Combined Spectroscopic and Calorimetric Studies to Reveal Absorption Mechanisms and Conformational Changes of Protein on Nanoporous Biomaterials

In this study the effect of surface modification of mesoporous silica nanoparticles (MSNs) on its adsorption capacities and protein stability after immobilization of beta-lactoglobulin B (BLG-B) was investigated. For this purpose, non-functionalized (KIT-6) and aminopropyl-functionalized cubic Ia3d mesoporous silica ([n-PrNH₂-KIT-6]) nanoparticles were used as nanoporous supports. Aminopropyl-functionalized mesoporous nanoparticles exhibited more potential candidates for BLG-B adsorption and minimum BLG leaching than non-functionalized nanoparticles. It was observed that the amount of adsorbed BLG is dependent on the initial BLG concentration for both KIT-6 and [n-PrNH₂-KIT-6] mesoporous nanoparticles. Also larger amounts of BLG-B on KIT-6 was immobilized upon raising the temperature of the medium from 4 to 55 °C while such increase was undetectable in the case of immobilization of BLG-B on the [n-PrNH₂-KIT-6]. At temperatures above 55 °C the amounts of adsorbed BLG on both studied nanomaterials decreased significantly. By Differential scanning calorimetry or DSC analysis the heterogeneity of the protein solution and increase in Tm may indicate that immobilization of BLG-B onto the modified KIT-6 results in higher thermal stability compared to unmodified one. The obtained results provide several crucial factors in determining the mechanism(s) of protein adsorption and stability on the nanostructured solid supports and the development of engineered nano-biomaterials for controlled drug-delivery systems and biomimetic interfaces for the immobilization of living cells.     

Size-dependent internal resonances and modal interactions in nonlinear dynamics of microcantilevers

The size-dependent internal energy transfer in the nonlinear dynamical behaviour of a microcantilever with an intermediate spring-support is investigated. A geometric size-dependent nonlinearity due to large changes in the curvature is taken into account in the longitudinal and transverse motions. Based on the modified couple stress theory, the potential energy of the system is developed; the kinetic energy is also constructed in term of the displacement field. The energy terms are balanced with the potential energy stored in the intermediate spring-support. The centreline-inextensibility assumption is applied leading to the continuous model of the system involving nonlinear inertial components as well as size-dependent nonlinear curvature components. Based on a weighted-residual technique, the continuous model is reduced and the resultant truncated model is solved via use of a continuation technique. The linear component of the truncated model is solved through an eigenvalue extraction method in order to verify the occurrence of internal energy transfer and modal interaction mechanisms. For the system tuned to internal resonances, the highly nonlinear dynamical response is obtained, taking into account both inertial and geometric (due to large rotations) nonlinearities. It is shown that taking into account the length-scale parameter changes the internal energy transfer mechanisms significantly.     

Resonant responses of three-layered shear-deformable microbeams

Microsystem Technologies - This paper analyses the coupled resonant motion of three-layered shear-deformable microbeams. On the basis of the modified couple stress theory, while both the rotational...     

Synthesis of nano β‐TCP and the effects on the mechanical and biological properties of β‐TCP/HDPE/UHMWPE nanocomposites

High density polyethylene/tricalcium phosphate/ultra high molecular weight polyethylene (TCP/HDPE/UHMWPE) Nanocomposite as an orthopedic biomaterial (with better properties toward TCP/HDPE composite) was obtained. To evaluate the capability of this nanocomposite as a material for bone tissue replacement, mechanical and biological assessments were performed. In this study, nanosize β‐TCP powders with average grain size of 100 nm were synthesized by chemical precipitation method and characterized by means of X‐ray diffraction (XRD), Fourier‐transform infrared spectroscopy (FTIR), and scanning electron microscopy (SEM). To evaluate the mechanical properties of this biomaterial, tensile properties were obtained for the material. Results showed that by increasing the weight percentage of β‐TCP, the elastic modulus increases, elongation at yield decreases and with no significant change in tensile strength. SEM micrographs of cryogenic fracture surface of samples indicated that distribution of nano powders in matrix is homogeneous. In vitro biological evaluations on the samples were done by performing cytotoxicity (MTT assay), alkaline phosphatase enzyme, and cell attachment tests. In all of the tests, osteoblast cells were used. Results of biological tests showed that the samples are biocompatible and they have no toxicity. Also, SEM observations demonstrated that the cells can attach to surface of nanocomposite samples, which reveals osteoconductivity of the surface. POLYM. COMPOS., 31:1745–1753, 2010. © 2010 Society of Plastics Engineers.     

