Temperature Activated Diffusion of Radicals through Ion Implanted Polymers

Abstract

Plasma immersion ion implantation (PIII) is a promising technique for immobilizing biomolecules on the surface of polymers. Radicals generated in a subsurface layer by PIII treatment diffuse throughout the substrate, forming covalent bonds to molecules when they reach the surface. Understanding and controlling the diffusion of radicals through this layer will enable efficient optimization of this technique. We develop a model based on site to site diffusion according to Fick's second law with temperature activation according to the Arrhenius relation. Using our model, the Arrhenius exponential prefactor (for barrierless diffusion), D0, and activation energy, EA, for a radical to diffuse from one position to another are found to be 3.11 × 10(-17) m(2) s(-1) and 0.31 eV, respectively. The model fits experimental data with a high degree of accuracy and allows for accurate prediction of radical diffusion to the surface. The model makes useful predictions for the lifetime over which the surface is sufficiently active to covalently immobilize biomolecules and it can be used to determine radical fluence during biomolecule incubation for a range of storage and incubation temperatures so facilitating selection of the most appropriate parameters.

Preserving the reactivity of coatings plasma deposited from oxazoline precursors − An in depth study

“…Reaction with long‐lived free radical diffusing from the bulk of the film to engage in covalent bond with the COOH‐AuNP such as those described by Bilek et al are also unlikely in the case of PPOx films which are not expected to have a highly unsaturated network facilitating the diffusion of unpaired electron through π conjugation. Moreover, we evidenced comparable binding rate for fresh and aged PPOx films for relatively short nanoparticle binding time, namely 1 h incubation, which is less than what would be expected for bulk radical to diffuse to the surface after 12 months storage at room temperature . Further investigation using established techniques such as electron spin resonance (ESR) or chemical derivatization with 2,2‐diphenyl‐1‐picrylhydrazyl (DPPH) to measure free radical density could shed light on the importance of free radical‐driven reaction on PPOx films .…”

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

“…35 Immobilizing biomolecules after short ageing times, however, ensures homogenous and robust surface coverage. Therefore, tropoelastin coating of the PIII treated surface is advantageous not only in promoting a greater degree of osteoblast-like cell proliferation but also in maintaining the functional stability of the material.…”

“…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. 36 Due to its increased surface hydrophilicity, modified chemical structure, and radical content, PIII treated PEEK has been associated with improved cell interactions.…”

“…As the bonds reform, reactive unpaired electrons are generated within the modified region. 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.…”

Electric fields control the orientation of peptides irreversibly immobilized on radical-functionalized surfaces

“…Radical-functionalized surfaces can be created on both non-polymeric 13 , 14 and carbon-rich polymeric surfaces 15 , 16 . The buried radicals are capable of diffusing to the surface 17 , where they react with biomolecules. The ion-treated surfaces are typically hydrophilic due to reactions with atmospheric oxygen 18 ; thus, the immobilized proteins do not suffer denaturation through physical interactions with the surface.…”