Involvement of N-cadherin/β-catenin interaction in the micro/nanotopography induced indirect mechanotransduction

Effect of polydimethylsiloxane surface morphology on osteogenic differentiation of mesenchymal stem cells through SIRT1 signalling pathway

Constructing surface topography with a certain roughness is a widely used, non-toxic, cost-effective and effective method for improving the microenvironment of cells, promoting the proliferation and osteogenic differentiation of mesenchymal stem cells (MSCs), and promoting the osseointegration of grafts and further improving their biocompatibility under clinical environmental conditions. SIRT1 plays an important regulatory role in the osteogenic differentiation of bone marrow-derived MSCs (BM-MSCs). However, it remains unknown whether SIRT1 plays an important regulatory role in the osteogenic differentiation of BM-MSCs with regard to surface morphology. Polydimethylsiloxane (PDMS) with different surface morphologies were prepared using different grits of sandpaper. The value for BMSCs added on different surfaces was detected by cell proliferation assays. RT-qPCR and Western blotting were performed to detect SIRT1 activation and osteogenic differentiation of MSCs. Osteogenesis of MSCs was detected by alkaline phosphatase (ALP) and alizarin red S staining. SIRT1 inhibition experiments were performed to investigate the role of SIRT1 in the osteogenic differentiation of MSCs induced by surface morphology. We found that BM-MSCs have better value and osteogenic differentiation ability on a surface with roughness of PDMS-1000M. SIRT1 showed higher gene and protein expression on a PDMS-1000M surface with a roughness of 13.741 ± 1.388 µm. The promotion of the osteogenic differentiation of MSCs on the PDMS-1000M surface was significantly decreased after inhibiting SIRT1 expression. Our study demonstrated that a surface morphology with certain roughness can activate the SIRT1 pathway of MSCs and promote the osteogenic differentiation of BMSCs via the SIRT1 pathway.

Mind the Viscous Modulus: The Mechanotransductive Response to the Viscous Nature of Isoelastic Matrices Regulates Stem Cell Chondrogenesis

The design of hydrogels as mimetics of tissues' matrices typically disregards the viscous nature of native tissues and focuses only on their elastic properties. In the case of stem cell chondrogenesis, this has led to contradictory results, likely due to unreported changes in the matrices' viscous modulus. Here, by employing isoelastic matrices with Young's modulus of ≈12 kPa, variations in viscous properties alone (i.e., loss tangent between 0.1 and 0.25) are demonstrated to be sufficient to drive efficient growth factor-free chondrogenesis of human mesenchymal stem cells, both in 2D and 3D cultures. The increase of the viscous component of RGD-functionalized polyacrylamide or polyethylene glycol maleimide hydrogels promotes a phenotype with reduced adhesion, alters mechanosensitive signaling, and boosts cell-cell contacts. In turn, this upregulates the chondrogenic transcription factor SOX9 and supports neocartilage formation, demonstrating that the mechanotransductive response to the viscous nature of the matrix can be harnessed to direct cell fate.

Biomaterial scaffolds in maxillofacial bone tissue engineering: A review of recent advances

Maxillofacial bone defects caused by congenital malformations, trauma, tumors, and inflammation can severely affect functions and aesthetics of maxillofacial region. Despite certain successful clinical applications of biomaterial scaffolds, ideal bone regeneration remains a challenge in maxillofacial region due to its irregular shape, complex structure, and unique biological functions. Scaffolds that address multiple needs of maxillofacial bone regeneration are under development to optimize bone regeneration capacity, costs, operational convenience. etc. In this review, we first highlight the special considerations of bone regeneration in maxillofacial region and provide an overview of the biomaterial scaffolds for maxillofacial bone regeneration under clinical examination and their efficacy, which provide basis and directions for future scaffold design. Latest advances of these scaffolds are then discussed, as well as future perspectives and challenges. Deepening our understanding of these scaffolds will help foster better innovations to improve the outcome of maxillofacial bone tissue engineering.

Investigation of nanotopography on SOCE mediated cell migration via live-cell : Imaging on opaque implant surface

The exploration of cell response to nanotopography has attracted considerable attentions for years. This article focuses on the influence of nanotopography on the intracellular Ca2+ dynamics, the most ubiquitous but ignored second messenger. The classic titanium nanotubes (NT) were fabricated by anodization to formulate nanoporous surfaces. Firstly, the store operative calcium entry (SOCE) in endoplasmic reticulum (ER) and functional Ca2+ release-activated Ca2+ (CRAC) channels were significantly enhanced on NT surfaces that revealed by live-cell Ca2+ imaging and fluorescence resonance energy transfer (FRET) identification of orai1-stim1 connection. To investigate the potential implication of Ca2+ elevation, the dynamic cell migration trajectory was monitored by a self-made holder, which could not only be suitable for the opaque implant surface but also guarantee the focus fields identical during samples shifting. The cell migration on NT surface was more vigorous and rapid, which was correlated with higher focal adhesion proteins expression, Ca2+-dependent calpain activity and stim1 level. In conclusion, this study has confirmed the novel ER Ca2+ hemostasis pathway on nanosurfaces and its crucial role in cell migration regulation, which may help for more biofavorable implant surface design.

Convergence of Calcium Channel Regulation and Mechanotransduction in Skeletal Regenerative Biomaterial Design

Cells are known to perceive their microenvironment through extracellular and intracellular mechanical signals. Upon sensing mechanical stimuli, cells can initiate various downstream signaling pathways that are vital to regulating proliferation, growth, and homeostasis. One such physiologic activity modulated by mechanical stimuli is osteogenic differentiation. The process of osteogenic mechanotransduction is regulated by numerous calcium ion channels-including channels coupled to cilia, mechanosensitive and voltage-sensitive channels, and channels associated with the endoplasmic reticulum. Evidence suggests these channels are implicated in osteogenic pathways such as the YAP/TAZ and canonical Wnt pathways. This review aims to describe the involvement of calcium channels in regulating osteogenic differentiation in response to mechanical loading and characterize the fashion in which those channels directly or indirectly mediate this process. The mechanotransduction pathway is a promising target for the development of regenerative materials for clinical applications due to its independence from exogenous growth factor supplementation. As such, also described are examples of osteogenic biomaterial strategies that involve the discussed calcium ion channels, calcium-dependent cellular structures, or calcium ion-regulating cellular features. Understanding the distinct ways calcium channels and signaling regulate these processes may uncover potential targets for advancing biomaterials with regenerative osteogenic capabilities.

