Current achievements and future perspectives in whole-organ bioengineering

Recent Advances in Liver Tissue Engineering as an Alternative and Complementary Approach for Liver Transplantation

Acute and chronic liver diseases cause significant morbidity and mortality worldwide, affecting millions of people. Liver transplantation is the primary intervention method, replacing a non-functional liver with a functional one. However, the field of liver transplantation faces challenges such as donor shortage, postoperative complications, immune rejection, and ethical problems. Consequently, there is an urgent need for alternative therapies that can complement traditional transplantation or serve as an alternative method. In this review, we explore the potential of liver tissue engineering as a supplementary approach to liver transplantation, offering benefits to patients with severe liver dysfunctions.

Vascular reconstruction of the decellularized biomatrix for whole-organ engineering-a critical perspective and future strategies

Whole-organ re-engineering is the most challenging goal yet to be achieved in tissue engineering and regenerative medicine. One essential factor in any transplantable and functional tissue engineering is fabricating a perfusable vascular network with macro- and micro-sized blood vessels. Whole-organ development has become more practical with the use of the decellularized organ biomatrix (DOB) as it provides a native biochemical and structural framework for a particular organ. However, reconstructing vasculature and re-endothelialization in the DOB is a highly challenging task and has not been achieved for constructing a clinically transplantable vascularized organ with an efficient perfusable capability. Here, we critically and articulately emphasized factors that have been studied for the vascular reconstruction in the DOB. Furthermore, we highlighted the factors used for vasculature development studies in general and their application in whole-organ vascular reconstruction. We also analyzed in detail the strategies explored so far for vascular reconstruction and angiogenesis in the DOB for functional and perfusable vasculature development. Finally, we discussed some of the crucial factors that have been largely ignored in the vascular reconstruction of the DOB and the future directions that should be addressed systematically.

Cell transplantation-based regenerative medicine in liver diseases

This review aims to evaluate the current preclinical state of liver bioengineering, the clinical context for liver cell therapies, the cell sources, the delivery routes, and the results of clinical trials for end-stage liver disease. Different clinical settings, such as inborn errors of metabolism, acute liver failure, chronic liver disease, liver cirrhosis, and acute-on-chronic liver failure, as well as multiple cellular sources were analyzed; namely, hepatocytes, hepatic progenitor cells, biliary tree stem/progenitor cells, mesenchymal stromal cells, and macrophages. The highly heterogeneous clinical scenario of liver disease and the availability of multiple cellular sources endowed with different biological properties make this a multidisciplinary translational research challenge. Data on each individual liver disease and more accurate endpoints are urgently needed, together with a characterization of the regenerative pathways leading to potential therapeutic benefit. Here, we critically review these topics and identify related research needs and perspectives in preclinical and clinical settings.

Decellularized Extracellular Matrix: The Role of This Complex Biomaterial in Regeneration

Organ transplantation is understood as a technique where an organ from a donor patient is transferred to a recipient patient. This practice gained strength in the 20th century and ensured advances in areas of knowledge such as immunology and tissue engineering. The main problems that comprise the practice of transplants involve the demand for viable organs and immunological aspects related to organ rejection. In this review, we address advances in tissue engineering for reversing the current challenges of transplants, focusing on the possible use of decellularized tissues in tissue engineering. We address the interaction of acellular tissues with immune cells, especially macrophages and stem cells, due to their potential use in regenerative medicine. Our goal is to exhibit data that demonstrate the use of decellularized tissues as alternative biomaterials that can be applied clinically as partial or complete organ substitutes.

iPSC-derived cells lack immune tolerance to autologous NK-cells due to imbalance in ligands for activating and inhibitory NK-cell receptors

BACKGROUND

Dozens of transplants generated from pluripotent stem cells are currently in clinical trials. The creation of patient-specific iPSCs makes personalized therapy possible due to their main advantage of immunotolerance. However, some reports have claimed recently that aberrant gene expression followed by proteome alterations and neoantigen formation can result in iPSCs recognition by autologous T-cells. Meanwhile, the possibility of NK-cell activation has not been previously considered. This study focused on the comparison of autologous and allogeneic immune response to iPSC-derived cells and isogeneic parental somatic cells used for reprogramming.

METHODS

We established an isogeneic cell model consisting of parental dermal fibroblasts, fibroblast-like iPSC-derivatives (iPS-fibro) and iPS-fibro lacking beta-2-microglobulin (B2M). Using the cells obtained from two patients, we analyzed the activation of autologous and allogeneic T-lymphocytes and NK-cells co-cultured with target cells.

RESULTS

Here we report that cells differentiated from iPSCs can be recognized by NK-cells rather than by autologous T-cells. We observed that iPS-fibro elicited a high level of NK-cell degranulation and cytotoxicity, while isogeneic parental skin fibroblasts used to obtain iPSCs barely triggered an NK-cell response. iPSC-derivatives with B2M knockout did not cause an additional increase in NK-cell activation, although they were devoid of HLA-I, the major inhibitory molecules for NK-cells. Transcriptome analysis revealed a significant imbalance of ligands for activating and inhibitory NK-cell receptors in iPS-fibro. Compared to parental fibroblasts, iPSC-derivatives had a reduced expression of HLA-I simultaneously with an increased gene expression of major activating ligands, such as MICA, NECTIN2, and PVR. The lack of inhibitory signals might be due to insufficient maturity of cells differentiated from iPSCs. In addition, we showed that pretreatment of iPS-fibro with proinflammatory cytokine IFNγ restored the ligand imbalance, thereby reducing the degranulation and cytotoxicity of NK-cells.

CONCLUSION

In summary, we showed that iPSC-derived cells can be sensitive to the cytotoxic potential of autologous NK-cells regardless of HLA-I status. Thus, the balance of ligands for NK-cell receptors should be considered prior to iPSC-based cell therapies. Trial registration Not applicable.

Tissue engineering of decellularized pancreas scaffolds for regenerative medicine in diabetes

Diabetes mellitus is a global disease requiring long-term treatment and monitoring. At present, pancreas or islet transplantation is the only reliable treatment for achieving stable euglycemia in Type I diabetes patients. However, the shortage of viable pancreata for transplantation limits the use of this therapy for the majority of patients. Organ decellularization and recellularization is emerging as a promising solution to overcome the shortage of viable organs for transplantation by providing a potential alternative source of donor organs. Several studies on decellularization and recellularization of rodent, porcine, and human pancreata have been performed, and show promise for generating usable decellularized pancreas scaffolds for subsequent recellularization and transplantation. In this state-of-the-art review, we provide an overview of the latest advances in pancreas decellularization, recellularization, and revascularization. We also discuss clinical considerations such as potential transplantation sites, donor source, and immune considerations. We conclude with an outlook on the remaining work that needs to be done in order to realize the goal of using this technology to create bioengineered pancreata for transplantation in diabetes patients. STATEMENT OF SIGNIFICANCE: Pancreas or islet transplantation is a means of providing insulin-independence in diabetes patients. However, due to the shortage of viable pancreata, whole-organ decellularization and recellularization is emerging as a promising solution to overcome organ shortage for transplantation. Several studies on decellularization and recellularization of rodent, porcine, and human pancreata have shown promise for generating usable decellularized pancreas scaffolds for subsequent recellularization and transplantation. In this state-of-the-art review, we highlight the latest advances in pancreas decellularization, recellularization, and revascularization. We also discuss clinical considerations such as potential transplantation sites, donor source, and immune considerations. We conclude with future work that needs to be done in order to realize clinical translation of bioengineered pancreata for transplantation in diabetes patients.

