Regulation of the behaviors of mesenchymal stem cells by surface nanostructured titanium

Polycrystalline particulates synthesized on zirconia for enhanced bioactivity: An in vitro study

Zirconia is a promising material for dental implant with its excellent biocompatibility, good mechanical properties, and esthetic effect similar to natural teeth. To improve the bioactivity and osteogenic properties of zirconia, pre-sintered zirconia discs were divided into C, T₃ , T₅ , and T₇ group. Group C was as control. T₃ , T₅ , and T₇ groups were soaked in hydrofluoric acid (HF) for 30, 50, and 70 s, respectively. Then, they were placed into CaCl₂ solution and heated in NaOH solution. After sintering, the samples were characterized by scanning electron microscopy, energy dispersive spectrometry, and X-ray diffraction, which confirmed the ZrO₂ polycrystalline particulates in situ synthesized on the treated sample discs. The surface roughness of the treated samples was increased with the prolonged of acid treatment time (p < .05), while the three-point bending strength did not decrease significantly (p > .05). MC3T3-E1 cells were cultured on zirconia discs to evaluate the bioactivity and osteogenic effect of modified zirconia. The living&dead fluorescence staining and CCK-8 assay showed that the specimens were non-toxic and significantly promoted cell proliferation. In addition, the cell proliferation was enhanced with the increase of zirconia surface roughness. Polycrystalline particles modified zirconia were beneficial to cell spreading. After osteogenic induction, MC3T3-E1 cells inoculated on modified zirconia exhibited higher alkaline phosphatase activity, mineralization activity and up-regulated osteogenesis-related gene expression. Above all, in situ synthesized polycrystalline particulates significantly improve the biological activity of zirconia, which will promote the widespread application of zirconia implants.

Functional engineering strategies of 3D printed implants for hard tissue replacement

Three-dimensional printing technology with the rapid development of printing materials are widely recognized as a promising way to fabricate bioartificial bone tissues. In consideration of the disadvantages of bone substitutes, including poor mechanical properties, lack of vascularization and insufficient osteointegration, functional modification strategies can provide multiple functions and desired characteristics of printing materials, enhance their physicochemical and biological properties in bone tissue engineering. Thus, this review focuses on the advances of functional engineering strategies for 3D printed biomaterials in hard tissue replacement. It is structured as introducing 3D printing technologies, properties of printing materials (metals, ceramics and polymers) and typical functional engineering strategies utilized in the application of bone, cartilage and joint regeneration.

Using a two-step method of surface mechanical attrition treatment and calcium ion implantation to promote the osteogenic activity of mesenchymal stem cells as well as biomineralization on a β-titanium surface

Combination of the SMAT technique and Ca-ion implantation produced a β-titanium alloy with a bioactive surface layer, which was proved to effectively promote the osteogenic activity of MSCs and Ca–P mineral deposition in vitro.

High-manganese and nitrogen stabilized austenitic stainless steel (Fe-18Cr-22Mn-0.65N): a material with a bright future for orthopedic implant devices

The rationale behind the success of nickel free or with extremely low nickel austenitic high manganese and nitrogen stabilized stainless steels is adverse influences of nickel ion on human body. Replacement of nickel by nitrogen and manganese provides a stable microstructure and facilitates better biocompatibility in respect of the conventional 316L austenitic stainless steel (316L SS). In this investigation, biocompatibility of the high-manganese and nitrogen stabilized (Fe-18Cr-22Mn-0.65N) austenitic stainless steel was studied and found highly promising.In vitrocell culture and cell proliferation (MTT) assays were performed on this stainless steel and assessed in respect of the 316L SS. Both the steels exhibited similar cell growth behavior. Furthermore, an enhancement was observed in cell proliferation on the Fe-18Cr-22Mn-0.65N SS after surface modification by ultrasonic shot peening (USP). The mean percent proliferation of the MG-63 cells increased from ≈88% for Un-USP to 98% and 105% for USP 3-2 and USP 2-2 samples, respectively for 5 d of incubation. Interestingly,in vivoanimal study performed in rabbits for 3 and 6 weeks showed callus formation and sign of union without any allergic reaction.

Innovative Surface Modification Procedures to Achieve Micro/Nano-Graded Ti-Based Biomedical Alloys and Implants

Due to the growing aging population of the world, and as a result of the increasing need for dental implants and prostheses, the use of titanium and its alloys as implant materials has spread rapidly. Although titanium and its alloys are considered the best metallic materials for biomedical applications, the need for innovative technologies is necessary due to the sensitivity of medical applications and to eliminate any potentially harmful reactions, enhancing the implant-to-bone integration and preventing infection. In this regard, the implant’s surface as the substrate for any reaction is of crucial importance, and it is accurately addressed in this review paper. For constructing this review paper, an internet search was performed on the web of science with these keywords: surface modification techniques, titanium implant, biomedical applications, surface functionalization, etc. Numerous recent papers about titanium and its alloys were selected and reviewed, except for the section on forthcoming modern implants, in which extended research was performed. This review paper aimed to briefly introduce the necessary surface characteristics for biomedical applications and the numerous surface treatment techniques. Specific emphasis was given to micro/nano-structured topographies, biocompatibility, osteogenesis, and bactericidal effects. Additionally, gradient, multi-scale, and hierarchical surfaces with multifunctional properties were discussed. Finally, special attention was paid to modern implants and forthcoming surface modification strategies such as four-dimensional printing, metamaterials, and metasurfaces. This review paper, including traditional and novel surface modification strategies, will pave the way toward designing the next generation of more efficient implants.

The Effects of Chemical Etching and Ultra-Fine Grain Structure of Titanium on MG-63 Cells Response

In this work, we study the influence of the surface properties of ultrafine grained (UFG) and coarse grained (CG) titanium on the morphology, viability, proliferation and differentiation of osteoblast-like MG-63 cells. Wet chemical etching in H2SO4/H2O2 and NH4OH/H2O2 solutions was used for producing surfaces with varying morphology, topography, composition and wettability. The topography and morphology have been studied by scanning electron microscopy (SEM) and atomic force microscopy (AFM). The composition was determined by time of flight mass-spectrometry (TOF-SIMS) and X-ray photoelectron spectroscopy (XPS). The results showed that it is possible to obtain samples with different compositions, hydrophilicity, topography and nanoscale or/and microscale structures by changing the etching time and the type of etching solution. It was found that developed topography and morphology can improve spreading and proliferation rate of MG-63 cells. A significant advantage of the samples of the UFG series in comparison with CG in adhesion, proliferation at later stages of cultivation (7 days), higher alkaline phosphatase (ALP) activity and faster achievement of its maximum values was found. However, there is no clear benefit of the UFG series on osteopontin (OPN) expression. All studied samples showed no cytotoxicity towards MG-63 cells and promoted their osteogenic differentiation.

