Production of decellularized porcine lung scaffolds for use in tissue engineering

Dynamic 3D in vitro lung models: applications of inorganic nanoparticles for model development and characterization

Being a vital organ exposed to the external environment, the lung is susceptible to a plethora of pathogens and pollutants. This is reflected in high incidences of chronic respiratory diseases, which remain a leading cause of mortality world-wide and pose a persistent global burden. It is thus of paramount importance to improve our understanding of these pathologies and provide better therapeutic options. This necessitates the development of representative and physiologically relevant in vitro models. Advances in bioengineering have enabled the development of sophisticated models that not only capture the three-dimensional architecture of the cellular environment but also incorporate the dynamics of local biophysical stimuli. However, such complex models also require novel approaches that provide reliable characterization. Within this review we explore how 3D bioprinting and nanoparticles can serve as multifaceted tools to develop such dynamic 4D printed in vitro lung models and facilitate their characterization in the context of pulmonary fibrosis and breast cancer lung metastasis.

High-frequency electric knife smoke particles: An experimental study on factors influencing emission characteristics

During surgery, the use of a high-frequency electric knife produces smoke, which can be harmful to the health of indoor medical staff and patients. The quantity and particle size distribution of smoke particles produced by different tissues may vary. Understanding the release characteristics of these smoke particles is necessary to clarify their impact on the surgical environment and to seek effective smoke control methods. A previous comparative analysis of human and pig tissues revealed that they share similar water and fat compositions in certain anatomical regions. In this study, we investigated the emission characteristics of smoke particles from various tissues of pigs (skeletal muscle, liver, kidney, skin, and subcutaneous fat) under different operating powers of an electric knife. We measured the indoor particle number concentration (particle concentration), and estimated the PM2.5 mass concentration (PM2.5 concentration), particle size distribution, and emission rate of the smoke particles. The study obtained the particle emission rates of different tissues under different electric knife operating powers, results of which showed that (1) during the operation of the electric knife, mainly small particles below 1 μm are produced. Among them, particles of 0.3 μm were the most abundant, with a particle concentration level of up to 109 particles/m3, accounting for 85.17-97.64% of the total particle number, and as the particle size increased, the particle concentration and percentage decreased significantly. (2) The water and fat compositions of different tissues influenced the indoor particle concentration and emission rate of the smoke emitted by the electric knife. Among different tissues, subcutaneous fat tissue had the lowest particle concentration and emission rate. (3) The electric knife operating power mainly affected particles below 1 μm, and except for kidney tissue, the indoor concentration and emission rate of these particle sizes were positively correlated with the power. The experimental results can provide data reference for the use of high-frequency electric knives in surgeries involving different human tissues in the operating room.

Animals in Respiratory Research

The respiratory barrier, a thin epithelial barrier that separates the interior of the human body from the environment, is easily damaged by toxicants, and chronic respiratory diseases are common. It also allows the permeation of drugs for topical treatment. Animal experimentation is used to train medical technicians, evaluate toxicants, and develop inhaled formulations. Species differences in the architecture of the respiratory tract explain why some species are better at predicting human toxicity than others. Some species are useful as disease models. This review describes the anatomical differences between the human and mammalian lungs and lists the characteristics of currently used mammalian models for the most relevant chronic respiratory diseases (asthma, chronic obstructive pulmonary disease, cystic fibrosis, pulmonary hypertension, pulmonary fibrosis, and tuberculosis). The generation of animal models is not easy because they do not develop these diseases spontaneously. Mouse models are common, but other species are more appropriate for some diseases. Zebrafish and fruit flies can help study immunological aspects. It is expected that combinations of in silico, in vitro, and in vivo (mammalian and invertebrate) models will be used in the future for drug development.

Decellularized bladder as scaffold to support proliferation and functionality of insulin-secreting pancreatic cells

Loss in the number or function of insulin-producing β-cells in pancreatic islets has been associated with diabetes mellitus. Although islet transplantation can be an alternative treatment, complications such as apoptosis, ischaemia and loss of viability have been reported. The use of decellularized organs as scaffolds in tissue engineering is of interest owing to the unique ultrastructure and composition of the extracellular matrix (ECM) believed to act on tissue regeneration. In this study, a cell culture system has been designed to study the effect of decellularized porcine bladder pieces on INS-1 cells, a cell line secreting insulin in response to glucose stimulation. Porcine bladders were decellularized using two techniques: a detergent-containing and a detergent-free methods. The resulting ECMs were characterized for the removal of both cells and dsDNA. INS-1 cells were not viable on ECM produced using detergent (i.e., sodium dodecyl sulfate). INS-1 cells were visualized following 7 days of culture on detergent-free decellularized bladders using a cell viability and metabolism assay (MTT) and cell proliferation quantified (CyQUANT™ NF Cell Proliferation Assay). Further, glucose-stimulated insulin secretion and immunostaining confirmed that cells were functional in response to glucose stimulation, as well as they expressed insulin and interacted with the detergent-free produced ECM, respectively.

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.

Decellularization compromises mechanical and structural properties of the native trachea

Tracheal replacement using tissue engineering technologies offers great potential to improve previously intractable clinical interventions, and interest in this area has increased in recent years. Many engineered airway constructs currently rely on decellularized native tracheas to serve as the scaffold for tissue repair. Yet, mechanical failure leading to airway narrowing and collapse remains a major cause of morbidity and mortality following clinical implantation of decellularized tracheal grafts. To understand better the factors contributing to mechanical failure in vivo, we characterized the histo-mechanical properties of tracheas following two different decellularization protocols, including one that has been used clinically. All decellularized tracheas deviated from native mechanical behavior, which may provide insights into observed in vivo graft failures. We further analyzed protein content by western blot and analyzed microstructure by histological staining and found that the specific method of decellularization resulted in significant differences in the depletion of proteoglycans and degradation of collagens I, II, III, and elastin. Taken together, this work demonstrates that the heterogeneous architecture and mechanical behavior of the trachea is severely compromised by decellularization. Such structural deterioration may contribute to graft failure clinically and limit the potential of decellularized native tracheas as viable long-term orthotopic airway replacements.

