Production and assessment of decellularized pig and human lung scaffolds

Decellularized extracellular matrix biomaterials for regenerative therapies: Advances, challenges and clinical prospects

Tissue engineering and regenerative medicine have shown potential in the repair and regeneration of tissues and organs via the use of engineered biomaterials and scaffolds. However, current constructs face limitations in replicating the intricate native microenvironment and achieving optimal regenerative capacity and functional recovery. To address these challenges, the utilization of decellularized tissues and cell-derived extracellular matrix (ECM) has emerged as a promising approach. These biocompatible and bioactive biomaterials can be engineered into porous scaffolds and grafts that mimic the structural and compositional aspects of the native tissue or organ microenvironment, both in vitro and in vivo. Bioactive dECM materials provide a unique tissue-specific microenvironment that can regulate and guide cellular processes, thereby enhancing regenerative therapies. In this review, we explore the emerging frontiers of decellularized tissue-derived and cell-derived biomaterials and bio-inks in the field of tissue engineering and regenerative medicine. We discuss the need for further improvements in decellularization methods and techniques to retain structural, biological, and physicochemical characteristics of the dECM products in a way to mimic native tissues and organs. This article underscores the potential of dECM biomaterials to stimulate in situ tissue repair through chemotactic effects for the development of growth factor and cell-free tissue engineering strategies. The article also identifies the challenges and opportunities in developing sterilization and preservation methods applicable for decellularized biomaterials and grafts and their translation into clinical products.

Lung viral infection modelling in a bioengineered whole-organ

Lung infections are one of the leading causes of death worldwide, and this situation has been exacerbated by the emergence of COVID-19. Pre-clinical modelling of viral infections has relied on cell cultures that lack 3D structure and the context of lung extracellular matrices. Here, we propose a bioreactor-based, whole-organ lung model of viral infection. The bioreactor takes advantage of an automated system to achieve efficient decellularization of a whole rat lung, and recellularization of the scaffold using primary human bronchial cells. Automatization allowed for the dynamic culture of airway epithelial cells in a breathing-mimicking setup that led to an even distribution of lung epithelial cells throughout the distal regions. In the sealed bioreactor system, we demonstrate proof-of-concept for viral infection within the epithelialized lung by infecting primary human airway epithelial cells and subsequently injecting neutrophils. Moreover, to assess the possibility of drug screening in this model, we demonstrate the efficacy of the broad-spectrum antiviral remdesivir. This whole-organ scale lung infection model represents a step towards modelling viral infection of human cells in a 3D context, providing a powerful tool to investigate the mechanisms of the early stages of pathogenic infections and the development of effective treatment strategies for respiratory diseases.

In vitro strategies for mimicking dynamic cell-ECM reciprocity in 3D culture models

The extracellular microenvironment regulates cell decisions through the accurate presentation at the cell surface of a complex array of biochemical and biophysical signals that are mediated by the structure and composition of the extracellular matrix (ECM). On the one hand, the cells actively remodel the ECM, which on the other hand affects cell functions. This cell-ECM dynamic reciprocity is central in regulating and controlling morphogenetic and histogenetic processes. Misregulation within the extracellular space can cause aberrant bidirectional interactions between cells and ECM, resulting in dysfunctional tissues and pathological states. Therefore, tissue engineering approaches, aiming at reproducing organs and tissues in vitro, should realistically recapitulate the native cell-microenvironment crosstalk that is central for the correct functionality of tissue-engineered constructs. In this review, we will describe the most updated bioengineering approaches to recapitulate the native cell microenvironment and reproduce functional tissues and organs in vitro. We have highlighted the limitations of the use of exogenous scaffolds in recapitulating the regulatory/instructive and signal repository role of the native cell microenvironment. By contrast, strategies to reproduce human tissues and organs by inducing cells to synthetize their own ECM acting as a provisional scaffold to control and guide further tissue development and maturation hold the potential to allow the engineering of fully functional histologically competent three-dimensional (3D) tissues.

A decellularized lung extracellular matrix/chondroitin sulfate/gelatin/chitosan-based 3D culture system shapes breast cancer lung metastasis

Distal metastasis of breast cancer is a primary cause of death, and the lung is a common metastatic target of breast cancer. However, the role of the lung niche in promoting breast cancer progression is not well understood. Engineered three-dimensional (3D) in vitro models capable of bridging this knowledge gap can be specifically designed to mimic crucial characteristics of the lung niche in a more physiologically relevant context than conventional two-dimensional systems. In this study, two 3D culture systems were developed to mimic the late stage of breast cancer progression at a lung metastatic site. These 3D models were created based on a novel decellularized lung extracellular matrix/chondroitin sulfate/gelatin/chitosan composite material and on a porcine decellularized lung matrix (PDLM), with the former tailored with comparable properties (stiffness, pore size, biochemical composition, and microstructure) to that of the in vivo lung matrix. The different microstructure and stiffness of the two types of scaffolds yielded diverse presentations of MCF-7 cells in terms of cell distribution, cell morphology, and migration. Cells showed better extensions with apparent pseudopods and more homogeneous and reduced migration activity on the composite scaffold compared to those on the PDLM scaffold. Furthermore, alveolar-like structures with superior porous connectivity in the composite scaffold remarkably promoted aggressive cell proliferation and viability. In conclusion, a novel lung matrix-mimetic 3D in vitro breast cancer lung metastasis model was developed to clarify the underlying correlativity between lung ECM and breast cancer cells after lung colonization. A better understanding of the effects of biochemical and biophysical environments of the lung matrix on cell behaviors can help elucidate the potential mechanisms of breast cancer progression and further improve target discovery of therapeutic strategies.

Decellularized Extracellular Matrix for Remodeling Bioengineering Organoid's Microenvironment

Over the past decade, stem cell- and tumor-derived organoids are the most promising models in developmental biology and disease modeling, respectively. The matrix is one of three main elements in the construction of an organoid and the most important module of its extracellular microenvironment. However, the source of the currently available commercial matrix, Matrigel, limits the application of organoids in clinical medicine. It is worth investigating whether the original decellularized extracellular matrix (dECM) can be exploited as the matrix of organoids and improving organoid construction are very important. In this review, tissue decellularization protocols and the characteristics of decellularization methods, the mechanical support and biological cues of extraccellular matrix (ECM), methods for construction of multifunctional dECM and responsive dECM hydrogel, and the potential applications of functional dECM are summarized. In addition, some expectations are provided for dECM as the matrix of organoids in clinical applications.

