Ultra-compact and polarization-insensitive silicon waveguide 3 × 3 star-crossing based on composite subwavelength grating metamaterials.

We present what we believe is the first report on a polarization-insensitive 3 × 3 silicon star-crossing utilizing a composite subwavelength metamaterial waveguide structure. Two different types of subwavelength grating metamaterials (nanohole grating and fan-shaped bent subwavelength grating) are respectively used to address diffraction issues in the crossing region and mode interference issues caused by a compact non-adiabatic design. This approach results in a device with an ultra-compact footprint of 12.68 × 10.98 µm2 on a standard 220 nm silicon-on-insulator (SOI) platform. Simulation results show low insertion loss (IL) values of <0.2 dB/0.3 dB and suppressed cross talk (CT) levels of <-27.2 dB/-23.6 dB for TE/TM polarizations across a wavelength range of 100 nm (1500-1600 nm). Experimental measurements of the fabricated devices confirm outstanding performance, with IL values of <0.35 dB/0.4 dB and CT levels of <-31.5 dB/-28.6 dB for TE/TM polarization in the C-band.

High-performance and ultra-wide bandwidth silicon TM polarizer with suppressed reflection utilizing a tailored contra-mode conversion Bragg grating.

We present a compact TM polarizer with high polarization extinction ratio (PER), low loss, and suppressed reflection over an ultra-wide bandwidth on a 220 nm silicon-on-insulator (SOI) platform. The device utilizes a contra-mode conversion Bragg grating (CMC-BG) with strong polarization dependence embedded in a multimode waveguide. Through a sophisticated grating design incorporating tailored chirping and apodization profiles to match modal properties, we have achieved, by simulation, a compact device footprint of 34.72 × 1.22 µm2 and an ultra-wide bandwidth of 346 nm with PER > 40 dB and an insertion loss (IL) < 1 dB, a 5-fold increase over our previous design. Particularly notable is the polarizer's ability to suppress reflection to <-15 dB across an extended bandwidth exceeding 450 nm. Experimental measurements confirm the excellent performance of the fabricated TM polarizer, with IL < 1.2 dB (0.5 dB) and PER > 30 dB over a bandwidth of 336 nm (268 nm).

All-silicon TM polarizer covering the 1260-1675†nm bandwidth using a band engineered subwavelength grating waveguide.

A TM polarizer working for whole optical communication bands with high performance is proposed on a 220-nm-thick silicon-on-insulator (SOI) platform. The device is based on polarization-dependent band engineering in a subwavelength grating waveguide (SWGW). By utilizing an SWGW with a relatively larger lateral width, an ultra-broad bandgap of ∼476 nm (1238 nm-1714nm) is obtained for the TE mode, while the TM mode is well supported in this range. Then, a novel tapered and chirped grating design is adopted for efficient mode conversion, which results in a polarizer with a compact footprint (3.0 µm × 18 µm), low insertion loss (IL < 1.15 dB) and high polarization extinction ratio (PER > 21 dB) covering O-U bands (1260 nm-1675 nm). Experimental results show that the fabricated device has an IL < 1.0 dB and PER > 22 dB over a 300- nm bandwidth, which is limited by our measurement setup. To the best of our knowledge, no TM polarizer on the 220-nm SOI platform with comparable performance covering O-U bands has ever been reported.

Experimental demonstration of a flexible and high-performance mode-order converter using subwavelength grating metamaterials.

