Porous lithium-doped hydroxyapatite scaffold seeded with hypoxia-preconditioned bone-marrow mesenchymal stem cells for bone-tissue regeneration

Lithium Promotes Osteogenesis via Rab11a-Facilitated Exosomal Wnt10a Secretion and β-Catenin Signaling Activation

Both bone mesenchymal stem cells (BMSCs) and their exosomes suggest promising therapeutic tools for bone regeneration. Lithium has been reported to regulate BMSC function and engineer exosomes to improve bone regeneration in patients with glucocorticoid-induced osteonecrosis of the femoral head. However, the mechanisms by which lithium promotes osteogenesis have not been elucidated. Here, we demonstrated that lithium promotes the osteogenesis of BMSCs via lithium-induced increases in the secretion of exosomal Wnt10a to activate Wnt/β-catenin signaling, whose secretion is correlated with enhanced MARK2 activation to increase the trafficking of the Rab11a and Rab11FIP1 complexes together with exosomal Wnt10a to the plasma membrane. Then, we compared the proosteogenic effects of exosomes derived from lithium-treated or untreated BMSCs (Li-Exo or Con-Exo) both in vitro and in vivo. We found that, compared with Con-Exo, Li-Exo had superior abilities to promote the uptake and osteogenic differentiation of BMSCs. To optimize the in vivo application of these hydrogels, we fabricated Li-Exo-functionalized gelatin methacrylate (GelMA) hydrogels, which are more effective at promoting osteogenesis and bone repair than Con-Exo. Collectively, these findings demonstrate the mechanism by which lithium promotes osteogenesis and the great promise of lithium for engineering BMSCs and their exosomes for bone regeneration, warranting further exploration in clinical practice.

Lithium prevents glucocorticoid-induced osteonecrosis of the femoral head by regulating autophagy

Autophagy may play an important role in the occurrence and development of glucocorticoid-induced osteonecrosis of the femoral head (GC-ONFH). Lithium is a classical autophagy regulator, and lithium can also activate osteogenic pathways, making it a highly promising therapeutic agent for GC-ONFH. We aimed to evaluate the potential therapeutic effect of lithium on GC-ONFH. For in vitro experiments, primary osteoblasts of rats were used for investigating the underlying mechanism of lithium's protective effect on GC-induced autophagy levels and osteogenic activity dysfunction. For in vivo experiments, a rat model of GC-ONFH was used for evaluating the therapeutic effect of oral lithium on GC-ONFH and underlying mechanism. Findings demonstrated that GC over-activated the autophagy of osteoblasts and reduced their osteogenic activity. Lithium reduced the over-activated autophagy of GC-treated osteoblasts through PI3K/AKT/mTOR signalling pathway and increased their osteogenic activity. Oral lithium reduced the osteonecrosis rates in a rat model of GC-ONFH, and restrained the increased expression of autophagy related proteins in bone tissues through PI3K/AKT/mTOR signalling pathway. In conclusion, lithium can restrain over-activated autophagy by activating PI3K/AKT/mTOR signalling pathway and up-regulate the expression of genes for bone formation both in GC induced osteoblasts and in a rat model of GC-ONFH. Lithium may be a promising therapeutic agent for GC-ONFH. However, the role of autophagy in the pathogenesis of GC-ONFH remains controversial. Studies are still needed to further explore the role of autophagy in the pathogenesis of GC-ONFH, and the efficacy of lithium in the treatment of GC-ONFH and its underlying mechanisms.

Metal ions: the unfading stars of bone regeneration-from bone metabolism regulation to biomaterial applications

In recent years, bone regeneration has emerged as a remarkable field that offers promising guidance for treating bone-related diseases, such as bone defects, bone infections, and osteosarcoma. Among various bone regeneration approaches, the metal ion-based strategy has surfaced as a prospective candidate approach owing to the extensive regulatory role of metal ions in bone metabolism and the diversity of corresponding delivery strategies. Various metal ions can promote bone regeneration through three primary strategies: balancing the effects of osteoblasts and osteoclasts, regulating the immune microenvironment, and promoting bone angiogenesis. In the meantime, the complex molecular mechanisms behind these strategies are being consistently explored. Moreover, the accelerated development of biomaterials broadens the prospect of metal ions applied to bone regeneration. This review highlights the potential of metal ions for bone regeneration and their underlying mechanisms. We propose that future investigations focus on refining the clinical utilization of metal ions using both mechanistic inquiry and materials engineering to bolster the clinical effectiveness of metal ion-based approaches for bone regeneration.

