Novel biodegradable fibres for applications in tissue engineering and drug delivery

The preparation and characterisation of novel biodegradable polymer fibres for application in tissue engineering and drug delivery are reported. Poly(e-caprolactone) (PCL) fibres were produced by wet spinning from solutions in acetone under low shear (gravity flow) conditions. The tensile strength and stiffness of as-spun fibres were highly dependent on the concentration of the spinning solution. Use of a 6% w/v solution resulted in fibres having strength and stiffness of 1.8 MPa and 0.01 GPa respectively, whereas these values increased to 9.9 MPa and 0.1 GPa when fibres were produced from 20% w/v solutions. Cold drawing to an extension of 500% resulted in further increases in fibre strength (up to 50 MPa) and stiffness (0.3 GPa). Hot drawing to 500% further increased the fibre strength (up to 81 MPa) and stiffness (0.5 GPa). The surface morphology of as-spun fibres was modified, to yield a directional grooved pattern by drying in contact with a mandrel having a machined topography characterised by a peak-peak separation of 91 mm and a peak height of 30 mm. Differential scanning calorimetery (DSC) analysis of as-spun fibres revealed the characteristic melting point of PCL at around 58°C and a % crystallinity of approximately 60%. The biocompatibility of as-spun fibres was assessed using cell culture. The number of attached 3T3 Swiss mouse fibroblasts, C2C12 mouse myoblasts and human umbilical vein endothelial cells (HUVECs) on as-spun, 500% cold drawn, and gelatin coated PCL fibres were observed. The results showed that the fibres promoted cell proliferation for 9 days in cell culture and was slightly lower than on tissue culture plastic. The morphology of all cell lines was assessed on the various PCL fibres using scanning electron microscopy. The cell function of HUVECs growing on the as-spun PCL fibres was evaluated. The ability HUVECs to induce an immune response when stimulated with lipopolysaccaride (LPS) and thereby to increase the amount of cell surface receptors was assessed by flow cytometry and reverse transcription-polymerase chain reaction (RT-PCR). The results showed that PCL fibres did not inhibit this function compared to TCP. As-spun PCL fibres were loaded with 1 % ovine albumin (OVA) powder, 1% OVA nanoparticles and 5% OVA nanoparticles by weight and the protein release was assessed in vitro. PCL fibres loaded with 1 % OVA powder released 70%, 1% OVA nanoparticle released 60% and the 5% OVA nanoparticle released 25% of their protein content over 28 days. These release figures did not alter when the fibres were subjected to lipase enzymatic degradation. The OVA released was examined for structural integrity by SDS-PAGE. This showed that the protein molecular weight was not altered after incorporation into the fibres. The bioactivity of progesterone was assessed following incorporation into PCL fibres. Results showed that the progesterone released had a pronounced effect on MCF-7 breast epithelial cells, inhibiting their proliferation. The PCL fibres display high fibre compliance, a potential for controlling the fibre surface architecture to promote contact guidance effects, favorable proliferation rate of fibroblasts, myoblasts and HUVECs and the ability to release pharmaceuticals. These properties recommended their use for 3-D scaffold production in soft tissue engineering and the fibres could also be exploited for controlled presentation and release of biopharmaceuticals such as growth factors.

A novel technique for polarisation mode dispersion measurements in optical fibres

A novel technique for determining the polarisation mode dispersion in optical fibres is described. The technique makes use of a sinusoidally frequency modulated source, and is applied to the measurement of the beat length of highly birefringent monomode fibre. The temporal delay between the two modes of the fibre is measured with a resolution of approximately ±0.6 ps.

Potential for broad range multiplexing of fibre Bragg gratings in polymer optical fibres and operation in the 700-nm wavelength range

