Systematic Comparison of Protocols for the Preparation of Human Articular Cartilage for Use as Scaffold Material in Cartilage Tissue Engineering

Bioactive scaffolds for tissue engineering: A review of decellularized extracellular matrix applications and innovations

Decellularized extracellular matrix (dECM) offers a three-dimensional, non-immunogenic scaffold, enriched with bioactive components, making it a suitable candidate for tissue regeneration. Although dECM-based scaffolds have been successfully implemented in preclinical and clinical settings within tissue engineering and regenerative medicine, the mechanisms of tissue remodeling and functional restoration are not fully understood. This review critically assesses the state-of-the-art in dECM scaffolds, including decellularization techniques for various tissues, quality control and cross-linking. It highlights the functional properties of dECM components and their latest applications in multiorgan tissue engineering and biomedicine. Additionally, the review addresses current challenges and limitations of decellularized scaffolds and offers perspectives on future directions in the field.

Exploiting the Potential of Decellularized Extracellular Matrix (ECM) in Tissue Engineering: A Review Study

While significant progress has been made in creating polymeric structures for tissue engineering, the therapeutic application of these scaffolds remains challenging owing to the intricate nature of replicating the conditions of native organs and tissues. The use of human-derived biomaterials for therapeutic purposes closely imitates the properties of natural tissue, thereby assisting in tissue regeneration. Decellularized extracellular matrix (dECM) scaffolds derived from natural tissues have become popular because of their unique biomimetic properties. These dECM scaffolds can enhance the body's ability to heal itself or be used to generate new tissues for restoration, expanding beyond traditional tissue transfers and transplants. Enhanced knowledge of how ECM scaffold materials affect the microenvironment at the injury site is expected to improve clinical outcomes. In this review, recent advancements in dECM scaffolds are explored and relevant perspectives are offered, highlighting the development and application of these scaffolds in tissue engineering for various organs, such as the skin, nerve, bone, heart, liver, lung, and kidney.

A Tissue-Engineered Construct Based on a Decellularized Scaffold and the Islets of Langerhans: A Streptozotocin-Induced Diabetic Model

Producing a tissue-engineered pancreas based on a tissue-specific scaffold from a decellularized pancreas, imitating the natural pancreatic tissue microenvironment and the islets of Langerhans, is one of the approaches to treating patients with type 1 diabetes mellitus (T1DM). The aim of this work was to investigate the ability of a fine-dispersed tissue-specific scaffold (DP scaffold) from decellularized human pancreas fragments to support the islets' survival and insulin-producing function when injected in a streptozotocin-induced diabetic rat model. The developed decellularization protocol allows us to obtain a scaffold with a low DNA content (33 [26; 38] ng/mg of tissue, p < 0.05) and with the preservation of GAGs (0.92 [0.84; 1.16] µg/mg, p < 0.05) and fibrillar collagen (273.7 [241.2; 303.0] µg/mg, p < 0.05). Rat islets of Langerhans were seeded in the obtained scaffolds. The rats with stable T1DM were treated by intraperitoneal injections of rat islets alone and islets seeded on the DP scaffold. The blood glucose level was determined for 10 weeks with a histological examination of experimental animals' pancreas. A more pronounced decrease in the recipient rats' glycemia was detected after comparing the islets seeded on the DP scaffold with the control injection (by 71.4% and 51.2%, respectively). It has been shown that the DP scaffold facilitates a longer survival and the efficient function of pancreatic islets in vivo and can be used to engineer a pancreas.

Development of bioactive solid-foam scaffolds from decellularized cartilage with chondrogenic and osteogenic properties

Full osteochondral regeneration remains a major clinical challenge. Among other experimental cartilage regenerative approaches, decellularized cartilage (DCC) is considered a promising material for generating potentially implantable scaffolds useful as cartilage repair strategy. In this work, we focus on screening and comparing different decellularization methods, aiming to generate DCC potentially useful in biomedical context, and therefore, with biological activity and functional properties in terms of induction of differentiation and regeneration. Data indicates that enzymatic and detergents-based decellularization methods differentially affect ECM components, and that it has consequences in further biological behavior. SDS-treated DCC powder is not useful to be further processed in 2D or 3D structures, because these structures tend to rapidly solubilize, or disaggregate, in physiologic media conditions. Conversely, Trypsin-treated DCC powders can be processed to mechanically stable 2D films and 3D solid-foam scaffolds, presumably due to partial digestion of collagens during decellularization, which would ease crosslinking at DCC during solubilization and processing. In vitro cell culture studies indicate that these structures are biocompatible and induce and potentiate chondrogenic differentiation. In vivo implantation of DCC derived 3D porous scaffolds in rabbit osteochondral defects induce subchondral bone regeneration and fibrocartilage tissue formation after implantation. Therefore, this work defines an optimal cartilage tissue decellularization protocol able to generate DCC powders processable to biocompatible and bioactive 2D and 3D structures. These structures are useful for in vitro cartilage research and in vivo subchondral bone regeneration, while hyaline cartilage regeneration with DCC alone as implantable material remains elusive.

