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Bioprinting is currently the most promising method to biofabricate complex tissues in vitro with the potential to transform the future of organ transplantation and drug discovery. Efforts to create such tissues are, however, almost exclusively based on animal-derived materials, like gelatin methacryloyl, which have demonstrated efficacy in bioprinting of complex tissues. While these materials are already used in clinical applications, uncertainty about their safety still remains due to their animal origin. Alternatively, synthetic bioinks are developed that match the printability of natural bioinks but lack their biological complexity, and thereby often fail to support cell growth and facilitate tissue formation. Additionally, most synthetic materials do not meet the mechanical demands to bioprint stable constructs while providing a suitable environment for cells to grow, limiting the number of available bioinks. To bridge this gap and synergize bioprinting and 3D cell culture, we developed a PEG-based bioink system to promote the growth and spreading of cell spheroids that consist of human primary endothelial cells and fibroblasts. The 3D bioprinted centimeter-scale constructs have a high shape fidelity and accelerated softening to provide sufficient space for cells to grow. Adjusting the rate of degradability, induced by the integration of ester-functionalized crosslinkers in addition to protease cleavable crosslinkers into the hydrogel network, improves the growth of spheroids in larger printed hydrogel constructs containing an interconnected channel structure. The perfusable constructs enable extensive spheroid sprouting and the formation of a cellular network upon fusion of sprouts as initial steps towards tissue formation with the potential for clinical translation., (Creative Commons Attribution license.)

Although micron-sized microgels have become important building blocks in regenerative materials, offering decisive interactions with living matter, their chemical composition mostly significantly varies when their network morphology is tuned. Since cell behavior is simultaneously affected by the physical, chemical, and structural properties of the gel network, microgels with variable morphology but chemical equivalence are of interest. This work describes a new method to produce thermoresponsive microgels with defined mechanical properties, surface morphologies, and volume phase transition temperatures. A wide variety of microgels is synthesized by crosslinking monomers or star polymers at different temperatures using thermally assisted microfluidics. The diversification of microgels with different network structures and morphologies but of chemical equivalence offers a new platform of microgel building blocks with the ability to undergo phase transition at physiological temperatures. The method holds high potential to create soft and dynamic materials while maintaining the chemical composition for a wide variety of applications in biomedicine., (© 2024 The Author(s). Angewandte Chemie International Edition published by Wiley-VCH GmbH.)

Recent studies show the importance of hydrogel geometry for various applications, such as encoding, micromachines, or tissue engineering. However, fabricating hydrogel structures with micrometer-sized features, advanced geometry, and precise control of porosity remains challenging. This work presents hierarchically structured hydrogels, so-called hydrogel patches, with internally deviating regions on a micron-scale. These regions are defined in a one-step, high-throughput fabrication process via stop-flow lithography. Between the specified projection pattern during fabrication, an interconnecting lower crosslinked and more porous hydrogel network forms, resulting in at least two degrees of crosslinking within the patches. A detailed investigation of patch formation is performed for two material systems and pattern variations, revealing basic principles for reliable patch formation. In addition to the two defined crosslinked regions, further regions are implemented in the patches by adapting the pattern accordingly. The variations in pattern geometry impact the mechanical characteristics of the hydrogel patches, which display pattern-dependent compression behavior due to predefined compression points. Cell culture on patches, as one possible application, reveals that the patch pattern determines the cell area of L929 mouse fibroblasts. These results introduce hierarchically structured hydrogel patches as a promising and versatile platform system with high customizability., (© 2024 The Author(s). Small published by Wiley‐VCH GmbH.)

Chronic kidney disease (CKD) affects more than 10% of the global population. As kidney function negatively correlates with the presence of interstitial fibrosis, the development of new anti-fibrotic therapies holds promise to stabilize functional decline in CKD patients. The goal of the study was to generate a scalable bioprinted 3-dimensional kidney tubulo-interstitial disease model of kidney fibrosis. We have generated novel human PDGFRβ + pericytes, CD10 + epithelial and CD31 + endothelial cell lines and compared their transcriptomic signature to their in vivo counterpart using bulk RNA sequencing in comparison to human kidney single cell RNA-sequencing datasets. This comparison indicated that the novel cell lines still expressed kidney cell specific genes and shared many features with their native cell-state. PDGFRβ + pericytes showed three-lineage differentiation capacity and differentiated towards myofibroblasts following TGFβ treatment. We utilized a fibrinogen/gelatin-based hydrogel as bioink and confirmed a good survival rate of all cell types within the bioink after printing. We then combined all three cells in a bioprinted model using separately printed compartments for tubule epithelium, and interstitial endothelium and pericytes. We confirmed that this 3D printed model allows to recapitulate key disease driving epithelial-mesenchymal crosstalk mechanisms of kidney fibrosis since injury of epithelial cells prior to bioprinting resulted in myofibroblast differentiation and fibrosis driven by pericytes after bioprinting. The bioprinted model was also scalable up to a 96-well format., Competing Interests: Declaration of competing interest The authors declare the following financial interests/personal relationships which may be considered as potential competing interests: Rafael Kramann reports financial support was provided by German Research FoundationDFGSFBTRR219. Rafael Kramann reports financial support was provided by CRU344 4288578857858. Rafael Kramann reports financial support was provided by CRU5011 445703531. Rafael Kramann reports a relationship with Sequantrix GmbH that includes: board membership and equity or stocks. Sikander Hayat reports a relationship with Sequantrix GmbH that includes: board membership and equity or stocks. If there are other authors, they declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 The Authors. Published by Elsevier Ltd.. All rights reserved.)

A novel approach to selectively modify narrow subareas of metallic nanostructures adjacent to plasmonic hotspots, where strong electromagnetic field amplification occurs upon localized surface plasmon (LSP) excitation, is reported. In contrast to surface plasmon-triggered polymerization, it relies on plasmonically enhanced multiphoton crosslinking (MPC) of polymer chains carrying photoactive moieties. When they are contacted with metallic nanostructures and irradiated with a femtosecond near-infrared beam resonantly coupled with LSPs, the enhanced field intensity locally exceeds the threshold and initiates MPC only at plasmonic hotspots. This concept is demonstrated by using gold nanoparticle arrays coated with two specifically designed polymers. Local MPC of a poly( N , N -dimethylacrylamide)-based copolymer with an anthraquinone crosslinker is shown via atomic force microscopy. Additionally, MPC is tested with a thermoresponsive poly( N -isopropylacrylamide)-based terpolymer. The reversible thermally induced collapse and swelling of the MPC-formed hydrogel at specific nanoparticle locations are confirmed by polarization-resolved localized surface plasmon resonance (LSPR) spectroscopy. These hybrid metallic/hydrogel materials can be further postmodified, offering attractive characteristics for future spectroscopic/bioanalytical applications., Competing Interests: The authors declare no competing financial interest., (© 2024 The Authors. Published by American Chemical Society.)

