Angiogenin-loaded fibrin/bone powder composite scaffold for vascularized bone regeneration

Microdroplets Encapsulated with NFATc1-siRNA and Exosomes-Derived from MSCs Onto 3D Porous PLA Scaffold for Regulating Osteoclastogenesis and Promoting Osteogenesis

Introduction

Osteoporotic-related fractures remains a significant public health concern, thus imposing substantial burdens on our society. Excessive activation of osteoclastic activity is one of the main contributing factors for osteoporosis-related fractures. While polylactic acid (PLA) is frequently employed as a biodegradable scaffold in tissue engineering, it lacks sufficient biological activity. Microdroplets (MDs) have been explored as an ultrasound-responsive drug delivery method, and mesenchymal stem cell (MSC)-derived exosomes have shown therapeutic effects in diverse preclinical investigations. Thus, this study aimed to develop a novel bioactive hybrid PLA scaffold by integrating MDs-NFATc1-silencing siRNA to target osteoclast formation and MSCs-exosomes (MSC-Exo) to influence osteogenic differentiation (MDs-NFATc1/PLA-Exo).

Methods

Human bone marrow-derived mesenchymal stromal cells (hBMSCs) were used for exosome isolation. Transmission electron microscopy (TEM) and confocal laser scanning microscopy were used for exosome and MDs morphological characterization, respectively. The MDs-NFATc1/PLA-Exo scaffold was fabricated through poly(dopamine) and fibrin gel coating. Biocompatibility was assessed using RAW 264.7 macrophages and hBMSCs. Osteoclast formations were examined via TRAP staining. Osteogenic differentiation of hBMSCs and cytokine expression modulation were also investigated.

Results

MSC-Exo exhibited a cup-shaped structure and effective internalization into cells, while MDs displayed a spherical morphology with a well-defined core-shell structure. Following ultrasound stimulation, the internalization study demonstrated efficient delivery of bioactive MDs into recipient cells. Biocompatibility studies indicated no cytotoxicity of MDs-NFATc1/PLA-Exo scaffolds in RAW 264.7 macrophages and hBMSCs. Both MDs-NFATc1/PLA and MDs-NFATc1/PLA-Exo treatments significantly reduced osteoclast differentiation and formation. In addition, our results further indicated MDs-NFATc1/PLA-Exo scaffold significantly enhanced osteogenic differentiation of hBMSCs and modulated cytokine expression.

Discussion

These findings suggest that the bioactive MDs-NFATc1/PLA-Exo scaffold holds promise as an innovative structure for bone tissue regeneration. By specifically targeting osteoclast formation and promoting osteogenic differentiation, this hybrid scaffold may address key challenges in osteoporosis-related fractures.

The Role of Vasculature and Angiogenic Strategies in Bone Regeneration

Bone regeneration is a complex process that involves various growth factors, cell types, and extracellular matrix components. A crucial aspect of this process is the formation of a vascular network, which provides essential nutrients and oxygen and promotes osteogenesis by interacting with bone tissue. This review provides a comprehensive discussion of the critical role of vasculature in bone regeneration and the applications of angiogenic strategies, from conventional to cutting-edge methodologies. Recent research has shifted towards innovative bone tissue engineering strategies that integrate vascularized bone complexes, recognizing the significant role of vasculature in bone regeneration. The article begins by examining the role of angiogenesis in bone regeneration. It then introduces various in vitro and in vivo applications that have achieved accelerated bone regeneration through angiogenesis to highlight recent advances in bone tissue engineering. This review also identifies remaining challenges and outlines future directions for research in vascularized bone regeneration.

HIF-1α and periodontitis: Novel insights linking host-environment interplay to periodontal phenotypes

Periodontitis, the sixth most prevalent epidemic disease globally, profoundly impacts oral aesthetics and masticatory functionality. Hypoxia-inducible factor-1α (HIF-1α), an oxygen-dependent transcriptional activator, has emerged as a pivotal regulator in periodontal tissue and alveolar bone metabolism, exerts critical functions in angiogenesis, erythropoiesis, energy metabolism, and cell fate determination. Numerous essential phenotypes regulated by HIF are intricately associated with bone metabolism in periodontal tissues. Extensive investigations have highlighted the central role of HIF and its downstream target genes and pathways in the coupling of angiogenesis and osteogenesis. Within this concise perspective, we comprehensively review the cellular phenotypic alterations and microenvironmental dynamics linking HIF to periodontitis. We analyze current research on the HIF pathway, elucidating its impact on bone repair and regeneration, while unraveling the involved cellular and molecular mechanisms. Furthermore, we briefly discuss the potential application of targeted interventions aimed at HIF in the field of bone tissue regeneration engineering. This review expands our biological understanding of the intricate relationship between the HIF gene and bone angiogenesis in periodontitis and offers valuable insights for the development of innovative therapies to expedite bone repair and regeneration.

