Stages Of Bone Repair Research Articles

Matrix Metalloproteinase-Responsive Hydrogel with On-Demand Release of Phosphatidylserine Promotes Bone Regeneration Through Immunomodulation.

Inflammation-responsive hydrogels loaded with therapeutic factors are effective biomaterials for bone tissue engineering and regenerative medicine. In this study, a matrix metalloproteinase (MMP)-responsive injectable hydrogel is constructed by integrating an MMP-cleavable peptide (pp) into a covalent tetra-armed poly-(ethylene glycol) (PEG) network for precise drug release upon inflammation stimulation. To establish a pro-regenerative environment, phosphatidylserine (PS) is encapsulated into a scaffold to form the PEG-pp-PS network, which could be triggered by MMP to release a large amount of PS during the early stage of inflammation and retain drug release persistently until the later stage of bone repair. The hydrogel is found to be mechanically and biologically adaptable to the complex bone defect area. In vivo and in vitro studies further demonstrated the ability of PEG-pp-PS to transform macrophages into the anti-inflammatory M2 phenotype and promote osteogenic differentiation, thus, resulting in new bone regeneration. Therefore, this study provides a facile, safe, and promising cell-free strategy on simultaneous immunoregulation and osteoinduction in bone engineering.

Electrospun Biomimetic Periosteum Capable of Controlled Release of Multiple Agents for Programmed Promoting Bone Regeneration.

The effective repair of large bone defects remains a major challenge due to its limited self-healing capacity. Inspired by the structure and function of the natural periosteum, an electrospun biomimetic periosteum is constructed to programmatically promote bone regeneration using natural bone healing mechanisms. The biomimetic periosteum is composed of a bilayer with an asymmetric structure in which an aligned electrospun poly(ε-caprolactone)/gelatin/deferoxamine (PCL/GEL/DFO) layer mimics the outer fibrous layer of the periosteum, while a random coaxial electrospun PCL/GEL/aspirin (ASP) shell and PCL/silicon nanoparticles (SiNPs) core layer mimics the inner cambial layer. The bilayer controls the release of ASP, DFO, and SiNPs to precisely regulate the inflammatory, angiogenic, and osteogenic phases of bone repair. The random coaxial inner layer can effectively antioxidize, promoting cell recruitment, proliferation, differentiation, and mineralization, while the aligned outer layer can promote angiogenesis and prevent fibroblast infiltration. In particular, different stages of bone repair are modulated in a rat skull defect model to achieve faster and better bone regeneration. The proposed biomimetic periosteum is expected to be a promising candidate for bone defect healing.

BONE REGENERATION AFTER IMPLANTATION OF CALCIUM PHOSPHATE CEMENTS BASED ON METASTABLE TRICALCIUM PHOSPHATE (IN VIVO EXPERIMENTAL STUDY)

Calcium phosphatCalcium phosphate cement (CPC) is a material used to fill bone defects. Its advantages include being able to fill irregularly shaped spaces, its similarity to bone tissue, and ease of biodegradation. However, insufficient durability and unpredictable rate of resorption limit CPC use. Objective. Study the dynamics of morphological changes in rat femurs after implanting two types of CPC based on metastable αʹ‒tricalcium phosphate(αʹ‒TCP) into defects in the distal metaphysis. Methods. 42 male white rats were used in the study. In each rat, defects were created in the distal metaphysis of the left femur and filled with one of the two types of CPC. The animals were split into two groups: І (n = 21) — CPC based on αʹ‒TCP powder; ІІ (n = 21) — CPС based on αʹ‒TCP powder reinforced with hydroxyapatite (HA) whiskers (4 % mass). Both varieties of CPC were developed and prepared at the Department of Solid-State Physics at the V. N. Karazin Kharkiv National University (Ukraine). 14, 30, and 60 days after the surgery, the animals were sacrificed, and histological analyses were performed. Results. For both types of CPC, inflammation was not observed in the region around the implant at 14, 30, or at 60 days. Bone tissue formed on the surface of the materials. The stages of bone repair were similar to the known stages of bone repair. As a result of the resorption of the CPC, 60 days after surgery the CPC comprised 26.83 % of the area of the defect in group I and 29.93 % in group II. The rest of the area was composed of lamellar bone. The two groups did not differ significantly in rate of CPC resorption or bone tissue formation. Conclusions. The two types of CPC studied, based on αʹ‒TCP (group I) and αʹ‒TCP reinforced with HA whiskers (group II), are biocompatible, osteoconductive, and osteoinductive. In addition, these materials are biodegradable and, with time, are replaced by bone tissue.

