Evaluation of osteogenesis and angiogenesis of icariin loaded on micro/nano hybrid structured hydroxyapatite granules as a local drug delivery system for femoral defect repair

Application of Antioxidant Compounds in Bone Defect Repair

Bone defects caused by trauma, tumor resection, and infections are significant clinical challenges. Excessive reactive oxygen species (ROS) usually accumulate in the defect area, which may impair the function of cells involved in bone formation, posing a serious challenge for bone repair. Due to the potent ROS scavenging ability, as well as potential anti-inflammatory and immunomodulatory activities, antioxidants play an indispensable role in the maintenance and protection of bone health and have gained increasing attention in recent years. This narrative review aims to give an overview of the main research directions on the application of antioxidant compounds in bone defect repair over the past decade. In addition, the positive effects of various antioxidants and their biomaterial delivery systems in bone repair are summarized to provide new insights for exploring antioxidant-based strategies for bone defect repair.

Integrated Janus nanofibers enabled by a co-shell solvent for enhancing icariin delivery efficiency

During the past several decades, nanostructures have played their increasing influences on the developments of novel nano drug delivery systems, among which, double-chamber Janus nanostructure is a popular one. In this study, a new tri-channel spinneret was developed, in which two parallel metal capillaries were nested into another metal capillary in a core-shell manner. A tri-fluid electrospinning was conducted with a solvent mixture as the shell working fluid for ensuring the formation of an integrated Janus nanostructure. The scanning electronic microscopic results demonstrated that the resultant nanofibers had a linear morphology and two distinct compartments within them, as indicated by the image of a cross-section. Fourier Transformation Infra-Red spectra and X-Ray Diffraction patterns verified that the loaded poorly water-soluble drug, i.e. icariin, presented in the Janus medicated nanofibers in an amorphous state, which should be attributed to the favorable secondary interactions between icariin and the two soluble polymeric matrices, i.e. hydroxypropyl methyl cellulose (HPMC) and polyvinylpyrrolidone (PVP). The in vitro dissolution tests revealed that icariin, when encapsulated within the Janus nanofibers, exhibited complete release within a duration of 5 min, which was over 11 times faster compared to the raw drug particles. Furthermore, the ex vivo permeation tests demonstrated that the permeation rate of icariin was 16.2 times higher than that of the drug powders. This improvement was attributed to both the rapid dissolution of the drug and the pre-release of the trans-membrane enhancer sodium lauryl sulfate from the PVP side of the nanofibers. Mechanisms for microformation, drug release, and permeation were proposed. Based on the methodologies outlined in this study, numerous novel Janus nanostructure-based nano drug delivery systems can be developed for poorly water-soluble drugs in the future.

Promoting osteogenesis and bone regeneration employing icariin-loaded nanoplatforms

There is an increasing demand for innovative strategies that effectively promote osteogenesis and enhance bone regeneration. The critical process of bone regeneration involves the transformation of mesenchymal stromal cells into osteoblasts and the subsequent mineralization of the extracellular matrix, making up the complex mechanism of osteogenesis. Icariin's diverse pharmacological properties, such as anti-inflammatory, anti-oxidant, and osteogenic effects, have attracted considerable attention in biomedical research. Icariin, known for its ability to stimulate bone formation, has been found to encourage the transformation of mesenchymal stromal cells into osteoblasts and improve the subsequent process of mineralization. Several studies have demonstrated the osteogenic effects of icariin, which can be attributed to its hormone-like function. It has been found to induce the expression of BMP-2 and BMP-4 mRNAs in osteoblasts and significantly upregulate Osx at low doses. Additionally, icariin promotes bone formation by stimulating the expression of pre-osteoblastic genes like Osx, RUNX2, and collagen type I. However, icariin needs to be effectively delivered to bone to perform such promising functions.Encapsulating icariin within nanoplatforms holds significant promise for promoting osteogenesis and bone regeneration through a range of intricate biological effects. When encapsulated in nanofibers or nanoparticles, icariin exerts its effects directly at the cellular level. Recalling that inflammation is a critical factor influencing bone regeneration, icariin's anti-inflammatory effects can be harnessed and amplified when encapsulated in nanoplatforms. Also, while cell adhesion and cell migration are pivotal stages of tissue regeneration, icariin-loaded nanoplatforms contribute to these processes by providing a supportive matrix for cellular attachment and movement. This review comprehensively discusses icariin-loaded nanoplatforms used for bone regeneration and osteogenesis, further presenting where the field needs to go before icariin can be used clinically.

