Recent advances of bone tissue engineering: carbohydrate and ceramic materials, fundamental properties and advanced biofabrication strategies ‒ a comprehensive review.

Bone is a dynamic tissue that can always regenerate itself through remodeling to maintain biofunctionality. This tissue performs several vital physiological functions. However, bone scaffolds are required for critical-size damages and fractures, and these can be addressed by bone tissue engineering. Bone tissue engineering (BTE) has the potential to develop scaffolds for repairing critical-size damaged bone. BTE is a multidisciplinary engineered scaffold with the desired properties for repairing damaged bone tissue. Herein, we have provided an overview of the common carbohydrate polymers, fundamental structural, physicochemical, and biological properties, and fabrication techniques for bone tissue engineering. We also discussed advanced biofabrication strategies and provided the limitations and prospects by highlighting significant issues in bone tissue engineering. There are several review articles available on bone tissue engineering. However, we have provided a state-of-the-art review article that discussed recent progress and trends within the last 3-5 years by emphasizing challenges and future perspectives.

The effect of a bionic bone ionic environment on osteogenesis, osteoimmunology, and in situ bone tissue engineering.

Bone, a mineralized tissue, continuously undergoes remodeling. It is a process that engages the mineralization and demineralization of the bone matrix, orchestrated by the interactions among cells and cell-secreted biomolecules under the bone ionic microenvironment (BIE). The osteoinductive properties of the demineralized organic bone matrix and many biological factors have been well-investigated. However, the impact of the bone ionic environment on cell differentiation and osteogenesis remains largely unknown. In this study, we extracted and isolated inorganic bone components (bone-derived monetite, BM) using a low-temperature method and, for the first time, investigated whether the BIE could actively affect cell differentiation and regulate osteoimmune reactions. It was evidenced that the BIE could foster the osteogenesis of human bone marrow stromal cells (hBMSCs) and promote hBMSCs mineralization without using osteogenic inductive agents. Interestingly, it was noted that BIE resulted in intracellular mineralization, evidenced by intracellular accumulation of carbonate hydroxyapatite similar to that oberved in osteoblasts cultured in osteoinductive media. Additionally, BIE was found to enhance osteogenesis by generating a favorable osteoimmune environment. In a rat calvarial bone defect model, the osteogenic capacity of BIE was evaluated using a collagen type I-impregnated BM (Col-BM) composite. It showed that Col-BM significantly promoted new bone formation in the critical-size bone defect areas. Taken together, this is the first study that investigated the influence of the BIE on osteogenesis, osteoimmunology, and in situ bone tissue engineering. The innate osteoinductive potential of inorganic bone components, both in vitro and in vivo, not only expands the understanding of the BIE on osteogenesis but also benefits future biomaterials engineering for bone tissue regeneration.

Accuracy of baseline low-dose computed tomography lung cancer screening: a systematic review and meta-analysis.

BACKGROUND: Screening using low-dose computed tomography (LDCT) is a more effective approach and has the potential to detect lung cancer more accurately. We aimed to conduct a meta-analysis to estimate the accuracy of population-based screening studies primarily assessing baseline LDCT screening for lung cancer. METHODS: MEDLINE, Excerpta Medica Database, and Web of Science were searched for articles published up to April 10, 2022. According to the inclusion and exclusion criteria, the data of true positives, false-positives, false negatives, and true negatives in the screening test were extracted. Quality Assessment of Diagnostic Accuracy Studies-2 was used to evaluate the quality of the literature. A bivariate random effects model was used to estimate pooled sensitivity and specificity. The area under the curve (AUC) was calculated by using hierarchical summary receiver-operating characteristics analysis. Heterogeneity between studies was measured using the Higgins I2 statistic, and publication bias was evaluated using a Deeks' funnel plot and linear regression test. RESULTS: A total of 49 studies with 157,762 individuals were identified for the final qualitative synthesis; most of them were from Europe and America (38 studies), ten were from Asia, and one was from Oceania. The recruitment period was 1992 to 2018, and most of the subjects were 40 to 75 years old. The analysis showed that the AUC of lung cancer screening by LDCT was 0.98 (95% CI: 0.96-0.99), and the overall sensitivity and specificity were 0.97 (95% CI: 0.94-0.98) and 0.87 (95% CI: 0.82-0.91), respectively. The funnel plot and test results showed that there was no significant publication bias among the included studies. CONCLUSIONS: Baseline LDCT has high sensitivity and specificity as a screening technique for lung cancer. However, long-term follow-up of the whole study population (including those with a negative baseline screening result) should be performed to enhance the accuracy of LDCT screening.