Review of recent developments in surface nanocrystallization of metallic biomaterials

Metallic materials are widely used to prepare implants for both short-term and long-term use in the human body. The performance of these implants is greatly influenced by their surface characteristics, which has motivated the development of several surface modification techniques. Surface severe plastic deformation (S2PD) techniques have emerged as promising strategies to enhance the performance of metallic biomaterials. They do not involve chemical modification of the surface and impart minimal changes to the surface topography. S2PD processes are based on the principle of generating nanocrystals at the surface, which can improve performance metrics, such as fatigue, wear, corrosion resistance, and biocompatibility through various mechanisms, such as surface hardening and alterations to the surface oxide layer. This review presents the state of the art on the development of different S2PD processes and their applications on metallic biomaterials. Brief descriptions of the different processes have been provided, followed by a discussion on the microstructural changes induced by these processes for different generations of biomaterials. The effect of S2PD on surface and bulk characteristics of the biomaterials and their performance is critically reviewed. As an emerging class of surface engineering techniques in biomaterials science, more work is needed to fully leverage their potential in this field, and these opportunities are discussed in this review.

The Anatase Phase of Nanotopography Titania with Higher Roughness Has Better Biocompatibility in Osteoblast Cell Morphology and Proliferation

Previous studies have concluded that surface-modified titanium oxide (titania, TiO2) surface properties promote osteoblast cell morphology and proliferation. To screen a suitable structured titania coating with the best biocompatibility to be used in dental implants, five titania films (two amorphous, one rutile, and two anatases) with different surfaces were successfully synthesized on polished titanium by radio frequency (RF) magnetron sputtering. We applied atomic force microscopy (AFM) and X-ray diffraction (XRD) to depict the formulations. Furthermore, MC3T3-E1, the mouse osteoblast precursor cell, was used to assess cell proliferation and observe morphologic changes at the film surface. The data indicated that the overall number of MC3T3-E1 cells on anatase films was significantly higher as compared with cells on rutile and amorphous films. Meanwhile, the actin filaments of the cells grown on the anatase phase films were well defined and fully spread. In addition, the film with higher roughness had enhanced biocompatibility than that with lower roughness. The results showed that the crystal phase and titania coated roughness had a greater influence on the biocompatibility of nanostructured titania film. The higher the roughness of the anatase phase was, the better bioactivity for the morphology and proliferation of osteoblast. This is a good surface-modified biological material and may have a good application prospect in dental implants.

Bioinformatics analysis and identification of circular RNAs promoting the osteogenic differentiation of human bone marrow mesenchymal stem cells on titanium treated by surface mechanical attrition

BACKGROUND

To analyze and identify the circular RNAs (circRNAs) involved in promoting the osteogenic differentiation of human bone mesenchymal stem cells (hBMSCs) on titanium by surface mechanical attrition treatment (SMAT).

METHODS

The experimental material was SMAT titanium and the control material was annealed titanium. Cell Counting Kits-8 (CCK-8) was used to detect the proliferation of hBMSCs, and alkaline phosphatase (ALP) activity and alizarin red staining were used to detect the osteogenic differentiation of hBMSCs on the sample surfaces. The bioinformatics prediction software miwalk3.0 was used to construct competing endogenous RNA (ceRNA) networks by predicting circRNAs with osteogenesis-related messenger RNAs (mRNAs) and microRNAs (miRNAs). The circRNAs located at the key positions in the networks were selected and analyzed by quantitative real-time PCR (QRT-PCR).

RESULTS

Compared with annealed titanium, SMAT titanium could promote the proliferation and osteogenic differentiation of hBMSCs. The total number of predicted circRNAs was 51. Among these, 30 circRNAs and 8 miRNAs constituted 6 ceRNA networks. Circ-LTBP2 was selected for verification. QRT-PCR results showed that the expression levels of hsa_circ_0032599, hsa_circ_0032600 and hsa_circ_0032601 were upregulated in the experimental group compared with those in the control group; the differential expression of hsa_circ_0032600 was the most obvious and statistically significant, with a fold change (FC) = 4.25 ± 1.60, p-values (p) < 0.05.

Enhanced durability, bio-activity and corrosion resistance of stainless steel through severe surface deformation

Owing to its good biocompatibility and low cost, stainless steel is one of the most widely utilized biomaterial. However, longtime assessment of stainless steel has shown problems related to material degradation, especially localized corrosion and bio-film formation. In addition, the leaching of toxic nickel and chromium ions from stainless steel leads to additional health complications. Here, we utilized submerged friction stir processing, a severe surface deformation technique for significantly enhancing its durability, bio-activity as well as antibacterial resistance. The processing was done with a wide variation in strain rates to produce tunable surface microstructure. High strain-rate processing resulted in nearly single-phase fine-grained microstructure, while slow strain-rate processing developed a dual-phase fine-grained microstructure. The bio-corrosion rate of processed steel was reduced by more than 60 % along with significant enhancement in the pitting resistance. The processed steel showed nearly no bacterial adhesion/biofilm formation, evaluated using S. aureus and E. coli bacterial strains. Further, the processed stainless steel surface demonstrated minimum leaching of the toxic elements, significantly enhancing its appeal for bio-implant applications. The observed behavior was explained based on the formation of a stable passive layer, rich in Cr₂O₃, as determined using x-ray photoelectron microscopy (XPS) and increased hydrophilicity.

