A microfluidics device to monitor platelet aggregation dynamics in response to strain rate micro-gradients in flowing blood

This paper reports the development of a platform technology for measuring platelet function and aggregation based on localized strain rate micro-gradients. Recent experimental findings within our laboratories have identified a key role for strain rate micro-gradients in focally triggering initial recruitment and subsequent aggregation of discoid platelets at sites of blood vessel injury. We present the design justification, hydrodynamic characterization and experimental validation of a microfluidic device incorporating contraction–expansion geometries that generate strain rate conditions mimicking the effects of pathological changes in blood vessel geometry. Blood perfusion through this device supports our published findings of both in vivo and in vitro platelet aggregation and confirms a critical requirement for the coupling of blood flow acceleration to downstream deceleration for the initiation and stabilization of platelet aggregation, in the absence of soluble platelet agonists. The microfluidics platform presented will facilitate the detailed analysis of the effects of hemodynamic parameters on the rate and extent of platelet aggregation and will be a useful tool to elucidate the hemodynamic and platelet mechano-transduction mechanisms, underlying this shear-dependent process.

A pilot randomized controlled crossover study comparing regional heparinization to regional citrate anticoagulation for continuous venovenous hemofiltration

OBJECTIVE: To evaluate the efficacy and safety of a regional heparinization and a regional citrate method of anticoagulation in CVVH.
DESIGN: Randomized controlled cross-over study.
SUBJECTS: Ten critically ill patients with acute renal failure.
SETTING: ICU of tertiary hospital.
INTERVENTION: CVVH was performed with pre-filter fluid replacement at 2000 ml/h and a blood flow rate of 150 ml/min. Regional heparinization was by the administration of heparin pre-filter at 1500 IU/h and protamine post-filter at 15 mg/h. Regional citrate anticoagulation was by means of a citrate-based replacement fluid (14 mmol/L) administered pre-dilution.
RESULTS: We studied nine males and one female. The mean age and APACHE II score were 70.5 and 17 respectively. Median circuit life was 13 hours (IQR 9.28) for the regional heparinization method compared to 17 hours (IQR 12,19.5) for the regional citrate method (p=0.77). There were no episodes of bleeding in either group.
CONCLUSION: Regional heparinization and regional citrate anticoagulation achieve similar circuit life in critically ill patients receiving CVVH.

Development of a novel pulsatile bioreactor for tissue culture

The construction of tissue-engineered parts such as heart valves and arteries requires more than just the seeding of cells onto a biocompatible/biodegradable polymeric scaffold. It is essential that the functionality and mechanical integrity of the cell-seeded scaffold be investigated in vitro prior to in vivo implantation. The correct hemodynamic conditioning would lead to the development of tissues with enhanced mechanical strength and cell viability. Therefore, a bioreactor that can simulate physiological conditions would play an important role in the preparation of tissue-engineered constructs. In this article, we present and discuss the design concepts and criteria, as well as the development, of a multifunctional bioreactor for tissue culture in vitro. The system developed is compact and easily housed in an incubator to maintain sterility of the construct. Moreover, the proposed bioreactor, in addition to mimicking in vivo conditions, is highly flexible, allowing different types of constructs to be exposed to various physiological flow conditions. Initial verification of the hemodynamic parameters using Laser doppler anemometry indicated that the bioreactor performed well and produced the correct physiological conditions.

Transient fluid–structure coupling for simulation of a trileaflet heart valve using weak coupling

In this article, a three-dimensional transient numerical approach coupled with fluid–structure interaction for the modeling of an aortic trileaflet heart valve at the initial opening stage is presented. An arbitrary Lagrangian–Eulerian kinematical description together with an appropriate fluid grid was used for the coupling strategy with the structural domain. The fluid dynamics and the structure aspects of the problem were analyzed for various Reynolds numbers and times. The fluid flow predictions indicated that at the initial leaflet opening stage a circulation zone was formed immediately downstream of the leaflet tip and propagated outward as time increased. Moreover, the maximum wall shear stress in the vertical direction of the leaflet was found to be located near the bottom of the leaflet, and its value decreased sharply toward the tip. In the horizontal cross section of the leaflet, the maximum wall shear stresses were found to be located near the sides of the leaflet.

Symbolic computation and perfect fluids in general relativity

Focuses on two areas within the field of general relativity. Firstly, the history and implications of the long-standing conjecture that general relativistic, shear-free perfect fluids which obey a barotropic equation of state p = p(w) such that w + p = 0, are either non-expanding or non-rotating. Secondly the application of the computer algebra system Maple to the area of tetrad formalisms in general relativity.