Mode-order converters, transforming a given mode into the desired mode, have an important implication for the multimode division multiplexing technology. Considerable mode-order conversion schemes have been reported on the silicon-on-insulator platform. However, most of them can only convert the fundamental mode to one or two specific higher-order modes with low scalability and flexibility, and the mode conversion between higher-order modes cannot be achieved unless a total redesign or a cascade is carried out. Here, a universal and scalable mode-order converting scheme is proposed by using subwavelength grating metamaterials (SWGMs) sandwiched by tapered-down input and tapered-up output tapers. In this scheme, the SWGMs region can convert, TEp mode guided from a tapered-down taper, into a TE0-like-mode-field (TLMF) and vice versa. Thereupon, a TEp-to-TEq mode conversion can be realized by a two-step process of TEp-to-TLMF and then TLMF-to-TEq, where input tapers, output tapers, and SWGMs are carefully engineered. As examples, the TE0-to-TE1, TE0-to-TE2, TE0-to-TE3, TE1-to-TE2, and TE1-to-TE3 converters, with ultracompact lengths of 3.436-7.71 µm, are reported and experimentally demonstrated. Measurements exhibit low insertion losses of < 1.8 dB and reasonable crosstalks of < -15 dB over 100-nm, 38-nm, 25-nm, 45-nm, and 24-nm working bandwidths. The proposed mode-order converting scheme shows great universality/scalability for on-chip flexible mode-order conversions, which holds great promise for optical multimode based technologies.

Sequential anti-inflammatory and osteogenic effects of a dual drug delivery scaffold loaded with parthenolide and naringin in periodontitis.

PURPOSE: Our pilot study showed that a 3-dimensional dual drug delivery scaffold (DDDS) loaded with Chinese herbs significantly increased the regenerated bone volume fraction. This study aimed to confirm the synergistic anti-inflammatory and osteogenic preclinical effects of this system. METHODS: The targets and pathways of parthenolide and naringin were predicted. Three cell models were used to assess the anti-inflammatory effects of parthenolide and the osteogenic effects of naringin. First, the distance between the cementoenamel junction and alveolar bone crest (CEJ-ABC) and the bone mineral density (BMD) of surgical defects were measured in a rat model of periodontitis with periodontal fenestration defects. Additionally, the mRNA expression levels of matrix metallopeptidase 9 (MMP9) and alkaline phosphatase (ALP) were measured. Furthermore, the number of inflammatory cells and osteoclasts, as well as the protein expression levels of tumor necrosis factor-alpha (TNF-α) and levels of ALP were determined. RESULTS: Target prediction suggested prostaglandin peroxidase synthase (PTGS2) as a potential target of parthenolide, while cytochrome P450 family 19 subfamily A1 (CYP19A1) and taste 2 receptor member 31 (TAS2R31) were potential targets of naringin. Parthenolide mainly targeted inflammation-related pathways, while naringin participated in steroid hormone synthesis and taste transduction. In vitro experiments revealed significant anti-inflammatory effects of parthenolide on RAW264.7 cells, and significant osteogenic effects of naringin on bone marrow mesenchymal stem cells and MC3T3-E1 cells. DDDS loaded with parthenolide and naringin decreased the CEJ-ABC distance and increased BMD and ALP levels in a time-dependent manner. Inflammation was significantly alleviated after 14 days of DDDS treatment. Additionally, after 56 days, the DDDS group exhibited the highest BMD and ALP levels. CONCLUSIONS: DDDS loaded with parthenolide and naringin in a rat model achieved significant synergistic anti-inflammatory and osteogenic effects, providing powerful preclinical evidence.

Highly scalable and flexible on-chip all-silicon mode filter using backward mode conversion gratings.

Mode filters are fundamental elements in a mode-division multiplexing (MDM) system for reducing modal cross-talk or realizing modal routing. However, the previously reported silicon mode filters can only filter one specific mode at a time and multiple modes filtering usually needs a cascade of several filters, which is adverse to highly integrated MDM systems. Here, we propose a unique concept to realize compact, scalable and flexible mode filters based on backward mode conversion gratings elaborately embedded in a multimode waveguide. Our proposed method is highly scalable for realizing a higher-order-mode-pass or band-mode-pass filter of any order and capable of flexibly filtering one or multiple modes simultaneously. We have demonstrated the concept through the design of four filters for different order of mode(s) and one mode demultiplexer based on such a filter, and the measurement of two fabricated 11µm length filters (TE1-pass/TE2-pass) show that an excellent performance of insertion loss <1.0dB/1.5dB and extinction ratio >29dB/28.5dB is achieved over a bandwidth of 51.2nm/48.3nm, which are competitive with the state-of-the-art.

