Controlling cell destruction using dielectrophoretic forces measures the factors that influence cell destruction during dielectrophoresis (DEP) experiments. A field-frequency window was identified that should be avoided to minimize cell damage or utilized to selectively destroy specific cell types. The width and location of this window depends on cell type properties like size, morphology, and dielectric properties, and is bounded by two characteristic frequencies - the DEP cross-over frequency and a frequency determined by the time constant that controls the frequency dependence of the induced field across the cell membrane. Operating in this window can minimize destruction by ensuring cells are not near electrodes, or exploit this window to selectively destroy cell types in a mixture.
Physical methods can be used to transfer genes into cells by transiently permeabilizing cell membranes. This allows naked DNA to enter cells. Key physical methods include electroporation, gene guns, ultrasound, and hydrodynamic delivery.
Electroporation uses short electrical pulses to create temporary pores in the cell membrane through which DNA can enter. Gene guns use compressed gas to accelerate DNA-coated gold or tungsten particles into cells. Ultrasound combines microbubbles and acoustic cavitation to permeabilize membranes for DNA uptake. Hydrodynamic delivery involves rapid injection of a large DNA solution volume to generate pressure forcing DNA into organ cells like hepatocytes. These methods show promise but also have limitations like tissue damage, shallow
This chapter discusses fractionated radiation and the dose-rate effect. It covers operational classifications of radiation damage including potentially lethal damage and sublethal damage. Fractionation allows for repair of sublethal damage through processes like reassortment and repopulation. The dose-rate effect results from increased repair at lower dose rates. Examples are provided for both in vitro and in vivo models. Brachytherapy techniques like intracavitary and interstitial brachytherapy are also summarized.
Complete Sequencing – Clifford Reid, PhD; CEO, Complete Genomics as presented at the Personalized Health Care Conference at Ohio State. Dr. Reid discussed what complete human sequencing looks like and costs now and in the near future.
This chapter discusses cell survival curves and the mechanisms of cell killing by radiation. It covers:
- The shape of the in vitro survival curve and models that describe it, such as the linear-quadratic and multitarget models.
- Mechanisms of cell killing including DNA damage, the bystander effect, apoptotic and mitotic death, autophagic cell death, and senescence.
- Survival curves vary between different mammalian cell types in culture but mitotic cells have similar radiosensitivity. Increased radiosensitivity correlates with increased apoptotic cell death.
- Oncogenes may increase radioresistance but their role in human tumors is unclear. Inherited syndromes involving DNA repair
On the All or Half Law of Recombinant DNA, Lentivus Transduction and some oth...Gang Zhang
Gang Zhang has extensive experience in research related to recombinant DNA, lentiviral transduction, CRISPR/Cas9 genome editing, and animal cloning. He received his PhD from Shandong Normal University and the Institute of Zoology, Chinese Academy of Sciences in 2005. Since then, he has held several postdoctoral and research positions focusing on topics such as neural stem cell differentiation, brain tumor cells, Parkinson's disease genes, and human integrin overexpression. Zhang has authored or co-authored several publications related to gene cloning techniques, lentiviral transduction, induced pluripotent stem cells, and animal cloning in mice. In this talk, he will discuss the "All or Half" law of
Perfluorocarbon nanoparticles can be used for cardiovascular disease diagnosis and treatment. They provide contrast for MRI and ultrasound imaging, and can target sites of thrombosis and angiogenesis. In animal models, fibrin-targeted perfluorocarbon nanoparticles accurately detected thrombi, while integrin-targeted nanoparticles identified neovascularization in atherosclerotic plaques. The nanoparticles allowed simultaneous 19F imaging and 1H MRI, providing anatomical and molecular pathology information. Anti-angiogenic drug-loaded nanoparticles reduced plaque growth in hyperlipidemic rabbits with a single dose, demonstrating the potential of targeted perfluorocarbon nanoparticles for cardiovascular disease applications.
This document discusses cell survival curves which describe the relationship between radiation dose and the proportion of cells that survive. It defines reproductive integrity and explains that proliferating cells are considered reproductively dead if they lose the capacity for sustained proliferation. Different models for describing survival curves are presented, including the linear quadratic model and multitarget model. The shape of typical survival curves is explained. The document also discusses various mechanisms of cell killing by radiation including DNA damage, the bystander effect, apoptotic death, and mitotic death.
This document discusses the radiobiological basis of fractionated radiation therapy. It covers the classic "4 R's" of radiobiology - repair, reassortment, repopulation and reoxygenation. Repair and reoxygenation make tumor cells more sensitive to radiation between fractions, while repopulation and reassortment make them more resistant. The document also proposes a "5th R" of radiossensitivity based on tissue maturity and metabolism. Finally, it briefly mentions the potential "6th R" of bystander effects and abscopal effects, where radiation triggers immune responses against distant tumor cells. Fractionation exploits repair in normal tissues while counteracting resistance mechanisms in tumors through its scheduling over multiple doses.
Physical methods can be used to transfer genes into cells by transiently permeabilizing cell membranes. This allows naked DNA to enter cells. Key physical methods include electroporation, gene guns, ultrasound, and hydrodynamic delivery.
Electroporation uses short electrical pulses to create temporary pores in the cell membrane through which DNA can enter. Gene guns use compressed gas to accelerate DNA-coated gold or tungsten particles into cells. Ultrasound combines microbubbles and acoustic cavitation to permeabilize membranes for DNA uptake. Hydrodynamic delivery involves rapid injection of a large DNA solution volume to generate pressure forcing DNA into organ cells like hepatocytes. These methods show promise but also have limitations like tissue damage, shallow
This chapter discusses fractionated radiation and the dose-rate effect. It covers operational classifications of radiation damage including potentially lethal damage and sublethal damage. Fractionation allows for repair of sublethal damage through processes like reassortment and repopulation. The dose-rate effect results from increased repair at lower dose rates. Examples are provided for both in vitro and in vivo models. Brachytherapy techniques like intracavitary and interstitial brachytherapy are also summarized.
Complete Sequencing – Clifford Reid, PhD; CEO, Complete Genomics as presented at the Personalized Health Care Conference at Ohio State. Dr. Reid discussed what complete human sequencing looks like and costs now and in the near future.
This chapter discusses cell survival curves and the mechanisms of cell killing by radiation. It covers:
- The shape of the in vitro survival curve and models that describe it, such as the linear-quadratic and multitarget models.
- Mechanisms of cell killing including DNA damage, the bystander effect, apoptotic and mitotic death, autophagic cell death, and senescence.
- Survival curves vary between different mammalian cell types in culture but mitotic cells have similar radiosensitivity. Increased radiosensitivity correlates with increased apoptotic cell death.
- Oncogenes may increase radioresistance but their role in human tumors is unclear. Inherited syndromes involving DNA repair
On the All or Half Law of Recombinant DNA, Lentivus Transduction and some oth...Gang Zhang
Gang Zhang has extensive experience in research related to recombinant DNA, lentiviral transduction, CRISPR/Cas9 genome editing, and animal cloning. He received his PhD from Shandong Normal University and the Institute of Zoology, Chinese Academy of Sciences in 2005. Since then, he has held several postdoctoral and research positions focusing on topics such as neural stem cell differentiation, brain tumor cells, Parkinson's disease genes, and human integrin overexpression. Zhang has authored or co-authored several publications related to gene cloning techniques, lentiviral transduction, induced pluripotent stem cells, and animal cloning in mice. In this talk, he will discuss the "All or Half" law of
Perfluorocarbon nanoparticles can be used for cardiovascular disease diagnosis and treatment. They provide contrast for MRI and ultrasound imaging, and can target sites of thrombosis and angiogenesis. In animal models, fibrin-targeted perfluorocarbon nanoparticles accurately detected thrombi, while integrin-targeted nanoparticles identified neovascularization in atherosclerotic plaques. The nanoparticles allowed simultaneous 19F imaging and 1H MRI, providing anatomical and molecular pathology information. Anti-angiogenic drug-loaded nanoparticles reduced plaque growth in hyperlipidemic rabbits with a single dose, demonstrating the potential of targeted perfluorocarbon nanoparticles for cardiovascular disease applications.
