Gary Pickrell

A review of bioactive glasses: Their structure, properties, fabrication and apatite formation

Bioactive glass and glass-ceramics are used in bone repair applications and are being developed for tissue engineering applications. Bioactive glasses/Bioglass are very attractive materials for producing scaffolds devoted to bone regeneration due to their versatile properties, which can be properly designed depending on their composition. An important feature of bioactive glasses, which enables them to work for applications in bone tissue engineering, is their ability to enhance revascularization, osteoblast adhesion, enzyme activity and differentiation of mesenchymal stem cells as well as osteoprogenitor cells. An extensive amount of research work has been carried out to develop silicate, borate/borosilicate bioactive glasses and phosphate glasses. Along with this, some metallic glasses have also been investigated for biomedical and technological applications in tissue engineering. Many trace elements have also been incorporated in the glass network to obtain the desired properties, which have beneficial effects on bone remodeling and/or associated angiogenesis. The motivation of this review is to provide an overview of the general requirements, composition, structure-property relationship with hydroxyapatite formation and future perspectives of bioglasses.Attention has also been given to developments of metallic glasses and doped bioglasses along with the techniques used for their fabrication.

Novel data processing techniques for dispersive white light interferometer

White light interferometry has been used in the sensing area for many years. A novel data processing method for demodulating the information from the interference spectrum of a white light system is presented. Compared with traditional algorithms, both high-resolution and large dynamic range have been achieved with a relatively low-cost system. Details of this arithmetic are discussed. A compact white light interferometric system employing this algorithm has been developed, combined with fiber Fabry-Perot sensors. A60.5-nm stability over 48 hours with a dynamic range on the order of tens of microns has been achieved with this system. The temperature dependence of this system has been analyzed, and a self-compensating data processing approach is adopted. Experimental results demonstrated a 61.5-nm shift in the temperature range of 10 to 45°C.

Random-hole optical fiber evanescent-wave gas sensing

Research on development of optical gas sensors based on evanescent-wave absorption in random-hole optical fibers is described. A process to produce random-hole optical fibers was recently developed that uses a novel in situ bubble formation technique. Gas molecules that exhibit characteristic vibrational absorption lines in the near-IR region that correspond to the transmission window for silica optical fiber have been detected through the evanescent field of the guided mode in the pore region. The presence of the gas molecules in the holes of the fiber appears as a loss at wavelengths that are characteristic of the particular gas species present in the holes. An experimental setup was constructed with these holey fibers for detection of acetylene gas. The results clearly demonstrate the characteristic absorptions in the optical spectra that correspond to the narrow-line absorptions of the acetylene gas, and this represents what is to our knowledge the first report of random-hole fiber gas sensing in the literature.

Novel techniques for the fabrication of holey optical fibers

Recently developed optical fibers rely on an array of air holes in the cladding to confine light to the fiber core as opposed to conventional telecommunications fibers that require a refractive index difference produced by different composition glasses in the core and cladding regions. Holey fibers have been fabricated by drawing an array of tubes stacked around a solid central core. In this paper, we describe a new technique to produce the holes (or pores) in the cladding region. These new fibers have been made by drawing a preform, consisting of a porous outer cladding region surrounding a solid central core region, into a fiber. During the fiber drawing process, the pores initially present in the preform cladding region are drawn into small, long, thin tubular pores. Controlling the dimensions and distribution of the pores in the preform can control the physical dimensions and distribution of the pores in the fiber. In some of the preforms, the porous cladding region in the preform was prepared by sol gel techniques. The preform fabrication process and fiber drawing process used to produce these new holey fibers as well as the results of the morphological study elucidating the size, shape and distribution of the porous phase are presented.

High-temperature fiber-tip pressure sensor

This paper presents a miniature fiber-optic high-temperature pressure sensor fabricated on the tip of a singlemode (SM) fiber by means of fusion splicing, cleaving, and wet chemical etching. A new approach was developed to simplify the fabrication and greatly improve the sensitivity. The sensor is made entirely of fused silica, whose high-temperature sensing capability is explored in detail for the first time. Two sensors were tested up to 611/spl deg/C and 710/spl deg/C, respectively, showing excellent repeatability better than 0.62% and 1.4%. The maximum operating temperature is limited by the mechanical creep of the fused silica diaphragm.

