Investigating Balloon-Vessel Contact Pressure Patterns in Angioplasty: In Silico Insights for Drug-Coated Balloons

Abstract

Drug-Coated Balloons have shown promising results as a minimally invasive approach to treat stenotic arteries, but recent animal studies have revealed limited, non-uniform coating transfer onto the arterial lumen. In vitro data suggested that local coating transfer tracks the local Contact Pressure (CP) between the balloon and the endothelium. Therefore, this work aimed to investigate in silico how different interventional and device parameters may affect the spatial distribution of CP during the inflation of an angioplasty balloon within idealized vessels that resemble healthy femoral arteries in size and compliance. An angioplasty balloon computational model was developed, considering longitudinal non-uniform wall thickness, due to its forming process, and the folding procedure of the balloon. To identify the conditions leading to non-uniform CP, sensitivity finite element analyses were performed comparing different values for balloon working length, longitudinally varying wall thickness, friction coefficient on the balloon-vessel interface, vessel wall stiffness and thickness, and balloon-to-vessel diameter ratio. Findings indicate a significant irregularity of contact between the balloon and the vessel, mainly affected by the balloon's unfolding and longitudinal thickness variation. Mirroring published data on coating transfer distribution in animal studies, the interfacial CP distribution was maximal at the middle of the balloon treatment site, while exhibiting a circumferential pattern of linear peaks as a consequence of the particular balloon-vessel interaction during unfolding. A high ratio of balloon-to-vessel diameter, higher vessel stiffness, and thickness was found to increase significantly the amplitude and spatial distribution of the CP, while a higher friction coefficient at the balloon-to-vessel interface further exacerbated the non-uniformity of CP. Evaluation of balloon design effects revealed that the thicker tapered part caused CP reduction in the areas that interacted with the extremities of the balloon, whereas total length only weakly impacted the CP. Taken together, this study offers a deeper understanding of the factors influencing the irregularity of balloon-tissue contact, a key step toward uniformity in drug-coating transfer and potential clinical effectiveness.

Keywords: Contact pressure; Drug-coated balloons; Drug-coating; Finite element simulations; Non-uniformity; Numerical.

Fig. 1

a Bottom—Dimensions of the angioplasty balloon model: “A” refers to the diameter of the catheter, “B” indicates the length of the taper on the balloon, and “C” represents the balloon diameter along the working length; the working length of the catheter was modified based on various values outlined in Table 1. Top—the three considered thickness variation cases. b Mechanical response of the three considered vessel material models

Fig. 2

a Mesh and boundary conditions adopted for the balloon numerical model, b Diagrammatic explanation of the Diameter Ratio, and c Mesh and boundary conditions adopted for the vessel numerical model

Fig. 3

Top: Relationship between the inflation pressure and the diameter (only after balloon distension) during a free expansion for the three balloon models with different thickness variations; Bottom: balloon behavior before its complete distention (Inflation pressure from 0 to 1.6 atm). The different unfolding configurations and the maximum distance from the axis are indicated. Step A reveals the initial unfolding movement during which the folds rotate around the central axis of the balloon. Subsequently, in step B, the balloon will start to distend until a circular cross-section is reached, where the balloon will start to increase the diameter of the cross-section. The values vary insignificantly with the different thickness variation conditions

Fig. 4

Early stages of the balloon expansion simulation along different expansion frames considering 40% DR. The figure unravels the different balloon-vessel configurations starting from the folded balloon (A) all the way until its complete distention (I). The presence of the vessel model increases the radial resistance of the system, resulting in a higher pressure required to distend the balloon compared to its free expansion process

Fig. 5

CP maps and the respective average values along the longitudinal and circumferential axis at different IPs for the control case simulation, while the last column depicts the concurrent configuration of the balloon. Linearly distributed imprints of the the folds are present even at high IPs, where the balloon has achieved its full distention. “A” and “C” on the top left of the figure denote the axial and circumferential direction of the artery respectively, while the right column shows the balloon’s configuration at the different IPs. A 10% variation of the wall thickness along the longitudinal axis of the balloon’s working length revealed a bell-shaped concentration of CP. This caused a circumferential non-uniformity of average CP

Fig. 6

Global average CP values among different conditions for various IPs. The observed increase in the average values of CPs at different IPs can be attributed to the following changes: a decrease in balloon thickness, an increase in balloon length, an increase in the friction coefficient, an increase in the diameter ratio, an increase in arterial stiffness, and an increase in arterial thickness. Among these factors, the diameter ratio and arterial stiffness were found to have a more significant impact on the average CP

Fig. 7

Color maps of different IPs with the respective developed CP maps on the vessel endoluminal area during the interaction with the DCB: a among the four different DR implemented (the last column represents the balloon configuration at the different IPs of the 40% DR case), b among the three different friction penalties considered, c among the three different vessel stiffness conditions assumed, d among the three different vessel thicknesses implemented in the simulations for different IP values, and e among the three different lengths implemented in the simulations for different IP values. The first column consistently represents the control condition, while alterations in CP amplitude produce distinct patterns of distribution. “A” and “C” on the top left of the figure denote the axial and circumferential direction of the vessel, respectively

Fig. 8

Left: Average CP values along the working length of the DCB among different numerically implemented thickness distributions at various IPs. CP was observed to be developed at low levels onto the endothelium located in the immediate vicinity of the proximal region of the balloon's working length. Moreover, the application of different degrees of balloon DR can lead to an eccentric distribution pattern of average CP across the vessel wall. Right: Average CPs along the circumferential axis of the vessel, among different IP values. The different blocks illustrate three of the DR conditions adopted in the simulations