Current Strategies for Tracheal Decellularization: A Systematic Review

The process of decellularization is crucial for producing a substitute for the absent tracheal segment, and the choice of agents and methods significantly influences the outcomes. This paper aims to systematically review the efficacy of diverse tracheal decellularization agents and methods using the PRISMA flowchart. Inclusion criteria encompassed experimental studies published between 2018 and 2023, written in English, and detailing outcomes related to histopathological anatomy, DNA quantification, ECM evaluation, and biomechanical characteristics. Exclusion criteria involved studies related to 3D printing, biomaterials, and partial decellularization. A comprehensive search on PubMed, NCBI, and ScienceDirect yielded 17 relevant literatures. The integration of various agents and methods has proven effective in the process of tracheal decellularization, highlighting the distinct advantages and drawbacks associated with each agent and method.

Decellularized extracellular matrix biomaterials for regenerative therapies: Advances, challenges and clinical prospects

Tissue engineering and regenerative medicine have shown potential in the repair and regeneration of tissues and organs via the use of engineered biomaterials and scaffolds. However, current constructs face limitations in replicating the intricate native microenvironment and achieving optimal regenerative capacity and functional recovery. To address these challenges, the utilization of decellularized tissues and cell-derived extracellular matrix (ECM) has emerged as a promising approach. These biocompatible and bioactive biomaterials can be engineered into porous scaffolds and grafts that mimic the structural and compositional aspects of the native tissue or organ microenvironment, both in vitro and in vivo. Bioactive dECM materials provide a unique tissue-specific microenvironment that can regulate and guide cellular processes, thereby enhancing regenerative therapies. In this review, we explore the emerging frontiers of decellularized tissue-derived and cell-derived biomaterials and bio-inks in the field of tissue engineering and regenerative medicine. We discuss the need for further improvements in decellularization methods and techniques to retain structural, biological, and physicochemical characteristics of the dECM products in a way to mimic native tissues and organs. This article underscores the potential of dECM biomaterials to stimulate in situ tissue repair through chemotactic effects for the development of growth factor and cell-free tissue engineering strategies. The article also identifies the challenges and opportunities in developing sterilization and preservation methods applicable for decellularized biomaterials and grafts and their translation into clinical products.

Subcutaneously Transplanted Fresh Cartilage in Allogeneic and Xenogeneic Immunocompetent Mouse

Cartilage is considered to be immune privileged in general. Clinically, live cells are removed from subcutaneously transplanted allogeneic cartilage mainly for preservation and for infection control. However, because maintaining cartilage feature requires live chondrocyte, it would be beneficial to subcutaneously transplant cartilage with live chondrocyte even if it was allogeneic. We harvested femoral head from 3-week-old male C57BL/6 mice, subcutaneously transplanted to 6-week-old male mice, BALB/c, BALB/c nu/nu, or C57BL/6-Tg (enhanced green fluorescent protein [EGFP] under the control of the CMV-IE enhancer, chicken beta-actin promoter, rabbit beta-globin genomic DNA [CAG promoter]), as allogeneic, allogeneic immunodeficient control, or syngeneic transplantation. We also transplanted cartilaginous particles from human induced pluripotent stem cells derived from human leukocyte antigen homozygous donor to 6-week-old male mice either BALB/c and BALB/c nu/nu as xenogeneic or xenogeneic immunodeficient control. The transplantation periods were 1, 2, 3, 4, 8, 12, and 24 weeks. As the result, we did not observe exposure of the transplant or apparent macroscopic inflammatory in all samples. Histological analysis suggested that the femoral head showed focal ossification and thinning in syngeneic transplantation. In allogeneic transplantation, slight invasion of CD3 (+) T cell and the denaturation of the cartilage were observed, suggesting immune reaction against allogeneic cartilage. In xenogeneic transplantation, slight invasion of CD3 (+) cell and CD4 (+) cell and the structure of the perichondrium-like tissue got unclear, suggesting slight immune reaction against xenogeneic cartilage. Our findings suggest that we should carefully investigate for appropriate procedure to control immune reaction against allogeneic cartilage with live chondrocyte and to maintain its cartilage feature for long time.

