Macroporous hydrogels derived from aqueous dynamic phase separation

A rapid interactive chitosan-based medium with antioxidant and pro-vascularization properties for infected burn wound healing

Large-pore hydrogels are better suited to meet the management needs of nutrient transportation and gas exchange between infected burn wounds and normal tissues. However, better construction strategies are required to balance the pore size and mechanical strength of hydrogels to construct a faster substance/gas interaction medium between tissues. Herein, we developed spongy large pore size hydrogel (CS-TA@Lys) with good mechanical properties using a simple ice crystal-assisted method based on chitosan (CS), incorporating tannic acid (TA) and ε-polylysine (Lys). A large-pore and mechanically robust hydrogel medium was constructed based on hydrogen bonding between CS molecules. On this basis, a pro-restorative functional platform with antioxidation and pro-vascularization was constructed using TA and Lys. In vitro experiments displayed that the CS-TA@Lys hydrogel possessed favorable mechanical properties and fast interaction performances. In addition, the CS-TA@Lys hydrogel possessed the capacity to remove intra/extracellular reactive oxygen species (ROS) and possessed antimicrobial and pro-angiogenic properties. In vivo experiments displayed that the CS-TA@Lys hydrogel inhibited wound inflammation and promoted wound vascularization. In addition, the CS-TA@Lys hydrogel showed the potential for rapid hemostasis. This study provides a potential functional wound dressing with rapid interaction properties for skin wound repair.

Porous Hydrogels for Immunomodulatory Applications

Cancer immunotherapy relies on the insight that the immune system can be used to defend against malignant cells. The aim of cancer immunotherapy is to utilize, modulate, activate, and train the immune system to amplify antitumor T-cell immunity. In parallel, the immune system response to damaged tissue is also crucial in determining the success or failure of an implant. Due to their extracellular matrix mimetics and tunable chemical or physical performance, hydrogels are promising platforms for building immunomodulatory microenvironments for realizing cancer therapy and tissue regeneration. However, submicron or nanosized pore structures within hydrogels are not favorable for modulating immune cell function, such as cell invasion, migration, and immunophenotype. In contrast, hydrogels with a porous structure not only allow for nutrient transportation and metabolite discharge but also offer more space for realizing cell function. In this review, the design strategies and influencing factors of porous hydrogels for cancer therapy and tissue regeneration are first discussed. Second, the immunomodulatory effects and therapeutic outcomes of different porous hydrogels for cancer immunotherapy and tissue regeneration are highlighted. Beyond that, this review highlights the effects of pore size on immune function and potential signal transduction. Finally, the remaining challenges and perspectives of immunomodulatory porous hydrogels are discussed.

Structuring gelatin methacryloyl - dextran hydrogels and microgels under shear

Gelatin methacryloyl (GelMA) is a widely used semi-synthetic polymer for a variety of bioapplications. However, the development of versatile GelMA hydrogels requires tuning of their microstructure. Herein, we report the possibility of preparing hydrogels with various microstructures under shear from an aqueous two-phase system (ATPS) consisting of GelMA and dextran. The influence of an applied preshear on dextran/GelMA droplets and bicontinuous systems is investigated by rheology that allows the application of a constant shear and is immediately followed by in situ UV-curing of the GelMA-rich phase. The microstructure of the resulting hydrogels is examined by confocal laser scanning microscopy (CLSM). The results show that the GelMA string phase and GelMA hydrogels with aligned bands can be formed depending on the concentration of dextran and the applied preshear. The influence of the pH of the ATPS is investigated and demonstrates the formation of multiple emulsions upon decreasing the charge density of GelMA. The preshearing of multiple emulsions, following gelation, leads to the formation of porous GelMA microgels. The diversity of the formed structures highlights the application potential of preshearing ATPS in the development of functional soft materials.

Cellular Architects at Work: Cells Building their Own Microgel Houses

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.