Effect of sulfonation time on physicochemical, osteogenic, antibacterial properties and biocompatibility of carbon fiber reinforced polyether ether ketone

The carbon fiber reinforced polyetheretherketone (CFR-PEEK) has been increasingly used in orthopedics dentistry due to its excellent biocompatibility and mechanical properties. However, the biological inertness and poor antibacterial activity limit its clinical applications. This paper focused on the performances of CFR-PEEK with porous morphology that were exposed to different sulfonation periods (1, 3, 5, and 10 min, corresponding to CP-S1, CP-S3, CP-S5, and CP-S10, respectively). Residual sulfuric acid was removed by acetone rinsing, NaOH immersion, and hydrothermal treatment before in vitro and in vivo studies. The results showed some significant difference in the physicochemical properties, including energy dispersive X-ray spectroscopy (EDS) map of sulfur atoms, X-ray photoelectron spectroscopy (XPS) of valences of sulfur ions, Fourier transformation infrared spectroscopy (FTIR), hydrophilicity, hardness, and elastic modulus among CP-S3, CP-S5, and CP-S10. However, CP-S5 and CP-S10 were more effective in promoting the proliferation, adhesion, and osteogenic differentiation of seeded bone mesenchymal stem cells (BMSCs) and growth inhibition of S. aureus and P. gingivalis compared with other groups. Furthermore, the CP-S5 and CP-S10 samples achieved better cranial bone repair than the non-sulfonation group in a rat model. Therefore, it can be inferred that both 5 and 10 min are viable sulfonation durations for 30% CFR-PEEK. These findings provide a theoretical basis for developing CFR-PEEK for clinical applications.

Topography-mediated immunomodulation in osseointegration; Ally or Enemy

Osteoimmunology is at full display during endosseous implant osseointegration. Bone formation, maintenance and resorption at the implant surface is a result of bidirectional and dynamic reciprocal communication between the bone and immune cells that extends beyond the well-defined osteoblast-osteoclast signaling. Implant surface topography informs adherent progenitor and immune cell function and their cross-talk to modulate the process of bone accrual. Integrating titanium surface engineering with the principles of immunology is utilized to harness the power of immune system to improve osseointegration in healthy and diseased microenvironments. This review summarizes current information regarding immune cell-titanium implant surface interactions and places these events in the context of surface-mediated immunomodulation and bone regeneration. A mechanistic approach is directed in demonstrating the central role of osteoimmunology in the process of osseointegration and exploring how regulation of immune cell function at the implant-bone interface may be used in future control of clinical therapies. The process of peri-implant bone loss is also informed by immunomodulation at the implant surface. How surface topography is exploited to prevent osteoclastogenesis is considered herein with respect to peri-implant inflammation, osteoclastic precursor-surface interactions, and the upstream/downstream effects of surface topography on immune and progenitor cell function.

In Situ Growth of Tunable Gold Nanoparticles by Titania Nanotubes Templated Electrodeposition for Improving Osteogenesis through Modulating Macrophages Polarization

Driving macrophages M2 polarization has attracted growing attention for improving osteogenesis. Here, the in situ growth of tunable gold nanoparticles (AuNPs) on titania nanotubes (TiNTs) array was realized by electrodeposition, with the guidance of TiNTs. The fabricated Au layer showed excellent biocompatibility with different osteoimmune effects. Briefly, the Au deposition on 5 and 10 V anodized TiNTs surface could induce RAW264.7 cells to M2 polarization, whereas the Au deposition on 20 V anodized TiNTs surface showed M1 polarization, as indicated by various markers determination through immunofluorescence staining, qPCR, Western blot, and ELISA. Furthermore, the osteogenic differentiation of MC3T3-E1 was significantly enhanced by the macrophages conditioned medium from the Au@10VNTs surface. The in vivo tests also confirmed denser and thicker new trabecula bone formation and more M2 macrophages infiltration both on and adjacent to the Au@10VNTs implant surface. In mechanism, the cytokine array analysis of macrophages conditioned medium from the Au@10VNTs surface revealed the upregulation of pro-healing cytokines such as IL-10 and VEGF and downregulation of pro-inflammatory cytokines such as IL-1β and MCSF. In addition, the NF-κB pathway was significantly inhibited. In conclusion, the electrodeposition of a Au layer guided by TiNTs is a promising strategy for reducing postoperative inflammatory reactions and improving osseointegration through modulating macrophages polarization.

Hydroxyapatite-modified micro/nanostructured titania surfaces with different crystalline phases for osteoblast regulation

Surface structures and physicochemical properties critically influence osseointegration of titanium (Ti) implants. Previous studies have shown that the surface with both micro- and nanoscale roughness may provide multiple features comparable to cell dimensions and thus efficiently regulate cell-material interaction. However, less attention has been made to further optimize the physicochemical properties (e.g., crystalline phase) and to further improve the bioactivity of micro/nanostructured surfaces. Herein, micro/nanostructured titania surfaces with different crystalline phases (amorphous, anatase and anatase/rutile) were prepared and hydroxyapatite (HA) nanorods were deposited onto the as-prepared surfaces by a spin-assisted layer-by-layer assembly method without greatly altering the initial multi-scale morphology and wettability. The effects of crystalline phase, chemical composition and wettability on osteoblast response were investigated. It is noted that all the micro/nanostructured surfaces with/without HA modification presented superamphiphilic. The activities of MC3T3-E1 cells suggested that the proliferation trend on the micro/nanostructured surfaces was greatly influenced by different crystalline phases, and the highest proliferation rate was obtained on the anatase/rutile surface, followed by the anatase; but the cell differentiation and extracellular matrix mineralization were almost the same among them. After ultrathin HA modification on the micro/nanostructured surfaces with different crystalline phases, it exhibited similar proliferation trend as the original surfaces; however, the cell differentiation and extracellular matrix mineralization were significantly improved. The results indicate that the introduction of ultrathin HA to the micro/nanostructured surfaces with optimized crystalline phase benefits cell proliferation, differentiation and maturation, which suggests a favorable biomimetic microenvironment and provides the potential for enhanced implant osseointegration in vivo.

