motility, CAR-T cell death, and CAR-T cell to target cell distances, followed by the capability to sort any desired CAR-T cell. The pipeline has the potential to further our understanding of T cell-based cancer immunotherapies and improve cell-therapy products for better patient outcomes.

Geometry effect in multi-step crossflow microfluidic devices for red blood cells separation and deformability assessment.

The efficient separation of blood components using microfluidic systems can help to improve the detection and diagnosis of several diseases, such as malaria and diabetes. Therefore, a novel multi-step microfluidic device, based on passive crossflow filters was developed. Three different designs were proposed, fabricated and tested in order to evaluate the most suitable geometry to perform, simultaneously, blood cells separation and cell deformability measurements. All the proposed geometries include a main channel and three sequential separation steps, all comprised of symmetrical crossflow filters, with multiple rows of pillars, to reduce the amount of red blood cells (RBCs) flowing to the outlets of the microfluidic device (MD). Sets of hyperbolic constrictions located at the outlets allow the assessment of cells deformability. Based on the proposed geometries, the three correspondent MD were evaluated and compared, by measuring the RBCs velocities, the cell-free layer (CFL) effect through the microchannels and by quantifying the amount of RBCs at the outlets. The results suggest that the proposed MD 3 configuration was the most effective one for the desired application, due to the formation of a wider CFL. As a result, a minor amount of RBCs flow through the hyperbolic contraction at the third separation level of the device. Nevertheless, for all the proposed geometries, the existence of three separation levels shows that it is possible to achieve a highly efficient cell separation. If needed, such microdevices have the potential for further improvements by increasing the number of separation levels, aiming the total separation of blood cells from plasma.

Screening of anti-atrophic peptides by using photo-cleavable peptide array and 96-well scale contractile human skeletal muscle atrophy models.

Skeletal muscle atrophy is characterized by decreases in protein content, myofiber diameter, and contractile force generation. As muscle atrophy worsens the quality of life, the development of anti-atrophic substances is desirable. In this study, we aimed to demonstrate a screening process for anti-atrophic peptides using photo-cleavable peptide array technology and human contractile atrophic muscle models. We developed a 96-well system and established a screening process with less variability. Dexamethasone-induced human atrophic tissue was constructed in the system. Eight peptides were selected from the literature and used for the screening of peptides for preventing the decrease of the contractile forces of tissues. The peptide QIGFIW, which showed preventive activity, was selected as the seed sequence. As a result of amino acid substitution, we obtained QIGFIQ as a peptide with higher anti-atrophic activity. These results indicate that the combinatorial use of the photo-cleavable peptide array technology and 96-well screening system could comprise a powerful approach to obtaining anti-atrophic peptides, and suggest that the 96-well screening system and atrophic model represent a practical and powerful tool for the development of drugs/functional food ingredients.

Human Blood Platelets Adsorption on Polymeric Materials for Liquid Biopsy.

Platelets are emerging as a promising source of blood biomarkers for several pathologies, including cancer. New automated techniques for easier manipulation of platelets in the context of lab-on-a-chips could be of great support for liquid biopsy. Here, several polymeric materials were investigated for their behavior in terms of adhesion and activation of human platelets. Polymeric materials were selected among the most used in microfabrication (PDMS, PMMA and COC) and commercial and home-made resins for 3D printing technology with the aim to identify the most suitable for the realization of microdevices for human platelets isolation and analysis. To visualize adherent platelets and their activation state scanning, electron microscopy was used, while confocal microscopy was used for evaluating platelets' features. In addition, atomic force microscopy was employed to further study platelets adherent to the polymeric materials. Polymers were divided in two main groups: the most prone to platelet adhesion and materials that cause few or no platelets to adhere. Therefore, different polymeric materials could be identified as suitable for the realization of microdevices aimed at capturing human platelets, while other materials could be employed for the fabrication of microdevices or parts of microdevices for the processing of platelets, without loss on surfaces during the process.

Bending for Better: Flexible Organic Single Crystals with Controllable Curvature and Curvature-Related Conductivity for Customized Electronic Devices.

Electronic microdevices of self-bending coronene crystals are developed to reveal an unexplored link between mechanical deformation and crystal function. First, a facile approach towards length/width/curvature-controllable micro-crystals through bottom-up solution crystallization was proposed for high processability and stability. The bending crystal devices show a significant increase beyond seven orders of magnitude in conductivity than the straight ones, providing the first example of deformation-induced function enhancement in crystal materials. Besides, double effects caused by bending, including the change of π electron level as well as the enhancement of carrier mobility, were determined, respectively by the X-ray photoelectric spectroscopy and X-ray crystallography to coexist, contributing to the conductivity improvement. Our findings will promote future creation of flexible organic crystal systems with deformation-enhanced functional features towards customized smart devices.

