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The tumor microenvironment presents spatiotemporal shifts in biomechanical properties with cancer progression. Hydrogel biomaterials like GelAGE offer the stiffness tuneability to recapitulate dynamic changes in tumor tissues by altering photo‐energy exposures. Here, a tuneable hydrogel with spatiotemporal control of stiffness and mesh‐network is developed. The volume of MCF7 spheroids encapsulated in a linear stiffness gradient demonstrates an inverse relationship with stiffness (p< 0.0001). As spheroids are exposed to increased crosslinking (stiffer) and greater mechanical confinement, spheroid stiffness increases. Protein expression (TRPV4, β1 integrin, E‐cadherin, and F‐actin) decreases with increasing stiffness while showing strong correlations to spheroid volume (r2> 0.9). To further investigate the role of volume, MCF7 spheroids are grown in a soft matrix for 5 days prior to a second polymerisation which presents a stiffness gradient to equally expanded spheroids. Despite being exposed to variable stiffness, these spheroids show even protein expression, confirming volume as a key regulator. Overall, this work showcases the versatility of GelAGE and demonstrates volume expansion as a key regulator of 3D mechanosensation in MCF7 breast cancer spheroids. This platform has the potential to further investigation into the role of stiffness and dimensionality in 3D spheroid culture for other types of cancers and diseases. There is a constant need for biomaterials that offer a high degree of tuneability to greater recapitulate the variable tissue properties noted in diseased tissues, such as breast cancer. Using a linear stiffness gradient GelAGE hydrogel, an increased density of mesh‐network results in restricted volume expansion of MCF7 spheroids and reduces key protein expression (TRPV4, β1 integrin, E‐cadherin, and F‐actin).

As emerging therapeutic factors, extracellular vesicles (EVs) offer significant potential for myocardial infarction (MI) treatment. Current delivery approaches for EVs involve either intra‐myocardial or intravenous injection, where both have inherent limitations for downstream clinical applications such as secondary tissue injury and low delivery efficiency. Herein, an injection‐free approach for delivering EVs onto the heart surface to treat MI is proposed. By spraying a mixture of EVs, gelatin methacryloyl (GelMA) precursors, and photoinitiators followed by visible light irradiation for 30 s, EVs are physically entrapped within the GelMA hydrogel network covering the surface of the heart, resulting in an enhanced retention rate. Moreover, EVs are gradually released from the hydrogel network through a combination of diffusion and/or enzymatic degradation of the hydrogel, and they are effectively taken up by the sprayed tissue area. More importantly, the released EVs further migrate deep into myocardium tissue, which exerts an improved therapeutic effect. In an MI‐induced mice model, the group treated with EVs‐laden GelMA hydrogels shows significant recovery in cardiac function after 4 weeks. The work demonstrates a new strategy for delivering EVs into cardiac tissues for MI treatment in a localized manner with high retention. Injection free delivery approach developed from this study can be utilized to deliver extracellular vesicles (EVs) in a localized and high retention manner. Delivered EVs are diffused into deep tissue region to achieve an uncompromised therapeutic effect. More importantly, in a myocardial infarction mice model, the cardiac function of mouse shows a significant improvement after the treatment.

3D Bioprinting The crosstalk between cells during microcapillary formation is highlighted in article 2101873by Khoon S. Lim and co‐workers. Mesenchymal stromal cells (red) building bridges to allow endothelial cells (green) to cross spatial gaps in biofabricated constructs for rapid vascularisation. Providing the right microenvironment is key to support cell‐driven microcapillary formation.

The principle challenge for engineering viable, cell‐laden hydrogel constructs of clinically‐relevant size, is rapid vascularization, in order to moderate the finite capacity of passive nutrient diffusion. A multiscale vascular approach, with large open channels and bulk microcapillaries may be an admissible approach to accelerate this process, promoting overall pre‐vascularization for long‐term viability of constructs. However, the limited availability of bioinks that possess suitable characteristics that support both fabrication of complex architectures and formation of microcapillaries, remains a barrier to advancement in this space. In this study, gelatin‐norbornene (Gel‐NOR) is investigated as a vascular bioink with tailorable physico‐mechanical properties, which promoted the self‐assembly of human stromal and endothelial cells into microcapillaries, as well as being compatible with extrusion and lithography‐based biofabrication modalities. Gel‐NOR constructs containing self‐assembled microcapillaries are successfully biofabricated with varying physical architecture (fiber diameter, spacing, and orientation). Both channel sizes and cell types affect the overall structural changes of the printed constructs, where cross‐signaling between both human stromal and endothelial cells may be responsible for the reduction in open channel lumen observed over time. Overall, this work highlights an exciting three‐way interplay between bioink formulation, construct design, and cell‐mediated response that can be exploited towards engineering vascular tissues. A multiscale vascular approach, with large open channels and bulk microcapillaries is an admissible approach to promote pre‐vascularization. Here, gelatin‐norbornene hydrogels are demonstrated to support cellular self‐assembly into capillaries, and shown to be applicable as a bioink in extrusion and lithography printing. Using this platform, an interplay between bioink formulation, construct physical architecture, and cell‐mediated response towards vascularization is uncovered.

Extrusion‐based 3D bioprinting is hampered by the inability to print materials of low‐viscosity. In this study, a single initiating system based on ruthenium (Ru) and sodium persulfate (SPS) is utilized for a sequential dual‐step crosslinking approach: 1) primary (partial) crosslinking in absence of light to alter the bioink's rheological profile for print fidelity, and 2) subsequent secondary post‐printing crosslinking for shape maintenance. Allyl‐functionalized gelatin (Gel‐AGE) is used as a bioink, allowing thiol‐ene click reaction between allyl moieties and thiolated crosslinkers. A systematic investigation of primary crosslinking reveals that a thiol‐persulfate redox reaction facilitates thiol‐ene crosslinking, mediating an increase in bioink viscosity that is controllable by tailoring the Ru/SPS, crosslinker, and/or Gel‐AGE concentrations. Thereafter, subsequent photoinitiated secondary crosslinking then facilitates maximum conversion of thiol‐ene bonds between AGE and thiol groups. The dual‐step crosslinking method is applicable to a wide biofabrication window (3–10 wt% Gel‐AGE) and is demonstrated to allow printing of low‐density (3 wt%) Gel‐AGE, normally exhibiting low viscosity (4 mPa s), with high shape fidelity and high cell viability (>80%) over 7 days of culture. The presented approach can therefore be used as a one‐pot system for printing low‐viscous bioinks without the need for multiple initiating systems, viscosity enhancers, or complex chemical modifications. Low density allyl‐functionalized gelatin bioinks are printable by step‐wise control of the degree of crosslinking to modify the rheological profile. The low‐density bioinks are irradiated with light to stabilize the construct, and are able to promote cell survival and function.