Icariin accelerates bone regeneration by inducing osteogenesis-angiogenesis coupling in rats with type 1 diabetes mellitus

BACKGROUND

Icariin (ICA), a natural flavonoid compound monomer, has multiple pharmacological activities. However, its effect on bone defect in the context of type 1 diabetes mellitus (T1DM) has not yet been examined.

AIM

To explore the role and potential mechanism of ICA on bone defect in the context of T1DM.

METHODS

The effects of ICA on osteogenesis and angiogenesis were evaluated by alkaline phosphatase staining, alizarin red S staining, quantitative real-time polymerase chain reaction, Western blot, and immunofluorescence. Angiogenesis-related assays were conducted to investigate the relationship between osteogenesis and angiogenesis. A bone defect model was established in T1DM rats. The model rats were then treated with ICA or placebo and micron-scale computed tomography, histomorphometry, histology, and sequential fluorescent labeling were used to evaluate the effect of ICA on bone formation in the defect area.

RESULTS

ICA promoted bone marrow mesenchymal stem cell (BMSC) proliferation and osteogenic differentiation. The ICA treated-BMSCs showed higher expression levels of osteogenesis-related markers (alkaline phosphatase and osteocalcin) and angiogenesis-related markers (vascular endothelial growth factor A and platelet endothelial cell adhesion molecule 1) compared to the untreated group. ICA was also found to induce osteogenesis-angiogenesis coupling of BMSCs. In the bone defect model T1DM rats, ICA facilitated bone formation and CD31hiEMCNhi type H-positive capillary formation. Lastly, ICA effectively accelerated the rate of bone formation in the defect area.

CONCLUSION

ICA was able to accelerate bone regeneration in a T1DM rat model by inducing osteogenesis-angiogenesis coupling of BMSCs.

Dual-functional 3D-printed porous bioactive scaffold enhanced bone repair by promoting osteogenesis and angiogenesis

The treatment of bone defects is a difficult problem in orthopedics. The excessive destruction of local bone tissue at defect sites destroys blood supply and renders bone regeneration insufficient, which further leads to delayed union or even nonunion. To solve this problem, in this study, we incorporated icariin into alginate/mineralized collagen (AMC) hydrogel and then placed the drug-loaded hydrogel into the pores of a 3D-printed porous titanium alloy (AMCI/PTi) scaffold to prepare a bioactive scaffold with the dual functions of promoting angiogenesis and bone regeneration. The experimental results showed that the ACMI/PTi scaffold had suitable mechanical properties, sustained drug release function, and excellent biocompatibility. The released icariin and mineralized collagen (MC) synergistically promoted angiogenesis and osteogenic differentiation in vitro. After implantation into a rabbit radius defect, the composite scaffold showed a satisfactory effect in promoting bone repair. Therefore, this composite dual-functional scaffold could meet the requirements of bone defect treatment and provide a promising strategy for the repair of large segmental bone defects in clinic.

Flavonoid-Loaded Biomaterials in Bone Defect Repair

Skeletons play an important role in the human body, and can form gaps of varying sizes once damaged. Bone defect healing involves a series of complex physiological processes and requires ideal bone defect implants to accelerate bone defect healing. Traditional grafts are often accompanied by issues such as insufficient donors and disease transmission, while some bone defect implants are made of natural and synthetic polymers, which have characteristics such as good porosity, mechanical properties, high drug loading efficiency, biocompatibility and biodegradability. However, their antibacterial, antioxidant, anti-inflammatory and bone repair promoting abilities are limited. Flavonoids are natural compounds with various biological activities, such as antitumor, anti-inflammatory and analgesic. Their good anti-inflammatory, antibacterial and antioxidant activities make them beneficial for the treatment of bone defects. Several researchers have designed different types of flavonoid-loaded polymer implants for bone defects. These implants have good biocompatibility, and they can effectively promote the expression of angiogenesis factors such as VEGF and CD31, promote angiogenesis, regulate signaling pathways such as Wnt, p38, AKT, Erk and increase the levels of osteogenesis-related factors such as Runx-2, OCN, OPN significantly to accelerate the process of bone defect healing. This article reviews the effectiveness and mechanism of biomaterials loaded with flavonoids in the treatment of bone defects. Flavonoid-loaded biomaterials can effectively promote bone defect repair, but we still need to improve the overall performance of flavonoid-loaded bone repair biomaterials to improve the bioavailability of flavonoids and provide more possibilities for bone defect repair.