An in vitro comparison of human corneal epithelial cell activity and inflammatory response on differently designed ocular amniotic membranes and a clinical case study

Amniotic membrane (AM) is a naturally derived biomaterial with biological and mechanical properties important to Ophthalmology. The epithelial side of the AM promotes epithelialization, while the stromal side regulates inflammation. However, not all AMs are equal. AMs undergo different processing with resultant changes in cellular content and structure. This study evaluates the effects of sidedness and processing on human corneal epithelial cell (HCEC) activity, the effect of processing on HCEC inflammatory response, and then a case study is presented. Three differently processed, commercially available ocular AMs were selected: (1) Biovance®3L Ocular, a decellularized, dehydrated human AM (DDHAM), (2) AMBIO2®, a dehydrated human AM (DHAM), and (3) AmnioGraft®, a cryopreserved human AM (CHAM). HCECs were seeded onto the AMs and incubated for 1, 4 and 7 days. Cell adhesion and viability were evaluated using alamarBlue assay. HCEC migration was evaluated using a scratch wound assay. An inflammatory response was induced by TNF-α treatment. The effect of AM on the expression of pro-inflammatory genes in HCECs was compared using quantitative polymerase chain reaction (qPCR). Staining confirmed complete decellularization and the absence of nuclei in DDHAM. HCEC activity was best supported on the stromal side of DDHAM. Under inflammatory stimulation, DDHAM promoted a higher initial inflammatory response with a declining trend across time. Clinically, DDHAM was used to successfully treat anterior basement membrane dystrophy. Compared with DHAM and CHAM, DDHAM had significant positive effects on the cellular activities of HCECs in vitro, which may suggest greater ocular cell compatibility in vivo.

Different Decellularization Methods in Bovine Lung Tissue Reveals Distinct Biochemical Composition, Stiffness, and Viscoelasticity in Reconstituted Hydrogels

Extracellular matrix (ECM)-derived hydrogels are in demand for use in lung tissue engineering to mimic the native microenvironment of cells in vitro. Decellularization of native tissues has been pursued for preserving organotypic ECM while eliminating cellular content and reconstitution into scaffolds which allows re-cellularization for modeling homeostasis, regeneration, or diseases. Achieving mechanical stability and understanding the effects of the decellularization process on mechanical parameters of the reconstituted ECM hydrogels present a challenge in the field. Stiffness and viscoelasticity are important characteristics of tissue mechanics that regulate crucial cellular processes and their in vitro representation in engineered models is a current aspiration. The effect of decellularization on viscoelastic properties of resulting ECM hydrogels has not yet been addressed. The aim of this study was to establish bovine lung tissue decellularization for the first time via pursuing four different protocols and characterization of reconstituted decellularized lung ECM hydrogels for biochemical and mechanical properties. Our data reveal that bovine lungs provide a reproducible alternative to human lungs for disease modeling with optimal retention of ECM components upon decellularization. We demonstrate that the decellularization method significantly affects ECM content, stiffness, and viscoelastic properties of resulting hydrogels. Lastly, we examined the impact of these aspects on viability, morphology, and growth of lung cancer cells, healthy bronchial epithelial cells, and patient-derived lung organoids.

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.

3D tissue-engineered lung models to study immune responses following viral infections of the small airways

Small airway infections caused by respiratory viruses are some of the most prevalent causes of illness and death. With the recent worldwide pandemic due to the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), there is currently a push in developing models to better understand respiratory diseases. Recent advancements have made it possible to create three-dimensional (3D) tissue-engineered models of different organs. The 3D environment is crucial to study physiological, pathophysiological, and immunomodulatory responses against different respiratory conditions. A 3D human tissue-engineered lung model that exhibits a normal immunological response against infectious agents could elucidate viral and host determinants. To create 3D small airway lung models in vitro, resident epithelial cells at the air-liquid interface are co-cultured with fibroblasts, myeloid cells, and endothelial cells. The air-liquid interface is a key culture condition to develop and differentiate airway epithelial cells in vitro. Primary human epithelial and myeloid cells are considered the best 3D model for studying viral immune responses including migration, differentiation, and the release of cytokines. Future studies may focus on utilizing bioreactors to scale up the production of 3D human tissue-engineered lung models. This review outlines the use of various cell types, scaffolds, and culture conditions for creating 3D human tissue-engineered lung models. Further, several models used to study immune responses against respiratory viruses, such as the respiratory syncytial virus, are analyzed, showing how the microenvironment aids in understanding immune responses elicited after viral infections.

