Decentralized Multi-Subgroup Formation Control With Connectivity Preservation and Collision Avoidance

This paper proposes a formation control algorithm to create separated multiple formations for an undirected networked multi-agent system while preserving the network connectivity and avoiding collision among agents. Through the modified multi-consensus technique, the proposed algorithm can simultaneously divide a group of multiple agents into any arbitrary number of desired formations in a decentralized manner. Furthermore, the agents assigned to each formation group can be easily reallocated to other formation groups without network topological constraints as long as the entire network is initially connected; an operator can freely partition agents even if there is no spanning tree within each subgroup. Besides, the system can avoid collision without loosing the connectivity even during the transient period of formation by applying the existing potential function based on the network connectivity estimation. If the estimation is correct, the potential function not only guarantees the connectivity maintenance but also allows some extra edges to be broken if the network remains connected. Numerical simulations are performed to verify the feasibility and performance of the proposed multi-subgroup formation control

Effect of RGD Peptide-Coated TiO 2

The purpose of this research was to characterize an Arg-Gly-Asp (RGD) peptide immobilized on TiO2 nanotubes. In addition, we investigated the effects of the RGD peptide-coated TiO2 nanotubes on the cellular response, proliferation, and functionality of osteogenic-induced human mesenchymal stem cells (hMSCs), which are osteoclasts that have been induced by bone marrow macrophages. The RGD peptide was grafted covalently onto the surface of TiO2 nanotubes based on the results of SEM, FT-IR, and XPS. Furthermore, the RGD peptide promoted the initial attachment and proliferation of the hMSCs, regardless of the size of the TiO2 nanotubes. However, the RGD peptide did not prominently affect the osteogenic functionality of the hMSCs because the peptide suppressed hMSC motility associated with osteogenic differentiation. The result of an in vitro osteoclast test showed that the RGD peptide accelerated the initial attachment of preosteoclasts and the formation of mature osteoclasts, which could resorb the bone matrix. Therefore, we believe that an RGD coating on TiO2 nanotubes synthesized on Ti implants might not offer significant acceleration of bone formation in vivo because osteoblasts and osteoclasts reside in the same compartment

Infrared-Mediated Drug Elution Activity of Gold Nanorod-Grafted TiO 2

The purpose of this research was to prepare gold nanorod- (GNR-) grafted TiO2 nanotubes by thiolactic acid treatment and evaluate remote-controlled drug elution and antibacterial activity by infrared (IR) light irradiation. Tetracycline used as an antibiotic was loaded into GNR-grafted TiO2 nanotubes by using 2 w/v% polylactic acid solutions. A near-IR laser (830 nm) was used for remote-controlled IR light irradiation. Results of SEM, TEM, XRD, and EDX revealed that GNR chemically bonded to the whole surface of the TiO2 nanotubes. An antibiotic release test revealed that on-off drug elution was triggered effectively by the photothermal effect of GNR grafted on TiO2 nanotubes. Furthermore, an antibacterial agar zone test indicated that the annihilated zone of Streptococcus mutans in the experimental group with IR light irradiation was significantly larger than that of the corresponding group without IR light irradiation (P<0.05). Therefore, GNR-grafted TiO2 nanotubes would be expected to extend the limited usage of TiO2, which show photocatalytic activity only within the ultraviolet (UV) to IR region, thereby allowing the development of novel fusion technologies in the field of implant materials

Titanium Oxide Nanotube Surface Topography and MicroRNA-488 Contribute to Modulating Osteogenesis

Understanding the biocomplexity of cell behavior in relation to the topographical characteristics of implants is essential for successful osseointegration with good longevity and minimum failure. Here, we investigated whether culture on titanium oxide (TiO2) nanotubes of various diameters could affect the behavior and differentiation of MC3T3-E1 cells. Among the tested nanotubes, those of 50 nm in diameter were found to trigger the expression of the osteoblast-specific transcription factors, sp7 and Dlx5, and upregulate the expression of alkaline phosphatase (ALP). Here, we report that miR-488 was significantly induced in osteoblasts cultured on 50 nm nanotubes and continued to increase with the progression of osteoblast differentiation. Furthermore, downregulation of miR-488 suppressed the expression levels of ALP and matrix metalloprotease-2 (MMP-2). This suppression of ALP transcription was overcome by treatment with the MMP-2 activator, bafilomycin A1. Collectively, these results suggest that 50 nm is the optimum TiO2 nanotube diameter for implants, and that modulation of miR-488 can change the differentiation activity of cells on TiO2 nanotubes. This emphasizes that we must fully understand the physicochemical properties of TiO2 nanotubes and the endogenous biomolecules that interact with such surfaces, in order to fully support their clinical application