Advances in Recellularization of Decellularized Liver Grafts with Different Liver (Stem) Cells: Towards Clinical Applications

Liver transplantation is currently the only curative therapy for patients with acute or chronic liver failure. However, a dramatic gap between the number of available liver grafts and the number of patients on the transplantation waiting list emphasizes the need for valid liver substitutes. Whole-organ engineering is an emerging field of tissue engineering and regenerative medicine. It aims to generate transplantable and functional organs to support patients on transplantation waiting lists until a graft becomes available. It comprises two base technologies developed in the last decade; (1) organ decellularization to generate a three-dimensional (3D) extracellular matrix scaffold of an organ, and (2) scaffold recellularization to repopulate both the parenchymal and vascular compartments of a decellularized organ. In this review article, recent advancements in both technologies, in relation to liver whole-organ engineering, are presented. We address the potential sources of hepatocytes and non-parenchymal liver cells for repopulation studies, and the role of stem-cell-derived liver progeny is discussed. In addition, different cell seeding strategies, possible graft modifications, and methods used to evaluate the functionality of recellularized liver grafts are outlined. Based on the knowledge gathered from recent transplantation studies, future directions are summarized.

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.

Lung organoids: current strategies for generation and transplantation

Lung diseases occupy a leading position in human morbidity and are the third leading cause of death. Often the chronic forms of these diseases do not respond to therapy, so that lung transplantation is the only treatment option. The development of cellular and biotechnologies offers a new solution-the use of lung organoids for transplantation in such patients. Here, we review types of lung organoids, methods of their production and characterization, and experimental works on transplantation in vivo. These results show the promise of work in this direction. Despite the current problems associated with a low degree of cell engraftment, immune response, and insufficient differentiation, we are confident that organoid transplantation will find it is clinical application.

Impact of Porcine Pancreas Decellularization Conditions on the Quality of Obtained dECM

Due to the limited number of organ donors, 3D printing of organs is a promising technique. Tissue engineering is increasingly using xenogeneic material for this purpose. This study was aimed at assessing the safety of decellularized porcine pancreas, together with the analysis of the risk of an undesirable immune response. We tested eight variants of the decellularization process. We determined the following impacts: rinsing agents (PBS/NH₃·H₂O), temperature conditions (4 °C/24 °C), and the grinding method of native material (ground/cut). To assess the quality of the extracellular matrix after the completed decellularization process, analyses of the following were performed: DNA concentration, fat content, microscopic evaluation, proteolysis, material cytotoxicity, and most importantly, the Triton X-100 content. Our analyses showed that we obtained a product with an extremely low detergent content with negligible residual DNA content. The obtained results confirmed the performed histological and immuno-fluorescence staining. Moreover, the TEM microscopic analysis proved that the correct collagen structure was preserved after the decellularization process. Based on the obtained results, we chose the most favorable variant in terms of quality and biology. The method we chose is an effective and safe method that gives a chance for the development of transplant and regenerative medicine.

Liver bioengineering: Recent trends/advances in decellularization and cell sheet technologies towards translation into the clinic

Development of novel technologies provides the best tissue constructs engineering and maximizes their therapeutic effects in regenerative therapy, especially for liver dysfunctions. Among the currently investigated approaches of tissue engineering, scaffold-based and scaffold-free tissues are widely suggested for liver regeneration. Analogs of liver acellular extracellular matrix (ECM) are utilized in native scaffolds to increase the self-repair and healing ability of organs. Native ECM analog could improve liver repairing through providing the supportive framework for cells and signaling molecules, exerting normal biomechanical, biochemical, and physiological signal complexes. Recently, innovative cell sheet technology is introduced as an alternative for conventional tissue engineering with the advantage of fewer scaffold restrictions and cell culture on a Thermo-Responsive Polymer Surface. These sheets release the layered cells through a temperature-controlled procedure without enzymatic digestion, while preserving the cell-ECM contacts and adhesive molecules on cell-cell junctions. In addition, several novelties have been introduced into the cell sheet and decellularization technologies to aid cell growth, instruct differentiation/angiogenesis, and promote cell migration. In this review, recent trends, advancements, and issues linked to translation into clinical practice are dissected and compared regarding the decellularization and cell sheet technologies for liver tissue engineering.

Whole Heart Engineering: Advances and Challenges

Bioengineering a solid organ for organ replacement is a growing endeavor in regenerative medicine. Our approach - recellularization of a decellularized cadaveric organ scaffold with human cells - is currently the most promising approach to building a complex solid vascularized organ to be utilized in vivo, which remains the major unmet need and a key challenge. The 2008 publication of perfusion-based decellularization and partial recellularization of a rat heart revolutionized the tissue engineering field by showing that it was feasible to rebuild an organ using a decellularized extracellular matrix scaffold. Toward the goal of clinical translation of bioengineered tissues and organs, there is increasing recognition of the underlying need to better integrate basic science domains and industry. From the perspective of a research group focusing on whole heart engineering, we discuss the current approaches and advances in whole organ engineering research as they relate to this multidisciplinary field's 3 major pillars: organ scaffolds, large numbers of cells, and biomimetic bioreactor systems. The success of whole organ engineering will require optimization of protocols to produce biologically-active scaffolds for multiple organ systems, and further technological innovation both to produce the massive quantities of high-quality cells needed for recellularization and to engineer a bioreactor with physiologic stimuli to recapitulate organ function. Also discussed are the challenges to building an implantable vascularized solid organ.

Decellularization Methods of Uterus in Tissue Engineering

A new field of investigation which aims to design tissues and organs similar to their native origin has been developed recently, named as regenerative medicine (tissue engineering and bio-engineering). Uterus is the main organ for regeneration and contributes in the fertility. At an ultimate level, the uterus plays a role in embryo implantation, sperm migration and fetal nutrition. Uterine congenital anomalies, attained uterine lesions and immune system disorders may affect such uterine functions preventing successful pregnancy. Due to following reasons, it is essential to consider regenerative medicine as a new approach for the treatment of uterine dysfunctions to overcome the failures that cannot be treated with clinical medication.

