The team, led by researchers including Tianhao Wang and Xiaoxiang Ren, defines its constructs as scaffold-guided engineered bone organoids, meaning the biomaterial establishes the initial three-dimensional architecture while the encapsulated cells progressively take over, depositing bone-specific extracellular matrix and driving mineralization. This dynamic remodeling is what separates a true organoid from a passive cell-laden scaffold. Conventional bone organoid platforms are largely built to push stem cells toward osteogenic differentiation, but they rarely incorporate immune components, a significant drawback given that macrophages must typically shift from a pro-inflammatory M1 state to a pro-regenerative M2 state to resolve inflammation, induce new vessel formation, and facilitate matrix remodeling during healing.

The new bioink blends three components in a carefully optimized ratio of 10 percent gelatin methacryloyl (GelMA), 1 percent Laponite synthetic nanoclay, and 40 percent aloe vera gel. Each ingredient earns its place through a defined function. GelMA, a photocrosslinkable derivative of gelatin, carries the arginine-glycine-aspartic acid cell-adhesion motif and offers tunable mechanics through rapid UV cross-linking. Laponite forms what materials scientists describe as a house-of-cards microstructure, imparting strong shear-thinning behavior that makes the ink extrusion-printable while boosting elastic modulus and toughness; its degradation products, magnesium and silicon ions, have independently been shown to foster a pro-regenerative microenvironment. Aloe vera serves as the immunologically active component, delivering bioactive polysaccharides such as acemannan along with phytosphingosine- and polyphenol-related metabolites identified by liquid chromatography-mass spectrometry.

Reaching that sweet-spot formulation required systematic trade-off analysis. Lower GelMA concentrations produced weak mechanical support and structural collapse, while higher levels restricted cell migration and matrix remodeling. Laponite at 1 percent elevated shape fidelity to a printability coefficient near 1.0, but higher loadings clogged nozzles and pushed cell viability below 80 percent through elevated shear stress. Aloe vera below the optimal threshold weakened immunomodulatory efficacy, whereas excess diluted the precursor and compromised cross-linking. The final formulation, seeded with rat bone marrow mesenchymal stem cells at one million cells per milliliter, yielded continuous filament deposition, precise architecture, and post-printing viability exceeding 90 percent, all without a single exogenous cytokine such as IL-4.

The printing parameters themselves are a study in delicacy. Constructs were extruded at 8 degrees Celsius to preserve gel consistency and prevent filament deformation, under pneumatic pressure of 0.2 to 0.3 megapascals at a speed of 4 millimeters per second, using a 21-gauge metal nozzle. A rectangular, eight-layer porous grid of 5 by 5 millimeters was built with 1.5-millimeter infill spacing and 90-degree interlayer rotation. Cross-linking used 365-nanometer UV light at just 5 percent intensity, applied for 10 seconds per layer with brief post-curing, enough to lock in shape without damaging the stem cells. Printed precursors then spent 24 hours in growth medium before switching to osteogenic induction medium supplemented with beta-glycerophosphate, ascorbic acid, and dexamethasone for up to 28 days.

In vitro, the organoids behaved as hoped. Alkaline phosphatase and Alizarin Red S staining documented progressive osteogenic differentiation and mineral deposition, confirmed by elevated expression of the master osteogenic markers OCN, RUNX2, and OPN and by micro-computed tomography detection of mineralized matrix. On the immune side, the constructs increased macrophage recruitment, invasion, and adhesion, and shifted the cells toward a CD206-positive, iNOS-low phenotype characteristic of pro-regenerative M2 macrophages, accompanied by reduced IL-1beta and increased IL-10 expression. Bulk RNA sequencing of implanted constructs revealed broad immune remodeling across Th1/Th2/Th17-related pathways and alterations in STAT6, NF-kappaB, PI3K/AKT, and RANKL-related signaling, consistent with enhanced pro-regenerative responses and dampened inflammation, though the authors caution these associations do not yet establish direct causality.

