https://researchbank.swinburne.edu.au/file/cfcb2291-f157-4ca4-937c-5cd1bbf218fd/1/PDF (Accepted manuscript).pdf

Biophysical Model of Bacterial Cell Interactions with Nanopatterned Cicada Wing Surfaces

The nanopattern on the surface of Clanger cicada (Psaltoda claripennis) wings represents the first example of a new class of biomaterials that can kill bacteria on contact based solely on its physical surface structure. As such, they provide a model for the development of novel functional surfaces that possess an increased resistance to bacterial contamination and infection. Their effectiveness against a wide spectrum of bacteria, however, is yet to be established. Here, the bactericidal properties of the wings were tested against several bacterial species, possessing a range of combinations of morphology and cell wall type. The tested species were primarily pathogens, and included Bacillus subtilis, Branhamella catarrhalis, Escherichia coli, Planococcus maritimus, Pseudomonas aeruginosa, Pseudomonas fluorescens, and Staphylococcus aureus. The wings were found to consistently kill Gram-negative cells (i.e., B. catarrhalis, E. coli, P. aeruginosa, and P. fluorescens), while Gram-positive cells (B. subtilis, P. maritimus, and S. aureus) remained resistant. The morphology of the cells did not appear to play any role in determining cell susceptibility. The bactericidal activity of the wing was also found to be quite efficient; 6.1 ± 1.5 × 106 P. aeruginosa cells in suspension were inactivated per square centimeter of wing surface after 30-min incubation. These findings demonstrate the potential for the development of selective bactericidal surfaces incorporating cicada wing nanopatterns into the design.

Selective bactericidal activity of nanopatterned superhydrophobic cicada Psaltoda claripennis wing surfaces

A model combining low-frequency complex conductivity and high-frequency permittivity is developed in the frequency range from 1 mHz to 1 GHz. The low-frequency conductivity depends on pore water and surface conductivities. Surface conductivity is controlled by the electrical diffuse layer, the outer component of the electrical double layer coating the surface of the minerals. The frequency dependence of the effective quadrature conductivity shows three domains. Below a critical frequency fp, which depends on the dynamic pore throat size Λ, the quadrature conductivity is frequency dependent. Between fp and a second critical frequency fd, the quadrature conductivity is generally well described by a plateau when clay minerals are present in the material. Clay-free porous materials with a narrow grain size distribution are described by a Cole-Cole model. The characteristic frequency fd controls the transition between double layer polarization and the effect of the high-frequency permittivity of the material. The Maxwell-Wagner polarization is found to be relatively negligible. For a broad range of frequencies below 1 MHz, the effective permittivity exhibits a strong dependence with the cation exchange capacity and the specific surface area. At high frequency, above the critical frequency fd, the effective permittivity reaches a high-frequency asymptotic limit that is controlled by the two Archie's exponents m and n like the low-frequency electrical conductivity. The unified model is compared with various data sets from the literature and is able to explain fairly well a broad number of observations with a very small number of textural and electrochemical parameters. It could be therefore used to interpret induced polarization, induction-based electromagnetic methods, and ground penetrating radar data to characterize the vadose zone.

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/2012WR012700

Effective conductivity and permittivity of unsaturated porous materials in the frequency range 1 mHz-1GHz.

Rock and Mineral Properties

The present study investigated the effects of microwave (MW) radiation applied under a sublethal temperature on Escherichia coli. The experiments were conducted at a frequency of 18 GHz and at a temperature below 40°C to avoid the thermal degradation of bacterial cells during exposure. The absorbed power was calculated to be 1,500 kW/m 3 , and the electric field was determined to be 300 V/m. Both values were theoretically confirmed using CST Microwave Studio 3D Electromagnetic Simulation Software. As a negative control, E. coli cells were also thermally heated to temperatures up to 40°C using Peltier plate heating. Scanning electron microscopy (SEM) analysis performed immediately after MW exposure revealed that the E. coli cells exhibited a cell morphology significantly different from that of the negative controls. This MW effect, however, appeared to be temporary, as following a further 10-min elapsed period, the cell morphology appeared to revert to a state that was identical to that of the untreated controls. Confocal laser scanning microscopy (CLSM) revealed that fluorescein isothiocyanate (FITC)conjugated dextran (150 kDa) was taken up by the MW-treated cells, suggesting that pores had formed within the cell membrane. Cell viability experiments revealed that the MW treatment was not bactericidal, since 88% of the cells were recovered after radiation. It is proposed that one of the effects of exposing E. coli cells to MW radiation under sublethal temperature conditions is that the cell surface undergoes a modification that is electrokinetic in nature, resulting in a reversible MW-induced poration of the cell membrane.