Unraveling the potential of 3D bioprinted immunomodulatory materials for regulating macrophage polarization: State-of-the-art in bone and associated tissue regeneration

Macrophage-assisted immunomodulation is an alternative strategy in tissue engineering, wherein the interplay between pro-inflammatory and anti-inflammatory macrophage cells and body cells determines the fate of healing or inflammation. Although several reports have demonstrated that tissue regeneration depends on spatial and temporal regulation of the biophysical or biochemical microenvironment of the biomaterial, the underlying molecular mechanism behind immunomodulation is still under consideration for developing immunomodulatory scaffolds. Currently, most fabricated immunomodulatory platforms reported in the literature show regenerative capabilities of a particular tissue, for example, endogenous tissue (e.g., bone, muscle, heart, kidney, and lungs) or exogenous tissue (e.g., skin and eye). In this review, we briefly introduced the necessity of the 3D immunomodulatory scaffolds and nanomaterials, focusing on material properties and their interaction with macrophages for general readers. This review also provides a comprehensive summary of macrophage origin and taxonomy, their diverse functions, and various signal transduction pathways during biomaterial-macrophage interaction, which is particularly helpful for material scientists and clinicians for developing next-generation immunomodulatory scaffolds. From a clinical standpoint, we briefly discussed the role of 3D biomaterial scaffolds and/or nanomaterial composites for macrophage-assisted tissue engineering with a special focus on bone and associated tissues. Finally, a summary with expert opinion is presented to address the challenges and future necessity of 3D bioprinted immunomodulatory materials for tissue engineering.

HIF-1α Regulates Bone Homeostasis and Angiogenesis, Participating in the Occurrence of Bone Metabolic Diseases

In the physiological condition, the skeletal system's bone resorption and formation are in dynamic balance, called bone homeostasis. However, bone homeostasis is destroyed under pathological conditions, leading to the occurrence of bone metabolism diseases. The expression of hypoxia-inducible factor-1α (HIF-1α) is regulated by oxygen concentration. It affects energy metabolism, which plays a vital role in preventing bone metabolic diseases. This review focuses on the HIF-1α pathway and describes in detail the possible mechanism of its involvement in the regulation of bone homeostasis and angiogenesis, as well as the current experimental studies on the use of HIF-1α in the prevention of bone metabolic diseases. HIF-1α/RANKL/Notch1 pathway bidirectionally regulates the differentiation of macrophages into osteoclasts under different conditions. In addition, HIF-1α is also regulated by many factors, including hypoxia, cofactor activity, non-coding RNA, trace elements, etc. As a pivotal pathway for coupling angiogenesis and osteogenesis, HIF-1α has been widely studied in bone metabolic diseases such as bone defect, osteoporosis, osteonecrosis of the femoral head, fracture, and nonunion. The wide application of biomaterials in bone metabolism also provides a reasonable basis for the experimental study of HIF-1α in preventing bone metabolic diseases.

Spatiotemporal correlation between HIF-1α and bone regeneration

Hypoxia-inducible factors (HIFs) are core regulators of the hypoxia response. HIF signaling is activated in the local physiological and pathological hypoxic environment, acting on downstream target genes to synthesize the corresponding proteins and regulate the hypoxic stress response. HIFs belong to the hypoxia-activated transcription family and contain two heterodimeric transcription factors, HIF-α and HIF-β. Under hypoxia, the dimer formed by HIF-α binding to HIF-β translocates into the nucleus and binds to the hypoxia response element (HRE) to induce transcription of a series of genes. HIF-1α plays an important role in innate bone development and acquired bone regeneration. HIF-1α promotes bone regeneration mainly through the following two pathways: (1) By regulating angiogenesis-osteoblast coupling to promote bone regeneration; and (2) by inducing metabolic reprogramming in osteoblasts, promoting cellular anaerobic glycolysis, ensuring the energy supply of osteoblasts under hypoxic conditions, and further promoting bone regeneration and repair. This article reviews recent basic research on HIF-1α and its role in promoting osteogenesis, discusses the possible molecular mechanisms, introduces the hypoxia-independent role of HIF-1α and reviews the application prospects of HIF-1α in tissue engineering.