This document discusses cell survival curves which describe the relationship between radiation dose and the proportion of cells that survive. It defines reproductive integrity and explains that proliferating cells are considered reproductively dead if they lose the capacity for sustained proliferation. Different models for describing survival curves are presented, including the linear quadratic model and multitarget model. The shape of typical survival curves is explained. The document also discusses various mechanisms of cell killing by radiation including DNA damage, the bystander effect, apoptotic death, and mitotic death.
This document discusses the radiobiological basis of fractionated radiation therapy. It covers the classic "4 R's" of radiobiology - repair, reassortment, repopulation and reoxygenation. Repair and reoxygenation make tumor cells more sensitive to radiation between fractions, while repopulation and reassortment make them more resistant. The document also proposes a "5th R" of radiossensitivity based on tissue maturity and metabolism. Finally, it briefly mentions the potential "6th R" of bystander effects and abscopal effects, where radiation triggers immune responses against distant tumor cells. Fractionation exploits repair in normal tissues while counteracting resistance mechanisms in tumors through its scheduling over multiple doses.
It describes relationship between radiation dose and the fraction of cells that “survive” that dose.
This is mainly used to assess biological effectiveness of radiation.
To understand it better, we need to know about a few basic things e.g.
Cell Death
Estimation of Survival / Plating Efficiency
Nature of Cell killing etc.
A cell survival curve is the relationship between the fraction of cells retaining their reproductive integrity and absorbed dose.
Conventionally, surviving fraction on a logarithmic scale is plotted on the Y-axis, the dose is on the X-axis . The shape of the survival curve is important.
The cell-survival curve for densely ionizing radiations (α-particles and low-energy neutrons) is a straight line on a log-linear plot, that is survival is an exponential function of dose.
The cell-survival curve for sparsely ionizing radiations (X-rays, gamma-rays has an initial slope, followed by a shoulder after which it tends to straighten again at higher doses.
1) The four Rs of radiobiology are repair, re-assortment, repopulation, and re-oxygenation. They influence how tumors and normal tissues respond to fractionated radiation treatment.
2) When radiation is delivered in two fractions separated by time, cell survival increases due to repair of sublethal damage between fractions. The increase peaks at 2-3 hours and then levels off due to repopulation.
3) Lowering the radiation dose rate generally decreases biological effects because it allows more time for repair of sublethal damage.
The document discusses cell survival curves, which describe the relationship between radiation dose and the proportion of cells that survive. It provides details on direct and indirect radiation action, modes of cell death including mitotic and apoptotic death, and how survival curves are plotted based on in vitro experiments. It also covers models used to describe survival curves, including the single-target model, multi-target single-hit model, and linear quadratic model which accounts for both single and double particle events. The linear quadratic model is now widely used to model the effects of radiation therapy on tumor cells and normal tissues.
This document provides an overview of key concepts in radiobiology, including:
1. Ionizing radiation can cause direct and indirect DNA damage. DNA is the main cellular target of radiation.
2. The biological effects of radiation are determined by factors like DNA break type, cell cycle radiosensitivity, and the advantages of dose fractionation such as allowing time for repair between fractions.
3. Fractionation exploits differences in recovery rates between normal and tumor tissues, allowing higher total doses to be delivered to tumors while sparing normal tissues.
Magnetofection is a novel nucleic acid delivery method that uses magnetic particles and magnetic force to enhance and target delivery. It works by associating nucleic acids or vectors with magnetic nanoparticles, then applying a magnetic field to concentrate the complexes onto target cells. This allows for rapid and efficient delivery with low toxicity. Magnetofection provides benefits like high transfection efficiency even with hard-to-transfect cells and low nucleic acid doses. Limitations include potential saturation effects and challenges targeting deep tissues or organs. Overall, magnetofection is a versatile and effective method for nucleic acid delivery.
1. The document discusses various strategies to overcome tumor hypoxia, including improving oxygen delivery to tumors, using hypoxic cell radiosensitizers, and hypoxia-activated cytotoxic drugs.
2. It provides examples of compounds that have shown promise in improving tumor oxygenation, such as motexafin gadolinium, as well as hypoxia-activated cytotoxic drugs like tirapazamine.
3. Hypoxia-selective gene therapy is also discussed as a potential strategy to selectively kill hypoxic tumor cells.
1. The document discusses the dose-rate effect, which is the change in biological response to radiation when the dose is delivered at different rates. A lower dose rate allows more time for repair of sublethal DNA damage between radiation events.
2. Survival curves become progressively shallower at lower dose rates as the shoulder disappears due to repair. An inverse dose-rate effect can also occur at very low dose rates.
3. Clinical data on brachytherapy implants show better tumor control at higher dose rates (>0.5 Gy/h) compared to lower dose rates, especially for doses <65 Gy. Larger tumors are associated with higher dose rates due to implant size.
Blots are techniques for transferring DNA, RNA and proteins onto a solid support (carrier) generally nylon or nitrocellulose membranes. so they can be separated, and often follows the use of a gel electrophoresis
This document discusses several topics related to molecular biology and DNA, including:
1) DNA structure, which involves double-stranded DNA containing genes that code for amino acids. 2) Chromosomes, which package DNA and contain telomeres that protect DNA during cell replication. 3) DNA replication and transcription, which allow DNA to direct protein synthesis. 4) Molecular techniques like electrophoresis, hybridization, and polymerase chain reaction that are used to study DNA.
Cell survival curves describe the relationship between radiation dose and the fraction of cells that survive that dose. The shape of the curve is influenced by many factors including:
1) The proliferative capacity of cells, with rapidly dividing cells being more radiosensitive.
2) The presence of oxygen, with hypoxic cells being more radioresistant.
3) Fractionation, with fractionated doses allowing more time for repair between exposures and resulting in a higher surviving fraction compared to a single dose.
4) Dose rate, with low dose rate irradiation resembling continuous fractionation and having less cell killing compared to an acute high dose rate.
Cell survival curves take different shapes for early-responding normal tissues dominated
The document discusses cell survival curves, which describe the relationship between radiation dose and the proportion of cells that survive. It defines key terms like clonogenic cells and explains the components of in vitro survival curves. It describes exponential and shoulder survival curves based on single-hit and multi-target theories. The mechanisms of cell killing like mitotic death and apoptosis are covered. Factors influencing radiosensitivity like dose rate, oxygen level and genetic mutations are summarized. Comparisons are made between survival curves of different mammalian cell types and microorganisms.
This document discusses principles of radiobiology including types of radiation, how radiation causes biological effects, and factors that affect radiobiological outcomes. It covers topics like linear energy transfer, relative biological effectiveness, oxygen enhancement ratio, and how tissue factors like the cell cycle, chromatin structure, and regeneration influence radiation responses in normal and tumor tissues. The key aims are to understand how radiation damages cells and tissues at the molecular, cellular, and physiological levels and how these principles apply clinically in areas like radiation therapy fractionation schedules and the risks of reirradiation.
This document summarizes key concepts regarding radiation-induced cell death and survival curves. It discusses how cell death is defined for differentiated and proliferating cells. The linear-quadratic model is then explained, which describes cell survival curves using alpha and beta coefficients. Various fractionation schemes and their resulting biological effective doses are calculated and compared for treating different head and neck cancers. The limitations of hypofractionation and importance of accounting for tumor proliferation are also covered.
This document discusses radiobiology principles related to radiation treatment of central nervous system tumors. It covers topics such as the cellular targets of radiation in brain and spinal cord tissue, factors that influence radiosensitivity, and the effects of radiation on different cell types in the CNS. It also summarizes studies on conventional fractionation schedules as well as hypofractionated and hyperfractionated regimens. The goal of altered fractionation is to improve tumor control while sparing normal tissues, though the evidence for benefits is mixed for most tumor types.