Bottom-Up Fabrication of Multilayer Enteric Devices for the Oral Delivery of Peptides.

PURPOSE: To develop a planar, asymmetric, micro-scale oral drug delivery vehicle by i) fabricating microdevice bodies with enteric materials, ii) efficiently and stably loading sensitive drug molecules, and iii) capping microdevices for controlled drug release. METHODS: Picoliter-volume inkjet printing was used to fabricate microdevices through additive manufacturing via drop-by-drop deposition of enteric polymer materials. Microdevice bodies with reservoirs are fabricated through deposition of an enteric polymer, Eudragit FS 30 D. A model API, insulin, was loaded into each microdevice and retained its stability during printing and release. Eudragit L 100 and/or S 100 were used to cap microdevices and control the kinetics of insulin release in simulated intestinal conditions. RESULTS: Microdevice morphologies and size can be tuned on the fly based on printing parameters to span from the microscale to the mesoscale. Insulin retained its stability throughout device fabrication and during in vitro release in simulated intestinal conditions. Insulin release kinetics, from burst release to no release, can be tailored by controlling the blend of the Eudragit capping material. CONCLUSION: This approach represents a uniquely scalable and flexible strategy for microdevice fabrication that overcomes limitations in loading sensitive biologics and in the tuneability of device geometries that are inherent to traditional microfabrication strategies.

Carbon-MEMS-Based Alternating Stacked MoS2 @rGO-CNT Micro-Supercapacitor with High Capacitance and Energy Density.

A novel process to fabricate a carbon-microelectromechanical-system-based alternating stacked MoS2 @rGO-carbon-nanotube (CNT) micro-supercapacitor (MSC) is reported. The MSC is fabricated by successively repeated spin-coating of MoS2 @rGO/photoresist and CNT/photoresist composites twice, followed by photoetching, developing, and pyrolysis. MoS2 @rGO and CNTs are embedded in the carbon microelectrodes, which cooperatively enhance the performance of the MSC. The fabricated MSC exhibits a high areal capacitance of 13.7 mF cm-2 and an energy density of 1.9 µWh cm-2 (5.6 mWh cm-3 ), which exceed many reported carbon- and MoS2 -based MSCs. The MSC also retains 68% of capacitance at a current density of 2 mA cm-2 (5.9 A cm-3 ) and an outstanding cycling performance (96.6% after 10 000 cycles, at a scan rate of 1 V s-1 ). Compared with other MSCs, the MSC in this study is fabricated by a low-cost and facile process, and it achieves an excellent and stable electrochemical performance. This approach could be highly promising for applications in integration of micro/nanostructures into microdevices/systems.

Biocontractile microfluidic channels for peristaltic pumping.

Bio-actuated micro-pumps do not need any external power source and pose no risk of electrical or heat shock for the biological materials in lab-on-chip systems. Several different designs of bio-actuated micro-pumps based on the use of the contractile force of cultured cardiomyocites have been proposed earlier. Here we present a novel type of a bio-actuated micro-pump representing a microfluidic channel with a contractile wall. The flow inside the channel is generated by the peristaltic movement of its wall caused by the propagation of an excitation-contraction wave along the channels surface. The directional flow generated by the pump was demonstrated by tracking of polystyrene microspheres, moving in the direction of the propagation of the excitation-contraction wave with an average velocity of 6-8 µm/min. The suggested design of a micro-pump allows the control of pumping direction, which might be useful for targeted delivery of fluids and substances in lab-on-chip systems. Prospects of future development and implementation of this kind of bio-actuated peristaltic pumps are discussed.

Flexible Fabrication of Shape-Controlled Collagen Building Blocks for Self-Assembly of 3D Microtissues.

Creating artificial tissue-like structures that possess the functionality, specificity, and architecture of native tissues remains a big challenge. A new and straightforward strategy for generating shape-controlled collagen building blocks with a well-defined architecture is presented, which can be used for self-assembly of complex 3D microtissues. Collagen blocks with tunable geometries are controllably produced and released via a membrane-templated microdevice. The formation of functional microtissues by embedding tissue-specific cells into collagen blocks with expression of specific proteins is described. The spontaneous self-assembly of cell-laden collagen blocks into organized tissue constructs with predetermined configurations is demonstrated, which are largely driven by the synergistic effects of cell-cell and cell-matrix interactions. This new strategy would open up new avenues for the study of tissue/organ morphogenesis, and tissue engineering applications.

Rapid, High-Throughput, and Direct Molecular Beacon Delivery to Human Cancer Cells Using a Nanowire-Incorporated and Pneumatic Pressure-Driven Microdevice.

