Mechanical properties and fibrin characteristics of endovascular coil–clot complexes: relevance to endovascular cerebral aneurysm repair paradigms

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.

Advances in Biomaterials and Technologies for Vascular Embolization

“…[107] After 3 h of clot formation, bare platinum coils increased clot stiffness almost eight times that of clot alone, while HydroCoil did not have a significant impact on clot modulus (Figure 4A). [107] After 3 days, the stiffness of the bare platinumcoil-clot complex reduced to the same order of the HydroCoil-clot system, whereas the sources that contributed to the stiffness of complex were totally different. In particular, the coil modulus determines the stiffness of the coil-clot complex while the fibrin network contributes to the clot modulus.…”

“…It has been reported that reduced aneurysm wall stress is associated with increased stiffness of the filling material. [106] Uniaxial compression tests were performed on coil-clot complexes [107] and clot stiffness was characterized by clot modulus (Young's modulus). [107] After 3 h of clot formation, bare platinum coils increased clot stiffness almost eight times that of clot alone, while HydroCoil did not have a significant impact on clot modulus (Figure 4A).…”

“…[106] Uniaxial compression tests were performed on coil-clot complexes [107] and clot stiffness was characterized by clot modulus (Young's modulus). [107] After 3 h of clot formation, bare platinum coils increased clot stiffness almost eight times that of clot alone, while HydroCoil did not have a significant impact on clot modulus (Figure 4A). [107] After 3 days, the stiffness of the bare platinumcoil-clot complex reduced to the same order of the HydroCoil-clot system, whereas the sources that contributed to the stiffness of complex were totally different.…”

Biophysical regulation of osteotomy healing: An animal study

“…The linearly elastic, isotropic properties used for the FE model were as follows: truss members were assigned a Young's modulus (E) and Poisson's ratio (ν) of cortical bone, 10 GPa and 0.33, respectively. E and ν of the day 1 content (fibrin) and day 2–3 content (fibrin + granulation tissue) of the osteotomies were 50 kPa and 0.33 and 0.1 MPa and 0.33, respectively. The distal‐most end of the maxillary structure was then fixed while a vertical bite force of 5 N was applied at the incisal end in a positive z‐direction, which simulated the incisal bite force in mice …”

Fibrin Matrices as (Injectable) Biomaterials: Formation, Clinical Use, and Molecular Engineering

“…Fibrin is a soft material, whose stiffness values can significantly overlap with those of most human tissues, with the notable exceptions of bone and fibrocartilage. A blood clot typically has a Young's modulus around 1 kPa and a shear modulus of a few hundreds Pa; platelet‐rich fibrin is very similar, for example, exhibiting a tensile elastic modulus of about 1 kPa with 3 mg mL −1 fibrinogen . At higher concentrations, for example, in fibrin glues, elastic moduli increase considerably; for example, an elastic modulus of about 100 kPa has been recorded for Tisseel …”