BZD9L1 benzimidazole analogue hampers colorectal tumor progression by impeding angiogenesis

BACKGROUND

The development of new vasculatures (angiogenesis) is indispensable in supplying oxygen and nutrients to fuel tumor growth. Epigenetic dysregulation in the tumor vasculature is critical to colorectal cancer (CRC) progression. Sirtuin (SIRT) enzymes are highly expressed in blood vessels. BZD9L1 benzimidazole analogue is a SIRT 1 and 2 inhibitor with reported anticancer activities in CRC. However, its role has yet to be explored in CRC tumor angiogenesis.

AIM

To investigate the anti-angiogenic potential of BZD9L1 on endothelial cells (EC) in vitro, ex vivo and in HCT116 CRC xenograft in vivo models.

METHODS

EA.hy926 EC were treated with half inhibitory concentration (IC₅₀) (2.5 μM), IC₅₀ (5.0 μM), and double IC₅₀ (10.0 μM) of BZD9L1 and assessed for cell proliferation, adhesion and SIRT 1 and 2 protein expression. Next, 2.5 μM and 5.0 μM of BZD9L1 were employed in downstream in vitro assays, including cell cycle, cell death and sprouting in EC. The effect of BZD9L1 on cell adhesion molecules and SIRT 1 and 2 were assessed via real-time quantitative polymerase chain reaction (qPCR). The growth factors secreted by EC post-treatment were evaluated using the Quantibody Human Angiogenesis Array. Indirect co-culture with HCT116 CRC cells was performed to investigate the impact of growth factors modulated by BZD9L1-treated EC on CRC. The effect of BZD9L1 on sprouting impediment and vessel regression was determined using mouse choroids. HCT116 cells were also injected subcutaneously into nude mice and analyzed for the outcome of BZD9L1 on tumor necrosis, Ki67 protein expression indicative of proliferation, cluster of differentiation 31 (CD31) and CD34 EC markers, and SIRT 1 and 2 genes via hematoxylin and eosin, immunohistochemistry and qPCR, respectively.

RESULTS

BZD9L1 impeded EC proliferation, adhesion, and spheroid sprouting through the downregulation of intercellular adhesion molecule 1, vascular endothelial cadherin, integrin-alpha V, SIRT1 and SIRT2 genes. The compound also arrested the cells at G1 phase and induced apoptosis in the EC. In mouse choroids, BZD9L1 inhibited sprouting and regressed sprouting vessels compared to the negative control. Compared to the negative control, the compound also reduced the protein levels of angiogenin, basic fibroblast growth factor, platelet-derived growth factor and placental growth factor, which then inhibited HCT116 CRC spheroid invasion in co-culture. In addition, a significant reduction in CRC tumor growth was noted alongside the downregulation of human SIRT1 (hSIRT1), hSIRT2, CD31, and CD34 EC markers and murine SIRT2 gene, while the murine SIRT1 gene remained unaffected, compared to vehicle control. Histology analyses revealed that BZD9L1 at low (50 mg/kg) and high (250 mg/kg) doses reduced Ki-67 protein expression, while BZD9L1 at the high dose diminished tumor necrosis compared to vehicle control.

CONCLUSION

These results highlighted the anti-angiogenic potential of BZD9L1 to reduce CRC tumor progression. Furthermore, together with previous anticancer findings, this study provides valuable insights into the potential of BZD9L1 to co-target CRC tumor vasculatures and cancer cells via SIRT1 and/or SIRT2 down-regulation to improve the therapeutic outcome.

