Co-encapsulation of anti-BMP2 monoclonal antibody and mesenchymal stem cells in alginate microspheres for bone tissue engineering

Mesenchymal Stem/Stromal Cells Microencapsulation for Cell Therapy

Cell microencapsulation is one of the most studied strategies to overcome the challenges associated with the implementation of mesenchymal stem/stromal cells (MSCs) in vivo. This approach isolates/shields donor MSCs from the host immune system using a semipermeable membrane that allows for the diffusion of gases, nutrients, and therapeutics, but not host immune cells. As a result, microencapsulated MSCs survive and engraft better after infusion, and they can be delivered specifically to the targeted site. Additionally, microencapsulation enables the co-culture of MSCs with different types of cells in a three-dimensional (3D) environment, allowing for better cellular interaction. Alginate, collagen, and cellulose are the most popular materials, and air jet extrusion, microfluidics, and emulsion are the most used techniques for MSC cell encapsulation in the literature. These materials and techniques differ in the size range of the resultant microcapsules and their compatibility with the applied materials. This review discusses various materials and techniques used for the microencapsulation of MSCs. We also shed light on the recent findings in this field, the advantages and drawbacks of using encapsulated MSCs, and the in vivo translation of the microencapsulated MSCs in cell therapy.

Advances in the application of hydrogel-based scaffolds for tendon repair

Tendon injuries often lead to joint dysfunction due to the limited self-regeneration capacity of tendons. Repairing tendons is a major challenge for surgeons and imposes a significant financial burden on society. Therefore, there is an urgent need to develop effective strategies for repairing injured tendons. Tendon tissue engineering using hydrogels has emerged as a promising approach that has attracted considerable interest. Hydrogels possess excellent biocompatibility and biodegradability, enabling them to create an extracellular matrix-like growth environment for cells. They can also serve as a carrier for cells or other substances to accelerate tendon repair. In the past decade, numerous studies have made significant progress in the preparation of hydrogel scaffolds for tendon healing. This review aims to provide an overview of recent research on the materials of hydrogel-based scaffolds used for tendon tissue engineering and discusses the delivery systems based on them.

Scaffold Application for Bone Regeneration with Stem Cells in Dentistry: Literature Review

Bone tissue injuries within oral and dental contexts often present considerable challenges because traditional treatments may not be able to fully restore lost or damaged bone tissue. Novel approaches involving stem cells and targeted 3D scaffolds have been investigated in the search for workable solutions. The use of scaffolds in stem cell-assisted bone regeneration is a crucial component of tissue engineering techniques designed to overcome the drawbacks of traditional bone grafts. This study provides a detailed review of scaffold applications for bone regeneration with stem cells in dentistry. This review focuses on scaffolds and stem cells while covering a broad range of studies explaining bone regeneration in dentistry through the presentation of studies conducted in this field. The role of different stem cells in regenerative medicine is covered in great detail in the reviewed literature. These studies have addressed a wide range of subjects, including the effects of platelet concentrates during dental surgery or specific combinations, such as human dental pulp stem cells with scaffolds for animal model bone regeneration, to promote bone regeneration in animal models. Noting developments, research works consider methods to improve vascularization and explore the use of 3D-printed scaffolds, secretome applications, mesenchymal stem cells, and biomaterials for oral bone tissue regeneration. This thorough assessment outlines possible developments within these crucial regenerative dentistry cycles and provides insights and suggestions for additional study. Furthermore, alternative creative methods for regenerating bone tissue include biophysical stimuli, mechanical stimulation, magnetic field therapy, laser therapy, nutritional supplements and diet, gene therapy, and biomimetic materials. These innovative approaches offer promising avenues for future research and development in the field of bone tissue regeneration in dentistry.

Multifunctional wet-adhesive chitosan/acrylic conduit for sutureless repair of peripheral nerve injuries

The incidence of peripheral nerve injury (PNI) is high worldwide, and a poor prognosis is common. Surgical closure and repair of the affected area are crucial to ensure the effective treatment of peripheral nerve injuries. Despite being the standard treatment approach, reliance on sutures to seal the severed nerve ends introduces several limitations and restrictions. This technique is intricate and time-consuming, and the application of threading and punctate sutures may lead to tissue damage and heightened tension concentrations, thus increasing the risk of fixation failure and local inflammation. This study aimed to develop easily implantable chitosan-based peripheral nerve repair conduits that combine acrylic acid and cleavable N-hydroxysuccinimide to reduce nerve damage during repair. In ex vivo tissue adhesion tests, the conduit achieved maximal interfacial toughness of 705 J m-2 ± 30 J m-2, allowing continuous bridging of the severed nerve ends. Adhesive repair significantly reduces local inflammation caused by conventional sutures, and the positive charge of chitosan disrupts the bacterial cell wall and reduces implant-related infections. This promises to open new avenues for sutureless nerve repair and reliable medical implants.

Hydrogel Microparticles for Bone Regeneration

Hydrogel microparticles (HMPs) stand out as promising entities in the realm of bone tissue regeneration, primarily due to their versatile capabilities in delivering cells and bioactive molecules/drugs. Their significance is underscored by distinct attributes such as injectability, biodegradability, high porosity, and mechanical tunability. These characteristics play a pivotal role in fostering vasculature formation, facilitating mineral deposition, and contributing to the overall regeneration of bone tissue. Fabricated through diverse techniques (batch emulsion, microfluidics, lithography, and electrohydrodynamic spraying), HMPs exhibit multifunctionality, serving as vehicles for drug and cell delivery, providing structural scaffolding, and functioning as bioinks for advanced 3D-printing applications. Distinguishing themselves from other scaffolds like bulk hydrogels, cryogels, foams, meshes, and fibers, HMPs provide a higher surface-area-to-volume ratio, promoting improved interactions with the surrounding tissues and facilitating the efficient delivery of cells and bioactive molecules. Notably, their minimally invasive injectability and modular properties, offering various designs and configurations, contribute to their attractiveness for biomedical applications. This comprehensive review aims to delve into the progressive advancements in HMPs, specifically for bone regeneration. The exploration encompasses synthesis and functionalization techniques, providing an understanding of their diverse applications, as documented in the existing literature. The overarching goal is to shed light on the advantages and potential of HMPs within the field of engineering bone tissue.

