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    Biomaterials

    (C-102) Adhesion Strength of Embolus Analogs on Common Biomaterials

    Friday, October 13, 2023
    9:30 AM – 10:30 AM PDT
    Location: Exhibit Hall - Row C - Poster # 102
    Introduction::

    Thrombus formation on blood-contacting medical devices is a common problem that can limit the success of such devices [1]. Clotting on devices poses a risk of clot embolization to the narrow blood vessels of the brain, heart, or other vital organs [1]. Furthermore, recent studies suggest that the mechanical properties of clots can influence the success of clot removal procedures [2]. Some studies have investigated quantification of the tensile and compressive properties of human blood clots, but adhesion strength of clots remains unexplored despite known thrombosis risk of cardiovascular devices [3]. For this reason, it is important to characterize the adhesion strength of blood clots in blood-contacting medical devices. This work aims to characterize adhesion of human embolus analogs on various biomaterials used in blood-contacting devices.



    Materials and Methods:: Blood was collected from human donors following an approved IRB protocol and was separated via centrifugation and reconstituted to 214 x 106 platelets per mL and 40% hematocrit. The blood was recalcified with 20 mM calcium chloride and 0.25 U/mL human thrombin. The recalcified blood (1 mL) was pipetted into cylindrical molds of 14 mm diameter and fitted on a 25 x 25 mm of biomaterial surface. The biomaterials considered for this study were polytetrafluorethylene (PTFE), poly ether ketone (PEEK), polyurethane (PU), nitinol, and titanium. Samples (n=6) were collected per material with replicates (n=6) for each surface. The blood samples were incubated at 37°C for 1 hour to form clots on the materials. The samples were loaded onto an Instron uniaxial load frame (Norwood, MA, USA). The top surface of the clot is attached to a vacuum fixture that applied a pressure of -200 mmHg, which is attached to the upper load cell of the frame. The sample was then loaded at 10% strain per second until the clot detached from the biomaterial.

    Results, Conclusions, and Discussions::

    Results: A mean detachment stress-strain plot for the clots adhered to each of the biomaterials is shown in Figure 1, where the peak of the trendlines indicates the clot detachment point. From the data, it was observed that blood clots attached to nitinol required a larger stress to detach from the surface than blood clots attached to titanium and polymeric surfaces. The mean detachment stress for nitinol and titanium were 0.68 ± 0.19 kPa and 0.52 ± 0.13 kPa, respectively. The mean detachment stress value of the polymeric biomaterials PTFE, PEEK, and PU were 0.50 ± 0.17 kPa, 0.46 ± 0.12 kPa, 0.44 ± 0.13 kPa, respectively. No significant differences were observed for the detachment stress values between titanium and the polymeric materials. The only significant difference in the detachment stress was noticed between nitinol than and polyurethane. The clots formed on titanium surface also had the highest mean detachment strain of 12.70 ± 3.53%. However, the largest mean modulus of the materials was noticed for the clots attached to nitinol (5.83 ± 1.97 kPa). 


    Conclusions: Although the trendlines for the detachment stress and strain show differences between materials, the differences between the polymeric materials and titanium were not significant. However, the only significant difference was observed between nitinol and polyurethane and that higher stress is required to detach the clots formed on nitinol surfaces than the clots on other biomaterials. The difference in detachment stress magnitude suggests blood clots adhere to nitinol more than titanium and other polymeric materials. Additionally, all materials demonstrate an irregular detachment pattern, suggesting an inhomogenous attachment at the clot-surface interface.


    This study has a few limitations that are worth considering. First, the blood embolus analogs used in this study were formed statically. The properties of statically formed embolus analogs can differ from dynamically formed clots. Second, the materials used in this study were not characterized and treated such that the surface is consistent with medical-grade devices. Nevertheless, this work provides an understanding of the adhesion of blood clot analogs on different biomaterials.


     



    Acknowledgements (Optional): :

    This research was supported, in part, by U.S. NIH HL146921, NSF CMMI-2017805, NIH T32GM108563, an Alfred P. Sloan Scholarship, and a Gates Millennium Scholarship. 



    References (Optional): :

    [1] Jaffer IH, et al., Medical Device-induced thrombosis: what causes it and how can we prevent it? Acta Biomaterialia. 2019; 94: 2-10


    [2] Boodt N, et al., Mechanical characterization of thrombi retrieved with endovascular thrombectomy in patients with acute ischemic stroke. Stroke. 2021; 52(8), 2510-2517


    [3] Cahalane, R.M.E, et al., Tensile and Compressive Mechanical Behaviour of Human Blood Clot Analogues. Annals of Biomedical Engineering. 2023; 51(8): 1759–1768.