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PubMed2000

Biomedical engineering: issues and opportunity.

As defined by the National Institutes of Health (NIH), bioengineering is an interdisciplinary field that applies physical, chemical, and mathematical sciences and engineering principles to the study of biology, medicine, behavior, and health. It advances knowledge from the molecular to the organ systems level, and develops new and novel biologics, materials, processes, implants, devices, and informational approaches for the prevention, diagnosis, and treatment of disease for patient rehabilitation and for improving health.

Biomedical Engineering↗
PubMed2002

Physico-chemical properties and degradability of non-woven hyaluronan benzylic esters as tissue engineering scaffolds.

The development of biocompatible materials which can be processed into three-dimensional scaffolds and the design of appropriate configurations in order to enable the cellular infiltration and proliferation is a major issue in the tissue engineering. The hyaluronan total benzyl ester (Hyaff 11) has been found to be suitable substrate to grow a variety of cell types. Since structural, physical, chemical and biological data can help for tailoring appropriate scaffold for tissue engineering, information on chemicophysical properties on degradability of hyaluronan total benzyl ester non-woven has been obtained. The thermal analysis, the evaluation of the surface chemical composition, the morphology, the mechanical behaviour and the swelling tests were carried out on these materials. The hyaluronan total benzyl ester non-woven showed a thermal stability up to 220 degrees C and the surface composition differed from that of the bulk for C-O and C-C contribution. No contaminant were detected. The non-woven swelled in culture medium. Moreover the mechanical tests showed that when submitted to a press treatment, the samples have best mechanical properties. The pressed Hyaff 11 non-woven undergoes degradation when exposed to DMEM. The frying and breaking of the fibres, a decrease of the mechanical properties and a molecular weight loss have been observed. First, the ester bond of the Hyaff 11 non-woven is hydrolysed and the benzylic alcohol is released and the low molecular weight values indicate that a cleavage of the polymer is promoted by the components of the culture medium. After 11 days, some fragments, constituted by hyaluronic acid with a molecular weight of 23,000 Da became soluble in the medium. No oligomer was detected.

Biocompatible Materials↗
PubMed2007

Efficient regeneration of NADPH using an engineered phosphite dehydrogenase.

The in situ regeneration of reduced nicotinamide cofactors (NAD(P)H) is necessary for practical synthesis of many important chemicals. Here, we report the engineering of a highly stable and active mutant phosphite dehydrogenase (12x-A176R PTDH) from Pseudomonas stutzeri and evaluation of its potential as an effective NADPH regeneration system in an enzyme membrane reactor. Two practically important enzymatic reactions including xylose reductase-catalyzed xylitol synthesis and alcohol dehydrogenase-catalyzed (R)-phenylethanol synthesis were used as model systems, and the mutant PTDH was directly compared to the commercially available NADP(+)-specific Pseudomonas sp. 101 formate dehydrogenase (mut Pse-FDH) that is widely used for NADPH regeneration. In both model reactions, the two regeneration enzymes showed similar rates of enzyme activity loss; however, the mutant PTDH showed higher substrate conversion and higher total turnover numbers for NADP(+) than mut Pse-FDH. The space-time yields of the product with the mutant PTDH were also up to fourfold higher than those with mut Pse-FDH. In particular, a space-time yield of 230 g L(-1) d(-1) xylitol was obtained with the mutant PTDH using a charged nanofiltration membrane, representing the highest productivity compared to other existing biological processes for xylitol synthesis based on yeast D-xylose converting strains or similar in vitro enzyme membrane reactor systems.

Enzyme Activation↗
PubMed2003

Greener by design.

Process simulation models and other design tools allow engineers to design, simulate, and optimize chemical processes. However, there is a critical need to incorporate green engineering into the design of these processes. This calls for extending the breadth of the design process. This paper presents an integrated framework for greener design. The framework starts the decision-making as early as the chemical and material selection stage and also includes management and planning decisions. The design goal is not restricted to profitability, but environmental and ecological objectives are also added. However, this integration poses challenging problem of discrete and continuous decisions, nonlinear models, and uncertainties. Furthermore, there are multiple and conflicting objectives to be considered. Therefore, the core of this integrated framework is the efficient algorithmic framework for multiobjective optimization under uncertainty. Two real world case studies are presented that illustrate the promise of such a framework.

Algorithms↗
PubMed1986

Production of drugs by microbial biosynthesis and biotransformation. Possibilities, limits and future developments (1st communication).