Biological Graft as an Innovative Biomaterial for Complex Skin Wound Treatment in Dogs: A Preliminary Report

Complex wounds in dogs are a recurrent problem in veterinary clinical application and can compromise skin healing; in this sense, tissue bioengineering focused on regenerative medicine can be a great ally. Decellularized and recellularized skin scaffolds are produced to be applied in different and complex canine dermal wounds in the present investigation. Dog skin fragments are immersed in a 0.5% sodium dodecyl sulfate (SDS) solution at room temperature and overnight at 4 °C for 12 days. Decellularized samples are evaluated by histological analysis, scanning electron microscopy (SEM) and gDNA quantification. Some fragments are also recellularized using mesenchymal stem cells (MSCs). Eight adult dogs are divided into three groups for the application of the decellularized (Group I, n = 3) and recellularized scaffolds (Group II, n = 3) on injured areas, and a control group (Group III, n = 2). Wounds are evaluated and measured during healing, and comparisons among the three groups are described. In 30- and 60-day post-grafting, the histopathological analysis of patients from Groups I and II shows similar patterns, tissue architecture preservation, epithelial hyperplasia, hyperkeratosis, edema, and mononuclear inflammatory infiltrate. Perfect integration between scaffolds and wounds, without rejection or contamination, are observed in both treated groups. According to these results, decellularized skin grafts may constitute a potential innovative and functional tool to be adopted as a promising dog cutaneous wound treatment. This is the first study that applies decellularized and recellularized biological skin grafts to improve the healing process in several complex wounds in dogs, demonstrating great potential for regenerative veterinary medicine progress.

Decellularized organ biomatrices facilitate quantifiable in vitro 3D cancer metastasis models

Metastatic cancers are chemoresistant, involving complex interplay between disseminated cancer cell aggregates and the distant organ microenvironment (extracellular matrix and stromal cells). Conventional metastasis surrogates (scratch/wound healing, Transwell migration assays) lack 3D architecture and ECM presence. Metastasis studies can therefore significantly benefit from biomimetic 3D in vitro models recapitulating the complex cascade of distant organ invasion and colonization by collective clusters of cells. We aimed to engineer reproducible and quantifiable 3D models of highly therapy-resistant cancer processes: (i) colorectal cancer liver metastasis; and (ii) breast cancer lung metastasis. Metastatic seeds are engineered using 3D tumor spheroids to recapitulate the 3D aggregation of cancer cells both in the tumor and in circulation throughout the metastatic cascade of many cancers. Metastatic soil was engineered by decellularizing porcine livers and lungs to generate biomatrix scaffolds, followed by extensive materials characterization. HCT116 colorectal and MDA-MB-231 breast cancer spheroids were generated on hanging drop arrays to initiate clustered metastatic seeding into liver and lung biomatrix scaffolds, respectively. Between days 3-7, biomatrix cellular colonization was apparent with increased metabolic activity and the presence of cellular nests evaluated via multiphoton microscopy. HCT116 and MDA-MB-231 cells colonized liver and lung biomatrices, and at least 15% of the cells invaded more than 20 μm from the surface. Engineered metastases also expressed increased signatures of genes associated with the metastatic epithelial to mesenchymal transition (EMT). Importantly, inhibition of matrix metalloproteinase-9 inhibited metastatic invasion into the biomatrix. Furthermore, metastatic nests were significantly more chemoresistant (>3 times) to the anti-cancer drug oxaliplatin, compared to 3D spheroids. Together, our data indicated that HCT116 and MDA-MB-231 spheroids invade, colonize, and proliferate in livers and lungs establishing metastatic nests in 3D settings in vitro. The metastatic nature of these cells was confirmed with functional readouts regarding EMT and chemoresistance. Modeling the dynamic metastatic cascade in vitro has potential to identify therapeutic targets to treat or prevent metastatic progression in chemoresistant metastatic cancers.

A decellularized flowable placental connective tissue matrix supports cellular functions of human tenocytes in vitro

Purpose

Injectable connective tissue matrices (CTMs) may promote tendon healing, given their minimally invasive properties, structural and biochemical extracellular matrix components, and capacity to fill irregular spaces. The purpose of this study is to evaluate the effects of placental CTMs on the cellular activities of human tenocytes. Decellularization, the removal of cells, cell fragments, and DNA from CTMs, has been shown to reduce the host’s inflammatory response. Therefore, the authors hypothesize that a decellularized CTM will provide a more cell-friendly matrix to support tenocyte functions.

Methods

Three human placental CTMs were selected for comparison: AmnioFill® (A-CTM), a minimally manipulated, non-viable cellular particulate, BioRenew™ (B-CTM), a liquid matrix, and Interfyl® (I-CTM), a decellularized flowable particulate. Adhesion and proliferation were evaluated using cell viability assays and tenocyte migration using a transwell migration assay. Gene expression of tenocyte markers, cytokines, growth factors, and matrix metalloprotease (MMP) in tenocytes were assessed using quantitative polymerase chain reaction.

Results

Although A-CTM supported more tenocyte adhesion, I-CTM promoted significantly more tenocyte proliferation compared with A-CTM and B-CTM. Unlike A-CTM, tenocyte migration was higher in I-CTM than the control. The presence of I-CTM also prevented the loss of tenocyte phenotype, attenuated the expression of pro-inflammatory cytokines, growth factors, and MMP, and promoted the expression of antifibrotic growth factor, TGFβ3.

Conclusion

Compared with A-CTM and B-CTM, I-CTM interacted more favorably with human tenocytes in vitro. I-CTM supported tenocyte proliferation with reduced de-differentiation and attenuation of the inflammatory response, suggesting that I-CTM may support tendon healing and regeneration in vivo.

Supplementary Information

The online version contains supplementary material available at 10.1186/s40634-022-00509-4.

