Ordinary and Activated Bone Grafts: Applied Classification and the Main Features

Endogenous Regeneration of Alveolar Bone by Decellularized Tooth Matrix

The efficiency of bone tissue regeneration by decellularized tooth matrix, demineralized tooth matrix, and commercial xenograft Bio-Oss Spongiosa was compared on the model of a critical-size circular defect in the alveolar bone of the upper jaw of adult Wistar rats. The defect healing dynamics was assessed using histological, histomorphometrical, and immunohistochemical methods on days 30 and 60. In contrast to demineralized matrix and commercial xenograft, decellularized matrix induces the formation of the new bone tissue by day 60. Decellularized matrix can be considered as a biomaterial for cell-free tissue engineering for alveolar bone restoration in dentistry and maxillofacial surgery.

BMP-2 (and partially GDF-5) coating significantly accelerates and augments bone formation close to hydroxyapatite/tricalcium-phosphate/brushite implant cylinders for tibial bone defects in senile, osteopenic sheep

Bilateral defects (diameter 8 mm) in the medial tibial head of senile, osteopenic female sheep (n = 48; 9.63 ± 0.10 years; mean ± SEM) were treated with hydroxyapatite (HA)/beta-tricalcium phosphate (β-TCP)/dicalcium phosphate dihydrate (DCPD; brushite) cylinders coated with BMP-2 (25 or 250 micrograms) or growth differentiation factor (GDF)-5 (125 or 1250 micrograms; left side); cylinders without BMP served as controls (right side). Three, 6, and 9 months post-operation (n = 6 each group), bone structure and formation were analyzed in vivo by X-ray and ex vivo by osteodensitometry, histomorphometry, and micro-computed tomography (micro-CT) at 3 and 9 months. Semi-quantitative X-ray evaluation showed significantly increasing bone densities around all implant cylinders over time. High-dose BMP-2-coated cylinders (3 and 9 months) and low-dose GDF-5-coated cylinders (3 and 6 months) demonstrated significantly higher densities than controls (dose-dependent for BMP-2 at 3 months). This was confirmed by osteodensitometry at 9 months for high-dose BMP-2-coated cylinders (and selected GDF-5 groups), and was again dose-dependent for BMP-2. Osteoinduction by BMP-2 was most pronounced in the adjacent bone marrow (dynamic histomorphometry/micro-CT). BMP-2 (and partially GDF-5) significantly increased the bone formation in the vicinity of HA/TCP/DCPD cylinders used to fill tibial bone defects in senile osteopenic sheep and may be suitable for surgical therapy of critical size, non-load-bearing bone defects in cases of failed tibial head fracture or defect healing.

[Advantages and disadvantages of bone graft materials activated by BMP-2 and constructs carrying its gene]

In the review gene constructs and proteins used to impart osteoinductive properties to bone graft materials are compared. On the basis of clinical and experimental data the experience and prospects of their application in maxillofacial surgery and dentistry are described. Information about complications associated with the use of bone morphogenetic protein-2 (BMP-2) and vectors carrying its gene is provided.

Comparative Efficiency of Gene-Activated Matrices Based on Chitosan Hydrogel and PRP Impregnated with BMP2 Polyplexes for Bone Regeneration

Gene therapy is one of the most promising approaches in regenerative medicine. Gene-activated matrices provide stable gene expression and the production of osteogenic proteins in situ to stimulate osteogenesis and bone repair. In this study, we developed new gene-activated matrices based on polylactide granules (PLA) impregnated with BMP2 polyplexes and included in chitosan hydrogel or PRP-based fibrin hydrogel. The matrices showed high biocompatibility both in vitro with mesenchymal stem cells and in vivo when implanted intramuscularly in rats. The use of porous PLA granules allowed the inclusion of a high concentration of polyplexes, and the introduction of the granules into hydrogel provided the gradual release of the plasmid constructs. All gene-activated matrices showed transfecting ability and ensured long-term gene expression and the production of target proteins in vitro. At the same time, the achieved concentration of BMP-2 was sufficient to induce osteogenic differentiation of MSCs. When implanted into critical-size calvarial defects in rats, all matrices with BMP2 polyplexes led to new bone formation. The most significant effect on osteoinduction was observed for the PLA/PRP matrices. Thus, the developed gene-activated matrices were shown to be safe and effective osteoplastic materials. PLA granules and PRP-based fibrin hydrogel containing BMP2 polyplexes were shown to be the most promising for future applications in bone regeneration.