The Localized Ionic Microenvironment in Bone Modelling/Remodelling: A Potential Guide for the Design of Biomaterials for Bone Tissue Engineering.

Bone is capable of adjusting size, shape, and quality to maintain its strength, toughness, and stiffness and to meet different needs of the body through continuous remodeling. The balance of bone homeostasis is orchestrated by interactions among different types of cells (mainly osteoblasts and osteoclasts), extracellular matrix, the surrounding biological milieus, and waste products from cell metabolisms. Inorganic ions liberated into the localized microenvironment during bone matrix degradation not only form apatite crystals as components or enter blood circulation to meet other bodily needs but also alter cellular activities as molecular modulators. The osteoinductive potential of inorganic motifs of bone has been gradually understood since the last century. Still, few have considered the naturally generated ionic microenvironment's biological roles in bone remodeling. It is believed that a better understanding of the naturally balanced ionic microenvironment during bone remodeling can facilitate future biomaterial design for bone tissue engineering in terms of the modulatory roles of the ionic environment in the regenerative process.

Osteoimmunomodulatory Nanoparticles for Bone Regeneration.

Treatment of large bone fractures remains a challenge for orthopedists. Bone regeneration is a complex process that includes skeletal cells such as osteoblasts, osteoclasts, and immune cells to regulate bone formation and resorption. Osteoimmunology, studying this complicated process, has recently been used to develop biomaterials for advanced bone regeneration. Ideally, a biomaterial shall enable a timely switch from early stage inflammatory (to recruit osteogenic progenitor cells) to later-stage anti-inflammatory (to promote differentiation and terminal osteogenic mineralization and model the microstructure of bone tissue) in immune cells, especially the M1-to-M2 phenotype switch in macrophage populations, for bone regeneration. Nanoparticle (NP)-based advanced drug delivery systems can enable the controlled release of therapeutic reagents and the delivery of therapeutics into specific cell types, thereby benefiting bone regeneration through osteoimmunomodulation. In this review, we briefly describe the significance of osteoimmunology in bone regeneration, the advancement of NP-based approaches for bone regeneration, and the application of NPs in macrophage-targeting drug delivery for advanced osteoimmunomodulation.

Liujunzi decoction exerts potent antitumor activity in oesophageal squamous cell carcinoma by inhibiting miR-34a/STAT3/IL-6R feedback loop, and modifies antitumor immunity.

BACKGROUND: Liujunzi decoction (LJZD), a traditional herbal formula and one of the most commonly used adjuvant medications for the treatment of oesophageal squamous cell carcinoma (ESCC), exerts good antitumor and immunomodulatory activity. However, its specific mechanism of action remains largely unclear. PURPOSE: In order to examine the potential primary and adjuvant antitumor mechanisms of LJZD, both in vitro and in vivo. METHODS: IL-6 and miR-34a inhibitors were used to activate the miR-34a/STAT3/IL-6R feedback loop to observe the effects of LJZD. A humanised mouse model with a functional human immune system was constructed to evaluate the antitumor efficacy of LJZD in vivo on xenograft tumours, which was compared to that of the positive control drug anti-PD-1 monoclonal antibodies (mAb). Finally, a co-culture system of peripheral blood mononuclear and tumour cells in vitro was used to analyse the cytotoxic activity of LJZD on T cells. RESULTS: LJZD significantly interfered with IL-6-induced activation of the miR-34a/STAT3/IL-6R feedback loop in ESCC by restoring the expression of the tumour suppressor miR-34a, and inhibited the proliferation of EC109 oesophageal cancer cells in a dose-dependant manner. Furthermore, LJZD effectively suppressed oesophageal tumour growth in vivo and alleviated organ injury and visceral index. Furthermore, LJZD boosted antitumor immunity by increasing IFN-γ expression and CD8+tumour-infiltrating lymphocytes (TILs) infiltration in the peripheral blood and tumour tissues, respectively, which may be related to a decrease in PD-1, but not PD-L1 expression. Finally, we confirmed that LJZD strengthens the killing ability of T cells by suppressing PD-1 expression in a co-culture system in vitro. CONCLUSION: LJZD exerts excellent antitumor effect by interfering with the miR-34a/STAT3/IL-6R feedback loop and augmenting antitumor immune responses. Which provides new insights into mechanisms for LJZD and sheds light on the multifaceted role of phytomedicine in cancer.