Refractive index and structural characteristics of optical polymers are strongly influenced by the thermal history of the material. Polymer optical fibres (POF) are drawn under tension, resulting in axial orientation of the polymer molecular chains due to their susceptibility to align in the fibre direction. This change in orientation from the drawing process results in residual strain in the fibre and also affects the transparency and birefringence of the material (1-3). PMMA POF has failure strain as high as over 100%. POF has to be drawn under low tension to achieve this value. The drawing tension affects the magnitude of molecular alignment along the fibre axis, thus affecting the failure strain. The higher the tension the lower the failure stain will be. However, the properties of fibre drawn under high tension can approach that of fibre drawn under low tension by means of an annealing process. Annealing the fibre can generally optimise the performance of POF while keeping most advantages intact. Annealing procedures can reduce index difference throughout the bulk and also reduce residual stress that may cause fracture or distortion. POF can be annealed at temperatures approaching the glass transition temperature (Tg) of the polymer to produce FBG with a permanent blue Bragg wave-length shift at room temperature. At this elevated temperature segmental motion in the structure results in a lower viscosity. The material softens and the molecular chains relax from the axial orientation causing shrinking of the fibre. The large attenuation of typically 1dB/cm in the 1550nm spectral region of PMMA POF has limited FBG lengths to less than 10cm. The more expensive fluorinated polymers with lower absorption have had no success as FBG waveguides. Bragg grating have been inscribed onto various POF in the 800nm spectral region using a 30mW continuous wave 325nm helium cadmium laser, with a much reduced attenuation coefficient of 10dB/m (5). Fabricating multiplexed FBGs in the 800nm spectral region in TOPAS and PMMA POF consistently has lead to fabrication of multiplexed FBG in the 700nm spectral region by a method of prolonged annealing. The Bragg wavelength shift of gratings fabricated in PMMA fibre at 833nm and 867nm was monitored whilst the POF was thermally annealed at 80°C. Permanent shifts exceeding 80nm into the 700nm spectral region was attained by both gratings on the fibre. The large permanent shift creates the possibility of multiplexed Bragg sensors operating over a broad range. -------------------------------------------------------------------------------------------------------------------- 1. Pellerin C, Prud'homme RE, Pézolet M. Effect of thermal history on the molecular orientation in polystyrene/poly (vinyl methyl ether) blends. Polymer. 2003;44(11):3291-7. 2. Dvoránek L, Machová L, Šorm M, Pelzbauer Z, Švantner J, Kubánek V. Effects of drawing conditions on the properties of optical fibers made from polystyrene and poly (methyl methacrylate). Die Angewandte Makromolekulare Chemie. 1990;174(1):25-39. 3. Dugas J, Pierrejean I, Farenc J, Peichot JP. Birefringence and internal stress in polystyrene optical fibers. Applied optics. 1994;33(16):3545-8. 4. Jiang C, Kuzyk MG, Ding JL, Johns WE, Welker DJ. Fabrication and mechanical behavior of dye-doped polymer optical fiber. Journal of applied physics. 2002;92(1):4-12. 5. Johnson IP, Webb DJ, Kalli K, Yuan W, Stefani A, Nielsen K, et al., editors. Polymer PCF Bragg grating sensors based on poly (methyl methacrylate) and TOPAS cyclic olefin copolymer2011: SPIE.

Sensing properties of germanate and tellurite glass optical fibres

Strain and thermal sensitivities of germanate and tellurite glass fibres were measured using a fibre Fabry-Perot (FFP) interferometer and fibre Bragg gratings (FBG). The strain phase sensitivity for germanate and tellurite fibre were 5900×103 rad/m and 5600×103 rad/m respectively at a central wavelength of 1540nm using FFP interferometer, which is consistent with the value of 1.22pm/µepsilon obtained for a germanate fibre FBG. The Young's modulus for germanate and tellurite fibre were also measured to be 58GPa and 37GPa. The thermal responses of germanate fibre were examined as 24.71 and 16.80 pm/°C at 1540nm and 1033nm wavelength using the FBG.

Potential for broad range multiplexing of fibre Bragg gratings in polymer optical fibres and operation in the 700-nm wavelength range

