Advanced Materials Technologies

3D printing has become a prevalent technology in many fields such as manufacturing, architecture, and electronics. This additive manufacturing technique is also widely used for biomedical research and clinical applications to prototype or assemble biomedical devices and tools. 3D printing-based strategies for biocompatible materials offer greater design flexibility, enhanced versatility, and faster results than traditional fabrication techniques, advantages that could be especially beneficial to the development of microfluidic chips. The ability to simply and efficiently produce new chip molds from computer aided design (CAD) models would significantly transform the development process and expand its accessibility by removing the need for more complex and expensive lithography methods. However, with standard processing strategies, the use of 3D printed molds for casting functioning chips is limited by the poor quality of prints achievable with widely available 3D printers. To mitigate this issue and facilitate rapid microfluidic device prototyping, we have developed a simple procedure to print microfluidic molds using a stereolithographic (SLA) printer and produce functional polydimethylsiloxane (PDMS) microfluidic chips with height and width feature dimensions as low as 75 {micro}m. Molds printed using a commercially available liquid photopolymer-based resin and processed using our strategy exhibited high dimensional fidelity to intended designs and significantly reduced average surface roughness (< 3 {micro}m). Here, we describe a streamlined post-print processing workflow for SLA molds and its efficacy in reducing surface roughness while preserving dimensional fidelity and then demonstrate its utility by prototyping and optimizing a microfluidic extracellular vesicle (EV)-exchange platform. Graphical AbstractRapid prototyping of microfluidic device features using stereolithographic 3D printing. O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=110 SRC="FIGDIR/small/662041v1_ufig1.gif" ALT="Figure 1"> View larger version (29K): org.highwire.dtl.DTLVardef@126ff02org.highwire.dtl.DTLVardef@1301c7forg.highwire.dtl.DTLVardef@19edb96org.highwire.dtl.DTLVardef@6256b5_HPS_FORMAT_FIGEXP M_FIG C_FIG

Despite technological advances, the fabrication of multiscale, multi-material, and topologically complex 3D structures using soft hydrogel bioinks remains a challenge due to the inherent trade-offs between print size/resolution, bioink properties, and design complexity. In this work, we combine additive (macroscale) digital light projection (DLP) mode with subtractive (microscale) two-photon ablation (TPA) mode with multi-material exchange capability. We identify ideal hydrogel bioink formulations that are compatible with both DLP and TPA modes of processing. Technical challenges related to multimodal fabrication such as alignment of multiscale topologies to facilitate seamless media perfusion, soft-hard multi-material printing to facilitate handling of mechanically weak hydrogel constructs, and hydrogel swelling during printing, were resolved. To highlight the novelty of this hybrid platform, we fabricated centimeter-scale bioink constructs with embedded microscale perfusable topologies that cannot be achieved by isolated use of either DLP or TPA modes. This includes simpler microfluidic chips with independently perfusable microchannels to more complex 3D constructs with embedded, multiscale, perfusable dual-fluidic circuits that mimic the alveoli-capillary interface, or microfluidic chips with endothelialized microchannels. The unique ability of this multimodal platform to mimic in vivo-like multiscale complexities can be potentially used to develop next-generation organ-on-chips.

Elastic porous membranes are essential components of mechanically active organ-on-a-chip and microphysiological system (MPS) platforms, where cyclic strain is required to recapitulate physiologically relevant tissue mechanics. However, existing fabrication methods are often difficult to reproduce, low throughput, or dependent on specialized infrastructure, limiting their adoption across laboratories. Many protocols also lack quality control steps for ensuring device assembling and reproducibility. In this paper, we present a robust and accessible fabrication and quality control workflow for the consistent production of elastic porous PDMS membranes. The method uses commercially available heat presses, release liners, and pre-patterned membrane wafers to enable rapid membrane molding. We describe a quality control framework, including visual verification of porous regions and wettability testing for surface activation, to ensure irreversible PDMS bonding and reliable device assembly. Together, this workflow improves fabrication yield, reduces device failure, and supports reproducible implementation of elastic porous membrane in organ-on-a-chip applications.