Human lung cell models to study aerosol delivery - considerations for model design and development

Human lung tissue models range from simple monolayer cultures to more advanced three-dimensional co-cultures. Each model system can address the interactions of different types of aerosols and the choice of the model and the mode of aerosol exposure depends on the relevant scenario, such as adverse outcomes and endpoints of interest. This review focuses on the functional, as well as structural, aspects of lung tissue from the upper airway to the distal alveolar compartments as this information is relevant for the design of a model as well as how the aerosol properties determine the interfacial properties with the respiratory wall. The most important aspects on how to design lung models are summarized with a focus on (i) choice of appropriate scaffold, (ii) selection of cell types for healthy and diseased lung models, (iii) use of culture condition and assembly, (iv) aerosol exposure methods, and (v) endpoints and verification process. Finally, remaining challenges and future directions in this field are discussed.

Lung Tissue Engineering: Toward a More Deliberate Approach

Chronic lung disease remains a leading cause of morbidity and mortality. Given the dearth of definitive therapeutic options, there is an urgent need to augment the pool of donor organs for transplantation. One strategy entails building a lung ex vivo in the laboratory. The past decade of whole lung tissue engineering has laid a foundation of systems and strategies for this approach. Meanwhile, tremendous progress in lung stem cell biology is elucidating cues contributing to alveolar repair, and speaks to the potential of whole lung regeneration in the future. This perspective discusses the key challenges facing the field and highlights opportunities to combine insights from biology with engineering strategies to adopt a more deliberate, and ultimately successful, approach to lung engineering.

Bioengineering lungs: An overview of current methods, requirements, and challenges for constructing scaffolds

Chronic respiratory diseases remain a significant health burden worldwide. The only option for individuals with end-stage lung failure remains Lung Transplantation. However, suitable organ donor shortages and immune rejection following transplantation remain a challenge. Since alternative options are urgently required to increase tissue availability for lung transplantation, researchers have been exploring lung bioengineering extensively, to generate functional, transplantable organs and tissue. Additionally, the development of physiologically-relevant artificial tissue models for testing novel therapies also represents an important step toward finding a definite clinical solution for different chronic respiratory diseases. This mini-review aims to highlight some of the most common methodologies used in bioengineering lung scaffolds, as well as the benefits and disadvantages associated with each method in conjunction with the current areas of research devoted to solving some of these challenges in the area of lung bioengineering.

Regenerative medicine: postnatal approaches

Paper 2 of the paediatric regenerative medicine Series focuses on recent advances in postnatal approaches. New gene, cell, and niche-based technologies and their combinations allow structural and functional reconstitution and simulation of complex postnatal cell, tissue, and organ hierarchies. Organoid and tissue engineering advances provide human disease models and novel treatments for both rare paediatric diseases and common diseases affecting all ages, such as COVID-19. Preclinical studies for gastrointestinal disorders are directed towards oesophageal replacement, short bowel syndrome, enteric neuropathy, biliary atresia, and chronic end-stage liver failure. For respiratory diseases, beside the first human tracheal replacement, more complex tissue engineering represents a promising solution to generate transplantable lungs. Genitourinary tissue replacement and expansion usually involve application of biocompatible scaffolds seeded with patient-derived cells. Gene and cell therapy approaches seem appropriate for rare paediatric diseases of the musculoskeletal system such as spinal muscular dystrophy, whereas congenital diseases of complex organs, such as the heart, continue to challenge new frontiers of regenerative medicine.

Extracellular Matrix Stiffness in Lung Health and Disease

The extracellular matrix (ECM) provides structural support and imparts a wide variety of environmental cues to cells. In the past decade, a growing body of work revealed that the mechanical properties of the ECM, commonly known as matrix stiffness, regulate the fundamental cellular processes of the lung. There is growing appreciation that mechanical interplays between cells and associated ECM are essential to maintain lung homeostasis. Dysregulation of ECM-derived mechanical signaling via altered mechanosensing and mechanotransduction pathways is associated with many common lung diseases. Matrix stiffening is a hallmark of lung fibrosis. The stiffened ECM is not merely a sequelae of lung fibrosis but can actively drive the progression of fibrotic lung disease. In this article, we provide a comprehensive view on the role of matrix stiffness in lung health and disease. We begin by summarizing the effects of matrix stiffness on the function and behavior of various lung cell types and on regulation of biomolecule activity and key physiological processes, including host immune response and cellular metabolism. We discuss the potential mechanisms by which cells probe matrix stiffness and convert mechanical signals to regulate gene expression. We highlight the factors that govern matrix stiffness and outline the role of matrix stiffness in lung development and the pathogenesis of pulmonary fibrosis, pulmonary hypertension, asthma, chronic obstructive pulmonary disease (COPD), and lung cancer. We envision targeting of deleterious matrix mechanical cues for treatment of fibrotic lung disease. Advances in technologies for matrix stiffness measurements and design of stiffness-tunable matrix substrates are also explored. © 2022 American Physiological Society. Compr Physiol 12:3523-3558, 2022.

Emerging Paradigms in Bioengineering the Lungs

In end-stage lung diseases, the shortage of donor lungs for transplantation and long waiting lists are the main culprits in the significantly increasing number of patient deaths. New strategies to curb this issue are being developed with the help of recent advancements in bioengineering technology, with the generation of lung scaffolds as a steppingstone. There are various types of lung scaffolds, namely, acellular scaffolds that are developed via decellularization and recellularization techniques, artificial scaffolds that are synthesized using synthetic, biodegradable, and low immunogenic materials, and hybrid scaffolds which combine the advantageous properties of materials in the development of a desirable lung scaffold. There have also been advances in the design of bioreactors in terms of providing an optimal regenerative environment for the maturation of functional lung tissue over time. In this review, the emerging paradigms in the field of lung tissue bioengineering will be discussed.

Natural Scaffolds Used for Liver Regeneration: A Narrative Update

Annually chronic liver diseases cause two million death worldwide. Although liver transplantation (LT) is still considered the best therapeutic option, the limited number of donated livers and lifelong side effects of LT has led researchers to seek alternative therapies. Tissue engineering (TE) as a promising method is considered for liver repair and regeneration. TE uses natural or synthetic scaffolds, functional somatic cells, multipotent stem cells, and growth factors to develop new organs. Biological scaffolds are notable in TE because of their capacity to mimic extracellular matrices, biodegradability, and biocompatibility. Moreover, natural scaffolds are classified based on their source and function in three separate groups. Hemostat-based scaffolds as the first group were reviewed for their application in coagulation in liver injury or surgery. Furthermore, recent studies showed improvement in the function of biological hydrogels in liver regeneration and vascularity. In addition, different applications of natural scaffolds were discussed and compared with synthetic scaffolds. Finally, we focused on the efforts to improve the performance of decellularized extracellular matrixes for liver implantation.