Lithium ion doped carbonated hydroxyapatite compositions: Synthesis, physicochemical characterisation and effect on osteogenic response in vitro

Hydroxyapatite is a commonly researched biomaterial for bone regeneration applications. To augment performance, hydroxyapatite can be substituted with functional ions to promote repair. Here, co-substituted lithium ion (Li⁺) and carbonate ion hydroxyapatite compositions were synthesised by an aqueous precipitation method. The co-substitution of Li⁺ and CO₃^2- is a novel approach that accounts for charge balance, which has been ignored in the synthesis of Li doped calcium phosphates to date. Three compositions were synthesised: Li⁺-free (Li 0), low Li⁺ (Li 0.25), and high Li⁺ (Li 1). Synthesised samples were sintered as microporous discs (70-75 % theoretical sintered density) prior to being ground and fractionated to produce granules and powders, which were then characterised and evaluated in vitro. Physical and chemical characterisation demonstrated that lithium incorporation in Li 0.25 and Li 1 samples approached design levels (0.25 and 1 mol%), containing 0.253 and 0.881 mol% Li⁺ ions, respectively. The maximum CO₃^2- ion content was observed in the Li 1 sample, with ~8 wt% CO₃, with the carbonate ions located on both phosphate and hydroxyl sites in the crystal structure. Measurement of dissolution products following incubation experiments indicated a Li⁺ burst release profile in DMEM, with incubation of 30 mg/ml sample resulting in a Li⁺ ion concentration of approximately 140 mM after 24 h. For all compositions evaluated, sintered discs allowed for favourable attachment and proliferation of C2C12 cells, human osteoblast (hOB) cells, and human mesenchymal stem cells (hMSCs). An increase in alkaline phosphatase (ALP) activity with Li⁺ doping was demonstrated in C2C12 cells and hMSCs seeded onto sintered discs, whilst the inverse was observed in hOB cells. Furthermore, an increase in ALP activity was observed in C2C12 cells and hMSCs in response to dissolution products from Li 1 samples which related to Li⁺ release. Complementary experiments to further investigate the findings from hOB cells confirmed an osteogenic role of the surface topography of the discs. This research has shown successful synthesis of Li⁺ doped carbonated hydroxyapatite which demonstrated cytocompatibility and enhanced osteogenesis in vitro, compared to Li⁺-free controls.

HIF signaling: A new propellant in bone regeneration

Bone tissue destruction leads to severe pain, physical flaws, and loss of motility. Bone repair using biocompatible and osteo-inductive scaffolds is regarded as a viable and potential therapeutic approach. However, for large-scale bone regeneration, oxygen and nutrient supply have become limiting factors. Further, a considerable need exists for recruited cell activities and blood vessel growth. Hypoxia-inducible factor (HIF) signaling pathways induced by hypoxia are involved in angiogenesis and osteogenesis. As an important transcription factor, HIF-1 functions by modulating vital genes, such as VEGF, PDK1, and EPO, and is a crucial regulator that influences the final fate of bone regeneration. Collectively, to achieve better osteogenesis results, the in-depth molecular mechanisms that underpin the links between materials, cells, and HIF signaling pathways must be determined. This review aimed to provide an in-depth insight into recent progress in HIF-regulated bone regeneration. Hypoxia and cellular oxygen-sensing mechanisms and their correlations with osteogenesis were determined, and recent studies on hypoxia-inducing and hypoxia-mimicking strategies were briefly described. Finally, the potential applications of HIF signaling in bone regeneration were highlighted. This review provides theoretical support for establishing a novel and viable bone repair strategy in the clinic by harnessing HIF signaling.