Reliable and scalable soft implantable neural interface fabrication remains a key challenge for chronic bioelectronic applications. Here, we present a transparent soft microelectrode fabricated with electrohydrodynamic (EHD) printing, utilizing the fluorinated polymer poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) and poly (3, 4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT: PSS) to form seamless, selectively patterned multilayer structures with low impedance and long-term stability. Controlled in situ curing during printing yields dense, void-free substrate and encapsulation layers, suppressing interfacial defects and ionic pathways, while maintaining high optical transparency (>60%) with PEDOT:PSS. The printed microelectrodes exhibit low impedance, high charge storage and injection capacities, and stable electrochemical behavior under biomimetic conditions. In addition, the devices demonstrate robust mechanical and electromechanical stability under cyclic deformation in both dry and wet environments, as well as under prolonged electrical stimulation. Accelerated aging studies project multi-year operational lifetimes, and in vitro/in vivo biocompatibility assessments confirm excellent tissue integration. These results establish EHD-printed fluorinated polymer-based microelectrodes as a scalable and durable platform for chronic implantable biointerfaces. ToC O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=182 SRC="FIGDIR/small/726391v1_ufig1.gif" ALT="Figure 1"> View larger version (79K): org.highwire.dtl.DTLVardef@152c58aorg.highwire.dtl.DTLVardef@126f1f5org.highwire.dtl.DTLVardef@1d743cforg.highwire.dtl.DTLVardef@1a4d743_HPS_FORMAT_FIGEXP M_FIG C_FIG This report presents an electrohydrodynamically printed transparent soft microelectrode for chronic purposes. Electrohydrodynamic printing promotes seamless multilayer structures with selective deposition and long-term mechanical stability. The devices show low impedance, high charge capacity, and robust electrochemical/electromechanical properties. Accelerated aging projects [~]7.2 year lifetimes, and XPS/SEM-EDS confirm strong ion barrier properties and biocompatibility for chronic implantation.

Organ-on-chip (OOC) technologies, also called microphysi-ological systems (MPS), offer dynamic microenvironments that improve upon static culture systems, yet widespread adoption has been hindered by fabrication complexity, reliance on poly-dimethylsiloxane (PDMS), and limited modularity. Here, we present a modular MPS platform designed for ease of use, re-producibility, and broad applicability. The system comprises layered elastomeric inserts for dual monolayer cell culture, which is clamped within a reusable acrylic cassette for perfusion studies. This enables researchers to decouple model establishment from flow experiments and streamline their work-flows. We validated the system using dual epithelial and en-dothelial cell co-culture under static and perfused conditions, including shear-induced alignment of HUVECs. Material testing confirmed biocompatibility, while vinyl cutting reproducibility demonstrated high manufacturing fidelity. The platform reliably supported long-term culture (up to 14 days), and the open insert format facilitated uniform seeding and imaging access. This approach enables parallelized experimentation, minimizes pump usage, and is well-suited for labs without microfabrication infrastructure. By combining fabrication flexibility with biological robustness, this work establishes a generalizable platform for modular tissue-chip development adapted to diverse organ systems and serves as a foundational framework for democratizing advanced in vitro model systems. O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=159 SRC="FIGDIR/small/651503v1_ufig1.gif" ALT="Figure 1"> View larger version (35K): org.highwire.dtl.DTLVardef@1e5fed3org.highwire.dtl.DTLVardef@bcf27eorg.highwire.dtl.DTLVardef@d46f33org.highwire.dtl.DTLVardef@d0912f_HPS_FORMAT_FIGEXP M_FIG C_FIG

