Miniature Wheel for Grinding of the Arterial Calcified Plaque

Abstract

Atherosclerosis is the accumulation of calcium and fatty tissue, often known as plaque, within the arterial wall. With the development of atherosclerosis, the plaque thickens and hardens the arterial wall, narrowing the arterial lumen and restricting blood flow. Plaque may calcify and harden over time, commonly occurring in the aging population. Atherectomy is a common and effective interventional cardiology procedure that uses a high-speed grinding wheel for treating the calcified plaque in coronary and peripheral arteries. However, even when using the smallest wheel currently available, complications such as restenosis, wheel entrapment, and vessel perforation can still occur. It is hypothesized that the forces exerted by the existing wheels are too large, causing potential vessel damage. There is a need for a miniature wheel to enhance the safety and efficacy of treating calcified plaque. Calcified plaque may also evolve to chronic total occlusion (CTO), which is defined as a total obstruction of an artery by the atherosclerotic plaque for a duration longer than three months with thrombolysis in myocardial infarction (TIMI) 0 flow. To treat CTO, percutaneous coronary intervention (PCI) has been utilized since the 1980s, which refers to a minimally invasive cardiovascular procedure to open the narrowed vessels and restore blood flow, including balloon angioplasty, stenting, and atherectomy. Treating CTO with PCI is challenging. When severe lesion calcification presents, the PCI-CTO procedure may fail because the existing microcatheters cannot follow the guidewire to pass cross the lesion or the balloon cannot be dilated successfully due to the resistance from the calcification. A device with high penetration ability is needed to cross the calcified CTO. This dissertation studies the fabrication and performance of a miniature wheel to cross through and grind the calcified plaque lesion with lower force to enhance procedural safety and overcome the clinical challenges of microcatheter-uncrossable and balloon-uncrossable lesions in the PCI treatment of CTO. First, a five-step nickel (Ni)-diamond electroplating method was developed to fabricate the miniature wheel. The electroplating parameters were optimized experimentally and the electroplating time to obtain the designed layer thickness was modeled based on Faraday’s law of electrolysis and the geometry of the drive shaft, wheel, and diamond grit. Second, the drilling and grinding performance of the miniature wheel integrated to an atherectomy device was tested on severely calcified plaque surrogates under both manual and automated modes. The associated force properties during the drilling and grinding processes were investigated. Wheel orbital motion was observed during grinding. Third, based on the observation that the wheel orbital motion gradually enlarges the surrogate lumen, the grinding threshold (maximum diameter achieved by grinding) of the miniature wheel was investigated via experiments and force analysis with a computational fluid dynamics (CFD) model to understand the grinding wheel motion and material removal mechanism. This study demonstrated that the proposed miniature wheel could effectively remove the calcified plaque surrogate through drilling and grinding. This research could lead to a more effective and safer device with sub-mm miniature diamond wheels to treat calcified lesions deep in coronary and peripheral arteries and offer a new PCI treatment approach for CTO to solve the problems of microcatheter-uncrossable and balloon-uncrossable lesions. Force analysis implied that in order to avoid excess force exerted by the grinding wheel, there is a trade-off when considering using low rotational speed at a given wheel size.