Introduction

Acute myocardial infarction (AMI) is characterized by irreversible ischemic necrosis of cardiomyocytes, primarily due to the abrupt cessation of coronary blood flow following thrombotic occlusion of an atherosclerotic artery.1 This process is initiated by plaque rupture or erosion, leading to platelet aggregation and intraluminal thrombus formation.2 Resultant oxygen deprivation triggers anaerobic metabolism, ATP depletion, and ultimately, myocyte death. The extent of myocardial injury depends on the duration and severity of ischemia, with transmural infarction representing the most severe form.3 A substantial proportion of myocardial infarction (MI) cases present without typical anginal symptoms, a clinical phenomenon termed “silent” myocardial ischemia.4 Myocardial infarction arises from the interplay of modifiable (eg, hypertension, diabetes, smoking) and non-modifiable (eg, age, chronic kidney disease) risk factors that drive endothelial dysfunction, atherosclerotic plaque progression, and inflammation-induced thrombosis, ultimately leading to coronary occlusion.5,6

Myocardial infarction is diagnosed through electrocardiographic changes and elevated cardiac biomarkers, primarily troponin and CK-MB. ECG differentiates STEMI from NSTEMI, guiding acute management strategies such as antiplatelet therapy, vasodilators, and supplemental oxygen.7 STEMI requires prompt reperfusion via primary PCI or, if unavailable, thrombolysis. PCI provides mechanical revascularization; thrombolysis enables pharmacologic clot dissolution. Treatment choice depends on ischemia duration, clinical status, and facility access, with both aiming to restore perfusion and minimize infarct size.8

PCI is indicated in high-risk patients with significant coronary artery disease to restore blood flow and prevent infarction.9 In diabetic patients with multivessel disease, CABG is preferred over PCI for more complete and durable revascularization.10,11 Even though these techniques dramatically lower the patient death rate,12 problems such hemorrhage, ischemia reperfusion damage, and coronary restenosis13,14 might happen at any time. New therapies focusing on angiogenesis, inflammation, and fibrosis after myocardial infarction aim to preserve cardiac function and reduce progression to heart failure.15,16 Ischemic hypoxia triggers cardiomyocyte apoptosis within hours to days post-MI, initiating inflammatory cell infiltration and cytokine release. This response drives granulation tissue formation via extracellular matrix deposition and activates reparative as well as maladaptive remodeling.17

To provide historical context, early pioneering work by Hu et al. (2011) demonstrated erythrocyte membrane-coated polymeric nanoparticles with extended circulation times, laying the foundation for the field of biomimetic nanocarriers.18 Recent advances in nanomedicine have introduced non-biomimetic platforms, including liposomes, polymeric nanoparticles, and inorganic carriers for myocardial infarction therapy, primarily aimed at enhancing pharmacokinetics and site-specific drug accumulation. Despite these benefits, such systems often encounter rapid clearance, limited myocardial targeting, and off-target immune activation. In contrast, macrophage membrane-coated nanocarriers (MM-NCs) exhibit superior biological interface compatibility by leveraging surface proteins that facilitate immune evasion, inflammation-responsive homing, and prolonged systemic retention.19,20 Moreover, understanding the temporal progression of myocardial infarction is crucial to optimizing therapeutic interventions. Clinically, myocardial infarction progresses through distinct temporal phases: an acute phase (hours to days) characterized by ischemia-reperfusion injury and inflammation, and a chronic phase (weeks to months) dominated by fibrotic remodeling and ventricular dilation. MM-NCs offer phase-specific therapeutic integration acutely, as modulators of post-reperfusion inflammation, and chronically, to attenuate maladaptive remodeling and promote cardiac repair. These attributes position MM-NCs as promising candidates to complement existing MI management protocols across its clinical timeline.21,22

Pathological Characteristics of Myocardial Ischemia and Infarction

The pathological definition of myocardial infarction centers on cardiomyocyte death caused by prolonged ischemia. Figure 1 depicts a schematic representation of the roles of cardiomyocytes, fibroblasts, immune cells, and endothelial subtypes in the progression and remodeling of the failing heart. Myocardial ischemia triggers ultrastructural changes within 10–15 minutes, including sarcolemmal disruption and mitochondrial swelling, visible via electron microscopy. While animal models show biochemical evidence of cell death within minutes, human myocardial necrosis develops over hours, progressing from subendocardial to transmural regions. This timeline can be altered by ischemic preconditioning, reduced oxygen demand, or collateral circulation. Modern diagnostics detect these changes through sensitive biomarkers and advanced imaging, identifying even minimal injury.23

Figure 1 Cellular contributors to the pathophysiology of heart failure: Cardiomyocytes respond to pathological stimuli through maladaptive hypertrophy or undergo cell death via necrotic or apoptotic mechanisms, contributing to contractile dysfunction and loss of viable myocardium. Fibroblasts, upon activation, differentiate into myofibroblasts and drive cardiac fibrosis, a hallmark of structural remodeling. The immune compartment, including infiltrating leukocytes, modulates myocardial injury and repair by secreting inflammatory cytokines, clearing cellular debris, and influencing the process of regeneration. Endothelial cells also play essential roles: vascular endothelial cells modulate cardiac function through paracrine signaling to adjacent cells, whereas lymphatic endothelial cells facilitate cardiac repair post-infarction by maintaining interstitial fluid homeostasis, promoting immune cell clearance, and secreting regenerative mediators. Adapted from He X, Du T, Long T, Liao X, Dong Y, Huang ZP. Signaling cascades in the failing heart and emerging therapeutic strategies. Signal Transduct Target Ther. 2022 Apr 23;7(1):134. © The Author(s) 2022.24 under the terms and conditions of the Creative Commons Attribution (CC BY) license (https://creativecommons.org/licenses/by/4.0/).