Effects of titanium with different micro/nano structures on the ability of osteoblasts to resist oxidative stress

Excessive accumulation of oxidative intermediates in the elderly significantly aggravates bone degradation and hinders the osseointegration of topological titanium (Ti) implants. Thus, it is of great significance to evaluate the antioxidant and osteoinduction capabilities of various nano, micro or micro/nano-composite structures under oxidative stress (OS) microenvironment. In this study, we discovered that 110 nm titania nanotubes (TNTs) enhanced the adsorption of fibronectin (FN) proteins onto smooth and rough titanium surfaces to varying degrees. Compared with Ti and 30 nm TNTs (T₃₀) groups, cells on 110 nm TNTs (T₁₁₀), microstructure/30 nm TNTs (M₃₀) and microstructure/110 nm TNTs (M₁₁₀) had smaller area, lower reactive oxygen species (ROS), and better proliferation/osteogenic differentiation abilities under OS condition, but there was no significant difference among the three groups. In addition, combined with our previous study, we suggested that T₁₁₀, M₃₀ and M₁₁₀ resistance to OS was also strongly associated with the high expression of FN-receptor integrin α5 or β1. All the findings indicated that the micro/nano-composed structures (M₃₀ & M₁₁₀) had similar anti-oxidation and osteogenesis abilities to T₁₁₀, which provided guidance for the application of different titanium implants with different topologies in the elderly.

ChondroGELesis: Hydrogels to harness the chondrogenic potential of stem cells

The extracellular matrix is a highly complex microenvironment, whose various components converge to regulate cell fate. Hydrogels, as water-swollen polymer networks composed by synthetic or natural materials, are ideal candidates to create biologically active substrates that mimic these matrices and target cell behaviour for a desired tissue engineering application. Indeed, the ability to tune their mechanical, structural, and biochemical properties provides a framework to recapitulate native tissues. This review explores how hydrogels have been engineered to harness the chondrogenic response of stem cells for the repair of damaged cartilage tissue. The signalling processes involved in hydrogel-driven chondrogenesis are also discussed, identifying critical pathways that should be taken into account during hydrogel design.

Micro/nano topography with altered nanotube diameter differentially trigger endoplasmic reticulum stress to mediate bone mesenchymal stem cell osteogenic differentiation

Micro/nano-topography (MNT) can promote osteogenic differentiation of stem cells, but the mechanism of topographical signaling transduction remains unclear. We have confirmed MNT, as a stressor, triggers endoplasmic reticulum (ER) stress and activates unfolded protein response in rat bone marrow mesenchymal stem cells, and such topography-induced ER stress promotes osteogenic differentiation. In order to reveal the influence of nanotube dimensions on ER stress, MNTs containing vertically oriented TiO2 nanotubes of diameters ranging from 30 nm to 100 nm were fabricated on pure titanium (Ti) foils, and ER stress and osteogenic differentiation of cells were systematically studied. After 12 h of cultivation, the transmission electron microscopy showed that cells on MNTs presented gross distortions of rough ER morphology containing the electron-dense material, and the expansion of the ER lumen became more pronounced as the dimension of nanotubes increased. Additionally, PCR and western blotting showed that the ER stress-related gene, the ER chaperone 78 kDa glucose-regulated protein, also known as binding-immunoglobulin protein (GRP78/BiP), was up-regulated, which was consistent with the osteogenesis-inducing ability of MNTs. Based on our previous studies, the findings in this article further revealed the mechanism for topographical cues modulating osteogenic differentiation of cells, which may provide an innovative approach for the optimal design of implant surface topography.

The Role of Autophagy in M2 Polarization of Macrophages Induced by Micro/Nano Topography

Background

The proper topography of implant surface can induce macrophages polarization, whereas the regulation mechanism has not been fully deciphered. The study aimed to examine the regulation mechanism of macrophages M2 polarization by titanium (Ti) implant surface micro/nano topography.

Results

Firstly, the titanium implant micropits-nanotubular surface with ~30 nm diameters (MNT) can induce the M2 polarization of RAW264.7 spontaneously, as indicated by the spindle-like cell morphological alteration and specific molecular marker arginase-1 (Arg1) expression. Next, the autophagic vacuoles (AVs) number is significantly increased on MNT surface, as confirmed by the monodansylcadaverine (MDC) and CYTO-ID staining as well as the transmission electron microscope (TEM) observation. In addition, increasing or decreasing the autophagosomes number by rapamycin or 3-methyladenine (3-MA) will result in augmentation or attenuation of Arg1. Furthermore, blocking the fusion between autophagosomes and lysosomes by bafilomycin also significantly reduces Arg1, even in the presence of rapamycin. Finally, the ERK phosphorylation is selectively upregulated on MNT surface and the AVs number and Arg1 expression are significantly suppressed by U0126 treatment.

Conclusion

Our findings suggest that the ERK-Beclin-1-autophagy axis may play a pivotal role in the regulation of M2 polarization induced by nanotopography.

ROS Dependent Wnt/β-Catenin Pathway and Its Regulation on Defined Micro-Pillars-A Combined In Vitro and In Silico Study

The physico-chemical surface design of implants influences the surrounding cells. Osteoblasts on sharp-edged micro-topographies revealed an impaired cell phenotype, function and Ca2+ mobilization. The influence of edges and ridges on the Wnt/β-catenin pathway in combination with the cells' stress response has not been clear. Therefore, MG-63 osteoblasts were studied on defined titanium-coated micro-pillars (5 × 5 × 5 µm) in vitro and in silico. MG-63s on micro-pillars indicated an activated state of the Wnt/β-catenin pathway. The β-catenin protein accumulated in the cytosol and translocated into the nucleus. Gene profiling indicated an antagonism mechanism of the transcriptional activity of β-catenin due to an increased expression of inhibitors like ICAT (inhibitor of β-catenin and transcription factor-4). Cells on pillars produced a significant reactive oxygen species (ROS) amount after 1 and 24 h. In silico analyses provided a detailed view on how transcriptional activity of Wnt signaling is coordinated in response to the oxidative stress induced by the micro-topography. Based on a coordinated expression of regulatory elements of the Wnt/β-catenin pathway, MG-63s are able to cope with an increased accumulation of β-catenin on micro-pillars and suppress an unintended target gene expression. Further, β-catenin may be diverted into other signaling pathways to support defense mechanisms against ROS.