Imaging-Guided Bioreactor for Generating Bioengineered Airway Tissue

Repeated injury to airway tissue can impair lung function and cause chronic lung disease, such as chronic obstructive pulmonary disease. Advances in regenerative medicine and bioreactor technologies offer opportunities to produce lab-grown functional tissue and organ constructs that can be used to screen drugs, model disease, and engineer tissue replacements. Here, a miniaturized bioreactor coupled with an imaging modality that allows in situ visualization of the inner lumen of explanted rat trachea during in vitro tissue manipulation and culture is described. Using this bioreactor, the protocol demonstrates imaging-guided selective removal of endogenous cellular components while preserving the intrinsic biochemical features and ultrastructure of the airway tissue matrix. Furthermore, the delivery, uniform distribution, and subsequent prolonged culture of exogenous cells on the decellularized airway lumen with optical monitoring in situ are shown. The results highlight that the imaging-guided bioreactor can potentially be used to facilitate the generation of functional in vitro airway tissues.

A Novel Bioreactor for Reconstitution of the Epithelium and Submucosal Glands in Decellularized Ferret Tracheas

Tracheal grafts introduce the possibility to treat airway pathologies that require resection. While there has been success with engraftment of the surface airway epithelium (SAE) onto decellularized tracheas, there has been minimal advancement in regenerating the submucosal glands (SMGs). We designed a cost-effective open-system perfusion bioreactor to investigate the engraftment potential of ferret SAEs and murine myoepithelial cells (MECs) on a partly decellularized ferret trachea with the goal of creating a fully functional tracheal replacement. An air-liquid interface was also arranged by perfusing humidified air through the lumen of a recellularized conduit to induce differentiation. Our versatile bioreactor design was shown to support the successful partial decellularization and recellularization of ferret tracheas. The decellularized grafts maintained biomechanical integrity and chondrocyte viability, consistent with other publications. The scaffolds supported SAE basal cell engraftment, and early differentiation was observed once an air-liquid interface had been established. Lastly, MEC engraftment was sustained, with evidence of diffuse SMG reconstitution. This model will help shed light on SMG regeneration and basal cell differentiation in vitro for the development of fully functional tracheal grafts before transplantation.

Novel Decellularization Method for Tissue Slices

Decellularization procedures have been developed and optimized for the entire organ or tissue blocks, by either perfusion of decellularizing agents through the tissue’s vasculature or submerging large sections in decellularizing solutions. However, some research aims require the analysis of native as well as decellularized tissue slices side by side, but an optimal protocol has not yet been established to address this need. Thus, the main goal of this work was to develop a fast and efficient decellularization method for tissue slices—with an emphasis on lung—while attached to a glass slide. To this end, different decellularizing agents were compared for their effectiveness in cellular removal while preserving the extracellular matrix. The intensity of DNA staining was taken as an indicator of remaining cells and compared to untreated sections. The presence of collagen, elastin and laminin were quantified using immunostaining and signal quantification. Scaffolds resulting from the optimized protocol were mechanically characterized using atomic force microscopy. Lung scaffolds were recellularized with mesenchymal stromal cells to assess their biocompatibility. Some decellularization agents (CHAPS, triton, and ammonia hydroxide) did not achieve sufficient cell removal. Sodium dodecyl sulfate (SDS) was effective in cell removal (1% remaining DNA signal), but its sharp reduction of elastin signal (only 6% remained) plus lower attachment ratio (32%) singled out sodium deoxycholate (SD) as the optimal treatment for this application (6.5% remaining DNA signal), due to its higher elastin retention (34%) and higher attachment ratio (60%). Laminin and collagen were fully preserved in all treatments. The SD decellularization protocol was also successful for porcine and murine (mice and rat) lungs as well as for other tissues such as the heart, kidney, and bladder. No significant mechanical differences were found before and after sample decellularization. The resulting acellular lung scaffolds were shown to be biocompatible (98% cell survival after 72 h of culture). This novel method to decellularize tissue slices opens up new methodological possibilities to better understand the role of the extracellular matrix in the context of several diseases as well as tissue engineering research and can be easily adapted for scarce samples like clinical biopsies.

Imaging-guided bioreactor for de-epithelialization and long-term cultivation of ex vivo rat trachea

Recent synergistic advances in organ-on-chip and tissue engineering technologies offer opportunities to create in vitro-grown tissue or organ constructs that can faithfully recapitulate their in vivo counterparts. Such in vitro tissue or organ constructs can be utilized in multiple applications, including rapid drug screening, high-fidelity disease modeling, and precision medicine. Here, we report an imaging-guided bioreactor that allows in situ monitoring of the lumen of ex vivo airway tissues during controlled in vitro tissue manipulation and cultivation of isolated rat trachea. Using this platform, we demonstrated partial removal of the rat tracheal epithelium (i.e., de-epithelialization) without disrupting the underlying subepithelial cells and extracellular matrix. Through different tissue evaluation assays, such as immunofluorescent staining, DNA/protein quantification, and electron beam microscopy, we showed that the epithelium of the tracheal lumen can be effectively removed with negligible disruption in the underlying tissue layers, such as cartilage and blood vessel. Notably, using a custom-built micro-optical imaging device integrated with the bioreactor, the trachea lumen was visualized at the cellular level, and removal of the endogenous epithelium and distribution of locally delivered exogenous cells were demonstrated in situ. Moreover, the de-epithelialized trachea supported on the bioreactor allowed attachment and growth of exogenous cells seeded topically on its denuded tissue surface. Collectively, the results suggest that our imaging-enabled rat trachea bioreactor and localized cell replacement method can facilitate creation of bioengineered in vitro airway tissue that can be used in different biomedical applications.

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.

Importance of the pig as a human biomedical model

[Figure: see text].

