Direct role of interrod spacing in mediating cell adhesion on Sr-HA nanorod-patterned coatings

Bioactive Porous Particles as Biological and Physical Stimuli for Bone Regeneration

Even though bony defects can be recovered to their original condition with full functionality, critical-sized bone injuries continue to be a challenge in clinical fields due to deficiencies in the scaffolding matrix and growth factors at the injury region. In this study, we prepared bone morphogenetic protein-2 (BMP-2)-loaded porous particles as a bioactive bone graft for accelerated bone regeneration. The porous particles with unique leaf-stacked morphology (LSS particles) were fabricated by a simple cooling procedure of hot polycaprolactone (PCL) solution. The unique leaf-stacked structure in the LSS particles provided a large surface area and complex release path for the sufficient immobilization of BMP-2 and sustained release of BMP-2 for 26 days. The LSS was also recognized as a topographical cue for cell adhesion and differentiation. In in vitro cell culture and in vivo animal study using a canine mandible defect model, BMP-2-immobilized LSS particles provided a favorable environment for osteogenic differentiation of stem cells and bone regeneration. In vitro study suggests a dual stimulus of bone mineral-like (leaf-stacked) structure (a physical cue) and continuously supplied BMP-2 (a biological cue) to be the cause of this improved healing outcome. Thus, LSS particles containing BMP-2 can be a promising bioactive grafting material for effective new bone formation.

Immunomodulation and osseointegration activities of Na2TiO3 nanorods-arrayed coatings doped with different Sr content

To endow Ti-based orthopedic implants immunomodulatory capability and thus enhanced osseointegration, different amounts of Sr are doped in Na2TiO3 nanorods in the arrays with identical nanotopographic parameters (rod diameter, length and inter-rod spacing) by substitution of Na+ using hydrothermal treatment. The obtained arrays are denoted as STSr2, STSr4, and STSr7, where the arabic numbers indicate the incorporating amounts of Sr in Na2TiO3. The modulation effects of the Sr-doped nanorods arrays on macrophage polarization and osteogenetic functions of osteoblasts are investigated, together with the array without Sr (ST). Moreover, osseointegration of these arrays are also assayed in rat femoral condyles. Sr-doped nanorods arrays accelerate M1 (pro-inflammatory phenotype)-to-M2 (anti-inflammatory phenotype) transformation of the adhered macrophages, enhancing secretion of pro-osteogenetic cytokines and growth factors (TGF-β1 and BMP2), moreover, the Sr doped arrays directly enhance osteogenetic functions of osteoblasts. The enhancement of paracrine of M2 macrophages and osteogenetic function of osteoblasts is promoted with the increase of Sr incorporating amounts. Consequently, Sr doped arrays show significantly enhanced osseointegration in vivo compared to ST, and STSr7 exhibits the best performance. Our work sheds a new light on the design of surface chemical components and structures for orthopedic implants to enhance their osseointegration.

Gold Nanorod Substrate for Rat Fetal Neural Stem Cell Differentiation into Oligodendrocytes

Gold nanorods (AuNRs) have been proposed to promote stem cell differentiation in vitro and in vivo. In this study, we examined a particular type of AuNR in supporting the differentiation of rat fetal neural stem cells (NSCs) into oligodendrocytes (ODCs). AuNRs were synthesized according to the seed-mediated method resulting in nanorods with an aspect ratio of around 3 (~12 nm diameter, 36 nm length) and plasmon resonance at 520 and 780 nm, as confirmed by transmission electron microscopy (TEM) and UV-vis spectroscopy, respectively. A layer-by-layer approach was used to fabricate the AuNR substrate on the functionalized glass coverslips. NSCs were propagated for 10 days using fibroblast growth factor, platelet-derived growth-factor-supplemented culture media, and differentiated on an AuNR or poly-D-lysine (PDL)-coated surface using differentiation media containing triiodothyronine for three weeks. Results showed that NSCs survived better and differentiated faster on the AuNRs compared to the PDL surface. By week 1, almost all cells had differentiated on the AuNR substrate, whereas only ~60% differentiated on the PDL surface, with similar percentages of ODCs and astrocytes. This study indicates that functionalized AuNR substrate does promote NSC differentiation and could be a viable tool for tissue engineering to support the differentiation of stem cells.

