Thermal Analysis for Cryosurgery of Nodular Basal Cell Carcinoma

Basel cell carcinoma (BCC) is the most common human skin malignancy. Its incidence has increased significantly in Australia, Europe and North America over the past decade. A number of modalities are currently used for treatment of BCC, including cryosurgery which offers a potential for high cure rate, low cost, minimal bleeding and good cosmetic effect. However, cryosurgery is not used frequently for BCC because no current method exists to design adequate treatment parameters. We present a numerical analysis on the thermal history of the target tissue during cryosurgery of a nodular BCC using liquid nitrogen (LN2) spray. The model uses Pennes equation to describe the heat transfer within the target tissue. A convective thermal boundary is used to describe the heat interaction between the tissue and LN2, and the apparent heat capacity method is applied to address the tissue phase change process. A parametric study is conducted on the convective heat transfer coefficient (hs: 104~106 W/m2·K), cooling site area (rs/R0: 0.5~1.0) and spray time (t: 0~30 sec.), with the objective to understand the thermal history during tissue freezing, including lethal temperature (-50 °C) and cooling rate (CR). Results demonstrate that propagation of the lethal isotherm is sensitive to the convective heat transfer coefficient, hs, with a range of 104~5×104 W/m2·K. Increasing the cooling site area can significantly enhance cooling efficiency, producing dramatic increase in the amount of tissue encompassed by the lethal isotherm. The cooling rate (CR) shows a highly dynamic distribution during the cooling process: the highest CR drops quickly from 140 °C/sec. (t=0.5 sec.) to 20 °C/sec. (t=5 sec.). The highest CR is initially located close to the cooling site but moves toward the inside of the tissue as treatment proceeds. The model presented herein provides a simulation tool for treatment planning of cryosurgery using LN2 spray, in which the protocol parameters, e.g. cooling site area and spray time, can be determined for an optimal outcome. The quantitative predictions on the propagation of lethal isotherm and the distribution of CR should help to optimize cryosurgery efficacy.

Monotonic Growth of Motile Microorganisms

The research results presented here are part of a more extensive effort regarding sustained bioconvection in porous media. Bioconvection is the phenomenon of gravity driven fluid motion due to buoyancy forces resulting from density differences between the fluid and motile micro-organisms suspended in the fluid. While the field of bio-convection in pure fluids emerged substantially over the past decade the corresponding effects of bio-convection in porous media received much less attention, despite the fact that micro-organisms grow naturally in porous environments; soil, food and human tissues serve as basic examples. The research focuses in two major new directions. The first deals with the theoretical and experimental investigation of bio-convection in porous media. The second major new direction is linked to the sustainability of the bio-convection motion. The existing work on bio-convection in both pure fluids and porous media exclude micro-organism growth during the bio-convection because the time scales concerned were very short. However, when the question of the sustainability of this convection over long times arises, microorganism growth has to be accounted for. If sustained bio-convection in porous media is possible it opens the avenue to investigate its impact on microbial proliferation in soil, food and human tissue, an important avenue for application of the theoretical results. Then, if bio-convection enhances microbial proliferation it may be undesirable in some cases, e.g. in food, or it might be desirable if specific micro-organisms that can be used for contaminated soil remediation will be "helped" by the bio-convection process to access contaminated regions in the soil. The theoretical and experimental results presented in this paper reflect the process of monotonic growth of motile microorganisms (e.g. the PAOI strain of Pseudomonas Aeruginosa) to be included in the bioconvection process. A new proposed model is shown to be the appropriate one to better reflect both conceptually as well as practically the microbial growth process.