Microparticle Hydrogel Material Properties Emerge from Mixing-Induced Homogenization in a Poly(ethylene glycol) and Dextran Aqueous Two-Phase System

Polymer-polymer aqueous two-phase systems (ATPSs) are attractive for microgel synthesis, but given the complexity of phase separation, predicting microgel material properties from ATPS formulations is not trivial. The objective of this study was to determine how the phase diagram of a poly(ethylene glycol) (PEG) and dextran ATPS is related to the material properties of PEG microgel products. PEG-dextran ATPSs were prepared from four-arm 20 kDa PEG-norbornene and 40 kDa dextran in phosphate buffered saline (PBS), and the phase diagram was constructed. PEG microgels were synthesized from five ATPS formulations using an oligopeptide cross-linker and thiol-norbornene photochemistry. Thermogravimetric analysis (TGA) revealed that the polymer concentration of microgel pellets linearly correlates with the average concentration of PEG in the ATPS rather than the separated phase compositions, as determined from the phase diagram. Atomic force microscopy (AFM) and bulk rheology studies demonstrated that the mechanical properties of microgels rely on both the average concentration of PEG in the ATPS and the ATPS volume ratio as determined from the phase diagram. These findings suggest that PEG-dextran ATPSs undergo homogenization upon mixing, which principally determines the material properties of the microgels upon gelation.

3D Printable Gelatin Methacryloyl (GelMA)-Dextran Aqueous Two-Phase System with Tunable Pores Structure and Size Enables Physiological Behavior of Embedded Cells In Vitro

The restricted porosity of most hydrogels established for in vitro 3D tissue engineering applications limits embedded cells with regard to their physiological spreading, proliferation, and migration behavior. To overcome these confines, porous hydrogels derived from aqueous two-phase systems (ATPS) are an interesting alternative. However, while developing hydrogels with trapped pores is widespread, the design of bicontinuous hydrogels is still challenging. Herein, an ATPS consisting of photo-crosslinkable gelatin methacryloyl (GelMA) and dextran is presented. The phase behavior, monophasic or biphasic, is tuned via the pH and dextran concentration. This, in turn, allows the formation of hydrogels with three distinct microstructures: homogenous nonporous, regular disconnected-pores, and bicontinuous with interconnected-pores. The pore size of the latter two hydrogels can be tuned from ≈4 to 100 µm. Cytocompatibility of the generated ATPS hydrogels is confirmed by testing the viability of stromal and tumor cells. Their distribution and growth pattern are cell-type specific but are also strongly defined by the microstructure of the hydrogel. Finally, it is demonstrated that the unique porous structure is sustained when processing the bicontinuous system by inkjet and microextrusion techniques. The proposed ATPS hydrogels hold great potential for 3D tissue engineering applications due to their unique tunable interconnected porosity.

A Facile Strategy for the Fabrication of Cell-laden Porous Alginate Hydrogels Based on Two-phase Aqueous Emulsions

Porous alginate hydrogels possess many advantages as cell carriers. However, current pore generation methods require either complex or harsh fabrication processes, toxic components, or extra purification steps, limiting the feasibility and affecting the cellular survival and function. In this study, a simple and cell-friendly approach to generate highly porous cell-laden alginate hydrogels based on two-phase aqueous emulsions is reported. The pre-gel solutions, which contain two immiscible aqueous phases of alginate and caseinate, are crosslinked by calcium ions. The porous structure of the hydrogel construct is formed by subsequently removing the caseinate phase from the ion-crosslinked alginate hydrogel. Those porous alginate hydrogels possess heterogeneous pores around 100 μm and interconnected paths. Human white adipose progenitors (WAPs) encapsulated in these hydrogels self-organize into spheroids and show enhanced viability, proliferation, and adipogenic differentiation, compared to non-porous constructs. As a proof of concept, this porous alginate hydrogel platform is employed to prepare core-shell spheres for coculture of WAPs and colon cancer cells, with WAP clusters distributed around cancer cell aggregates, to investigate cellular crosstalk. This efficacious approach is believed to provide a robust and versatile platform for engineering porous-structured alginate hydrogels for applications as cell carriers and in disease modeling.

Coacervation-Mediated Cytocompatible Formation of Supramolecular Hydrogels with Self-Evolving Macropores for 3D Multicellular Spheroid Culture

Coacervation driven liquid-liquid phase separation of biopolymers has aroused considerable attention for diverse applications, especially for the construction of microstructured polymeric materials. Herein, a coacervate-to-hydrogel transition strategy is developed to create macroporous hydrogels (MPH), which are formed via the coacervation process of supramolecular assemblies (SA) built by the host-guest complexation between γ-cyclodextrin and anthracene dimer. The weak and reversible supramolecular crosslinks endow the SA with liquid-like rheological properties, which facilitate the formation of SA-derived macroporous coacervates and the subsequent transition to MPH (pore size ≈ 100 µm). The excellent structural dynamics (derived from SA) and the cytocompatible void-forming process of MPH can better accommodate the dramatic volumetric expansion associated with colony growth of encapsulated multicellular spheroids compared with the non-porous static hydrogel with similar initial mechanical properties. The findings of this work not only provide valuable guidance to the design of biomaterials with self-evolving structures but also present a promising strategy for 3D multicellular spheroid culture and other diverse biomedical applications.