3D Bioprinting Strategies, Challenges, and Opportunities to Model the Lung Tissue Microenvironment and Its Function

Human lungs are organs with an intricate hierarchical structure and complex composition; lungs also present heterogeneous mechanical properties that impose dynamic stress on different tissue components during the process of breathing. These physiological characteristics combined create a system that is challenging to model in vitro. Many efforts have been dedicated to develop reliable models that afford a better understanding of the structure of the lung and to study cell dynamics, disease evolution, and drug pharmacodynamics and pharmacokinetics in the lung. This review presents methodologies used to develop lung tissue models, highlighting their advantages and current limitations, focusing on 3D bioprinting as a promising set of technologies that can address current challenges. 3D bioprinting can be used to create 3D structures that are key to bridging the gap between current cell culture methods and living tissues. Thus, 3D bioprinting can produce lung tissue biomimetics that can be used to develop in vitro models and could eventually produce functional tissue for transplantation. Yet, printing functional synthetic tissues that recreate lung structure and function is still beyond the current capabilities of 3D bioprinting technology. Here, the current state of 3D bioprinting is described with a focus on key strategies that can be used to exploit the potential that this technology has to offer. Despite today's limitations, results show that 3D bioprinting has unexplored potential that may be accessible by optimizing bioink composition and looking at the printing process through a holistic and creative lens.

The Potential Contribution of Biopolymeric Particles in Lung Tissue Regeneration of COVID-19 Patients

The lung is a vital organ that houses the alveoli, which is where gas exchange takes place. The COVID-19 illness attacks lung cells directly, creating significant inflammation and resulting in their inability to function. To return to the nature of their job, it may be essential to rejuvenate the afflicted lung cells. This is difficult because lung cells need a long time to rebuild and resume their function. Biopolymeric particles are the most effective means to transfer developing treatments to airway epithelial cells and then regenerate infected lung cells, which is one of the most significant symptoms connected with COVID-19. Delivering biocompatible and degradable natural biological materials, chemotherapeutic drugs, vaccines, proteins, antibodies, nucleic acids, and diagnostic agents are all examples of these molecules' usage. Furthermore, they are created by using several structural components, which allows them to effectively connect with these cells. We highlight their most recent uses in lung tissue regeneration in this review. These particles are classified into three groups: biopolymeric nanoparticles, biopolymeric stem cell materials, and biopolymeric scaffolds. The techniques and processes for regenerating lung tissue will be thoroughly explored.

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.

Development of novel apoptosis-assisted lung tissue decellularization methods

Decellularized tissues hold great potential for both regenerative medicine and disease modeling applications. The acellular extracellular matrix (ECM)-enriched scaffolds can be recellularized with patient-derived cells prior to transplantation, or digested to create thermally-gelling ECM hydrogels for 3D cell culture. Current methods of decellularization clear cellular components using detergents, which can result in loss of ECM proteins and tissue architectural integrity. Recently, an alternative approach utilizing apoptosis to decellularize excised murine sciatic nerves resulted in superior ECM preservation, cell removal, and immune tolerance in vivo. However, this apoptosis-assisted decellularization approach has not been optimized for other tissues with a more complex geometry, such as lungs. To this end, we developed an apoptosis-assisted lung tissue decellularization method using a combination of camptothecin and sulfobetaine-10 (SB-10) to induce apoptosis and facilitate gentle and effective removal of cell debris, respectively. Importantly, combination of the two agents resulted in superior cell removal and ECM preservation compared to either of the treatments alone, presumably because of pulmonary surfactants. In addition, our method was superior in cell removal compared to a previously established detergent-based decellularization protocol. Furthermore, thermally-gelling lung ECM hydrogels supported high viability of rat lung epithelial cells for up to 2 weeks in culture. This work demonstrates that apoptosis-based lung tissue decellularization is a superior technique that warrants further utilization for both regenerative medicine and disease modeling purposes.

Advanced single-cell technologies to guide the development of bioengineered lungs

Lung transplantation remains the only viable option for individuals suffering from end-stage lung failure. However, a number of current limitations exist including a continuing shortage of suitable donor lungs and immune rejection following transplantation. To address these concerns, engineering a decellularized biocompatible lung scaffold from cadavers reseeded with autologous lung cells to promote tissue regeneration is being explored. Proof-of-concept transplantation of these bioengineered lungs into animal models has been accomplished. However, these lungs were incompletely recellularized with resulting epithelial and endothelial leakage and insufficient basement membrane integrity. Failure to repopulate lung scaffolds with all of the distinct cell populations necessary for proper function remains a significant hurdle for the progression of current engineering approaches and precludes clinical translation. Advancements in 3D bioprinting, lung organoid models, and microfluidic device and bioreactor development have enhanced our knowledge of pulmonary lung development, as well as important cell-cell and cell-matrix interactions, all of which will help in the path to a bioengineered transplantable lung. However, a significant gap in knowledge of the spatiotemporal interactions between cell populations as well as relative quantities and localization within each compartment of the lung necessary for its proper growth and function remains. This review will provide an update on cells currently used for reseeding decellularized scaffolds with outcomes of recent lung engineering attempts. Focus will then be on how data obtained from advanced single-cell analyses, coupled with multiomics approaches and high-resolution 3D imaging, can guide current lung bioengineering efforts for the development of fully functional, transplantable lungs.

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.

