Surface Modification of PTFE and NiTi Alloy for Their Biomedical Application


Student thesis: Doctoral Thesis

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Awarding Institution
Award date18 Jul 2017


Surface modification is an effective and economical way to either enhance the biological performance of biomaterials without influencing the bulk attributes or endow the existing biomaterials with new properties for a special needs. In this work, surface modification techniques are utilized to treat polytetrafluoroethylene (PTFE) and NiTi alloy, in order to circumvent the disadvantages of PTFE in cardiovascular application and to prepare the NiTi alloy to be the electrode used in biosensor. Specifically, there are three parts in this thesis. The first two parts demonstrate the treatment of PTFE by plasma immersion ion implantation (PIII) and the functionalization of the treated surface by linker-free covalent immobilization of heparin, CD47, as well as SDF-1α for the cardiovascular application. The third part shows a simple one-step electrochemical potential cycling technique to prepare NiTi alloy to be an effective electrode for the non-enzymatic glucose biosensor.
Firstly, the PTFE surface is engineered by nitrogen PIII, after which morphologies of quasi-ordered “protrusions and valleys” in the scale of hundreds of nanometers emerge. The PIII treatment also greatly changes the surface composition and chemical states thus altering the wettability of the surface from about 120°to be nearly superhydrophobic (147 ± 3°). More importantly, the PIII treatment alters the inherent inertness of PTFE to be biocompatible, which is adequate for rapid endothelialization, as revealed by the remarkably enhanced adhesion, spreading, proliferation, migration, as well as nitric oxide production of human umbilical vein endothelial cells cultured on treated surface.
Secondly, a versatile "implantation-incubation" approach is developed to further functionalize the PTFE. After nitrogen (N2 ) PIII treatment, the abundant free radicals generated underneath the surface continuously migrate to the surface and react with environmental molecules. Taking advantage of this mechanism, various biomolecules with different functions can be steadily immobilized on the surface of PTFE by simple solution immersion. As examples, three typical biomolecules, heparin, SDF-1α , and CD47 are covalently grafted onto the PTFE. In addition to retaining the bioactivity, the surface-functionalized PTFE exhibits reduced thrombogenicity, facilitates the recruitment of endothelial progenitor cells and even alleviates the inflammatory immune responses of monocytesmacrophages, hence is promising for the development of small-diameter prosthetic vascular grafts with good long-term patency.
Thirdly, a one-step potential cycling technique for in situ synthesis of electroactive Ni(OH)2 and protective TiO2 composite film on NiTi alloy is developed. The Ni(OH)2/TiO2 composite film can be used directly as the electrode in a non-enzymatic glucose sensor. This binder-free sensor boasts a high glucose sensitivity of 192 μA mM-1 cm-2 , short response time of less than 1 s, and detection limit of 8 μM. In addition, the stable and protective TiO2 extends the linear range to 14 mM and provides excellent long-term stability. This novel fabrication method not only simplifies the preparation of high-performance non-enzymatic glucose sensing materials, but also can be readily extended to the fabrication of other transition metal-based biosensors.
In summary, plasma-based modification is an effective way to improve the cytocompatibility of PTFE and endow PTFE special ability to immobilize various biomolecules covalently without using chemical crosslinker, and the electrochemical treatment of NiTi alloy provides a simple and novel strategy to prepare the electrode for a non-enzymatic glucose sensor.

    Research areas

  • PTFE, Surface modification, Plasma immersion ion implantation, Covalent immobilization, Multi-functionalization