Strategies for in situ tissue engineering of vascularized bone regeneration (Review)

Numerous physiological processes occur following bone fracture, including inflammatory cell recruitment, vascularization, and callus formation and remodeling. In particular circumstances, such as critical bone defects or osteonecrosis, the regenerative microenvironment is compromised, rendering endogenous stem/progenitor cells incapable of fully manifesting their reparative potential. Consequently, external interventions, such as grafting or augmentation, are frequently necessary. In situ bone tissue engineering (iBTE) employs cell-free scaffolds that possess microenvironmental cues, which, upon implantation, redirect the behavior of endogenous stem/progenitor cells towards a pro-regenerative inflammatory response and reestablish angiogenesis-osteogenesis coupling. This process ultimately results in vascularized bone regeneration (VBR). In this context, a comprehensive review of the current techniques and modalities in VBR-targeted iBTE technology is provided.

Polymeric and Composite Carriers of Protein and Non-Protein Biomolecules for Application in Bone Tissue Engineering

Conventional intake of drugs and active substances is most often based on oral intake of an appropriate dose to achieve the desired effect in the affected area or source of pain. In this case, controlling their distribution in the body is difficult, as the substance also reaches other tissues. This phenomenon results in the occurrence of side effects and the need to increase the concentration of the therapeutic substance to ensure it has the desired effect. The scientific field of tissue engineering proposes a solution to this problem, which creates the possibility of designing intelligent systems for delivering active substances precisely to the site of disease conversion. The following review discusses significant current research strategies as well as examples of polymeric and composite carriers for protein and non-protein biomolecules designed for bone tissue regeneration.

Icariin: A Potential Alternative Against Osteoporosis

Osteoporosis is a metabolic skeletal disorder characterized by increased fragility and fracture risk as s result of reduced bone mineral density and microstructural destruction and caused a heavy burden on families and society. Current medicines, on the other hand, have some limitations, with side effects and doubts regarding long-term efficacy being highlighted. Studies seeking for natural constituents as potential treatment options therefore come into focus. Icariin is a phytochemical derived from a traditional Chinese medicine, Herba epimedium, that has been used to treat orthopedic disorders in ancient China for thousands of years, including osteoporosis, osteoarthritis, and fracture. Icariin belongs to a category of prenylated flavonoids and has been shown to help reduce osteoporosis bone loss while having relatively low side effects. Icariin's anti-osteoporosis properties manifest in a variety of ways, like promoting osteogenesis, suppressing osteoclastogenesis and bone resorption, regulating migration, proliferation, and differentiation of mesenchymal stem cells, enhancing angiogenesis, anti-inflammation, and antioxidation. These procedures entail a slew of critical signaling pathways, such as PPARγ, ERα/AKT/β-catenin, and MAPK. Therefore, icariin can be an applicable alternative to improve osteoporosis although the underlying mechanisms have yet to be fully understood. In this study, we searched using the terms “icariin” and “osteoporosis,” and included 64 articles meeting the inclusion criteria and reviewed the research of icariin in anti-osteoporosis over the last 10 years, and discussed new prospects for future study. Therefore, this review may provide some references for further studies.

Aptamer/Hydroxyapatite-Functionalized Titanium Substrate Promotes Implant Osseointegration via Recruiting Mesenchymal Stem Cells

Endowing bone regeneration materials with both stem cell recruitment and osteoinduction properties is a key factor in promoting osseointegration of titanium (Ti) implants. In this study, Apt19s-grafted oxidized hyaluronic acid (OHA) was deposited onto a protein-mediated biomineralization hydroxyapatite (HAp) coating of Ti. HAp was achieved by the treatment of lysozyme and tris(2-carboxyethyl) phosphonate mixture and then soaked in calcium ion (Ca²⁺) solution to obtain functional Ti substrate (Ti/HAp/OHA-Apt). In vitro studies confirmed that Ti/HAp/OHA-Apt could effectively maintain the sustained release of Apt19s from Ti for 7 days. The released Apt19s significantly enhanced the migration of bone marrow mesenchymal stem cells (MSCs), which was reflected by the experiment of transwell assay, wound healing, and zymogram detection. Compared with pure Ti, Ti/HAp/OHA-Apt was able to adjust the adsorption of functional proteins at the Ti-based interface to expose their active sites, which significantly increased the expression of adhesion-associated proteins (vinculin and tensin) in MSCs to promote their adhesion on Ti-based interface. In vitro cell experiments of alkaline phosphatase activity staining, mineralization detection, and expression of osteogenesis-related genes showed that Ti/HAp/OHA-Apt significantly enhanced the osteogenic differentiation ability of MSCs, which may be highly related to the porous structure of hydroxyapatite on Ti interface. In vivo test of Micro-CT, H&E staining, and histochemical staining further confirmed that Ti/HAp/OHA-Apt was able to promote MSC recruitment at the peri-implant interface to form new bone. This work provides a new approach to develop functional Ti-based materials for bone defect repair.