Advances and Prospects in Materials for Craniofacial Bone Reconstruction

The craniofacial region is composed of 23 bones, which provide crucial function in keeping the normal position of brain and eyeballs, aesthetics of the craniofacial complex, facial movements, and visual function. Given the complex geometry and architecture, craniofacial bone defects not only affect the normal craniofacial structure but also may result in severe craniofacial dysfunction. Therefore, the exploration of rapid, precise, and effective reconstruction of craniofacial bone defects is urgent. Recently, developments in advanced bone tissue engineering bring new hope for the ideal reconstruction of the craniofacial bone defects. This report, presenting a first-time comprehensive review of recent advances of biomaterials in craniofacial bone tissue engineering, overviews the modification of traditional biomaterials and development of advanced biomaterials applying to craniofacial reconstruction. Challenges and perspectives of biomaterial development in craniofacial fields are discussed in the end.

Integrated Osteoinductive Factors─Exosome@MicroRNA-26a Hydrogel Enhances Bone Regeneration

MicroRNAs (miRNAs) are a new therapeutic tool that can target multiple genes by inducing translation repression and target mRNA degradation. Although miRNAs have gained significant attention in oncology and in work on genetic disorders and autoimmune diseases, their application in tissue regeneration remains hindered by several challenges, such as miRNA degradation. Here, we reported Exosome@MicroRNA-26a (Exo@miR-26a), an osteoinductive factor that can be substituted for routinely used growth factors, which was constructed using bone marrow stem cell (BMSC)-derived exosomes and microRNA-26a (miR-26a). Exo@miR-26a-integrated hydrogels significantly promoted bone regeneration when implanted into defect sites; as the exosome stimulated angiogenesis, miR-26a promoted osteogenesis while the hydrogel enabled a site-directed release. Moreover, BMSC-derived exosomes further facilitated healthy bone regeneration by repressing osteoclast differentiation-related genes rather than damaging osteoclasts. Taken together, our findings demonstrate the promising potential of Exo@miR-26a for bone regeneration and provide a new strategy for the application of miRNA therapy in tissue engineering.

Preparation of Cell-Loaded Microbeads as Stable and Injectable Delivery Platforms for Tissue Engineering

Cell transplants in therapeutic studies do not preserve their long-term function inside the donor body. In mesenchymal stem cell (MSC) transplants, transplanted cells disperse through the body and are prone to degradation by immune cells after the transplant process. Various strategies, such as usage of the immunosuppressive drugs to eliminate allograft rejection, are designed to increase the efficiency of cell therapy. Another strategy is the construction of biomimetic encapsulates using polymeric materials, which isolate stem cells and protect them from environmental effects. In this study, fibroblasts (L929) and MSCs were investigated for their improved viability and functionality once encapsulated inside the alginate microbeads under in vitro conditions for up to 12 days of incubation. Thus, uniform and injectable (<200 µm) cell-loaded microbeads were constructed by the electrostatically assisted spraying technique. Results showed that both L929 and MSCs cells continue their metabolic activity inside the microbeads during the incubation periods. Glucose consumption and lactic acid production levels of both cell lines were consistently observed. The released cell number on day 12 was found to be increased compared to day 0. Protein expression levels of both groups increased every day with the expected doubling rate. Hence, this strategy with a simple yet clever design to encapsulate either MSCs or L929 cells might outstand as a potential cell delivery platform for cell therapy-based tissue engineering.

Osteogenesis Enhancement with 3D Printed Gene-Activated Sodium Alginate Scaffolds

Natural and synthetic hydrogel scaffolds containing bioactive components are increasingly used in solving various tissue engineering problems. The encapsulation of DNA-encoding osteogenic growth factors with transfecting agents (e.g., polyplexes) into such scaffold structures is one of the promising approaches to delivering the corresponding genes to the area of the bone defect to be replaced, providing the prolonged expression of the required proteins. Herein, a comparative assessment of both in vitro and in vivo osteogenic properties of 3D printed sodium alginate (SA) hydrogel scaffolds impregnated with model EGFP and therapeutic BMP-2 plasmids was demonstrated for the first time. The expression levels of mesenchymal stem cell (MSC) osteogenic differentiation markers Runx2, Alpl, and Bglap were evaluated by real-time PCR. Osteogenesis in vivo was studied on a model of a critical-sized cranial defect in Wistar rats using micro-CT and histomorphology. The incorporation of polyplexes comprising pEGFP and pBMP-2 plasmids into the SA solution followed by 3D cryoprinting does not affect their transfecting ability compared to the initial compounds. Histomorphometry and micro-CT analysis 8 weeks after scaffold implantation manifested a significant (up to 46%) increase in new bone volume formation for the SA/pBMP-2 scaffolds compared to the SA/pEGFP ones.

Fabrication and Performance Evaluation of Gelatin/Sodium Alginate Hydrogel-Based Macrophage and MSC Cell-Encapsulated Paracrine System with Potential Application in Wound Healing

A gelatin/sodium alginate-based hydrogel microsphere has been fabricated after reaction condition optimization. Macrophages (RAW246.7) and adipose mesenchymal stem cells (ADSC) have been subsequently encapsulated in the microsphere in order to construct a 3D paracrine system for wound healing treatment. The synthesized microsphere displayed neglectable cytotoxicity toward both encapsulated cells until 10 days of incubation, indicating promising biocompatibility of the microsphere. A qRT-PCR and ELISA experiment revealed positive regulation of cytokines (Arg-1, IL-6, IL-8, IL-10, bFGF, HGF, VEGF, TLR-1, and CXCL13) expression regarding macrophage phenotype transformation and anti-inflammatory performance both inside the microsphere and in the microenvironment of established in vitro inflammatory model. Additionally, positive tendency of cytokine expression benefit wound healing was more pronounced in a fabricated 3D paracrine system than that of a 2D paracrine system. Furthermore, the 3D paracrine system exhibited more efficiently in the wound healing rate compared to the 2D paracrine system in an in vitro model. These results suggested the current paracrine system could be potentially used as a robust wound healing dressing.

