The molecule at the heart of the study is AICAR, a well-known activator of AMPK, an enzyme often described as the cell’s central metabolic switch. When the researchers treated human umbilical vein endothelial cells with AICAR under inflammatory conditions designed to mimic the diabetic wound environment, AMPK phosphorylation rose more than threefold. The effects cascaded through the cells’ mitochondria: transmission electron microscopy showed preserved mitochondrial ultrastructure instead of the swelling and shrinkage seen in untreated controls, respiratory-chain complexes I through V became more active, and ATP production roughly doubled. Mitochondrial membrane potential increased, mitochondrial mass expanded, and levels of damaging mitochondrial superoxide fell.

Metabolic readouts confirmed that AICAR had shifted endothelial cells into a genuinely high-energy state. The NAD+/NADH ratio rose while the lactate/pyruvate ratio fell, both changes pointing toward enhanced oxidative phosphorylation and suppressed glycolysis. Critically, these effects disappeared when the cells were co-treated with Compound C, an AMPK inhibitor, establishing that the metabolic transformation was AMPK-dependent. Energized endothelial cells also became better builders of blood vessels: they produced more VEGF, migrated faster across scratch wounds, formed more extensive tube networks on Matrigel, and stimulated denser vessel growth in the chick chorioallantoic membrane assay.

But the most striking discovery came from the cells’ secretions. Exosomes, nanosized vesicles that ferry proteins and genetic material between cells, are increasingly recognized as key mediators of intercellular communication in tissue repair. When the team isolated exosomes from AICAR-treated endothelial cells, dubbed AI-EXO, they found that AICAR stimulation increased exosome yield roughly threefold and boosted bioactive protein content 2.2-fold compared with exosomes from untreated cells. Mass spectrometry confirmed that no residual AICAR was encapsulated inside the vesicles, meaning their biological activity came entirely from their own cargo.

Proteomic profiling of AI-EXO revealed a distinct molecular signature, with growth arrest-specific protein 6, or GAS6, standing out among the most significantly upregulated proteins. GAS6 is a secreted ligand with well-documented anti-inflammatory and tissue-protective effects, and it signals through MER, a receptor of the TAM family expressed on macrophages. The researchers hypothesized that AI-EXO might use GAS6 to push macrophages out of their destructive pro-inflammatory M1 state and into the pro-healing M2 state, a transition that is notoriously impaired in diabetes.

The evidence was compelling. When inflammatory M1 macrophages were treated with AI-EXO, the proportion of iNOS-positive M1 cells plummeted to 4.8 percent while Arg-1-positive M2 cells surged to 41.3 percent, yielding an M2-to-M1 ratio of about 8.60, compared with roughly 0.30 in controls. To prove GAS6 was the culprit, the team silenced the GAS6 gene in endothelial cells before AICAR treatment; the resulting exosomes lost nearly all of their reprogramming power. Adding recombinant GAS6 back restored the effect, and blocking either MER or its downstream target AKT with pharmacological inhibitors likewise abolished the M1-to-M2 shift. A GAS6-neutralizing antibody provided independent confirmation that the vesicles’ immunomodulatory function depends specifically on this protein.

With the mechanism established in vitro, the researchers built a delivery system to translate it into living wounds. Using melt electrospinning writing, a high-precision 3D printing technique, they fabricated porous polycaprolactone scaffolds coated with a GelMA hydrogel loaded with AICAR, creating a patch designated MEWs + GelMA@AI. The scaffold released AICAR sustainably for approximately 15 days, and its compressive modulus of about 217 kilopascals provided mechanical stability without excessive stiffness. Endothelial cells cultured on the patch under inflammatory conditions showed a survival rate of nearly 95 percent, well above the 78 percent seen on plain scaffolds, and attached in far greater numbers.

The real test came in diabetic rats, whose diabetes was induced with streptozotocin and a high-sugar, high-fat diet. Full-thickness wounds treated with the AICAR-loaded patch closed significantly faster than wounds in all control groups, including those receiving systemic AICAR injections. Histology told the story beneath the surface: less inflammatory-cell infiltration, denser collagen deposition on Masson’s trichrome staining, and markedly increased CD31-positive neovascularization. Immunofluorescence of wound tissue on day 14 showed the same macrophage shift seen in the dish, with more F4/80-positive Arg-1-positive M2 cells and fewer F4/80-positive iNOS-positive M1 cells. When the researchers added a MER inhibitor to the patch, these benefits largely vanished, confirming that the GAS6/MER/AKT pathway drives the healing response in vivo.

