Hamed Shahsavan

Conformal adhesion enhancement on biomimetic microstructured surfaces.

Inspired by the superior adhesive ability of the gecko foot pad, we report an experimental study of conformal adhesion of a soft elastomer thin film on biomimetic micropatterned surfaces (micropillars), showing a remarkable adhesion enhancement due to the surface patterning. The adhesion of a low-surface-energy poly(dimethylsiloxane) tape to a SU-8 micropatterned surface was found be able to increase by 550-fold as the aspect ratio increases from 0 to 6. The dependency of the adhesion enhancement on the aspect ratio is highly nonlinear. A series of peeling experiment coupled with optical interference imaging were performed to investigate the adhesion enhancement as a function of the height of the micropillars and the associated delamination mechanisms. Local elastic energy dissipation, side-wall friction, and plastic deformations were analyzed and discussed in terms of their contributions to the adhesion enhancement. We conclude that the local adhesion and friction events of pulling micropillars out of the embedded polymer film play a primary role in the observed adhesion enhancement. The technical implications of this local friction-based adhesion enhancement mechanism were discussed for the effective assembly of similar or dissimilar material components at small scales. The combined use of the micro/nanostructured surfaces with the van der Waals interactions seem to be a potentially more universal solution than the conventional adhesive bonding technology, which depends on the chemical and viscoelastic properties of the materials.

Smart Muscle-Driven Self-Cleaning of Biomimetic Microstructures from Liquid Crystal Elastomers

Muscle-driven actuation of biomimetic microfibrillar structures is achieved using integrative soft-lithography on a backing splayed liquid-crystal elastomer (LCE). Variation in the backing LCE layer thickness yields different modes of thermal deformation from a pure bend to a twist-bend. Muscular motion and dynamic self-cleaning of gecko toe pads are mimicked via this mechanism.

Thermally Active Liquid Crystal Network Gripper Mimicking the Self-Peeling of Gecko Toe Pads

Self-peeling of gecko toes is mimicked by integration of film-terminated fibrillar adhesives to hybrid nematic liquid crystal network (LCN) cantilevers. A soft gripper is developed based on the gecko-inspired attachment/detachment mechanism. Performance of the fabricated gripper for transportation of thin delicate objects is evaluated by the optimum mechanical strength of the LCN and the maximum size of the adhesive patch.

Biologically inspired enhancement of pressure-sensitive adhesives using a thin film-terminated fibrillar interface

A hybrid adhesive structure consisting of an array of elastic biomimetic micropillars and a thin viscoelastic terminal film was designed and fabricated. A remarkable adhesion enhancement and a crack propagation modulation were observed, indicating a synergistic effect between the elastic fibrillar structures and the viscoelastic terminal film.

Bacterial Networks on Hydrophobic Micropillars

Bacteria have evolved as intelligent microorganisms that can colonize and form highly structured and cooperative multicellular communities with sophisticated singular and collective behaviors. The initial stages of colony formation and intercellular communication are particularly important to understand and depend highly on the spatial organization of cells. Controlling the distribution and growth of bacterial cells at the nanoscale is, therefore, of great interest in understanding the mechanisms of cell-cell communication at the initial stages of colony formation. Staphyloccocus aureus, a ubiquitous human pathogen, is of specific clinical importance due to the rise of antibiotic resistant strains of this species, which can cause life-threatening infections. Although several methods have attempted to pattern bacterial cells onto solid surfaces at single cell resolution, no study has truly controlled the 3D architectures of growing colonies. Herein, we present a simple, low-cost method to pattern S. aureus bacterial colonies and control the architecture of their growth. Using the wetting properties of micropatterened poly(dimethyl siloxane) platforms, with help from the physiological activities of the S. aureus cells, we fabricated connected networks of bacterial microcolonies of various sizes. Unlike conventional heterogeneous growth of biofilms on surfaces, the patterned S. aureus microcolonies in this work grow radially from nanostrings of a few bacterial cells, to form micrometer-thick rods when provided with a nutrient rich environment. This simple, efficient, and low-cost method can be used as a platform for studies of cell-cell communication phenomena, such as quorum sensing, horizontal gene transfer, and metabolic cross-feeding especially during initial stages of colony formation.

Simulation-based design of thermally-driven actuators using liquid crystal elastomers

ABSTRACT Liquid crystal elastomers (LCEs) are a class of soft functional materials which exhibit complex mechanical responses to external stimuli. Their promise for technological applications is difficult to realise in practice due to the complexity of design, fabrication and performance quantification of these materials. In order to address these issues, simulation-based methods are necessary to both enhance and accelerate the design process, compared to traditional experimentation alone. This work presents such an approach using a hyperelastic solid mechanics model and experimental measurement of material parameters for a thermotropic LCE. The simulation method is validated using existing experimental data of the thermomechanical response of an LCE-based cantilever resulting from a hybrid-aligned nematic texture imposed during crosslinking. The validated method is then used to perform a proof-of-concept design process of an LCE multilegged gripper in order to determine optimal design parameters for gripper performance. The simulation method and results presented in this work represent a significant step towards simulation-based design of LCE materials, which has the potential to overcome the complexity and cost of the LCE design process. Graphical Abstract

Application of wide-band liquid crystal reflective windows in building energy efficiency: a case study of educational buildings

The purpose of this article is to study the impact of seven different window systems on overall energy consumption of educational buildings. In particular, four of the windows are non-traditional liquid crystal base, namely 1) Tunable, 2) Broadband Type 1, 3) Broadband Type 2, and 4) Broadband Type 3. For the purpose of simulation, a LEED Gold certified building located at a major university in the U.S. was modeled, benchmarked, and calibrated. Then several scenarios according to window choices haven been tested, both in actual and different climate zones. The results show, Broadband Type 2 and Type 3 can make a significant impact in reducing building energy consumption. Their contribution is higher for projects located in hotter climates.

Biomimicry: Smart Muscle‐Driven Self‐Cleaning of Biomimetic Microstructures from Liquid Crystal Elastomers (Adv. Mater. 43/2015)

Smart, muscle-driven self-cleaning of biomimetic microstructures is achieved using a hybrid aligned liquid-crystal elastomer (LCE). By varying the thickness of the splayed LCE backing layer, bend and twist-bend deformations are achieved to mimic the scrolling motions of gecko toes. The results presented by A. Jákli, B. Zhao, and co-workers on page 6828 can be a stepping stone for the development of next-generation gecko-inspired fibrillar adhesives.