Transparent PDMS Bioreactors for the Fabrication and Analysis of Multi-Layer Pre-vascularized Hydrogels Under Continuous Perfusion

Tissue engineering in combination with stem cell technology has the potential to revolutionize human healthcare. It aims at the generation of artificial tissues that can mimic the original with complex functions for medical applications. However, even the best current designs are limited in size, if the transport of nutrients and oxygen to the cells and the removal of cellular metabolites waste is mainly dependent on passive diffusion. Incorporation of functional biomimetic vasculature within tissue engineered constructs can overcome this shortcoming. Here, we developed a novel strategy using 3D printing and injection molding technology to customize multilayer hydrogel constructs with pre-vascularized structures in transparent Polydimethysiloxane (PDMS) bioreactors. These bioreactors can be directly connected to continuous perfusion systems without complicated construct assembling. Mimicking natural layer-structures of vascular walls, multilayer vessel constructs were fabricated with cell-laden fibrin and collagen gels, respectively. The multilayer design allows functional organization of multiple cell types, i.e., mesenchymal stem cells (MSCs) in outer layer, human umbilical vein endothelial cells (HUVECs) the inner layer and smooth muscle cells in between MSCs and HUVECs layers. Multiplex layers with different cell types showed clear boundaries and growth along the hydrogel layers. This work demonstrates a rapid, cost-effective, and practical method to fabricate customized 3D-multilayer vascular models. It allows precise design of parameters like length, thickness, diameter of lumens and the whole vessel constructs resembling the natural tissue in detail without the need of sophisticated skills or equipment. The ready-to-use bioreactor with hydrogel constructs could be used for biomedical applications including pre-vascularization for transplantable engineered tissue or studies of vascular biology.

Protocols for the preparation and characterization of decellularized tissue and organ scaffolds for tissue engineering

Extracellular matrix (ECM) scaffolds are extensively used in tissue engineering studies and numerous clinical applications for tissue and organ reconstructions. Due to the global severe shortage of human tissues and organs, xenogeneic biomaterials are a common source for human tissue engineering and regenerative medicine applications. Traditional methods for decellularization often disrupt the 3D architecture and damage the structural integrity of the ECM scaffold. To efficiently obtain natural ECM scaffolds from animal tissues and organs with intact architecture, we have developed a platform decellularization process using supercritical CO₂ and tested its potential application in tissue engineering. A combination of human mesenchymal stem cells with a decellularized dermal matrix scaffold allowed complete regeneration of skin structure in a porcine full-thickness wound model.

Recognized trophoblast-like cells conversion from human embryonic stem cells by BMP4 based on convolutional neural network

The use of models of stem cell differentiation to trophoblastic cells provides an effective perspective for understanding the early molecular events in the establishment and maintenance of human pregnancy. In combination with the newly developed deep learning technology, the automated identification of this process can greatly accelerate the contribution to relevant knowledge. Based on the transfer learning technique, we used a convolutional neural network to distinguish the microscopic images of Embryonic stem cells (ESCs) from differentiated trophoblast -like cells (TBL). To tackle the problem of insufficient training data, the strategies of data augmentation were used. The results showed that the convolutional neural network could successfully recognize trophoblast cells and stem cells automatically, but could not distinguish TBL from the immortalized trophoblast cell lines in vitro (JEG-3 and HTR8-SVneo). We compare the recognition effect of the commonly used convolutional neural network, including DenseNet, VGG16, VGG19, InceptionV3, and Xception. This study extends the deep learning technique to trophoblast cell phenotype classification and paves the way for automatic bright-field microscopic image analysis of trophoblast cells in the future.

Refunctionalization of Decellularized Organ Scaffold of Pancreas by Recellularization: Whole Organ Regeneration into Functional Pancreas

BACKGROUND

Tissue engineering centers on creating a niche similar to the natural one, with a purpose of developing an organ construct. A natural scaffold can replace none while creating a scaffold unique to each tissue in composition, architecture and cues that regulate the character of cells.

METHODS

Whole pancreas from mouse was decellularized using detergent and enzymes, followed by recellularizing with MSC from human placenta. This construct was transplanted in streptozotocin induced diabetic mice. Histopathology of both decellularized and recellularized transplanted pancreas and qPCR analysis were performed to assess its recovery.

RESULTS

Decellularization removes the cells leaving behind extracellular matrix rich natural scaffold. After reseeding with mesenchymal stem cells, these cells differentiate into pancreas specific cells. Upon transplantation in streptozotocin induced diabetic mice, this organ was capable of restoring its histomorphology and functioning. Restoration of endocrine (islets), the exocrine region (acinar) and vascular network was seen in transplanted pancreas. The process of functional recovery of endocrine system took about 20 days when the mice start showing blood glucose reduction, though none achieved gluconormalization.

CONCLUSION

Natural decellularized scaffolds of soft organs can be refunctionalized using recipient's mesenchymal stem cells to restore structure and function; and counter immune problems arising during transplantation.

Advances in Pluripotent Stem Cells: History, Mechanisms, Technologies, and Applications

Over the past 20 years, and particularly in the last decade, significant developmental milestones have driven basic, translational, and clinical advances in the field of stem cell and regenerative medicine. In this article, we provide a systemic overview of the major recent discoveries in this exciting and rapidly developing field. We begin by discussing experimental advances in the generation and differentiation of pluripotent stem cells (PSCs), next moving to the maintenance of stem cells in different culture types, and finishing with a discussion of three-dimensional (3D) cell technology and future stem cell applications. Specifically, we highlight the following crucial domains: 1) sources of pluripotent cells; 2) next-generation in vivo direct reprogramming technology; 3) cell types derived from PSCs and the influence of genetic memory; 4) induction of pluripotency with genomic modifications; 5) construction of vectors with reprogramming factor combinations; 6) enhancing pluripotency with small molecules and genetic signaling pathways; 7) induction of cell reprogramming by RNA signaling; 8) induction and enhancement of pluripotency with chemicals; 9) maintenance of pluripotency and genomic stability in induced pluripotent stem cells (iPSCs); 10) feeder-free and xenon-free culture environments; 11) biomaterial applications in stem cell biology; 12) three-dimensional (3D) cell technology; 13) 3D bioprinting; 14) downstream stem cell applications; and 15) current ethical issues in stem cell and regenerative medicine. This review, encompassing the fundamental concepts of regenerative medicine, is intended to provide a comprehensive portrait of important progress in stem cell research and development. Innovative technologies and real-world applications are emphasized for readers interested in the exciting, promising, and challenging field of stem cells and those seeking guidance in planning future research direction.

Decellularization and recellularization of the ovary for bioengineering applications; studies in the mouse

BACKGROUND

Fertility preservation is particularly challenging in young women diagnosed with hematopoietic cancers, as transplantation of cryopreserved ovarian cortex in these women carries the risk for re-introducing cancer cells. Therefore, the construction of a bioengineered ovary that can accommodate isolated small follicles was proposed as an alternative to minimize the risk of malignancy transmission. Various options for viable bioengineered scaffolds have been reported in the literature. Previously, we reported three protocols for producing mouse ovarian scaffolds with the decellularization technique. The present study examined these scaffolds further, specifically with regards to their extracellular composition, biocompatibility and ability to support recellularization with mesenchymal stem cells.