Tracking and monitoring the intracellular behavior of mRNA is of paramount importance for understanding real-time gene expression in cell biology. To detect specific mRNA sequences, molecular beacons (MBs) have been widely employed as sensing probes. Although numerous strategies for MB delivery into the target cells have been reported, many issues such as the cytotoxicity of the carriers, dependence on the random probability of MB transfer, and critical cellular damage still need to be overcome. Herein, we have developed a nanowire-incorporated and pneumatic pressure-driven microdevice for rapid, high-throughput, and direct MB delivery to human breast cancer MCF-7 cells to monitor survivin mRNA expression. The proposed microdevice is composed of three layers: a pump-associated glass manifold layer, a monolithic polydimethylsiloxane (PDMS) membrane, and a ZnO nanowire-patterned microchannel layer. The MB is immobilized on the ZnO nanowires by disulfide bonding, and the glass manifold and PDMS membrane serve as a microvalve, so that the cellular attachment and detachment on the MB-coated nanowire array can be manipulated. The combination of the nanowire-mediated MB delivery and the microvalve function enable the transfer of MB into the cells in a controllable way with high cell viability and to detect survivin mRNA expression quantitatively after docetaxel treatment.

Elevating Platinum to Volumetric Capacitance: High Surface Area Electrodes through Reactive Pt Sputtering.

Platinum is the most widespread electrode material used for implantable biomedical and neuroelectronic devices, motivating exploring ways to improve its performance and understand its fundamental properties. Using reactive magnetron sputtering, PtOx is prepared, which upon partial reduction yields a porous thin-film form of platinum with favorable properties, notably record-low impedance values outcompeting other reports for platinum-based electrodes. It is established that its high electrochemical capacitance scales with thickness, in the way of volumetric capacitor materials like IrOx and poly(3,4-ethylenedioxythiophene), PEDOT. Unlike these two well-known analogs, however, it is found that PtOx capacitance is not caused by reversible pseudofaradaic reactions but rather due to high surface area. In contrast to IrOx, PtOx is not a reversible valence-change oxide, but rather a porous form of platinum. The findings show that this oxygen-containing form of Pt can place Pt electrodes on a level competitive with IrOx and PEDOT. Due to its relatively low cost and ease of preparation, PtOx can be a good choice for microfabricated bioelectronic devices.

Microfluidic reactor designed for time-lapsed imaging of pretreatment and enzymatic hydrolysis of lignocellulosic biomass.

The effect of tissue-specific biochemical heterogeneities of lignocellulosic biomass on biomass deconstruction is best understood through confocal laser scanning microscopy (CLSM) combined with immunohistochemistry. However, this process can be challenging, given the fragility of plant materials, and is generally not able to observe changes in the same section of biomass during both pretreatment and enzymatic hydrolysis. To overcome this challenge, a custom polydimethylsiloxane (PDMS) microfluidic imaging reactor was constructed using standard photolithographic techniques. As proof of concept, CLSM was performed on 60 µm-thick corn stem sections during pretreatment and enzymatic hydrolysis using the imaging reactor. Based on the fluorescence images, the less lignified parenchyma cell walls were more susceptible to pretreatment than the lignin-rich vascular bundles. During enzymatic hydrolysis, the highly lignified protoxylem cell wall was the most resistant, remaining unhydrolyzed even after 48 h. Therefore, imaging thin whole biomass sections was useful to obtain tissue-specific changes during biomass deconstruction.

Computational Fluid-Structure Interaction in Microfluidics.

Micro elastofluidics is a transformative branch of microfluidics, leveraging the fluid-structure interaction (FSI) at the microscale to enhance the functionality and efficiency of various microdevices. This review paper elucidates the critical role of advanced computational FSI methods in the field of micro elastofluidics. By focusing on the interplay between fluid mechanics and structural responses, these computational methods facilitate the intricate design and optimisation of microdevices such as microvalves, micropumps, and micromixers, which rely on the precise control of fluidic and structural dynamics. In addition, these computational tools extend to the development of biomedical devices, enabling precise particle manipulation and enhancing therapeutic outcomes in cardiovascular applications. Furthermore, this paper addresses the current challenges in computational FSI and highlights the necessity for further development of tools to tackle complex, time-dependent models under microfluidic environments and varying conditions. Our review highlights the expanding potential of FSI in micro elastofluidics, offering a roadmap for future research and development in this promising area.

Recent Advances in Alginate-Based Hydrogels for Cell Transplantation Applications.

