The study of respiratory diseases has long relied on simplified cell cultures and animal models, each with inherent limitations. Traditional two-dimensional (2D) cell monolayers fail to replicate the complex three-dimensional architecture and cell–cell interactions of the human lung, while animal models often diverge in key physiological responses. Over the past decade, advances in tissue engineering, biomaterials, and microfluidics have converged to produce sophisticated three-dimensional (3D) lung models that better mimic native tissue. Among these, vascularized lung models—engineered constructs that incorporate functional blood vessel networks—stand out as a transformative tool. By recapitulating the intimate relationship between lung epithelium and the surrounding microvasculature, these platforms enable researchers to study disease mechanisms, test drug candidates, and explore therapeutic targets with unprecedented fidelity. This article delves into the state-of-the-art techniques for building vascularized lung models, the major challenges that remain, and the profound impact these models are having on respiratory disease research.

The Critical Role of Vascularization in Lung Biology

The human lung is one of the most highly vascularized organs in the body. Its primary function—gas exchange—depends on a vast network of capillaries that wrap around alveoli, the tiny air sacs where oxygen and carbon dioxide are exchanged. This vascular bed is not merely a passive conduit; it actively participates in immune surveillance, fluid balance, and the pathophysiology of many lung diseases. For example, during an acute respiratory infection such as COVID-19, the virus first targets the epithelium but rapidly triggers endothelial dysfunction, leading to microvascular thrombosis and severe inflammation. Similarly, in pulmonary fibrosis, aberrant angiogenesis and vessel remodeling contribute to disease progression. Without a vascular component, conventional in vitro models cannot replicate these critical interactions, limiting their ability to predict human responses. Vascularized lung models aim to bridge this gap by providing a perfusable, living vasculature that supports epithelial tissues and enables the study of blood–air barrier function, immune cell trafficking, and drug transport.

Technological Approaches for Engineering Vascularized Lung Models

Several complementary engineering strategies have emerged to create functional vascular networks within lung tissue constructs. Each approach offers distinct advantages in terms of throughput, structural complexity, and physiological relevance.

3D Bioprinting

Bioprinting uses computer-controlled deposition of cell-laden hydrogels (bioinks) to build tissue constructs layer by layer. For vascularized lung models, researchers typically print a scaffold that includes both airway lumens and parallel or branching channels intended to become blood vessels. Bioinks are formulated with extracellular matrix (ECM) components such as collagen, fibrin, or gelatin methacrylate, and are often loaded with endothelial cells (e.g., human umbilical vein endothelial cells or lung microvascular endothelial cells) along with epithelial cells. A key advantage of bioprinting is the ability to achieve high spatial resolution and replicate the hierarchical branching of lung vasculature. Recent work has demonstrated bioprinted alveolar models with a perfusable, endothelial-lined network that sustains epithelial viability for weeks (Science, 2019). Challenges remain in achieving the fine capillary-scale diameters (5–10 µm) needed for physiological relevance, but advances in multi-material printing and sacrificial fiber techniques are steadily overcoming these limitations.

Microfluidic Devices (Lung-on-a-Chip)

Lung-on-a-chip technology couples microfluidic channels with a porous membrane lined by lung epithelial cells on one side and endothelial cells on the opposite side. This configuration creates a miniature blood–air barrier that can be mechanically stretched to simulate breathing motions. By flowing culture medium through the “vascular” channel, researchers can model shear stress, drug delivery, and immune cell adhesion. A seminal example is the human lung-on-a-chip developed by Huh et al., which recapitulated the lung microenvironment and was used to study pulmonary edema and nanoparticle toxicity (Nature Medicine, 2008). More recent iterations incorporate microvessel networks that self-assemble from endothelial cells within a hydrogel-filled chamber, allowing for true 3D vascularization. These microfluidic platforms are ideal for high-throughput drug screening and mechanistic studies because they require very few cells and offer precise control over biochemical and biomechanical cues.