/pdf/specific-electromagnetic-effects-of-microwave-radiation-on-4bnmcekjb4.pdf

Specific Electromagnetic Effects of Microwave Radiation on Escherichia coli

A method for calculating the complex dielectric permittivity of an anisotropic wood structure at microwave frequencies is presented. A numerical model for describing the 3D wood structure containing fibers, rays, vessels and cracks with changeable dimensions and material composition is built. This model is introduced into an efficient solver that calculates the effective dielectric constant of any 3D structure of dielectric materials. Using our numerical model we succeeded in theoretically reproducing the results of recent measurements of the dielectric permittivity of wood, in various directions and various moisture contents. The qualitative agreement is realistic, reproducing all the trends of the changes in ɛ as the direction of the electric field and the moisture content are varied. The quantitative agreement is practical and reliable for engineering calculations with an average deviation of ±10% in ɛ′ and ±5% in ɛ′′. As microwave processing of wood involves internal temperatures as high as 150°C and pressures of up to 5 atm, the dielectric properties of wood were also calculated with the same numerical model by simulating high internal temperature and pressure. A comparison between the calculated and measured values shows once again how accurate the model reproduces the empirical study.

Modeling the dielectric properties of wood

The present study developed and verified a ‘cold’ microwave (MW) treatment that could lead to the inactivation of two common pathogenic species of bacteria, Escherichia coli and Staphylococcus aureus, in raw meats. A number of experimental conditions were designed and tested to maximise MW exposure without overheating the samples. The non-thermal effect was maximised by multiple exposure to attain efficient MW threshold intensities. It was shown that at sub-lethal temperatures repeated exposure using high frequency MW radiation was significantly more effective in decontaminating bacteria in raw meats compared to a single exposure. It was concluded that non thermal inactivation of pathogenic bacteria in raw meats could be achieved at defined conditions using high frequency MW radiation.

https://researchbank.swinburne.edu.au/file/027785d5-3348-4c5b-a811-bb5c1bba7632/1/PDF (Published version).pdf

Development of a Microwave Treatment Technique for Bacterial Decontamination of Raw Meat

A method for measuring the dielectric permittivity of thick pieces of wood is presented together with a description of the software required to extract the dielectric parameters from the measured quantities via the solution of a transcendental equation in the complex plane. This specific experimental method was adopted as it is suitable for extension to measurements at elevated temperatures and pressures. The measuring procedure, the numeric scheme, and a general analysis of the solutions are demonstrated by a series of measurements conducted on soda lime glass. First results of Blue Gum (Eucalyptus globulus) wood measurements are also presented and reveal a strong dependence of the dielectric permittivity on the electric field direction and sample moisture content.

Measuring the dielectric properties of wood at microwave frequencies

Bioprosthetic valves created from chemically treated natural tissues such as bovine pericardial biomaterial are used as heart valve scaffolds. Methods currently available for sterilization of biomaterial for transplantation include the application of gamma radiation and chemical sterilants. These techniques, however, can be problematic because they can be expensive and lead to a reduction in tissue integrity. Therefore, improved techniques are needed that are cost effective and do not disrupt the physical properties, functionality, and lifespan of the valvular leaflets. This study examined a novel technique using nonthermal microwave radiation that could lead to the inactivation of bacteria in bovine pericardial biomaterial without compromising valve durability. Two common pathogenic species of bacteria, Escherichia coli and Staphylococcus aureus, were used as test microorganisms. Optimized microwave parameters were used to determine whether inactivation of pathogenic bacteria from bovine pericardium could be achieved. In addition, the effect of microwave sterilization on tissue integrity was examined. The mechanical properties (assessed using dynamic mechanical analysis) and tensile strength testing (using a Universal Tensile Tester) as well as thermal analysis (using thermogravimetric analysis and differential scanning calorimetry) indicated that microwave sterilization did not compromise the functionality of bovine pericardial biomaterial. Scanning electron microscopy imaging and cytotoxicity testing also confirmed that the structure and biocompatibility of transplant biomaterial remained unaltered after the sterilization process. Results from the application of this new microwave (MW) sterilization technique to bovine pericardium showed that near-complete inactivation of the contaminant bacteria was achieved. It is concluded that nonthermal inactivation of pathogenic bacteria from bovine pericardial biomaterial could be achieved using microwave radiation.