Micropatterning techniques for 3D cell cultures enable the recreation of tissue-level structures, but their combination with well-defined, microscale fluidic systems for perfusion remains challenging. To address this technological gap, we developed a user-friendly in-situ micropatterning protocol that integrates photolithography of crosslinkable, cell-laden hydrogels with a simple microfluidic housing, and tested the impact of crosslinking chemistry on stability and spatial resolution. Working with gelatin functionalized with photo-crosslinkable moieties, we found that inclusion of cells at high densities ([&ge;] 107/mL) during crosslinking did not impede thiol-norbornene gelation, but decreased the storage moduli of methacryloyl hydrogels. Hydrogel composition and light dose were selected to match the storage moduli of soft tissues. The cell-laden precursor solution was flowed into a microfluidic chamber and exposed to 405 nm light through a photomask to generate the desired pattern. The on-chip 3D cultures were self-standing, and the designs were interchangeable by simply swapping out the photomask. Thiol-ene hydrogels yielded highly accurate feature sizes from 100 - 900 m in diameter, whereas methacryloyl hydrogels yielded slightly enlarged features. Furthermore, only thiol-ene hydrogels were mechanically stable under perfusion overnight. Repeated patterning readily generated multi-region cultures, either separately or adjacent, including non-linear boundaries that are challenging to obtain on-chip. As a proof-of-principle, primary human T cells, were patterned on-chip with high regional specificity. Viability remained high (> 85%) after overnight culture with constant perfusion. We envision that this technology will enable researchers to pattern 3D cultures under fluidic control in biomimetic geometries that were previously difficult to obtain.

The foreign body response to implanted materials often complicates the functionality of sensitive biomedical devices. For cochlear implants, this response can reduce device performance, battery life and preservation of residual acoustic hearing. As a permanent and passive solution to the foreign body response, this work investigates ultra-low-fouling poly(carboxybetaine methacrylate) (pCBMA) thin film hydrogels that are simultaneously photo-grafted and photo-polymerized onto polydimethylsiloxane (PDMS). The cellular anti-fouling properties of these coatings are robustly maintained even after six-months subcutaneous incubation and over a broad range of cross-linker compositions. On pCBMA-coated PDMS sheets implanted subcutaneously, capsule thickness and inflammation are reduced significantly in comparison to uncoated PDMS or coatings of polymerized poly(ethylene glycol dimethacrylate) (pPEGDMA) or poly(hydroxyethyl methacrylate) (pHEMA). Further, capsule thickness is reduced over a wide range of pCBMA cross-linker compositions. On cochlear implant electrode arrays implanted subcutaneously for one year, the coating bridges over the exposed platinum electrodes and dramatically reduces the capsule thickness over the entire implant. Coated cochlear implant electrode arrays could therefore lead to persistent improved performance and reduced risk of residual hearing loss. More generally, the in vivo anti-fibrotic properties of pCBMA coatings also demonstrate potential to mitigate the fibrotic response on a variety of sensing/stimulating implants. Graphical Abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=75 SRC="FIGDIR/small/518125v1_ufig1.gif" ALT="Figure 1"> View larger version (27K): org.highwire.dtl.DTLVardef@1d92121org.highwire.dtl.DTLVardef@e2ca3org.highwire.dtl.DTLVardef@948783org.highwire.dtl.DTLVardef@14ce647_HPS_FORMAT_FIGEXP M_FIG C_FIG

Bespoke cell culture devices are essential for tissue engineering applications. Traditional manufacturing methods for cell culture accessories involve injection molding and machining, which are too costly and time-consuming to implement for producing custom designs in small batches, and/or while testing the usefulness of a new design before mass producing it. Materials typically used for rapid design iteration, like poly(dimethylsiloxane) (PDMS) elastomers, surmount this issue but present new challenges of affinity for hydrophobic small molecules and sub-optimal interactions with sensitive cell types. Here, we propose polycarbonate (PC) thermoforming as a solution for creating customized transparent and autoclavable accessories. We demonstrate that optimized preheating of PC overcomes issues with bubbling during thermoforming. The use of high heat deflection temperature (HDT) resins allows these PC devices to be thermoformed off molds created by Digital Light Processing (DLP) 3D prints, enabling rapid prototyping of the PC. Using this approach, we fabricated custom PC well plate inserts. These inserts combine many advantages of tissue culture polystyrene (negligible absorption of hydrophobic molecules, transparency, rigidity) and elastomers (ease of creating bespoke devices, ability to be sterilized by autoclaving) and are compatible with a variety of cell biology applications, including human induced pluripotent stem cells (iPSC) culture. PC inserts also supported iPSC differentiation into cardiomyocytes (iPS-CM) and micro-patterning of iPS-CM into cardiospheres. This low cost, customizable approach holds promise for a variety of bioengineering applications.

