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

The trend of allogeneic tendon decellularization: literature review

Tendon injuries repair is a significant burden for orthopaedic surgeons. Finding a proper graft material to repair tendon is one of the main challenges in orthopaedics, for which the requirement of substitute for tendon repair would be different for each clinical application. Among biological scaffolds, the use of decellularized tendon increasingly represents an interesting approach to treat tendon injuries and several articles have investigated the approaches of tendon decellularization. To understand the outcomes of the the approaches of tendon decellularization on effect of tendon transplantation, a literature review was performed. This review was conducted by searching in Pubmed and Embase and 64 studies were included in this study. The findings revealed that the common approaches to decellularize tendon include chemical, physical, and enzymatic decellularization methods or their combination. With the development of tissue engineering, researchers also put forward new theories such as automatic acellular machine, 3D printing technology to manufacture acellular scaffold.

Bioengineering and Clinical Translation of Human Lung and its Components

Clinical lung transplantation has rapidly established itself as the gold standard of treatment for end-stage lung diseases in a restricted group of patients since the first successful lung transplant occurred. Although significant progress has been made in lung transplantation, there are still numerous obstacles on the path to clinical success. The development of bioartificial lung grafts using patient-derived cells may serve as an alternative treatment modality; however, challenges include developing appropriate scaffold materials, advanced culture strategies for lung-specific multiple cell populations, and fully matured constructs to ensure increased transplant lifetime following implantation. This review highlights the development of tissue-engineered tracheal and lung equivalents over the past two decades, key problems in lung transplantation in a clinical environment, the advancements made in scaffolds, bioprinting technologies, bioreactors, organoids, and organ-on-a-chip technologies. The review aims to fill the lacuna in existing literature toward a holistic bioartificial lung tissue, including trachea, capillaries, airways, bifurcating bronchioles, lung disease models, and their clinical translation. Herein, the efforts are on bridging the application of lung tissue engineering methods in a clinical environment as it is thought that tissue engineering holds enormous promise for overcoming the challenges associated with the clinical translation of bioengineered human lung and its components.

Development and evaluation of a novel combined perfusion decellularization heart-lung model for tissue engineering of bioartificial heart-lung scaffolds

BACKGROUND

Bioengineered transplantable heart-lung scaffolds could be potentially lifesaving in a large number of congenital and acquired cardiothoracic disorders including terminal heart-lung disease.

METHODS

We decellularized heart-lung organ-blocks from rats (n = 10) by coronary and tracheal perfusion with ionic detergents in a modified Langendorff circuit.

RESULTS

In the present project, we were able to achieve complete decellularization of the heart-lung organ-block. Decellularized heart-lung organ-blocks lacked intracellular components but maintained structure of the cellular walls with collagen and elastic fibers.

CONCLUSIONS

We present a novel model of combined perfusion and decellularization of heart-lung organ-blocks. This model is the first step on the pathway to creating bioengineered transplantable heart-lung scaffolds. We believe that further development of this technology could provide a life-saving conduit, significantly reducing the risks of heart-lung failure surgery and improving postoperative quality of life.

Functional acellular matrix for tissue repair

In view of their low immunogenicity, biomimetic internal environment, tissue- and organ-like physicochemical properties, and functionalization potential, decellularized extracellular matrix (dECM) materials attract considerable attention and are widely used in tissue engineering. This review describes the composition of extracellular matrices and their role in stem-cell differentiation, discusses the advantages and disadvantages of existing decellularization techniques, and presents methods for the functionalization and characterization of decellularized scaffolds. In addition, we discuss progress in the use of dECMs for cartilage, skin, nerve, and muscle repair and the transplantation or regeneration of different whole organs (e.g., kidneys, liver, uterus, lungs, and heart), summarize the shortcomings of using dECMs for tissue and organ repair after refunctionalization, and examine the corresponding future prospects. Thus, the present review helps to further systematize the application of functionalized dECMs in tissue/organ transplantation and keep researchers up to date on recent progress in dECM usage.

Bioactive Cell-Derived ECM Scaffold Forms a Unique Cellular Microenvironment for Lung Tissue Engineering