Protein-Delivering Nanocomplexes with Fenton Reaction-Triggered Cargo Release to Boost Cancer Immunotherapy

Immunotherapeutic efficacy of tumors based on immune checkpoint blockade (ICB) therapy is frequently limited by an immunosuppressive tumor microenvironment and cross-reactivity with normal tissues. Herein, we develop reactive oxygen species (ROS)-responsive nanocomplexes with the function of ROS production for delivery and triggered release of anti-mouse programmed death ligand 1 antibody (αPDL1) and glucose oxidase (GOx). GOx and αPDL1 were complexed with oligomerized (-)-epigallocatechin-3-O-gallate (OEGCG), which was followed by chelation with Fe³⁺ and coverage of the ROS-responsive block copolymer, POEGMA-b-PTKDOPA, consisting of poly(oligo(ethylene glycol)methacrylate) (POEGMA) and the block with thioketal bond-linked dopamine moieties (PTKDOPA) as the side chains. After intravenous injection, the nanocomplexes show prolonged circulation in the bloodstream with a half-life of 8.72 h and efficient tumor accumulation. At the tumor sites, GOx inside the nanocomplexes can produce H₂O₂ via oxidation of glucose for Fenton reaction to generate hydroxyl radicals (•OH) which further trigger the release of the protein cargos through ROS-responsive cleavage of thioketal bonds. The released GOx improves the production efficiency of •OH to kill cancer cells for release of tumor-associated antigens via chemodynamic therapy (CDT). The enhanced immunogenic cell death (ICD) can activate the immunosuppressive tumor microenvironment and improve the immunotherapy effect of the released αPDL1, which significantly suppresses primary and metastatic tumors. Thus, the nanocomplexes with Fenton reaction-triggered protein release show great potentials to improve the immunotherapeutic efficacy of ICB via combination with CDT.

The use of heparin/polycation coacervate sustain release system to compare the bone regenerative potentials of 5 BMPs using a critical sized calvarial bone defect model

Nonunion following bone fracture and segmental bone defects are challenging clinical conditions. To combat this clinical dilemma, development of new bone tissue engineering therapies using biocompatible materials to deliver bone growth factors is desirable. This aim of this study is to use a heparin/polycation coacervate sustained-release platform to compare 5 bone morphogenetic proteins (BMPs) for promoting bone defect healing in a critical sized calvarial defect model. The in vitro 3D osteogenic pellet cultures assays demonstrated that BMPs 2, 4, 6, 7 and 9 all enhanced mineralization in vitro compared to the control group. BMP2 resulted in higher mineralized volume than BMP4 and BMP6. All BMPs and the control group activated the pSMAD5 signaling pathway and expressed osterix (OSX). The binding of BMP2 with coacervate significantly increased the coacervate average particle size. BMP2, 4, 6, & 7 bound to coacervate significantly increased the Zeta potential of the coacervate while BMP9 binding showed insignificant increase. Furthermore, using a monolayer culture osteogenic assay, it was found that hMDSCs cultured in the coacervate BMP2 osteogenic medium expressed higher levels of RUNX2, OSX, ALP and COX-2 compared to the control and BMPs 4, 6, 7 & 9. Additionally, the coacervate complex can be loaded with up to 2 μg of BMP proteins for sustained release. In vivo, when BMPs were delivered using the coacervate sustained release system, BMP2 was identified to be the most potent BMP promoting bone regeneration and regenerated 10 times of new bone than BMPs 4, 6 & 9. BMP7 also stimulated robust bone regeneration when compared to BMPs 4, 6 & 9. The quality of the newly regenerated bone by all BMPs delivered by coacervate is equivalent to the host bone consisting of bone matrix and bone marrow with normal bone architecture. Although the defect was not completely healed at 6 weeks, coacervate sustain release BMPs, particularly BMP2 and BMP7, could represent a new strategy for treatment of bone defects and non-unions.

Interaction of alginate with nano-hydroxyapatite-collagen using strontium provides suitable osteogenic platform

Background

Hydrogels based on organic/inorganic composites have been at the center of attention for the fabrication of engineered bone constructs. The establishment of a straightforward 3D microenvironment is critical to maintaining cell-to-cell interaction and cellular function, leading to appropriate regeneration. Ionic cross-linkers, Ca²⁺, Ba²⁺, and Sr²⁺, were used for the fabrication of Alginate-Nanohydroxyapatite-Collagen (Alg-nHA-Col) microspheres, and osteogenic properties of human osteoblasts were examined in in vitro and in vivo conditions after 21 days.

Results

Physicochemical properties of hydrogels illustrated that microspheres cross-linked with Sr²⁺ had reduced swelling, enhanced stability, and mechanical strength, as compared to the other groups. Human MG-63 osteoblasts inside Sr²⁺ cross-linked microspheres exhibited enhanced viability and osteogenic capacity indicated by mineralization and the increase of relevant proteins related to bone formation. PCR (Polymerase Chain Reaction) array analysis of the Wnt (Wingless-related integration site) signaling pathway revealed that Sr²⁺ cross-linked microspheres appropriately induced various signaling transduction pathways in human osteoblasts leading to osteogenic activity and dynamic growth. Transplantation of Sr²⁺ cross-linked microspheres with rat osteoblasts into cranium with critical size defect in the rat model accelerated bone formation analyzed with micro-CT and histological examination.

Conclusion

Sr²⁺ cross-linked Alg-nHA-Col hydrogel can promote functionality and dynamic growth of osteoblasts.

Graphical Abstract

Supplementary Information

The online version contains supplementary material available at 10.1186/s12951-022-01511-9.

Whitlockite-Enabled Hydrogel for Craniofacial Bone Regeneration

Growth-factor-free bone regeneration remains a challenge in craniofacial engineering. Here, we engineered an osteogenic niche composed of a commercially modified alginate hydrogel and whitlockite microparticles (WHMPs), which impart tunable physicochemical properties that can direct osteogenesis of human gingival mesenchymal stem cells (GMSCs). Our in vitro studies demonstrate that WHMPs induce osteogenesis of GMSCs more effectively than previously demonstrated hydroxyapatite microparticles (HApMPs). Alginate-WHMP hydrogels showed higher elasticity without any adverse effects on the viability of the encapsulated GMSCs. Moreover, the alginate-WHMP hydrogels upregulate the mitogen-activated protein kinase (MAPK) pathway, which in turn orchestrates several osteogenic markers, such as RUNX2 and OCN, in the encapsulated GMSCs. Concurrent coculture studies with human osteoclasts demonstrate that GMSCs encapsulated in alginate-WHMP hydrogels downregulate osteoclastic activity, potentially due to release of Mg2+ ions from the WHMPs along with secretion of osteoprotegerin from the GMSCs. In vivo studies demonstrated that the GMSCs encapsulated in our osteogenic niche were able to promote bone repair in calvarial defects in murine models. Altogether, our results confirmed the development of a promising treatment modality for craniofacial bone regeneration based on an injectable growth-factor-free hydrogel delivery system.