A New Sono-Chemo Sensitizer Overcoming Tumor Hypoxia for Augmented Sono/Chemo-Dynamic Therapy and Robust Immune-Activating Response.

Novel sonosensitizers with intrinsic characteristics for tumor diagnosis, efficient therapy, and tumor microenvironment regulation are appealing in current sonodynamic therapy. Herein, a manganese (Mn)-layered double hydroxide-based defect-rich nanoplatform is presented as a new type of sono-chemo sensitizer, which allows ultrasound to efficiently trigger reactive oxygen species generation for enhanced sono/chemo-dynamic therapy. Moreover, such a nanoplatform is able to relieve tumor hypoxia and achieve augmented singlet oxygen production via catalyzing endogenous H2 O2 into O2 . On top of these actions, the released Mn2+ ions and immune-modulating agent significantly intensify immune activation and reverse the immunosuppressive tumor microenvironment to the immunocompetent one. Consequently, this nanoplatform exhibits excellent anti-tumor efficacy and effectively suppresses both primary and distant tumor growth, demonstrating a new strategy to functionalize nanoparticles as sono-chemo sensitizers for synergistic combination cancer therapy.

Current Advances in 3D Dynamic Cell Culture Systems.

The traditional two-dimensional (2D) cell culture methods have a long history of mimicking in vivo cell growth. However, these methods cannot fully represent physiological conditions, which lack two major indexes of the in vivo environment; one is a three-dimensional 3D cell environment, and the other is mechanical stimulation; therefore, they are incapable of replicating the essential cellular communications between cell to cell, cell to the extracellular matrix, and cellular responses to dynamic mechanical stimulation in a physiological condition of body movement and blood flow. To solve these problems and challenges, 3D cell carriers have been gradually developed to provide a 3D matrix-like structure for cell attachment, proliferation, differentiation, and communication in static and dynamic culture conditions. 3D cell carriers in dynamic culture systems could primarily provide different mechanical stimulations which further mimic the real in vivo microenvironment. In this review, the current advances in 3D dynamic cell culture approaches have been introduced, with their advantages and disadvantages being discussed in comparison to traditional 2D cell culture in static conditions.

O2-Supplying Nanozymes Alleviate Hypoxia and Deplete Lactate to Eliminate Tumors and Activate Antitumor Immunity.

Direct hypoxia alleviation and lactate depletion in the tumor microenvironment (TME) are promising for effective cancer therapy but still very challenging. To address this challenge, the current research directly reshapes the TME for inhibiting tumor growth and activating the antitumor immunity using a drug-free nanozyme. Herein, the acid-sensitive nanozymes were constructed based on peroxidized layered double hydroxide nanoparticles for O2 self-supply and self-boosted lactate depletion. The coloading of partially cross-linked catalase and lactate oxidase enabled the acid-sensitive nanozymes to promote three reactions, that is, (1) H2O2 generation from MgO2 hydrolysis (30% at pH 7.4 vs 63% at pH 6.0 in 8 h); (2) O2 generation from H2O2 (12% at pH 7.4 vs 21% at pH 6.0 in 2 h); and (3) lactate depletion by in situ generated O2 (50% under hypoxia vs 75% under normoxia in 24 h in vitro) in parallel or tandem. These promoted reactions together efficiently induced colon cancer cell apoptosis under the hypoxic conditions, significantly inhibited tumor growth (>95%), and suppressed distant tumor growth upon seven administrations in every 3 days and moreover transformed the immunosuppressive tumor into "hot" one in the colon tumor-bearing mouse model. This is the first example for a nanozyme that supplies sufficient O2 for hypoxia relief and lactate depletion, thus providing a new insight into drug-free nanomaterial-mediated TME-targeted cancer therapy.