Before the advent of alchemy the therapeutic aids for man and animals consisted exclusively of using natural products in many different forms. Chemical syntheses have been used for little more than 100 years as a means of obtaining drugs. The discovery of penicillin and the first industrial production of this compound in 1941/42 opened the door to a third way for the preparation of drugs by exploitation of the manifold biosynthetic capabilities of microorganisms to produce antibiotics or more recently other pharmacologically active substances. The selective use of individual enzymatic transformation stages with microorganisms in chemical production pathways in particular by biotransformations of steroids in 1950 expanded the field of biotechnological production of pharmaceuticals. The increasing knowledge in the regulation of the biosynthesis of primary and secondary metabolites, the growing experience in the use of microorganisms as biocatalysts and source of valuable enzymes and the development of new economical technical procedures raised the number and volume of drugs prepared by microbial biosynthesis and biotransformation. The modern method of the genetic engineering supported by the chemical DNA-synthesis enabled the preparation of important proteohormones and physiologically active peptides in microorganisms. Finally, the development of monoclonal antibodies, although at present still formed in mammalian cells, will lead to new ways of therapy in future. A review is given on the present state of biotechnological productions of antibiotics, vitamins, steroids, alkaloids, amino acids and pharmaceutical enzymes combined with new developments in the preparation of blood factors, enzyme inhibitors, hormones and physiologically active peptides and the possible future use of monoclonal antibodies.

Anti-Bacterial Agents↗
PubMed2003

Global incorporation of norleucine in place of methionine in cytochrome P450 BM-3 heme domain increases peroxygenase activity.

In this study we have replaced all 13 methionine residues in the cytochrome P450 BM-3 heme domain (463 amino acids) with the isosteric methionine analog norleucine. This experiment has provided a means of testing the functional limits of globally incorporating into an enzyme an unnatural amino acid in place of its natural analog, and also an efficient way to test whether inactivation during peroxide-driven P450 catalysis involves methionine oxidation. Although there was no increase in the stability of the P450 under standard reaction conditions (in 10 mM hydrogen peroxide), complete substitution with norleucine resulted in nearly two-fold-increased peroxygenase activity. Thermostability was significantly reduced. The fact that the enzyme can tolerate such extensive amino acid replacement suggests that we can engineer enzymes with unique chemical properties via incorporation of unnatural amino acids while retaining or improving catalytic properties. This system also provides a platform for directing enzyme evolution using an extended set of protein building blocks.

Culture Media↗
PubMed2004

Laboratory evolution of cytochrome p450 BM-3 monooxygenase for organic cosolvents.

Cytochrome p450 BM-3 (EC 1.14.14.1) catalyzes the hydroxylation and/or epoxidation of a broad range of substrates, including alkanes, alkenes, alcohols, fatty acids, amides, polyaromatic hydrocarbons, and heterocycles. For many of these notoriously water-insoluble compounds, p450 BM-3's K(m) values are in the millimolar range. Polar organic cosolvents are therefore added to increase substrate solubility and achieve high catalytic efficiency. Using p450 BM-3 as a catalyst for these important transformations requires that we improve its ability to tolerate the cosolvents. By directed evolution, we improved the activity of p450 BM-3 in the presence of dimethylsulfoxide (DMSO) and tetrahydrofuran (THF), achieving increases in specific activity up to 10-fold in 2% (v/v) THF and 6-fold in 25% (v/v) DMSO. The engineered p450 BM-3's are also significantly more resistant to acetone, acetonitrile, dimethylformamide, and ethanol as cosolvents in the reaction.

Bacillus megaterium↗
PubMed2006

The role of pair dispersion in turbulent flow.

Mixing and transport in turbulent flows-which have strong local concentration fluctuations-are essential in many natural and industrial systems including reactions in chemical mixers, combustion in engines and burners, droplet formation in warm clouds, and biological odor detection and chemotaxis. Local concentration fluctuations, in turn, are intimately tied to the problem of the separation of pairs of fluid elements. We have measured this separation rate in an intensely turbulent laboratory flow and have found, in quantitative agreement with the seminal predictions of Batchelor, that the initial separation of the pair plays an important role in the subsequent spreading of the fluid elements. These results have surprising consequences for the decay of concentration fluctuations and have applications to biological and chemical systems.

Journal Article↗
PubMed2004

Emission comparison of urban bus engine fueled with diesel oil and 'biodiesel' blend.

