RamanSPy: An Open-Source Python Package for Integrative Raman Spectroscopy Data Analysis.

Raman spectroscopy is a nondestructive and label-free chemical analysis technique, which plays a key role in the analysis and discovery cycle of various branches of science. Nonetheless, progress in Raman spectroscopic analysis is still impeded by the lack of software, methodological and data standardization, and the ensuing fragmentation and lack of reproducibility of analysis workflows thereof. To address these issues, we introduce RamanSPy, an open-source Python package for Raman spectroscopic research and analysis. RamanSPy provides a comprehensive library of tools for spectroscopic analysis that supports day-to-day tasks, integrative analyses, the development of methods and protocols, and the integration of advanced data analytics. RamanSPy is modular and open source, not tied to a particular technology or data format, and can be readily interfaced with the burgeoning ecosystem for data science, statistical analysis, and machine learning in Python. RamanSPy is hosted at https://github.com/barahona-research-group/RamanSPy, supplemented with extended online documentation, available at https://ramanspy.readthedocs.io, that includes tutorials, example applications, and details about the real-world research applications presented in this paper.

Magnetically driven formation of 3D freestanding soft bioscaffolds.

3D soft bioscaffolds have great promise in tissue engineering, biohybrid robotics, and organ-on-a-chip engineering applications. Though emerging three-dimensional (3D) printing techniques offer versatility for assembling soft biomaterials, challenges persist in overcoming the deformation or collapse of delicate 3D structures during fabrication, especially for overhanging or thin features. This study introduces a magnet-assisted fabrication strategy that uses a magnetic field to trigger shape morphing and provide remote temporary support, enabling the straightforward creation of soft bioscaffolds with overhangs and thin-walled structures in 3D. We demonstrate the versatility and effectiveness of our strategy through the fabrication of bioscaffolds that replicate the complex 3D topology of branching vascular systems. Furthermore, we engineered hydrogel-based bioscaffolds to support biohybrid soft actuators capable of walking motion triggered by cardiomyocytes. This approach opens new possibilities for shaping hydrogel materials into complex 3D morphologies, which will further empower a broad range of biomedical applications.

Microfibrous Scaffolds Guide Stem Cell Lumenogenesis and Brain Organoid Engineering.

3D organoids are widely used as tractable in vitro models capable of elucidating aspects of human development and disease. However, the manual and low-throughput culture methods, coupled with a low reproducibility and geometric heterogeneity, restrict the scope and application of organoid research. Combining expertise from stem cell biology and bioengineering offers a promising approach to address some of these limitations. Here, melt electrospinning writing is used to generate tuneable grid scaffolds that can guide the self-organization of pluripotent stem cells into patterned arrays of embryoid bodies. Grid geometry is shown to be a key determinant of stem cell self-organization, guiding the position and size of emerging lumens via curvature-controlled tissue growth. Two distinct methods for culturing scaffold-grown embryoid bodies into either interconnected or spatially discrete cerebral organoids are reported. These scaffolds provide a high-throughput method to generate, culture, and analyze large numbers of organoids, substantially reducing the time investment and manual labor involved in conventional methods of organoid culture. It is anticipated that this methodological development will open up new opportunities for guiding pluripotent stem cell culture, studying lumenogenesis, and generating large numbers of uniform organoids for high-throughput screening.

Organoids/organs-on-a-chip: new frontiers of intestinal pathophysiological models.

Organoids/organs-on-a-chip open up new frontiers for basic and clinical research of intestinal diseases. Species-specific differences hinder research on animal models, while organoids are emerging as powerful tools due to self-organization from stem cells and the reproduction of the functional properties in vivo. Organs-on-a-chip is also accelerating the process of faithfully mimicking the intestinal microenvironment. And by combining organoids and organ-on-a-chip technologies, they further are expected to serve as innovative preclinical tools and could outperform traditional cell culture models or animal models in the future. Above all, organoids/organs-on-a-chip with other strategies like genome editing, 3D printing, and organoid biobanks contribute to modeling intestinal homeostasis and disease. Here, the current challenges and future trends in intestinal pathophysiological models will be summarized.

Assembly of Fillable Microrobotic Systems by Microfluidic Loading with Dip Sealing.

