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Johari N.,Isfahan University of Technology | Fathi M.H.,Isfahan University of Technology | Golozar M.A.,Isfahan University of Technology | Erfani E.,Tehran University of Medical Sciences | And 2 more authors.
Journal of Materials Science: Materials in Medicine | Year: 2012

In this study, biodegradation and biocompatibility of novel poly(ε-caparolactone)/nano fluoridated hydroxyapatite (PCL-FHA) scaffolds were investigated. The FHA nanopowders were prepared via mechanical alloying method and had a chemical composition of Ca 10 (PO 4) 6OH 2-xF x (where x values were selected equal to 0.5 and 2.0). In order to fabricate PCL-FHA scaffolds, 10, 20, 30 and 40 wt% of the FHA were added to the PCL. The PCL-FHA scaffolds were produced by the solvent casting/ particulate leaching using sodium chloride particles (with diameters of 300-500 lm) as the porogen. The phase structure, microstructure and morphology of the scaffolds were evaluated using X-ray diffraction, Fourier transform infrared spectroscopy and scanning electron microscopy techniques. Porosity of the scaffolds was measured using the Archimedes' Principle. In vitro degradation of PCL- FHA scaffolds was studied by incubating the samples in phosphate buffered saline at 37°C and pH 7.4 for 30 days. Moreover, biocompatibility was evaluated by MTT assay after seeding and culture of osteoblast-like cells on the scaffolds. Results showed that the osteoblast-like cells attached to and proliferated on PCL-FHA and increasing the porosity of the scaffolds increased the cell viability. Also, degradation rate of scaffolds were increased with increasing the fluorine content in scaffolds composition. © 2012 Springer Science+Business Media, LLC. Source


Krishnan J.,Center for Process Systems Engineering | Krishnan J.,Imperial College London
Industrial and Engineering Chemistry Research | Year: 2011

There has been a considerable effort in the past decade to understand different aspects of cellular processes from both a reverse engineering and, more recently, a synthetic perspective. In this article I provide a perspective on aspects of cellular signal processing which involve traditional chemical engineering elements (reactions, transport, control) and their variants, along with additional ingredients, sometimes combined in unusual ways. I also compare and contrast certain basic aspects of chemical engineering and cellular signal processing in areas of mutual overlap. © 2011 American Chemical Society. Source


Alam-Nazki A.,Center for Process Systems Engineering | Krishnan J.,Center for Process Systems Engineering | Krishnan J.,Imperial College London
BMC Systems Biology | Year: 2012

Background: Spatial signal transduction plays a vital role in many intracellular processes such as eukaryotic chemotaxis, polarity generation and cell division. Furthermore it is being increasingly realized that the spatial dimension to signalling may play an important role in other apparently purely temporal signal transduction processes. It is increasingly being recognized that a conceptual basis for studying spatial signal transduction in signalling networks is necessary.Results: In this work we examine spatial signal transduction in a series of standard motifs/networks. These networks include coherent and incoherent feedforward, positive and negative feedback, cyclic motifs, monostable switches, bistable switches and negative feedback oscillators. In all these cases, the driving signal has spatial variation. For each network we consider two cases, one where all elements are essentially non-diffusible, and the other where one of the network elements may be highly diffusible. A careful analysis of steady state signal transduction provides many insights into the behaviour of all these modules. While in the non-diffusible case for the most part, spatial signalling reflects the temporal signalling behaviour, in the diffusible cases, we see significant differences between spatial and temporal signalling characteristics. Our results demonstrate that the presence of diffusible elements in the networks provides important constraints and capabilities for signalling.Conclusions: Our results provide a systematic basis for understanding spatial signalling in networks and the role of diffusible elements therein. This provides many insights into the signal transduction capabilities and constraints in such networks and suggests ways in which cellular signalling and information processing is organized to conform to or bypass those constraints. It also provides a framework for starting to understand the organization and regulation of spatial signal transduction in individual processes. © 2012 Alam-Nazki and Krishnan; licensee BioMed Central Ltd. Source


Krishnan J.,Center for Process Systems Engineering | Krishnan J.,Imperial College London | Alam-Nazki A.,Center for Process Systems Engineering
Journal of Theoretical Biology | Year: 2011

Many important cellular processes rely on cellular responses to spatially graded signals. This response may be either attractive, indicating a positive bias, or repulsive indicating a negative bias. In this paper we consider cells which exhibit both repulsive and attractive gradient sensing responses and aim to uncover the underlying design principles and features of how the networks are wired which could allow a cell to exhibit both responses. We use a modular approach to examine different configurations which will allow for a cell to exhibit both responses and analyse how this depends on the basic characteristics of gradient sensing and downstream signal propagation. Overall our analysis provides insights into how gradient responses can be switched and the key factors which affect this switching. © 2010 Elsevier Ltd. Source


Suwanmajo T.,Center for Process Systems Engineering | Krishnan J.,Center for Process Systems Engineering | Krishnan J.,Imperial College London
Journal of the Royal Society Interface | Year: 2013

Multi-site phosphorylation systems are repeatedly encountered in cellular biologyandmulti-sitemodification is a basic building blockofpost-translational modification. In this paper, we demonstrate how distributive multi-site modification mechanisms by a single kinase/phosphatase pair can lead to biphasic/ partial biphasic dose-response characteristics for the maximally phosphorylated substrate at steady state. We use simulations and analysis to uncover a hidden competing effect which is responsible for this and analyse how it may be accentuated.We build on this to analyse different variants of multi-site phosphorylation mechanisms showing that some mechanisms are intrinsically not capable of displaying this behaviour. This provides both a consolidated understanding of howand under what conditions biphasic responses are obtained in multi-site phosphorylation and a basis for discriminating between different mechanisms based on this. We also demonstrate how this behaviour may be combined with other behaviour such as threshold and bistable responses, demonstrating the capacity of multi-site phosphorylation systems to act as complex molecular signal processors. © 2013 The Author(s) Published by the Royal Society. All rights reserved. Source

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