Introduction to Macrophage Membrane-Coated Nanocarriers as an Innovative Solution

Traditional drug delivery systems face significant limitations, including systemic toxicity, nonspecific distribution, rapid clearance, poor bioavailability, and delayed therapeutic onset. To address these challenges in myocardial infarction treatment, targeted drug delivery to the ischemic myocardium has emerged as a critical therapeutic strategy. Recent advances highlight biomimetic nanoparticle platforms as a promising approach, offering enhanced precision, prolonged circulation, and improved therapeutic efficacy for cardiac repair.25 Biomimetic nanoparticles inherit special biofunctions from the original cells, including long circulation times, active targeting capabilities, and high biocompatibility, while retaining the beneficial physical characteristics of conventional nanoparticles. This is achieved by fusing bioactive cell components onto the surfaces of synthetic nanoparticles.18,26Figure 2 depicts cell membrane-coated nanoparticles combine customizable synthetic cores with biologically derived membrane coatings, enabling tailored functionalities for targeted biomedical applications. Red blood cell membrane-coated nanoparticles, for instance, have a half-life of up to 40 hours and can improve blood circulation. 10 Porous silicon nanoparticles coated with leukocyte membranes show effective accumulation at tumor locations and extended circulation durations.27 Nanoparticles enclosed in neutrophil membranes can alleviate inflammatory arthritis.28 Furthermore, injured blood arteries can be selectively adhered to by platelet membrane-coated nanoparticles.29

Figure 2 Cell membrane-coated nanoparticles combine customizable synthetic cores with biologically functionalized coatings, where core material selection depends on application needs while membrane wrappings (eg, from RBCs, WBCs, or stem cells) confer source cell-specific properties. This modular design enables tailored biomedical functionality, from targeted drug delivery to immune modulation. Adapted from Krishnan N, Fang RH, Zhang L. Cell membrane-coated nanoparticles for the treatment of cancer. Clin Transl Med. 2023 Jun;13(6):e1285. © 2023 The Authors. Clinical and Translational Medicine published by John Wiley & Sons Australia, Ltd on behalf of Shanghai Institute of Clinical Bioinformatics,30 under the terms and conditions of the Creative Commons Attribution (CC BY) license (https://creativecommons.org/licenses/by/4.0/).

Macrophages, as an immune cells, are the main mediators of inflammation and tissue repair.31Figure 3 represents schematic overview of macrophage crosstalk with neutrophils, eosinophils, basophils, and T cells regulating inflammatory resolution and reparative polarization post-MI. In different phases of myocardial infraction, macrophages have been involved.32,33 The infarcted myocardium exhibits rapid recruitment of inflammatory monocytes within 30 minutes post-MI, which subsequently differentiate into macrophages and localize predominantly within the ischemic core and margin zones.34 These macrophages have very vital role in promoting cardiac repair and for removing necrotic cellular debris.35,36 Adhesion molecules, such as PSGL-1 and LAF-1 facilitates the transfer of monocyte-derived macrophages.37 Macrophage membranes (MM) are potential candidates to target injured myocardium because these intrinsic surface proteins bind to vascular cell adhesion molecules-1 (ICAM-1, VCAM-1), which are substantially increased in damaged endothelial cells during MI27. Additionally, by helping polymer nanoparticles avoid immune clearance, this MM coating technique may improve their biocompatibility.

Figure 3 Immunoregulatory interactions between macrophages and immune cells in the infarcted myocardium. Neutrophil-derived extracellular DNA promotes macrophage polarization through activation of the toll-like receptor 9 (TLR9) pathway. Additionally, neutrophil secretion of neutrophil gelatinase-associated lipocalin (NGAL) enhances macrophage efferocytosis capacity by upregulating the Mer tyrosine kinase (MertK) receptor. In turn, macrophages limit excessive neutrophil infiltration by releasing matrix metalloproteinase-12 (MMP-12). Crosstalk with adaptive immune cells is also critical: regulatory T cells (Tregs) secrete interleukin-35 (IL-35), which triggers glycoprotein 130 (GP130)-dependent signaling via interleukin-12 receptor beta 2 (IL-12Rβ2) in macrophages, resulting in phosphorylation of signal transducer and activator of transcription 1 and 4 (STAT1 and STAT4), and subsequent upregulation of C-X3-C motif chemokine receptor 1 (CX3CR1) and transforming growth factor-beta 1 (TGF-β1). Furthermore, macrophage-derived interleukin-5 (IL-5) promotes eosinophil accumulation, which drives macrophage phenotypic switching through the interleukin-4/signal transducer and activator of transcription 6 (IL-4/STAT6) axis. Basophils also contribute to alternative macrophage activation by secreting interleukin-4 (IL-4) and interleukin-13 (IL-13). Collectively, these interactions orchestrate the balance between pro-inflammatory and reparative macrophage states during myocardial infarction healing. Adapted from Jian Y, Zhou X, Shan W et al. Crosstalk between macrophages and cardiac cells after myocardial infarction. Cell Commun Signal. 2023 May 11;21(1):109. © The Author(s) 2023,38 under the terms and conditions of the Creative Commons Attribution (CC BY) license (https://creativecommons.org/licenses/by/4.0/).

Certain receptors, such as CXCR4, CXCR2, interleukin (IL)-1R, and tumor necrosis factor (TNF)-R, are found in the membrane of macrophages. Consequently, nanoparticles coated with macrophage membranes exhibit biomimetic properties similar to those of macrophages found in nature.39,40 Macrophage membrane-coated VEGF sustained-release PLGA nanoparticles can migrate more specifically towards the inflammatory site when CXCR2 and CXCR4 receptors are present,39,40 and.41 This allows the particles to accumulate in the infarcted myocardium and guarantees that VEGF is continuously released in the infarcted area, which promotes neovascularization. The enhanced biosafety profile of biomimetic membrane-coated nanoparticles is one of their most convincing benefits over alternative VEGF delivery techniques to the infarcted myocardium.42 Conventional physical methods needed the modification of paramagnetic nanoparticles (Fe3O4) in order to concentrate them in the infarcted myocardium via magnetic targeting.43 There is a chance of further cardiac injury because this technique has been linked to myocardial iron overload.44 In contrast to immunoliposome-based delivery systems, biomimetic membrane-coated PLGA nanoparticles offer superior sustained-release capabilities while maintaining targeted delivery properties.45

