In Situ Recruitment of Human Bone Marrow-Derived Mesenchymal Stem Cells Using Chemokines for Articular Cartilage Regeneration

Ion Channels as a Therapeutic Target: Drug Design and Pharmacological Investigation

This Special Issue intends to illustrate the novelties in the field of ion channels [...].

Effect of autologous lyophilized platelet‑rich fibrin on the reconstruction of osteochondral defects in rabbits

Osteochondral defects caused by degenerative diseases of joints, traumas and inflammation are important issues in clinical practice. Different types of autologous platelet concentrate (PCs) are used in bone and cartilage regeneration. The present study aimed to investigate the effect of lyophilized platelet-rich fibrin (L-PRF) on the repair of osteochondral defects in rabbits. L-PRF was first prepared from fresh PRF (F-PRF) through freeze-drying, and histological and microstructural observations were performed to compare the characteristics of L-PRF and F-PRF. Thereafter, these bioactive scaffolds were implanted into osteochondral defects surgically created in rabbits to assess their effects on tissue repair using micro-CT scanning, histological observations and the evaluation scoring method for cartilage repair established by the International Cartilage Repair Society (ICRS). L-PRF had a histological structure similar to F-PRF. At 16 weeks after implantation surgery, full-thickness osteochondral defects with a diameter of 5 mm and a depth of 4 mm were well-filled with newly regenerated tissues, exhibiting the simultaneous regeneration of avascular articular cartilage and well-vascularized subchondral bone, as proven through macroscopic and microscopic observations in PRF-treated groups compared with that in the untreated group. The application of L-PRF and F-PRF for osteochondral defects in rabbits contributed to massive host remodeling and reconstruction of osteochondral tissues, thus offering a prospective bioactive scaffold for the simultaneous reconstruction of articular cartilage and subchondral bone tissue.

Hypoxic Extracellular Matrix Preserves Its Competence after Expansion of Human MSCs under Physiological Hypoxia In Vitro

Tissue-relevant O2 levels are considered as an important tool for the preconditioning of multipotent mesenchymal stromal cells (MSCs) for regenerative medicine needs. The present study investigated the quality and functions of the extracellular matrix (ECM) of MSCs under low O2 levels. Human adipose tissue-derived MSCs were continuously expanded under normoxia (20% O2, N) or "physiological" hypoxia (5% O2, Hyp). Decellularized ECM (dcECM) was prepared. The structure of the dcECM was analyzed using confocal laser and scanning electron microscopy. Collagen, dcECM-N, and dcECM-Hyp were recellularized with MSC-N and further cultured at normoxia. The efficacy of adhesion, spreading, growth, osteogenic potential, and paracrine activity of recellularized MSC-N were evaluated. At low O2, the dcECM showed an increased alignment of fibrillar structures and provided accelerated spreading of MSC-N, indicating increased dcECM-Hyp stiffness. We described O2-dependent "ECM-education" of MSC-N when cultured on dcECM-Hyp. This was manifested as attenuated spontaneous osteo-commitment, increased susceptibility to osteo-induction, and a shift in the paracrine profile. It has been suggested that the ECM after physiological hypoxia is able to ensure the maintenance of a low-commitment state of MSCs. DcECM, which preserves the competence of the natural microenvironment of cells and is capable of "educating" others, appears to be a prospective tool for guiding cell modifications for cell therapy and tissue engineering.

Cartilage Tissue Engineering in Practice: Preclinical Trials, Clinical Applications, and Prospects

Articular cartilage defects significantly compromise the quality of life in the global population. Although many strategies are needed to repair articular cartilage, including microfracture, autologous osteochondral transplantation, and osteochondral allograft, the therapeutic effects remain suboptimal. In recent years, with the development of cartilage tissue engineering, scientists have continuously improved the formulations of therapeutic cells, biomaterial-based scaffolds, and biological factors, which have opened new avenues for better therapeutics of cartilage lesions. This review focuses on advances in cartilage tissue engineering, particularly in preclinical trials and clinical applications, prospects, and challenges.

Engineered biochemical cues of regenerative biomaterials to enhance endogenous stem/progenitor cells (ESPCs)-mediated articular cartilage repair

As a highly specialized shock-absorbing connective tissue, articular cartilage (AC) has very limited self-repair capacity after traumatic injuries, posing a heavy socioeconomic burden. Common clinical therapies for small- to medium-size focal AC defects are well-developed endogenous repair and cell-based strategies, including microfracture, mosaicplasty, autologous chondrocyte implantation (ACI), and matrix-induced ACI (MACI). However, these treatments frequently result in mechanically inferior fibrocartilage, low cost-effectiveness, donor site morbidity, and short-term durability. It prompts an urgent need for innovative approaches to pattern a pro-regenerative microenvironment and yield hyaline-like cartilage with similar biomechanical and biochemical properties as healthy native AC. Acellular regenerative biomaterials can create a favorable local environment for AC repair without causing relevant regulatory and scientific concerns from cell-based treatments. A deeper understanding of the mechanism of endogenous cartilage healing is furthering the (bio)design and application of these scaffolds. Currently, the utilization of regenerative biomaterials to magnify the repairing effect of joint-resident endogenous stem/progenitor cells (ESPCs) presents an evolving improvement for cartilage repair. This review starts by briefly summarizing the current understanding of endogenous AC repair and the vital roles of ESPCs and chemoattractants for cartilage regeneration. Then several intrinsic hurdles for regenerative biomaterials-based AC repair are discussed. The recent advances in novel (bio)design and application regarding regenerative biomaterials with favorable biochemical cues to provide an instructive extracellular microenvironment and to guide the ESPCs (e.g. adhesion, migration, proliferation, differentiation, matrix production, and remodeling) for cartilage repair are summarized. Finally, this review outlines the future directions of engineering the next-generation regenerative biomaterials toward ultimate clinical translation.

The Effect of CaV1.2 Inhibitor Nifedipine on Chondrogenic Differentiation of Human Bone Marrow or Menstrual Blood-Derived Mesenchymal Stem Cells and Chondrocytes

Cartilage is an avascular tissue and sensitive to mechanical trauma and/or age-related degenerative processes leading to the development of osteoarthritis (OA). Therefore, it is important to investigate the mesenchymal cell-based chondrogenic regenerating mechanisms and possible their regulation. The aim of this study was to investigate the role of intracellular calcium (iCa2+) and its regulation through voltage-operated calcium channels (VOCC) on chondrogenic differentiation of mesenchymal stem/stromal cells derived from human bone marrow (BMMSCs) and menstrual blood (MenSCs) in comparison to OA chondrocytes. The level of iCa2+ was highest in chondrocytes, whereas iCa2+ store capacity was biggest in MenSCs and they proliferated better as compared to other cells. The level of CaV1.2 channels was also highest in OA chondrocytes than in other cells. CaV1.2 antagonist nifedipine slightly suppressed iCa2+, Cav1.2 and the proliferation of all cells and affected iCa2+ stores, particularly in BMMSCs. The expression of the CaV1.2 gene during 21 days of chondrogenic differentiation was highest in MenSCs, showing the weakest chondrogenic differentiation, which was stimulated by the nifedipine. The best chondrogenic differentiation potential showed BMMSCs (SOX9 and COL2A1 expression); however, purposeful iCa2+ and VOCC regulation by blockers can stimulate a chondrogenic response at least in MenSCs.

