Adult Stem Cells for Bone Regeneration and Repair

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.

Stem Cells and Acellular Preparations in Bone Regeneration/Fracture Healing: Current Therapies and Future Directions

Bone/fracture healing is a complex process with different steps and four basic tissue layers being affected: cortical bone, periosteum, fascial tissue surrounding the fracture, and bone marrow. Stem cells and their derivatives, including embryonic stem cells, induced pluripotent stem cells, mesenchymal stem cells, hematopoietic stem cells, skeletal stem cells, and multipotent stem cells, can function to artificially introduce highly regenerative cells into decrepit biological tissues and augment the healing process at the tissue level. Stem cells are molecularly and functionally indistinguishable from standard human tissues. The widespread appeal of stem cell therapy lies in its potential benefits as a therapeutic technology that, if harnessed, can be applied in clinical settings. This review aims to establish the molecular pathophysiology of bone healing and the current stem cell interventions that disrupt or augment the bone healing process and, finally, considers the future direction/therapeutic options related to stem cells and bone healing.

Comparing the bone regeneration potential between a trabecular bone and a porous scaffold through osteoblast migration and differentiation: A multiscale approach

Both cell migration and osteogenic differentiation are critical for successful bone regeneration. Therefore, understanding the mechanobiological aspects that govern these two processes is essential in designing effective scaffolds that promote faster bone regeneration. Studying these two factors at different locations is necessary to manage bone regeneration in various sections of a scaffold. Hence, a multiscale computational model was used to observe the mechanical responses of osteoblasts placed in different positions of the trabecular bone and gyroid scaffold. Fluid shear stresses in scaffolds at cell seeded locations (representing osteogenic differentiation) and strain energy densities in cells at cell substrate interface (representing cell migration) were observed as mechanical response parameters in this study. Comparison of these responses, as two critical factors for bone regeneration, between the trabecular bone and gyroid scaffold at different locations, is the overall goal of the study. This study reveals that the gyroid scaffold exhibits higher osteogenic differentiation and cell migration potential compared to the trabecular bone. However, the responses in the gyroid only mimic the trabecular bone in two out of nine positions. These findings can guide us in predicting the ideal cell seeded sites within a scaffold for better bone regeneration and in replicating a replaced bone condition by altering the physical parameters of a scaffold.

Towards Stem Cell Therapy for Critical-Sized Segmental Bone Defects: Current Trends and Challenges on the Path to Clinical Translation

The management and reconstruction of critical-sized segmental bone defects remain a major clinical challenge for orthopaedic clinicians and surgeons. In particular, regenerative medicine approaches that involve incorporating stem cells within tissue engineering scaffolds have great promise for fracture management. This narrative review focuses on the primary components of bone tissue engineering-stem cells, scaffolds, the microenvironment, and vascularisation-addressing current advances and translational and regulatory challenges in the current landscape of stem cell therapy for critical-sized bone defects. To comprehensively explore this research area and offer insights for future treatment options in orthopaedic surgery, we have examined the latest developments and advancements in bone tissue engineering, focusing on those of clinical relevance in recent years. Finally, we present a forward-looking perspective on using stem cells in bone tissue engineering for critical-sized segmental bone defects.

Stem Cell and Regenerative Therapies for the Treatment of Osteoporotic Vertebral Compression Fractures

Osteoporotic vertebral compression fractures (OVCFs) significantly increase morbidity and mortality, presenting a formidable challenge in healthcare. Traditional interventions such as vertebroplasty and kyphoplasty, despite their widespread use, are limited in addressing the secondary effects of vertebral fractures in adjacent areas and do not facilitate bone regeneration. This review paper explores the emerging domain of regenerative therapies, spotlighting stem cell therapy's transformative potential in OVCF treatment. It thoroughly describes the therapeutic possibilities and mechanisms of action of mesenchymal stem cells against OVCFs, relying on recent clinical trials and preclinical studies for efficacy assessment. Our findings reveal that stem cell therapy, particularly in combination with scaffolding materials, holds substantial promise for bone regeneration, spinal stability improvement, and pain mitigation. This integration of stem cell-based methods with conventional treatments may herald a new era in OVCF management, potentially improving patient outcomes. This review advocates for accelerated research and collaborative efforts to translate laboratory breakthroughs into clinical practice, emphasizing the revolutionary impact of regenerative therapies on OVCF management. In summary, this paper positions stem cell therapy at the forefront of innovation for OVCF treatment, stressing the importance of ongoing research and cross-disciplinary collaboration to unlock its full clinical potential.

Osteosarcoma cell death induced by innovative scaffolds doped with chemotherapeutics

Osteosarcoma (OS) cancer treatments include systemic chemotherapy and surgical resection. In the last years, novel treatment approaches have been proposed, which employ a drug-delivery system to prevent offside effects and improves treatment efficacy. Locally delivering anticancer compounds improves on high local concentrations with more efficient tumour-killing effect, reduced drugs resistance and confined systemic effects. Here, the synthesis of injectable strontium-doped calcium phosphate (SrCPC) scaffold was proposed as drug delivery system to combine bone tissue regeneration and anticancer treatment by controlled release of methotrexate (MTX) and doxorubicin (DOX), coded as SrCPC-MTX and SrCPC-DOX, respectively. The drug-loaded cements were tested in an in vitro model of human OS cell line SAOS-2, engineered OS cell line (SAOS-2-eGFP) and U2-OS. The ability of doped scaffolds to induce OS cell death and apoptosis was assessed analysing cell proliferation and Caspase-3/7 activities, respectively. To determine if OS cells grown on doped-scaffolds change their migratory ability and invasiveness, a wound-healing assay was performed. In addition, the osteogenic potential of SrCPC material was evaluated using human adipose derived-mesenchymal stem cells. Osteogenic markers such as (i) the mineral matrix deposition was analysed by alizarin red staining; (ii) the osteocalcin (OCN) protein expression was investigated by enzyme-linked immunosorbent assay test, and (iii) the osteogenic process was studied by real-time polymerase chain reaction array. The delivery system induced cell-killing cytotoxic effects and apoptosis in OS cell lines up to Day 7. SrCPC demonstrates a good cytocompatibility and it induced upregulation of osteogenic genes involved in the skeletal development pathway, together with OCN protein expression and mineral matrix deposition. The proposed approach, based on the local, sustained release of anticancer drugs from nanostructured biomimetic drug-loaded cements is promising for future therapies aiming to combine bone regeneration and anticancer local therapy.

Antimicrobial peptides in bone regeneration: mechanism and potential

INTRODUCTION

Antimicrobial peptides (AMPs) are small-molecule peptides with a unique antimicrobial mechanism. Other notable biological activities of AMPs, including anti-inflammatory, angiogenesis, and bone formation effects, have recently received widespread attention. These remarkable bioactivities, combined with the unique antimicrobial mechanism of action of AMPs, have led to their increasingly important role in bone regeneration.

AREAS COVERED

In this review, on the one hand, we aimed to summarize information about the AMPs that are currently used for bone regeneration by reviewing published literature in the PubMed database. On the other hand, we also highlight some AMPs with potential roles in bone regeneration and their possible mechanisms of action.

EXPERT OPINION

The translation of AMPs to the clinic still faces many problems, but their unique antimicrobial mechanisms and other conspicuous biological activities suggest great potential. An in-depth understanding of the structure and mechanism of action of AMPs will help us to subsequently combine AMPs with different carrier systems and perform structural modifications to reduce toxicity and achieve stable release, which may be a key strategy for facilitating the translation of AMPs to the clinic.