This chapter discusses oxygen effect and reoxygenation in radiobiology. It describes how oxygen enhances the effects of radiation, known as the oxygen effect. The mechanism is that oxygen reacts with free radicals produced by radiation, causing more DNA damage. Tumor hypoxia is common, caused by both chronic and acute mechanisms. Chronic hypoxia results from limited oxygen diffusion in tumors. Acute hypoxia occurs when blood vessels temporarily close. Techniques to measure tumor oxygenation include oxygen probes and hypoxia markers. Reoxygenation is the process where hypoxic tumor cells become oxygenated after radiation, which is important for fractionated radiotherapy. The time and extent of reoxygenation varies between different tumor types.
Grid therapy is a type of spatially fractionated radiation therapy that delivers high doses of radiation to cancer tumors. It involves using a lead grid with cylindrical holes to break the radiation beam into small dose clusters, allowing higher total doses to be delivered safely. Some key advantages are that small volumes of skin can tolerate high doses, tumor cells are more likely to be killed through reoxygenation, and cytokines released may enhance a bystander effect against tumor cells. Modern linear accelerators can provide spatial fractionation using multileaf collimators instead of physical grids. Grid therapy remains beneficial for treating large, bulky sarcomas and cancers of the head and neck.
Nanopore sequencing is a fourth generation DNA sequencing technique that involves monitoring changes in electric current as DNA molecules pass through nanopores. There are two main types of nanopores: biological nanopores made of protein complexes like alpha-hemolysin, and solid state nanopores made in thin silicon nitride membranes. Nanopore sequencing has advantages of being label-free, producing long reads at high throughput with low material requirements, but challenges include slowing DNA translocation and reducing noise. Potential applications are in single molecule sensing for analysis of biomolecules.
The 4 Rs of radiobiology are repair, reoxygenation, redistribution, and repopulation. Repair refers to the ability of cells to repair radiation damage over hours through pathways like base excision repair. Redistribution occurs as cells in different phases of the cell cycle are irradiated, with some phases being more radioresistant. Repopulation is the regrowth of cells after irradiation, with tumors potentially repopulating faster than normal tissues. Reoxygenation occurs as hypoxic tumor cells reoxygenate over hours to days, allowing radiation to better damage them in subsequent fractions. Understanding the 4 Rs helps explain fractionated radiotherapy dosing.
Cell survival curves show the relationship between radiation dose and the proportion of cells that survive. For low linear energy transfer (LET) radiation like X-rays, the curve starts with a shoulder region followed by an exponential decrease in survival fraction. The linear-quadratic model describes cell survival as an exponential function of dose, with parameters α and β representing linear and quadratic components of cell killing. Fractionation reduces cell survival more than single high doses by allowing repair of sublethal damage between fractions. Hypoxic cells are less sensitive initially but may reoxygenate and become sensitive to later fractions. Mitotic cell death is the most common mode of radiation-induced cell death in tumor cells.
It describes relationship between radiation dose and the fraction of cells that “survive” that dose.
This is mainly used to assess biological effectiveness of radiation.
To understand it better, we need to know about a few basic things e.g.
Cell Death
Estimation of Survival / Plating Efficiency
Nature of Cell killing etc.
A cell survival curve is the relationship between the fraction of cells retaining their reproductive integrity and absorbed dose.
Conventionally, surviving fraction on a logarithmic scale is plotted on the Y-axis, the dose is on the X-axis . The shape of the survival curve is important.
The cell-survival curve for densely ionizing radiations (α-particles and low-energy neutrons) is a straight line on a log-linear plot, that is survival is an exponential function of dose.
The cell-survival curve for sparsely ionizing radiations (X-rays, gamma-rays has an initial slope, followed by a shoulder after which it tends to straighten again at higher doses.
1) The four Rs of radiobiology are repair, re-assortment, repopulation, and re-oxygenation. They influence how tumors and normal tissues respond to fractionated radiation treatment.
2) When radiation is delivered in two fractions separated by time, cell survival increases due to repair of sublethal damage between fractions. The increase peaks at 2-3 hours and then levels off due to repopulation.
3) Lowering the radiation dose rate generally decreases biological effects because it allows more time for repair of sublethal damage.
The document discusses cell survival curves, which describe the relationship between radiation dose and the proportion of cells that survive. It provides details on direct and indirect radiation action, modes of cell death including mitotic and apoptotic death, and how survival curves are plotted based on in vitro experiments. It also covers models used to describe survival curves, including the single-target model, multi-target single-hit model, and linear quadratic model which accounts for both single and double particle events. The linear quadratic model is now widely used to model the effects of radiation therapy on tumor cells and normal tissues.
This document provides an overview of key concepts in radiobiology, including:
1. Ionizing radiation can cause direct and indirect DNA damage. DNA is the main cellular target of radiation.
2. The biological effects of radiation are determined by factors like DNA break type, cell cycle radiosensitivity, and the advantages of dose fractionation such as allowing time for repair between fractions.
3. Fractionation exploits differences in recovery rates between normal and tumor tissues, allowing higher total doses to be delivered to tumors while sparing normal tissues.
Magnetofection is a novel nucleic acid delivery method that uses magnetic particles and magnetic force to enhance and target delivery. It works by associating nucleic acids or vectors with magnetic nanoparticles, then applying a magnetic field to concentrate the complexes onto target cells. This allows for rapid and efficient delivery with low toxicity. Magnetofection provides benefits like high transfection efficiency even with hard-to-transfect cells and low nucleic acid doses. Limitations include potential saturation effects and challenges targeting deep tissues or organs. Overall, magnetofection is a versatile and effective method for nucleic acid delivery.
1. The document discusses various strategies to overcome tumor hypoxia, including improving oxygen delivery to tumors, using hypoxic cell radiosensitizers, and hypoxia-activated cytotoxic drugs.
2. It provides examples of compounds that have shown promise in improving tumor oxygenation, such as motexafin gadolinium, as well as hypoxia-activated cytotoxic drugs like tirapazamine.
3. Hypoxia-selective gene therapy is also discussed as a potential strategy to selectively kill hypoxic tumor cells.
1. The document discusses the dose-rate effect, which is the change in biological response to radiation when the dose is delivered at different rates. A lower dose rate allows more time for repair of sublethal DNA damage between radiation events.
2. Survival curves become progressively shallower at lower dose rates as the shoulder disappears due to repair. An inverse dose-rate effect can also occur at very low dose rates.
3. Clinical data on brachytherapy implants show better tumor control at higher dose rates (>0.5 Gy/h) compared to lower dose rates, especially for doses <65 Gy. Larger tumors are associated with higher dose rates due to implant size.
Blots are techniques for transferring DNA, RNA and proteins onto a solid support (carrier) generally nylon or nitrocellulose membranes. so they can be separated, and often follows the use of a gel electrophoresis
This document discusses several topics related to molecular biology and DNA, including:
1) DNA structure, which involves double-stranded DNA containing genes that code for amino acids. 2) Chromosomes, which package DNA and contain telomeres that protect DNA during cell replication. 3) DNA replication and transcription, which allow DNA to direct protein synthesis. 4) Molecular techniques like electrophoresis, hybridization, and polymerase chain reaction that are used to study DNA.
Cell survival curves describe the relationship between radiation dose and the fraction of cells that survive that dose. The shape of the curve is influenced by many factors including:
1) The proliferative capacity of cells, with rapidly dividing cells being more radiosensitive.
2) The presence of oxygen, with hypoxic cells being more radioresistant.
3) Fractionation, with fractionated doses allowing more time for repair between exposures and resulting in a higher surviving fraction compared to a single dose.
4) Dose rate, with low dose rate irradiation resembling continuous fractionation and having less cell killing compared to an acute high dose rate.
Cell survival curves take different shapes for early-responding normal tissues dominated
The document discusses cell survival curves, which describe the relationship between radiation dose and the proportion of cells that survive. It defines key terms like clonogenic cells and explains the components of in vitro survival curves. It describes exponential and shoulder survival curves based on single-hit and multi-target theories. The mechanisms of cell killing like mitotic death and apoptosis are covered. Factors influencing radiosensitivity like dose rate, oxygen level and genetic mutations are summarized. Comparisons are made between survival curves of different mammalian cell types and microorganisms.
