Development of a bioresorbable self-expanding microstent for interventional applications - an innovative approach for stent-assisted coiling.

OBJECTIVES: Stent-assisted coiling prevents coil migration in broad-based intracranial aneurysms. So far, only permanent metal stents are approved for intracranial use. Bioresorbable stents allow a new therapeutic approach that may prevent the need for lifelong anticoagulation. We developed a neurovascular bioresorbable microstent (NBRS) and compared it in vitro to the commercial Neuroform EZ stent. MATERIALS AND METHODS: The self-expanding NBRS design is oriented on the Neuroform EZ stent. Poly L-lactic acid (PLLA) was used to manufacture semi-finished products in a dipping process. For the compensation of the inferior material properties of PLLA, design adjustments were made. The NBRS were cut by means of femtosecond (fs) laser and were morphologically and mechanically compared in vitro to the Neuroform EZ stent. In vitro implantation of an NBRS was performed using a complex patient-specific 3D-printed aneurysm model. In addition, an in vitro coiling procedure to assess the stent's ability to support a coil package was conducted. RESULTS: The NBRS could be reproducibly manufactured and had high quality regarding surface morphology. The radial force at the indicated vessel diameter of 3.0 mm was slightly higher for the Neuroform EZ stent compared to the NBRS. The self-expansion ability of the NBRS could be proven. The kink behavior of the NBRS was comparable to that of the Neuroform EZ stent, so no vessel lumen size reduction is expected. The stents showed identical deformation under local compression of 25 % based on the initial diameter, resulting in maximum forces of 24 ±â€Š5 mN (Neuroform EZ) and 8 ±â€Š2 mN (NBRS). The implanted NBRS expanded uniformly, and proper vessel wall adaptation was observed. The NBRS has the ability to retain a coil package. CONCLUSION: This study reported a reproducible manufacturing process for the developed NBRS as well as mechanical and morphological in vitro tests. Furthermore, successful NBRS implantation into a complex patient-specific vessel model was presented as proof of concept. The promising results of this study, also considering the commercial Neuroform EZ stent, support the idea of fully biodegradable microstents for intracranial aneurysm treatment. KEY POINTS: · High-performance polymer-based self-expanding neurovascular microstents were manufactured with good reproducibility.. · The bioresorbable microstent meets the requirements to pass through narrow radii.. · Implantability in a patient-specific and close-to-physiology vascular in vitro model was proven..

Revisiting SFA stent technology: an updated overview on mechanical stent performance.

OBJECTIVES: The study investigated mechanical parameters of stent systems indicated for treatment of femoropopliteal (FP) arterial disease to support interpretation of clinical results and the related causalities. METHODS: Eight stent system types of same dimensions were investigated (n=2). Parameters were the profile of stent delivery system (SDS), radiopacity, trackability and pushability, bending stiffness (flexibility) and axial stiffness of expanded stents, length change during expansion, radial force, crush resistance, strut thickness and general surface condition. RESULTS: The trackability ranged from 0.237 to 0.920 N and the pushability was 47.9-67.6 %. The bending stiffness of SDS was between 108.42 and 412.68 N mm2. The length change during stent release to 5 mm was low, with one exception. The bending stiffness of the expanded stents was 2.73-41.67 N mm2. The normalized radial forces at 5 mm diameter ranged from 0.133 N/mm to 0.503 N/mm. During non-radial compression by 50 %, the forces were 3.07-8.42 N, with one exception (58.7 N). The strut thickness was 153-231 µm. CONCLUSIONS: Large differences occurred for flexibility, radial force and length change during expansion. The data should be used when choosing the proper device for restoring vascular function.

Initial Clinical Results and In Vitro Testing of the New CGuard MicroNet-Covered "One-Size-Fits-All" Carotid Stent.