Seamless and early gap healing of osteochondral defects by autologous mosaicplasty combined with bioactive supramolecular nanofiber-enabled gelatin methacryloyl (BSN-GelMA) hydrogel

Autologous mosaicplasty is a common approach used to treat osteochondral defects in clinical practice. Gap integration between host and transplanted plugs requires bone tissue reservation and hyaline cartilage regeneration without uneven surface, graft necrosis and sclerosis. However, poor gap integration is a serious concern, which eventually leads to deterioration of joint function. To deal with such complications, this study has developed a strategy to effectively enhance integration of the gap region following mosaicplasty by applying injectable bioactive supramolecular nanofiber-enabled gelatin methacryloyl (GelMA) hydrogel (BSN-GelMA). A rabbit osteochondral defect model demonstrated that BSN-GelMA achieved seamless osteochondral healing in the gap region between plugs of osteochondral defects following mosaicplasty, as early as six weeks. Moreover, the International Cartilage Repair Society score, histology score, glycosaminoglycan content, subchondral bone volume, and collagen II expression were observed to be the highest in the gap region of BSN-GelMA treated group. This improved outcome was due to bio-interactive materials, which acted as tissue fillers to bridge the gap, prevent cartilage degeneration, and promote graft survival and migration of bone marrow mesenchymal stem cells by releasing bioactive supramolecular nanofibers from the GelMA hydrogel. This study provides a powerful and applicable approach to improve gap integration after autologous mosaicplasty. It is also a promising off-the-shelf bioactive material for cell-free in situ tissue regeneration.

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A novel strategy that can effectively enhance post-mosaicplasty interstitial integration was developed.

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The bioactive supramolecular nanofibers (BSN) exhibited comparable bioactivity to insulin-like growth factor-1 (IGF-1).

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The BSN-GelMA hydrogel is a promising off-the-shelf bioactive material for cell-free in situ tissue regeneration.

Hyaline Cartilage Microtissues Engineered from Adult Dedifferentiated Chondrocytes: Safety and Role of WNT Signaling

The repair of damaged articular cartilage is an unmet medical need. Chondrocyte-based cell therapy has been used to repair cartilage for over 20 years despite current limitations. Chondrocyte dedifferentiation upon expansion in monolayer is well known and is the main obstacle to their use as cell source for cartilage repair. Consequently, current approaches often lead to fibrocartilage, which is biomechanically different from hyaline cartilage and not effective as a long-lasting treatment. Here, we describe an innovative 3-step method to engineer hyaline-like cartilage microtissues, named Cartibeads, from high passage dedifferentiated chondrocytes. We show that WNT5A/5B/7B genes were highly expressed in dedifferentiated chondrocytes and that a decrease of the WNT signaling pathway was instrumental for full re-differentiation of chondrocytes, enabling production of hyaline matrix instead of fibrocartilage matrix. Cartibeads showed hyaline-like characteristics based on GAG quantity and type II collagen expression independently of donor age and cartilage quality. In vivo, Cartibeads were not tumorigenic when transplanted into SCID mice. This simple 3-step method allowed a standardized production of hyaline-like cartilage microtissues from a small cartilage sample, making Cartibeads a promising candidate for the treatment of cartilage lesions.

Strategies for Articular Cartilage Repair and Regeneration

Articular cartilage is an avascular tissue, with limited ability to repair and self-renew. Defects in articular cartilage can induce debilitating degenerative joint diseases such as osteoarthritis. Currently, clinical treatments have limited ability to repair, for they often result in the formation of mechanically inferior cartilage. In this review, we discuss the factors that affect cartilage homeostasis and function, and describe the emerging regenerative approaches that are informing the future treatment options.

Synovial Fluid Mesenchymal Stem Cells for Knee Arthritis and Cartilage Defects: A Review of the Literature

Mesenchymal stem cells (MSCs) are adult stem cells that have the ability to self-renew and differentiate into several cell lineages including adipocytes, chondrocytes, tenocytes, bones, and myoblasts. These properties make the cell a promising candidate for regenerative medicine applications, especially when dealing with sports injuries in the knee. MSCs can be isolated from almost every type of adult tissue. However, most of the current research focuses on MSCs derived from bone marrow, adipose, and placenta derived products. Synovial fluid-derived MSCs (SF-MSCs) are relatively overlooked but have demonstrated promising therapeutic properties including possessing higher chondrogenic proliferation capabilities than other types of MSCs. Interestingly, SF-MSC population has shown to increase exponentially in patients with joint injury or disease, pointing to a potential use as a biomarker or as a treatment of some orthopaedic disorders. In this review, we go over the current literature on synovial fluid-derived MSCs including the characterization, the animal studies, and discuss future perspectives.

Endogenous Repair and Regeneration of Injured Articular Cartilage: A Challenging but Promising Therapeutic Strategy

Articular cartilage (AC) has a very limited intrinsic repair capacity after injury or disease. Although exogenous cell-based regenerative approaches have obtained acceptable outcomes, they are usually associated with complicated procedures, donor-site morbidities and cell differentiation during ex vivo expansion. In recent years, endogenous regenerative strategy by recruiting resident mesenchymal stem/progenitor cells (MSPCs) into the injured sites, as a promising alternative, has gained considerable attention. It takes full advantage of body's own regenerative potential to repair and regenerate injured tissue while avoiding exogenous regenerative approach-associated limitations. Like most tissues, there are also multiple stem-cell niches in AC and its surrounding tissues. These MSPCs have the potential to migrate into injured sites to produce replacement cells under appropriate stimuli. Traditional microfracture procedure employs the concept of MSPCs recruitment usually fails to regenerate normal hyaline cartilage. The reasons for this failure might be attributed to an inadequate number of recruiting cells and adverse local tissue microenvironment after cartilage injury. A strategy that effectively improves local matrix microenvironment and recruits resident MSPCs may enhance the success of endogenous AC regeneration (EACR). In this review, we focused on the reasons why AC cannot regenerate itself in spite of potential self-repair capacity and summarized the latest developments of the three key components in the field of EACR. In addition, we discussed the challenges facing in the present EACR strategy. This review will provide an increasing understanding of EACR and attract more researchers to participate in this promising research arena.