Chronic lung diseases are one of the leading causes of death worldwide. Lung transplantation is currently the only causal therapeutic for lung diseases, which is restricted to end-stage disease and limited by low access to donor lungs. Lung tissue engineering (LTE) is a promising approach to regenerating a replacement for at least a part of the damaged lung tissue. Currently, lung regeneration is limited to a simplified local level (e.g., alveolar−capillary barrier) due to the sophisticated and complex structure and physiology of the lung. Here, we introduce an extracellular matrix (ECM)-integrated scaffold using a cellularization−decellularization−recellularization technique. This ECM-integrated scaffold was developed on our artificial co-polymeric BETA (biphasic elastic thin for air−liquid interface cell culture conditions) scaffold, which were initially populated with human lung fibroblasts (IMR90 cell line), as the main generator of ECM proteins. Due to the interconnected porous structure of the thin (<5 µm) BETA scaffold, the cells can grow on and infiltrate into the scaffold and deposit their own ECM. After a mild decellularization procedure, the ECM proteins remained on the scaffold, which now closely mimicked the cellular microenvironment of pulmonary cells more realistically than the plain artificial scaffolds. We assessed several decellularization methods and found that 20 mM NH4OH and 0.1% Triton X100 with subsequent DNase treatment completely removed the fibroblasts (from the first cellularization) and maintains collagen I and IV as the key ECM proteins on the scaffold. We also showed the repopulation of the primary fibroblast from human (without chronic lung disease (non-CLD) donors) and human bronchial epithelial (16HBE14o−) cells on the ECM-integrated BETA scaffold. With this technique, we developed a biomimetic scaffold that can mimic both the physico-mechanical properties and the native microenvironment of the lung ECM. The results indicate the potential of the presented bioactive scaffold for LTE application.

Fabrication of vitamin K3-carnosine peptide-loaded spun silk fibroin fibers/collagen bi-layered architecture for bronchopleural fistula tissue repair and regeneration applications

Bronchial and pleural injuries with persistent air leak pose a threat in the repair and regeneration of pulmonary diseases. The need to arrive at a highly efficient therapy for closure of bronchopleural fistula (BPF) so as to effectively suppress inflammation, infection and repair the damaged pleural space caused by cancer as well as contractile restoration of bronchopleural scars remain a significant clinical challenge. Herein, we have designed and developed potent bioactive vitamin K3 carnosine peptide (VKC)-loaded spun SF fibroin fibers/collagen bi-layered 3D scaffold for bronchopleural fistula tissue engineering applications. The VKC drug showed excellent cell viability in human bronchial epithelial cells (HBECs), in addition to its pronounced higher cytotoxicity against the A549 lung cancer cell line with an IC₅₀ of 5 μg/mL. Furthermore, VKC displayed a strong affinity with the catalytic site of EGFR (PDB ID: 1M17) and VEGFR2 (PDB ID: 4AGD, 4ASD) receptors in molecular docking studies. Following which the spun SF-VKC (primary layer) and collagen film (top layer) constructed bi-layered CSVKC were structurally elucidated and its morphological, physicochemical and biological characterizations were well examined. The bi-layered scaffold showed superior biocompatibility and cell migration ability in HBECs than other scaffolds. Interestingly, the CSVKC revealed rapid HBECs motility towards scratched regions for fast healing in vitro bronchial tissue engineering. In vivo biocompatibility and angiogenesis studies of the prepared scaffolds were evaluated and the results obtained demonstrated excellent new tissue formation and neovascularization in the bi-layered architecture rather than others. Therefore, our results suggest that the potent antibacterial and anticancer therapeutic agent (VKC)-impregnated silk fibroin fibers/collagen bi-layered 3D biomaterial could be useful in treating cancerous BPF and pulmonary diseases in future.

Decellularized extracellular matrix scaffolds: Recent trends and emerging strategies in tissue engineering

The application of scaffolding materials is believed to hold enormous potential for tissue regeneration. Despite the widespread application and rapid advance of several tissue-engineered scaffolds such as natural and synthetic polymer-based scaffolds, they have limited repair capacity due to the difficulties in overcoming the immunogenicity, simulating in-vivo microenvironment, and performing mechanical or biochemical properties similar to native organs/tissues. Fortunately, the emergence of decellularized extracellular matrix (dECM) scaffolds provides an attractive way to overcome these hurdles, which mimic an optimal non-immune environment with native three-dimensional structures and various bioactive components. The consequent cell-seeded construct based on dECM scaffolds, especially stem cell-recellularized construct, is considered an ideal choice for regenerating functional organs/tissues. Herein, we review recent developments in dECM scaffolds and put forward perspectives accordingly, with particular focus on the concept and fabrication of decellularized scaffolds, as well as the application of decellularized scaffolds and their combinations with stem cells (recellularized scaffolds) in tissue engineering, including skin, bone, nerve, heart, along with lung, liver and kidney.