Surface sulfonation and nitrification enhance the biological activity and osteogenesis of polyetheretherketone by forming an irregular nano-porous monolayer

Polyether-ether-ketone (PEEK) is becoming a popular component of clinical spinal and orthopedic applications, but its practical use suffers from several limitations. In this study, irregular nano-porous monolayer with differently functional groups was formed on the surface of PEEK through sulfonation and nitrification. The surface characteristics were detected by field-emission scanning electron microscopy, atomic force microscopy, energy-dispersive X-ray spectrometry, water contact angle measurements and Fourier transform infrared spectroscopy. In vitro cellular behaviors were evaluated by cell adhesion, morphological changes, proliferation, alkalinity, phosphatase activity, real-time RT-PCR and western blot analyses. In vivo osseointegration was examined through micro-CT and histological assessments. Our results reveal that the irregular nano-porous of PEEK affect the biological properties. High-temperature hydrothermal NP treatment induced early osteogenic differentiation and early osteogenesis. Modification by sulfonation and nitrification can broaden the use of PEEK in orthopedic and dental applications. This study provides a theoretical basis for the wider clinical application of PEEK. a To obtain a uniform porous structure, PEEK samples were treated by concentrated sulfuric acid and fuming nitric acid (82-80%) with magnetic stirring sequentially. b Effects of nanopores on biological behavior of bMSCS.

Cation Channel Transient Receptor Potential Vanilloid 4 Mediates Topography-Induced Osteoblastic Differentiation of Bone Marrow Stem Cells

Micro/nanotopographies (MNTs) have been reported to enhance the osseointegration of biomaterials and modulate cell functions, but the underlying mechanisms are incompletely understood. We hypothesized that transient receptor potential vanilloid 4 (TRPV4) may mediate the topographically induced osteoblastic differentiation of bone marrow stem cells (BMSCs) by regulating the NFATc1 and Wnt/β-catenin signaling. To test this hypothesis, murine BMSCs were cultured on polished titanium (Ti) discs (PT) and Ti discs carrying titania nanotubes (i.e., MNTs) with diameters of ∼30 and ∼100 nm (termed TNT-30 and TNT-100, respectively). It was found that the MNTs (in particular TNT-100) promoted the expression and activation of TRPV4. Inhibition of TRPV4 in BMSCs cultured on TNT-100 reduced the expression of osteoblastic genes and the gene expression and protein levels of NFATc1 and Wnt3a/β-catenin and also decreased nuclear translocation of NFATc1 and β-catenin (all vs uninhibited BMSCs). Conversely, activation of TRPV4 in BMSCs cultured on PT increased the expression of the osteoblastic gene and the gene expression and protein level of NFATc1 and Wnt3a/β-catenin and also enhanced the nuclear translocation of NFATc1 and β-catenin (all vs unactivated BMSCs). These differences suggest that the MNTs promoted TRPV4 expression and activation to enhance intracellular Ca²⁺, which further increased the nuclear translocation of NFATc1 and stimulated the Wnt/β-catenin signaling, thus leading to upregulated expression of osteoblastic genes. These results indicate TRPV4 to be a mediator in MNT-induced osteoblastic differentiation of BMSCs.

AMOT130/YAP pathway in topography-induced BMSC osteoblastic differentiation

Micro/nano-topography (MNT) is an important variable affecting osseointegration of bone biomaterials, but the underlying mechanisms are not fully understood. We probed the role of a AMOT130/YAP pathway in osteoblastic differentiation of bone marrow mesenchymal stems cultured on titanium (Ti) carrying MNTs. Ti surfaces with two well-defined MNTs (TiO2 nanotubes of different diameters and wall thicknesses) were prepared by anodization. Rat BMSCs were cultured on flat Ti and Ti surfaces carrying MNTs, and cell behaviors (i.e., morphology, F-actin development, osteoblastic differentiation, YAP localization) were studied. Ti surfaces carrying MNTs increased F-actin formation, osteoblastic gene expression, and protein AMOT130 production in BMSCs (all vs. flat Ti), and the surface carrying larger nantubes was more effective, confirming osteoblastic differentiation induced by MNTs. Elevation of the AMOT130 level (by inhibiting its degradation) increased the osteoblastic gene expression, F-actin formation, and nuclear localization of YAP. These show that, AMOT130/YAP is an important pathway mediating the translation of MNT signals to BMSC osteoblastic commitment, likely via the cascade: AMOT130 promotion of F-actin formation, increased YAP nuclear import, and activation of osteoblastic gene expression.

Titanium-based implant comprising a porous microstructure assembled with nanoleaves and controllable silicon-ion release for enhanced osseointegration

Osseointegration is crucial for early fixation as well as for long-term implantation success, hence numerous efforts have been made to tune the surface topography or chemical composition of biomedical implants to improve osseointegration. In this work, various nanostructures, including nanoflocs, nanobundles, nanorods, and nanoleaves, were introduced to the surface of silicon (Si)-incorporated microporous structure to form Si-incorporated micro-nano hierarchical structures on titanium (Ti)-based implants. The osseointegration of the implants were systemically assessed in vivo and in vitro. The in vitro evaluations showed that the nanostructures promoted the protein adsorption, thus modulating the early cellular responses, including the attachment and spreading of osteoblasts and human endothelial cells (HUVECs), and subsequent cell proliferation and differentiation. Furthermore, compared with the single microporous structure, the nanostructures located over the microporous structure protected the Si ions from quick release and allowed the long-term sustained Si-ions release, which further contributed to the proliferation and differentiation of osteoblasts and vascular endothelial growth factor (VEGF) secretion as well as the tube formation of HUVECs. Collectively, the favorable nano-surface structures, especially the nanoleaves structure, and the constant Si-ion release together led to robust osteogenic and angiogenic activities. More importantly, in vivo micro-CT evaluation and histological observations further verified that the Si-incorporated micro-nano hierarchical implant with nanoleaves structure could efficiently promote new bone formation, thus indicating it was an attractive candidate as a next-generation bone-implant material.

