Role of silk fibroin and rice starch on some physical properties of hydroxyapatite‐based composites

The role of organic blends of silk fibroin (SF) and rice starch (RS) in bone composites based on inorganic hydroxyapatite (HA) is studied. The physical property of HA‐based composites prepared by using the sol–gel method from Ca(OH)₂ and H₃PO₄ in ethanol and water solvent (4 : 1 volume ratio) could be improved by adding SF and RS (1 : 2 weight ratio) to HA (7 : 3 weight ratio). The Fourier transform infrared spectrometer spectrum shows that the SF and RS organic phases are blended homogeneously into the HA crystal structure. Addition of SF increases the pore size and surface area of the composites, as measured by Brunauer–Emmett–Teller method, but their pore volume is slightly decreased. The values of lattice parameters, crystallinity, and crystallite size, as determined from the field‐emission scanning electron microscope, transmission electron microscope, and X‐ray diffractometer results, increase after adding RS. The results are agreeable with the increase of their compressive strength and Young's modulus. Thus, the improved physical property of the prepared HA–SF/RS composites is better suited as bone‐filling material than the standard HA or HA‐based composites with either SF or RS only. Therefore, due to its low cost, biocompatibility, and nontoxicity, this innovative solution could be worth taken under consideration by the restorative dental and orthopedic implants industry. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42722.     

New exponential passivity of BAM neural networks with time-varying delays

In this paper, the exponential passivity for bidirectional associative memory (BAM) neural networks with time-varying delays is considered. In our study, the lower and upper bounds of the activation functions are allowed to be either positive, negative or zero. By constructing new and improved Lyapunov–Krasovskii functional and introducing free-weighting matrices, a new and improved delay-dependent exponential passivity criterion for BAM neural networks with time-varying delays is derived in the form of linear matrix inequality (LMI). A numerical example is given to show that the derived condition is less conservative than some existing results given in the literature.

     

Robust Finite‐Time Control for Linear Time‐Varying Delay Systems With Bounded Control

This paper develops a novel finite‐time control design for linear systems subject to time‐varying delay and bounded control. Based on the Lyapunov‐like functional method and using a result on bounding estimation of integral inequality, we provide some sufficient conditions for designing state feedback controllers that guarantee the robust finite‐time stabilization with guaranteed cost control. The conditions are obtained in terms of linear matrix inequalities (LMIs), which can be determined by utilizing the MATLAB LMI Control Toolbox. A numerical example is given to show the effectiveness of the proposed method.     

Fibroin membrane preparation and stabilization by polyethylene glycol diglycidyl ether

Membranes prepared by drying aqueous Bombyx mori silk fibroin (SF) solution and modified silk fibroin (MSF) solutions, prepared by adding the low molecular weight crosslinking agent, polyethylene glycol diglycidyl ether (PEGDE) MW 526, 0–10% w/w, were investigated by Scanning Electron Microscopy (SEM), Fourier Transform Infrared (FTIR) spectroscopy, and UV–vis spectroscopy. Weight gain in aqueous solutions and their mechanical properties (tensile strength, elongation, and Young's modulus) were then characterized. SEM measurements revealed greater porosity in MSF membranes. IR spectra showed transformation from the largely α‐helical/random coil structures in SF membranes to predominantly β‐sheet in MSF membranes. Results from UV–vis spectroscopy showed that the MSF membranes were largely insoluble within the pH range of 4–10. Water absorbability of the MSF membranes improved with increasing the amounts of cross‐linker, up to 4%. The MSF membranes showed greater pliability and tenacity, but lower tensile strength, with increasing PEGDE concentrations. In the wet condition, PEGDE levels up to 4% can improve both tensile strength and tenacity of the MSF membrane, but higher levels (up to 10%) did not significantly change these properties. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci 2008