Microporous annealed particle (MAP) scaffolds are investigated for their application as injectable 3D constructs in the field of regenerative medicine and tissue repair. While available MAP scaffolds provide a stable interlinked matrix of microgels for cell culture, the infiltration depth and space for cells to grow inside the scaffolds is pre-determined by the void fraction during the assembly. In the case of MAP scaffolds fabricated from interlinked spherical microgels, a cellularity gradient can be observed with the highest cell density on the scaffold surface. Additionally, the interlinked microgel network limits the ability of cells to remodel their environment, which contradicts native tissue dynamics. In this work, a cell-induced interlinking method for MAP scaffold formation is established, which avoids the necessity of chemical crosslinkers and pre-engineered pores to achieve micro- or macropores in these 3D frameworks. This method enables cells to self-organize with microgels into dynamic tissue constructs, which can be further controlled by altering the microgel properties, the cell/microgel ratio, and well shape. To form a cell-induced interlinked scaffold, the cells are mixed with dextran-based microgels and function as a glue between the microgels, resulting in a more homogenous cell distribution throughout the scaffold with efficient cell-cell interactions., (© 2023 The Authors. Advanced Healthcare Materials published by Wiley‐VCH GmbH.)

Fibrosis represents the uncontrolled replacement of parenchymal tissue with extracellular matrix (ECM) produced by myofibroblasts. While genetic fate-tracing and single-cell RNA-Seq technologies have helped elucidate fibroblast heterogeneity and ontogeny beyond fibroblast to myofibroblast differentiation, newly identified fibroblast populations remain ill defined, with respect to both the molecular cues driving their differentiation and their subsequent role in fibrosis. Using an unbiased approach, we identified the metalloprotease ADAMTS12 as a fibroblast-specific gene that is strongly upregulated during active fibrogenesis in humans and mice. Functional in vivo KO studies in mice confirmed that Adamts12 was critical during fibrogenesis in both heart and kidney. Mechanistically, using a combination of spatial transcriptomics and expression of catalytically active or inactive ADAMTS12, we demonstrated that the active protease of ADAMTS12 shaped ECM composition and cleaved hemicentin 1 (HMCN1) to enable the activation and migration of a distinct injury-responsive fibroblast subset defined by aberrant high JAK/STAT signaling.

Biomedical applications such as drug delivery, tissue engineering, and functional surface coating rely on switchable adsorption and desorption of specialized guest molecules. Poly(dehydroalanine), a polyzwitterion containing pH-dependent positive and negative charges, shows promise for such reversible loading, especially when integrated into a gel network. Herein, we present the fabrication of poly(dehydroalanine)-derived gels of different size scales and evaluate them with respect to their practical use in biomedicine. Already existing protocols for bulk gelation were remodeled to derive suitable reaction conditions for droplet-based microfluidic synthesis. Depending on the layout of the microfluidic chip, microgels with a size of approximately 30 μm or 200 μm were obtained, whose crosslinking density can be increased by implementing a multi-arm crosslinker. We analyzed the effects of the crosslinker species on composition, permeability, and softness and show that the microgels exhibit advantageous properties inherent to zwitterionic polymer systems, including high hydrophilicity as well as pH- and ionic strength-sensitivity. We demonstrate pH-regulated uptake and release of fluorescent model dyes before testing the adsorption of a small antimicrobial peptide, LL-37. Quantification of the peptide accommodated within the microgels reveals the impact of size and crosslinking density of the microgels. Biocompatibility of the microgels was validated by cell tests.

Mesenchymal stem cells (MSCs) have the potential to differentiate into multiple lineages and can be harvested relatively easily from adults, making them a promising cell source for regenerative therapies. While it is well-known how to consistently differentiate MSCs into adipose, chondrogenic, and osteogenic lineages by treatment with biochemical factors, the number of studies exploring how to achieve this with mechanical signals is limited. A relatively unexplored area is the effect of cyclic forces on the MSC differentiation. Recently, our group developed a thermoresponsive N -ethyl acrylamide/ N -isopropylacrylamide (NIPAM/NEAM) hydrogel supplemented with gold nanorods that are able to convert near-infrared light into heat. Using light pulses allows for local hydrogel collapse and swelling with physiologically relevant force and frequency. In this study, MSCs are cultured on this hydrogel system with a patterned surface and exposed to intermittent or continuous actuation of the hydrogel for 3 days to study the effect of actuation on MSC differentiation. First, cells are harvested from the bone marrow of three donors and tested for their MSC phenotype, meeting the following criteria: the harvested cells are adherent and demonstrate a fibroblast-like bipolar morphology. They lack the expression of CD34 and CD45 but do express CD73, CD90, and CD105. Additionally, their differentiation potential into adipogenic, chondrogenic, and osteogenic lineages is validated by the addition of standardized differentiation media. Next, MSCs are exposed to intermittent or continuous actuation, which leads to a significantly enhanced cell spreading compared to nonactuated cells. Moreover, actuation results in nuclear translocation of Runt-related transcription factor 2 and the Yes-associated protein. Together, these results indicate that cyclic mechanical stimulation on a soft, ridged substrate modulates the MSC fate commitment in the direction of osteogenesis.

Microbubbles (MB) are used as ultrasound (US) contrast agents in clinical settings because of their ability to oscillate upon exposure to acoustic pulses and generate nonlinear responses with a stable cavitation profile. Polymeric MB have recently attracted increasing attention as molecular imaging probes and drug delivery agents based on their tailorable acoustic responses, high drug loading capacity, and surface functionalization capabilities. While many of these applications require MB to be functionalized with biological ligands, the impact of bioconjugation on polymeric MB cavitation and acoustic properties remains poorly understood. Hence, we here evaluated the effects of MB shell hydrolysis and subsequent streptavidin conjugation on the acoustic behavior of poly(butyl cyanoacrylate) (PBCA) MB. We show that upon biofunctionalization, MB display higher acoustic stability, stronger stable cavitation, and enhanced second harmonic generation. Furthermore, functionalized MB preserve the binding capabilities of streptavidin conjugated on their surface. These findings provide insights into the effects of bioconjugation chemistry on polymeric MB acoustic properties, and they contribute to improving the performance of polymer-based US imaging and theranostic agents.

