Introduction of vasculature in engineered three-dimensional tissue

Temperature-modulated separation of vascular cells using thermoresponsive-anionic block copolymer-modified glass

Introduction

Vascular tissue engineering is a key technology in the field of regenerative medicine. In tissue engineering, the separation of vascular cells without cell modification is required, as cell modifications affect the intrinsic properties of the cells. In this study, we have developed an effective method for separating vascular cells without cell modification, using a thermoresponsive anionic block copolymer.

Methods

A thermoresponsive anionic block copolymer, poly(acrylic acid)-b-poly(N-isopropylacryl-amide) (PAAc-b-PNIPAAm), with various PNIPAAm segment lengths, was prepared in two steps: atom transfer radical polymerization and subsequent deprotection. Normal human umbilical vein endothelial cells (HUVECs), normal human dermal fibroblasts, and human aortic smooth muscle cells (SMCs) were seeded onto the prepared thermoresponsive anionic block copolymer brush-modified glass. The adhesion behavior of cells on the copolymer brush was observed at 37 °C and 20 °C.

Results

A thermoresponsive anionic block copolymer, poly(acrylic acid)-b-poly(N-isopropylacrylamide) (PAAc-b-PNIPAAm), with various PNIPAAm segment lengths was prepared. The prepared copolymer-modified glass exhibited anionic properties attributed to the bottom PAAc segment of the copolymer brush. On the PAAc-b-PNIPAAm, which had a moderate PNIPAAm length, a high adhesion ratio of HUVECs and low adhesion ratio of SMCs were observed at 37 °C. By reducing temperature from 37 °C to 20 °C, the adhered HUVECs were detached, whereas the SMCs maintained adhesion, leading to the recovery of purified HUVECs by changing the temperature.

Conclusions

The prepared thermoresponsive anionic copolymer-modified glass could be used to separate HUVECs and SMCs by changing the temperature without modifying the cell surface. Therefore, the developed cell separation method will be useful for vascular tissue engineering.

Current methods for fabricating 3D cardiac engineered constructs

3D cardiac engineered constructs have yielded not only the next generation of cardiac regenerative medicine but also have allowed for more accurate modeling of both healthy and diseased cardiac tissues. This is critical as current cardiac treatments are rudimentary and often default to eventual heart transplants. This review serves to highlight the various cell types found in cardiac tissues and how they correspond with current advanced fabrication methods for creating cardiac engineered constructs capable of shedding light on various pathologies and providing the therapeutic potential for damaged myocardium. In addition, insight is given toward the future direction of the field with an emphasis on the creation of specialized and personalized constructs that model the region-specific microtopography and function of native cardiac tissues.

Potential strategies to prevent encrustations on urinary stents and catheters - thinking outside the box: a European network of multidisciplinary research to improve urinary stents (ENIUS) initiative

Introduction: Urinary stents have been around for the last 4 decades, urinary catheters even longer. They are associated with infections, encrustation, migration, and patient discomfort. Research efforts to improve them have shifted onto molecular and cellular levels. ENIUS brought together translational scientists to improve urinary implants and reduce morbidity.Methods & materials: A working group within the ENIUS network was tasked with assessing future research lines for the improvement of urinary implants.Topics were researched systematically using Embase and PubMed databases. Clinicaltrials.gov was consulted for ongoing trials.Areas covered: Relevant topics were coatings with antibodies, enzymes, biomimetics, bioactive nano-coats, antisense molecules, and engineered tissue. Further, pH sensors, biodegradable metals, bactericidal bacteriophages, nonpathogenic uropathogens, enhanced ureteric peristalsis, electrical charges, and ultrasound to prevent stent encrustations were addressed.Expert opinion: All research lines addressed in this paper seem viable and promising. Some of them have been around for decades but are yet to proceed to clinical application (i.e. tissue engineering). Others are very recent and, at least in urology, still only conceptual (i.e. antisense molecules). Perhaps the most important learning point resulting from this pan-European multidisciplinary effort is that collaboration between all stakeholders is not only fruitful but also truly essential.