MATERIAL AND METHODS

Three decellularization protocols based on 0.5% sodium dodecyl sulfate (Protocol 1; P1), or 2% sodium deoxycholate (P2), or a combination of the two detergents (P3) were applied to produce three types of scaffolds. The levels of collagen, elastin and sulfated glycosaminoglycans (sGAGs) were quantified in the remaining extracellular matrix. Detailed immunofluorescence and scanning electron microscopy imaging were conducted to assess the morphology and recellularization efficiency of the constructs after 14 days in vitro utilizing red fluorescent protein-labelled mesenchymal stem cells.

RESULTS

All protocols efficiently removed the DNA while the elastin content was not significantly reduced during the procedures. The SDS-protocol (P1) reduced the sGAG and the collagen content more than the SDC-protocol (P2). All scaffolds were biocompatible and recellularization was successful, particularly in several P2-derived scaffolds. The cells were extensively distributed throughout the constructs, with a denser distribution observed towards the ovarian cortex. The cell density was not significantly different (400 to 550 cells/mm²) between scaffold types. However, there was a tendency towards a higher cell density in the SDC-derived constructs. Scanning electron microscope images showed fibrous scaffolds with a dense repopulated surface structure.

CONCLUSIONS

While there were differences in the key structural macromolecules between protocols, all scaffolds were biocompatible and showed effective recellularization. The results indicate that our SDC-protocol might be better than our SDS-protocol. However, additional studies are necessary to determine their suitability for attachment of small follicles and folliculogenesis.

Multicentric Study to Evaluate Mexican Medical Students' Knowledge of Transplants and Organ Donation

INTRODUCTION

Transplants and organ donation are greatly aided by future medical professionals having adequate knowledge of this topic. This study aimed to elucidate the level of Mexican medical students' knowledge in the field of transplants and organ donation.

MATERIALS AND METHODS

The evaluation instrument was designed and validated. The design used simple sampling with replacement, selecting a random sample of 5 universities from among the institutional members of the Mexican Association of Departments and Schools of Medicine (Asociación Mexicana de Facultades y Escuelas de Medicina [AMFEM]). The sample was composed of 3214 medical students. Measures of central tendency were determined, and the mean scores obtained across the different universities were compared using a Kruskal-Wallis test. The odds ratio was calculated for the students whose school or department included instruction on transplants and donation within their curriculum. Kendall correlation was used for the students' academic grade level and score. All analyses considered a threshold of P < .05.

RESULTS

A questionnaire was administered to a sample of 2563 students to evaluate their knowledge of transplants and organ donation. The average score was 4.02 on a scale of 0 to 10 (standard deviation 0.03), with a 95% confidence interval (3.96-4.08). Students whose school or department taught the subject of transplants and donations within their curriculum obtained an odds ratio of 1.44 (P = .0000822).

CONCLUSIONS

The findings of this study suggest that medical students in Mexico do not have sufficient knowledge of transplants and organ donation.

Three-dimensional spheroids of mesenchymal stem/stromal cells promote osteogenesis by activating stemness and Wnt/β-catenin

Mesenchymal stem/stromal cells (MSCs) are multipotent and self-renewal cells that are widely used in regenerative medicine. The culture of three-dimensional (3D) spheroid MSCs more accurately mimics the biological microenvironment. However, it is unclear which key molecules are responsible for the cell fate control of MSCs during 3D spheroid formation and their impact on the functional characteristics of these stem cells. Furthermore, it remains unclear what effects 3D spheroid MSC transplantation has on new bone formation compared with that of 2D monolayer MSCs. We assessed whether the osteogenerative potential of 3D spheroid MSCs is greater than that of 2D monolayer MSCs in vitro. In addition, to elucidate the ability of 3D spheroid MSCs to regenerate bone, we examined the effects of transplanting wild-type (WT) or knockout (KO) spheroid MSCs on new bone formation in mice calvarial defect model in vitro. The 3D spheroid MSC culture dramatically upregulated into stemness markers compared with the 2D monolayer MSC culture. In contrast, BMP-2 significantly increased the osteogenesis-related molecules in the 3D spheroid MSCs but, in turn, downregulated the stemness markers. BMP-2 activated Smad1/5 together with Wnt/β-catenin in 3D spheroid MSCs. Transplantation of these MSCs into aged mice with calvarial defects promoted new bone formation compared with that of 2D monolayer MSCs. In contrast, transplantation of 3D or 2D β-catenin knockout MSCs induced little new bone formation. The 3D spheroid MSC culture had higher stemness compared with the 2D monolayer MSC culture. The culture of 3D spheroid MSCs rapidly promoted osteoblastogenesis and bone formation through synergistic activation of the Wnt/β-catenin pathway in vitro. The transformation of 3D spheroid, but not 2D monolayer, MSCs promoted new bone regeneration in vivo. These results indicate that transplantation of 3D spheroid MSCs in regeneration therapy contributes to a shorter regenerative healing process, including new bone formation.

A Hepatic Scaffold from Decellularized Liver Tissue: Food for Thought

Allogeneic liver transplantation is still deemed the gold standard solution for end-stage organ failure; however, donor organ shortages have led to extended waiting lists for organ transplants. In order to overcome the lack of donors, the development of new therapeutic options is mandatory. In the last several years, organ bioengineering has been extensively explored to provide transplantable tissues or whole organs with the final goal of creating a three-dimensional growth microenvironment mimicking the native structure. It has been frequently reported that an extracellular matrix-based scaffold offers a structural support and important biological molecules that could help cellular proliferation during the recellularization process. The aim of the present review is to underline the recent developments in cell-on-scaffold technology for liver bioengineering, taking into account: (1) biological and synthetic scaffolds; (2) animal and human tissue decellularization; (3) scaffold recellularization; (4) 3D bioprinting; and (5) organoid technology. Future possible clinical applications in regenerative medicine for liver tissue engineering and for drug testing were underlined and dissected.

Methods to generate tissue-derived constructs for regenerative medicine applications

The shortage of donor organs for transplantation remains a continued problem for patients with irreversible end-stage organ failure. Tissue engineering and regenerative medicine aims to develop therapies to provide viable solutions for these patients. Use of decellularized tissue scaffolds has emerged as an attractive approach to generate tissue constructs that mimic native tissue architecture and vascular networks. The process of decellularization which involves the removal of resident cellular components from donor tissues has been successfully translated to the clinic for applications in patients. However, transplantation of bioengineered solid organs using this approach remains a challenge as the process requires repopulating target cells to achieve functioning organs. This article presents a comprehensive overview of the methods used to achieve decellularization, the types of decellularizing agents, and the potential cell sources that could be used to achieve tissue function. Understanding the mechanism of action of the decellularizing agent and the processing methods will provide the optimal results for applications.

Regenerative Medicine: Taming the Chimaera

In this issue of Stem Cell Reports, Hamanaka et al. (2018) describe the generation of chimeric mice with all vascular endothelial cells derived from pluripotent stem cells. This approach is desirable to prevent immune rejection when human stem cells are combined with animal embryos to grow human organs in animals.