Bioactive natural compounds as potential medications for osteogenic effects in a molecular docking approach

Bone defect repair and fracture healing are critical challenges in clinical treatments. Bioactive natural compounds are potential resources for medications for osteogenic effects. We have identified icariin, the effective ingredient of Epimedium pubescens, to promote osteogenic differentiation of bone mesenchymal stem cells (BMSCs) and repair bone defects. To explore more natural compounds with the potential modality for bone repair, in the present study, we employed an icariin-induced gene expression pattern as an osteogenic model and screened the Connectivity Map database for small molecules with gene expression signatures similar to this model. We verified the effectiveness of this molecule docking approach by introducing hydroxycholesterol, the second highest score of the similarity to icariin, into the osteoinductive experiments in vitro and demonstrated its excellent osteogenic effect on BMSCs compared with a BMP-2-positive control group. Based on the compatible result of hydroxycholesterol, subsequently, ginsenoside Rb1 was chosen as the most drug-like natural compound among the molecule docking results from icariin. Finally, ginsenoside Rb1 was demonstrated to promote the expression of osteoblastic genes and ALP activity in vitro and repair the calvarial defect of rats in vivo. The study aimed to provide diverse choices for clinical application in bone repair and functional regeneration.

Angiogenic and Osteogenic Effects of Flavonoids in Bone Regeneration

Bone is a highly vascularised tissue that relies on a close spatial and temporal interaction between blood vessels and bone cells. As a result, angiogenesis is critical for bone formation and healing. The vascular system supports bone regeneration by delivering oxygen, nutrients, and growth factors, as well as facilitating efficient cell-cell contact. Most clinical applications of engineered bone grafts are hampered by insufficient vascularization after implantation. Over the last decade, a number of flavonoids have been reported to have osteogenic-angiogenic potential in bone regeneration because of their excellent bioactivity, low cost, availability, and minimal in vivo toxicity. During new bone formation, the osteoinductive nature of certain flavonoids is involved in regulating multiple signaling pathways contributing toward the osteogenic-angiogenic coupling. This review briefly outlines the osteogenic-angiogenic potential of those flavonoids and the mechanisms of their action in promoting bone regeneration. However, further studies are needed to investigate their delivery strategies and establish their clinical efficacy. This article is protected by copyright. All rights reserved.

TiO2 Nanotubes Functionalized with Icariin for an Attenuated In Vitro Immune Response and Improved In Vivo Osseointegration

Due to their superior mechanical and chemical properties, titanium (Ti) and its alloys have been widely used as orthopedic implantable devices. However, their bioinertness represents a limitation, which can be overcome by employing various surface modifications, such as TiO₂ nanotube (TNT) fabrication via electrochemical anodization. Anodic TNTs present tunable dimensions and unique structures, turning them into feasible drug delivery platforms. In the present work, TNTs were loaded with icariin (Ica) through an adhesive intermediate layer of polydopamine (DP), and their in vitro and in vivo biological performance was evaluated. The successful fabrication of the modified surfaces was verified by scanning electron microscopy (SEM), atomic force microscopy (AFM), Fourier transform infrared spectroscopy (FTIR), and contact angle measurements (CA), while the in vitro release of Ica was evaluated via UV-VIS spectrophotometry. In terms of in vitro behaviour, comparative studies on RAW 264.7 macrophages demonstrated that the TNT substrates, especially TNT-DP-Ica, elicited a lower inflammatory response compared to the Ti support. Moreover, the in vivo implantation studies evinced generation of a reduced fibrotic capsule around this implant and increased thickness of the newly formed bone tissue at 1 month and 3 months post-implantation, respectively. Overall, our results indicate that the controlled release of Ica from TNT surfaces could result in an improved osseointegration process.

Strategies for Enhancing Vascularization of Biomaterial-Based Scaffold in Bone Regeneration

Despite the recent advances in reconstructive orthopedics; fracture union is a challenge to bone regeneration. Concurrent angiogenesis is a complex process governed by events, delicately entwined with osteogenesis. However, poorly perfused scaffolds have lower success rates; necessitating the need for a better vascular component, which is important for the delivery of nutrients, oxygen, waste elimination, recruitment of cells for optimal bone repair. This review highlights the latest strategies to promote biomaterial-based scaffold vascularization by incorporation of cells, growth factors, inorganic ions, etc. into natural or synthetic polymers, ceramic materials, or composites of organic and inorganic compounds. Furthermore, it emphasizes structural modifications, biophysical stimuli, and natural molecules to fabricate scaffolds aiding the genesis of dense vascularization following their implantation to manifest a compatible regenerative microenvironment without graft rejection.