Copper-Lithium-Doped Nanohydroxyapatite Modulates Mesenchymal Stem Cells Homing to Treat Glucocorticoids-Related Osteonecrosis of the Femoral Head

In situ tissue regeneration has been demonstrated to promote bone repair. To identify a better approach for treating osteonecrosis of the femoral head (ONFH), we prepared scaffolds using copper-lithium-doped nanohydroxyapatite (Cu-Li-nHA), which has the potential to modulate mesenchymal stem cells (MSCs) homing. The scaffold was fabricated using the gas foaming method and the migration, angiogenesis, and osteogenesis activities of MSCs were detected using Transwell assays, tube formation assays, alkaline phosphatase and alizarin red S staining, respectively. We then implanted the Cu-Li-nHA scaffold into the femoral heads of ONFH rabbits, and CFSE labeled exogenous MSCs were injected intravenously to verify cell homing. The repair effect was subsequently examined using micro-CT and histological analysis in vivo. The results showed that Cu-Li-nHA significantly promoted MSCs migration and homing by upregulating the HIF-1α/SDF-1 pathway. The Cu-Li-nHA group showed optimal osteogenesis and angiogenesis and greater improvements in new bone formation in ONFH rabbits. To summarize, Cu-Li-nHA promoted homing and induced the osteogenic differentiation of MSCs, thereby enhancing bone regeneration during ONFH repair. Thus, Cu-Li-nHA implantation may serve as a potential therapeutic strategy for ONFH in the future.

Understanding Zinc-Doped Hydroxyapatite Structures Using the First-Principles Calculations and Convolutional Neural Network Algorithm

Element doping is widely used to improve the performance of materials by changing their intrinsic properties. However, the lack of direct crystallographic structures for dopants has restricted the effective high-throughput...

Delivery of MiR335-5p-Pendant Tetrahedron DNA Nanostructures Using an Injectable Heparin Lithium Hydrogel for Challenging Bone Defects in Steroid-Associated Osteonecrosis

Corticosteroids-induced Dickkopf-1 (DKK1) upregulation and Wnt signaling inhibition result in bone metabolism disorder and steroid-associated osteonecrosis (SAON). Implanting biomaterials to regulate the Wnt pathway is a promising method to repair challenging bone defects associated with SAON. Here, tetrahedral DNA nanostructures (TDNs) are fabricated as gene carriers to deliver MiR335-5p, which targets DKK1 translation. Heparin lithium hydrogel (Li-hep-gel) is synthesized to act as a lithium and MiR@TDNs delivery agent. Finally, the repair effects on challenging bone defect in SAON using a MiR@TDNs/Li-hep-gel composite are assessed in vivo. The results reveal that MiR@TDNs are absorbed by bone mesenchymal stem cells (BMSCs) and increase cell viability and reduce apoptosis. Moreover, MiR@TDNs promote alkaline phosphatase expression and calcium nodular deposition, decrease lipid droplet expression of BMSCs, and improve vascular endothelial growth factor secretion and vascular-like structure formation in vitro. After MiR@TDNs/Li-hep-gel is implanted into the SAON model, the internal bone defect of osteonecrosis is repaired with a large area of new bone accompanied with neovascularization and reduced empty lacunae. In conclusion, MiR@TDNs/Li-hep-gel can provide dual delivery of lithium and MiR@TDNs, which synergistically upregulate the Wnt signaling pathway, enhancing bone regeneration in challenging bone defects, and can be potentially used in SAON repair.

Porous copper- and lithium-doped nano-hydroxyapatite composite scaffold promotes angiogenesis and bone regeneration in the repair of glucocorticoids-induced osteonecrosis of the femoral head

Glucocorticoids-induced osteonecrosis of the femoral head (GIONFH) is a common refractory disease. In the present study, we aimed to synthesize the nano-hydroxyapatite-copper-lithium (Cu-Li-nHA) composite porous scaffold to promote osteogenesis and angiogenesis functions to repair GIONFH by regulating the Wnt/β-catenin and HIF-1α/VEGF pathways. The physicochemical property of the scaffold was characterized and their osteogenic and angiogenic effects were tested through a serial of experimentsin vitroandin vivo. Results showed that 0.25% Cu-Li-nHA scaffolds possessed the highest mechanical and biocompatibilityin vitro. Then the 0.25% Cu-Li-nHA scaffolds significantly enhanced the new bone formation on defects in GIONFH rabbitsin vivo. Moreover, the scaffold could increase the expression of osteogenic and angiogenic factors along with the activation of factors in Wnt/β-catenin and HIF-1α/VEGF pathwaysin vitroandin vivo. In conclusion, the 0.25% Cu-Li-nHA scaffold could improve the osteogenesis and angiogenesis by upregulating the Wnt/β-catenin and HIF-1α/VEGF pathways which benefited to repair the GIONFH in rabbit models.