Decellularization of cartilage microparticles: Effects of temperature, supercritical carbon dioxide and ultrasound on biochemical, mechanical, and biological properties

One of the approaches to restoring the structure of damaged cartilage tissue is an intra-articular injection of tissue-engineered medical products (TEMPs) consisting of biocompatible matrices loaded with cells. The most interesting are the absorbable matrices from decellularized tissues, provided that the cellular material is completely removed from them with the maximum possible preservation of the structure and composition of the natural extracellular matrix. The present study investigated the mechanical, biochemical, and biological properties of decellularized porcine cartilage microparticles (DCMps) obtained by techniques, differing only in physical treatments, such as freeze-thaw cycling (Protocol 1), supercritical carbon dioxide fluid (Protocol 2) and ultrasound (Protocol 3). Full tissue decellularization was achieved, as confirmed by the histological analysis and DNA quantification, though all the resultant DCMps had reduced glycosaminoglycans (GAGs) and collagen. The elastic modulus of all DCMp samples was also significantly reduced. Most notably, DCMps prepared with Protocol 3 significantly outperformed other samples in viability and the chondroinduction of the human adipose-derived stem cells (hADSCs), with a higher GAG production per DNA content. A positive ECM staining for type II collagen was also detected only in cartilage-like structures based on ultrasound-treated DCMps. The biocompatibility of a xenogenic DCMps obtained with Protocol 3 has been confirmed for a 6-month implantation in the thigh muscle tissue of mature rats (n = 18). Overall, the results showed that the porcine cartilage microparticles decellularized by a combination of detergents, ultrasound and DNase could be a promising source of scaffolds for TEMPs for cartilage reconstruction.

Decellularized ECM hydrogels: prior use considerations, applications, and opportunities in tissue engineering and biofabrication

Tissue development, wound healing, pathogenesis, regeneration, and homeostasis rely upon coordinated and dynamic spatial and temporal remodeling of extracellular matrix (ECM) molecules. ECM reorganization and normal physiological tissue function, require the establishment and maintenance of biological, chemical, and mechanical feedback mechanisms directed by cell-matrix interactions. To replicate the physical and biological environment provided by the ECM in vivo, methods have been developed to decellularize and solubilize tissues which yield organ and tissue-specific bioactive hydrogels. While these biomaterials retain several important traits of the native ECM, the decellularizing process, and subsequent sterilization, and solubilization result in fragmented, cleaved, or partially denatured macromolecules. The final product has decreased viscosity, moduli, and yield strength, when compared to the source tissue, limiting the compatibility of isolated decellularized ECM (dECM) hydrogels with fabrication methods such as extrusion bioprinting. This review describes the physical and bioactive characteristics of dECM hydrogels and their role as biomaterials for biofabrication. In this work, critical variables when selecting the appropriate tissue source and extraction methods are identified. Common manual and automated fabrication techniques compatible with dECM hydrogels are described and compared. Fabrication and post-manufacturing challenges presented by the dECM hydrogels decreased mechanical and structural stability are discussed as well as circumvention strategies. We further highlight and provide examples of the use of dECM hydrogels in tissue engineering and their role in fabricating complex in vitro 3D microenvironments.

Decellularization of Articular Cartilage: A Hydrochloric Acid-Based Strategy

Removing cellular material from a tissue, a process called decellularization, reduces the risk of adverse host reactions, allows for efficient decontamination, and extends the shelf-life of the matrix. It facilitates the use of cartilage tissue as human-derived allograft, thus providing the field of cartilage regeneration with a biomaterial unmatched in its similarity to native cartilage in terms of structure, composition, and mechanical properties.The dense extracellular matrix of articular cartilage requires a particularly thorough process to achieve the removal of cells, cell debris, and reagents used in the process. In our studies (Nürnberger et al., EBioMedicine 64:103196, 2021; Schneider et al., Tissue Eng Part C Methods 22(12):1095-1107, 2016), we have successfully developed a protocol for achieving decellularization via physical, chemical, and enzymatic steps. Combining freeze-thaw cycles for devitalization, hydrochloric acid as decellularization agent and the enzymatic removal of glycosaminoglycans, results in an acellular scaffold that is fully biocompatible and promotes cellular attachment. The structure and sophisticated architecture of collagen type II is left intact.This chapter provides a comprehensive guide to the steps and reagents needed to decellularize articular cartilage. In addition to the standard decell-deGAG protocol, a fast option is given which is suitable for thin specimen. Histological evaluation is presented to illustrate treatment success.

