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The objective of this study was to develop a thermo-mechanical strategy to create a radial elasticity gradient in a β metastable Ti-Nb-Zr alloy, and to characterize it in terms of microstructural and mechanical properties. A first investigation was conducted on thin samples of Ti-20Nb-6Zr (at.%) submitted to various thermo-mechanical treatments. Microstructure-properties relationships and elastic variability of this alloy were determined performing uniaxial tensile tests, X-ray diffraction and scanning and transmission electron microscopies. Based on these preliminary results, mechanical deformation was identified as a potential way to lower the elastic modulus of the alloy. In order to create elastically graded pieces, shot-peening was therefore carried out on thicker samples to engender surface deformation. In this second part of the work, local mechanical properties were evaluated by instrumented micro-indentation. Experimental observations demonstrated that shot-peening enabled to locally induce martensitic transformation on surface, and a decrease in indentation elastic modulus from 85 to 65 GPa over 400 μm was highlighted. Surface deformation proved to be an efficient way of creating an elasticity gradient in β metastable titanium alloys. This combination of material and process could be suitable to produce dental implants with mechanically enhanced biocompatibility.

Well-designed microscopic elasticity gradients on cell culture substrate can be an useful platform for investigating the mechanics of cell movements. To understand mechanical aspect of cell movement, we have focused on durotaxis which is a form of cell migration guided by elasticity gradient on extracellular millieu. To systematically investigate the effect of the elasticity gradient on emergence of cell polarity that determines direction of cell movement, we have originally developed microelastically-patterned hydrogel substrate, which enable manipulating the cell durotaxis. Width, strength, and curvature of the elasticity gradient around the elasticity transition region could be successfully designed by employing the mask-free photolithographic microelasticity patterning system. In this mini-review, the following three issues are discussed: 1) determining a threshold strength of elasticity gradient that induces durotaxis, 2) designing an asymmetric elastic gradient that rectifies durotactic cells, and 3) investigating how the durotaxis depends on curvatures on the elasticity boundaries. [ABSTRACT FROM AUTHOR]

In this work the novel method to create PDMS substrates with continuous and discrete elasticity gradients of different shapes and dimensions over the large areas was introduced. Elastic properties of the sample were traced using force spectroscopy (FS) and quantitative imaging (QI) mode of atomic force microscopy (AFM). Then, fluorescence microscopy was applied to investigate the effect of elastic properties on proliferation of bladder cancer cells (HCV29). Obtained results show that cancerous cells proliferate significantly more effective on soft PDMS, whereas the stiff one is almost cell-repellant. This strong impact of substrate elasticity on cellular behavior is driving force enabling precise positioning of cells. [ABSTRACT FROM AUTHOR]

Controlled surface patterns are useful in a wide range of applications including flexible electronics, elastomeric optics, fluidic channels, surface engineering, measurement technique, biological templates, stamps, and sensors. In this work, we report on the controlled formation of surface patterns in metal films deposited on elasticity-gradient polydimethylsiloxane (PDMS) substrates. Because of the temperature gradient during the curing process, the PDMS substrate in each sample successively changes from a purely liquid state at one side to a purely elastic state at the opposite side. It is found that surface folds appear in the liquid or viscous PDMS region while wrinkles form in the elastic region. In the transition region from the liquid to elastic PDMS, a nested pattern (i.e., the coexisting of folds and wrinkles) can be observed. The folding wave is triggered by the intrinsic stress during the film deposition and its wavelength is independent of the film thickness. The wrinkling wave is induced by the thermal compression after deposition and its wavelength is proportional to the film thickness. The report in this work could promote better understanding of the effect of substrate elasticity on the surface patterns and fabrication of such patterns (folds and wrinkles) by tuning the substrate property.