A bone regeneration strategy via dual delivery of demineralized bone matrix powder and hypoxia-pretreated bone marrow stromal cells using an injectable self-healing hydrogel

Demineralized bone matrix (DBM) powder is a potential alternative bone grafting material due to its bone regeneration capacity when the supply of autogenous bone is insufficient. However, the use of DBM powder alone remains challenging in many aspects in the clinic, such as its unstable osteoinductivity due to inactivation of growth factors during the preparation process, lack of bone regeneration cells, and difficulty in handling. Herein, we report a strategy that adopts a dual delivery of DBM powder and hypoxia-pretreated bone marrow stromal cells (BMSCs) using an injectable self-healing hydrogel to enhance bone regeneration and repair a cranial bone defect in a rabbit model. The injectable self-healing hydrogel was prepared based on a double crosslinking architecture, which comprised a dynamically cross-linked Schiff-base network as a self-healing component and a borax ion cross-linked physical network that strengthened its mechanical properties. The handling of the DBM powder was improved by mixing with the hydrogel, and, more importantly, the expression of osteocalcin (OCN) and vascular endothelial growth factor (VEGF) of the encapsulated BMSCs in the hydrogel was significantly up-regulated after hypoxia-pretreatment. The in vivo study demonstrated that the use of the hydrogel alone cannot heal the cranial bone defect, while the hydrogel/BMSC composite could increase the bone formation but was inferior to the hydrogel/DBM composite. Finally, the hydrogel/DBM/BMSC composite exhibited the best bone defect repairing effects among all groups. Overall, our results demonstrate that this dual delivery approach is a promising strategy to enhance bone regeneration for bone defect repair.

Hypoxia Enhanced Bone Regeneration Through the HIF-1α/β-Catenin Pathway in Femoral Head Osteonecrosis

BACKGROUND

Osteonecrosis of the femoral head (ONFH) is a common disease. Transplantation of bone marrow stem cells (BMSCs) is a promising method to treat ONFH but is impeded by the low survival rate and deficiency of cell bioactivity.

METHODS

We performed hypoxic preprocessing to treat BMSCs and assessed cell viability, apoptosis, differentiation, and growth factor expression in vitro. Subsequently, we constructed the ONFH model and delivered hypoxia-pretreated BMSCs to the rabbit femoral head after core decompression surgery, evaluating its effects on bone regeneration and ONFH repair. Six weeks later, micro-computed tomography (CT) and histopathology were performed to evaluate ONFH repair.

RESULTS

Our findings demonstrated that hypoxic preprocessing promoted the viability of BMSCs, increased the expression of hypoxia-inducible factor-1 alpha (HIF-1α), vascular endothelial growth factor (VEGF), alkaline phosphatase (ALP), calcium deposition, and enhanced the formation of vessels-shaped structures. In an in vivo study, micro-CT observations demonstrated that the bone volume was increased in the hypoxia BMSCs group. Histological examination revealed reduced cellular apoptosis, lower empty lacunae rate, enhanced bone formation, and stronger trabecular bone in the hypoxia BMSCs group when compared with those transplanted with normoxia treated BMSCs. Additionally, immunological assessment of the hypoxia BMSCs group demonstrated increased expression of HIF-1α and β-catenin, as well as increased VEGF, ALP, osteocalcin (OCN), and collagen type I (Col-1).

CONCLUSIONS

Collectively, our findings indicated that hypoxia stimulated angiogenesis and bone regeneration via the HIF-1/β-catenin pathway in BMSCs and that the delivery of hypoxia-pretreated BMSCs contributed to the treatment of early ONFH.

