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Original research
Mechanical properties and fibrin characteristics of endovascular coil–clot complexes: relevance to endovascular cerebral aneurysm repair paradigms
  1. Kevin J Haworth1,2,
  2. Christopher R Weidner2,
  3. Todd A Abruzzo1,3,
  4. Jason T Shearn2,
  5. Christy K Holland1,2
  1. 1Division of Cardiovascular Health and Disease, Department of Internal Medicine, University of Cincinnati, Cincinnati, Ohio, USA
  2. 2Biomedical Engineering Program, University of Cincinnati, Cincinnati, Ohio, USA
  3. 3Department of Neurosurgery, University of Cincinnati, Cincinnati, Ohio, USA
  1. Correspondence to Dr Kevin J Haworth, University of Cincinnati, Department of Internal Medicine, Cardiovascular Center Room 3939, 231 Albert Sabin Way, Cincinnati, OH 45267-0586, USA; kevin.haworth{at}uc.edu

Abstract

Background Although coil embolization is known to prevent rebleeding from acutely ruptured cerebral aneurysms, the underlying biological and mechanical mechanisms have not been characterized. We sought to determine if microcoil-dependent interactions with thrombus induce structural and mechanical changes in the adjacent fibrin network. Such changes could play an important role in the prevention of aneurysm rebleeding.

Methods The stiffness of in vitro human blood clots and coil–clot complexes implanted into aneurysm phantoms were measured immediately after formation and after retraction for 3 days using unconfined uniaxial compression assays. Scanning electron microscopy of the coil–clot complexes showed the effect of coiling on clot structure.

Results The coil packing densities achieved were in the range of clinical practice. Bare platinum coils increased clot stiffness relative to clot alone (Young's modulus 6.9 kPa and 0.83 kPa, respectively) but did not affect fibrin structure. Hydrogel-coated coils prevented formation of a clot and had no significant effect on clot stiffness (Young's modulus 2 kPa) relative to clot alone. Clot age decreased fiber density by 0.2 fibers/µm2 but not the stiffness of the bare platinum coil–clot complex.

Conclusions The stiffness of coil–clot complexes is related to the summative stiffness of the fibrin network and associated microcoils. Hydrogel-coated coils exhibit significantly less stiffness due to the mechanical properties of the hydrogel and the inhibition of fibrin network formation by the hydrogel. These findings have important implications for the design and engineering of aneurysm occlusion devices.

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