Three-dimensional bioprinting of a full-thickness functional skin model using acellular dermal matrix and gelatin methacrylamide bioink

Treatment of full-thickness skin defects still presents a significant challenge in clinical practice. Three-dimensional (3D) bioprinting technique offers a promising approach for fabricating skin substitutes. However, it is necessary to identify bioinks that have both sufficient mechanical properties and desirable biocompatibilities. In this study, we successfully fabricated acellular dermal matrix (ADM) and gelatin methacrylamide (GelMA) bioinks. The results demonstrated that ADM preserved the main extracellular matrix (ECM) components of the skin and GelMA had tunable mechanical properties. Both bioinks with shear-thinning properties were suitable for 3D bioprinting and GelMA bioink exhibited high printability. Additionally, the results revealed that 20% GelMA with sufficient mechanical properties was suitable to engineer epidermis, 1.5% ADM and 10% GelMA displayed relatively good cytocompatibilities. Here, we proposed a new 3D structure to simulate natural full-thickness skin, which included 20% GelMA with HaCaTs as an epidermal layer, 1.5% ADM with fibroblasts as the dermis, and 10% GelMA mesh with human umbilical vein endothelial cells (HUVECs) as the vascular network and framework. We demonstrated that this 3D bioprinting functional skin model (FSM) could not only promote cell viability and proliferation, but also support epidermis reconstruction in vitro. When transplanted in vivo, the FSM could maintain cell viability for at least 1 week. Furthermore, the FSM promoted wound healing and re-epithelization, stimulated dermal ECM secretion and angiogenesis, and improved wound healing quality. The FSM may provide viable functional skin substitutes for future clinical applications. STATEMENT OF SIGNIFICANCE: We propose a new 3D structure to simulate natural full-thickness skin, which included 20% GelMA with HaCaTs as an epidermal layer, 1.5% ADM with fibroblasts as the dermis, and 10% GelMA mesh with HUVECs as the vascular network. It could not only maintain a moist microenvironment and barrier function, but also recreate the natural skin microenvironment to promote cell viability and proliferation. This may provide viable functional skin substitutes for future clinical applications.

Effectiveness of a biodegradable 3D polylactic acid/poly(ɛ-caprolactone)/hydroxyapatite scaffold loaded by differentiated osteogenic cells in a critical-sized radius bone defect in rat

The effects of a scaffold made of polylactic acid, poly (ɛ-caprolactone) and hydroxyapatite by indirect 3D printing method with and without differentiated bone cells was tested on the regeneration of a critical radial bone defect in rat. The scaffold characterization and mechanical performance were determined by the rheology, scanning electron microscopy, energy-dispersive X-ray spectroscopy, X-ray diffraction, and Fourier transform infrared spectrometry. The defects were created in forty Wistar rats which were randomly divided into the untreated, autograft, scaffold cell-free, and differentiated bone cell-seeded scaffold groups (n = 10 in each group). The expression level of angiogenic and osteogenic markers, analyzed by quantitative real time-polymerase chain reaction (in vitro), significantly improved (p < 0.05) in the scaffold group compared to the untreated one. Radiology and computed tomography scan demonstrated a significant improvement in the cell-seeded scaffold group compared to the untreated one (p < 0.001). Biomechanical, histopathological, histomorphometric, and immunohistochemical investigations showed significantly better regeneration scores in the cell-seeded scaffold and autograft groups compared to the untreated group (p < 0.05). The cell-seeded scaffold and autograft groups did show comparable results on the 80^th day post-treatment (p > 0.05), however, most results in the scaffold group were significantly higher than the untreated group (p < 0.05). Differentiated bone cells can enhance bone regeneration potential of the scaffold.

Bone Vasculature and Bone Marrow Vascular Niches in Health and Disease

Bone vasculature and bone marrow vascular niches supply oxygen, nutrients, and secrete angiocrine factors required for the survival, maintenance, and self-renewal of stem and progenitor cells. In the skeletal system, vasculature creates nurturing niches for bone and blood-forming stem cells. Blood vessels regulate hematopoiesis and drive bone formation during development, repair, and regeneration. Dysfunctional vascular niches induce skeletal aging, bone diseases, and hematological disorders. Recent cellular and molecular characterization of the bone marrow microenvironment has provided unprecedented insights into the complexity, heterogeneity, and functions of the bone vasculature and vascular niches. The bone vasculature is composed of distinct vessel subtypes that differentially regulate osteogenesis, hematopoiesis, and disease conditions in bones. Further, bone marrow vascular niches supporting stem cells are often complex microenvironments involving multiple different cell populations and vessel subtypes. This review provides an overview of the emerging vascular cell heterogeneity in bone and the new roles of the bone vasculature and associated vascular niches in health and disease. © 2020 The Authors. Journal of Bone and Mineral Research published by Wiley Periodicals LLC on behalf of American Society for Bone and Mineral Research (ASBMR).

