Disordered Topography Mediates Filopodial Extension and Morphology of Cells on Stiff Materials

In cell–material interactions, cells use filopodia to sense external biochemical and mechanical cues, and subsequently dictate their survival. In an effort toward understanding how disordered topography of stiff materials influences filopodial recognition, diamond films with grain sizes varying from nano‐ to micrometers are fabricated for the investigation of osteoblast filopodial extension. Interestingly, straight filopodia with pronounced cell–substrate adhesion are observed on a nanocrystalline diamond (NCD) region, whereas filopodia on a microcrystalline diamond (MCD) surface only adhere to, and get deflected by, large diamond grains. More importantly, filopodia on NCD keep propagating with a constant velocity, whereas the same process takes place in a slow and intermittent manner on MCD. A theoretical model is also developed and it suggests that the contact between the disordered topography and the filopodial tip plays a key role in altering filopodial growth dynamics. In particular, it is predicted that large surface asperities can block the movement of the filopodial tip, delay its extension, and cause bending of the structure, in quantitative agreement with experimental observations. These findings reveal previously underappreciated effects of random, stiff topographies on the response of cells, and hence can provide new insights for the design of future implant biomaterials.     

A novel approach to analyse adhesive layer strain field in a stepped lap repaired carbon fiber reinforced polymer panel using digital image correlation

Abstract

The present work focuses on the critical strain analysis of thin adhesive layer present in single-sided stepped lap-repaired carbon fibre-reinforced polymer panels subjected to tensile loading. Digital image correlation technique is used for acquiring both the global and local whole field strain, to obtain the longitudinal, peel, and shear strain distribution over the adhesive layer. The evolution of strain field with increasing load is captured to predict its mechanical behaviour. Magnified optics is used to capture the localized strain field at critical zones. Step corners are identified as critical zones of damage. Debonding is observed as the primary source of damage in the adhesive layer. Overall, the load displacement behaviour and damage mechanism are captured from the experiment. A numerical study based on finite-element analysis is carried out for validating the experimental results. In the numerical study, the adhesive layer is modelled using zero thickness contact element with cohesive behaviour to mimic disbonding. The cohesive zone properties for mode-I and mode-II loading are experimentally obtained from DCBt to ENF test respectively. Microscopic load vs. displacement curve obtained from an experiment is found to be in good correlation with FE estimates.     

Comparison of the Microstructures and Mechanical Properties in the Overlapping Region of Low Carbon Steel Additive Bead Fabricated by WAAM and FSP

Metallurgical and Materials Transactions A - The periodic structural characteristics of the grains in the overlapping region of the WAAM deposited additive bead translate into spatially dependent...