Development and Application of Endothelial Cells Derived From Pluripotent Stem Cells in Microphysiological Systems Models

The vascular endothelium is present in all organs and blood vessels, facilitates the exchange of nutrients and waste throughout different organ systems in the body, and sets the tone for healthy vessel function. Mechanosensitive in nature, the endothelium responds to the magnitude and temporal waveform of shear stress in the vessels. Endothelial dysfunction can lead to atherosclerosis and other diseases. Modeling endothelial function and dysfunction in organ systems in vitro, such as the blood–brain barrier and tissue-engineered blood vessels, requires sourcing endothelial cells (ECs) for these biomedical engineering applications. It can be difficult to source primary, easily renewable ECs that possess the function or dysfunction in question. In contrast, human pluripotent stem cells (hPSCs) can be sourced from donors of interest and renewed almost indefinitely. In this review, we highlight how knowledge of vascular EC development in vivo is used to differentiate induced pluripotent stem cells (iPSC) into ECs. We then describe how iPSC-derived ECs are being used currently in in vitro models of organ function and disease and in vivo applications.

Glycolytic inhibition by resveratrol prevents myoblast cell death caused by glucose deprivation and hypoxia; a possible application to the three-dimensional tissue construction

Decreased cell viability resulting from a severe condition of nutrients deprivation and hypoxia has been the major obstacle in three-dimensional (3D) tissue construction. Therefore, technical improvement which prevents cell death caused by starvation and low oxygen is desired for the development of large, thick tissues. We focused on the anti-glycolytic effect of resveratrol (RSV), a naturally-occurring polyphenol known as a caloric restriction mimetic, and investigated its cytoprotective effect in two-dimensional (2D) and 3D-cell culture using H9c2 rat myoblast cells. Glucose deprivation by culturing with low glucose media caused time- and dose-dependent cell death in H9c2 cells. In contrast, RSV treatment at 100 μM significantly increased the cell viability by preventing cell death. RSV showed anti-glycolytic effect associated with a down-regulation of glycolytic genes (GLUT1, PKM2) and glucose uptake activity, and increased the activation of AMP-activated protein kinase (AMPK), an essential cellular energy sensor activated in the condition of energy deprivation. RSV treatment markedly improved the viability of myoblast cells cultured in a hypoxic, low glucose condition and attenuated the up-regulation of glycolytic genes by hypoxic response. In 3D-cultured model, spheroids constructed with RSV-treated cells showed improved cell viability and intact histological appearance compared with control. These results suggest that glycolytic inhibition by RSV decreases the glucose usage of myoblast cells, therefore, prevents cell death caused by nutrient deprivation and hypoxic condition. Our finding provides useful information to improve cell viability in a condition that nutrients and oxygen are low in supply, and be a possible application to the 3D-tissue construction.

A Gelatin Hydrogel Nonwoven Fabric Facilitates Metabolic Activity of Multilayered Cell Sheets

IMPACT STATEMENT

This study introduces the utility of gelatin hydrogel nonwoven fabrics (GHNFs) for cell sheet engineering. The GHNF had the mechanical property strong enough to hold by forceps even in the swollen condition. The cell sheet harvest and transfer processes were performed simpler and faster than those without using the GHNF. The GHNF facilitates the metabolic activity of three-layered cell sheets, and the cell migration from cell sheets into the GHNF was observed. The GHNF is a promising material used to support cell sheets during the process of assemble formulation and contributes to the improved biological functions of tissue-like cell constructs.

Human pluripotent stem cell-derived cardiomyocytes for studying energy metabolism

Cardiomyocyte energy metabolism is altered in heart failure, and primary defects of metabolic pathways can cause heart failure. Studying cardiac energetics in rodent models has principal shortcomings, raising the question to which extent human induced pluripotent stem cell derived cardiomyocytes (hiPSC-CM) can provide an alternative. As metabolic maturation of CM occurs mostly after birth during developmental hypertrophy, the immaturity of hiPSC-CM is an important limitation. Here we shortly review the physiological drivers of metabolic maturation and concentrate on methods to mature hiPSC-CM with the goal to benchmark the metabolic state of hiPSC-CM against in vivo data and to see how far known abnormalities in inherited metabolic disorders can be modeled in hiPSC-CM. The current data indicate that hiPSC-CM, despite their immature, approximately mid-fetal state of energy metabolism, faithfully recapitulate some basic metabolic disease mechanisms. Efforts to improve their metabolic maturity are underway and shall improve the validity of this model.

