Recent advancements in decellularized matrix technology for bone tissue engineering

The native extracellular matrix (ECM) provides a matrix to hold tissue/organ, defines the cellular fate and function, and retains growth factors. Such a matrix is considered as a most biomimetic scaffold for tissue engineering due to the biochemical and biological components, 3D hierarchical structure, and physicomechanical properties. Several attempts have been performed to decellularize allo- or xeno-graft tissues and used them for bone repairing and regeneration. Decellularized ECM (dECM) technology has been developed to create an in vivo-like microenvironment to promote cell adhesion, growth, and differentiation for tissue repair and regeneration. Decellularization is mediated through physical, chemical, and enzymatic methods. In this review, we describe the recent progress in bone decellularization and their applications as a scaffold, hydrogel, bioink, or particles in bone tissue engineering. Furthermore, we address the native dECM limitations and the potential of non-bone dECM, cell-based ECM, and engineered ECM (eECM) for in vitro osteogenic differentiation and in vivo bone regeneration.

Relevant biological processes for tissue development with stem cells and their mechanistic modeling: A review

A potential alternative for tissue transplants is tissue engineering, in which the interaction of cells and biomaterials can be optimized. Tissue development in vitro depends on the complex interaction of several biological processes such as extracellular matrix synthesis, vascularization and cell proliferation, adhesion, migration, death, and differentiation. The complexity of an individual phenomenon or of the combination of these processes can be studied with phenomenological modeling techniques. This work reviews the main biological phenomena in tissue development and their mathematical modeling, focusing on mesenchymal stem cell growth in three-dimensional scaffolds.

Transferable Matrixes Produced from Decellularized Extracellular Matrix Promote Proliferation and Osteogenic Differentiation of Mesenchymal Stem Cells and Facilitate Scale-Up

Decellularized extracellular matrixes (dECM) derived from mesenchymal stem cell (MSC) cultures have recently emerged as cell culture substrates that improve the proliferation, differentiation, and maintenance of MSC phenotype during ex vivo expansion. These biomaterials have considerable potential in the fields of stem cell biology, tissue engineering, and regenerative medicine. Processing the dECMs into concentrated solutions of biomolecules that enable the useful properties of the native dECM to be transferred to a new surface via a simple adsorption step would greatly increase the usefulness and impact of this technology. The development of such solutions, hereafter referred to as transferable matrixes, is the focus of this article. In this work, we produced transferable matrixes from dECM derived from two human placental MSC cell lines (DMSC23 and CMSC29) using pepsin digestion (P-ECM), urea extraction (U-ECM), and mechanical homogenization in acetic acid (AA-ECM). Native dECMs improved primary DMSC proliferation as well as osteogenic and adipogenic differentiation, compared with traditional expansion procedures. Interestingly, tissue culture plastic coated with P-ECM was able to replicate the proliferative effects of native dECM, while U-ECM was able to replicate osteogenic differentiation. These data illustrate the feasibility of producing dECM-derived transferable matrixes that replicate key features of the native matrixes and show that different processing techniques produce transferable matrixes with varying bioactivities. Additionally, these transferable matrixes are able to coat 1.3-5.2 times the surface area covered by the native dECM, facilitating scale-up of this technology.

Decellularized orthopaedic tissue-engineered grafts: biomaterial scaffolds synthesised by therapeutic cells

In orthopaedic surgery, the reconstruction of musculoskeletal defects is a constant challenge.

Enhanced bone repair induced by human adipose-derived stem cells on osteogenic extracellular matrix ornamented small intestinal submucosa

AIM

Our aim was to design an osteogenic extracellular matrix (ECM) coated bioscaffold and to apply it to critical bone defect repair with adipose-derived stem cells (ADSCs).

MATERIALS & METHODS

Morphology of scaffolds was scanned by scanning electron microscope. Cell adhesion, proliferation and osteogenic differentiation of ADSCs on ECM-small intestinal submucosa (SIS) were evaluated by immunofluorescences staining, cell counting kit-8 and real-time qPCR, respectively. A mouse calvarial defect model was used to assess effects on bone regeneration in vivo.

RESULTS

Abundant ECM was coated on SIS, which facilitated cell adhesion and proliferation of ADSCs. ECM-SIS induced osteogenic differentiation of ADSCs even without osteogenic inductive factors. Bone regeneration in vivo was enhanced by ECM-SIS + ADSCs via BMP/SMAD pathway.

CONCLUSION

This work suggested a biofabricated SIS scaffold coated with osteogenic ECM-facilitated bone regeneration with ADSCs synergistically.