Ceramic Scaffolds in a Vacuum Suction Handle for Intraoperative Stromal Cell Enrichment

During total joint replacement, high concentrations of mesenchymal stromal cells (MSCs) are released at the implantation site. They can be found in cell–tissue composites (CTC) that are regularly removed by surgical suction. A surgical vacuum suction handle was filled with bone substitute granules, acting as a filter allowing us to harvest CTC. The purpose of this study was to investigate the osteopromotive potential of CTC trapped in the bone substitute filter material during surgical suction. In the course of 10 elective total hip and knee replacement surgeries, β-tricalcium-phosphate (TCP) and cancellous allograft (Allo) were enriched with CTC by vacuum suction. Mononuclear cells (MNC) were isolated from the CTC and investigated towards cell proliferation and colony forming unit (CFU) formation. Furthermore, MSC surface markers, trilineage differentiation potential and the presence of defined cytokines were examined. Comparable amounts of MNC and CFUs were detected in both CTCs and characterized as MSC‰ of MNC with 9.8 ± 10.7‰ for the TCP and 12.8 ± 10.2‰ for the Allo (p = 0.550). CTCs in both filter materials contain cytokines for stimulation of cell proliferation and differentiation (EGF, PDGF-AA, angiogenin, osteopontin). CTC trapped in synthetic (TCP) and natural (Allo) bone substitute filters during surgical suction in the course of a joint replacement procedure include relevant numbers of MSCs and cytokines qualified for bone regeneration.

Effectiveness of mesenchymal stem cell-seeded onto the 3D polylactic acid/polycaprolactone/hydroxyapatite scaffold on the radius bone defect in rat

PURPOSE

The importance of regeneration in large bone defects forces the orthopedic surgeons to search for a proper methodology. The present experiment evaluated the capability of polylactic acid/polycaprolactone/hydroxyapatite (PLA/PCL/HA) scaffold loaded with and without mesenchymal stem cells (MSCs) on bone regeneration.

METHODS

Fourier transform infrared spectrometry, X-ray diffraction, scanning electron microscopy, and rheology methodologies were used to characterize the scaffold. Forty Wistar rats were randomly divided into the four groups including the untreated defects as the control group and three other groups in which the bone defects were treated with autologous bones (autograft group), the PLA/PCL/HA scaffolds (PLA/PCL/HA group), and the MSCs-seeded scaffolds (MSCs-seeded PLA/PCL/HA group).

RESULTS

Based on the qRT-PCR results, significantly higher expression levels of osteocalcin, osteopontin, and CD31 were seen in the cell-seeded scaffold group compared to the control group (P < 0.05). The CT scanning and radiographic images depicted significantly more newly formed bonny tissue in the MSCs-loaded scaffold and autograft groups than the untreated group (P < 0.001). The immunohistochemistry, biomechanical, histopathologic, and histomorphometric evaluations demonstrated significantly improved regeneration in the autograft and MSCs-loaded scaffold groups compared to the non-treated group (P < 0.05). There were significant differences between the scaffold and untreated groups in all in vivo evaluations (P < 0.05).

CONCLUSION

The MSCs enhanced bone healing potential of the PLA/PCL/HA scaffold and the MSCs-seeded scaffold was comparable to the autograft as the golden treatment regimen (P > 0.05).

A novel method to improve the osteogenesis capacity of hUCMSCs with dual-directional pre-induction under screened co-culture conditions

OBJECTIVES

Mesenchymal stem cells (MSCs) based therapy for bone regeneration has been regarded as a promising method in the clinic. However, hBMSCs with invasive harvesting process and undesirable proliferation rate hinder the extensive usage. HUCMSCs of easier access and excellent performances provide an alternative for the fabrication of tissue-engineered bone construct. Evidence suggested the osteogenesis ability of hUCMSCs was weaker than that of hBMSCs. To address this issue, a co-culture strategy of osteogenically and angiogenically induced hUCMSCs has been proposed since thorough vascularization facilitates the blood-borne nutrition and oxygen to transport in the scaffold, synergistically expediting the process of ossification.

MATERIALS AND METHODS

Herein, we used osteogenic- and angiogenic-differentiated hUCMSCs for co-culture in screened culture medium to elevate the osteogenic capacity with in vitro studies and finally coupled with 3D TCP scaffold to repair rat's critical-sized calvarial bone defect. By dual-directional induction, hUCMSCs could differentiate into osteoblasts and endothelial cells, respectively. To optimize the co-culture condition, gradient ratios of dual-directional differentiated hUCMSCs co-cultured under different medium were studied to determine the appropriate condition.