This document discusses principles of radiobiology including types of radiation, how radiation causes biological effects, and factors that affect radiobiological outcomes. It covers topics like linear energy transfer, relative biological effectiveness, oxygen enhancement ratio, and how tissue factors like the cell cycle, chromatin structure, and regeneration influence radiation responses in normal and tumor tissues. The key aims are to understand how radiation damages cells and tissues at the molecular, cellular, and physiological levels and how these principles apply clinically in areas like radiation therapy fractionation schedules and the risks of reirradiation.
This document summarizes key concepts regarding radiation-induced cell death and survival curves. It discusses how cell death is defined for differentiated and proliferating cells. The linear-quadratic model is then explained, which describes cell survival curves using alpha and beta coefficients. Various fractionation schemes and their resulting biological effective doses are calculated and compared for treating different head and neck cancers. The limitations of hypofractionation and importance of accounting for tumor proliferation are also covered.
This document discusses radiobiology principles related to radiation treatment of central nervous system tumors. It covers topics such as the cellular targets of radiation in brain and spinal cord tissue, factors that influence radiosensitivity, and the effects of radiation on different cell types in the CNS. It also summarizes studies on conventional fractionation schedules as well as hypofractionated and hyperfractionated regimens. The goal of altered fractionation is to improve tumor control while sparing normal tissues, though the evidence for benefits is mixed for most tumor types.
This chapter discusses oxygen effect and reoxygenation in radiobiology. It describes how oxygen enhances the effects of radiation, known as the oxygen effect. The mechanism is that oxygen reacts with free radicals produced by radiation, causing more DNA damage. Tumor hypoxia is common, caused by both chronic and acute mechanisms. Chronic hypoxia results from limited oxygen diffusion in tumors. Acute hypoxia occurs when blood vessels temporarily close. Techniques to measure tumor oxygenation include oxygen probes and hypoxia markers. Reoxygenation is the process where hypoxic tumor cells become oxygenated after radiation, which is important for fractionated radiotherapy. The time and extent of reoxygenation varies between different tumor types.
Grid therapy is a type of spatially fractionated radiation therapy that delivers high doses of radiation to cancer tumors. It involves using a lead grid with cylindrical holes to break the radiation beam into small dose clusters, allowing higher total doses to be delivered safely. Some key advantages are that small volumes of skin can tolerate high doses, tumor cells are more likely to be killed through reoxygenation, and cytokines released may enhance a bystander effect against tumor cells. Modern linear accelerators can provide spatial fractionation using multileaf collimators instead of physical grids. Grid therapy remains beneficial for treating large, bulky sarcomas and cancers of the head and neck.
Nanopore sequencing is a fourth generation DNA sequencing technique that involves monitoring changes in electric current as DNA molecules pass through nanopores. There are two main types of nanopores: biological nanopores made of protein complexes like alpha-hemolysin, and solid state nanopores made in thin silicon nitride membranes. Nanopore sequencing has advantages of being label-free, producing long reads at high throughput with low material requirements, but challenges include slowing DNA translocation and reducing noise. Potential applications are in single molecule sensing for analysis of biomolecules.
The 4 Rs of radiobiology are repair, reoxygenation, redistribution, and repopulation. Repair refers to the ability of cells to repair radiation damage over hours through pathways like base excision repair. Redistribution occurs as cells in different phases of the cell cycle are irradiated, with some phases being more radioresistant. Repopulation is the regrowth of cells after irradiation, with tumors potentially repopulating faster than normal tissues. Reoxygenation occurs as hypoxic tumor cells reoxygenate over hours to days, allowing radiation to better damage them in subsequent fractions. Understanding the 4 Rs helps explain fractionated radiotherapy dosing.
Cell survival curves show the relationship between radiation dose and the proportion of cells that survive. For low linear energy transfer (LET) radiation like X-rays, the curve starts with a shoulder region followed by an exponential decrease in survival fraction. The linear-quadratic model describes cell survival as an exponential function of dose, with parameters α and β representing linear and quadratic components of cell killing. Fractionation reduces cell survival more than single high doses by allowing repair of sublethal damage between fractions. Hypoxic cells are less sensitive initially but may reoxygenate and become sensitive to later fractions. Mitotic cell death is the most common mode of radiation-induced cell death in tumor cells.
This document discusses the design of a geographic information system (GIS) software platform integrated with a decision support system (DSS) for use in e-government applications in China. It proposes a new approach that tightly integrates DSS techniques with GIS techniques to provide comprehensive information and decision-making services to governments. The platform uses a uniform database design and data management approach. It is developed using a component-based approach to achieve close integration of GIS and DSS functions. The platform adopts a client-server architecture for applications and a client-server structure for system maintenance.
A new study of dss based on neural network and data miningAttaporn Ninsuwan
This document proposes using neural networks and data mining to support intelligent decision support systems (IDSS). It discusses how neural networks can help with knowledge learning, problem solving abilities, and real-time processing. Data mining can be used for analysis, clustering, and concept description. The paper then presents a framework for an IDSS combining neural networks, data mining, reasoning, and natural language processing. It provides an example application to evaluate using marsh gas instead of oil and natural gas in China.
Investigación en electromicrobiología en donde se utilizan Bacterias especiales para generar electricidad y limpiar agua residual. Electromicrobiology research
The document discusses the patch clamp technique, which allows the study of single or multiple ion channels in cells. It was developed in the late 1970s/early 1980s by Erwin Neher and Bert Sakmann, who received the Nobel Prize for this work. There are different configurations of patch clamp including cell-attached, whole-cell, outside-out, and inside-out. The technique involves pressing a glass pipette against a cell to form an electrical seal and record currents. It has applications in studying ion channels in excitable cells and the effects of drugs.
- Cell survival curves relate the radiation dose to the proportion of cells that survive. They are generated through in vitro experiments where cells are exposed to radiation doses and then assessed for their ability to proliferate into colonies.
- The linear-quadratic model describes cell survival as having both a linear component related to single radiation hits and a quadratic component related to multiple radiation hits. It is used to design fractionated radiotherapy regimens and understand acute vs late tissue responses.
- Key factors in the model include the alpha coefficient representing intrinsic radiosensitivity, the beta coefficient representing repair capacity, and the alpha/beta ratio which indicates the dose where linear and quadratic death are equal.
Segmenting Epithelial Cells in High-Throughput RNAi Screens (Miaab 2011)Kevin Keraudren
This document summarizes a proposed method for segmenting epithelial cells in high-throughput RNAi screens using image analysis. The method uses a pipeline that includes pre-processing images using filters to reduce noise and enhance cell structures, segmenting nuclei, generating an edge map of cell-cell contacts, and performing an adaptive watershed segmentation to extract three structures: cell-cell contacts, nuclei, and cell walls. The method is shown to accurately segment these structures and provide reliable quantification of markers in different experimental conditions, distinguishing effects of depleting different actin-binding proteins on cell-cell adhesion receptors and the cytoskeleton.
Bio-impedance detector for Staphylococcus aureus exposed to magnetic fieldsجنة الربيع
This document discusses a study that used bioimpedance measurements to analyze the effect of magnetic fields on the growth of Staphylococcus aureus bacteria. The study found that exposure to DC magnetic fields caused impedance to fall, indicating inhibited bacterial growth. In contrast, exposure to AC magnetic fields caused impedance to increase, enhancing bacterial growth. An impedance system was constructed to measure the impedance of bacterial samples over time and under different magnetic field conditions. Statistical analysis found significant differences in impedance between control samples and samples exposed to DC or AC magnetic fields.
This document summarizes a research paper that proposes using dielectrophoresis in a microfluidic device to separate live and dead biological cells. It describes how an applied non-uniform electric field can induce dipole moments in cells, causing them to be attracted to either high or low field regions depending on their dielectric properties. The document outlines the design of a microfluidic device with a 3D electrode structure intended to exploit these differences and separate live and dead mammalian cells based on their dielectric behavior over 50-70 kHz frequencies.