Bone repair potential of collagen-poly(3-hydroxybutyrate)-carbon nanotubes scaffold loaded with mesenchymal stem cells for the reconstruction of critical-sized mandibular defects

The poor structural stability of collagen (COL) upon hydration poses a significant challenge in tissue engineering (TE). To overcome this limitation, the incorporation of hydrophobic polymers such as poly(3-hydroxybutyrate) (PHB), and nanomaterials such as carbon nanotubes (CNTs) has been explored. In this study, we investigated the physical, chemical, and biological characteristics of COL-based scaffolds modified with PHB and CNTs for bone tissue engineering (BTE) applications. The tensile strength analysis revealed a substantial improvement in the ultimate tensile strength with the addition of 10 % PHB and 4 % CNTs. Scanning electron microscopy (SEM) images depicted a denser and more compact structure resulting from the presence of PHB and CNTs, enhancing the scaffold's mechanical properties. Fourier-transform infrared spectroscopy (FTIR) confirmed the successful incorporation of PHB and CNTs into the composite scaffold, maintaining the chemical integrity of COL. Stereological studies also conducted in a rat model with induced critical-sized bone defects in the mandibular bone further emphasize the substantial increase in bone formation and reduction in defect volume achieved by the scaffold loaded with stem cells. These findings underscore the promising approach to enhance bone healing, using COL-based scaffolds loaded with stem cells, and the favorable results obtained in this study can contribute to the advancement of BTE strategies.

Titanium-Doped Diamond-like Carbon Layers as a Promising Coating for Joint Replacements Supporting Osteogenic Differentiation of Mesenchymal Stem Cells

Diamond-like carbon (DLC) layers are known for their high corrosion and wear resistance, low friction, and high biocompatibility. However, it is often necessary to dope DLC layers with additional chemical elements to strengthen their adhesion to the substrate. Ti-DLC layers (doped with 0.4, 2.1, 3.7, 6.6, and 12.8 at.% of Ti) were prepared by dual pulsed laser deposition, and pure DLC, glass, and polystyrene (PS) were used as controls. In vitro cell-material interactions were investigated with an emphasis on cell adhesion, proliferation, and osteogenic differentiation. We observed slightly increasing roughness and contact angle and decreasing surface free energy on Ti-DLC layers with increasing Ti content. Three-week biological experiments were performed using adipose tissue-derived stem cells (ADSCs) and bone marrow mesenchymal stem cells (bmMSCs) in vitro. The cell proliferation activity was similar or slightly higher on the Ti-doped materials than on glass and PS. Osteogenic cell differentiation on all materials was proved by collagen and osteocalcin production, ALP activity, and Ca deposition. The bmMSCs exhibited greater initial proliferation potential and an earlier onset of osteogenic differentiation than the ADSCs. The ADSCs showed a slightly higher formation of focal adhesions, higher metabolic activity, and Ca deposition with increasing Ti content.

BMP-2-immobilized PCL 3D printing scaffold with a leaf-stacked structure as a physically and biologically activated bone graft

Although three-dimensional (3D) printing techniques are used to mimic macro- and micro-structures as well as multi-structural human tissues in tissue engineering, efficient target tissue regeneration requires bioactive 3D printing scaffolds. In this study, we developed a bone morphogenetic protein-2 (BMP-2)-immobilized polycaprolactone (PCL) 3D printing scaffold with leaf-stacked structure (LSS) (3D-PLSS-BMP) as a bioactive patient-tailored bone graft. The unique LSS was introduced on the strand surface of the scaffold via heating/cooling in tetraglycol without significant deterioration in physical properties. The BMP-2 adsorbed on3D-PLSS-BMPwas continuously released from LSS over a period of 32 d. The LSS can be a microtopographical cue for improved focal cell adhesion, proliferation, and osteogenic differentiation.In vitrocell culture andin vivoanimal studies demonstrated the biological (bioactive BMP-2) and physical (microrough structure) mechanisms of3D-PLSS-BMPfor accelerated bone regeneration. Thus, bioactive molecule-immobilized 3D printing scaffold with LSS represents a promising physically and biologically activated bone graft as well as an advanced tool for widespread application in clinical and research fields.

Investigation of background, novelty and recent advance of iron (II,III) oxide- loaded on 3D polymer based scaffolds as regenerative implant for bone tissue engineering: A review

Bone tissue engineering had crucial role in the bone defects regeneration, particularly when allograft and autograft procedures have limitations. In this regard, different types of scaffolds are used in tissue regeneration as fundamental tools. In recent years, magnetic scaffolds show promising applications in different biomedical applications (in vitro and in vivo). As superparamagnetic materials are widely considered to be among the most attractive biomaterials in tissue engineering, due to long-range stability and superior bioactivity, therefore, magnetic implants shows angiogenesis, osteoconduction, and osteoinduction features when they are combined with biomaterials. Furthermore, these scaffolds can be coupled with a magnetic field to enhance their regenerative potential. In addition, magnetic scaffolds can be composed of various combinations of magnetic biomaterials and polymers using different methods to improve the magnetic, biocompatibility, thermal, and mechanical properties of the scaffolds. This review article aims to explain the use of magnetic biomaterials such as iron (II,III) oxide (Fe2O3 and Fe3O4) in detail. So it will cover the research background of magnetic scaffolds, the novelty of using these magnetic implants in tissue engineering, and provides a future perspective on regenerative implants.

Three-Dimensional Modeling with Osteoblast-like Cells under External Magnetic Field Conditions Using Magnetic Nano-Ferrite Particles for the Development of Cell-Derived Artificial Bone

The progress in artificial bone research is crucial for addressing fractures and bone defects in the aging population. However, challenges persist in terms of biocompatibility and structural complexity. Nanotechnology provides a promising avenue by which to overcome these challenges, with nano-ferrite particles (NFPs) exhibiting superparamagnetic properties. The ability to control cell positioning using a magnetic field opens up new possibilities for customizing artificial bones with specific shapes. This study explores the biological effects of NFPs on osteoblast-like cell lines (MC3T3-E1), including key analyses, such as cell viability, cellular uptake of NFPs, calcification processes, cell migration under external magnetic field conditions, and three-dimensional modeling. The results indicate that the impact of NFPs on cell proliferation is negligible. Fluorescence and transmission electron microscopy validated the cellular uptake of NFPs, demonstrating the potential for precise cell positioning through an external magnetic field. Under calcification-inducing conditions, the cells exhibited sustained calcification ability even in the presence of NFPs. The cell movement analysis observed the controlled movement of NFP-absorbing cells under an external magnetic field. Applying a magnetic field along the z-axis induced the three-dimensional shaping of cells incorporating NFPs, resulting in well-arranged z-axis directional patterns. In this study, NFPs demonstrated excellent biocompatibility and controllability under an external magnetic field, laying the foundation for innovative treatment strategies for customizing artificial bones.

Mechanical loading intensities affect the release of extracellular vesicles from mouse bone marrow-derived hematopoietic progenitor cells and change their osteoclast-modulating effect

Low-intensity loading maintains or increases bone mass, whereas lack of mechanical loading and high-intensity loading decreases bone mass, possibly via the release of extracellular vesicles by mechanosensitive bone cells. How different loading intensities alter the biological effect of these vesicles is not fully understood. Dynamic fluid shear stress at low intensity (0.7 ± 0.3 Pa, 5 Hz) or high intensity (2.9 ± 0.2 Pa, 1 Hz) was used on mouse hematopoietic progenitor cells for 2 min in the presence or absence of chemical compounds that inhibit release or biogenesis of extracellular vesicles. We used a Receptor activator of nuclear factor kappa-Β ligand-induced osteoclastogenesis assay to evaluate the biological effect of different fractions of extracellular vesicles obtained through centrifugation of medium from hematopoietic stem cells. Osteoclast formation was reduced by microvesicles (10 000× g) obtained after low-intensity loading and induced by exosomes (100 000× g) obtained after high-intensity loading. These osteoclast-modulating effects could be diminished or eliminated by depletion of extracellular vesicles from the conditioned medium, inhibition of general extracellular vesicle release, inhibition of microvesicle biogenesis (low intensity), inhibition of ESCRT-independent exosome biogenesis (high intensity), as well as by inhibition of dynamin-dependent vesicle uptake in osteoclast progenitor cells. Taken together, the intensity of mechanical loading affects the release of extracellular vesicles and change their osteoclast-modulating effect.