In this report, a versatile method is demonstrated to create colloidal suprastructures by assembly and supramolecular interlinking of microgels using droplet-based microfluidics. The behavior of the microgels is systematically investigated to evaluate the influence of their concentration on their distribution between the continuous, the droplet phase, and the interface. At low concentrations, microgels are mainly localized at the water-oil interface whereas an excess of microgels results, following the complete coverage of the water-oil interface, in their distribution in the continuous phase. To stabilize the colloidal suprastructure, on-chip gelation is introduced by adding natural polyphenol tannic acid (TA) in the water phase. TA forms interparticle linking between the poly(N-vinylcaprolactam) (PVCL) microgels by supramolecular interactions. The combination of supramolecular interlinking with the variation of the microgel concentration in microfluidic droplets enables on-chip fabrication of defined colloidal suprastructures with morphologies ranging from colloidosomes to colloidal supraballs. The obtained supracolloidal structures exhibit a pH-responsive behavior with a disintegration at alkaline conditions within a scale of seconds. The destabilization process results from the deprotonation of phenolic groups and destruction of hydrogen bonds with PVCL chains at higher pH., (© 2023 The Authors. Small published by Wiley-VCH GmbH.)

Microgels are water-swollen, crosslinked polymers that are widely used as colloidal building blocks in scaffold materials for tissue engineering and regenerative medicine. Microgels can be controlled in their stiffness, degree of swelling, and mesh size depending on their polymer architecture, crosslink density, and fabrication method-all of which influence their function and interaction with the environment. Currently, there is a lack of understanding of how the polymer composition influences the internal structure of soft microgels and how this morphology affects specific biomedical applications. In this report, we systematically vary the architecture and molar mass of polyethylene glycol-acrylate (PEG-Ac) precursors, as well as their concentration and combination, to gain insight in the different parameters that affect the internal structure of rod-shaped microgels. We characterize the mechanical properties and diffusivity, as well as the conversion of acrylate groups during photopolymerization, in both bulk hydrogels and microgels produced from the PEG-Ac precursors. Furthermore, we investigate cell-microgel interaction, and we observe improved cell spreading on microgels with more accessible RGD peptide and with a stiffness in a range of 20 kPa to 50 kPa lead to better cell growth., (© 2023 The Authors. Angewandte Chemie International Edition published by Wiley-VCH GmbH.)

Nanofibrous scaffolds are widely investigated for tendon tissue engineering due to their porous structure, high flexibility, and the ability to guide cells in a preferred direction. Previous research has shown that providing a microenvironment similar to in vivo settings improves tissue regeneration. Therefore, in this work, ingenious multicomponent nanoyarn scaffolds that mimic the fibrillar and tubular structures of tendons are developed for the first time through electrospinning and bundling nanoyarns followed by electrospinning of a nanofibrous shell around the bundle. Multicomponent nanoyarn scaffolds out of poly(ε-caprolactone) with varying porosity, density, and diameter were successfully produced by coelectrospinning with water-soluble poly(2-ethyl-2-oxazoline) as a sacrificial component. The diameter and fiber orientation of the nanoyarns were successfully tuned based on parameter-morphology models obtained by the design of experiments. Cyclic bending tests were performed, indicating that the flexibility of the multicomponent nanoyarn scaffolds depends on the morphology and can be tuned through controlling the number of nanoyarns in the bundle and the porosity. Indirect and direct cell culture tests using mouse and equine tendon cells revealed excellent cytocompatibility of the nanofibrous products and demonstrated the potential of the nanoyarns to guide the growing cells along the nanofiber direction, which is crucial for tendon tissue engineering.

Recreating human tissues and organs in the petri dish to establish models as tools in biomedical sciences has gained momentum. These models can provide insight into mechanisms of human physiology, disease onset, and progression, and improve drug target validation, as well as the development of new medical therapeutics. Transformative materials play an important role in this evolution, as they can be programmed to direct cell behavior and fate by controlling the activity of bioactive molecules and material properties. Using nature as an inspiration, scientists are creating materials that incorporate specific biological processes observed during human organogenesis and tissue regeneration. This article presents the reader with state-of-the-art developments in the field of in vitro tissue engineering and the challenges related to the design, production, and translation of these transformative materials. Advances regarding (stem) cell sources, expansion, and differentiation, and how novel responsive materials, automated and large-scale fabrication processes, culture conditions, in situ monitoring systems, and computer simulations are required to create functional human tissue models that are relevant and efficient for drug discovery, are described. This paper illustrates how these different technologies need to converge to generate in vitro life-like human tissue models that provide a platform to answer health-based scientific questions., (© 2023 The Authors. Advanced Healthcare Materials published by Wiley-VCH GmbH.)

Today's living world is enriched with a myriad of natural biological designs, shaped by billions of years of evolution. Unraveling the construction rules of living organisms offers the potential to create new materials and systems for biomedicine. From the close examination of living organisms, several concepts emerge: hierarchy, pattern repetition, adaptation, and irreducible complexity. All these aspects must be tackled to develop transformative materials with lifelike behavior. This perspective article highlights recent progress in the development of transformative biohybrid systems for applications in the fields of tissue regeneration and biomedicine. Advances in computational simulations and data-driven predictions are also discussed. These tools enable the virtual high-throughput screening of implant design and performance before committing to fabrication, thus reducing the development time and cost of biomimetic and biohybrid constructs. The ongoing progress of imaging methods also constitutes an essential part of this matter in order to validate the computation models and enable longitudinal monitoring. Finally, the current challenges of lifelike biohybrid materials, including reproducibility, ethical considerations, and translation, are discussed. Advances in the development of lifelike materials will open new biomedical horizons, where perhaps what is currently envisioned as science fiction will become a science-driven reality in the future., (© 2023 The Authors. Advanced Healthcare Materials published by Wiley-VCH GmbH.)

Therapeutic antibodies are the key treatment option for various cytokine-mediated diseases, such as rheumatoid arthritis, psoriasis, and inflammatory bowel disease. However, systemic injection of these antibodies can cause side effects and suppress the immune system. Moreover, clearance of therapeutic antibodies from the blood is limiting their efficacy. Here, water-swollen microgels are produced with a size of 25 µm using droplet-based microfluidics. The microgels are functionalized with TNFα antibodies to locally scavenge the pro-inflammatory cytokine TNFα. Homogeneous distribution of TNFα-antibodies is shown throughout the microgel network and demonstrates specific antibody-antigen binding using confocal microscopy and FLIM-FRET measurements. Due to the large internal accessibility of the microgel network, its capacity to bind TNFα is extremely high. At a TNFα concentration of 2.5 µg mL -1 , the microgels are able to scavenge 88% of the cytokine. Cell culture experiments reveal the therapeutic potential of these microgels by protecting HT29 colorectal adenocarcinoma cells from TNFα toxicity and resulting in a significant reduction of COX II and IL8 production of the cells. When the microgels are incubated with stimulated human macrophages, to mimic the in vivo situation of inflammatory bowel disease, the microgels scavenge almost all TNFα that is produced by the cells., (© 2023 The Authors. Advanced Healthcare Materials published by Wiley-VCH GmbH.)

