A New Method for Free Vibration Analysis of Triangular Isotropic and Orthotropic Plates of Isosceles Type Using an Accurate Series Solution

In this paper, a new method based on an accurate analytical series solution for free vibration of triangular isotropic and orthotropic plates is presented. The proposed solution is expressed in terms of undetermined arbitrary coefficients, which are exactly satisfied by the governing differential equation in free vibration. The approach used is based on an innovative extension of the superposition method through the application of a modified system of trigonometric functions. The boundary conditions for bending displacements and bending rotations on the sides of the triangular plate led to an infinite system of linear algebraic equations in terms of the undetermined coefficients. Following this development, the paper then presents an algorithm to solve the boundary value problem for isotropic and orthotropic triangular plates for any kinematic boundary conditions. Of course, the boundary conditions with zero displacements and zero rotations on all sides correspond to the case when the plate is fully clamped all around. The convergence of the proposed method is examined by numerical simulation applying stringent accuracy requirements to fulfill the prescribed boundary conditions. Some of the computed numerical results are compared with published results and finally, the paper draws significant conclusions

Dynamic stiffness matrix of a conical bar using the Rayleigh-Love theory with applications

Based on the Rayleigh-Love theory, the dynamic stiffness matrix of a conical bar in longitudinal vibration is developed for the investigation of free vibration and response characteristics of such bars and their assemblies. First the governing differential equation of motion in free longitudinal vibration of a conical bar using the Rayleigh-Love theory which accounts for the inertia effects due to transverse or lateral deformations is derived by applying Hamilton's principle. Next, for harmonic oscillation, the governing differential equation is recast in the form of Legendre's equation, providing a series solution connected by integration constants. The expressions for the amplitudes of displacements and forces are then obtained by means of the series solution. Finally, the frequency dependent dynamic stiffness matrix is formulated by relating the amplitudes of forces to those of the corresponding displacements at the ends of the conical bar and thereby eliminating the integration constants. As an established solution technique, the Wittrick-Williams algorithm is applied to the resulting dynamic stiffness matrix when computing the natural frequencies and mode shapes of some illustrative examples. The theory is also applied to investigate the response of a cantilever conical Rayleigh-Love bar with a harmonically varying load applied at the tip. The results computed from the Rayleigh-Love model based dynamic stiffness theory are compared and contrasted with those computed from conventional classical theory with significant conclusions drawn

Carrageenan-based hydrogels for the controlled delivery of PDGF-BB in bone tissue engineering applications

One of the major drawbacks found in most bone tissue engineering approaches developed so far consists in the lack of strategies to promote vascularisation. Some studies have addressed different issues that may enhance vascularisation in tissue engineered constructs, most of them involving the use of growth factors (GFs) that are involved in the restitution of the vascularity in a damaged zone. The use of sustained delivery systems might also play an important role in the re-establishment of angiogenesis. In this study, !-carrageenan, a naturally occurring polymer, was used to develop hydrogel beads with the ability to incorporate GFs with the purpose of establishing an effective angiogenesis mechanism. Some processing parameters were studied and their influence on the final bead properties was evaluated. Platelet derived growth factor (PDGF-BB) was selected as the angiogenic factor to incorporate in the developed beads, and the results demonstrate the achievement of an efficient encapsulation and controlled release profile matching those usually required for the development of a fully functional vascular network. In general, the obtained results demonstrate the potential of these systems for bone tissue engineering applications.This work was supported by the European NoE EXPERTISSUES (NMP3-CT-2004-500283), the European STREP HIPPOCRATES (NMP3-CT-2003-505758), and by the Portuguese Foundation for Science and Technology (FCT) through the project PTDC/FIS/68517/2006 and through the V. Espirito Santo's Ph.D. grant (SFRH/BD/39486/2007)

Designing Bioactive Delivery Systems for Tissue Regeneration

The direct infusion of macromolecules into defect sites generally does not impart adequate physiological responses. Without the protection of delivery systems, inductive molecules may likely redistribute away from their desired locale and are vulnerable to degradation. In order to achieve efficacy, large doses supplied at interval time periods are necessary, often at great expense and ensuing detrimental side effects. The selection of a delivery system plays an important role in the rate of re-growth and functionality of regenerating tissue: not only do the release kinetics of inductive molecules and their consequent bioactivities need to be considered, but also how the delivery system interacts and integrates with its surrounding host environment. In the current review, we describe the means of release of macromolecules from hydrogels, polymeric microspheres, and porous scaffolds along with the selection and utilization of bioactive delivery systems in a variety of tissue-engineering strategies

Chemical Recycling of High-Molecular-Weight Organosilicon Compounds in Supercritical Fluids

The main known patterns of thermal and/or catalytic destruction of high-molecular-weight organosilicon compounds are considered from the viewpoint of the prospects for processing their wastes. The advantages of using supercritical fluids in plastic recycling are outlined. They are related to a high diffusion rate, efficient extraction of degradation products, the dependence of solvent properties on pressure and temperature, etc. A promising area for further research is described concerning the application of supercritical fluids for processing the wastes of organosilicon macromolecular compounds