/pdf/a-new-sterilization-technique-of-bovine-pericardial-benf930m4b.pdf

A New Sterilization Technique of Bovine Pericardial Biomaterial Using Microwave Radiation

Through its industrial applications potential (i.e. drying, stress relief, structural modification for impregnation, bending and surface treatments to enhance coating), microwave processing could offer a powerful materialprocessing tool to wood industry. In order to scale up a microwave process, the development of the exploratory process to production scale has to be performed. This research basically depends on microwave-material interaction understanding. The main effect of microwave-material interaction is the conversion of microwave energy into heat within the material due to the absorption of the electromagnetic energy through the dielectric properties of the material. Wood is a very complex material with poor thermal conductivity and permeability. As a result, under the various industrial microwave processes, temperature within wood may range from 100o to 170oC giving rise to internal wood pressure of up to 7 atm. Variety of methods for measuring the relative complex permittivity has been described in the specialised literature. However, to obtain the dielectric properties of wood which are relevant to microwave heating, measurements at elevated temperatures and pressures have to be performed. Such research has not been undertaken before and requires the design of new equipment. The aim of this paper is to present a specially made device and the appropriate measuring procedure for measuring the dielectric properties of wood under high temperatures and pressures. To measure the dielectric permittivity of wood at microwave frequency of 2.45 GHz and under high temperatures and pressures, the short-circuit line measurement technique was selected due to its well suitability for high temperature measurements. The experimental set-up (Figure 1) consists of a VNA (HP 8720C) system connected to a standard waveguide which for high pressure and temperature convenience was extended with a special designed high-pressure cavity. Used as the sample holder, the cavity was manufactured from stainless steel waveguide with build-in pressure applicator and Pyrex pressure window (transparent to microwave and resistant to 150°C and 5 atm.). The cavity is ended with an attachable fixed short-circuit. The sample temperature is progressively increased by means of an electrical heater placed underneath the sample holder. An immersion probe inserted within the sample detects and reads the temperature. As the measurement aim is to simultaneously perform internal wood temperature and pressure of about 150°C and 5 atm. respectively, air pressure is applied inside the cavity and it is controlled by the pressure gauge. Figure 1: Experimental set-up For such configuration, when a wood sample of a certain thickness, which perfectly fits the sample holder cross section, is placed to the left of the shortcircuit, the VNA system measures the 1-port scattering parameters (which in this case is the reflection coefficient S11). Since the reflectivity at a point within the transmission line is related to the impedance at that point, the procedure used to determine the wood sample permittivity is based on the impedance change caused by the presence of the wood within the rectangular cavity. To solve the final Fiber optic thermometer Specimen holder VNA (HP 8720C) Electrical heater Temperature probe equation (a transcendental equation in the complex plan) which involves the sample length and reflection coefficient and from which the value of permittivity is extracted, a computer program solver was developed. Through its configuration, the solver gives all solutions in a given domain of the complex plane and each solution is obtained within an accuracy of 10. However, since the number of solutions is infinite, one has to make sure that the “right” physical solution for permittivity is one of the numerical solutions obtained. In principle, to peak the physical solution among all the mathematical solutions of the transcendental equation, another sample with a different thickness should be measured. The experience could also point out the physical solution. The method described above is suitable for measuring the dielectric permittivity of wood as long as the calibration of the measuring device includes elements like pressure windows, pumping air holes, etc. However, a special attention has to be directed to the measuring device calibration. Due to the thermal expansion of the pressure cavity components, the initial calibration precision is changing during the measurement process and will directly affect the results accuracy. Several measurements were performed on Mountain Ash (Eucalyptus regnans) wood samples with oven dry density of 0.75g/cm and different moisture contents (MCs). First results for permittivity (Fig. 2) were obtained in radial direction and for different temperatures and related pressures. Figure 2: Mountain Ash dielectric parameters at high temperatures and pressures Dielectric Parameters Mountain Ash: ρ0=0.75 g/cm , radial direction -

/pdf/measuring-the-dielectric-properties-of-australian-wood-2aucnxpkfg.pdf

Yury Shramkov

Papers

Modeling the dielectric properties of wood

Development of a Microwave Treatment Technique for Bacterial Decontamination of Raw Meat

Measuring the dielectric properties of wood at microwave frequencies

A New Sterilization Technique of Bovine Pericardial Biomaterial Using Microwave Radiation

Measuring the dielectric properties of Australian wood species