A novel temperature-insensitive optical fiber pressure sensor for harsh environments

A novel diaphragm-based miniature optical fiber pressure sensor has been shown to work at temperatures up to 700/spl deg/C with a sensitivity of 2.93 nm/psi and a resolution of 0.01 psi (68.9 Pa). A passive temperature compensation scheme was used to reduce the temperature dependence to 0.0076 psi//spl deg/C (52.4 Pa//spl deg/C). The sensor exhibited a linear response in the available testing range from 0 to 200 psi (1.38 MPa), and being composed entirely of fused silica, the sensors structure is very reliable, corrosion resistant, and immune to electromagnetic interference.

Single-crystal sapphire fiber-based strain sensor for high-temperature applications

Single-crystal sapphire fibers have a very high melting point (up to 2050/spl deg/C), which renders them a very good candidate for sensing applications at a very high temperature. We present in this paper the recent work of developing single-crystal sapphire fiber extrinsic Fabry-Perot interferometric strain sensors based on the white-light interferometric spectrum demodulation technique. Prototype sapphire strain sensors were fabricated and tested at high temperatures up to 1004/spl deg/C. The preliminary experimental results indicate that the sensors are promising to be used under high-temperature environments for making strain measurements with strain measurement resolution of 0.2-/spl mu/ strain.

Signal-processing algorithm for white-light optical fiber extrinsic Fabry–Perot interferometric sensors

We present a novel signal-processing algorithm for single-mode optical fiber extrinsic Fabry-Perot interferometric sensors that can achieve both high-resolution, absolute measurement of the cavity length and a large dynamic measurement range simultaneously. The algorithm is based on an accurate model of the characteristics of a fiber-optic sensor that takes into account the phase shift that is due to the coupling of light reflected at the second surface to the lead-in fiber end.

Silica-antibiotic hybrid nanoparticles for targeting intracellular pathogens.

ABSTRACT We investigated the capability of biodegradable silica xerogel as a novel carrier of antibiotic and the efficacy of treatment compared to that with the same dose of free drug against murine salmonellosis. The drug molecules (31%) entrapped in the sol-gel matrix remained in biologically active form, and the bactericidal effect was retained upon drug release. The in vitro drug release profiles of the gentamicin from the xerogel and that from the xerogel-polyethylene glycol (PEG) were distinctly different at pH 7.4. A delayed release of gentamicin was observed from the silica xerogel network (57% in 33 h), and with the addition of 2% PEG, the release rate reached 90% in 33 h. Administration of two doses of the silica xerogel significantly reduced the Salmonella enterica serovar Typhimurium load in the spleens and livers of infected AJ 646 mice. The silica xerogel and xerogel-PEG achieved a 0.45-log and a 0.41-log reduction in the spleens, respectively, while for the free drug there was no reduction. On the other hand, silica xerogel and xerogel-PEG achieved statistically significant 1.13-log and 1.15-log reductions in the livers, respectively, while for the free drug the reduction was a nonsignificant value of 0.07 log. This new approach, which utilizes a room-temperature synthetic route for incorporating therapeutic drugs into the silica matrix, should improve the capability for targeting intracellular pathogens.

Microstructural analysis of random hole optical fibers

A new type of optical fiber, the random hole optical fiber, has been fabricated and consists of a solid silica central core region surrounded by a porous silica cladding region. The holes present in the cladding region are random in both spatial location and in size, varying from approximately 25 nm to 2.5 microns in radius. Over a thousand holes are present in the fiber. The spectral attenuation in the fiber was measured to be about 2.0 dB/m at 1550 nm. The fibers were prepared by the incorporation of a gas producing agent in the optical fiber preform, which generated the holes in situ during the fiber drawing process.