G K Suraishkumar

Human skull bone is a three-layered structure with a compliant viscoelastic cancellous bone layer sandwiched between elastic compact layers. The objective of the work was to check whether the skull bone is innately optimized with respect to the various geometrical and material parameters and to find out the parameters with which they are optimized. The effect of varying the thickness of layers and short time modulus of the interlayer are studied for optimality using finite element analysis of the skull subjected to low-velocity impact. Results show that they are optimized to meet different objectives. © Woodhead Publishing Ltd.

Liquid phase oxygen supply strategy (LPOS), in which hydrogen peroxide (H2O2) is used to supply oxygen to the bioreactor, leads to low cell productivity despite high specific productivities of relevant metabolites. We hypothesized that high H2O2 concentrations in the feed-zone led to local cell death, which in turn, lead to lower cell productivity. To test the hypothesis, a mathematical model was developed. Bacillus subtilis 168 was used as the model system in this study. The model simulations of cell concentrations in the bioreactor-zone were verified with the experimental results. The feed-zone H2O2 concentrations remained 12-14 times higher than bulk bioreactor concentrations. The high local concentrations are expected to cause local cell killing, which explains the decrease in overall cell production by 50% at 300 rpm compared to conventional cultivation. Further, among the four different feed strategies studied using the model, dissolved oxygen (DO) controlled H2O2 feed strategy caused least local cell killing and improved overall cell production by 34%. © 2007 Springer-Verlag.

The photosynthetic machinery of Spirulina maxima was studied when subjected to induced reactive oxygen species (ROS) to examine the organism's responses to stress. Significant decreases in both photosynthetic efficiency and growth rate were observed. Exposure to 0.01 mmol H2O2/(g cell), which induced the lowest specific intracellular ROS level (siROS) led to a 15% decrease in specific growth rate; an increase in siROS by 70-fold led to a 25% decrease in specific growth rate. Similarly, siROS induced by 0.01 mmol H 2O2/(g cell) led to 15% inhibition in photosynthetic efficiency, while an increase in siROS by 40- or 70-fold led to about 60% inhibition in photosynthetic efficiency. To further understand the effects of induced ROS on photosynthetic machinery, we performed a detailed pigmentation analysis as well as analyzed Phycobilisomes (PBS), Photosystem II (PSII), and Photosystem I (PSI), the three important components of cyanobacterial photosynthetic apparatus. We found carotenoids (beta-carotene and lutein) to be most sensitive to siROS. Also, specific levels of phycocyanin and allophycocyanin, which are important PBS pigments, decreased significantly in response to H2O2. Further, electron transport assays revealed that ROS cause damage primarily to PSII, whereas they do not significantly affect PSI in comparison; siROS induced by 0.01 mmol H 2O2/(g cell) led to a 15% inhibition of PSII, and increase in siROS by 9-, 40-, and 70-fold led to 22%, 36%, and 46% inhibition, respectively. © 2006 Wiley Periodicals, Inc.

Bone is a hierarchical bio-composite, and has a staggered arrangement of soft protein molecules interspaced with hard mineral platelets at the fine ultrastructure level. The investigation into reasons for high fracture toughness of bio-composites such as bone requires consideration of properties at the different levels of hierarchy. In this work, the analysis is done at the continuum level, but the properties used are appropriate to that of the level considered. In this way, the properties at the fine ultrastructure level of bone is considered in the stress distribution analysis of a platelet adjacent to the broken platelet. Results show the influence of overlapping in determining the nature of stress distribution. This could play an important part in the fracture toughness of bio-composites. Copyright © 2007 Tech Science Press.

In this study, biosorption of Cu(II) was investigated in a column of pretreated Aspergillus niger biomass. The breakthrough was measured as a function of influent flow rate and bed height for a feed solution at 10 mg/l metal ion concentration. Biosorption was evaluated in terms of the equilibrium capacity of the column and the amount of metal loading on the A. niger surface. It has been observed that pretreatment of the biomass enhanced the activity of the surface reactive groups and hence the uptake. The breakthrough data obtained was described by bed depth service time (BDST) and Thomas models. The amount of copper adsorbed per gram of pretreated A. niger was 13.4 ± 0.60 mg/g. The sorbed copper was eluted from the column using 0.1N HCl in five consecutive sorption-desorption cycles. For the same initial metal ion concentration, a packed column reactor shows more uptake of Cu(II) in comparison to a batch reactor. © 2008 Elsevier B.V. All rights reserved.

Biocomposites such as bone exhibit synergistic superior mechanical properties compared to its constituents, protein (collagen) and mineral (hydroxyapatite). The importance of properties of constituents at the submicron scale with regard to the toughness and strength of bone is investigated employing a discrete lattice model. The results show that matrix failure as opposed to platelet breakage provides better toughness to the bone. There is a fairly sudden increase in the toughness of bone when the strength of mineral platelet to that of protein crosses a particular critical value. These could provide clues to the preparation of ultra-tough artificial composites and the treatment of diseases related to fragility of bone. © 2008 World Scientific Publishing Company.