Decellularized Lung Scaffolds

Whole-organ decellularization uses detergents to remove all cellular material from a donor lung (human or animal), leaving behind the ECM scaffold—a precisely structured framework composed of collagen, elastin, laminin, and other proteins. This scaffold retains the native lung architecture, including the vascular tree down to the alveolar level. Researchers then repopulate the scaffold with endothelial cells seeded through the vascular route and epithelial cells through the airway route. The resulting construct can be cultured under perfusion in a bioreactor, yielding a functional lung model with an intact vascular network. This approach has shown promise for studying tissue remodeling in fibrosis and for evaluating the effects of biomaterials on cell behavior (Biomaterials, 2012). However, challenges include achieving complete recellularization and maintaining long-term sterility, and donor availability remains limited.

Self-Assembling and Organoid Approaches

Recent progress in stem cell biology has enabled the generation of lung organoids—3D structures derived from pluripotent stem cells or adult stem cells that self-organize into airway and alveolar epithelium. When co-cultured with endothelial cells and supporting stromal cells in a hydrogel, these organoids can form rudimentary vascular networks. While the resulting vessels are not as orderly as those in bioprinted or decellularized constructs, they provide a valuable model for studying development, genetic disorders, and early-stage infections. Combining organoids with microfluidic perfusion can improve vascular maturation. The major advantage of organoid-based models is their patient-specific potential, enabling personalized medicine approaches for respiratory diseases (Stem Cell Reports, 2021).

Overcoming Key Challenges in Model Development

Despite remarkable progress, building a fully functional, long-lasting vascularized lung model remains a formidable engineering challenge. Several specific hurdles must be addressed before these models can be broadly adopted for drug development and clinical research.

Replicating Hierarchical Vasculature

The lung’s vascular tree is exquisitely organized: large arteries and veins branch down to capillaries that form a dense mesh around each alveolus. 3D bioprinting can reproduce coarse branching patterns but struggles with capillary-scale dimensions. Decellularized scaffolds preserve the native architecture but are limited by donor variability and the difficulty of fully recellularizing the capillary bed. Strategies such as sacrificial printing (using templating materials that dissolve to leave channels) and angiogenic sprouting (allowing endothelial cells to self-organize into capillary networks) are being combined to achieve multiscale vasculature. The use of pro-angiogenic growth factors (VEGF, angiopoietin-1) and matrix metalloproteinase-responsive hydrogels further promotes capillary formation.

Ensuring Long-Term Perfusion and Viability

For a vascularized model to be useful for chronic disease studies or repeated drug dosing, the vascular network must remain patent (open and functional) for weeks. Cell-lined channels can be blocked by thrombus formation or vessel regression in the absence of appropriate shear stress signals. Researchers address this by optimizing flow rates, adding anticoagulant factors (heparin, albumin), and using bioreactors that mimic the pulsatile nature of cardiac perfusion. Hypoxia is another concern—thick constructs suffer from oxygen gradients. Engineering oxygen-generating biomaterials or incorporating red blood cells into the perfusate can help maintain viability.

Integrating Airway and Vascular Compartments

The key functional unit of the lung is the alveolar–capillary interface, where air on one side meets blood on the other. Most models separate these two compartments with a porous membrane (in microfluidic chips) or by seeding airway and vascular cells on opposite sides of a thin scaffold. Achieving a thin (< 10 µm) barrier that permits gas diffusion while preventing fluid leakage is technically demanding. Designs that use electrospun nanofiber membranes or ultra-thin hydrogels show promise in mimicking the native basement membrane.

Incorporating Immune Cells and Disease States

Many respiratory diseases involve complex immune responses—macrophages, neutrophils, and T cells traffic through the vasculature and interact with the epithelium. Adding immune cells to a vascularized lung model introduces another layer of complexity because these cells require appropriate chemokine gradients and adhesion molecules. Researchers now routinely co-culture peripheral blood mononuclear cells or specific immune subtypes in the vascular channel. Additionally, to model diseases such as asthma, COPD, or cystic fibrosis, the epithelium can be derived from patient-specific induced pluripotent stem cells (iPSCs) carrying known mutations. These patient-derived vascularized models offer a unique platform for studying genetic susceptibility and testing personalized therapies.

