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Protein Adsorption onTo CHarged surfacES

Periodic Reporting for period 1 - PATCHES (Protein Adsorption onTo CHarged surfacES)

Reporting period: 2018-05-16 to 2020-05-15

PATCHES focused on a multi-scale hybrid computation/experimental study of the tribologically induced surface charge of different biocompatible materials when subjected to common mechanical contacts such as sliding and fracture. Mechanical contacts are, indeed, known to affect the distribution of the charge on the materials surface and the redistribution of charged groups at the interface between proteins and surface and this is a key factor in the adsorption of the proteins, thus of materials biocompatibility. The study was conducted using Density Functional Theory (DFT) calculations and Molecular Dynamics (MD) simulation methods and the computational models were validated by experimental tests.

Overall the project met the main objective of designing a multi-scale hybrid
computation/experimental method to analyse the surface charge of biocompatible materials for typical contact conditions. Specifically, this was achieved through two main objectives: i) simulating the charge density of different bio-materials, such as diamond, amorphous silica and diamond-like-carbon (DLC) as subjected to sliding and fracture and comparing the results with experimental measurements; ii) using the evaluated charge distribution to study how it affects the adsorption of saliva proteins onto the surface of the set of biomaterials considered.

The results obtained from the analysis of the amorphous silica and the PTFE bulk at high pressure phase are one of the kinds. In fact, the amorphous silica results were obtained after a long computational calculation time, over a year, a study which was never done before and unlikely to be repeated. The PTFE structural values, instead, are a fundamental source for the scientific community because they will be the starting point for the modelling of a material to be used in a wide range of studies. Moreover, because of its unique properties PTFE is a major material for various other applications, in particular for green energy nanogenerators, which are devices that convert mechanical energy into electricity, and they are used for the development of smart cities. Therefore, the results of this study can also be exploited for environment climate challenges.
To start, DFT methods were employed to identify the stable structural configuration of diamond surface and its electronic characteristics. This initial study showed that diamond surface tends to have a negative charge distribution under mechanical stress conditions which is well comparable with the experimental analysis. Therefore, the multi-scale method was validated and completed to be used for the analysis of the other materials. This outcome was presented at STLE Tribology Frontiers Conference 2018 and the results are publicly available in a peer-reviewed journal paper, “A Combined Experimental and Theoretical Study on the Mechanisms Behind Tribocharging Phenomenon and the Influence of Triboemission”, Tribology Online, 14 (5), 367-374, 2019.

The comparison of the computational analysis of the other materials with the experimental results showed that the multiscale method can be also used for complex materials such as amorphous silica. The analysis of this last also unravelled for the first time the mechanism behind material transfer and how this influences the transfer and distribution of the charge. This outcome was disseminated at Notte dei Ricercatori 2018 and ITC conference 2019 and will be published in an extra peer reviewed publication currently in submission to the journal Physical Review Letters with the title “Evolution of the structural and electronic properties of amorphous silica undergoing mechanical stresses on long-time period: an ab initio study”.

The analysis on the PTFE revealed its tendency of acquiring negative charge which is the key property of a biomaterial. These outcomes are published in a journal paper titled “First-Principles Insights into the Structural and Electronic Properties of Polytetrafluoroethylene in Its High-Pressure Phase (Form III)”, The Journal of Physical Chemistry C 123 (10), 6250-6255, 2019. This paper is a fundamental resource for the scientific community because it gives numerical values of the PTFE structure. The additional study on defective surfaces showed that defects on the surface favour the capability of the PTFE to acquire negative charge, thus, they are expected to favour proteins absorption. Results of this study will be published in an extra peer reviewed publication currently under review to the journal Polymers with the title “Ab initio study of Polytetrafluoroethylene defluorination and its possible effects on tribocharging”. The outcomes were disseminated at MOBT Conference 2019.

An additional study was also conducted to analyse the adhesion of the PTFE with common metals usually used for bio-implants. It has been found that the adhesion of PTFE depends on the paired material and it can be increased by modifying the PTFE structure, i.e. by defluorination. Therefore, this multiscale method can be used for the innovation of new materials that can be tailored for various applications. The results of this study will be published in an extra peer reviewed publication currently under submission to the high impact factor journal Nano Energy with the title “The correlation between adhesion and electric charge and its influence on PTFE coating on common bio-implants metals”

The experimental analysis of the adhesion of proteins was assessed by means of laser induced fluorescence technique coupled with fluorescent dye and a tribometer. Among the materials chosen PTFE was unravelled to be the most promising bio compatible material as expected from the computational analysis. This outcome results in the final validation of the multi-scale model.
This multi-scale method contributes to the actual state of art of tribocharging as a tool to measure at atomic level the charge distribution of a material when undergoes to mechanical stresses. Furthermore, it can be also used for complex materials such as amorphous silica. In particular, the results obtained for this last are one of the kinds in the scientific community because of the long computational time needed. Results from the PTFE study, instead, substantially contributed to state of art of the structural and electronic characteristic of this widely used material. In addition to its importance as biocompatible material PTFE is one of the most used materials for innovative technologies such as green batteries. The development of these devices is aiming to transition from fossil energy to green energy with the scope of fighting climate change. PATCHES made it possible the advancement in the field of technology innovation for both medical and green applications.

The work delivered by the project has been published in prestigious peer reviewed journals as open source for a wide scientific audience. As the project focused on truly understanding the charge distribution of materials undergone mechanical stresses and in case of bio-environment how the proteins interact with surfaces, the outcome produced is benefit the broader biomedical scientific and industrial community. The multiscale model, main outcome of the project, is available to the wider scientific community as a standalone open-source tool.
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