Third-order optical nonlinear studies of Cobalt (II) Schiff base complex bearing triphenylphosphine using Differential Optical Kerr Gate and Z-scan studies

The third-order optical nonlinearity of the composite film of coordination complex [CoLPPh₃Cl] (L = N-(2-pyridyl)-N′-(salicylidene)hydrazine) and PMMA has been investigated by using Differential Optical Kerr Gate (DOKG) and Z-scan measurements. Large value of the third-order nonlinear optical susceptibility (χ⁽³⁾) of the order of 10^?10 esu was measured and its nonlinear response time was found to be faster than or comparable to the laser pulse width (90 fs) used. The single beam Z-scan technique was used to investigate the nonlinear absorption property of the composite near 800 nm. The sample exhibit saturable absorption. The nonlinear absorption coefficient of sample is found to be ?32 cm/GW.     

Studies on carboxy‐terminated liquid natural rubber in NBR

Maleic anhydride was chemically attached to depolymerized natural rubber by a photochemical reaction. The product Carboxy Terminated Liquid Natural Rubber (CTNR) was characterized by ¹H‐NMR, IR, GPC, and TGA. The efficiency and permanence of CTNR were compared with conventional plasticizers in NBR vulcanizates. This polymeric plasticizer was found to be less volatile and more resistant to oil extraction. The vulcanizates showed improved aging resistance compared to vulcanizates containing conventional plasticizers. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 84: 261–267, 2002; DOI 10.1002/app.10322     

Electron Paramagnetic Resonance and optical absorption spectra of Cr(III) ions in alkali cadmium borosulphate glasses

The Electron Paramagnetic Resonance (EPR) spectrum at 9.205 GHz and at 300 K has been examined for a series of Cr³⁺ ions doped alkali cadmium borosulphate [R₂SO₄-CdSO₄-B₂O₃ (R=Li,Na,K or Cs)] glasses. The low field EPR spectral resonance lines are attributed to isolated Cr³⁺ ions where as the high field spectral resonance lines are attributed to exchange coupled pairs of Cr³⁺ ions. The absorption spectra of Cr³⁺ ions ions in these glasses show two broad bands characteristic of Cr³⁺ ions in octahedral symmetry. The bands are slightly shifted to higher wavelength side from Li glass to Cs glass. From the optical spectra the crystal field parameter Dq and the Racah interelectronic repulsion parameters B and C are evaluated. From the EPR and optical data, it is concluded that, the site symmetry around the Cr³⁺ ions is octahedral and the nature of bonding is predominantly covalent in nature.     

Aloe vera incorporated biomimetic nanofibrous scaffold: a regenerative approach for skin tissue engineering

Aloe vera (AV) is one of the medicinal herbs with a well-established spectrum of wound healing, antimicrobial and anti-inflammatory property. AV-mediated therapeutics present significant tissue regenerative activity by modulating the inflammatory and proliferative phases of wound healing. The purpose of the present work was to combine the biological properties of AV and the advantages of electrospun meshes to prepare a potent transdermal biomaterial. The polycaprolactone (PCL) containing 5 and 10 wt % of lyophilized powder of AV was studied for electrospinning into nanoscale fiber mats and compared with PCL/Collagen blend for dermal substitutes. SEM revealed the average diameters of PCL, PCL-AV 5 %, PCL-AV 10 % and PCL/Collagen nanofiber scaffolds in the range of 519 ± 28, 264 ± 46, 215 ± 63 and 249 ± 52 nm, respectively. PCL-AV 10 % nanofiber scaffolds showed finer fiber morphology with improved hydrophilic properties and higher tensile strength of 6.28 MPa with a Young’s modulus of 16.11 MPa desirable for skin tissue engineering. The nanofibers were then used to investigate differences in biological responses in terms of proliferation and cell morphology of mice dermal fibroblasts. It was found that PCL-AV 10 % nanofibrous matrix favored cell proliferation compared to other scaffolds which almost increased linearly by (p ≤ 0.01) 17.79 % and (p ≤ 0.01) 21.28 % compared to PCL on sixth and ninth day. CMFDA dye expression, secretion of collagen and F-actin expression were significantly increased in PCL-AV 10 % scaffolds compared to other nanofibrous scaffolds. The obtained results proved that the PCL-AV 10 % nanofibrous scaffold is a potential biomaterial for skin tissue regeneration.     

