Grain Size Dependent Mechanical Properties in Nanophase Materials

Micro-Tensile Testing of Nanocrystalline Al/Zr Alloys

A novel micro testing machine has been used to perform tensile tests on nanocrystalline Al/Zr microsamples with grain sizes ranging from 10 to 250 nm. The problems associated with testing such small specimens (200μm × 200μm in the gage section) were overcome by using a contact-free interferometrie strain gage (ISDG) and alignment and low friction loading were assured by use of a linear air bearing. The postulated relationship between yield stress and hardness was investigated and will be discussed. The effect of the microstructure and the grain size of the compacts on their mechanical behaviour are also analysed.

Enhanced functions of vascular and bladder cells on poly-lactic-co-glycolic acid polymers with nanostructured surfaces

Polymers currently utilized for tissue engineering applications do not possess surfaces with nanostructured features. However, the tissue that the polymers will replace is composed of proteins that have nanometer dimensions. Undoubtedly, in situ, cells are accustomed to interacting with surface roughness values in the nanometer regime due to the presence of such proteins in natural tissue. Therefore, the objective of this paper was to design, synthesize and evaluate (using in vitro cellular models) poly-lactic-co-glycolic acid (PLGA) with nanostructured surface features to serve as the next generation of more efficient tissue engineered materials. For this purpose, nanostructured PLGA was created by treating conventional PLGA with various concentrations of NaOH for select periods of time. To eliminate surface chemistry changes created though the etching process, PLGA was cast from silastic molds of NaOH-treated nanostructured PLGA. Results provided the first evidence of increased numbers of vascular cells (specifically, endothelial and aortic smooth muscle cells) and bladder smooth muscle cells on nanostructured compared with conventional PLGA substrates. For this reason, the present results suggest, for the first time, that PLGA should incorporate a high degree of nanostructured surface roughness to enhance tissue regeneration for vascular and bladder applications.

Adhesion of Pseudomonas fluorescens onto nanophase materials

Nanobiotechnology is a growing area of research, primarily due to the potentially numerous applications of new synthetic nanomaterials in engineering/science. Although various definitions have been given for the word 'nanomaterials' by many different experts, the commonly accepted one refers to nanomaterials as those materials which possess grains, particles, fibres, or other constituent components that have one dimension specifically less than 100 nm. In biological applications, most of the research to date has focused on the interactions between mammalian cells and synthetic nanophase surfaces for the creation of better tissue engineering materials. Although mammalian cells have shown a definite positive response to nanophase materials, information on bacterial interactions with nanophase materials remains elusive. For this reason, this study was designed to assess the adhesion of Pseudomonas fluorescens on nanophase compared to conventional grain size alumina substrates. Results provide the first evidence of increased adhesion of Pseudomonas fluorescens on alumina with nanometre compared to conventional grain sizes. To understand more about the process, polymer (specifically, poly-lactic-co-glycolic acid or PLGA) casts were made of the conventional and nanostructured alumina surfaces. Results showed similar increased Pseudomonas fluorescens capture on PLGA casts of nanostructured compared to conventional alumina as on the alumina itself. For these reasons, a key material property shown to enhance bacterial adhesion was elucidated in this study for both polymers and ceramics: nanostructured surface features.

Increased osteoblast function on PLGA composites containing nanophase titania

Nanotechnology creates materials that potentially outperform, at several boundaries, existing materials in terms of mechanical, electrical, catalytic, and optical properties. However, despite their promise to mimic the surface roughness cells experience in vivo, the use of nanophase materials in biological applications remains to date largely unexplored. The objective of the present in vitro study was, therefore, to determine whether when added to a polymer scaffold, nanophase compared to conventional ceramics enhance functions of osteoblasts (or bone-forming cells). Results from this study provided the first evidence that functions (specifically, adhesion, synthesis of alkaline phosphatase, and deposition of calcium-containing mineral) of osteoblasts increased on poly-lactic-co-glycolic acid (PLGA) scaffolds containing nanophase compared to conventional grain size titania with greater weight percentage (from 10-30 wt %). Because the chemistry, material phase, porosity (%), and pore size of the composites were similar, this study implies that the surface features created by adding nanophase compared to conventional titania was a key parameter that enhanced functions of osteoblasts. In this manner, the study adds another novel property of nanophase ceramics: their ability to promote osteoblast functions in vitro when added to a polymer scaffold. For this reason, nanophase ceramics (and nanomaterials in general) deserve further attention as orthopedic tissue engineering materials.