Bio-Activation of Polyether Ether Ketone Using Plasma Immersion Ion Implantation: A Kinetic Model

Abstract

Plasma immersion ion implantation (PIII) is used in this study to improve the surface bioactivity of polyether ether ketone (PEEK) by modifying the chemical structure and introducing radicals. The kinetic properties of the treated surface are characterised here, allowing for tuning of the PIII process in order to produce PEEK with optimised bioactivity. The optimum PIII ion fluence for PEEK is determined to be 1 × 1016 ions/cm2. A model is proposed that accounts for the decay of radicals, nitrogen loss, oxygen incorporation and changes in surface energy within the structure. The model is based on the premise that there is a distribution of local chemical environments produced by PIII. The distribution of chemical environments results in a bioactive surface that has a long shelf life, compatible with clinical needs.

Plasma ion implantation enabled bio-functionalization of PEEK improves osteoblastic activity

“…Bare PIII treated PEEK promoted 134 6 39% and 70 6 8% higher proliferation at day 7 compared to the untreated surface with and without BSA blocking, respectively. This significant increase indicates that the improved hydrophilicity and chemical modification previously reported as a result of PIII treatment of PEEK 36 create an improved cytocompatible environment. By day 7, the tropoelastin coated surfaces further augmented cell proliferation by 54 6 5% over the unblocked untreated PEEK, 176 6 82% over BSA-blocked untreated PEEK, 24 6 2% over unblocked PIII treated PEEK, and 83 6 27% over BSA-blocked PIII treated PEEK.…”

“…37 The generation and final concentration of radicals present in a sub-surface layer are functions of ion fluence, which in turn are functions of treatment time. 36 To ensure that the surfaces were sufficiently activated with radicals and coated with a full monolayer of tropoelastin, a PIII treatment time of 800 s and a tropoelastin coating concentration of 20 lg/ml were selected for subsequent experiments.…”

“…33,34 These unpaired electrons are present in radicals that diffuse throughout the polymer to covalently react with molecules at the surface, 35 such as atmospheric oxygen 36 or biomolecules in solution. 37 PEEK, PIII treated under identical conditions as utilized in this study, exhibits dynamic properties characterized by progressive oxidation of the surface 36 and a decreasing concentration of radicals. 35 These dynamic surface properties stabilize after 7 days to produce a stable hydrophilic surface.…”

“…35 These dynamic surface properties stabilize after 7 days to produce a stable hydrophilic surface. 36 Due to its increased surface hydrophilicity, modified chemical structure, and radical content, PIII treated PEEK has been associated with improved cell interactions. 38,39 Previous studies of PIII treated PEEK with nitrogen plasma have shown improved hydrophilicity and anti-bacterial and cell interaction properties in general 21,40,41 but have not investigated functionalization of the surface for specific applications.…”

Force fields for simulating the interaction of surfaces with biological molecules

“…Their bulk properties are best considered with coarse-grain approaches [19], inherently unsuitable for determining the effect of specific functional group interactions. An added difficulty in simulating these systems is the presence of contaminants, and also the heterogeneity introduced by surface treatments, such as by plasma [51]. Given that there is no atomic structure for these materials, researchers have turned to SAMs of alkanes that can be more easily controlled in experiment, and more explicitly defined in simulation.…”