A non-linear mathematical model using optical sensor to predict heart decellularization efficacy

One of the main problems of the decellularization technique is the subjectivity of the final evaluation of its efficacy in individual organs. This problem can result in restricted cell repopulation reproducibility and worse responses to transplant tissues. Our proposal is to analyze the optical profiles produced by hearts during perfusion decellularization, as an additional method for evaluating the decellularization process of each individual organ. An apparatus comprised of a structured LED source and photo detector on an adjustable base was developed to capture the relationship between transmitted light during the perfusion of murine hearts, and residual DNA content. Voltage-time graphic records were used to identify a nonlinear mathematical model to discriminate between decellularizations with remaining DNA above (Incomplete Decellularization) and below (Complete Decellularization) the standardized limits. The results indicate that temporal optical evaluation of the process enables inefficient cell removal to be predicted in the initial stages, regardless of the apparent transparency of the organ. Our open system also creates new possibilities to add distinct photo detectors, such as for specific wavelengths, image acquisition, and physical-chemical evaluation of the scaffold, in order to collect different kinds of information, from dozens of studies. These data, when compiled and submitted to machine learning techniques, have the potential to initiate an exponential advance in tissue bioengineering research.

Immune responses towards bioengineered tissues and strategies to control them

PURPOSE OF REVIEW

Research into development of artificial tissues and bioengineered organs to replace physiological functions of injured counterparts has highlighted a previously underestimated challenge for its clinical translatability: the immune response against biomaterials. Herein, we will provide an update and review current knowledge regarding this important barrier to regenerative medicine.

RECENT FINDINGS

Although a clear understanding of the immune reactivity against biomaterials remains elusive, accumulating evidence indicates that innate immune cells, primarily neutrophils and macrophages, play a key role in the initial phases of the immune response. More recently, data have shown that in later phases, T and B cells are also involved. The use of physicochemical modifications of biomaterials and cell-based strategies to modulate the host inflammatory response is being actively investigated for effective biomaterial integration.

SUMMARY

The immune response towards biomaterials and bioengineered organs plays a crucial role in determining their utility as transplantable grafts. Expanding our understanding of these responses is necessary for developing protolerogenic strategies and delivering on the ultimate promise of regenerative medicine.

Naturally-Derived Biomaterials for Tissue Engineering Applications

Naturally-derived biomaterials have been used for decades in multiple regenerative medicine applications. From the simplest cell microcarriers made of collagen or alginate, to highly complex decellularized whole-organ scaffolds, these biomaterials represent a class of substances that is usually first in choice at the time of electing a functional and useful biomaterial. Hence, in this chapter we describe the several naturally-derived biomaterials used in tissue engineering applications and their classification, based on composition. We will also describe some of the present uses of the generated tissues like drug discovery, developmental biology, bioprinting and transplantation.

Decellularization of the mouse ovary: comparison of different scaffold generation protocols for future ovarian bioengineering

Background

In order to preserve fertility in young women with disseminated cancer, e.g. leukemia, an approach that has been suggested is to retransplant isolated small follicles within an ovarian matrix free from malignant cells and with no risk for contamination. The present study evaluates the first step to create a bioengineered ovarian construct that can act as growth-supporting tissue for isolated small follicles that are dependent on a stroma for normal follicular maturation. The present study used the intact mouse ovary to develop a mouse ovarian scaffold through various protocols of decellularization.

Material and methods

Potential Immunogenic DNA and intracellular components were removed from whole mouse ovaries by agitation in a 0.5% sodium dodecyl sulfate solution (Protocol 1; P1), or in a 2% sodium deoxycholate solution (P2) or by a combination of the two (P3). The remaining decelluralized ovarian extracellular matrix structure was then assessed based on the DNA- and protein content, and was further evaluated histologically by haematoxylin and eosin-, Verhoeff’s van gieson- (for elastin), Masson’s trichrome- (for collagens) and Alcian blue (for glycosaminoglycans) staining. We also evaluated the decellularization efficiency using the mild detergent Triton-X100 (1%).

Results

Sodium dodecyl sulfate efficiently removed DNA and intracellular components from the ovarian tissue but also significantly reduced the integrity of the remaining ovarian extracellular matrix. Sodium deoxycholate, a considerably milder detergent compared to sodium dodecyl sulfate, preserved the ovarian extracellular matrix better, evident by a more distinct staining for glycosaminoglycan, collagen and elastic fibres. Triton-X100 was found ineffective as a decellularization reagent for mouse ovaries in our settings.

Conclusions

The sodium dodecyl sulfate generated ovarian scaffolds contained minute amounts of DNA that may be an advantage to evade a detrimental immune response following engraftment. The sodium deoxycholate generated ovarian scaffolds had higher donor DNA content, yet, retained the extracellular composition better and may therefore have improved recellularization and other downstream bioengineering applications. These two novel types of mouse ovarian scaffolds serve as promising scaffold-candidates for future ovarian bioengineering experiments.

Evaluating two ovarian decellularization methods in three species

Since there is dearth of practical ways to obtain mature follicles from cryopreserved or native ovarian tissues, especially in patients suffering from ovarian dysfunction, tissue engineering may help in restoring ovarian function and/or fertility. In the present study, the effects of sodium dodecyl sulfate (SDS) and sodium hydroxide (NaOH) on the decellularization of ovarian tissues were studied in order to ascertain their suitability in creating suitable bioscaffolds. Cells were removed from the ovarian tissues of mouse, sheep and human. The samples were distributed among three groups, viz., control (not treated), SDS and NaOH treated. Qualitative histological evaluations, quantitative assessments (nuclear contents, collagen and glycosaminoglycan), immunohistochemistry staining (for laminin, fibronectin and Collagen I), cell viability and scanning electron microscopic (SEM) assays were performed for all experimental groups. Finally, suspensions of mouse ovarian cells were injected into human NaOH treated scaffolds and subsequently auto-transplanted to ovariectomized mice. H&E and IHC staining (GDF-9) were performed on human recellularized NaOH treated scaffolds 1 month after auto-transplantation. Although histological studies and quantitative evaluations confirmed the successful decellularization and presence of key factors in ovarian scaffolds under both treatment methods, NaOH showed more interesting outcomes. Cell metabolic activity in sheep and human ovaries treated with NaOH was statistically (p < 0.05) higher than for SDS treated samples after 72 h. Moreover, spherical associations with cuboidal cells in human NaOH treated scaffolds were observed and this follicular reconstruction was also confirmed by GDF-9. NaOH was found to be more suitable than SDS for the decellularization of ovarian tissues and it supports follicular reconstruction better than SDS. This is a valuable finding in tissue engineering research and can help in the creation of appropriate ovarian bioscaffolds.