Nanostructured titanium regulates osseointegration via influencing macrophage polarization in the osteogenic environment

Introduction

Fabricating nanostructured surface topography represents the mainstream approach to induce osteogenesis for the next-generation bone implant. In the past, the bone implant was designed to minimize host repulsive reactions in order to acquire biocompatibility. However, increasing reports indicate that the absence of an appropriate immune response cannot acquire adequate osseointegration after implantation in vivo.

Materials and methods

We prepared different topographies on the surface of titanium (Ti) specimens by grinding, etching and anodizing, and they were marked as polished specimen (P), specimen with nanotubes (NTs) in small diameters (NT-30) and specimen with NTs in large diameters (NT-100). We evaluated the ability of different topographies of the specimen to induce osteogenic differentiation of mice bone marrow mesenchymal stem cells (BMSCs) in vitro and to induce osseointegration in vivo. Furthermore, we investigated the effect of different topographies on the polarization and secretion of macrophages, and the effect of macrophage polarization on topography-induced osteogenic differentiation of mice BMSCs. Finally, we verified the effect of macrophage polarization on topography-induced osseointegration in vivo by using Cre*RBP-J^fl/fl mice in which classically activated macrophage was restrained.

Results

The osteogenic differentiation of mice BMSCs induced by specimen with different topographies was NT-100>NT-30>P, while the osseointegration induced by specimen with different topographies in vivo was NT-30>NT-100>P. In addition, specimen of NT-30 could induce more macrophages to M2 polarization, while specimen of P and NT-100 could induce more macrophages to M1 polarization. When co-culture mice BMSCs and macrophages on specimen with different topographies, the osteogenic differentiation of mice BMSCs was NT-30>NT-100≥P. The osseointegration induced by NT-100 in Cre*RBP-J^fl/fl mice was much better than that of wild type mice.

Conclusion

It is suggested that the intrinsic immunomodulatory effects of nanomaterials are not only crucial to evaluate the in vivo biocompatibility but also required to determine the final osseointegration. To clarify the immune response and osseointegration may be beneficial for the designation and optimization of the bone implant.

Calcium-MicroRNA Complex-Functionalized Nanotubular Implant Surface for Highly Efficient Transfection and Enhanced Osteogenesis of Mesenchymal Stem Cells

Controlling mesenchymal stem cell (MSC) differentiation by RNA interference (RNAi) is a promising approach for next-generation regenerative medicine. However, efficient delivery of RNAi therapeutics is still a limiting factor. In this study, we have developed a simple, biocompatible, and highly effective delivery method of small RNA therapeutics into human MSCs (hMSCs) from an implant surface by calcium ions. First, we demonstrated that simple Ca/siRNA targeting green fluorescent protein (GFP) nanocomplexes were able to efficiently silence GFP in GFP-expressing hMSCs with adequate Ca²⁺ concentration (>5 mM). In addition, a single transfection could obtain a long-lasting silencing effect for more than 2 weeks. All three of the main endocytosis pathways (clathrin- and caveolin-mediated endocytosis and macropinocytosis) were involved in the internalization of the Ca/siRNA complexes by MSCs, and macropinocytosis plays the most dominant role. Furthermore, the Ca/siRNA complexes could be efficiently loaded onto the titanium implant surface when pretreated with anodization to create a nanotube (NT) layer. Because of the hydrophilic property of the NT surface, the Ca/siRNA was quickly loaded (less than 4 h) with high efficiency (nearly 100%), forming an even amorphous coating. The Ca/siRNA-coated NT surface showed an initial burst release of 80% of the siRNA complexes over 2 h, which is adequate to achieve robust gene silencing of attached hMSCs. To demonstrate the therapeutic potential of our Ca/siRNA coating technology, Ca/antimiR-138 complexes were loaded on to the NT surface, which strongly enhanced the osteogenic differentiation of hMSCs. In conclusion, our findings suggest that Ca²⁺ is an effective and biocompatible carrier to deliver small RNA therapeutics into hMSCs, both in solution and from functionalized surfaces, which provides a novel approach to control the MSC differentiation and tissue regeneration.

Tuning surface properties of bone biomaterials to manipulate osteoblastic cell adhesion and the signaling pathways for the enhancement of early osseointegration

Osteoblast cell adhesion is the initial step of early osseointegration responding to bone material implants. Enhancing the osteoblastic cell adhesion has become one of the prime aims when optimizing the surface properties of bone biomaterials. The traditional strategy focuses in improving the physical attachment of osteoblastic cells onto the surfaces of biomaterials. However, instead of a simple cell physical attachment, the osteoblastic cell adhesion has been revealed to be a sophisticated system. Despite the well-documented effect of bone biomaterial surface modifications on adhesion, few studies have focused on the underlying molecular mechanisms. Physicochemical signals from biomaterials can be transduced into intracellular signaling network and further initiate the early response cascade towards the implants, which includes cell survival, migration, proliferation, and differentiation. Adhesion is vital in determining the early osseointegration between host bone tissue and implanted bone biomaterials via regulating involving signaling pathways. Therefore, the modulation of early adhesion behavior should not simply target in physical attachment, but emphasize in the manipulation of downstream signaling pathways, to regulate early osseointegration. This review firstly summarized the basic biological principles of osteoblastic cell adhesion process and the activated downstream cell signaling pathways. The effects of different biomaterial physicochemical properties on osteoblastic cell adhesion were then reviewed. This review provided up-to-date research outcomes in the adhesion behavior of osteoblastic cells on bone biomaterials with different physicochemical properties. The strategy is optimised from traditionally focusing in physical cell adhesion to the proposed strategy that manipulating cell adhesion and the downstream signaling network for the enhancement of early osseointegration.