Viscoelastically coupled size-dependent behaviour of imperfect extensible microbeams

This paper aims at investigating the size-dependent nonlinear behaviour of a viscoelastic imperfect extensible microbeam taking into account both transverse and longitudinal displacements and inertia. The size-dependent potential energy is formulated in the framework of the modified couple stress theory. The works due to the viscous parts of the stress tensor and the deviatoric part of the couple stress tensor are obtained in terms of system parameters. The kinetic energy as well as the work of external dynamic loading is obtained as functions of the displacement field. Hamilton’s principle is employed in order to balance the work and energy terms which results in the coupled nonlinear equations of motion for the longitudinal and transverse directions. A high-dimensional weighted-residual technique is employed so as to discretise the coupled equations of longitudinal and transverse motions and hence the continuous system with infinite number of degrees of freedom is truncated into a reduced-order model with sufficient degrees of freedom for accurate results capable of capturing almost all modal interactions. This high-dimensional nonlinear coupled reduced-order model is solved for the fundamental coupled nonlinear resonant response via use of a continuation method as well as direct time integration for response characterisation with special consideration to the coupled effect of the viscousity, initial imperfection, and length-scale parameter on the system response in the longitudinal and transverse directions. It is shown that the deviation between the response of viscoelastic and elastic systems is substantial for fairly large excitation forces.     

Coupled size-dependent behavior of shear deformable microplates

The aim of the present study is to investigate the nonlinear motion characteristics of a shear deformable microplate based on the modified couple stress theory. The microplate is modeled via the third-order shear deformation theory retaining in-plane displacements and inertia. Using the Lagrange equations together with an assumed-mode method, five sets of second-order nonlinear ordinary differential equations of motion with coupled terms are obtained. These five sets of equations (two for the in-plane motions, one for the out-of-plane motion, and two for rotations) are transformed into ten sets of first-order nonlinear ordinary differential equations. These resultant equations are then solved by means of a direct time integration technique and the pseudo-arclength continuation method in order to analyze the nonlinear response of the system. Apart from the nonlinear analysis, the linear natural frequencies of the system are obtained using an eigenvalue analysis. Results are shown through frequency–response and force–response curves. Points of interest in the parameter space in the form of time histories, phase-plane portraits, and fast Fourier transforms are also highlighted. Moreover, a comparison is made between the motion characteristics of the system based on the modified couple stress and classical continuum theories.     

Optimal contract design for effort-averse sensors

ABSTRACT

A central planner wishes to engage a collection of sensors to measure a quantity. Each sensor seeks to trade-off the effort it invests to obtain and report a measurement, against contracted reward. Assuming that measurement quality improves as a sensor increases the effort it invests, the problem of the reward contract design is investigated. To this end, a game is formulated between the central planner and the sensors. Using this game, it is established that the central planner can enhance the quality of the estimate by rewarding each sensor based on the distance between the average of the received measurements and the measurement provided by the sensor. Optimal contracts are designed from the perspective of the budget required to achieve a specified level of error performance.     

Optimal structured static state-feedback control design with limited model information for fully-actuated systems

We introduce the family of limited model information control design methods, which construct controllers by accessing the plant’s model in a constrained way, according to a given design graph. We investigate the closed-loop performance achievable by such control design methods for fully-actuated discrete-time linear time-invariant systems, under a separable quadratic cost. We restrict our study to control design methods which produce structured static state feedback controllers, where each subcontroller can at least access the state measurements of those subsystems that affect its corresponding subsystem. We compute the optimal control design strategy (in terms of the competitive ratio and domination metrics) when the control designer has access to the local model information and the global interconnection structure of the plant-to-be-controlled. Finally, we study the trade-off between the amount of model information exploited by a control design method and the best closed-loop performance (in terms of the competitive ratio) of controllers it can produce.     

Size-dependent behaviour of electrically actuated microcantilever-based MEMS

In this paper, the nonlinear size-dependent static and dynamic behaviours of a microelectromechanical system under an electric excitation are investigated. A microcantilever is considered for the modelling of the deformable electrode of the MEMS. The governing equation of motion is derived based on the modified couple stress theory (MCST), a non-classical model capable of capturing small-size effects. With the aid of a high-dimensional Galerkin scheme, the nonlinear partial differential equation governing the motion of the deformable electrode is converted into a reduced-order model of the system. Then, the pseudo-arclength continuation technique is used to solve the governing equations. In order to investigate the static behaviour and static pull-in instabilities, the system is excited only by the electrostatic actuation (i.e., a DC voltage). The results obtained for the static pull-in instability predicted by both the classical theory and MCST are compared. In the second stage of analysis, the nonlinear dynamic behaviour of the deformable electrode due to the AC harmonic actuation is investigated around the deflected configuration, incorporating size dependence.