Bioinformatics analysis and identification of genes and molecular pathways in steroid-induced osteonecrosis of the femoral head

Background

Steroid-induced osteonecrosis of the femoral head (ONFH) is a common hip joint disease and is difficult to be diagnosed early. At present, the pathogenesis of steroid-induced ONFH remains unclear, and recognized and effective diagnostic biomarkers are deficient. The present study aimed to identify potentially important genes and signaling pathways involved in steroid-induced ONFH and investigate their molecular mechanisms.

Methods

Microarray data sets GSE123568 (peripheral blood) and GSE74089 (cartilage) were obtained from the Gene Expression Omnibus database, including 34 ONFH samples and 14 control samples. Morpheus software and Venn diagram were used to identify DEGs and co-expressed DEGs, respectively. Besides, we conducted Kyoto Encyclopedia of Genome (KEGG) and gene ontology (GO) pathway enrichment analysis. We construct a protein-protein interaction (PPI) network through GEO2R and used cytoHubba to divide the PPI network into multiple sub-networks. Additionally, quantitative real-time polymerase chain reaction (qRT-PCR) was performed to verify the bioinformatics analysis results.

Results

A total of 118 intersecting DEGs were obtained between the peripheral blood and cartilage samples, including 40 upregulated genes and 78 downregulated genes. Then, GO and KEGG pathway enrichment analysis revealed that upregulated DEGs focused on the signaling pathways related to staphylococcus aureus infection, leishmaniasis, antigen processing, and presentation, as well as asthma and graft-versus-host disease. Downregulated genes were concentrated in the FoxO signaling pathway, AMPK signaling pathway, signaling pathway regulating stem cell pluripotency, and mTOR signaling pathway. Some hub genes with high interactions such as CXCR1, FPR1, MAPK1, FOXO3, FPR2, CXCR2, and TYROBP were identified in the PPI network. The results of qRT-PCR demonstrated that CXCR1, FPR1, and TYROBP were upregulated while MAPK1 was downregulated in peripheral blood of steroid-induced ONFH patients. This was consistent with the bioinformatics analysis.

Conclusions

The present study would provide novel insight into the genes and associated pathways involved in steroid-induced ONFH. CXCR1, FPR1, TYROBP, and MAPK1 may be used as potential drug targets and biomarkers for the diagnosis and prognosis of steroid-induced ONFH.

Research Progress on Stem Cell Therapies for Articular Cartilage Regeneration

Injury of articular cartilage can cause osteoarthritis and seriously affect the physical and mental health of patients. Unfortunately, current surgical treatment techniques that are commonly used in the clinic cannot regenerate articular cartilage. Regenerative medicine involving stem cells has entered a new stage and is considered the most promising way to regenerate articular cartilage. In terms of theories on the mechanism, it was thought that stem cell-mediated articular cartilage regeneration was achieved through the directional differentiation of stem cells into chondrocytes. However, recent evidence has shown that the stem cell secretome plays an important role in biological processes such as the immune response, inflammation regulation, and drug delivery. At the same time, the stem cell secretome can effectively mediate the process of tissue regeneration. This new theory has attributed the therapeutic effect of stem cells to their paracrine effects. The application of stem cells is not limited to exogenous stem cell transplantation. Endogenous stem cell homing and in situ regeneration strategies have received extensive attention. The application of stem cell derivatives, such as conditioned media, extracellular vesicles, and extracellular matrix, is an extension of stem cell paracrine theory. On the other hand, stem cell pretreatment strategies have also shown promising therapeutic effects. This article will systematically review the latest developments in these areas, summarize challenges in articular cartilage regeneration strategies involving stem cells, and describe prospects for future development.

Stem cell recruitment based on scaffold features for bone tissue engineering

Stem-cell based therapy strategies are promising approaches for the treatment of bone defects. However, extensive cell expansion steps, the low rate of cell survival and uncontrolled differentiation of stem cells transplanted into the body currently remain key challenges in advancing stem cell therapeutics. An alternative strategy is to use specifically designed bone scaffolds to recruit endogenous stem cells upon implantation and to stimulate new bone formation and remodeling. Stem cell recruitment based on scaffold features for bone tissue engineering relies on the development of scaffolds that can effectively mobilize and recruit endogenous stem cells to the implantation site. This article addresses the recent advances in the recruitment of endogenous stem cells in applications of bone scaffolds, particularly focusing on chemical modification and physical characteristic modification of the scaffold for endogenous stem cell homing and recruitment. Finally, the continuing challenges and future directions of scaffold-based stem cell recruitment are discussed.

Comparison of concentrated fresh mononuclear cells and cultured mesenchymal stem cells from bone marrow for bone regeneration

Autologous bone marrow mononuclear cell (BMMNC) transplantation has been widely studied in recent years. The fresh cell cocktail in BMMNCs, without going through the in vitro culture process, helps to establish a stable microenvironment for osteogenesis, and each cell type may play a unique role in bone regeneration. Our study compared the efficacy of concentrated fresh BMMNCs and cultured bone marrow‐derived mesenchymal stem cells (BMSCs) in Beagle dogs for the first time. Fifteen‐millimeter segmental bone defects were created in the animals' tibia bones. In BMMNCs group, the defects were repaired with concentrated fresh BMMNCs combined with β‐TCP (n = 5); in cultured BMSC group, with in vitro cultured and osteo‐induced BMSCs combined with β‐TCP (n = 5); in scaffold‐only group, with a β‐TCP graft alone (n = 5); and in blank group, nothing was grafted (n = 3). The healing process was monitored by X‐rays and single photon emission computed tomography. The animals were sacrificed 12 months after surgery and their tibias were harvested and analyzed by microcomputed tomography and hard tissue histology. Moreover, the microstructure, chemical components, and microbiomechanical properties of the regenerated bone tissue were explored by multiphoton microscopy, Raman spectroscopy and nanoindentation. The results showed that BMMNCs group promoted much more bone regeneration than cultured BMSC group. The grafts in BMMNCs group were better mineralized, and they had collagen arrangement and microbiomechanical properties similar to the contralateral native tibia bone. These results indicate that concentrated fresh bone marrow mononuclear cells may be superior to in vitro expanded stem cells in segmental bone defect repair.