Targeting macrophage endocytosis via platelet membrane coating for advanced osteoimmunomodulation.

The identification, uptake, and clearance of nanoparticles (NPs) by phagocytes are critical in NP-based therapeutics. The cell membrane coating technique has recently emerged as an ideal surface modification approach to help NP bypass phagocytosis. CD47, a regulatory protein for phagocytosis, is a cell surface glycoprotein expressed on all cell types, including platelets. Herein, we enclosed bioactive glass (BG) with a platelet membrane to bestow BG with unique cell surface functions for immune evasion and immunomodulation. Compared with the uncoated particles, platelet membrane-coated BG shows reduced cellular uptake and can generate an immune environment favorable for osteogenesis. This is evidenced by the triggering of robust osteogenic differentiation in bone mesenchymal stromal cells, suggesting the synergistic effect of platelet membrane and BG in bone regeneration. These collectively indicate that cell membrane coating is a promising approach to enhance the therapeutic efficacy of biomaterials and thus provide new insight into biomaterial-mediated bone regeneration.

The Hollow Porous Sphere Cell Carrier for the Dynamic Three-Dimensional Cell Culture.

Large-scale mammalian cell culture is essential in cell therapy, vaccine production, and the manufacturing of therapeutic protein drugs. Due to the adherent growth characteristic of most mammalian cell types, the combination of cell carrier and bioreactor is a common choice in large-scale mammalian cell culture. Current cell carriers developed by polymer crosslinking, lithography, or emulsion drops are unable to obtain a structure with uniformed porous structure and porous interior design, which results in an inhomogeneous culture condition for cells and therefore cannot ensure an optimal dynamic culture condition for cell proliferation, matrix production, and cell differentiation. In addition, the fluidic shear stress (a standard mechanical stimulation in bioreactor culture) and inner-carrier velocity (to ensure nutrient transport and waste exchange), which influence cell viability and growth, are not well-controlled/analyzed due to an irregular porous structure with these traditionally synthesized cell carriers. To solve these problems, we designed four types of hollow porous spheres (HPS, 1.0 cm diameter) with different porous structures. To investigate the impacts of porous structure on surface shear stress and inner velocity, computational fluid dynamics (CFD) simulations were conducted to analyze the liquid flow behavior in HPSs, based on which an optimal structure with minimal surface shear stress and best inner velocity was obtained and fabricated using fused deposition modeling three-dimensional (3D) printing technology. Inspired by the industrial large-scale culture system, a novel 3D dynamic culture system was then established using HPSs to seed the cells, which were then placed in a mini bioreactor on a tube roller. CFD analysis showed that under 0.1 m/s water flow, the shear stress at most surface areas from four HPSs was lower than 20 dynes/cm2, which suggests that the HPSs should provide protection against physical stress to the cells living on the scaffold surface. A dynamic cell seeding was developed and refined using the 3D culture system, which increased the 32% seeding efficiency of MC3T3 cells compared to the traditional static cell seeding method. The cell proliferation analysis demonstrated that HPSs could speed up cell growth in dynamic cell culture. The HPS with a honeycomb-like structure showed the highest inner pore velocity (CFD analysis) and achieved the fastest cell proliferation and the highest cell viability. Overall, our study, for the first time, developed a 3D printed HPS cell culture device with a uniformed porous structure, which can effectively facilitate cell adhesion and proliferation in the dynamic cultural environment, thereby could be considered an ideal carrier candidate.

Corrigendum: Micro-Nano Bioactive Glass Particles Incorporated Porous Scaffold for Promoting Osteogenesis and Angiogenesis in vitro.

[This corrects the article DOI: 10.3389/fchem.2019.00186.].

Current Development of Nano-Drug Delivery to Target Macrophages.

Macrophages are the most important innate immune cells that participate in various inflammation-related diseases. Therefore, macrophage-related pathological processes are essential targets in the diagnosis and treatment of diseases. Since nanoparticles (NPs) can be preferentially taken up by macrophages, NPs have attracted most attention for specific macrophage-targeting. In this review, the interactions between NPs and the immune system are introduced to help understand the pharmacokinetics and biodistribution of NPs in immune cells. The current design and strategy of NPs modification for specific macrophage-targeting are investigated and summarized.