Safety data were reassuring. Fasting blood glucose and body weight showed no significant differences between groups, indicating that neither local nor systemic AICAR delivery disturbed systemic metabolism. Histological examination of major organs revealed no abnormalities, and the patch actually lowered local glucose concentrations within the wound tissue, partially reversing the hyperglycemic microenvironment that sabotages repair. The authors note important caveats, however: the streptozotocin rat model does not fully capture the comorbidities, infection and neuropathy of human diabetic ulcers, the in vitro work relied on immortalized cell lines, and the isolated exosome preparations contain a heterogeneous mix of vesicle subtypes whose individual contributions remain to be disentangled.

Even so, the study represents a notable conceptual advance. It is the first work to identify the GAS6/MER/AKT axis as the link between the metabolic state of endothelial cells and macrophage reprogramming in chronic wounds, framing tissue repair as an immunometabolic conversation between cell types. By pairing a metabolism-centered intervention with a biodegradable scaffold that releases its payload over weeks, the researchers offer a template for dual-targeted wound therapy, one that simultaneously rebuilds vasculature and recalibrates immunity. For the millions of patients whose wounds refuse to heal, that combination of vascular and immune repair, delivered from a single patch, could eventually change the trajectory of diabetic wound care.

Subject of Research: AICAR-loaded scaffolds promoting diabetic wound healing through endothelial energy metabolism, exosomal GAS6 signaling and macrophage reprogramming

Article Title: AICAR-induced energy supply and paracrine activity of endothelial cells accelerate chronic diabetic wound healing by promoting angiogenesis and modulating macrophage reprogramming

Article References: Su, H., Liu, C., Cheng, Y., Cheng, W., Xu, A., Hu, D., Shi, H., Huang, M., Yuan, H., Huang, C., Huang, Y., Su, S., Duan, C., & Feng, X. (2026). AICAR-induced energy supply and paracrine activity of endothelial cells accelerate chronic diabetic wound healing by promoting angiogenesis and modulating macrophage reprogramming. Materials Today Bio, 41, Article 103743. https://doi.org/10.1016/j.mtbio.2026.103743

Image Credits: AI Generated

DOI: 10.1016/j.mtbio.2026.103743

Keywords: diabetic wounds, AICAR, AMPK, exosomes, GAS6, macrophage polarization, angiogenesis, MER/AKT signaling, GelMA hydrogel, melt electrospinning, tissue engineering, immunometabolism

The scale of the problem is enormous. Roughly 50 million people sustain traumatic brain injuries annually, and the global economic burden exceeds 400 billion US dollars. Surgeons can relieve pressure and clinicians can manage symptoms with osmotic agents, diuretics, and glucocorticoids, but none of these supports repair of the injured tissue. The real killers are the secondary cascades that unfold over hours to days: rising intracranial pressure, cerebral edema, breakdown of the blood-brain barrier, ischemia, redox imbalance, and a self-reinforcing wave of neuroinflammation. Edema and inflammation feed each other. A leaky barrier lets immune cells and plasma flood into brain tissue, swelling activates resident microglia, and the inflammatory signals they release further destabilize the endothelial tight junctions that hold the barrier together. Breaking that loop is a central therapeutic goal.

Cannabidiol, or CBD, has long been an attractive candidate for exactly this job. It is anti-inflammatory, antioxidant, and non-intoxicating, and the team’s earlier work showed that CBD restores blood-brain barrier integrity after brain injury through the PGE2-EP2-cAMP pathway while also damping microglial activation. The obstacle has always been delivery. Because CBD is highly lipophilic, intraperitoneal injection sends much of the drug into adipose tissue rather than the brain. Oral dosing loses more than 70 percent of the compound to first-pass metabolism in the liver. Intravenous injection achieves full bioavailability but suffers from a short half-life and demands professional administration, an awkward constraint in acute care. None of the conventional routes keeps therapeutic levels of CBD parked at a contused cortex for the critical first days.

The researchers’ solution was a sponge made of gelatin methacryloyl, or GelMA, a photocrosslinkable hydrogel already used in drug delivery, ophthalmic therapy, and cardiac repair. The team synthesized GelMA by reacting gelatin with methacrylic anhydride, confirmed the modification with proton nuclear magnetic resonance spectroscopy and infrared spectroscopy, and screened twelve candidate formulations by varying the gelatin-to-anhydride ratio and ultraviolet crosslinking time. They judged each variant on swelling behavior, mass loss in simulated body fluid, and microstructure imaged by scanning electron microscopy. The winning formulation swelled only modestly, between 13 and 25 percent, retained a porous interconnected architecture, and fully degraded within five days under the tested conditions, a profile suited to a temporary implant that releases drug and then disappears.

Loading the sponge with CBD changed none of those material properties. Infrared spectra of the finished product showed the hydroxyl and aliphatic carbon-hydrogen stretching peaks characteristic of cannabidiol, while swelling and degradation curves remained essentially identical to the blank scaffold. Ultraperformance liquid chromatography measured encapsulation efficiencies between roughly 50 and 63 percent, with batch-to-batch variation below 3 percent and, remarkably, center-to-periphery drug ratios of almost exactly one, meaning the CBD was distributed evenly through each sponge. In a release assay, about 22 percent of the payload emerged in the first two hours, followed by a steady trickle that reached roughly 58 percent at 24 hours and 80 percent by 72 hours, precisely the sustained profile the early post-injury phase demands.

