Three-Dimensional Microfabrication System for Biodegradable Microdevices With High-Resolution and Bio-Applicability

Biodegradable polymers are employed in medicine and its further application is expected with eagerness. But the lack of an appropriate processing method retards the progress. To overcome this problem, we have developped a novel three-dimensional microfabrication system. The system design allows us the processing of the free three-dimensional micro-level forms by stacking up melted polymers from the nozzle. Different from the conventional method, we adopted a batch process to supply materials in order to eliminate the prior process that required toxic solvents. In addition, it is possible to handle almost all biodegradable thermoplastic resins by adopting this system. A single layer from the piled-up layers of extruded lines was observed to evaluate the resolution. The lateral and depth resolutions attained are 40 μm and 45 μm, respectively. Biodegradable polymers enable three-dimensional microstructures such as micro-pipes, micro-bends, and micro-coil springs to be manufactured in less than 15 min. The biocompatibility of the newly fabricated structure was evaluated using a cell line (PC12). For this purpose, a small vessel, with a transparent base, was fabricated using PLA and cells were cultivated in it. The results were then compared with the results obtained using the standard method. The mechanical strength of our microstructures was evaluated using a tensile strength test. The tensile strength of the microstructure was lower than the one obtained from the conventional method, but has enough strength for fabrication of medical devices. Our system renders it possible to produce toxic-free, as well as transparent and leakage-free devices. Our system is expected to have potential applications in optimum design and fabrication of implantable devices, especially in tissue engineering.

Mechanical Neural Growth Models

Critical to being able to control the growth patterns of cell-based sensors is being able to understand how the cytoskeleton of the cell maintains its structure and integrity both under mechanical load and in a load-free environment. Our approach to a better understanding of cell growth is to use a computer simulation that incorporates the primary structures, microtubules, necessary for growth along with their observed behaviors and experimentally determined mechanical properties. Microtubules are the main compressive structural support elements for the axon of a neuron and are created via polymerization of α-β tubulin dimers. Our de novo simulation explores the mechanics of the forces between microtubules and the membrane. We hypothesize that axonal growth is most influenced by the location and direction of the force exerted by the microtubule on the membrane, and furthermore that the interplay of forces between microtubules and the inner surface of the cell membrane dictates the polar structure of axons. The simulation will be used to understand cytoskeletal mechanics for the purpose of engineering cells to be used as sensors.

Micromachined Electrical Conductivity Probe for RF Ablation of Tumors

RF ablation is an important technique in cancer treatment. It has been proposed that the effective area treated via RF ablation can be increased by increasing the local electrical conductivity. This is achieved by injection of NaCl solution into the tissue. For an accurate and effective RF ablation treatment using this new method, it is necessary to measure the local electrical conductivity, which varies spatially due to diffusion of sodium chloride. In this paper, we propose a micro probe to measure the local tissue electrical conductivity. The probe consists of two in-plane miniature electrodes separated by a small gap. When the electrodes are in contact with the tissue, the electrical resistance across them can be used to calculate the electrical conductivity. The probe is fabricated by standard photolithography techniques. The substrate material is polyimide and the electrodes are made of gold. A four-electrode probe is used to calibrate the new electrical conductivity micro probe using different concentrations of saline water. The resistance measurements are carried out using an impedance analyzer on different frequencies. The frequency of choice for RF ablation of tumors is 500k Hz and is the one selected for calibration and testing. The micro-probe calibration is then verified by measuring electrical conductivity of a phantom and comparing it with the result measured by the four-electrode probe. Finally, some in vivo tests are performed and the results are compared with literate data.

