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.

In vitro simulator with numerical stress analysis for evaluation of stent-assisted coiling embolization in cerebral aneurysm treatments

There are several complications associated with Stent-assisted Coil Embolization (SACE) in cerebral aneurysm treatments, due to damaging operations by surgeons and undesirable mechanical properties of stents. Therefore, it is necessary to develop an in vitro simulator that provides both training and research for evaluating the mechanical properties of stents.

Double stent-retriever technique in endovascular treatment of middle cerebral artery saddle embolus

Ischemic stroke is a major public health problem worldwide, considered as the third most costly health condition in developed countries, with urgent reperfusion remaining the paramount goal for its treatment. In line with the results of recent randomized control trials, the introduction of stent retrievers was a major advancement in the treatment of stroke; however, interventionalists sometimes encounter thrombi not-retrievable by applying conventional techniques. In this article, we present a case treated by an innovative double-stent retrieval in Y-configuration that may potentially help other clinicians in similar situations.

A biomechanically optimized knitted stent using a bio-inspired design approach

Vascular implants have always been a key area of research in medical textiles. Knitted structures have been proven to be suitable for stent applications on the basis of their looped mesh geometry, structural flexibility and ease of manufacturing. However, there are biomechanical constraints of plain knit constructions that can result in clinical complications after implantation and hence cannot be ignored. This study reports a new segmented knit design inspired by structural metamerism observed in the body design of some invertebrate animals. Metamerism is the phenomenon of having a linear series of body segments fundamentally similar in structure, but assigned to perform different functions. It was hypothesized that utilization of this simple and yet effective biological design approach in stent construction could improve the degree of control for optimizing stent biomechanical properties. The proposed segmented stent was constructed by incorporating an elastic filament component into a polyethylene terephthalate knitted stent at specific intervals along its length, also known as the ‘Plating Technique’. This technique generates a structure with alternately arranged stiff and elastic knitted sections which equip the stent with vital structural support and volumetric compliance properties, respectively. The stent design parameters (filament diameter, loop length, segmentation plan) were optimized to achieve significantly better biomechanical performance (bending flexibility, compression resistance, volumetric expansion, longitudinal extensibility) than a plain knit stent.

Lifestyle pattern change in males following percutaneous transluminal coronary angioplasty/intracoronary stenting

tilizing a naturalistic inquiry approach, a semi-structured interview schedule and non-probability purposive sampling, this study provided detail on the rationale and influences behind the decisions of four males participants to change or not change their lifestyle patterns 3 months after a percutaneous transluminal coronary angioplasty/intracoronary stent procedure. One of the participants made a noticeable lifestyle pattern change in this period. The remaining participants failed to exhibit any discernible lifestyle pattern change or had continued with their previous behaviours. Results suggest a new 'positive' psychological health perspective, family considerations, return-to-work issues and a reluctance to participate in cardiac rehabilitation as the major factors influencing lifestyle pattern change. Because nurses spend the greatest amount of time with percutaneous transluminal coronary angioplasty/intracoronary stent patients during hospitalization, they have the best opportunity to provide up-to-date and relevant information to patients that will enable them to then make decisions concerning cardiac healthy lifestyle changes.

In vitro studying corrosion behaviour of biocorrodible Mg alloys

The idea of bioabsorbable/biocorrodible stents has gained increasing attention in the last decade. Permanent coronary stents, traditionally made from 316L grade stainless steel, are routinely used for the treatment of blocked arteries. However, these stents can cause complications such as restenosis, thrombosis and the need for the patient to undergo prolonged antiplatelet therapy. Biodegradable metal stents provide an opportunity for the stent to remain in place for a period to ensure restoration of function and then degrade through a carefully controlled bio-corrosion process. Among the number of potentially suitable materials, Magnesium alloys have shown great promise as a stent material due to their non-toxicity [1] and the corrosion rates attainable in biological environments. However, a carefully controlled corrosion process is essential in order to avoid hyper hydrogen generation and the fatal consequences that follow. In addition uniform corrosion is a basic requirement to maintain the mechanical integrity and load bearing characteristics. Work being undertaken in our laboratories focuses on controlling the corrosion behaviour of magnesium in a simulated biological environment in the presence of protein. In the investigation reported here the Mg alloy has been examined using Scanning Electrochemical Microscope (SECM) to visualize the corrosion process and identify the corrosion pattern. Complementary bulk electrochemical techniques (EIS and potentiodynamic polarization) have been used to acquire kinetic and mechanistic information. Early results obtained by SECM have revealed the tendency towards pitting corrosion in the early stages which subsequently develops in to filiform corrosion.