Compression Bioreactor-Based Mechanical Loading Induces Mobilization of Human Bone Marrow-Derived Mesenchymal Stromal Cells into Collagen Scaffolds In Vitro

Articular cartilage (AC) is an avascular tissue composed of scattered chondrocytes embedded in a dense extracellular matrix, in which nourishment takes place via the synovial fluid at the surface. AC has a limited intrinsic healing capacity, and thus mainly surgical techniques have been used to relieve pain and improve function. Approaches to promote regeneration remain challenging. The microfracture (MF) approach targets the bone marrow (BM) as a source of factors and progenitor cells to heal chondral defects in situ by opening small holes in the subchondral bone. However, the original function of AC is not obtained yet. We hypothesize that mechanical stimulation can mobilize mesenchymal stromal cells (MSCs) from BM reservoirs upon MF of the subchondral bone. Thus, the aim of this study was to compare the counts of mobilized human BM-MSCs (hBM-MSCs) in alginate-laminin (alginate-Ln) or collagen-I (col-I) scaffolds upon intermittent mechanical loading. The mechanical set up within an established bioreactor consisted of 10% strain, 0.3 Hz, breaks of 10 s every 180 cycles for 24 h. Contrary to previous findings using porcine MSCs, no significant cell count was found for hBM-MSCs into alginate-Ln scaffolds upon mechanical stimulation (8 ± 5 viable cells/mm³ for loaded and 4 ± 2 viable cells/mm³ for unloaded alginate-Ln scaffolds). However, intermittent mechanical stimulation induced the mobilization of hBM-MSCs into col-I scaffolds 10-fold compared to the unloaded col-I controls (245 ± 42 viable cells/mm³ vs. 22 ± 6 viable cells/mm³, respectively; p-value < 0.0001). Cells that mobilized into the scaffolds by mechanical loading did not show morphological changes. This study confirmed that hBM-MSCs can be mobilized in vitro from a reservoir toward col-I but not alginate-Ln scaffolds upon intermittent mechanical loading, against gravity.

Cell-derived decellularized extracellular matrix scaffolds for articular cartilage repair

Articular cartilage repair remains a great clinical challenge. Tissue engineering approaches based on decellularized extracellular matrix (dECM) scaffolds show promise for facilitating articular cartilage repair. Traditional regenerative approaches currently used in clinical practice, such as microfracture, mosaicplasty, and autologous chondrocyte implantation, can improve cartilage repair and show therapeutic effect to some degree; however, the long-term curative effect is suboptimal. As dECM prepared by proper decellularization procedures is a biodegradable material, which provides space for regeneration tissue growth, possesses low immunogenicity, and retains most of its bioactive molecules that maintain tissue homeostasis and facilitate tissue repair, dECM scaffolds may provide a biomimetic microenvironment promoting cell attachment, proliferation, and chondrogenic differentiation. Currently, cell-derived dECM scaffolds have become a research hotspot in the field of cartilage tissue engineering, as ECM derived from cells cultured in vitro has many advantages compared with native cartilage ECM. This review describes cell types used to secrete ECM, methods of inducing cells to secrete cartilage-like ECM and decellularization methods to prepare cell-derived dECM. The potential mechanism of dECM scaffolds on cartilage repair, methods for improving the mechanical strength of cell-derived dECM scaffolds, and future perspectives on cell-derived dECM scaffolds are also discussed in this review.

Endogenous cell recruitment strategy for articular cartilage regeneration

In the absence of timely and proper treatments, injuries to articular cartilage (AC) can lead to cartilage degeneration and ultimately result in osteoarthritis. Regenerative medicine and tissue engineering techniques are emerging as promising approaches for AC regeneration and repair. Although the use of cell-seeded scaffolds prior to implantation can regenerate and repair cartilage lesions to some extent, these approaches are still restricted by limited cell sources, excessive costs, risks of disease transmission and complex manufacturing practices. Recently developed acellular scaffold approaches that rely on the recruitment of endogenous cells to the injured sites avoid these drawbacks and offer great promise for in situ AC regeneration. Multiple endogenous stem/progenitor cells (ESPCs) are found in joint-resident niches and have the capability to migrate to sites of injury to participate in AC regeneration. However, the natural recruitment of ESPCs is insufficient, and the local microenvironment is hostile after injury. Hence, an endogenous cell recruitment strategy based on the combination of chemoattractants and acellular scaffolds to effectively and specifically recruit ESPCs and improve local microenvironment may provide new insights into in situ AC regeneration. This review provides a brief overview of: (1) the status of endogenous cell recruitment strategy; (2) the subpopulations, potential migration routes (PMRs) of joint-resident ESPCs and their immunomodulatory and reparative effects; (3) chemoattractants and their potential adverse effects; (4) scaffold-based drug delivery systems (SDDSs) that are utilized for in situ AC regeneration; and (5) the challenges and future perspectives of endogenous cell recruitment strategy for AC regeneration. STATEMENT OF SIGNIFICANCE: Although the endogenous cell recruitment strategy for articular cartilage (AC) regeneration has been investigated for several decades, much work remains to be performed in this field. Future studies should have the following aims: (1) reporting the up-to-date progress in the endogenous cell recruitment strategies; (2) determining the subpopulations of ESPCs, the cellular and molecular mechanisms underlying the migration of these cells and their anti-inflammatory, immunomodulatory and reparative effects; (3) elucidating the chemoattractants that enhance ESPC recruitment and their potential adverse effects; and (4) developing advanced SDDSs for chemoattractant dispatch. Herein, we present a systematic overview of the aforementioned issues to provide a better understanding of endogenous cell recruitment strategies for AC regeneration and repair.

Implementation of Endogenous and Exogenous Mesenchymal Progenitor Cells for Skeletal Tissue Regeneration and Repair

Harnessing adult mesenchymal stem/progenitor cells to stimulate skeletal tissue repair is a strategy that is being actively investigated. While scientists continue to develop creative and thoughtful ways to utilize these cells for tissue repair, the vast majority of these methodologies can ultimately be categorized into two main approaches: (1) Facilitating the recruitment of endogenous host cells to the injury site; and (2) physically administering into the injury site cells themselves, exogenously, either by autologous or allogeneic implantation. The aim of this paper is to comprehensively review recent key literature on the use of these two approaches in stimulating healing and repair of different skeletal tissues. As expected, each of the two strategies have their own advantages and limitations (which we describe), especially when considering the diverse microenvironments of different skeletal tissues like bone, tendon/ligament, and cartilage/fibrocartilage. This paper also discusses stem/progenitor cells commonly used for repairing different skeletal tissues, and it lists ongoing clinical trials that have risen from the implementation of these cells and strategies. Lastly, we discuss our own thoughts on where the field is headed in the near future.

miR-200a contributes to the migration of BMSCs induced by the secretions of E. faecalis via FOXJ1/NFκB/MMPs axis

Background

Upon migrating to the injured sites, bone marrow mesenchymal stem cells (BMSCs) play critical roles in the repair of bone lesion caused by chronic apical periodontitis. Emerging evidences have shown that Enterococcus faecalis is always associated with apical periodontitis, especially refractory apical periodontitis. But the mechanism underlying how Enterococcus faecalis affects the migration of BMSCs remains unclear.