Microrobots can provide spatiotemporally well-controlled cargo delivery that can improve therapeutic efficiency compared to conventional drug delivery strategies. Robust microfabrication methods to expand the variety of materials or cargoes that can be incorporated into microrobots can greatly broaden the scope of their functions. However, current surface coating or direct blending techniques used for cargo loading result in inefficient loading and poor cargo protection during transportation, which leads to cargo waste, degradation and non-specific release. Herein, a versatile platform to fabricate fillable microrobots using microfluidic loading and dip sealing (MLDS) is presented. MLDS enables the encapsulation of different types of cargoes within hollow microrobots and protection of cargo integrity. The technique is supported by high-resolution 3D printing with an integrated microfluidic loading system, which realizes a highly precise loading process and improves cargo loading capacity. A corresponding dip sealing strategy is developed to encase and protect the loaded cargo whilst maintaining the geometric and structural integrity of the loaded microrobots. This dip sealing technique is suitable for different materials, including thermal and light-responsive materials. The MLDS platform provides new opportunities for microrobotic systems in targeted drug delivery, environmental sensing, and chemically powered micromotor applications.

Puffball-Inspired Microrobotic Systems with Robust Payload, Strong Protection, and Targeted Locomotion for On-Demand Drug Delivery.

Microrobots are recognized as transformative solutions for drug delivery systems (DDSs) because they can navigate through the body to specific locations and enable targeted drug release. However, their realization is substantially limited by insufficient payload capacity, unavoidable drug leakage/deactivation, and strict modification/stability criteria for drugs. Natural puffballs possess fascinating features that are highly desirable for DDSs, including a large fruitbody for storing spores, a flexible protective cap, and environmentally triggered release mechanisms. This report presents a puffball-inspired microrobotic system which incorporates an internal chamber for loading large drug quantities and spatial drug separation, and a near-infrared-responsive top-sealing layer offering strong drug protection and on-demand release. These puffball-inspired microrobots (PIMs) display tunable loading capacities up to high concentrations and enhanced drug protection with minimal drug leakage. Upon near-infrared laser irradiation, on-demand drug delivery with rapid release efficiency is achieved. The PIMs also demonstrate translational motion velocities, switchable motion modes, and precise locomotion under a rotating magnetic field. This work provides strong proof-of-concept for a DDS that combines the superior locomotion capability of microrobots with the unique characteristics of puffballs, thereby illustrating a versatile avenue for development of a new generation of microrobots for targeted drug delivery.

Fabrication of Biomaterials and Biostructures Based On Microfluidic Manipulation.

Biofabrication technologies are of importance for the construction of organ models and functional tissue replacements. Microfluidic manipulation, a promising biofabrication technique with micro-scale resolution, can not only help to realize the fabrication of specific microsized structures but also build biomimetic microenvironments for biofabricated tissues. Therefore, microfluidic manipulation has attracted attention from researchers in the manipulation of particles and cells, biochemical analysis, tissue engineering, disease diagnostics, and drug discovery. Herein, biofabrication based on microfluidic manipulation technology is reviewed. The application of microfluidic manipulation technology in the manufacturing of biomaterials and biostructures with different dimensions and the control of the microenvironment is summarized. Finally, current challenges are discussed and a prospect of microfluidic manipulation technology is given. The authors hope this review can provide an overview of microfluidic manipulation technologies used in biofabrication and thus steer the current efforts in this field.

Nitrite-responsive hydrogel for long-term and smart control of cyanobacteria bloom.

Frequent cyanobacteria bloom has caused serious environmental consequences and economic loss, especially in aquaculture. Direct algaecide addition, the most commonly used method, suffered from the poor control and overdose of algaecide. In this manuscript, we designed a smart nitrite-responsive hydrogel (DHPG) loading algaecide (BZK@DHPG) based on selective crosslinker: a kind of dihydropyridine derivatives termed DHPL. The network of the polymer could be decomposed by the nitrite-induced cleavage of DHPL. Compared to the traditional method, BZK@DHPG can adjust releasing speed according to the concentration of NO2-, the marker of cyanobacteria bloom level, and elongate the releasing time. Furthermore, BZK@DHPG could shift the effective dose of algaecide much ahead of the safety threshold, thus reducing deterioration of water quality caused by the overdose of algaecide.

Composable microfluidic spinning platforms for facile production of biomimetic perfusable hydrogel microtubes.

Microtissues with specific structures and integrated vessels play a key role in maintaining organ functions. To recapitulate the in vivo environment for tissue engineering and organ-on-a-chip purposes, it is essential to develop perfusable biomimetic microscaffolds. We developed facile all-aqueous microfluidic approaches for producing perfusable hydrogel microtubes with diverse biomimetic sizes and shapes. Here, we provide a detailed protocol describing the construction of the microtube spinning platforms, the assembly of microfluidic devices, and the fabrication and characterization of various perfusable hydrogel microtubes. The hydrogel microtubes can be continuously generated from microfluidic devices due to the crosslinking of alginate by calcium in the coaxial flows and collecting bath. Owing to the mild all-aqueous spinning process, cells can be loaded into the alginate prepolymer for microtube spinning, which enables the direct production of cell-laden hydrogel microtubes. By manipulating the fluid dynamics at the microscale, the composable microfluidic devices and platforms can be used for the facile generation of six types of biomimetic perfusable microtubes. The microfluidic platforms and devices can be set up within 3 h from commonly available and inexpensive materials. After 10-20 min required to adjust the platform and fluids, perfusable hydrogel microtubes can be generated continuously. We describe how to characterize the microtubes using scanning electron or confocal microscopy. As an example application, we describe how the microtubes can be used for the preparation of a vascular lumen and how to perform barrier permeability tests of the vascular lumen.