Sponge-Like Macroporous Hydrogel with Antibacterial and ROS Scavenging Capabilities for Diabetic Wound Regeneration

Hydrogels with soft and wet properties have been intensively investigated for chronic disease tissue repair. Nevertheless, tissue engineering hydrogels containing high water content are often simultaneously suffered from low porous size and low water-resistant capacities, leading to undesirable surgery outcomes. Here, a novel sponge-like macro-porous hydrogel (SM-hydrogel) with stable macro-porous structures and anti-swelling performances is developed via a facile, fast yet robust approach induced by Ti₃ C₂ MXene additives. The MXene-induced SM-hydrogels (80% water content) with 200-300 µm open macropores, demonstrating ideal mass/nutrient infiltration capability at ≈20-fold higher water/blood-transport velocity over that of the nonporous hydrogels. Moreover, the highly strong interactions between MXene and polymer chains endow the SM-hydrogels with excellent anti-swelling capability, promising equilibrium SM-hydrogels with identical macro-porous structures and toughened mechanical performances. The SM-hydrogel with versatile functions such as facilitating mass transport, antibacterial (bacterial viability in (Acrylic acid-co-Methacrylamide dopamine) copolymer-Ti₃ C₂ MXene below 25%), and reactive oxygen species scavenging capacities (96% scavenging ratio at 120 min) synergistically promotes diabetic wound healing (compared with non-porous hydrogels the wound closure rate increased from 39% to 81% within 7 days). Therefore, the durable SM-hydrogels exhibit connective macro-porous structures and bears versatile functions induced by MXene, demonstrating its great potential for wound tissue engineering.

In situ multimodal transparent electrophysiological hydrogel for in vivo miniature two-photon neuroimaging and electrocorticogram analysis

Hydrogels are widely used in nerve tissue repair and show good histocompatibility. There remain, however, challenges with hydrogels for applications related to neural signal recording, which requires a tissue-like biomechanical property, high optical transmission, and low impedance. Here, we describe a transparent hydrogel that is highly biocompatible and has a low Young's modulus (0.15 MPa). Additionally, it functions well as an implantable electrode, as it conformably adheres to brain tissue, results in minimal inflammation and has a low impedance of 150 Ω at 1 kHz. Its high transmittance, corresponding to 93.35% at a wavelength of 300 nm to 1100 nm, supports its application in two-photon imaging. Consistent with these properties, this flexible multimodal transparent electrophysiological hydrogel (MTEHy) electrode was able to record neuronal Ca²⁺ activity using miniature two-photon microscopy. It also used to monitor electrocorticogram (ECoG) activity in real time in freely moving mice. Moreover, its compatibility with magnetic resonance imaging (MRI), indicates that MTEHy is a new tool for studying activity in the cerebral cortex. STATEMENT OF SIGNIFICANCE: : Future brain science research requires better-performing implantable electrodes to detect neuronal signaling in the brain. In this study, we developed a new hydrogel material, MTEHy-3, that shows high biocompatibility, high optical transmittance (93.35%) and a low Young's modulus (0.15 MPa). Using as high-biocompatible metal-free hydrogel electrode, MTEHy-3 can be implanted for a long time to study the cerebral cortex, and synchronously record the Ca²⁺ signaling activity of individual neurons and monitor electrocorticogram activity through ionic conduction in freely moving mice. At the same time, non-metallic MTEHy-3 is also suitable for magnetic resonance imaging. Thus MTEHy-3 provides one in situ multimodal tool to detect neuronal signaling with both high spatial resolution and high temporal resolution in the brain.