Surface tension provides microbubbles (MB) with a perfect spherical shape. Here, we demonstrate that MB can be engineered to be nonspherical, endowing them with unique features for biomedical applications. Anisotropic MB were generated via one-dimensionally stretching spherical poly(butyl cyanoacrylate) MB above their glass transition temperature. Compared to their spherical counterparts, nonspherical polymeric MB displayed superior performance in multiple ways, including i) increased margination behavior in blood vessel-like flow chambers, ii) reduced macrophage uptake in vitro, iii) prolonged circulation time in vivo, and iv) enhanced blood-brain barrier (BBB) permeation in vivo upon combination with transcranial focused ultrasound (FUS). Our studies identify shape as a design parameter in the MB landscape, and they provide a rational and robust framework for further exploring the application of anisotropic MB for ultrasound-enhanced drug delivery and imaging applications.

Continuous flow manufacturing (CFM) has shown remarkable advantages in the industrial-scale production of drug-loaded nanomedicines, including mRNA-based COVID-19 vaccines. Thus far, CFM research in nanomedicine has mainly focused on the initial particle formation step, while post-formation production steps are hardly ever integrated. The opportunity to implement in-line quality control of critical quality attributes merits closer investigation. Here, we designed and tested a CFM setup for the manufacturing of liposomal nanomedicines that can potentially encompass all manufacturing steps in an end-to-end system. Our main aim was to elucidate the key composition and process parameters that affect the physicochemical characteristics of the liposomes. Total flow rate, lipid concentration and residence time of the liposomes in a high ethanol environment ( i.e. , above 20% v/v) emerged as critical parameters to tailor liposome size between 80 and 150 nm. After liposome formation, the pressure and the surface area of the filter in the ultrafiltration unit were critical parameters in the process of clearing the dispersion from residual ethanol. As a final step, we integrated in-line measurement of liposome size and residual ethanol content. Such in-line measurements allow for real-time monitoring and in-process adjustment of key composition and process parameters.

Growing millimeter-scaled functional tissue remains a major challenge in the field of tissue engineering. Therefore, microporous annealed particles (MAPs) are emerging as promising porous biomaterials that are formed by assembly of microgel building blocks. To further vary the pore size and increase overall MAP porosity of mechanically stable scaffolds, rod-shaped microgels with high aspect ratios up to 20 are chemically interlinked into highly porous scaffolds. Polyethylene glycol based microgels (width 10 µm, lengths up to 200 µm) are produced via in-mold polymerization and covalently interlinked into stable 3D scaffolds via epoxy-amine chemistry. For the first time, MAP porosities can be enhanced by increasing the microgel aspect ratio (mean pore sizes ranging from 39 to 82 µm, porosities from 65 to 90%). These porosities are significantly higher compared to constructs made from spherical or lower aspect ratio rod-shaped microgels. Rapid filling of the pores by either murine or primary human fibroblasts is ensured as cells migrate and grow extensively into these scaffolds. Overall, this study demonstrates that highly porous, stable macroporous hydrogels can be achieved with a very low partial volume of synthetic, high aspect ratio microgels, leading to large empty volumes available for cell ingrowth and cell-cell interactions., (© 2022 The Authors. Advanced Healthcare Materials published by Wiley-VCH GmbH.)

Gas-filled microbubbles (MB) are routinely used in the clinic as ultrasound contrast agents. MB are also increasingly explored as drug delivery vehicles based on their ultrasound stimuli-responsiveness and well-established shell functionalization routes. Broadening the range of MB properties can enhance their performance in both imaging and drug delivery applications. This can be promoted by systematically varying the reagents used in the synthesis of MB, which in the case of polymeric MB include surfactants. We therefore set out to study the effect of key surfactant characteristics, such as the chemical structure, molecular weight, and hydrophilic-lipophilic balance on the formation of poly(butyl cyanoacrylate) (PBCA) MB, as well as on their properties, including shell thickness, drug loading capacity, ultrasound contrast, and acoustic stability. Two different surfactant families ( i.e. , Triton X and Tween) were employed, which show opposite molecular weight vs hydrophilic-lipophilic balance trends. For both surfactant types, we found that the shell thickness of PBCA MB increased with higher-molecular-weight surfactants and that the resulting MB with thicker shells showed higher drug loading capacities and acoustic stability. Furthermore, the higher proportion of smaller polymer chains of the Triton X-based MB (as compared to those of the Tween-based ones) resulted in lower polymer entanglement, improving drug loading capacity and ultrasound contrast response. These findings open up new avenues to fine-tune the shell properties of polymer-based MB for enhanced ultrasound imaging and drug delivery applications.

The intracellular environment is crowded with macromolecules that influence biochemical equilibria and biomacromolecule diffusion. The incorporation of such crowding in synthetic cells would be needed to mimic the biochemistry of living cells. However, only a few methods provide crowded artificial cells, moreover providing cells with either heterogeneous size and composition or containing a significant oil fraction. Therefore, a method that generates monodisperse liposomes with minimal oil content and tunable macromolecular crowding using polydimethylsiloxane (PDMS)-based microfluidics is presented. Lipid stabilized water-in-oil-in-water emulsions that are stable for at least several months and with a high macromolecular crowder concentration that can be controlled with the external osmolality are formed. A crucial feature is that the oil phase can be removed using high flow conditions at any point after production, providing the highly crowded liposomes. Genetically encoded macromolecular crowding sensors show that the high level of macromolecular crowding in the emulsions is fully retained throughout the generation of minimal-oil lipid bilayers. This modular and robust platform will serve the study of biochemistry under physiologically relevant crowding conditions., (© 2022 The Authors. Advanced Science published by Wiley-VCH GmbH.)