Dual-Functionalized Graphene Oxide Based siRNA Delivery System for Implant Surface Biomodification with Enhanced Osteogenesis

Surface functionalization by small interfering RNA (siRNA) is a novel strategy for improved implant osseointegration. A gene delivery system with safety and high transfection activity is a crucial factor for an siRNA-functionalized implant to exert its biological function. To this end, polyethylene glycol (PEG) and polyethylenimine (PEI) dual-functionalized graphene oxide (GO; nGO-PEG-PEI) may present a promising siRNA vector. In this study, nanosized nGO-PEG-PEI was prepared and optimized for siRNA delivery. Titania nanotubes (NTs) fabricated by anodic oxidation were biomodified with nGO-PEG-PEI/siRNA by cathodic electrodeposition, designated as NT-GPP/siRNA. NT-GPP/siRNA possessed benign cytocompatibility, as evaluated by cell adhesion and proliferation. Cellular uptake and knockdown efficiency of the NT-GPP/siRNA were assessed by MC3T3-E1 cells, which exhibited high siRNA delivery efficiency and sustained target gene silencing. Casein kinase-2 interacting protein-1 (Ckip-1) is a negative regulator of bone formation. siRNA-targeting Ckip-1 (siCkip-1) was introduced to the implant, and a series of in vitro and in vivo experiments were carried out to evaluate the osteogenic capacity of NT-GPP/siCkip-1. NT-GPP/siCkip-1 dramatically improved the in vitro osteogenic differentiation of MC3T3-E1 cells in terms of improved osteogenesis-related gene expression, and increased alkaline phosphatase (ALP) production, collagen secretion, and extracellular matrix (ECM) mineralization. Moreover, NT-GPP/siCkip-1 led to apparently enhanced in vivo osseointegration, as indicated by histological staining and EDX line scanning. Collectively, these findings suggest that NT-GPP/siRNA represents a practicable and promising approach for implant functionalization, showing clinical potential for dental and orthopedic applications.

Self-assembled N-cadherin mimetic peptide hydrogels promote the chondrogenesis of mesenchymal stem cells through inhibition of canonical Wnt/β-catenin signaling

N-cadherin, a transmembrane protein and major component of adherens junction, mediates cell-cell interactions and intracellular signaling that are important to the regulation of cell behaviors and organ development. Previous studies have identified mimetic peptides that possess similar bioactivity as that of N-cadherin, which promotes chondrogenesis of human mesenchymal stem cells (hMSCs); however, the molecular mechanism remains unknown. In this study, we combined the N-cadherin mimetic peptide (HAVDI) with the self-assembling KLD-12 peptide: the resultant peptide is capable of self-assembling into hydrogels functionalized with N-cadherin peptide in phosphate-buffered saline (PBS) at 37 °C. Encapsulation of hMSCs in these hydrogels showed enhanced expression of chondrogenic marker genes and deposition of cartilage specific extracellular matrix rich in proteoglycan and Type II Collagen compared to control hydrogels, with a scrambled-sequence peptide after 14 days of chondrogenic culture. Furthermore, western blot showed a significantly higher expression of active glycogen synthase kinase-3β (GSK-3β), which phosphorylates β-catenin and facilitates ubiquitin-mediated degradation, as well as a lower expression of β-catenin and LEF1 in the N-cadherin peptide hydrogels versus controls. Immunofluorescence staining revealed significantly less nuclear localization of β-catenin in N-cadherin mimetic peptide hydrogels. Our findings suggest that N-cadherin peptide hydrogels suppress canonical Wnt signaling in hMSCs by reducing β-catenin nuclear translocation and the associated transcriptional activity of β-catenin/LEF-1/TCF complex, thereby enhancing the chondrogenesis of hMSCs. Our biomimetic self-assembled peptide hydrogels can serve as a tailorable and versatile three-dimensional culture platform to investigate the effect of biofunctionalization on stem cell behavior.

Directing the osteoblastic and chondrocytic differentiations of mesenchymal stem cells: matrix vs. induction media

While both induction culture media and matrix have been reported to regulate the stem cell fate, little is known about which factor plays a more decisive role in directing the MSC differentiation lineage as well as the underlying mechanisms. To this aim, we seeded MSCs on HA-collagen and HA-synthetic hydrogel matrixes, which had demonstrated highly different potentials toward osteoblastic and chondrocytic differentiation lineages, respectively, and cultured them with osteogenic, chondrogenic and normal culture media, respectively. A systematic comparison has been carried out on the effects of induction media and matrix on MSC adhesion, cytoskeleton organization, proliferation, and in particular differentiation into the osteoblastic and chondrocytic lineages. The results demonstrated that the matrix selection had a much more profound effect on directing the differentiation lineage than the induction media did. The strong modulation effect on the transcription activities might be the critical factor contributing to the above observations in our study, where canonical Wnt-β-Catenin signal pathway was directly involved in the matrix-driven osteoblastic differentiation. Such findings not only provide a critical insight on natural cellular events leading to the osteoblastic and chondrocytic differentiations, but also have important implications in biomaterial design for tissue engineering applications.

Investigation of silk fibroin nanoparticle-decorated poly(l-lactic acid) composite scaffolds for osteoblast growth and differentiation

Attempts to reflect the physiology of organs is quite an intricacy during the tissue engineering process. An ideal scaffold and its surface topography can address and manipulate the cell behavior during the regeneration of targeted tissue, affecting the cell growth and differentiation significantly. Herein, silk fibroin (SF) nanoparticles were incorporated into poly(l-lactic acid) (PLLA) to prepare composite scaffolds via phase-inversion technique using supercritical carbon dioxide (SC-CO2). The SF nanoparticle core increased the surface roughness and hydrophilicity of the PLLA scaffolds, leading to a high affinity for albumin attachment. The in vitro cytotoxicity test of SF/PLLA scaffolds in L929 mouse fibroblast cells indicated good biocompatibility. Then, the in vitro interplay between mouse preosteoblast cell (MC3T3-E1) and various topological structures and biochemical cues were evaluated. The cell adhesion, proliferation, osteogenic differentiation and their relationship with the structures as well as SF content were explored. The SF/PLLA weight ratio (2:8) significantly affected the MC3T3-E1 cells by improving the expression of key players in the regulation of bone formation, ie, alkaline phosphatase (ALP), osteocalcin (OC) and collagen 1 (COL-1). These results suggest not only the importance of surface topography and biochemical cues but also the potential of applying SF/PLLA composite scaffolds as biomaterials in bone tissue engineering.

Hierarchical macropore/nano surface regulates stem cell fate through a ROCK-related signaling pathway

Synergistic cytoskeleton distribution accompanying higher ROCK activity activated FAK-ERK1/2 signaling pathway and promotion of BMSC osteogenesis on hierarchical surface.