Advances in the roles of ATF4 in osteoporosis

Osteoporosis (OP) is characterized by reduced bone mass, decreased strength, and enhanced bone fragility fracture risk. Activating transcription factor 4 (ATF4) plays a role in cell differentiation, proliferation, apoptosis, redox balance, amino acid uptake, and glycolipid metabolism. ATF4 induces the differentiation of bone marrow mesenchymal stem cells (BM-MSCs) into osteoblasts, increases osteoblast activity, and inhibits osteoclast formation, promoting bone formation and remodeling. In addition, ATF4 mediates the energy metabolism in osteoblasts and promotes angiogenesis. ATF4 is also involved in the mediation of adipogenesis. ATF4 can selectively accumulate in osteoblasts. ATF4 can directly interact with RUNT-related transcription factor 2 (RUNX2) and up-regulate the expression of osteocalcin (OCN) and osterix (Osx). Several upstream factors, such as Wnt/β-catenin and BMP2/Smad signaling pathways, have been involved in ATF4-mediated osteoblast differentiation. ATF4 promotes osteoclastogenesis by mediating the receptor activator of nuclear factor κ-B (NF-κB) ligand (RANKL) signaling. Several agents, such as parathyroid (PTH), melatonin, and natural compounds, have been reported to regulate ATF4 expression and mediate bone metabolism. In this review, we comprehensively discuss the biological activities of ATF4 in maintaining bone homeostasis and inhibiting OP development. ATF4 has become a therapeutic target for OP treatment.

Effects of Aging on Osteosynthesis at Bone-Implant Interfaces

Joint replacement is a common surgery and is predominantly utilized for treatment of osteoarthritis in the aging population. The longevity of many of these implants depends on bony ingrowth. Here, we provide an overview of current techniques in osteogenesis (inducing bone growth onto an implant), which is affected by aging and inflammation. In this review we cover the biologic underpinnings of these processes as well as the clinical applications. Overall, aging has a significant effect at the cellular and macroscopic level that impacts osteosynthesis at bone-metal interfaces after joint arthroplasty; potential solutions include targeting prolonged inflammation, preventing microbial adhesion, and enhancing osteoinductive and osteoconductive properties.

Neuro-bone tissue engineering: emerging mechanisms, potential strategies, and current challenges

The skeleton is a highly innervated organ in which nerve fibers interact with various skeletal cells. Peripheral nerve endings release neurogenic factors and sense skeletal signals, which mediate bone metabolism and skeletal pain. In recent years, bone tissue engineering has increasingly focused on the effects of the nervous system on bone regeneration. Simultaneous regeneration of bone and nerves through the use of materials or by the enhancement of endogenous neurogenic repair signals has been proven to promote functional bone regeneration. Additionally, emerging information on the mechanisms of skeletal interoception and the central nervous system regulation of bone homeostasis provide an opportunity for advancing biomaterials. However, comprehensive reviews of this topic are lacking. Therefore, this review provides an overview of the relationship between nerves and bone regeneration, focusing on tissue engineering applications. We discuss novel regulatory mechanisms and explore innovative approaches based on nerve-bone interactions for bone regeneration. Finally, the challenges and future prospects of this field are briefly discussed.

Bone repair and key signalling pathways for cell-based bone regenerative therapy: A review

Advances in cell-based regenerative therapy create new opportunities for the treatment of bone-related disorders and injuries, by improving the reparative phase of bone healing. Apart from the classical approach of bone grafting, the application of cell-based therapies, particularly stem cells (SCs), has gained a lot of attention in recent years. SCs play an important role in regenerative therapy due to their excellent ability to differentiate into bone-forming cells. Regeneration of new bone is regulated by a wide variety of signalling molecules and intracellular networks, which are responsible for coordinating cellular processes. The activated signalling cascade is significantly involved in cell survival, proliferation, apoptosis, and interaction with the microenvironment and other types of cells within the healing site. Despite the increasing evidence from studies conducted on signalling pathways associated with bone formation, the exact mechanism involved in controlling the differentiation stage of transplanted cells is not well understood. Identifying the key activated pathways involved in bone regeneration may allow for precise manipulation of the relevant signalling molecules within the progenitor cell population to accelerate the healing process. The in-depth knowledge of molecular mechanisms would be advantageous in improving the efficiency of personalised medicine and targeted therapy in regenerative medicine. In this review, we briefly introduce the theory of bone repair mechanism and bone tissue engineering followed by an overview of relevant signalling pathways that have been identified to play an important role in cell-based bone regenerative therapy.

Differentiation of osteoblasts: the links between essential transcription factors

Osteoblasts, cells derived from mesenchymal stem cells (MSCs) in the bone marrow, are cells responsible for bone formation and remodeling. The differentiation of osteoblasts from MSCs is triggered by the expression of specific genes, which are subsequently controlled by pro-osteogenic pathways. Mature osteoblasts then differentiate into osteocytes and are embedded in the bone matrix. Dysregulation of osteoblast function can cause inadequate bone formation, which leads to the development of bone disease. Various key molecules are involved in the regulation of osteoblastogenesis, which are transcription factors. Previous studies have heavily examined the role of factors that control gene expression during osteoblastogenesis, both in vitro and in vivo. However, the systematic relationship of these transcription factors remains unknown. The involvement of ncRNAs in this mechanism, particularly miRNAs, lncRNAs, and circRNAs, has been shown to influence transcriptional factor activity in the regulation of osteoblast differentiation. Here, we discuss nine essential transcription factors involved in osteoblast differentiation, including Runx2, Osx, Dlx5, β-catenin, ATF4, Ihh, Satb2, and Shn3. In addition, we summarize the role of ncRNAs and their relationship to these essential transcription factors in order to improve our understanding of the transcriptional regulation of osteoblast differentiation. Adequate exploration and understanding of the molecular mechanisms of osteoblastogenesis can be a critical strategy in the development of therapies for bone-related diseases.Communicated by Ramaswamy H. Sarma.

Electrospun Scaffolds of Polylactic Acid, Collagen, and Amorphous Calcium Phosphate for Bone Repair

Most electrospun scaffolds for bone tissue engineering typically use hydroxyapatite (HA) or beta tricalcium phosphate (β-TCP). However, the biological activity of these crystalline compounds can be limited due to their low solubility. Therefore, amorphous calcium phosphate (ACP) may be an alternative in bone repair scaffolds. This study analyzes the morphology, porosity, mechanical strength, and surface chemistry of electrospun scaffolds composed of polylactic acid and collagen integrated with hydroxyapatite (MHAP) or amorphous calcium phosphate (MACP). In addition, the in vitro biocompatibility, osteogenic differentiation, and growth factor production associated with bone repair using human Wharton's jelly-derived mesenchymal stem cells (hWJ-MSCs) are evaluated. The results show that the electrospun MHAP and MACP scaffolds exhibit a fibrous morphology with interconnected pores. Both scaffolds exhibit favorable biocompatibility and stimulate the proliferation and osteogenesis of hWJ-MSCs. However, cell adhesion and osteocalcin production are greater in the MACP scaffold compared to the MHAP scaffold. In addition, the MACP scaffold shows significant production of bone-repair-related growth factors such as transforming growth factor-beta 1 (TGF-β1), providing a solid basis for its use in bone tissue engineering.

