Molecular Biomarkers for In Vitro Thrombogenicity Assessment of Medical Device Materials.

To develop standardized in vitro thrombogenicity test methods for evaluating medical device materials, three platelet activation biomarkers, beta-thromboglobulin (β-TG), platelet factor 4 (PF4), soluble p-selectin (CD62P), and a plasma coagulation marker, thrombin-antithrombin complex (TAT), were investigated. Whole blood, drawn from six healthy human volunteers into Anticoagulant Citrate Dextrose Solution A was recalcified and heparinized over a concentration range of 0.5-1.

Development of a large diameter in vitro flow loop thrombogenicity test system.

Background: To accommodate a wider range of medical device sizes, a larger in vitro flow loop thrombogenicity test system using 9.5 -mm inner diameter (ID) tubing was developed and evaluated based on our previously established 6.4 -mm ID tubing system.

In vitro test methods for evaluating high molecular weight polyethylene oxide polymer induced hemolytic and thrombotic potential.

To combat opioid abuse, the U.S. Food and Drug Administration (FDA) released a comprehensive action plan to address opioid addiction, abuse, and overdose that included increasing the prevalence of abuse-deterrent formulations (ADFs) in opioid tablets.

In Vitro Thrombogenicity Testing of Biomaterials in a Dynamic Flow Loop: Effects of Length and Quantity of Test Samples.

The results of in vitro dynamic thrombogenicity testing of biomaterials and medical devices can be significantly impacted by test conditions. To develop and standardize a robust dynamic in vitro thrombogenicity tool, the key test parameters need to be appropriately evaluated and optimized. We used a flow loop test system previously developed in our laboratory to investigate the effects of sample length and the number of samples per test loop on the thrombogenicity results.

Effect of Temperature on Thrombogenicity Testing of Biomaterials in an In Vitro Dynamic Flow Loop System.

To develop and standardize a reliable in vitro dynamic thrombogenicity test protocol, the key test parameters that could impact thrombus formation need to be investigated and understood. In this study, we evaluated the effect of temperature on the thrombogenic responses (thrombus surface coverage, thrombus weight, and platelet count reduction) of various materials using an in vitro blood flow loop test system. Whole blood from live sheep and cow donors was used to assess four materials with varying thrombogenic potentials: negative-control polytetrafluoroethylene (PTFE), positive-control latex, silicone, and high-density polyethylene (HDPE).

Results of the Interlaboratory Computational Fluid Dynamics Study of the FDA Benchmark Blood Pump.

Computational fluid dynamics (CFD) is widely used to simulate blood-contacting medical devices. To be relied upon to inform high-risk decision making, however, model credibility should be demonstrated through validation. To provide robust data sets for validation, researchers at the FDA and collaborators developed two benchmark medical device flow models: a nozzle and a centrifugal blood pump.

Comparison of animal and human blood for in vitro dynamic thrombogenicity testing of biomaterials.

Background: To determine suitable alternatives to human blood for in vitro dynamic thrombogenicity testing of biomaterials, four different animal blood sources (ovine, bovine, and porcine blood from live donors, and abattoir porcine blood) were compared to fresh human blood.

Methods: To account for blood coagulability differences between individual donors and species, each blood pool was heparinized to a donor-specific concentration immediately before testing in a dynamic flow loop system. The target heparin level was established using a static thrombosis pre-test.

The effect of blood viscosity on shear-induced hemolysis using a magnetically levitated shearing device.

Introduction: Blood contacting medical devices, including rotary blood pumps, can cause shear-induced blood damage that may lead to adverse effects in patients. Due in part to an inadequate understanding of how cell-scale fluid mechanics impact red blood cell membrane deformation and damage, there is currently not a uniformly accepted engineering model for predicting blood damage caused by complex flow fields within ventricular assist devices (VADs).

Methods: We empirically investigated hemolysis in a magnetically levitated axial Couette flow device typical of a rotary VAD.

Platelet and leukocyte count assay for thrombogenicity screening of biomaterials and medical devices: Evaluation and improvement of ASTM F2888 test standard.