Microfluidic systems incorporating or contained within hydrogels are important in creating microphysiological systems (MPSs). Often naturally derived hydrogels are used, as their inherent bioactivity supports dynamic cellular behaviors. Hydrogel biomaterials that are partly or fully synthetic are desirable in engineering systems with specific, designed properties, though they typically lack bioactive features of natural materials without additional molecular design. In particular, permissive biomaterials enable physiologically relevant dynamic cellular behaviors. Granular hydrogels offer inherent permissiveness, owning to porosity between particles and dynamic behaviors in the absence of interparticle crosslinking. However, applying these in MPS to model tissues requires stable channels to perfuse fluid in these dynamic systems. Here, we establish channels within granular hydrogels to enable perfusion through spatially controlled interparticle crosslinking. Selective crosslinking allowed for the formation of stable channels while allowing the microparticles of a granular hydrogel between two channels to remained uncrosslinked. This allowed spatiotemporal control of signals within an environment established from microparticles without interparticle crosslinking. Fluorescently tagged molecules allowed for the visualization of controlled soluble gradients between two channels within the device. Additionally, embedded 3D printing processes can be used to specify material composition within the system, demonstrating integrated technology for engineering well-defined hydrogel systems. Integrated microfluidic-based control over soluble signals in a system that is compatible with 3D printing processes will establish a basis for building MPSs for broad applications, and the ability to maintain granular systems in culture without interparticle crosslinking will enable design of synthetic hydrogels that access unique dynamic properties within these systems.

Stereolithography (SLA) 3D printing has become increasingly popular for fabricating microfluidic devices, with applications including hydrogel patterning and tissue modeling. In open-channel systems with surface tension-driven flow, 3D-printer-induced discrepancies in channel surface texture can significantly impact fluid flow and device performance. While previous work has focused on comparing different 3D printing methods for microchannel fabrication, the effect of device orientation during SLA printing on microchannel morphology and capillary-driven flow has not been systematically evaluated. Furthermore, there is minimal research elucidating the influence of channel surface texture on the flow of biologically relevant hydrogel precursors commonly used in organ-on-a-chip applications. Herein, we investigated the impact of print orientation on channel morphology, fluid wetting behavior, and fluid flow by comparing laser SLA-based parts where the length of the channel was tilted at 0{degrees}, 15{degrees}, 45{degrees}, or 90{degrees} during printing. We demonstrated that channel floor surface texture is greatly affected by print orientation: the highest axial surface roughness was measured in 15{degrees} printed channels, and the highest axial surface tortuosity-which describes the real length along the surface-was measured in 45{degrees} printed channels. Print angles of 15{degrees} and 45{degrees} also resulted in asymmetric roughness of the channel floor, which caused asymmetric wetting of glycerol solution. Surface tension-driven flow of glycerol solution, agarose precursor solution, and collagen precursor solution was affected by print orientation, in which the 45{degrees} printed flow devices had slowest flow for all test fluids. Root mean square roughness was not a reliable predictor of slower flow; instead, surface tortuosity should be considered. Potential alternatives to better theoretically model how print angle-induced surface texture affects open-channel flow are discussed as well. These findings provide a framework of fabrication considerations for laser SLA printing of open microchannels that can also be applied to other layer-by-layer, vat photopolymerization-based 3D printing technologies.

The development of microphysiological cell culture models (MPMs) that align with the throughput demands of drug and chemical testing are needed to help reduce animal testing, aide in the discovery of new drugs, and identify harmful chemical exposures. To address this need, we have developed a process for rapid prototyping MPM devices using computer numerical control (CNC) micromilling of commercially available microplates. Microchannels are cut out of the existing microplate structure and ports are drilled into the bottom of the wells to interface the wells. To test versatility and benchmark to another rapid-prototyping approach, we manufactured common microfluidic features into microplates using four different CNC mills as well as a 3D printer. Cell viability was assessed for polystyrene (PS) well plates and two 3D printed resins (MED610 and VeroClear) with the PS showing >2.5-fold increase in cell growth after three days. Machines were tested on their ability to create common device features including a traditional microfluidic device as well as a custom design incorporating complex geometries. Features were measured by confocal microscopy. We found that features including 1000{micro}m ports, 800{micro}m microchannels, 200{micro}m phase-guides, and 500{micro}m post arrays were machined and the range of CVs for features were 1.02-4.42, 1.32-3.50, 2.34-16.58, 6.25-16.40 respectively, while the 3D printed features exhibited maximal CVs of 20.98, 11.68, 23.60, and 10.01 for the same features. Predictably, more expensive machines generally showed higher accuracy and lower variation, but many features could be created accurately and precisely by inexpensive (<$3000) machines facilitating the broader use of this technology to create a user customizable platform to support the prototyping, development, and testing of human relevant models with broad applications across the life sciences. Graphical abstractMultiple CNC mills are assessed on accuracy and precision of microfluidic features of interest for microphysiological model development creation. O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=112 SRC="FIGDIR/small/615399v1_ufig1.gif" ALT="Figure 1"> View larger version (42K): org.highwire.dtl.DTLVardef@1be08eorg.highwire.dtl.DTLVardef@33b0a4org.highwire.dtl.DTLVardef@192167borg.highwire.dtl.DTLVardef@200b7_HPS_FORMAT_FIGEXP M_FIG C_FIG

