Microwave photonics interrogation for multiplexing fiber Fabry-Perot sensors.

A microwave photonics interrogation system for multiplexing fiber Fabry-Perot (FP) sensors is demonstrated in this paper. Different from previous FP demodulation schemes, this system aims at quasi-distributed sensing networks composed of FP sensors with a short effective cavity length less than 1 mm. With the help of a dispersion element, the superimposed reflected spectrum from FP sensors based on a hollow core fiber (HCF) can be converted into separate response passbands in the frequency domain simultaneously, whose center frequency will shift linearly with the variations of environment. The experimental results exhibit high linearity and interrogation ability for both the all-FP multiplexing system and hybrid multiplexing system. A strain interrogation sensitivity of 0.938 kHz/µÉ› and temperature sensitivity of -0.699 MHz/°C have been realized, corresponding to a FP cavity length demodulation sensitivity of 1.563 MHz/µm. Furthermore, numerical studies about the impacts of the HCF-FP spectrum envelope on the RF response passband, as well as the theoretical minimum detectable cavity length and multiplexing capacity of the system, are also carried out.

Macro-bending measurement based on a correlated FLRD system with an ASE source.

A passive correlated fiber loop ringdown (FLRD) system based on an amplified spontaneous emission (ASE) source is proposed and experimentally demonstrated for macro-bending measurement. Due to the randomness of spontaneous emission, the autocorrelation coefficient of ASE has an extremely narrow FWHM (0.114 ns), which allows shorter fiber loop and higher sensitivity. The experimental results show that our system with a fiber length of 2.1 m can identify the bending within tens of nanoseconds. When the bending diameter remains 2.5 cm, the sensitivity of bending turns reaches 0.0017ns-1/turn. This system provides an effective solution for fast bending fault diagnosis.

Ultrawide temperature range operation of SPR sensor utilizing a depressed double cladding fiber coated with Au-Polydimethylsiloxane.

A surface plasmon resonance (SPR) temperature sensor on the basis of depressed double cladding fiber (DDCF) is theoretically proposed and experimentally demonstrated for the first time. Simulation analysis implies that the SPR fiber optic structure consisting of a multimode fiber (MMF) inserted into an 8 mm long DDCF is highly sensitive to the refractive index (RI) of the surrounding environment, owing to their mismatched cores, large discrepancy in cladding diameters, and the depressed inner cladding in DDCF. The experimental results further verify that the highest RI sensitivity is 7002 nm/RIU established with a 50nm Au coated DDCF-SPR sensor. Additionally, the temperature sensitivity reaches up to -2.27 nm/°C within a wide working temperature range of -30 to 330 °C by combining polydimethylsiloxane (PDMS) film as the temperature sensitive material with DDCF-Au architecture. The integrated PDMS, Au and DDCF temperature sensor possesses high performance in terms of sensing capability and physical construction, opening a route to their potential applications in other types of sensors.

Exploring the dark side of MTT viability assay of cells cultured onto electrospun PLGA-based composite nanofibrous scaffolding materials.

One major method used to evaluate the biocompatibility of porous tissue engineering scaffolding materials is MTT (3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) assay. The MTT cell viability assay is based on the absorbance of the dissolved MTT formazan crystals formed in living cells, which is proportional to the number of viable cells. Due to the strong dye sorption capability of porous scaffolding materials, we propose that the cell viability determined from the MTT assay is likely to give a false negative result. In this study, we aim to explore the effect of the adsorption of MTT formazan on the accuracy of the viability assay of cells cultured onto porous electrospun poly(lactic-co-glycolic acid) (PLGA) nanofibers, HNTs (halloysite nanotubes)/PLGA, and CNTs (multiwalled carbon nanotubes)/PLGA composite nanofibrous mats. The morphology of electrospun nanofibers and L929 mouse fibroblasts cultured onto the nanofibrous scaffolds were observed using scanning electron microscopy. The viability of cells proliferated for 3 days was evaluated through the MTT assay. In the meantime, the adsorption of MTT formazan onto the same electrospun nanofibers was evaluated and the standard concentration-absorbance curve was obtained in order to quantify the contribution of the adsorbed MTT formazan during the MTT cell viability assay. We show that the PLGA, and the HNTs- or CNTs-doped PLGA nanofibers display appreciable MTT formazan dye sorption, corresponding to 35.6-50.2% deviation from the real cell viability assay data. The better dye sorption capability of the nanofibers leads to further deviation from the real cell viability. Our study gives a general insight into accurate MTT cytotoxicity assessment of various porous tissue engineering scaffolding materials, and may be applicable to other colorimetric assays for analyzing the biological properties of porous scaffolding materials.

Controlled release and antibacterial activity of antibiotic-loaded electrospun halloysite/poly(lactic-co-glycolic acid) composite nanofibers.