An oral delivery vehicle based on konjac glucomannan acetate targeting the colon for inflammatory bowel disease therapy.

Orally administered colon-targeted delivery vehicles are of major importance in the treatment of inflammatory bowel disease (IBD). However, it remains a challenge to maintain the integrity of such delivery vehicles during treatment, particularly in the gastric environment, which may cause untimely drug release before reaching the targeted colon. Herein, an oral colon-targeted drug delivery system (OCDDS) based on acetylated konjac glucomannan (AceKGM) has been developed in this work, which accomplishes colonic localization release and targets local inflammatory macrophages. The AceKGM nanoparticle-loading curcumin (Cur) was successfully fabricated by emulsion solvent evaporation techniques. DLS, AFM, and SEM were used in order to evaluate the nanoparticles' diameter as well as their in vitro drug release profile, and reactive oxygen species (ROS) scavenging results showed that the OCDDS considerably retained the activity of Cur treated with simulated gastric fluid (SGF) and controllably released in simulated intestinal fluid (SIF). In addition, the adhesion experiment results indicated that the nanoparticle could accumulate on the colonic macrophages. Evaluations in colitis mice showed that the treatment significantly alleviated the symptoms of colitis by decreasing the local level of myeloperoxidase (MPO) and the disease activity index (DAI) score in mice. In summary, the results of our research demonstrate that Cur-AceKGM nanoparticles exhibit significantly improved therapeutic efficacy compared to orally administered free Cur and can be developed as an effective drug delivery vehicle for IBD treatment.

Compact and ultra-broadband all-silicon TM-pass and TE-reflected polarizer using grating based weakly coupled nanowires.

On-chip silicon polarizers with broad operating bandwidth and compact footprint have recently attracted increasing attention for their applications in large capacity and high density integrated optical systems. However, strong waveguide dispersion usually limits the bandwidth of the silicon polarizers, especially for the TM-pass polarizers. In this paper, we overcome the bandwidth limit of the TM polarizer by utilizing a novel waveguide structure composed of two weakly coupled nanowires with gratings sandwiched in between. Such a structure can effectively enlarge the bandgap for the undesired TE polarized light, while act as a low loss subwavelength metamaterial for TM polarized light over an extremely large wavelength range. In simulation, we obtain a compact polarizer of 13.6 µm × 1.3 µm in size with an ultra-broad operating bandwidth of ∼362 nm for extinction ratios (ERs) >21 dB and insertion losses (ILs) <1 dB, which covers E-, S-, C-, L-, and U-bands and part of O-band. The measurements of fabricated devices show that the device performed well in the test wavelength range from 1300 to 1600 nm with an ER >15 dB and an average IL ∼1 dB, consistent with the simulation results. This work paves a new way for designing compact and ultra-broadband on-chip polarizers.

In vivo and in vitro evaluation of chitosan-modified bioactive glass paste for wound healing.

In this work, the role of chitosan (CS) in improving the properties of bioactive glass (BG) paste for wound healing was studied. Based on in vitro evaluation, it was found that the addition of CS neutralizes the pH value from 11.0 to 7.5, which did not lead to decreasing the bioactivity of BG paste in vitro. The rheological properties showed that the composite paste had higher bio-adhesion and better affinity with the skin surface than either CS or the BG paste. The antibacterial property evaluation showed that the composite paste had stronger antibacterial activity than either CS or BG paste and promoted the proliferation of HUVECs (human umbilical vein endothelial cells) and HaCat (human immortalized keratinocyte cells). Comparatively, the effect of promoting the proliferation of HUVECs is more significant than that of HaCat. The burn-wound model of rat was developed for evaluating in vivo activity, and the addition of CS effectively promoted wound healing without obvious inflammation according to the IL-1ß and IL-6 staining. This novel paste is expected to provide a promising alternative for wound healing.

Reduced graphene oxide-coated electrospun fibre: effect of orientation, coverage and electrical stimulation on Schwann cells behavior.