Synergistic effects of laminin-1 peptides, VEGF and FGF9 on salivary gland regeneration

Hyposalivation is associated with radiation therapy, Sjögren's syndrome and/or aging, and is a significant clinical problem that decreases oral health and overall health in many patients and currently lacks effective treatment. Hence, methods to regenerate salivary glands and restore saliva secretion are urgently needed. To this end, this study describes the modification of fibrin hydrogels with a combination of laminin-1 peptides (YIGSR and A99) and human growth factors (vascular endothelial growth factor and fibroblast growth factor 9) to enhance regeneration in a salivary gland injury mouse model. Our results indicate that these fortified hydrogels enhanced angiogenesis and neurogenesis while promoting formation of acinar structures, thereby leading to enhanced saliva secretion. Such functional recovery indicates salivary gland regeneration and suggests that our technology may be useful in promoting gland regeneration and reversing hyposalivation in a clinical setting. STATEMENT OF SIGNIFICANCE: We engineered Fibrin Hydrogels (FH) to contain multiple regenerative cues including laminin-1 peptides (L_1p) and growth factors (GFs). L_1p and GF modified FH were used to induce salivary gland regeneration in a wounded mouse model. Treatment with L_1p and GF modified FH promoted salivary epithelial tissue regeneration, vascularization, neurogenesis and healing as compared to L_1p-FH or FH alone. Results indicate that L_1p and GF modified FH can be used for future therapeutic applications.

Construction of Pedicled Smooth Muscle Tissues by Combining the Capsule Tissue and Cell Sheet Engineering

The survival of engineered tissue requires the formation of its own capillary network, which can anastomose with the host vasculature after transplantation. Currently, while many strategies, such as modifying the scaffold material, adding endothelial cells, or angiogenic factors, have been researched, engineered tissue implanted in vivo cannot timely access to sufficient blood supply, leading to ischemic apoptosis or shrinkage. Constructing vascularized engineered tissue with its own axial vessels and subsequent pedicled transfer is promising to solve the problem of vascularization in tissue engineering. In this study, we used the tissue expander capsule as a novel platform for vascularizing autologous smooth muscle cell (SMC) sheets and fabricating vascularized engineered tissue with its own vascular pedicle. First, we verified which time point was the most effective for constructing an axial capsule vascular bed. Second, we compared the outcome of SMC sheet transplantation onto the expander capsule and classical dorsal subcutaneous tissue, which was widely used in other studies for vascularization. Finally, we transplanted multilayered SMC sheets onto the capsule bed twice to verify the feasibility of fabricating thick pedicled engineered smooth muscle tissues. The results indicated that the axial capsule tissue could be successfully induced, and the capsule tissue 1 week after full expansion was the most vascularized. Quantitative comparisons of thickness, vessel density, and apoptosis of cell sheet grafts onto two vascular beds proved that the axial capsule vascular bed was more favorable to the growth and vascularization of transplants than classical subcutaneous tissue. Furthermore, thick vascularized smooth muscle tissues with the vascular pedicle could be constructed by multi-transplanting cell sheets onto the capsule bed. The combination of axial capsule vascular bed and cell sheet engineering may provide an efficient strategy to overcome the problem of slow or insufficient vascularization in tissue engineering.

Pathological Process of Prompt Connection between Host and Donor Tissue Vasculature Causing Rapid Perfusion of the Engineered Donor Tissue after Transplantation

The shortage of donors for transplantation therapy is a serious issue worldwide. Tissue engineering is considered a potential solution to this problem. Connection and perfusion in engineered tissues after transplantation is vital for the survival of the transplanted tissue, especially for tissues requiring blood perfusion to receive nutrients, such as the heart. A myocardial cell sheet containing an endothelial cell network structure was fabricated in vitro using cell sheet technology. Transplantation of the three-dimensional (3D) tissue by layering myocardial sheets could ameliorate ischemic heart disease in a rat model. The endothelial cell network in the 3D tissue was able to rapidly connect to host vasculature and begin perfusion within 24 h after transplantation. In this review, we compare and discuss the engineered tissue⁻host vasculature connection process between tissue engineered constructs with hydrogels and cell sheets by histological analysis. This review provides information that may be useful for further improvements of in vivo engineered tissue vascularization techniques.

Engineering a microcirculation for perfusion control of ex vivo-assembled organ systems: Challenges and opportunities

Donor organ shortage remains a clear problem for many end-stage organ patients around the world. The number of available donor organs pales in comparison with the number of patients in need of these organs. The field of tissue engineering proposes a plausible solution. Using stem cells, a patient's autologous cells, or allografted cells to seed-engineered scaffolds, tissue-engineered constructs can effectively supplement the donor pool and bypass other problems that arise when using donor organs, such as who receives the organ first and whether donor organ rejection may occur. However, current research methods and technologies have been unable to successfully engineer and vascularize large volume tissue constructs. This review examines the current perfusion methods for ex vivo organ systems, defines the different types of vascularization in organs, explores various strategies to vascularize ex vivo organ systems, and discusses challenges and opportunities for the field of tissue engineering.