Decellularized Tissues for Wound Healing: Towards Closing the Gap Between Scaffold Design and Effective Extracellular Matrix Remodeling

The absence or damage of a tissue is the main cause of most acute or chronic diseases and are one of the appealing challenges that novel therapeutic alternatives have, in order to recover lost functions through tissue regeneration. Chronic cutaneous lesions are the most frequent cause of wounds, being a massive area of regenerative medicine and tissue engineering to have efforts to develop new bioactive medical products that not only allow an appropriate and rapid healing, but also avoid severe complications such as bacterial infections. In tissue repair and regeneration processes, there are several overlapping stages that involve the synergy of cells, the extracellular matrix (ECM) and biomolecules, which coordinate processes of ECM remodeling as well as cell proliferation and differentiation. Although these three components play a crucial role in the wound healing process, the ECM has the function of acting as a biological platform to permit the correct interaction between them. In particular, ECM is a mixture of crosslinked proteins that contain bioactive domains that cells recognize in order to promote migration, proliferation and differentiation. Currently, tissue engineering has employed several synthetic polymers to design bioactive scaffolds to mimic the native ECM, by combining biopolymers with growth factors including collagen and fibrinogen. Among these, decellularized tissues have been proposed as an alternative for reconstructing cutaneous lesions since they maintain the complex protein conformation, providing the required functional domains for cell differentiation. In this review, we present an in-depth discussion of different natural matrixes recently employed for designing novel therapeutic alternatives for treating cutaneous injuries, and overview some future perspectives in this area.

Advanced In Vitro Lung Models for Drug and Toxicity Screening: The Promising Role of Induced Pluripotent Stem Cells

The substantial socioeconomic burden of lung diseases, recently highlighted by the disastrous impact of the coronavirus disease 2019 (COVID-19) pandemic, accentuates the need for interventive treatments capable of decelerating disease progression, limiting organ damage, and contributing to a functional tissue recovery. However, this is hampered by the lack of accurate human lung research models, which currently fail to reproduce the human pulmonary architecture and biochemical environment. Induced pluripotent stem cells (iPSCs) and organ-on-chip (OOC) technologies possess suitable characteristics for the generation of physiologically relevant in vitro lung models, allowing for developmental studies, disease modeling, and toxicological screening. Importantly, these platforms represent potential alternatives for animal testing, according to the 3Rs (replace, reduce, refine) principle, and hold promise for the identification and approval of new chemicals under the European REACH (registration, evaluation, authorization and restriction of chemicals) framework. As such, this review aims to summarize recent progress made in human iPSC- and OOC-based in vitro lung models. A general overview of the present applications of in vitro lung models is presented, followed by a summary of currently used protocols to generate different lung cell types from iPSCs. Lastly, recently developed iPSC-based lung models are discussed.

Microvascular fluid flow in ex vivo and engineered lungs

In recent years, it has become common to experiment with ex vivo perfused lungs for organ transplantation and to attempt regenerative pulmonary engineering using decellularized lung matrices. However, our understanding of the physiology of ex vivo organ perfusion is imperfect; it is not currently well understood how decreasing microvascular barrier affects the perfusion of pulmonary parenchyma. In addition, protocols for lung perfusion and organ culture fluid-handling are far from standardized, with widespread variation on both basic methods and on ideally controlled parameters. To address both of these deficits, a robust, noninvasive, and mechanistic model is needed which is able to predict microvascular resistance and permeability in perfused lungs while providing insight into capillary recruitment. Although validated mathematical models exist for fluid flow in native pulmonary tissue, previous models generally assume minimal intravascular leak from artery to vein and do not assess capillary bed recruitment. Such models are difficult to apply to both ex vivo lung perfusions, in which edema can develop over time and microvessels can become blocked, and to decellularized ex vivo organomimetic cultures, in which microvascular recruitment is variable and arterially perfused fluid enters into the alveolar space. Here, we develop a mathematical model of pulmonary microvascular fluid flow which is applicable in both instances, and we apply our model to data from native, decellularized, and regenerating lungs under ex vivo perfusion. The results provide substantial insight into microvascular pressure-flow mechanics, while producing previously unknown output values for tissue-specific capillary-alveolar hydraulic conductivity, microvascular recruitment, and total organ barrier resistance.NEW & NOTEWORTHY We present a validated model of pulmonary microvascular fluid mechanics and apply this model to study the effects of increased capillary permeability in decellularized and regenerating lungs. We find that decellularization alters microvascular steady-state mechanics and that re-endothelialization partially rescues key biologic parameters. The described model provides powerful insight into intraorgan microvascular dynamics and may be used to guide regenerative engineering experiments. We include all data and derivations necessary to replicate this work.

Development of a Cell-Based Biosensor for Residual Detergent Detection in Decellularized Scaffolds

Ex vivo engineering of organs that uses decellularized whole organs as a scaffold with autologous stem cells is a potential alternative to traditional transplantation. However, one of the main challenges in this approach is preparing cytocompatible scaffolds. So far, high-precision and specific evaluation methods have not been developed for this purpose. Cell-based biosensors (CBBs) are promising tools to measure analytes with high sensitivity and specificity in a cost-effective and noninvasive manner. In this paper, using the NF-κB inducible promoter we developed a CBB for residual detergent detection. Proximal and core sections of the inducible promoter, containing NF-κB binding sequence, are designed and cloned upstream of the reporter gene (secreted alkaline phosphatase (SEAP)). After transfection into HEK293 cells, stable and reliable clones were selected. After confirmation of induction of this gene construct by sodium dodecyl sulfate (SDS), the stability and function of cells treated by qPCR and SEAP activity were measured. This biosensor was also used to evaluate the cytocompatibility of decellularized tissue. Results showed that the developed biosensor could detect very small amounts of SDS detergent (3.467 pM). It has the best performance 8 h after exposure to detergent, and its stability in high passage numbers was not significantly reduced. Applying this biosensor on decellularized tissues showed that SEAP activity higher than 4.36 (U/L) would lead to a viability reduction of transplanted cells below 70%. This paper presents a novel method to evaluate the cytocompatibility of decellularized tissues. The developed CBB can detect residual detergents (such as SDS) in tissues with high sensitivity and efficiency.

