Articles

Reducing In-Stent Restenosis through Novel Stent Flow Field Augmentation

Eoin Murphy et al. — Mon, 10 Dec 2012 07:45:14 PST

In-stent restenosis (ISR), manifested as a re-narrowing of the arterial lumen post-implantation of a stent, is a detrimental limitation of stent technology. Understanding and consequently devising ways of reducing the frequency of ISR has been a continuing goal of research into improved stent designs. The biological processes that can lead to ISR have been found to be partially flow dependent with the local hemodynamics at the arterial wall of crucial importance. This paper investigates these biological processes and their instigating factors. Furthermore, the history and theory behind three stent technologies which endeavour to reduce ISR rates through stent flow field augmentation are presented: a flow divider which increases the blood-flow velocity and consequently the wall shear stress through a stented region, and two novel stent technologies which induce helical flow that mimics the natural blood flow present in healthy arteries. This paper serves as a thorough introduction to both the investigation of ISR, particularly the influence of the local hemodynamics, and to the three novel stent technologies which aim to reduce ISR rates.

Ablation of Chronic Total Occlusions Using Kilohertz-Frequency Mechanical Vibrations in Minimally Invasive Angioplasty Procedures.

Garrett McGuinness et al. — Tue, 26 Jun 2012 05:34:37 PDT

Certain minimally invasive cardiology procedures, such as balloon angioplasty and stent implantation, critically require that the site of an arterial blockage be crossed by an intraluminal guidewire. Plaques resulting in near or totally occluded arteries are known as chronic total occlusions (CTOs), and crossing them with conventional guidewires is a significant challenge. Among the most promising proposed solutions is the delivery of high power, low frequency ultrasonic vibrations to the occlusion site via an intraluminal wire waveguide. The vibrating distal-tip of the ultrasound wire waveguide is used to transmit energy to the surrounding plaques, tissues and fluids in order to ablate or weaken atherosclerotic plaque. Potential mechanisms of interaction with the plaque and adjacent fluids identified in the literature include; (i) direct contact with the waveguide distal tip, (ii) subcavitational acoustic fluid pressure fluctuations, (iii) cavitation, and (iv) acoustic streaming. This article will summarize developments in this area over more than two decades, describing experimental methods for device performance characterization, preclinical tests, early clinical investigations and, later, full clinical trials. The article will also review theoretical foundations, and numerical models suitable for device design and analysis. Finally, important issues for future research and for the development of this technology will be considered.

Increased Susceptibility of Arterial Tissue to Wire Perforation with the Application of High Frequency Mechanical Vibrations

Mark Wylie et al. — Tue, 31 Jan 2012 03:54:35 PST

High frequency mechanical vibrations (20–50 kHz), delivered via small diameter flexible wire waveguides represent a minimally invasive technology for the treatment of chronic total occlusions (CTOs) and in other tissue ablation applications. Tissue disruption is reported to be caused by repetitive mechanical contact and cavitation. This work focuses on the effects of vibrating wire waveguides in contact with arterial tissue. An apparatus with clinically relevant parameters was used, characterized as operating at 22.5 kHz and delivering amplitudes of vibration of 17.8 - 34.3 µm (acoustic intensity, I_SATA: 1.03 - 3.83 W/cm²) via 1.0 mm diameter waveguides. Inertial cavitation (in water at 37⁰C) was determined to occur above amplitudes of vibration greater than 31.4 µm (I_SATA = 3.21 W/cm²). The energized waveguides were advanced through tissue samples (porcine aorta) and the force profiles were measured for a range of acoustic intensities. The results show that the tissue perforation initiation force, perforation initiation energy and total energy required to perforate the tissue reduces with increasing acoustic intensity. No significant reduction in perforation force or energy was observed in the inertial cavitation region. Multistage perforation was evident through the force profile and histological examination of the tissue samples post wire waveguide perforation.

The Effect of Physiological Cyclic Stretch on the Cell Morphology, Cell Orientation and Protein Expression of Endothelial Cells

V. Barron et al. — Wed, 23 Mar 2011 03:24:14 PDT

In vivo, endothelial cells are constantly exposed to pulsatile shear and tensile stresses. The main aim of this study was to design and build a physiological simulator, which reproduced homogenous strain proﬁles of the tensile strain experienced in vivo, and to investigate the effect of this cyclic tensile strain on the cell morphology, cell orientation and protein expression of endothelial cells. The biological response of human umbilical vein endothelial cells to a uniaxial cyclic stretch, in this newly developed simulator, was examined experimentally using immunohistostaining and confocal imaging and it was

found that the cells elongated and oriented at 58.9± 4.5. This value was compared to a mathematical model where it was revealed that endothelial cells would orient at an angle of 60. This model also revealed that endothelial cells have an axial strain threshold value of 1.8% when exposed to a 10% cyclic strain at 1 Hz for 3 h. Cells cultured under conditions of cyclic strain showed increased ICAM-1 immunostaining when compared to static cells whereas, a marked decrease in the levels of VCAM-1 receptor staining was also observed. Haemodynamic stresses can modulate the endothelial cell adhesion response in vivo thus, taken together; this data validates the bioreactor as replicating the physiological environment.