Dynamic Digital Image Correlation of a Dynamic Physical Model of the Vocal Folds

An experimental study of the vibratory deformation of the human vocal folds was conducted. Experiments were performed using model vocal folds [1, 2], Fig. 1, made of silicone rubber implemented into an air supply system, Fig. 2. The material used to cast the model is an isotropic homogeneous material, [3] with a tangent modulus E=5 kPa at ε = 0, i.e. elastic properties similar to those of the human vocal fold cover [4]. The advantages of the use of model larynx systems over the use of excised larynges include easy accessibility to fundamental studies of the vocal fold vibration without invasive testing. Acoustic analysis of voice or electroglottography provide certain insight into voice production processes but optical techniques for the study of vocal fold vibrations have drawn considerable attention. Videoendoscopy, stroboscopy, high-speed photography, and kymography have shown to provide a visual impression of vocal fold dynamics but are limited in providing insight into the fundamental deformation processes of the vocal folds. Quantitative measures of deformation have been conducted through micro-suture techniques but are invasive and allows for measurements of only view image points. Laser triangulation is non-invasive but is limited to only one local measurement point. Here, digital image correlation technique with the software VIC 3D [5] is applied. For the experimental set-up see Fig. 2. The analysis consists of (1) stereo correlation to obtain in-plane displacements and (2) stereo triangulation step to obtain out-of-plane deformation. For the stereo correlation images of the object at two different stages of deformation are compared. A point in the image of the undeformed object is matched with the corresponding point in the deformed stage. “Subsets” of digital images are traced via their gray value distribution from the undeformed reference image to the deformed image. The uniqueness of the matching is enabled by the creation of a speckle pattern on the object’s surface. Here, a white pigment is mixed into the silicone rubber and subsequently black enamel paint is sprayed onto the superior surface of the vocal folds. The stereo triangulation requires two images of the object at each stage of deformation. These are obtained in a single CCD frame by placing a beam splitter in the optical axis between camera and object. These images provide a “left” and “right” view of the model larynx. Thus, the deformed shape of the vocal folds can be obtained. The method allows for noninvasive measurement of the full-field displacement fields. Images of the superior surface of the model larynx are obtained by the use of a high speed digital camera with a frame rate of 3000 frames per second allowing for more than 30 image frames for each vibration cycle. For the 3D digital image correlation analysis two images of the object are obtained for each time instance as a beam splitter is placed in the optical axis between the camera and the model larynx. Phonation frequencies and onset pressure are given in Fig. 3, showing that the model larynx behavior is close to actual physiological data. Figs 4(a) and (b) provide superior views of the model larynx at maximum glottal opening and at glottal closure, respectively. As one example of measured strain fields, Figs 5(a) and (b) depict the distributions of the transverse strain component, on the glottal surface in a contour plot on the deformed superior surface. The knowledge of the distribution of this strain component is relevant to the assessment of the impact of vocal fold collision on potential tissue damage. In the position of maximum opening the vocal folds are deformed by a combination of a bulging-type deformation and the opening movement. At this time instance, the transverse strains at the medial surface are found to be negative, an indication of Poisson’s deformation. During the closing stage, vocal folds collide and simultaneously a mode 3 vibration pattern emerges. Closure of the glottal opening is not complete and two incomplete closure areas are formed during the closure stage. These open areas are located at the anterior and posterior ends of the model larynx, see Fig. 4(b). The finding of this type of incomplete closure is agreement with both actual glottal measurements [6] and 3D finite element simulations of [7]. Transverse strains during that stage are now positive and considerably larger that during the opening stage. Finally, Fig. 6 depicts the time evolution of the out of plane displacements along the medial surface for the closing phase and Fig. 7 depicts the maximum values of the longitudinal strain (at the coronal section of the medial surface) in dependence of the flow rate. These examples of measurements indicate that the DIC method is promising for studies of vocal fold dynamics.

Automated Sample Preparation System for Rapid Biological Threat Detection

Rapid, automated sample preparation of bacterial cells and spores is required for threat analysis by remotely deployed chemical and biological warning systems. Sandia is designing, building, and testing an automated front-end sample preparation system based on miniature and microfluidic components, with the goal of concentrating bacterial species collected from the air, harvesting and solubilizing proteins from them, and delivering them to Sandia’s MicroChemLab capillary gel electrophoresis system1,2 for analysis (Fig. 1). Miniature, motorized valves and pumps control flow between system components connected by fused silica capillaries (Fig. 4). Sample processing modules include concentration by dielectrophoresis in an array of insulating posts or by mechanical filtration; heat-activated chemical lysis; mechanical filtration; removal of chemical lysis agents by size exclusion chromatography (SEC); and in-capillary fluorescent labeling.