Influence of transverse vibrations on convective heat transfer in parallel flow tube-in-tube heat exchanger

Tube-in-tube heat exchangers are widely used in food processing industries and wastewater treatment for both heating and cooling. Enhancement techniques namely active, passive, and compound are developed to reduce the thermal resistance in heat exchangers by improving convective heat transfer with or without increase in surface area. The present experimental study is aimed at analyzing the influence of vibrations on the convective heat transfer of a parallel flow tube-in-tube heat exchanger. The heat exchanger is placed in horizontal position and is subjected to transverse vibrations under turbulent fluid flow conditions. Experiments were performed at four frequencies (20, 40, 60, and 100 Hz), three amplitudes (1, 2, and 3 m/s²), and three vibration generator positions along its length, in the Reynolds number range of 10 710 to 21 420. An enhancement in Nusselt number is found with vibration than without vibration throughout the entire range of Reynolds numbers. A maximum enhancement of 33% at 40 Hz frequency, 3 m/s² amplitude, and vibration generator position at three-fourth of the tube length was observed. Empirical correlations are developed for Nusselt number to determine the heat transfer coefficient with vibration with an error of $\pm$10%.     

Conductive electrospun PANi-PEO/TiO2 fibrous membrane for photo catalysis

The integration of electrospinning and electrospraying to prepare the fibrous catalytic filter membrane is demonstrated. The non-conductive polyethylene oxide (PEO) is blended with (±)-camphor-10-sulfonic acid (CSA) doped conductive polyaniline (PANi) for electrospinning. The conductive CSA/PANi-PEO composite fibers are produced upon electrospinning, which are used as the conductive collector for electrospraying process by which titanium dioxide (TiO₂) nanoparticles (NPs) are sprayed and allowed to adsorb on the fibers. The degree of adsorption and dispersion of nano TiO₂ catalysts on the surface of the CSA/PANi-PEO fibers exhibit a stronger dependence on weight percentage (wt%) of PANi in PEO solution and the strength of electrical conductivity of the fibers used during electrospraying. CSA/PANi-PEO fibers as collector reduce the wastage of TiO₂ NPs during electrospraying to lesser than 5%. Among the three different composition of PANi studied, PEO with 12 wt% PANi yields very uniform diameter and beads-free fibrous structure with higher electrical conductivity. 12 wt% CSA/PANi-PEO fibrous membrane is found to support for greater dispersion of TiO₂ NPs. The photocatalytic activity of the as-prepared TiO₂-PANi-PEO catalytic membrane is tested against the toxicant simulant 2-chloroethyl phenyl sulfide (CEPS) under the ultraviolet light irradiation. It is observed that the TiO₂ nanoparticles catalysts embedded PANi-PEO fibrous membrane decontaminated the toxicant CEPS significantly, which is due to uniform dispersion of the catalysts produced by the methodology.     