Future Perspectives in Small-Diameter Vascular Graft Engineering

The increased demands of small-diameter vascular grafts (SDVGs) globally has forced the scientific society to explore alternative strategies utilizing the tissue engineering approaches. Cardiovascular disease (CVD) comprises one of the most lethal groups of non-communicable disorders worldwide. It has been estimated that in Europe, the healthcare cost for the administration of CVD is more than 169 billion €. Common manifestations involve the narrowing or occlusion of blood vessels. The replacement of damaged vessels with autologous grafts represents one of the applied therapeutic approaches in CVD. However, significant drawbacks are accompanying the above procedure; therefore, the exploration of alternative vessel sources must be performed. Engineered SDVGs can be produced through the utilization of non-degradable/degradable and naturally derived materials. Decellularized vessels represent also an alternative valuable source for the development of SDVGs. In this review, a great number of SDVG engineering approaches will be highlighted. Importantly, the state-of-the-art methodologies, which are currently employed, will be comprehensively presented. A discussion summarizing the key marks and the future perspectives of SDVG engineering will be included in this review. Taking into consideration the increased number of patients with CVD, SDVG engineering may assist significantly in cardiovascular reconstructive surgery and, therefore, the overall improvement of patients' life.

Novel Lung Tropic Adeno-Associated Virus Capsids for Therapeutic Gene Delivery

Efforts to identify mutations that underlie inherited genetic diseases combined with strides in the development of gene therapy vectors over the last three decades have culminated in the approval of several adeno-associated virus (AAV)-based gene therapies. Genetic diseases that manifest in the lung such as cystic fibrosis (CF) and surfactant deficiencies, however, have so far proven to be elusive targets. Early clinical trials in CF using AAV serotype 2 (AAV2) achieved safety, but not efficacy endpoints; however, importantly, these studies provided critical information on barriers that need to be surmounted to translate AAV lung gene therapy toward clinical success. Bolstered with an improved understanding of AAV biology and more clinically relevant lung models, next-generation molecular biology and bioinformatics approaches have given rise to novel AAV capsid variants that offer improvements in transduction efficiency, immunological profile, and the ability to circumvent physical barriers in the lung such as mucus. This review discusses the principal limiting barriers to clinical success in lung gene therapy and focuses on novel engineered AAV capsid variants that have been developed to overcome those challenges.

Whole Organ Engineering: Approaches, Challenges, and Future Directions

End-stage organ failure remains a leading cause of morbidity and mortality across the globe. The only curative treatment option currently available for patients diagnosed with end-stage organ failure is organ transplantation. However, due to a critical shortage of organs, only a fraction of these patients are able to receive a viable organ transplantation. Those patients fortunate enough to receive a transplant must then be subjected to a lifelong regimen of immunosuppressant drugs. The concept of whole organ engineering offers a promising alternative to organ transplantation that overcomes these limitations. Organ engineering is a discipline that merges developmental biology, anatomy, physiology, and cellular interactions with enabling technologies such as advanced biomaterials and biofabrication to create bioartificial organs that recapitulate native organs in vivo. There have been numerous developments in bioengineering of whole organs over the past two decades. Key technological advancements include (1) methods of whole organ decellularization and recellularization, (2) three-dimensional bioprinting, (3) advanced stem cell technologies, and (4) the ability to genetically modify tissues and cells. These advancements give hope that organ engineering will become a commercial reality in the next decade. In this review article, we describe the foundational principles of whole organ engineering, discuss key technological advances, and provide an overview of current limitations and future directions.

Platform Effects on Regeneration by Pulmonary Basal Cells as Evaluated by Single-Cell RNA Sequencing

Cell-based therapies have shown promise for treating myriad chronic pulmonary diseases through direct application of epithelial progenitors or by way of engineered tissue grafts or whole organs. To elucidate environmental effects on epithelial regenerative outcomes in vitro, here, we isolate and culture a population of pharmacologically expanded basal cells (peBCs) from rat tracheas. At peak basal marker expression, we simultaneously split peBCs into four in vitro platforms: organoid, air-liquid interface (ALI), engineered trachea, and engineered lung. Following differentiation, these samples are evaluated using single-cell RNA sequencing (scRNA-seq) and computational pipelines are developed to compare samples both globally and at the population level. A sample of native rat tracheal epithelium is also evaluated by scRNA-seq as a control for engineered epithelium. Overall, this work identifies platform-specific effects that support the use of engineered models to achieve the most physiologic differential outcomes in pulmonary epithelial regenerative applications.

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.

Non-invasive and real-time measurement of microvascular barrier in intact lungs

Microvascular leak is a phenomenon witnessed in multiple disease states. In organ engineering, regaining a functional barrier is the most crucial step towards creating an implantable organ. All previous methods of measuring microvascular permeability were either invasive, lengthy, introduced exogenous macromolecules, or relied on extrapolations from cultured cells. We present here a system that enables real-time measurement of microvascular permeability in intact rat lungs. Our unique system design allows direct, non-invasive measurement of average alveolar and capillary pressures, tracks flow paths within the organ, and enables calculation of lumped internal resistances including microvascular barrier. We first describe the physiology of native and decellularized lungs and the inherent properties of the extracellular matrix as functions of perfusion rate. We next track changing internal resistances and flows in injured native rat lungs, resolving the onset of microvascular leak, quantifying changing vascular resistances, and identifying distinct phases of organ failure. Finally, we measure changes in permeability within engineered lungs seeded with microvascular endothelial cells, quantifying cellular effects on internal vascular and barrier resistances over time. This system marks considerable progress in bioreactor design for intact organs and may be used to monitor and garner physiological insights into native, decellularized, and engineered tissues.