Fetal Lung Tissue Engineering

Lung transplantation may be considered as a final treatment option for diseases such as chronic lung disease, pulmonary hypertension, bronchopulmonary dysplasia, pulmonary fibrosis, and end-stage lung disease. The five-year survival rate of lung transplants is nearly 50%. Unfortunately, many patients will die before a suitable lung donor can be found. Importantly, the shortage of donor organs has been a significant problem in lung transplantation. The tissue engineering approach uses de- and recellularization of lung tissue to create functional lung substitutes to overcome donor lung limitations. Decellularization is hope for generating an intact ECM in the development of the engineered lung. The goal of decellularization is to prepare a suitable scaffold of lung tissue that contains an appropriate framework for the functionality of regenerated lung tissue. In this chapter, we aim to describe the decellularization protocols for lung tissue regenerative purposes.

Advanced human-relevant in vitro pulmonary platforms for respiratory therapeutics

Over the past years, advanced in vitro pulmonary platforms have witnessed exciting developments that are pushing beyond traditional preclinical cell culture methods. Here, we discuss ongoing efforts in bridging the gap between in vivo and in vitro interfaces and identify some of the bioengineering challenges that lie ahead in delivering new generations of human-relevant in vitro pulmonary platforms. Notably, in vitro strategies using foremost lung-on-chips and biocompatible "soft" membranes have focused on platforms that emphasize phenotypical endpoints recapitulating key physiological and cellular functions. We review some of the most recent in vitro studies underlining seminal therapeutic screens and translational applications and open our discussion to promising avenues of pulmonary therapeutic exploration focusing on liposomes. Undeniably, there still remains a recognized trade-off between the physiological and biological complexity of these in vitro lung models and their ability to deliver assays with throughput capabilities. The upcoming years are thus anticipated to see further developments in broadening the applicability of such in vitro systems and accelerating therapeutic exploration for drug discovery and translational medicine in treating respiratory disorders.

Decellularized human-sized pulmonary scaffolds for lung tissue engineering: a comprehensive review

The ultimate goal of lung bioengineering is to produce transplantable lungs for human beings. Therefore, large-scale studies are of high importance. In this paper, we review the investigations on decellularization and recellularization of human-sized lung scaffolds. First, studies that introduce new ways to enhance the decellularization of large-scale lungs are reviewed, followed by the investigations on the xenogeneic sources of lung scaffolds. Then, decellularization and recellularization of diseased lung scaffolds are discussed to assess their usefulness for tissue engineering applications. Next, the use of stem cells in recellularizing acellular lung scaffolds is reviewed, followed by the case studies on the transplantation of bioengineered lungs. Finally, the remaining challenges are discussed, and future directions are highlighted.

Platforms to test the temporospatial capabilities of carrier systems in delivering growth factors to benefit vascular bioengineering

In this study we produced a set of in vitro culture platforms to model vascular cell responses to growth factors and factor delivery vehicles. Two of the systems (whole vessel and whole lung vascular development) were supported by microfluidic systems facilitating media circulation and waste removal. We assessed vascular endothelial growth factor (VEGF) delivery by Pluronic F-127 hydrogel, 30 nm pore-sized microparticles (MPs), 60 nm pore-sized MP or a 50/50 mixture of 30 and 60 nm pore-sized MP. VEGF was delivered to porcine acellular lung vascular scaffolds (2.5 cm² square pieces or whole 3D segments of acellular blood vessels) as well as whole acellular lung scaffolds. Scaffold-cell attachment was examined as was vascular tissue formation. We showed that a 50/50 mixture of 30 and 60 nm pore-sized silicon wafer MPs allowed for long-term release of VEGF within the scaffold vasculature and supported vascular endothelial tissue development during in vitro culture.

Recent Advancements in Engineered Biomaterials for the Regeneration of Female Reproductive Organs

Various gynecologic diseases and chemoradiation or surgery for the management of gynecologic malignancies may damage the uterus and ovaries, leading to clinical problems such as infertility or early menopause. Embryo or oocyte cryopreservation-the standard method for fertility preservation-is not a feasible option for patients who require urgent treatment because the procedure requires ovarian stimulation for at least several days. Hormone replacement therapy (HRT) for patients diagnosed with premature menopause is contraindicated for patients with estrogen-dependent tumors or a history of thrombosis. Furthermore, these methods cannot restore the function of the uterus and ovaries. Although autologous transplantation of cryopreserved ovarian tissue is being attempted, it may re-introduce malignant cells after cancer treatment. With the recent development in regenerative medicine, research on engineered biomaterials for the restoration of female reproductive organs is being actively conducted. The use of engineered biomaterials is a promising option in the field of reproductive medicine because it can overcome the limitations of current therapies. Here, we review the ideal properties of biomaterials for reproductive tissue engineering and the recent advancements in engineered biomaterials for the regeneration of female reproductive organs.

Advances in bioreactors for lung bioengineering: From scalable cell culture to tissue growth monitoring

Lung bioengineering has emerged to resolve the current lung transplantation limitations and risks, including the shortage of donor organs and the high rejection rate of transplanted lungs. One of the most critical elements of lung bioengineering is bioreactors. Bioreactors with different applications have been developed in the last decade for lung bioengineering approaches, aiming to produce functional reproducible tissue constructs. Here, the current status and advances made in the development and application of bioreactors for bioengineering lungs are comprehensively reviewed. First, bioreactor design criteria are explained, followed by a discussion on using bioreactors as a culture system for scalable expansion and proliferation of lung cells, such as producing epithelial cells from induced pluripotent stem cells (iPSCs). Next, bioreactor systems facilitating and improving decellularization and recellularization of lung tissues are discussed, highlighting the studies that developed bioreactors for producing engineered human-sized lungs. Then, monitoring bioreactors are reviewed, showing their ability to evaluate and optimize the culture conditions for maturing engineered lung tissues, followed by an explanation on the ability of ex vivo lung perfusion systems for reconditioning the lungs before transplantation. After that, lung cancer studies simplified by bioreactors are discussed, showing the potentials of bioreactors in lung disease modeling. Finally, other platforms with the potential of facilitating lung bioengineering are described, including the in vivo bioreactors and lung-on-a-chip models. In the end, concluding remarks and future directions are put forward to accelerate lung bioengineering using bioreactors.