An appropriate preclinical thrombogenicity evaluation of a blood-contacting device is important to reduce thrombosis and thromboembolism risks to patients. The in vitro platelet and leukocyte count assay, as described in the ASTM F2888 test standard, aims to assess thrombogenic potentials of blood-contacting materials. The goals of this study were to evaluate whether this standardized test method can effectively differentiate materials with different thrombogenic potentials and to investigate the impact of anticoagulation conditions on test sensitivity.

Preclinical Device Thrombogenicity Assessments: Key Messages From the 2018 FDA, Industry, and Academia Forum.

Device-related thrombosis and thromboembolic complications remain a major clinical concern and often impact patient morbidity and mortality. Thus, improved preclinical thrombogenicity assessment methods that better predict clinical outcomes and enhance patient safety are needed. However, there are several challenges and limitations associated with developing and performing preclinical thrombogenicity assessments on the bench and in animals (e.

An In Vitro Blood Flow Loop System for Evaluating the Thrombogenicity of Medical Devices and Biomaterials.

A reliable in vitro dynamic test method to evaluate device thrombogenicity is very important for the improvement of the design and safety of blood-contacting medical devices, while reducing the use of animal studies. In this study, a recirculating flow loop system was developed for thrombogenicity testing, using donor sheep blood anticoagulated with Anticoagulant Citrate Dextrose Solution A (ACDA) and used within 24-36 hr postdraw. Immediately before testing, the blood was recalcified and heparinized to a donor-specific target concentration.

Inter-Laboratory Characterization of the Velocity Field in the FDA Blood Pump Model Using Particle Image Velocimetry (PIV).

Purpose: A credible computational fluid dynamics (CFD) model can play a meaningful role in evaluating the safety and performance of medical devices. A key step towards establishing model credibility is to first validate CFD models with benchmark experimental datasets to minimize model-form errors before applying the credibility assessment process to more complex medical devices. However, validation studies to establish benchmark datasets can be cost prohibitive and difficult to perform.

Renal Toxicodynamic Effects of Extracellular Hemoglobin After Acute Exposure.

Plasma hemoglobin (Hb) is elevated in some hematologic disease states, during exposures to certain toxicants, and with the use of some medical devices. Exposure to free Hb can precipitate oxidative reactions within tissues and alter the normal physiological function of critical organ systems. As kidney structures can be highly sensitive to Hb exposures, we evaluated the acute dose dependent renal toxicologic response to purified Hb isolated from RBCs.

Predicting Plasma Free Hemoglobin Levels in Patients Due to Medical Device-Related Hemolysis.

Blood passage through medical devices can cause hemolysis and increased levels of plasma free hemoglobin (pfH) that may lead to adverse effects such as vasoconstriction and renal tubule injury. Although the hemolytic potential of devices is typically characterized in vitro using animal blood, the results can be impacted by various blood parameters, such as donor species. Moreover, it is unclear how to relate measured in vitro hemolysis levels to clinical performance because pfH accumulation in vivo depends on both hemolysis rate and availability of plasma haptoglobin (Hpt) that can bind and safely eliminate pfH.

Use of the FDA nozzle model to illustrate validation techniques in computational fluid dynamics (CFD) simulations.

A "credible" computational fluid dynamics (CFD) model has the potential to provide a meaningful evaluation of safety in medical devices. One major challenge in establishing "model credibility" is to determine the required degree of similarity between the model and experimental results for the model to be considered sufficiently validated. This study proposes a "threshold-based" validation approach that provides a well-defined acceptance criteria, which is a function of how close the simulation and experimental results are to the safety threshold, for establishing the model validity.

FDA Benchmark Medical Device Flow Models for CFD Validation.

Computational fluid dynamics (CFD) is increasingly being used to develop blood-contacting medical devices. However, the lack of standardized methods for validating CFD simulations and blood damage predictions limits its use in the safety evaluation of devices. Through a U.

Effects of nanotopography on the in vitro hemocompatibility of nanocrystalline diamond coatings.