Biomimetic porous titanium scaffolds for orthopaedic and dental applications

The development of artificial organs and implants for replacement of injured and diseased hard tissues such as bones, teeth and joints is highly desired in orthopedic surgery. Orthopedic prostheses have shown an enormous success in restoring the function and offering high quality of life to millions of individuals each year. Therefore, it is pertinent for an engineer to set out new approaches to restore the normal function of impaired hard tissues.

Over the last few decades, a large number of metals and applied materials have been developed with significant improvement in various properties in a wide range of medical applications. However, the traditional metallic bone implants are dense and often suffer from the problems of adverse reaction, biomechanical mismatch and lack of adequate space for new bone tissue to grow into the implant. Scientific advancements have been made to fabricate porous scaffolds that mimic the architecture and mechanical properties of natural bone. The porous structure provides necessary framework for the bone cells to grow into the pores and integrate with host tissue, known as osteointegration. The appropriate mechanical properties, in particular, the low elastic modulus mimicking that of bone may minimize or eliminate the stress-shielding problem. Another important approach is to develop biocompatible and corrosion resistant metallic materials to diminish or avoid adverse body reaction. Although numerous types of materials can be involved in this fast developing field, some of them are more widely used in medical applications. Amongst them, titanium and some of its alloys provide many advantages such as excellent biocompatibility, high strength-to-weight ratio, lower elastic modulus, and superior corrosion resistance, required for dental and orthopedic implants. Alloying elements, i.e. Zr, Nb, Ta, Sn, Mo and Si, would lead to superior improvement in properties of titanium for biomedical applications.

New processes have recently been developed to synthesize biomimetic porous titanium scaffolds for bone replacement through powder metallurgy. In particular, the space holder sintering method is capable of adjusting the pore shape, the porosity, and the pore size distribution, notably within the range of 200 to 500 m as required for osteoconductive applications. The present chapter provides a review on the characteristics of porous metal scaffolds used as bone replacement as well as fabrication processes of porous titanium (Ti) scaffolds through a space holder sintering method. Finally, surface modification of the resultant porous Ti scaffolds through a biomimetic chemical technique is reviewed, in order to ensure that the surfaces of the scaffolds fulfill the requirements for biomedical applications.

In vitro strain measurements in cerebral aneurysm models for cyber-physical diagnosis

Background: The development of new diagnostic technologies for cerebrovascular diseases requires an understanding of the mechanism behind the growth and rupture of cerebral aneurysms. To provide a comprehensive diagnosis and prognosis of this disease, it is desirable to evaluate wall shear stress, pressure, deformation and strain in the aneurysm region, based on information provided by medical imaging technologies. Methods: In this research, we propose a new cyber-physical system composed of in vitro dynamic strain experimental measurements and computational fluid dynamics (CFD) simulation for the diagnosis of cerebral aneurysms. A CFD simulation and a scaled-up membranous silicone model of a cerebral aneurysm were completed, based on patient-specific data recorded in August 2008. In vitro blood flow simulation was realized with the use of a specialized pump. A vision system was also developed to measure the strain at different regions on the model by way of pulsating blood flow circulating inside the model. Results: Experimental results show that distance and area strain maxima were larger near the aneurysm neck (0.042 and 0.052), followed by the aneurysm dome (0.023 and 0.04) and finally the main blood vessel section (0.01 and 0.014). These results were complemented by a CFD simulation for the addition of wall shear stress, oscillatory shear index and aneurysm formation index. Diagnosis results using imaging obtained in August 2008 are consistent with the monitored aneurysm growth in 2011. Conclusion: The presented study demonstrates a new experimental platform for measuring dynamic strain within cerebral aneurysms. This platform is also complemented by a CFD simulation for advanced diagnosis and prediction of the growth tendency of an aneurysm in endovascular surgery.

Analytical thermal study on nonlinear fundamental heat transfer cases using a novel computational technique

In this paper a novel computational technique called Parameterized Perturbation Method (PPM) is used to obtain the solutions of nonlinear fundamental heat conduction equations. Three well known problems in the area of heat transfer are addressed to be solved. An analytical investigation is carried out for: (a) the temperature distribution in a fin with a temperature-dependent thermal conductivity, (b) the cooling of the lumped system with variable specific heat, and (c) the temperature distribution of a convective-radiative fin. The validity of the results of PPM solution was verified via comparison with numerical results obtained using a fourth order Runge-Kutta method. These comparisons revealed that PPM is a powerful approach for solving these problems. Also, the results showed that the main attributions of this method are very straightforward calculations and low computational burden compared to previous analytical and numerical approaches.