Effect of ultrasonic shot peening duration on microstructure, corrosion behavior and cell response of cp-Ti

Surface mechanical attrition treatment (SMAT) of metallic biomaterials has gained significant importance due to its ability to develop nano structure in the surface region. In the present study, the microstructural changes and corrosion behavior of the commercially pure titanium (cp-Ti), following different durations of ultrasonic shot peening (USSP) has been investigated. cp-Ti was shot peened for different durations from 0 to 120 s and the treated samples were examined for microstructural changes in the surface region, cell viability and corrosion behavior. Cell viability was considerably increased after USSP for 60-120 s, exhibiting maximum for the 90 s of USSP. The passivation tendency was also improved with peening duration up to 90 s, however, it declined for longer duration of USSP. The beneficial effects of USSP may be attributed to nano structuring in the surface region and development of higher positive potentials at the USSP treated surface. Transmission Electron Microscope (TEM) examination of the USSPed surface revealed dislocation entanglement and substructure. Also, higher surface volta potential was observed over the USSPed sample exhibiting better cell proliferation. The present work is corollary to previous work of the group and mainly discusses the role of USSP duration, as a process parameter, on the cell viability and corrosion resistance of cp-Ti.

The Implication of Spatial Statistics in Human Mesenchymal Stem Cell Response to Nanotubular Architectures

INTRODUCTION

In recent years there has been ample interest in nanoscale modifications of synthetic biomaterials to understand fundamental aspects of cell-surface interactions towards improved biological outcomes. In this study, we aimed at closing in on the effects of nanotubular TiO2 surfaces with variable nanotopography on the response on human mesenchymal stem cells (hMSCs). Although the influence of TiO2 nanotubes on the cellular response, and in particular on hMSC activity, has already been addressed in the past, previous studies overlooked critical morphological, structural and physical aspects that go beyond the simple nanotube diameter, such as spatial statistics.

METHODS

To bridge this gap, we implemented an extensive characterization of nanotubular surfaces generated by anodization of titanium with a focus on spatial structural variables including eccentricity, nearest neighbour distance (NND) and Voronoi entropy, and associated them to the hMSC response. In addition, we assessed the biological potential of a two-tiered honeycomb nanoarchitecture, which allowed the detection of combinatory effects that this hierarchical structure has on stem cells with respect to conventional nanotubular designs. We have combined experimental techniques, ranging from Scanning Electron (SEM) and Atomic Force (AFM) microscopy to Raman spectroscopy, with computational simulations to characterize and model nanotubular surfaces. We evaluated the cell response at 6 hrs, 1 and 2 days by fluorescence microscopy, as well as bone mineral deposition by Raman spectroscopy, demonstrating substrate-induced differential biological cueing at both the short- and long-term.

RESULTS

Our work demonstrates that the nanotube diameter is not sufficient to comprehensively characterize nanotubular surfaces and equally important parameters, such as eccentricity and wall thickness, ought to be included since they all contribute to the overall spatial disorder which, in turn, dictates the overall bioactive potential. We have also demonstrated that nanotubular surfaces affect the quality of bone mineral deposited by differentiated stem cells. Lastly, we closed in on the integrated effects exerted by the superimposition of two dissimilar nanotubular arrays in the honeycomb architecture.

DISCUSSION

This work delineates a novel approach for the characterization of TiO2 nanotubes which supports the incorporation of critical spatial structural aspects that have been overlooked in previous research. This is a crucial aspect to interpret cellular behaviour on nanotubular substrates. Consequently, we anticipate that this strategy will contribute to the unification of studies focused on the use of such powerful nanostructured surfaces not only for biomedical applications but also in other technology fields, such as catalysis.

Surface mechanical attrition treatment of low modulus Ti-Nb-Ta-O alloy for orthopedic applications

Surface mechanical attrition treatment (SMAT) is recognized as a surface severe plastic deformation (SPD) method that is effective in improving the surface-dependent mechanical and functional properties of conventional metallic biomaterials. In this study, we aimed to systemically investigate the effect of SMAT on the physical, electrochemical, tribological and biological performances of a newly developed low modulus β Ti-Nb-Ta-O alloy with two different microstructures, namely, single phase β-treated and dual phase β + α aged. The microhardness results showed considerable hardening for the β-treated condition due to formation of deformation substructures; that was associated with increased corrosion resistance resulting from a stronger and denser passive layer on the surface, as revealed by Tafel polarization, impedance studies and Mott-Scottky plots. The wear volume loss during fretting in serum solution was found to decrease by 46% while friction coefficient decreased only marginally, due to presence of a harder and more brittle surface. In the β + α condition of the alloy, minimal hardening was observed due to coarsening of the precipitates during SMAT. However, this also reduced the number of α-β interfaces, which in turn minimized the tendency for galvanic corrosion resulting in lower corrosion rate after SMAT. Wear resistance was enhanced after SMAT, with 32% decrease in wear volume loss and 21% decrease in friction coefficient resulted due to improved ductility on the surface. The attachment and growth of osteoblasts on the alloys in vitro were not affected by SMAT and was comparable to that on commercially pure Ti. Taken together, these results provide new insights into the effects of surface SPD of low modulus β- Ti alloys for orthopedic applications and underscore the importance of the initial microstructure in determining the performance of the alloy.

On the Use of Functionally Graded Materials to Differentiate the Effects of Surface Severe Plastic Deformation, Roughness and Chemical Composition on Cell Proliferation

Additive manufacturing allows the manufacture of parts made of functionally graded materials (FGM) with a chemical gradient. This research work underlines that the use of FGM makes it possible to study mechanical, microstructural or biological characteristics while minimizing the number of required samples. The application of severe plastic deformation (SPD) by surface mechanical attrition treatment (SMAT) on FGM brings new insights on a major question in this field: which is the most important parameter between roughness, chemistry and microstructure modification on biocompatibility? Our study demonstrates that roughness has a large impact on adhesion while microstructure refinement plays a key role during the early stage of proliferation. After several days, chemistry is the main parameter that holds sway in the proliferation stage. With this respect, we also show that niobium has a much better biocompatibility than molybdenum when alloyed with titanium.

Oriented Cell Alignment Induced by a Nanostructured Titanium Surface Enhances Expression of Cell Differentiation Markers

A key factor for dental implant success is a good sealing between the implant surface and both soft (gum) and hard (bone) tissues. Surface nanotopography can modulate cell response through mechanotransduction. The main objective of this research was the development of nanostructured titanium (Ti) surfaces that promote both soft and hard tissue integration with potential application in dental implants. Nanostructured Ti surfaces were developed by electrochemical anodization-nanopores (NPs) and nanonets (NNs)-and characterized by atomic force microscopy, scanning electronic microscopy, and contact angle analysis. In addition, nanoparticle release and apoptosis activation were analyzed on cell culture. NP surfaces showed nanoparticle release, which increased in vitro cell apoptosis. Primary human gingival fibroblasts (hGFs) and human bone marrow mesenchymal stem cells (hBM-MSCs) were used to test cell adhesion, cytotoxicity, metabolic activity, and differentiation markers. Finally, cell orientation on the different surfaces was analyzed using a phalloidin staining. NN surfaces induced an oriented alignment of both cell types, leading in turn to an improved expression of differentiation markers. Our results suggest that NN structuration of Ti surfaces has great potential to be used for dental implant abutments to improve both soft and hard tissue integration.

