Propidium iodide solution

At 72 h post-transfection, 1 × 10⁶ transfected cells were washed 2 times with cold BioLegend cell staining buffer (420201, BioLegend, San Diego, CA, USA) and resuspended in 100 µL of Annexin V Binding buffer (42220, BioLegend). The whole suspension was then treated with 5 µL of APC Annexin V (640920, BioLegend) and 10 µL of Propidium Iodide solution (421301, BioLegend) and incubated in the dark for 15 min. After that, 400 µL of Annexin V Binding buffer (42220, BioLegend) was added, and the apoptotic cells were measured by BD FACSCalibur™ Flow Cytometer (BD Biosciences, San Jose, CA, USA).
For cell cycle progression, 1 × 10⁶ transfected cells were washed 1 time with cold PBS. Then, 1 mL of cold 70% ethanol was added dropwise to the cell pellet and fixed at 4 °C for 30 min. After that, the fixed cells were collected and resuspended in 1 mL of PBS. The fixed cells were then treated with 50 µL of 100 µg/mL RNase A (Thermo Scientific, Boston, MA, USA), 425 µL of cell staining buffer (420201, BioLegend), and 25 µL of Propidium Iodide solution (421301, BioLegend). Finally, cell cycle profile analysis was measured by using BD FACSCalibur™ Flow Cytometer (BD Biosciences).

Two platforms were used to elucidate the transcriptional changes and cellular landscape of CMs and cardiac immune cells. The hearts collected from mice of different groups were subjected to Langendorff retrograde perfusion by sequential calcium-free solution and enzymatic digestion (0.03 g BSA and 0.03 g collagenase dissolved in 45 mL of Ca²⁺-free solution). The tissue was blown, filtered, and centrifuged (100× g for 3 min) to obtain a single-cell suspension of CMs. To obtain additional immune cells, five hearts from each group were cut in isotonic PBS (supplemented with 0.5% BSA) and digested with collagenase 4 (Worthington, Cat#: Ls004188) for 45 min at 37 °C. After filtering and red blood cell lysis, the cell suspension was labeled with 1 µL/100 uL CD45-BV421 antibody (BioLegend, Cat#: 103134) and propidium iodide solution (BioLegend, Cat#: 421301) and subjected to fluorescence-activated cell sorting to acquire PI^-CD45⁺ live immune cells. Peripheral immune cells were obtained at different time points by collecting blood from the angular veins of FM mice. The cells were labeled with 1 µL/100 µL of CD45-BV421 antibody (BioLegend, Cat#: 103134) and propidium iodide solution (BioLegend, Cat# 421301) and subjected to fluorescence-activated cell sorting after red blood cell lysis.

Sodium alginate and gelatin were purchased from Sigma–Aldrich (St. Louis, MO, USA). Dopamine hydrochloride (DA, 98%) and Tris(hydroxymethyl) aminomethane (extra pure, 99.5%) were obtained from J&K scientific Ltd. (Shanghai, China). Methacrylic acid copolymer type C (Eudragit L100-55, MAC) was from yingdemaofeng pharmaceuticals Co. Ltd. (Guangdong, China). Polycaprolactone (PCL), 1-Hydroxybenzotriazole (HOBT), and dimethylformamide (DMF) were purchased from Macklin Chemical Reagent Co. Ltd. (Shanghai, China). Doxorubicin hydrochloride (DOX·HCl), paclitaxel (PTX), and 1-Ethyl-3-(3-dimethlaminopropyl)-carbodiimide hydrochloride (EDCI) were obtained from Aladdin Chemical Reagent Co. Ltd. (Shanghai, China). Dulbecco’s modified Eagle medium (DMEM), penicillin, Trypsin-EDTA solution, and sterilized fetal bovine serum (FBS) were purchased from Solarbio (Beijing, China). Propidium iodide solution was purchased from BioLegend (San Diego, CA, USA). Mouse breast cancer (4T1) cells were obtained from Cyagen (Shanghai, China). Cell Counting kit-8 was obtained from ZomanBio (Beijing, China).