Functional acellular matrix for tissue repair

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

Direct 3D printing of decellularized matrix embedded composite polycaprolactone scaffolds for cartilage regeneration

Treatment options for large osteochondral injuries (OCIs) are limited by donor tissue scarcity, morbidity, and anatomic mismatch. 3D printing technology can produce patient-specific scaffolds to address these large defects. Thermoplastics like polycaprolactone (PCL) offer necessary mechanical properties, but lack bioactivity. We fabricated 3D printed PCL scaffolds embedded with polylactic acid microspheres containing decellularized cartilage matrix (DM). DM incorporation within polylactic acid microspheres prevented its thermal degradation during the 3D printing process. The scaffolds replicated the mechanical properties of native cartilage and demonstrated controlled release of DM proteins. Human mesenchymal stem cells (hMSCs) seeded on the composite scaffolds with DM and cultured in basal media self-assembled into aggregates mimicking mesenchymal condensates during embryonic development. The DM composite scaffolds also induced higher expression of biochemical markers of cartilage development than controls, providing evidence for their translational application in the treatment of OCIs. The present study demonstrates the potential of direct incorporation of DM with thermoplastics for 3D printing of patient-specific scaffolds for osteochondral regeneration.

Preparation and Application of Decellularized ECM-Based Biological Scaffolds for Articular Cartilage Repair: A Review

Cartilage regeneration is dependent on cellular-extracellular matrix (ECM) interactions. Natural ECM plays a role in mechanical and chemical cell signaling and promotes stem cell recruitment, differentiation and tissue regeneration in the absence of biological additives, including growth factors and peptides. To date, traditional tissue engineering methods by using natural and synthetic materials have not been able to replicate the physiological structure (biochemical composition and biomechanical properties) of natural cartilage. Techniques facilitating the repair and/or regeneration of articular cartilage pose a significant challenge for orthopedic surgeons. Whereas, little progress has been made in this field. In recent years, with advances in medicine, biochemistry and materials science, to meet the regenerative requirements of the heterogeneous and layered structure of native articular cartilage (AC) tissue, a series of tissue engineering scaffolds based on ECM materials have been developed. These scaffolds mimic the versatility of the native ECM in function, composition and dynamic properties and some of which are designed to improve cartilage regeneration. This review systematically investigates the following: the characteristics of cartilage ECM, repair mechanisms, decellularization method, source of ECM, and various ECM-based cartilage repair methods. In addition, the future development of ECM-based biomaterials is hypothesized.

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.

Relation between micro- and nanostructure features and biological properties of the decellularized rat liver

Organ decellularization is one of the promising technologies of regenerative medicine, which allows obtaining cell-free extracellular matrix (ECM), which provide preservation of the composition, architecture, vascular network and biological activity of the ECM. The method of decellularization opens up wide prospects for its practical application not only in the field of creating full-scale bioengineered structures, but also in the manufacture of vessels, microcarriers, hydrogels, and coatings. The main goal of our work was the investigation of structure and biological properties of lyophilized decellularized Wistar rat liver fragments (LDLFs), as well as we assessed the regenerative potential of the obtained ECM. We obtained decellularized liver of a Wistar rat, the vascular network and the main components of the ECM of tissue were preserved. H&E staining of histological sections confirmed the removal of cells. DNA content of ECM is equal to 0.7% of native tissue DNA content. Utilizing scanning probe nanotomogrphy method, we showed sinuous, rough topography and highly nanoporous structure of ECM, which provide high level of mouse 3T3 fibroblast and Hep-G₂cells biocompatibility. Obtained LDLF had a high regenerative potential, which we studied in an experimental model of a full-thickness rat skin wound healing: we observed the acceleration of wound healing by 2.2 times in comparison with the control.