The osteogenesis of Ginsenoside Rb1 incorporated silk/micro-nano hydroxyapatite/sodium alginate composite scaffolds for calvarial defect

Ginsenoside Rb1, the effective constituent of ginseng, has been demonstrated to play favorable roles in improving the immunity system. However, there is little study on the osteogenesis and angiogenesis effect of Ginsenoside Rb1. Moreover, how to establish a delivery system of Ginsenoside Rb1 and its repairment ability in bone defect remains elusive. In this study, the role of Ginsenoside Rb1 in cell viability, proliferation, apoptosis, osteogenic genes expression, ALP activity of rat BMSCs were evaluated firstly. Then, micro-nano HAp granules combined with silk were prepared to establish a delivery system of Ginsenoside Rb1, and the osteogenic and angiogenic effect of Ginsenoside Rb1 loaded on micro-nano HAp/silk in rat calvarial defect models were assessed by sequential fluorescence labeling, and histology analysis, respectively. It revealed that Ginsenoside Rb1 could maintain cell viability, significantly increased ALP activity, osteogenic and angiogenic genes expression. Meanwhile, micro-nano HAp granules combined with silk were fabricated smoothly and were a delivery carrier for Ginsenoside Rb1. Significantly, Ginsenoside Rb1 loaded on micro-nano HAp/silk could facilitate osteogenesis and angiogenesis. All the outcomes hint that Ginsenoside Rb1 could reinforce the osteogenesis differentiation and angiogenesis factor’s expression of BMSCs. Moreover, micro-nano HAp combined with silk could act as a carrier for Ginsenoside Rb1 to repair bone defect.

Bioactive strontium ions/ginsenoside Rg1-incorporated biodegradable silk fibroin-gelatin scaffold promoted challenging osteoporotic bone regeneration

Autogenous healing of osteoporotic fractures is challenging, as the regenerative capacity of bone tissues is impaired by estrogen reduction and existed pro-inflammatory cytokines. In this study, a biofunctional ginsenoside Rg1 and strontium-containing mineral (SrHPO₄, SrP)-incorporated biodegradable silk fibroin-gelatin (SG) scaffold (Rg1/SrP/SG) was developed to stimulate the osteoporotic bone repair. The incorporation of 15 wt% SrP significantly enhanced the mechanical strength, stimulated the osteogenic differentiation of mouse bone marrow mesenchymal stem cells, and suppressed the osteoclastogenesis of RAW264.7 in a concentration-related manner. The loading of Rg1 in SG and 15SrP/SG scaffolds obviously promoted the angiogenesis of human umbilical vein endothelial cells via activating the expression of vascular endothelial growth factor and basic fibroblast growth factor genes and proteins. The bioactive strontium ions (Sr²⁺) and Rg1 released from the scaffolds together mediated lipopolysaccharide-treated macrophages polarizing into M2 type. They downregulated the expression of inflammatory-related genes (interleukin (IL)-1β, tumor necrosis factor α, and IL-6) and stimulated the expression of genes related to anti-inflammation (Arginase and IL-10) as well as bone repair (BMP-2 and PDGF-BB) in the macrophages. The in vivo results also displayed that SrP and Rg1 significantly promoted the bone repair effect of SG scaffolds in osteoporotic critical-sized calvarial defects. Besides, the degradation rate of the scaffolds was close to the bone regeneration rate. Therefore, the simultaneous addition of SrP and Rg1 is a promising way for facilitating the osteoporotic bone repair activity of SG scaffolds via promoting the osteogenesis and angiogenesis, as well as inhibiting the osteoclastogenesis and inflammation.

Hydrogel Encapsulation of Mesenchymal Stem Cells and Their Derived Exosomes for Tissue Engineering

Tissue engineering has been an inveterate area in the field of regenerative medicine for several decades. However, there remains limitations to engineer and regenerate tissues. Targeted therapies using cell-encapsulated hydrogels, such as mesenchymal stem cells (MSCs), are capable of reducing inflammation and increasing the regenerative potential in several tissues. In addition, the use of MSC-derived nano-scale secretions (i.e., exosomes) has been promising. Exosomes originate from the multivesicular division of cells and have high therapeutic potential, yet neither self-replicate nor cause auto-immune reactions to the host. To maintain their biological activity and allow a controlled release, these paracrine factors can be encapsulated in biomaterials. Among the different types of biomaterials in which exosome infusion is exploited, hydrogels have proven to be the most user-friendly, economical, and accessible material. In this paper, we highlight the importance of MSCs and MSC-derived exosomes in tissue engineering and the different biomaterial strategies used in fabricating exosome-based biomaterials, to facilitate hard and soft tissue engineering.

