Materials such as sedimentary rocks, pharmaceutical tablets, plastic bonded explosives, biscuits, concretes, nacre, solid propellants, seashells and asphalts can be treated as particulate composites that consist of particles of high volume fraction, matrixes of thin layer and interfaces of high specific surface area. Mechanical behaviour of highly packed particulate composites is the theme of this issue of Journal Club forum.

Ionic polymer-metal composite (IPMC) is a polyelectrolyte (usually Nafion or Femion swollen by simple salt solution) strip or membrane with both sides plated with metal electrodes. It is a particular design of electroactive-polymer device rather than a new class of material. When a voltage is applied between its electrodes, it will bend toward either electrode depending on the polarity (anode for a negatively charged gel), and the magnitude of deformation could be controlled by the electric signal.  Reversely, the deformation of an IPMC can generate electric signal or even energy output [1-4].  Therefore IPMC has recently becomes a hot topic in actuation, sensor and energy harvesting applications, especially when integrated with the characteristics of certain gels that are responsive to other environmental stimuli such as pH value or temperature.

Welcome to the January 2010 issue! In the issue of May 2007 , Prof. Xiaodong Li outlined the existing experimental methods for mechanical characterization of 1D nanostructures. In this issue, I will discuss along the same line but focus on experimental methods enabled by microelectromechanical systems (MEMS).

Welcome to the forum! Discussion topics were suggested initially as follow:

Metal foams, cell deformation (bending, buckling, plasticity and fracture), constitutive stress-strain behaviour of cellular materials, energy absorption, hypervelocity impact, shock wave behaviour, 1D shock modelling, shock attenuation, shock enhancement, Material Point Method (MPM) simulation and microscopic tomography experimental observation;

*This issue of the Journal Club has been prepared as a group by Ankush Aggarwal, Mo Bai, Mainak Sarkar, and Jee E Rim, and with comments and suggestions from Bill Klug .

Many musculoskeletal soft tissues, such as tendons, ligaments, meniscus and cartilage are inhomogeneous. Hence, during mechanical loading it is likely that a nonuniform strain pattern occurs within the tissue. These nonuniform strain patterns may assist in successful load transmission and minimize rupture of the tissue during physiological loading. Determination of local material properties will likely be important for successful function and design of tissue engineered replacements. In the late 1980’s uniaxial tensile tests were conducted using a video camera in conjunction with surface markers to document local strain distributions on the surface of ligaments. Photoelasticity has also been used to document local strain patterns.

Before we start this issue of J-club, I would like to recommend Prof. Langer's lecture for his MRS Von Hippel Award in the 2005 MRS Fall Meeting (Langer, 2006). His lecture not only delineated the history of the new exciting field of drug delivery and controlled release, but also told us many interesting stories happened in his career development. With Prof. Langer's pioneer work, many new materials are developed for designing new drug delivery and controlled drug release systems.

Welcome to the May 2007 issue. This issue focuses on experimental nanomechanics of nanobuilding blocks. The extremely small dimensions of nanobuilding blocks (for instance, nanoparticles, nanotubes, and nanowires) have imposed great challenges to many existing instruments, methodologies, and even theories.  In this issue, we will discuss – (1) experimental techniques and (2) size-effects. 

The molecular building blocks of a cell include:

♦ membrane components (e.g. fatty acids and phospholipids)
♦ biopolymers (e.g. proteins)
♦ genetic blueprint (e.g. DNA and RNA)

In a previous issue of the journal club, John Dolbow has discussed computational mechanics of biomembrane. I would like to discuss the mechanics issues of proteins and DNA (RNA) from an analytical perspective.