RESULTS

It revealed that the osteogenic- and angiogenic-induced hUCMSCs mixed with the ratio of 3:1 co-cultured in the mixed medium of osteogenic induction medium to endothelial cell induction medium of 3:1 possessed more mineralization nodules. Similarly, ALP and osteogenesis/angiogenesis-related genes expressions were relatively higher. Further evidence of bone defect repair with 3D printed TCP of 3:1 group exhibited better restoration outcomes.

CONCLUSIONS

Our work demonstrated a favourable and convenient approach of dual-directional differentiated hUCMSCs co-culture to improve the osteogenesis, establishing a novel way to fabricate tissue-engineered bone graft with 3D TCP for large bone defect augmentation.

Bonding Strength of Universal Adhesives to Indirect Substrates: A Meta-Analysis of in Vitro Studies

PURPOSE

To evaluate the in vitro bond strength of universal adhesive systems to indirect substrates.

MATERIAL AND METHODS

Two reviewers performed a literature search up to March 2018 in seven databases: PubMed, Web of Science, SciELO, Scopus, LILACS, IBECS, and BBO. The review included studies that compared the bond strength of universal adhesives and well-established material-specific primers to indirect substrates: lithium disilicate ceramic, yttrium-stabilized zirconium dioxide ceramic, leucite-reinforced ceramic, feldspathic porcelain, polymer infiltrated ceramic material, resin composite or metal alloys. Analyses were carried out using RevMan 5.3.5. A global comparison was performed with the standardized mean difference using a random-effects models at a significance level of p < 0.05.

RESULTS

A total of 45 studies were included in the qualitative analysis, and the meta-analysis was performed with 42 studies. Bond strength to glass-based ceramics and alloys was improved with the use of a specific-primer as separate step before the bonding procedures (lithium disilicate, p < 0.001; alloys, p < 0.001). The bond strength to zirconium substrates was improved with the use of universal adhesives (p < 0.001). For bond strength to composite resin as indirect substrate, universal adhesives performed in a manner similar to that of the material-specific primer (p = 0.11).

CONCLUSIONS

The clinical procedure of luting zirconia and resin composite restorations could be simplified by using single-bottle universal adhesives. However, the ability of universal adhesives to achieve an adequate and durable bond to glass-based ceramics and alloys appears to be limited.

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'.

Recent Advances in Scaffold Design and Material for Vascularized Tissue-Engineered Bone Regeneration

Bone tissue is a highly vascularized tissue and concomitant development of the vascular system and mineralized matrix requires a synergistic interaction between osteogenesis and angioblasts. Several strategies have been applied to achieve vascularized tissue-engineered bone, including the addition of cytokines as well as pre-vascularization strategies and co-culture systems. However, the scaffold is another extremely important component to consider, and development of vascularized bone scaffolds remains one of the greatest challenges for engineering clinically relevant bone substitutes. Here, this review highlights the biomaterial selection, preparation of pre-vascularized scaffolds, composition modification of the scaffold, structural design, and the comprehensive use of the above synergistic modifications of scaffold materials for vascular scaffolds in bone tissue engineering. Moreover, a strategy is proposed for the design of future scaffold structures, in which promoting the regeneration of vascularized bone by regulating the microenvironment should be the main focus. This overview can help illuminate progress in this field and identify the most recently developed scaffolds that show the greatest potential for achieving clinically vascularized bone.

Angiogenin production in response to hypoxia and l-mimosine in periodontal fibroblasts

BACKGROUND

A major mediator of angiogenesis is angiogenin, which is expressed in the early phase of healing in oral tissue engineering strategies. It is unclear how angiogenin is regulated in the periodontal tissue. The objective of this study was to reveal the regulation of angiogenin in response to hypoxia and the hypoxia mimetic agent l-mimosine in periodontal fibroblasts.

METHODS

Human fibroblasts of the periodontal ligament (PDLF) and the gingiva (GF) in monolayer and spheroid cultures were exposed to hypoxia or l-mimosine. The production of angiogenin was evaluated at mRNA and protein levels with reverse transcription quantitative polymerase chain reaction and enzyme-linked immunosorbent assays, respectively. Echinomycin, an inhibitor of hypoxia-inducible factor (HIF)-1 activity, was used to test the involvement of HIF-1.