A narrative overview of utilizing biomaterials to recapitulate the salient regenerative features of dental-derived mesenchymal stem cells

Tissue engineering approaches have emerged recently to circumvent many limitations associated with current clinical practices. This elegant approach utilizes a natural/synthetic biomaterial with optimized physiomechanical properties to serve as a vehicle for delivery of exogenous stem cells and bioactive factors or induce local recruitment of endogenous cells for in situ tissue regeneration. Inspired by the natural microenvironment, biomaterials could act as a biomimetic three-dimensional (3D) structure to help the cells establish their natural interactions. Such a strategy should not only employ a biocompatible biomaterial to induce new tissue formation but also benefit from an easily accessible and abundant source of stem cells with potent tissue regenerative potential. The human teeth and oral cavity harbor various populations of mesenchymal stem cells (MSCs) with self-renewing and multilineage differentiation capabilities. In the current review article, we seek to highlight recent progress and future opportunities in dental MSC-mediated therapeutic strategies for tissue regeneration using two possible approaches, cell transplantation and cell homing. Altogether, this paper develops a general picture of current innovative strategies to employ dental-derived MSCs combined with biomaterials and bioactive factors for regenerating the lost or defective tissues and offers information regarding the available scientific data and possible applications.

BMP2 immune complexes promote new bone formation by facilitating the direct contact between osteoclasts and osteoblasts

BMP2 antibody is proposed as a promising replacement for rhBMP2 in bone tissue engineering. Although studies have demonstrated its osteoinductive efficacy, the underlying osteogenic mechanism and adverse reactions of specific BMP2 antibody are not clarified yet, making it difficult to optimize the antibody for future application. By establishing BMP2 immune complexes (BMP2-ICs) ex vivo, we were able to introduce BMP2-ICs directly in vivo and found that BMP2-ICs promoted bone formation while suppressing osteoclastogenesis. However, ex vivo osteoclastogenic assays showed that BMP2-ICs promoted osteoclastogenesis by binding FcγR and activating PLCγ2 phosphorylation. Given that BMP2-ICs react with osteoblast and osteoclast lineage cells by the conjugated BMP2 domain and the Fc domain respectively, we introduced BMP2-ICs into coculture system of the two lineage cells and found that BMP2-ICs promoted osteogenesis while suppressing osteoclastogenesis by facilitating osteoblast-osteoclast contact and activating the EphrinB2-EphB4 signaling. This bidirectional function of BMP2-ICs was reproduced in the cranial bone resorption model, where osteoblast and osteoclast lineage cells co-localized. This study excluded the hidden problem of osteoclast overactivation that usually comes with rhBMP2 and clarified the first evidence of the mechanism of antibody-mediated bone regeneration, suggesting BMP2-ICs may present a promising therapy for bone diseases related with disrupted osteoclast-osteoblast interaction.

Preparation of Alginate-Based Biomaterials and Their Applications in Biomedicine

Alginates are naturally occurring polysaccharides extracted from brown marine algae and bacteria. Being biocompatible, biodegradable, non-toxic and easy to gel, alginates can be processed into various forms, such as hydrogels, microspheres, fibers and sponges, and have been widely applied in biomedical field. The present review provides an overview of the properties and processing methods of alginates, as well as their applications in wound healing, tissue repair and drug delivery in recent years.

One-Step All-Aqueous Interfacial Assembly of Robust Membranes for Long-Term Encapsulation and Culture of Adherent Stem/Stromal Cells

The therapeutic effectiveness and biological relevance of technologies based on adherent cells depend on platforms that enable long-term culture in controlled environments. Liquid-core capsules have been suggested as semipermeable moieties with spatial homogeneity due to the high mobility of all components in their core. The lack of cell-adhesive sites in liquid-core structures often hampers their use as platforms for stem cell-based technologies for long-term survival and cell-directed self-organization. Here, the one-step fast formation of robust polymeric capsules formed by interfacial complexation of oppositely charged polyelectrolytes in an all-aqueous environment, compatible with the simultaneous encapsulation of mesenchymal stem/stromal cells (MSCs) and microcarriers, is described. The adhesion of umbilical cord MSCs to polymeric microcarriers enables their aggregation and culture for more than 21 days in capsules prepared either manually by dropwise addition, or by scalable electrohydrodynamic atomization, generating robust and stable capsules. Cell aggregation and secretion overtime can be tailored by providing cells with static or dynamic (bioreactor) environments.

New insight of immuno-engineering in osteoimmunomodulation for bone regeneration

With the continuous development of bone tissue engineering, the importance of immune response in bone tissue regeneration is gradually recognized. The new bone tissue engineering products should possess immunoregulatory functions, harmonizing the interactions between the bone's immune defense and regeneration systems, and promoting tissue regeneration. This article will interpret the relationship between the bone immune system, bone tissue regeneration, as well as the immunoregulatory function of bone biomaterials and seed stem cells in bone tissue engineering. This review locates arears for foucusing efforts at providing novel designs ideas about the development of immune-mediation targeted bone tissue engineering products and the evaluation strategy for the osteoimmunomodulation property of bone biomaterials.

The osteogenic differentiation of human dental pulp stem cells in alginate-gelatin/Nano-hydroxyapatite microcapsules

Background

Microcapsule is considered as a promising 3D microenvironment for Bone Tissue Engineering (BTE) applications. Microencapsulation of cells in an appropriate scaffold not only protected the cells against excess stress but also promoted cell proliferation and differentiation. Through the current study, we aimed to microcapsulate the human Dental Pulp Stem Cells (hDPSCs) and evaluated the proliferation and osteogenic differentiation of those cells by using MTT assay, qRT-PCR, Alkaline phosphatase, and Alizarine Red S.

Results

The SEM results revealed that Alg/Gel microcapsules containing nHA showed a rough and more compact surface morphology in comparison with the Alg/Gel microcapsules. Moreover, the microencapsulation by Alg/Gel/nHA could improve cell proliferation and induce osteogenic differentiation. The cells cultured in the Alg/Gel and Alg/Gel/nHA microcapsules showed 1.4-fold and 1.7-fold activity of BMP-2 gene expression more in comparison with the control group after 21 days. The mentioned amounts for the BMP-2 gene were 2.5-fold and 4-fold more expression for the Alg/Gel and Alg/Gel/nHA microcapsules after 28 days. The nHA, addition to hDPSCs-laden Alg/Gel microcapsule, could up-regulate the bone-related gene expressions of osteocalcin, osteonectin, and RUNX-2 during the 21 and 28 days through the culturing period, too. Calcium deposition and ALP activities of the cells were observed in accordance with the proliferation results as well as the gene expression analysis.

Conclusion

The present study demonstrated that microencapsulation of the hDPSCs inside the Alg/Gel/nHA hydrogel could be a potential approach for regenerative dentistry in the near future.