This document discusses several key concepts in radiobiology including:
1. The interaction of radiation with cells is probabilistic, with damage occurring through direct and indirect action. Indirect action involves free radicals produced by radiation interacting with water molecules within cells.
2. Different phases of the cell cycle have differing radiosensitivities, with G2/M being most sensitive. Fractionated radiation can exploit this through redistribution effects.
3. The linear quadratic model describes cell survival curves and accounts for both single-hit and double-hit damage from radiation. It is used to calculate biologically equivalent doses.
4. Mechanisms like reoxygenation between fractions can improve the therapeutic ratio by making tumor cells
International Journal of Engineering Research and Development (IJERD)IJERD Editor
This summary provides the key details about the document in 3 sentences:
The document analyzes the surface tension of osteoblast cells in a microchip. It studies how electrical pulses, electrode configuration, microchannel dimensions, and suspension media properties affect the surface tension of the inner and outer layers of osteoblast cell membranes. The document develops a 3D microfluidic model and electrical circuit model to investigate the membrane surface tension and how it is impacted by various parameters like pulse characteristics, electrodes, microchannel, and suspension media.
Chapter 5 -repair or radiation damage and dose-rate effect - jtlJohn Lucas
The document summarizes various pathways for repairing DNA damage from radiation: base excision repair removes inappropriate bases; nucleotide excision repair removes bulky adducts like pyrimidine dimers. Mismatch repair fixes base-base mismatches. Non-homologous end joining and homologous recombination repair double-strand breaks, with the former being error-prone and active in G1, and the latter being error-free using a sister chromatid template and most active in G2 phase. Certain syndromes like ataxia-telangiectasia and LIG4 syndrome result from defects in these pathways and cause radiation sensitivity.
The patch clamp technique allows for high-resolution recording of ion channel currents. It involves using a glass pipette to form a high-resistance seal with a cell membrane, isolating a small portion of the membrane. This enables measurement of the electric current passing through individual or small groups of ion channels as voltages are varied. The technique was developed in the late 1970s and has provided insights into the functions of many ion channels in excitable cells like neurons.
This document discusses radiation-induced cell kill and damage. It begins by outlining the topics to be covered, including DNA damage by ionizing radiation, chromosome damage and repair, cell survival curves, and the clinical response of normal tissues to radiation exposure. It then covers various topics in depth, such as the direct and indirect action of ionizing radiation on DNA, the role of linear energy transfer (LET), different types of DNA damage and repair mechanisms, chromosome aberrations, and cell survival curves. The goal of radiotherapy is explained as maximizing tumor kill while minimizing damage to normal tissues.
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The document studies the window effect of rectangular electrical pulses on the membrane potential of an osteoblast cell modeled as a dielectric. It presents an equivalent circuit model of the cell subjected to time domain electric fields such as rectangular pulses. The model includes separate charging time constants and relaxation times for the inner and outer cell membranes. Simulation results show that shorter pulse durations selectively affect the inner membrane more than the outer membrane, while longer pulses can fully charge both membranes. The window effect provides insight into bioelectric phenomena like electroporation and nanopore formation, with applications to cancer treatment.
DIELECTROPHORETIC DEFORMATION OF ERYTHROCYTES ON TRANSPARENT INDIUM TIN OXIDE...Larry O'Connell
1. The document presents a protocol for patterning transparent indium tin oxide (ITO) electrodes and investigates their efficacy for dielectrophoretically deforming erythrocytes compared to existing gold electrodes.
2. ITO electrodes were fabricated through a multi-step reactive ion etching process involving photoresist patterning and chromium/nickel masking layers. The transparent ITO electrodes allow full visualization of adhered cells, unlike opaque gold electrodes.
3. Erythrocytes suspended in a glucose solution were dielectrophoretically deformed at increasing electric field strengths on the ITO electrodes. Images were captured at each voltage step to measure cell deformation without occlusion from the electrodes.
DNA repair is a collection of processes cells use to identify and correct damage to DNA. Each day, human cells can experience up to 1 million instances of DNA damage from normal metabolic processes and environmental factors like UV light and radiation. When repair processes fail and damaged cells do not undergo apoptosis, irreparable DNA damage can occur, potentially leading to mutations, senescence, apoptosis, or cancer. The ability of a cell to repair DNA is vital to the functioning of the organism, and deficiencies in repair pathways can influence lifespan. In 2015, the Nobel Prize in Chemistry recognized Tomas Lindahl, Paul Modrich, and Aziz Sancar for their work elucidating molecular mechanisms of DNA repair.
Effects of Electromagnetism Exposure on Human EnvironmentKenko95
This document provides an overview of electromagnetism including its sources, uses, and effects. It discusses that electromagnetism comes from both natural sources like lightning and the Earth's magnetic field as well as artificial human-made sources like power outlets and mobile phones. The document also reviews several studies that have investigated both the potential harmful effects of electromagnetic exposure as well as some beneficial effects such as its use in suppressing cancer cell growth and reducing chemotherapy toxicity. While some research has linked electromagnetic fields to health issues, other studies have not found clear evidence of harm.
Physical methods can be used to transfer genes into cells by creating transient defects in cell membranes through which naked DNA can enter. These include electroporation, gene guns, ultrasound, and hydrodynamic delivery.
Electroporation uses short pulses of high voltage to carry DNA across cell membranes. Gene guns use compressed gas to accelerate DNA-coated metal particles into cells. Ultrasound uses microbubbles and acoustic cavitation to enhance DNA delivery. Hydrodynamic delivery involves high-pressure injection of DNA solution into an organ to enter cells.
These physical methods show promise for gene transfer but also have limitations like tissue damage, shallow penetration depth, and low efficiency that need addressing for clinical use.
Physical methods can be used to transfer genes into cells by creating transient defects in cell membranes through which naked DNA can enter. These include electroporation, gene guns, ultrasound, and hydrodynamic delivery.
Electroporation uses short pulses of high voltage to carry DNA across cell membranes. Gene guns use compressed gas to accelerate DNA-coated metal particles into cells. Ultrasound uses microbubbles and acoustic cavitation to enhance DNA delivery. Hydrodynamic delivery involves high-pressure injection of DNA solution into an organ to enter cells.
These physical methods show promise for gene transfer but also have limitations like tissue damage, shallow penetration depth, or low efficiency that need addressing for clinical use.
Gene cloning involves producing exact copies of a gene using genetic engineering techniques. It involves isolating the gene of interest from one organism and inserting it into a vector, which is then introduced into a host organism where the gene can be replicated. There are several methods used to transfer genes between organisms or cells, including bacterial transformation, electroporation, transfection, and microinjection. Bacterial transformation involves directly taking up exogenous DNA, electroporation uses an electric pulse to create pores for DNA entry, while transfection introduces nucleic acids into eukaryotic cells using chemical reagents or viruses.
This document is a table of contents and introduction for a book titled "jQuery Fundamentals" by Rebecca Murphey. The book covers jQuery basics, core concepts, events, effects, Ajax, plugins, and advanced topics. It includes over 50 code examples to demonstrate jQuery syntax and techniques. The book is available under a Creative Commons license and the source code is hosted on GitHub.
This document provides a preface and table of contents for a book on jQuery concepts. The preface explains that the book is intended to teach intermediate and advanced jQuery concepts through code examples. It highlights some stylistic approaches used in the book, such as emphasizing code over text explanations and using color coding. It also defines some key terms that will be used, and recommends reviewing the jQuery documentation and understanding how the text() method works before reading the book. The table of contents then outlines the book's 12 chapters and their respective sections, which cover topics like selecting, traversing, manipulating, events, plugins and more.
This document proposes techniques for embedding unique codewords in electronic documents to discourage illicit copying and distribution. It describes three coding methods - line-shift coding, word-shift coding, and feature coding - that alter document formatting or text elements in subtle, hard-to-detect ways. Experimental results show the line-shift coding method can reliably decode documents even after photocopying, enabling identification of the intended recipient. The techniques aim to make unauthorized distribution at least as difficult as obtaining documents legitimately from the publisher.
