Silicon is an important material not only for semiconductor applications, but also for the development of novel bioinspired and biomimicking materials and structures or drug delivery systems in the context of nanomedicine. For these applications, a thorough understanding of the fracture behavior of the material is critical. In this paper we address this issue by investigating a fundamental issue of the mechanical properties of silicon, its behavior under extreme mechanical loading. Earlier experimental work has shown that at low temperatures, silicon is a brittle material that fractures catastrophically like glass once the applied load exceeds a threshold value. At elevated temperatures, however, the behavior of silicon is ductile. This brittle-to-ductile transition (BDT) has been observed in many experimental studies of single crystals of silicon. However, the mechanisms that lead to this change in behavior remain questionable, and the atomic-scale phenomena are unknown. Here we report for the first time the direct atomistic simulation of the nucleation of dislocations from a crack tip in silicon only due to an increase of the temperature, using large-scale atomistic simulation with the first principles based ReaxFF force field. By raising the temperature in a computational experiment with otherwise identical boundary conditions, we show that the material response changes from brittle cracking to emission of a dislocation at the crack tip, representing evidence for a potential mechanisms of dislocation mediated ductility in silicon.

We have performed the finite element simulations to study the binding reaction kinetics of the analyte-ligand protein pairs, C-reactive protein (CRP) and anti-CRP, in a reaction chamber of a biosensor. For diffusion limited reactions, diffusion boundary layers often develop on the reaction surface, thus hindering the reaction. To enhance the efficiency of a biosensor, a non-uniform AC electric field is applied to induce the electrothermal force which stirs the flow field. Biosensors with different arrangements of the electrode pairs and the reaction surface are designed to study the effects of geometric configurations on the binding efficiency. The maximum initial slope of the binding curve can be 6.94 times of the field-free value in the association phase, under an AC field of 15 rms and an operating frequency of 100 kHz. With the electrothermal effect, it is possible to use a slower flow and save much sample consumption without sacrificing the performance of a biosensor. Several design factors not studied in our previous works such as the thermal boundary conditions are discussed.

Polymer micro- and nanotubes are of growing interest for design of microfluidic devices, chromatography, biotechnology, medicine chemical sensors, etc. One approach for the design of tubes is based on use of self-rolling thin films. Here we overview our recent progress in the fabrication of polymeric self-rolling tube.

Here we report an epoch-making simple fabrication for wrinkle formation. The present wrinkle formation process is a solution for controlling the area, shape and direction of wrinkle area by forming wrinkles on the liquid state polydimethylsiloxane directly exposed to sputtered metal particles in the low vacuum plasma chamber in various vacuum states and deposition conditions. Also the process allows us to make extremely flexible metal thin film electrode with approved adhesion. These bring us possibilities of actual electrical and biological applications.

We have investigated the possibility of using the protease enzyme thermolysin to catalyse the synthesis and gelation of ionic-complementary peptides from non-gelling peptide precursors. In the described system, thermolysin was added at a fixed concentration (0.3 mg mL−1) to solutions (25 - 100 mg mL−1) of a short tetra-peptide FEFR. Initially, the protease partially hydrolysed the tetrapeptide into di-peptides in all samples. Subsequently, longer peptide sequences were found to form through reverse-hydrolysis and their stability was found to be dependent on their self-assembling properties. The sequences that self-assembled into anti-parallel β-sheet rich fibres became the stable products for the reverse hydrolysis reaction, while the others formed were unstable and disappeared with increasing incubation time. Ultimately, the main product of the system was octa-peptide, which suggests that it represents the thermodynamically favoured product of this dynamic library.

In many biological applications, such as cell therapy and drug delivery, there is a need to enhance diffusion by enabling chemical transport in all three dimensions. We highlight this need by comparing diffusion in a conventional two-dimensional (2D) microwell with diffusion in a three-dimensional (3D) cubic microwell using numerical simulations. We also describe the fabrication of hollow polymeric (and biocompatible) cubic microwells and microwell arrays. We emphasize that since the assembly process is compatible with 2D lithographic patterning, porosity can be precisely patterned in all three dimensions. Hence, this platform provides considerable versatility for a variety of applications.