RESULTS

Our data show that hypoxia and l-mimosine can increase angiogenin mRNA and protein levels in PDLF monolayer cultures. In GF monolayer cultures, we found an increase of angiogenin at the mRNA level in response to hypoxia. The increase of angiogenin can be blocked by inhibition of HIF-1 signaling via echinomycin. In PDLF and GF spheroid cultures, the impact of hypoxia and l-mimosine did not reach the level of significance.

CONCLUSION

Hypoxia and the hypoxia mimetic agent l-mimosine can increase the production of angiogenin via HIF-1 signaling in PDLF monolayer cultures but not in spheroid cultures. GF were less sensitive to the impact of hypoxia and l-mimosine. Overall, these results suggest a link between hypoxia, HIF-1 signaling and angiogenin in the periodontium.

Histological and structural evaluation of growth hormone and PLGA incorporation in macroporous scaffold of α-tricalcium phosphate cement

An in vivo study was conducted to evaluate the effects of the incorporation of fibers of poly(lactic acid-co-glycolic acid, PLGA) and poly(isoprene) blend and recombinant human growth hormone (rhGH) in a macroporous scaffold of α-tricalcium phosphate cement (α-TCP) samples inserted into calvarial defects (8 mm in diameter) of 48 Wistar rats. The samples of α-TCP + PLGA/poly(isoprene) blend fibers were also submitted to a mechanical test of flexural strength. The animals of the different experimental groups [1] α-TCP (n = 6); [2] α-TCP + PLGA/poly(isoprene) blend fibers (n = 6); [3] α-TCP + rhGH, (n = 6) and [4] α-TCP + PLGA/poly(isoprene) blend fibers + rhGH, (n = 6) (the numbers within square brackets identify the experimental groups), after two weeks (subdivision "a") and four weeks (subdivision "b"), were euthanized and the implants removed for histological analysis. There was no statistical difference (p > 0.05) between the samples with and without fibers in the mechanical test. Light microscopy revealed good integration of the material in the host tissue, represented by tissue penetration into the macropores and adequate angiogenesis. In the two-week period, the groups [3a] and [4a] were significantly superior (p < 0.05) to the other groups with regard to angiogenesis and bone neoformation. In the four-week period, the group [3b] was significantly superior (p < 0.05) to the other groups with regard to bone neoformation. We conclude that the macroporous α-TCP scaffold used in this study has low mechanical resistance, is biocompatible and has significantly improved the osteoconductive capacity when rhGH is incorporated into its structure.

Natural and synthetic polymers/bioceramics/bioactive compounds-mediated cell signalling in bone tissue engineering

Bone is a highly integrative and dynamic tissue of the human body. It is continually remodeled by bone cells such as osteoblasts, osteoclasts. When a fraction of a bone is damaged or deformed, stem cells and bone cells under the influence of several signaling pathways regulate bone regeneration at the particular locale. Effective therapies for bone defects can be met via bone tissue engineering which employs drug delivery systems with biomaterials to enhance cellular functions by acting on signaling pathways such as Wnt, BMP, TGF-β, and Notch. This review provides the current understanding of polymers/bioceramics/bioactive compounds as scaffolds in activation of signaling pathways for the formation of bone.

L-mimosine and hypoxia can increase angiogenin production in dental pulp-derived cells

Background

Angiogenin is a key molecule in the healing process which has been successfully applied in the field of regenerative medicine. The role of angiogenin in dental pulp regeneration is unclear. Here we aimed to reveal the impact of the hypoxia mimetic agent L-mimosine (L-MIM) and hypoxia on angiogenin in the dental pulp.

Methods

Human dental pulp-derived cells (DPC) were cultured in monolayer and spheroid cultures and treated with L-MIM or hypoxia. In addition, tooth slice organ cultures were applied to mimic the pulp-dentin complex. We measured angiogenin mRNA and protein levels using qPCR and ELISA, respectively. Inhibitor studies with echinomycin were performed to reveal the role of hypoxia-inducible factor (HIF)-1 signaling.

Results

Both, L-MIM and hypoxia increased the production of angiogenin at the protein level in monolayer cultures of DPC, while the increase at the mRNA level did not reach the level of significance. The increase of angiogenin in response to treatment with L-MIM or hypoxia was reduced by echinomycin. In spheroid cultures, L-MIM increased angiogenin at protein levels while the effect of hypoxia was not significant. Angiogenin was also expressed and released in tooth slice organ cultures under normoxic and hypoxic conditions and in the presence of L-MIM.