Design, Simulation and Testing of Shape Memory Alloy Actuator for Mixing Two Solutions in High-Pressure Optical Cell for Biophysical Studies

Window-type high-pressure optical cells (HPOC) such as the one designed by Paladini and Weber [Rev. Sci. Instrum. 52, (1981) p. 419] have provided biophysicists a powerful tool to understand the structure-function relationships of biological molecules. However, the conventional HPOC is only good for single solution testing and does not allow for quick mixing and stirring of additional components while the sample is under pressure. To mix two solutions under pressure, Zhou et al [Rev. Sci. Instrum. 69, (1998) p. 3958] developed a laser activated dual chamber HPOC. However, the expensive laser device and its unavailability in most laboratories make the application difficult. In a later study, Zhou et al. [Rev. Sci. Instrum. 71, (2000) p. 4249] introduced shape memory alloy (SMA) as an actuator to unplug a urethane stopper with a biasing spring for agitation. The drawback is that the biasing spring blocks the observing light beam and creates unwanted reflections. This research is to construct an actuator with concentric SMA spring and compressive biasing spring: an SMA helical tensile spring to pull out the stopper to let two solutions mix; and a helical compressive spring to bias and to agitate solutions, and to leave the lower half cuvette clear for optical observation. Due to the limited space in the cuvette, the alignment of two springs is critical for both motion and heat response to activate each spring separately. This paper discusses the design of SMA actuator, SMA spring testing and mixing testing by the SMA spring actuator. Since SMA (nickel-titanium) spring is not solderable and crimping method is limited due to the space, a conductive adhesive is used not only to fix the alignment between springs and cap, but also to conduct electric current. Spring force testing was done by INSTRON. Mixing testing used flourescein intensity change to trace the mixing process. The bio-compatibility of the nickel-titanium SMA with proteins and phospholipids has also been tested.

Microfabricated Electrode Array Compatible With Optical Imaging of Intrinsic Signals During Somatosensory Stimulation and Cortical Spreading Depression

Accurate interpretation of functional brain images requires knowledge of the relationship between neurons and their supporting cells and vasculature. Our understanding of this complex and dynamic system would improve if we measure multiple aspects of brain function simultaneously. We have developed a semi-transparent electrode array which allows for concurrent multi-site electrophysiological recording and high-resolution optical imaging of intrinsic signals. The 8-channel electrode array is fabricated on a transparent glass substrate with platinum recording surfaces. We map stimulus-induced field potentials (evoked potentials) and changes in cerebral blood volume in rat somatosensory cortex. We also examine the evolution of these responses during the neuro-pathological state of cortical spreading depression. We have developed a planar multi-electrode array that is fully compatible with Optical imaging of Intrinsic Signals. It provides a sensitive and reliable tool to use in the study of neurovascular coupling in brain activation.

Grasping Contact Analysis of Viscoelastic Materials With Applications in Minimally Invasive Surgery

This paper presents a method to determine the contact force and pressure on the surface of viscoelastic objects grasped by an endoscopic grasper, used in Minimally Invasive Surgery (MIS). Normally, an endoscopic grasper is corrugated (teeth-like) in order to grasp slippery tissues. It is highly important to avoid damage to the tissues during grasping and manipulation in endoscopic surgery. Therefore, it is essential to determine the exact contact force on the surface of the tissue. To this end, initially a comprehensive closed form analysis of grasping contact force and pressure on elastic and particularly viscoelastic materials which have similar behavior as that of biological tissues is studied. The behavior of a rigid grasper with wedge-like teeth, when pressed into a delayed elasticity material is being examined. Initially, a single wedge penetrating into a solid is studied and then is extended to the grasper. The elastic wedge indentation is the basis of this study and the effects of time are included in the equations by considering the corresponding integral operator from viscoelastic stress-stain relations. Under the action of a constant normal load, the penetration of the indenter and the contact area will change. In this research, the variation of the contact area with time and the grasping contact force is studied. The results of this study which provides a closed form expression for grasping contact force and contact area are compared with those from elastic analysis.

Polymer Grippers as End-Effectors for Biological Sample Manipulation

We report the development of completely releasable SU-8 based polymer microgripper and the manipulation of normal rat kidney (NRK) cells suspended in phosphate buffered saline (PBS) solution using a generic biological sample manipulator, which incorporates such a polymer microgripper as an end-effector. The electrically insulative polymer gripper consists of a thick (~50 μm), patterned high aspect ratio (~5:1) layer of SU-8 as the structural layer and a thin nickel layer as the electrothermal heating layer. The fabricated polymer gripper was completely released from the substrate and mounted onto a ceramic pad. The gripper was characterized in air and PBS, and the displacement at the tips was 12 μm for 0.5 V in air and for 2 V in PBS. The mounted gripper was assembled as end-effector onto a biological nano-manipulator (L200, Zyvex Corporation, Richardson, TX). Pick-and-place of a single cell from a cluster of suspended cells in aqueous medium has been demonstrated using this set-up.