Macroporous Aligned Hydrogel Microstrands for 3D Cell Guidance

Tissue engineering strongly relies on the use of hydrogels as highly hydrated 3D matrices to support the maturation of laden cells. However, because of the lack of microarchitecture and sufficient porosity, common hydrogel systems do not provide physical cell-instructive guidance cues and efficient transport of nutrients and oxygen to the inner part of the construct. A controlled, organized cellular alignment and resulting alignment of secreted ECM are hallmarks of muscle, tendons, and nerves and play an important role in determining their functional properties. Although several strategies to induce cellular alignment have been investigated in 2D systems, the generation of cell-instructive 3D hydrogels remains a challenge. Here, we report on the development of a simple and scalable method to efficiently generate highly macroporous constructs featuring aligned guidance cues. A precross-linked bulk hydrogel is pressed through a grid with variable opening sizes, thus deconstructing it into an array of aligned, high aspect ratio microgels (microstrands) with tunable diameter that are eventually stabilized by a second photoclick cross-linking step. This method has been investigated and optimized both in silico and in vitro, thereby leading to conditions with excellent viability and organized cellular alignment. Finally, as proof of concept, the method has been shown to direct aligned muscle tissue maturation. These findings demonstrate the 3D physical guidance potential of our system, which can be used for a variety of anisotropic tissues and applications.

Temperature-Responsive Aldehyde Hydrogels with Injectable, Self-Healing, and Tunable Mechanical Properties

Injectable and self-healing hydrogels with exemplary biocompatibility and tunable mechanical properties are urgently needed due to their significant advantages for tissue engineering applications. Here, we report a new temperature-responsive aldehyde hydrogel with dual physical-cross-linked networks and injectable and self-healing properties prepared from an ABA-type triblock copolymer, poly{[FPMA(4-formylphenyl methacrylate)-co-DEGMA[di(ethylene glycol) methyl ether methacrylate]-b-MPC(2-methacryloyloxyethyl phosphorylcholine)-b-(FPMA-co-DEGMA)}. The thermoresponsive poly(DEGMA) segments drive the dehydration and hydrophobic interaction, enabling polymer chain winding as the first cross-linking network, when the temperature is raised above the critical gelation temperature. Meanwhile, the benzaldehyde groups offer physical interactions, including hydrogen bonding and hydrophobic and π-π stacking interactions as the second cross-linking network. When increasing the benzaldehyde content in the triblock copolymers from 0 to 8.2 mol %, the critical gelation temperature of the resulted hydrogels dropped from 35.5 to 19.9 °C and the mechanical modulus increased from 21 to 1411 Pa. Owing to the physical-cross-linked networks, the hydrogel demonstrated excellent injectability and self-healing properties. The cell viabilities tested from MTT assays toward both normal lung fibroblast cells (MRC-5) and cancerous cervical (HeLa) cells were found to be 100 and 101%, respectively, for varying polymer concentrations up to 1 mg/mL. The 3D cell encapsulation of the hydrogels was evaluated by a cytotoxicity Live/Dead assay, showing 92% cell viability. With these attractive physiochemical and biological properties, this temperature-responsive aldehyde hydrogel can be a promising candidate as a cell scaffold for tissue engineering.

Increased connectivity of hiPSC-derived neural networks in multiphase granular hydrogel scaffolds

To reflect human development, it is critical to create a substrate that can support long-term cell survival, differentiation, and maturation. Hydrogels are promising materials for 3D cultures. However, a bulk structure consisting of dense polymer networks often leads to suboptimal microenvironments that impedes nutrient exchange and cell-to-cell interaction. Herein, granular hydrogel-based scaffolds were used to support 3D human induced pluripotent stem cell (hiPSC)-derived neural networks. A custom designed 3D printed toolset was developed to extrude hyaluronic acid hydrogel through a porous nylon fabric to generate hydrogel granules. Cells and hydrogel granules were combined using a weaker secondary gelation step, forming self-supporting cell laden scaffolds. At three and seven days, granular scaffolds supported higher cell viability compared to bulk hydrogels, whereas granular scaffolds supported more neurite bearing cells and longer neurite extensions (65.52 ± 11.59 μm) after seven days compared to bulk hydrogels (22.90 ± 4.70 μm). Long-term (three-month) cultures of clinically relevant hiPSC-derived neural cells in granular hydrogels supported well established neuronal and astrocytic colonies and a high level of neurite extension both inside and beyond the scaffold. This approach is significant as it provides a simple, rapid and efficient way to achieve a tissue-relevant granular structure within hydrogel cultures.

