Kieran Lau

Modulating how macrophages sense mechanical cues offers a novel strategy to control fibrosis around implanted biomaterials. We term this approach ‘mechano-immunotherapy’, which involves the desensitization of immune mechanosensory pathways to control the host response. Here, we use RN-1734 (RN), a model small molecule to demonstrate the proof-of-concept that pharmacologically disrupting macrophage mechanosensation can mitigate fibrosis. In vitro, RN reduced calcium influx and pro-inflammatory cytokine secretion in J774. a2 macrophages. These effects were strictly context-dependent with efficacy observed only in macrophages on high-stiffness (10% w/v) GelMA hydrogels, with no significant impact on those in softer (5% w/v) hydrogels. In vivo, RN selectively attenuated fibrotic capsule formation around implanted electrospun scaffolds but not smooth hydrogels. Notably, despite hydrogels releasing ∼6-fold more drug than scaffolds, fibrosis was reduced only in the scaffold group, suggesting that therapeutic efficacy is driven by the inhibition of high mechanosensory input rather than the loaded drug concentration alone. Spatial transcriptomics revealed that macrophages acted as the primary mechanosensors at the tissue-implant interface. Unsupervised global principal component analysis revealed that RN acted predominantly on early day 3 macrophages. The strongest effect was observed in surface-adhered mechanosensitive macrophages, where RN treatment enhanced their M2-like phenotype and promoted their dispersal from clustered aggregates into broader distribution within the scaffold. This redistribution was accompanied by a marked reduction in the recruitment of interstitial macrophages from the surrounding tissue, which were enriched for matrix-forming gene signatures. Together, these findings suggest that pharmacological desensitization of immune mechanosensors may represent a promising, context-specific approach to improve biomaterial integration.

3D bioprinting is known for its high precision and reproducibility in fabricating complex and customized biomedical constructs. However, its applications are limited by their static nature; i.e., unlike native tissues, they cannot change shape or functionality over time. To overcome this, 4D bioprinting has emerged as a groundbreaking strategy by incorporating time as the fourth dimension, enabling dynamic structures that adapt in response to stimuli, thereby more accurately replicating living tissues. The success of 4D bioprinting hinges on the development of advanced smart bioinks, as their physicochemical properties uniquely dictate the shape‐morphing behavior, functionality, and performance of bioprinted constructs. These bioinks must be precisely engineered to respond to specific stimuli. This review first introduces 4D bioprinting technologies for tissue engineering scaffolds. We then outline essential requirements for smart bioinks and highlight how AI, particularly machine learning, is revolutionizing their design. Additionally, we examine widely used biomaterials for 4D bioprinting and discuss promising candidates for 4D printing. We also present cutting‐edge bioink applications in tissue engineering, drug screening, and disease modeling, showcasing their potential in regenerative medicine and personalized therapeutics. Finally, we discuss current challenges and future perspectives, underscoring the transformative impact of smart bioinks and 4D bioprinting on biomedical innovation.

The clinical potential of mesenchymal stromal/stem cells (MSCs) is limited by the mismatch between their low abundance in adult tissue and the high doses required for treatment. Conventional cell expansion systems that rely on repeated supplementation with labile, soluble growth factors are inefficient and costly. Moreover, the majority of transplanted MSCs exhibit poor survival post-delivery, undermining therapeutic outcomes and exacerbating cell supply challenges. Three-dimensional (3D) polymeric scaffolds, with high surface-area-to-volume ratios, offer a promising strategy for enhancing both cell expansion and delivery. However, their bioinert nature and limited functionalization options have hindered translation. Here, we present a dual-purpose macroporous polycaprolactone (PCL) scaffold, homogeneously activated using long-lived surface-embedded radicals, to enable the one-step covalent immobilization of fibroblast growth factor 2 (FGF2) throughout its internal architecture. This approach preserves the degradability of PCL, while enhancing FGF2 stability and bioavailability. The resulting biofunctional scaffold supports labor-efficient, spatially uniform MSC expansion with a 99% reduction in FGF2 usage, compared to serial cultures on planar surfaces in FGF2-supplemented media. In addition, when used as a cell delivery vehicle, the scaffold enhances MSC survival and retention after implantation. The generation of such multifunctional 3D materials has broad implications for improving the feasibility, accessibility, and impact of cell therapies and offers a blueprint for the robust, cost-effective biofunctionalization of other biomedically relevant porous materials.