Biomineralization: From Material Tactics to Biological Strategy

Biomineralization is an important tactic by which biological organisms produce hierarchically structured minerals with marvellous functions. Biomineralization studies typically focus on the mediation function of organic matrices on inorganic minerals, which helps scientists to design and synthesize bioinspired functional materials. However, the presence of inorganic minerals may also alter the native behaviours of organic matrices and even biological organisms. This progress report discusses the latest achievements relating to biomineralization mechanisms, the manufacturing of biomimetic materials and relevant applications in biological and biomedical fields. In particular, biomineralized vaccines and algae with improved thermostability and photosynthesis, respectively, demonstrate that biomineralization is a strategy for organism evolution via the rational design of organism-material complexes. The successful modification of biological systems using materials is based on the regulatory effect of inorganic materials on organic organisms, which is another aspect of biomineralization control. Unlike previous studies, this study integrates materials and biological science to achieve a more comprehensive view of the mechanisms and applications of biomineralization.

Generating and characterizing the mechanical properties of cell-derived matrices using atomic force microscopy

Mechanical interaction between cells and their surrounding extracellular matrix (ECM) controls key processes such as proliferation, differentiation and motility. For many years, two-dimensional (2D) models were used to better understand the interactions between cells and their surrounding ECM. More recently, variation of the mechanical properties of tissues has been reported to play a major role in physiological and pathological scenarios such as cancer progression. The 3D architecture of the ECM finely tunes cellular behavior to perform physiologically relevant tasks. Technical limitations prevented scientists from obtaining accurate assessment of the mechanical properties of physiologically realistic matrices. There is therefore a need for combining the production of high-quality cell-derived 3D matrices (CDMs) and the characterization of their topographical and mechanical properties. Here, we describe methods that allow to accurately measure the young modulus of matrices produced by various cellular types. In the first part, we will describe and review several protocols for generating CDMs matrices from endothelial, epithelial, fibroblastic, muscle and mesenchymal stem cells. We will discuss tools allowing the characterization of the topographical details as well as of the protein content of such CDMs. In a second part, we will report the methodologies that can be used, based on atomic force microscopy, to accurately evaluate the stiffness properties of the CDMs through the quantification of their young modulus. Altogether, such methodologies allow characterizing the stiffness and topography of matrices deposited by the cells, which is key for the understanding of cellular behavior in physiological conditions.

Decellularized ECM effects on human mesenchymal stem cell stemness and differentiation

Microenvironment extracellular matrices (ECMs) influence cell adhesion, proliferation and differentiation. The ECMs of different microenvironments have distinctive compositions and architectures. This investigation addresses effects ECMs deposited by a variety of cell types and decellularized with a cold-EDTA protocol have on multipotent human mesenchymal stromal/stem cell (hMSC) behavior and differentiation. The cold-EDTA protocol removes intact cells from ECM, with minimal ECM damage and contamination. The decellularized ECMs deposited by cultured hMSCs, osteogenic hMSCs, and two smooth muscle cell (SMC) lines were tested for distinctive effects on the behavior and differentiation of early passage ('naïve') hMSC plated and cultured on the decellularized ECMs. Uninduced hMSC decellularized ECM enhanced naïve hMSC proliferation and cell motility while maintaining stemness. Decellularized ECM deposited by osteogenic hMSCs early in the differentiation process stimulated naïve hMSCs osteogenesis and substrate biomineralization in the absence of added dexamethasone, but this osteogenic induction potential was lower in ECMs decellularized later in the osteogenic hMSC differentiation process. Decellularized ECMs deposited by two smooth muscle cell lines induced naïve hMSCs to become smooth muscle cell-like with distinctive phenotypic characteristics of contractile and synthetic smooth muscle cells. This investigation demonstrates a useful approach for obtaining functional cell-deposited ECM and highlights the importance of ECM specificity in influencing stem cell behavior.

Cell-derived matrices for tissue engineering and regenerative medicine applications

The development and application of decellularized extracellular matrices (ECM) has grown rapidly in the fields of cell biology, tissue engineering and regenerative medicine in recent years. Similar to decellularized tissues and whole organs, cell-derived matrices (CDMs) represent bioactive, biocompatible materials consisting of a complex assembly of fibrillar proteins, matrix macromolecules and associated growth factors that often recapitulate, at least to some extent, the composition and organization of native ECM microenvironments. The unique ability to engineer CDMs de novo based on cell source and culture methods makes them an attractive alternative to conventional allogeneic and xenogeneic tissue-derived matrices that are currently harvested from cadaveric sources, suffer from inherent heterogeneity, and have limited ability for customization. Although CDMs have been investigated for a number of biomedical applications, including adhesive cell culture substrates, synthetic scaffold coatings, and tissue engineered products, such as heart valves and vascular grafts, the state of the field is still at a relatively nascent stage of development. In this review, we provide an overview of the various applications of CDM and discuss successes to date, current limitations and future directions.

