title: Non-linear time domain model of electropermeabilization: Effect of extracellular conductivity and applied electric field parameters

authors: Talele, Sadhana

subjects: electroporation

abstract: This paper describes simulation results obtained from a previously reported numerical model for a single cell exposed to an arbitrary waveform electric field pulse. This paper concentrates on how the efficiency of electroporation related applications can be significantly improved by appropriately adjusting the parameters of applied electric field and conductivity of the external medium, σe. Emphasis is given here on the normalization of the degree of electroporation for a range of cell radii.
The simulated results indicate that it may be difficult for cells of substantially different sizes to be close to uniformly electroporated if surrounded by media with a conductivity higher than around 5*10⁻³ S/m for 100 kHz bipolar pulses, or 0.2 S/m for 1 MHz bipolar pulses. To achieve as normalized as possible electroporation for the radii/size variation required in any particular application, using a lower σe would be preferable. There is, however, a limit to how low the external conductivity can be made, as the applied electric field amplitude must stay within practical limits. Considering 3*10¹³ pores/m² as a nominal pore density N for approximately optimum electroporation, σe could be as low as 0.08 S/m for a 7.5 µm cell radius with a peak electric field of 1.2*10⁵V/m (depending on the pulse shape and frequency). For a 15 µm cell radius, σe could be as low as 0.05 S/m (depending on the pulse shape and frequency). It is seen that the relative difference of N between the two cell sizes investigated is consistently lower for a bipolar sine wave electric field compared to a bipolar square wave electric field, even though the square wave electric field peak amplitude is always lower for an equivalent N.

text: Non-linear time domain model of electropermeabilization: Effect of extracellular conductivity and applied electric field parameters This paper describes simulation results obtained from a previously reported numerical model for a single cell exposed to an arbitrary waveform electric field pulse. This paper concentrates on how the efficiency of electroporation related applications can be significantly improved by appropriately adjusting the parameters of applied electric field and conductivity of the external medium, σe. Emphasis is given here on the normalization of the degree of electroporation for a range of cell radii.
The simulated results indicate that it may be difficult for cells of substantially different sizes to be close to uniformly electroporated if surrounded by media with a conductivity higher than around 5*10⁻³ S/m for 100 kHz bipolar pulses, or 0.2 S/m for 1 MHz bipolar pulses. To achieve as normalized as possible electroporation for the radii/size variation required in any particular application, using a lower σe would be preferable. There is, however, a limit to how low the external conductivity can be made, as the applied electric field amplitude must stay within practical limits. Considering 3*10¹³ pores/m² as a nominal pore density N for approximately optimum electroporation, σe could be as low as 0.08 S/m for a 7.5 µm cell radius with a peak electric field of 1.2*10⁵V/m (depending on the pulse shape and frequency). For a 15 µm cell radius, σe could be as low as 0.05 S/m (depending on the pulse shape and frequency). It is seen that the relative difference of N between the two cell sizes investigated is consistently lower for a bipolar sine wave electric field compared to a bipolar square wave electric field, even though the square wave electric field peak amplitude is always lower for an equivalent N.

year: 2008

title: Strengthening Rotationally Moulded Products: Development of a Rotomouldable Thermoplastic Composite

authors: Betschart, Paul Josef

subjects: rotational moulding

abstract: Rotational moulding is a process with a range of unique benefits, currently experiencing significant growth within industry. A primary limitation of the process, however, is the restricted range of suitable materials and the subsequent limitations placed upon the mechanical performance of rotationally moulded products.
The aim of this research project was to develop a rotational moulding material which possessed substantially improved mechanical properties over conventional, rotationally moulded polyethylene grades. This was attempted through the development of a fibre-reinforced thermoplastic composite which was amenable to the rotational moulding process. Although the development of rotationally moulded composites has been previously reported in literature, these materials have largely proven to be unsatisfactory in terms of mechanical performance. 
The composite material developed here is distinct from those previously reported in that it utilises melt-compounded composite granules of a significantly larger size than are normally considered suitable for rotational moulding. These granules are intended to be moulded as an inner layer within a rotationally moulded product, with the outer moulded layer formed from conventional, unfilled polymer powder. In this way, the average length of the fibres within the moulded article is maximised while retaining the benefits of the melt-compounding process and giving an excellent external moulded finish. In order to achieve a sufficient degree of composite granule flow and coalescence during rotational moulding, it was found necessary to base the composite granules on high melt-flow, injection moulding grades of polypropylene and polyethylene. The most successful of the resultant composite materials was shown to be superior to the previously utilised rotational moulding grade of unfilled, high-density polyethylene by approximately 65% in offset yield strength (0.5% offset) and over 95% in tensile modulus.

text: Strengthening Rotationally Moulded Products: Development of a Rotomouldable Thermoplastic Composite Rotational moulding is a process with a range of unique benefits, currently experiencing significant growth within industry. A primary limitation of the process, however, is the restricted range of suitable materials and the subsequent limitations placed upon the mechanical performance of rotationally moulded products.
The aim of this research project was to develop a rotational moulding material which possessed substantially improved mechanical properties over conventional, rotationally moulded polyethylene grades. This was attempted through the development of a fibre-reinforced thermoplastic composite which was amenable to the rotational moulding process. Although the development of rotationally moulded composites has been previously reported in literature, these materials have largely proven to be unsatisfactory in terms of mechanical performance. 
The composite material developed here is distinct from those previously reported in that it utilises melt-compounded composite granules of a significantly larger size than are normally considered suitable for rotational moulding. These granules are intended to be moulded as an inner layer within a rotationally moulded product, with the outer moulded layer formed from conventional, unfilled polymer powder. In this way, the average length of the fibres within the moulded article is maximised while retaining the benefits of the melt-compounding process and giving an excellent external moulded finish. In order to achieve a sufficient degree of composite granule flow and coalescence during rotational moulding, it was found necessary to base the composite granules on high melt-flow, injection moulding grades of polypropylene and polyethylene. The most successful of the resultant composite materials was shown to be superior to the previously utilised rotational moulding grade of unfilled, high-density polyethylene by approximately 65% in offset yield strength (0.5% offset) and over 95% in tensile modulus.

year: 2008

title: Te Hokinga ki te Pā Harakeke

authors: Hohepa, Margie Kahukura

abstract: 'Tiakina Te Pā Harakeke' investigates the collective values that nourish and enhances the well-being of tamariki Māori as taonga within our whānau, hapū and iwi. lt explores ways in which Māori values and tikanga are harnessed in contemporary whānau contexts to provide safe, vibrant and enriched childrearing. parenting and child-focussed strategies.

text: Te Hokinga ki te Pā Harakeke 'Tiakina Te Pā Harakeke' investigates the collective values that nourish and enhances the well-being of tamariki Māori as taonga within our whānau, hapū and iwi. lt explores ways in which Māori values and tikanga are harnessed in contemporary whānau contexts to provide safe, vibrant and enriched childrearing. parenting and child-focussed strategies.

year: 2014