Towards Acoustic Vibration as a Diagnostic Tool for Spinal Fractures

The diagnostic tools for clinicians to detect vertebral body fractures are limited to radiation technologies1, such as X-ray and CT. The objective is to identify shape changes that reflect bone tissue failure. Because this method is subjective, only crude changes of 15% and more in vertebral height can be detected2. From in-vitro laboratory experiments it is know that the ultimate load is reached at deformations much less than 5%, and is generally detected before any shape changes are visible in radiographic images3. Acoustic vibration is a promising technique to detect changes in material integrity and quality. The overall goal of this study was to investigate the use of acoustic vibration to detect spinal fractures.

Fluorescent Melting Curve Analysis Compatible With a Flowing Polymerase Chain Reactor

A primary tool for analysing PCR product is the Fluorescent Melting Curve Analysis (FMCA). The temperature at which a double helix DNA strand denatures depends both on its length and base pair composition. Accurate measurement of this melting temperature using fluorescence allows estimations be made regarding DNA product length and composition. Current progress in development of PCR thermal cyclers has been primarily aimed at micro-channel based flowing devices. This paper addresses the challenges associated with performing FMCA analysis which is compatible with the output from a flowing PCR thermocycler. Two PCR products of significantly different lengths and base pair composition are compared using space domain FMCA. Results allow for differentiation of the PCR product, and compare favourably with results from a commercial thermal cycler. The successful application of FMCA within a channel shows its potential for use in high throughput flow based total analysis systems (μTAS).

Prototype of Microcapsule Including a Gas Bubble for Developing Shock Wave Drug Delivery Systems

This paper describes the trial of making microcapsules including a bubble for shock wave drug delivery systems and evaluation of their mechanical properties. We have proposed drug delivery systems (DDS) using shock waves in order to apply micro/nano technology in the fields of biomedical engineering. In this system, a microcapsule including a gas bubble is flown in the blood vessel, and finally broken by shock induced microjet, then drug is reached to the affected part in the body as same as traditional DDS. In this paper, the mechanism for deformation and disintegration of capsules in our previous works is reviewed, and the trials of making special microcapsules are discussed. To determine Young’s modulus of capsule membrane mentioned above, the membrane is deformed by the aspiration device and the deformation is compared with computational result by FEM.

An Ultrasonic Based System to Measure Inter Spinous Process Distance in Humans: A Pilot Study

The objective of this research project was to develop an ultrasonic based testing system and evaluate its application on human volunteers to locate and assess the distance between adjacent lumbar vertebrae. Tests were performed on ten volunteers aged between 19 and 29 years old during two sessions. The participants were asked to lie face down on a table with lower back section uncovered while the tests were executed. A computer controlled ultrasonic system was designed for this application. A single element 3.5 MHz immersion transducer held by a customized assembly was used to propagate and receive the ultrasonic signals. The transducer was moved along the assembly to fully scan at least two contiguous spinous processes. A Lab view based program was designed to generate a two-dimensional image (B-scan) that display the shape and position of the bone tips as well as the distance between them. The standard deviation obtained from the measurements of the distance between the tips of the spinous processes of human subjects, in a given session ranged from 0.1–0.48mm. The difference between two sessions had a mean of 0.85–0.95 mm and a standard deviation of 0.87–1.03mm with reliability coefficients greater than 0.95. The study demonstrated the viability of utilizing ultrasound to precisely measure the distance between spinous processes of adjacent lumbar vertebrae.

Dynamic Response of Normal and Osteoporotic Trabecular Bone by Vibration Analysis

Osteoporosis afflicts about 200 million people worldwide; and osteoporotic fractures are in the millions annually in the US alone and cost tens of billions of dollars [1]. Characterization of bone quality in osteoporotic patients is important with respect to monitoring treatment efficacy, though currently quite limited. While some technical hurdles in developing a noninvasive diagnostic tool using low frequency vibration have been overcome, changes in the frequency response signal of bone have not been investigated at the various bone organizational levels. Our principal hypothesis is that the vibrational modes of bone tissue change significantly with the deterioration of bone micro-architecture and that these modes can be captured by noninvasive sensors.