Electrical signals are present in the extracellular spaces between neural cells. To mimic the electrophysiological environment for peripheral nerve regeneration, this study was intended to investigate how conductive graphene-based fibrous scaffolds with aligned topography regulate Schwann cell behavior in vitro via electrical stimulation (ES). To this end, randomly- and uniaxially-aligned polycaprolactone fibrous scaffolds were fabricated by electrospinning, followed by coating with reduced graphene oxide (rGO) via vacuum filteration. SEM revealed that rGO was successfully coated on the fibers without changing their alignment, and also brought about an improvement in mechanical properties and hydrophilicity. The electrical conductivity of the rGO-coated fibrous scaffold was up to 0.105 S m-1. When Schwann cells were seeded on the scaffolds and stimulated by 10 mV in vitro, it was found that either the alignment of the fibers or ES led to a higher level of proliferation and nerve growth factor (NGF) expression of Schwann cells. Further, ES at the aligned fibrous topography enhanced the expression of NGF, the proliferation of Schwann cells, and enhanced the cell migration rate by more than 60% compared to either ES or the oriented fibers alone. The application of exogenous electric cues mediated by templated biomaterials provides profound insights for nerve regeneration.

Synergetic effect of growth factor and topography on fibroblast proliferation.

An innovative basic fibroblast growth factor (bFGF)-loaded polycaprolactone (PCL) fibrous membrane with highly aligned structure is developed for guided tissue regeneration (GTR). The aligned membrane is fabricated by electrospinning. In order to make efficient use of bFGF, PCL electrospun fibrous membrane is firstly surface-coated by self-polymerization of dopamine, and followed by immobilization of heparin via covalent conjugation to the polydopamine (PDA) layer. Subsequently, bFGF is loaded by binding to heparin. The loading yield of bFGF on heparin-immobilized PDA-coated PCL membrane significantly increases to around 7 times as compared with that of pure PCL membrane. NIH-3T3 cells show an enhanced proliferation and exhibit a stretched morphology aligned along the direction of the fibers on the aligned membranes. However, aligned bFGF-loaded PCL membrane exhibit a similar morphology but a highest cell density prolonged till 9 days. The synergetic effect of growth factor and topography would effectively regulate cell proliferation.

Bioadaptive nanorod array topography of hydroxyapatite and TiO2 on Ti substrate to preosteoblast cell behaviors.

Bioadaptive nanostructure coatings of hydroxyapatite (HAP) and TiO2 on titanium (Ti) implants are essential for biomaterial-tissue osteointegration. However, there is no specific report, so far, that focuses on the different influences of the two bioadaptive coatings on preosteoblast behaviors. Herein, adhesion, proliferation, and osteogenic potential of preosteoblast on HAP and TiO2 coatings with nanorod array topography were studied. XRD, TEM, and SAED analysis indicated that rod-like HAP nanoarray and anatase TiO2 nanoarray coatings were fabricated successfully, and there was insignificant difference in roughness and fibronectin adsorption of the two coatings. Adhesion and proliferation of MC3T3-E1 cells on the two coatings were of no significant difference, besides a larger projected area of the cells on HAP coating. MC3T3-E1 cells cultured on the HAP coating displayed significantly higher expression of runt-related transcription factor-2 (Runx2), osteocalcin (OCN) and collagen type-1 (Col I) after culture for 21 days compared with those on TiO2 coating, except alkaline phosphatase (ALP). This study provides beneficial suggestion for intelligent selection of biocoatings.

Synergetic effect of chemical and topological signals of gingival regeneration scaffold on the behavior of human gingival fibroblasts.

