Mechanical-Bending-Induced Fluorescence Enhancement in Plastically Flexible Crystals of a GFP Chromophore Analogue.

Single crystals of optoelectronic materials that respond to external stimuli, such as mechanical, light, or heat, are immensely attractive for next generation smart materials. Here we report single crystals of a green fluorescent protein (GFP) chromophore analogue with irreversible mechanical bending and associated unusual enhancement of the fluorescence, which is attributed to the strained molecular packing in the perturbed region. Soft crystalline materials with such fluorescence intensity modulations occurring in response to mechanical stimuli under ambient pressure conditions will have potential implications for the design of technologically relevant tunable fluorescent materials.

Development of nano-porous hydroxyapatite coated e-glass for potential bone-tissue engineering application: An in vitro approach.

To reconstruct the defects caused by craniectomies autologous, bone grafting was usually used, but they failed most commonly due to bone resorption, infections and donor-site morbidity. In the present investigation, an effort has been made for the first time to check the feasibility and advantage of using hydroxyapatite (HAp) coated e-glass as component of bone implants. Sol-gel synthesized coatings were found to be purely hydroxyapatite from XRD with graded and interconnected pores all over the surface observable in TEM. The interconnected porous nature of ceramics are found to increase bioactivity by acting to up-regulate the process of osseointegration through enhanced nutrient transfer and induction of angiogenesis. From TEM studies and nano indentation studies, we have shown that pores were considered to be appropriate for nutrient supply without compromising the strength of sample while in contact with physiological fluid. After SBF immersion test, porous surface was found to be useful for nucleation of apatite crystals, hence increasing the feasibility and bioactivity of sample. However, our quasi-dynamic study showed less crystallization but had significant formation of apatite layer. Overall, the in vitro analyses show that HAp coated e-glass leads to significant improvement of implant properties in terms of biocompatibility, cell viability and proliferation, osteoinductivity and osteoconductivity. HAp coating of e-glass can potentially be utilized in fabricating durable and strong bioactive non-metallic implants and tissue engineering scaffolds.

Mechanical Actuation and Patterning of Rewritable Crystalline Monomer-Polymer Heterostructures via Topochemical Polymerization in a Dual-Responsive Photochromic Organic Material.

The dark-orange monomer single crystals of 1,1'-dioxo-1H-2,2'-biindene-3,3'-diyldidodecanoate (BIT-dodeca2) convert to a transparent single-crystalline polymer (PBIT-dodeca2) material via a single-crystal-to-single-crystal (SCSC) polymerization reaction under sunlight, which then undergoes reverse thermal transformation into BIT-dodeca2 single crystals, leading to reversible photo-/thermochromism, coupled with mechanical actuation. We exploit the properties of this unique material to demonstrate the formation of monomer-polymer heterostructures in selected regions of single crystals with micrometer-scale precision using a laser. This is the first example of heterostructure patterning involving monomer-polymer domains in single crystals. We reveal that the speed of photomechanical bending induced by the polymerization reaction in this example is comparable to those of the well-known diarylethene derivatives, in which electrocyclic ring-closing-ring-opening reactions operate. Furthermore, we characterize the distinct mechanical properties of the monomer and polymer using a quantitative nanoindentation technique as well as demonstrate photopatterning on a monomer-coated paper for potential use in security devices. These crystals with several advantages, such as photomechanical bending (weight lifting) even when the crystal size is large, responsiveness to both UV and visible light, distinct solubilities (the polymer is insoluble, whereas the monomer is soluble in most organic solvents) and colors, provide unique opportunities for their use at different length scales of the sample (µm to mm) for various purposes.

Nano- and micro-tribological behaviours of plasma nitrided Ti6Al4V alloys.

Plasma nitriding of the Ti-6Al-4V alloy (TA) sample was carried out in a plasma reactor with a hot wall vacuum chamber. For ease of comparison these plasma nitrided samples were termed as TAPN. The TA and TAPN samples were characterized by XRD, Optical microscopy, FESEM, TEM, EDX, AFM, nanoindentation, micro scratch, nanotribology, sliding wear resistance evaluation and in vitro cytotoxicity evaluation techniques. The experimental results confirmed that the nanohardness, Young's modulus, micro scratch wear resistance, nanowear resistance, sliding wear resistance of the TAPN samples were much better than those of the TA samples. Further, when the data are normalized with respect to those of the TA alloy, the TAPN sample showed cell viability about 11% higher than that of the TA alloy used in the present work. This happened due to the formation of a surface hardened embedded nitrided metallic alloy layer zone (ENMALZ) having a finer microstructure characterized by presence of hard ceramic Ti2N, TiN etc. phases in the TAPN samples, which could find enhanced application as a bioimplant material.

ROS mediated high anti-bacterial efficacy of strain tolerant layered phase pure nano-calcium hydroxide.