Nanocrystalline diamond (NCD) coatings have been investigated for improved wear resistance and enhanced hemocompatibility of cardiovascular devices. The goal of this study was to evaluate the effects of NCD surface nanotopography on in vitro hemocompatibility. NCD coatings with small (NCD-S) and large (NCD-L) grain sizes were deposited using microwave plasma chemical vapor deposition and characterized using scanning electron microscopy, atomic force microscopy, contact angle testing, and Raman spectroscopy.

Analysis of Transitional and Turbulent Flow Through the FDA Benchmark Nozzle Model Using Laser Doppler Velocimetry.

Transitional and turbulent flow through a simplified medical device model is analyzed as part of the FDA's Critical Path Initiative, designed to improve the process of bringing medical products to market. Computational predictions are often used in the development of devices and reliable in vitro data is needed to validate computational results, particularly estimations of the Reynolds stresses that could play a role in damaging blood elements. The high spatial resolution of laser Doppler velocimetry (LDV) is used to collect two component velocity data within the FDA benchmark nozzle model.

A Reusable, Compliant, Small Volume Blood Reservoir for In Vitro Hemolysis Testing.

Bench-top in vitro hemolysis testing is a fundamental tool during the design and regulatory safety evaluation of blood-contacting medical devices. While multiple published experimental protocols exist, descriptions of the test loop reservoir remain ambiguous. A critical fixture within the circuit, there is no readily available blood reservoir that ensures thorough mixing and complete air evacuation: two major factors which can affect results.

Time-Resolved Particle Image Velocimetry Measurements with Wall Shear Stress and Uncertainty Quantification for the FDA Nozzle Model.

We present advanced particle image velocimetry (PIV) processing, post-processing, and uncertainty estimation techniques to support the validation of computational fluid dynamics analyses of medical devices. This work is an extension of a previous FDA-sponsored multi-laboratory study, which used a medical device mimicking geometry referred to as the FDA benchmark nozzle model. Experimental measurements were performed using time-resolved PIV at five overlapping regions of the model for Reynolds numbers in the nozzle throat of 500, 2000, 5000, and 8000.

Verification Benchmarks to Assess the Implementation of Computational Fluid Dynamics Based Hemolysis Prediction Models.

As part of an ongoing effort to develop verification and validation (V&V) standards for using computational fluid dynamics (CFD) in the evaluation of medical devices, we have developed idealized flow-based verification benchmarks to assess the implementation of commonly cited power-law based hemolysis models in CFD. Verification process ensures that all governing equations are solved correctly and the model is free of user and numerical errors. To perform verification for power-law based hemolysis modeling, analytical solutions for the Eulerian power-law blood damage model (which estimates hemolysis index (HI) as a function of shear stress and exposure time) were obtained for Couette and inclined Couette flow models, and for Newtonian and non-Newtonian pipe flow models.

Multilaboratory study of flow-induced hemolysis using the FDA benchmark nozzle model.

Multilaboratory in vitro blood damage testing was performed on a simple nozzle model to determine how different flow parameters and blood properties affect device-induced hemolysis and to generate data for comparison with computational fluid dynamics-based predictions of blood damage as part of an FDA initiative for assessing medical device safety. Three independent laboratories evaluated hemolysis as a function of nozzle entrance geometry, flow rate, and blood properties. Bovine blood anticoagulated with acid citrate dextrose solution (2-80 h post-draw) was recirculated through nozzle-containing and paired nozzle-free control loops for 2 h.

In vitro shear stress-induced platelet activation: sensitivity of human and bovine blood.

As platelet activation plays a critical role in physiological hemostasis and pathological thrombosis, it is important in the overall hemocompatibility evaluation of new medical devices and biomaterials to assess their effects on platelet function. However, there are currently no widely accepted in vitro test methods to perform this assessment. In an effort to develop effective platelet tests for potential use in medical device evaluation, this study compared the sensitivity of platelet responses to shear stress stimulation of human and bovine blood using multiple platelet activation markers.