In vitro methodology for medical device material thrombogenicity assessments: A use condition and bioanalytical proof‐of‐concept approach

FIGURE 1. Mixing motion applied in the tube model. Left = Nutation; Right = Combined tilting and rotation

FIGURE 2. Design of dynamic pulsatile closed loop model (left). The loop contains two injection/withdraw ports (Port 1 [6:00 position] and Port 2 [12:00 position] and a check valve (at 3:00 position; enlargement at right). A repeating (specified) pulse of rotation in the clockwise direction followed by a (specified) pause causes the small check valve to close and open, respectively, and the blood to flow in pulsatile fashion via angular momentum

FIGURE 3. The generic in vitro case study experimental design. This design involves testing a positive control (pos cntl), a No Material negative control (neg cntl), a biomaterial control (PE), and a legally marketed comparator device (LMCD) material alongside the test material (Test) at two heparin levels (where use conditions indicate test devices/materials may be used with and without anticoagulation). It specifies testing with blood from two donors, and potential repeat runs (allowing n = 2 or n = 4) to increase robustness and confidence in results. This gives a Materialx2x2x2 full factorial design that involves 4–8 separate small volume blood draws (bd; i.e., bd1 to bd8)

FIGURE 4. In vitro material thrombogenicity results for MTES3 showing (a) TAT, (b), F1.2, and (c), βTG responses to test materials across the variables Model, Heparin level, and Donor (A and D). Models: Tube model using VF blood filling with rocker‐roller mixing and loop model using pulsatile flow. Exposure ratio: 6.0 cm2/ml whole blood. PE, polyethylene; Pebax, polyether block amide; PEU, polyurethane; PEU+H, polyurethane with a heparin coating; No Material, Tube or Loop model without any test or control materials present. ANOVA showed the Donor factor to be significant only in the βTG measurements. ◯ = Donor A data; ● = Donor D data. (Heparin): Low = 1.0 U/ml; High = 2.0 U/ml. TAT, thrombin‐antithrombin complex; F1.2, prothrombin fragment F1.2; βTG, β‐thromboglobulin

FIGURE 5. In vitro material thrombogenicity results for Case Study 4 showing (a), TAT, (b), F1.2, and (c), βTG responses in both Tube and Loop models to the test and various control materials. Scoring according to Table 5 reveals Test Material 4 (Test‐4) to be: 0–1 (TAT), 0–1 (F1.2), and 1–2 (βTG). LMCD, legally marketed comparator device/material; PE, polyethylene; No Material, Tube or Loop model without any materials present. ◯ = Donor A data; ● = Donor D data. [Heparin]: Low = 1.0 U/ml; High = 2.0 U/ml. TAT, thrombin‐antithrombin complex; F1.2, prothrombin fragment F1.2; βTG, β‐thromboglobulin

FIGURE 6. In vitro material thrombogenicity results for Case Study 6 showing the TAT responses to the test and various control materials. Scoring according to Table 5 reveals Test Device 6 (Test‐6) to be of moderate thrombogenicity concern, having TAT scores of 3 in blood from both donors. LMCD, legally marketed comparator device/material (two were used in this study–LMCD‐6A and LMCD‐6B); PE, polyethylene; No Material, tube model without any materials present. ● = Donor A Run 1, ■ = Donor A Run 2, ◯ = Donor D Run 1, □ = Donor D Run 2. Heparin anticoagulation was set at [Heparin] = 0.6 U/ml

FIGURE 7. Representative images from devices/materials examined in in vitro Case Studies 1, 2, 3, and 6. LMCD, legally marketed comparator device; PE, polyethylene; No Material, no test or control material present

FIGURE 8. Representative explant images of some of the devices examined in the in vivo studies. Case Study 1 shows images of two Test Devices. Case Study 4 shows the Test Device (white catheter without thrombus) alongside the LMCD. Case Study 5 shows images of two Test Devices. Case Study 6 shows the LMCD alongside the Test Device (white catheter). NAVI scores for in vivo Case Studies 2 and 3 were estimated from References 16 and 18, respectively. The latter references should be consulted for in vivo images of these devices. LMCD, legally marketed comparator device; NAVI, nonanticoagulated venous implant