Optimal UAV Deployment and Resource Management in UAV Relay Networks.

UAV equipped three-dimensional (3D) wireless networks can provide a solution for the requirements of 5G communications, such as enhanced Mobile Broadband (eMBB) and massive Machine Type Communications (mMTC). Especially, the introduction of an unmanned aerial vehicle (UAV) as a relay node can improve the connectivity, extend the terrestrial base station (BS) coverage and enhance the throughput by taking advantage of a strong air-to-ground line of sight (LOS) channel. In this paper, we consider the deployment and resource allocation of UAV relay network (URN) to maximize the throughput of user equipment (UE) within a cell, while guaranteeing a reliable transmission to UE outside the coverage of BS. To this end, we formulate joint UAV deployment and resource allocation problems, whose analytical solutions can be hardly obtained, in general. We propose a fast and practical algorithm to provide the optimal solution for the number of transmit time slots and the UAV relay location in a sequential manner. The transmit power at BS and UAV is determined in advance based on the availability of channel state information (CSI). Simulation results demonstrate that the proposed algorithms can significantly reduce the computational effort and complexity to determine the optimal UAV location and transmit time slots over an exhaustive search.

Polarization-selective four-wave mixing in a degenerate multi-level system.

This paper describes the first observation of polarization-selective four-wave mixing signals in conventional coupling-probe spectroscopy, specifically, saturation absorption spectroscopy in 85Rb atoms. The four-wave mixing signal is induced by two counter-propagating laser beams in a degenerate multi-level atomic system, involving the F g = 3 → F e = 2 , 3 , and 4 transitions of the 85Rb D2 line. Consequently, the four-wave mixing signals copropagating along the probe beam induce polarization rotation of a linearly polarized probe beam. To distinguish these four-wave mixing signals from the resulting probe beam, we detect the polarization components orthogonal to the polarization direction of the input probe beam, depending on the linear polarization angles between the probe and coupling beams. The experimental findings demonstrate excellent agreement with theoretical results.

Dynamic polarization response of polarization-maintaining fibers by periodic thermal cycling method.

We report a periodic thermal cycling method to investigate the dynamic response of the polarization of a laser propagating through polarization-maintaining (PM) optical fiber, driven by periodic weak temperature modulation. Consequently, temperature modulation on the surface of the coating material of the PM fiber was found to cause a continuous periodic change in the polarization state of the output laser without approaching the steady state of the resulting dynamic polarization response. Additionally, the response was found to depend on the temperature-modulation frequency and amplitude. These experimental results are qualitatively in good agreement with that of the simple theoretical model. Our research would be applied not only to the method of measuring properties of a PM optical fiber by utilizing the continuous modulation of the differential refractive index with a wide modulation-frequency range but also to various applications of the dynamic control of the periodic refractive index in materials.

Incorporation of Calcium Sulfate Dihydrate into Hydroxyapatite Microspheres To Improve the Release of Bone Morphogenetic Protein-2 and Accelerate Bone Regeneration.

In this study, hydroxyapatite (HA)-based microspheres with the ability to deliver bone morphogenetic protein-2 (BMP-2) were developed for accelerating bone regeneration. The incorporation of calcium sulfate dihydrate (CSD) in the HA matrix improved the rate of BMP-2 release from the microspheres. Under physiological conditions, the CSD fully degraded within 7 days and generated pore channels in the microspheres. The porosity and pore size of the HA-CSD microspheres after CSD degradation were 34.3% ± 4.2% and 11.5 ± 2.4 µm, respectively, significantly larger than those of the HA microspheres (23.9% ± 3.1% and 8.7 ± 0.9 µm, respectively). The increased porosity directly affected the rate of BMP-2 release from the microspheres. An in vitro experiment showed that both the BMP-2 release rate and the total amount of BMP-2 released increased considerably when incorporating the HA microspheres with CSD. BMP-2 was released slowly from the HA microspheres for up to 6 weeks. BMP-2 release was notably improved in the HA-CSD biphasic microspheres compared to the microspheres without CSD; the rate of release was 2.4-times faster due to the pores created by CSD dissolution after 7 days. Prior to animal testing, in vitro cell tests were performed to evaluate the biocompatibility of the HA-CSD microspheres. During CSD dissolution, biocompatible bone-like apatite precipitated on the cell surfaces, and preosteoblasts grew on the microspheres. In vivo experiments using a rabbit lateral femoral condyle defect model demonstrated that the level of bone regeneration was significantly enhanced by mineralization on the surface, generated additional pores as well as improved BMP-2 release behavior. The HA-CSD microspheres accelerated new bone growth to fill the entire defect in 6 weeks, corresponding to a 170% improvement in performance compared to the HA microspheres.

Facile strategy involving low-temperature chemical cross-linking to enhance the physical and biological properties of hyaluronic acid hydrogel.

