Woon T. Ang

Applications of Ultrasound to Enhance Mycophenolic Acid Production

Reducing production costs for fermentation-based drugs (e.g., antibiotics) is crucial for the long-term sustainability of healthcare. In this study, we propose a novel low-intensity pulsed ultrasound (LIPUS) stimulation scheme using a nominal frequency of 1.5 MHz with a 20% duty cycle (200 μs ultrasound on and 800 μs ultrasound off) to increase production of fermentation-based drugs. We chose Penicillium brevicompactum as a model system to demonstrate the performance of our LIPUS system. Penicillium brevicompactum can produce mycophenolic acid (MPA), an immunosuppressive agent commonly used to prevent rejection after organ transplantation. We have stimulated Penicillium brevicompactum in 50 mL shake flasks using LIPUS during its fermentation. After a series of screening experiments to optimize ultrasound parameters (e.g., ultrasound intensities, treatment duration and treatment frequency per day), it was concluded that ultrasound stimulation can increase MPA production by as much as 60% when treated eight times a day for 10-min durations at an intensity (spatial peak temporal average) of 200 mW/cm(2). These findings elucidate a new approach to reduce the cost of producing fermentation-based drugs.

Design and Implementation of Therapeutic Ultrasound Generating Circuit for Dental Tissue Formation and Tooth-Root Healing

Biological tissue healing has recently attracted a great deal of research interest in various medical fields. Trauma to teeth, deep and root caries, and orthodontic treatment can all lead to various degrees of root resorption. In our previous study, we showed that low-intensity pulsed ultrasound (LIPUS) enhances the growth of lower incisor apices and accelerates their rate of eruption in rabbits by inducing dental tissue growth. We also performed clinical studies and demonstrated that LIPUS facilitates the healing of orthodontically induced teeth-root resorption in humans. However, the available LIPUS devices are too large to be used comfortably inside the mouth. In this paper, the design and implementation of a low-power LIPUS generator is presented. The generator is the core of the final intraoral device for preventing tooth root loss and enhancing tooth root tissue healing. The generator consists of a power-supply subsystem, an ultrasonic transducer, an impedance-matching circuit, and an integrated circuit composed of a digital controller circuitry and the associated driver circuit. Most of our efforts focus on the design of the impedance-matching circuit and the integrated system-on-chip circuit. The chip was designed and fabricated using 0.8- ¿m high-voltage technology from Dalsa Semiconductor, Inc. The power supply subsystem and its impedance-matching network are implemented using discrete components. The LIPUS generator was tested and verified to function as designed and is capable of producing ultrasound power up to 100 mW in the vicinity of the transducers resonance frequency at 1.5 MHz. The power efficiency of the circuitry, excluding the power supply subsystem, is estimated at 70%. The final products will be tailored to the exact size of teeth or biological tissue, which is needed to be used for stimulating dental tissue (dentine and cementum) healing.

Applications of low-intensity pulsed ultrasound to increase monoclonal antibody production in CHO cells using shake flasks or wavebags.

Many technologies, such as cell line screening and host cell engineering, culture media optimization and bioprocess optimization, have been proposed to increase monoclonal antibody (mAb) production in Chinese Hamster Ovary (CHO) cells. Unlike the existing biochemical approaches, we investigated stimulation using low-intensity pulsed ultrasound (LIPUS) as a purely physical approach, offering enhanced scalability, contamination control and cost-efficiency, while demonstrating significantly increased cell growth and antibody production. It was found that daily ultrasound treatments at 40 mW/cm(2) for 5 min during cell culture increased the production of human anti-IL-8 antibody by more than 30% using 10 or 30 mL shake flasks. Further increasing the ultrasound dosage (either intensities or the treatment duration) did not appreciably increase cell growth or antibody production, however feeding the culture with additional highly-concentrated nutrients, glucose and amino acids (glutamine in this case), did further increase cell growth and antibody titer to 35%. Similar ultrasound treatments (40 mW/cm(2), 5 min per day) when scaled up to larger volume wavebags, resulted in a 25% increase in antibody production. Increased antibody production can be attributed to both elevated cell count and the ultrasound stimulation. Theoretical study of underlying mechanisms was performed through the simulations of molecular dynamics using the AMBER software package, with results showing that LIPUS increases cell permeability. The significance of this study is that LIPUS, as a physical-based stimulation approach, can be externally applied to the cell culture without worrying about contamination. By combining with the existing technologies in antibody production, LIPUS can achieve additional mAb yields. Because it can be easily integrated with existing cell culture apparatuses, the technology is expected to be more acceptable by the end users.

Ensemble Dependent Matrix Methodology for Probabilistic-Based Fault-tolerant Nanoscale Circuit Design

Two probabilistic-based models, namely the ensemble-dependent matrix model (Chen and Li, 2006), (Patel et al., 2003) and the Markov random field model (Chen et al., 2003), have been proposed to deal with faults in nanoscale system. The MRF design can provide excellent noise tolerance in nanoscale circuit design. However, it is complicated to be applied to model circuit behavior at system level. Ensemble dependent matrix methodology is more effective and suitable for CAD tools development and to optimize nanoscale circuit and system design. In this paper, we show that the ensemble-dependent matrices describe the actual circuit performances when signal errors are present. We then propose a new criterion to compare circuit error-tolerance capability. We also prove that the matrix model and the Markov model converge when signals are digital

A clock-fault tolerant architecture and circuit for reliable nanoelectronics system