This document discusses the field of computer forensics. It defines computer forensics as the collection, preservation, and analysis of computer-related evidence. The goal is to provide solid legal evidence that can be admitted in court and understood by laypeople. Computer forensics is used to investigate various incidents including human behavior like fraud, physical events like hardware failures, and organizational issues like staff changes. It aims to determine the root cause of system disruptions and failures.
This document discusses techniques for data hiding, which involves embedding additional data into digital media files like images, audio, or text. It describes several constraints on data hiding, such as the amount of data to hide, ensuring the data remains intact if the file is modified, and preventing unauthorized access to the hidden data. The document outlines traditional and novel data hiding techniques and evaluates them for applications like copyright protection, tamper-proofing, and adding supplemental data to files. It also discusses tradeoffs between hiding more data versus making the data more robust against modifications to the file.
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Steganography has been used for over 2500 years to hide secret messages. The paper explores steganography's history from ancient times through modern digital applications. It discusses early examples like Johannes Trithemius' steganographic treatise in the 15th century. Modern uses include microdots, digital images, audio, and digital watermarks for copyright protection. Terrorist groups may use steganography but there is no public evidence yet. Steganography continues to evolve with technology while attackers work to defeat new techniques.
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This document discusses the topic of steganography, which is hiding secret messages within other harmless messages. It outlines different techniques for hiding messages in text, images, and audio files. For text, it describes line shift coding, word shift coding, and feature coding methods. For images, it explains least significant bit insertion and exploiting the limitations of the human visual system. For audio, it mentions low-bit encoding and other techniques like phase coding and spread spectrum. It also discusses steganalysis, which aims to detect and destroy hidden messages within files.
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3) Protocols for secure communication like HTTPS, digital certificates, and single sign-on systems.
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This document discusses the discrete-time Fourier transform (DTFT). It begins by introducing the DTFT and how it can be used to represent aperiodic signals as the sum of complex exponentials. Several properties of the DTFT are then discussed, including linearity, time/frequency shifting, periodicity, and conjugate symmetry. Examples are provided to illustrate how to compute the DTFT of simple signals. The document also discusses how the DTFT can be used to represent periodic signals and impulse trains.
This document discusses the continuous-time Fourier transform. It begins by developing the Fourier transform representation of aperiodic signals as the limit of Fourier series coefficients as the period increases. It then defines the Fourier transform pairs and discusses properties like convergence. Several examples of calculating the Fourier transform of common signals like exponentials, pulses and periodic signals are provided. Key concepts like the sinc function are also introduced.
Chapter3 - Fourier Series Representation of Periodic SignalsAttaporn Ninsuwan
This document discusses Fourier series representation of periodic signals. It introduces continuous-time periodic signals and their representation as a linear combination of harmonically related complex exponentials. The coefficients in the Fourier series representation can be determined by multiplying both sides of the representation by complex exponentials and integrating over one period. The key steps are: 1) multiplying both sides by e-jω0t, 2) integrating both sides from 0 to T=2π/ω0, and 3) using the fact that the integral equals T when k=n and 0 otherwise to obtain an expression for the coefficients an. Examples are provided to illustrate these concepts.
Chapter3 - Fourier Series Representation of Periodic Signals
Leukemia dep-force
1. Controlling cell destruction using dielectrophoretic
forces
A. Menachery and R. Pethig
Abstract: Measurements are reported of the main factors, namely the AC voltage frequency and
magnitude, that were observed to influence the number of cells destroyed during dielectrophoresis
(DEP) experiments on Jurkat T cells and HL60 leukemia cells. Microelectrodes of interdigitated
and quadrupolar geometries were used. A field-frequency window has been identified that should
be either avoided or utilised, depending on whether or not cell damage is to be minimised or is a
desired objective. The width and location of this frequency window depends on the cell type, as
defined by cell size, morphology and dielectric properties, and is bounded by two characteristic
frequencies. These frequencies are the DEP cross-over frequency, where a cell makes the transition
from negative to positive DEP, and a frequency determined by the time constant that controls the
frequency dependence of the field induced across the cell membrane. When operating in this
frequency window, and for the microelectrode designs used in this work, cell destruction can be
minimised by ensuring that cells are not directed by positive DEP to electrode edges where fields
exceeding 30–40 kV/m are generated. Alternatively, this field-frequency window can be exploited to
selectively destroy specific cell types in a cell mixture.
1 Introduction have been successfully cultured following their DEP
enrichment from bone marrow and peripheral stem cell
The possibility that, under certain conditions, cells may be harvests [3]. Fibroblasts can be successfully cultivated,
irreversibly damaged as a result of exposure to dielectro- without significant change in their viability, motility,
phoresis (DEP) forces is well known to workers in the field, anchorage or cell-cycle time, when exposed to DEP fields
but is often not reported. The desired objective in many continuously over a period of 3 days [4]. Although very
DEP experiments is to use radio-frequency electric fields to small increases were observed in the stress-related gene c-fos
selectively isolate, concentrate, or purify target bioparticles expression levels for glioma and neuroblastoma cells
from prepared or natural fluid suspensions. Examples separated by DEP, subsequent culturing experiments
include the isolation of cancer cells, fetal cells, stem cells demonstrated that there were no effects on cell growth [5].
or bacteria from blood for further analysis or potential The highest reported fluid flow rate for DEP cell separation
therapeutic purposes. Maintaining cell viability is an appears to be 2.5 ml/min [6]. Because of the relatively small
important objective in such cases. For some of our previous dimensions of a typical DEP separation chamber, this flow
studies, the frequency and voltage of the applied electrical rate is well within the limits for laminar flow and
signals were programmed to avoid regimes where cell corresponds to a shear stress exerted on the cells of around
damage had been observed [1]. For other envisaged 0.3 N/m2. This is well below the shear stress of 150 N/m2
applications of DEP, as for example to facilitate the release required to damage erythrocytes [7] or of 20 N/m2 for T
of proteins or DNA from target cells, utilising such cells [8].
frequency-voltage regimes to achieve selective cell destruc- Cell membranes can also be disrupted by forced
tion may be a desired objective. oscillation at frequencies greater than around 10 kHz, and
DEP-induced cell damage can arise from at least three this is the basis for using high-power sonication to
main sources: (i) effects associated with the cells being disintegrate cells. Cell destruction by DEP is more subtle,
suspended in a non-physiological medium; (ii) stress and is primarily related to a field-induced breakdown of the
induced by the applied electric field; and (iii) shear stresses physical integrity of the plasma membrane, as evidenced by
associated with fluid flow. Workers in the field are now the fact that the internal structure of the cell appears (under
competent in their choice of cell suspending media and phase-contrast microscopy) to remain intact for some time
applied signal voltages, so that under gentle DEP conditions and is even manipulable by DEP [9]. A related topic is
cell viability can be readily maintained. For example, the electroporation (also called electropermeabilisation) of cells,
viability of erythrocytes separated from leukemia cells has which is typically achieved by subjecting cells to electric
been verified using trypan blue dye [2] and CD34+ cells pulses of field strengths ranging from around 5 MV/m (for
microsecond pulses) down to 0.1 MV/m (for millisecond
r IEE, 2005
pulses) [10]. Field-frequency maps have also been produced
IEE Proceedings online no. 20050010
of the observed probability of AC electromediated cell
doi:10.1049/ip-nbt:20050010
bursting [11].