The in vivo results are where the platform becomes genuinely striking. When implanted subcutaneously into nude mice, the organoid precursors matured into bone-like tissue, organizing type 1 collagen and periostin into structured extracellular matrix, forming vinculin-positive focal adhesions, and sprouting prominent surface capillaries alongside internal CD31-positive microvascular networks. The team then moved to the decisive test: bilateral 5-millimeter critical-sized calvarial defects in rats, wounds too large to heal on their own. By eight weeks, the aloe-containing organoids had promoted more robust bone regeneration than GelMA-only or GelMA/Laponite control scaffolds, with improved mineralized bone formation, closer integration with host tissue, and CD206-positive macrophages populating the repair site. Histology of major organs and routine blood biochemistry revealed no obvious systemic toxicity.

The authors are candid about the platform’s limits. The protocol models macrophage-mediated regulation only; neutrophils, osteoclasts, T cells, and other stromal populations were not systematically incorporated, and the use of immunodeficient nude mice precludes assessment of adaptive immunity. Late-stage osteocyte maturation and lacuno-canalicular network organization remain uncharacterized, and the eight-week observation window captures only early-to-intermediate regeneration, leaving scaffold degradation kinetics, vascular stabilization, and biomechanical load-bearing integration for future studies extending to 12 to 24 weeks and, ultimately, large-animal models. Batch-to-batch consistency of aloe vera gel also emerges as a critical quality-control point, since variability in its bioactive constituents could weaken macrophage polarization.

Even so, the implications extend well beyond the skull. The researchers envision adapting the bioink to model immune-dysregulated orthopedic diseases such as rheumatoid arthritis and osteoporosis by incorporating patient-derived macrophages, synovial fibroblasts, or osteoclast precursors. Adding chondrogenic factors like TGF-beta3 could generate cartilage organoids, while the same immunoregulatory chemistry might improve wound repair and reduce scarring in skin models. Because the constructs simultaneously promoted bone formation and vascularization in vivo, the system could also help solve the vascularization bottleneck that plagues the engineering of many other tissues. Multi-nozzle bioprinting and microfluidic culture could eventually arrange bone-forming, vascular, and marrow-like compartments in spatially organized, immunocompetent constructs. For a field long tethered to an ill-defined gel extracted from mouse tumors, a printable, plant-powered alternative that teaches immune cells to heal rather than inflame marks a genuinely consequential turn in the organoid revolution.

Subject of Research: Fabrication of immune-regulatory bone organoids using a plant-based GelMA/Laponite/Aloe vera bioink

Article Title: Protocol for fabricating immune-regulatory bone organoids via plant-based bioinks

Article References: Wang, T., Gao, G., Zhang, X., Huo, K., Liu, C., Geng, Z., Bai, L., Zhang, H., Liu, H., Xu, K., Lai, Y., Wang, J., Jing, Y., He, C., Wang, G., Su, J., & Ren, X. (2026). Protocol for fabricating immune-regulatory bone organoids via plant-based bioinks. iScience, 29(11), Article 117866. https://doi.org/10.1016/j.isci.2026.117866

Image Credits: AI Generated

DOI: 10.1016/j.isci.2026.117866

Keywords: bone organoids, bioink, Aloe vera, GelMA, Laponite, 3D bioprinting, macrophage polarization, osteoimmunology, bone regeneration, Matrigel-free, tissue engineering, calvarial defect

The research, led by Hao Pan, Jiefeng Huang, Haoze Zhu, Xiaokun Li, and Cailong Liu, builds on a conceptual shift that has been gathering momentum in regenerative medicine. Bone repair is increasingly understood not as a purely osteogenic event but as an immunoregenerative one. Successful healing requires the temporally orchestrated resolution of inflammation, recruitment and differentiation of osteoprogenitor cells, formation of vascular networks, deposition of extracellular matrix, and eventual mineral maturation. At the center of this cascade sit macrophages—the immune cells that flood any injury site within hours. Early on, pro-inflammatory macrophages clear debris and defend against pathogens, but if that inflammatory state persists, it amplifies cytokine release, kills off osteoprogenitors, suppresses angiogenesis, and stalls bone bridging. When macrophages transition in time toward a reparative, so-called M2 phenotype, they instead secrete signals that resolve inflammation, remodel matrix, stabilize vessels, and drive osteogenic differentiation.