Bone Tissue Engineering Scaffolds: Function of Multi-Material Hierarchically Structured Scaffolds.

Bone tissue engineering (BTE) is a topic of interest for the last decade, and advances in materials, processing techniques, and the understanding of bone healing pathways have opened new avenues of research. The dual responsibility of BTE scaffolds in providing load-bearing capability and interaction with the local extracellular matrix to promote bone healing is a challenge in synthetic scaffolds. This article describes the usage and processing of multi-materials and hierarchical structures to mimic the structure of natural bone tissues to function as bioactive and load-bearing synthetic scaffolds. The first part of this literature review describes the physiology of bone healing responses and the interactions at different stages of bone repair. The following section reviews the available literature on biomaterials used for BTE scaffolds followed by some multi-material approaches. The next section discusses the impact of the scaffold's structural features on bone healing and the necessity of a hierarchical distribution in the scaffold structure. Finally, the last section of this review highlights the emerging trends in BTE scaffold developments that can inspire new tissue engineering strategies and truly develop the next generation of synthetic scaffolds.

Abnormal Variations of the Key Genes in Osteoporotic Fractures.

The classical osteoporotic signaling pathways include the four key genes (LRP5, Runx2, Osterix, and RANKL) influencing the regulation of osteogenesis and osteoclastogenesis. This study investigates the expression of these four genes associated with bone remodeling during fracture healing. Ovariectomized rats as an osteoporotic group were randomly divided into three groups-group A, group B, and group C. Nonosteoporotic rats as the control group were likewise divided into three groups A0, B0, and C0, using the same method. The rats were killed on the third day of fractures in groups A and A0, on the seventh day of fractures in groups B and B0, and on the fourteenth day of fractures in groups C and C0. The bone specimens were taken from the femoral fracture site, and the expression level of each gene in the bone specimens was detected using RT-qPCR, Western blotting, and immunohistochemistry. LRP5, Runx2, and Osterix expressions were decreased in osteoporotic rat fractures and then increased over time. The expression of RANKL was elevated in osteoporotic rat bone specimens, which decreased after that. The expressions of the four genes varied with time after fracture, which could be associated with the various stages of bone repair. The four genes can inform practice in ideal interventions in the prevention and management of osteoporosis.

Towards in silico Models of the Inflammatory Response in Bone Fracture Healing.

In silico modeling is a powerful strategy to investigate the biological events occurring at tissue, cellular and subcellular level during bone fracture healing. However, most current models do not consider the impact of the inflammatory response on the later stages of bone repair. Indeed, as initiator of the healing process, this early phase can alter the regenerative outcome: if the inflammatory response is too strongly down- or upregulated, the fracture can result in a non-union. This review covers the fundamental information on fracture healing, in silico modeling and experimental validation. It starts with a description of the biology of fracture healing, paying particular attention to the inflammatory phase and its cellular and subcellular components. We then discuss the current state-of-the-art regarding in silico models of the immune response in different tissues as well as the bone regeneration process at the later stages of fracture healing. Combining the aforementioned biological and computational state-of-the-art, continuous, discrete and hybrid modeling technologies are discussed in light of their suitability to capture adequately the multiscale course of the inflammatory phase and its overall role in the healing outcome. Both in the establishment of models as in their validation step, experimental data is required. Hence, this review provides an overview of the different in vitro and in vivo set-ups that can be used to quantify cell- and tissue-scale properties and provide necessary input for model credibility assessment. In conclusion, this review aims to provide hands-on guidance for scientists interested in building in silico models as an additional tool to investigate the critical role of the inflammatory phase in bone regeneration.