Achievement of gingiva regeneration poses a substantial challenge for dental aesthetics and periodontal disease repair, but reports of a bioactive and easily available gingival regeneration scaffold are rare. Cell behaviors can be affected by multiple kinds of bioactive signals; thus, it is important to explore the effects of the chemical and topological signals of the scaffold on the behavior of human gingival fibroblasts (HGFs). We hypothesized that the synergetic effect of the chemical and topological scaffold signals were beneficial to gingival regeneration. In this study, HGF behavior on random/aligned poly (e-caprolactone) (PCL) and polydopamine (PDA)-coated PCL electrospun scaffolds was investigated in a common medium and in basic fibroblast growth factor (bFGF) medium. The results showed that the synergistic effect of three signals was better than that of one or two signals. The cell proliferation of the aligned scaffold group was higher than that of the random scaffold, and the PCL/PDA-Aligned+bFGF group showed the highest cell proliferation. Even if two chemical signals were present, the HGFs still maintained an ordered distribution on the aligned scaffold. Cell differentiation and protein secretion analysis indicated that gene and protein expression of focal adhesion kinase and fibronectin were the highest in the PCL/PDA-Aligned+bFGF group. Taken together, the chemical and topographic signals within the electrospun scaffold were considered to display a synergistic effect on HGF behaviors, suggesting the potential usefulness of the PCL/PDA-Aligned+bFGF scaffold for gingiva tissue engineering.

A study on graphene composites for peripheral nerve injury repair under electrical stimulation.

Electrical stimulation (ES) provides an effective alternative to peripheral nerve repair via conductive scaffolds. The aim of the present study is to investigate a graphene (GR)/thermoplastic polyurethane (TPU) composite for the repair of peripheral nerve injury under ES. To this end, conductive composite membranes were fabricated by blending GR (2, 4 and 6 wt%) with TPU. GR maintains its own structure in the composite and enhances the mechanical and electrical properties of the composite. The composites with excellent biocompatibility had a hemolysis rate of less than 5%. As a result, the 4GR-TPU (4 wt% GR) sample with enhanced mechanical properties possessed the highest conductivity value of 33.45 ± 0.78 S m-1. Compared with the non-conductive sample, 4GR-TPU was favorable for the viability of Schwann cells (SCs) under ES. When different voltages of ES were applied, a direct current of 10 mV was more suitable for the growth and proliferation of SCs. This study provides beneficial information for peripheral nerve repair via ES.

Fabrication of two distinct hydroxyapatite coatings and their effects on MC3T3-E1 cell behavior.

How the surface topography of hydroxyapatite (HAP) coatings remodels hard tissue is of utmost importance and a contributing factor to ambiguity regarding this subject. Here, HAP coatings with different topographies of a rod-like nanoarray with c-axis orientation and a flake-like micro-flower array with a(b)-axis orientation on a Ti substrate were synthesized via hydrothermal-electrodeposition by controlling the concentration of electrolytes. XRD, TEM and SAED analyses indicated that the rod-like HAP nanoarray was predominant with an orientation of (001), while the HAP micro-flower samples were based on an orientation of (100). Compared to the flake-like HAP, the rod-like nanoarray HAP possessed better hydrophilic properties and lower roughness, which not only enhanced adsorption of specific fibronectin proteins but also promoted the spreading and growth of MC3T3-E1 cells. Runx2, alkaline phosphatase, collagen and osteocalcin were also analyzed by RT-PCR on the two distinctive HAP-coated samples. MC3T3-E1 cells on the rod-like nanoarray coating had higher osteo-related gene expression. This finding suggested that the ordered assembly structure of the HAP might cause topography-dependent coordination with biomolecules for enhancing osteoblast-like cell proliferation and osteogenic differentiation. This study provided an understanding of the surface's features for biomaterials to ensure better bioactivity.

Dual drug loaded coaxial electrospun PLGA/PVP fiber for guided tissue regeneration under control of infection.

Electrospinning promisingly fabricate mats for Guided Tissue Regeneration (GTR). Due to a chronic inflammatory pathology in periodontal, it is highly desirable to develop a novel GTR mats to realize tissue regeneration under control of infection. In the study, coaxial electrospinning was firstly conducted to fabricate dual drug loaded fiber mats with core/shell structure. Naringin-loaded polyvinylpyrrolidone was designed as core fiber to enrich tissue regeneration and metronidazole-loaded poly(lactic-co-glycolic acid) as shell fiber to inhibit bacterial. TEM revealed that the fibers with distinct core/shell structure were in an outer diameter of 1.5-1.7 µm with an inner diameter of <1.0 µm. The loading of dual drug decreased the tensile strength and elongation of the coaxial fiber mats. On in vitro assessment, metronidazole had a short-term release while naringin had a long-term release behavior in all the coaxial mats. The colonization of anaerobic bacteria on the mats effectively were inhibited over 21 days. Furthermore, the dual drug loaded coaxial fiber mats were observed to positively supported the adhesion and proliferation of MC3T3-E1 and was conductive to high alkaline phosphatase express. Thus, a simple and effective coaxial electrospinning approach was demonstrated for the fabrication of anti-infective GTR mats with promoting tissue regeneration.