A Monocular Marker-Free Gait Measurement System

Jane Courtney et al. — Tue, 25 Jan 2011 06:17:50 PST

This paper presents a new, user-friendly, portable motion capture and gait analysis system for capturing and analyzing human gait, designed as a telemedicine tool to monitor remotely the progress of patients through treatment. The system requires minimal user input and simple single-camera filming (which can be acquired from a basic webcam) making it very accessible to nontechnical, nonclinical personnel. This system can allow gait studies to acquire a much larger data set and allow trained gait analysts to focus their skills on the interpretation phase of gait analysis. The design uses a novel motion capture method derived from spatiotemporal segmentation and model-based tracking. Testing is performed on four monocular, sagittal-view, sample gait videos. Results of modeling, tracking, and analysis stages are presented with standard gait graphs and parameters compared to manually acquired data.

Drug-Eluting Stents for Coronary Artery Disease: a Review

David Martin et al. — Fri, 14 Jan 2011 03:08:36 PST

Over the past decade the introduction of drug-eluting stents (DESs) has revolutionised the treatment of coronary artery disease. However, in recent years concern has arisen over the long-term safety and efficacy of DESs due to the occurrence of late adverse clinical events such as stent thrombosis. With this concern in mind, research and development is currently centred on increasing the long-term safety and efficacy of DESs. The aim of this paper is to provide a thorough review of currently approved and promising investigational DESs. With dozens of companies involved in the development of new and innovative anti-restenotic agents, polymeric coatings and stent platforms, it is intended that this review paper will provide a clear indication of how DESs are currently evolving and prove a valuable reference tool for future research in this area.

Preliminary Results for a Monocular Marker-Free Gait Measurement System

Jane Courtney et al. — Thu, 13 Jan 2011 07:13:57 PST

This paper presents results from a novel monocular marker-free gait measurement system. The system was designed for physical and occupational therapists to monitor the progress of patients through therapy. It is based on a novel human motion capture method derived from model-based tracking. Testing is performed on two monocular, sagittal-view, sample gait videos – one with both the environment and the subject’s appearance and movement restricted and one in a natural environment with unrestricted clothing and motion. Results of the modelling, tracking and analysis stages are presented along with standard gait graphs and parameters.

Computational Structural Modelling of Coronary Stent Deployment: A Review

David Martin et al. — Fri, 19 Nov 2010 07:10:44 PST

The finite element (FE) method is a powerful investigative tool in the field of biomedical engineering, particularly in the analysis of medical devices such as coronary stents whose performance is extremely difficult to evaluate in vivo. In recent years, a number of FE studies have been carried out to simulate the deployment of coronary stents, and the results of these studies have been utilised to assess and optimise the performance of these devices. The aim of this paper is to provide a thorough review of the state-of-the-art research in this area, discussing the aims, methods and conclusions drawn from a number of significant studies. It is intended that this paper will provide a valuable reference for future research in this area.

A Linear Finite Element Acoustic Fluid-Structure Model of Ultrasonic Angioplasty in Vivo

Mark Wylie et al. — Fri, 23 Jul 2010 01:36:03 PDT

The delivery of high-power ultrasonic energy via small diameter wire waveguides represents a new alternative therapy for the treatment of chronic totally occluded arteries (CTOs). This type of energy manifests itself as a mechanical vibration at the distal-tip of the waveguide with amplitudes of vibration up to 60 µm and at frequencies of 20- 50 kHz. Disruption of diseased tissue is reported to be a result of direct mechanical ablation, cavitation, pressure components and acoustic streaming and that ablation was only evident above the cavitation threshold. This work presents a linear finite element acoustic fluid-structure model of an ultrasonic angioplasty waveguide in vivo. The model was first verified against a reported analytical solution for an oscillating sphere. It was determined that 140 elements per wavelength (EPW) were required to predict the pressure profile generated by the wire waveguide distal-tip. Implementing this EPW count, the pressure field surrounding a range of distal-tip geometries was modelled. For validation, a model was developed with parameters based on a bench-top experiment from the literature of an ultrasonic wire waveguide in a phantom leg. This model showed good correlation with the experimental measurements. These models may aid in the further development of this technology.

Links with Canada Benefit DIT Prosthesis Research

Colm O'Kane — Fri, 28 May 2010 07:25:08 PDT

Colm O’Kane is a lecturer in the School of Manufacturing and Design Engineering and a member of the DIT Biomedical Device and Assistive Technology Research Group. He is currently engaged in PhD research in the field of knee prosthesis development, focused on developing optimised strategies for partial and total joint replacements used in treatment of osteoarthritis of the knee joint. This article is an account of a research scholarship sponsored by the CHC Helicopter Corporation and awarded by the Ireland Canada University Foundation (ICUF). This foundation awards annual scholarships for research visits between Ireland and Canada with the aspiration of fostering links between the two countries’ research communities.