Targeted Deletion of CD11b+ Macrophage Subtypes alter the Acute Inflammatory Cytokine Response In Bone Healing

Abstract Any immunological or inflammatory dysregulation can impair the bone healing process. Macrophages (MØ) are immune cells specialized for phagocytosis and assist in all stages of bone repair. MØs are often divided into two main subsets, MØ1, pro-inflammatory M1 macrophages and MØ2, anti-inflammatory or resolving M2 macrophages. Our preliminary data demonstrates that MØ1 to MØ2 polarization occurs following femur fracture during the first 7 days post-fracture and is associated with a specific cytokine expression profile over time. Other studies have demonstrated that dysregulated inflammation can impair fracture healing outcomes in normal mice. We hypothesize that targeted depletion of CD11b+ MØ cells will reduce the acute inflammatory response, alter the normal cytokine expression profile, and interfere with the bone healing response. Therefore, the bone marrow of mice depleted of CD11b+ MØ cells were compared to normal mice following femur fracture at days 0, 1, 2, and 4 using established methods. MØ subtypes were identified using flow cytometry and cytokine expression was quantified using Luminex. The data demonstrated that after fracture, the CD11b+ MØ depleted group had significantly less MØ1s, F480+/CD86+/MHC classII+/CD11b+ cells when compared to controls at all timepoints. MØ cytokine expression profiles were found to be altered in the control fractures when compared to the CD11b+ MØ depleted fractures. Our results demonstrate that MØ subsets contribute substantially to the signaling mechanisms that guide the acute inflammatory phase of bone healing. Proper modulation of macrophage polarization may be useful to develop novel treatment strategies to improve healing when the immune system or inflammation is dysregulated.

Periostin in Bone Regeneration.

Bone regeneration is an efficient regenerative process depending on the recruitment and activation of skeletal stem cells that allowcartilage and bone formation leading to fracture consolidation. Periosteum, the tissue located at the outer surface of bone is now recognized as an essential player in the bone repair process and contains skeletal stem cells with high regenerative potential. The matrix composition of the periosteum defines its roles in bone growth, in cortical bone modeling and remodeling in response to mechanical strain, and in bone repair. Periostinis a key extracellular matrix component of the periosteum involved in periosteum functions. In this chapter, we summarize the current knowledge on the bone regeneration process, the role of the periosteum and skeletal stem cells, and Periostin functions in this context. The matricellular protein Periostinhas several roles through all stages of bone repair: in the early days of repair during the initial activation of stem cells within periosteum, in the active phase of cartilage and bone deposition in the facture callus, and in the final phase of bone bridging and reconstitution of the stem cell pool within periosteum.

Interosseous electrostimulation in a model of lengthening with external fixation

Abstract Background A fracture repair involves complex cellular processes. However, despite optimal treatment, some fractures heal slowly or do not repair. These complications support the need for innovative therapies. Electromagnetic stimulation is a non-invasive technology that could have a direct impact on many cellular pathways. Objective To demonstrate the effectiveness of electro-stimulation by alternating current applied during bone elongation to accelerate the consolidation process for 30 days in an animal model. Materials and methods A device with closed circuit and graduated voltage was designed and kept in contact with the external fixator. Group A was elongated without electro-stimulation and group B was electro-stimulated since the beginning of the distraction. Radiographs were taken at 15 and 30 days post-surgical. Haematoxylin and eosin staining and Masson's trichrome stain were performed. Results No significant difference were observed in bone density of group A (4.05±3.24, p = 0.163). In group B there was a significant difference (61.06±20.17, p = 0.03) in bone density. Group A maintained a fibrous tissue repair, with areas of cartilage and bone matrix. Group B had more organised tissue in the stages of bone repair. Conclusion Because there is a significant difference in the growth and callus formation at 15 and 30 days between groups, electro-stimulation could be considered as an adjuvant during bone elongation.

Modulation of fixation stiffness from flexible to stiff in a rat model of bone healing

Background and purpose — Constant fixator stiffness for the duration of healing may not provide suitable mechanical conditions for all stages of bone repair. We therefore investigated the influence of stiffening fixation on callus stiffness and morphology in a rat diaphyseal osteotomy model to determine whether healing time was shortened and callus stiffness increased through modulation of fixation from flexible to stiff.Material and methods — An external unilateral fixator was applied to the osteotomized femur and stiffened by decreasing the offset of the inner fixator bar at 3, 7, 14, and 21 days after operation. After 5 weeks, the rats were killed and healing was evaluated with mechanical, histological, and microcomputed tomography methods. Constant fixation stiffness control groups with either stiff or flexible fixation were included for comparison.Results — The callus stiffness of the stiff group and all 4 experimental groups was greater than in the flexible group. The callus of the flexible group was larger but contained a higher proportion of unmineralized tissue and cartilage. The stiff and modulated groups (3, 7, 14, and 21 days) all showed bony bridging at 5 weeks, as well as signs of callus remodeling. Stiffening fixation at 7 and 14 days after osteotomy produced the highest degree of callus bridging. Bone mineral density in the fracture gap was highest in animals in which the fixation was stiffened after 14 days.Interpretation — The predicted benefit of a large robust callus formed through early flexible fixation could not be shown, but the benefits of stabilizing a flexible construct to achieve timely healing were demonstrated at all time points.