Research progress in decellularized extracellular matrix-derived hydrogels

Decellularized extracellular matrix (dECM) is widely used in regenerative medicine as a scaffold material due to its unique biological activity and good biocompatibility. Hydrogel is a three-dimensional network structure polymer with high water content and high swelling that can simulate the water environment of human tissues, has good biocompatibility, and can exchange nutrients, oxygen, and waste with cells. At present, hydrogel is the ideal biological material for tissue engineering. In recent years, rapid development of the hydrogel theory and technology and progress in the use of dECM to form hydrogels have attracted considerable attention to dECM hydrogels as an innovative method for tissue engineering and regenerative medicine. This article introduces the classification of hydrogels, and focuses on the history and formation of dECM hydrogels, the source of dECM, the application of dECM hydrogels in tissue engineering and the commercial application of dECM materials.

Host Response to Biomaterials for Cartilage Tissue Engineering: Key to Remodeling

Biomaterials play a core role in cartilage repair and regeneration. The success or failure of an implanted biomaterial is largely dependent on host response following implantation. Host response has been considered to be influenced by numerous factors, such as immune components of materials, cytokines and inflammatory agents induced by implants. Both synthetic and native materials involve immune components, which are also termed as immunogenicity. Generally, the innate and adaptive immune system will be activated and various cytokines and inflammatory agents will be consequently released after biomaterials implantation, and further triggers host response to biomaterials. This will guide the constructive remolding process of damaged tissue. Therefore, biomaterial immunogenicity should be given more attention. Further understanding the specific biological mechanisms of host response to biomaterials and the effects of the host-biomaterial interaction may be beneficial to promote cartilage repair and regeneration. In this review, we summarized the characteristics of the host response to implants and the immunomodulatory properties of varied biomaterial. We hope this review will provide scientists with inspiration in cartilage regeneration by controlling immune components of biomaterials and modulating the immune system.

Enhanced articular cartilage decellularization using a novel perfusion-based bioreactor method

Current decellularization methods for articular cartilages require many steps, various and high amounts of detergents, and a relatively long time to produce decellularized scaffolds. In addition, such methods often damage the essential components and the structure of the tissue. This study aims to introduce a novel perfusion-based bioreactor (PBB) method to decellularize bovine articular cartilages efficiently while reducing the harmful physical and chemical steps as well as the duration of the process. This leads to better preservation of the structure and the essential components of the native tissue. Firstly, a certain number of channels (Ø 180 μm) were introduced into both sides of cylindrical articular bovine cartilage disks (5 mm in diameter and 1 mm in thickness). Next, the disks were decellularized in the PBB and a shaker as the control. Using the PBB method resulted in ∼90% reduction of DNA content in the specimens, which was significantly higher than those of the shaker results with ∼60%. Also, ∼50% sulfated glycosaminoglycan (sGAG) content and ∼92% of the compression properties were maintained implying the efficient preservation of the structure and components of the scaffolds. Moreover, the current study indicated that the PBB specimens supported the adherence and proliferation of the new cells effectively. In conclusion, the results show that the use of PBB method increases the efficiency of producing decellularized cartilage scaffolds with a better maintenance of essential components and structure, while reducing the chemicals and steps required for the process. This will pave the way for producing close-to-natural scaffolds for cartilage tissue engineering.

Repopulation of decellularised articular cartilage by laser-based matrix engraving

BACKGROUND

In spite of advances in the treatment of cartilage defects using cell and scaffold-based therapeutic strategies, the long-term outcome is still not satisfying since clinical scores decline years after treatment. Scaffold materials currently used in clinical settings have shown limitations in providing suitable biomechanical properties and an authentic and protective environment for regenerative cells. To tackle this problem, we developed a scaffold material based on decellularised human articular cartilage.

METHODS

Human articular cartilage matrix was engraved using a CO₂ laser and treated for decellularisation and glycosaminoglycan removal. Characterisation of the resulting scaffold was performed via mechanical testing, DNA and GAG quantification and in vitro cultivation with adipose-derived stromal cells (ASC). Cell vitality, adhesion and chondrogenic differentiation were assessed. An ectopic, unloaded mouse model was used for the assessment of the in vivo performance of the scaffold in combination with ASC and human as well as bovine chondrocytes. The novel scaffold was compared to a commercial collagen type I/III scaffold.