Methods

The effects of Enterococcus faecalis supernatants on the migration of BMSCs were determined by transwell migration assays. miRNA sequencing was performed to detect the significantly differentially expressed miRNAs of BMSCs. Proteomics analysis was used to detect the protein expression alterations of BMSCs. Luciferase report assays were deployed to verify the targets of miRNA. Western blot analysis was performed to examine the expressions of matrix metalloproteinases-3, matrix metalloproteinases-9, Forkhead Box Protein J1 (FOXJ1), and nuclear factor kappa B (NFκB). The activations of NFκB were detected by luciferase assays with NFκBluc reporter.

Results

We found that Enterococcus faecalis supernatants could promote the migration of BMSCs. The upregulation of miR-200a-3p in this process contributed to BMSC migration through downregulating its target Forkhead Box Protein J1. Moreover, FOXJ1/ NFκB axis was found to regulate matrix metalloproteinases (MMPs) in this process.

Conclusions

These results above suggest that miR-200a contributes to the migration of BMSCs induced by the secretions of E. faecalis via FOXJ1/NFκB/MMPs axis.

Clinical Application Status of Articular Cartilage Regeneration Techniques: Tissue-Engineered Cartilage Brings New Hope

Hyaline articular cartilage lacks blood vessels, lymphatics, and nerves and is characterised by limited self-repair ability following injury. Traditional techniques of articular cartilage repair and regeneration all have certain limitations. The development of tissue engineering technology has brought hope to the regeneration of articular cartilage. The strategies of tissue-engineered articular cartilage can be divided into three types: “cell-scaffold construct,” cell-free, and scaffold-free. In “cell-scaffold construct” strategies, seed cells can be autologous chondrocytes or stem. Among them, some commercial products with autologous chondrocytes as seed cells, such as BioSeed®-C and CaReS®, have been put on the market and some products are undergoing clinical trials, such as NOVOCART® 3D. The stem cells are mainly pluripotent stem cells and mesenchymal stem cells from different sources. Cell-free strategies that indirectly utilize the repair and regeneration potential of stem cells have also been used in clinical settings, such as TruFit and MaioRegen. Finally, the scaffold-free strategy is also a new development direction, and the short-term repair results of related products, such as NOVOCART® 3D, are encouraging. In this paper, the commonly used techniques of articular cartilage regeneration in surgery are reviewed. By studying different strategies and different seed cells, the clinical application status of tissue-engineered articular cartilage is described in detail.

A sericin/ graphene oxide composite scaffold as a biomimetic extracellular matrix for structural and functional repair of calvarial bone

Bone defects affect millions of people worldwide each year, leading to severe disabilities. Biomimetic scaffolds mediated tissue regeneration represents a promising alternative for bone repair. However, the major problem associated with most currently clinical available artificial bone substitutes (scaffolds) is that they mainly possess filling function but lack of osteo-induction abilities. Therefore, development of biomaterials with osteo-induction property for effective bone regeneration is highly desired. Methods: We report the design and fabrication of a photo-crosslinked sericin methacryloyl (SerMA)/ graphene oxide (GO) hydrogel (SMH/GO) as a biomimetic scaffold for the functional repair of the bone. The mechanical strength, degradation and biocompatibility behavior of SMH/GO hydrogel were measured in vitro. The effect of SMH/GO hydrogel on BMSCs proliferation, migration, osteogenesis differentiation was assessed. After that, SMH/GO-2 was used as an artificial bone substitute for bone regeneration after calvarial defects and effect on bone repair was evaluated by histological, X-Ray and microCT analysis. Furthermore, the potential mechanism of SMH/GO hydrogel regulating BMSCs migration and differentiation was investigated by RNA sequencing. Results: This scaffold has good biocompatibility, cell adhesive property, proliferation- and migration-promoting effects, and osteogenic induction property. After being implanted in a rat calvarial defect model, this SMH/GO scaffold effectively promotes new bone regeneration and achieves structural and functional repair within 12 weeks by inducing autologous bone marrow-derived mesenchymal stem cells (BMSCs) differentiation. By utilizing cell-biological assays and RNA sequencing, we reveal its possible regeneration mechanisms: the SMH/GO hydrogel regulates BMSCs migration and osteo-differentiation via activating MAPK, TNF, and chemokine signaling for bone regeneration. Conclusion: Aiming to meet clinical demands and overcome current limitations of existing artificial bones, we have developed a new type of sericin/ graphene oxide composite scaffold and provided histological, functional, and molecular evidence demonstrating that it is capable of effectively repairing defective bones by inducing autologous BMSCs directional migration and osteogenic differentiation.

Articular cartilage regeneration: The role of endogenous mesenchymal stem/progenitor cell recruitment and migration

BACKGROUND

Trauma- or osteoarthritis-related cartilage damage resulted in functional decline of joints and heavy burden of public health. Recently, the reparative role of mesenchymal stem/progenitor cells (MSCs) in articular cartilage (AC) reconstruction is drawing more and more attention.

OBJECTIVE

To provide a review on (1) the locations and categories of joint-resident MSCs, (2) the regulation of chondrogenic capacities of MSCs, (3) the migratory approaches of MSCs to diseased AC and regulatory mechanisms.

METHODS

PubMed and Web of Science were searched for English-language articles related to MSC recruitment and migration for AC repair until June 2019. The presence of various MSCs in or around joints, the potential approaches to diseased AC` and the regenerative capacities of MSCs were reviewed.

RESULTS

Various intra- and peri-articular MSCs, with inherent migratory potentials, are present in multiple stem cell niches in or around joints. The recruitment and migration of joint-resident MSCs play crucial roles in endogenous AC repair. Multiple recruiting signals, such as chemokines, growth factors, etc., emerge during the development of AC diseases and participate in the regulation of MSC mobilization. Motivated MSCs could migrate into cartilage lesions and then exert multiple reparative potentials, including extracellular matrix (ECM) reconstruction and microenvironment modulation.

CONCLUSION

In general, AC repair based on endogenous MSC recruitment and migration is a feasible strategy, and a promising research field. Furthermore, endogenous AC repair mediated by native MSCs would provide new opportunities to efficient preventative or therapeutic options for AC diseases.