Electroestimulación interósea en un modelo de elongación con fijación externa

BackgroundA fracture repair involves complex cellular processes. However, despite optimal treatment, some fractures heal slowly or do not repair. These complications support the need for innovative therapies. Electromagnetic stimulation is a non-invasive technology that could have a direct impact on many cellular pathways. ObjectiveTo demonstrate the effectiveness of electro-stimulation by alternating current applied during bone elongation to accelerate the consolidation process for 30 days in an animal model. Materials and methodsA device with closed circuit and graduated voltage was designed and kept in contact with the external fixator. Group A was elongated without electro-stimulation and group B was electro-stimulated since the beginning of the distraction. Radiographs were taken at 15 and 30 days post-surgical. Haematoxylin and eosin staining and Masson's trichrome stain were performed. ResultsNo significant difference were observed in bone density of group A (4.05±3.24, P=0.163). In group B there was a significant difference (61.06±20.17, P=0.03) in bone density. Group A maintained a fibrous tissue repair, with areas of cartilage and bone matrix. Group B had more organised tissue in the stages of bone repair. ConclusionBecause there is a significant difference in the growth and callus formation at 15 and 30 days between groups, electro-stimulation could be considered as an adjuvant during bone elongation.

Grain boundary corrosion of highly porous ceramic TiO2 foams is reduced by annealing and quenching

Porous bioceramics, such as scaffolds, can be used for bone regeneration. Bioceramics are instantly attacked by body fluids, macrophages and osteoclasts during stages of bone repair. Acidic microenvironments generated by these cells may amplify the well-known effect of grain boundary dissolution. Grain boundary corrosion in such porous scaffolds can have significant impact on the mechanical strength due to the high surface area of the scaffold. Corrosive media were found to significantly affect the mechanical strength of highly porous TiO2 scaffolds. Compressive strength decreased significantly after 12h in an aqueous acidic solution with a reduction to 35±10% after 8 weeks immersion time. Following post-sintering heat treatments by combining air quenching and annealing, the strength was maintained throughout a corrosion period of 8 weeks in acidic environment. Impurity segregation to the grain boundaries and thus, susceptibility to grain boundary corrosion was reduced by the synergistic effect of both heat treatments.

Analysis of the Early Stages of Osseointegration in Two Surfaces Dental Implants: Pilot Study

Objective: The aim of this article is to compare two surface treatment types of the dental implants inserted in tibiae of rabbits on the early stages of the bone repair considering the pattern of maturation of collagen fibers and the osseointegration process. Materials and methods: 10 modSAE (sandblast and acid etched modified) and 10 AO (anodic oxidation) implants were evaluated such as bone-implant contact (BIC), and collagen fiber orientation verified by circular polarized light (BICCPL). The results were measured at 7, 21 and 42 postoperative days. Results: The modSAE implants induced greater BIC at all times observed. The BICCPL analysis revealed the both implants showed a maturation pattern collagen fiber formation. However, BICCPL values of modSAE were higher than AO values at 21 days. Conclusions: In conclusion, the topography and surface characteristic of modSAE implant showed a tendency to improve bone tissue integration and also contributes to maturation of collagen fibers. This fact was evidenced at 21 days. The study shows the influence of topography and surface treatment of titanium dental implants in different stages of bone repair.

Effect of Recombinant Human Growth Hormone on Osseointegration of Titanium Implants: A Histologic and Biomechanical Study in Rabbits.