Boron-incorporated micro/nano-topographical calcium silicate coating dictates osteo/angio-genesis and inflammatory response toward enhanced osseointegration

Orthopedic implant coatings with optimal surface features to achieve favorable osteo/angio-genesis and inflammatory response would be of great importance. However, to date, few coatings are capable of fully satisfying these requirements. In this work, to take advantage of the structural complexity of micro/nano-topography and benefits of biological trace elements, two types of boron-containing nanostructures (nanoflakes and nanolamellars) were introduced onto plasma-sprayed calcium silicate (F-BCS and L-BCS) coatings via hydrothermal treatment. The C-CS coating using deionized water as hydrothermal medium served as control. Boron-incorporated CS coating stimulated osteoblastic differentiation of bone marrow-derived mesenchymal stem cells (BMSCs). Specifically, the combination of β1 integrin-vinculin-mediated cell spreading and activation of bone morphogenetic protein signaling pathway acted synergistically to cause significant upregulation of runt-related transcription factor 2 (RUNX2) protein and Runx2 gene expression in BMSCs on the F-BCS coating surface, which induced the transcription of downstream osteogenic differentiation marker genes. F-BCS coating allowed specific boron ion release, which favored angiogenesis as evidenced by the enhanced migration and tube formation of human umbilical vein endothelial cells in the coating extract. Boron-incorporated coatings significantly suppressed the expression of toll-like receptor adaptor genes in RAW264.7 macrophages and subsequently the degradation of nuclear factor-κB inhibitor α, accompanied by the inactivation of the downstream pro-inflammatory genes. In vivo experiments confirmed that F-BCS-coated Ti implant possessed enhanced osseointegration compared with L-BCS- and C-CS-coated implants. These data highlighted the synergistic effect of specific nanotopography and boron release from orthopedic implant coating on improvement of osseointegration.

Enhancing Neurogenesis of Neural Stem Cells Using Homogeneous Nanohole Pattern-Modified Conductive Platform

Biocompatible platforms, wherein cells attach and grow, are important for controlling cytoskeletal dynamics and steering stem cell functions, including differentiation. Among various components, membrane integrins play a key role in focal adhesion of cells (18-20 nm in size) and are, thus, highly sensitive to the nanotopographical features of underlying substrates. Hence, it is necessary to develop a platform/technique that can provide high flexibility in controlling nanostructure sizes. We report a platform modified with homogeneous nanohole patterns, effective in guiding neurogenesis of mouse neural stem cells (mNSCs). Sizes of nanoholes were easily generated and varied using laser interference lithography (LIL), by changing the incident angles of light interference on substrates. Among three different nanohole patterns fabricated on conductive transparent electrodes, 500 nm-sized nanoholes showed the best performance for cell adhesion and spreading, based on F-actin and lamellipodia/filopodia expression. Enhanced biocompatibility and cell adhesion of these nanohole patterns ultimately resulted in the enhanced neurogenesis of mNSCs, based on the mRNAs expression level of the mNSCs marker and several neuronal markers. Therefore, platforms modified with homogeneous nanohole patterns fabricated by LIL are promising for the precise tuning of nanostructures in tissue culture platforms and useful for controlling various differentiation lineages of stem cells.

Lateral Spacing of TiO2 Nanotubes Modulates Osteoblast Behavior

Titanium dioxide (TiO2) nanotube coated substrates have revolutionized the concept of implant in a number of ways, being endowed with superior osseointegration properties and local drug delivery capacity. While accumulating reports describe the influence of nanotube diameter on cell behavior, little is known about the effects of nanotube lateral spacing on cells involved in bone regeneration. In this context, in the present study the MC3T3-E1 murine pre-osteoblast cells behavior has been investigated by using TiO2 nanotubes of ~78 nm diameter and lateral spacing of 18 nm and 80 nm, respectively. Both nanostructured surfaces supported cell viability and proliferation in approximately equal extent. However, obvious differences in the cell spreading areas, morphologies, the organization of the actin cytoskeleton and the pattern of the focal adhesions were noticed. Furthermore, investigation of the pre-osteoblast differentiation potential indicated a higher capacity of larger spacing nanostructure to enhance the expression of the alkaline phosphatase, osteopontin and osteocalcin osteoblast specific markers inducing osteogenic differentiation. These findings provide the proof that lateral spacing of the TiO2 nanotube coated titanium (Ti) surfaces has to be considered in designing bone implants with improved biological performance.