Bioengineered functional humanized livers: An emerging supportive modality to bridge the gap of organ transplantation for management of end-stage liver diseases

End stage liver diseases (ESLD) represent a major, neglected global public health crisis which requires an urgent action towards finding a proper cure. Orthotropic liver transplantation has been the only definitive treatment modality for ESLD. However, shortage of donor organs, timely unavailability, post-surgery related complications and financial burden on the patients limits the number of patients receiving the transplants. Since last two decades cell-based therapies have revolutionized the field of organ/tissue regeneration. However providing an alternative organ source to address the donor liver shortage still poses potential challenges. The developments made in this direction provide useful futuristic approaches, which could be translated into pre-clinical and clinical settings targeting appropriate applications in specific disease conditions. Earlier studies have demonstrated the applicability of this particular approach to generate functional organ in rodent system by connecting them with portal and hepatic circulatory networks. However, such strategy requires very high level of surgical expertise and also poses the technical and financial questions towards its future applicability. Hence, alternative sites for generating secondary organs are being tested in several types of disease conditions. Among different sites, omentum has been proved to be more appropriate site for implanting several kinds of functional tissue constructs without eliciting much immunological response. Hence, omentum may be considered as better site for transplanting humanized bioengineered ex vivo generated livers, thereby creating a secondary organ at intra-omental site. However, the expertise for generating such bioengineered organs are limited and only very few centres are involved for investigating the potential use of such implants in clinical practice due to gap between the clinical transplant surgeons and basic scientists working on the concept evolution. Herein we discuss the recent advances and challenges to create functional secondary organs through intra-omental transplantation of ex vivo generated bioengineered humanized livers and their further application in the management of ESLD as a supportive bridge for organ transplantation.

The potential of human induced pluripotent stem cells for modelling diabetic wound healing in vitro

Impaired wound healing and ulceration caused by diabetes mellitus, is a significant healthcare burden, markedly impairs quality of life for patients, and is the major cause of amputation worldwide. Current experimental approaches used to investigate the complex wound healing process often involve cultures of fibroblasts and/or keratinocytes in vitro, which can be limited in terms of complexity and capacity, or utilisation of rodent models in which the mechanisms of wound repair differ substantively from that in humans. However, advances in tissue engineering, and the discovery of strategies to reprogramme adult somatic cells to pluripotency, has led to the possibility of developing models of human skin on a large scale. Generation of induced pluripotent stem cells (iPSCs) from tissues donated by diabetic patients allows the (epi)genetic background of this disease to be studied, and the ability to differentiate iPSCs to multiple cell types found within skin may facilitate the development of more complex skin models; these advances offer key opportunities for improving modelling of wound healing in diabetes, and the development of effective therapeutics for treatment of chronic wounds.

Reconstruction of structure and function in tissue engineering of solid organs: Toward simulation of natural development based on decellularization

Failure of solid organs, such as the heart, liver, and kidney, remains a major cause of the world's mortality due to critical shortage of donor organs. Tissue engineering, which uses elements including cells, scaffolds, and growth factors to fabricate functional organs in vitro, is a promising strategy to mitigate the scarcity of transplantable organs. Within recent years, different construction strategies that guide the combination of tissue engineering elements have been applied in solid organ tissue engineering and have achieved much progress. Most attractively, construction strategy based on whole-organ decellularization has become a popular and promising approach, because the overall structure of extracellular matrix can be well preserved. However, despite the preservation of whole structure, the current constructs derived from decellularization-based strategy still perform partial functions of solid organs, due to several challenges, including preservation of functional extracellular matrix structure, implementation of functional recellularization, formation of functional vascular network, and realization of long-term functional integration. This review overviews the status quo of solid organ tissue engineering, including both advances and challenges. We have also put forward a few techniques with potential to solve the challenges, mainly focusing on decellularization-based construction strategy. We propose that the primary concept for constructing tissue-engineered solid organs is fabricating functional organs based on intact structure via simulating the natural development and regeneration processes.

The rat pancreatic body tail as a source of a novel extracellular matrix scaffold for endocrine pancreas bioengineering

Background

Regenerative medicine and tissue engineering are promising approaches for organ transplantation. Extracellular matrix (ECM) based scaffolds obtained through the decellularization of natural organs have become the preferred platform for organ bioengineering. In the field of pancreas bioengineering, acellular scaffolds from different animals approximate the biochemical, spatial and vascular relationships of the native extracellular matrix and have been proven to be a good platform for recellularization and in vitro culture. However, artificial endocrine pancreases based on these whole pancreatic scaffolds have a critical flaw, specifically their difficult in vivo transplantation, and connecting their vessels to the recipient is a major limitation in the development of pancreatic tissue engineering. In this study, we focus on preparing a novel acellular extracellular matrix scaffold derived from the rat pancreatic body tail (pan-body-tail ECM scaffold).

Results

Several analyses confirmed that our protocol effectively removes cellular material while preserving ECM proteins and the native vascular tree. DNA quantification demonstrated an obvious reduction of DNA compared with that of the natural organ (from 931.9 ± 267.8 to 11.7 ± 3.6 ng/mg, P < 0.001); the retention of the sGAG in the decellularized pancreas (0.878 ± 0.37) showed no significant difference from the natural pancreas (0.819 ± 0.1) (P > 0.05). After transplanted with the recellularized pancreas, fasting glucose levels declined to 9.08 ± 2.4 mmol/l within 2 h of the operation, and 8 h later, they had decreased to 4.7 ± 1.8 mmol/l (P < 0.05).

Conclusions

The current study describes a novel pancreatic ECM scaffold prepared from the rat pancreatic body tail via perfusion through the left gastric artery. We further showed the pioneering possibility of in vivo circulation-connected transplantation of a recellularized pancreas based on this novel scaffold. By providing such a promising pancreatic ECM scaffold, the present study might represent a key improvement and have a positive impact on endocrine pancreas bioengineering.

Mechanistics of biomass discharge during whole-heart decellularization

Whole-organ engineering-based on the functional repopulation of acellular whole-organ scaffolds derived from perfusion-based in toto decellularization of the specific organ system-is one of the most promising fields in tissue engineering. However, to date, we still have hardly any insights into the process of perfusion-based scaffold generation itself, with human-scale scaffolds usually obtained by adoption of small animal decellularization models, although those organs are of decreased biomass and potentially different biological characteristics. Therefore, in this study we analyzed perfusion-based human-scale whole-heart decellularization by evaluating and comparing the dynamics of biomass discharge and its kinetic characteristics during in toto decellularization of ovine and rodent hearts, while introducing a theoretical model of biomass depletion during perfusion-based whole-heart decellularization. Our results suggest highly varying process characteristics for the in toto decellularization of individual human-scale organs, such as protein discharge kinetics or time-dependent viscoelasticity of formed debris, despite seemingly consistent inter-sample decellularization efficacy, as evaluated by conventional disruptive analysis of obtained ECM scaffolds. Hence, the here exposed insights into the mechanistics of whole-heart decellularization as well as the introduced non-disruptive process accompanying tools may help to monitor and further optimize the decellularization process, especially with regards to human-scale scaffold production.