Degradation properties of chitosan microspheres/poly(L-lactic acid) composite in vitro and in vivo.

Poly(L-lactic acid) (PLLA) is a popular biodegradable polymer, but the accumulated acid production by degradation is a bottleneck for its extended utilization. In this study, chitosan microspheres (CSMs) were introduced into PLLA porous matrices to manipulate the acid microclimate from PLLA degradation. In vitro and in vivo degradation were, respectively, performed in PBS and implanted into rat's subcutaneous. The results indicated that pH of CSMs/PLLA composites remained stable of around 7.50 in vitro until six weeks. With the increasing of CSMs, mass loss, water absorption of the composites increased, while Mv of PLLA decreased during in vitro test. Furthermore, CSMs/PLLA composites degradation in vivo could be speeded by the introduction of CSMs via obvious morphological destroy under H&E staining observation. These results indicated that incorporation of CSMs not only buffered the acidic microclimate but also improved the degradation of PLLA. The tunable degradation behavior and moderate degradation microclimate of CSMs/PLLA composites developed in the study would provide benefits for its biomedical application.

Study on structure, mechanical property and cell cytocompatibility of electrospun collagen nanofibers crosslinked by common agents.

Collagen electrospun scaffolds properly reproduce the framework of the extracellular matrix (ECM) of tissues that are natural with the fibrous morphology of the protein by coupling large biomimetism of the biological material. However, traditional solvents employed for collagen electrospinning lead to poor mechanical attributes and bad hydro-stability. In this work, by N-(3-dimethylaminopropyl)-N'-ethylcarbodiimide hydrochloride with N-hydroxysulfosuccinimide (EDC-NHS), glutaraldehyde (GTA) and genipin (GP) respectively, electrospun collagen fibers cross-linked, effectively stabilized the fiber morphology over 2months and improved the mechanical properties in both dry and wet state, especially EDC-NHS with large ultimate tensile stress and εb. The secondary structure of collagen structure still remained and had no obvious difference among various crosslinked samples according to FTIR. On the cell assessment, electrospun collagen fibers crosslinked by EDC-NHS, GTA and GP, were found to support cell adhesion, spreading and proliferation of MC3T3-E1. By contrast, GTA was more effective in preserving explicit fibrous morphology with a relatively lower cell viability both in FBS and BSA soaked mats. Interestingly, GP also had the similar cytocompatibility of MC3T3-E1 as EDC-NHS did. The study proved the feasibility of chemical crosslinker to electrospun collagen for biomedical application.

In vitro evaluation of electrospun PLGA/PLLA/PDLLA blend fibers loaded with naringin for guided bone regeneration.

The present study was to evaluate fiber mesh loaded with naringin via electrospinning to guide bone regeneration in vitro. The naringin-loaded fiber mesh was prepared via elctrospinning of PLGA, PLLA, PDLLA blending solution with naringin. SEM showed that naringin decreased the fiber's diameter according to the concentration of naringin. After 20 days' degradation in PBS, the drug-loaded fiber meshes still kept their stability with about 10% decrease in tensile strength. In vitro release experiments showed a sustained and steady naringin releasing profile with little initial burst releasing. Compared to the mats without naringin, the fiber mats loaded with naringin showed the most pronounced enhancement of cell growth when MC3T3-E1 cells were cultured on the fiber mats. The blend fiber loaded with naringin has optimized physical properties and sustained release profile in vitro. The study presents a promising fibrous mesh material for guided bone regeneration therapy.