According to reports, when macrophages are exposed to endotoxins like LPS, they begin secreting many cytokines, including interleukins and TNFα, within 4 to 5 hours.46 Based on findings it is suggested that the duration of lipopolysaccharide (LPS) induction was systematically varied to optimize membrane-bound tumor necrosis factor-alpha (TNFα) expression on macrophage surfaces. These modified membranes demonstrated time-dependent antiproliferative effects against HeLa, MCF-7, and MDA-MB-231 cancer cell lines, confirming preserved bioactivity. Subsequent mechanical extrusion of the LPS-activated macrophage membranes produced functional nanovesicles for targeted therapeutic applications.47

Role of Macrophages in Inflammation and Repair After MI

Infarct macrophages orchestrate debris clearance via phagocytosis (necrotic material/matrix fragments) and efferocytosis (apoptotic cells). This dual function resolves inflammation while promoting repair, with efferocytosis additionally suppressing pro-inflammatory cascade. In vivo studies demonstrate infarct macrophages actively phagocytose dying cardiomyocytes and neutrophils, confirming their essential role in debris clearance. Impaired phagocytic capacity disrupts inflammation resolution and tissue repair, directly linking macrophage function to cardiac recovery post-infarction.48–50

Infarct macrophages adopt reparative M2 phenotypes through efferocytosis-induced anti-inflammatory signaling, lymphocyte/neutrophil crosstalk via contact or soluble factors, and neutrophil-derived NGAL that enhances efferocytosis. This multilevel regulation ensures timely inflammation resolution and tissue repair.51 The recruitment of anti-inflammatory T cell subsets particularly regulatory T cells (Tregs), further promotes macrophage polarization toward a reparative phenotype through multiple mechanisms: paracrine IL-10 signaling and direct cell-contact-mediated interactions. These coordinated immunomodulatory actions enhance the transition to an M2-like macrophage state critical for cardiac repair.52 Cytokine activation in the infarct microenvironment triggers infarct macrophages to generate endogenous anti-inflammatory signals that block proinflammatory pathways. The activation of IL-1 receptor-associated kinase (IRAK)-M by infarct macrophages has been demonstrated to prevent inflammatory activity induced by TLRs and IL-1, protecting the infarcted heart from damaging remodeling.53 Transforming growth factor (TGF)-bs, IL-4, IL-10, and IL-13 are among the anti-inflammatory cytokines that are induced by the infarct and collectively prevent proinflammatory macrophage activation.54 Both increased de novo production55 and activation of latent reserves56 in the infarcted heart activate TGF-b signaling cascades, which may be crucial in mediating the anti-inflammatory effects of macrophages.57–59 It was discovered that TGF-b activates Smad3 signaling but not Smad2 signaling, which results in anti-inflammatory effects on infarct macrophages.60,61 The modulation of transcription factors belonging to the IRF family may be one way whereby secreted mediators affect the phenotypic and functional character of infarct macrophages.62

Monocyte/Macrophage Response After MI

During the acute phase of myocardial ischemia, neutrophils rapidly infiltrate the infarcted myocardium through a well-orchestrated adhesion cascade, achieving maximal accumulation within 24 hours post-occlusion. This recruitment is mechanistically governed by selectin-mediated rolling (L- and P-selectin), firm adhesion via intercellular adhesion molecule-1 (ICAM-1), and chemotactic gradient formation by interleukin-8 (CXCL8) and CXCL1, which collectively guide neutrophils from the vasculature into the ischemic tissue.63 The post-infarct cellular infiltrate is predominantly composed of monocytes and their macrophage derivatives. Extensive studies in both rodent and large animal models have characterized the temporal dynamics, persistence, and functional significance of these phagocytic populations in cardiac repair and remodeling processes.64,65 Studies demonstrate that monocytes and macrophages play pivotal roles in orchestrating infarct healing and regulating cellular recruitment during the initial 14-day post-MI period. Monocyte infiltration into the infarct zone depends critically on the MCP-1/CCR2 chemokine axis, as evidenced by impaired recruitment in germline CCR2/MCP-1 knockout models. Additionally, upregulated expression of adhesion molecules - particularly vascular cell adhesion molecule 1 (VCAM-1) on activated endothelium facilitates leukocyte extravasation into ischemic myocardium.64,66 VCAM-1-mediated monocyte recruitment via VLA-4 binding paradoxically worsens ischemia-reperfusion injury, as activated neutrophils and macrophages release cytotoxic ROS and proteases that injure viable cardiomyocytes. Preclinical evidence confirms that modulating this inflammatory response reduces infarct expansion (measured by infarct size/area-at-risk ratio), highlighting the therapeutic potential of targeted anti-inflammatory approaches in reperfusion injury.67,68

The clinical translatability of these approaches remains unestablished, with an unclear role for reparative monocytes in injury modulation. Non-reperfused MI models show dichotomous results monocyte/macrophage infiltration associates with both improved healing (via tissue remodeling) and worsened dysfunction (through inflammatory exacerbation).64,69–72 Effective infarct healing demands balanced monocyte/macrophage activity, merging inflammation and repair, particularly in unreperfused MI, where scar formation requires phagocyte-driven clearance. Excessive suppression or amplification of this response impairs remodeling, mirroring macrophages’ dual roles in skin wounds. Thus, therapeutic strategies must preserve this equilibrium to avoid disrupting the phased transition from debris removal to fibrosis:73–75 Proteases like matrix metalloproteinases,76–78 urokinase-type plasminogen activator, and cathepsins are released by the cells, which break down the preexisting collagen network and promote cell movement;76 phagocytose apoptotic and necrotic myocytes and neutrophils and other debris;79 release inflammatory mediators like inducible nitrous oxide synthase, reactive oxygen species, interferon, TNF-, IL-1, IL-6, and macrophage inflammatory protein 1;80 promote angiogenesis through the secretion of vascular endothelial growth factor and fibroblast growth factor;81 transport reparative enzymes and prosurvival factors like transglutaminases; stimulate collagen synthesis and deposition by myofibroblasts through the release of transforming growth factor and fibroblast growth factor.63,82

Nanofibers serve as versatile scaffolds in regenerative medicine, particularly for skin, bone, vascular, and nerve tissues, due to their highly porous and interconnected architecture. This unique structure facilitates efficient nutrient exchange, waste removal, and cellular communication while mimicking the natural extracellular matrix to guide tissue regeneration. Their adaptable composition and tunable physical properties allow customization for diverse therapeutic applications.83 Unlike solid Macrophage biology and its role in MI.