Purpose: To evaluate a MicroNet-covered stent designed for the carotid artery with the new ability to adjust to different vessel diameters. Materials and Methods: Thirty consecutive patients (mean age 72.1±7.7 years; 26 men) with symptomatic stenosis (86.3%±6.4%) of the internal carotid artery were treated with the new self-adjusting nitinol stent, which has a self-expanding, open-cell design covered by an outer conformable layer (MicroNet). The only stent used was the "One-Size-Fits-All" CGuard stent with lengths of 30 or 40 mm. In bench testing, the chronic outward force of the One-Size-Fits-All stent was determined with a segmented head radial force test device. The stent was deployed directly into the test device at a diameter of 5.0 mm, and the chronic outward force was measured up to 10.0 mm, the maximum expansion of the stent. Results: The stent was successfully implanted in all 30 patients without periprocedural complications, including no neurological events within 30 days. The chronic outward force normalized by stent length demonstrated a near-equivalent radial force outcome: The stent displayed only a minor difference between the minimal radial force at 9.0 mm (0.195 N/mm) and the maximal radial force at 5.5 mm (0.330 N/mm). Conclusion: The new self-adjusting, MicroNet-covered stent has high conformability combined with an almost equivalent radial force at expansion diameters ranging from 5.5 to 9.0 mm. The first clinical results demonstrate that the new One-Size-Fits-All stent can be safely implanted in internal carotid arteries with reference diameters within this range.

Mechanical behavior of in vivo degraded second generation resorbable magnesium scaffolds (RMS).

Resorbable magnesium scaffolds are used for the treatment of atherosclerotic coronary vascular disease and furthermore, for vascular restoration therapy. Recently, the first-in-man clinical studies with Magmaris showed promising results regarding the target lesion failure as well as vasomotion properties after 12 and 24 month. The consistency of in vivo degraded magnesium alloys in a cardiovascular environment is qualitatively described in literature, but only little has been disclosed about the actual change in mechanical properties and the behavior of the magnesium alloy degradation products. In the present study, uncoated magnesium scaffolds 3.0 × 20 mm were implanted in coronary arteries of two healthy Goetinnger mini-swine. The scaffolds were explanted to evaluate the mechanical properties of the degraded magnesium scaffolds after 180 days in vivo. Ex vivo sample preparation and test conditions were adapted to a customized compression test setup which was developed to investigate the micro-scale scaffold fragments (width 225 ±â€¯75 µm, thickness 150 µm). As reference bare undegraded magnesium scaffold fragments were tested. Mechanical parameters relating to force as a function of displacement were determined for both sample groups. The undegraded samples showed no fracturing at the maximum applied force of 8 N, whereas the in vivo degraded test samples showed forces of 0.411 ±â€¯0.197 N at the first fracturing and a maximum force of 0.956 ±â€¯0.525 N. The deformation work, calculated as area beneath the force-displacement curve, of the in vivo degraded test samples was reduced by approximately 87-88% compared to the undegraded samples (5.20 mN mm and 40.79 mN mm, both at 7.5% deformation). The indication for a complete loss of structural integrity through a reduction of mechanical properties after a certain degradation time increases the chance to restore vascular function and physiological vasomotion in the stented vessel compartment.

Direct comparison of coronary bare metal vs. drug-eluting stents: same platform, different mechanics?

BACKGROUND: Drug-eluting stents (DES) compared to bare metal stents (BMS) have shown superior clinical performance, but are considered less suitable in complex cases. Most studies do not distinguish between DES and BMS with respect to their mechanical performance. The objective was to obtain mechanical parameters for direct comparison of BMS and DES. METHODS: In vitro bench tests evaluated crimped stent profiles, crossability in stenosis models, elastic recoil, bending stiffness (crimped and expanded), and scaffolding properties. The study included five pairs of BMS and DES each with the same stent platforms (all n = 5; PRO-Kinetic Energy, Orsiro: BIOTRONIK AG, Bülach, Switzerland; MULTI-LINK 8, XIENCE Xpedition: Abbott Vascular, Temecula, CA; REBEL Monorail, Promus PREMIER, Boston Scientific, Marlborough, MA; Integrity, Resolute Integrity, Medtronic, Minneapolis, MN; Kaname, Ultimaster: Terumo Corporation, Tokyo, Japan). Statistical analysis used pooled variance t tests for pairwise comparison of BMS with DES. RESULTS: Crimped profiles in BMS groups ranged from 0.97 ± 0.01 mm (PRO-Kinetic Energy) to 1.13 ± 0.01 mm (Kaname) and in DES groups from 1.02 ± 0.01 mm (Orsiro) to 1.13 ± 0.01 mm (Ultimaster). Crossability was best for low profile stent systems. Elastic recoil ranged from 4.07 ± 0.22% (Orsiro) to 5.87 ± 0.54% (REBEL Monorail) including both BMS and DES. The bending stiffness of crimped and expanded stents showed no systematic differences between BMS and DES neither did the scaffolding. CONCLUSIONS: Based on in vitro measurements BMS appear superior to DES in some aspects of mechanical performance, yet the differences are small and not class uniform. The data provide assistance in selecting the optimal system for treatment and assessment of new generations of bioresorbable scaffolds. TRIAL REGISTRATION: not applicable.