Polymer self-assembly is a crucial process in materials engineering. Currently, almost all polymer self-assembly is limited to non-covalent bonding methods, even though these methods have drawbacks as they require complicated synthesis techniques and produce relatively unstable structures. Here, a novel mechanism of covalent polymer self-assembly is discovered and employed to address drawbacks of non-covalent polymer self-assembly. A simple ketone homopolymer is found to self-assemble into nano- to macroscale hydrogels during covalent crosslinking. In contrast to non-covalent self-assembly, the covalent self-assembly is independent of and unaffected by solvent conditions (e.g., polarity and ionic strength) and does not require additional agents, e.g., organic solvents and surfactants. The covalent polymer self-assembly is subjected to a new mechanism of control by tuning the covalent crosslinking rate. This leads to nanogels with an unprecedented and tightly controlled range of dimensions from less than 10 nm to above 100 nm. Moreover, the crosslinking rate also regulates the assembly behavior of microgels fabricated by microfluidics. The microgels self-assemble into granular fibers, which is 3D printed into stable porous scaffolds. The novel covalent polymer assembly method has enormous potential to revolutionize multiscale materials fabrication for applications in drug delivery, tissue engineering, and many other fields., (© 2022 The Authors. Advanced Materials published by Wiley-VCH GmbH.)

A two-component system of functionalized microgels from microfluidics allows for fast interlinking into 3D macroporous constructs in aqueous solutions without further additives. Continuous photoinitiated on-chip gelation enables variation of the microgel aspect ratio, which determines the building block properties for the obtained constructs. Glycidyl methacrylate (GMA) or 2-aminoethyl methacrylate (AMA) monomers are copolymerized into the microgel network based on polyethylene glycol (PEG) star-polymers to achieve either epoxy or amine functionality. A focusing oil flow is introduced into the microfluidic outlet structure to ensure continuous collection of the functionalized microgel rods. Based on a recent publication, microgel rod-based constructs result in larger pores of several hundred micrometers and, at the same time, lead to overall higher scaffold stability in comparison to a spherical-based model. In this way, it is possible to produce higher-volume constructs with more free volume while reducing the amount of material required. The interlinked macroporous scaffolds can be picked up and transported without damage or disintegration. Amine and epoxy groups not involved in interlinking remain active and can be used independently for post-modification. This protocol describes an optimized method for the fabrication of microgel rods to form macroporous interlinked scaffolds that can be utilized for subsequent cell experiments.

In this work, a two component microgel assembly using soft anisometric microgels that interlink to create a 3D macroporous construct for cell growth is reported. Reactive microgel rods with variable aspect ratio are produced via microfluidics in a continuous plug-flow on-chip gelation method by photoinitiated free-radical polymerization of star-polyethylene glycol-acrylate with glycidyl methacrylate or 2-aminoethyl methacrylate comonomers. The resulting complementary epoxy- and amine-functionalized microgels assemble and interlink with each other via a ring opening reaction, resulting in macroporous constructs with pores up to several hundreds of micrometers. The level of crosslinking depends on the functionalization degree of the microgels, which also affects the stiffness and cell adhesiveness of the microgels when modified with the cell-adhesive GRGDS-PC peptide. Therefore, 3D spreading and growth of cells inside the macroporous structure is influenced not only by the presence of macropores but also by the mechanical and biochemical properties of the individual microgels., (© 2022 The Authors. Advanced Science published by Wiley-VCH GmbH.)

Microgels are crosslinked, water-swollen networks with a 10 nm to 100 µm diameter and can be modified chemically or biologically to render them biocompatible for advanced clinical applications. Depending on their intended use, microgels require different mechanical and structural properties, which can be engineered on demand by altering the biochemical composition, crosslink density of the polymer network, and the fabrication method. Here, the fundamental aspects of microgel research and development, as well as their specific applications for theranostics and therapy in the clinic, are discussed. A detailed overview of microgel fabrication techniques with regards to their intended clinical application is presented, while focusing on how microgels can be employed as local drug delivery materials, scavengers, and contrast agents. Moreover, microgels can act as scaffolds for tissue engineering and regeneration application. Finally, an overview of microgels is given, which already made it into pre-clinical and clinical trials, while future challenges and chances are discussed. This review presents an instructive guideline for chemists, material scientists, and researchers in the biomedical field to introduce them to the fundamental physicochemical properties of microgels and guide them from fabrication methods via characterization techniques and functionalization of microgels toward specific applications in the clinic., (© 2021 The Authors. Advanced Healthcare Materials published by Wiley-VCH GmbH.)

In nerve regeneration, scaffolds play an important role in providing an artificial extracellular matrix with architectural, mechanical, and biochemical cues to bridge the site of injury. Directed nerve growth is a crucial aspect of nerve repair, often introduced by engineered scaffolds imparting linear tracks. The influence of physical cues, determined by well-defined architectures, has been mainly studied for implantable scaffolds and is usually limited to continuous guiding features. In this report, the potential of short anisometric microelements in inducing aligned neurite extension, their dimensions, and the role of vertical and horizontal distances between them, is investigated. This provides crucial information to create efficient injectable 3D materials with discontinuous, in situ magnetically oriented microstructures, like the Anisogel. By designing and fabricating periodic, anisometric, discreet guidance cues in a high-throughput 2D in vitro platform using two-photon lithography techniques, the authors are able to decipher the minimal guidance cues required for directed nerve growth along the major axis of the microelements. These features determine whether axons grow unidirectionally or cross paths via the open spaces between the elements, which is vital for the design of injectable Anisogels for enhanced nerve repair., (© 2021 The Authors. Advanced Healthcare Materials published by Wiley-VCH GmbH.)

Nerve regeneration scaffolds often consist of soft hydrogels modified with extracellular matrix (ECM) proteins or fragments, as well as linear and cyclic peptides. One of the commonly used integrin-mediated cell adhesive peptide sequences is Arg-Gly-Asp (RGD). Despite its straightforward coupling mechanisms to artificial extracellular matrix (aECM) constructs, linear RGD peptides suffer from low stability towards degradation and lack integrin selectivity. Cyclization of RGD improves the affinity towards integrin subtypes but lacks selectivity. In this study, a new class of short bicyclic peptides with RGD in a cyclic loop and 'random screened' tri-amino acid peptide sequences in the second loop is investigated as a biochemical cue for cell growth inside three-dimensional (3D) synthetic poly(ethylene glycol) (PEG)-based Anisogels. These peptides impart high integrin affinity and selectivity towards either αvβ3 or α5β1 integrin subunits. Enzymatic conjugation of such bicyclic peptides to the PEG backbone enables the formulation of an aECM hydrogel that supports nerve growth. Furthermore, different proteolytic cleavable moieties are incorporated and compared to promote cell migration and proliferation, resulting in enhanced cell growth with different degradable peptide crosslinkers. Mouse fibroblasts and primary nerve cells from embryonic chick dorsal root ganglions (DRGs) show superior growth in bicyclic RGD peptide conjugated gels selective towards αvβ3 or α5β1, compared to monocyclic or linear RGD peptides, with a slight preference to αvβ3 selective bicyclic peptides in the case of nerve growth. Synthetic Anisogels, modified with bicyclic RGD peptides and containing short aligned, magneto-responsive fibers, show oriented DRG outgrowth parallel to the fibers. This report shows the potential of PEG hydrogels coupled with bicyclic RGD peptides as an aECM model and paves the way for a new class of integrin selective biomolecules for cell growth and nerve regeneration.