A potential approach for treating spinal cord injuries is the implantation of human induced pluripotent stem cells-derived spinal cord progenitor cells (SCPCs) encapsulated in hydrogels. Digital light processing (DLP) enables the fabrication of scaffolds with high microchannel packing density, which are essential for neurofilament infiltration. In this study, SCPCs were encapsulated in gelatin methacrylate (GelMA)-based bioinks for single-layer printing via DLP bioprinting to incorporate human SCPCs within microchannel scaffolds at a reduced printing time. Mechanical properties were evaluated through degradation studies and compression testing, revealing that while the presence of poly(ethylene glycol) diacrylate improved printability and scaffold stability, it adversely affected cell survival. Scaffolds with higher GelMA concentration (10%) induced greater extent of motor neuronal differentiation as compared to those with 7.5% GelMA concentration (9.4 ± 5.1% vs 3.70 ± 2.6%, p < 0.001). In contrast, the scaffolds with lower GelMA concentration increased interneuron differentiation compared to those with higher GelMA concentration (7.3 ± 1.7% vs 1.6 ± 1.8%, p < 0.01), indicating that stiffness and GelMA content may modulate SCPC differentiation to specific neural subtypes. Overall, the encapsulation of SCPCs within the GelMA microchannel scaffold highlights the significance of material composition and stiffness in 3D printability and neuronal differentiation for spinal cord injury treatment.

An optically active antibacterial ruthenium(II) phenanthroline complex (tris(3,4,7,8‐tetramethyl‐1,10‐phenanthroline) ruthenium(II) dichloride), is investigated for its potential as a multifunctional photo‐initiator. Antibacterial and cytotoxic studies indicated that the complex is biologically active, and viable below <0.5 mm. The complex is shown to photo‐polymerize gelatin using visible light in a similar manner to tris(2,2′‐bipyridyl)ruthenium(II) dichloride and is demonstrated to retain antibacterial activity post‐fabrication of a gelatin hydrogel. Incorporation of the photo‐initiator into the interstitial fluid of a hybrid gelatin granular scaffold generated a multifunctional scaffold that retained cell viability and exhibited injectable properties.

RNA interference (RNAi)-mediated gene silencing is a promising therapeutic approach to treat various diseases, but safe and efficient delivery remains a major challenge to its clinical application. Non-viral gene vectors, such as poly(β-amino esters) (pBAEs), have emerged as a potential candidate due to their biodegradability, low toxicity profile, ease of synthesis, and high gene transfection efficiency for both DNA and siRNA delivery. However, achieving significant gene silencing using pBAEs often requires a large amount of polymer carrier (with polymer/siRNA weight ratio >100) or high siRNA dose (>100 nM), which might potentially exacerbate toxicity concerns during delivery. To overcome these barriers, we designed and optimized a series of hyperbranched pBAEs capable of efficiently condensing siRNA and achieving excellent silencing efficiency at a lower polymer/siRNA weight ratio (w/w) and siRNA dose. Through modulation of monomer combinations and branching density, we identified the top-performing hyperbranched pBAEs, named as h(A2B3)-1, which possess good siRNA condensation ability, low cytotoxicity, and high cellular uptake efficiency. Compared with Lipofectamine 2000, h(A2B3)-1 achieved lower cytotoxicity and higher siRNA silencing efficiency in HeLa cells at a polymer/siRNA weight ratio of 30 and 30 nM siRNA dose. Notably, h(A2B3)-1 enhanced the gene uptake in primary neural cells and effectively silenced the target gene in hard-to-transfect primary cortical neurons and oligodendrocyte progenitor cells, with gene knockdown efficiencies of 34.8 and 53.4% respectively. By incorporating a bioreducible disulfide compartment into the polymer backbone, the cytocompatibility of the h(A2B3)-1 was greatly enhanced while maintaining their good transfection efficiency. Together, the low cytotoxicity and high siRNA transfection efficiency of hyperbranched h(A2B3)-1 in this study demonstrated their great potential as a non-viral gene vector for efficient siRNA delivery and RNAi-mediated gene silencing. This provides valuable insight into the future development of safe and efficient non-viral siRNA delivery systems as well as their translation into clinical applications.

Silk fibroin hydrogels are extensively explored for tissue engineering and regenerative medicine as an artificial extracellular matrix (ECM) that can support tissue growth. However, the nanometer pore size of hydrogels limits adequate cell, tissue, and vascular infiltration. Microgel scaffolds are an emerging class of microporous biomaterials formed by annealing small microscale hydrogels (microgels) into a 3D construct. In this work, silk microgels are generated using a microfluidic device that allows tuning of the microgel diameter (100–400 µm) and are stabilized via visible light‐initiated photo‐crosslinking of native tyrosine residues in silk. Microgels are then covalently annealed using silk solution as glue and the same cytocompatible visible light‐initiated crosslinking to form microgel scaffolds. Unlike the nano‐porosity of bulk photo‐crosslinked silk hydrogels, the microgel scaffolds have an average pore diameter of 29 ± 17 or 192 ± 81 µm depending on the microgel size, with enhanced mechanical properties compared to bulk hydrogels. This microporosity supports enhanced cell spreading and proliferation in vitro and increases scaffold remodeling in vivo, encouraging improved tissue infiltration and matrix deposition. The microgel size and material format also affect inflammatory responses in vivo. This work demonstrates that silk microgels and microgel scaffolds are promising candidates for tissue engineering and regenerative medicine applications.