Introduction:: Cardiovascular disease is the number one cause of death in many countries. In many cases, it is closely related to internal plaque buildup on the vessel wall, referred to as atherosclerosis. One of the popular options for relieving this issue is to use vascular grafts to reopen the narrowed section or bypass the stenosed vessel. However, even if patients scheduled post-surgical surveillance routines, complications, such as pain, limb swelling, strokes, and heart attacks, can occur between sequential checkups which compromise the patient’s health or even threaten the patient's life. To address this issue, a dynamic continuous monitoring system is necessary. In most surveillance systems proposed by researchers for vascular grafts, the measurement of blood flow is the main criterion in the design. As stenosis occurs, the amount of blood passing through a unit length can reflect the percentage of flow reduction and the extent of severity of the stenosis. Currently, mainstream models utilize diffraction-grating transducers, electromagnetic rings, and/or piezoelectric pressure sensors. However, even with advanced flexible materials, these add-on devices either compromise the mechanical performance of the vascular graft or limit the compliance of the implant. As a result, we are proposing in this study to design and fabricate a blood flow measuring device which is completely incorporated into the textile-based vascular graft.
Materials and Methods:: The blood flow sensor is consisted of a PU core yarn, and a layer of conductive polymer, polypyrrole, synthesized on the outer side. The PU core supplies the elasticity of the strain sensor. The conductive polymer takes the responsibility of relating pressure level to resistance change yields from the stretch. The prepared sensor retains the shape of filament yarn, which facilitates the process of integration into a knitted PET vascular graft. With minimum tension applied, the sensor can be inserted into the loop structure by the weft insertion technique. An in vitro evaluation of the vascular prosthesis deployed with a phantom vessel was used to verify the effect of the stretchable strain sensor. Controlled blood flow was replicated at normal to extreme blood flow scenarios.
Results, Conclusions, and Discussions:: The conductive layer of polypyrrole was successfully synthesized on the surface of PU yarn (Fig.1a). The SEM pictures showed that the polypyrrole layer displayed uniform coverage and conformed tightly to the contours of the filaments of the PU yarn. During stretching, the polypyrrole layer underwent deformation according to the elastic properties of the core yarn. As the PU-polypyrrole strain sensor extended, the resistance of the sensor itself increased with strain due to micro-cracks of the polypyrrole material (Fig.1b). The change of resistance for the strain sensor increased 54 times when the yarn was stretched from 1inch to 1.25inch. Thus, when this sensor is inserted circumferentially into the wall of a knitted vascular graft, the stretched and relaxed displacement data from the strain sensor will be measured and recorded as changes in modulated electrical output (Fig.1c), which will be then converted into changes in blood pressure. When two or more of the strain sensors are inserted along the knitted graft, the pressure variance along the graft can be profiled to indicate flow characteristics, revealing the potential of restenosis of the implanted graft. Therefore, the knitted vascular graft with an integrated stretch sensor can be applied in an in vitro model. Various stroke rhythms and volumes of blood per stroke will be modulated, so as to calibrate the stretch sensor.
In this study, we fabricated a conductive textile sensor that reflected and recorded blood pressure in real time. By utilizing pressure changes along the vascular graft, the characteristics of blood flow can be depicted. It is expected that the signal resolution will display minimal drift and/or distortion along the vascular graft. Consequently, patients can self-monitor their vascular prosthesis after implantation of vascular grafts and seek medical intervention as necessary prior to the onset of critical conditions.