Tissue regeneration of sensitive tissues calls for injectable scaffolds, which are minimally invasive and offer minimal damage to the native tissues. However, most of these systems are inherently isotropic and do not mimic the complex hierarchically ordered nature of the native extracellular matrices. This review focuses on the different approaches developed in the past decade to bring in some form of anisotropy to the conventional injectable tissue regenerative matrices. These approaches include introduction of macroporosity, in vivo pattering to present biomolecules in a spatially and temporally controlled manner, availability of aligned domains by means of self-assembly or oriented injectable components, and in vivo bioprinting to obtain structures with features of high resolution that resembles native tissues. Toward the end of the review, different techniques to produce building blocks for the fabrication of heterogeneous injectable scaffolds are discussed. The advantages and shortcomings of each approach are discussed in detail with ideas to improve the functionality and versatility of the building blocks., (© 2021 The Authors. Advanced Healthcare Materials published by Wiley-VCH GmbH.)

Many applications of responsive microgels rely on the fast adaptation of the polymer network. However, the underlying dynamics of the de-/swelling process of the gels have not been fully understood. In the present work, we focus on the collapse kinetics of poly- N -isopropylacrylamide (pNIPAM) microgels due to cononsolvency. Cononsolvency means that either of the pure solvents, e.g., pure water or pure methanol, act as a so-called good solvent, leading to a swollen state of the polymer network. However, in mixtures of water and methanol, the previously swollen network undergoes a drastic volume loss. To further elucidate the cononsolvency transition, pNIPAM microgels with diameters between 20 and 110 μm were synthesized by microfluidics. To follow the dynamics, pure water was suddenly exchanged with an unfavorable mixture of 20 mol% methanol (solvent-jump) within a microfluidic channel. The dynamic response of the microgels was investigated by optical and fluorescence microscopy and Raman microspectroscopy. The experimental data provide unique and detailed insight into the size-dependent kinetics of the volume phase transition due to cononsolvency. The change in the microgel's diameter over time points to a two-step process of the microgel collapse with a biexponential behavior. Furthermore, the dependence between the two time constants from this biexponential behavior and the microgel's diameter in the collapsed state deviates from the square-power law proposed by Tanaka and Fillmore [ J. Chem. Phys. 1979, 70, 1214-1218]. The deviation is discussed considering the adhesion-induced deformation of the gels and the physical processes underlying the collapse.

Human in vitro tissues are extracorporeal 3D cultures of human cells embedded in biomaterials, commonly hydrogels, which recapitulate the heterogeneous, multiscale, and architectural environment of the human body. Contemporary strategies used in 3D tissue and organ engineering integrate the use of automated digital manufacturing methods, such as 3D printing, bioprinting, and biofabrication. Human tissues and organs, and their intra- and interphysiological interplay, are particularly intricate. For this reason, attentiveness is rising to intersect materials science, medicine, and biology with arts and informatics. This report presents advances in computational modeling of bioink polymerization and its compatibility with bioprinting, the use of digital design and fabrication in the development of fluidic culture devices, and the employment of generative algorithms for modeling the natural and biological augmentation of in vitro tissues. As a future direction, the use of serially linked in vitro tissues as human body-mimicking systems and their application in drug pharmacokinetics and metabolism, disease modeling, and diagnostics are discussed., (© 2020 The Authors. Advanced Healthcare Materials published by Wiley-VCH GmbH.)

The filtration performance of soft colloid suspensions suffers from the agglomeration of the colloids on the membrane surface as filter cakes. Backflushing of fluid through the membrane and cross-flow flushing across the membrane are widely used methods to temporally remove the filter cake and restore the flux through the membrane. However, the phenomena occurring during the recovery of the filtration performance are not yet fully described. In this study, we filtrate poly(N-isopropylacrylamide) microgels and analyze the filter cake in terms of its composition and its dynamic mobility during removal using on-line laser scanning confocal microscopy. First, we observe uniform cake build-up that displays highly ordered and amorphous regions in the cake layer. Second, backflushing removes the cake in coherent pieces and their sizes depend on the previous cake build-up. And third, cross-flow flushing along the cake induces a pattern of longitudinal ridges on the cake surface, which depends on the cross-flow velocity and accelerates cake removal. These observations give insight into soft colloid filter cake arrangement and reveal the cake's unique behaviour exposed to shear-stress.

Directing cells is essential to organize multi-cellular organisms that are built up from subunits executing specific tasks. This guidance requires a precisely controlled symphony of biochemical, mechanical, and structural signals. While many guiding mechanisms focus on 2D structural patterns or 3D biochemical gradients, injectable material platforms that elucidate how cellular processes are triggered by defined 3D physical guiding cues are still lacking but crucial for the repair of soft tissues. Herein, a recently developed anisotropic injectable hybrid hydrogel (Anisogel) contains rod-shaped microgels that orient in situ by a magnetic field and has propelled studying 3D cell guidance. Here, the Anisogel is used to investigate the dependence of axonal guidance on microgel dimensions, aspect ratio, and distance. While large microgels result in high material anisotropy, they significantly reduce neurite outgrowth and thus the guidance efficiency. Narrow and long microgels enable strong axonal guidance with maximal outgrowth including cell sensing over distances of tens of micrometers in 3D. Moreover, nerve cells decide to orient inside the Anisogel within the first three days, followed by strengthening of the alignment, which goes along with oriented fibronectin deposition. These findings demonstrate the potential of the Anisogel to tune structural and mechanical parameters for specific applications., (© 2020 The Authors. Published by Wiley-VCH GmbH.)