Previous attempts to exploit this plasticity have relied on small molecules, inorganic ions, or cytokines embedded in scaffolds. Such agents diffuse rapidly, act through narrow signaling channels, and cannot reproduce the rich paracrine language that reparative immune cells actually speak. The new work turns instead to small extracellular vesicles, or sEVs—nanoscale, membrane-bound packets that cells use to ship proteins, lipids, mRNAs, and microRNAs to one another. Because their cargo reflects the physiological state of the parent cell, sEVs can regulate recipient cells through multiple targets and pathways simultaneously. Macrophage-derived vesicles are especially attractive: their composition and function track the macrophage’s polarization status, and M2 macrophage exosomes have already been shown to restore osteoimmune balance and accelerate fracture healing, even under diabetic conditions where inflammatory dysregulation cripples bone repair.

Native sEVs, however, suffer from well-known weaknesses: modest yields, heterogeneous bioactivity, inefficient uptake by target cells, and rapid clearance after injection. The team’s solution was a two-step engineering scheme. First, they polarized RAW264.7 murine macrophages with interleukin-4 to generate reparative M2-like cells, confirmed by upregulation of the M2 markers Mrc1 and Arg1, elevated CD206 expression, and increased secretion of the anti-inflammatory cytokines IL-10 and TGF-β. Then they subjected these cells to 24 hours of hypoxic preconditioning in a sealed low-oxygen system, mimicking the low oxygen tension characteristic of injury niches. Western blotting confirmed accumulation of HIF-1α, the master hypoxia-responsive transcription factor, verifying that the donor cells had mounted a hypoxia program before releasing their vesicles.

The hypoxic treatment produced a striking and therapeutically useful side effect: apoptotic mimicry. Annexin V staining revealed a time-dependent externalization of phosphatidylserine on the donor macrophages, reaching 50.6 percent Annexin V-positive, membrane-intact cells at 24 hours. Phosphatidylserine is the classic eat-me lipid that dying cells display to trigger efferocytosis—the engulfment of apoptotic material—and, crucially, this recognition is not merely a cleanup mechanism. PS-mediated uptake actively drives anti-inflammatory, pro-resolving responses in phagocytes. Confocal imaging confirmed that the purified vesicles, dubbed M2-HP-Apo-sEVs, retained this PS-enriched membrane. Transmission electron microscopy showed typical rounded, cup-shaped nanovesicles of roughly 148 to 151 nanometers, and marker analysis confirmed enrichment of the EV proteins CD81 and ALIX with no detectable calnexin contamination. Notably, hypoxia also boosted vesicle yield per donor cell—without degrading purity, as shown by a stable particle-to-protein ratio—likely because hypoxic signaling accelerates endosomal trafficking and multivesicular body turnover.

Functionally, the engineered vesicles outperformed their normoxic counterparts at every checkpoint. In flow-cytometric uptake assays, macrophages internalized M2-HP-Apo-sEVs far more readily than standard M2-sEVs, an advantage the team traced in part to the MerTK receptor, a phosphatidylserine-binding efferocytic receptor. When the researchers partially silenced Mertk with siRNA, the uptake advantage vanished and the two vesicle types became indistinguishable in their immunomodulatory effects—strong evidence that PS-MerTK recognition underlies the enhanced activity, though the authors caution that incomplete knockdown and the absence of direct PS-blocking experiments mean other pathways likely contribute. In lipopolysaccharide-stimulated inflammatory macrophages, M2-HP-Apo-sEVs suppressed the pro-inflammatory genes Il1b and Nos2 more strongly than ordinary M2-sEVs while boosting Arg1 and Mrc1, shifting secreted cytokines away from IL-6 and IL-1β and toward IL-10 and TGF-β, and flipping surface marker expression from CD86 toward CD206. In short, the vesicles did not merely dampen inflammation—they actively converted inflammatory macrophages into a pro-resolving, tissue-repairing state.

The benefits rippled outward to the two other cell lineages that bone regeneration depends on. In bone marrow mesenchymal stem cells, M2-HP-Apo-sEVs produced the strongest alkaline phosphatase activity at day seven of osteogenic induction and the most abundant mineralized nodule formation by day fourteen, alongside coordinated upregulation of Alpl, Runx2, Opn, Ocn, and Bmp2 and intensified BMP2 protein staining. In human umbilical vein endothelial cells, the vesicles drove proliferation in EdU assays, accelerated migration in Transwell chambers, and produced denser, more interconnected capillary-like networks with significantly more nodes, junctions, and branches. This triple action—immune resolution, osteogenesis, and angiogenesis—reflects the emerging principle of osteo–immuno–angiogenic coupling, in which macrophages, stem cells, and vessels reinforce one another rather than operating as isolated modules.