Advancing Dentistry through Bioprinting: Personalization of Oral Tissues

Despite significant advancements in dental tissue restoration and the use of prostheses for addressing tooth loss, the prevailing clinical approaches remain somewhat inadequate for replicating native dental tissue characteristics. The emergence of three-dimensional (3D) bioprinting offers a promising innovation within the fields of regenerative medicine and tissue engineering. This technology offers notable precision and efficiency, thereby introducing a fresh avenue for tissue regeneration. Unlike the traditional framework encompassing scaffolds, cells, and signaling factors, 3D bioprinting constitutes a contemporary addition to the arsenal of tissue engineering tools. The ongoing shift from conventional dentistry to a more personalized paradigm, principally under the guidance of bioprinting, is poised to exert a significant influence in the foreseeable future. This systematic review undertakes the task of aggregating and analyzing insights related to the application of bioprinting in the context of regenerative dentistry. Adhering to PRISMA guidelines, an exhaustive literature survey spanning the years 2019 to 2023 was performed across prominent databases including PubMed, Scopus, Google Scholar, and ScienceDirect. The landscape of regenerative dentistry has ushered in novel prospects for dentoalveolar treatments and personalized interventions. This review expounds on contemporary accomplishments and avenues for the regeneration of pulp-dentin, bone, periodontal tissues, and gingival tissues. The progressive strides achieved in the realm of bioprinting hold the potential to not only enhance the quality of life but also to catalyze transformative shifts within the domains of medical and dental practices.

Human Mesenchymal Stem Cells and Innovative Scaffolds for Bone Tissue Engineering Applications

Stem cell-based therapy is a significant topic in regenerative medicine, with a predominant role being played by human mesenchymal stem cells (hMSCs). The hMSCs have been shown to be suitable in regenerative medicine for the treatment of bone tissue. In the last few years, the average lifespan of our population has gradually increased. The need of biocompatible materials, which exhibit high performances, such as efficiency in bone regeneration, has been highlighted by aging. Current studies emphasize the benefit of using biomimetic biomaterials, also known as scaffolds, for bone grafts to speed up bone repair at the fracture site. For the healing of injured bone and bone regeneration, regenerative medicine techniques utilizing a combination of these biomaterials, together with cells and bioactive substances, have drawn a great interest. Cell therapy, based on the use of hMSCs, alongside materials for the healing of damaged bone, has obtained promising results. In this work, several aspects of cell biology, tissue engineering, and biomaterials applied to bone healing/regrowth will be considered. In addition, the role of hMSCs in these fields and recent progress in clinical applications are discussed. Impact Statement The restoration of large bone defects is both a challenging clinical issue and a socioeconomic problem on a global scale. Different therapeutic approaches have been proposed for human mesenchymal stem cells (hMSCs), considering their paracrine effect and potential differentiation into osteoblasts. However, different limitations are still to be overcome in using hMSCs as a therapeutic opportunity in bone fracture repair, including hMSC administration methods. To identify a suitable hMSC delivery system, new strategies have been proposed using innovative biomaterials. This review provides an update of the literature on hMSC/scaffold clinical applications for the management of bone fractures.

Microneedle-based cell delivery and cell sampling for biomedical applications

Cell-based therapeutics are novel therapeutic strategies that can potentially treat many presently incurable diseases through novel mechanisms of action. Cell therapies may benefit from the ease, safety, and efficacy of administering therapeutic cells. Despite considerable recent technological and biological advances, several barriers remain to the clinical translation and commercialization of cell-based therapies, including low patient compliance, personal handling inconvenience, poor biosafety, and limited biocompatibility. Microneedles (MNs) are emerging as a promising biomedical device option for improved cell delivery with little invasion, pain-free administration, and simplicity of disposal. MNs have shown considerable promise in treating a wide range of diseases and present the potential to improve cell-based therapies. In this review, we first summarized the latest advances in the various types of MNs developed for cell delivery and cell sampling. Emphasis was given to the design and fabrication of various types of MNs based on their structures and materials. Then we focus on the recent biomedical applications status of MNs-mediated cell delivery and sampling, including tissue repair (wound healing, heart repair, and endothelial repair), cancer treatment, diabetes therapy, cell sampling, and other applications. Finally, the current status of clinical application, potential perspectives, and the challenges for clinical translation are also highlighted.

Biotherapeutic Applications of Platelet-Rich Plasma in Regenerative Medicine

BACKGROUND

Platelet-rich plasma (PRP), a blood-based product containing platelets and growth factors, is being utilized to treat numerous non-hemostatic disorders. Studies have explored the use of PRP to provide rapid repair, healing, and recovery from various injuries; some studies mentioned the effectiveness of PRP as compared with other forms of treatment like the use of hyaluronic acid. Commercially available PRP systems are available now, and each varies from one another depending on how it is prepared, thus causing variations in platelet concentration and growth factor content. These variations also implicated different therapeutic applications.

METHODS

The paper reviews the various applications of PRP, including factors to consider before using PRP therapy, and provides an extensive list of PRP applications.

RESULTS

The administration of PRP as a standalone treatment or as a co-therapy results in observed positive outcomes. However, there is a lack of standardization for PRP preparation, increasing the risks for heterogeneity and bias amongst results.

CONCLUSION

The use of PRP is indeed an option for regenerative therapy, but more research is needed before it can fully be recommended as a primary treatment modality.

Investigation of Bone Regeneration Efficacy of New Bovine Bone Minerals in a Canine Mandibular Critical Defect Model

This study aims to investigate the bone regeneration effect of bovine hydroxyapatite-processed biomaterials Bone-XB and S1-XB in a beagle mandibular defect model. A total of four saddle-type critical sizes (15 mm × 10 mm) bone defects are created in each dog: two defects in the left mandible and two defects in the right mandible. The defect control (DC) group is kept unfilled, and the other three defects are filled with three different biomaterials as follows: positive control Bio-Oss (Bio-Oss group), Bone-XB (XB group), and S1-XB (S1-XB group). Bone regeneration is evaluated by radiography, micro-computed tomography, and histological analysis. It is revealed that Bone-XB and S1-XB significantly increase newly formed bone, defect filling percentage, and bone healing score compared to the DC group, which is confirmed by bone microstructure augmentation (bone volume/total volume, trabecular number, and trabecular thickness). Interestingly, no significant differences are observed between the Bone-XB, S1-XB, and Bio-Oss groups. It is suggested that Bone-XB or S1-XB stimulates bone regeneration demonstrated by the increase in newly formed bone and bone microstructure, thereby improving bone defect filling, which is equivalent to the Bio-Oss. Therefore, bovine hydroxyapatite-processed Bone-XB or S1-XB can be considered effective biomaterials for correcting critical-size bone defects or fractures.

Recent Advances in Bioengineering Bone Revascularization Based on Composite Materials Comprising Hydroxyapatite

The natural healing process of bone is impaired in the presence of tumors, trauma, or inflammation, necessitating external assistance for bone regeneration. The limitations of autologous/allogeneic bone grafting are still being discovered as research progresses. Bone tissue engineering (BTE) is now a crucial component of treating bone injuries and actively works to promote vascularization, a crucial stage in bone repair. A biomaterial with hydroxyapatite (HA), which resembles the mineral makeup of invertebrate bones and teeth, has demonstrated high osteoconductivity, bioactivity, and biocompatibility. However, due to its brittleness and porosity, which restrict its application, scientists have been prompted to explore ways to improve its properties by mixing it with other materials, modifying its structural composition, improving fabrication techniques and growth factor loading, and co-cultivating bone regrowth cells to stimulate vascularization. This review scrutinizes the latest five-year research on HA composite studies aimed at amplifying vascularization in bone regeneration.