Due to discrepancies in manufacturing process and the probabilistic nature of quantum mechanical phenomenon, nanoelectronic devices cannot be made as reliable as current microelectronic devices. As a result, fault-tolerant architectures are a prerequisite to building reliable electronic systems from these unreliable nanoelectronic devices. One important design aspect of nanoelectronic architecture that demands attentive consideration is clock generation and distribution. Various defects and interference such as doping discrepancies, supply noise and cross-talks could lead to clock irregularity and malformed clock signals, thus resulting in faulty operations of sequential circuits. Generally, these errors are not readily amenable to efficient correction using error-correcting codes known to date. In this paper, we propose a novel fault-tolerant architecture for a parallel computation structure. The fault-tolerance capabilities built into this architecture allow for effective remedy against the deleterious effects of random clock abnormality and reduce the probability of computational errors. Central to the operation of the proposed fault-tolerant architecture is a novel clock-fault detection circuitry. In order to illustrate the fault- tolerance capability rendered by the detection circuitry, an error probability analysis is performed. Finally, a prototype CMOS design of this proposed circuit that consists of only 28 transistors and 2 capacitors is presented. Our simulation shows that with only a two-fold increase in hardware counts, the proposed architecture can gain significant fault-tolerance capability.

System-on-chip ultrasonic transducer for dental tissue formation and stem cell growth and differentiation

Conventional ultrasound designs are used for medical therapeutics including different tissue healing and medical imaging. Recently, we discovered that the low intensity pulsed ultrasound (LIPUS) can help stimulate dental and bone tissue growth. However, the size of available ultrasound devices is too large to fit inside the mouth.,. In this paper, we present the design of a system-on-chip ultrasonic device for dental tissue formation and stem cell growth differentiation. The device helps tissue healing by stimulating formation of new blood vessels and different tissue matrix formation, like bone, dentin and cementum. Testing results show that our prototype device can stimulate stem cells to grow and differentiate into bone forming cells.

An efficient methodology to evaluate nanoscale circuit fault-tolerance performance based on belief propagation

As silicon circuits quickly approach their physical limitations, researchers are actively looking for novel building blocks to develop nanocircuits. However, future nanoelectronic circuits are more error-prone than conventional CMOS designs because of their self-assembly design. To help design fault-tolerant nanoscale circuits, new circuit design and testing tools are needed. In this paper, an efficient methodology to evaluate nanoscale circuit fault tolerance based on belief propagation (BP) algorithm is proposed. Compared with existing approaches, the BP algorithm is more efficient in terms of memory requirements and CPU times. The proposed methodology can be easily run on multiple CPUs to achieve parallel processing and thus further reduces simulation time.

Design and Characterization of a Close-Proximity Thermoacoustic Sensor

Although the radiation force balance is the gold standard for measuring ultrasound intensity, it cannot be used for real-time monitoring in certain settings, for example, bioreactors or in the clinic to measure ultrasound intensities during treatment. Foreseeing these needs, we propose a close-proximity thermoacoustic sensor. In this article, we describe the design, characterization, testing and implementation of such a sensor. We designed a 20-mm-diameter plexiglass sensor with a 2-mm-long absorber and tested it against low-intensity pulsed ultrasound generated at a 1.5-MHz frequency, 20% duty cycle, 1-kHz pulse repetition frequency and intensities between 30 and 120 mW/cm(2). The sensor captures the beam, converts the ultrasound power into heat and indirectly measures the spatial-average time-average ultrasound intensity (Isata) by dividing the calculated power by the beam cross section (or the nominal area of the transducers). A thin copper sheet was attached to the back face of the sensor with thermal paste to increase heat diffusivity 1000-fold, resulting in uniform temperature distribution across the back face. An embedded system design was implemented using an Atmel microcontroller programmed with a least-squares algorithm to fit measured temperature-versus-time data to a model describing the temperature rise averaged across the back side of the sensor in relation to the applied ultrasound intensity. After it was calibrated to the transducer being measured, the thermoacoustic sensor was able to measure ultrasound intensity with an average error of 5.46% compared with readings taken using a radiation force balance.

Close-proximity, real-time thermoacoustic sensors: Design, characterization, and testing

This paper describes the design, characterization, and testing of a close-proximity, real-time thermoacoustic sensor for ultrasound intensity measurements. Plexiglass sensors, 20 mm diameter and 3.3 mm length, absorbed ultrasound with a frequency of 1.5 MHz, a 20% duty cycle, and a 1 kHz pulse repetition frequency, at intensities between 30 and 100 mW/cm2. An embedded system design fit thermistor temperature data to a curve relating the temperature rise averaged across the backside of the sensor to the applied ultrasound intensity, and calculated the corresponding ultrasound intensity. Good linearity was demonstrated between the ultrasound intensity measured using a radiation force balance, and intensity measured using the thermoacoustic sensor when placed in contact with the acoustic transducer: accuracy within 5% of the target value and standard deviation of 4.55% or less. The sensor has an operational temperature range of 22°C to 26°C. This design makes for a quick and convenient method of checking ultrasound intensity, and also presents the possibility of integrated sensor and ultrasound generator systems using feedback loops to achieve auto-calibration.

Developing a thermoacoustic sensor adaptive to ambient temperatures

In this paper, a simple and adaptive thermoacoustic sensor was designed to measure Low Intensity Pulsed Ultrasound (LIPUS). Compared to other thermoacoustic sensor designs, our novelty lies in (i) integrating an ultrasound medium layer during the measurement to simplify the complicated set-up procedures and (ii) taking the effect of ambient temperatures into design consideration. After measuring temperature increases with various ambient temperatures under different ultrasound intensities, a relationship among ultrasound intensities, ambient temperatures and coefficients of temporal temperature changes was calculated. Our improved design has made the sensor easy to operate and its performance more accurate and consistent than the thermoacoustic sensor designs without considering ambient temperatures. In all, our improved design greatly enhances the thermoacoustic sensor in practical ultrasound calibration.