In Vitro Characteristics of Porcine Tendon Hydrogel for Tendon Regeneration

Decellularization and Their Significance for Tissue Regeneration in the Era of 3D Bioprinting

Three-dimensional bioprinting is an emerging technology that has high potential application in tissue engineering and regenerative medicine. Increasing advancement and improvement in the decellularization process have led to an increase in the demand for using a decellularized extracellular matrix (dECM) to fabricate tissue engineered products. Decellularization is the process of retaining the extracellular matrix (ECM) while the cellular components are completely removed to harvest the ECM for the regeneration of various tissues and across different sources. Post decellularization of tissues and organs, they act as natural biomaterials to provide the biochemical and structural support to establish cell communication. Selection of an effective method for decellularization is crucial, and various factors like tissue density, geometric organization, and ECM composition affect the regenerative potential which has an impact on the end product. The dECM is a versatile material which is added as an important ingredient to formulate the bioink component for constructing tissue and organs for various significant studies. Bioink consisting of dECM from various sources is used to generate tissue-specific bioink that is unique and to mimic different biometric microenvironments. At present, there are many different techniques applied for decellularization, and the process is not standardized and regulated due to broad application. This review aims to provide an overview of different decellularization procedures, and we also emphasize the different dECM-derived bioinks present in the current global market and the major clinical outcomes. We have also highlighted an overview of benefits and limitations of different decellularization methods and various characteristic validations of decellularization and dECM-derived bioinks.

Exploring polysaccharide and protein-enriched decellularized matrix scaffolds for tendon and ligament repair: A review

Tissue engineering (TE) has become a primary research topic for the treatment of diseased or damaged tendon/ligament (T/L) tissue. T/L injuries pose a severe clinical burden worldwide, necessitating the development of effective strategies for T/L repair and tissue regeneration. TE has emerged as a promising strategy for restoring T/L function using decellularized extracellular matrix (dECM)-based scaffolds. dECM scaffolds have gained significant prominence because of their native structure, relatively high bioactivity, low immunogenicity, and ability to function as scaffolds for cell attachment, proliferation, and differentiation, which are difficult to imitate using synthetic materials. Here, we review the recent advances and possible future prospects for the advancement of dECM scaffolds for T/L tissue regeneration. We focus on crucial scaffold properties and functions, as well as various engineering strategies employed for biomaterial design in T/L regeneration. dECM provides both the physical and mechanical microenvironments required by cells to survive and proliferate. Various decellularization methods and sources of allogeneic and xenogeneic dECM in T/L repair and regeneration are critically discussed. Additionally, dECM hydrogels, bio-inks in 3D bioprinting, and nanofibers are briefly explored. Understanding the opportunities and challenges associated with dECM-based scaffold development is crucial for advancing T/L repairs in tissue engineering and regenerative medicine.

Decellularization of Dense Regular Connective Tissue-Cellular and Molecular Modification with Applications in Regenerative Medicine

Healing of dense regular connective tissue, due to a high fiber-to-cell ratio and low metabolic activity and regeneration potential, frequently requires surgical implantation or reconstruction with high risk of reinjury. An alternative to synthetic implants is using bioscaffolds obtained through decellularization, a process where the aim is to extract cells from the tissue while preserving the tissue-specific native molecular structure of the ECM. Proteins, lipids, nucleic acids and other various extracellular molecules are largely involved in differentiation, proliferation, vascularization and collagen fibers deposit, making them the crucial processes in tissue regeneration. Because of the multiple possible forms of cell extraction, there is no standardized protocol in dense regular connective tissue (DRCT). Many modifications of the structure, shape and composition of the bioscaffold have also been described to improve the therapeutic result following the implantation of decellularized connective tissue. The available data provide a valuable source of crucial information. However, the wide spectrum of decellularization makes it important to understand the key aspects of bioscaffolds relative to their potential use in tissue regeneration.

The Ethical Implications of Tissue Engineering for Regenerative Purposes: A Systematic Review

Tissue Engineering (TE) is a branch of Regenerative Medicine (RM) that combines stem cells and biomaterial scaffolds to create living tissue constructs to restore patients' organs after injury or disease. Over the last decade, emerging technologies such as 3D bioprinting, biofabrication, supramolecular materials, induced pluripotent stem cells, and organoids have entered the field. While this rapidly evolving field is expected to have great therapeutic potential, its development from bench to bedside presents several ethical and societal challenges. To make sure TE will reach its ultimate goal of improving patient welfare, these challenges should be mapped out and evaluated. Therefore, we performed a systematic review of the ethical implications of the development and application of TE for regenerative purposes, as mentioned in the academic literature. A search query in PubMed, Embase, Scopus, and PhilPapers yielded 2451 unique articles. After systematic screening, 237 relevant ethical and biomedical articles published between 2008 and 2021 were included in our review. We identified a broad range of ethical implications that could be categorized under 10 themes. Seven themes trace the development from bench to bedside: (1) animal experimentation, (2) handling human tissue, (3) informed consent, (4) therapeutic potential, (5) risk and safety, (6) clinical translation, and (7) societal impact. Three themes represent ethical safeguards relevant to all developmental phases: (8) scientific integrity, (9) regulation, and (10) patient and public involvement. This review reveals that since 2008 a significant body of literature has emerged on how to design clinical trials for TE in a responsible manner. However, several topics remain in need of more attention. These include the acceptability of alternative translational pathways outside clinical trials, soft impacts on society and questions of ownership over engineered tissues. Overall, this overview of the ethical and societal implications of the field will help promote responsible development of new interventions in TE and RM. It can also serve as a valuable resource and educational tool for scientists, engineers, and clinicians in the field by providing an overview of the ethical considerations relevant to their work. Impact statement To our knowledge, this is the first time that the ethical implications of Tissue Engineering (TE) have been reviewed systematically. By gathering existing scholarly work and identifying knowledge gaps, this review facilitates further research into the ethical and societal implications of TE and Regenerative Medicine (RM) and other emerging biomedical technologies. Moreover, it will serve as a valuable resource and educational tool for scientists, engineers, and clinicians in the field by providing an overview of the ethical considerations relevant to their work. As such, our review may promote successful and responsible development of new strategies in TE and RM.