Decellularization of porcine whole lung to obtain a clinical-scale bioengineered scaffold

Whole-organ engineering is emerging as an alternative source for xenotransplantation in end-stage diseases. Utilization of decellularized whole lung scaffolds created by detergent perfusion is an effective strategy for organ replacement. In the current study, we attempted to decellularize porcine whole lungs to generate an optimal and reproducible decellularized matrix for future clinical use. Porcine whole lungs were decellularized via perfusion of various detergents (sodium dodecyl sulfate (SDS)/Triton X-100, sodium lauryl ether sulfate (SLES)/Triton X-100, dextrose/SDS/Triton X-100 and dextrose/SLES/Triton X-100) through the pulmonary artery and bronchus of the lung. The decellularized scaffolds were evaluated for decellularization efficiency, extracellular matrix (ECM) component preservation, xenoantigen removal and compatibility. The resulting lung scaffolds obtained from treatment with the dextrose/SLES/Triton X-100 cocktail showed minimal residual cellular components and xenoantigens, including DNA and protein, and good preservation of ECM composition. Evaluation of the porcine lung ECM by specific staining and immunofluorescence confirmed that the three-dimensional ultrastructure of the ECM was noticeably preserved in the SLES-treated groups. In addition, the decellularized lung scaffolds originating from the dextrose/SLES/Triton X-100 cocktail supported cell adhesion and growth. In summary, the novel detergent SLES alleviated the damage to retain a better-preserved ECM than SDS. Sequential Triton X-100 perfusion eliminated SLES. Moreover, performing dextrose perfusion in advance further protected scaffold components, especially collagen. We developed an optimal dextrose/SLES/Triton X-100 cocktail method that can be used for the decellularization of porcine whole lung to obtain a clinical-scale bioengineered scaffold.

From Submerged Cultures to 3D Cell Culture Models: Evolution of Nasal Epithelial Cells in Asthma Research and Virus Infection

Understanding the response to viral infection in the context of respiratory diseases is of significant importance. Recently, there has been more focus on the role of the nasal epithelium in disease modeling. Here, we provide an overview of different submerged, organotypic 3D and spheroid cell culture models of nasal epithelial cells, which were used to study asthma and allergy with a special focus on virus infection. In detail, this review summarizes the importance, benefits, and disadvantages of patient-derived cell culture models of nasal- and bronchial epithelial cells, including a comparison of these cell culture models and a discussion on why investigators should consider using nasal epithelial cells in their research. Exposure experiments, simple virus transduction analyses as well as genetic studies can be performed in these models, which may provide first insights into the complexity of molecular signatures and may open new doors for drug discovery and biomarker research.

Post-decellularization techniques ameliorate cartilage decellularization process for tissue engineering applications

Due to the current lack of innovative and effective therapeutic approaches, tissue engineering (TE) has attracted much attention during the last decades providing new hopes for the treatment of several degenerative disorders. Tissue engineering is a complex procedure, which includes processes of decellularization and recellularization of biological tissues or functionalization of artificial scaffolds by active cells. In this review, we have first discussed those conventional steps, which have led to great advancements during the last several years. Moreover, we have paid special attention to the new methods of post-decellularization that can significantly ameliorate the efficiency of decellularized cartilage extracellular matrix (ECM) for the treatment of osteoarthritis (OA). We propose a series of post-decellularization procedures to overcome the current shortcomings such as low mechanical strength and poor bioactivity to improve decellularized ECM scaffold towards much more efficient and higher integration.

3D printing in the battle against COVID-19

Coronavirus disease 2019 (COVID-19) that is SARS-CoV-2, previously called 2019-nCoV, is a kind of human infectious disease caused by severe acute respiratory syndrome coronavirus. Based on the prompt increase of human infection rate, COVID-19 outbreak was distinguished as a pandemic by the World Health Organization (WHO). By 2020, COVID-19 becomes a major health problem all around the world. Due to the battle against COVID-19, there are some adversities that are encountered with. The most significant difficulty is the lack of equipment for the COVID-19 battle. Lately, there is not sufficient personal protective equipment (PPE) for hospital workers on the front lines in this terrifying time. All around the world, hospitals are overwhelmed by the volume of patients and the lack of personal protective equipment including face masks, gloves, eye protection and clothing. In addition, the lack of nasal swabs, which are necessary components, that are used for testing is another issue that is being faced. There are a small number of respirators, which are emergency devices that help patients breathe for a short period of time. To overcome the limited number of equipment available, the foremost solution can be 3D printing that allows three-dimensional renderings to be realized as physical objects with the use of a printer and that revolutionized prototyping. Low-cost desktop 3D printers allow economical 3D models and guides but have less quality approvals. 3D printing is already well integrated into the process of COVID-19 battle by manufacturing the equipment that are convenient. The goals of this review are to explore the techniques of 3D printing for the equipment that are used for COVID-19 battle and evaluate the materials that are used for manufacturing and the manufactured equipment. Lastly, the advantages and disadvantages of 3D printing are figured out.

An Early Stage Researcher's Primer on Systems Medicine Terminology

Background: Systems Medicine is a novel approach to medicine, that is, an interdisciplinary field that considers the human body as a system, composed of multiple parts and of complex relationships at multiple levels, and further integrated into an environment. Exploring Systems Medicine implies understanding and combining concepts coming from diametral different fields, including medicine, biology, statistics, modeling and simulation, and data science. Such heterogeneity leads to semantic issues, which may slow down implementation and fruitful interaction between these highly diverse fields. Methods: In this review, we collect and explain more than100 terms related to Systems Medicine. These include both modeling and data science terms and basic systems medicine terms, along with some synthetic definitions, examples of applications, and lists of relevant references. Results: This glossary aims at being a first aid kit for the Systems Medicine researcher facing an unfamiliar term, where he/she can get a first understanding of them, and, more importantly, examples and references for digging into the topic.

Current Advances in 3D Tissue and Organ Reconstruction

Bi-dimensional culture systems have represented the most used method to study cell biology outside the body for over a century. Although they convey useful information, such systems may lose tissue-specific architecture, biomechanical effectors, and biochemical cues deriving from the native extracellular matrix, with significant alterations in several cellular functions and processes. Notably, the introduction of three-dimensional (3D) platforms that are able to re-create in vitro the structures of the native tissue, have overcome some of these issues, since they better mimic the in vivo milieu and reduce the gap between the cell culture ambient and the tissue environment. 3D culture systems are currently used in a broad range of studies, from cancer and stem cell biology, to drug testing and discovery. Here, we describe the mechanisms used by cells to perceive and respond to biomechanical cues and the main signaling pathways involved. We provide an overall perspective of the most recent 3D technologies. Given the breadth of the subject, we concentrate on the use of hydrogels, bioreactors, 3D printing and bioprinting, nanofiber-based scaffolds, and preparation of a decellularized bio-matrix. In addition, we report the possibility to combine the use of 3D cultures with functionalized nanoparticles to obtain highly predictive in vitro models for use in the nanomedicine field.