Extraction and Characterization of Novel Natural Hydroxyapatite Bioceramic by Thermal Decomposition of Waste Ostrich Bone

A novel natural hydroxyapatite (HAp) bioceramic was extracted from the ostrich cortical bone by the thermal decomposition method. HAp was characterized by different analytical tools such as thermogravimetric analysis (TGA), Fourier-transform infrared spectroscopy (FTIR), X-ray diffraction (XRD) analysis, and scanning electron microscopy (SEM). Removal of organic impurities from the bone powder was confirmed by TGA analysis. FTIR spectra of HAp confirmed the presence of the major functional groups such as phosphate (PO₄³⁻), hydroxyl (OH⁻), and carbonate (CO₃²⁻) in the bioceramic. The XRD data revealed that the HAp was the crystalline phase obtained by calcination of the bone powder at 950°C, and the SEM analyses confirmed the typical plate-like texture of the nanosized HAp crystals.

In vitro effects of the co-release of icariin and strontium from bioactive glass submicron spheres on the reduced osteogenic potential of rat osteoporotic bone marrow mesenchymal stem cells

Osteoporosis is a metabolic disease that affects bone tissue and is highly associated with bone fractures. Typical osteoporosis fracture treatments, such as bisphosphonates and hormone replacement, present important challenges because of their low bioavailability on the site of action. Options to overcome this issue are systems for the local release of therapeutic agents such as bioactive glasses containing therapeutic molecules and ions. These agents are released during the dissolution process, combining the drugs and ion therapeutic effects for osteoporosis treatment. Among the therapeutic agents that can be applied for bone repair are strontium (Sr) ion and phytopharmaceutical icariin, which have shown potential to promote healthy bone marrow stem cells osteogenic differentiation, increase bone formation and prevent bone loss. Submicron Sr-containing bioactive glass mesoporous spheres with sustained ion release capacity were obtained. Icariin was successfully incorporated into the particles, and the glass composition influenced the icariin incorporation efficiency and release rates. In this work, for the first time, Sr and icariin were incorporated into bioactive glass submicron mesoporous spheres and the in vitro effects of the therapeutic agents release were evaluated on the reduced osteogenic potential of rat osteoporotic bone marrow mesenchymal stem cells, and results showed an improvement on the reduced differentiation potential.

Nanotechnology for angiogenesis: opportunities and challenges

Angiogenesis plays a critical role within the human body, from the early stages of life (i.e., embryonic development) to life-threatening diseases (e.g., cancer, heart attack, stroke, wound healing). Many pharmaceutical companies have expended huge efforts on both stimulation and inhibition of angiogenesis. During the last decade, the nanotechnology revolution has made a great impact in medicine, and regulatory approvals are starting to be achieved for nanomedicines to treat a wide range of diseases. Angiogenesis therapies involve the inhibition of angiogenesis in oncology and ophthalmology, and stimulation of angiogenesis in wound healing and tissue engineering. This review aims to summarize nanotechnology-based strategies that have been explored in the broad area of angiogenesis. Lipid-based, carbon-based and polymeric nanoparticles, and a wide range of inorganic and metallic nanoparticles are covered in detail. Theranostic and imaging approaches can be facilitated by nanoparticles. Many preparations have been reported to have a bimodal effect where they stimulate angiogenesis at low dose and inhibit it at higher doses.

The role of antimiR-26a-5p/biphasic calcium phosphate in repairing rat femoral defects