Paper received 24th May 2005
We now intend to analyse the conditions, in terms of the
The authors are with the School of Informatics, University of Wales, Bangor,
strength and frequency of the applied AC field, under which
Dean Street, Bangor, Gwynedd, LL57 1UT, UK two different cell types (human T cells and HL60 leukemia
E-mail: ron@informatics.bangor.ac.uk cells) can be observed to burst during routine DEP
IEE Proc.-Nanobiotechnol., Vol. 152, No. 4, August 2005 145
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2. experiments. This analysis will provide insights into the references cited therein as:
main factors that can be controlled to either minimise or to 1:5ðR=dÞE cos y
achieve selected cell destruction using dielectrophoresis. Em ðo; yÞ ¼ ð4Þ
1 þ jot
2 Theory The factor R/d is the ratio of the cell radius R to the
membrane thickness d (B5 nm) and y is the polar angle
As described in standard texts e.g. [12] the total force, per with respect to the field direction. The time constant t is
unit volume, acting on a dielectric particle subjected to an given by:
external electric field E is given by: 2si se R
t ¼ RCm þ sm ð5Þ
eo 2 eo si þ2se d
2 der
Fv ¼ rE À E rer þ r E g ð1Þ where si, sm, and se are the conductivities of the cell interior
2 2 dg
(cytoplasm), cell membrane and extracellular medium,
In this equation, r represents the net charge density carried respectively. Cm is the membrane capacitance whose value
by the particle, e0 is the permittivity of free space, er and g is principally determined by the morphology of the cell in
are the relative permittivity and density of the particle terms of the presence of microvilli, blebs or membrane
material, respectively, and r is the grad vector operator. folds, for example, and to a good approximation can be
The first term of (1) is thus the electrophoretic force acting determined experimentally from the expression [20]:
on a charged particle, whereas the second term is a force pffiffiffi
2
that will appear if the particle is composed of a dielectrically Cm ¼ se ð6Þ
inhomogeneous material. The last term gives a volume force 2pRfxo
in an inhomogeneous electric field and hence represents the In this equation, fxo is the frequency (the so-called DEP
DEP force [13], where the factor der/dg is given by the cross-over frequency) where the cell exhibits a transition
Clausius-Mossotti relationship that (erÀ1)/(eo+2) should be from negative to positive DEP. Equation (4) predicts that at
proportional to the density of the material [14]. low frequencies (oto1) the field Em acting across a cell
A rigorous way to apply (1) utilises the Maxwell stress membrane can exceed the applied field E by a factor of 103
tensor to determine the time-averaged mechanical forces or greater, depending on cell size.
and torques (tensions acting along field lines and pressures
acting perpendicular to them) exerted by an electric field on 3 Experimental
the surface and within the body of a particle [12, 15]. This
method involves determining difficult integrals that incor- 3.1 Cell samples
porate pressure-like variables that are difficult to test Human T lymphocytes (Jurkat E6-1) and leukemia cells
experimentally, so that for most practical applications the (HL60) were obtained from the American Type Culture
Maxwell stress tensor formulation is not ‘user friendly’. The Collection (ATCC: TIB-152) and the European Collection
so-called ‘effective dipole’ method gives the same results as of Cell Cultures (ECACC: 85011431), respectively. The T
the more rigorous Maxwell stress tensor method, and has cells were grown in RPMI media containing modified
the advantage that it uses simple concepts and relatively RPMI-1640 (ATCC) supplemented with 10% fetal bovine
straightforward analyses [16]. Based on this theory the time- serum (ATCC), 100 U/ml penicillin, and 100 mg/ml strepto-
averaged DEP force, acting on a homogeneous spherical mycin (Gibco/BRL). The HL60 cells were grown in RPMI-
particle of radius R suspended in a medium of relative 1640 media (Sigma) supplemented with 10% fetal bovine
permittivity em, is given by: serum (Sigma), 1 mM glutamine and 20 mM hepes buffer
(Sigma). A humidified incubator was used, and maintained
hFDEP i ¼ 2peo em R3 Re½f ðeà ފrjEj2 ð2Þ at 371C, with 5% CO2, 95% air.
Immediately before the DEP experiments, the cells were
where E is the root-mean-squared amplitude of the applied washed twice with 10 ml of an isotonic low conductivity
AC field. Re½f ðeà ފ is the real part of the Clausius-Mossotti media containing 8.6% w/w sucrose, 0.3% w/w dextrose,
factor: and 1.0 mg/ml BSA (Sigma), pH 7.4. The conductivity of
à this media was adjusted to 40 mS/m at 251C, by adding
e À eà modified Eagle’s minimum essential media (Sigma) at a
f ðeÃ Þ ¼ Ãc e
ð3Þ
ec þ 2eÃ
e ratio of about 40:1, and using a YSI 3200 conductivity
instrument with an Orion 018012 conductivity flow cell.
and is bounded by the values À0:5 Re½f ðeà ފ 1:0. After washing, the cells were suspended in the 40 mS/m
Positive values signify a positive DEP (cells attracted to media. The osmolality of the cell suspensions remained near
high-field regions at electrode edges) and negative values 296 mmol/kg, as determined using a Vapro 5520 vapour
give a negative DEP (cells repelled from electrode edges). pressure osmometer. The osmolality and conductivity of the
The factors eà and eà are the cell and extracellular medium
c e cell suspensions were checked before and after each DEP
complex permittivities, respectively, defined by eà ¼ e À experiment.
jðs=oÞ with e being the permittivity, s the conductivity, o
pffiffiffiffiffiffiffi
the radian frequency (2pf) and j ¼ À1. 3.2 Dielectrophoresis and cell bursting
To obtain a significant DEP force, the factor r7E72 in (2) observations
should be of the order of 1013 V2/m3, which, depending Two microelectrode designs were employed in the experi-
on the electrode geometry, can correspond to an applied ments, namely the interdigitated-castellated and quadrupo-
field of the order of 10 kV/m or lower [17]. The reason lar (polynomial) geometries shown in Fig. 1. The
a relatively weak DEP field can cause electrical damage interdigitated electrodes were fabricated with a character-
to a cell is because the field is ‘amplified’ in the form of a istic dimension of 80 mm defining the castellation geometry
potential induced across the cell membrane. For a model, [21], and for the quadrupole design [22] the distance
spherical, cell the frequency dependence of the field Em between opposing electrode tips was 400 mm. The electrode
acting across the membrane is given by [18, 19] and material was gold, 70 nm thick, vacuum evaporated onto a
146 IEE Proc.-Nanobiotechnol., Vol. 152, No. 4, August 2005
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3. 300
31.8
distance, µm
A 200 27.2
22.7
18.1
A 13.6
9.1
100
4.5
0
0 100 200 300 400
distance, µm
Fig. 2 The electric field contours (in kilovolts per metre)
generated by the interdigitated electrodes with an applied sinusoidal
B
AC voltage of 1 V (peak)
600
11.3
500 11.3
9.1
400
B
distance, µm
6.8
Fig. 1 The interdigitated and quadrupole electrodes used in these 300
studies are shown on the top and bottom, respectively. The
characteristic dimension defining the interdigitated castellations 2.3
was 80 mm, and the distance between opposing quadrupole electrode 200
11.3
tips was 400 mm. Cells are shown being attracted to the electrode
18 .1
edges under the influence of positive DEP, cell bursts events were 100
13.6
most common in regions such as those marked A and B 9.1
15.8
0
0 100 200 300 400 500 600
5 nm thick seed layer of chromium on a glass microscope distance, µm
slide substrate. Further details of these electrode designs,
their fabrication, and how they are used for DEP Fig. 3 The field contours (in kilovolts per metre) generated by the
experiments, have been given elsewhere [21, 22]. quadrupolar electrodes with an applied sinusoidal AC voltage of 1 V
The data collected for cell bursting events were obtained (peak)
during experiments performed primarily to characterise the
DEP properties of T cells and HL60 cells. The results
obtained for the T cells have been reported elsewhere [20] from field contour maps of the form shown in Figs. 2 and 3.
and during the course of these experiments approximately These maps were obtained using the Femlab Electromag-
5% of the cells burst on approaching the (polynomial netics Module (COMSOL, Inc.) in conjunction with the
design) electrode edges under the influence of a positive Matlab (The Math Works, Inc.) environment, for a 1 V
DEP force. In these experiments the location of each cell peak sinusoidal signal applied to the electrodes, and as a
could be continuously tracked, and a value for the diameter function of height (up to 15 mm) above the electrode plane.
of each cell could be determined to within 70.25 mm [20]. Most of the experiments were performed with an applied
The observations made of the location of the cells when AC sinusoidal voltage in the range 2–6 V (peak), and simple
they burst, and of the magnitude and frequency of the linear scalings of the contours given in Figs. 2 and 3 were
applied AC voltages, constitute the bulk of the data adopted to accommodate these different voltages. One
presented in this study. Cell bursting events for a smaller experiment was performed to induce increased numbers of
number of T cells were also observed using the inter- HL60 cell bursting events, by increasing the interdigitated
digitated electrode geometry. The data collected for the electrode voltage up to 12 V (peak).