M1 (Pro-Inflammatory) vs M2 (Anti-Inflammatory) Macrophage

In order to promote an inflammatory response in the wounded tissues, macrophages or monocytes first polarize into a pro-inflammatory (M1) phenotype and then change into an anti-inflammatory (M2) phenotype for tissue regeneration.84,85 The uncontrolled inflammation caused by the M1 phenotype results in a severe foreign body reaction, where macrophages aggregate to form massive cells called foreign body granuloma with fibrous encapsulation.86,87 Biomaterials can guide post-infarct healing by modulating macrophage polarization through engineered physical (stiffness, topography) and biochemical (cytokine release, ECM mimicry) properties. These precisely designed matrices promote regenerative M2 phenotypes while suppressing damaging inflammation, shifting from passive scaffolds to active immunomodulatory platforms that orchestrate cardiac repair.88,89 Biomaterial design critically influences macrophage polarization through specific physical cues: implants with sharp edges, high stiffness, moderate roughness, and small-scale topography (nanofibers/micropores) promote pro-inflammatory M1 responses, while smooth surfaces, low stiffness, high roughness, and macro-scale architecture (large fibers/pores) favor anti-inflammatory M2 phenotypes. These structural parameters enable targeted immunomodulation to control foreign body reactions and tissue repair processes.90 While early approaches focused on immunosuppression, current evidence highlights that a controlled, transient inflammatory response is essential for effective myocardial regeneration. Given the critical role of M1-to-M2 transitions in post-MI healing, targeted delivery systems capable of modulating this shift while minimizing systemic toxicity are urgently needed this is where macrophage membrane-coated nanocarriers offer significant promise. However, recent evidence highlights that controlled early inflammation is indispensable for effective tissue regeneration, shifting the paradigm toward immunomodulatory biomaterial design rather than immunosuppression polycaprolactone (PCL) implants, nanofibrous PCL scaffolds demonstrate superior biocompatibility, as evidenced by host cell infiltration in murine subcutaneous models. This structural advantage promotes a more favorable tissue response through improved biomaterial-tissue integration.91 Electrospun nanofibers enable bioactive molecule delivery but their hydrophobicity limits cell adhesion, risking fibrosis. Surface modifications can enhance biocompatibility while preserving its function.92,93 Peptides, intercellular adhesion molecule-1, epidermal growth factors, antigen-mimetic GM3-lactone molecules, granulocyte colony-stimulating factors, and proteins (EphA5-Fc and ephrin A5-Fc) have all been functionalized into the nanofibers to improve cellular interactions.94–98 Additionally, immunoregulatory substances like mechano-growth factor (MGF) and interleukin-4 (IL-4) can be added to the exterior of electrospun nanofibers to encourage macrophages to transition to the M2 phenotype.99,100 To prevent protein denaturation during physical and chemical processes, nanofibrous scaffolds have been coated with synthetic lipid bilayers.101 According to a recent study, macrophages are promoted to the M2 phenotype by PCL scaffolds functionalized with mesenchymal stromal exosomes.102 PCL/nano-hydroxyapatite-incorporated chitin-derived hydrogels loaded with mesenchymal stem cells induce macrophages to adopt an M2 phenotype, which improves bone regeneration.103

The Role of M1 and M2 Macrophages in MI

Macrophage polarization critically regulates wound healing and tissue regeneration across physiological contexts.104 Despite incomplete understanding of polarization pathways, macrophage modulation represents a promising therapeutic strategy for diseases requiring tissue regeneration.105–107 MI represents a prime candidate for macrophage polarization therapy, as temporal control of M1-to-M2 transition could simultaneously resolve inflammation and promote myocardial regeneration.108 Cardiac macrophages exhibit transcriptional and functional heterogeneity beyond M1/M2 dichotomies, with infarcted hearts containing distinct subsets (eg, CCR2+ vs TIMD4+ macrophages) that differentially contribute to inflammation, clearance, and fibrosis.109

According to mouse models, cardiac resident macrophages make up 6–8% of non-cardiomyocytes and come from two different lineages: fetal monocytes in the postnatal phase and erythromyeloid progenitors in the yolk sac during early embryogenesis.33,110 The expression of CCR2 distinguishes these two groups of macrophages from one another. Therefore, macrophages generated from the yolk sac are CCR2-, while macrophages derived from monocytes are CCR2+.110 CCR2-macrophages are mainly found in the heart’s myocardium and are renewed by self-renewal, whereas CCR2+ macrophages are mainly concentrated in the endocardium and are restored by the recruitment of circulating monocytes.111,112 Based on the expression of MHC-II and Ly6C, CCR2-macrophages are further divided into three subsets: MHC-IIhigh, MHC-IIlow, and Ly6C+.113 Overall, resident cardiac macrophages can be divided into four subsets: CCR2-MHC-IIhigh, CCR2-MHC-IIlow, CCR2-Ly6C+, and CCR2+ macrophages, based on the surface markers described. However, a study conducted recently by Dick and associates has offered a rather different explanation of the local cardiac macrophage morphologies. The scientists used genetic fate mapping, long-term parabiosis studies, and single-cell RNA sequencing in mice to identify four subsets of macrophages in an adult heart: TIMD4+LYVE1+MHC-IIlowCCR2– macrophages, TIMD4−LYVE1–MHC-IIhighCCR2 macrophages, and two CCR2+MHC-IIhigh subsets. Blood monocytes are the only ones that can restore CCR2+MHC-IIhigh subsets, and circulating monocytes may partially replace TIMD4−LYVE1–MHC-IIhighCCR2− macrophages. It was shown that TIMD4+LYVE1+MHC-IIlowCCR2– macrophages are maintained by local proliferation distinct from circulating monocytes.36

Since animals with lower levels of macrophages exhibit poorer wound recovery, macrophages are most likely the primary source of growth factors needed for scar formation.114–120 By phagocytosing necrotic cells and releasing angiogenic and growth factors, macrophages in the post-MI LV primarily aid in wound repair. Macrophages travel in response to signals from the injured myocardium, including those from resident cells (myocytes) and acute inflammatory cells (neutrophils). The local production of adhesion molecules, chemo attractants, and other proteins attracts macrophages to the injury site and the surrounding border zone.121 In turn, activated macrophages generate a variety of cytokines, chemokines, and proteases, including MMPs.122,123

As master regulators of post-MI inflammation, macrophages dictate clinical outcomes through phased activities: early debris clearance (preventing secondary necrosis) and late matrix remodeling (preventing wall thinning). Therapeutic strategies now target their polarization dynamics rather than global suppression.124 Reperfusion accelerates and amplifies the inflammatory response in ischemic tissue, yet paradoxically enhances healing outcomes. Early clinical trials demonstrated that anti-inflammatory therapy with methylprednisolone increased mortality due to left ventricular rupture, underscoring the essential role of inflammation in post-ischemic repair.125Figure 4 represents key features and roles of M1 versus M2 macrophage polarization during myocardial infarction-related inflammation and tissue repair.

