1. Biomechanical Assessment of Bioresorbable Devices
Nicolas Foin, MSc, PhD
Adj. Associate Professor
NATIONAL HEART CENTRE SINGAPORE/
DUKE-NUS MEDICAL SCHOOL

2. Nicolas Foin, MSc, PhD
No relevant financial relationships in the context of this presentation
Speaker’s Honorarium: Abbott Vascular, Biotronik
from Feb 2017: Philips-Volcano

3. Agenda
Biomechanical attributes and limitations with current generation BRS
Next Gen thin-strut BRS: What improvements to expect

4. BRS mechanical strength is determined by:
Biodegradable Materials
BRS mechanical strength
is determined by:
SCAFFOLD MATERIAL
PROCESSING
SCAFFOLD DESIGN
STRUT THICKNESS – WIDTH
Courtesy Zeus Biomaterials
- Thermal treatment (Annealing)
- Polymer orientation/stretching

5. Material Strength and Strut thickness
COBALT CHROMIUM
STAINLESS STEEL MG
PLA POLYMER
Adapted from Meyer-Kobbe, PCR, 2015

6. 1. BRS radial force compared with metallic stent
Adapted from Meyer-Kobbe,
PCR, 2015
Foin et al. 2015
Oberhauser. EuroIntervention (2009) Vol. 5 F15-F22

7. Insights From Absorb trials
Serruys, 2015

8. Insights from expansion in an Asymmetric Lesion Model
Bioabsorbable Vascular Scaffold Radial Expansion and Conformation Compared to a Metallic platform
Insights from expansion in an Asymmetric Lesion Model
In a model fibrotic lesion:
Higher Eccentricity with BVS
Smaller MLD compared with Metal
Residual stenosis hard to correct after BVS implantation
“what you prep is what you get “
Angiographic predictors of BVS Thrombosis, T. Gori, PCR 2015
Foin, Lee, Bourantas, et al. Euroint 2016

9. 2. “Footprint”, or Strut to Artery Ratio
Surface of the vessel wall covered by stent material
Angiographic predictors of BVS Thrombosis, T. Gori, PCR 2015
Puricel. J Am Coll Cardiol 2016;67:921–31
Magmaris 3.0 Mg
20%
Foin et al, J Am Coll Cardiol

10. 3. Post-Expansion

11. Area to improve: In-vitro BVS post-expansion
Post-expansion of a 3.0mm BVS scaffold deployed within a silicon lesion model
Limit on BRS post-dilatation
Lesser overexpansion is possible in presence of a lesion
Respect manufacturer recommendation for BVS : Maximal 0.5mm Overexpansion above scaffold nominal size
Foin et al. Euroint. Mar 2016

12. 4. Evolution in strut thickness from DES to BRS
Int J. Cardiology 2014

13. Strut Thickness Impacts Healing
Large Struts associated with delayed strut coverage and healing
More Endothelialization
% Strut Coverage
Alternative title –
Thicker Struts associated with delayed strut coverage and healing
ABSORB™ Stent
Biomatrix™ Stent
SYNERGY™ Stent
150 µm (0.0059”)
120 µm (0.0047”)
74 µm* (0.0029”)
Uncovered struts predictive of late stent thrombosis 1
* Strut thickness for small vessel model is 74μm, Workhorse model is 79μm and large vessel is 81μm. 1. Finn A, Joner M et al, Circulation 2007;115:
Rabbit Model. Presented by Renu Virmani, MD. TCTAP 2014.

14. Impact of Strut Thickness on Thrombogenicity
Thicker struts associated with increased acute thrombogenicity
SYNERGY
BVS
Thick Strut DES
Thin Strut DES
Koskinas et al
Top Figure: Thick, rectangular struts promote stent thrombogenicity. High endothelial shear stress (ESS) on top of struts activates platelets to release adenosine diphosphate (ADP), a potent platelet aggregation promoter. Recirculation zones with low ESS downstream of the strut increase local concentration of activated platelets, retard re endothelialization, and attenuate the production of natural anticoagulants.
Bottom Figure: Thin, circular struts retain physiologic ESS, which favors platelet quiescence on top of struts and enhances re-endothelialization and production of antithrombotic factors downstream of struts.
Red circle activated platelet; Red line quiescent platelet.
ESS endothelial shear stress; NO nitric oxide; PGI2 prostacyclin; tPA tissue plasminogen activator; vWF von Willebrand factor.
Koskinas et al. J Am Coll Cardiol 2012;59:1337–49
Michael Joner, MD, EuroPCR 2014
Thrombus formation assessed by immunofluorescence staining for platelet marker CD61 after 1 hour in ex-vivo pig AV shunt model 14

15. Serruys, Chevalier, TCT 2016

16. Impact of Malapposition on Thrombogenicity
Malapposition impacts more acute thrombogenicity than Strut size

17. II. Next GEN BRS: The thinner the better ?

18. BRS Scaffolds under Development
Updated Foin et al., TCT 2016, Int J Card. 2016

19. What to expect from new thin-strut BRS ?
1st Gen
Thick strut
2nd Gen
Thin strut
+ Radial Force
+ Prevent elastic recoil
- Low Deliverability
- Higher Neointimal area
Flow disturbances
High SAR
+ Deliverability + Flexibility
+ Lesser Neointima area
+ Lesser Flow disturbances
Radial strength ?
Risk of elastic recoil ?
If the material remains the same, reducing strut thickness will also reduces scaffold strength
Thinner strut BRS reduces flow disturbances
BVS
160 um
Next Gen
100 um
Xience
Foin, Soh, Leo, Torii 2015

20. Progression of Oriented Tubing for BRS
Control of polymer morphology enables biaxial orientation to create stronger and tougher polymer tubing with thinner walls which translates to thinner BRS struts.
Courtesy Zeus Biomaterials
Material -Design – Process Improvements can reduce strut thickness while maintaining good scaffolding mechanical ppties

21. Impact of Strut Thickness on Radial Strength ?
Nef, Foin, PCR 2016
81 um
150 um
120 um
150 um
Material CoCr PLLA PLLA PLLA
*DESolve Cx is not available for sale.
Data on file at Elixir Medical

22. Summary: BRS Biomechanical Assessment:
Current and next Gen Thin-strut designs
BRS behave very differently than metallic DES
Current gen BRS:
Full lesion preparation is mandatory: under-expansion leads to high SAR/footprint and unfavorable outcome
Post-dilatation is recommended to optimise BRS apposition and reduce flow disturbance.
Large profile/Strut thickness does remain a limitation
Newer Thin-strut BRS platforms are emerging with strut thickness reduced to um: Radial Force, Expansion and fracture resistance need to be at least equivalent to 1st gen BRS
Advantages of thin-strut BRS struts:
1. Improved Deliverability
2. Better strut-wall hemodynamic environment
3. Faster coverage
> All of which should translate in improved clinical results (trials on the way!)

23. Thank you ! This research was conducted at NHCS/ Duke-NUS,
Acknowledgements: J. Ng ; S. Lu; H.Y. Ang; D.R. Lee; A. Mattesini; G. Caizzano; G. Lan; J. E. Davies; C Di Mario; M. Joner; Y.Onuma; P. Wong ; H. Nef; P.W. Serruys