Graphical abstract

Gingiva-derived Mesenchymal Stem Cells and Their Potential Applications in Oral and Maxillofacial Diseases

BACKGROUND

Stem cells are undifferentiated cells with multilineage differentiation potential. They can be collected from bone marrow, fat, amniotic fluid, and teeth. Stem cell-based therapies have been widely used to treat multiple diseases, such as cardiac disease, and hematological disorders. The cells may also be beneficial for controlling the disease course and promoting tissue regeneration in oral and maxillofacial diseases. Oral-derived gingival mesenchymal stem cells are easy to access and the donor sites heal rapidly without a scar. Such characteristics demonstrate the beneficial role of GMSCs in oral and maxillofacial diseases.

OBJECTIVE

We summarize the features of GMSCs, including their self-renewal, multipotent differentiation, immunomodulation, and anti-inflammation properties. We also discuss their applications in oral and maxillofacial disease treatment and tissue regeneration.

CONCLUSION

GMSCs are easily harvestable adult stem cells with outstanding proliferation, differentiation, and immunomodulation characteristics. A growing body of evidence indicates that GMSCs have strong potential use in accelerating wound healing and promoting the regeneration of bone defects, periodontium, oral neoplasms, salivary glands, peri-implantitis, and nerves. Moreover, alginate, polylactic acid and polycaprolactone can be used as biodegradable scaffolds for GMSC encapsulation. Various growth factors can be applied to the corresponding scaffolds to obtain the desired GMSC differentiation and phenotypes. Three-dimensional spheroid culture systems could optimize GMSC properties and improve the performance of the cells in tissue engineering. The immunomodulatory property of GMSCs in controlling oral and maxillofacial inflammation needs further research.

Functionalized Scaffold and Barrier Membrane with Anti-BMP-2 Monoclonal Antibodies for Alveolar Ridge Preservation in a Canine Model

Introduction

The aim of this study was to investigate the ability of anti-bone morphogenetic protein 2 monoclonal antibody (anti-BMP-2 mAb) to functionalize scaffolds to mediate bone regeneration in a canine model.

Materials and Methods

The mandibular right premolar 4 (PM4) was extracted in eight beagle dogs and grafted with anti-BMP-2 mAb+anorganic bovine bone mineral with 10% collagen (ABBM-C) and porcine bilayer native collagen membrane (CM). The ABBM-C and CM were functionalized with either anti-BMP-2 mAb (test group) or an isotype matched control mAb (control group). Animals were euthanized at 12 weeks for radiographic, histologic, and histomorphometric analyses. Outcomes were compared between groups.

Results

3D imaging using cone beam computed tomography (CBCT) revealed that sites treated with ABBM-C and CM functionalized with anti-BMP-2 mAb exhibited significantly more remaining bone width near the alveolar crest, as well as buccal bone height, compared with control groups. Histologic and histomorphometric analyses demonstrated that in anti-BMP-2 mAb-treated sites, total tissue volume was significantly higher in the coronal part of the alveolar bone crest compared with control sites. In anti-BMP-2 mAb-treated sites, bone formation was observed under the barrier membrane.

Conclusion

Functionalization of the ABBM-C scaffold and CM appeared to have led to bone formation within healing alveolar bone sockets.

The sialylation profile of IgG determines the efficiency of antibody directed osteogenic differentiation of iMSCs by modulating local immune responses and osteoclastogenesis

Antibody-mediated osseous regeneration (AMOR) has been proved as a promising strategy for osteogenic differentiation of induced pluripotent stem cells derived MSCs (iMSCs). The key characteristic of antibody that determines the AMOR potential is largely unknown. The glycosylation profile of immunoglobulin G (IgG) represents a key checkpoint that determines its effector functions. Herein, we modified the sialylation profile of BMP2 antibodies to investigate the effects of glycosylation on antibody-mediated osteogenic differentiation of iMSCs. We found that over-sialylated BMP2 antibodies stimulated the highest amount of new bone while those non- or low-sialylated led to bone porosity and collapse. The immune response aroused by BMP2 immune complexes (BMP2-ICs) was intensified by desialylation, which contributed to an environment that favored osteoclastogenesis while inhibited osteoblastogenesis. In vitro study further demonstrated that the osteogenic potential of BMP2-ICs was not significantly affected by the degree of sialylation. On the other hand, BMP2-ICs could stimulate osteoclastogenesis by binding FcγRs on preosteoclasts directly, which was significantly intensified by desialylation and attenuated by over-sialylation. Bone defects implanted with alginate microbeads loaded with iMSCs and over-sialylated antibodies showed more bone formation than those sites with non- or low sialylated antibodies. Taken together, our study demonstrated that sialylation profile is one of the traits that decide the AMOR potential of BMP2 antibodies. Enhancement of sialylation may be a promising strategy to optimize antibody for iMSCs application in bone tissue engineering. STATEMENT OF SIGNIFICANCE: Antibody-mediated osseous regeneration (AMOR) is a promising strategy for bone tissue engineering that takes advantage of the specific reactivity of antibodies to sequester endogenous BMP2 and present it to osteoprogenitor cells. We previously demonstrated that BMP2 immune complex can drive iPSCs derived MSCs to osteogenic lineage. In this study, we analyze the effects of glycosylation profile on antibody directed osteogenic differentiation of iMSCs because glycosylation profile represents a key checkpoint that determines the effector functions of antibodies, and it is susceptible to variations in different clones. The results showed that sialylation profile is one of the traits that decides the AMOR potential of BMP2 antibody, and the enhancement of sialylation maybe a promising strategy to optimize antibodies for AMOR.

Designing Microgels for Cell Culture and Controlled Assembly of Tissue Microenvironments

Micron-sized hydrogels, termed microgels, are emerging as multifunctional platforms that can recapitulate tissue heterogeneity in engineered cell microenvironments. The microgels can function as either individual cell culture units or can be assembled into larger scaffolds. In this manner, individual microgels can be customized for single or multi-cell co-culture applications, or heterogeneous populations can be used as building blocks to create microporous assembled scaffolds that more closely mimic tissue heterogeneities. The inherent versatility of these materials allows user-defined control of the microenvironments, from the order of singly encapsulated cells to entire three-dimensional cell scaffolds. These hydrogel scaffolds are promising for moving towards personalized medicine approaches and recapitulating the multifaceted microenvironments that exist in vivo.