Figure 4 Functional roles and phenotypic transitions of macrophages in myocardial injury and repair. Following cardiomyocyte damage, peripheral monocytes are recruited to the injured myocardium, where they differentiate into pro-inflammatory M1 macrophages. These macrophages activate key signaling pathways, including the C-C motif chemokine ligand 2 (CCL2) and nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB) pathways, resulting in elevated secretion of tumor necrosis factor-alpha (TNF-α), interleukin-1 beta (IL-1β), and interleukin-6 (IL-6). This pro-inflammatory response exacerbates cardiomyocyte necrosis and hinders tissue repair. Over time, M1 macrophages undergo phenotypic switching to reparative M2 macrophages, a transition mediated in part by the cannabinoid receptor type 2 (CB2) signaling axis, which promotes resolution of inflammation and supports tissue remodeling. M2 macrophages suppress pro-inflammatory cytokines, facilitate tissue repair by promoting angiogenesis and fibroblast activation, and share functional characteristics with resident cardiac macrophages that support myocardial regeneration. Adapted from Chen G, Jiang H, Yao Y, Tao Z, Chen W, Huang F, Chen X. Macrophage, a potential targeted therapeutic immune cell for cardiomyopathy. Front Cell Dev Biol. 2022 Sep 30;10:908790. Copyright © 2022 Chen, Jiang, Yao, Tao, Chen, Huang and Chen.126 under the terms and conditions of the Creative Commons Attribution (CC BY) license (https://creativecommons.org/licenses/by/4.0/).

M-CSF administration post-MI enhances macrophage recruitment, improving functional recovery and accelerating infarct repair. Conversely, in cryoinjury models, clodronate liposome-mediated macrophage depletion impairs wound healing, underscoring their essential role in cardiac repair.71,127,128 Post-MI healing requires inflammatory chemotaxis: apoptotic neutrophils induce endothelial/monocytic adhesion molecule expression (ICAM-1, β2 integrins), enabling macrophage infiltration. These cells coordinate essential repair processes, underscoring inflammation’s dual role in injury and recovery.129 Activated macrophages secrete over 150 distinct proteins cytokines, chemokines, and growth factors, underscoring their central role in immune regulation and tissue remodeling.130 Among the proteins released are IL-1 α and β, IL-6, TNFα, and the macrophage inflammatory proteins 1α, 1β, 2α, and 2β 90.131 The release of growth factors and cytokines at the site of injury controls the fibroblast proliferation, angiogenesis, and inflammatory component.125

Enhancing Drug Delivery and Immune Evasion, Macrophage Membranes Coated with Nanocarriers

Macrophage membrane-coated nanomaterials inherit the biological functions of natural membranes, enhancing biocompatibility, immune evasion, and targeted delivery to inflammatory and malignant tissues. This biomimetic strategy has shown therapeutic potential across diverse pathologies, including cancer, infectious diseases, cardiovascular disorders, neurological conditions, and immune dysregulation. The preserved surface receptors such as integrins (eg, α4β1), MAC-1 (CD11b/CD18), and CSF1R enable nanoparticle homing to disease sites (eg, tumors, infected tissues) through innate recognition pathways.125

Atherosclerosis (AS) is a chronic inflammatory vasculopathy characterized by lipid-rich plaque accumulation within the arterial intima. This process is initiated when endothelial cells, stimulated by oxidized low-density lipoprotein (Ox-LDL), overexpress adhesion molecules (eg, VCAM-1, ICAM-1) and generate excessive reactive oxygen species (ROS), thereby recruiting immune cells (monocytes, T cells) that perpetuate vascular inflammation and plaque progression.132 Local inflammation contributes to arterial lumen narrowing and plaque destabilization, leading to stroke and other fatal cardiovascular events.133 Integrin α4 and β1, two crucial leukocyte receptors on the macrophage membrane, draw macrophages to atherosclerotic plaques by recognizing VCAM-1 on the surface of vascular endothelial cells.134,135 Fe3O4 is a typical magnetic resonance imaging (MRI) agent. It was discovered that Fe3O4 nanoparticles coated with a RAW264.7 membrane (Fe3O4@M) were successful in focusing on the first phases of AS.136 Fe3O4@Ms was more effective at imaging than Fe3O4@PEG and was safer for research items in vivo or in vitro when compared to the traditional MR agent. The molecular mechanism analysis demonstrated that macrophages’ upregulation of integrins α4 and β1 specifically identified VCAM-1 on endothelial cells. In order to target atherosclerotic lesions, Wang et al created a macrophage membrane coating on the surface of rapamycin-loaded PLGA (MM/RAPNPs).137

Fabrication of Macrophage Cell Membrane-Coated Systems

There are a few sequential procedures needed to fabricate MCM-coated NPs. This is accomplished by applying a nanovesicle formed from MCM to the previously constructed NP inner core. In order to create MCM-coated NPs, the preparation steps include 1) removing the outer membrane and isolating membrane vesicles, also known as “ghost cells”, 2) choosing and creating the NP core, and 3) fusing the MCM nanovesicles with the NP core via coextrusion, sonication, or electrostatic interaction.138,139 The source cells have been emptied and their intracellular contents extracted using a variety of delicate methods that cause cell lysis and disturb the cell structure.

