Computational study of clot formation in aneurysms treated with shape memory polymer foam

Hemostatic shape memory polymer foams with improved survival in a lethal traumatic hemorrhage model

Although there are many hemostatic agents available for use on the battlefield, uncontrolled hemorrhage is still the primary cause of preventable death. Current hemostatic dressings include QuikClot® Combat Gauze (QCCG) and XStat®, which have inadequate success in reducing mortality. To address this need, a new hemostatic material was developed using shape memory polymer (SMP) foams, which demonstrate biocompatibility, rapid clotting, and shape recovery to fill the wound site. SMP foam hemostatic efficacy was examined in a lethal, noncompressible porcine liver injury model over 6 h following injury. Wounds were packed with SMP foams, XStat, or QCCG and compared in terms of time to bleeding cessation, total blood loss, and animal survival. The hemostatic material properties and in vitro blood interactions were also characterized. SMP foams decreased blood loss and active bleeding time in comparison with XStat and QCCG. Most importantly, SMP foams increased the 6 h survival rate by 50% and 37% (vs. XStat and QCCG, respectively) with significant increases in survival times. Based upon in vitro characterizations, this result is attributed to the low stiffness and shape filling capabilities of SMP foams. This study demonstrates that SMP foams have promise for improving upon current clinically available hemostatic dressings and that hemostatic material properties are important to consider in designing devices for noncompressible bleeding control. STATEMENT OF SIGNIFICANCE: Uncontrolled hemorrhage is the leading cause of preventable death on the battlefield, and it accounts for approximately 1.5 million deaths each year. New biomaterials are required for improved hemorrhage control, particularly in noncompressible wounds in the torso. Here, we compared shape memory polymer (SMP) foams with two clinical dressings, QuikClot Combat Gauze and XStat, in a pig model of lethal liver injury. SMP foam treatment reduced bleeding times and blood loss and significantly improved animal survival. After further material characterization, we determined that the improved outcomes with SMP foams are likely due to their low stiffness and controlled shape change after implantation, which enabled their delivery to the liver injuries without inducing further wound tearing. Overall, SMP foams provide a promising option for hemorrhage control.

Characterization of shape memory polymer foam hemostats in in vitro hemorrhagic wound models

Shape memory polymer foam hemostats are a promising option for future hemorrhage control in battlefield wounds. To enable their use as hemostatic devices, they must be optimized in terms of formulation and architecture, and their safety and efficacy must be characterized in animal models. Relevant in vitro models can be used for device optimization to help mitigate the excess use of animals and reduce costs of clinical translation. In this work, a simplified gunshot wound model and a grade V liver injury model were constructed. The models were used to characterize the effects of shape memory polymer foam hemostat geometry on wall pressures, application/removal times, hemorrhage (fluid loss), and fluid absorption in comparison with clinical controls. It was found that there is no benefit in over-sizing the hemostatic device relative to wound volume and that geometry effects are dependent upon the wound type. These models provide a rapid means for elucidation of promising hemostat geometries and formulations for use in future in vivo testing.