Rapid Fabrication, Microstructure, and in Vitro and in Vivo Investigations of a High-Performance Multilayer Coating with External, Flexible, and Silicon-Doped Hydroxyapatite Nanorods on Titanium

A high-performance multilayer coating with external, flexible, and silicon-doped hydroxyapatite (Si-HA) nanorods was designed using bionics. Plasma electrolytic oxidation (PEO) and the microwave hydrothermal (MH) method were used to rapidly deposit this multilayer coating on a titanium (Ti) substrate, applied for 5 and 10 min, respectively. The bioactive multilayer coating was composed of four layers, and the outermost layer was an external growth layer that consisted of many Si-HA nanorods with a single-crystal structure. The Si-HA nanorods exhibited good flexibility, likely because of their complete single-crystal structures, smooth surfaces, and suitable diameters and lengths. This multilayer coating with a high surface energy was superhydrophilic and exhibited good in vitro bioactivities, such as good apatite formation ability, good cell spreading, and high osteogenic gene expression levels. After implantation in the tibia of rabbits for 16 weeks, almost no soft tissues were formed at the MH treated PEO implant-bone interface. A direct bone contact interface was formed by a bridging effect of the flexible Si-HA nanorods, which further produced a high implant-bone interface bonding strength. The current results demonstrated that the bioactive multilayer layers with the flexible Si-HA nanorods displayed a very good osseointegration ability, showing promising applications in the biomedical field.

Surface Immobilization of TiO2 Nanotubes with Bone Morphogenetic Protein-2 Synergistically Enhances Initial Preosteoblast Adhesion and Osseointegration

Although titanium (Ti) alloys have been widely used as implant materials, the bioinertness of pristine Ti impairs their bioactivity and early osseointegration. In the present work, we prepared TiO₂ nanotubes (TNT) layer on the titanium (Ti) surface by anodic oxidation. The anodized surface was functionalized with human bone morphogenetic protein-2 coating to form the hBMP-2/TNT surface. The release behavior of hBMP-2 on the hBMP-2/TNT surface displayed a controlled and sustained pattern, compared to that on the hBMP-2/Ti surface, which showed a rapid release. In vitro cellular activity tests demonstrated that both TNT and hBMP-2/Ti surfaces, particularly the hBMP-2/TNT surface, enhanced adhesion, proliferation, and differentiation of osteoblast cells. Increased cell adhesion, improved cytoskeleton organization, and immunofluorescence staining of vinculin were observed on the modified surfaces. The TNT, hBMP-2/Ti, and hBMP-2/TNT surfaces, especially the hBMP-2/TNT surface, further displayed an upregulated gene expression of adhesion and osteogenic markers vinculin, collagen type 1, osteopontin, and osteocalcin, compared to the pristine Ti surface. In vivo experiments using a rat model demonstrated that the TNT and hBMP-2/Ti surfaces, in particular the hBMP-2/TNT surface, improved osseointegration and showed a superior bone bonding ability compared to Ti. Our study revealed a synergistic role played by TiO₂ nanotubes nanotopography and hBMP-2 in promoting initial osteoblast adhesion, proliferation, differentiation, and osseointegration, thus suggesting a promising method for better modifying the implant surface.

Participation of integrin β3 in osteoblast differentiation induced by titanium with nano or microtopography

The major role of integrins is to mediate cell adhesion but some of them are involved in the osteoblasts-titanium (Ti) interactions. In this study, we investigated the participation of integrins in osteoblast differentiation induced by Ti with nanotopography (Ti-Nano) and with microtopography (Ti-Micro). By using a PCR array, we observed that, compared with Ti-Micro, Ti-Nano upregulated the expression of five integrins in mesenchymal stem cells, including integrin β3, which increases osteoblast differentiation. Silencing integrin β3, using CRISPR-Cas9, in MC3T3-E1 cells significantly reduced the osteoblast differentiation induced by Ti-Nano in contrast to the effect on T-Micro. Concomitantly, integrin β3 silencing downregulated the expression of integrin αv, the parent chain that combines with other integrins and several components of the Wnt/β-catenin and BMP/Smad signaling pathways, all involved in osteoblast differentiation, only in cells cultured on Ti-Nano. Taken together, our results showed the key role of integrin β3 in the osteogenic potential of Ti-Nano but not of Ti-Micro. Additionally, we propose a novel mechanism to explain the higher osteoblast differentiation induced by Ti-Nano that involves an intricate regulatory network triggered by integrin β3 upregulation, which activates the Wnt and BMP signal transductions. © 2019 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 107A: 1303-1313, 2019.