Enhancement of Migration and Tenogenic Differentiation of Macaca Mulatta Tendon-Derived Stem Cells by Decellularized Tendon Hydrogel

Decellularized tendon hydrogel from human or porcine tendon has been manufactured and found to be capable of augmenting tendon repair in vivo. However, no studies have clarified the effect of decellularized tendon hydrogel upon stem cell behavior. In the present study, we developed a new decellularized tendon hydrogel (T-gel) from Macaca mulatta, and investigated the effect of T-gel on the proliferation, migration and tenogenic differentiation of Macaca mulatta tendon-derived stem cells (mTDSCs). The mTDSCs were first identified to have universal stem cell characteristics, including clonogenicity, expression of mesenchymal stem cell and embryonic stem cell markers, and multilineage differentiation potential. Decellularization of Macaca mulatta Achilles tendons was confirmed to be effective by histological staining and DNA quantification. The resultant T-gel exhibited highly porous structure or similar nanofibrous structure and approximately swelling ratio compared to the collagen gel (C-gel). Interestingly, stromal cell-derived factor-1 (SDF-1) and fibromodulin (Fmod) inherent in the native tendon extracellular matrix (ECM) microenvironment were retained and the values of SDF-1 and Fmod in the T-gel were significantly higher than those found in the C-gel. Compared with the C-gel, the T-gel was found to be cytocompatible with NIH-3T3 fibroblasts and displayed good histocompatibility when implanted into rat subcutaneous tissue. More importantly, it was demonstrated that the T-gel supported the proliferation of mTDSCs and significantly promoted the migration and tenogenic differentiation of mTDSCs compared to the C-gel. These findings indicated that the T-gel, with its retained nanofibrous structure and some bioactive factors of native tendon ECM microenvironment, represents a promising hydrogel for tendon regeneration.

Pancreatic extracellular matrix and platelet-rich plasma constructing injectable hydrogel for pancreas tissue engineering

The development of pancreatic extracellular matrices enriched with insulin-secreting β-cells is a promising tissue engineering approach to treat type 1 diabetes. However, its long-term therapeutic efficacy is restricted by the defensive mechanism of host immune response and the lack of developed vascularization as appropriate after transplantation. Platelet-rich plasma (PRP), as an autologous platelet concentrate, contains a large number of active factors that are essential for the cell viability, vascularization, and immune regulation. In this study, we have incorporated pancreatic extracellular matrix (PEM) with PRP to develop a three-dimensional (3D) injectable PEM-PRP hydrogel to coculture and transplant rat insulinoma cells (INS-1) and human umbilical vein endothelial cells (HUVECs). Results from this study demonstrated that PEM-PRP hydrogel mimicked the biochemical compositions of native extracellular matrices, and possessed the enhanced elastic modulus and resistance to enzymatic degradation that enabled biomaterials to maintain its volume and slowly degrade. Additionally, PEM-PRP hydrogel could release growth factors in a sustained manner. In vitro, PEM-PRP hydrogel significantly promoted the viability, insulin-secreting function, and insulin gene expression of gel encapsulated INS-1 cells. Moreover, HUVECs encapsulated in PEM-PRP hydrogel were found to constitute many lumen-like structures and exhibited high expression of proangiogenic genes. In vivo transplantation of PEM-PRP hydrogel encapsulated with INS-1 cells and HUVECs improved the viability of INS-1 cells, promoted vascularization, inhibited the host inflammatory response, and reversed hyperglycemia of diabetic rats. Our study suggests that the PEM-PRP hydrogel offers excellent biocompatibility and proangiogenic property, and may serve as an effective biomaterial platform to maintain the long-term survival and function of insulin-secreting β cells.

Extracellular matrix hydrogel therapies: In vivo applications and development

Decellularized extracellular matrix (ECM) has been widely used for tissue engineering applications and is becoming increasingly versatile as it can take many forms, including patches, powders, and hydrogels. Following additional processing, decellularized ECM can form an inducible hydrogel that can be injected, providing for new minimally-invasive procedure opportunities. ECM hydrogels have been derived from numerous tissue sources and applied to treat many disease models, such as ischemic injuries and organ regeneration or replacement. This review will focus on in vivo applications of ECM hydrogels and functional outcomes in disease models, as well as discuss considerations for clinical translation.

STATEMENT OF SIGNIFICANCE

Extracellular matrix (ECM) hydrogel therapies are being developed to treat diseased or damaged tissues and organs throughout the body. Many ECM hydrogels are progressing from in vitro models to in vivo biocompatibility studies and functional models. There is significant potential for clinical translation of these therapies since one ECM hydrogel therapy is already in a Phase 1 clinical trial.