RELATIONSHIP OF PLATELET ADHESION WITH SURFACE TOPOGRAPHY IN THE PENN STATE PEDIATRIC VENTRICULAR ASSIST DEVICE

Open Access
Author:
Mueser, Ashlyn S
Area of Honors:
Biomedical Engineering
Degree:
Bachelor of Science
Document Type:
Thesis
Thesis Supervisors:
  • Keefe Manning, Thesis Supervisor
  • William O Hancock, Honors Advisor
Keywords:
  • PVAD
  • Platelet Adhesion
  • Surface Topography
  • Pediatric Ventricular Assist Devices
Abstract:
Between 1999 and 2006, 535 children died while waiting for a heart while 3,098 children were listed on the heart transplant list.1 In 2015, 385 hearts were transplanted in children; 321 children remain on the waiting list.2 As a result, there is a need for a pediatric ventricular assist device (PVAD) as a bridge-to-transplant. The Penn State PVAD has been designed with this goal in mind; however, like all ventricular assist devices, thrombosis is a major problem that can lead to device failure, heart attack, and stroke. One possible theory for thrombus formation within the Penn State PVAD is the surface roughness of the polymer blood sac causing platelet and fibrin deposits. Penn State PVADs, explanted from ovine trials at the Penn State Hershey Medical Center, are analyzed for a relationship between surface topography of the polymer blood sac with thrombus formation. This is done by analyzing the same sac using three microscopy techniques. The samples are labeled immunofluorescently using an indirect method with anti-CD41 and Alexa Fluor 555 to label platelets and anti-fibrinogen and Alexa Fluor 488 to label fibrin and evaluated using confocal microscopy to determine if platelets and fibrin are present on the surface. The fluorescence structures are confirmed using environmental scanning electron microscopy. After all biologics are degraded, the surface topography is captured using optical profilometry with surface roughness parameters, such as root mean squared (RMS), roughness average (Ra), ten-point height (Rz), and Swedish height (H). Macroscopic clots are found only at the ports of the device, whereas microscopic deposits are observed throughout the sac. The surface under macroscopic clot locations are leading to higher surface roughness parameters than both microscopic deposit locations and control surfaces. The average RMS value for macroscopic clots are about 51% higher than microscopic deposits, and about 93% higher than the control. Similar trends are obtained for Ra, Rz, and H. To further the analysis beyond topography data, correlations between images captured with confocal, ESEM and optical profilometry are made to draw conclusions regarding the defects possibly causing deposits. Scuffing and scratches are found on 3 of the 5 samples where macroscopic clots were located and on 5 of the 11 microscopic deposit locations. Flow regime within the device and factors from the animal studies, such as study duration, may both play a role in thrombus formation. The overall results of this analysis conclude that the surface topography does impact thrombus formation within the Penn State PVAD.