Transport of bacteria is an important aspect from scientific, industrial and environmental point of view. In this work, a one-dimensional mathematical model based on linear equilibrium adsorption of bacteria has been developed to predict bacterial transport through porous media. This model is more realistic than existing models because of its coupling both physicochemical and biological phenomena. Two important biological phenomena, the growth and decay of bacterial cells and chemotactic/chemotaxis of bacteria along with physicochemical properties have been adequately incorporated which are quite new aspects in our model. In agreement with experimental study by [D.K. Powelson, R.J. Simpson, C.P. Gerba, J. Environ. Qual. 19 (1990) 396], model simulations indicated that enhancement of breakthrough occurs due to increase in flow velocity, cell concentration, substrate concentration, respectively. It has also been found that chemo tactic has a significant effect on bacterial transport, especially under conditions of considerable substrate gradient and at low pore velocity. The importance of threshold concentration of captured cells (σ0) on bacterial transport has also been identified which is also a new aspect in our model. © 2005 Elsevier B.V. All rights reserved.

Sustainable development requires wastewater management. Heavy metals such as copper, cadmium, lead and zinc are the critical metals in wastewater. The treatment of wastewater is vital functions in any society; hence securing them for current and future generations is an important part of sustainable development. The main objective of this work is to increase water use efficiency and recycling water which is an integrated approach to sustainable development. In this present work, copper biosorption by formalin washed Aspergillus niger was characterized. The nature and binding mechanism of chemical groups in the formalin washed biomass responsible for copper biosorption was investigated as a function of pH and metal concentration, combined with Scanning Electron Micrograph (SEM), Image Analysis System (IAS), a nitrogen adsorption-desorption technique and Fourier transform infrared spectroscopy (FTIR). The retention capacity of the biomass was determined at pH 6.0 to be equal to 23.62 mg of copper/g of biomass. The Langmuir and Freundlich isotherm equations were then used to describe the behavior of the system. Based on the experimental data and surface analysis an efficient method was established for copper removal from wastewater so that it can be reused for domestic cleaning and industrial reuse.

Treatment of microbial cultures with chemical agents such as hydrogen peroxide (H2O2) and hypochlorous acid (HOCl) induces production of reactive oxygen species (ROS) in culture. These ROS inducing (treatment) agents increased the growth rate as well as the maximum specific levels of extracellular enzymes such as α-amylase and protease in Bacillus subtilis cultures. Treatment with hypochlorous acid increased maximum specific α-amylase level by 2.2-fold and maximum specific protease level by 2.6-fold, respectively. Similarly, treatment with H2O2 increased specific α-amylase and specific protease level by 1.5- and 1.9-fold, respectively. Increases in specific enzyme levels were correlated with levels of specific intracellular ROS in cultures. The mechanism of increase in enzyme productivity under induced oxidative stress was also traced at the genetic level through analysis of available microarray data. The microarray data showed an induced level of signal peptidase gene (sipT), which is the most important secretory apparatus component, and suggested that increased efficiency of secretory apparatus as a result of treatments with ROS inducing agents also leads to increased productivity of α-amylase. © 2004 Elsevier Ltd. All rights reserved.

A multi-objective optimization formulation that reflects the multi-substrate optimization in a multi-product fermentation is proposed in this work. This formulation includes the application of ε-constraint to generate the trade-off solution for the enhancement of one selective product in a multi-product fermentation, with simultaneous minimization of the other product within a threshold limit. The formulation has been applied to the fed-batch fermentation of Aspergillus niger that produces a number of enzymes during the course of fermentation, and of these, catalase and protease enzyme expression have been chosen as the enzymes of interest. Also, this proposed formulation has been applied in the environment of three control variables, i.e. the feed rates of sucrose, nitrogen source and oxygen and a set of trade-off solutions have been generated to develop the pareto-optimal curve. We have developed and experimentally evaluated the optimal control profiles for multiple substrate feed additions in the fed-batch fermentation of A. niger to maximize catalase expression along with protease expression within a threshold limit and vice versa. An increase of about 70% final catalase and 31% final protease compared to conventional fed-batch cultivation were obtained. Novel methods of oxygen supply through liquid-phase H2O2 addition have been used with a view to overcome limitations of aeration due to high gas-liquid transport resistance. The multi-objective optimization problem involved linearly appearing control variables and the decision space is constrained by state and end point constraints. The proposed multi-objective optimization is solved by differential evolution algorithm, a relatively superior population-based stochastic optimization strategy. © Springer-Verlag 2005.