Construction of Complex Structures Containing Micro-Pits and Nano-Pits on the Surface of Titanium for Cytocompatibility Improvement

The surface topography of medical implants plays an important role in the regulation of cellular responses. Microstructure and nanostructure surfaces have been proved to enhance cell spreading and proliferation with respect to smooth surfaces. In this study, we fabricated a new structure including micro-pits and nano-pits on the surface of titanium via sandblasting, acid etching and chemical oxidation to investigate the influence of composite structures on cell behavior. Meanwhile, the surface properties and corrosion resistance of treated samples were also tested. The micro/nanostructured titanium surface comprising of micro-pits and nano-pits presented enhanced roughness and hydrophilicity. In addition, the corrosion resistance of the titanium substrate with micro-pits and nano-pits was significantly improved compared to that of polished titanium. More importantly, the micro/nanostructured titanium surface proved a good interfacial environment to promote osteoblast functions such as cell adhesion and spreading. Taken together, these results showed that the construction of micro/nanostructure on the titanium surface is an effective modification strategy to improve osteoblast cell responses.

Enhanced antibacterial properties and the cellular response of stainless steel through friction stir processing

Biofilm related bacterial infection is one of the primary causes of implant failure. Limiting bacterial adhesion and colonization of pathogenic bacteria is a challenging task in health care. Here, a highly simplistic processing technique for imparting antibacterial properties on a biomedical grade stainless steel is demonstrated. Low-temperature high strain-rate deformation achieved using submerged friction stir processing resulted in a nearly single phase ultra-fine grain structure. The processed stainless steel demonstrated improved antibacterial properties for both Gram-positive and Gram-negative bacteria, significantly impeding biofilm formation during the in vitro study. Also, the processed stainless steel showed better compatibility with human fibroblasts manifested through apparent cell spreading and proliferation. The substantial antibacterial properties of the processed steel are explained in terms of the favorable electronic characteristics of the metal-oxide and by using classical Derjaguin-Landau-Verwey-Overbeek (DLVO) and the extended DLVO (XDLVO) approach at the cell-substrate interface.

Enhanced in-vitro osteoblastic functions on β-type titanium alloy using surface mechanical attrition treatment

To improve the osseointegration of titanium based implants, we herein modified Ti-25Nb-3Mo-2Sn-3Zr, a β-type titanium alloy by means of surface mechanical attrition treatment (SMAT). X-ray diffraction and transmission electron microscope results jointly indicate that SMAT process refined the average grain size of β phase in the surface layer of the alloy from about 110 μm to 26 nm. Besides, the surface properties and in-vitro cell culture tests of the SMAT-processed samples were investigated compared to those on the non-treated samples. Atomic force microscope and hydrophilicity tests revealed that the SMAT-processed surface was much rougher and hydrophilic than the non-treated surface. In vitro experimental results showed that SMAT-processed surface promoted adsorption of total protein as well as anchoring proteins such as vitronectin and fibronectin on its surface from cell culture medium, furthermore, significant improvements of osteoblast adhesion, proliferation, differentiation and extracellular mineralization were also found on the SMAT-processed surface compared to the non-treated surface. This could be attributed to the grain refinement as well as increased surface hydrophilicity and roughness after SMAT process. Our study provides a promising means of surface modification for future use in biomedical application.

Deferoxamine loaded titania nanotubes substrates regulate osteogenic and angiogenic differentiation of MSCs via activation of HIF-1α signaling

To develop biomaterials for inducing osteogenic and angiogenic differentiation of mesenchymal stem cells (MSCs) is crucial for bone repair. In this study, we employed titania nanotubes (TNT) as drug nanoreservoirs to load deferoxamine (DFO), and then deposited chitosan (Chi) and gelatin (Gel) multilayer as coverage structure via layer-by-layer (LBL) assembly technique, resulting in TNT-DFO-LBL substrates. Scanning electron microscopy (SEM), atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS) and contact angle measurements were employed to characterize the physical and chemical properties of the substrates. The results proved the successful fabrication of multilayer coating on TNT array. DFO released from the TNT arrays in a sustained manner. The drug-device combination titanium (Ti) substrates positively improved the adhesion, proliferation, osteogenic/angiogenic differentiation of MSCs and mediated the growth behavior of human umbilical vein endothelial cells (HUVECs). Moreover, the TNT-DFO-LBL substrates up-regulated osteogenic and angiogenic differentiation related genes expression of MSCs by activating HIF-1α signaling pathway. The approach presents here has a potential impact on the development of high quality Ti-based orthopedic implants.

Topographical cues of direct metal laser sintering titanium surfaces facilitate osteogenic differentiation of bone marrow mesenchymal stem cells through epigenetic regulation

OBJECTIVES

To investigate the role of hierarchical micro/nanoscale topography of direct metal laser sintering (DMLS) titanium surfaces in osteogenic differentiation of bone marrow mesenchymal stem cells (BMSCs), as well as the possible underlying epigenetic mechanism.

MATERIALS AND METHODS

Three groups of titanium specimens were prepared, including DMLS group, sandblasted, large-grit, acid-etched (SLA) group and smooth titanium (Ti) group. BMSCs were cultured on discs followed by surface characterization. Cell adhesion and proliferation were examined by SEM and CCK-8 assay, while osteogenic-related gene expression was detected by real-time RT-PCR. Immunofluorescence, western blotting and in vivo study were also performed to evaluate the potential for osteogenic induction of materials. In addition, to investigate the underlying epigenetic mechanisms, immunofluorescence and western blotting were performed to evaluate the global level of H3K4me3 during osteogenesis. The H3K4me3 and H3K27me3 levels at the promoter area of the osteogenic gene Runx2 were detected by ChIP assay.

RESULTS

The DMLS surface exhibits greater protein adsorption ability and shows better cell adhesion performance than SLA and Ti surfaces. Moreover, both in vitro and in vivo studies demonstrated that the DMLS surface is more favourable for the osteogenic differentiation of BMSCs than SLA and Ti surfaces. Accordingly, osteogenesis-associated gene expression in BMSCs is efficiently induced by a rapid H3K27 demethylation and increase in H3K4me3 levels at gene promoters upon osteogenic differentiation on DMLS titanium surface.