A Scaffold- and Serum-Free Method to Mimic Human Stable Cartilage Validated by Secretome

A stabilized cartilage construct without signs of hypertrophy in chondrocytes is still a challenge. Suspensions of adipose stem/stromal cells (ASCs) and cartilage progenitor cells (CPCs) were seeded into micromolded nonadhesive hydrogel to produce spheroids (scaffold- and serum-free method) characterized by size, immunohistochemistry, fusion, and biomechanical properties. After cell dissociation, they were characterized for mesenchymal cell surface markers, cell viability, and quantitative real-time polymerase chain reaction. Both targeted and nontargeted (shotgun mass spectrometry) analyses were conducted on the culture supernatants. Induced ASC spheroids (ø = 350 μm) showed high cell viability and CD73 downregulation contrasting to CD90. The transforming growth factor (TGF)-β3/TGF-β1 ratio and SOX9 increased (p < 0.05), whereas interleukin (IL)-6, IL-8, RUNX2, and ALPL decreased. Induced ASC spheroids were able to completely fuse and showed a higher force required to compression at day 14 (p < 0.0001). Strong collagen type II in situ was associated with gradual decrease of collagen type X and a lower COLXA1 gene expression at day 14 compared with day 7 (p = 0.0352). The comparison of the secretome content of induced and non-induced ASCs and CPCs identified 138 proteins directly relevant to chondrogenesis of 704 proteins in total. Although collagen X was absent, thrombospondin-1 (TSP-1), described as antiangiogenic and antihypertrophic, and cartilage oligomeric matrix protein (COMP), a biomarker of chondrogenesis, were upregulated in induced ASC spheroids. Our scaffold- and serum-free method mimics stable cartilage acting as a tool for biomarker discovery and for regenerative medicine protocols. Impact Statement Promising adult stem cell sources for cartilage regeneration include adipose stem/stromal cells (ASCs) from subcutaneous adipose tissue. Our main objective was the development of a reproducible and easy-to-handle scaffold- and serum-free method to obtain stable cartilage from induced ASC spheroids. In addition to targeted protein profiling and biomechanical analysis, we provide the first characterization of the secretome composition for ASC spheroids, providing a useful tool to monitor in vitro chondrogenesis and a noninvasive quality control of tissue-engineered constructs. Furthermore, our secretome analysis revealed a potential novel biomarker-thrombospondin-1 (TSP-1), known by its antiangiogenic properties and recently described as an antihypertrophic protein.

CCL21/CCR7 axis regulating juvenile cartilage repair can enhance cartilage healing in adults

Juvenile tissue healing is capable of extensive scarless healing that is distinct from the scar-forming process of the adult healing response. Although many growth factors can be found in the juvenile healing process, the molecular mechanisms of juvenile tissue healing are poorly understood. Here we show that juvenile mice deficient in the chemokine receptor CCR7 exhibit diminished large-scale healing potential, whereas CCR7-depleted adult mice undergo normal scar-forming healing similar to wild type mice. In addition, the CCR7 ligand CCL21 was transiently expressed around damaged cartilage in juvenile mice, whereas it is rarely expressed in adults. Notably, exogenous CCL21 administration to adults decreased scar-forming healing and enhanced hyaline-cartilage repair in rabbit osteochondral defects. Our data indicate that the CCL21/CCR7 axis may play a role in the molecular control mechanism of juvenile cartilage repair, raising the possibility that agents modulating the production of CCL21 in vivo can improve the quality of cartilage repair in adults. Such a strategy may prevent post-traumatic arthritis by mimicking the self-repair in juvenile individuals.

Cartilaginous extracellular matrix derived from decellularized chondrocyte sheets for the reconstruction of osteochondral defects in rabbits

Cartilaginous extracellular matrix (ECM) materials derived from decellularized native articular cartilage are widely used in cartilage regeneration. However, it is difficult for endogenous cells to migrate into ECM derived from native cartilage owing to its nonporous structure and dense nature. Moreover, current decellularization approaches frequently lead to architectural breakdown and potential loss of surface composition of ECM. To solve this problem, we aimed to establish a novel biological ECM scaffold from chondrocyte sheets for cartilage regeneration. We cultured chondrocytes harvested from the auricular cartilage of 4-week-old New Zealand rabbits and enabled them to form cell sheets. These sheets were decellularized using sodium dodecyl sulfate (SDS) with three different concentrations, namely, 1%, 5%, and 10%, followed by 1% Triton X-100 and deoxyribonuclease enzyme solution. In vitro microstructural examination and mechanical tests demonstrated that 1% SDS not only removed chondrocytes completely but also maintained the native architecture and composition of ECM, thus avoiding the use of high-concentration SDS. Application of decellularized chondrocyte sheets for osteochondral defects in rabbits resulted in substantial host remodeling and variant regeneration of osteochondral tissues. One percent SDS-treated decellularized chondrocyte sheets contributed to the superior reconstruction of osteochondral defects as compared with 5% and 10% SDS groups, which includes vascularized subchondral bone, articular cartilage with adequate thickness, and integration with host tissues. Furthermore, ECM from 1% SDS significantly increased the migrating potential of bone marrow mesenchymal stem cells (BMSCs) in vitro. RT-PCR and western blot also revealed that ECM increased the expression of SOX-9 in BMSCs, whereas it decreased COL-X expression. In conclusion, our results suggested that the chondrocyte sheets decellularized with 1% SDS preserved the integrity and bioactivity, which favored cell recruitment and enabled osteochondral regeneration in the knee joints of rabbits, thus offering a promising approach for articular cartilage reconstruction without cell transplantation. STATEMENT OF SIGNIFICANCE: Although biological extracellular matrix (ECM) derived from decellularized native cartilage has been widely used in cartilage regeneration, it is difficult for endogenous cells to migrate into ECM owing to its dense nature. Moreover, current decellularization approaches lead to architectural breakdown of ECM. This study established a novel biological ECM from decellularized chondrocyte sheets for cartilage regeneration. Our results suggested that cartilaginous ECM favored cell recruitment and enabled osteochondral regeneration in rabbits, thus offering a promising approach for articular cartilage reconstruction without cell transplantation. SDS 1% adequately decellularized the chondrocytes in cell sheets, whereas it maintained the native architecture and composition of ECM, thereby avoiding the use of high-concentration SDS and providing a new way to acquire cartilaginous ECM.

TGFβ3 recruits endogenous mesenchymal stem cells to initiate bone regeneration

Background

The recruitment of a sufficient number of endogenous mesenchymal stem cells (MSCs) is the first stage of in-situ tissue regeneration. Transforming growth factor beta-3 (TGFβ3) could recruit stem or progenitor cells and endothelial cells to participate in tissue regeneration. However, the mechanism of TGFβ3 recruiting MSCs toward bone regeneration has remained obscure.

