Jet Blown PTFE for Control of Biocompatibility

Open Access
Author:
Leibner, Evan Scott
Graduate Program:
Chemistry
Degree:
Doctor of Philosophy
Document Type:
Dissertation
Date of Defense:
July 13, 2009
Committee Members:
  • John V Badding, Dissertation Advisor
  • John V Badding, Committee Chair
  • Michael Pishko, Committee Member
  • Erwin A Vogler, Committee Member
  • James Bernhard Anderson, Committee Member
  • Paul Wencil Brown, Committee Member
Keywords:
  • Hemocompatible
  • Polytetrafluoroethylene
  • Jet Blowing
  • Potein Adsorption
Abstract:
The development of fully hemocompatible cardiovascular biomaterials will have a major impact on the practice of modern medicine. Current artificial surfaces, unlike native vascular surfaces, are not able to control clot and thrombus formation. Protein interactions are an important component in hemocompatibility and can result in decreased patency due to thrombus formation or surface passivation which can improve endothelization. It is believed that controlling these properties, specifically the nanometer sizes of the fibers on the material's surface, will allow for better control of biological responses. The biocompatibility of Teflon, a widely used polymer for vascular grafts, would be improved with nanostructured control of surface features. Due to the difficultly in processing polytetrafluoroethylene (PTFE), it has not been possible to create nanofibrous PTFE surfaces. The novel technique of Jet Blowing allows for the formation of nanostructured PTFE (nPTFE). A systematic investigation into controlling polymer properties by varying the processing conditions of temperature, pressure, and gas used in the Jet Blowing allows for an increased understanding of the effects of plasticization on the material’s properties. This fundamental understanding of the material science behind the Jet Blowing process has enabled control of the micro and nanoscale structure of nPTFE. While protein adsorption, a key component of biocompatibility, has been widely studied, it is not fully understood. Major problems in the field of biomaterials include a lack of standard protocols to measure biocompatibility, and inconstant literature on protein adsorption. A reproducible protocol for measuring protein adsorption onto superhydrophobic surfaces (ePTFE and nPTFE) has been developed. Both degassing of PBS buffer solutions and evacuation of the air around the expanded PTFE (ePTFE) prior to contact with protein solutions are essential. Protein adsorption experiments show a four-fold difference in the measure of proteins adsorbed using radiometry (I-125 labeled human serum albumin (HSA)) and electrophoresis (unlabeled HSA). This provides evidence that the standard method of radiolabeled protein for measuring adsorption does not fully account for changes to the HSA molecules due to labeling. The differences between measured protein values can be attributed to the radiolabel affecting the HSA hydrophobicity resulting in a change in the protein’s interactions with the hydrophobic surface. Additionally, our work has provided repeatable results showing that the amount of protein adsorbed onto the polymer surface, after washing, accounted for only 65% of the amount of protein that was removed from solution based on depletion analysis. This implies that measurement of the amount of strongly bound protein on the material significantly underestimates the actual amount of protein adsorbing into the surface region of the material interface. HSA adsorption isotherms demonstrate an increase in protein adsorption capacity on the nPTFE surface compared to adsorption on the same surface area of ePTFE. Preliminary cell work shows that the nPTFE surfaces had a larger number of cells growing on the surface of the material when compared to ePTFE surfaces. The research also shows that while most endothelial cells were not viable on the ePTFE surface after 96 hours, they remained alive on the nPTFE surface during that same time period. Surface functionalization using ammonia plasma has been performed. X-ray photoelectron spectroscopy (XPS) analysis revealed the presence of amine groups on the nPTFE surface. The amine groups can be used to couple polypeptides onto the PTFE surface in the future. The selection of different peptides will allow for selective control of cell adhesion. This research shows that nPTFE has potential for improved biocompatibility over standard ePTFE, based on increased protein adsorption capacity, increased viability of endothelial cells, and the ability to plasma modify the PTFE surface.