Interventional Cardiology
Figure 3: BioMime Sirolimus-eluting Stent Construction
SEM of BioMime surface
BioMime Sirolimus-eluting Stent – Primary Device Description
The BioMime SES is made of the following components: •
• •
stent – NexGen™ Cobalt Chromium Coronary Stent System; drug – sirolimus (Rapamycin) 1.25µg/mm2; and
polymer – BioPoly™, the biodegradable co-polymer combination of poly-L-lactic acid (PLLA) and poly-L-glycolic acid (PLGA).
The Right Stent Architecture The BioMime SES (see Figure 3) employs the CE-marked NexGen Cobalt Chromium Coronary Stent System – a novel concept conceived to minimise intra-arterial injury.
Stent cross-section
Ultra-low strut thickness 65µm Co–Cr L605 struts
Sirolimus (1.25µg/mm2 ) +
biodegradable polymer coating
The design stretches the boundaries of structural engineering with an ultra-low strut thickness (65µm) stent maintained across all 54 dimensions without any loss in radial strength. On bench testing, NexGen demonstrates a high radial strength of 1.1 bar with a mean recoil of
Figure 4: Morphology-mediated Expansion Crimped stent
The novel stent design ensures a morphology-mediated expansion27 (see Figure 4) due to a hybrid cell design structure (open-cell configurations in the centre and closed at the edges). This unique method of expansion eliminates the classic dog-boning seen in conventional designs and also ensures minimal edge injury.27 Furthermore, the struts have unique strut width variability (see Figure 5), which ensures flexibility while retaining high radial strength. Evidently, due to these features, the stent demonstrates superior acute gain (see Figure 6) and complete wall apposition. Thus, it appears to endothelialise quickly (see Figure 7) in porcine coronary artery models at 28 days.27
Morphology-mediated expansion™
The stent delivery system also ensures minimal arterial injury. The semi-compliant rapid exchange balloon catheter shoulders are carefully constructed short tapers and abrupt with a marginal over- hang (see Figure 8). This allows for high trackability and deliverability at the same time, minimising any chance of balloon-related edge injury.27
Fully expanded stent
Figure 5: Strut Width Variability in NexGen™ Cobalt–Chromium Stent
The resultant stent system has a predictably low injury profile. Simons et al. have proved through their experimental work that topography of the stent as measured by its strut thickness has a direct impact on endothelialisation,28
and Kastrati et al. have proved
through the Intracoronary Stenting and Angiographic Results: Strut Thickness Effect on Restenosis Outcome (ISAR-STEREO)29 STEREO 230
and ISAR Y-connector S-link Mirror polish
Figure 6: Optimal Scaffolding with a Metal-to-artery Ratio of ~14%
trials that low strut thickness stents, irrespective of the stent design, are associated with a significant reduction of angiographic and clinical restenosis after coronary stenting. In an interesting pre-clinical evaluation undertaken in a porcine coronary artery model, low strut thickness (65µm) NexGen™ stents were compared with high strut thickness (91µm) Driver stent (Medtronic, US). Piglets were sacrificed at 28 and 90 days to appraise the biocompatibility. The primary end-point was mid in-stent neointimal thickness. Histomorphometric analysis at 28 days showed significant differences in mid-stent neointimal thickness: 0.18±0.08mm for NexGen segments versus 0.30±0.41mm for Driver segments; p=0.03 favouring thinner strut cobalt chromium stents (see Figure 9). This beneficial result was maintained at 90 days: 0.09±0.04mm for NexGen segments versus 0.25±0.03mm for Driver segments.27
This study corroborates earlier stated results obtained in humans by Kastrati et al., which allowed for predictability in
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