Evaluation methods as quality control in the generation of decellularized peripheral nerve allografts

Nowadays, the high incidence of peripheral nerve injuries and the low success ratio of surgical treatments are driving research to the generation of novel alternatives to repair critical nerve defects. In this sense, tissue engineering has emerged as a possible alternative with special attention to decellularization techniques. Tissue decellularization offers the possibility to obtain a cell-free, natural extracellular matrix (ECM), characterized by an adequate 3D organization and proper molecular composition to repair different tissues or organs, including peripheral nerves. One major problem, however, is that there are no standard quality control methods to evaluate decellularized tissues. Therefore, in this review, a brief description of current strategies for peripheral nerve repair is given, followed by an overview of different decellularization methods used for peripheral nerves. Furthermore, we extensively discuss the available and currently used methods to demonstrate the success of tissue decellularization in terms of the cell removal, preservation of essential ECM molecules and maintenance or modification of biomechanical properties. Finally, orientative guidelines for the evaluation of decellularized peripheral nerve allografts are proposed.

Lung bioengineering: advances and challenges in lung decellularization and recellularization

PURPOSE OF REVIEW

Bioengineering the lung based on its natural extracellular matrix (ECM) offers novel opportunities to overcome the shortage of donors, to reduce chronic allograft rejections, and to improve the median survival rate of transplanted patients. During the last decade, lung tissue engineering has advanced rapidly to combine scaffolds, cells, and biologically active molecules into functional tissues to restore or improve the lung's main function, gas exchange. This review will inspect the current progress in lung bioengineering using decellularized and recellularized lung scaffolds and highlight future challenges in the field.

RECENT FINDINGS

Lung decellularization and recellularization protocols have provided researchers with tools to progress toward functional lung tissue engineering. However, there is continuous evolution and refinement particularly for optimization of lung recellularization. These further the possibility of developing a transplantable bioartificial lung.

SUMMARY

Bioengineering the lung using recellularized scaffolds could offer a curative option for patients with end-stage organ failure but its accomplishment remains unclear in the short-term. However, the state-of-the-art of techniques described in this review will increase our knowledge of the lung ECM and of chemical and mechanical cues which drive cell repopulation to improve the advances in lung regeneration and lung tissue engineering.

Extracellular matrix stiffness regulates human airway smooth muscle contraction by altering the cell-cell coupling

For an airway or a blood vessel to narrow, there must be a connected path that links the smooth muscle (SM) cells with each other, and transmits forces around the organ, causing it to constrict. Currently, we know very little about the mechanisms that regulate force transmission pathways in a multicellular SM ensemble. Here, we used extracellular matrix (ECM) micropatterning to study force transmission in a two-cell ensemble of SM cells. Using the two-SM cell ensemble, we demonstrate (a) that ECM stiffness acts as a switch that regulates whether SM force is transmitted through the ECM or through cell-cell connections. (b) Fluorescent imaging for adherens junctions and focal adhesions show the progressive loss of cell-cell borders and the appearance of focal adhesions with the increase in ECM stiffness (confirming our mechanical measurements). (c) At the same ECM stiffness, we show that the presence of a cell-cell border substantially decreases the overall contractility of the SM cell ensemble. Our results demonstrate that connectivity among SM cells is a critical factor to consider in the development of diseases such as asthma and hypertension.

Harnessing Human Decellularized Blood Vessel Matrices and Cellular Construct Implants to Promote Bone Healing in an Ex Vivo Organotypic Bone Defect Model

Decellularized matrices offer a beneficial substitute for biomimetic scaffolds in tissue engineering. The current study examines the potential of decellularized placental vessel sleeves (PVS) as a periosteal protective sleeve to enhance bone regeneration in embryonic day 18 chick femurs contained within the PVS and cultured organotypically over a 10 day period. The femurs are inserted into decellularized biocompatibility-tested PVS and maintained in an organotypic culture for a period of 10 days. In femurs containing decellularized PVS, a significant increase in bone volume (p < 0.001) is evident, demonstrated by microcomputed tomography (µCT) compared to femurs without PVS. Histological and immunohistological analyses reveal extensive integration of decellularized PVS with the bone periosteum, and enhanced conservation of bone architecture within the PVS. In addition, the expressions of hypoxia inducible factor-1 alpha (HIF-1α), type II collagen (COL-II), and proteoglycans are observed, indicating a possible repair mechanism via a cartilaginous stage of the bone tissue within the sleeve. The use of decellularized matrices like PVS offers a promising therapeutic strategy in surgical tissue replacement, promoting biocompatibility and architecture of the tissue as well as a factor-rich niche environment with negligible immunogenicity.

The Research of Acellular Pancreatic Bioscaffold as a Natural 3-Dimensional Platform In Vitro

OBJECTIVE

The aim of the study was to investigate the biochemical and functional properties of a rat acellular pancreatic bioscaffolds (APBs).

METHODS

Fresh pancreata from 10 rats were soaked and perfused through portal veins using Easy-Load Digital Drive peristaltic pumps. The histological structure, extracellular matrix composition, and the DNA content of the APBs were evaluated. Biocompatibility studies had also been performed. The proliferation and differentiation of AR42J pancreatic acinar cells were assessed.

RESULTS

The pancreatic tissue became translucent after decellularization. There were no visible vascular endothelial cells, cellular components, or cracked cellular debris. The extracellular matrix components were not decreased after decellularization (P > 0.05); however, the DNA content was decreased significantly (P < 0.05). The subcutaneous implantation sites showed low immunological response and low cytotoxicity around the APB. The proliferation rate was higher and the apoptosis rate was lower when AR42J cells were cultured on APB (P < 0.05). The gene expression and the protein expression were higher for the APB group (P < 0.001).

CONCLUSIONS

Our findings support the biological utility of whole pancreas APBs as biomaterial scaffolds, which provides an improved approach for regenerative medicine.