The chemical and toxicological characteristics of emissions from an urban bus engine fueled with diesel and biodiesel blend were studied. Exhaust gases were produced by a turbocharged EURO 2 heavy-duty diesel engine, operating in steady-state conditions on the European test 13 mode cycle (ECE R49). Regulated and unregulated pollutants, such as carcinogenic polycyclic aromatic hydrocarbons (PAHs) and nitrated derivatives (nitro-PAHs), carbonyl compounds and light aromatic hydrocarbons were quantified. Mutagenicity of the emissions was evaluated by the Salmonella typhimurium/mammalian microsome assay. The effect of the fuels under study on the size distribution of particulate matter (PM) was also evaluated. The use of biodiesel blend seems to result in small reductions of emissions of most of the aromatic and polyaromatic compounds; these differences, however, have no statistical significance at 95% confidence level. Formaldehyde, on the other hand, has a statistically significant increase of 18% with biodiesel blend. In vitro toxicological assays show an overall similar mutagenic potency and genotoxic profile for diesel and biodiesel blend emissions. The electron microscopy analysis indicates that PM for both fuels has the same chemical composition, morphology, shape and granulometric spectrum, with most of the particles in the range 0.06-0.3 microm.

Chemical Fractionation↗
PubMed2004

Engineering protein A affinity chromatography.

Staphylococcal protein A can selectively interact with immunoglobulins. This protein is widely used as a ligand for affinity chromatography to purify therapeutic antibodies on an industrial scale. This type of affinity chromatography constitutes a generic step in processing antibodies. Questions of scale-up, design of chromatographic conditions, clearance of adventitious agents and operational modes, such as continuous operation or purification of antibodies in expanded-bed mode, will be addressed in this review.

Antibodies, Monoclonal↗
PubMed2003

Microfluidic patterning of cells in extracellular matrix biopolymers: effects of channel size, cell type, and matrix composition on pattern integrity.

The organization of cells within an extracellular matrix is critical to promote appropriate cellular interactions and tissue function in vivo. The ability to design and create biologically relevant cellular arrangements via microfluidic patterning on surfaces provides new capabilities for tissue engineering and biomimetics. The purpose of this article is to describe techniques using microfluidic patterning of three-dimensional biopolymer matrices to improve cellular pattern integrity and to provide microscale control over cellular microenvironments. Results demonstrated that the incorporation of extracellular matrix biopolymers in cell microfluidic patterning results in a more stable pattern of adherent human endothelial cells than patterning without matrix components after several days in vitro. This may be important for carrying out long-term biological experiments and tissue engineering in vitro. Moreover, chemical components in the patterned biopolymer matrices, such as collagen, chitosan, and fibronectin, influenced the ability of the matrices to control cell migration and pattern stability over time. Thus, microfluidic patterning of cells in extracellular matrix biopolymers was shown to be useful in patterning multiple cell types in well-defined three-dimensional geometries.

Biopolymers↗
PubMed2005

Composition, toxicity, and mutagenicity of particulate and semivolatile emissions from heavy-duty compressed natural gas-powered vehicles.

Particulate matter (PM) and vapor-phase semivolatile organic compounds (SVOC) were collected from three buses fueled by compressed natural gas. The bus engines included a well-functioning, conventional engine; a "high emitter" engine; and a new technology engine with an oxidation catalyst. Chemical analysis of the emissions showed differences among these samples, with the high emitter sample containing markers of engine oil constituents. PM + SVOC samples were also collected for mutagenicity and toxicity testing. Extraction efficiencies from the collection media were lower than for similarly collected samples from gasoline or diesel vehicles. Responses to the recovered samples were compared on the basis of exhaust volume, to incorporate the emission rates into the potency factors. Mutagenicity was assessed by Salmonella reverse mutation assay. Mutagenicity was greatest for the high emitter sample and lowest for the new technology sample. Metabolic activation reduced mutagenicity in strain TA100, but not TA98. Toxicity, including inflammation, cytotoxicity, and parenchymal changes, was assessed 24 h after intratracheal instillation into rat lungs. Lung responses were generally mild, with little difference between the responses to equivalent volumes of emissions from the normal emitter and the new technology, but greater responses for the high emitter. These emission sample potencies are further compared on the basis of recovered mass with previously reported samples from normal and high-emitter gasoline and diesel vehicles. While mutagenic potencies for the CNG emission samples were similar to the range observed in the gasoline and diesel emission samples, lung toxicity potency factors were generally lower than those for the gasoline and diesel samples.

Air Pollutants↗
PubMed2004

Poly(phosphoester) ionomers as tissue-engineering scaffolds.