Here, we present a novel strategy to fabricate hyaluronic acid (HA) hydrogels with excellent physical and biological properties. The cross-linking of HA hydrogel by butanediol diglycidyle ether (BDDE) was characterized under different reaction temperatures, and the resulting physical properties (i.e., the storage modulus and swelling ratio) were measured. The ratio between the cross-linking rate (a strengthening effect) and the hydrolysis rate (a weakening effect) was much greater with lower cross-linking temperatures after sufficient cross-linking time, resulting in a noticeably higher storage modulus. As the cross-linking temperature decreased, the formed HA hydrogel structure became denser with smaller pores. Moreover, the introduction of low-temperature HA cross-linking strategy also resulted in an enhanced several important characteristics of HA hydrogels including its enzymatic resistivity and its ability to elicit a cellular response. These results indicate the performance of HA hydrogels can be markedly enhanced without further additives or modifications, which is expected to contribute to the advancement of applications of HA hydrogels in all industrial fields.

Hyaluronic acid-hydroxyapatite nanocomposite hydrogels for enhanced biophysical and biological performance in a dermal matrix.

A hyaluronic acid (HAc)-hydroxyapatite (HAp) nanocomposite (HAc-nanoHAp) hydrogel was fabricated through an in situ precipitation process for mechanical and biological enhancement as a soft tissue augmentation product. In this study, these composite hydrogel fillers were analyzed from three different perspectives and compared with pure HAc hydrogel for soft tissue augmentation application: (1) rheological behaviors, (2) in vivo lateral diffusion under mouse skin, and (3) wrinkle improvement in a photo-aged mouse model. HAc-nanoHAp provided great improvement to wrinkles because of its higher stiffness and gel cohesiveness in comparison with that of pure HAc. HAc-nanoHAp also presented great enhancement in strengthening the dermal matrix by stimulating the synthesis of collagen and elastin. Thus, HAc-nanoHAp filler has great potential as a soft tissue augmentation product, improving the biophysical and biological performance in skin tissue. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 105A: 3315-3325, 2017.

Cytocompatibility of Ti3AlC2, Ti3SiC2, and Ti2AlN: In Vitro Tests and First-Principles Calculations.

Herein, the cytocompatibility of selected MAX phases, Ti3AlC2, Ti3SiC2, and Ti2AlN, were systematically evaluated using in vitro tests for the first time. These phases were anoxic to preosteoblasts and fibroblasts. Compared with the strong viable fibroblasts, the different cellular responses of these materials were clearly distinguishable for the preosteoblasts. Under an osteoblastic environment, Ti2AlN exhibited better cell proliferation and differentiation performance than Ti3AlC2 and Ti3SiC2. Moreover, the performance was superior to that of a commercial Ti-6Al-4V alloy and comparable to that of pure Ti. A possible mechanism was suggested based on the different surface oxidation products, which were determined from the binding energy of adsorbed Ca2+ ions using first-principles calculations. Compared with the partially oxidized TiCxOy layer on Ti3AlC2 and Ti3SiC2, the partially oxidized TiNxOy layer on the Ti2AlN had a stronger affinity to the Ca2+ ions, which indicated the good cytocompatibility of Ti2AlN.

Multiscale porous titanium surfaces via a two-step etching process for improved mechanical and biological performance.

Titanium (Ti)-based dental implants with multiscale surface topography have attracted great attention as a promising approach to enhance fixation and long-term stability of the implants, through the synergistic effect of nano- and microscale surface roughness, for accelerated bone regeneration and improved mechanical interlocking. However, structural integrity and mechanical stability of the multiscale roughened Ti surface under deformation need to be considered because significant deformation of dental implants is often induced during the surgical operation. Therefore, in this study, a well-defined nanoporous structure was directly introduced onto micro-roughened Ti surfaces through target-ion induced plasma sputtering (TIPS) with a tantalum (Ta) target, following sand-blasted, large-grit and acid-etching (SLA). This two-step etching process successfully created multiscale surface roughness on Ti with a minimal change of the pre-formed microscale roughness. Moreover, TIPS allowed the Ti surface to possess good mechanical stability under deformation and improved hydrophilicity, through altering the surface chemistry of brittle and hydrophobic SLA-treated Ti without formation of the interface between nanoporous and microporous structures. The in vitro and in vivo tests confirmed that multiscale roughened Ti significantly enhanced osteoblast attachment, proliferation and differentiation, which eventually led to improved bone regeneration and osseointegration, compared to smooth and micro-roughened Ti.

Long-lasting and bioactive hyaluronic acid-hydroxyapatite composite hydrogels for injectable dermal fillers: Physical properties and in vivo durability.

Hyaluronic acid (HAc)-hydroxyapatite (HAp) composite hydrogels were developed to improve the biostability and bioactivity of HAc for dermal filler applications. Two kinds of HAc-HAp composite fillers were generated: HAcmicroHAp and HAc-nanoHAp composites. HAc-microHAp was fabricated by mixing HAp microspheres with HAc hydrogels, and HAc-nanoHAp was made by in situ precipitation of nano-sized HAp particles in HAc hydrogels. Emphasis was placed on the effect of HAp on the durability and bioactivity of the fillers. Compared with the pure HAc filler, all of the HAc-HAp composite fillers exhibited significant improvements in volumetric maintenance based on in vivo tests owing to their reduced water content and higher degree of biointegration between the filler and surrounding tissues. HAc-HAp composite fillers also showed noticeable enhancement in dermis recovery, promoting collagen and elastic fiber formation. Based on their long-lasting durability and bioactivity, HAc-HAp composite fillers have great potential for soft tissue augmentation with multifunctionality.