High-throughput selection of cells based on accumulated growth and division using PicoShell particles

Production of high-energy lipids by microalgae may provide a sustainable energy source that can help tackle climate change. However, microalgae engineered to produce more lipids usually grow slowly, leading to reduced overall yields. Unfortunately, culture vessels used to select cells based on growth while maintaining high biomass production, such as well plates, water-in-oil droplet emulsions, and nanowell arrays, do not provide production-relevant environments that cells experience in scaled-up cultures (e.g., bioreactors or outdoor cultivation farms). As a result, strains that are developed in the laboratory may not exhibit the same beneficial phenotypic behavior when transferred to industrial production. Here, we introduce PicoShells, picoliter-scale porous hydrogel compartments, that enable >100,000 individual cells to be compartmentalized, cultured in production-relevant environments, and selected based on growth and bioproduct accumulation traits using standard flow cytometers. PicoShells consist of a hollow inner cavity where cells are encapsulated and a porous outer shell that allows for continuous solution exchange with the external environment. PicoShells allow for cell growth directly in culture environments, such as shaking flasks and bioreactors. We experimentally demonstrate that Chlorella sp., Saccharomyces cerevisiae, and Chinese hamster ovary cells, used for bioproduction, grow to significantly larger colony sizes in PicoShells than in water-in-oil droplet emulsions (P < 0.05). We also demonstrate that PicoShells containing faster dividing and growing Chlorella clonal colonies can be selected using a fluorescence-activated cell sorter and regrown. Using the PicoShell process, we select a Chlorella population that accumulates chlorophyll 8% faster than does an unselected population after a single selection cycle.

PEG-based Cleavable Hydrogel Microparticles with controlled porosity for permiselective trafficking of biomolecular complexes in biosensing applications

In the last decade, PEG-based hydrogels have been extensively used for the production of microparticles for biosensing applications. The biomolecule accessibility and mass transport rate represent key parameters for the...

A paintable ophthalmic adhesive with customizable properties based on symmetrical/asymmetrical cross-linking

In situ and efficient incision sealing for ophthalmic surgery remains unresolved. Current commercially available gel adhesives often suffer from unsuitable gelation time, difficulty in micro-delivery, and mismatched degradation period, leading to difficulties for application in ocular tissue areas. Herein, a novel hydrogel adhesive was developed based on the simultaneous crosslinking of poly(lysine) (PLL) and lysine (Lys) with an end-modified active ester multi-arm polyethylene glycol (PEG) via the amidation reaction, where the residual terminal active ester of PEG can also bond to amino groups on tissue to provide strong adhesion. Due to the different molecular structures around their amino groups, PLL and Lys can crosslink with 4-arm-PEG-NHS (active ester) respectively, to form symmetrical and asymmetrical crosslinking networks, which exhibit various mechanical properties. Therefore, just by adjusting PLL/Lys ratios, the PEG-PLL-Lys hydrogel can easily possess a suitable gelation time, appropriate mechanical properties and matched degradation rate. As a result, a paintable, readily accessible and biocompatible ophthalmic tissue adhesive (sealant) is prepared for sealing ocular tissue incision. Considering the simple strategy and outstanding performance, the PEG-PLL-Lys hydrogel is promising for clinical transformation.

Modelling the central nervous system: tissue engineering of the cellular microenvironment

With the increasing prevalence of neurodegenerative diseases, improved models of the central nervous system (CNS) will improve our understanding of neurophysiology and pathogenesis, whilst enabling exploration of novel therapeutics. Studies of brain physiology have largely been carried out using in vivo models, ex vivo brain slices or primary cell culture from rodents. Whilst these models have provided great insight into complex interactions between brain cell types, key differences remain between human and rodent brains, such as degree of cortical complexity. Unfortunately, comparative models of human brain tissue are lacking. The development of induced Pluripotent Stem Cells (iPSCs) has accelerated advancement within the field of in vitro tissue modelling. However, despite generating accurate cellular representations of cortical development and disease, two-dimensional (2D) iPSC-derived cultures lack an entire dimension of environmental information on structure, migration, polarity, neuronal circuitry and spatiotemporal organisation of cells. As such, researchers look to tissue engineering in order to develop advanced biomaterials and culture systems capable of providing necessary cues for guiding cell fates, to construct in vitro model systems with increased biological relevance. This review highlights experimental methods for engineering of in vitro culture systems to recapitulate the complexity of the CNS with consideration given to previously unexploited biophysical cues within the cellular microenvironment.