To evaluate the action of recombinant human growth hormone (rhGH) on osseointegration of titanium implants in rabbits. Fourteen adult New Zealand rabbits, aged 30 weeks, were used in the study, and randomly divided into 2 groups. In each animal, 2 (2.2 mm × 6 mm) pure titanium implants were placed in the left tibia. In one group (test group), 1 IU (0.3 mg) of rhGH as a lyophilized powder was applied to each osteotomy site prior to implant placement. Only titanium implants were placed in osteotomy sites of the other group (control). Animals were humanely killed at 14 and 42 days after surgery, and samples were then prepared for histologic analysis and biomechanical test. The biomechanical test showed tensile pull-out stress values of 33.88 N/cm(2) for controls and 59.26 N/cm(2) for the rhGH group at 14 days and 25.99 N/cm(2) and 29.69 N/cm(2) for the control and the test group, respectively, at 42 days. Scanning electron microscope analysis showed more uniform and abundant bone tissue in contact with the implants for the test group at 14 days, and no differences between groups at 42 days. Furthermore, histologic analysis also showed accelerated bone repair in 14 days and a more advanced stage of bone remodeling for the rhGH-treated group when compared to controls after 42 days of repair. Such results show that the topical use of rhGH induces new bone formation in the early stages of bone repair and hence accelerates osseointegration of titanium dental implants.

Codepositon of Dopamine/Calcium on Titanium to Enhancing Implant Integration

Calcium plays an important role in various stages of bone repair. Surface calcium modification is a common method to improve the biocompatibility of titanium implant. In this work, anovel facile codeposition dopamine/calcium on titanium alloy method for orthopedics applications was developed. SEM-EDS results showed calcium microspheres uniformly deposited on titanium surface with dopamine. Water contact angle showed the dopamine/calcium modification layer improved the bare titanium surface hydrophobic property. And the dopamine/calcium coating enhanced the cell proliferation by MTT test. The ALP gene expression also showed the dopamine/calcium coating may enhance the cell early differentiation. Such facile method has great potential in titanium applications.

IN VIVO EFFECTS OF LOW FREQUENCY LOW ENERGY PULSING ELECTROMAGNETIC FIELDS ON GENE EXPRESSION DURING THE INFLAMMATION PHASE OF BONE REPAIR

It has been widely demonstrated that pulsed low-frequency electromagnetic fields (PEMFs) positively affect bone repair. The aim of this study is to highlight if PEMFs influence cell metabolic activity during the replacement of the blood clot with granulation tissue in the inflammation phase of bone repair. Four equal transcortical holes were made, at the same diaphyseal level, in both metacarpals (McIII) of five male adult horses. The left McIII were exposed to PEMFs 24 hr/day; the right untreated McIII were used as controls. Eight days after surgery, the horses were sacrificed. We investigated the effect of PEMFs on 1) histological aspects of the lesion, 2) histochemical detection of the bone marker alkaline phosphatase, and 3) molecular markers as tumor necrosis factor-α (TNF-α), interleukin-6 (IL-6) and transforming growth factor-β1 (TGF-β) by reverse transcriptase-polymerase chain reaction amplification (RT-PCR).The histological analysis indicates that the blood clot, in both PEMF treated and control holes, is being replaced by granulation tissue extending from the endosteal towards the periosteal side of the lesion. TALP positive areas do not exactly correspond to the areas where fibroblasts are present, these being wider than the former. The study of the expression of the mRNA of TGF-β1 shows no differences between treated holes and control ones. The expression of TNF-α and IL-6 however, is not univocal, being sometimes more expressed, sometimes less in treated or control holes. These data show that PEMFs exposure affects the expression of inflammatory cytokines (TNF-α and IL-6) during the very early stages of bone repair. On the contrary TFG β expression and histological findings are not modified by PEMF exposure at least in this experimental condition.

Pulsed Electromagnetic Fields Modulate Enzymatic Actmty During the Early Stages of Bone Repair

The goal of this study was to investigate whether PEMFs influence enzymatic activities during the early stages of bone repair. Two transcortical holes (4.5 mm diameter) were drilled at the same diaphyseal level in the lateral margin of the right and left metacarpal bone (McIII) of six adult male horses. The left McIII were exposed to PEMFs (75 Hz; 2.8 mT, 1.3 ms impulse width) 24 h/day; the right untreated McIII were used as controls. Horses were sacrificed 8 and 15 days after the operation. The bone segments containing the holes were fixed, dehydrated in ethanol solutions, and, undecalcified, embedded in methylmethacrylate. The midlongitudinal sections of the holes were either stained with soluidine blue or processed for evaluation of the total alkaline phosphatase (TALP) and the tartrate-resistant acid phosphatase (TRAP). In PEMF-treated holes we found: (1) TALP is strongly positive with respect to the controls; (b) the newly formed bony trabeculae are more abundant than in the controls; (c) in both tre...