CONCLUSIONS

Topographical cues of DMLS surfaces have greater potential for the induction of osteogenic differentiation of BMSCs than SLA and Ti surfaces both in vitro and in vivo. A potential epigenetic mechanism is that the appropriate topography allows rapid H3K27 demethylation and an increased H3K4me3 level at the promoter region of osteogenesis-associated genes during the osteogenic differentiation of BMSCs.

Investigation of osteogenic responses of Fe-incorporated micro/nano-hierarchical structures on titanium surfaces

Fe incorporated micro/nano topographical titanium substrates are fabricated to synergistically regulate osteogenic responses in vitro and osseointegration in vivo.

Octopod PtCu Nanoframe for Dual-Modal Imaging-Guided Synergistic Photothermal Radiotherapy

Heavy atom nanoparticles have high X-ray absorption capacity and near infrared (NIR) photothermal conversion efficiency, which could be used as radio-sensitizers. We hypothesized that concave PtCu octopod nanoframes (OPCNs) would be an efficient nanoplatform for synergistic radio-photothermal tumor ablation.

Methods: In this study, we newly exploited a folic acid-receptor (FR) mediated photothermal radiotherapy nanoagent base on OPCNs. OPCNs were synthesized with a hydrothermal method and then modified with polyethylene glycol (PEG) and folic acid (FA). A series of physical and chemical characterizations, cytotoxicity, targeting potential, endocytosis mechanism, biodistribution, systematic toxicological evaluation, pharmacokinetics, applications of OPCNs-PEG-FA for in vitro and in vivo infrared thermal imaging (ITI)/photoacoustic imaging (PAI) dual-modal imaging and synergistic photothermal radiotherapy against tumor were carried out.

Results: The OPCNs-PEG-FA demonstrated good biocompatibility, strong NIR absorption and X-ray radio-sensitization, which enabling it to track and visualize tumor in vivo via ITI/PAI dual-modal imaging. Moreover, the as-synthesized OPCNs-PEG-FA exhibited remarkable photothermal therapy (PTT) and radiotherapy (RT) synergistic tumor inhibition when treated with NIR laser and X-ray.

Conclusion: A novel multifunctional theranostic nanoplatform based on OPCNs was designed and developed for dual-modal image-guided synergistic tumor photothermal radiotherapy.

Friction Stir Processing of Stainless Steel for Ascertaining Its Superlative Performance in Bioimplant Applications

Substrate-cell interactions for a bioimplant are driven by substrate's surface characteristics. In addition, the performance of an implant and resistance to degradation are primarily governed by its surface properties. A bioimplant typically degrades by wear and corrosion in the physiological environment, resulting in metallosis. Surface engineering strategies for limiting degradation of implants and enhancing their performance may reduce or eliminate the need for implant removal surgeries and the associated cost. In the current study, we tailored the surface properties of stainless steel using submerged friction stir processing (FSP), a severe plastic deformation technique. FSP resulted in significant microstructural refinement from 22 μm grain size for the as-received alloy to 0.8 μm grain size for the processed sample with increase in hardness by nearly 1.5 times. The wear and corrosion behavior of the processed alloy was evaluated in simulated body fluid. The processed sample demonstrated remarkable improvement in both wear and corrosion resistance, which is explained by surface strengthening and formation of a highly stable passive layer. The methylthiazol tetrazolium assay demonstrated that the processed sample is better in supporting cell attachment, proliferation with minimal toxicity, and hemolysis. The athrombogenic characteristic of the as-received and processed samples was evaluated by fibrinogen adsorption and platelet adhesion via the enzyme-linked immunosorbent assay and lactate dehydrogenase assay, respectively. The processed sample showed less platelet and fibrinogen adhesion compared with the as-received alloy, signifying its high thromboresistance. The current study suggests friction stir processing to be a versatile toolbox for enhancing the performance and reliability of currently used bioimplant materials.

TiO2 nanorod arrays modified Ti substrates promote the adhesion, proliferation and osteogenic differentiation of human periodontal ligament stem cells

Nanostructure coating on titanium (Ti) implants is well known as a cue for directing osteoblast behavior and function. However, effects of nanostructure coatings on dental stem cells have been rarely explored. In this work, assembled TiO₂ nanorod arrays (TNRs) were fabricated on the polished Ti substrates using hydrothermal and sintering methods. The adhesion, morphology, proliferation and osteogenic differentiation of human periodontal ligament stem cells (PDLSCs) seeded onto TNRs substrates were evaluated. Ti substrates were used as control. Rougher TNRs showed better hydrophilicity and protein adsorption capacity compared with Ti control. When seeded on TNRs substrates, PDLSCs exhibited more stretched morphology and higher proliferation rate. Cytoskeletal F-actin expression was markedly promoted for PDLSCs cultured on TNRs substrates under osteogenic induction. Alkaline phosphatase (ALP) activity and mineral deposition were also enhanced by TNRs. Moreover, osteogenesis-related markers of ALP, runt related transcription factor 2 (Runx2) and osteopontin (OPN) of PDLSCs cultured on TNRs substrates were significantly up-regulated at both gene and protein levels when compared to Ti substrates. In conclusion, the unique structure of TNRs provided a biocompatible platform for modulating morphology and function of PDLSCs. The promotion of osteogenic differentiation indicated that the surface modification of implants with TNRs may improve the osteogenic activity of implants and the bone-implant integration in future clinical applications.