Methods

We estimated the promigratory property of TGFβ3 on human bone marrow MSCs (hBMSCs) cocultured with the vascular cells (human umbilical artery smooth muscle cells or human umbilical vein endothelial cells) or not by Transwell assay. After the addition of the inhibitor (SB431542) or Smad3 siRNA, the levels of MCP1 and SDF1 in coculture medium were tested by ELISA kit, and then the migratory signaling pathway of hBMSCs induced by TGFβ3 was investigated by western blot analysis. In vivo, a 2-mm FVB/N mouse femur defect model was used to evaluate chemokine secretion, endogenous cell homing, and bone regeneration induced by scaffolds loading 1 μg TGFβ3 through qPCR, immunofluorescent staining, immunohistochemical analysis, and Micro-CT, compared to the vehicle group.

Results

TGFβ3 (25 ng/ml) directly showed a nearly 40% increase in migrated hBMSCs via the TGFβ signaling pathway, compared to the vehicle treatment. Then, in the coculture system of hBMSCs and vascular cells, TGFβ3 further upregulated nearly 3-fold MCP1 secretion from vascular cells in a Smad3-dependent manner, to indirectly enhance nearly more than 50% of migrated hBMSCs. In vivo, TGFβ3 delivery improved MCP1 expression by nearly 7.9-fold, recruited approximately 2.0-fold CD31⁺ vascular cells and 2.0-fold Sca-1⁺ PDGFR-α⁺ MSCs, and achieved 2.5-fold bone volume fraction (BV/TV) and 2.0-fold bone mineral density, relative to TGFβ3-free delivery.

Conclusions

TGFβ3, as a MSC homing molecule, recruited MSCs to initiate bone formation in the direct-dependent and indirect-dependent mechanisms. This may shed light on the improvement of MSC homing in bone regeneration.

Regenerative approaches for cartilage repair in the treatment of osteoarthritis

Osteoarthritis (OA) as a debilitating affliction of joints currently affects millions of people and remains an unsolved problem. The disease involves multiple cellular and molecular pathways that converge on the progressive destruction of cartilage. Activation of cartilage regenerative potential and specific targeting pathogenic mediators have been the major focus of research efforts aimed at slowing the progression of cartilage degeneration and preserve joint function. This review will summarize recent key discoveries toward better understanding of the complex mechanisms behind OA development and highlight the latest advances in basic and clinical research in the approach for cartilage regeneration. Prospectively, more potent therapeutic strategies against progressive cartilage deterioration may use a combination of cytotherapy, pharmacotherapy, and bioscaffoldings for improved chondrogenic differentiation and stem/progenitor cell homing as well as the concomitant reduced enzymatic matrix degradation and inflammation. Further, treatments need to be provided with increased preciseness of targeted therapy. One might expect that the regenerative therapies could potentially control or even possibly cure OA if performed at early stages of the disease.

Mesenchymal Stem Cell Alterations in Bone Marrow Lesions in Patients With Hip Osteoarthritis

Objective

In patients with osteoarthritis (OA), bone marrow lesions (BMLs) are intimately linked to disease progression. We hypothesized that aberrant multipotential stromal cell (also known as mesenchymal stem cell [MSC]) responses within bone tissue contributes to BML pathophysiology. The aim of this study was to investigate BML and non‐BML native subchondral bone MSCs for numeric, topographic, in vitro functional, and gene expression differences.

Methods

Ex vivo 3T magnetic resonance imaging (MRI) of the femoral heads of 20 patients with hip OA was performed. MRI‐determined BML and non‐BML regions were excised and enzymatically treated to extract cells and quantify MSCs using flow cytometry and colony‐forming unit–fibroblast (CFU‐F) assay. Immunohistochemical analysis was performed to determine in vivo CD271+ MSC distribution. Culture‐expanded CD271+ cells were analyzed for tripotentiality and gene expression.

Results

BML regions were associated with greater trabecular bone area and cartilage damage compared with non‐BML regions. The proportion of CD45−CD271+ MSCs was higher in BML regions compared with non‐BML regions (median difference 5.6‐fold; P < 0.001); the CFU‐F assay showed a similar trend (median difference 4.3‐fold; P = 0.013). Immunohistochemistry revealed CD271+ cell accumulation in bone adjacent to cartilage defects and areas of osteochondral angiogenesis. BML MSCs had lower proliferation and mineralization capacities in vitro and altered expression of TNFSF11/RANKL and CXCR4/stromal cell–derived factor 1 receptor. OA MSCs showed up‐regulated transcripts for CXCR1 and CCR6 compared with MSCs derived from healthy or osteoporotic bone.

Conclusion

This study is the first to show numeric and topographic alterations in native MSCs in the diseased bone of patients with hip OA. Given the associated functional perturbation of MSCs, these data suggest that subchondral bone MSC manipulation may be an OA treatment target.

MIF-Induced Stromal PKCβ/IL8 Is Essential in Human Acute Myeloid Leukemia

Acute myeloid leukemia (AML) cells exhibit a high level of spontaneous apoptosis when cultured in vitro but have a prolonged survival time in vivo, indicating that tissue microenvironment plays a critical role in promoting AML cell survival. In vitro studies have shown that bone marrow mesenchymal stromal cells (BM-MSC) protect AML blasts from spontaneous and chemotherapy-induced apoptosis. Here, we report a novel interaction between AML blasts and BM-MSCs, which benefits AML proliferation and survival. We initially examined the cytokine profile in cultured human AML compared with AML cultured with BM-MSCs and found that macrophage migration inhibitory factor (MIF) was highly expressed by primary AML, and that IL8 was increased in AML/BM-MSC cocultures. Recombinant MIF increased IL8 expression in BM-MSCs via its receptor CD74. Moreover, the MIF inhibitor ISO-1 inhibited AML-induced IL8 expression by BM-MSCs as well as BM-MSC-induced AML survival. Protein kinase C β (PKCβ) regulated MIF-induced IL8 in BM-MSCs. Finally, targeted IL8 shRNA inhibited BM-MSC-induced AML survival. These results describe a novel, bidirectional, prosurvival mechanism between AML blasts and BM-MSCs. Furthermore, they provide biologic rationale for therapeutic strategies in AML targeting the microenvironment, specifically MIF and IL8. Cancer Res; 77(2); 303-11. ©2016 AACR.

