Mechanically robust neuroprotective stent by sequential Mg ions release for ischemic stroke therapy

Abstract

Most acute ischemic stroke patients with large vessel occlusion require stent implantation post-thrombectomy for complete recanalization, yet they exhibit a high rate of poor prognosis due to ischemia-reperfusion injury. Thus, combining reperfusion therapy with neuroprotective treatment offers significant advantages. This study introduces a novel Mg²⁺ eluting stent by incorporating neuroprotective MgSO₄ particles into a PLCL (poly (l-lactide-co-ε-caprolactone)) substrate using 3D printing technology. A novel MgSO₄-particle/Mg²⁺-ions combined-mechanical reinforcement mechanism was introduced. Subsequently, the neuroprotective efficacy of the stents was validated through oxygen-glucose deprivation/reoxygenation-injured neuron cells in vitro and via the transient middle cerebral artery occlusion rat model to emulate human brain ischemia/reperfusion injury in vivo. The staged-release of Mg²⁺ is supposed to provide sequential neuroprotection that aligns with the treatment window for acute ischemic stroke. This study marks the first development of biodegradable neuroprotective brain stents and presents an effective strategy to alleviate cerebral ischemia-reperfusion injury.

Fig. 1. Schematic illustration of the study design.

Preparation: PLCL is synthesized via copolymerization of L-lactide and ε-caprolactone. Magnesium sulfate (MgSO₄) powder is mixed into the molten PLCL to form PLCL/MgSO₄ composites with varying MgSO₄ concentrations. The composite is extruded as a hot-melt filament through a 3D printer nozzle, adhering to either a rotating rod or previously deposited filaments, ultimately fabricating stents. Implantation: A middle cerebral artery occlusion (MCAO) rat model is established. The fabricated stents are implanted into the common carotid artery (CCA). Neuroprotection: Mg²⁺ ions (blue spheres) released from the stent migrate with blood flow into the infarcted region (gray area). There, they antagonize Ca²⁺ overload and scavenge reactive oxygen species (ROS) in damaged neurons, exerting a neuroprotective effect.

Fig. 2. Characterization of the PLCLxMS stents.

A Surface morphology of PLCLxMS (x = 0, 5, 10, 15, 20, 25) stents (SEM images). Each experiment was repeated 3 times independently with similar results. B Elemental mapping on the PLCL10MS stent surface. Each experiment was repeated 3 times independently with similar results. C Fourier transform infrared spectroscopy (FTIR) analysis. D X-ray diffractometer (XRD) spectra. E Differential scanning calorimeter (DSC) curves. F Thermogravimetric analysis (TGA) thermograph. Source data are provided as a Source Data file.

Fig. 3. Staged in vitro degradation behavior of the PLCLxMS stents in PBS solution at different time points.

A Schematic diagram of Mg²⁺ release and degradation of PLCLxMS stent struts from cross-sectional perspective. B Staged-cumulative release curve of Mg²⁺ at different stages. C Staged-Mg²⁺ release rate over 56 days. D Surface and cross-sectional morphology of the PLCL10MS stents after immersion in PBS for 7 days. E Simulation of Mg²⁺ dissolution and concentration change in PLCL5MS composites. F Simulated release curves of Mg²⁺ during immersion of composites with varying MgSO₄ contents, based on diffusion theory. Source data and exact P values are provided as a Source data file. One-way analysis of variance (ANOVA) with a Tukey/Games-Howell post hoc test for multiple comparisons. Sample size: n = 3 biologically independent replicates. **P < 0.01, ***P < 0.001, Burst vs. Fast group; # P < 0.05, ## P < 0.01, ### P < 0.001, Fast vs. Stable group; §§ P < 0.01, §§§ P < 0.001, Stable vs. Burst group. Data are presented as mean values ± SD.

Fig. 4. Mechanical properties of PLCLxMS composites and stents.

A Tensile test device for PLCLxMS sheets. B Stress-strain curve of PLCLxMS sheets. C The calculated Young’s modulus of PLCLxMS sheets. D SEM images and EDS mapping of the fracture topography of PLCL5MS and PLCL25MS sheets post-tensile test. E Radial force test device. F Radial force with compression of PLCLxMS stents. G The maximum radial force with compression of PLCLxMS stents. H Simulated body stress distribution in PLCLxMS stents when compressed to 70% of their original diameter. I Simulated radial force with compression of PLCLxMS stents. Source data and exact P values are provided as a Source data file. One-way analysis of variance (ANOVA) with a Tukey/Games-Howell post hoc test for multiple comparisons. Sample size: n = 3 biologically independent replicates. ***P < 0.001, PLCL vs. PLCL5MS group; PLCL vs. PLCL10MS group; PLCL vs. PLCL25MS group. Data are presented as mean values ± SD.

Fig. 5. Investigation into mechanical strengthening mechanisms during PLCL degradation.