Conclusions

L-MIM and hypoxia modulate production of angiogenin via HIF-1 differentially and the response depends on the culture model. Given the role of angiogenin in regeneration the here presented results are of high relevance for pre-conditioning approaches for cell therapy and tissue engineering in the field of regenerative endodontics.

In Vitro and In Vivo Evaluation of Commercially Available Fibrin Gel as a Carrier of Alendronate for Bone Tissue Engineering

Alendronate (ALN) is a bisphosphonate drug that is widely used for the treatment of osteoporosis. Furthermore, local delivery of ALN has the potential to improve the bone regeneration. This study was designed to investigate an ALN-containing fibrin (fibrin/ALN) gel and evaluate the effect of this gel on both in vitro cellular behavior using human mesenchymal stem cells (hMSCs) and in vivo bone regenerative capacity. Fibrin hydrogels were fabricated using various ALN concentrations (10-7-10-4 M) with fibrin glue and the morphology, mechanical properties, and ALN release kinetics were characterized. Proliferation and osteogenic differentiation of and cytotoxicity in fibrin/ALN gel-embedded hMSCs were examined. In vivo bone formation was evaluated using a rabbit calvarial defect model. The fabricated fibrin/ALN gel was transparent with Young's modulus of ~13 kPa, and these properties were not affected by ALN concentration. The in vitro studies showed sustained release of ALN from the fibrin gel and revealed that hMSCs cultured in fibrin/ALN gel showed significantly increased proliferation and osteogenic differentiation. In addition, microcomputed tomography and histological analysis revealed that the newly formed bone was significantly enhanced by implantation of fibrin/ALN gel in a calvarial defect model. These results suggest that fibrin/ALN has the potential to improve bone regeneration.

Effects of Sr-HT-Gahnite on osteogenesis and angiogenesis by adipose derived stem cells for critical-sized calvarial defect repair

Tissue engineering strategies to construct vascularized bone grafts are now attracting much attention. Strontium-hardystonite-Gahnite (Sr-HT-Gahnite) is a strong, highly porous, and biocompatible calcium silicate based bio-ceramic that contains strontium and zinc ions. Adipose derived stem cells (ASCs) have been demonstrated to have the ability in promoting osteogenesis and angiogenesis. In this study, the effects of Sr-HT-Gahnite on cell morphology, cell proliferation, and osteogenic differentiation of ASCs were systematically investigated. The cell proliferation, migration and angiogenic differentiation of human umbilical vein endothelial cell (HUVECs) were studied. Beta-tricalcium phosphate/hydroxyapatite (TCP/HA) bioceramic scaffolds were set as the control biomaterial. Both bio-ceramics exhibited no adverse influence on cell viability. The Sr-HT-Gahnite scaffolds promoted cell attachment and alkaline phosphatase (ALP) activity of ASCs. The Sr-HT-Gahnite dissolution products enhanced ALP activity, matrix mineralization, and angiogenic differentiation of ASCs. They could also improve cell proliferation, migration, and angiogenic differentiation of HUVECs. Levels of in vivo bone formation with Sr-HT Gahnite were significantly higher than that for TCP/HA. The combination of Sr-HT-Gahnite and ASCs promoted both osteogenesis and angiogenesis in vivo study, compared to Sr-HT-Gahnite and TCP/HA bio-ceramics when administered alone, suggesting Sr-HT-Gahnite can act as a carrier for ASCs for construction of vascularized tissue-engineered bone.

Synergistic Effects of Vascular Endothelial Growth Factor on Bone Morphogenetic Proteins Induced Bone Formation In Vivo: Influencing Factors and Future Research Directions

Vascular endothelial growth factor (VEGF) and bone morphogenetic proteins (BMPs), as key mediators in angiogenesis and osteogenesis, are used in a combined delivery manner as a novel strategy in bone tissue engineering. VEGF has the potential to enhance BMPs induced bone formation. Both gene delivery and material-based delivery systems were incorporated in previous studies to investigate the synergistic effects of VEGF and BMPs. However, their results were controversial due to variation of methods incorporated in different studies. Factors influencing the synergistic effects of VEGF on BMPs induced bone formation were identified and analyzed in this review to reduce confusion on this issue. The potential mechanisms and directions of future studies were also proposed here. Further investigating mechanisms of the synergistic effects and optimizing these influencing factors will help to generate more effective bone regeneration.

