Evaluation of a Desktop 3D Printed Rigid Refractive-Indexed-Matched Flow Phantom for PIV Measurements on Cerebral Aneurysms

Purpose Fabrication of a suitable flow model or phantom is critical to the study of biomedical fluid dynamics using optical flow visualization and measurement methods. The main difficulties arise from the optical properties of the model material, accuracy of the geometry and ease of fabrication. Methods Conventionally an investment casting method has been used, but recently advancements in additive manufacturing techniques such as 3D printing have allowed the flow model to be printed directly with minimal post-processing steps. This study presents results of an investigation into the feasibility of fabrication of such models suitable for particle image velocimetry (PIV) using a common 3D printing Stereolithography process and photopolymer resin. Results An idealised geometry of a cerebral aneurysm was printed to demonstrate its applicability for PIV experimentation. The material was shown to have a refractive index of 1.51, which can be refractive matched with a mixture of de-ionised water with ammonium thiocyanate (NH4SCN). The images were of a quality that after applying common PIV pre-processing techniques and a PIV cross-correlation algorithm, the results produced were consistent within the aneurysm when compared to previous studies. Conclusions This study presents an alternative low-cost option for 3D printing of a flow phantom suitable for flow visualization simulations. The use of 3D printed flow phantoms reduces the complexity, time and effort required compared to conventional investment casting methods by removing the necessity of a multi-part process required with investment casting techniques

A Comprehensive Flow Study of the 12 cc Penn State Pulsatile Pediatric Ventricular Assist Device

While medical options for children born with congenital heart defects include transplantation, the amount of available organs remains limited. This lack of donors led to the development of the National Institute of Health’s National Heart, Lung and Blood Institute Pediatric Circulatory Support Program. Contracts have been awarded to five teams with the task of creating novel support systems for children, ranging from 2 to 25 kg [1]. As part of this program, Penn State has developed a 12 cc pulsatile pediatric ventricular assist device (PVAD), based on the successful 70 cc Pierce-Donachy adult assist device. During the process of reducing the volume of the device for pediatric use, changes were made to the design including altering the angles of the inlet and outlet ports. Previous two-dimensional flow visualization in the PVAD by Manning et al. had shown that these changes led to an increased three-dimensionality of the flow, the influence of which required further investigation [2]. It is important to characterize the fluid dynamics of the flow field inside assist devices such as the PVAD because certain characteristics including high blood residence time, stagnant flow and wall shear rates below 500 s−1 can lead to an increased propensity of thrombus deposition [3,4].</jats:p

Flow Visualization of a Pediatric Ventricular Assist Device During Stroke Volume Reductions Related to Weaning

The aim of this study is to define the fluid mechanics of a pulsatile pneumatically driven pediatric ventricular assist device (PVAD), for the reduced flow rates encountered during device weaning and myocardial recovery, and relate the results to the potential for thromboembolic events. We place an acrylic model of the PVAD in a mock circulatory loop filled with a viscoelastic blood analog and operate at four stroke volumes (SVs), each with two different filling conditions, to mimic how the flow rate of the device may be reduced. Particle image velocimetry is used to acquire flow field data. We find that a SV reduction method provides better rotational flow and higher wall shear rates than a beat rate reduction method; that a quick filling condition with a compressed diastolic time is better than a slow filling condition; and, that a reduction in SV to 40% led to greatly reduced fluid movement and wall shear rates that could increase the thrombogenicity of the device. SV reduction is a viable option for flow reduction during weaning, however, it does lead to significant changes to the device flow field and future studies are needed to develop operational protocols for the PVAD during bridge-to-recovery

In Vitro Viscoelastic Flow Measurements of a Pediatric End-to-Side Anastomosis to the 12cc Penn State Ventricular Assist Device

Congenital cardiovascular defects are the leading cause of infant mortality due to birth defects, accounting for 29% of all birth defect-related infant deaths [1]. Each year over 35,000 babies are born with heart defects in the United States. A quarter of these patients require invasive treatment [2]. Although transplantation has proven to be a viable option for recovery, it is limited by an inadequate supply of donor organs. The average wait time for a transplant in 2005 was 107 days, and without the availability of transplants, approximately 40% of infants in need of a cardiovascular transplant may die [3,4].</jats:p

The Fluid Dynamic Effects Within the 12cc Penn State Pediatric Ventricular Assist Device When Altering the End Diastolic Delay

Congenital heart disease is the most common and leading cause of birth-defect related deaths [1]. While many of these patients have damaged or deformed hearts that require transplantation, recovery may be possible for a select population [2]. Extracorporeal membrane oxygenation or ventricular assist devices are often used in a bridge-to-recovery situation to sustain a patient with the expectation of recovery of natural ventricular function [3].</jats:p

The Challenges of Developing a Pediatric Ventricular Assist Device From a Fluid Dynamics Perspective

As a medical device proves successful in adult patients, it is anticipated that a similar solution for pediatrics may be developed. However, in many cases this task has proved to be much more complex than simply scaling the device down for a miniature adult patient. Pediatric patients present a unique set of characteristics and constraints not seen in adults. These include a large range of sizes from infants to adolescents, the possible growth of the patient during use, possible anatomical deformities and a body that has not fully matured.</jats:p

A Fluid Dynamics Study Focusing on Wall Shear Rates Within the Penn State 12 cc Pulsatile Pediatric Ventricular Assist Device: A Comparison of Mechanical Heart Valve Types

Previous studies have shown that the interrelated flow characteristics necessary for the prevention of thrombosis in a pulsatile ventricular assist device (VAD) are a strong inlet jet, a late diastolic recirculating flow, and adequate wall washing (greater than 500 s−1). Particle image velocimetry was used to compare the flow fields in the chamber of the 12 cc Penn State pediatric pulsatile VAD using two valves: Björk-Shiley Monostrut (BSM) tilting-disc valves at the inlet and outlet and Carbomedics (CM) bi-leaflet valves at the inlet and outlet. In conjunction with the flow evaluation, wall shear data were calculated and analyzed to help to quantify wall washing. The major orifice inlet jet of the device containing BSM valves was more intense which led to better circulation and wall washing than the three jets produced by the CM valves Regurgitation through the CM valve was observed and served as a significant hindrance to the development of the rotational flow.</jats:p

Impact of Outlet Valve Orientation on Fluid Dynamics of the 12 cc Penn State Pediatric Ventricular Assist Device

Congenital cardiovascular defects are the leading cause of death among live births [1]. These defects involve the interior walls of the heart, valves, arteries, and veins and change the normal flow of blood through the heart and into the systemic system. Fortunately, several options exist for the more than 35,000 children born with congenital heart disease. Ventricular assist devices (VADs) currently hold the most promise for bridge-to-transplant treatment; however, a major problem for these devices is thrombus formation and deposition.</jats:p