Fabrication of nanofiber-based drug delivery system with controlled release property is of general interest in biomedical sciences. In this study, we prepared an antibiotic drug tetracycline hydrochloride (TCH)-loaded halloysite nanotubes/poly(lactic-co-glycolic acid) composite nanofibers (TCH/HNTs/PLGA), and evaluated the drug release and antibacterial activity of this drug delivery system. The structure, morphology, and mechanical properties of the formed electrospun TCH/HNTs/PLGA composite nanofibrous mats were characterized using scanning electron microscopy (SEM), Fourier transform infrared spectroscopy, and tensile testing. We show that the incorporation of TCH-loaded HNTs within the PLGA nanofibers is able to improve the tensile strength and maintain the three-dimensional structure of the nanofibrous mats. In vitro viability assay and SEM morphology observation of mouse fibroblast cells cultured onto the fibrous scaffolds demonstrate that the developed TCH/HNTs/PLGA composite nanofibers are cytocompatible. More importantly, the TCH/HNTs/PLGA composite nanofibers are able to release the antibacterial drug TCH in a sustained manner for 42 days and display antimicrobial activity solely associated with the encapsulated TCH drug. With the improved mechanical durability, sustained drug release profile, good cytocompatibility, and non-compromised therapeutic efficacy, the developed composite electrospun nanofibrous drug delivery system may be used as therapeutic scaffold materials for tissue engineering and drug delivery applications.

Carbon nanotube-incorporated multilayered cellulose acetate nanofibers for tissue engineering applications.

We report the fabrication of a novel carbon nanotube-containing nanofibrous polysaccharide scaffolding material via the combination of electrospinning and layer-by-layer (LbL) self-assembly techniques for tissue engineering applications. In this approach, electrospun cellulose acetate (CA) nanofibers were assembled with positively charged chitosan (CS) and negatively charged multiwalled carbon nanotubes (MWCNTs) or sodium alginate (ALG) via a LbL technique. We show that the 3-dimensional fibrous structures of the CA nanofibers do not appreciably change after the multilayered assembly process except that the surface of the fibers became much rougher than that before assembly. The incorporation of MWCNTs in the multilayered CA fibrous scaffolds tends to endow the fibers with improved mechanical property and promote fibroblast attachment, spreading, and proliferation when compared with CS/ALG multilayer-assembled fibrous scaffolds. The approach to engineering the nanofiber surfaces via LbL assembly likely provides many opportunities for new scaffolding materials design in various tissue engineering applications.

Biocompatibility of electrospun halloysite nanotube-doped poly(lactic-co-glycolic acid) composite nanofibers.

Organic/inorganic hybrid nanofiber systems have generated great interest in the area of tissue engineering and drug delivery. In this study, halloysite nanotube (HNT)-doped poly(lactic-co-glycolic acid) (PLGA) composite nanofibers were fabricated via electrospinning and the influence of the incorporation of HNTs within PLGA nanofibers on their in vitro biocompatibility was investigated. The morphology, mechanical and thermal properties of the composite nanofibers were characterized by scanning electron microscopy (SEM), tensile test, differential scanning calorimetry and thermogravimetric analysis. The adhesion and proliferation of mouse fibroblast cells cultured on both PLGA and HNT-doped PLGA fibrous scaffolds were compared through 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide assay of cell viability and SEM observation of cell morphology. We show that the morphology of the PLGA nanofibers does not appreciably change with the incorporation of HNTs, except that the mean diameter of the fibers increased with the increase of HNT incorporation in the composite. More importantly, the mechanical properties of the nanofibers were greatly improved. Similar to electrospun PLGA nanofibers, HNT-doped PLGA nanofibers were able to promote cell attachment and proliferation, suggesting that the incorporation of HNTs within PLGA nanofibers does not compromise the biocompatibility of the PLGA nanofibers. In addition, we show that HNT-doped PLGA scaffolds allow more protein adsorption than those without HNTs, which may provide sufficient nutrition for cell growth and proliferation. The developed electrospun HNT-doped composite fibrous scaffold may find applications in tissue engineering and pharmaceutical sciences.

Improved cellular response on multiwalled carbon nanotube-incorporated electrospun polyvinyl alcohol/chitosan nanofibrous scaffolds.

We report the fabrication of multiwalled carbon nanotube (MWCNT)-incorporated electrospun polyvinyl alcohol (PVA)/chitosan (CS) nanofibers with improved cellular response for potential tissue engineering applications. In this study, smooth and uniform PVA/CS and PVA/CS/MWCNTs nanofibers with water stability were formed by electrospinning, followed by crosslinking with glutaraldehyde vapor. The morphology, structure, and mechanical properties of the formed electrospun fibrous mats were characterized using scanning electron microscopy, Fourier transform infrared spectroscopy, and mechanical testing, respectively. We showed that the incorporation of MWCNTs did not appreciably affect the morphology of the PVA/CS nanofibers; importantly the protein adsorption ability of the nanofibers was significantly improved. In vitro cell culture of mouse fibroblasts (L929) seeded onto the electrospun scaffolds showed that the incorporation of MWCNTs into the PVA/CS nanofibers significantly promoted cell proliferation. Results from this study hence suggest that MWCNT-incorporated PVA/CS nanofibrous scaffolds with small diameters (around 160 nm) and high porosity can mimic the natural extracellular matrix well, and potentially provide many possibilities for applications in the fields of tissue engineering and regenerative medicine.