A new model of chronic peripheral nerve compression for basic research and pharmaceutical drug testing

Aim: To develop a consistent model to standardize research in the field of chronic peripheral nerve neuropathy. Methods: The left sciatic nerve of 8-week-old Sprague-Dawley rats was compressed using a customized instrument leaving a defined post injury nerve lumen (400 μm, 250 μm, 100 μm, 0 μm) for 6 weeks. Sensory and motor outcomes were measured weekly, and histomorphology and electrophysiology after 6 weeks. Results: The findings demonstrated compression depth-dependent sensory and motor pathologies. Quantitative measurements revealed a significant myelin degeneration, axon irregularities and muscle atrophy. At the functional level, we highlighted the dynamics of the different injury profiles. Conclusion: Our novel model of chronic peripheral nerve compression is a useful tool for research on pathophysiology and new therapeutic approaches.

Axon Growth of CNS Neurons in Three Dimensions Is Amoeboid and Independent of Adhesions

During development of the central nervous system (CNS), neurons polarize and rapidly extend their axons to assemble neuronal circuits. The growth cone leads the axon to its target and drives axon growth. Here, we explored the mechanisms underlying axon growth in three dimensions. Live in situ imaging and super-resolution microscopy combined with pharmacological and molecular manipulations as well as biophysical force measurements revealed that growth cones extend CNS axons independent of pulling forces on their substrates and without the need for adhesions in three-dimensional (3D) environments. In 3D, microtubules grow unrestrained from the actomyosin cytoskeleton into the growth cone leading edge to enable rapid axon extension. Axons extend and polarize even in adhesion-inert matrices. Thus, CNS neurons use amoeboid mechanisms to drive axon growth. Together with our understanding that adult CNS axons regenerate by reactivating developmental processes, our findings illuminate how cytoskeletal manipulations enable axon regeneration in the adult CNS.

PEG-interpenetrated genipin-crosslinked dual-sensitive hydrogel/nanostructured lipid carrier compound formulation for topical drug administration

PEG-interpenetrated dual-sensitive hydrogels that load nano lipid carrier (NLC) were researched and developed for topical drug administration. Natural antioxidant α-lipoic acid (ALA) was selected as our model drug. The α-lipoic acid (ALA) nano lipid carrier was successfully prepared by hot melt emulsification and ultrasonic dispersion method, and the physicochemical properties of the nano lipid carrier were investigated, including morphology, particle distribution, polydispersity coefficient, zeta potential and encapsulation efficiency. Carboxymethyl chitosan and poloxamer 407 contributed to pH- and temperature-sensitive properties in the hydrogel, respectively. Natural non-toxic cross-linking agent genipin reacted with carboxymethyl chitosan to form the hydrogel. Poly ethylene glycol (PEG), a polymer compound with good water solubility and biocompatibility, interpenetrated the hydrogel and influenced the mechanical strength and drug release behaviour. FI-IR test verified the successful synthesis of the hydrogel. The rheological parameters indicated that the mechanical strength of the hydrogel was positively correlated with the amount of PEG, and the in vitro dissolution profiles demonstrated that the increasement of PEG could accelerate the drug release rate. The compatibility of the drug delivery system was verified with cells and mice model. Topical delivery of ALA in solution, NLC and NLC-gel was investigated in-vitro.

Electrophysiology Read-Out Tools for Brain-on-Chip Biotechnology

Brain-on-Chip (BoC) biotechnology is emerging as a promising tool for biomedical and pharmaceutical research applied to the neurosciences. At the convergence between lab-on-chip and cell biology, BoC couples in vitro three-dimensional brain-like systems to an engineered microfluidics platform designed to provide an in vivo-like extrinsic microenvironment with the aim of replicating tissue- or organ-level physiological functions. BoC therefore offers the advantage of an in vitro reproduction of brain structures that is more faithful to the native correlate than what is obtained with conventional cell culture techniques. As brain function ultimately results in the generation of electrical signals, electrophysiology techniques are paramount for studying brain activity in health and disease. However, as BoC is still in its infancy, the availability of combined BoC-electrophysiology platforms is still limited. Here, we summarize the available biological substrates for BoC, starting with a historical perspective. We then describe the available tools enabling BoC electrophysiology studies, detailing their fabrication process and technical features, along with their advantages and limitations. We discuss the current and future applications of BoC electrophysiology, also expanding to complementary approaches. We conclude with an evaluation of the potential translational applications and prospective technology developments.