Refractive index and structural characteristics of optical polymers are strongly influenced by the thermal history of the material. Polymer optical fibres (POF) are drawn under tension, resulting in axial orientation of the polymer molecular chains due to their susceptibility to align in the fibre direction. This change in orientation from the drawing process results in residual strain in the fibre and also affects the transparency and birefringence of the material (1-3). PMMA POF has failure strain as high as over 100%. POF has to be drawn under low tension to achieve this value. The drawing tension affects the magnitude of molecular alignment along the fibre axis, thus affecting the failure strain. The higher the tension the lower the failure stain will be. However, the properties of fibre drawn under high tension can approach that of fibre drawn under low tension by means of an annealing process. Annealing the fibre can generally optimise the performance of POF while keeping most advantages intact. Annealing procedures can reduce index difference throughout the bulk and also reduce residual stress that may cause fracture or distortion. POF can be annealed at temperatures approaching the glass transition temperature (Tg) of the polymer to produce FBG with a permanent blue Bragg wave-length shift at room temperature. At this elevated temperature segmental motion in the structure results in a lower viscosity. The material softens and the molecular chains relax from the axial orientation causing shrinking of the fibre. The large attenuation of typically 1dB/cm in the 1550nm spectral region of PMMA POF has limited FBG lengths to less than 10cm. The more expensive fluorinated polymers with lower absorption have had no success as FBG waveguides. Bragg grating have been inscribed onto various POF in the 800nm spectral region using a 30mW continuous wave 325nm helium cadmium laser, with a much reduced attenuation coefficient of 10dB/m (5). Fabricating multiplexed FBGs in the 800nm spectral region in TOPAS and PMMA POF consistently has lead to fabrication of multiplexed FBG in the 700nm spectral region by a method of prolonged annealing. The Bragg wavelength shift of gratings fabricated in PMMA fibre at 833nm and 867nm was monitored whilst the POF was thermally annealed at 80°C. Permanent shifts exceeding 80nm into the 700nm spectral region was attained by both gratings on the fibre. The large permanent shift creates the possibility of multiplexed Bragg sensors operating over a broad range. -------------------------------------------------------------------------------------------------------------------- 1. Pellerin C, Prud'homme RE, Pézolet M. Effect of thermal history on the molecular orientation in polystyrene/poly (vinyl methyl ether) blends. Polymer. 2003;44(11):3291-7. 2. Dvoránek L, Machová L, Šorm M, Pelzbauer Z, Švantner J, Kubánek V. Effects of drawing conditions on the properties of optical fibers made from polystyrene and poly (methyl methacrylate). Die Angewandte Makromolekulare Chemie. 1990;174(1):25-39. 3. Dugas J, Pierrejean I, Farenc J, Peichot JP. Birefringence and internal stress in polystyrene optical fibers. Applied optics. 1994;33(16):3545-8. 4. Jiang C, Kuzyk MG, Ding JL, Johns WE, Welker DJ. Fabrication and mechanical behavior of dye-doped polymer optical fiber. Journal of applied physics. 2002;92(1):4-12. 5. Johnson IP, Webb DJ, Kalli K, Yuan W, Stefani A, Nielsen K, et al., editors. Polymer PCF Bragg grating sensors based on poly (methyl methacrylate) and TOPAS cyclic olefin copolymer2011: SPIE.

Sensing properties of germanate and tellurite glass optical fibres

Strain and thermal sensitivities of germanate and tellurite glass fibres were measured using a fibre Fabry-Perot (FFP) interferometer and fibre Bragg gratings (FBG). The strain phase sensitivity for germanate and tellurite fibre were 5900×103 rad/m and 5600×103 rad/m respectively at a central wavelength of 1540nm using FFP interferometer, which is consistent with the value of 1.22pm/µepsilon obtained for a germanate fibre FBG. The Young's modulus for germanate and tellurite fibre were also measured to be 58GPa and 37GPa. The thermal responses of germanate fibre were examined as 24.71 and 16.80 pm/°C at 1540nm and 1033nm wavelength using the FBG.

Enhanced spectral compression in nonlinear optical fibres

We propose two new approaches to enhance the spectral compression process arising from nonlinear pulse propagation in an optical fibre. We numerically show that an additional sinusoidal temporal phase modulation of the pulse enables efficient reduction of the intensity level of side lobes in the spectrum. Another strategy is to select a regime of propagation in which normal group-velocity dispersion reshapes the initial stretched pulse to a near-Fourier-transform-limited rectangular waveform.

Fuzzy Logic Foundations and Industrial Applications (ed. D. Ruan), Springer US, 1996, ISBN: 978-0-7923-9774-8 [Book review]

Abstract not available

Electrospinning of polymeric composites with GRMs for different industrial applications

Electrospinning is the most common and industrially scalable technique for the production of polymeric nanofibers. Currently, nanocomposites are drawing much interest for their excellent properties in terms of flexibility, electrical conductivity and high surface area, which enhances the interaction with the surrounding environment. The objective of this thesis was the optimization of different electrospinning setups for the production of nanostructured polymeric composites using graphene-related materials as nanofillers. Such composites were obtained using different polymers as matrix (polyamide 6, polyinylidene fluoride and polylactic acid) that were selected and combined with the appropriate reinforcements based on their properties and their interest for specific applications. Moreover, this study highlighted the possibility to tune the morphology and size of the produced nanofibers by the addition of appropriate nanofillers even in low amounts. The addition of only 0.5% of GO allowed the production of smooth nanofibers with diameters up to 75% thinner (in the case of PLA) than the ones obtained from the pristine polymer. PVdF was charged with GO to produce triboelectric materials that can be exploited in a wearable nanogenerator for the conversion of human motion energy in electrical energy. The addition of GO improved the open-circuit voltage and power-output of a generator prototype by 3.5 times. Electrospun PA6 membranes were coated with rGO using a simple two-step technique to produce conductive textiles for wearable electronic applications. The sheet resistance of the produced materials was measured in approximately 500 Ω/sq and their resistance to washing and bending was successfully tested. These materials could be exploited as strain sensors or heating elements in smart textiles. PLA was co-electrospun with GO and cellulose nanofibers to produce high-surface area and porosity mats that could be exploited for the production of functionalized highly selective adsorption membranes with low pressure drops.