These methods include the use of a Dounce homogenizer, sonication, extrusion, freeze-thaw cycles, and hypotonic lysis buffer. To preserve the cell membranes’ biofunctionality for fruitful biological interactions, these methods preserve the proteins that make up the surface membrane.138 To fabricate macrophage membrane-coated nanoparticles (MCM-NPs), the plasma membranes of isolated macrophages must be extracted. Unlike red blood cells, nucleated white blood cells require more complex protocols due to their intracellular components. Membrane isolation typically involves cell disruption methods such as hypotonic lysis and extrusion, followed by purification through differential centrifugation.140

Isolated membranes are physically extruded through polycarbonate membranes with defined pore sizes and then sonicated to form nanoscale vesicles that preserve the native proteolipid profile of MCMs. These vesicles are subsequently fused with nanoparticle (NP) cores pre-loaded with diagnostic or therapeutic payloads. A variety of core materials have been employed, including lipid-based NPs, gold NPs, Fe₃O₄ NPs, mesoporous silica NPs, upconversion NPs (UCNPs), and other inorganic platforms. Organic polymeric cores such as PLGA, albumin, and chitosan NPs have also been widely reported.141 In situ packaging of nanoparticles (NPs) via live-cell treatment enables the production of high-quality, membrane-wrapped NPs, preserving membrane integrity and surface protein functionality. For example, PLGA NPs loaded with rapamycin—an mTOR inhibitor—were encapsulated using macrophage-derived membranes to actively target atherosclerotic lesions. This dual-targeting strategy leverages macrophage surface α4β1 integrins and chemokine receptors, which bind VCAM-1 and inflammatory cytokines on activated endothelium, respectively. The resultant biomimetic NPs demonstrated effective in vivo accumulation in atherosclerotic plaques and reduced phagocytosis in vitro. Additionally, combining simvastatin with apolipoprotein A-I peptide (AP) enhanced foam cell cholesterol efflux and attenuated inflammatory cytokine expression, significantly reducing lesion formation. These findings underscore the therapeutic potential of macrophage membrane-coated nanoplatforms for targeted atherosclerosis diagnosis and treatment.142

Acute ischemic stroke, primarily caused by thrombotic occlusion of cerebral vessels, remains a leading cause of mortality globally. Therapeutic strategies aim to preserve neurons within the ischemic penumbra. A biomimetic nanosystem, Ma@(MnO2 + FTY), was developed by coating fingolimod-loaded manganese dioxide (MnO2) nanospheres with macrophage membranes to target inflamed brain regions. Leveraging macrophage-mediated inflammation-homing, the system exhibited enhanced biocompatibility, prolonged circulation, and selective accumulation in ischemic lesions. MnO2 scavenged excess ROS by converting H2O2 into O2, mitigating oxidative stress, while fingolimod promoted M1-to-M2 microglial polarization, shifting the proinflammatory microenvironment toward a neuroprotective state. This dual mechanism led to significant neuroprotection and lesion-targeting in vivo, positioning Ma@(MnO2 + FTY) as a promising synergistic therapy for acute ischemic stroke.143

Types of Core Nanocarriers

Lipid nanocarriers’ pharmacokinetics and biodistribution are dictated by their composition, size, surface charge, and steric stabilization. These factors influence plasma protein interactions, MPS clearance, and organ targeting. PEGylation reduces opsonization but does not prevent hepatic elimination. Administration routes alter systemic exposure: i.v. delivery leads to rapid organ distribution, while s.c. or i.m. routes may favor slower absorption and lymphatic transport. Additionally, lipid–drug affinity and membrane fluidity affect drug retention and release dynamics.144

The non-specific adsorption of charged nanoparticles onto phospholipid bilayers results in steric and electrostatic repulsions. These adsorbed nanoparticles work density-dependently to prevent liposomes from combining to form larger vesicles.145 Stabilizers promote lipid surface remodeling at nanoparticle adsorption sites, reducing interfacial tension and enhancing liposomal stability.146 This stabilization strategy, utilizing nanoparticles such as polystyrene, gold, and silica, facilitates the development of advanced liposome formulations with enhanced drug delivery performance.145 Stabilizing liposomes with nanoparticles allows precise modulation of surface charge and charge density, enabling stimuli-responsive attachment and detachment. This facilitates controlled liposome fusion and intelligent, on-demand cargo release. For instance, at neutral pH, carboxyl-modified gold nanoparticles adsorbed on liposomal surfaces inhibit membrane fusion. Lipid–polymer hybrid nanoparticles further enable systematic analysis of surface functionalities; studies have employed them to assess immunocompatibility of terminal groups such as methoxyl, carboxyl, and amine moieties.147

Polymeric nanoparticles offer tunable physicochemical and drug release properties through control of size, surface charge, hydrophobicity, and stimuli-responsive behavior. Surface functionalization with polymer end groups or conjugation with targeting ligands such as antibodies, peptides, or small molecules—enables tissue- or receptor-specific delivery. Their high surface-area-to-volume ratio enhances epithelial interaction and facilitates both receptor-mediated and nonspecific uptake. Polymeric NPs can encapsulate diverse therapeutics, including small molecules, biologics, and nucleic acids (eg, siRNA, DNA), and are often composed of biodegradable, FDA-approved materials suitable for clinical application.148

Lipid-Core Polymeric Micelles for Intracellular Drug Delivery

Endocytosis-mediated lysosomal degradation limits therapeutic micelle efficacy. Enhancing intracellular delivery can be achieved by targeting ligands (eg, mAb 2C5) and controlling micelle surface charge. Positively charged nanoparticles show increased cellular uptake via endocytosis, the primary mechanism for cationic lipid–DNA complexes. Lipofectin® (DOTMA/DOPE), a cationic lipid formulation, enhances intracellular drug and DNA delivery by promoting endosomal membrane disruption and endosomal escape. PEG-PE micelles carry a net negative charge, reducing cellular internalization. Incorporating cationic lipids into PEG-PE micelles neutralizes this charge, enhancing uptake and facilitating endosomal escape. Paclitaxel-loaded PEG-PE/LL (Lipofectin® lipids) micelles exhibited improved cytoplasmic distribution and higher in vitro cytotoxicity in BT-20 breast cancer and A2780 ovarian cancer cells, compared to PEG-PE micelles without cationic lipids or free paclitaxel. MTT assay results showed IC50 values for paclitaxel-loaded PEG-PE/LL micelles at 1.2 µM (A2780) and 6.4 µM (BT-20), significantly lower than free drug (22.5 µM and 24.3 µM, respectively) and non-cationic PEG-PE micelles (5.8 µM and 9.5 µM). This highlights the role of surface charge modulation and endosomal escape in enhancing micellar drug delivery and anticancer efficacy.149