Reduced Graphene Oxide-Encapsulated Microfiber Patterns Enable Controllable Formation of Neuronal-Like Networks

Scaffold-guided formation of neuronal-like networks, especially under electrical stimulation, can be an appealing avenue toward functional restoration of injured nervous systems. Here, 3D conductive scaffolds are fabricated based on printed microfiber constructs using near-field electrostatic printing (NFEP) and graphene oxide (GO) coating. Various microfiber patterns are obtained from poly(l-lactic acid-co-caprolactone) (PLCL) using NFEP and complexity is achieved via modulating the fiber overlay angles (45°, 60°, 75°, 90°), fiber diameters (15 to 148 µm), and fiber spatial organization (spider web and tubular structure). Upon coating GO onto PLCL microfibers via a layer-by-layer (L-b-L) assembly technique and in situ reduction into reduced GO (rGO), the obtained conductive scaffolds, with 25-50 layers of rGO, demonstrate superior conductivity (≈0.95 S cm-1 ) and capability of inducing neuronal-like network formation along the conductive microfibers under electrical stimulation (100-150 mV cm-1 ). Both electric field (0-150 mV cm-1 ) and microfiber diameter (17-150 µm) affect neurite outgrowth (PC-12 cells and primary mouse hippocampal neurons) and the formation of orientated neuronal-like networks. With further demonstration of such guidance to neuronal cells, these conductive scaffolds may see versatile applications in nerve regeneration and neural engineering.

Screening method to identify hydrogel formulations that facilitate myotube formation from encapsulated primary myoblasts

Hydrogel-based three-dimensional (3D) cellular models are attractive for bioengineering and pharmaceutical development as they can more closely resemble the cellular function of native tissue outside of the body. In general, these models are composed of tissue specific cells embedded within a support material, such as a hydrogel. As hydrogel properties directly affect cell function, hydrogel composition is often tailored to the cell type(s) of interest and the functional objective of the model. Here, we develop a parametric analysis and screening method to identify suitable encapsulation conditions for the formation of myotubes from primary murine myoblasts in methacryloyl gelatin (GelMA) hydrogels. The effect of the matrix properties on the myotube formation was investigated by varying GelMA weight percent (wt%, which controls gel modulus), cell density, and Matrigel concentration. Contractile myotubes form via myoblast fusion and are characterized by myosin heavy chain (MyHC) expression. To efficiently screen the gel formulations, we developed a fluorescence-based plate reader assay to quantify MyHC staining in the gel samples, as a metric of myotube formation. We observed that lower GelMA wt% resulted in increased MyHC staining (myotube formation). The cell density did not significantly affect MyHC staining, while the inclusion of Matrigel increased MyHC staining, however, a concentration dependent effect was not observed. These findings were supported by the observation of spontaneously contracting myotubes in samples selected in the initial screen. This work provides a method to rapidly screen hydrogel formulations for the development of 3D cellular models and provides specific guidance on the formulation of gels for myotube formation from primary murine myoblasts in 3D.

Granular Cellulose Nanofibril Hydrogel Scaffolds for 3D Cell Cultivation

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.

Spatiotemporally Controlled Photoresponsive Hydrogels: Design and Predictive Modeling from Processing through Application

Photoresponsive hydrogels (PRHs) are soft materials whose mechanical and chemical properties can be tuned spatially and temporally with relative ease. Both photo-crosslinkable and photodegradable hydrogels find utility in a range of biomedical applications that require tissue-like properties or programmable responses. Progress in engineering with PRHs is facilitated by the development of theoretical tools that enable optimization of their photochemistry, polymer matrices, nanofillers, and architecture. This review brings together models and design principles that enable key applications of PRHs in tissue engineering, drug delivery, and soft robotics, and highlights ongoing challenges in both modeling and application.