FINDINGS

Crossed line engravings of the matrix allowed for a most regular and ubiquitous distribution of cells and chemical as well as enzymatic matrix treatment was performed to increase cell adhesion. The biomechanical characteristics of this novel scaffold that we term CartiScaff were found to be superior to those of commercially available materials. Neo-tissue was integrated excellently into the scaffold matrix and new collagen fibres were guided by the laser incisions towards a vertical alignment, a typical feature of native cartilage important for nutrition and biomechanics. In an ectopic, unloaded in vivo model, chondrocytes and mesenchymal stromal cells differentiated within the incisions despite the lack of growth factors and load, indicating a strong chondrogenic microenvironment within the scaffold incisions. Cells, most noticeably bone marrow-derived cells, were able to repopulate the empty chondrocyte lacunae inside the scaffold matrix.

INTERPRETATION

Due to the better load-bearing, its chondrogenic effect and the ability to guide matrix-deposition, CartiScaff is a promising biomaterial to accelerate rehabilitation and to improve long term clinical success of cartilage defect treatment.

FUNDING

Austrian Research Promotion Agency FFG ("CartiScaff" #842455), Lorenz Böhler Fonds (16/13), City of Vienna Competence Team Project Signaltissue (MA23, #18-08).

Repopulation of decellularised articular cartilage by laser-based matrix engraving

Background

In spite of advances in the treatment of cartilage defects using cell and scaffold-based therapeutic strategies, the long-term outcome is still not satisfying since clinical scores decline years after treatment. Scaffold materials currently used in clinical settings have shown limitations in providing suitable biomechanical properties and an authentic and protective environment for regenerative cells. To tackle this problem, we developed a scaffold material based on decellularised human articular cartilage.

Methods

Human articular cartilage matrix was engraved using a CO₂ laser and treated for decellularisation and glycosaminoglycan removal. Characterisation of the resulting scaffold was performed via mechanical testing, DNA and GAG quantification and in vitro cultivation with adipose-derived stromal cells (ASC). Cell vitality, adhesion and chondrogenic differentiation were assessed. An ectopic, unloaded mouse model was used for the assessment of the in vivo performance of the scaffold in combination with ASC and human as well as bovine chondrocytes. The novel scaffold was compared to a commercial collagen type I/III scaffold.

Findings

Crossed line engravings of the matrix allowed for a most regular and ubiquitous distribution of cells and chemical as well as enzymatic matrix treatment was performed to increase cell adhesion. The biomechanical characteristics of this novel scaffold that we term CartiScaff were found to be superior to those of commercially available materials. Neo-tissue was integrated excellently into the scaffold matrix and new collagen fibres were guided by the laser incisions towards a vertical alignment, a typical feature of native cartilage important for nutrition and biomechanics. In an ectopic, unloaded in vivo model, chondrocytes and mesenchymal stromal cells differentiated within the incisions despite the lack of growth factors and load, indicating a strong chondrogenic microenvironment within the scaffold incisions. Cells, most noticeably bone marrow-derived cells, were able to repopulate the empty chondrocyte lacunae inside the scaffold matrix.

Interpretation

Due to the better load-bearing, its chondrogenic effect and the ability to guide matrix-deposition, CartiScaff is a promising biomaterial to accelerate rehabilitation and to improve long term clinical success of cartilage defect treatment.

Funding

Austrian Research Promotion Agency FFG (“CartiScaff” #842455), Lorenz Böhler Fonds (16/13), City of Vienna Competence Team Project Signaltissue (MA23, #18-08)

A novel 3D histotypic cartilage construct engineered by supercritical carbon dioxide decellularized porcine nasal cartilage graft and chondrocytes exhibited chondrogenic capability in vitro

