Mechanical and in vitro evaluation of an experimental canine patent ductus arteriosus occlusion device

Abstract

Patent ductus arteriosus (PDA) is a congenital cardiovascular malformation in which a fetal connection between the aorta and pulmonary artery remains patent after birth. This defect commonly results in clinical complications, even death, necessitating closure. Surgical ligation is the most common treatment but requires a thoracotomy and is therefore invasive. A minimally invasive option is preferable. A prototype device for PDA occlusion which utilizes shape memory polymer foams has been developed and evaluated using mechanical and in vitro experiments. Removal force and radial pressure measurements show that the prototype device exhibited a lower removal force and radial pressure than a commercially available device. The in vitro experiments conducted within simplified and physiological PDA models showed that the prototype does not migrate out of position into the pulmonary artery at either physiological or elevated pressures in multiple model configurations. While the radial pressure and removal force were lower than commercial devices, the device performed acceptably in the in vitro benchtop experiments warranting further prototype development.

Keywords: ACDO; Patent ductus arteriosus; Shape memory polymer.

Fig. 1

NFC shape setting procedure. (A) Laser cut nitinol tubing with SS spacers positioned and gauge pin placed within lumen. (B) Interior SS spacer positioned in proximal struts. (C) Tube is compressed axially so proximal cage opens. (D) Tube is compressed axially further to expand distal struts.

Fig. 2

PDA device comparison. (A) 6 mm ACDO (sized at the device waist); (B) NFC, foam compressed; (C) NFC foam expanded. (Same scale across frames).

Fig. 3

Simplified PDA model geometries. Dimensions and shapes based upon common canine PDA shapes (Miller et al., 2006).

Fig. 4

Radial pressure testing setup. (A) Blockwise RJA62 J-Crimp™ Radial Compression Station attached to Instron Test Frame. (B) Enlarged, front view of compression blades, set to 5 mm diameter, with NFC deployed. (C) Side view schematic of deployed NFC within compression station showing constrained distal cage.

Fig. 5

Schematic of flow loop used for in vitro testing.

Fig. 6

Average radial pressure. Average radial pressure of the NFC compared to the ACDO at each ampulla ID tested.

Fig. 7

Average removal force. Average removal force of the NFC and ACDO for each simplified vessel geometry.

Fig. 8

Device stability in the IIA (A.1–A.3), IIB (B.1–B.3), and WA (C.1–C.3) models. Flow is from left to right. Images recorded after device subjected to labeled pressures for five minutes.

Fig. 9

NFC deployment (NFC 1) into physiological model under fluoroscopic guidance. (A) NFC in catheter. (B) Distal cage deployed from catheter. (C) NFC placement against pulmonic ostium of model. (D) Proximal cage delivered and device released. White arrow indicates distal cage during deployment and positioning.

Fig. 10

Tungsten-doped foam visibility under fluoroscopic guidance during NFC 4 delivery. (A) NFC in catheter. (B) Proximal cage deployment, foam begins to expand. (C) NFC deployed, foam expansion indicated by reduction in the radiographic contrast of foam. White arrow indicates foam location.

Fig. 11

Flow reduction comparison. Images were collected at the time when max contrast was present in ampulla as determined by visual inspection. (A) Model without a device present to provide a baseline image. (B) Model with the ACDO positioned. (C) and (D) NFC devices with a 6 mm diameter and 8 mm diameter SMP foam respectively. (E) and (F) NFC 4 subject to a 100 mmHg and 200 mmHg pressure gradient respectively.