Nitrite-Responsive Hydrogel: Smart Drug Release Depending on the Severity of the Nitric Oxide-Related Disease.

Nitric oxide (NO) is known as one of the most important biomarkers of many diseases. However, the development of NO-triggered drug releasing platforms is challenging due to the low concentration and short lifetime of NO in vivo. In this work, a novel nitrite (NO2-)-responsive hydrogel (DHPL-GEL), which can be used for smart drug release depending on the severity of the NO-related disease, is demonstrated. A dihydropyridine cross-linking agent is designed to construct DHPL-GEL to enable the responsive degradation of the hydrogel triggered by NO2-. On-demand release of the drug loaded in DHPL-GEL was observed under the stimulation of various concentrations of NO2- at the physiological level both in vitro and in vivo. In the inflammatory arthritis rat model, the DHPL-GEL drug delivery system showed a better therapeutic effect and less side effects than the traditional therapy and nonresponsive hydrogel drug delivery system, demonstrating the promising application of the NO2--responsive hydrogel for the treatment of NO-related diseases.

h-FIBER: Microfluidic Topographical Hollow Fiber for Studies of Glomerular Filtration Barrier.

Kidney-on-a-chip devices may revolutionize the discovery of new therapies. However, fabricating a 3D glomerulus remains a challenge, due to a requirement for a microscale soft material with complex topography to support cell culture in a native configuration. Here, we describe the use of microfluidic spinning to recapitulate complex concave and convex topographies over multiple length scales, required for biofabrication of a biomimetic 3D glomerulus. We produced a microfluidic extruded topographic hollow fiber (h-FIBER), consisting of a vessel-like perfusable tubular channel for endothelial cell cultivation, and a glomerulus-like knot with microconvex topography on its surface for podocyte cultivation. Meter long h-FIBERs were produced in microfluidics within minutes, followed by chemically induced inflation for generation of topographical cues on the 3D scaffold surface. The h-FIBERs were assembled into a hot-embossed plastic 96-well plate. Long-term perfusion, podocyte barrier formation, endothelialization, and permeability tests were easily performed by a standard pipetting technique on the platform. Following long-term culture (1 month), a functional filtration barrier, measured by the transfer of albumin from the blood vessel side to the ultrafiltrate side, suggested the establishment of an engineered glomerulus.

Engineering of Hydrogel Materials with Perfusable Microchannels for Building Vascularized Tissues.

Vascular systems are responsible for various physiological and pathological processes related to all organs in vivo, and the survival of engineered tissues for enough nutrient supply in vitro. Thus, biomimetic vascularization is highly needed for constructing both a biomimetic organ model and a reliable engineered tissue. However, many challenges remain in constructing vascularized tissues, requiring the combination of suitable biomaterials and engineering techniques. In this review, the advantages of hydrogels on building engineered vascularized tissues are discussed and recent engineering techniques for building perfusable microchannels in hydrogels are summarized, including micromolding, 3D printing, and microfluidic spinning. Furthermore, the applications of these perfusable hydrogels in manufacturing organ-on-a-chip devices and transplantable engineered tissues are highlighted. Finally, current challenges in recapitulating the complexity of native vascular systems are discussed and future development of vascularized tissues is prospected.

Microfluidics for Biosynthesizing: from Droplets and Vesicles to Artificial Cells.

Fabrication of artificial biomimetic materials has attracted abundant attention. As one of the subcategories of biomimetic materials, artificial cells are highly significant for multiple disciplines and their synthesis has been intensively pursued. In order to manufacture robust "alive" artificial cells with high throughput, easy operation, and precise control, flexible microfluidic techniques are widely utilized. Herein, recent advances in microfluidic-based methods for the synthesis of droplets, vesicles, and artificial cells are summarized. First, the advances of droplet fabrication and manipulation on the T-junction, flow-focusing, and coflowing microfluidic devices are discussed. Then, the formation of unicompartmental and multicompartmental vesicles based on microfluidics are summarized. Furthermore, the engineering of droplet-based and vesicle-based artificial cells by microfluidics is also reviewed. Moreover, the artificial cells applied for imitating cell behavior and acting as bioreactors for synthetic biology are highlighted. Finally, the current challenges and future trends in microfluidic-based artificial cells are discussed. This review should be helpful for researchers in the fields of microfluidics, biomaterial fabrication, and synthetic biology.