Regenerative medicine requires scaffolds of divergent physicochemical properties for different tissue-engineering applications. To this end, a series of biodegradable poly(phosphoester) ionomers of the general composition [p(BHET-EOP-HOP/TC)] was synthesized, with BHET(bis-hydroxyl ethylene phosphate):EOP(ethylene phosphate):HOP(free phosphate) ratios of 60:20:20, 70:10:20, and 75:5:20, respectively. The 60/20/20 ionomer possessed the best tensile properties, exhibiting an average tensile modulus of 68 MPa and strain at break of 31%. Calcium treatment of the ionomer films led to significantly higher hardness and elastic moduli as measured by indentation. Calcium binding was evident from the increase in glass transition and melting temperatures, and a shift in the P-->O absorption in the FTIR spectrum. Stable N-hydroxysuccinimide ester (NHS) of the ionomers could be synthesized to facilitate derivatization, as demonstrated by conjugation of GRGDS in this study. The polymers conjugated with NHS were hydrolyzed in a biphasic mode, with a fast initial phase occurring in the first few hours, followed by a slower phase in the next few days. These ionomers represent a novel class of biomaterials with readily controllable physical and chemical attributes for tissue engineering.

Biocompatible Materials↗
PubMed2005

Advances in synthetic biology: on the path from prototypes to applications.

Synthetic biology combines knowledge from various disciplines including molecular biology, engineering, mathematics and physics to design and build novel proteins, genetic circuits and metabolic networks. Early efforts aimed at altering the behavior of individual elements have now evolved to focus on the construction of complex networks in single-cell and multicellular systems. Recent achievements include the development of sophisticated non-native behaviors such as bi-stability, oscillations, proteins customized for biosensing, optimized drug synthesis and programmed spatial pattern formation. The de novo construction of such systems offers valuable quantitative insight into naturally occurring information processing activities. Furthermore, as the techniques for system design, synthesis and optimization mature, we will witness a rapid growth in the capabilities of synthetic systems with a wide-range of applications.

Gene Expression Regulation↗
PubMed2006

Engineering and public health at CDC.

Engineering is the application of scientific and technical knowledge to solve human problems. Using imagination, judgment, and reasoning to apply science, technology, mathematics, and practical experience, engineers develop the design, production, and operation of useful objects or processes. During the 1940s, engineers dominated the ranks of CDC scientists. In fact, the first CDC director, Assistant Surgeon General Mark Hollis, was an engineer. CDC engineers were involved in malaria control through the elimination of standing water. Eventually the CDC mission expanded to include prevention and control of dengue, typhus, and other communicable diseases. The development of chlorination, water filtration, and sewage treatment were crucial to preventing waterborne illness. Beginning in the 1950s, CDC engineers began their work to improve public health while developing the fields of environmental health, industrial hygiene, and control of air pollution. Engineering disciplines represented at CDC today include biomedical, civil, chemical, electrical, industrial, mechanical, mining, and safety engineering. Most CDC engineers are located in the National Institute for Occupational Safety and Health (NIOSH) and the Agency for Toxic Substances and Disease Registry (ATSDR). Engineering research at CDC has a broad stakeholder base. With the cooperation of industry, labor, trade associations, and other stakeholders and partners, current work includes studies of air contaminants, mining, safety, physical agents, ergonomics, and environmental hazards. Engineering solutions remain a cornerstone of the traditional "hierarchy of controls" approach to reducing public health hazards.

Centers for Disease Control and Prevention, U.S.↗
PubMed2005

Schwarz meets Schwann: design and fabrication of biomorphic tissue engineering scaffolds.

Tissue engineering is a discipline at the leading edge of the field of computer assisted intervention. This multidisciplinary engineering science is based on the notion of design and fabrication of scaffolds- porous, three-dimensional "trellis-like" biomimetic structures that, on implantation, provide a viable environment to recuperate and regenerate damaged cells. Existing CAD-based approaches produce porous labyrinths with contra-naturam straight edges. The biomorphic geometry that mimics the secundam-naturam substrate would be one that is continuous through all space, partitioned into two not-necessarily-equal sub-spaces by a non-intersecting, two-sided surface. Minimal surfaces are ideal to describe such a space. We present results on the premier attempt in computer controlled fabrication and mechanical characterization of Triply Periodic Minimal Surfaces [TPMS]. This initiative is a significant step to link Schwann's 1838 cell theory with Schwarz's discovery of TPMS in 1865 to fabricate the previously elusive optimal biomorphic tissue analogs.

Biocompatible Materials↗