To keep the vesicles where they are needed, the team embedded them in gelatin methacryloyl (GelMA), a photocrosslinkable hydrogel that combines cell-adhesive motifs with tunable degradation. Scanning electron microscopy showed that vesicle loading did not disrupt the hydrogel’s interconnected porous architecture, and release experiments in collagenase-containing medium demonstrated progressive, sustained vesicle liberation over seven days, governed by enzymatic degradation of the matrix. The construct was then tested in a demanding model: a five-millimeter critical-sized calvarial defect in mice, filled in situ with photocrosslinked hydrogel. Twelve weeks later, micro-computed tomography revealed minimal spontaneous healing in the GelMA-only group, substantial improvement with ordinary M2-sEVs, and the most extensive defect filling and radiographic bridging with the hypoxia-programmed vesicles. Quantitative analysis confirmed significantly better bone volume fraction, mineral density, trabecular number, and trabecular thickness, with reduced trabecular separation.

Tissue-level analyses told a coherent mechanistic story. Immunofluorescence of regenerated calvarial tissue showed reduced CD86 and increased CD206, indicating that the macrophage phenotype shift survived implantation; BMP2 and the endothelial marker CD31 were both elevated, evidencing coupled osteogenesis and vascularization; and H&E plus Masson’s trichrome staining revealed more continuous tissue bridging and richer collagen matrix in the M2-HP-Apo-sEV group. Gene expression in the defect tissue mirrored the in vitro findings, with inflammatory transcripts down and reparative, angiogenic, and osteogenic transcripts up. Examination of heart, liver, spleen, lung, and kidney showed no overt histopathological abnormalities at the twelve-week endpoint, offering preliminary reassurance on biocompatibility.

The authors are candid about limitations: the in vivo evidence rests on a single murine model at a single time point; the vesicles came from a cell line rather than primary human macrophages; the oxygen level during preconditioning was not continuously controlled; ultracentrifugation cannot fully resolve apoptosis-associated vesicle subpopulations; and the specific cargo—protein, lipid, or RNA—responsible for the effects remains unidentified. Clinical translation will also demand GMP-compatible manufacturing, closed processing systems, and rigorous lot-release criteria. Even so, the study delivers a compelling proof of concept: by programming donor macrophages with hypoxia, borrowing the apoptotic eat-me signal to hijack the immune system’s own resolution machinery, and parking the resulting nanovesicles in a degradable hydrogel, the researchers have assembled a cell-free platform that teaches the wound to heal itself. If the approach generalizes to load-bearing defects and larger animals, it could reshape how surgeons think about the impossible hole in the bone—not as a gap to be filled, but as an immune conversation waiting to be redirected.

Subject of Research: Hypoxia-programmed apoptotic-mimetic M2 macrophage-derived small extracellular vesicles delivered in GelMA hydrogels for immunoregenerative repair of critical-sized bone defects

Article Title: Hypoxia-programmed apoptotic-mimetic M2 macrophage-derived small extracellular vesicles for hydrogel-mediated immunoregenerative bone repair

Article References: Pan, H., Huang, J., Zhu, H., Chen, L., Huang, S., Huang, Y., Zhu, X., Li, X., & Liu, C. (2026). Hypoxia-programmed apoptotic-mimetic M2 macrophage-derived small extracellular vesicles for hydrogel-mediated immunoregenerative bone repair. Materials Today Bio, 41, Article 103696. https://doi.org/10.1016/j.mtbio.2026.103696

Image Credits: AI Generated

DOI: 10.1016/j.mtbio.2026.103696

Keywords: extracellular vesicles, macrophages, M2 polarization, hypoxia preconditioning, phosphatidylserine, efferocytosis, MerTK, GelMA hydrogel, bone regeneration, osteogenesis, angiogenesis, calvarial defect