Three-Dimensional Cell Cultures: The Bridge between In Vitro and In Vivo Models

Although historically, the traditional bidimensional in vitro cell system has been widely used in research, providing much fundamental information regarding cellular functions and signaling pathways as well as nuclear activities, the simplicity of this system does not fully reflect the heterogeneity and complexity of the in vivo systems. From this arises the need to use animals for experimental research and in vivo testing. Nevertheless, animal use in experimentation presents various aspects of complexity, such as ethical issues, which led Russell and Burch in 1959 to formulate the 3R (Replacement, Reduction, and Refinement) principle, underlying the urgent need to introduce non-animal-based methods in research. Considering this, three-dimensional (3D) models emerged in the scientific community as a bridge between in vitro and in vivo models, allowing for the achievement of cell differentiation and complexity while avoiding the use of animals in experimental research. The purpose of this review is to provide a general overview of the most common methods to establish 3D cell culture and to discuss their promising applications. Three-dimensional cell cultures have been employed as models to study both organ physiology and diseases; moreover, they represent a valuable tool for studying many aspects of cancer. Finally, the possibility of using 3D models for drug screening and regenerative medicine paves the way for the development of new therapeutic opportunities for many diseases.

The Potential of miR-21 in Stem Cell Differentiation and its Application in Tissue Engineering and Regenerative Medicine

MicroRNAs (miRNAs) and long non-coding RNAs (lncRNAs) are two important types of non-coding RNAs that are not translated into protein. These molecules can regulate various biological processes, including stem cell differentiation and self-renewal. One of the first known miRNAs in mammals is miR-21. Cancer-related studies have shown that this miRNA has proto-oncogene activity and is elevated in cancers. However, it is confirmed that miR-21 inhibits stem cell pluripotency and self-renewal and induces differentiation by targeting various genes. Regenerative medicine is a field of medical science that tries to regenerate and repair damaged tissues. Various studies have shown that miR-21 plays an essential role in regenerative medicine by affecting stem cell proliferation and differentiation. In this review, we will discuss the function of miR-21 in regenerative medicine of the liver, nerve, spinal cord, wound, bone, and dental tissues. In addition, the function of natural compounds and lncRNAs will be analyzed as potential regulators of miR-21 expression in regenerative medicine.

Biofunctionalization with Cissus quadrangularis Phytobioactives Accentuates Nano-Hydroxyapatite Based Ceramic Nano-Cement for Neo-Bone Formation in Critical Sized Bone Defect

Developing biofunctionalized ceramic bone substitutes with phytobioactives for their sustained delivery is highly desired to enhance the osteo-active potential of ceramic bone substitutes, reduce the systemic toxicity of synthetic drugs, and increase the bioavailability of phytobioactives. The present work highlights the local delivery of phytobioactives of Cissus quadrangularis (CQ) through nano-hydroxyapatite (nHAP) based ceramic nano-cement. The phytoconstituent profiling represented the optimized CQ fraction to be rich in osteogenic polyphenols and flavonoids like quercetin, resveratrol, and their glucosides. Further, CQ phytobioactives-based formulation was biocompatible, increased bone formation, calcium deposition, proliferation, and migration of cells with simultaneous alleviation of cellular oxidative stress. In the in vivo critical-sized bone defect model, enhanced formation of highly mineralized tissue (BV mm³) in CQ phytobioactives functionalized nano-cement (10.5 ± 2 mm³) were observed compared to the control group (6.5 ± 1.2 mm³). Moreover, the addition of CQ phytobioactives to the bone nano-cement increased the fractional bone volume (BV/TV%) to 21 ± 4.2% compared to 13.1 ± 2.5% in non-functionalized nano-cement. The results demonstrated nHAP-based nano-cement as a carrier for phytobioactives which could be a promising approach for neo-bone formation in different bone defect conditions.

Protease-degradable hydrogels with multifunctional biomimetic peptides for bone tissue engineering

Mimicking bone extracellular matrix (ECM) is paramount to develop novel biomaterials for bone tissue engineering. In this regard, the combination of integrin-binding ligands together with osteogenic peptides represents a powerful approach to recapitulate the healing microenvironment of bone. In the present work, we designed polyethylene glycol (PEG)-based hydrogels functionalized with cell instructive multifunctional biomimetic peptides (either with cyclic RGD-DWIVA or cyclic RGD-cyclic DWIVA) and cross-linked with matrix metalloproteinases (MMPs)-degradable sequences to enable dynamic enzymatic biodegradation and cell spreading and differentiation. The analysis of the intrinsic properties of the hydrogel revealed relevant mechanical properties, porosity, swelling and degradability to engineer hydrogels for bone tissue engineering. Moreover, the engineered hydrogels were able to promote human mesenchymal stem cells (MSCs) spreading and significantly improve their osteogenic differentiation. Thus, these novel hydrogels could be a promising candidate for applications in bone tissue engineering, such as acellular systems to be implanted and regenerate bone or in stem cells therapy.

Adipose delivered stem cells protect liver after ischemia-reperfusion injury by controlling autophagy

OBJECTIVE

Ischemia-reperfusion(I/R) injury is an unavoidable side effect of liver surgery and transplantation. A potentially useful tool for cellular therapy and tissue engineering is adipose-derived stem cells (ADSCs).The process of autophagy is used by the cell to break down inappropriate molecules.The study's goal was to examine the impact of ADSCs on the autophagic pathway after rat hepatic ischemia-reperfusion injury.

MATERIAL AND METHODS

Thirty male rats used in our study were divided into control, ADSC, ischemia, I/R, and I/R+ ADSC groups (n = 6). Liver tissues were stained with hematoxylin-eosin and histological changes were evaluated with Suzuki scoring. Immunoexpressions of transforming growth factor (TGF-β) and autophagy markers LC3B, p62 were analyzed using the immunohistochemical method.

RESULTS

As a result of histological evaluation the ischemia and I/R groups displayed sinusoid congestion, vacuolization, and necrosis in liver tissues. We showed that the immunostaining of LC3B and TGF- β were elevated, and p62 decreased in the rat liver from ischemia and I/R groups when compared to the control group.

CONCLUSION

ADSCs reduced the excessive level of autophagy and structural damage to hepatocytes and the pathological alterations in the liver after ıschemia-reperfusion injury.

Mesenchymal-Stromal-Cell-Conditioned Media and Their Implication for Osteochondral Regeneration

Despite significant advances in biomedical research, osteochondral defects resulting from injury, an autoimmune condition, cancer, or other pathological conditions still represent a significant medical problem. Even though there are several conservative and surgical treatment approaches, in many cases, they do not bring the expected results and further permanent damage to the cartilage and bones occurs. Recently, cell-based therapies and tissue engineering have gradually become promising alternatives. They combine the use of different types of cells and biomaterials to induce regeneration processes or replace damaged osteochondral tissue. One of the main challenges of this approach before clinical translation is the large-scale in vitro expansion of cells without changing their biological properties, while the use of conditioned media which contains various bioactive molecules appears to be very important. The presented manuscript provides a review of the experiments focused on osteochondral regeneration by using conditioned media. In particular, the effect on angiogenesis, tissue healing, paracrine signaling, and enhancing the properties of advanced materials are pointed out.