Inducing Temporal and Reversible Autophagy by Nanotopography for Potential Control of Cell Differentiation

Tuning autophagy has become a new strategy to control cell differentiation in tissue engineering. The nanosized surface is well-known for its ability to interfere with intracellular procedures, while its role in autophagy regulation is unclear. In this study, we found that a nanotube (NT) structure was able to induce enhanced mTOR-independent autophagy in osteoblasts compared to a flat surface. Further analysis revealed that autophagy was temporally promoted by NTs in the initial day contact and it was also reversible by exchanging the substrate nanotopographies. Actin filaments were significantly dispersed and there were numerous filopodia on the leading edge of cells grown on the NT surface. Intracellular Ca²⁺ was significantly increased on the NT surface. Moreover, the phenomenon was also found on different nanotopographies as well as in different cell lines. These indicated that cell membrane stretching might be the central regulation factor. Finally, we found that the NT surface exhibited enhanced autophagy-dependent osteogenic differentiation efficacy. In addition, the enhancement on NT surface could be remembered. In conclusion, the nanotopographic surface is able to induce temporal, reversible, and memorable autophagy via cell membrane stretching, which may be used as a versatile method to control cell differentiation.

Improved rhBMP-2 function on MBG incorporated TiO2 nanorod films

In the process of biomaterials mediated bone regeneration, rhBMP-2 delivery at efficient dose in sustained kinetics is crucial for promoting cell osteogenic differentiation. Meanwhile, surface morphology of the biomaterials could regulate cellular responses as well as strengthen the rhBMP-2 interaction with cells for better bone induction. Herein, TiO₂ nanorod films with varied mesoporous bioactive glass (MBG) incorporation amount were designed to strengthen the efficacy of rhBMP-2, basing on optimized loading/release behaviors and surface nanostructure cooperatively. The MBG incorporation improved rhBMP-2 loading amount and regulated its release behavior. Consequently, the osteogenic differentiation of bone marrow-derived mesenchymal stem cells (BMSCs) on the incorporated films was extremely enhanced, and the incorporated nanorod film with 200nm MBG thickness exhibited the best osteoinduction effect. However, MBG film and the incorporated nanorod film had the same loading amount of rhBMP-2, the latter showed a much higher expression of 7-day osteogenic differentiation index than the former, which could be attributed to the synergistic effect of optimized rhBMP-2 release behavior and surface morphology. The MBG incorporated TiO₂ nanorod films here presents a promising strategy for enhancing osteoinduction through optimized rhBMP-2 release behavior.

Additively Manufactured Macroporous Titanium with Silver-Releasing Micro-/Nanoporous Surface for Multipurpose Infection Control and Bone Repair - A Proof of Concept

Restoring large-scale bone defects, where osteogenesis is slow while infections lurk, with biomaterials represents a formidable challenge in orthopedic clinics. Here, we propose a scaffold-based multipurpose anti-infection and bone repairing strategy to meet such restorative needs. To do this, personalized multifunctional titanium meshes were produced through an advanced additive manufacturing process and dual "TiO₂-poly(dopamine)/Ag (nano)" post modifications, yielding macroporous constructs with micro-/nanoporous walls and nanosilver bullets immobilized/embedded therein. Ultrahigh loading capacity and durable release of Ag⁺ were accomplished. The scaffolds were active against planktonic/adherent bacteria (Gram-negative and positive) for up to 12 weeks. Additionally, they not only defended themselves from biofilm colonization but also helped destroy existing biofilms, especially in combination with antibiotics. Further, the osteoblasts/bacteria coculture study displayed that the engineered surfaces aided MG-63 cells to combat bacterial invasion. Meanwhile, the scaffolds elicited generally acceptable biocompatibility (cell adhesion, proliferation, and viability) and hastened osteoblast differentiation and maturation (alkaline phosphatase production, matrix secretion, and calcification), by synergy of micro-/nanoscale topological cues and bioactive catecholamine chemistry. Although done ex vivo, these studies reveal that our three-in-one strategy (infection prophylaxis, infection fighting, and bone repair) has great potential to simultaneously prevent/combat infections and bridge defected bone. This work provides new thoughts to the use of enabling technologies to design biomaterials that resolve unmet clinical needs.

Effects of hierarchical micro/nano-topographies on the morphology, proliferation and differentiation of osteoblast-like cells

Coating the surfaces of titanium-based implants with appropriate hierarchical micro/nano-topographies resembling the structure of natural bone significantly enhances their biological performance. However, the relationship between nanostructures surfaces and their effects on modulating cellular response is not clearly understood. Moreover, it is not clear whether the surface chemistry or topography is the main factor on modulating cellular behavior, because the commonly used surface modification techniques for titanium-based implants simultaneously modify surface topography and chemistry. The aim of this study is to investigate osteoblast-like cell adhesion, proliferation and differentiation on hierarchical micro/nano-topographies with similar surface chemistry but different nano-scale features. Micro-arc oxidation and post hydrothermal treatment were employed to fabricate micro/nano-topographies on titanium. According to the morphological features, they were classified as microcrater (micro-topography), nanoplate (hierarchical topography with nanoplates) and nanoleaf (hierarchical topography with nanoleaves). The response of osteoblast like cells (SaOS-2) was studied on each surface after sputtering with a thin layer of gold (Au) to minimize the influence of surface chemistry. The morphological evaluation after histochemical staining revealed that the adherent cells were polygonal-shaped on microcrater surface, roundish on nanoplate surface and elongated on nanoleaf surface. Additionally, compared to microcrater surface, nanoplate surface slowed down cell proliferation and exhibited no enhancement on cell differentiation. However, nanoleaf surface supported cell proliferation and promoted cell differentiation. The results indicate that tuning morphological features of nanostructures on micro-topography can serve as a promising strategy to specifically modulate cellular response, such as cell morphology, proliferation, differentiation and mineralization.