Recent Advances in Modified Cellulose for Tissue Culture Applications

Tissue engineering is a rapidly advancing field in regenerative medicine, with much research directed towards the production of new biomaterial scaffolds with tailored properties to generate functional tissue for specific applications. Recently, principles of sustainability, eco-efficiency and green chemistry have begun to guide the development of a new generation of materials, such as cellulose, as an alternative to conventional polymers based on conversion of fossil carbon (e.g., oil) and finding technologies to reduce the use of animal and human derived biomolecules (e.g., foetal bovine serum). Much of this focus on cellulose is due to it possessing the necessary properties for tissue engineering scaffolds, including biocompatibility, and the relative ease with which its characteristics can be tuned through chemical modification to adjust mechanical properties and to introduce various surface modifications. In addition, the sustainability of producing and manufacturing materials from cellulose, as well as its modest cost, makes cellulose an economically viable feedstock. This review focusses specifically on the use of modified cellulose materials for tissue culturing applications. We will investigate recent techniques used to promote scaffold function through physical, biochemical and chemical scaffold modifications, and describe how these have been utilised to reduce reliance on the addition of matrix ligands such as foetal bovine serum.

Metabolic Reprogramming and the Recovery of Physiological Functionality in 3D Cultures in Micro-Bioreactors

The recovery of physiological functionality, which is commonly seen in tissue mimetic three-dimensional (3D) cellular aggregates (organoids, spheroids, acini, etc.), has been observed in cells of many origins (primary tissues, embryonic stem cells (ESCs), induced pluripotent stem cells (iPSCs), and immortal cell lines). This plurality and plasticity suggest that probably several basic principles promote this recovery process. The aim of this study was to identify these basic principles and describe how they are regulated so that they can be taken in consideration when micro-bioreactors are designed. Here, we provide evidence that one of these basic principles is hypoxia, which is a natural consequence of multicellular structures grown in microgravity cultures. Hypoxia drives a partial metabolic reprogramming to aerobic glycolysis and an increased anabolic synthesis. A second principle is the activation of cytoplasmic glutaminolysis for lipogenesis. Glutaminolysis is activated in the presence of hypo- or normo-glycaemic conditions and in turn is geared to the hexosamine pathway. The reducing power needed is produced in the pentose phosphate pathway, a prime function of glucose metabolism. Cytoskeletal reconstruction, histone modification, and the recovery of the physiological phenotype can all be traced to adaptive changes in the underlying cellular metabolism. These changes are coordinated by mTOR/Akt, p53 and non-canonical Wnt signaling pathways, while myc and NF-kB appear to be relatively inactive. Partial metabolic reprogramming to aerobic glycolysis, originally described by Warburg, is independent of the cell’s rate of proliferation, but is interwoven with the cells abilities to execute advanced functionality needed for replicating the tissues physiological performance.

Biomimetic matrix fabricated by LMP-1 gene-transduced MC3T3-E1 cells for bone regeneration

Bone healing is regulated by multiple microenvironmental signals provided by the extracellular matrix (ECM). This study aimed to mimic the native osteoinductive microenvironment by developing an ECM using gene-transduced cells. The LIM mineralization protein-1 (LMP-1) gene was transferred to murine pre-osteoblast cells (MC3T3-E1) using lentiviral vectors. Western blotting assay indicated that the MC3T3-E1 cells expressed an increased level of bone morphologic protein-2, -4 and -7 (BMP-2, -4 and -7) after LMP-1 gene transduction. The transduced cells were then seeded into calcined bovine bone scaffolds and cultured for 7, 14, and 21 days to construct ECMs on the scaffolds. The ECM-scaffold composites were then decellularized using the freeze-drying method. Scaffolds without ECM deposition were used as controls. The composites and controls were implanted into critical-sized bone defects created in the distal femurs of New Zealand rabbits. Twelve weeks after the surgery, both microcomputed tomography and histologic results indicated that the 7-day-cell-modified ECM-scaffold composites induced bone regeneration with significantly larger volume, trabecular thickness and connectivity than the controls. However, the 14- and 21-day-cell-modified ECM-scaffold composites triggered sustained inflammation response even at 12 weeks after the surgery and showed less bone ingrowth and integration than their 7-day-cell-modified counterparts. In conclusion, these results highlight the viable gene transfer techniques for manipulating cells in a constructed microenvironment of ECM for bone regeneration. However, the unresolved inflammation relating to the duration of ECM modification needs to be considered.

A transatlantic perspective on 20 emerging issues in biological engineering

Advances in biological engineering are likely to have substantial impacts on global society. To explore these potential impacts we ran a horizon scanning exercise to capture a range of perspectives on the opportunities and risks presented by biological engineering. We first identified 70 potential issues, and then used an iterative process to prioritise 20 issues that we considered to be emerging, to have potential global impact, and to be relatively unknown outside the field of biological engineering. The issues identified may be of interest to researchers, businesses and policy makers in sectors such as health, energy, agriculture and the environment.

Regenerative immunology: the immunological reaction to biomaterials

Regenerative medicine promises to meet two of the most urgent needs of modern organ transplantation, namely immunosuppression-free transplantation and an inexhaustible source of organs. Ideally, bioengineered organs would be manufactured from a patient's own biomaterials-both cells and the supporting scaffolding materials in which cells would be embedded and allowed to mature to eventually regenerate the organ in question. While some groups are focusing on the feasibility of this approach, few are focusing on the immunogenicity of the scaffolds that are being developed for organ bioengineering purposes. This review will succinctly discuss progress in the understanding of immunological characteristics and behavior of different scaffolds currently under development, with emphasis on the extracellular matrix scaffolds obtained decellularized animal or human organs which seem to provide the ideal template for bioengineering purposes.

"Tissue Papers" from Organ-Specific Decellularized Extracellular Matrices

Using an innovative, tissue-independent approach to decellularized tissue processing and biomaterial fabrication, the development of a series of "tissue papers" derived from native porcine tissues/organs (heart, kidney, liver, muscle), native bovine tissue/organ (ovary and uterus), and purified bovine Achilles tendon collagen as a control from decellularized extracellular matrix particle ink suspensions cast into molds is described. Each tissue paper type has distinct microstructural characteristics as well as physical and mechanical properties, is capable of absorbing up to 300% of its own weight in liquid, and remains mechanically robust (E = 1-18 MPa) when hydrated; permitting it to be cut, rolled, folded, and sutured, as needed. In vitro characterization with human mesenchymal stem cells reveals that all tissue paper types support cell adhesion, viability, and proliferation over four weeks. Ovarian tissue papers support mouse ovarian follicle adhesion, viability, and health in vitro, as well as support, and maintain the viability and hormonal function of nonhuman primate and human follicle-containing, live ovarian cortical tissues ex vivo for eight weeks postmortem. "Tissue papers" can be further augmented with additional synthetic and natural biomaterials, as well as integrated with recently developed, advanced 3D-printable biomaterials, providing a versatile platform for future multi-biomaterial construct manufacturing.

Emerging advancements in liver regeneration and organogenesis as tools for liver replacement

PURPOSE OF REVIEW

Although the liver possesses a unique, innate ability to regenerate through mass compensation, transplantation remains the only therapy when damage outpaces regeneration, or liver metabolic capacity is irreversibly impacted. Recent insight from developmental biology has greatly influenced the advancement of alternative options to transplantation in these settings.