The present work provides the first ever report on extraordinarily high antibacterial efficacy of phase pure micro-layered calcium hydroxide nanoparticles (LCHNPs) even under dark condition. The LCHNPs synthesized especially in aqueous medium by a simple, inexpensive method show adequate mechanical properties along with the presence of a unique strain tolerant behaviour. The LCHNPs are characterized by FTIR, Raman spectroscopy, XRD, Rietveld analysis, FE-SEM, TEM, TG-DTA, surface area, particle size distribution, zeta potential analysis and nanoindentation techniques. The LCHNPs have 98.1% phase pure hexagonal Ca(OH)2 as the major phase having micro-layered architecture made up of about ~100-200nm thick individual nano-layers. The nanomechanical properties e.g., nanohardness (H) and Young's modulus (E) of the LCHNPs are found to have a unique load independent behavior. The dielectric responses (e.g., dielectric constant and dielectric loss) and antibacterial properties are evaluated for such LCHNPs. Further, the LCHNPs show much better antibacterial potency against both gram-positive e.g., Staphylococcus aureus (S. aureus) and gram-negative e.g., Pseudomonas putida (P. putida) bacteria even in dark especially, with the lowest ever reported MIC value (e.g., 1 µg ml-1) against the P. putida bacterial strain and exhibit ROS mediated antibacterial proficiency. Finally, such LCHNPs has almost ~8-16% inhibition efficacy towards the development of biofilm of these microorganisms quantified by colorimetric detection process. So, such LCHNPs may find potential applications in the areas of healthcare industry and environmental engineering.

Nanotribological response of a plasma nitrided bio-steel.

AISI 316L is a well known biocompatible, austenitic stainless steel (SS). It is thus a bio-steel. Considering its importance as a bio-prosthesis material here we report the plasma nitriding of AISI 316L (SS) followed by its microstructural and nanotribological characterization. Plasma nitriding of the SS samples was carried out in a plasma reactor with a hot wall vacuum chamber. For ease of comparison these plasma nitrided samples were termed as SSPN. The experimental results confirmed the formations of an embedded nitrided metal layer zone (ENMLZ) and an interface zone (IZ) between the ENMLZ and the unnitrided bulk metallic layer zone (BMLZ) in the SSPN sample. These ENMLZ and IZ in the SSPN sample were richer in iron nitride (FeN) chromium nitride (CrN) along with the austenite phase. The results from nanoindentation, microscratch, nanoscratch and sliding wear studies confirmed that the static contact deformation resistance, the microwear, nanowear and sliding wear resistance of the SSPN samples were much better than those of the SS samples. These results were explained in terms of structure-property correlations.

Nanocolumnar Crystalline Vanadium Oxide-Molybdenum Oxide Antireflective Smart Thin Films with Superior Nanomechanical Properties.

Vanadium oxide-molybdenum oxide (VO-MO) thin (21-475 nm) films were grown on quartz and silicon substrates by pulsed RF magnetron sputtering technique by altering the RF power from 100 to 600 W. Crystalline VO-MO thin films showed the mixed phases of vanadium oxides e.g., V2O5, V2O3 and VO2 along with MoO3. Reversible or smart transition was found to occur just above the room temperature i.e., at ~45-50 °C. The VO-MO films deposited on quartz showed a gradual decrease in transmittance with increase in film thickness. But, the VO-MO films on silicon exhibited reflectance that was significantly lower than that of the substrate. Further, the effect of low temperature (i.e., 100 °C) vacuum (10-5 mbar) annealing on optical properties e.g., solar absorptance, transmittance and reflectance as well as the optical constants e.g., optical band gap, refractive index and extinction coefficient were studied. Sheet resistance, oxidation state and nanomechanical properties e.g., nanohardness and elastic modulus of the VO-MO thin films were also investigated in as-deposited condition as well as after the vacuum annealing treatment. Finally, the combination of the nanoindentation technique and the finite element modeling (FEM) was employed to investigate yield stress and von Mises stress distribution of the VO-MO thin films.

Nanomechanical responses of human hair.

Here we report the first ever studies on nanomechanical properties e.g., nanohardness and Young׳s modulus for human hair of Indian origin. Three types of hair samples e.g., virgin hair samples (VH), bleached hair samples (BH) and Fe-tannin complex colour treated hair samples (FT) with the treatment by a proprietary hair care product are used in the present work. The proprietary hair care product involves a Fe-salt based formulation. The hair samples are characterized by optical microscopy, atomic force microscopy, field emission scanning electron microscopy, energy dispersive X-ray spectroscopy (EDAX) genesis line map, EDAX spot mapping, nanoindentation, tensile fracture, and X-ray diffraction techniques. The nanoindentation studies are conducted on the cross-sections of the VH, BH and FT hair samples. The results prove that the nanomechanical properties e.g., nanohardness and Young׳s modulus are sensitive to measurement location e.g., cortex or medulla and presence or absence of the chemical treatment. Additional results obtained from the tensile fracture experiments establish that the trends reflected from the evaluations of the nanomechanical properties are general enough to hold good. Based on these observations a schematic model is developed. The model explains the present results in a qualitative yet satisfactory manner.