With its exceptional biocompatibility, alginate emerged as a highly promising biomaterial for a large range of applications in regenerative medicine. Whether in the form of microparticles, injectable hydrogels, rigid scaffolds, or bioinks, alginate provides a versatile platform for encapsulating cells and fostering an optimal environment to enhance cell viability. This review aims to highlight recent studies utilizing alginate in diverse formulations for cell transplantation, offering insights into its efficacy in treating various diseases and injuries within the field of regenerative medicine.

Evolution of the Microrobots: Stimuli-Responsive Materials and Additive Manufacturing Technologies Turn Small Structures into Microscale Robots.

The development of functional microsystems and microrobots that have characterized the last decade is the result of a synergistic and effective interaction between the progress of fabrication techniques and the increased availability of smart and responsive materials to be employed in the latter. Functional structures on the microscale have been relevant for a vast plethora of technologies that find application in different sectors including automotive, sensing devices, and consumer electronics, but are now also entering medical clinics. Working on or inside the human body requires increasing complexity and functionality on an ever-smaller scale, which is becoming possible as a result of emerging technology and smart materials over the past decades. In recent years, additive manufacturing has risen to the forefront of this evolution as the most prominent method to fabricate complex 3D structures. In this review, we discuss the rapid 3D manufacturing techniques that have emerged and how they have enabled a great leap in microrobotic applications. The arrival of smart materials with inherent functionalities has propelled microrobots to great complexity and complex applications. We focus on which materials are important for actuation and what the possibilities are for supplying the required energy. Furthermore, we provide an updated view of a new generation of microrobots in terms of both materials and fabrication technology. While two-photon lithography may be the state-of-the-art technology at the moment, in terms of resolution and design freedom, new methods such as two-step are on the horizon. In the more distant future, innovations like molecular motors could make microscale robots redundant and bring about nanofabrication.

Optical Active Meta-Surfaces, -Substrates, and Single Quantum Dots Based on Tuning Organic Composites with Graphene.

In this communication, the design and fabrication of optical active metamaterials were developed by the incorporation of graphene and joining it to different substrates with variable spectroscopical properties. It focuses on how graphene and its derivatives could generate varied optical setups and materials considering modified and enhanced optics within substrates and surfaces. In this manner, it is discussed how light could be tuned and modified along its path from confined nano-patterned surfaces or through a modified micro-lens. In addition to these optical properties generated from the physical interaction of light, it should be added that the non-classical light pathways and quantum phenomena could participate. In this way, graphene and related carbon-based materials with particular properties, such as highly condensed electronics, pseudo-electromagnetic properties, and quantum and luminescent properties, could be incorporated. Therefore, the modified substrates could be switched by photo-stimulation with variable responses depending on the nature of the material constitution. Therefore, the optical properties of graphene and its derivatives are discussed in these types of metasurfaces with targeted optical active properties, such as within the UV, IR, and terahertz wavelength intervals, along with their further properties and respective potential applications.

Impact of Microdevice Geometry on Transit and Retention in the Murine Gastrointestinal Tract.

Oral protein delivery technologies often depend on encapsulating or enclosing the protein cargo to protect it against pH-driven degradation in the stomach or enzymatic digestion in the small intestine. An emergent methodology is to encapsulate therapeutics in microscale, asymmetric, planar microparticles, referred to as microdevices. Previous work has shown that, compared to spherical particles, planar microdevices have longer residence times in the GI tract, but it remains unclear how specific design choices (e.g., material selection, particle diameter) impact microdevice behavior in vivo. Recent advances in microdevice fabrication through picoliter printing have expanded the range of device sizes that can be fabricated in a rapid manner. However, relatively little work has explored how device size governs their behavior in the intestinal environment. In this study, we probe the impact of geometry of planar microdevices on their transit and accumulation in the murine GI tract. Additionally, we present a strategy to label, image, and quantify these distributions in intact tissue in a continuous manner, enabling a more detailed understanding of device distribution and transit kinetics than previously possible. We show that smaller particles (194.6 ± 7 µm.diameter) tend to empty from the stomach faster than midsize (293.2 ± 7 µm.diameter) and larger devices (440.9 ± 9 µm.diameter) and that larger devices distribute more broadly in the GI tract and exit slower than other geometries. In general, we observed an inverse correlation between device diameter and GI transit rate. These results inform the future design of drug delivery systems, using particle geometry as an engineering design parameter to control device accumulation and distribution in the GI tract. Additionally, our image analysis process provides greater insight into the tissue level distribution and transit of particle populations. Using this technique, we demonstrate that microdevices act and translocate independently, as opposed to transiting in one homogeneous mass, meaning that target sites will likely be exposed to devices multiple times over the course of hours post administration. This imaging technique and associated findings enable data-informed design of future particle delivery systems, allowing orthogonal control of transit and distribution kinetics in vivo independent of material and cargo selection.