Surface topographies at micro- and nanoscales can influence different cellular behavior, such as their growth rate and directionality. While different techniques have been established to fabricate 2-dimensional flat substrates with nano- and microscale topographies, most of them are prone to high costs and long preparation times. The 2.5-dimensional fiber platform presented here provides knowledge on the effect of the combination of fiber alignment, inter-fiber distance (IFD), and fiber surface topography on contact guidance to direct neurite behavior from dorsal root ganglia (DRGs) or dissociated primary neurons. For the first time, the interplay of the micro-/nanoscale topography and IFD is studied to induce linear nerve growth, while controlling branching. The results demonstrate that grooved fibers promote a higher percentage of aligned neurite extension, compensating the adverse effect of increased IFD. Accordingly, maximum neurite extension from primary neurons is achieved on grooved fibers separated by an IFD of 30 μm, with a higher percentage of aligned neurons on grooved fibers at a large IFD compared to porous fibers with the smallest IFD of 10 µm. We further demonstrate that the neurite "decision-making" behavior on whether to cross a fiber or grow along it is not only dependent on the IFD but also on the fiber surface topography. In addition, axons growing in between the fibers seem to have a memory after leaving grooved fibers, resulting in higher linear growth and higher IFDs lead to more branching. Such information is of great importance for new material development for several tissue engineering applications. STATEMENT OF SIGNIFICANCE: One of the key aspects of tissue engineering is controlling cell behavior using hierarchical structures. Compared to 2D surfaces, fibers are an important class of materials, which can emulate the native ECM architecture of tissues. Despite the importance of both fiber surface topography and alignment to direct growing neurons, the current state of the art did not yet study the synergy between both scales of guidance. To achieve this, we established a solvent assisted spinning process to combine these two crucial features and control neuron growth, alignment, and branching. Rational design of new platforms for various tissue engineering and drug discovery applications can benefit from such information as it allows for fabrication of functional materials, which selectively influence neurite behavior., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2020. Published by Elsevier Ltd.)

The replacement of diseased and damaged organs remains an challenge in modern medicine. However, through the use of tissue engineering techniques, it may soon be possible to (re)generate tissues and organs using artificial scaffolds. For example, hydrogel networks made from hydrophilic precursor solutions can replicate many properties found in the natural extracellular matrix (ECM) but often lack the dynamic nature of the ECM, as many covalently crosslinked hydrogels possess elastic and static networks with nanoscale pores hindering cell migration without being degradable. To overcome this, macroporous colloidal hydrogels can be prepared to facilitate cell infiltration. Here, an easy method is presented to fabricate granular cellulose nanofibril hydrogel (CNF) scaffolds as porous networks for 3D cell cultivation. CNF is an abundant natural and highly biocompatible material that supports cell adhesion. Granular CNF scaffolds are generated by pre-crosslinking CNF using calcium and subsequently pressing the gel through micrometer-sized nylon meshes. The granular solution is mixed with fibroblasts and crosslinked with cell culture medium. The obtained granular CNF scaffold is significantly softer and enables well-distributed fibroblast growth. This cost-effective material combined with this efficient and facile fabrication technique allows for 3D cell cultivation in an upscalable manner., (© 2020 The Authors. Published by Wiley-VCH GmbH.)

To replicate functional liver tissue in vitro for drug testing or transplantation, 3D tissue engineering requires representative cell models as well as scaffolds that not only promote tissue production but also are applicable in a clinical setting. Recently, adult liver-derived liver organoids are found to be of much interest due to their genetic stability, expansion potential, and ability to differentiate toward a hepatocyte-like fate. The current standard for culturing these organoids is a basement membrane hydrogel like Matrigel (MG), which is derived from murine tumor material and apart from its variability and high costs, possesses an undefined composition and is therefore not clinically applicable. Here, a cellulose nanofibril (CNF) hydrogel is investigated with regard to its potential to serve as an alternative clinical grade scaffold to differentiate liver organoids. The results show that its mechanical properties are suitable for differentiation with overall, either equal or improved, functionality of the hepatocyte-like cells compared to MG. Therefore, and because of its defined and tunable chemical definition, the CNF hydrogel presents a viable alternative to MG for liver tissue engineering with the option for clinical use., (© 2020 The Authors. Published by WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Stop-flow lithography (SFL) has emerged as a facile high-throughput fabrication method for μm-sized anisometric particles; yet, the fabrication of soft, anisometric microgels has not frequently been addressed in the literature. Furthermore, and to the best of the authors' knowledge, no soft, complex-shaped microgels with temperature-responsive behavior have been fabricated with this technology before. However, such microgels have tremendous potential as building blocks and actuating elements in rapidly developing fields, such as tissue engineering and additive manufacturing of soft polymeric building blocks, bio-hybrid materials, or soft micro-robotics. Given their great potential, we prove in this work that SFL is a viable method for the fabrication of soft, temperature-responsive, and complex-shaped microgels. The microgels, fabricated in this work, consist of poly(N-isopropylacrylamide) (pNIPAm), which is crosslinked with N,N'-methylenebis(acrylamide). The results confirm that the shape of the pNIPAm microgels is determined by the transparency mask, used in SFL. Furthermore, it is shown that, in order to realize stable microgels, a minimum threshold of crosslinker concentration of 2 wt% is required. Above this threshold, the stiffness of pNIPAm microgels can be deliberately altered by adjusting the concentration of the crosslinker. The fabricated pNIPAm microgels show the targeted temperature-responsive behavior. Within this context, temperature-dependent reversible swelling is confirmed, even for fractal-like geometries, such as micro snowflakes. Thus, these microgels provide the targeted unique combination of softness, shape complexity, and temperature responsiveness and increase the freedom of design for actuated building blocks.

In the past decade, anisometric rod-shaped microgels have attracted growing interest in the materials-design and tissue-engineering communities. Rod-shaped microgels exhibit outstanding potential as versatile building blocks for 3D hydrogels, where they introduce macroscopic anisometry, porosity, or functionality for structural guidance in biomaterials. Various fabrication methods have been established to produce such shape-controlled elements. However, continuous high-throughput production of rod-shaped microgels with simultaneous control over stiffness, size, and aspect ratio still presents a major challenge. A novel microfluidic setup is presented for the continuous production of rod-shaped microgels from microfluidic plug flow and jets. This system overcomes the current limitations of established production methods for rod-shaped microgels. Here, an on-chip gelation setup enables fabrication of soft microgel rods with high aspect ratios, tunable stiffness, and diameters significantly smaller than the channel diameter. This is realized by exposing jets of a microgel precursor to a high intensity light source, operated at specific pulse sequences and frequencies to induce ultra-fast photopolymerization, while a change in flow rates or pulse duration enables variation of the aspect ratio. The microgels can assemble into 3D structures and function as support for cell culture and tissue engineering., (© 2019 DWI - Leibniz Institute for Interactive Materials. Published by WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Double emulsions are useful geometries as templates for core-shell particles, hollow sphere capsules, and for the production of biomedical delivery vehicles. In microfluidics, two approaches are currently being pursued for the preparation of microfluidic double emulsion devices. The first approach utilizes soft lithography, where many identical double-flow-focusing channel geometries are produced in a hydrophobic silicone matrix. This technique requires selective surface modification of the respective channel sections to facilitate alternating wetting conditions of the channel walls to obtain monodisperse double emulsion droplets. The second technique relies on tapered glass capillaries, which are coaxially aligned, so that double emulsions are produced after flow focusing of two co-flowing streams. This technique does not require surface modification of the capillaries, as only the continuous phase is in contact with the emulsifying orifice; however, these devices cannot be fabricated in a reproducible manner, which results in polydisperse double emulsion droplets, if these capillary devices were to be parallelized. Here, we present 3D printing as a means to generate four identical and parallelized capillary device architectures, which produce monodisperse double emulsions with droplet diameters in the range of 500 µm. We demonstrate high throughput synthesis of W/O/W and O/W/O double emulsions, without the need for time-consuming surface treatment of the 3D printed microfluidic device architecture. Finally, we show that we can apply this device platform to generate hollow sphere microgels.