Correction: Hydrogel microfibers with perfusable folded channels for tissue constructs with folded morphology.

[This corrects the article DOI: 10.1039/C8RA04192J.].

Microfabrication of AngioChip, a biodegradable polymer scaffold with microfluidic vasculature.

Microengineered biomimetic systems for organ-on-a-chip or tissue engineering purposes often fail as a result of an inability to recapitulate the in vivo environment, specifically the presence of a well-defined vascular system. To address this limitation, we developed an alternative method to cultivate three-dimensional (3D) tissues by incorporating a microfabricated scaffold, termed AngioChip, with a built-in perfusable vascular network. Here, we provide a detailed protocol for fabricating the AngioChip scaffold, populating it with endothelial cells and parenchymal tissues, and applying it in organ-on-a-chip drug testing in vitro and surgical vascular anastomosis in vivo. The fabrication of the AngioChip scaffold is achieved by a 3D stamping technique, in which an intricate microchannel network can be embedded within a 3D scaffold. To develop a vascularized tissue, endothelial cells are cultured in the lumen of the AngioChip network, and parenchymal cells are encapsulated in hydrogels that are amenable to remodeling around the vascular network to form functional tissues. Together, these steps yield a functional, vascularized network in vitro over a 14-d period. Finally, we demonstrate the functionality of AngioChip-vascularized hepatic and cardiac tissues, and describe direct surgical anastomosis of the AngioChip vascular network on the hind limb of a Lewis rat model.

Necklace-Like Microfibers with Variable Knots and Perfusable Channels Fabricated by an Oil-Free Microfluidic Spinning Process.

Fiber materials with different structural features, which in many cases endow the fibers extraordinary functions, are drawing considerable attention from biomedical and material researchers. Here, perfusable necklace-like knotted microfibers are presented for the first time. Additionally, a novel microfluidic spinning method facilitates the production of variable knots and channels. Not only spindle-, but also hemisphere- and petal-knotted microfibers can be controllably fabricated. Generation and perfusion of both Janus channels and helical channel in the knotted microfibers are also shown. With no need of oil and surfactant, the spinning process is highly cytocompatible. The potential bioengineering and biomedical application of the knotted hollow microfiber is demonstrated by its cell-encapsulation feasibility and the unique liver acinus-like diffusion gradient in the knot. The merits of perfusability, cytocompatibility, and structural diversity of the microfibers may open more avenues for further material and biomedical investigation.

Hydrogel microfibers with perfusable folded channels for tissue constructs with folded morphology.

Fiber-based materials with microchannels have drawn considerable attention in recent years owing to their ability to mimic intrinsic morphologies of living tissues. Folded morphologies, which are common in vivo, such as in skeletal muscle capillaries and intestine luminal endoderm, play important roles in the achievement of tissue functions. Here, microfibers with folded hollow channels are fabricated. Channel morphologies, such as straight-folded, double-folded and double-helical channels, can be regulated by adjusting flow conditions in the microfluidic devices. To further demonstrate the potential to be used in tissue engineering, intestine and skeletal muscle constructs are fabricated using these microfibers as building blocks. Furthermore, the properties of perfusability, permeability, cytocompatibility and weavability of the microfibers are evaluated. The asymmetric molecular distributions in the microfibers provide promising platforms for the study of nutrient exchange and energy supplement between normal and tortuous tissues. The new features of biofibers and proof-of-concept of tissue constructs with folded morphologies may contribute to the development of regenerative medicine and drug screening in the future.

Bioinspired Microfibers with Embedded Perfusable Helical Channels.

Materials with microchannels have attracted increasing attention due to their promising perfusability and biomimetic geometry. However, the fabrication of microfibers with more geometrically complex channels in the micro- or nanoscale remains a big challenge. Here, a novel method for generating scalable microfibers with consecutive embedded helical channels is presented using an easily made coaxial microfluidic device. The characteristics of the helical channel can be accurately controlled by simply adjusting the flow rate ratio of the fluids. The mechanism of the helix formation process is theorized with newly proposed heterogenerated rope-coil effect, which enhances the tunability of helical patterns and promotes the comprehension of this abnormal phenomenon. Based on this effect, microfibers with embedded Janus channels and even double helical channels are generated in situ by changing the design of the device. The uniqueness and potential applications of these tubular microfibers are also demonstrated by biomimetic supercoiling structures as well as the perfusable and permeable spiral vessel.