We understand few details about how the arrangement and interactions of cell wall polymers produce the mechanical properties of primary cell walls. Consequently, we cannot quantitatively assess if proposed wall structures are mechanically reasonable or assess the effectiveness of proposed mechanisms to change mechanical properties. As a step to remedying this, we developed WallGen, a Fortran program (available on request) building virtual cellulose-hemicellulose networks by stochastic self-assembly whose mechanical properties can be predicted by finite element analysis. The thousands of mechanical elements in the virtual wall are intended to have one-to-one spatial and mechanical correspondence with their real wall counterparts of cellulose microfibrils and hemicellulose chains. User-defined inputs set the properties of the two polymer types (elastic moduli, dimensions of microfibrils and hemicellulose chains, hemicellulose molecular weight) and their population properties (microfibril alignment and volume fraction, polymer weight percentages in the network). This allows exploration of the mechanical consequences of variations in nanostructure that might occur in vivo and provides estimates of how uncertainties regarding certain inputs will affect WallGen's mechanical predictions. We summarize WallGen's operation and the choice of values for user-defined inputs and show that predicted values for the elastic moduli of multinet walls subject to small displacements overlap measured values. "Design of experiment" methods provide systematic exploration of how changed input values affect mechanical properties and suggest that changing microfibril orientation and/or the number of hemicellulose cross-bridges could change wall mechanical anisotropy.Plant scientists have long studied how primary wall structure influences mechanical properties (Preston, 1974). In this work, we develop methods to predict the elastic modulus for layered networks of cellulose microfibrils (CMFs) cross-linked by hemicellulose (HC) chains when they are subject to small imposed displacements.Polysaccharides provide over 90% of wall mass and therefore are likely to dominate wall mechanics. Two distinct but probably interacting (Zykwinska et al., 2005) networks are recognized: a cellulose-hemicellulose (CHC) network and a pectin network. Pectins can be removed by mutations, allowing measurements of the mechanical properties of the CHC network (Ryden et al., 2003) that can be compared with predicted values. The two networks probably make roughly comparable mechanical contributions in pectin-rich dicots (Ryden et al., 2003), but the CHC network presumably dominates in monocots with pectin-poor, type II walls (Carpita and Gibeaut, 1993;Rose, 2003). Plant cells align CMFs (Baskin, 2005) but not noncellulosic polysaccharides such as pectins and HCs. CMF alignment, therefore, underlies the structural and mechanical anisotropy seen in many cell walls.In principle, wall structure can predict mechanical properties, a multiscale modeling problem of the type...

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Development of a new steerable electrode array with embedded nitinol shape memory alloy actuators is described in this paper. The risk of damaging the basilar membrane during insertion of electrode array into the human cochlear is expected to be significantly reduced with the ability to redirect the tip of the electrode array at the critical hook region. The final position of this electrode array can also be adjusted to lie beneath the basilar membrane inside the scala tympani for delivery of neurotrophins (growth factors). The bending behaviour of the steerable electrode array and its trajectories during insertion into the scale tympani were predicted using a 3D finite element model. Results from the model have shown that the new electrode array can be steered through the critical 'hook' region and be accurately positioned for delivery of neurotrophins.

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