An enzymatically cross-linked polyethylene glycol (PEG)-based hydrogel was engineered to promote and align nerve cells in a three-dimensional manner. To render the injectable, otherwise bioinert, PEG-based material supportive for cell growth, its mechanical and biochemical properties were optimized. A recombinant fibronectin fragment (FNIII9*-10/12-14) was coupled to the PEG backbone during gelation to provide cell adhesive and growth factor binding domains in close vicinity. Compared to full-length fibronectin, FNIII9*-10/12-14 supports nerve growth at similar concentrations. In a 3D environment, only the ultrasoft 1 w/v% PEG hydrogels with a storage modulus of ∼10 Pa promoted neuronal growth. This gel was used to establish the first fully synthetic, injectable Anisogel by the addition of magnetically aligned microelements, such as rod-shaped microgels or short fibers. The Anisogel led to linear neurite extension and represents a large step in the direction of clinical translation with the opportunity to treat acute spinal cord injuries.

Polydimethylsiloxane (PDMS) is a synthetic material with excellent properties for biomedical applications because of its easy fabrication method, high flexibility, permeability to oxygen, transparency, and potential to produce high-resolution structures in the case of lithography. However, PDMS needs to be modified to support homogeneous cell attachments and spreading. Even though many physical and chemical methods, like plasma treatment or extracellular matrix coatings, have been developed over the last decades to increase cell-surface interactions, these methods are still very time-consuming, often not efficient enough, complex, and can require several treatment steps. To overcome these issues, we present a novel, robust, and fast one-step PDMS coating method using engineered anchor peptides fused to the cell-adhesive peptide sequence (glycine-arginine-glycine-aspartate-serine, GRGDS). The anchor peptide attaches to the PDMS surface predominantly by hydrophobic interactions by simply dipping PDMS in a solution containing the anchor peptide, presenting the GRGDS sequence on the surface available for cell adhesion. The binding performance and kinetics of the anchor peptide to PDMS are characterized, and the coatings are optimized for efficient cell attachment of fibroblasts and endothelial cells. Additionally, the applicability is proven using PDMS-based directional nanotopographic gradients, showing a lower threshold of 5 μm wrinkles for fibroblast alignment.

Human induced pluripotent stem cells (hiPSCs) are used as an alternative for human embryonic stem cells. Cardiomyocytes derived from hiPSCs are employed in cardiac tissue regeneration constructs due to the heart's low regeneration capacity after infarction. A coculture of hiPSC-CM and primary dermal fibroblasts is encapsulated in injectable poly(ethylene glycol)-based microgels via microfluidics to enhance the efficiency of regenerative cell transplantations. The microgels are prepared via Michael-type addition of multi-arm PEG-based molecules with an enzymatically degradable peptide as a cross-linker and modified with a cell-adhesive peptide. Cell-cell interactions and, consequently, cell viability are improved by a thin extracellular matrix (ECM) coating formed on the cell surfaces via layer-by-layer (LbL) deposition. The beating strength of encapsulated cardiomyocytes (∼60 BPM) increases by 2-fold compared to noncoated cells. The combination of microfluidics with the LbL technique offers a new technology to fabricate functional cardiac mini tissues for cell transplantation therapies.

Cells feel the forces exerted on them by the surrounding extracellular matrix (ECM) environment and respond to them. While many cell fate processes are dictated by these forces, which are highly synchronized in space and time, abnormal force transduction is implicated in the progression of many diseases (muscular dystrophy, cancer). However, material platforms that enable transient, cyclic forces in vitro to recreate an in vivo-like scenario remain a challenge. Here, we report a hydrogel system that rapidly beats (actuates) with spatio-temporal control using a near infra-red light trigger. Small, user-defined mechanical forces (~nN) are exerted on cells growing on the hydrogel surface at frequencies up to 10 Hz, revealing insights into the effect of actuation on cell migration and the kinetics of reversible nuclear translocation of the mechanosensor protein myocardin related transcription factor A, depending on the actuation amplitude, duration and frequency.

A metal-organic gel (metallogel) based on the new tetracarboxyl ligand N 1 , N 4 -(diterephthalic acid)terephthalamide in combination with chromium(III) has been converted into its xero- and aerogel and demonstrated to have excellent specific sorption properties for dyes in its metallogel state, where fuchsine is adsorbed faster than the two other dyes, calcein and disulfine blue, and for water, sulfur dioxide and carbon dioxide in its xero- and aerogel state. The metallogel showed very good shape retention and could be extruded from molds in designed shapes. In a rheology experiment, the storage modulus was determined to be 1440 Pa, and the metallogel is elastic up to 3 Hz, breaking at strains higher than 0.3%. Additional metallogels utilizing the same ligand with a wide range of metal ions (Al(III), Fe(III), Co(III), In(III), and Hg(II)) have also been synthesized, and the aluminum and mixed aluminum-chromium derivative were also converted into its aerogel. The highly porous Cr, Al, and AlCr metal-organic aerogels proved stable against water vapor in a physisorption experiment and were used to model breakthrough curves for SO 2 /CO 2 gas mixtures with the idealized adsorbed solution theory from their physisorption isotherms. The breakthrough simulation utilized SO 2 /CO 2 equivalencies from a real world application and showed effective retention of SO 2 from the gas mixture. Furthermore, the materials in this work exhibit the highest SO 2 uptake values for metal-organic aerogels so far (up to 116.8 cm 3 g -1 , or 23.4 wt %).