Over the past decade, the integration of microgel-based granular hydrogels in biomedical technologies has experienced substantial growth due to the numerous benefits microgels offer. However, the inability to easily adopt uniform microgel fabrication workflows at scale constitutes a major bottleneck, or in some cases, a barrier-to-entry that stunts further growth of the field. The gold-standard technique for emulsion-based microgel production is through microfluidic droplet-generating devices that produce liquid gel precursor droplets that gel post-production. However, traditional microfluidic workflows often require multiple independent flows and controlled pressure sources, along with a steep learning curve in using microfluidics to achieve uniform droplet sizes reproducibly and repeatedly. This difficulty in adopting microgel fabrication is further compounded by low throughput and the extensive flow rate calibration required when switching to new formulations (e.g., material type, droplet size). In this work, we present a step-emulsion system that bridges the gap by providing a robust and simple setup. We experimentally characterize and evaluate how flow and outlet channel dimension contribute to the generation of uniform droplet populations at specific sizes. With our large dataset consisting of various outlet channel dimensions, we evaluated outlet channel geometrical impacts (height, width, cross-sectional area, aspect-ratio, etc.) on gel precursor droplet size and generation throughput. We demonstrate robust, highly compatible, and repeatably uniform droplet generation from various gel precursor polymer backbones, users with varying microfluidics experience, and a wide viscosity range, including alginate solutions with 650 times the viscosity of water. Furthermore, we confirmed consistent gel precursor droplet generation outcomes driven by a constant flow source (syringe pump) and by direct manual injection as a simple and highly adoptable option for the generation of gel precursor droplets. This platform is ideal for researchers seeking rapid and easy microgel fabrication, regardless of microfluidics experience.

This paper focuses on the design, fabrication, and characterization of a platform aiming to dynamically culture cells under mechanical stimulation. The platform, made of polymethylmethacrylate (PMMA), allows real-time mechanical stimuli, providing valuable insights for living tissue models. Through mechanical testing and dynamic microfluidic tests, the chip functionality was assessed. The experimental results validation showcases the potential of the device in mimicking physiological conditions, offering a promising avenue for pharmaceutical testing advancement.