Bioactive glass activates VEGF paracrine signaling of cardiomyocytes to promote cardiac angiogenesis.

The heart contains a wide range of cell types, which are not isolated but interact with one another via multifarious paracrine, autocrine and endocrine factors. In terms of cardiac angiogenesis, previous studies have proved that regulating the communication between cardiomyocytes and endothelial cells is efficacious to promote capillary formation. Firstly, this study investigated the effect and underlying mechanism of bioactive glass (BG) acted on vascular endothelial growth factor (VEGF) paracrine signaling in cardiomyocytes. We found that bioactive ions released from BG significantly promoted the VEGF production and secretion of cardiomyocytes. Subsequently, we proved that cardiomyocyte-derived VEGF played an important role in mediating the behavior of endothelial cells. Further research showed that the phosphoinositide 3-kinase (PI3K)/protein kinase B (Akt)/hypoxia-inducible factor 1α (HIF-1α) signaling pathway was upregulated by BG, which was involved in VEGF expression of cardiomyocytes. This study revealed that by means of modulating cellular crosstalk via paracrine signaling of host cells in heart is a new direction for the application of BGs in cardiac angiogenesis.

Macrophages at Low-Inflammatory Status Improved Osteogenesis via Autophagy Regulation.

Accumulating evidence indicates that the interaction between immune and skeletal systems is vital in bone homeostasis. However, the detailed mechanisms between macrophage polarization and osteogenic differentiation of mesenchymal stromal cells (bone marrow-derived stromal cells [BMSCs]) remain largely unknown. We observed enhanced macrophage infiltration along with bone formation in vivo, which showed a transition from early-stage M1 phenotype to later stage M2 phenotype, cells at the transitional stage expressed both M1 and M2 markers that actively participated in osteogenesis, which was mimicked by stimulating macrophages with lower inflammatory stimulus (compared with typical M1). Using conditioned medium (CM) from M0, typical M1, low-inflammatory M1 (M1semi), and M2 macrophages, it was found that BMSCs treated with M1semi CM showed significantly induced migration, osteogenic differentiation, and mineralization, compared with others. Along with the induced osteogenesis, the autophagy level was the highest in M1semi CM-treated BMSCs, which was responsible for BMSC migration and osteogenic differentiation, as autophagy interruption significantly abolished this effect. This study indicated that low-inflammatory macrophages could activate autophagy in BMSCs to improve osteogenesis.

Coaxial nanofibrous scaffolds mimicking the extracellular matrix transition in the wound healing process promoting skin regeneration through enhancing immunomodulation.

Numerous studies have shown that scaffolds incorporated with extracellular matrix (ECM) proteins could regulate cell behaviors and improve wound healing. However, most ECM-containing scaffolds fail to capture the dynamic features of the native ECM. In this regard, nanofibrous scaffolds which mimic the composition transition of the ECM during wound healing may have great potential in promoting skin regeneration through dynamically modulating the microenvironment. Herein, we report a novel skin ECM-biomimetic coaxial nanofibrous scaffold for the repair of chronic wounds. Two essential ECM proteins, fibrinogen and collagen I, were incorporated into the shell and the core of nanofibers, respectively, to mimic the sequential appearance of fibrinogen and collagen I in the wound healing process. The regulation of the biomimetic coaxial scaffolds on adipose-derived mesenchymal stromal cells (ASCs) was compared with that of the PLGA/fibrinogen, PLGA/collagen I and PLGA uniaxial scaffolds. Our results showed that the biomimetic coaxial scaffolds remarkably promoted the immunomodulatory paracrine secretion of ASCs. By incubating macrophages with ASC conditioned medium, the enhanced immunomodulation of ASCs on the biomimetic coaxial scaffolds was confirmed by the enhanced M1-to-M2 polarization of macrophages. Furthermore, the biomimetic coaxial scaffolds effectively promoted wound repair through resolving inflammation in diabetic rats. These findings helped reveal the role of the dynamic ECM change in regulating wound healing and suggest the potential utility of the biomimetic coaxial scaffolds as a promising alternative to treat chronic wounds.