Osseointegration of Implants Surface-Treated with Various Diameters of TiO 2

The aim of this study was to evaluate the osseointegration of implants which were surface-treated with various diameters of TiO2 nanotubes (30 nm, 70 nm, and 100 nm) in rabbit. Resorbable blast media (RBM) surfaced implants (Osstem, Busan, Korea) 3.5 mm in diameter and 8.5 mm in length were designated as the control group and the implants surface-treated with various diameters of nanotubes (30 nm, 70 nm, and 100 nm) with the same shapes were designated as the experimental groups. The implants were maintained unloaded for 4 and 12 weeks. After this period, the animals were sacrificed and micro-CT analysis, histomorphometric analysis (bone to implant contact (BIC), bone volume (BV)), and removal torque test were performed. Micro-CT analysis, histomorphometric analysis, and removal torque test results all showed the similar pattern, showing that 70 nm experimental group had the highest value at 4 weeks while 30 nm experimental group had the highest value at 12 weeks. Therefore, on the basis of the results above, it can be concluded that 30 nm and 70 nm TiO2 nanotubes may have positive effects on osteogenesis and osseointegration depending on the healing time

The Evaluation of Osseointegration of Dental Implant Surface with Different Size of TiO 2

With the development of nanotechnology, many researches have shown that nanometer-scaled materials especially TiO2 nanotube have a positive effect on cellular behavior and surface characteristics of implant, which are considered to be crucial factors in osseointegration. However, it has not yet been verified which nanotube size is effective in osseointegration in vivo. The aim of this study was to evaluate the effect of implant surface-treated with different size of TiO2 nanotubes on osseointegration in rat femur. The customized implants (threaded and nonthreaded type), surface-treated with different diameter of TiO2 nanotubes (30 nm, 50 nm, 70 nm, and 100 nm nanotube), were placed on both sides of the femur of 50 male Sprague-Dawley rats (6 weeks old). Rats were sacrificed at 2 and 6 weeks following surgery; then the specimens were collected by perfusion fixation and the osseointegration of implants was evaluated by radiographic and histologic analyses and removal torque value test. The mean of bone area (%) and the mean of removal torque were different in each group, indicating that the difference in TiO2 nanotube size may influence new bone formation and osseointegration in rats

UV Photocatalysis of Bone Marrow-Derived Macrophages on TiO2 Nanotubes Mediates Intracellular Ca2+ Influx via Voltage-Gated Ca2+ Channels

Titanium (Ti) possesses excellent properties for use in dental implants but has low osteogenic surface properties that result in limiting rapid osseointegration. The physiological interaction between the surface of the implant material and bone cells, especially osteoclasts, is a crucial factor in determining successful osseointegration. However, the details of such an interaction remain elusive. Here, we demonstrated that nanotopography on the Ti surface is a crucial factor for modulating intracellular signal transduction in bone marrow-derived macrophages (BMMs). To define this, intracellular Ca2+ and ROS were simultaneously measured in BMMs that were seeded on polished Ti and TiO2 nanotubes. We found that UV photocatalysis of TiO2 immediately elicits intracellular calcium concentration ([Ca2+]i) increase and intracellular reactive oxygen species concentration ([ROS]i) reduction in cells on TiO2 nanotubes. UV photocatalysis-mediated [Ca2+]i increase is dependent on extracellular and intracellular ROS generation. Furthermore, extracellular Ca2+ influx through voltage-gated calcium channels (VGCCs) is critical for the UV photocatalysis-mediated [Ca2+]i increase, while phospholipase C (PLC) activation is not required. Considering the physiological roles of Ca2+ signaling in BMMs and osteoclastogenesis, nanotopography on the Ti surface should be considered an important factor that can influence successful dental implantation

The Effect of Covalently Immobilized FGF-2 on Biphasic Calcium Phosphate Bone Substitute on Enhanced Biological Compatibility and Activity

The purpose of this research was to covalently graft fibroblast growth factor 2 (FGF-2) onto biphasic calcium phosphate (BCP) via a bifunctional cross-linker technique and to estimate the optimal dose of FGF-2 resulting in the best osteogenic differentiation of human mesenchymal stem cells (hMSCs). SEM observation revealed that the surface of the 100 ng FGF-2 coated BCP was completely covered with the nanoparticles expected to be from the silane coupling agent. XRD, FT-IR, and XPS analysis showed that silane treatment, bifunctional cross-linker coating, and FGF-2 covalent grafts were conducted successfully without deforming the crystalline structure of BCP. An MTT assay demonstrated that FGF-2 coated BCP had good biocompatibility, regardless of the concentration of FGF-2, after 24 or 48 h of incubation. An alkaline phosphatase (ALP) activity assay (14 days of incubation) and the ALP gene expression level of real-time PCR analysis (7 days of incubation) revealed that 50, 100, and 200 ng FGF-2 coated BCP induced the highest activities among all experimental groups and control group (P<0.05). Thus, low concentrations of FGF-2 facilitated excellent osteogenesis and were effective at enhancing osteogenic potential. Also, the bifunctional cross-linker technique is expected to be a more feasible way to induce osteogenic differentiation while minimizing the risk of FGF-2 overdose