Bone Augmentation for Implant Placement: Recent Advances

There are various advancements in biomaterials and methods for bone augmentation. This article aims to review the recent advances in bone augmentation for dental implants. Relevant articles on bone augmentation for dental implants were searched in PubMed/Medline, Scopus, Google Scholar, and Science Direct published in English literature published between January 1996 and March 2021. Relevant studies on bone grafts for dental implants were included and critically analyzed in this review. Various biomaterials can be used to augment bone for implant placement. Each graft procedure has advantages and disadvantages in each clinical application and needs to choose the graft material with a high success rate and less morbidity.

Bone Graft Options in Spinal Fusion: A Review of Current Options and the Use of Mesenchymal Cellular Bone Matrices

BACKGROUND

Spinal fusion is the mainstay treatment for various spinal conditions ranging from lumbar and cervical stenosis to degenerative spondylolisthesis as well as extensive deformity corrections. A new emerging category of allograft is cellular bone matrices (CBMs), which take allogeneic mesenchymal stem cells and incorporate them into an osteoconductive and osteoinductive matrix. This study reviewed the current spinal fusion options and new emerging treatment options.

METHODS

Articles were searched using PubMed. The search included English publications since January 1, 2014, using the search terms "cellular bone matrix," "mesenchymal stem cells spinal fusion," "spinal arthrodesis AND mesenchymal stem cells," and "spine fusion AND cellular bone matrix."

RESULTS

Spinal fusion is accomplished through the use of allografts, autografts, and bone graft substitutes in combination or alone. An emerging category of allograft is CBMs, in which an osteoconductive and osteoinductive matrix is filled with mesenchymal stem cells. Studies demonstrate that CBMs have achieved equivalent or better fusion rates compared with traditional options for anterior cervical discectomy and fusions and posterolateral lumbar fusions; however, the studies have been retrospective and lacking control groups and therefore not ideal.

CONCLUSIONS

Many treatment options have been successfully used in spinal fusion. Newer allografts such as CBMs have shown promising results in both animal and clinical studies. Further research is needed to determine the therapeutic dose of mesenchymal stem cells delivered within CBMs.

Nanocomposites of Chitosan/Graphene Oxide/Titanium Dioxide Nanoparticles/Blackberry Waste Extract as Potential Bone Substitutes

New technologies based on nanocomposites of biopolymers and nanoparticles inspired by the nature of bone structure have accelerated their application in regenerative medicine, thanks to the introduction of reinforcing properties. Our research incorporated chitosan (CS) covalently crosslinked with glutaraldehyde (GLA) beads with graphene oxide (GO) nanosheets, titanium dioxide nanoparticles (TiO₂), and blackberry processing waste extract (BBE) and evaluated them as partial bone substitutes. Skullbone defects in biomodels filled with the scaffolds showed evidence through light microscopy, scanning electron microscopy, histological studies, soft tissue development with hair recovery, and absence of necrotic areas or aggressive infectious response of the immune system after 90 days of implantation. More interestingly, newly formed bone was evidenced by elemental analysis and Masson trichromacy analysis, which demonstrated a possible osteoinductive effect from the beads using the critical size defect experimental design in the biomodels. The results of this research are auspicious for the development of bone substitutes and evidence that the technologies for tissue regeneration, including chitosan nanocomposites, are beneficial for the adhesion and proliferation of bone cells.

Bone Grafts and Substitutes in Dentistry: A Review of Current Trends and Developments

After tooth loss, bone resorption is irreversible, leaving the area without adequate bone volume for successful implant treatment. Bone grafting is the only solution to reverse dental bone loss and is a well-accepted procedure required in one in every four dental implants. Research and development in materials, design and fabrication technologies have expanded over the years to achieve successful and long-lasting dental implants for tooth substitution. This review will critically present the various dental bone graft and substitute materials that have been used to achieve a successful dental implant. The article also reviews the properties of dental bone grafts and various dental bone substitutes that have been studied or are currently available commercially. The various classifications of bone grafts and substitutes, including natural and synthetic materials, are critically presented, and available commercial products in each category are discussed. Different bone substitute materials, including metals, ceramics, polymers, or their combinations, and their chemical, physical, and biocompatibility properties are explored. Limitations of the available materials are presented, and areas which require further research and development are highlighted. Tissue engineering hybrid constructions with enhanced bone regeneration ability, such as cell-based or growth factor-based bone substitutes, are discussed as an emerging area of development.