Although miRNAs have been implicated in the osteogenic differentiation of stem cells, their role in bone repair and reconstruction in tissue‑engineered bone grafts remains unclear. We previously reported that microRNA (miR)‑26a‑5p inhibited the osteogenic differentiation of adipose‑derived mesenchymal stem cells (ADSCs), and that antimiR‑26a‑5p exerted the opposite effect. In the present study, the role of miR‑26a‑5p‑ and antimiR‑26a‑5p‑modified ADSCs combined with biphasic calcium phosphate (BCP) scaffolds was evaluated in a rat femur defect model. The aim of the present study was to improve the understanding of the role of miR‑26a‑5p in bone regeneration in vivo, as well as to provide a new method to optimize the osteogenic ability of BCPs. ADSCs were infected with Lv‑miR‑26a‑5p, Lv‑miR‑NC, Lv‑antimiR‑26a‑5p or Lv‑antimiR‑NC respectively, and then combined with BCP scaffolds to repair rat femoral defects. Using X‑rays, micro‑computed tomography and histology at 2, 4, and 8 weeks postoperatively, the quantity and rate of bone regeneration were analyzed, revealing that they were the highest in animals treated with antimiR‑26a‑5p and the lowest in the miR‑26a‑5p treatment group. The expression levels of osteocalcin, collagen I, Runt‑related transcription factor 2, Wnt family member 5A and calmodulin‑dependent protein kinase II proteins were positively correlated with the bone formation rate. Taken together, the present results demonstrated that miR‑26a‑5p inhibited bone formation while antimiR‑26a‑5p accelerated bone formation via the Wnt/Ca2+ signaling pathway. Therefore, antimiR‑26a‑5p‑modified ADSCs combined with BCP scaffolds may be used to construct an effective tissue‑engineering bone graft for bone repair and reconstruction.

Dual functional approaches for osteogenesis coupled angiogenesis in bone tissue engineering

Bone fracture healing is a multistep and overlapping process of inflammation, angiogenesis and osteogenesis. It is initiated by inflammation, causing the release of various cytokines and growth factors. It leads to the recruitment of stem cells and formation of vasculature resulting in the functional bone formation. This combined phenomenon is used by bone tissue engineers from past few years to address the problem of vasculature and osteogenic differentiation during bone regeneration. In this review, we have discussed all major studies reporting the dual functioning approach to promote osteogenesis coupled angiogenesis using various scaffolds. These scaffolds are broadly classified into four types based on the nature of their structural and functional components. The functionality of the scaffold is either due to the structural components or the loaded cargo which conducts or induces the coupled functionality. Dual delivery system for osteoinductive and angioinductive factors ensures the co-delivery of two different types of molecules to induce osteogenesis and angiogenesis. Single delivery scaffold for angioinductive and osteoinductive molecule releases single type of molecules which could induce both angiogenesis and osteogenesis. Osteoconductive scaffold consisted of bone constituents releases angioinductive factors. Osteoconductive and angioconductive scaffold composed of components which provide the native substrate features for osteogenesis and angiogenesis. This review article also discusses the studies highlighting the synergism of physico-chemical stimuli as dual functioning feature to enhance angiogenesis and osteogenesis simultaneously. In addition, this article covers one of the least discussed area of the bone regeneration i.e. 'cartilage formation as a median between angiogenesis and osteogenesis'.

Amorphous carbon modification on implant surface: a general strategy to enhance osteogenic differentiation for diverse biomaterials via FAK/ERK1/2 signaling pathways

Amorphous carbon coatings enhance osteogenic differentiation via FAK/ERK1/2 signaling pathways.

Study of the osteogenesis effect of icariside II and icaritin on canine bone marrow mesenchymal stem cells

This study aimed to identify the osteogenesis effect of icariside II (ICSII) and icaritin (ICT) in vitro. Bone marrow mesenchymal stem cells (BMSCs) were treated with ICSII and ICT in order to detect the proliferation and differentiation of BMSCs, the expression of the osteogenesis-related proteins with or without osteogenic medium (OM) and genes, Runt-related transcription factor 2 (Runx-2), osteocalcin (OCN), osteopontin (OPN), osterix, and basic fibroblast growth factor (bFGF), and the phosphorylation levels of mitogen-activated protein kinase (MAPK). We found that the optical density increased and alkaline phosphatase decreased after the BMSCs were treated with different concentrations of ICSII; however, ICT showed an opposing effect. The formation of calcium nodules was observed after the BMSCs were treated with ICSII and ICT. The expression level of osteogenesis-related proteins was enhanced following treatment with both ICSII or ICT, while the expression level of the osteogenesis-related genes Runx-2, OCN, OPN, osterix, and bFGF significantly increased with ICSII treatment (P < 0.05), and only Runx-2 and bFGF significantly increased (P < 0.01) with ICT. The expression of osteogenic differentiation-related proteins (except OPN) following treatment with ICSII + OM or ICT + OM was not notably increased. Both ICSII and ICT elevated the phosphorylation levels of MAPK/ERK, which was attenuated by GDC-0994 (an inhibitor of MAPK/ERK). Collectively, these data indicate that ICSII and ICT facilitate orientation osteogenic differentiation of BMSCs, which is most likely via the MAPK/ERK pathway. OM did not synergistically enhance the osteogenesis effect of ICSII and ICT.