RECENT FINDINGS

Factors known to direct liver cell specification, expansion, and differentiation have been used to generate hepatocyte-like cells from stem and somatic cells for developing cell therapies. Additionally, interactions between hepatic epithelial and nonepithelial cells key to establishing hepatic architecture have been used in tissue engineering approaches to advance self-organizing hepatic organoids and bioartificial liver devices. Simultaneously, recent clinically applicable advances in human hepatocyte transplantation and promotion of innate hepatic regeneration have been limited.

SUMMARY

Although mature hepatocytes have the potential to bridge to, or replace whole organ transplantation, limits in the ability to obtain healthy cells, stabilize in-vitro expansion, cryopreserve, and alleviate rejection, still exist. Alternative sources for generating hepatocytes hold promise for cell therapy and tissue engineering. These may allow generation of autologous or universal donor cells that eliminate the need for immunosuppression; however, limits exist regarding hepatocyte maturity and efficacy at liver repopulation, as well as applicability to human chronic liver disease.

Collagenase treatment enhances proteomic coverage of low-abundance proteins in decellularized matrix bioscaffolds

There is great interest in the application of advanced proteomic techniques to characterize decellularized tissues in order to develop a deeper understanding of the effects of the complex extracellular matrix (ECM) composition on the cellular response to these pro-regenerative bioscaffolds. However, the identification of proteins in ECM-derived bioscaffolds is hindered by the high abundance of collagen in the samples, which can interfere with the detection of lower-abundance constituents that may be important regulators of cell function. To address this limitation, we developed a novel multi-enzyme digestion approach using treatment with a highly-purified collagenase derived from Clostridium Histolyticum to selectively deplete collagen from ECM-derived protein extracts, reducing its relative abundance from up to 90% to below 10%. Moreover, we applied this new method to characterize the proteome of human decellularized adipose tissue (DAT), human decellularized cancellous bone (DCB), and commercially-available bovine tendon collagen (BTC). We successfully demonstrated with all three sources that collagenase treatment increased the depth of detection and enabled the identification of a variety of signaling proteins that were masked by collagen in standard digestion protocols with trypsin/LysC, increasing the number of proteins identified in the DAT by ∼2.2 fold, the DCB by ∼1.3 fold, and the BTC by ∼1.6 fold. In addition, quantitative proteomics using label-free quantification demonstrated that the DAT and DCB extracts were compositionally distinct, and identified a number of adipogenic and osteogenic proteins that were consistently more highly expressed in the DAT and DCB respectively. Overall, we have developed a new processing method that may be applied in advanced mass spectrometry studies to improve the high-throughput proteomic characterization of bioscaffolds derived from mammalian tissues. Further, our study provides new insight into the complex ECM composition of two human decellularized tissues of interest as cell-instructive platforms for regenerative medicine.

A Drug-Induced Hybrid Electrospun Poly-Capro-Lactone: Cell-Derived Extracellular Matrix Scaffold for Liver Tissue Engineering

Liver transplant is the only treatment option for patients with end-stage liver failure, however, there are too few donor livers available for transplant. Whole organ tissue engineering presents a potential solution to the problem of rapidly escalating donor liver shortages worldwide. A major challenge for liver tissue engineers is the creation of a hepatocyte microenvironment; a niche in which liver cells can survive and function optimally. While polymers and decellularized tissues pose an attractive option for scaffold manufacturing, neither alone has thus far proved sufficient. This study exploited cell's native extracellular matrix (ECM) producing capabilities using two different histone deacetylase inhibitors, and combined these with the customizability and reproducibility of electrospun polymer scaffolds to produce a "best of both worlds" niche microenvironment for hepatocytes. The resulting hybrid poly-capro-lactone (PCL)-ECM scaffolds were validated using HepG2 hepatocytes. The hybrid PCL-ECM scaffolds maintained hepatocyte growth and function, as evidenced by metabolic activity and DNA quantitation. Mechanical testing revealed little significant difference between scaffolds, indicating that cells were responding to a biochemical and topographical profile rather than mechanical changes. Immunohistochemistry showed that the biochemical profile of the drug-derived and nondrug-derived ECMs differed in ratio of Collagen I, Laminin, and Fibronectin. Furthermore, the hybrid PCL-ECM scaffolds influence the gene expression profile of the HepG2s drastically; with expression of Albumin, Cytochrome P450 Family 1 Subfamily A Polypeptide 1, Cytochrome P450 Family 1 Subfamily A Polypeptide 2, Cytochrome P450 Family 3 Subfamily A Polypeptide 4, Fibronectin, Collagen I, and Collagen IV undergoing significant changes. Our results demonstrate that drug-induced hybrid PCL-ECM scaffolds provide a viable, translatable platform for creating a niche microenvironment for hepatocytes, supporting in vivo phenotype and function. These scaffolds offer great potential for tissue engineering and regenerative medicine strategies for whole organ tissue engineering.

Decellularized Human Liver Is Too Heterogeneous for Designing a Generic Extracellular Matrix Mimic Hepatic Scaffold

Decellularized human livers are considered the perfect extracellular matrix (ECM) surrogate because both three-dimensional architecture and biological features of the hepatic microenvironment are thought to be preserved. However, donor human livers are in chronically short supply, both for transplantation or as decellularized scaffolds, and will become even scarcer as life expectancy increases. It is hence of interest to determine the structural and biochemical properties of human hepatic ECM to derive design criteria for engineering biomimetic scaffolds. The intention of this work was to obtain quantitative design specifications for fabricating scaffolds for hepatic tissue engineering using human livers as a template. To this end, hepatic samples from five patients scheduled for hepatic resection were decellularized using a protocol shown to reproducibly conserve matrix composition and microstructure in porcine livers. The decellularization outcome was evaluated through histological and quantitative image analyses to evaluate cell removal, protein, and glycosaminoglycan content per unit area. Applying the same decellularization protocol to human liver samples obtained from five different patients yielded five different outcomes. Only one liver out of five was completely decellularized, while the other four showed different levels of remaining cells and matrix. Moreover, protein and glycosaminoglycan content per unit area after decellularization were also found to be patient- (or donor-) dependent. This donor-to-donor variability of human livers thus precludes their use as templates for engineering a generic "one-size fits all" ECM-mimic hepatic scaffold.

Uterus transplantation and beyond

Uterus transplantation is today the only available treatment for absolute uterine factor infertility which is caused by either congenital/surgical uterine absence or that a present uterus is non-functioning. Structured animal-based research, from rodents to nonhuman primates, was the scientific basis for a successful introduction of uterus transplantation as a clinical procedure. The patient groups for uterus transplantation, the preclinical research and data from the published human cases will be covered herein. During recent years the concept of bioengineering of organs and tissues has emerged. Creation of a bioengineered uterus is in the initial research state, with experiments performed in rodents. The research that has been performed to create a bioengineered uterus will be summarized. In conclusion, uterus transplantation is now a clinical experimental procedure for treatment of uterine factor infertility. In parallel to the establishment of this combined assisted reproduction technique and transplantation procedure as a routine clinical procedure, we predict that uterus bioengineering will develop further towards introduction within the human setting, but that this process will take several years.