Engineered macroporous hydrogel scaffolds via pickering emulsions stabilized by MgO nanoparticles promote bone regeneration

Hydrogels are appealing biomaterials for regenerative medicine since biomimetic modifications of their polymeric network can provide unique physical properties and emulate the native extracellular matrix (ECM). Meanwhile, therapeutic metal ions, such as magnesium ions (Mg²⁺), not only regulate cellular behaviours but also stimulate local bone formation and healing. However, the absence of a meaningful macroporous structure and the uncompromising mechanical strength are still challenges. Herein, we designed a macroporous composite hydrogel based on mild and fast thiol-ene click reactions. The Pickering emulsion method was adopted to form a macroporous structure and introduce MgO nanoparticles (NPs). The results show that the composite hydrogel possesses good mechanical strength and an evenly distributed macroporous structure. MgO NPs stabilized at the oil/water interface not only function as effective emulsion stabilizers, but also enhance the mechanical properties of hydrogels and mediate the sustained release of Mg²⁺. In vitro cell experiments demonstrated that the composite hydrogel displays good biocompatibility. More importantly, the release of Mg²⁺ ions from hydrogels can effectively promote the osteogenic differentiation of BMSCs. Furthermore, an in vivo study showed that macroporous hydrogels can provide a good extracellular matrix microenvironment for in situ osteogenesis and accelerate bone tissue regeneration.

Coupling PEG-LZM polymer networks with polyphenols yields suturable biohydrogels for tissue patching

Poor mechanical performances severely limit the application of hydrogels in vivo; for example, it is difficult to perform a very common suturing operation on hydrogels during surgery. There is a growing demand to improve the mechanical properties of hydrogels for broadening their clinical applications. Natural polyphenols can match the potential toughening sites in our previously reported PEG-lysozyme (LZM) hydrogel because polyphenols have unique structural units including a hydroxyl group and an aromatic ring that can interact with PEG via hydrogen bonding and form hydrophobic interactions with LZM. By utilizing polyphenols as noncovalent crosslinkers, the resultant PEG-LZM-polyphenol hydrogel presents super toughness and high elasticity in comparison to pristine PEG-LZM with no obvious changes in the initial shape, and it can even withstand the high pressure from sutures. At the same time, the mechanical properties could be widely adjusted by varying the polyphenol concentration. Interestingly, the PEG-LZM-polyphenol hydrogel has a higher water content than other polyphenol-toughened hydrogels, which may better meet the clinical needs for hydrogel materials. Besides, the introduction of polyphenols endows the hydrogel with improved antibacterial and anti-inflammatory abilities. Finally, the PEG-LZM-polyphenol (tannic acid) hydrogel was demonstrated to successfully patch a rabbit myocardial defect by suturing for 4 weeks and improve the wound healing and heart function recovery compared to autologous muscle patches.

Reverse engineering human brain evolution using organoid models

Primate brains vary dramatically in size and organization, but the genetic and developmental basis for these differences has been difficult to study due to lack of experimental models. Pluripotent stem cells and brain organoids provide a potential opportunity for comparative and functional studies of evolutionary differences, particularly during the early stages of neurogenesis. However, many challenges remain, including isolating stem cell lines from additional great ape individuals and species to capture the breadth of ape genetic diversity, improving the reproducibility of organoid models to study evolved differences in cell composition and combining multiple brain regions to capture connectivity relationships. Here, we describe strategies for identifying evolved developmental differences between humans and non-human primates and for isolating the underlying cellular and genetic mechanisms using comparative analyses, chimeric organoid culture, and genome engineering. In particular, we focus on how organoid models could ultimately be applied beyond studies of progenitor cell evolution to decode the origin of recent changes in cellular organization, connectivity patterns, myelination, synaptic development, and physiology that have been implicated in human cognition.

Peptide-Fluorophore Hydrogel as a Signal Boosting Approach in Rapid Detection of Cancer DNA

Cancer is a major health risk in the modern society that requires rapid, reliable, and inexpensive diagnostics. Because of the low abundance of cancer DNA in biofluids, current detection methods require DNA amplification. The amplification can be challenging; it provides only relative quantification and extends time and cost of an assay. Herein, we report a new oligonucleotide hybridization platform for amplification-free detection of human cancer DNA. Using a large PEG-capture probe allows rapid separation of the bound (mutant) versus unbound (wild type) DNA. Next, a supramolecular hydrogel forming peptide attached to a detection oligonucleotide probe serves as a signal amplification tool. Having screened multiple short peptides and fluorophores, we identified the system P1 + cyanine 3.5 that allows for sensitive quantitative detection of mutation L858R in EGFR oncogene. The peptide-fluorophore-based assay provides absolute target DNA quantification at the detection limit of 20 ng cancer DNA versus >500 ng for Cy3.5-labeled oligonucleotide in only 1 hour.