HL60 cells were all made using interdigitated electrodes,
and in these experiments the locations of the cells and their 4 Results
diameters (70.5 mm) were determined using a simple video
imaging method. Cell bursting was observed to occur most The cell bursting events, in terms of the local fields
often (but not always) in the inter-electrode regions marked experienced by the cells and the frequencies of the applied
‘A’ and ‘B’ in Fig. 1, for the interdigitated and quadrupolar voltages, are shown in Fig. 4. HL60 cell bursting events for
electrodes, respectively. the experiments where the voltage was increased up to 12 V
The magnitudes of the local electric fields imposed on the (peak) are not included in this Figure (but see Fig. 6). The
cells at the time of their observed bursting were deduced data points for the HL60 and T cells can be seen to fall into
IEE Proc.-Nanobiotechnol., Vol. 152, No. 4, August 2005 147
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4. 100
6
MD A435 cells [11]
(200 kHz, 58 mS/m)
percentage of cells destroyed, %
log applied field E, V/m
80
5
60 T cells [11]
4 (2 MHz, 55.7 mS/m)
HL 60 T cells
40
3
20
HL60 cells
4 5 6 7 (100 kHz, 38 mS/m)
log frequency, Hz 0
4 5 6
Fig. 4 Values of the local field and voltage signal frequency at log field, V/m
which HL60 and T cells were observed to burst in a suspending
electrolyte of conductivity 40 mS/m. The HL60 data points were Fig. 6 Results extracted from [11] on the electromediated
obtained using the interdigitated electrode design. Both quadrupole bursting of T cells and breast cancer cells (MDA-MB-435) are
(filled circles) and interdigitated (open circles) electrodes were used shown with our cell bursting data for HL60 cells. The conductivities
for the T cell studies of the suspending media are given, and the AC frequency values cited
correspond to those where cell bursting was most probable for each
cell type
9 respectively. The average cell radius was taken as 5.2 mm
[20], to give t ¼ 9.5 Â 10À7 s for the time constant of the T
cells. For the HL60 cells the value for Cm was obtained
log membrane field Em, V/m
8 HL 60 from measurement of the cross-over frequency fxo for 90
E = 30 kV/m cells that did not burst. Observed values for fxo ranged from
7
57–93 kHz, and gave an average value close to 75 kHz. The
fxo: HL60 T cells radii of the HL60 cells were determined to range from 6.0–
E = 40 kV/m 7.5 mm (70.25 mm) with an average value close to 6.75 mm.
f xo: T cells
6 This gives a Cm value of 17.8 mF/m2 for the HL60 cells, and
a corresponding time constant value t ¼ 1.66 Â 10À6 s.
HL 60 T cells The average radii and time constant values (5.2 mm,
5 9.5 Â 10À7 s; 6.75 mm, 1.66 Â 10À6 s, for the T and HL60
cells, respectively) were used in (4) to create the curves
4 5 6 7
drawn in Fig. 5 to show how the membrane field generated
log frequency, Hz
parallel to the applied field varies as a function of frequency.
Fig. 5 Values obtained from (4), using the field-frequency data These curves are plotted in Fig. 5 for values of external field
given in Fig. 4, for the induced field membrane at the time of cell of 30 and 40 kV/m for the HL60 and T cells, respectively.
bursting. Also shown are the DEP cross-over (fxo) frequency range The cross-over frequency ranges, where cells exhibited a
values measured for the HL60 and T cells that did not burst. The change from negative to positive DEP with increasing
solid curve shows how the membrane field varies with frequency for frequency, are also shown in Fig. 5 for the HL60 cells
the HL60 cells for an applied local field of 30 kV/m and a suspending (fxoB60–90 kHz) and T cells (fxoB110–190 kHz).
medium conductivity of 40 mS/m. The dotted line gives the same
information for T cells in a local field of 40 kV/m
5 Discussions and conclusions
The data shown in Fig. 4 indicate that in our DEP
fairly distinct field-frequency windows. The fact that the experiments a small number (B5%) of cells in suspension
results obtained for the T cells did not depend on whether were induced to burst if they were directed by positive DEP
polynomial or interdigitated electrodes were employed towards regions at the electrode edges where the local
indicates that difference in cell type, rather than choice of sinusoidal fields exceeded a value of about 30 kV/m. For
electrode geometry, determined the different experimental cells suspended in an isotonic electrolyte of conductivity
parameters observed for cell bursting. 40 mS/m and with applied AC voltages between 1 and 6 V
The data of Fig. 4 has been used to produce Fig. 5, to (pk), very few cell bursting events were observed in the
show values of the membrane field generated parallel to the frequency range from 10 kHz up to the cross-over frequency
applied field (i.e. y ¼ 0) in each cell at the instant of their fxo where the cells made the transition from negative to
bursting. These calculations employed (4) and required the positive DEP. We assume that in this lower frequency range
value of the cell radius (which was measured in the the cells were directed away from the electrode edges and
experiments) as well as the membrane capacitance Cm to de- were never subjected to field stresses greater than 30 kV/m.
termine the time constant t given by (5). For the T cells, the From Fig. 5 the critical membrane field for the onset of
value for Cm was taken as the average value 13.24 mF/m2 cell destruction for both the HL60 and T cells is of the order
determined in [20] for the large number (4600) of cells of 108 V/m for frequencies just slightly above their respective
that did not burst during the experiments. In (5) the fxo cross-over frequencies, and progressively drops (to a
experimental value of 40 mS/m was used for the conductiv- value of the order of 107 V/m for T cells) as the frequency is
ity se of the external suspending medium, and values of raised above fxo. This suggests that a combination of
0.7 S/m and 5 Â 10À7 S/m were assumed for the conductiv- stresses induced by both the increase of the membrane field
ities si and sm of the cell interior and membrane, stress and the DEP force acting on the cell leads to cell
148 IEE Proc.-Nanobiotechnol., Vol. 152, No. 4, August 2005
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5. destruction. At frequencies just above the cross-over result:
frequency fxo it is common in DEP experiments to observe
cells spinning at electrode edges under the influence of an fmf 2se
fxo ¼ pffiffiffi 1 þ ð8Þ
induced rotational torque. Such behaviour can result in 2 si
significant shear forces on the cell membrane, resulting in
cell damage [1]. Above a certain frequency, however, where Equation (8) teaches that the close relationships between the
the membrane field falls below 107 V/m, the DEP force DEP cross-over frequency and the fall in membrane fields
acting alone is not sufficient to initiate cell destruction. A shown in Fig. 5 can be expected to hold for the range
previous report [11] has described unpublished work to (1–200 mS/m) of medium conductivities commonly
show that different cell types have characteristically different employed in DEP experiments on cells.
susceptibilities to destruction by AC fields. Although the
experimental details of this earlier work are not provided, 6 Acknowledgments
some interesting comparisons can be made with our work
presented here. As shown in Fig. 6, T cells and breast cancer We thank Dr Sally Cotterill and Brenda Kusler for their
cells subjected to an AC field exhibited maximum cell work with cell cultures, and Drs Mark Talary and Richard
damage at frequencies around 2 MHz and 200 kHz, Lee for their help with the dielectrophoresis experiments.
respectively [11]. This mirrors the different field-frequency Part of this work was funded by the National Foundation
windows for cell destruction of HL60 and T cells shown in for Cancer Research.
Figs. 4 and 5, and suggests that in this earlier work [11] the
applied fields were not uniform and that DEP forces could
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IEE Proc.-Nanobiotechnol., Vol. 152, No. 4, August 2005 149
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