Enhanced Osseointegration of Hierarchically Structured Ti Implant with Electrically Bioactive SnO2-TiO2 Bilayered Surface

The poor osseointegration of Ti implant significantly compromise its application in load-bearing bone repair and replacement. Electrically bioactive coating inspirited from heterojunction on Ti implant can benefit osseointegration but cannot avoid the stress shielding effect between bone and implant. To resolve this conflict, hierarchically structured Ti implant with electrically bioactive SnO₂-TiO₂ bilayered surface has been developed to enhance osseointegration. Benefiting from the electric cue offered by the built-in electrical field of SnO₂-TiO₂ heterojunction and the topographic cue provided by the hierarchical surface structure to bone regeneration, the osteoblastic function of basic multicellular units around the implant is significantly improved. Because the individual TiO₂ or SnO₂ coating with uniform surface exhibits no electrical bioactivity, the effects of electric and topographic cues to osseointegration have been decoupled via the analysis of in vivo performance for the placed Ti implant with different surfaces. The developed Ti implant shows significantly improved osseointegration with excellent bone-implant contact, improved mineralization of extracellular matrix, and increased push-out force. These results suggest that the synergistic strategy of combing electrical bioactivity with hierarchical surface structure provides a new platform for developing advanced endosseous implants.

Effects of titanium surface roughness on the mediation of osteogenesis via modulating the immune response of macrophages

Osteoblastic lineage cells are commonly used to evaluate the in vitro osteogenic ability of bone biomaterials. However, contradictory results obtained from in vivo and in vitro studies are not uncommon. With the increasing understanding of osteoimmunology, the immune response has been recognized as playing an important role in bone regeneration. In this study, we examined the effect of submicron-scaled titanium surface roughness (ranging from approximately 100 to 400 nm) on the response of osteoblasts and macrophages. The results showed that osteoblast differentiation enhanced with increased surface roughness of titanium substrates. The cytoskeleton of macrophages altered with the variation in titanium surface roughness. The production of cytokines (TNF-α, IL-6, IL-4 and IL-10) could be regulated by titanium surface roughness. Moreover, macrophages cultured on titanium surfaces exhibited a tendency to polarize to M1 phenotype with the increase of surface roughness. Material/macrophage conditioned medium tended to promote osteoblast differentiation with the increase of surface roughness. The results indicate that increasing surface roughness in the submicron range is beneficial for osteogenesis via modulating the immune response of macrophages. Modifying biomaterial surfaces based on their immunomodulatory effects is considered as a novel strategy for the improvement of their biological performance.

Silver-nanoparticles-modified biomaterial surface resistant to staphylococcus: new insight into the antimicrobial action of silver

Titanium implants are widely used clinically, but postoperative implant infection remains a potential severe complication. The purpose of this study was to investigate the antibacterial activity of nano-silver(Ag)-functionalized Ti surfaces against epidemic Staphylococcus from the perspective of the regulation of biofilm-related genes and based on a bacteria-cell co-culture study. To achieve this goal, two representative epidemic Staphylococcus strains, Staphylococcus epidermidis (S. epidermidis, RP62A) and Staphylococcus aureus (S. aureus, USA 300), were used, and it was found that an Ag-nanoparticle-modified Ti surface could regulate the expression levels of biofilm-related genes (icaA and icaR for S. epidermidis; fnbA and fnbB for S. aureus) to inhibit bacterial adhesion and biofilm formation. Moreover, a novel bacteria-fibroblast co-culture study revealed that the incorporation of Ag nanoparticles on such a surface can help mammalian cells to survive, adhere and spread more successfully than Staphylococcus. Therefore, the modified surface was demonstrated to possess a good anti-infective capability against both sessile bacteria and planktonic bacteria through synergy between the effects of Ag nanoparticles and ion release. This work provides new insight into the antimicrobial action and mechanism of Ag-nanoparticle-functionalized Ti surfaces with bacteria-killing and cell-assisting capabilities and paves the way towards better satisfying the clinical needs.