Photo-crosslinkable hydrogels are widely employed in biofabrication and tissue engineering as they provide spatiotemporal control over gelation. Most conventional photo-curing hydrogel systems rely upon small-molecule photoinitiators which, upon activation by (ultra)violet irradiation, generate free radicals to initiate polymerization. Such an approach can induce oxidative stress and DNA damage, significantly limiting their use in sensitive biological applications. Here, we present a photoinitiator-free, gelatin-based hydrogel system functionalized with acrylamidylpyrene groups (Gel-Pyr), which undergoes photocrosslinking via a visible-light-induced [2+2] cycloaddition reaction. Gel-Pyr exhibits rapid gelation kinetics, tuneable mechanical properties, facile temporal control over photocrosslinking, and long-term structural stability (>30 days) in cell culture conditions. Rheological analyses reveal pronounced shear-thinning behaviour at room temperature, enabling extrusion-based 3D bioprinting of multilayered constructs with high structural fidelity. Fine strand resolution (<400 {micro}m) is achieved in bioprinted crosshatch structures, enabling sufficient nutrient diffusion for cell support. Encapsulation of human mesenchymal stem cells (hMSCs) within both bulk and printed constructs maintains >80% viability over 7 days, demonstrating robust cytocompatibility. By eliminating UV exposure and free radicals, this visible-light-responsive hydrogel platform offers a facile and cytoprotective alternative to other hydrogel systems. Table of ContentA visible light-crosslinkable, initiator-free gelatin-based hydrogel (Gel-Pyr) is developed using acrylamidylpyrene functionalization. This radical-free system enables rapid crosslinking under cytocompatible reaction conditions and offers excellent printability, tuneable mechanics, and long-term stability. Gel-Pyr supports high cell viability and precision bioprinting, positioning it as a promising platform for tissue engineering and in vitro biofabrication. O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=181 SRC="FIGDIR/small/691472v1_ufig1.gif" ALT="Figure 1"> View larger version (55K): org.highwire.dtl.DTLVardef@168fbd5org.highwire.dtl.DTLVardef@16d7e7forg.highwire.dtl.DTLVardef@18beea3org.highwire.dtl.DTLVardef@1e02cd9_HPS_FORMAT_FIGEXP M_FIG C_FIG

Climate change-driven increases in forest fires pose a major global health risk due to exposure to smoke containing hazardous gases and fine particulates, emphasizing the need for physiologically relevant in vitro airway models for studying smoke-induced responses. Microfluidic lung-on-a-chip technologies provide a strong foundation for in vitro airway modeling and ongoing developments are expanding their ability to incorporate multicellular organization, extracellular matrix complexity, and physiologically relevant exposure methods. This work presents the optimization and integration of a photopolymerizable gelatin methacrylate (GelMA)-based hydrogel into a microfluidic airway-on-a-chip that models the human small conducting airways and supports controlled aerosol exposure to wood smoke. The GelMA hydrogel was optimized to support fibroblast encapsulation, endothelial, and epithelial adhesion and robust mechanical stability. The device combines the hydrogel with a compartmentalized microchannel layout, and sacrificial molding to create a 3D organotypic airway culture featuring a multilayer architecture, 3D stromal matrix, and a perfusable vasculature-like lumen. Coupling the platform with a custom aerosol exposure system enables precise, biomimetic exposure to whole wood smoke. Proof-of-concept studies using transforming growth factor beta1 (TGF-{beta}1) and whole wood smoke elicited expected inflammatory and fibrotic responses, validating the platforms physiological relevance for inhalation studies and investigating smoke-induced airway remodeling and inflammation.

Innovative techniques for gene editing have enabled accurate animal models of human diseases to be established. In order for these methods to be successfully adopted in the scientific community, the optimization of procedures used for breeding genetically altered mice is required. Among these, the in vitro fertilization (IVF) procedure is still suboptimal and the culture methods do not guarantee the development of competent embryos. Critical aspects in traditional in vitro embryo culture protocols include the use of mineral oil and the stress induced by repetitive handling of the embryos. A new microfluidic system was designed to allow for efficient in vitro culture of mouse embryos. Harmful fluidic stress and plastic toxicity were excluded by completing the industry gold standard Mouse Embryo Assay. The potential competence of the embryos developed in the device was quantified in terms of blastocyst rate, outgrowth assay, energy substrate metabolism and expression of genes related to implantation potential. Mass spectrometry analyses identified plastic-related compounds released in medium, and confirmed leaching of low molecular weight species into the culture medium that might be associated to un-crosslinked PDMS. Finally, these data show the potential for the system to study preimplantation embryo development and to improve human IVF techniques.

