Comparative study of collagen and gelatin in chitosan-based hydrogels for effective wound dressing: Physical properties and fibroblastic cell behavior.

The influence of collagen as an effective substitute for gelatin was investigated on properties of chitosan/gelatin hydrogels for fibroblasts growth and attachment for wound dressing applications. We synthesized hydrogels based on chitosan associated with collagen and gelatin biopolymers (in the ratio of 1:5 and 1:1, respectively). The hydrogels properties such as morphology, swelling ratio, mechanical characteristics, water vapor loss, water vapor transmission rate (WVTR), and biodegradation were analyzed. 1 × 105 human fibroblasts were seeded per ml of hydrogels and maintained for 7 days. Cell viability was assessed by using MTT. The presence of collagen caused reduced swelling ratio, and biodegradation rate compared to chitosan/gelatin hydrogels (p < 0.05). The introduction of collagen into chitosan hydrogels improved the mechanical strength compared to gelatin. Hydrogels with collagen possessed an optimum WVTR compared to the chitosan group and hydrogels with gelatin (p < 0.05). Analyzing the morphology of hydrogels revealed that the addition of collagen leads to a homogenous and interconnected structure. Collagen impregnation promoted cell survival and attachment compared with chitosan hydrogels after 7 days (p < 0.05). Collectively, these results demonstrated the potential of the chitosan/collagen hydrogels for wound dressing applications.

Schottky-contact plasmonic dipole rectenna concept for biosensing.

Nanoantennas are key optical components for several applications including photodetection and biosensing. Here we present an array of metal nano-dipoles supporting surface plasmon polaritons (SPPs) integrated into a silicon-based Schottky-contact photodetector. Incident photons coupled to the array excite SPPs on the Au nanowires of the antennas which decay by creating "hot" carriers in the metal. The hot carriers may then be injected over the potential barrier at the Au-Si interface resulting in a photocurrent. High responsivities of 100 mA/W and practical minimum detectable powers of -12 dBm should be achievable in the infra-red (1310 nm). The device was then investigated for use as a biosensor by computing its bulk and surface sensitivities. Sensitivities of ∼ 250 nm/RIU (bulk) and ∼ 8 nm/nm (surface) in water are predicted. We identify the mode propagating and resonating along the nanowires of the antennas, we apply a transmission line model to describe the performance of the antennas, and we extract two useful formulas to predict their bulk and surface sensitivities. We prove that the sensitivities of dipoles are much greater than those of similar monopoles and we show that this difference comes from the gap in dipole antennas where electric fields are strongly enhanced.

Periodic plasmonic nanoantennas in a piecewise homogeneous background.

Periodic rectangular gold nanomonopoles and nanodipoles in a piecewise inhomogeneous background, consisting of a silicon substrate and a dielectric (aqueous) cover, have been investigated extensively via 3D finite-difference time-domain simulations. The transmittance, reflectance and absorptance response of the nanoantennas were studied as a function of their geometry (length, width, thickness, gap) and found to vary very strongly. The nanoantennas were found to resonate in a single surface plasmon mode supported by the corresponding rectangular cross-section nanowire waveguide, identified as the sa(b)(0) mode [Phys. Rev. B 63, 125417 (2001)]. We determine the propagation characteristics of this mode as a function of nanowire cross-section and wavelength, and we relate the modal results to the performance of the nanoantennas. An approximate expression resting on modal results is proposed for the resonant length of nanomonopoles, and a simple equivalent circuit, also resting on modal results, but involving transmission lines and a capacitor (modelling the gap) is proposed to determine the resonant wavelength of nanodipoles. The expression and the circuit yield results that are in good agreement with the full computations, and thus will prove useful in the design of nanoantennas.