Bringing a Gene-Activated Bone Substitute Into Clinical Practice: From Bench to Bedside

Bone grafting and reconstruction are still challenging in clinical practice because of the limitations of bone autografts and the drawbacks of currently approved bone substitutes. We thus developed a gene-activated bone substitute based on octacalcium phosphate and naked plasmid DNA carrying the vascular endothelial growth factor gene. This advanced combined therapy medicinal product had no cytotoxic effects in vitro, slightly decreased bone marrow mesenchymal stromal cell (MSC) doubling time, and was characterized by a prolonged level of gene construct delivery in vivo in a luciferase bioimaging assay. In the model of critically sized cranial bone defects in rabbits, the gene-activated matrix increased bone tissue formation through angiogenesis induction. After preclinical studies, we conducted an open-label non-randomized clinical trial (NCT03076138). The primary study outcome was the proportion of patients with newly formed bone tissue within the surgical area as measured by computed tomography within 6 months after surgery. The main secondary outcomes included frequencies of adverse events (AEs) and serious adverse events (SAEs) as well as the surgical failure rate. After completing the clinical trial, the patients had dental implants placed in the bone grafting area, and trephine biopsy samples were collected. In total, 20 patients with alveolar ridge atrophy (n = 16) and jaw bone defects (n = 4) were enrolled in the study. There were no AEs or SAEs during the clinical trial or the follow-up period (30 months). In all patients, newly formed tissues with a bone density of 908.13 ± 114.40 HU were detected within the zone of bone grafting. There were no significant differences between the subgroups of patients with atrophy and bone defects: 915.28 ± 125.85 and 879.56 ± 48.36 HU, respectively (p = 0.60). Histological analysis showed that the bone grafting area comprised newly formed bone tissue with some fragments of the gene-activated bone substitute partially resorbed and integrated with bone, without fibrous tissue in between. The preclinical data and clinical trial results proved the feasibility, safety, and efficacy of the investigated material for jaw bone grafting, allowing us to bring the world's first gene-activated bone substitute from bench to bedside.

Two Decades of Global Progress in Authorized Advanced Therapy Medicinal Products: An Emerging Revolution in Therapeutic Strategies

The introduction of advanced therapy medicinal products (ATMPs) to the global pharma market has been revolutionizing the pharmaceutical industry and has opened new routes for treating various types of cancers and incurable diseases. In the past two decades, a noticeable part of clinical practices has been devoting progressively to these products. The first step to develop such an ATMP product is to be familiar with other approved products to obtain a general view about this industry trend. The present paper depicts an overall perspective of approved ATMPs in different countries, while reflecting the degree of their success in a clinical point of view and highlighting their main safety issues and also related market size as a whole. In this regard, published articles regarding safety, efficacy, and market size of approved ATMPs were reviewed using the search engines PubMed, Scopus, and Google Scholar. For some products which the related papers were not available, data on the relevant company website were referenced. In this descriptive study, we have introduced and classified approved cell, gene, and tissue engineering-based products by different regulatory agencies, along with their characteristics, manufacturer, indication, approval date, related regulatory agency, dosage, product description, price and published data about their safety and efficacy. In addition, to gain insights about the commercial situation of each product, we have gathered accessible sale reports and market size information that pertain to some of these products.

Development prospects of curable osteoplastic materials in dentistry and maxillofacial surgery

The article presents classification of the thermosetting materials for bone augmentation. The physical, mechanical, biological, and clinical properties of such materials are reviewed. There are two main types of curable osteoplastic materials: bone cements and hydrogels. Compared to hydrogels, bone cements have high strength features, but their biological properties are not ideal and must be improved. Hydrogels are biocompatible and closely mimic the extracellular matrix. They can be used as cytocompatible scaffolds for tissue engineering, as can protein- and nucleic acid-activated structures. Hydrogels may be impregnated with osteoinductors such as proteins and genetic vectors without conformational changes. However, the mechanical properties of hydrogels limit their use for load-bearing bone defects. Thus, improving the strength properties of hydrogels is one of the possible strategies to achieve the basis for an ideal osteoplastic material.