Lithium and Copper Induce the Osteogenesis-Angiogenesis Coupling of Bone Marrow Mesenchymal Stem Cells via Crosstalk between Canonical Wnt and HIF-1α Signaling Pathways

The combination of osteogenesis and angiogenesis dual-delivery trace element-carrying bioactive scaffolds and stem cells is a promising method for bone regeneration and repair. Canonical Wnt and HIF-1α signaling pathways are vital for BMSCs' osteogenic differentiation and secretion of osteogenic factors, respectively. Simultaneously, lithium (Li) and copper (Cu) can activate the canonical Wnt and HIF-1α signaling pathway, respectively. Moreover, emerging evidence has shown that the canonical Wnt and HIF signaling pathways are related to coupling osteogenesis and angiogenesis. However, it is still unclear whether the lithium- and copper-doped bioactive scaffold can induce the coupling of the osteogenesis and angiogenesis in BMSCs and the underlying mechanism. So, we fabricated a lithium- (Li⁺-) and copper- (Cu²⁺-) doped organic/inorganic (Li 2.5-Cu 1.0-HA/Col) scaffold to evaluate the coupling osteogenesis and angiogenesis effects of lithium and copper on BMSCs and further explore its mechanism. We investigated that the sustained release of lithium and copper from the Li 2.5-Cu 1.0-HA/Col scaffold could couple the osteogenesis- and angiogenesis-related factor secretion in BMSCs seeding on it. Moreover, our results showed that 500 μM Li⁺ could activate the canonical Wnt signaling pathway and rescue the XAV-939 inhibition on it. In addition, we demonstrated that the 25 μM Cu²⁺ was similar to 1% oxygen environment in terms of the effectiveness of activating the HIF-1α signaling pathway. More importantly, the combination stimuli of Li⁺ and Cu²⁺ could couple the osteogenesis and angiogenesis process and further upregulate the osteogenesis- and angiogenesis-related gene expression via crosstalk between the canonical Wnt and HIF-1α signaling pathway. In conclusion, this study revealed that lithium and copper could crosstalk between the canonical Wnt and HIF-1α signaling pathways to couple the osteogenesis and angiogenesis in BMSCs when they are sustainably released from the Li-Cu-HA/Col scaffold.

Biological Roles and Delivery Strategies for Ions to Promote Osteogenic Induction

Bone is the most studied tissue in the field of tissue regeneration. Even though it has intrinsic capability to regenerate upon injury, several pathologies and injuries could hamper the highly orchestrated bone formation and resorption process. Bone tissue engineering seeks to mimic the extracellular matrix of the tissue and the different biochemical pathways that lead to successful regeneration. For many years, the use of extrinsic factors (i.e., growth factors and drugs) to modulate these biological processes have been the preferred choice in the field. Even though it has been successful in some instances, this approach presents several drawbacks, such as safety-concerns, short release profile and half-time life of the compounds. On the other hand, the use of inorganic ions has attracted significant attention due to their therapeutic effects, stability and lower biological risks. Biomaterials play a key role in such strategies where they serve as a substrate for the incorporation and release of the ions. In this review, the methodologies used to incorporate ions in biomaterials is presented, highlighting the osteogenic properties of such ions and the roles of biomaterials in controlling their release.

Therapeutic Metallic Ions in Bone Tissue Engineering: A Systematic Review of The Literature

An important field of bone tissue engineering (BTE) concerns the design and fabrication of smart scaffolds capable of inducing cellular interactions and differentiation of osteo-progenitor cells. One of these additives that has gained growing attention is metallic ions as therapeutic agents (MITAs). The specific biological advantage that these ions bring to scaffolds as well as other potential mechanical, and antimicrobial enhancements may vary depending on the ion entity, fabrication method, and biomaterials used. Therefore, this article provides an overview on current status of In-vivo application of MITAs in BTE and the remaining challenges in the field. Electronic databases, including PubMed, Scopus, Science direct and Cochrane library were searched for studies on MITAs treatments for BTE. We searched for articles in English from January-2000 to October-2019. Abstracts, letters, conference papers and reviews, In-vitro studies, studies on alloys and studies investigating effects other than enhancement of new bone formation (NBF) were excluded. A detailed summary of relevant metallic ions with specific scaffold material and design, cell type, animal model and defect type, the implantation period, measured parameters and obtained qualitative and quantitative results is presented. No ideal material or fabrication method suited to deliver MITAs can yet be agreed upon, but an investigation into various systems and their drawbacks or potential advantages can lead the future research. A tendency to enhance NBF with MITAs can be observed in the studies. However, this needs to be validated with further studies comparing various ions with each other in the same animal model using critical-sized defects.