The combined effects of nanotopography and Sr ion for enhanced osteogenic activity of bone marrow mesenchymal stem cells (BMSCs)

Both surface topography and chemistry have a significant influence on the biological performance of orthopedic implant coatings. In our study, a surface modification strategy embodying bioactive trace element incorporation and nanotopography construction was employed to enhance the osteogenic activity of calcium silicate (Ca-Si) coatings. We developed strontium-loaded nanolayer on plasma sprayed Ca-Si (CS) coating via hydrothermal treatment which was denoted as Sr-NT-CS. The original CS coating and the CS coating modified with similar nanotopography (NT-CS) were studied in parallel. We investigated the cellular effects of surface topography and released Sr ion on the adhesion, proliferation, differentiation, and mineralization of BMSCs and the associated molecular mechanisms. The results indicated that the nanotopography activated integrin β1, promoted the spread of BMSCs into a polygonal osteoblastic shape, and induced higher levels of collagen secretion. The Sr incorporation stimulated osteogenic differentiation and mineralization as indicated by the increases in ALP activity and mineralized nodules formation. The examination of gene expressions revealed that Sr ion exerted the effects by interacting with extracellular calcium sensitive receptor (CaSR), and combined with the nanotopographical cue for the up-regulation of osteogenic master transcription factor Runx2. The promoted Runx2 subsequently affected osteoblast (OB) marker genes (BMP-2, BSP, OPN, and OCN), thus driving BMSCs to differentiate into OBs. Moreover, the Sr incorporation inhibited osteoclastogenesis, as indicated by the down-regulation of interleukin-6 (IL-6) and the inhibition of RANKL/RANK system. Those results suggested that our developed Sr-NT-CS coating have combined the effects of nanotopography and Sr ion for enhanced osteogenic activity of BMSCs.

Evaluating the osseointegration of nanostructured titanium implants in animal models: Current experimental methods and perspectives (Review)

The aim of this paper is to review the experimental methods currently being used to evaluate the osseointegration of nanostructured titanium implants using animal models. The material modifications are linked to the biocompatibility of various types of oral implants, such as laser-treated, acid-etched, plasma-coated, and sand-blasted surface modifications. The types of implants are reviewed according to their implantation site (endoosseous, subperiosteal, and transosseous implants). The animal species and target bones used in experimental implantology are carefully compared in terms of the ratio of compact to spongy bone. The surgical technique in animal experiments is briefly described, and all phases of the histological evaluation of osseointegration are described in detail, including harvesting tissue samples, processing undemineralized ground sections, and qualitative and quantitative histological assessment of the bone-implant interface. The results of histological staining methods used in implantology are illustrated and compared. A standardized and reproducible technique for stereological quantification of bone-implant contact is proposed and demonstrated. In conclusion, histological evaluation of the experimental osseointegration of dental implants requires careful selection of the experimental animals, bones, and implantation sites. It is also advisable to use larger animal models and older animals with a slower growth rate rather than small or growing experimental animals. Bones with a similar ratio of compact to spongy bone, such as the human maxilla and mandible, are preferred. A number of practical recommendations for the experimental procedures, harvesting of samples, tissue processing, and quantitative histological evaluations are provided.

Manipulating mammalian cell by phase transformed titanium surface fabricated through ultra-short pulsed laser synthesis

Developing cell sensitive indicators on interacting substrates that allows specific cell manipulation by a combination of physical, chemical or mechanical cues is a challenge for current biomaterials. Hence, various fabrication approaches have been created on a variety of substrates to mimic or create cell specific cues. However, to achieve cell specific cues a multistep process or a post-chemical treatment is often necessitated. So, a simple approach without any chemical or biological treatment would go a long way in developing bio-functionalized substrates to effectively modulate cell adhesion and interaction. The present investigation is aimed to study the manipulative activity induced by phase transformed titanium surface. An ultra-short laser is used to fabricate the phase transformed titanium surface where a polymorphic titanium oxide phases with titanium monoxide (TiO), tri-titanium oxide (Ti3O) and titanium dioxide (TiO2) have been synthesized on commercially pure titanium. Control over oxide phase transformed area was demonstrated via a combination of laser scanning time (laser pulse interaction time) and laser pulse widths (laser pulse to pulse separation time). The interaction of phase transformed titanium surface with NIH3T3 fibroblasts and MC3T3-E1 osteoblast cells developed a new bio-functionalized platforms on titanium based biomaterials to modulate cell migration and adhesion. The synthesized phase transformed titanium surface on the whole appeared to induce directional cues for cell migration with unique preferential cell adhesion unseen by other fabrication approaches. The precise bio-functionalization controllability exhibited during fabrication offers perceptible edge for developing a variety of smart bio-medical devices, implants and cardiovascular stents where the need in supressing specific cell adhesion and proliferation is of great demand.

Regulation of local bone remodeling mediated by hybrid multilayer coating embedded with hyaluronan-alendronate/BMP-2 nanoparticles on Ti6Al7Nb implants

Hyaluronate-alendronate/BMP-2 nanoparticles were inserted into Gel/Chi multilayers on Ti6Al7Nb for enhancing BMP-2 stability and promoting local osteogenesis under osteoporosis.

Osteogenic differentiation and proliferation of bone marrow-derived mesenchymal stromal cells on PDLLA + BMP-2-coated titanium alloy surfaces

RhBMP-2 is clinically applied to enhance bone healing and used in combination with titanium fixation implants. The purpose of this in vitro study was to compare the osteogenic differentiation and proliferation of hMSC on native polished versus sandblasted titanium surfaces (TS) and to test their behavior on pure poly-D,L-lactide (PDLLA) coated as well as PDLLA + rhBMP-2 coated TS. Furthermore, the release kinetics of PDLLA + rhBMP-2-coated TS was investigated. Human bone marrow cells were obtained from three different donors (A: male, 16 yrs; B: male, 27 yrs, C: male, 49 yrs) followed by density gradient centrifugation and flow cytometry with defined antigens. The cells were seeded on native polished and sandblasted TS, PDLLA-coated TS and PDLLA + rhBMP-2-coated TS. Osteogenic differentiation (ALP specific activity via ALP and BCA assay) and proliferation (LDH cytotoxicity assay) was examined on day 7 and 14 and release kinetics of rhBMP-2 was investigated on day 3, 7, 10, and 14. We found significant higher ALP specific activity and LDH activity on native polished compared to native sandblasted surfaces. PDLLA led to decreased ALP specific and LDH activity on both surface finishes. Additional rhBMP-2 slightly diminished this effect. RhBMP-2-release from coated TS decreased nearly exponentially with highest concentrations at the beginning of the cultivation period. The results of this in vitro study suggest that native TS stimulate hMSC significantly stronger toward osteogenic differentiation and proliferation than rhBMP-2 + PDLLA-layered TS in the first 14 days of cultivation. The PDLLA-layer seems to inhibit local hMSC differentiation and proliferation.

