Layer-by-layer heparinization of decellularized liver matrices to reduce thrombogenicity of tissue engineered grafts

Biomedical Application of Decellularized Scaffolds

Tissue loss and end-stage organ failure are serious health problems across the world. Natural and synthetic polymer scaffold material based artificial organs play an important role in the field of tissue engineering and organ regeneration, but they are not from the body and may cause side effects such as rejection. In recent years, the biomimetic decellularized scaffold based materials have drawn great attention in the tissue engineering field for their good biocompatibility, easy modification, and excellent organism adaptability. Therefore, in this review, we comprehensively summarize the application of decellularized scaffolds in tissue engineering and biomedicine in recent years. The preparation methods, modification strategies, construction of artificial tissues, and application in biomedical applications are discussed. We hope that this review will provide a useful reference for research on decellularized scaffolds and promote their application tissue engineering.

Advances in lung bioengineering: Where we are, where we need to go, and how to get there

Lung transplantation is the only potentially curative treatment for end-stage lung failure and successfully improves both long-term survival and quality of life. However, lung transplantation is limited by the shortage of suitable donor lungs. This discrepancy in organ supply and demand has prompted researchers to seek alternative therapies for end-stage lung failure. Tissue engineering (bioengineering) organs has become an attractive and promising avenue of research, allowing for the customized production of organs on demand, with potentially perfect biocompatibility. While breakthroughs in tissue engineering have shown feasibility in practice, they have also uncovered challenges in solid organ applications due to the need not only for structural support, but also vascular membrane integrity and gas exchange. This requires a complex engineered interaction of multiple cell types in precise anatomical locations. In this article, we discuss the process of creating bioengineered lungs and the challenges inherent therein. We summarize the relevant literature for selecting appropriate lung scaffolds, creating decellularization protocols, and using bioreactors. The development of completely artificial lung substitutes will also be reviewed. Lastly, we describe the state of current research, as well as future studies required for bioengineered lungs to become a realistic therapeutic modality for end-stage lung disease. Applications of bioengineering may allow for earlier intervention in end-stage lung disease and have the potential to not only halt organ failure, but also significantly reverse disease progression.

In-Vitro Endothelialization Assessment of Heparinized Bovine Pericardial Scaffold for Cardiovascular Application

(1) Background: Hemocompatibility is a critical challenge for tissue-derived biomaterial when directly contacting the bloodstream. In addition to surface modification with heparin, endothelialization of the grafted material is suggested to improve long-term clinical efficacy. This study aimed to evaluate the ability to endothelialize in vitro of heparinized bovine pericardial scaffolds. (2) Methods: bovine pericardial scaffolds were fabricated and heparinized using a layer-by-layer assembly technique. The heparinized scaffolds were characterized for heparin content, surface morphology, and blood compatibility. Liquid extraction of the samples was prepared for cytotoxicity testing on human endothelial cells. The in-vitro endothelialization was determined via human endothelial cell attachment and proliferation on the scaffold. (3) Results: The heparinized bovine pericardial scaffold exhibited a heparin coating within its microfiber network. The scaffold surface immobilized with heparin performed good anti-thrombosis and prevented platelet adherence. The proper cytotoxicity impact was observed for a freshly used heparinized sample. After 24 h washing in PBS 1X, the cell compatibility of the heparinized scaffolds was improved. In-vitro examination results exhibited human endothelial cell attachment and proliferation for 7 days of culture. (4) Conclusions: Our in-vitro analysis provided evidence for the scaffold's ability to support endothelialization, which benefits long-term thromboresistance.

Recent Advances in Liver Engineering With Decellularized Scaffold

Liver transplantation is currently the only effective treatment for patients with end-stage liver disease; however, donor liver scarcity is a notable concern. As a result, extensive endeavors have been made to diversify the source of donor livers. For example, the use of a decellularized scaffold in liver engineering has gained considerable attention in recent years. The decellularized scaffold preserves the original orchestral structure and bioactive chemicals of the liver, and has the potential to create a de novo liver that is fit for transplantation after recellularization. The structure of the liver and hepatic extracellular matrix, decellularization, recellularization, and recent developments are discussed in this review. Additionally, the criteria for assessment and major obstacles in using a decellularized scaffold are covered in detail.