Enhanced Osteogenic Activity of TiO2 Nanorod Films with Microscaled Distribution of Zn-CaP

The topography at the micro-/nanoscale level and bioactive composition of material surfaces have been thought to play vital roles in their interactions with cells. However, it is still a challenge to further modify special topography with biodegradable composition or vice versa. In this study, TiO2 nanorod films covered with microscale-distributed Zn-containing calcium phosphate (Zn-CaP) were prepared, trying to create a micro-/nanoscale topography and Zn(2+) release capability. MC3T3-E1 cells cultured on TiO2 nanorod film with sparsely distributed Zn-CaP (TiO2/S-ZCP) had significantly higher biological responses than those on the films with densely distributed Zn-CaP (TiO2/D-ZCP) and fully covered Zn-CaP (F-ZCP). TiO2/S-ZCP film was demonstrated to facilitate osteogenic differentiation much more strongly than F-ZCP and TiO2/D-ZCP films based on evaluations of ALP, related gene expressions, and extracellular matrix mineralization. The higher osteogenic differentiation on TiO2/S-ZCP film is ascribed to the micro-/nanoscale topography from Zn-CaP coverage promoting cell adhesion and filopodia extension, and inducing differentiation-orientation in the initial stage. And consequently Zn(2+) release results in enhancement of differentiation. Therefore, we believe that better organization of the micro-/nanotopography and bioactive ion release on the surface would be a promising way to enhance osteogenic activity for orthopedic and dental implants.

PELA microspheres with encapsulated arginine-chitosan/pBMP-2 nanoparticles induce pBMP-2 controlled-release, transfected osteoblastic progenitor cells, and promoted osteogenic differentiation

Repair of the bone injury remains a challenge in clinical practices. Recent progress in tissue engineering and therapeutic gene delivery systems have led to promising new strategies for successful acceleration of bone repair process. The aim of this study was to create a controlled-release system to slowly release the arginine-chitosan/plasmid DNA nanoparticles encoding BMP-2 gene (Arg-CS/pBMP-2 NPs), efficiently transfect osteoblastic progenitor cells, secrete functional BMP-2 protein, and promote osteogenic differentiation. In this study, chitosan was conjugated with arginine to generate arginine-chitosan polymer (Arg-CS) for gene delivery. Mix the Arg-CS with pBMP-2 to condense pBMP-2 into nano-sized particles. In vitro transfection assays demonstrated that the transfection efficiency of Arg-CS/pBMP-2 nanoparticles and the expression level of BMP-2 was obviously exceed control groups. Further, PELA microspheres as the controlled-release carrier for the nanoparticles were used to encapsulate Arg-CS/pBMP-2 NPs. We demonstrated that the Arg-CS/pBMP-2 NPs could slowly release from the PELA microspheres at least for 42 d. During the co-culture with the PELA microspheres, the content of BMP-2 protein secreted by MC3T3-E1 reached the peak at 7 d. After 21d, the secretion of BMP-2 protein still maintain a higher level. The alkaline phosphatase activity, alizarin red staining, and osteogenesis-related gene expression by real-time quantitative PCR analysis all showed the PELA microspheres entrapping with Arg-CS/pBMP-2 NPs can obviously induce the osteogenic differentiation. The results indicated that the Arg-CS is a suitable gene vector which can promote the gene transfection. And the novel PELA microspheres-nanoparticle controlled-release system has potential clinical application in the future after further research.

Design of Decorin-Based Peptides That Bind to Collagen I and their Potential as Adhesion Moieties in Biomaterials

Mimicking the binding epitopes of protein-protein interactions by using small peptides is important for generating modular biomimetic systems. A strategy is described for the design of such bioactive peptides without accessible structural data for the targeted interaction, and the effect of incorporating such adhesion peptides in complex biomaterial systems is demonstrated. The highly repetitive structure of decorin was analyzed to identify peptides that are representative of the inner and outer surface, and it was shown that only peptides based on the inner surface of decorin bind to collagen. The peptide with the highest binding affinity for collagen I, LHERHLNNN, served to slow down the diffusion of a conjugated dye in a collagen gel, while its dimer could physically crosslink collagen, thereby enhancing the elastic modulus of the gel by one order of magnitude. These results show the potential of the identified peptides for the design of biomaterials for applications in regenerative medicine.

Effect of Octacalcium-Phosphate-Modified Micro/Nanostructured Titania Surfaces on Osteoblast Response

Surface structures and properties of titanium implants play a vital role in successful bone replacement. To mimic the natural bone structure, some strategies have recently focused on the preparation of multiscaled morphology on medical titanium and shown some promising results; however, relatively few efforts have been made for further enhancing the biocompatibility of such a hierarchical hybrid structure without compromising the superior bioactivity of the starting micro/nano roughness. In this study, a thin ribbonlike octacalcium phosphate (OCP) coating was electrodeposited on a hierarchically structured titania surface, maintaining its micro/nanospongelike morphology. It is indicated that the micro/nanostructured surface with deposited OCP showed an improved biomineralization ability, in comparison to that without OCP modification, when immersed in simulated body fluid (SBF). Further evaluations of cellular activities demonstrated that the introduction of OCP to the micro/nano spongelike-structured surface remarkably enhanced MC3T3-E1 cell proliferation, alkaline phosphatase activity, and extracellular matrix mineralization compared to that of cells on the micro/nanospongelike titania surface during 14 days of culturing. Meanwhile, the OCP-deposited micro/nanostructured surface displayed much a smaller passive current density and lower current response to the applied potential, resulting in the improvement of corrosion resistance. All of the evaluations suggested that the modification of the OCP coating on the prepared micro/nanospongelike titania is of superior chemical stability, biomineralization, and osteoblast activities, which indicates a favorable implant microenvironment for osseointegration in vivo.

N-cadherin-based adherens junction regulates the maintenance, proliferation, and differentiation of neural progenitor cells during development

This review addresses our current understanding of the regulatory mechanism by which N-cadherin, a classical cadherin, affects neural progenitor cells (NPCs) during development. N-cadherin is responsible for the integrity of adherens junctions (AJs), which develop in the sub-apical region of NPCs in the neural tube and brain cortex. The apical domain, which contains the sub-apical region, is involved in the switching from symmetric proliferative division to asymmetric neurogenic division of NPCs. In addition, N-cadherin-based AJ is deeply involved in the apico-basal polarity of NPCs and the regulation of Wnt-β-catenin, hedgehog (Hh), and Notch signaling. In this review, we discuss the roles of N-cadherin in the maintenance, proliferation, and differentiation of NPCs through components of AJ, β-catenin and αE-catenin.