Has carotid artery stenting found its place? A 10-year regional centre perspective

The post-Carotid Revascularization Endarterectomy versus Stenting Trial era has seen a dramatic decline in the practice of carotid artery stenting (CAS). A retrospective review of prospectively collected CAS outcomes over a 10-year period by a single operator was undertaken to determine if this change in practice is justified and to identify the place of carotid stenting in current practice.

A new design concept for knitted external vein-graft support mesh

Autologous vein-graft failure significantly limits the long-term efficacy of coronary artery bypass procedures. The major cause behind this complication is biomechanical mismatch between the vein and coronary artery. The implanted vein experiences a sudden increase (10-12 fold) in luminal pressures. The resulting vein over-distension or 'ballooning' initiates wall thickening phenomenon and ultimate occlusion. Therefore, a primary goal in improving the longevity of a coronary bypass procedure is to inhibit vein over-distension using mechanical constriction. The idea of using an external vein-graft support mesh has demonstrated sustained benefits and wide acceptance in experimental studies. Nitinol based knitted structures have offered more promising mechanical features than other mesh designs owing to their unique loosely looped construction. However, the conventional plain knit construction still exhibits limitations (radial compliance, deployment ease, flexibility, and bending stresses) which limit this design from proving its real clinical advantage. The new knitted mesh design presented in this study is based on the concept of composite knitting utilising high modulus (nitinol and polyester) and low modulus (polyurethane) material components. The experimental comparison of the new design with a plain knit design demonstrated significant improvement in biomechanical (compliance, flexibility, extensibility, viscoelasticity) and procedural (deployment limit) parameters. The results are indicative of the promising role of new mesh in restoring the lost compliance and pulsatility of vein-graft at high arterial pressures. This way it can assist in controlled vein-graft remodelling and stepwise restoration of vein mechanical homoeostasis. Also, improvement in deployment limit parameter offers more flexibility for a surgeon to use a wide range of vein diameters, which may otherwise be rendered unusable for a plain knit mesh.

Medical textiles as vascular implants and their success to mimic natural arteries

Vascular implants belong to a specialised class of medical textiles. The basic purpose of a vascular implant (graft and stent) is to act as an artificial conduit or substitute for a diseased artery. However, the long-term healing function depends on its ability to mimic the mechanical and biological behaviour of the artery. This requires a thorough understanding of the structure and function of an artery, which can then be translated into a synthetic structure based on the capabilities of the manufacturing method utilised. Common textile manufacturing techniques, such as weaving, knitting, braiding, and electrospinning, are frequently used to design vascular implants for research and commercial purposes for the past decades. However, the ability to match attributes of a vascular substitute to those of a native artery still remains a challenge. The synthetic implants have been found to cause disturbance in biological, biomechanical, and hemodynamic parameters at the implant site, which has been widely attributed to their structural design. In this work, we reviewed the design aspect of textile vascular implants and compared them to the structure of a natural artery as a basis for assessing the level of success as an implant. The outcome of this work is expected to encourage future design strategies for developing improved long lasting vascular implants.

Gender difference in treatment and mortality of patients with ST-segment elevation myocardial infarction admitted to Victorian public hospitals: A retrospective database study.

BACKGROUND: Death from acute coronary syndrome (ACS) is avoidable with early reperfusion therapy, however, evidence suggests inequity in women's ACS treatment within a number of international healthcare systems, when compared to men's. Research indicates mortality rates are higher in some age groups of women when compared to men for the sub-group of ACS known as ST-segment elevation myocardial infarction (STEMI). OBJECTIVE: To determine whether patient sex was associated with patterns of reperfusion treatment variation or increased inhospital mortality in patients with STEMI. METHODS: We undertook retrospective analyses on a government database for patients admitted to Victorian public hospitals with STEMI. Patients were categorised into two age groups: 18-64 and 65-84 years (inclusive), to determine whether patient sex and these age groups influenced treatment from 2005 to 2008 and mortality from 2005 to 2010. RESULTS: Both younger and older women received less frequent angioplasty with stent and more often received no reperfusion treatment than men in corresponding younger and older age groups (p=0.006 and p<0.001, respectively). Overall, women in both age groups were more likely to die inhospital than men from equivalent age groups with STEMI (p<0.001, both groups). CONCLUSIONS: Proportionately, both younger and older women received less interventional reperfusion therapy for STEMI than their male cohorts, and died more often during admission than men. Further research needs to be undertaken to verify the findings and causes, and guide future research to ensure application of evidence to treatment in patients with STEMI.

