The bending properties of catheters and stents have a big influence on their success during clinical application. Whereas bending stiffness directly affects the trackability of catheters, stents underlie bending when used for renal, superficial femoral or femoro-popliteal arteries, respectively. A three-point bending test setup according to ASTM F2606 was implemented into a universal testing machine and was validated regarding influence parameters such as accuracy of force measurement, test speed and span length. The bending stiffness can be calculated from the initial linear portion of the force-deflection curve. Furthermore, a multi-cycle approach was developed to evaluate the bending properties at large deformations revealing the deflection depending peak load as well as deflection depending elastic recovery rate after unloading. Within this study samples with a length of 120 cm from the proximal region of a commercial coronary balloon catheter were used. Influence of test speed was not significant. However, bending stiffness increased with increasing span length. For multi-cycle measurements a constant test speed and constant span length was used. Test results showed an increasing plastic deformation and peak load as well as a decreasing elastic recovery rate as expected. The presented test method can be used for catheters as well as stents with a length diameter ration of at least 4:1.

Transcatheter aortic valve replacement (TAVR) has become the standard treatment of multimorbid patients with severe aortic valve stenosis. One frequently observed complication after TAVR procedure is the occurence of paravalvular leakage (PVL). PVL is caused by a gap between the vessel wall and the TAVR stent, enabling blood to flow from the aorta back to the ventricle during diastolic phase. A high PVL rate leads to increased mortality of TAVR patients. To avoid this complication, pericardial skirts were developed by manufacturers to seal the leakage gap. Furthermore, the aim is to improve the conforming expansion of the TAVR stent to the vessel wall, especially for the self-expanding TAVR consisting of nitinol. One factor for the expansion is the size and shape of the TAVR stent cells, which vary between 9 and 15 cells around the circumference of established TAVR devices. To quantify the impact of different cell sizes on the occurence of PVL, we performed numerical studies with different TAVR designs and investigated the PVL for each TAVR design. For this purpose, we developed three different TAVR designs with 9, 12 and 15 stent cells around the circumference of the TAVR. These were deployed into a generic aortic root model with standardized calcification in the annulus region using finite element simulations. Afterwards, the PVL was calculated using numerical flow simulations. We found that the TAVR stent design with nine cells had the highest PVL rate (11.2mLs−1). In contrast, the TAVR stent design with 15 cells had the lowest PVL (4.8mLs−1). Our study thus showed a decisive impact of cell size on the sealing behavior of the TAVR stent and, accordingly, the PVL.

Due to promising results, the patient cohort for transcather aortic valve replacement (TAVR) has been extended in recent years to include patients with a bicuspid aortic valve (BAV). There are different types of BAV. One variant is the tricommisural bicuspid aortic valve (TBAV). BAV have an increased risk of post-TAVR complications such as paravalvular leakage. In the case of paravalvular leakage, blood flows past the prosthesis back into the ventricle during diastole. Clinically, patients with BAV are often predilated.

For this reason, we want to investigate how pre-dilatation of BAV can affect the leakage rate. A simplified model is used for pre-dilatition, where the calcification nodule is cut along the free edge of the leaflets before the deployment.

In order to evaluate the effects of this method, a deployment simulation was carried out for both geometries using an explicit calculation. A flow simulation was then performed to determine the paravalvular leakage.

The pre-dilatation allows the leaflets to move independently of each other. Without pre-dilatation, the TAVR cannot fully expanded. The leakage rate is higher for the BAV than for the

predilated geometry (53.1mLs−1 vs. 19.4mLs−1).

In this model, we have shown the effect of pre-dilatition on implantation results.

Introduction

The ingress of bodily fluids into active implantable medical devices (AIMDs) poses a significant risk of failure. Delamination progresses along metal-polymer junctions of electrodes and conductive pathways leading to leakage currents and insulation faults, potentially causing device failure. However, understanding these delamination mechanisms is difficult due to the complex electrochemical-diffusive processes involved. To address this challenge a standardized test method and specimen were developed to investigate diffusion-based delamination processes of the polymer-metal interface. Medical grade materials were chosen for better transferability to real AIMD.

Method

As it is common in AIMD, such as cochlear implants, a medical grade silicone and platinum were chosen. Since the test uses a chemical reaction of the metallic surface to visualize diffusion in the silicone-platinum-interface, an indicator structure was added onto the platinum using PVD. For this study copper was chosen as it yields an intense color change in the chemical reaction and allows the corrosion process to be visualized without the use of hazardous chemicals simply by color-change. The test-specimens were immersed in a potassium sulfide solution serving as corroding agent. This way the corrosion time of the metallic layer was reduced to a few seconds, allowing an isolated investigation on delamination and diffusion phenomena. During the experiment, images were taken with a time-lapse camera, on which the progress of the diffusion front in the interface was observed. The images were analyzed in an automated Matlab script.

Results

The indicator structure was suitable to visualize and investigate the diffusion processes in the silicone-platinum interface. The experiments showed a high permeability and diffusion rate for ionic molecules that penetrate from the water into the interface.

Conclusion

The developed test has the potential to provide a better understanding of the degradation processes in the metal-polymer interface of AIMD. Furthermore, the test can be adapted for other substances by a suitable choice of indicator structures to investigate the diffusion rates in the interface for different substances.

For treating idiopathic sudden sensorineural hearing loss, prednisolone is commonly used. However, systemic or middle ear injections often lead to insufficient drug delivery to the inner ear, causing ineffective treatment and systemic side effects. An implant inserted into the middle ear and delivering the drug directly to the inner ear offers a promising solution, providing controlled, long-term drug release with potentially better efficacy and fewer side effects. Individualized implants made of prednisolone-containing silicone can optimize inner ear treatment by fitting the patient's middle ear anatomy.

To gauge the properties of prednisolone-21-hydrogen succinate containing silicone, samples with different geometries and drug concentrations have been 3D printed. The shore hardness of samples with three different drug concentration was assessed. Three different shapes with four different drug concentrations were incubated in artificial perilymph for up to 56 days to evaluate the release rates. The resulting eluates were analysed via Ultra high precision liquid chromatography coupled with a time-of-flight micro-mass spectrometer.

Samples were softer when a higher drug concentration was used. A high burst release of prednisolone after one hour was measured. Afterwards the release rates decreased and reached a relative constant rate after ten days and stayed there for at least another 46 days. The release rates were multiple times higher, when the samples had a higher surface to volume ratio. The softer the sample, the higher was the release rate, unproportional to the concentration increase.