Physical/Chemical Properties and Resorption Behavior of a Newly Developed Ca/P/S-Based Bone Substitute Material

Properly regulating the resorption rate of a resorbable bone implant has long been a great challenge. This study investigates a series of physical/chemical properties, biocompatibility and the behavior of implant resorption and new bone formation of a newly developed Ca/P/S-based bone substitute material (Ezechbone^® Granule CBS-400). Experimental results show that CBS-400 is comprised majorly of HA and CSD, with a Ca/P/S atomic ratio of 54.6/39.2/6.2. After immersion in Hank’s solution for 7 days, the overall morphology, shape and integrity of CBS-400 granules remain similar to that of non-immersed samples without showing apparent collapse or disintegration. With immersion time, the pH value continues to increase to 6.55 after 7 days, and 7.08 after 14 days. Cytotoxicity, intracutaneous reactivity and skin sensitization tests demonstrate the good biocompatibility features of CBS-400. Rabbit implantation/histological observations indicate that the implanted granules are intimately bonded to the surrounding new bone at all times. The implant is not merely a degradable bone substitute, but its resorption and the formation of new cancellous bone proceed at the substantially same pace. After implantation for 12 weeks, about 85% of the implant has been resorbed. The newly-formed cancellous bone ratio quickly increases to >40% at 4 weeks, followed by a bone remodeling process toward normal cancellous bone, wherein the new cancellous bone ratio gradually tapers down to about 30% after 12 weeks.

3D Printed Gene-activated Octacalcium Phosphate Implants for Large Bone Defects Engineering

The aim of the study was the development of three-dimensional (3D) printed gene-activated implants based on octacalcium phosphate (OCP) and plasmid DNA encoding VEGFA. The first objective of the present work involved design and fabrication of gene-activated bone substitutes based on the OCP and plasmid DNA with VEGFA gene using 3D printing approach of ceramic constructs, providing the control of its architectonics compliance to the initial digital models. X-ray diffraction, scanning electron microscopy (SEM), Fourier transform infrared spectroscopy, and compressive strength analyses were applied to investigate the chemical composition, microstructure, and mechanical properties of the experimental samples. The biodegradation rate and the efficacy of plasmid DNA delivery in vivo were assessed during standard tests with subcutaneous implantation to rodents in the next stage. The final part of the study involved substitution of segmental tibia and mandibular defects in adult pigs with 3D printed gene-activated implants. Biodegradation, osteointegration, and effectiveness of a reparative osteogenesis were evaluated with computerized tomography, SEM, and a histological examination. The combination of gene therapy and 3D printed implants manifested the significant clinical potential for effective bone regeneration in large/critical size defect cases.

Injectable porcine bone demineralized and digested extracellular matrix-PEGDA hydrogel blend for bone regeneration

Extracellular matrix (ECM) has a major role in the structural support and cellular processes of organs and tissues. Proteins extracted from the ECM have been used to fabricate different scaffolds for tissue engineering applications. The aims of the present study were to extract, characterize and fabricate a new class of hydrogel with proteins isolated from pig bone ECM and combine them with a synthetic polymer so it could be used to promote bone regeneration. Porcine bone demineralized and digested extracellular matrix (pddECM) containing collagen type I was produced, optimized and sterilized with high pressurized CO₂ method. The pddECM was further blended with 20% w/v polyethylene glycol diacrylate (PEGDA) to create an injectable semi interpenetrating polymer network (SIPN) scaffold with enhanced physicochemical properties. The blend tackled the shortfall of natural polymers, such as lack of structural stability and fast degradation, preserving its structure in more than 90% after 30 days of incubation; thus, increasing the material endurance in a simulated physiological environment. The manufactured injectable hydrogel showed high cytocompatibility with hOb and SaOs-2 cells, promoting osteogenic proliferation within 21 days of culture. The hydrogel had a high compression modulus of 520 kPa, low swelling (5.3 mg/mg) and millimetric volume expansion (19.5%), all of which are favorable characteristics for bone regeneration applications.

Review of the Pathways Involved in the Osteogenic Differentiation of Adipose-Derived Stem Cells

Grafts and prosthetic materials used for the repair of bone defects are often accompanied by comorbidity and rejection. Therefore, there is an immense need for novel approaches to combating the issues surrounding such defects. Because of their accessibility, substantial proportion, and osteogenic differentiation potential, adipose-derived stem cells (ASCs) make for an ideal source of bone tissue in regenerative medicine. However, efficient induction of ASCs toward an osteoblastic lineage in vivo is met with challenges, and many signaling pathways must come together to secure osteoblastogenesis. Among them are bone morphogenic protein, wingless-related integration site protein, Notch, Hedgehog, fibroblast growth factor, vascular endothelial growth factor, and extracellular regulated-signal kinase. The goal of this literature review is to conglomerate the present research on these pathways to formulate a better understanding of how ASCs are most effectively transformed into bone in the context of tissue engineering.