Enhanced In Vivo Vascularization of 3D-Printed Cell Encapsulation Device Using Platelet-Rich Plasma and Mesenchymal Stem Cells

The current standard for cell encapsulation platforms is enveloping cells in semipermeable membranes that physically isolate transplanted cells from the host while allowing for oxygen and nutrient diffusion. However, long-term viability and function of encapsulated cells are compromised by insufficient oxygen and nutrient supply to the graft. To address this need, a strategy to achieve enhanced vascularization of a 3D-printed, polymeric cell encapsulation platform using platelet-rich plasma (PRP) and mesenchymal stem cells (MSCs) is investigated. The study is conducted in rats and, for clinical translation relevance, in nonhuman primates (NHP). Devices filled with PRP, MSCs, or vehicle hydrogel are subcutaneously implanted in rats and NHP and the amount and maturity of penetrating blood vessels assessed via histopathological analysis. In rats, MSCs drive the strongest angiogenic response at early time points, with the highest vessel density and endothelial nitric oxide synthase (eNOS) expression. In NHP, PRP and MSCs result in similar vessel densities but incorporation of PRP ensues higher levels of eNOS expression. Overall, enrichment with PRP and MSCs yields extensive, mature vascularization of subcutaneous cell encapsulation devices. It is postulated that the individual properties of PRP and MSCs can be leveraged in a synergistic approach for maximal vascularization of cell encapsulation platforms.

Translating Basic Research into Safe and Effective Cell-based Treatments for Respiratory Diseases

Respiratory diseases, such as chronic obstructive pulmonary disease and pulmonary fibrosis, result in severely impaired quality of life and impose significant burdens on healthcare systems worldwide. Current disease management involves pharmacologic interventions, oxygen administration, reduction of infections, and lung transplantation in advanced disease stages. An increasing understanding of mechanisms of respiratory epithelial and pulmonary vascular endothelial maintenance and repair and the underlying stem/progenitor cell populations, including but not limited to airway basal cells and type II alveolar epithelial cells, has opened the possibility of cell replacement-based regenerative approaches for treatment of lung diseases. Further potential for personalized therapies, including in vitro drug screening, has been underscored by the recent derivation of various lung epithelial, endothelial, and immune cell types from human induced pluripotent stem cells. In parallel, immunomodulatory treatments using allogeneic or autologous mesenchymal stromal cells have shown a good safety profile in clinical investigations for acute inflammatory conditions, such as acute respiratory distress syndrome and septic shock. However, as yet, no cell-based therapy has been shown to be both safe and effective for any lung disease. Despite the investigational status of cell-based interventions for lung diseases, businesses that market unproven, unlicensed and potentially harmful cell-based interventions for respiratory diseases have proliferated in the United States and worldwide. The current status of various cell-based regenerative approaches for lung disease as well as the effect of the regulatory environment on clinical translation of such approaches are presented and critically discussed in this review.

Bioengineering the Blood-gas Barrier

The pulmonary blood-gas barrier represents a remarkable feat of engineering. It achieves the exquisite thinness needed for gas exchange by diffusion, the strength to withstand the stresses and strains of repetitive and changing ventilation, and the ability to actively maintain itself under varied demands. Understanding the design principles of this barrier is essential to understanding a variety of lung diseases, and to successfully regenerating or artificially recapitulating the barrier ex vivo. Many classical studies helped to elucidate the unique structure and morphology of the mammalian blood-gas barrier, and ongoing investigations have helped to refine these descriptions and to understand the biological aspects of blood-gas barrier function and regulation. This article reviews the key features of the blood-gas barrier that enable achievement of the necessary design criteria and describes the mechanical environment to which the barrier is exposed. It then focuses on the biological and mechanical components of the barrier that preserve integrity during homeostasis, but which may be compromised in certain pathophysiological states, leading to disease. Finally, this article summarizes recent key advances in efforts to engineer the blood-gas barrier ex vivo, using the platforms of lung-on-a-chip and tissue-engineered whole lungs. © 2020 American Physiological Society. Compr Physiol 10:415-452, 2020.

Limitations of recellularized biological scaffolds for human transplantation

A shortage of donor organs for transplantation and the dependence of the recipients on immunosuppressive therapy have motivated researchers to consider alternative regenerative approaches. The answer may reside in acellular scaffolds generated from cadaveric human and animal tissues. Acellular scaffolds are expected to preserve the architectural and mechanical properties of the original organ, permitting cell attachment, growth, and differentiation. Although theoretically, the use of acellular scaffolds for transplantation should pose no threat to the recipient's immune system, experimental data have revealed significant immune responses to allogeneic and xenogeneic transplanted scaffolds. Herein, we review the various factors of the scaffold that could trigger an inflammatory and/or immune response, thereby compromising its use for human transplant therapy. In addition, we provide an overview of the major cell types that have been considered for recellularization of the scaffold and their potential contribution to triggering an immune response.

Using GRGDSPC peptides to improve re-endothelialization of decellularized pancreatic scaffolds

Engineering of functional vascularized pancreatic tissues offers an alternative way to solve the perpetual shortage of organs for transplantation. However, revascularization remains a major bottleneck in biological engineering, which limited the further clinical applications of this strategy. In this study, an efficient approach for enhancing re-endothelialization of rat decellularized pancreatic scaffolds (DPS) was presented, by conjugating with GRGDSPC peptide to maximize coverage of the vessel walls with human umbilical vein endothelial cells (HUVECs). First, pancreas was perfused with 1% Triton X-100 and 0.1% ammonium hydroxide to remove the cellular components. Subsequently, GRGDSPC was covalently coupled to the vasculature of DPS and re-seeded with HUVECs via perfusion of the portal vein in the bioreactor. After the re-endothelialized scaffolds were created, in vitro and in vivo experiments were undertaken to evaluate the angiogenesis. Our results demonstrated that GRGDSPC-conjugated scaffolds could support the survival and accelerated the proliferation of HUVECs; angiogenesis was also significantly improved over untreated scaffolds. In conclusion, GRGDSPC-conjugated scaffolds showed great potential for the generation of functional bioengineered pancreatic tissue suitable for long-term transplantation.