A low-cost intelligent gas sensing device for military applications

The field of electronic noses and gas sensing has been developing rapidly since the introduction of the silicon based sensors. There are numerous systems that can detect and indicate the level of a specific gas. We introduce here a system that is low power, small and cheap enough to be used in mobile robotic platforms while still being accurate and reliable enough for confident use. The design is based around a small circuit board mounted in a plastic case with holes to allow the sensors to protrude through the top and allow the natural flow of gas evenly across them. The main control board consists of a microcontroller PCB with surface mount components for low cost and power consumption. The firmware of the device is based on an algorithm that uses an Artificial Neural Network (ANN) which receives input from an array of gas sensors. The various sensors feeding the ANN allow the microcontroller to determine the gas type and quantity. The Testing of the device involves the training of the ANN with a number of different target gases to determine the weightings for the ANN. Accuracy and reliability of the ANN is validated through testing in a specific gas filled environment.

Microprocessor-based insulin delivery device with amperometric glucose sensing

This paper details the design of a closed-loop insulin delivery device, consisting of a glucose sensing circuit, and a basic microprocessor-based syringe pump. The glucose sensing circuit contains the required components to interface with CGMS's glucose sensor assembly, while the syringe pump design uses microprocessor to allow flexible control over the pump driver. Instrumentation developed in this paper provides a ready reference to other researchers on the construction of a closed-loop insulin delivery apparatus with amperometric glucose sensor.

Wear in centrifugal slurry pumps

The project improves understanding of wear in slurry pumps. By measuring actual pump wear and microscopically examining worn surfaces, a clearer picture emerged of wear modes and mechanisms for different materials. This enables improved guidelines for material selection and modifications to hydraulic shape that increased pump wear life.

Neural net device for IED gas identification

Most of the embedded systems that detect gases today are for specific types and indicate the levels of the gas present with their standard sensors. We introduce here an adaptable system that can detect and distinguish the type of gas in a volatile environment such as searching for Improvised Explosive Devices (IEDs). This is achieved with a small device mounted on a mobile robot through the use of an algorithm that is an Artificial Neural Network (ANN). The input layer to the ANN is an array of environmental and gas sensors. The small device, comprising of a multilayer circuit board with sensors in a rugged lightweight case, mounts on the mobile robot and communicates the gaseous data to the robot.

The ANN is implemented in the hardware of a FPGA with the control of the ANN being achieved through the configurable processor and memory. Calibration and testing of the device involves the training of device and the ANN with specific target gases. The Accuracy of the device is validated through lab testing against high-end gas test instruments with known concentrations of gases.

Data-driven computation of contact dynamics during two-point manipulation of deformable objects

This study represents a preliminary step towards data-driven computation of contact dynamics during manipulation of deformable objects at two points of contact. A modeling approach is proposed that characterizes the individual interaction at both points and the mutual effects of the two interactions on each other via a set of parameters. Both global as well as local coordinate systems are tested for encoding the contact mechanics. Artificial neural networks are trained on simulated data to capture the object behavior. A comparison of test data with the output of the trained system reveals a mean squared error percentage between 1% and 3% for simple interactions.

Design and properties of a new hybrid stent-graft device

This PhD work explored a novel bio-inspired approach for designing artificial blood vessel implants known as stent-grafts. The design was inspired from body design of a caterpillar. This design concept induced natural flexibility and expandability property in the new stent-graft, which is considered critical in deciding long-term health of treated patients.

RF rectifiers for EM power harvesting in a deep brain stimulating device

A passive deep brain stimulation (DBS) device can be equipped with a rectenna, consisting of an antenna and a rectifier, to harvest energy from electromagnetic fields for its operation. This paper presents optimization of radio frequency rectifier circuits for wireless energy harvesting in a passive head-mountable DBS device. The aim is to achieve a compact size, high conversion efficiency, and high output voltage rectifier. Four different rectifiers based on the Delon doubler, Greinacher voltage tripler, Delon voltage quadrupler, and 2-stage charge pumped architectures are designed, simulated, fabricated, and evaluated. The design and simulation are conducted using Agilent Genesys at operating frequency of 915 MHz. A dielectric substrate of FR-4 with thickness of 1.6 mm, and surface mount devices (SMD) components are used to fabricate the designed rectifiers. The performance of the fabricated rectifiers is evaluated using a 915 MHz radio frequency (RF) energy source. The maximum measured conversion efficiency of the Delon doubler, Greinacher tripler, Delon quadrupler, and 2-stage charge pumped rectifiers are 78, 75, 73, and 76 % at -5 dBm input power and for load resistances of 5-15 kΩ. The conversion efficiency of the rectifiers decreases significantly with the increase in the input power level. The Delon doubler rectifier provides the highest efficiency at both -5 and 5 dBm input power levels, whereas the Delon quadrupler rectifier gives the lowest efficiency for the same inputs. By considering both efficiency and DC output voltage, the charge pump rectifier outperforms the other three rectifiers. Accordingly, the optimised 2-stage charge pumped rectifier is used together with an antenna to harvest energy in our DBS device.