Applications in Respiratory Disease Research

Vascularized lung models are already being deployed to study a range of respiratory conditions, often revealing mechanisms that would remain hidden in simpler systems.

COVID-19 and Viral Infections

The COVID-19 pandemic highlighted the need for human-relevant models to study viral tropism and pathogenesis. SARS-CoV-2 infects both epithelial and endothelial cells, and the resulting vascular damage is a major driver of disease severity. Lung-on-a-chip models have been used to recapitulate the infection process, showing that the virus damages endothelial barriers and promotes immune cell adhesion (Nature Biomedical Engineering, 2021). These platforms allow researchers to evaluate antiviral drugs and antibody therapies in a system that captures the critical endotheliopathy seen in patients, offering an advantage over standard epithelial-only cultures.

Idiopathic Pulmonary Fibrosis (IPF)

IPF is a progressive, fatal disease characterized by excessive scarring and alveolar destruction. Vascular remodeling in IPF is abnormal, with regions of capillary rarefaction and aberrant angiogenesis contributing to disease progression. Using decellularized lung scaffolds repopulated with IPF-derived cells, researchers have observed that diseased fibroblasts induce a pro-fibrotic microenvironment that can be attenuated by blocking specific signaling pathways. Vascularized model systems also enable the testing of anti-fibrotic drugs like pirfenidone and nintedanib in a more realistic tissue context, potentially reducing the high failure rate of preclinical compounds.

Lung Cancer

Lung tumors are highly dependent on the surrounding vasculature for nutrients and oxygen, as well as for metastatic dissemination. Vascularized lung models can be used to study tumor cell extravasation, the formation of pre-metastatic niches, and the efficacy of anti-angiogenic therapies. By incorporating patient-derived tumor cells into a vascularized construct, researchers can create a “tumor-on-a-chip” that recapitulates key features of the tumor microenvironment, such as hypoxia, interstitial fluid pressure, and immune cell infiltration. These models have been instrumental in understanding resistance to checkpoint inhibitors and identifying combination therapies that enhance treatment response.

Future Directions and Clinical Translation

As the field matures, several exciting avenues are opening up. The integration of organ-on-a-chip technology with machine learning could allow high-throughput screening of thousands of compounds against patient-specific vascularized lung models, accelerating drug discovery. Advances in bioprinting with in situ crosslinking may soon enable the fabrication of complete, perfusable lung lobes that could one day serve as transplantable grafts. Furthermore, combining vascularized lung models with other organ models (liver, heart, kidney) on a single microfluidic platform—the so-called “body-on-a-chip”—promises to capture systemic drug effects and toxicity more realistically.

Regulatory agencies such as the U.S. Food and Drug Administration (FDA) are increasingly acknowledging the value of microphysiological systems (MPS) as alternatives to animal testing. Recent legislation, including the FDA Modernization Act 2.0, encourages the use of MPS data for drug approval. This shift in regulatory attitude will likely drive investment and accelerate the translation of vascularized lung models from academic labs into commercial drug development pipelines.

Conclusion

Developing vascularized lung models is a quintessential example of how biomedical engineering can address fundamental challenges in disease research. By faithfully replicating the blood–air interface and the dynamic interplay between epithelial, endothelial, and immune cells, these models provide a powerful toolkit for studying respiratory diseases and evaluating therapeutics. While hurdles related to vascular architecture, long-term stability, and immune integration persist, the pace of innovation is rapid. As these models become more standardized, scalable, and accessible, they will not only deepen our understanding of lung biology but also reduce reliance on animal testing and bring safer, more effective treatments to patients faster.