Method to decellularize the human chorion membrane

The human placenta is considered a biological waste, thus it is a great source of extracellular matrix (ECM) proteins. The human chorion membrane (HCM) is a membrane that composes the human placenta and is constituted by collagens type I, II, IV, V and VI, fibronectin and laminin. To the best of our knowledge, the potential of HCM alone is largely unexplored as a substrate to be used in tissue engineering and regenerative medicine. In this work, we describe, for the first time, the process and method to decellularize the chorion membrane alone. To verify the success of the decellularization protocol, the presence and distribution of cell nuclei and double-stranded DNA were quantified and analyzed by DAPI staining, PicoGreen and electrophoresis. After the decellularization protocol an ECM compact and handleably membrane is obtained, the decellularized human chorion membrane (dHCM).

High-Performance Acellular Tissue Scaffold Combined with Hydrogel Polymers for Regenerative Medicine

Decellularization of tissues provides extracellular matrix (ECM) scaffolds for regeneration therapy and an experimental model to understand ECM and cellular interactions. However, decellularization often causes microstructure disintegration and reduction of physical strength, which greatly limits the use of this technique in soft organs or in applications that require maintenance of physical strength. Here, we present a new tissue decellularization procedure, namely CASPER (Clinically and Experimentally Applicable Acellular Tissue Scaffold Production for Tissue Engineering and Regenerative Medicine), which includes infusion and hydrogel polymerization steps prior to robust chemical decellularization treatments. Polymerized hydrogels serve to prevent excessive damage to the ECM while maintaining the sophisticated structures and biological activities of ECM components in various organs, including soft tissues such as brains and embryos. CASPERized tissues were successfully recellularized to stimulate a tissue-regeneration-like process after implantation without signs of pathological inflammation or fibrosis in vivo, suggesting that CASPERized tissues can be used for monitoring cell-ECM interactions and for surrogate organ transplantation.

Lung tissue bioengineering for chronic obstructive pulmonary disease: overcoming the need for lung transplantation from human donors

Introduction: Chronic obstructive pulmonary disease (COPD) affects more than 380 million people, causing more than 3 million deaths annually worldwide. Despite this enormous burden, currently available therapies are largely limited to symptom control. Lung transplant is considered for end-stage disease but is severely limited by the availability of human organs. Furthermore, the pre-transplant course is a complex orchestration of locating and harvesting suitable lungs, and the post-transplant course is complicated by rejection and infection. Lung tissue bioengineering has the potential to relieve the organ shortage and improve the post-transplant course by generating patient-specific lungs for transplant. Additionally, emerging progenitor cell therapies may facilitate in vivo regeneration of pulmonary tissue, obviating the need for transplant. Areas Covered: We review several lung tissue bioengineering approaches including the recellularization of decellularized scaffolds, 3D bioprinting, genetically-engineered xenotransplantation, blastocyst complementation, and direct therapy with progenitor cells. Articles were identified by searching relevant terms (see Key Words) in the PubMed database and selected for inclusion based on novelty and uniqueness of their approach. Expert Opinion: Lung tissue bioengineering research is in the early stages. Of the methods reviewed, only direct cell therapy has been investigated in humans. We anticipate a minimum of 5-10 years before human therapy will be feasible.

Decellularization and recellularization of cornea: Progress towards a donor alternative

The global shortage of donor corneas for transplantation has led to corneal bioengineering being investigated as a method to generate transplantable tissues. Decellularized corneas are among the most promising materials for engineering corneal tissue since they replicate the complex structure and composition of real corneas. Decellularization is a process that aims to remove cells from organs or tissues resulting in a cell-free scaffold consisting of the tissues extracellular matrix. Here different decellularization techniques are described, including physical, chemical and biological methods. Analytical techniques to confirm decellularization efficiency are also discussed. Different cell sources for the recellularization of the three layers of the cornea, recellularization methods used in the literature and techniques used to assess the outcome of the implantation of such scaffolds are examined. Studies involving the application of decellularized corneas in animal models and human clinical studies are discussed. Finally, challenges for this technology are explored involving scalability, automatization and regulatory affairs.

Tissue-Engineered Grafts from Human Decellularized Extracellular Matrices: A Systematic Review and Future Perspectives

Tissue engineering and regenerative medicine involve many different artificial and biologic materials, frequently integrated in composite scaffolds, which can be repopulated with various cell types. One of the most promising scaffolds is decellularized allogeneic extracellular matrix (ECM) then recellularized by autologous or stem cells, in order to develop fully personalized clinical approaches. Decellularization protocols have to efficiently remove immunogenic cellular materials, maintaining the nonimmunogenic ECM, which is endowed with specific inductive/differentiating actions due to its architecture and bioactive factors. In the present paper, we review the available literature about the development of grafts from decellularized human tissues/organs. Human tissues may be obtained not only from surgery but also from cadavers, suggesting possible development of Human Tissue BioBanks from body donation programs. Many human tissues/organs have been decellularized for tissue engineering purposes, such as cartilage, bone, skeletal muscle, tendons, adipose tissue, heart, vessels, lung, dental pulp, intestine, liver, pancreas, kidney, gonads, uterus, childbirth products, cornea, and peripheral nerves. In vitro recellularizations have been reported with various cell types and procedures (seeding, injection, and perfusion). Conversely, studies about in vivo behaviour are poorly represented. Actually, the future challenge will be the development of human grafts to be implanted fully restored in all their structural/functional aspects.

Equine lung decellularization: a potential approach for in vitro modeling the role of the extracellular matrix in asthma

Contrary to conventional research animals, horses naturally develop asthma, a disease in which the extracellular matrix of the lung plays a significant role. Hence, the horse lung extracellular matrix appears to be an ideal candidate model for in vitro studying the mechanisms and potential treatments for asthma. However, so far, such model to study cell–extracellular matrix interactions in asthma has not been developed. The aim of this study was to establish a protocol for equine lung decellularization that maintains the architecture of the extracellular matrix and could be used in the future as an in vitro model for therapeutic treatment in asthma. For this the equine lungs were decellularized by sodium dodecyl sulfate detergent perfusion at constant gravitational pressure of 30 cmH₂O. Lung scaffolds were assessed by immunohistochemistry (collagen I, III, IV, laminin, and fibronectin), scanning electron microscopy, and DNA quantification. Their mechanical property was assessed by measuring lung compliance using the super-syringe technique. The optimized protocol of lung equine decellularization was effective to remove cells (19.8 ng/mg) and to preserve collagen I, III, IV, laminin, and fibronectin. Moreover, scanning electron microscopy analysis demonstrated maintained microscopic lung structures. The decellularized lungs presented lower compliance compared to native lung. In conclusion we described a reproducible decellularization protocol that can produce an acellular equine lung feasible for the future development of novel treatment strategies in asthma.