Isolation and Coating of Macrophage Membranes Around the Nanocarriers

Macrophage-based delivery systems are emerging as targeted strategies for transporting therapeutics to tumor microenvironments and sites of inflammation, potentially enhancing efficacy while minimizing off-target effects. These approaches include: (1) drug delivery using live macrophages; (2) utilization of macrophage-derived extracellular vesicles (EVs) and EV-mimetic nanoparticles; (3) delivery via proteolipid nanovesicles isolated from macrophages; and (4) macrophage cell membrane (MCM)-coated nanoparticles.150,151 Macrophages’ intrinsic ability to infiltrate hypoxic tumor regions enables targeted delivery of tirapazamine-loaded PLGA nanoparticles to hypoxic zones in 4T1 breast cancer models, enhancing intratumoral drug accumulation and tumor growth inhibition in vivo. Various nanomaterials have been successfully encapsulated within live macrophages for biomedical applications. For example, macrophages loaded with MFe₃O₄-Cy5.5 photothermal nanoprobes demonstrate effective blood-brain barrier penetration and enable targeted photothermal ablation of gliomas.142

After manufacture, the membrane and inner core NPs must be joined to form a membrane-coated core and cell membrane biomimetic NPs. There are several methods for creating cell-membrane coated NPs. In situ packaging (by natural endocytosis and exocytosis), coextrusion (by mechanical force), extrusion/sonication and stir (by ultrasonic energy/endocytosis and exocytosis), extrusion/electroporation and extrusion/microfluidic electroporation (by electric pulse), and extrusion/sonication and freeze-thaw/sonication (by ultrasonic energy)152 are some of the suggested methods that have gained widespread recognition. Co-extrusion, sometimes referred to as co-injection, is the technique of using an extruder and an auxiliary system to continuously fill one material with another in order to create a single product out of two separate materials. However, some products are made using the so-called “true co-extrusion” process, which combines two extruders to extrude two products into one at the same time. The generated nanoparticles are mechanically extruded onto membranes in therapeutic settings. For several minutes before bath sonication, the “NP-membrane” mixture is repeatedly extruded through porous membranes of different diameters. For NPs to accomplish the vesicle-particle fusion, they must cross through a lipid bilayer. Following many extrusions, the precipitates are gathered and employed as final products, while the excess vesicles are centrifuged and disposed of.153

Co-extrusion methodology has been used to coat NPs with RBCs (eg, on PLGA, AuNP, Mesoporous silica, Cu2-xSe, upconversion NP, and nano pharmaceuticals), platelets (on magnetic NPs), cancer cells (on PLGA, gold NPs, and PGL), stem cells (on gelatin NPs), and immune cells (on liposome and PLGA). Recently, erythrocyte membrane-disguised anti-cancer drug delivery systems were created by co-extrusion coating red blood cell membrane-derived vesicles (RDVs) with poly (acrylic acid)-cysteine hydrochloride-D-α-tocopherol succinate (PAAssVES) nanoparticles (NPs). Polycarbonate membranes were used in this application to create homogenous, consistent, and co-extruded mixtures of RDVs and sorafenib (SFN)-PAAssVES NPs. In a different application, MDA-MB-231 breast cancer cell-derived CCM vesicles were used to coat and co-extrusion TOPSi 22 NPs. These NPs were subsequently ingested in polymeric particles of AcDEX or SpAcDEX.154 Synthetic liposomes are frequently prepared by coextrusion, in which the mechanical force exerted breaks down the membrane’s integrity and permits reconstruction around the NP core. Creating multi-layer and multifunctional structures, cutting down on the number of steps, and enabling tailored performance through the use of specific membranes are some advantages of co-extrusion technology. Through extrusion/sonication, NPs have been coated with RBCs (on PLGA and metal-organic framework), stem cells, platelets and platelet/RBCs (on PLGA), cancer cells (on liposome and mesoporous silica NPs), and immune cells (on PLGA). Ultrasonic energy induces the assembly of core nanoparticles and cell membranes into core–shell nanostructures, offering several advantages. This method preserves nanoparticle properties akin to physical extrusion while minimizing material loss. It also enables fusion of multiple cell membranes, integrating diverse functionalities. By combining membrane characteristics such as stability and charge asymmetry with nanoparticle structural integrity, this approach achieves right-side-out membrane orientation and favorable energetic configuration. Additional membrane-coating techniques include freeze-thaw/sonication (eg, platelet coating on PLGA), extrusion/sonication with stirring (platelet coating on nanogel and dextran), extrusion/electroporation (platelet coating on Au nanorods), and in situ packaging (RBC coating on perfluorocarbon-PLGA and cancer cell coating on PLGA).152