Extracellular vesicles: From bone development to regenerative orthopedics

Regenerative medicine aims to promote the replacement of tissues lost to damage or disease. While positive outcomes have been observed experimentally, challenges remain in their clinical translation. This has led to growing interest in applying extracellular vesicles (EVs) to augment or even replace existing approaches. Through the engineering of culture environments or direct/indirect manipulation of EVs themselves, multiple avenues have emerged to modulate EV production, targeting, and therapeutic potency. Drives to modulate release using material systems or functionalize implants for improved osseointegration have also led to outcomes that could have real-world impact. The purpose of this review is to highlight advantages in applying EVs for the treatment of skeletal defects, outlining the current state of the art in the field and emphasizing avenues for further investigation. Notably, the review identifies inconsistencies in EV nomenclature and outstanding challenges in defining a reproducible therapeutic dose. Challenges also remain in the scalable manufacture of a therapeutically potent and pure EV product, with a need to address scalable cell sources and optimal culture environments. Addressing these issues will be critical if we are to develop regenerative EV therapies that meet the demands of regulators and can be translated from bench to bedside.

Therapeutic effects of MSCs, genetically modified MSCs, and NFĸB-inhibitor on chronic inflammatory osteolysis in aged mice

The number of total joint replacements is increasing, especially in elderly patients, and so too are implant-related complications such as prosthesis loosening. Wear particles from the prosthesis induce a chronic inflammatory reaction and subsequent osteolysis, leading to the need for revision surgery. This study investigated the therapeutic effect of NF-ĸB decoy oligodeoxynucleotides (ODN), mesenchymal stem cells (MSCs), and genetically-modified NF-ĸB sensing interleukin-4 over-secreting MSCs (IL4-MSCs) on chronic inflammation in aged mice. The model was generated by continuous infusion of contaminated polyethylene particles into the intramedullary space of the distal femur of aged mice (15-17 months old) for 6 weeks. Local delivery of ODN showed increased bone mineral density (BMD), decreased osteoclast-like cells, increased alkaline phosphatase (ALP)-positive area, and increased M2/M1 macrophage ratio. Local injection of MSCs and IL4-MSCs significantly decreased osteoclast-like cells and increased the M2/M1 ratio, with a greater trend for IL4-MSCs than MSCs. MSCs significantly increased ALP-positive area and BMD values compared with the control. The IL4-MSCs demonstrated higher values for both ALP-positive area and BMD. These findings demonstrated the therapeutic effects of ODN, MSCs, and IL4-MSCs on chronic inflammatory osteolysis in aged mice. The two MSC-based therapies were more effective than ODN in increasing the M2/M1 macrophage ratio, reducing bone resorption, and increasing bone formation. Specifically, MSCs were more effective in increasing bone formation, and IL4-MSCs were more effective in mitigating inflammation. This study suggests potential therapeutic strategies for treating wear particle-associated inflammatory osteolysis after arthroplasty in the elderly.

LncRNA HOTAIRM1 promotes dental follicle stem cell-mediated bone regeneration by regulating HIF-1α/KDM6/EZH2/H3K27me3 axis

Large bone defect reconstruction undergoes hypoxia and remains a major practical challenge. Bone tissue engineering with a more promising stem cell source facilitates the development of better therapeutic outcomes. Human dental follicle stem cells (hDFSCs) with superior multipotency, osteogenic capacity, and accessibility have been proven a promising cell source for bone regeneration. We previously identified a novel long noncoding RNA (lncRNA), HOTAIRM1, to be highly expressed in hDFSCs. Here we found that HOTAIRM1 overexpressed hDFSCs promoted bone regeneration in rat critical-size calvarial defect model. Mechanically, HOTAIRM1 was induced in hDFSCs under hypoxic conditions and activated HIF-1α. RNA-sequencing analysis indicated that HOTAIRM1 upregulated oxygen-sensing histone demethylases KDM6A/B and suppressed methyltransferase EZH2 via targeting HIF-1α. The osteogenic differentiation of hDFSCs was accompanied with demethylation of H3K27, and HOTAIRM1 overexpression decreased the distribution of H3K27me3 in osteogenic genes, including ALP, M-CSF, Wnt-3a, Wnt-5a, Wnt-7a, and β-catenin, thus promoted their transcription. Our study provided evidence that HOTAIRM1 upregulated KDM6A/B and inhibited EZH2 in a HIF-1α dependent manner to enhance the osteogenesis of hDFSCs. HOTAIRM1-mediated hDFSCs may serve as a promising therapeutic approach to promote bone regeneration in clinical practice.

Slipper Limpet (Crepidula fornicata) Shells Support In Vitro Osteogenesis of Human Adipose-Derived Stem Cells

This study aimed to investigate a cost-effective alternative to man-made calcium phosphate ceramics for treating bone defects. The slipper limpet is an invasive species in European coastal waters, and its shells composed of calcium carbonate could potentially be a cost-effective source of bone graft substitutes. This research analyzed the mantle of the slipper limpet (Crepidula fornicata) shells to enhance in vitro bone formation. Discs machined from the mantle of C. fornicata were analyzed using scanning electron microscopy with energy dispersive spectroscopy (SEM-EDS), X-ray crystallography (XRD), Fourier-transform infrared spectroscopy (FT-IR) and profilometry. Calcium release and bioactivity were also studied. Cell attachment, proliferation, and osteoblastic differentiation (RT-qPCR and alkaline phosphatase activity) were measured in human adipose-derived stem cells grown on the mantle surface. The mantle material was mainly composed of aragonite and showed a sustained Ca²⁺ release at physiological pH. In addition, apatite formation was observed in simulated body fluid after three weeks, and the materials supported osteoblastic differentiation. Overall, our findings suggest the mantle of C. fornicata shows potential as a material for fabricating bone graft substitutes and structural biomaterials for bone regeneration.

3D printing of conch-like scaffolds for guiding cell migration and directional bone growth

Regeneration of severe bone defects remains an enormous challenge in clinic. Developing regenerative scaffolds to directionally guide bone growth is a potential strategy to overcome this hurdle. Conch, an interesting creature widely spreading in ocean, has tough spiral shell that can continuously grow along the spiral direction. Herein, inspired by the physiological features of conches, a conch-like (CL) scaffold based on β-TCP bioceramic material was successfully prepared for guiding directional bone growth via digital light processing (DLP)-based 3D printing. Benefiting from the spiral structure, the CL scaffolds significantly improved cell adhesion, proliferation and osteogenic differentiation in vitro compared to the conventional 3D scaffolds. Particularly, the spiral structure in the scaffolds could efficiently induce cells to migrate from the bottom to the top of the scaffolds, which was like “cells climbing stairs”. Furthermore, the capability of guiding directional bone growth for the CL scaffolds was demonstrated by a special half-embedded femoral defects model in rabbits. The new bone tissue could consecutively grow into the protruded part of the scaffolds along the spiral cavities. This work provides a promising strategy to construct biomimetic biomaterials for guiding directional bone tissue growth, which offers a new treatment concept for severe bone defects, and even limb regeneration.

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A conch-like scaffold was firstly developed for guiding directional bone growth.

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The CL scaffolds efficiently induced cells “climbing stairs”- like-migrating.

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The CL scaffolds showed improved bioactivities benefited from the spiral structure.

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This work provided a new treatment concept for severe bone defects.

The Osteogenic Role of Biomaterials Combined with Human-Derived Dental Stem Cells in Bone Tissue Regeneration

The use of stem cells in regenerative medicine had great potential for clinical applications. However, cell delivery strategies have critical importance in stimulating the differentiation of stem cells and enhancing their potential to regenerate damaged tissues. Different strategies have been used to investigate the osteogenic potential of dental stem cells in conjunction with biomaterials through in vitro and in vivo studies. Osteogenesis has a broad implication in regenerative medicine, particularly for maxillofacial defects. This review summarizes some of the most recent developments in the field of tissue engineering using dental stem cells.