Clinical Results and Mechanical Properties of the Carotid CGUARD Double-Layered Embolic Prevention Stent.

PURPOSE: To report early clinical outcomes with a novel double-layer stent for the internal carotid artery (ICA) and the in vitro investigation of the stent's mechanical properties. METHODS: A prospective single-center study enrolled 30 consecutive patients (mean age 73.1±6.3 years; 21 men) with symptomatic (n=25) or high-grade (n=5) ICA stenosis treated with the new double-layer carotid CGUARD Embolic Prevention System (EPS) stent, which has an inner open-cell nitinol design with an outer closed-cell polyethylene terephthalate layer. The average stenosis of the treated arteries was 84.1%±7.9% with a mean lesion length of 16.6±2.1 mm. In the laboratory, 8×40-mm stents where tested in vitro with respect to their radial force during expansion, the bending stiffness of the stent system and the expanded stent, as well as the collapse pressure in a thin and flexible sheath. The wall adaptation was assessed using fluoroscopy after stent release in step and curved vessel models. RESULTS: The stent was successfully implanted in all patients. No peri- or postprocedural complications occurred; no minor or major stroke was observed in the 6-month follow-up. The bending stiffness of the expanded stent was 63.1 N·mm2 and (not unexpectedly) was clearly lower than that of the stent system (601.5 N·mm2). The normalized radial force during expansion of the stent to 7.0 mm, consistent with in vivo sizing, was relatively high (0.056 N/mm), which correlates well with the collapse pressure of 0.17 bars. Vessel wall adaptation was harmonic and caused no straightening of the vessel after clinical application. CONCLUSION: Because of its structure, the novel CGUARD EPS stent is characterized by a high flexibility combined with a high radial force and very good plaque coverage. These first clinical results demonstrate a very safe implantation behavior without any stroke up to 6 months after the procedure.

In vitro performance investigation of bioresorbable scaffolds - Standard tests for vascular stents and beyond.

BACKGROUND/PURPOSE: Biodegradable polymers are the main materials for coronary scaffolds. Magnesium has been investigated as a potential alternative and was successfully tested in human clinical trials. However, it is still challenging to achieve mechanical parameters comparative to permanent bare metal (BMS) and drug-eluting stents (DES). As such, in vitro tests are required to assess mechanical parameters correlated to the safety and efficacy of the device. METHODS/MATERIALS: In vitro bench tests evaluate scaffold profiles, length, deliverability, expansion behavior including acute elastic and time-dependent recoil, bending stiffness and radial strength. The Absorb GT1 (Abbott Vascular, Temecula, CA), DESolve (Elixir Medical Corporation, Sunnyvale, CA) and the Magmaris (BIOTRONIK AG, Bülach, Switzerland) that was previously tested in the BIOSOLVE II study, were tested. RESULTS: Crimped profiles were 1.38±0.01mm (Absorb GT1), 1.39±0.01mm (DESolve) and 1.44±0.00mm (Magmaris) enabling 6F compatibility. Trackability was measured depending on stiffness and force transmission (pushability). Acute elastic recoil was measured at free expansion and within a mock vessel, respectively, yielding results of 5.86±0.76 and 5.22±0.38% (Absorb), 7.85±3.45 and 9.42±0.21% (DESolve) and 5.57±0.72 and 4.94±0.31% (Magmaris). Time-dependent recoil (after 1h) was observed for the Absorb and DESolve scaffolds but not for the Magmaris. The self-correcting wall apposition behavior of the DESolve did not prevent time-dependent recoil under vessel loading. CONCLUSIONS: The results of the suggested test methods allow assessment of technical feasibility based on objective mechanical data and highlight the main differences between polymeric and metallic bioresorbable scaffolds.