Microbial Dynamics Subject to Metabolic Mass Transfer

Accounting for metabolic mass transfer and abiotic resource dynamics is not common in modeling microbial population growth. In this paper it is demonstrated that the latter is an essential feature that needs to be considered if reliable results are sought. The results of a model that takes the metabolic mass transfer and abiotic resource dynamics into account are shown to capture a variety of features that appear in experiments such as a Lag phase, a Logarithmic Inflection Point, growth followed by decline and oscillations. The results have a wide variety of implications and applications, from food microbiology and wine fermentation, up to human cell growth, where the latter includes tumor growth.

Modeling of the Dynamic Surface Profile in Magnetic Fluid Mirrors

Magnetic fluid deformable mirrors (MFDMs) present a simple alternative to the expensive and delicate wavefront correctors currently in use in adaptive optics (AO) systems. Such mirrors are particularly suitable for retinal imaging AO systems. The practical implementation of a retinal imaging AO system incorporating a MFDM requires an effective control system to control the shape of the mirror surface. The real-time control of the mirror surface requires a model of the mirror that can be used to determine the dynamic response of the mirror to a magnetic field applied as the control input. This paper presents such a model that not only determines the dynamic response of the MFDM but also takes into account the unique requirements of the retinal imaging application of the mirrors. The mirror is modeled as a horizontal layer of a magnetic fluid. The dynamic response of the mirror to the applied magnetic field is represented by the deflection of the free surface of the layer. The surface deflection is determined by the modal analysis of the coupled fluid-magnetic system. Considering the requirements of the retinal imaging application, the effects of surface tension and depth of the fluid layer are duly represented in the model. The mirror model is described in a state-space form and can be readily used in the design of a controller to regulate the mirror surface shape.

Quantifying the Effect of Pressure Oscillations on the Respiratory System: An Engineering Approach

The use of respiratory support devices using pressure oscillations has been shown to improve alveolar recruitment in animals and provide clinical benefits over traditional ventilators to infants with respiratory distress syndrome (RDS). The interactions and mechanisms of human lungs with such "bubble oscillation" (BO) devices is unknown. A simple mathematical model of the respiratory system and a BO type device is developed to explore the use of a new assessment parameter to study the effect of the pressure oscillations on lung performance. A mean square spectral density (MSSD) approach is employed in an attempt to observe the contribution of each pressure oscillation frequency on the work rate of unhealthy lungs. Further improvements to the respiratory system model are suggested for more detailed studies into human lung interactions with BO type devices.

Modeling of a Novel Multi-Jet Emitter for ESI-MS Applications

This paper presents the concept and simulation of a novel multiple electrospray emitters for electrospray ionization mass spectrometric (ESI-MS) applications. The proposed emitter is based on an array of carbon nanofibers (CNF) vertically grown around the orifice of a microscale thermoplastic capillary. The electrospray ionization process is simulated using a CFD code that utilizes Taylor-Melcher leaky-dielectric formulations for the electrohydrodynamics and volume-of-fluid (VOF) method for tracking the interface. The modeling results predict that under steady state conditions, individual cone-jets are established around each of the CNFs resulting in an array of electrosprays. Effects of several design and operational parameters on the electrospray performance are thoroughly investigated. The results of the present study will facilitate design, fabrication and experiments using the CNF emitter. Higher spray current and lower jet diameter indicate that the proposed emitter can perform equivalent to nanospray emitters exhibiting improved MS sensitivity while using a microscale orifice. Use of microscale orifice benefits in terms of higher sample throughput and eliminates potential clogging problem inherent in nanoscale capillaries. Overall, the proposed emitter is believed to be a suitable candidate for ESI-MS applications.