Augmentative and reconstructive rhinoplasty surgical procedures use autologous tissue grafts or synthetic grafts to repair the nasal defect and aesthetic reconstruction. Donor site trauma and morbidity are common in autologous grafts. The desperate need for the production of grafted 3D cartilage tissues as rhinoplasty grafts without the adverse effect is the need of the hour. In the present study, we developed a bioactive 3D histotypic construct engineered with the various ratio of adipose-derived stem cells (ADSC) and chondrocytes together with decellularized porcine nasal cartilage graft (dPNCG). We decellularized porcine nasal cartilage using supercritical carbon dioxide (SCCO2) extraction technology. dPNCG was characterized by H&E, DAPI, alcian blue staining, scanning electron microscopy and residual DNA content, which demonstrated complete decellularization. 3D histotypic constructs were engineered using dPNCG, rat ADSC and chondrocytes with different percentage of cells and cultured for 21 days. dPNCG together with 100% chondrocytes produced a solid mass of 3D histotypic cartilage with significant production of glycosaminoglycans. H&E and alcian blue staining showed an intact mass, with cartilage granules bound to one another by extracellular matrix and proteoglycan, to form a 3D structure. Besides, the expression of chondrogenic markers, type II collagen, aggrecan and SOX-9 were elevated indicating chondrocytes cultured on dPNCG substrate facilitates the synthesis of type II collagen along with extracellular matrix to produce 3D histotypic cartilage. To conclude, dPNCG is an excellent substrate scaffold that might offer a suitable environment for chondrocytes to produce 3D histotypic cartilage. This engineered 3D construct might serve as a promising future candidate for cartilage tissue engineering in rhinoplasty.

Decellularized Extracellular Matrix-based Bioinks for Engineering Tissue- and Organ-specific Microenvironments

Biomaterials-based biofabrication methods have gained much attention in recent years. Among them, 3D cell printing is a pioneering technology to facilitate the recapitulation of unique features of complex human tissues and organs with high process flexibility and versatility. Bioinks, combinations of printable hydrogel and cells, can be utilized to create 3D cell-printed constructs. The bioactive cues of bioinks directly trigger cells to induce tissue morphogenesis. Among the various printable hydrogels, the tissue- and organ-specific decellularized extracellular matrix (dECM) can exert synergistic effects in supporting various cells at any component by facilitating specific physiological properties. In this review, we aim to discuss a new paradigm of dECM-based bioinks able to recapitulate the inherent microenvironmental niche in 3D cell-printed constructs. This review can serve as a toolbox for biomedical engineers who want to understand the beneficial characteristics of the dECM-based bioinks and a basic set of fundamental criteria for printing functional human tissues and organs.

Recellularization of auricular cartilage via elastase-generated channels

Decellularized tissue matrices are promising substrates for tissue generation by stem cells to replace poorly regenerating tissues such as cartilage. However, the dense matrix of decellularized cartilage impedes colonisation by stem cells. Here, we show that digestion of elastin fibre bundles traversing auricular cartilage creates channels through which cells can migrate into the matrix. Human chondrocytes and bone marrow-derived mesenchymal stromal cells efficiently colonise elastin-treated scaffolds through these channels, restoring a glycosaminoglycan-rich matrix and improving mechanical properties while maintaining size and shape of the restored tissue. The scaffolds are also rapidly colonised by endogenous cartilage-forming cells in a subcutaneously implanted osteochondral biopsy model. Creating channels for cells in tissue matrices may be a broadly applicable strategy for recellularization and restoration of tissue function.

Decellularized cartilage as a prospective scaffold for cartilage repair

Articular cartilage lacks self-healing capacity, and there is no effective therapy facilitating cartilage repair. Osteoarthritis (OA) due to cartilage defects represents large and increasing healthcare burdens worldwide. Nowadays, the generation of scaffolds to preserve bioactive factors and the biophysical environment has received increasing attention. Furthermore, improved decellularization technology has provided novel insights into OA treatment. This review provides a comparative account of different cartilage defect therapies. Furthermore, some recent effective decellularization protocols have been discussed. In particular, this review focuses on the decellularization ratio of each protocol. Moreover, these protocols were compared particularly on the basis of immunogenicity and mechanical functionality. Further, various recellularization methods have been enlisted and the reparative capacity of decellularized cartilage scaffolds is evaluated herein. The advantages and limitations of different recellularization processes have been described herein. This provides a basis for the generation of decellularized cartilage scaffolds, thereby potentially promoting the possibility of decellularization as a clinical therapeutic target.