Engineering liver microtissues for disease modeling and regenerative medicine

The burden of liver diseases is increasing worldwide, accounting for two million deaths annually. In the past decade, tremendous progress has been made in the basic and translational research of liver tissue engineering. Liver microtissues are small, three-dimensional hepatocyte cultures that recapitulate liver physiology and have been used in biomedical research and regenerative medicine. This review summarizes recent advances, challenges, and future directions in liver microtissue research. Cellular engineering approaches are used to sustain primary hepatocytes or produce hepatocytes derived from pluripotent stem cells and other adult tissues. Three-dimensional microtissues are generated by scaffold-free assembly or scaffold-assisted methods such as macroencapsulation, droplet microfluidics, and bioprinting. Optimization of the hepatic microenvironment entails incorporating the appropriate cell composition for enhanced cell-cell interactions and niche-specific signals, and creating scaffolds with desired chemical, mechanical and physical properties. Perfusion-based culture systems such as bioreactors and microfluidic systems are used to achieve efficient exchange of nutrients and soluble factors. Taken together, systematic optimization of liver microtissues is a multidisciplinary effort focused on creating liver cultures and on-chip models with greater structural complexity and physiological relevance for use in liver disease research, therapeutic development, and regenerative medicine.

Hemocompatibility improvement of decellularized spleen matrix for constructing transplantable bioartificial liver

Thrombogenicity is the predominant obstacle to successful implantation of decellularized spleen matrix (DSM). The aim of this study was to construct a transplantable functional bioartificial liver (BAL) with the use of DSM. This was achieved by layer-by-layer electrostatic immobilization technique by using poly dimethyl diallyl ammonium chloride and heparin. After heparin immobilization, DSM gradually turned from translucent into completely opaque milky white. Toluidine blue staining showed strong positive staining of the entire coated DSM. In vitro diluted blood perfusion test showed that the splenic arterial pressure of the heparin-coated DSM was much lower than that of the non-coated DSM (p < 0.01). Then, we heterotopically transplanted the modified DSM into rat hepatic injury model for 6 h to evaluate the hemocompatibility in vivo. Overall, HE staining and vWF immunohistochemistry all confirmed that heparin-coated DSM has a satisfactory anticoagulant effect. Based on the heparin-coated DSM, BALs were built with the use of rat primary hepatocytes. Our results demonstrate that these heparin-coated BALs satisfied anticoagulant effects even after 6 h. Immunofluorescence of ALB and G6PC also showed that hepatocytes in heparin-coated BAL have significantly higher cell viability and function than the non-coated group. However, serum analysis did not indicate a significant difference between the two groups but a slight trend of improvement with respect to serum albumin (p = 0.156) and aspartate transaminase (p = 0.140). In conclusion, we demonstrated that the BAL constructed by heparin-coated DSM can exert satisfactory short-term anticoagulant effects and can compensate for a certain degree of liver function.

Recent Advances in Decellularization and Recellularization for Tissue-Engineered Liver Grafts

Liver transplantation from deceased or living human donors remains the only proven option for patients with end-stage liver disease. However, the shortage of donor organs is a significant clinical concern that has led to the pursuit of tissue-engineered liver grafts generated from decellularized liver extracellular matrix and functional cells. Investigative efforts on optimizing both liver decellularization and recellularization protocols have been made in recent decades. In the current review, we briefly summarize these advances, including the generation of high-quality liver extracellular matrix scaffolds, evaluation criteria for quality control, modification of matrix for enhanced properties, and reseeding strategies. These efforts to optimize the methods of decellularization and recellularization lay the groundwork towards generating a transplantable, human-sized liver graft for the treatment of patients with severe liver disease.