Gender difference in the use of coronary interventions for patients with acute coronary syndrome: experience from a major metropolitan hospital in Melbourne, Australia

BACKGROUND: Literature suggests an ongoing gender disparity in the use of coronary angiography and subsequent interventions among patients with acute coronary syndrome (ACS). OBJECTIVES: The study aimed to examine gender differences in the use of coronary interventions amongst patients with acute coronary syndrome (ACS) admitted to a major metropolitan hospital in Melbourne during the period 2009-2012. METHODS: We undertook a retrospective analysis of a hospital database of 2096 ACS patients. ACS included unstable angina (UA), ST-segment-elevation myocardial infarction (STEMI) and non-STEMI (NSTEMI). RESULTS: The mean age of the patients was 64.3 years and 624 (30%) were women. Half of them were diagnosed as NSTEMI, 23% as STEMI and 25% as UA. Compared to men, women were older at admission, less likely to be diagnosed with STEMI and less likely to smoke. No gender difference was observed for severe co-morbidities or use of coronary angiography. Women diagnosed with STEMI were 39% less likely to receive an angioplasty stent (adjusted odds ratio 0.61, 95% confidence intervals 0.39-0.96) and 66% less likely to receive grafts (adjusted OR 0.34, 95% CIs 0.13-0.93). Women diagnosed with NSTEMI were 44% less likely to receive grafts (adjusted OR 0.56, 95% CIs 0.37-0.83). Younger women aged 35-49 years were less likely to receive an angioplasty stent, and older women >50 years were less likely to receive grafts. CONCLUSIONS: Adherence to guideline based treatment will help to ensure knowledge translation from guideline to practice. Further research investigating symptom presentation, use of non-invasive tests and medical management of ACS by gender may further explain gender difference for coronary interventions.

Effect of polymer microstructure on the docetaxel release and stability of polyurethane formulation

PurSil®AL20 (PUS), a copolymer of 4,4'-dicyclohexylmethane diisocyanate (HMDI), 1,4-butane diol (BD), poly-tetramethylene oxide (PTMO) and poly-dimethyl siloxane (PDMS) was investigated for stability as a vehicle for Docetaxel (DTX) delivery through oesophageal drug eluting stent (DES). On exposure to stability test conditions, it was found that DTX release rate declined at 4 and 40 °C. In order to divulge reasons underlying this, changes in DTX solid state as well as PUS microstructure were followed. It was found that re-crystallization of DTX in PDMS rich regions was reducing the drug release at both 4 °C and 40 °C samples. So far microstructural features have not been correlated with stability and drug release, and in this study we found that at 40 °C increase in microstructural domain sizes and the inter-domain distances (from ∼85 Å to 129 Å) were responsible for hindering the DTX release in addition to DTX re-crystallization.

In vitro and in vivo assessment of docetaxel formulation developed for esophageal stents

Esophageal cancer (EC) mostly affects the elderly population and is frequently diagnosed at an advanced stage. Self-expanding metal stents (SEMS) are the most popular mode of palliation, but they are associated with reocclusion caused by tumor growth. To overcome this problem, docetaxel (DTX)-loaded polyurethane formulations were prepared for stent application. The films were evaluated against the cancer cell lines, OE-19 and OE-21, and normal esophageal cell line Het-1A. The DTX and the formulations were evaluated in vitro for the cytotoxicity and in vivo in nude mice. It was found that DTX and the formulations have a weak activity against the EC cell lines and an even weaker activity against Het-1A cell line. Preliminary in vivo studies showed skin toxicity in nude mice necessitating modification of the formulation. Reevaluation in a mouse xenograft model resulted in toxicity at high dose formulations while the low dose formulation exhibited modest advantage over commercial IV formulation; however, there was no significant difference between the commercial IV and blank formulation. DTX combination with an anti-cancer agent having complementary mode of action and non-overlapping toxicity could yield better outcome in future.