Strontium-substituted sub-micron bioactive glasses inhibit ostoclastogenesis through suppression of RANKL-induced signaling pathway.

Strontium-substituted bioactive glass (Sr-BG) has shown superior performance in bone regeneration. Sr-BG-induced osteogenesis has been extensively studied; however, Sr-BG-mediated osteoclastogenesis and the underlying molecular mechanism remain unclear. It is recognized that the balance of osteogenesis and osteoclastogenesis is closely related to bone repair, and the receptor activators of nuclear factor kappaB ligand (RANKL) signaling pathway plays a key role of in the regulation of osteoclastogenesis. Herein, we studied the potential impact and underling mechanism of strontium-substituted sub-micron bioactive glass (Sr-SBG) on RANKL-induced osteoclast activation and differentiation in vitro. As expected, Sr-SBG inhibited RANKL-mediated osteoclastogenesis significantly with the experimental performance of decreased mature osteoclasts formation and downregulation of osteoclastogenesis-related gene expression. Furthermore, it was found that Sr-SBG might suppress osteoclastogenesis by the combined effect of strontium and silicon released through inhibition of RANKL-induced activation of p38 and NF-κB pathway. These results elaborated the effect of Sr-SBG-based materials on osteoclastogenesis through RANKL-induced downstream pathway and might represent a significant guidance for designing better bone repair materials.

Substrate stiffness affects the immunosuppressive and trophic function of hMSCs via modulating cytoskeletal polymerization and tension.

Mesenchymal stem cells (MSCs) have broad therapeutic potential due to their ability to secrete bioactive factors that are immunomodulatory and trophic (regenerative). In this study, polyacrylamide (PAAm) hydrogels with different stiffness are used as a model to explore the effects of substrate stiffness on the paracrine function of human mesenchymal stem cells (hMSCs). Human MSCs cultured on soft substrates produced significantly higher levels of immunomodulatory and trophic factors compared with hMSCs cultured on rigid substrates. The enhanced paracrine function of hMSCs is further confirmed by the M2 phenotypic polarization observed in macrophages, as well as the accelerated chemotactic migration and angiogenesis capacity observed in human umbilical vein endothelial cells (HUVECs) after treatment with conditioned media (CM) collected from hMSCs cultured on soft substrates. Furthermore, the inhibited secretion of immunosuppressive and trophic factors by hMSCs cultured on rigid substrates is largely rescued by treatment with Lat.A, a cytoskeletal polymerization inhibitor. Similar results are observed after treatment with either myosin (Blebbi) or ROCK (Y27632) inhibitors. These results demonstrate that substrate stiffness is a key modulator of the paracrine function of hMSCs and highlight the potential utility of promoting tissue repair through stiffness-regulated paracrine signaling in MSCs.

Micro-Nano Bioactive Glass Particles Incorporated Porous Scaffold for Promoting Osteogenesis and Angiogenesis in vitro.

Constructing the interconnected porous biomaterials scaffolds with osteogenesis and angiogenesis capacity is extremely important for efficient bone tissue engineering. Herein, we fabricated a bioactive micro-nano composite scaffolds with excellent in vitro osteogenesis and angiogenesis capacity, based on poly (lactic-co-glycolic acid) (PLGA) incorporated with micro-nano bioactive glass (MNBG). The results showed that the addition of MNBG enlarged the pore size, increased the compressive modulus (4 times improvement), enhanced the physiological stability and apatite-forming ability of porous PLGA scaffolds. The in vitro studies indicated that the PLGA-MNBG porous scaffold could enhance the mouse bone mesenchymal stem cells (mBMSCs) attachment, proliferation, and promote the expression of osteogenesis marker (ALP). Additionally, PLGA-MNBG could also support the attachment and proliferation of human umbilical vein endothelial cells (HUVECs), and significantly enhanced the expression of angiogenesis marker (CD31) of HUVECs. The as-prepared bioactive PLGA-MNBG nanocomposites scaffolds with good osteogenesis and angiogenesis probably have a promising application for bone tissue regeneration.