CXCL12/CXCR4 Axis Regulates Aggrecanase Activation and Cartilage Degradation in a Post-Traumatic Osteoarthritis Rat Model

We evaluated the role of the CXCL12/CXCR4 (C-X-C motif chemokine ligand 12/C-X-C chemokine receptor type 4) axis in aggrecanase-mediated cartilage degradation, and explored the underlying mechanism in a post-traumatic osteoarthritis rat model. Expression of CXCL12/CXCR4 and ADAMTS-5 was analyzed in the knees of osteoarthritic and non-arthritic rats using Western blot, ELISA, immunohistochemistry and immunofluorescence. Rodent studies were performed using Sprague-Dawley rats, with animals divided into three groups: Destabilization of the medial meniscus/AMD3100-treated (DMM/AMD3100-treated), DMM/PBS-treated, and sham controls. Rats were sacrificed after eight weeks, and samples were collected for histology and immunohistochemistry analyses. IL-1-pretreated primary chondrocytes were cultured with untreated control, CXCL12a, siNC + CXCL12a, or siRNA CXCR4 + CXCL12a, and analyzed for expression of relevant markers and cellular pathways. Higher levels of CXCL12 were detected in the knee fluid of osteoarthritic subjects, with strong staining for CXCR4 in chondrocytes and CXCL12 in synoviocytes together with enhanced expression of ADAMTS-5. DMM/AMD3100-treated rats showed a significantly reduced immunological response, with minimal evidence of pathology in both histological and immunohistochemical analyses. Treatment with CXCL12a increased the expression of ACAN, RUNX-2, and ADAMTS-4/5 in IL-1-pretreated primary chondrocytes, together with a decrease in the expression of SOX-9. Molecular analyses revealed strong induction of NF-κB activation, along with phosphorylation of MAPKs, and activation of canonical Wnt/β-catenin signaling. In conclusion, inhibition of SDF-1α/CXCR4 signaling axis was able to inhibit aggrecanase expression and lessen cartilage degeneration in post-traumatic osteoarthritis rats.

Cell Therapy Products in Menopausal Medicine

The incidence of postmenopausal diseases increases with the age of women. In this review, we introduce cell therapy products, a new treatment for postmenopausal osteoporosis, which often occurs in postmenopausal women. We also figure out the trends of research on cell therapy products and emphasize the necessity and importance of this research for researchers and postmenopausal women. Finally, we suggest the direction for improvement of postmenopausal osteoporosis and research on cell therapy products. We investigated which medication have been used so far. We also examined the development and technical problems of technologies that are currently in use.

Cell recruiting chemokine-loaded sprayable gelatin hydrogel dressings for diabetic wound healing

In this study, we developed horseradish peroxidase (HRP)-catalyzed sprayable gelatin hydrogels (GH) as a bioactive wound dressing that can deliver cell-attracting chemotactic cytokines to the injured tissues for diabetic wound healing. We hypothesized that topical administration of chemokines using GH hydrogels might improve wound healing by inducing recruitment of the endogenous cells. Two types of chemokines (interleukin-8; IL-8, macrophage inflammatory protein-3α; MIP-3α) were simply loaded into GH hydrogels during in situ cross-linking, and then their wound-healing effects were evaluated in streptozotocin-induced diabetic mice. The incorporation of chemokines did not affect hydrogels properties including swelling ratio and mechanical stiffness, and the bioactivities of IL-8 and MIP-3α released from hydrogel matrices were stably maintained. In vivo transplantation of chemokine-loaded GH hydrogels facilitated cell infiltration into the wound area, and promoted wound healing with enhanced re-epithelialization/neovascularization and increased collagen deposition, compared with no treatment or the GH hydrogel alone. Based on our results, we suggest that cell-recruiting chemokine-loaded GH hydrogel dressing can serve as a delivery platform of various therapeutic proteins for wound healing applications.

STATEMENT OF SIGNIFICANCE

Despite development of materials combined with therapeutic agents for diabetic wound treatment, impaired wound healing by insufficient chemotactic responses still remain as a significant problem. In this study, we have developed enzyme-catalyzed gelatin (GH) hydrogels as a sprayable dressing material that can deliver cell-attracting chemokines for diabetic wound healing. The chemotactic cytokines (IL-8 and MIP-3α) were simply loaded within hydrogel during in situ gelling, and wound healing efficacy of chemokine-loaded GH hydrogels was investigated in STZ-induced diabetic mouse model. These hydrogels significantly promoted wound-healing efficacy with faster wound closure, neovascularization, and thicker granulation. Therefore, we expect that HRP-catalyzed in situ forming GH hydrogels can serve as an injectable/sprayable carrier of various therapeutic agents for wound healing applications.

Advancing biomaterials of human origin for tissue engineering

Biomaterials have played an increasingly prominent role in the success of biomedical devices and in the development of tissue engineering, which seeks to unlock the regenerative potential innate to human tissues/organs in a state of deterioration and to restore or reestablish normal bodily function. Advances in our understanding of regenerative biomaterials and their roles in new tissue formation can potentially open a new frontier in the fast-growing field of regenerative medicine. Taking inspiration from the role and multi-component construction of native extracellular matrices (ECMs) for cell accommodation, the synthetic biomaterials produced today routinely incorporate biologically active components to define an artificial in vivo milieu with complex and dynamic interactions that foster and regulate stem cells, similar to the events occurring in a natural cellular microenvironment. The range and degree of biomaterial sophistication have also dramatically increased as more knowledge has accumulated through materials science, matrix biology and tissue engineering. However, achieving clinical translation and commercial success requires regenerative biomaterials to be not only efficacious and safe but also cost-effective and convenient for use and production. Utilizing biomaterials of human origin as building blocks for therapeutic purposes has provided a facilitated approach that closely mimics the critical aspects of natural tissue with regard to its physical and chemical properties for the orchestration of wound healing and tissue regeneration. In addition to directly using tissue transfers and transplants for repair, new applications of human-derived biomaterials are now focusing on the use of naturally occurring biomacromolecules, decellularized ECM scaffolds and autologous preparations rich in growth factors/non-expanded stem cells to either target acceleration/magnification of the body's own repair capacity or use nature's paradigms to create new tissues for restoration. In particular, there is increasing interest in separating ECMs into simplified functional domains and/or biopolymeric assemblies so that these components/constituents can be discretely exploited and manipulated for the production of bioscaffolds and new biomimetic biomaterials. Here, following an overview of tissue auto-/allo-transplantation, we discuss the recent trends and advances as well as the challenges and future directions in the evolution and application of human-derived biomaterials for reconstructive surgery and tissue engineering. In particular, we focus on an exploration of the structural, mechanical, biochemical and biological information present in native human tissue for bioengineering applications and to provide inspiration for the design of future biomaterials.

Cell-free macro-porous fibrin scaffolds for in situ inductive regeneration of full-thickness cartilage defects

Macro-porous fibrin scaffold was fabricated and used to induce cartilage regenerationin situwithout pre-loaded cells or growth factors.