Recent Trends in Three-Dimensional Bioinks Based on Alginate for Biomedical Applications

Three-dimensional (3D) bioprinting is an appealing and revolutionary manufacturing approach for the accurate placement of biologics, such as living cells and extracellular matrix (ECM) components, in the form of a 3D hierarchical structure to fabricate synthetic multicellular tissues. Many synthetic and natural polymers are applied as cell printing bioinks. One of them, alginate (Alg), is an inexpensive biomaterial that is among the most examined hydrogel materials intended for vascular, cartilage, and bone tissue printing. It has also been studied pertaining to the liver, kidney, and skin, due to its excellent cell response and flexible gelation preparation through divalent ions including calcium. Nevertheless, Alg hydrogels possess certain negative aspects, including weak mechanical characteristics, poor printability, poor structural stability, and poor cell attachment, which may restrict its usage along with the 3D printing approach to prepare artificial tissue. In this review paper, we prepare the accessible materials to be able to encourage and boost new Alg-based bioink formulations with superior characteristics for upcoming purposes in drug delivery systems. Moreover, the major outcomes are discussed, and the outstanding concerns regarding this area and the scope for upcoming examination are outlined.

Structures, properties and application of alginic acid: A review

Alginic acid is a natural polysaccharide, which has been widely concerned and applied due to its excellent water solubility, film formation, biodegradability and biocompatibility. This paper briefly describes the source, properties, structure and application of sodium alginate by summarizing and analyzing the current literature. This paper reviews the application of sodium alginate in the fields of food industry, catalyst, health, water treatment, packaging, immobilized cells, and looks forward to its application prospects.

Microenvironment Can Induce Development of Auditory Progenitor Cells from Human Gingival Mesenchymal Stem Cells

Sensorineural hearing loss in mammals occurs due to irreversible damage to the sensory epithelia of the inner ear and has very limited treatment options. The ability to regenerate the auditory progenitor cells is a promising approach for the treatment of sensorineural hearing loss; therefore, finding an appropriate and easily accessible stem cell source for restoring the sense of hearing would be of great interest. Here, we proposed a novel easy-to-access source of cells with the ability to recover auditory progenitor cells. In this study, gingival mesenchymal stem cells (GMSCs) were utilized, as these cells have high self-renewal and multipotent differentiation capacity and can be obtained easily from the oral cavity or discarded tissue samples at dental clinics. To manipulate the biophysical properties of the cellular microenvironment for promoting GMSC differentiation toward the target cells, we also tried to propose a candidate biomaterial. GMSCs in combination with an appropriate scaffold material can, therefore, present advantageous therapeutic options for a number of conditions. Here, we report the potential of GMSCs to differentiate into auditory progenitor cells while supporting them with an optimized three-dimensional scaffold and certain growth factors. A hybrid hydrogel scaffold based on peptide modified alginate and Matrigel was used here in addition to the presence of fibroblast growth factor-basic (bFGF), insulin-like growth factor (IGF), and epidermal growth factor (EGF). Our in vitro and in vivo studies confirmed the auditory differentiation potential of GMSCs within the engineered microenvironment.

Rational design of type-IA receptor-derived cyclic peptides to target human bone morphogenic protein 2

Human bone morphogenetic protein 2 (BMP2) is a bone-growth regulatory factor involved in the formation of bone and cartilage, and has been recogn ized as an attractive therapeutic target for a variety of bone diseases and defects. Here, we report successful design of a head-to-tail cyclic peptide based on crystal structure to target BMP2. Computational alanine scanning identifies two hotspot regions at the crystal complex interface of BMP2 with its type-IA receptor; promising one is stripped from the interface to derive a linear self-inhibitory peptide RPS2^[r78-94] that covers residues 78-94 of the receptor protein. Dynamics simulation and energetics analysis reveal that the peptide is highly flexible in isolated state and cannot spontaneously bind to BMP2. The RPS2^[r78-94] peptide is further extended from its N- and C-termini until reaching two spatially vicinal residues 74 and 98 in the crystal structure of intact BMP2-receptor complex system, consequently resulting in a longer peptide RPS2^[r74-98], which is then cyclized in a head-to-tail manner to obtain its cyclic counterpart cycRPS2^[r74-98]. Computational analysis suggests that the cyclic peptide can well maintain in a conformation similar with its active conformation in complex crystal structure, exhibiting a smaller disorder and a larger potency than its linear counterpart. Further assays confirm that the two linear peptides RPS2^[r78-94] and RPS2^[r74-98]are nonbinders of BMP2, whereas, as designed, the cyclic peptide cycRPS2^[r74-98] can bind to BMP2 with a moderate affinity. The cyclic peptide is expected as a lead molecular entity to develop new and potent peptide-based drugs for BMP2-targeted therapy.

Anti-fibrotic mechanisms of exogenously-expanded mesenchymal stromal cells for fibrotic diseases

Most chronic diseases involving inflammation have a fibrotic component that involves remodeling and excess accumulation of extracellular matrix components. Left unchecked, fibrosis leads to organ failure and death. Mesenchymal stromal cells (MSCs) are emerging as a potent cell-based therapy for a wide spectrum of fibrotic conditions due to their immunomodulatory, anti-inflammatory and anti-fibrotic properties. This review provides an overview of known mechanisms by which MSCs mediate their anti-fibrotic actions and in relation to animal models of pulmonary, liver, renal and cardiac fibrosis. Recent MSC clinical trials results in liver, lung, skin, kidney and hearts are discussed and next steps for future MSC-based therapies including pre-activated or genetically-modified cells, or extracellular vesicles are also considered.

Bacterial cellulose membrane functionalized with hydroxiapatite and anti-bone morphogenetic protein 2: A promising material for bone regeneration

Bone tissue engineering seeks to adequately restore functions related to physical and biological properties, aiming at a repair process similar to natural bone. The use of compatible biopolymers, such as bacterial cellulose (BC), as well as having interesting mechanical characteristics, presents a slow in vivo degradation rate, and the ability to be chemically modified. To promote better bioactivity towards BC, we synthesized an innovative BC membrane associated to hydroxyapatite (HA) and anti-bone morphogenetic protein antibody (anti-BMP-2) (BC-HA-anti-BMP-2). We present the physical-chemical, biological and toxicological characterization of BC-HA-anti-BMP-2. Presence of BC and HA components in the membranes was confirmed by SEM-EDS and FTIR assays. No toxic potential was found in MC3T3-E1 cells by cytotoxicity assays (XTT Assay and Clonogenic Survival), genotoxicity (Comet Assay) and mutagenicity (Cytokinesis-blocked micronucleus Test). The in vitro release kinetics of anti-BMP-2 antibodies detected gradually reducing antibody levels, reducing approximately 70% in 7 days and 90% in 14 days. BC-HA-anti-BMP-2 increased SPP1, BGLAP, VEGF, ALPL, RUNX2 and TNFRSF11B expression, genes involved in bone repair and also increased mineralization nodules and phosphatase alcalin (ALP) activity levels. In conclusion, we developed BC-HA-anti-BMP-2 as an innovative and promising biomaterial with interesting physical-chemical and biological properties which may be a good alternative to treatment with commercial BMP-2 protein.