Engineered three-dimensional scaffolds for enhanced bone regeneration in osteonecrosis

Osteonecrosis, which is typically induced by trauma, glucocorticoid abuse, or alcoholism, is one of the most severe diseases in clinical orthopedics. Osteonecrosis often leads to joint destruction, and arthroplasty is eventually required. Enhancement of bone regeneration is a critical management strategy employed in osteonecrosis therapy. Bone tissue engineering based on engineered three-dimensional (3D) scaffolds with appropriate architecture and osteoconductive activity, alone or functionalized with bioactive factors, have been developed to enhance bone regeneration in osteonecrosis. In this review, we elaborate on the ideal properties of 3D scaffolds for enhanced bone regeneration in osteonecrosis, including biocompatibility, degradability, porosity, and mechanical performance. In addition, we summarize the development of 3D scaffolds alone or functionalized with bioactive factors for accelerating bone regeneration in osteonecrosis and discuss their prospects for translation to clinical practice.

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Engineered three-dimensional scaffolds boost bone regeneration in osteonecrosis.

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The ideal properties of three-dimensional scaffolds for osteonecrosis treatment are discussed.

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Bioactive factors-functionalized three-dimensional scaffolds are promising bone regeneration devices for osteonecrosis management.

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The challenges and opportunities of engineered three-dimensional scaffolds for osteonecrosis therapy are predicted.

Evaluation of the degradation, biocompatibility and osteogenesis behavior of lithium-doped calcium polyphosphate for bone tissue engineering

BACKGROUND

Calcium polyphosphate (CPP) is a commonly used biomaterial in bone tissue engineering, but CPP is insufficient in osteoinduction. This study aimed to fabricate lithium doped CPP (LiCPP) scaffolds and assess their characterization, degradation, biocompatibility and osteogenesis behavior for bone tissue engineering.

METHODS

The novel scaffold was characterized by XRD, FTIR and SEM. The porosity, cell mediated degradation behavior and mechanical properties were also investigated. Meanwhile, cell proliferation activity and adhesion in vitro was exploited. Finally, osteogenesis the LiCPP scaffolds in vitro and in vivo was researched.

RESULTS

The outcomes revealed that low-content Li doping had no significant influence on the structure of CPP. The results of cells mediated degradation experiments from the weight loss and the release of ions indicated that Li doped CPP improved biological degradation. The compressive strength of CPP with 66% porosity was improved to 7 MPa. Cells proliferation experiment and adhesion experiment demonstrated 2.0%LiCPP scaffold was most beneficial to cell growth and attachment. Furthermore, Li doped CPP up-regulated Wnt signal pathway when co-cultured with MG63 and increased osteogenic marker ALP expression and calcium phosphate deposition in vitro. At the same time, new bone formation in vivo was also enhanced by using LiCPP scaffolds and the 2.0%LiCPP scaffolds obtained best osteogenesis outcomes.

CONCLUSION

The results obtained in our study suggest that 2.0%LiCPP scaffold could benefit from improving the osteogenesis behavior and is a promising biomaterial for bone repairing applications.

Comprehensive In Vitro Testing of Calcium Phosphate-Based Bioceramics with Orthopedic and Dentistry Applications

Recently, a large spectrum of biomaterials emerged, with emphasis on various pure, blended, or doped calcium phosphates (CaPs). Although basic cytocompatibility testing protocols are referred by International Organization for Standardization (ISO) 10993 (parts 1-22), rigorous in vitro testing using cutting-edge technologies should be carried out in order to fully understand the behavior of various biomaterials (whether in bulk or low-dimensional object form) and to better gauge their outcome when implanted. In this review, current molecular techniques are assessed for the in-depth characterization of angiogenic potential, osteogenic capability, and the modulation of oxidative stress and inflammation properties of CaPs and their cation- and/or anion-substituted derivatives. Using such techniques, mechanisms of action of these compounds can be deciphered, highlighting the signaling pathway activation, cross-talk, and modulation by microRNA expression, which in turn can safely pave the road toward a better filtering of the truly functional, application-ready innovative therapeutic bioceramic-based solutions.

