Plasma-Engineered Polyetheretherketone for Orthopedic Application


Student thesis: Doctoral Thesis

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Award date31 Jul 2020


Surface properties and structures of biomaterials can be modified through surface engineering techniques, such as self-assembly monolayer and plasma treatment. Polyetheretherketone (PEEK) is a semi-crystalline, bioinert polymer, which has desirable biocompatible and mechanical properties, however, the antibacterial and osteoconductive properties should be improved for better application in orthopedics. In this thesis, some array structures are constructed through the self-assembly monolayer and plasma processing to modify the biological properties of PEEK, such as the antibacterial activity and osteoblast growth.

This thesis consists of three sections. The first section details the preparation of pillar-like and cone-like arrays derived from the cicada wing via the self-assembly monolayer of polystyrene micro/nanospheres and plasma etching. The bacterial killing mechanism of nanoarrays mimics the cicada wing, showing a penetrating phenomenon, whereas microarrays with a hybrid structure distort and kill E. coli more effectively. Due to the improved surface energy and hydrophilicity of the structure, these arrays are regarded as an appropriate platform for osteoblasts to spread, attach, and proliferate compared to the pristine PEEK. Besides the pillar arrays, the sheet-like and nanolamellar structure are also of great significance to biomaterial research, due to the special morphology and surface property. The orientation of these arrays may also be associated with the surface interfacial interaction with cells and bacteria. Based on these hypotheses, fish scale mimicked and nacre simulated nanolamellar arrays were prepared by etching PEEK to a different crystalline degree using argon plasma. The vertically aligned nacre porous structure was more effective at killing gram-positive and gram-negative bacteria compared to the fish scale mimicked array, however, both structures improved the proliferation and differentiation of osteoblasts as well as alkaline phosphatase (ALP) activity. These outcomes are consistent with the inflammatory response and osseointegration test in vivo, as discussed in the second section.

For a better understanding of the influence of surface properties on bacterial killing and osteoblast activity, the pillar and nanolamellar arrays of PEEK were coated with diamond-like carbon (DLC) for in vitro studies in the last section. Moreover, the deposition time significantly affects the morphology of the lamellae but has less impact on the pillar array, which in turn influences osteoblast proliferation and bactericidal activity. Regarding the mechanism, the mechanical properties and roughness contributed to improved cell proliferation. Consequently, the DLC coated patterns further improved osteoblast growth in a topography dependent mechanism.

In summary, the surface morphology and property of PEEK can be greatly improved by plasma techniques for better application as a biomaterial. This work demonstrated the importance of surface structures on the antibacterial activity and osseointegration of PEEK, providing insights into the interfacial interaction between cells, bacteria, and biomaterials, as well as offering some new designs for other polymeric biomaterials, especially semi-crystalline polymers.