Drug-loaded/grafted peptide-modified porous PEEK to promote bone tissue repair and eliminate bacteria

Bone restoration and related infection in bone defect repair remain thorny problems in clinical practice. Herein, a drug-loaded (chlorogenic acid, CGA)/grafted peptide (BFP) hydrogel system supported on a sulfonated polyetheretherketone (SPEEK) surface is constructed to address the problem of large-scale defects and related infections in clinical bone implantation. Briefly, the encapsulated chlorogenic acid is released during hydrogel degradation and can inhibit the growth of bacteria and provide a bacteria-free environment for new bone formation. In vitro experiments and cell adhesion/proliferation evaluation reveal that the chlorogenic acid-sodium alginate-peptide bridging system shows better bioaffinity than the control groups due to the BFP peptide on the surface of the hydrogel. In addition, bacterial experiments suggest that the released chlorogenic acid has excellent antibacterial activity against gram-negative and gram-positive bacteria. Therefore, the hydrogel bridging system has a prospective application in clinical applications for bone repair.

Mineralized Polysaccharide Transplantation Modules Supporting Human MSC Conversion into Osteogenic Cells and Osteoid Tissue in a Non-Union Defect

Regenerative orthopedics needs significant devices to transplant human stem cells into damaged tissue and encourage automatic growth into replacements suitable for the human skeleton. Soft biomaterials have similarities in mechanical, structural and architectural properties to natural extracellular matrix (ECM), but often lack essential ECM molecules and signals. Here we engineer mineralized polysaccharide beads to transform MSCs into osteogenic cells and osteoid tissue for transplantation. Bone morphogenic proteins (BMP-2) and indispensable ECM proteins both directed differentiation inside alginate beads. Laminin and collagen IV basement membrane matrix proteins fixed and organized MSCs onto the alginate matrix, and BMP-2 drove differentiation, osteoid tissue self-assembly, and small-scale mineralization. Augmentation of alginate is necessary, and we showed that a few rationally selected small proteins from the basement membrane (BM) compartment of the ECM were sufficient to upregulate cell expression of Runx-2 and osteocalcin for osteoid formation, resulting in Alizarin red-positive mineral nodules. More significantly, nested BMP-2 and BM beads added to a non-union skull defect, self-generated osteoid expressing osteopontin (OPN) and osteocalcin (OCN) in a chain along the defect, at only four weeks, establishing a framework for complete regeneration expected in 6 and 12 weeks. Alginate beads are beneficial surgical devices for transplanting therapeutic cells in programmed (by the ECM components and alginate-chitosan properties) reaction environments ideal for promoting bone tissue.

Nano-hydroxyapatite-alginate-gelatin microcapsule as a potential osteogenic building block for modular bone tissue engineering

To develop osteogenic building blocks for modular bone tissue engineering applications, influence of gelatin as cell adhesive molecule and nano-hydroxyapatite (nHA) as osteoconductive component was examined on alginate-based hydrogel properties and microencapsulated osteoblast-like cell behavior by using factorial experimental design technique. nHA and alginate showed a statistically significant impact on swelling reduction, and improvement of stability and mechanical strength of hydrogels, respectively. Gelatin influence, however, was in a reverse manner. nHA played imperative roles in promoting microencapsulated osteoblastic cell proliferation and function due to its bioactivity and mechanical strength improvement of hydrogels to the modulus range of mineralized bone tissue in vivo. The results and their statistical analysis also revealed the importance of interaction effect of gelatin and nHA. Proliferation and osteogenic function of the cells fluctuated with increasing gelatin concentration of microcapsules in the presence of nHA, demonstrating that hydrogel properties should be balanced to provide an efficient 3D osteoconductive microcapsule. Alginate (1%)-gelatin (2.5%)-nHA (0.5%) microcapsule with compressive modulus of 0.19 MPa ± 0.02, swelling ratio of 52% ± 8 (24 h) and degradation rate of 12% ± 4 (96 h) revealed a maximum performance for the cell proliferation and function, indicating a potential microcapsule composition to prepare building blocks for modular bone tissue engineering.

Simvastatin delivery on PEEK for bioactivity and osteogenesis enhancements

A strategy developed for obtaining positive cellular responses remains to be focused in the filed of functional biomimetics. In this study, a hydrogel covered simvastatin-loaded polyetheretherketone (PEEK) bio-composites was constructed with the purpose of bone tissue regeneration therapy. Briefly, a three-dimensional (3D) porous structure was fabricated on PEEK surface; then the substrate was functionalized with the poly(L-lactic acid)/simvastatin porous film and hyaluronic acid hydrogel subsequently. In vitro cell attachment, proliferation, and cytoskeletal observation experiments reveal that our scaffolds show better bio-affinity due to the layer of hyaluronic acid hydrogel compared with control. Furthermore, the alkaline phosphatase activity, calcium mineral deposition evaluation, and gene expression for osteogenic potential all exhibit that the superior osteogenic differentiation of MC3T3-E1 pre-osteoblasts on our scaffolds. Therefore, our PEEK samples loaded with simvastatin and covered with hyaluronic acid hydrogel hold great potential in clinical applications for bone repair.

Therapeutic antibody directed osteogenic differentiation of induced pluripotent stem cell derived MSCs

Induced pluripotent stem cells (iPSCs) are regarded as a new cell source for regenerative medicine. Recent advances in tissue engineering have brought to light the therapeutic application of induced pluripotent stem cells (iPSCs) in bone defect repair. However, a safe and efficient way to differentiate iPSCs into osteogenic lineage remains to be a major challenge. Here we describe an approach using anti-BMP2 antibodies (Abs) to mediate osteogenic differentiation of iPSC-derived mesenchymal stromal cells (iMSCs). We first proved that 3G7 (an anti-BMP2 Ab) not only bound to BMP2, but also allowed the bound BMP2 to engage the BMP2 receptors on iMSCs. Subcutaneous implantation sites loaded with iMSCs + 3G7 group showed significant bone formation and vascularization in mice while those sites with exogenous BMP2 exhibited dystrophic calcification and significantly lower vascularization. Our in vitro study demonstrated that the anti-BMP2 Ab/BMP2 immune complex were capable of dictating the acquisition of osteogenic phenotype of iMSCs and subsequent mineralization. The study provided the first evidence of antibody-mediated differentiation of iMSCs and osseous regeneration in vivo. This novel strategy takes full advantage of the endogenous bioactive molecules for osseous regeneration and its potential therapeutic application is promising.