Decellularized matrices in regenerative medicine

Of all biologic matrices, decellularized extracellular matrix (dECM) has emerged as a promising tool used either alone or when combined with other biologics in the fields of tissue engineering or regenerative medicine - both preclinically and clinically. dECM provides a native cellular environment that combines its unique composition and architecture. It can be widely obtained from native organs of different species after being decellularized and is entitled to provide necessary cues to cells homing. In this review, the superiority of the macro- and micro-architecture of dECM is described as are methods by which these unique characteristics are being harnessed to aid in the repair and regeneration of organs and tissues. Finally, an overview of the state of research regarding the clinical use of different matrices and the common challenges faced in using dECM are provided, with possible solutions to help translate naturally derived dECM matrices into more robust clinical use.

STATEMENT OF SIGNIFICANCE

Ideal scaffolds mimic nature and provide an environment recognized by cells as proper. Biologically derived matrices can provide biological cues, such as sites for cell adhesion, in addition to the mechanical support provided by synthetic matrices. Decellularized extracellular matrix is the closest scaffold to nature, combining unique micro- and macro-architectural characteristics with an equally unique complex composition. The decellularization process preserves structural integrity, ensuring an intact vasculature. As this multifunctional structure can also induce cell differentiation and maturation, it could become the gold standard for scaffolds.

Bioengineered lungs generated from human iPSCs-derived epithelial cells on native extracellular matrix

The development of an alternative source for donor lungs would change the paradigm of lung transplantation. Recent studies have demonstrated the potential feasibility of using decellularized lungs as scaffolds for lung tissue regeneration and subsequent implantation. However, finding a reliable cell source and the ability to scale up for recellularization of the lung scaffold still remain significant challenges. To explore the possibility of regeneration of human lung tissue from stem cells in vitro, populations of lung progenitor cells were generated from human iPSCs. To explore the feasibility of producing engineered lungs from stem cells, we repopulated decellularized human lung and rat lungs with iPSC-derived epithelial progenitor cells. The iPSCs-derived epithelial progenitor cells lined the decellularized human lung and expressed most of the epithelial markers when were cultured in a lung bioreactor system. In decellularized rat lungs, these human-derived cells attach and proliferate in a manner similar to what was observed in the decellularized human lung. Our results suggest that repopulation of lung matrix with iPSC-derived lung epithelial cells may be a viable strategy for human lung regeneration and represents an important early step toward translation of this technology.

Preparation of Decellularized Lung Matrices for Cell Culture and Protein Analysis

The limited available treatment options for patients with chronic lung diseases, such as fibrosis, lead to poor prognosis after diagnosis and short survival rates. An exciting new bioengineering approach utilizes de- and recellularization of lung tissue to potentially overcome donor organ shortage and immune reactions toward the received transplant. The goal of decellularization is to create a scaffold which contains the necessary framework for stability and functionality for regenerating lung tissue while removing immunomodulatory factors by removal of cells. After decellularization, the scaffold could be re-functionalized by repopulation with the patient's own stem/progenitor cells to create a fully functional organ or can be used as ex vivo models of disease. In this chapter the decellularization of lung tissue from multiple species (i.e., rodents, pigs, and humans) as well as disease states such as fibrosis is described. We discuss and describe the various quality control measures which should be used to characterize decellularized scaffolds, methods for protein analysis of the remaining scaffold, and methods for recellularization of scaffolds.

Lung regeneration: steps toward clinical implementation and use

PURPOSE OF REVIEW

Whole lung tissue engineering is a relatively new area of investigation. In a short time, however, the field has advanced quickly beyond proof of concept studies in rodents and now stands on the cusp of wide-spread scale up to large animal studies. Therefore, this technology is ever closer to being directly clinically relevant.

RECENT FINDINGS

The main themes in the literature include refinement of the fundamental components of whole lung engineering and increasing effort to direct induced pluripotent stem cells and lung progenitor cells toward use in lung regeneration. There is also increasing need for and emphasis on functional evaluation in the lab and in vivo, and the use of all of these tools to construct and evaluate forthcoming clinically scaled engineered lung.

SUMMARY

Ultimately, the goal of the research described herein is to create a useful clinical product. In the intermediate time, however, the tools described here may be employed to advance our knowledge of lung biology and the organ-specific regenerative capacity of lung stem and progenitor cells.

Vascularization of three-dimensional engineered tissues for regenerative medicine applications

Engineering of three-dimensional (3D) tissues is a promising approach for restoring diseased or dysfunctional myocardium with a functional replacement. However, a major bottleneck in this field is the lack of efficient vascularization strategies, because tissue constructs produced in vitro require a constant flow of oxygen and nutrients to maintain viability and functionality. Compared to angiogenic cell therapy and growth factor treatment, bioengineering approaches such as spatial micropatterning, integration of sacrificial materials, tissue decellularization, and 3D bioprinting enable the generation of more precisely controllable neovessel formation. In this review, we summarize the state-of-the-art approaches to develop 3D tissue engineered constructs with vasculature, and demonstrate how some of these techniques have been applied towards regenerative medicine for treatment of heart failure.

STATEMENT OF SIGNIFICANCE

Tissue engineering is a promising approach to replace or restore dysfunctional tissues/organs, but a major bottleneck in realizing its potential is the challenge of creating scalable 3D tissues. Since most 3D engineered tissues require a constant supply of nutrients, it is necessary to integrate functional vasculature within the tissues in order to facilitate the transport of nutrients. To address these needs, researchers are employing biomaterial engineering and design strategies to foster vessel formation within 3D tissues. This review highlights the state-of-the-art bioengineering tools and technologies to create vascularized 3D tissues for clinical applications in regenerative medicine, highlighting the application of these technologies to engineer vascularized cardiac patches for treatment of heart failure.