Synergetic topography and chemistry cues guiding osteogenic differentiation in bone marrow stromal cells through ERK1/2 and p38 MAPK signaling pathway

Both the topographic surface and chemical composition modification can enhance rapid osteogenic differentiation and bone formation. Till now, the synergetic effects of topography and chemistry cues guiding biological responses have been rarely reported. Herein, the ordered micro-patterned topography and classically essential trace element of strontium (Sr) ion doping were selected to imitate topography and chemistry cues, respectively. The ordered micro-patterned topography on Sr ion-doped bioceramics was successfully duplicated using the nylon sieve as the template. Biological response results revealed that the micro-patterned topography design or Sr doping could promote cell attachment, ALP activity, and osteogenic differentiation of bone marrow-derived mesenchymal stem cells (BMSCs). Most importantly, the samples both with micro-patterned topography and Sr doping showed the highest promotion effects, and could synergistically activate the ERK1/2 and p38 MAPK signaling pathways. The results suggested that the grafts with both specific topography and chemistry cues have synergetic effects on osteogenic activity of BMSCs and provide an effective approach to design functional bone grafts and cell culture substrates.

Nanocomposite Porous Microcarriers Based on Strontium-Substituted HA- g-Poly(γ-benzyl-l-glutamate) for Bone Tissue Engineering

Porous microcarriers have aroused increasing attention recently, which can create a protected environment for sufficient cell seeding density, facilitate oxygen and nutrient transfer, and well support the cell attachment and growth. In this study, porous microcarriers fabricated from the strontium-substituted hydroxyapatite- graft-poly(γ-benzyl-l-glutamate) (Sr10-HA- g-PBLG) hybrid nanocomposite were developed. The surface grating of PBLG, the micromorphology and element distribution, mechanical strength, in vitro degradation, and Sr²⁺ ion release of the obtained Sr10-HA- g-PBLG porous microcarriers were investigated, respectively. The grafting ratio and the molecular weight of the grafted PBLG of Sr10-HA- g-PBLG could be effectively controlled by varying the initial ratio of BLG-NCA to Sr10-HA-NH₂. The microcarriers exhibited a highly porous and interconnected microstructure with the porosity of about 90% and overall density of 1.03-1.06 g/cm³. Also, the degradation rate of Sr10-HA-PBLG microcarriers could be effectively controlled and long-term Sr²⁺ release was obtained. The Sr10-HA-PBLG microcarriers allowed cells adhesion, infiltration, and proliferation and promoted the osteogenic differentiation of rabbit adipose-derived stem cells (ADSCs). Successful healing of femoral bone defect was proved by injection of the ADSCs-seeded Sr10-HA-PBLG microcarriers in a rabbit model.

One-dimensional hydroxyapatite materials: preparation and applications

As one of the biominerals, hydroxyapatite (HAP) plays important roles in biology, and inspires researchers to investigate HAP-based materials for the applications in various biomedical fields. Among them, one-dimensional (1-D) micro-/nanostructured HAP materials have attracted great interest in the last decades. This review summarizes the preparation and applications of 1-D HAP materials, and discusses different aspects of 1-D HAP materials. Various synthetic methods have been developed to prepare 1-D HAP materials with different morphologies, sizes, surface properties and crystallinities. In addition, elements-substituted 1-D HAP materials and composites have also been prepared. Surfactants and additives are usually adopted to control the nucleation and growth of 1-D HAP materials, but the related mechanisms are not very clear yet. The applications of 1-D HAP materials have been widely investigated, and the biomedical applications show great prospect but still need further improvements. A new kind of highly flexible fire-resistant inorganic paper made of ultralong HAP nanowires has been developed and is a promising alternative of the traditional cellulose paper for valuable archives and important documents. Regardless of the advances, further studies should be made for preparing 1-D HAP materials with controlled structures, sizes and morphologies and for boosting their various applications.

Effects of HAp and TCP in constructing tissue engineering scaffolds for bone repair

TCP possesses superior long-term effects in structuring tissue engineering scaffold for bone repair compared to HAp, though TCP lags behind HAp in the early repair period.

The effect of quercetin delivery system on osteogenesis and angiogenesis under osteoporotic conditions

Bone regeneration under osteoporotic conditions with impaired angiogenesis, osteogenesis and remodeling represents a great challenge.

Strontium (Sr) strengthens the silicon (Si) upon osteoblast proliferation, osteogenic differentiation and angiogenic factor expression

Sr strengthens the Si upon osteoblast proliferation, osteogenic differentiation and angiogenic factor expression via Si and Sr released from Si/Sr co-substituted hydroxyapatite bioceramic materials.