Cross-platform mechanical characterization of lung tissue

Published data on the mechanical strength and elasticity of lung tissue is widely variable, primarily due to differences in how testing was conducted across individual studies. This makes it extremely difficult to find a benchmark modulus of lung tissue when designing synthetic extracellular matrices (ECMs). To address this issue, we tested tissues from various areas of the lung using multiple characterization techniques, including micro-indentation, small amplitude oscillatory shear (SAOS), uniaxial tension, and cavitation rheology. We report the sample preparation required and data obtainable across these unique but complimentary methods to quantify the modulus of lung tissue. We highlight cavitation rheology as a new method, which can measure the modulus of intact tissue with precise spatial control, and reports a modulus on the length scale of typical tissue heterogeneities. Shear rheology, uniaxial, and indentation testing require heavy sample manipulation and destruction; however, cavitation rheology can be performed in situ across nearly all areas of the lung with minimal preparation. The Young's modulus of bulk lung tissue using micro-indentation (1.4±0.4 kPa), SAOS (3.3±0.5 kPa), uniaxial testing (3.4±0.4 kPa), and cavitation rheology (6.1±1.6 kPa) were within the same order of magnitude, with higher values consistently reported from cavitation, likely due to our ability to keep the tissue intact. Although cavitation rheology does not capture the non-linear strains revealed by uniaxial testing and SAOS, it provides an opportunity to measure mechanical characteristics of lung tissue on a microscale level on intact tissues. Overall, our study demonstrates that each technique has independent benefits, and each technique revealed unique mechanical features of lung tissue that can contribute to a deeper understanding of lung tissue mechanics.

Production and transplantation of bioengineered lung into a large-animal model

The inability to produce perfusable microvasculature networks capable of supporting tissue survival and of withstanding physiological pressures without leakage is a fundamental problem facing the field of tissue engineering. Microvasculature is critically important for production of bioengineered lung (BEL), which requires systemic circulation to support tissue survival and coordination of circulatory and respiratory systems to ensure proper gas exchange. To advance our understanding of vascularization after bioengineered organ transplantation, we produced and transplanted BEL without creation of a pulmonary artery anastomosis in a porcine model. A single pneumonectomy, performed 1 month before BEL implantation, provided the source of autologous cells used to bioengineer the organ on an acellular lung scaffold. During 30 days of bioreactor culture, we facilitated systemic vessel development using growth factor–loaded microparticles. We evaluated recipient survival, autograft (BEL) vascular and parenchymal tissue development, graft rejection, and microbiome reestablishment in autografted animals 10 hours, 2 weeks, 1 month, and 2 months after transplant. BEL became well vascularized as early as 2 weeks after transplant, and formation of alveolar tissue was observed in all animals (n = 4). There was no indication of transplant rejection. BEL continued to develop after transplant and did not require addition of exogenous growth factors to drive cell proliferation or lung and vascular tissue development. The sterile BEL was seeded and colonized by the bacterial community of the native lung.

How to build a lung: latest advances and emerging themes in lung bioengineering

Chronic respiratory diseases remain a major cause of morbidity and mortality worldwide. The only option at end-stage disease is lung transplantation, but there are not enough donor lungs to meet clinical demand. Alternative options to increase tissue availability for lung transplantation are urgently required to close the gap on this unmet clinical need. A growing number of tissue engineering approaches are exploring the potential to generate lung tissue ex vivo for transplantation. Both biologically derived and manufactured scaffolds seeded with cells and grown ex vivo have been explored in pre-clinical studies, with the eventual goal of generating functional pulmonary tissue for transplantation. Recently, there have been significant efforts to scale-up cell culture methods to generate adequate cell numbers for human-scale bioengineering approaches. Concomitantly, there have been exciting efforts in designing bioreactors that allow for appropriate cell seeding and development of functional lung tissue over time. This review aims to present the current state-of-the-art progress for each of these areas and to discuss promising new ideas within the field of lung bioengineering.

Impact of different intratracheal flows during lung decellularization on extracellular matrix composition and mechanics

Aim: To evaluate different intratracheal flow rates on extracellular matrix content and lung mechanics in an established lung decellularization protocol. Materials & methods: Healthy mice were used: 15 for decellularization and five to serve as controls. Fluids were instilled at 5, 10 and 20 ml/min flow rates through tracheal cannula and right ventricular cavity (0.5 ml/min) in all groups. Results: The 20 ml/min rate better preserved collagen content in decellularized lungs. Elastic fiber content decreased at 5 and 10 ml/min, but not at 20 ml/min, compared with controls. Chondroitin, heparan and dermatan content was reduced after decellularization. Conclusion: An intratracheal flow rate of 20 ml/min was associated with lower resistance and greater preservation of collagen to that observed in ex vivo control lungs.

Avian lungs: A novel scaffold for lung bioengineering

Allogeneic lung transplant is limited both by the shortage of available donor lungs and by the lack of suitable long-term lung assist devices to bridge patients to lung transplantation. Avian lungs have different structure and mechanics resulting in more efficient gas exchange than mammalian lungs. Decellularized avian lungs, recellularized with human lung cells, could therefore provide a powerful novel gas exchange unit for potential use in pulmonary therapeutics. To initially assess this in both small and large avian lung models, chicken (Gallus gallus domesticus) and emu (Dromaius novaehollandiae) lungs were decellularized using modifications of a detergent-based protocol, previously utilized with mammalian lungs. Light and electron microscopy, vascular and airway resistance, quantitation and gel analyses of residual DNA, and immunohistochemical and mass spectrometric analyses of remaining extracellular matrix (ECM) proteins demonstrated maintenance of lung structure, minimal residual DNA, and retention of major ECM proteins in the decellularized scaffolds. Seeding with human bronchial epithelial cells, human pulmonary vascular endothelial cells, human mesenchymal stromal cells, and human lung fibroblasts demonstrated initial cell attachment on decellularized avian lungs and growth over a 7-day period. These initial studies demonstrate that decellularized avian lungs may be a feasible approach for generating functional lung tissue for clinical therapeutics.