The enhancer landscape predetermines the skeletal regeneration capacity of stromal cells

Multipotent stromal cells are considered attractive sources for cell therapy and tissue engineering. Despite numerous experimental and clinical studies, broad application of stromal cell therapeutics is not yet emerging. A major challenge is the functional diversity of available cell sources. Here, we investigated the regenerative potential of clinically relevant human stromal cells from bone marrow (BMSCs), white adipose tissue, and umbilical cord compared with mature chondrocytes and skin fibroblasts in vitro and in vivo. Although all stromal cell types could express transcription factors related to endochondral ossification, only BMSCs formed cartilage discs in vitro that fully regenerated critical-size femoral defects after transplantation into mice. We identified cell type-specific epigenetic landscapes as the underlying molecular mechanism controlling transcriptional stromal differentiation networks. Binding sites of commonly expressed transcription factors in the enhancer and promoter regions of ossification-related genes, including Runt and bZIP families, were accessible only in BMSCs but not in extraskeletal stromal cells. This suggests an epigenetically predetermined differentiation potential depending on cell origin that allows common transcription factors to trigger distinct organ-specific transcriptional programs, facilitating forward selection of regeneration-competent cell sources. Last, we demonstrate that viable human BMSCs initiated defect healing through the secretion of osteopontin and contributed to transient mineralized bone hard callus formation after transplantation into immunodeficient mice, which was eventually replaced by murine recipient bone during final tissue remodeling.

Enzyme-Cleaved Bone Marrow Transplantation Improves the Engraftment of Bone Marrow Mesenchymal Stem Cells

Mesenchymal stem cell (MSC) therapy is a promising approach to curing bone diseases and disorders. In treating genetic bone disorders, MSC therapy is local or systemic transplantation of isolated and in vitro proliferated MSC rather than bone marrow transplantation. Recent evidence showed that bone marrow MSC engraftment to bone regeneration has been controversial in animal and human studies. Here, our modified bone marrow transplantation (BMT) method solved this problem. Like routine BMT, our modified method involves three steps: (i) isolation of bone marrow cells from the donor, (ii) whole-body lethal irradiation to the recipient, and (iii) injection of isolated bone marrow cells into irradiated recipient mice via the tail vein. The significant modification is imported at the bone marrow isolation step. While the bone marrow cells are flushed out from the bone marrow with the medium in routine BMT, we applied the enzymes' (collagenase type 4 and dispase) integrated medium to wash out the bone marrow cells. Then, cells were incubated in enzyme integrated solution at 37°C for 10 minutes. This modification designated BMT as collagenase-integrated BMT (c-BMT). Notably, successful engraftment of bone marrow MSC to the new bone formation, such as osteoblasts and chondrocytes, occurs in c-BMT mice, whereas routine BMT mice do not recruit bone marrow MSC. Indeed, flow cytometry data showed that c-BMT includes a higher proportion of LepR⁺, CD51⁺, or RUNX2⁺ non-hematopoietic cells than BMT. These findings suggested that c-BMT is a time-efficient and more reliable technique that ensures the disaggregation and collection of bone marrow stem cells and engraftment of bone marrow MSC to the recipient. Hence, we proposed that c-BMT might be a promising approach to curing genetic bone disorders. © 2023 The Authors. JBMR Plus published by Wiley Periodicals LLC on behalf of American Society for Bone and Mineral Research.

Thermo-Responsive Nanocomposite Bioink with Growth-Factor Holding and its Application to Bone Regeneration

Three-dimensional (3D) bioprinting, which is being increasingly used in tissue engineering, requires bioinks with tunable mechanical properties, biological activities, and mechanical strength for in vivo implantation. Herein, a growth-factor-holding poly(organophosphazene)-based thermo-responsive nanocomposite (TNC) bioink system is developed. The mechanical properties of the TNC bioink are easily controlled within a moderate temperature range (5-37 °C). During printing, the mechanical properties of the TNC bioink, which determine the 3D printing resolution, can be tuned by varying the temperature (15-30 °C). After printing, TNC bioink scaffolds exhibit maximum stiffness at 37 °C. Additionally, because of its shear-thinning and self-healing properties, TNC bioinks can be extruded smoothly, demonstrating good printing outcomes. TNC bioink loaded with bone morphogenetic protein-2 (BMP-2) and transforming growth factor-beta1 (TGF-β1), key growth factors for osteogenesis, is used to print a scaffold that can stimulate biological activity. A biological scaffold printed using TNC bioink loaded with both growth factors and implanted on a rat calvarial defect model reveals significantly improved bone regenerative effects. The TNC bioink system is a promising next-generation bioink platform because its mechanical properties can be tuned easily for high-resolution 3D bioprinting with long-term stability and its growth-factor holding capability has strong clinical applicability.

Differential regulation of skeletal stem/progenitor cells in distinct skeletal compartments

Skeletal stem/progenitor cells (SSPCs), characterized by self-renewal and multipotency, are essential for skeletal development, bone remodeling, and bone repair. These cells have traditionally been known to reside within the bone marrow, but recent studies have identified the presence of distinct SSPC populations in other skeletal compartments such as the growth plate, periosteum, and calvarial sutures. Differences in the cellular and matrix environment of distinct SSPC populations are believed to regulate their stemness and to direct their roles at different stages of development, homeostasis, and regeneration; differences in embryonic origin and adjacent tissue structures also affect SSPC regulation. As these SSPC niches are dynamic and highly specialized, changes under stress conditions and with aging can alter the cellular composition and molecular mechanisms in place, contributing to the dysregulation of local SSPCs and their activity in bone regeneration. Therefore, a better understanding of the different regulatory mechanisms for the distinct SSPCs in each skeletal compartment, and in different conditions, could provide answers to the existing knowledge gap and the impetus for realizing their potential in this biological and medical space. Here, we summarize the current scientific advances made in the study of the differential regulation pathways for distinct SSPCs in different bone compartments. We also discuss the physical, biological, and molecular factors that affect each skeletal compartment niche. Lastly, we look into how aging influences the regenerative capacity of SSPCs. Understanding these regulatory differences can open new avenues for the discovery of novel treatment approaches for calvarial or long bone repair.

A Review of Biomimetic and Biodegradable Magnetic Scaffolds for Bone Tissue Engineering and Oncology

Bone defects characterized by limited regenerative properties are considered a priority in surgical practice, as they are associated with reduced quality of life and high costs. In bone tissue engineering, different types of scaffolds are used. These implants represent structures with well-established properties that play an important role as delivery vectors or cellular systems for cells, growth factors, bioactive molecules, chemical compounds, and drugs. The scaffold must provide a microenvironment with increased regenerative potential at the damage site. Magnetic nanoparticles are linked to an intrinsic magnetic field, and when they are incorporated into biomimetic scaffold structures, they can sustain osteoconduction, osteoinduction, and angiogenesis. Some studies have shown that combining ferromagnetic or superparamagnetic nanoparticles and external stimuli such as an electromagnetic field or laser light can enhance osteogenesis and angiogenesis and even lead to cancer cell death. These therapies are based on in vitro and in vivo studies and could be included in clinical trials for large bone defect regeneration and cancer treatments in the near future. We highlight the scaffolds' main attributes and focus on natural and synthetic polymeric biomaterials combined with magnetic nanoparticles and their production methods. Then, we underline the structural and morphological aspects of the magnetic scaffolds and their mechanical, thermal, and magnetic properties. Great attention is devoted to the magnetic field effects on bone cells, biocompatibility, and osteogenic impact of the polymeric scaffolds reinforced with magnetic nanoparticles. We explain the biological processes activated due to magnetic particles' presence and underline their possible toxic effects. We present some studies regarding animal tests and potential clinical applications of magnetic polymeric scaffolds.