Promoting angiogenesis with mesoporous microcarriers through a synergistic action of delivered silicon ion and VEGF

Angiogenic capacity of biomaterials is a key asset to drive vascular ingrowth during tissue repair and regeneration. Here we design a unique angiogenic microcarrier based on sol-gel derived mesoporous silica. The microspheres offer a potential angiogenic stimulator, Si ion, 'intrinsically' within the chemical structure. Furthermore, the highly mesoporous nature allows the loading and release of angiogenic growth factor 'extrinsically'. The Si ion is released from the microcarriers at therapeutic ranges (over a few ppm per day), which indeed up-regulates the expression of hypoxia inducing factor 1α (HIF1α) and stabilizes it by blocking HIF-prolyl hydroxylase 2 (PHD2) in HUVECs. This in turn activates the expression of a series of proangiogenic molecules, including bFGF, VEGF, and eNOS. VEGF is incorporated effectively within the mesopores of microcarriers and is then released continuously over a couple of weeks. The Si ion and VEGF released from the microcarriers synergistically stimulate endothelial cell functions, such as cell migration, chemotactic homing, and tubular networking. Furthermore, in vivo neo-blood vessel sprouting in chicken chorioallantoic membrane model is significantly promoted by the Si/VEGF releasing microcarriers. The current study demonstrates the synergized effects of Si ion and angiogenic growth factor through a biocompatible mesoporous microsphere delivery platform, and the concept provided here may open the door to a new co-delivery system of utilizing ions with growth factors for tissue repair and regeneration.

Investigation of angiogenesis in bioactive 3-dimensional poly(d,l-lactide-co-glycolide)/nano-hydroxyapatite scaffolds by in vivo multiphoton microscopy in murine calvarial critical bone defect

Reconstruction of critical size bone defects remains a major clinical challenge because of poor bone regeneration, which is usually due to poor angiogenesis during repair. Satisfactory vascularization is a prerequisite for the survival of grafts and the integration of new tissue with existing tissue. In this work, we investigated angiogenesis in 3D scaffolds by in vivo multiphoton microscopy during bone formation in a murine calvarial critical bone defect model and evaluated bone regeneration 8weeks post-implantation. The continuous release of bioactive lentiviral vectors (LV-pdgfb) from the scaffolds could be detected for 5days in vitro. In vivo, the released LV-pdgfb transfected adjacent cells and expressed PDGF-BB, facilitating angiogenesis and enhancing bone regeneration. The expression of both pdgfb and the angiogenesis-related genes vWF and VEGFR2 was significantly increased in the pdgfb gene-carrying scaffold (PHp) group. In addition, microCT scanning and histomorphology results proved that there was more new bone ingrowth in the PHp group than in the PLGA/nHA (PH) and control groups. MicroCT parameters, including BMD, BV/TV, Tb.Sp, and Tb.N indicated that there was significantly more new bone formation in the PHp group than in the other groups. With regard to neovascularization, 8weeks post-implantation, blood vessel areas (BVAs) were 9428±944μm(2), 4090±680.3μm(2), and none in the PHp, PH, and control groups, respectively. At each time point, BVAs in the PHp scaffolds were significantly higher than in the PH scaffolds. To our knowledge, this is the first use of multiphoton microscopy in bone tissue-engineering to investigate angiogenesis in scaffolds in vivo. This method represents a valuable tool for investigating neovascularization in bone scaffolds to determine if a certain scaffold is beneficial to neovascularization. We also proved that delivery of the pdgfb gene alone can improve both angiogenesis and bone regeneration Acronyms.

STATEMENT OF SIGNIFICANCE

Reconstruction of critical size bone defects remains a major clinical challenge because of poor bone regeneration, which is usually due to poor angiogenesis during repair. Satisfactory vascularization is a prerequisite for the survival of grafts and the integration of new tissue with existing tissue. In this work, we investigated angiogenesis in 3D scaffolds by in vivo multiphoton microscopy during bone formation in a murine calvarial critical bone defect model and evaluated bone regeneration 8weeks post-implantation. To verify that pdgfb-expressing vectors carried by the scaffolds can promote angiogenesis in 3D-printed scaffolds in vivo, we monitored angiogenesis within the implants by multiphoton microscopy. To our knowledge, this is the first study to dynamically investigate angiogenesis in bone tissue engineering scaffolds in vivo.