Hydroxyapatite-nanotube composites and coatings for orthopedic applications

Hydroxyapatite (HA) has received wide attention in orthopedics, due to its biocompatibility and osseointegration ability. Despite these advantages, the brittle nature and low fracture toughness of HA often results in rapid wear and premature fracture of implant. Hence, there is a need to improve the fracture toughness and wear resistance of HA without compromising its biocompatibility. The aim of the current research is to explore the potential of nanotubes as reinforcement to HA for orthopedic implants. HA- 4 wt.% carbon nanotube (CNT) composites and coatings are synthesized by spark plasma sintering and plasma spraying respectively, and investigated for their mechanical, tribological and biological behavior. CNT reinforcement improves the fracture toughness (\u3e90%) and wear resistance (\u3e66%) of HA for coating and free standing composites. CNTs have demonstrated a positive influence on the proliferation, differentiation and matrix mineralization activities of osteoblasts, during in-vitro biocompatibility studies. In-vivo exposure of HA-CNT coated titanium implant in animal model (rat) shows excellent histocompatibility and neobone integration on the implant surface. The improved osseointegration due to presence of CNTs in HA is quantified by the adhesion strength measurement of single osteoblast using nano-scratch technique. Considering the ongoing debate about cytotoxicity of CNTs in the literature, the present study also suggests boron nitride nanotube (BNNT) as an alternative reinforcement. BNNT with the similar elastic modulus and strength as CNT, were added to HA. The resulting composite having 4 wt.% BNNTs improved the fracture toughness (∼85%) and wear resistance (∼75%) of HA in the similar range as HA-CNT composites. BNNTs were found to be non-cytotoxic for osteoblasts and macrophages. In-vitro evaluation shows positive role of BNNT in osteoblast proliferation and viability. Apatite formability of BNNT surface in ∼4 days establishes its osseointegration ability

Microstructure dependent elastic modulus variation in NiTi shape memory alloy

Modulus variation of NiTi shape memory alloy has been investigated at microstructural level through nano dynamical mechanical analysis and compared with bulk experimental measurements. The differences between the modulus values at the macro and micro level as well as within the micro level are discussed and the corresponding variations have been explained based on the crystal structure, orientation and misorientation. The experimental results confirm a higher modulus value for the martensite phase that is in agreement with the theoretical predictions. (C) 2015 Elsevier B. V. All rights reserved

Nutraceutical regulation of miRNAs involved in neurodegenerative diseases and brain cancers

The human brain is a well-connected, intricate network of neurons and supporting glial cells. Neurodegenerative diseases arise as a consequence of extensive loss of neuronal cells leading to disruption of their natural structure and function. On the contrary, rapid proliferation and growth of glial as well as neuronal cells account for the occurrence of malignancy in brain. In both cases, the molecular microenvironment holds pivotal importance in the progression of the disease. MicroRNAs (miRNA) are one of the major components of the molecular microenvironment. miRNAs are small, noncoding RNAs that control gene expression post-transcriptionally. As compared to other tissues, the brain expresses a substantially high number of miRNAs. In the early stage of neurodegeneration, miRNA expression upregulates, while in oncogenesis, miRNA expression is gradually lost. Neurodegeneration and brain cancer is presumed to be under the influence of identical pathways of cell proliferation, differentiation and cell death which are tightly regulated by miRNAs. It has been confirmed experimentally that miRNA expression can be regulated by nutraceuticals - macronutrients, micronutrients or natural products derived from food; thereby making dietary supplements immensely significant for targeting miRNAs having altered expression patterns during neurodegeneration or oncogenesis. In this review, we will discuss in detail, about the common miRNAs involved in brain cancers and neurodegenerative diseases along with the comprehensive list of miRNAs involved separately in both pathological conditions. We will also discuss the role of nutraceuticals in the regulation of those miRNAs which are involved in both of these pathological conditions

Cold Sprayed Aluminum Based Glassy Coating: Synthesis, Wear And Corrosion Properties

Al-based glassy coatings were synthesized using cold spraying technique to protect 6061 aluminum surface from wear and corrosion. Gas atomized Al90.05Y4.4Ni4.3Co0.9Sc0.35 (at.%) powder was used as the starting powder. Dense (98%) coatings with a uniform thickness of ~250μm were deposited. The coatings retained the glassy structure of the powder with few nanocrystals embedded in the amorphous matrix. Ball-on-disk wear of the coatings showed 600% improvement in the wear resistance as compared to 6061Al substrate. Potentiodynamic studies of the coatings in varying NaCl concentrations displayed 5 times better corrosion resistance than 6061 Al substrate, which was attributed to the active passivation and the chemical homogeneity of the coatings.© 2013 Elsevier B.V

Carbon Nanotube Toughened Hydroxyapatite By Spark Plasma Sintering: Microstructural Evolution And Multiscale Tribological Properties

Carbon nanotube (CNT) reinforced hydroxyapatite (HA) composite synthesized using spark plasma sintering is investigated in this study. Quantitative microstructural analysis suggests that CNTs play a role in grain boundary pinning and are responsible for the improved densification and retention of nanostructure throughout the thickness of the sintered pellet. HA crystal forms coherent interface with the CNT, resulting in a strong interfacial bond. The uniform distribution of 4 wt.% CNTs in the HA matrix, good interfacial bonding and fine HA grain size help to improve the fracture toughness by 92% and elastic modulus by 25% as compared to the HA matrix without CNT. Toughening mechanisms have been explained in terms of interfacial shear strength and pull-out energy of CNT from the HA matrix. CNT plays a major role in improving the wear resistance of HA matrix at both macro- and nano-scale. It is concluded that graphene layer removal from the CNT surface occurs during macro-wear, but not for nano-wear. Thus, the coefficient of friction (CoF) in HA-CNT decreases in macro-wear due to lubrication available through delaminated graphene layers. © 2010 Elsevier Ltd. All rights reserved

Apatite Formability Of Boron Nitride Nanotubes

This study investigates the ability of boron nitride nanotubes (BNNTs) to induce apatite formation in a simulated body fluid environment for a period of7, 14 and 28days. BNNTs, when soaked in the simulated body fluid, are found to induce hydroxyapatite (HA) precipitation on their surface. The precipitation process has an initial incubation period of ∼ 4.6 days. The amount of HA precipitate increases gradually with the soaking time. High resolution TEM results indicated a hexagonal crystal structure of HA needles. No specific crystallographic orientation relationship is observed between BNNT and HA, which is due to the presence of a thin amorphous HA layer on the BNNT surface that disturbs a definite orientation relationship. © 2011 IOP Publishing Ltd