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Thrombogenicity Testing for Blood-Contacting
Medical Devices in an in vitro Human Blood-Loop
Yan Chen, PhD
American Preclinical Services
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Advances in Cardiovascular Medical Devices
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Thrombogenicity TestISO 10993-4 thrombogenicity testing is widely used for meeting regulatory requirements for approval of blood-contacting medical devices.
– Thrombosis deposition
– Thromboembolism
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In vivo Thrombogenicity • In vivo implant in clinical relevant location
• In vivo thrombogenicity study– NAVI (Non-anticoagulated venous implant)
– AVI (Anticoagulated venous implant)
– NAAI (Non-Anticoagulated arterial implant)
– AAI (Anticoagulated arterial implant)
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Limitations of in vivo Model
• Acknowledged by only a few regulatory bodies
• Controversy and caveats with the methodology
– The implant position
– The implant technique
– The extent of device-vessel wall contact (Tissue Factor)
– The explant technique
– Failure of LMCD
– Hydrophilic surface
– Statistical power
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1Wolf, M. F., and Anderson, J. M., 2012, “Practical Approach to Blood Compatibility Assessments: General Considerations and Standards,” Biocompatibility and Performance of Medical Devices, J.-P. Boutrand, ed., Woodhead Publishing, Oxford, UK.
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In vitro Ovine Blood Loop
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Journal of Medical Devices:
Special Issue on Cardiovascular Device
Development
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3RS Award for in vitro Alternative Assay
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In vitro Human Blood Loop
Enhanced potential for prediction of clinical risk
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In vitro Blood Loop Configuration
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Typical Assay Design
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Blood Collection/Qualification
• Drawn from healthy donors
• Final heparin 0.7 IU per mL
• Time from collection to loading of the loop (~3 hours)
• Baseline ACT (120 – 250 seconds)
• Minimal of three donors
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Temperature Control
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Study Assessment• Thrombus formation
– % surface area coverage
• Non-adherent thrombus– Weights of non-adherent thrombus
• Blood characterization – Complete blood counts (CBC)
– Activated clotting time (ACT)
– Platelet counts
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In situ Visual Observation
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Quantitative Thrombus Assessment
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Insertion Site
= test device (Total Length = 10 cm)
= Thrombus formation
: Thrombus on segment: for 50% coverage
for 100% coverage
Cross section View - Example for Calculating Coverage
𝟑.𝟏𝒄𝒎 𝒙 𝟓𝟎% + 𝟏𝒄𝒎 𝒙 𝟏𝟎𝟎%
𝟏𝟎𝒄𝒎= 26% coverage
3.1cm 1.0 cm
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Positive and Negative Controls (N=13 studies)
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Non-Adherent Thrombus
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Weights of recovered non-adherent thrombus fromseveral sets of assays were evaluated and in only oneinstance (a positive control loop from one individualassay) was any non-adherent thrombus visible. Inthis single instance, the observed weight ofthrombus was <10 mg.
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Complete Blood Count
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Blood ACT Values
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B a s e lin e N e g a t iv e C o n tr o l P o s it iv e C o n tr o l
0
1 0 0
2 0 0
3 0 0
4 0 0
AC
T (
se
co
nd
s)
± s
tde
v
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Blood Platelet Counts
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B a s e lin e N e g a tiv e C o n tro ls P o s it iv e C o n tro ls
0
2 0 0
4 0 0
6 0 0
Pla
tele
t C
ou
nt
(10
00
's p
er µ
L)
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In vivo – in vitro Comparison• The implant position
– Uniform and consistent blood flow, Controlled tubing diameter
• The implant technique – Controlled deployment procedure
• The extent of device-vessel wall contact (Tissue Factor)– Minimal tubing wall contacting, no TF components
• The explant technique– In situ thrombus observation, non-adherent thrombus quantification
• Failure of LMCD– ?– Positive and negative control
• Hydrophilic surface– Non-adherent thrombus quantification
• Statistical power– Minimal of there different donors, up to 3 replicates per loop
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Acknowledgement
• Dr. Mark E. Smith
• Dr. Michael L. Conforti
• Sarah E. Howard
• Matthew R. Cunningham
• Abigail C. Beltrame
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