Sonochemical nanostructuring of titanium for regulation of human mesenchymal stem cells behavior for implant development

The influence of surface nanotopography of sonochemically generated mesoporous titania coatings (TMS) on the adhesion, proliferation, and osteogenic differentiation of human mesenchymal stem cells (hMSCs) have been investigated in vitro for the first time. It has been revealed that adhesion and proliferation of hMSCs is higher on disordered TMS surfaces compared to smooth polished titania surface after five days of incubation. Surprisingly, the sonochemically generated disordered nanotopography induces the differentiation of hMSCs into osteogenic direction in the absence of osteogenic medium in 14 days of incubation. Thus sonochemical nanostructuring of titanium based implants stimulates the regenerative process of bone tissue.

Low oxygen tension modulates the osteogenic differentiation of mouse embryonic stem cells

This study examined the effects of low oxygen tension on the osteogenic differentiation of embryonic stem cells (ESCs) in a three-dimensional culture system. The high expression levels of hypoxia-related proteins hypoxia-inducible factor-1α and vascular endothelial growth factor were first validated in ESCs subjected to hypoxic conditions compared with normoxic controls. The osteogenic differentiation of hypoxic ESCs with either osteogenic or osteogenic factor-free media was subsequently evaluated by measuring alkaline phosphatase activity, intracellular calcium levels, matrix mineralization, and the protein levels of osteogenic markers Runt-related transcription factor 2 and osterix. We confirmed that hypoxia significantly stimulated ESC osteogenic activity; the strongest stimulation of ESC osteogenesis was exerted when cells were grown in osteogenic media. To identify differentially expressed genes associated with hypoxia-induced ESC differentiation, we performed microarray analysis of ESCs cultured in osteogenic media under normoxic and hypoxic conditions. This study demonstrated that differences in oxygen tension induced the differential expression of genes known to play roles in such processes as skeletal system development and signaling pathways for bone morphogenetic protein, Wnt, Notch, mitogen-activated protein kinase, and integrin. These findings reveal the effects of low oxygen tension on osteogenic progression in ESCs and provide insight into the molecular pathways that regulate ESC differentiation following exposure to hypoxia.

Matrix Metalloproteinases in Bone Resorption, Remodeling, and Repair

Matrix metalloproteinases (MMPs) are the major protease family responsible for the cleavage of the matrisome (global composition of the extracellular matrix (ECM) proteome) and proteins unrelated to the ECM, generating bioactive molecules. These proteins drive ECM remodeling, in association with tissue-specific and cell-anchored inhibitors (TIMPs and RECK, respectively). In the bone, the ECM mediates cell adhesion, mechanotransduction, nucleation of mineralization, and the immobilization of growth factors to protect them from damage or degradation. Since the first description of an MMP in bone tissue, many other MMPs have been identified, as well as their inhibitors. Numerous functions have been assigned to these proteins, including osteoblast/osteocyte differentiation, bone formation, solubilization of the osteoid during bone resorption, osteoclast recruitment and migration, and as a coupling factor in bone remodeling under physiological conditions. In turn, a number of pathologies, associated with imbalanced bone remodeling, arise mainly from MMP overexpression and abnormalities of the ECM, leading to bone osteolysis or bone formation. In this review, we will discuss the functions of MMPs and their inhibitors in bone cells, during bone remodeling, pathological bone resorption (osteoporosis and bone metastasis), bone repair/regeneration, and emergent roles in bone bioengineering.

World's First Clinical Case of Gene-Activated Bone Substitute Application

Treatment of patients with large bone defects is a complex clinical problem. We have initiated the first clinical study of a gene-activated bone substitute composed of the collagen-hydroxyapatite scaffold and plasmid DNA encoding vascular endothelial growth factor. The first patient with two nonunions of previously reconstructed mandible was enrolled into the study. Scar tissues were excised; bone defects (5–14 mm) between the mandibular fragments and nonvascularized rib-bone autograft were filled in with the gene-activated bone substitute. No adverse events were observed during 12 months of follow-up. In 3 months, the average density of newly formed tissues within the implantation zone was 402.21 ± 84.40 and 447.68 ± 106.75 HU in the frontal and distal regions, respectively, which correlated with the density of spongy bone. Complete distal bone defect repair with vestibular and lingual cortical plates formation was observed in 6 and 12 months after surgery; thereby the posterior nonunion was successfully eliminated. However, there was partial resorption of the proximal edge of the autograft entailed to relapse of the anterior nonunion. Thus, the first clinical data on the safety and efficacy of the gene-activated bone substitute were obtained. Given a high complexity of the clinical situation the treatment, results might be considered as promising. NCT02293031.