Use of precisely sculptured thin film (STF) substrates with generalized ellipsometry to determine spatial distribution of adsorbed fibronectin to nanostructured columnar topographies and effect on cell adhesion

Sculptured thin film (STF) substrates consist of nanocolumns with precise orientation, intercolumnar spacing, and optical anisotropy, which can be used as model biomaterial substrates to study the effect of homogenous nanotopogrophies on the three-dimensional distribution of adsorbed proteins. Generalized ellipsometry was used to discriminate between the distributions of adsorbed FN either on top of or within the intercolumnar void spaces of STFs, afforded by the optical properties of these precisely crafted substrates. Generalized ellipsometry indicated that STFs with vertical nanocolumns enhanced total FN adsorption two-fold relative to flat control substrates and the FN adsorption studies demonstrate different STF characteristics influence the degree of FN immobilization both on top and within intercolumnar spaces, with increasing spacing and surface area enhancing total protein adsorption. Mouse fibroblasts or mouse mesenchymal stem cells were subsequently cultured on STFs, to investigate the effect of highly ordered and defined nanotopographies on cell adhesion, spreading, and proliferation. All STF nanotopographies investigated in the absence of adsorbed FN were found to significantly enhance cell adhesion relative to flat substrates; and the addition of FN to STFs was found to have cell-dependent effects on enhancing cell-material interactions. Furthermore, the amount of FN adsorbed to the STFs did not correlate with comparative enhancements of cell-material interactions, suggesting that nanotopography predominantly contributes to the biocompatibility of homogenous nanocolumnar surfaces. This is the first study to correlate precisely defined nanostructured features with protein distribution and cell-nanomaterial interactions. STFs demonstrate immense potential as biomaterial surfaces for applications in tissue engineering, drug delivery, and biosensing.

Nanostructured Architectures by Assembling Polysaccharide-Coated BSA Nanoparticles for Biomedical Application

Nanostructured architectures are produced on Ti surfaces by layer-by layer (LbL) self-assembling of polysaccharide-coated BSA nanoparticles (BNPs), which created cellular microenvironments mimicking natural extracellular matrix. The BMP-2 encapsulated BNPs are prepared by a desolvation method, and are further coated by chitosan (CHI) coatings to obtain positively charged NPs (CBNPs). Vancomycin (Van) encapsulated CBNPs are obtained by the same method and subsequently coated by oxidized alginate (OALG) to obtain negatively charged NPs (OCBNPs). The CBNPs and OCBNPs are assembled on Ti surfaces to construct nanostructured coatings via electrostatic and covalent interactions. The nanostructured architectures realize the sustained release of BMP-2 and Van for a long term. Bone marrow stromal cells (BMSCs) culture tests confirm that the bare nanostructured architectures intrinsically facilitate attachment, proliferation, and differentiation of cells, which is attributed to the nanoscale porous structures that are similar to the size of cellular filopodia. Incorporating BMP-2 into the nanostructured architectures significantly enhances osteogenetic differentiation of BMSCs, which reveals the synergistic effects of nanostructures and growth factors on cell activity. The antibacterial tests indicate that controlled release of Van has good antibacterial ability against Staphylococcus epidermidis, while not affecting the normal biological activity of BMSCs.

Mesenchymal stem cell growth behavior on micro/nano hierarchical surfaces of titanium substrates

Surface topography of an orthopedic implant plays an essential role in the regulation of bone formation with surrounding bone tissue. To investigate the effects of surface topography of titanium (Ti) substrates on cellular behavior of mesenchymal stem cells (MSCs), a series of micro/nano hierarchical structures were fabricated onto micro-structured titanium (Micro-Ti) substrates via a sol-gel method with spin-coat technique. Scanning electron microscopy (SEM), surface profiler, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and water contact angle measurement were employed to certify the successful fabrication of micro/nano hierarchical structures with the presence of various nano-sized TiO2 grains (20 nm, 40 nm and 80 nm, respectively) onto micro-structured surfaces. The formation mechanism of the micro/nano hierarchical structures was proposed. Moreover, the effects of those hierarchical structures on the growth behavior of MSCs were evaluated both on cellular and molecular levels in vitro. The results confirmed that micro/nano hierarchical structures with large grains (80 nm) greatly promoted the proliferation and differentiation of MSCs comparing with other small grains (20 nm and 40 nm). The study provides an alternative for the fabrication of hierarchically structured Ti implants for potential orthopedic application.

Enhanced osteogenesis on titanium implants by UVB photofunctionalization of hydrothermally grown TiO₂ coatings

Even though Ti-based implants are the most used materials for hard tissue replacement, they may present lack of osseointegration on the long term, due to their inertness. Hydrothermal treatment (HT) is a useful technique for the synthesis of firmly attached, highly crystalline coatings made of anatase titanium dioxide (TiO2), providing favorable nanoroughness and higher exposed surface area, as well as greater hydrophilicity, compared to the native amorphous oxide on pristine titanium. The hydrophilicity drops even more by photofunctionalization of the nanostructured TiO2-anatase coatings under UV light. Human mesenchymal stem cells exhibited a good response to the combination of the positive surface characteristics, especially in respect to the UVB pre-irradiation. The results showed that the cells were not harmed in terms of viability; even more, they were encouraged to differentiate in osteoblasts and to become osteogenically active, as confirmed by the calcium ion uptake and the formation of well-mineralized, bone-like nodule structures. In addition, the enrichment of hydroxyl groups on the HT-surfaces by UVB photofunctionalization accelerated the cell differentiation process and greatly improved the osteogenesis in comparison with the nonirradiated samples. The optimal surface characteristics of the HT-anatase coatings as well as the high potentiality of the photo-induced hydrophilicity, which was reached during a relatively short pre-irradiation time (5 h) with UVB light, can be correlated with better osseointegration ability in vivo; among the samples, the superior biological behavior of the roughest and most hydrophilic HT coating makes it a good candidate for further studies and applications.