Surface Functionalization to Improve Targeting and Drug Release

The structure of the NP surface plays a critical role in determining the effectiveness of NPs both in vitro and in vivo because it affects how they interact with blood proteins, the immune system, and tumor tissue. Figure 5 is an Illustration of macrophage membrane-coated nanoparticles engineered for immune evasion and targeted delivery in inflammatory conditions such as myocardial infarction. Hydrophilic polymers, particularly polyethylene glycol (PEG, ~2–20 kDa), are the most commonly used surface coatings for nanoparticles (NPs). PEG forms a steric barrier that reduces plasma protein adsorption (opsonization) and delays immune clearance, thus prolonging NP circulation and enhancing tumor accumulation. Besides PEG, other hydrophilic polymers such as dextran, chitosan, hyaluronic acid (HA), polyvinyl pyrrolidone (PVP), polyvinyl alcohol (PVA), polyamino acids, and poloxamers have been employed as stealth coatings. An alternative stealth strategy involves coating NPs with biomimetic materials that mimic “self” components recognized by the immune system, thereby evading clearance. Examples include porphyrin-like lipoproteins (PLP), membrane proteins such as CD47, and intact red blood cell membranes. However, the “PEG dilemma” highlights a trade-off: while PEG improves NP circulation time, its presence can hinder NP interaction with target cells, reducing cellular uptake and therapeutic efficacy.155 To overcome the PEG dilemma, nanoparticles (NPs) are functionalized with cell- or receptor-specific ligands, enhancing targeted cellular interaction and uptake by tumor tissues. Ligand decoration also facilitates drug delivery to metastatic or poorly vascularized tumors where the enhanced permeability and retention (EPR) effect is insufficient. These ligands recognize specific markers on cancer cell surfaces or intracellular organelles, promoting receptor-mediated endocytosis. Enhanced cellular internalization improves therapeutic efficacy, particularly when drug targets are intracellular or when cancer cells exhibit drug efflux. Lipid-based nanocarriers have attracted significant interest due to their favorable properties, including low toxicity, improved bioavailability, biocompatibility, controlled drug release, high loading capacity, gastrointestinal stability, and scalability. Their excipients critically influence carrier characteristics and are vital for optimizing drug therapeutic outcomes. These systems effectively deliver hydrophilic, lipophilic, and amphiphilic drugs via various administration routes.156

Figure 5 Conceptual overview of engineered cell membrane-camouflaged nanomaterials. The illustration highlights the design principle of coating synthetic nanoparticle cores with natural cell membranes, such as those derived from macrophages, to enhance biocompatibility, prolong systemic circulation, and enable targeted delivery through membrane-bound recognition ligands. Adapted from Guan X, Xing S, Liu Y. Engineered Cell Membrane-Camouflaged Nanomaterials for Biomedical Applications. Nanomaterials (Basel). 2024 Feb 23;14(5):413. © 2024 by the authors.157 Licensee MDPI, Basel, Switzerland under the terms and conditions of the Creative Commons Attribution (CC BY) license (https://creativecommons.org/licenses/by/4.0/).

Modifying nanocarriers with cell membranes is an effective strategy due to their long circulation, biosafety, biocompatibility, and biodegradability. The adhesive properties of cell membranes enhance antibiotic localization and site-specific delivery. Moreover, membrane coatings mimic host–pathogen interactions, improving bacterial targeting and binding.158 Developing efficient nanocarriers requires overcoming complex biological barriers to maximize therapeutic efficacy. White blood cell-derived nanoparticles (WBC-NPs) offer unique advantages, including reduced phagocytic clearance via self-recognition, enhanced trans-endothelial transport, and targeted delivery to diseased sites through inherent cellular surface ligands. These properties have enabled WBC-NPs to be explored for drug delivery in bacterial infections, cancer, and inflammatory diseases, particularly by targeting inflammatory microenvironments.159

Mechanisms of Action in Myocardial Infarction Therapy

The targeting efficiency of macrophage membrane-coated DiD nanoparticles (MM/DiDNPs) to injured myocardium was assessed using a myocardial infarction (MI) mouse model. Mice received intravenous injections of DiDNPs or MM/DiDNPs one day post-MI. Fluorescence imaging at 6 hours post-injection showed that MM/DiDNPs accumulated in the infarcted myocardium with an average intensity 1.5-fold higher than DiDNPs alone. At 12 hours, fluorescence predominantly localized to the liver, spleen, lungs, and kidneys, indicating clearance via the reticuloendothelial system, consistent with previous reports highlighting macrophage-mediated nanoparticle phagocytosis in the liver and spleen.160,161 Macrophage membrane-coated nanoparticles (MM/DiDNPs) reduce off-target accumulation and associated toxicity by lowering nonspecific uptake in key organs. Fluorescence signals in the liver and spleen were significantly decreased for MM/DiDNPs compared to DiDNPs. Therapeutic efficacy of MM/RESNPs was evaluated in a myocardial infarction (MI) mouse model via tail vein injection of saline, RES, RESNPs, or MM/RESNPs. After 28 days, echocardiography revealed that MM/RESNPs significantly improved cardiac function, with left ventricular ejection fraction (EF%) and fractional shortening (FS%) increased by approximately 1.46- and 1.56-fold over the RES group (p < 0.05, p < 0.001). MM/RESNPs also showed superior improvements in EF%, and reductions in left ventricular internal diameter in systole (LVIDs) and end-systolic volume (ESV), indicating enhanced contractile function. Histological analyses using Masson’s trichrome and TTC staining confirmed reduced fibrosis and infarct size, underscoring the therapeutic advantage of macrophage membrane coating in cardiac repair.37

Prolonged Circulation: Immune Evasion via Macrophage-Derived Proteins (Eg, CD47)

Macrophage membranes express receptors such as CXCR4, CXCR2, IL-1R, and TNF-R, conferring biomimetic targeting capabilities to macrophage membrane-coated nanoparticles. VEGF-loaded PLGA nanoparticles coated with macrophage membranes exhibit enhanced homing to inflammatory sites via CXCR2 and CXCR4 interactions, enabling targeted accumulation and sustained VEGF release within infarcted myocardium to promote neovascularization. This biomimetic coating improves the biosafety profile compared to other VEGF delivery methods. MI involves complex inflammatory responses, with M1 macrophages dominating early post-infarct phases and exacerbating cardiomyocyte injury through pro-inflammatory cytokine release. Promoting polarization from M1 to reparative M2 macrophages during early MI stages is critical for improved cardiac repair and prognosis.42 Recent studies indicate that M1 macrophages primarily promote angiogenesis initiation, while M2 macrophages support vessel maturation and stabilization. Prolonged M1 macrophage activity leads to the degradation of existing vasculature, highlighting the importance of timely M1-to-M2 polarization following myocardial ischemia/reperfusion (MI/R) injury. The macrophage phenotypic switch is regulated by diverse signals, but further research is needed to determine the optimal timing for therapeutic interventions targeting this transition to maximize treatment efficacy.162

Targeted Drug Delivery: Homing to Inflamed MI Sites

Characteristics of Drug Delivery Systems For targeted delivery to areas of vascular injury and inflammation, a variety of DDS classes have been employed, including liposomes, polymeric nanopa