STATEMENT OF SIGNIFICANCE

Induced pluripotent stem cells (iPSCs) and its derived cells hold significant promise for the treatment of bone defects. In present study, we carried out the concept of antibody-mediated bone regeneration into the iPSC research for the first time. We demonstrated that anti-BMP2 Ab/BMP2 immune complex was capable of promoting osteogenic differentiation of iPSC-derived MSCs (iMSCs), likely through the classical BMP2/Smad1/Runx2 pathway. Subcutaneous co-delivery of iMSCs and anti-BMP2 Abs resulted in significant bone formation and vascularization. These findings suggested antibody mediated osteogenic differentiation may be a favorable approach for iPSC-based bone tissue engineering.

Antibody-Mediated Osseous Regeneration for Bone Tissue Engineering in Canine Segmental Defects

Among many applications of therapeutic monoclonal antibodies (mAbs), a unique approach for regenerative medicine has entailed antibody-mediated osseous regeneration (AMOR). In an effort to identify a clinically relevant model of craniofacial defect, the present study investigated the efficacy of mAb specific for bone morphogenetic protein- (BMP-) 2 to repair canine segmental mandibular continuity defect model. Accordingly, a 15 mm unilateral segmental defect was created in mandible and fixated with a titanium plate. Anorganic bovine bone mineral with 10% collagen (ABBM-C) was functionalized with 25 μg/mL of either chimeric anti-BMP-2 mAb or isotype-matched mAb (negative control). Recombinant human (rh) BMP-2 served as positive control. Morphometric analyses were performed on computed tomography (CT) and histologic images. Bone densities within healed defect sites at 12 weeks after surgery were 1360.81 ± 10.52 Hounsfield Unit (HU), 1044.27 ± 141.16 HU, and 839.45 ± 179.41 HU, in sites with implanted anti-BMP-2 mAb, rhBMP-2, and isotype mAb groups, respectively. Osteoid bone formation in anti-BMP-2 mAb (42.99% ± 8.67) and rhBMP-2 (48.97% ± 2.96) groups was not significantly different but was higher (p < 0.05) than in sites with isotype control mAb (26.8% ± 5.35). In view of the long-term objective of translational application of AMOR in humans, the results of the present study demonstrated the feasibility of AMOR in a large clinically relevant animal model.

Human Periodontal Ligament- and Gingiva-derived Mesenchymal Stem Cells Promote Nerve Regeneration When Encapsulated in Alginate/Hyaluronic Acid 3D Scaffold

Repair or regeneration of damaged nerves is still a challenging clinical task in reconstructive surgeries and regenerative medicine. Here, it is demonstrated that periodontal ligament stem cells (PDLSCs) and gingival mesenchymal stem cells (GMSCs) isolated from adult human periodontal and gingival tissues assume neuronal phenotype in vitro and in vivo via a subcutaneous transplantation model in nude mice. PDLSCs and GMSCs are encapsulated in a 3D scaffold based on alginate and hyaluronic acid hydrogels capable of sustained release of human nerve growth factor (NGF). The elasticity of the hydrogels affects the proliferation and differentiation of encapsulated MSCs within scaffolds. Moreover, it is observed that PDLSCs and GMSCs are stained positive for βIII-tubulin, while exhibiting high levels of gene expression related to neurogenic differentiation (βIII-tubulin and glial fibrillary acidic protein) via quantitative polymerase chain reaction (qPCR). Western blot analysis shows the importance of elasticity of the matrix and the presence of NGF in the neurogenic differentiation of encapsulated MSCs. In vivo, immunofluorescence staining for neurogenic specific protein markers confirms islands of dense positively stained structures inside transplanted hydrogels. As far as it is known, this study is the first demonstration of the application of PDLSCs and GMSCs as promising cell therapy candidates for nerve regeneration.

Reconstruction of Craniomaxillofacial Bone Defects Using Tissue-Engineering Strategies with Injectable and Non-Injectable Scaffolds

Engineering craniofacial bone tissues is challenging due to their complex structures. Current standard autografts and allografts have many drawbacks for craniofacial bone tissue reconstruction; including donor site morbidity and the ability to reinstate the aesthetic characteristics of the host tissue. To overcome these problems; tissue engineering and regenerative medicine strategies have been developed as a potential way to reconstruct damaged bone tissue. Different types of new biomaterials; including natural polymers; synthetic polymers and bioceramics; have emerged to treat these damaged craniofacial bone tissues in the form of injectable and non-injectable scaffolds; which are examined in this review. Injectable scaffolds can be considered a better approach to craniofacial tissue engineering as they can be inserted with minimally invasive surgery; thus protecting the aesthetic characteristics. In this review; we also focus on recent research innovations with different types of stem-cell sources harvested from oral tissue and growth factors used to develop craniofacial bone tissue-engineering strategies.

Stem cell-based bone regeneration in diseased microenvironments: Challenges and solutions

Restoration of extensive bone loss and defects remain as an unfulfilled challenge in modern medicine. Given the critical contributions to bone homeostasis and diseases, mesenchymal stem cells (MSCs) have shown great promise to jumpstart and facilitate bone healing, with immense regenerative potential in both pharmacology-based endogenous MSC rescue/mobilization in skeletal diseases and emerging application of MSC transplantation in bone tissue engineering and cytotherapy. However, efficacy of MSC-based bone regeneration was not always achieved; particularly, fulfillment of MSC-mediated bone healing in diseased microenvironments of host comorbidities remains as a major challenge. Indeed, impacts of diseased microenvironments on MSC function rely not only on the dynamic regulation of resident MSCs by surrounding niche to convoy pathological signals of bone, but also on the profound interplay between transplanted MSCs and recipient components that mediates and modulates therapeutic effects on skeletal conditions. Accordingly, novel solutions have recently been developed, including improving resistance of MSCs to diseased microenvironments, recreating beneficial microenvironments to guarantee MSC-based regeneration, and usage of subcellular vesicles of MSCs in cell-free therapies. In this review, we summarize state-of-the-art knowledge regarding applications and challenges of MSC-mediated bone healing, further offering principles and effective strategies to optimize MSC-based bone regeneration in aging and diseases.