Engineered decellularized matrices to instruct bone regeneration processes

Despite the significant progress in the field of bone tissue engineering, cell-based products have not yet reached the stage of clinical adoption. This is due to the uncertain advantages from the standard-of-care, combined with challenging cost-and regulatory-related issues. Novel therapeutic approaches could be based on exploitation of the intrinsic regenerative capacity of bone tissue, provided the development of a deeper understanding of its healing mechanisms. While it is well-established that endogenous progenitors can be activated toward bone formation by overdoses of single morphogens, the challenge to stimulate the healing processes by coordinated and controlled stimulation of specific cell populations remains open. Here, we review the recent approaches to generate osteoinductive materials based on the use of decellularized extracellular matrices (ECM) as reservoirs of multiple factors presented at physiological doses and through the appropriate ligands. We then propose the generation of customized engineered and decellularized ECM (i) as a tool to better understand the processes of bone regeneration and (ii) as safe and effective "off-the-shelf" bone grafts for clinical use. This article is part of a Special Issue entitled Stem Cells and Bone.

Ornamenting 3D printed scaffolds with cell-laid extracellular matrix for bone tissue regeneration

3D printing technique is the most sophisticated technique to produce scaffolds with tailorable physical properties. But, these scaffolds often suffer from limited biological functionality as they are typically made from synthetic materials. Cell-laid mineralized ECM was shown to be potential for improving the cellular responses and drive osteogenesis of stem cells. Here, we intend to improve the biological functionality of 3D-printed synthetic scaffolds by ornamenting them with cell-laid mineralized extracellular matrix (ECM) that mimics a bony microenvironment. We developed bone graft substitutes by using 3D printed scaffolds made from a composite of polycaprolactone (PCL), poly(lactic-co-glycolic acid) (PLGA), and β-tricalcium phosphate (β-TCP) and mineralized ECM laid by human nasal inferior turbinate tissue-derived mesenchymal stromal cells (hTMSCs). A rotary flask bioreactor was used to culture hTMSCs on the scaffolds to foster formation of mineralized ECM. A freeze/thaw cycle in hypotonic buffer was used to efficiently decellularize (97% DNA reduction) the ECM-ornamented scaffolds while preserving its main organic and inorganic components. The ECM-ornamented 3D printed scaffolds supported osteoblastic differentiation of newly-seeded hTMSCs by upregulating four typical osteoblastic genes (4-fold higher RUNX2; 3-fold higher ALP; 4-fold higher osteocalcin; and 4-fold higher osteopontin) and increasing calcium deposition compared to bare 3D printed scaffolds. In vivo, in ectopic and orthotopic models in rats, ECM-ornamented scaffolds induced greater bone formation than that of bare scaffolds. These results suggest a valuable method to produce ECM-ornamented 3D printed scaffolds as off-the-shelf bone graft substitutes that combine tunable physical properties with physiological presentation of biological signals.

Strategies for controlled delivery of growth factors and cells for bone regeneration

The controlled delivery of growth factors and cells within biomaterial carriers can enhance and accelerate functional bone formation. The carrier system can be designed with pre-programmed release kinetics to deliver bioactive molecules in a localized, spatiotemporal manner most similar to the natural wound healing process. The carrier can also act as an extracellular matrix-mimicking substrate for promoting osteoprogenitor cellular infiltration and proliferation for integrative tissue repair. This review discusses the role of various regenerative factors involved in bone healing and their appropriate combinations with different delivery systems for augmenting bone regeneration. The general requirements of protein, cell and gene therapy are described, with elaboration on how the selection of materials, configurations and processing affects growth factor and cell delivery and regenerative efficacy in both in vitro and in vivo applications for bone tissue engineering.

Enhancing the biological performance of synthetic polymeric materials by decoration with engineered, decellularized extracellular matrix

Materials based on synthetic polymers can be extensively tailored in their physical properties but often suffer from limited biological functionality. Here we tested the hypothesis that the biological performance of 3D synthetic polymer-based scaffolds can be enhanced by extracellular matrix (ECM) deposited by cells in vitro and subsequently decellularized. The hypothesis was tested in the context of bone graft substitutes, using polyesterurethane (PEU) foams and mineralized ECM laid by human mesenchymal stromal cells (hMSC). A perfusion-based bioreactor system was critically employed to uniformly seed and culture hMSC in the scaffolds and to efficiently decellularize (94% DNA reduction) the resulting ECM while preserving its main organic and inorganic components. As compared to plain PEU, the decellularized ECM-polymer hybrids supported the osteoblastic differentiation of newly seeded hMSC by up-regulating the mRNA expression of typical osteoblastic genes (6-fold higher bone sialoprotein; 4-fold higher osteocalcin and osteopontin) and increasing calcium deposition (6-fold higher), approaching the performance of ceramic-based materials. After ectopic implantation in nude mice, the decellularized hybrids induced the formation of a mineralized matrix positively immunostained for bone sialoprotein and resembling an immature osteoid tissue. Our findings consolidate the perspective of bioreactor-based production of ECM-decorated polymeric scaffolds as off-the-shelf materials combining tunable physical properties with the physiological presentation of instructive biological signals.