Repopulation of an auricular cartilage scaffold, AuriScaff, perforated with an enzyme combination

Biomaterials currently in use for articular cartilage regeneration do not mimic the composition or architecture of hyaline cartilage, leading to the formation of repair tissue with inferior characteristics. In this study we demonstrate the use of "AuriScaff", an enzymatically perforated bovine auricular cartilage scaffold, as a novel biomaterial for repopulation with regenerative cells and for the formation of high-quality hyaline cartilage. AuriScaff features a traversing channel network, generated by selective depletion of elastic fibers, enabling uniform repopulation with therapeutic cells. The complex collagen type II matrix is left intact, as observed by immunohistochemistry, SEM and TEM. The compressive modulus is diminished, but three times higher than in the clinically used collagen type I/III scaffold that served as control. Seeding tests with human articular chondrocytes (hAC) alone and in co-culture with human adipose-derived stromal/stem cells (ASC) confirmed that the network enabled cell migration throughout the scaffold. It also guides collagen alignment along the channels and, due to the generally traverse channel alignment, newly deposited cartilage matrix corresponds with the orientation of collagen within articular cartilage. In an osteochondral plug model, AuriScaff filled the complete defect with compact collagen type II matrix and enabled chondrogenic differentiation inside the channels. Using adult articular chondrocytes from bovine origin (bAC), filling of even deep defects with high-quality hyaline-like cartilage was achieved after 6 weeks in vivo. With its composition and spatial organization, AuriScaff provides an optimal chondrogenic environment for therapeutic cells to treat cartilage defects and is expected to improve long-term outcome by channel-guided repopulation followed by matrix deposition and alignment. STATEMENT OF SIGNIFICANCE: After two decades of tissue engineering for cartilage regeneration, there is still no optimal strategy available to overcome problems such as inconsistent clinical outcome, early and late graft failures. Especially large defects are dependent on biomaterials and their scaffolding, guiding and protective function. Considering the currently used biomaterials, structure and mechanical properties appear to be insufficient to fulfill this task. The novel scaffold developed within this study is the first approach enabling the use of dense cartilage matrix, repopulate it via channels and provide the cells with a compact collagen type II environment. Due to its density, it also provides better mechanical properties than materials currently used in clinics. We therefore think, that the auricular cartilage scaffold (AuriScaff) has a high potential to improve future cartilage regeneration approaches.

Tissue-Engineered Grafts from Human Decellularized Extracellular Matrices: A Systematic Review and Future Perspectives

Tissue engineering and regenerative medicine involve many different artificial and biologic materials, frequently integrated in composite scaffolds, which can be repopulated with various cell types. One of the most promising scaffolds is decellularized allogeneic extracellular matrix (ECM) then recellularized by autologous or stem cells, in order to develop fully personalized clinical approaches. Decellularization protocols have to efficiently remove immunogenic cellular materials, maintaining the nonimmunogenic ECM, which is endowed with specific inductive/differentiating actions due to its architecture and bioactive factors. In the present paper, we review the available literature about the development of grafts from decellularized human tissues/organs. Human tissues may be obtained not only from surgery but also from cadavers, suggesting possible development of Human Tissue BioBanks from body donation programs. Many human tissues/organs have been decellularized for tissue engineering purposes, such as cartilage, bone, skeletal muscle, tendons, adipose tissue, heart, vessels, lung, dental pulp, intestine, liver, pancreas, kidney, gonads, uterus, childbirth products, cornea, and peripheral nerves. In vitro recellularizations have been reported with various cell types and procedures (seeding, injection, and perfusion). Conversely, studies about in vivo behaviour are poorly represented. Actually, the future challenge will be the development of human grafts to be implanted fully restored in all their structural/functional aspects.

Optimization of Human Myocardium Decellularization Method for the Construction of Implantable Patches

Cardiac tissue engineering by means of synthetic or natural scaffolds combined with stem/progenitor cells is emerging as the response to the unsatisfactory outcome of approaches based solely on the injection of cells. Parenchymal and supporting cells are surrounded, in vivo, by a specialized and tissue-specific microenvironment, consisting mainly of extracellular matrix (ECM) and soluble factors incorporated in the ECM. Since the naturally occurring ECM is the ideal platform for ensuring cell engraftment, survival, proliferation, and differentiation, the acellular native ECM appears by far the most promising and appealing substrate among all biomaterials tested so far. To obtain intact scaffold of human native cardiac ECM while preserving its composition, we compared the decellularized ECM (d-ECM) produced through five different protocols of decellularization (named Pr1, Pr2, Pr3, Pr4, and Pr5) in terms of efficiency of decellularization, composition, and three-dimensional architecture of d-ECM scaffolds and of their suitability for cell repopulation. The decellularization procedures proved substantially different. Specifically, only three, of the five protocols tested, proved effective in producing thoroughly acellular d-ECM. In addition, the d-ECM delivered differed in architecture and composition and, more importantly, in its ability to support engraftment, survival, and differentiation of cardiac primitive cells in vitro.