Safety testing came next, and it was thorough. Extracts of the sponge were applied to hippocampal neurons, astrocytes, and brain endothelial cells; viability remained high up to 5 micrograms per milliliter, defining a safe exposure window, while hemolysis assays with rat red blood cells showed rates below 5 percent. The team then implanted the sponges into rats subjected to a standardized weight-drop cortical contusion and tracked CBD with high-resolution liquid chromatography mass spectrometry. The pharmacokinetic contrast with conventional dosing was striking. After intraperitoneal injection, CBD in the injured cortex peaked at about 91 nanograms per gram and faded quickly. With the sponge, cortical concentrations reached about 251 nanograms per gram and remained detectable for the entire 48-hour observation window, while blood levels stayed low, an inversion of exposure that concentrates the drug at the lesion and spares the rest of the body. Serum chemistry and organ histology showed no treatment-related abnormalities.

The therapeutic results followed. Forty-eight hours after injury, rats receiving the medium and high doses of the CBD sponge scored significantly better on a standardized neurological deficit scale, traveled farther in open-field tests, and explored the open arms of an elevated plus maze more readily than injured controls, with mannitol and injected CBD providing comparable but generally weaker benefits. Under the microscope, the treated cortex retained orderly neuronal architecture and intact Nissl bodies, showed fewer TUNEL-positive apoptotic cells, and released lower levels of neuron-specific enolase and S-100 calcium-binding protein beta, two canonical markers of neural damage. The blank sponge alone conferred little benefit, indicating that sustained CBD release, not the scaffold itself, drove the protection.

Mechanistically, the study points to the blood-brain barrier and the water channel aquaporin-4. Treated rats had less brain water content and far less Evans blue dye leaking across the barrier, alongside restored expression of the tight junction proteins ZO-1, occludin, and claudin-5. Molecular docking predicted that CBD binds aquaporin-4 with a binding energy of minus 6.7 kilocalories per mole, and surface plasmon resonance confirmed a measurable micromolar interaction with a dissociation constant of 56.6 micromolar. After injury, aquaporin-4 shifted away from vascular endothelial structures and toward reactive, GFAP-positive astrocytes; the sponge reversed that redistribution, reduced astrocytic overactivation, and preserved endothelial markers. On the inflammatory front, the treatment lowered interleukin-6, interleukin-1 beta, and tumor necrosis factor-alpha, raised the anti-inflammatory interleukin-10, and calmed Iba-1-stained microglia. RNA sequencing of the injured cortex identified nearly 800 differentially expressed genes and pointed to dampened NF-kappaB and TNF signaling alongside enhanced PI3K-Akt survival signaling, changes the authors confirmed by Western blot and quantitative PCR.

The authors are careful about the limits of their work. The study captured only the acute, two-day phase, leaving long-term cognitive and behavioral recovery untested, and the local and injected CBD regimens were not matched for dose or exposure, so some benefits may reflect the delivery platform rather than the drug alone. No formal power calculation was performed, and the transcriptomic analysis omitted the blank-sponge and injected-CBD groups. Even so, the concept is compelling: a cheap, photocrosslinkable gelatin sponge that turns a one-shot drug depot into a 48-hour local infusion, right where edema and inflammation are born. If future studies with exposure-matched controls and longer follow-up bear out these results, the humble gelatin sponge could become a serious contender in the long-delayed search for the first true neuroprotective therapy for traumatic brain injury.

Subject of Research: Local delivery of cannabidiol using a GelMA hydrogel sponge to treat cerebral edema and neuroinflammation after traumatic brain injury

Article Title: In situ delivery of cannabidiol-loaded GelMA sponge attenuates cerebral edema and neuroinflammation in traumatic brain injury

Article References: Li, H., Luo, X., Cao, Y., Jiang, H., Guo, Z., Zhu, Y., Zhang, L., Li, Z., Li, J., Wu, H., & Li, P. (2026). In situ delivery of cannabidiol-loaded GelMA sponge attenuates cerebral edema and neuroinflammation in traumatic brain injury. Materials Today Bio, 41, Article 103721. https://doi.org/10.1016/j.mtbio.2026.103721

Image Credits: AI Generated

DOI: 10.1016/j.mtbio.2026.103721

Keywords: traumatic brain injury, cannabidiol, GelMA hydrogel, drug delivery, cerebral edema, blood-brain barrier, neuroinflammation, aquaporin-4, microglia, NF-kappaB signaling, biomaterials, rat model

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