Microfluidic mixing was applied to conventional acid pasting process to re-crystallize organic nanocrystals of Titanyl phthalocyanine (TiOPc). TiOPc nanocrystals were re-crystallized in a two step process. Seed particles were prepared by mixing TiOPc, dissolved in concentrated sulfuric acid with deionized water using high speed microchannel mixers. Seed particles were then subjected to post-precipitation treatment to achieve final crystalline product. Effects of seed preparation conditions, such as mixing efficiency (mixer type) and mixing temperature on the structure of final product were studied. Time evolution of optical absorption spectra was examined with a view to elucidate structure evolution during early stages of seed formation process.

Several different hydrogel compositions have been incorporated into magnetic vesicle gels and the resulting “smart” biomaterials assessed as cell culture scaffolds. The compatibility of these hydrogels with the “smart” component of these biomaterials, thermally sensitive vesicles (TSVs) crosslinked by magnetic nanoparticles, was assessed by the leakage of fluorescent 5/6-carboxyfluorescein from the TSVs under cell culture conditions. Subsequently the ability of the hydrogels to support 3T3 fibroblast and chondrocyte viability was assessed. These studies revealed that alginate-based gels were the most compatible with both the TSVs and the cultured cells, with an alginate:fibronectin mix proving to be the most versatile. Nonetheless these studies also suggest that TSV composition needs to be modified to improve the performance of these “smart” cell culture scaffolds in future applications.

Stem cell transplantation holds tremendous potential for the treatment of various trauma and diseases. However, the therapeutic efficacy is often limited by poor and unpredictable post-transplantation cell survival. While hydrogels are thought to be ideal scaffolds, the sol-gel phase transitions required for cell encapsulation within commercially available biomatrices such as collagen and Matrigel often rely on non-physiological environmental triggers (e.g., pH and temperature shifts), which are detrimental to cells. To address this limitation, we have designed a novel class of protein biomaterials: Mixing-Induced Two-Component Hydrogels (MITCH) that are recombinantly engineered to undergo gelation by hetero-assembly upon mixing at constant physiological conditions, thereby enabling simple, biocompatible cell encapsulation and transplantation protocols. Building upon bio-mimicry and precise molecular-level design principles, the resulting hydrogels have tunable viscoelasticity consistent with simple polymer physics considerations. MITCH are reproducible across cell-culture systems, supporting growth of human endothelial cells, rat mesenchymal stem cells, rat neural stem cells, and human adipose-derived stem cells. Additionally, MITCH promote the differentiation of neural progenitors into neuronal phenotypes, which adopt a 3D-branched morphology within the hydrogels.

Silver nanoparticles coated by a layer of gold (Ag@Au) have received much attention because of their potential application as ultra sensitive probes for the detection of biologically important molecules such as DNA, proteins, amino acids and many others. However, the ability to control the size, shape, and monodispersity of the Ag@Au structure has met with limited success. In our own research we have addressed this challenge by creating an aqueous wet chemical synthesis technique towards size and shape controllable Ag@Au nanoparticles. These materials are highly interesting because of the tunable silver core size, and the tunable gold shell thickness, opening many avenues to the modification of the particle properties in terms of bio-molecular sensing. The resulting nanoparticle probes were functionalized with two complementary stranded DNA oligonucleotides. When combined, the complementary strands hybridized, causing the Ag@Au nanoparticles to assemble into large nano-structures. The presence of the oligonucleotide was confirmed through a series of techniques including UV-Vis and Raman spectroscopy, as well as TEM, XPS, DLS, and many others. The results reflect the role that the nanoparticle physical properties play in the detection of the bio-molecules, as well as elucidate the characteristics of the bio-molecule/nanoparticle interaction.