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Original research
Characterization of strut indentation during mechanical thrombectomy in acute ischemic stroke clot analogs
  1. Fiona M Weafer1,2,
  2. Sharon Duffy2,
  3. Ines Machado3,
  4. Gillian Gunning2,
  5. Pasquale Mordasini4,
  6. Ellen Roche1,5,6,
  7. Peter E McHugh1,
  8. Michael Gilvarry2
  1. 1 College of Engineering and Informatics, National University of Ireland, Galway, Ireland
  2. 2 Cerenovus, Galway Neuro Technology Centre, Galway, Ireland
  3. 3 Instituto Superior Técnico, Universidade de Lisboa, Lisboa, Portugal
  4. 4 Department of Diagnostic and Interventional Neuroradiology, University of Bern, Bern, Switzerland
  5. 5 Department of Mechanical Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts, USA
  6. 6 Institute for Medical Engineering Science, Massachusetts Institute of Technology, Cambridge, Massachusetts, USA
  1. Correspondence to Dr Fiona M Weafer, National University of Ireland, Galway, Ireland; fiona.weafer{at}gmail.com

Abstract

Background Although it is common practice to wait for an ‘embedding time’ during mechanical thrombectomy (MT) to allow strut integration of a stentriever device into an occluding thromboembolic clot, there is a scarcity of evidence demonstrating the value or optimal timing for the wide range of thrombus compositions. This work characterizes the behavior of clot analogs of varying fibrin and cellular compositions subject to indentation forces and embedding times representative of those imparted by a stentriever during MT. The purpose of this study is to quantify the effect of thrombus composition on device strut embedding, and to examine the precise nature of clot integration into a stentriever device at a microstructural level.

Method Clot analogs with 0% (varying densities), 5%, 40%, and 80% red blood cell (RBC) content were created using ovine blood. Clot indentation behavior during an initial load application (loading phase) followed by a 5-min embedding time (creep phase) was analyzed using a mechanical tester under physiologically relevant conditions. The mechanism of strut integration was examined using micro-computed tomography (µCT) with an EmboTrap MT device (Cerenovus, Galway, Ireland) deployed in each clot type. Microstructural clot characteristics were identified using scanning electron microscopy (SEM).

Results Compressive clot stiffness measured during the initial loading phase was shown to be lowest in RBC-rich clots, with a corresponding greatest maximum indentation depth. Meanwhile, additional depth achieved during the simulated embedding time was most pronounced in fibrin-rich clots. SEM imaging identified variations in microstructural mechanisms (fibrin stretching vs rupturing) which was dependent on fibrin:cellular content, while µCT analysis demonstrated the mechanism of strut integration was predominantly the formation of surface undulations rather than clot penetration.

Conclusions Disparities in indentation behavior between clot analogs were attributed to varying microstructural features induced by the cellular:fibrin content. Greater indentation was identified in clots with higher RBC content, but with an increased level of fibrin rupture, suggesting an increased propensity for fragmentation. Additional embedding time improves strut integration, especially in fibrin-rich clots, through the mechanism of fibrin stretching with the majority of additional integration occurring after 3 mins. The level of thrombus incorporation into the EmboTrap MT device (Cerenovus, Galway, Ireland) was primarily influenced by the stentriever design, with increased integration in regions of open architecture.

  • stroke
  • thrombectomy
  • device
  • intervention
  • stent

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Footnotes

  • Contributors FMW: Experimental conception and design, data collection and analysis, manuscript writing and editing. SD: Clot preparation. IM: Assisted with µCT analysis. GG: Data interpretation. PM: Data interpretation, manuscript editing. ETR: Experimental conception and design, data interpretation, manuscript editing. PMc: Data interpretation. MG: Experimental conception and design, data interpretation and manuscript editing.

  • Funding This work was supported by Cerenovus, Galway and the National University of Ireland, Galway.

  • Competing interests FMW, SD, GMG, MG report a financial relationship with Cerenovus outside the submitted work.

  • Patient consent Not required.

  • Provenance and peer review Not commissioned; externally peer reviewed.

  • Data sharing statement Please contact the corresponding author with data sharing requests.