Biomimetic material strategies for cardiac tissue engineering

Cardiovascular disease precedes many serious complications including myocardial infarction (MI) and it remains a major problem for the global community. Adult mammalian heart has limited ability to regenerate and compensate for the loss of cardiomyocytes. Restoration of cardiac function by replacement of diseased myocardium with functional cardiomyocytes is an intriguing strategy because it offers a potential cure for MI. Biomaterials are fabricated in nanometer scale dimensions by combining the chemical, biological, mechanical and electrical aspects of material for potential tissue engineering (TE) applications. Synthetic polymers offer advantageous in their ability to tailor the mechanical properties, and natural polymers offer cell recognition sites necessary for cell, adhesion and proliferation. Cardiac tissue engineering (TE) aim for the development of a bioengineered construct that can provide physical support to the damaged cardiac tissue by replacing certain functions of the damaged extracellular matrix and prevent adverse cardiac remodeling and dysfunction after MI. Electrospun nanofibers are applied as heart muscle patches, while hydrogels serve as a platform for controlled delivery of growth factors, prevent mechanical complications and assist in cell recruitment. This article reviews the applications of different natural and synthetic polymeric materials utilized as cardiac patches, injectables or 3D constructs for cardiac TE. Smart organization of nanoscale assemblies with synergistic approaches of utilizing nanofibers and hydrogels could further advance the field of cardiac tissue engineering. Rapid innovations in biomedical engineering and cell biology will bring about new insights in the development of optimal scaffolds and methods to create tissue constructs with relevant contractile properties and electrical integration to replace or substitute the diseased myocardium.     

Elastomeric electrospun scaffolds of poly(<Emphasis Type="SmallCaps">l</Emphasis>-lactide-<Emphasis Type="Italic">co</Emphasis>-trimethylene carbonate) for myocardial tissue engineering

In myocardial tissue engineering the use of synthetically bioengineered flexible patches implanted in the infarcted area is considered one of the promising strategy for cardiac repair. In this work the potentialities of a biomimetic electrospun scaffold made of a commercial copolymer of (l)-lactic acid with trimethylene carbonate (P(l)LA-co-TMC) are investigated in comparison to electrospun poly(l)lactic acid. The P(l)LA-co-TMC scaffold used in this work is a glassy rigid material at room temperature while it is a rubbery soft material at 37°C. Mechanical characterization results (tensile stress–strain and creep-recovery measurements) show that at 37°C electrospun P(l)LA-co-TMC displays an elastic modulus of around 20 MPa and the ability to completely recover up to 10% of deformation. Cell culture experiments show that P(l)LA-co-TMC scaffold promotes cardiomyocyte proliferation and efficiently preserve cell morphology, without hampering expression of sarcomeric alpha actinin marker, thus demonstrating its potentialities as synthetic biomaterial for myocardial tissue engineering.     

Evaluation of the Biocompatibility of PLACL/Collagen Nanostructured Matrices with Cardiomyocytes as a Model for the Regeneration of Infarcted Myocardium

Pioneering research suggests various modes of cellular therapeutics and biomaterial strategies for myocardial tissue engineering. Despite several advantages, such as safety and improved function, the dynamic myocardial microenvironment prevents peripherally or locally administered therapeutic cells from homing and integrating of biomaterial constructs with the infarcted heart. The myocardial microenvironment is highly sensitive due to the nanoscale cues that it exerts to control bioactivities, such as cell migration, proliferation, differentiation, and angiogenesis. Nanoscale control of cardiac function has not been extensively analyzed in the field of myocardial tissue engineering. Inspired by microscopic analysis of the ventricular organization in native tissue, a scalable in‐vitro model of nanoscale poly(L ‐lactic acid)‐co ‐poly(? ‐caprolactone)/collagen biocomposite scaffold is fabricated, with nanofibers in the order of 594 ± 56 nm to mimic the native myocardial environment for freshly isolated cardiomyocytes from rabbit heart, and the specifically underlying extracellular matrix architecture: this is done to address the specificity of the underlying matrix in overcoming challenges faced by cellular therapeutics. Guided by nanoscale mechanical cues provided by the underlying random nanofibrous scaffold, the tissue constructs display anisotropic rearrangement of cells, characteristic of the native cardiac tissue. Surprisingly, cell morphology, growth, and expression of an interactive healthy cardiac cell population are exquisitely sensitive to differences in the composition of nanoscale scaffolds. It is shown that suitable cell–material interactions on the nanoscale can stipulate organization on the tissue level and yield novel insights into cell therapeutic science, while providing materials for tissue regeneration.