Proliferation and stemness preservation of human adipose-derived stem cells by surface-modified in situ TiO₂ nanofibrous surfaces

Two important criteria of an ideal biomaterial in the field of stem cells research are to regulate the cell proliferation without the loss of its pluripotency and to direct the differentiation into a specific cell lineage when desired. The present study describes the influence of TiO2 nanofibrous surface structures on the regulation of proliferation and stemness preservation of adipose-derived stem cells (ADSCs). TiO2 nanofiber arrays were produced in situ onto Ti-6Al-4V substrate via a thermal oxidation process and the successful fabrication of these nanostructures was confirmed by field emission scanning electron microscopy (FESEM), energy dispersive spectrometer (EDS), X-ray diffractometer (XRD), and contact angle measurement. ADSCs were seeded on two types of Ti-6Al-4V surfaces (TiO2 nanofibers and flat control), and their morphology, proliferation, and stemness expression were analyzed using FESEM, AlamarBlue assay, flow cytometry, and quantitative real-time polymerase chain reaction (qRT-PCR) after 2 weeks of incubation, respectively. The results show that ADSCs exhibit better adhesion and significantly enhanced proliferation on the TiO2 nanofibrous surfaces compared to the flat control surfaces. The greater proliferation ability of TiO2 nanofibrous surfaces was further confirmed by the results of cell cycle assay. More importantly, TiO2 nanofibrous surfaces significantly upregulate the expressions of stemness markers Sox-2, Nanog3, Rex-1, and Nestin. These results demonstrate that TiO2 nanofibrous surfaces can be used to enhance cell adhesion and proliferation while simultaneously maintaining the stemness of ADSCs, thereby representing a promising approach for their potential application in the field of bone tissue engineering as well as regenerative therapies.

Regulation of the migration of endothelial cells by a gradient density of vascular endothelial growth factor

To investigate the effect of the surface gradient density of growth factor on the migration of endothelial cells (ECs), an approach to fabricate a gradient density of vascular endothelial growth factor (VEGF) onto silicon slides has been developed in this study. Our approach involves gradual injection of 3-glycidoxypropyltrimeth oxysilane (GPTMS) and then back filling with 3-triethoxysilylpropyl succinicanhydride (TESPSA) to produce a gradient density of carboxyl groups (-COOH) onto the silicon slides. The -COOH moieties were then activated for the immobilization of VEGF, which leading to a surface gradient density of VEGF. The successful formation of both carboxyl and VEGF gradient densities were confirmed by contact angle measurement, confocal laser scanning microscopy (CLSM) and X-ray photoelectron spectroscopy (XPS), respectively. The treated silicon slide displayed a gradient density of VEGF from 54 to 132 ng/cm2 with a slope of 7.8 ng/cm2/mm. ECs cultured on the surface gradient density of VEGF demonstrated preferential orientation and an enhanced directional migration behavior. Up to 72% of cells migrated towards the region with high surface density of VEGF. However, the gradient density of VEGF had no significant effect on the cell migration rate. The study provides an alternative to explore chemical-directing cells migration, which is essentially important for understanding cell migration/in-growth behavior for angiogenesis involved in implant technology.

Cell response to nanocrystallized metallic substrates obtained through severe plastic deformation

Cell-substrate interface is known to control the cell response and subsequent cell functions. Among the various biophysical signals, grain structure, which indicates the repeating arrangement of atoms in the material, has also proved to play a role of significant importance in mediating the cell activities. Moreover, refining the grain size through severe plastic deformation is known to provide the processed material with novel mechanical properties. The potential application of such advanced materials as biomedical implants has recently been evaluated by investigating the effect of different substrate grain sizes on a wide variety of cell activities. In this review, recent advances in biomedical applications of severe plastic deformation techniques are highlighted with special attention to the effect of the obtained nano/ultra-fine-grain size on cell-substrate interactions. Various severe plastic deformation techniques used for this purpose are discussed presenting a brief description of the mechanism for each process. The results obtained for each treatment on cell morphology, adhesion, proliferation, and differentiation, as well as the in vivo studies, are discussed. Finally, the advantages and challenges regarding the application of these techniques to produce multifunctional bio-implant materials are addressed.

Assessment of cellular viability on calcium sulphate/hydroxyapatite injectable scaffolds

Cements for maxillofacial reconstruction of jaw defects through calcification of rotated muscle have been tested. The objective of this study was to investigate the visibility of loading of two types of commercially available cements, Cerament(™) Spine Support and Cerament Bone Void Filler with mesenchymal cells and cytokines (bone morphogenetic protein) to act as a biomimetic scaffolding for future clinical application. Determination of basic biocompatibility (cell viability) using methyl thiazolyl tetrazolium and live/dead assay was carried out using MG-63 cells at various time points. Next, in order to inform potential subsequent in vivo experiments, a collagen tissue mimic was used for characterization of rabbit mesenchymal stromal cells using immunofluorescent cytoskeleton staining, and simultaneous and then sequential injection of Cerament Spine Support cement and cells into collagen gels. Results indicated that Cerament Spine Support was more biocompatible and that sequential injection of cement and then rabbit mesenchymal stromal cells into the tissue mimics is an optimal approach for clinical applications.

The Control of Mesenchymal Stromal Cell Osteogenic Differentiation through Modified Surfaces

Stem cells continue to receive widespread attention due to their potential to revolutionise treatments in the fields of both tissue engineering and regenerative medicine. Adult stem cells, specifically mesenchymal stromal cells (MSCs), play a vital role in the natural events surrounding bone healing and osseointegration through being stimulated to differentiate along their osteogenic lineage and in doing so, they form new cortical and trabecular bone tissue. Understanding how to control, manipulate, and enhance the intrinsic healing events modulated through osteogenic differentiation of MSCs by the use of modified surfaces and biomaterials could potentially advance the fields of both orthopaedics and dentistry. This could be by either using surface modification to generate greater implant stability and more rapid healing following implantation or the stimulation of MSCs ex vivo for reimplantation. This review aims to gather publications targeted at promoting, enhancing, and controlling the osteogenic differentiation of MSCs through biomaterials, nanotopographies, and modified surfaces for use in implant procedures.

Nano size effects of TiO2 nanotube array on the glioma cells behavior

In order to investigate the interplay between the cells and TiO₂ nanotube array, and to explore the ability of cells to sense the size change in nano-environment, we reported on the behavior of glioma C6 cells on nanotube array coatings in terms of proliferation and apoptosis. The behavior of glioma C6 cells was obviously size-dependent on the coatings; the caliber with 15 nm diameter provided effective spacing to improve the cells proliferation and enhanced the cellular activities. C6 cells’ biological behaviors showed many similar tendencies to many phorocytes; the matching degree of geometry between nanotube and integrin defined that a spacing of 15 nm was optimal for inducing signals to nucleus, which results in achieving maximum activity of glioma cells. In addition, the immune behavior of cells was studied, a variety of inflammatory mediator’s gene expression levels were controlled by the nanoscale dimension, the expressions of IL-6 and IL-10 were higher on 30 nm than on 15 nm nanotube.