Research Progress of Macrophages in Bone Regeneration

Bone tissue regeneration plays an increasingly important role in contemporary clinical treatment. The reconstruction of bone defects remains a huge challenge for clinicians. Bone regeneration is regulated by the immune system, in which inflammation is an important regulating factor in bone formation and remodeling. As the main cells involved in inflammation, macrophages play a key role in osteogenesis by polarizing into different phenotypes during different stages of bone regeneration. Considering this, this review mainly summarizes the function of macrophage in bone regeneration based on mesenchymal stem cells (MSCs), osteoblasts, osteoclasts, and vascular cells. In conclusion, anti-inflammatory macrophages (M2) have a greater potentiality to promote bone regeneration than M0 and classically activated proinflammatory macrophages (M1). In the fracture and bone defect models, tissue engineering materials can induce the transition from M1 to M2, alter the bone microenvironment, and promote bone regeneration through interactions with bone-related cells and blood vessels. The review provides a further understanding of macrophage polarization behavior in the evolving field of bone immunology.

One-Step Preparation of an Injectable Hydrogel Scaffold System Capable of Sequential Dual-Growth Factor Release to Maximize Bone Regeneration

Numerous growth factors are involved in the natural bone healing process, which is precisely controlled in a time- and concentration-dependent manner. Mimicking the secretion pattern of growth factors could be an effective means to maximize the bone regeneration effect. However, achieving the sequential delivery of various growth factors without the use of multiple materials or complex scaffold designs is challenging. Herein, an injectable poly(organophosphazene) hydrogel scaffold (IPS) encapsulating bone morphogenetic protein (BMP)-2 and TGFβ-1 (IPS_BT) is studied to mimic the sequential secretion of growth factors involved in natural bone healing. The IPS_BT system is designed to release TGFβ-1 slowly while retaining BMP-2 for a longer period of time. When IPS_BT is injected in vivo, the hydrogel is replaced by bone tissue. In addition, angiogenic (CD31 and alpha-smooth muscle actin (α-SMA)) and stemness (Nanog and SOX2) markers are highly upregulated in the early stages of bone regeneration. The IPS system developed here has promising applications in tissue engineering because 1) various amounts of the growth factors can be loaded in one step, 2) the release pattern of each growth factor can be controlled via differences in their molecular interactions, and 3) the injected IPS can be degraded and replaced with regenerated bone tissue.

Bone regeneration in osteoporosis: opportunities and challenges

Osteoporosis is a bone disorder characterised by low bone mineral density, reduced bone strength, increased bone fragility, and impaired mineralisation of bones causing an increased risk of bone fracture. Several therapies are available for treating osteoporosis which include bisphosphonates, anti-resorptive agents, oestrogen modulators, etc. These therapies primarily focus on decreasing bone resorption and do not assist in bone regeneration or offering permanent curative solutions. Additionally, these therapies are associated with severe adverse events like thromboembolism, increased risk of stroke, and hypocalcaemia. To overcome these limitations, bone regenerative pathways and approaches are now considered to manage osteoporosis. The bone regenerative pathways involved in bone regeneration include wingless-related integration site/β-catenin signalling pathway, notch signalling pathway, calcium signalling, etc. The various regenerative approaches which possess potential to heal and replace the bone defect site include scaffolds, cements, cell therapy, and other alternative medicines. The review focuses on describing the challenges and opportunities in bone regeneration for osteoporosis.

Ceria-based coatings on magnesium alloys for biomedical applications: a literature review

Magnesium alloys are being studied for use in temporary orthopedic implants because of their mechanical properties, which are similar to those of human bone, and their good biocompatibility. However, their application is limited due to their rapid degradation, and early loss of their mechanical properties, decreasing the stability of the implant and its proper synchronization with tissue regeneration. In this regard, various surface coatings have been used to improve their biological, physico-chemical and biodegradation properties. Currently, one of the most explored strategies is using smart coatings because of their self-healing properties that can slow down the corrosion process of Mg and its alloys. Ceria-based materials show promise as coatings for these alloys. Their unique redox capacity not only provides Mg alloys with good self-healing properties but also interesting biological properties, which are described in this paper. Despite this, some problems and challenges related to the biocompatibility and application of these materials in coatings remain unsolved. In this article, a critical review is presented summarizing the most representative literature on ceria-based coatings on Mg alloys for their potential use as biomaterials. The results show that ceria is a versatile material that may be used in industrial and biomedical applications.

Role of Enterococcus faecalis in refractory apical periodontitis: from pathogenicity to host cell response

BACKGROUND

Refractory apical periodontitis (RAP) is an oral infectious disease characterised by persistent inflammation, progressive alveolar bone destruction, and delayed bone healing. RAP has received increasing attention, because it cannot be cured after repeated root canal therapies. The aetiology of RAP is related to the complex interplay between the pathogen and its host. However, the exact pathogenesis of RAP remains unclarified and includes several factors, such as microorganism immunogenicity, host immunity and inflammation, and tissue destruction and repair. Enterococcus faecalis is the dominant pathogen involved in RAP, and has evolved multiple strategies to ensure survival, which cause persistent intraradicular and extraradicular infections.

OBJECTIVE

To review the crucial role of E. faecalis in the pathogenesis of RAP, and open new avenues for prevention and treatment of RAP.

METHODS

The PubMed and Web of Science databases were searched for pertinent publications, employing the search terms "Enterococcus faecalis", "refractory apical periodontitis", "persistent periapical periodontitis", "pathogenicity", "virulence", "biofilm formation", "dentine tubule", "immune cell", "macrophage", and "osteoblast".

RESULTS AND CONCLUSION

Besides its high pathogenicity due to various virulence mechanisms, E. faecalis modulates the macrophage and osteoblast responses, including regulated cell death, cell polarisation, cell differentiation, and inflammatory response. An in-depth understanding of the multifaceted host cell responses modulated by E. faecalis will help to design potential future therapeutic strategies and overcome the challenges of sustained infection and delayed tissue healing in RAP.

Repairing a critical cranial defect using WISP1-pretreated chondrocyte scaffolds

In cranial flat bone fractures, spontaneous bone repair will occur only when the fracture ends are in close contact. However, in cases wherein bone discontinuity is extensive, surgical interventions are often required. To this end, autologous bone is harvested and surgically integrated into the site of fracture. Here we propose to use cartilage, as an alternative autologous source, to promote cranial fracture repair. The advantage of this approach is the potential reduction in donor site morbidity, likely due to the avascular and aneural nature of cartilage. As a first step we attempted to induce cartilage mineralization in vitro, using micromass primary chondrocyte cultures, incubated with BMP2 and/or WISP1, which were examined histologically following a 3-week culture period. Next, chondrocyte seeded collagen scaffolds were evaluated in vitro for expression profiles and ALP activity. Finally, chondrocyte-seeded collagen scaffolds were implanted in a Lewis rats 8 mm critical calvaria defect model, which was imaged via live CT for 12 weeks until sacrifice. End points were analyzed for microCT, histology, and serum levels of bone related markers. Micromass cultures exhibited an osseous inducing trend following WISP1 administration, which was maintained in chondrocyte seeded scaffolds. Accordingly, in vivo analysis was carried out to assess the impact of WISP1-pretreated chondrocytes (WCS) versus untreated chondrocytes (UCS) in calvaria defect model and compared to untreated control comprised of a defect-associated blood clot (BC) or empty collagen scaffold (CS) implant. Live CT and microCT exhibited higher mineralization volumes in critical defect implanted with UCS, with some structural improvements in WCS. Histological analysis exhibited higher anabolic bone formation in WCS and trabecular bone was detected in WCS and UCS groups. Chondrocytes implanted into critical cranial defect expedite the formation of native-like osseous tissue, especially after WISP1 priming in culture. Ultimately, these data support the use of autologous chondrocytes to repair critical maxillofacial defects.