Icariin-loaded porous scaffolds for bone regeneration through the regulation of the coupling process of osteogenesis and osteoclastic activity

Objective

Icariin (IC) promotes osteogenic differentiation, and it may be a potential small molecule drug for local application in bone regeneration. Icariin-loaded hydroxyapatite/alginate (IC/HAA) porous composite scaffolds were designed in this study for the potential application of the sustainable release of icariin and subsequent bone regeneration.

Methods

An icariin-loaded hydroxyapatite/alginate porous composite scaffold was prepared and characterized by SEM and HPLC for morphology and release behavior, respectively. The mechanical properties, degradation in PBS and cytotoxicity on BMSCs were also evaluated by MTT assay, compression strength and calculation of weight remaining ratio, respectively. Rabbit BMSCs were cocultured with IC/HAA scaffolds, and ALP activity and Alizarin Red staining were performed to evaluate osteogenic differentiation induction. The mRNA and protein expression level of an osteogenic gene was detected by RT-PCR and Western blotting, respectively. In vivo animal models of critical bone defects in the radius of rabbit were used. Four and 12 weeks after the implantation of IC/HAA scaffolds in the bone defect, radiographic images of the radius were obtained and scored by using the Lane and Sandhu X-ray scoring system. Tissue samples were also evaluated using H&E and Masson staining, and an osteogenic gene and Wnt signaling pathway genes were detected.

Results

A hydroxyapatite/alginate (HAA) porous composite scaffold-loaded icariin was fabricated using a freeze-drying method. Our data indicated that the icariin was loaded in alginate scaffold without compromising the macro/microstructure or mechanical properties of the scaffold. Notably, the IC/HAA promoted the proliferation of rBMSCs without exerting cytotoxicity on rBMSCs. In vivo, rabbit radius bone defect experiments demonstrated that the IC/HAA scaffold exhibited better capacity for bone regeneration than HAA, and IC/HAA upregulated the relative expression levels of an osteogenic gene and the Wnt signaling pathway genes. Most notably, the IC/HAA scaffold also inhibited osteoclast activity in vivo.

Conclusion

Our data suggests a promising application for the use of HAA scaffolds to load icariin and promote bone regeneration in situ through mediation of the coupling processes of osteogenesis induction and osteoclast activity inhibition.

Cationic Substitutions in Hydroxyapatite: Current Status of the Derived Biofunctional Effects and Their In Vitro Interrogation Methods

High-performance bioceramics are required for preventing failure and prolonging the life-time of bone grafting scaffolds and osseous implants. The proper identification and development of materials with extended functionalities addressing socio-economic needs and health problems constitute important and critical steps at the heart of clinical research. Recent findings in the realm of ion-substituted hydroxyapatite (HA) could pave the road towards significant developments in biomedicine, with an emphasis on a new generation of orthopaedic and dentistry applications, since such bioceramics are able to mimic the structural, compositional and mechanical properties of the bone mineral phase. In fact, the fascinating ability of the HA crystalline lattice to allow for the substitution of calcium ions with a plethora of cationic species has been widely explored in the recent period, with consequent modifications of its physical and chemical features, as well as its functional mechanical and in vitro and in vivo biological performance. A comprehensive inventory of the progresses achieved so far is both opportune and of paramount importance, in order to not only gather and summarize information, but to also allow fellow researchers to compare with ease and filter the best solutions for the cation substitution of HA-based materials and enable the development of multi-functional biomedical designs. The review surveys preparation and synthesis methods, pinpoints all the explored cation dopants, and discloses the full application range of substituted HA. Special attention is dedicated to the antimicrobial efficiency spectrum and cytotoxic trade-off concentration values for various cell lines, highlighting new prophylactic routes for the prevention of implant failure. Importantly, the current in vitro biological tests (widely employed to unveil the biological performance of HA-based materials), and their ability to mimic the in vivo biological interactions, are also critically assessed. Future perspectives are discussed, and a series of recommendations are underlined.