Large scale cell-laden hydrogel models hold great promise for tissue repair and organ transplantation, but their fabrication is faced with challenges in achieving clinically-relevant size and hierarchical structures. 3D bioprinting is an emerging technology, but its application in large, solid hydrogel fabrication has been limited by the slow printing speed that can affect the part quality and the biological activity of the encapsulated cells. Here we present a Fast hydrogeL prOjection stereolithogrAphy Technology (FLOAT) that allows the creation of a centimeter-sized, multiscale solid hydrogel model within minutes. Through precisely controlling the photopolymerization condition, we established low suction force-driven, high-velocity flow of the hydrogel prepolymer that supports the continuous replenishment of the prepolymer solution below the curing part and the nonstop part growth. We showed that this process is unique to the hydrogel prepolymer without externally supplemented oxygen. The rapid printing of centimeter-sized hydrogel models using FLOAT was shown to significantly reduce the part deformation and cellular injury caused by the prolonged exposure to the environmental stresses in layer-by-layer based printing methods. Media perfusion in the printed vessel network was shown to promote cell survival and metabolic function in the deep core of the large-sized hydrogel model over long term. The FLOAT is compatible with multiple photocurable hydrogel materials and the printed scaffold supports the endothelialization of prefabricated vascular channels. Together, these studies demonstrate a rapid 3D hydrogel printing method and highlight the potential of this method in the fabrication of large-sized engineered tissue models.

In vitro three-dimensional (3D) cell models have been accepted to better recapitulate aspects of in vivo organ environment than 2D cell culture. Currently, the production of these complex in vitro 3D cell models with multiple cell types and microenvironments remains challenging and prone to human error. Here we report a versatile bioink comprised of a 4-arm PEG based polymer with distal maleimide derivatives as the main ink component and a bis-thiol species as the activator that crosslinks the polymer to form the hydrogel in less than a second. The rapid gelation makes the polymer system compatible with 3D bioprinting. The ink is combined with a drop-on-demand 3D bioprinting platform consisting of eight independently addressable nozzles and high-throughput printing logic for creating complex 3D cell culture models. The combination of multiple nozzles and fast printing logic enables the rapid preparation of many complex 3D structures comprising multiple hydrogel environments in the one structure in a standard 96-well plate format. The platform compatibility for biological applications was validated using pancreatic ductal adenocarcinoma cancer (PDAC) cells with their phenotypic responses controlled by tuning the hydrogel microenvironment.

Central airway obstruction is a life-threatening disorder causing a high physical and psychological burden to patients due to severe breathlessness and impaired quality of life. Standard-of-care airway stents are silicone tubes, which cause immediate relief, but are prone to migration, especially in growing patients, and require additional surgeries to be removed, which may cause further tissue damage. Customized airway stents with tailorable bioresorbability that can be produced in a reasonable time frame would be highly needed in the management of this disorder. Here, we report poly(D,L-lactide-co-{varepsilon}-caprolactone) methacrylate blends-based biomedical inks and their use for the rapid fabrication of customized and bioresorbable airway stents. The 3D printed materials are cytocompatible and exhibit silicone-like mechanical properties with suitable biodegradability. In vivo studies in healthy rabbits confirmed biocompatibility and showed that the stents stayed in place for 7 weeks after which they became radiographically invisible. The developed biomedical inks open promising perspectives for the rapid manufacturing of the customized medical devices for which high precision, tuneable elasticity and predictable degradation are sought-after.

Engineered in vitro platforms are powerful systems to study information flow in the nervous system. While existing polydimethylsiloxane (PDMS)-based microfluidic platforms offer precise architectures, the cultured neurons grow on two-dimensional (2D) planar multielectrode arrays (MEA). To mimic the native microenvironment, where neurons grow in three-dimensional (3D) extracellular matrices (ECM), 3D hydrogels can be designed to encapsulate cells and enable physiologically-mimicked behaviors. Here, we describe hydroMEA, a 3D platform fabricated by placing PDMS microstructures on a high-density MEA and filled with a desired hydrogel, to offer controlled topologies, physiologically-relevant microenvironments, and real-time electrophysiological measurements. First, we developed a gelatin methacryloyl (GelMA) hydrogel with incorporated ECM components and tuned the mechanical properties to match those of nerve tissue. The hydrogel was able to support: 1) the growth of iPSC-derived sensory neurons (hSNs) for >100 days; 2) co-cultures of hSN with human embryonic stem cell-derived Schwann cells (hSCs), to enable reliable 3D myelination. Next, hydroMEA were prepared for topologically- defined 3D growth and myelination in designated compartments. Finally, electrophysiological evaluation of hSN-hSCs co-cultures revealed increased conduction speeds indicating functional myelin. This platform is a promising tool to study cell-cell interactions and to functionally evaluate the effect of pharmacological compounds in a more translational manner.