Placental tissue stem cells and their role in neonatal diseases

Neonatal diseases such as hypoxic ischemic encephalopathy, diseases of prematurity and congenital disorders carry increased morbidity and mortality. Despite technological advancements, their incidence remains largely unabated. Stem cell (SC) interventions are novel therapies in the neonatal world. In pre-clinical models of neonatal diseases, SC applications have shown encouraging results. SC sources vary, with the bone marrow being the most utilized. However, the ability to harvest bone marrow SCs from neonates is limited. Placental-tissue derived SCs (PTSCs), provide an alternative and highly attractive source. Human placentas, the cornerstone of fetal survival, are abundant with such cells. Comparing to adult pools, PTSCs exhibit increased potency, decreased immunogenicity and stronger anti-inflammatory effects. Several types of PTSCs have been identified, with mesenchymal stem cells being the most utilized population. This review will focus on PTSCs and their pre-clinical and clinical applications in neonatology.

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.

Elastin in healthy and diseased lung

Elastic fibers are an essential part of the pulmonary extracellular matrix (ECM). Intact elastin is required for normal function and its damage contributes profoundly to the etiology and pathology of lung disease. This highlights the need for novel lung-specific imaging methodology that enables high-resolution 3D visualization of the ECM. We consider elastin's involvement in chronic respiratory disease and examine recent methods for imaging and modeling of the lung in the context of advances in lung tissue engineering for research and clinical application.

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.

Xenogeneic stem cell transplantation: Research progress and clinical prospects

Organ transplantation is the ultimate treatment for end-stage diseases such as heart and liver failure. However, the severe shortage of donor organs has limited the organ transplantation progress. Xenogeneic stem cell transplantation provides a new strategy to solve this problem. Researchers have shown that xenogeneic stem cell transplantation has significant therapeutic effects and broad application prospects in treating liver failure, myocardial infarction, advanced type 1 diabetes mellitus, myelosuppression, and other end-stage diseases by replacing the dysfunctional cells directly or improving the endogenous regenerative milieu. In this review, the sources, problems and solutions, and potential clinical applications of xenogeneic stem cell transplantation will be discussed.

Building three-dimensional lung models for studying pharmacokinetics of inhaled drugs

Drug development is a critical step in the development pipeline of pharmaceutical industry, commonly performed in traditional cell culture and animal models. Though, those models hold critical gapsin the prediction and the translation of human pharmacokinetic (PK) and pharmacodynamics (PD) parameters. The advances in tissue engineering have allowed the combination of cell biology with microengineering techniques, offering alternatives to conventional preclinical models. Organ-on-a-chips and three-dimensional (3D) bioprinting models present the potentialityof simulating the physiological and pathological microenvironment of living organs and tissues, constituting this way,more realistic models for the assessment of absorption, distribution, metabolism and excretion (ADME) of drugs. Therefore, this review will focus on lung-on-a-chip and 3D bioprinting techniques for developing lung models that can be usedfor predicting PK/PD parameters.

Standardization of Microcomputed Tomography for Tracheal Tissue Engineering Analysis

Tracheal tissue engineering has become an active area of interest among clinical and scientific communities; however, methods to evaluate success of in vivo tissue-engineered solutions remain primarily qualitative. These evaluation methods have generally relied on the use of photographs to qualitatively demonstrate tracheal patency, endoscopy to image healing over time, and histology to determine the quality of the regenerated extracellular matrix. Although those generally qualitative methods are valuable, they alone may be insufficient. Therefore, to quantitatively assess tracheal regeneration, we recommend the inclusion of microcomputed tomography (μCT) to quantify tracheal patency as a standard outcome analysis. To establish a standard of practice for quantitative μCT assessment for tracheal tissue engineering, we recommend selecting a constant length to quantify airway volume. Dividing airway volumes by a constant length provides an average cross-sectional area for comparing groups. We caution against selecting a length that is unjustifiably large, which may result in artificially inflating the average cross-sectional area and thereby diminishing the ability to detect actual differences between a test group and a healthy control. Therefore, we recommend selecting a length for μCT assessment that corresponds to the length of the defect region. We further recommend quantifying the minimum cross-sectional area, which does not depend on the length, but has functional implications for breathing. We present empirical data to elucidate the rationale for these recommendations. These empirical data may at first glance appear as expected and unsurprising. However, these standard methods for performing μCT and presentation of results do not yet exist in the literature, and are necessary to improve reporting within the field. Quantitative analyses will better enable comparisons between future publications within the tracheal tissue engineering community and empower a more rigorous assessment of results. Impact statement The current study argues for the standardization of microcomputed tomography (μCT) as a quantitative method for evaluating tracheal tissue-engineered solutions in vivo or ex vivo. The field of tracheal tissue engineering has generally relied on the use of qualitative methods for determining tracheal patency. A standardized quantitative evaluation method currently does not exist. The standardization of μCT for evaluation of in vivo studies would enable a more robust characterization and allow comparisons between groups within the field. The impact of standardized methods within the tracheal tissue engineering field as presented in the current study would greatly improve the quality of published work.