A Staged-radial force of PLCLxMS stents measured after immersion for 7, 14, 28 and 56 days. B FTIR spectra of PLCL5MS stents after immersion for 7 days (Fast) and 56 days (Stable). C Schematic diagram illustrating experiments and conjectures to investigate the reinforcement mechanism of Mg²⁺ during PLCL degradation (Created in BioRender). D Hardness of the PLCL surface after immersion in various solutions. E FTIR spectra of the PLCL surface post-immersion. F, G High-resolution O1s XPS spectra of PLCL following immersion. Source data and exact P values are provided as a Source data file. One-way analysis of variance (ANOVA) with a Tukey/Games-Howell post hoc test for multiple comparisons. Sample size: n = 4 biologically independent replicates. *P < 0.05, PLCL vs. Deioinzed water group or PLCL vs. MgSO₄ solution group; ### P < 0.001, Deioinzed water vs. MgSO₄ solution group. Data are presented as mean values ± SD.

Fig. 6. In vitro neuroprotection analysis using the OGD/R cell model.

A Schematic of the cell OGD experiment. B Cell viability was assessed by CCK-8 assays. C Relative LDH concentration released from the neuron to the supernatant. D Typical images of intracellular Ca²⁺ observed by fluorescent microscopy; scale bars: 20 µm. E Quantification of relative fluorescence intensity of intracellular Ca²⁺. F Relative fluorescence intensity of ROS in neurons. G Changes in cell apoptosis detected by flow cytometry. H Quantification of apoptosis rate from (G). Source data and exact P values are provided as a Source data file. One-way analysis of variance (ANOVA) with a Tukey/Games-Howell post hoc test for multiple comparisons. Sample size: n = 5 biologically independent replicates. *P < 0.05, **P < 0.01, ***P < 0.001 vs. OGD/R group. NS, not significant. Data are presented as mean values ± SD.

Fig. 7. In vivo neuroprotection analysis of PLCLxMS in tMCAO rat models on the 7 days after ischemia/reperfusion injury.

A Schematic diagram of stent strut implantation process. B Brain slices stained with TTC to differentiate between healthy tissue (red) and damaged tissue (white). C Quantification of brain infarct volume from (B). D, E Brain slices with Nissl staining and quantification of Nissl bodies; scale bars: 1 mm and 25 µm. F Evaluation of brain water content ratio. G Representative Evans blue extravasation image illustrating blood-brain barrier disruption. H Quantification of cerebral Evans blue content. I Measurements of CBF before, during, and after surgery. J Comparison of relative CBF across groups. Source data and exact P values are provided as a Source data file. Two-way analysis of variance (ANOVA) with a Tukey/Games-Howell post hoc test for multiple comparisons. Sample size: n = 6 biologically independent replicates. *P < 0.05, **P < 0.01, ***P < 0.001, tMCAO+PLCL5MS or tMCAO+PLCL10MS vs. tMCAO group; # P < 0.05, ## P < 0.01, ### P < 0.001, c or tMCAO+PLCL10MS vs. tMCAO+PLCL group; §P < 0.05, §§ P < 0.01, §§§ P < 0.001, tMCAO+PLCL10MS vs. tMCAO+PLCL5MS. Data are presented as mean values ± SD.

Fig. 8. Behavioral evaluation of tMCAO rat models implanted with PLCLxMS wires after ischemia/reperfusion injury.

A Longa score assessment. B, C Results from the Rotarod test. D–F Adhesive contact and removal test performance before stroke and up to 14 days post-stroke. G Open field test conducted 7 days post-stroke. H Walking distance and time in the open field. I Magnesium concentration in the blood and ipsilateral infarction brain (IIB) of rats at 1 and 7 days post-implantation of PLCLxMS wires. Source data and exact P values are provided as a Source data file. Two-way analysis of variance (ANOVA) with a Tukey/Games-Howell post hoc test for multiple comparisons. Sample size: n = 12 for neurological tests, biologically independent replicates; n = 3 for magnesium content measurement tests, biologically independent replicates. **P < 0.01, ***P < 0.001, tMCAO+PLCL5MS or tMCAO+PLCL10MS vs. tMCAO group; # P < 0.05, ## P < 0.01, ### P < 0.001, tMCAO+PLCL5MS or tMCAO+PLCL10MS vs. tMCAO+PLCL group; § P < 0.05, §§ P < 0.01, §§§ P < 0.001, tMCAO+PLCL10MS vs. tMCAO+PLCL5MS. Data are presented as mean values ± SD.

Fig. 9. Illustration of the time-matched release of Mg²⁺ with the treatment windows for AIS.

Stage 1: The “Burst” stage of Mg²⁺ release corresponds to the hyperacute stage of AIS characterized by severe neural injury. The stent exhibits a substantial initial burst release of Mg²⁺, which provides high-dose neuroprotective effects by rapidly diffusing across the compromised BBB to target ischemic death neurons. Stage 2: The “Fast” stage of Mg²⁺ release corresponds to the acute stage of AIS characterized by cerebral edema formation. Mg²⁺ is released at a controlled yet therapeutically effective rate—reduced from the “Burst” stage but maintained at levels sufficient to support neural repair mechanisms including BBB and neuronal repair. The presence of Mg²⁺ attenuates secondary injury while facilitating progressive neuronal recovery. Stage 3: The “Stable” stage of Mg²⁺ release corresponds to the subacute stage of AIS characterized by active brain tissue remodeling. Mg²⁺ release kinetics transition to a slow, sustained profile, ultimately achieving dynamic equilibrium. BBB integrity is restored, and neuronal recovery advances. The radial force of the stent is significantly reduced.