# KRSR and RGD Adsorption on TiO2 and Influence of Ion Concentration: A Molecular Dynamics Study

## TL;DR

This study uses molecular dynamics to compare how two peptides, KRSR and RGD, adsorb on TiO2 surfaces under varying salt concentrations, revealing differences in their sensitivity to ionic strength.

## Contribution

The study introduces a detailed molecular dynamics analysis of peptide adsorption on TiO2 under variable physiological salt conditions.

## Key findings

- KRSR shows reduced surface contact persistence at higher salt concentrations, while RGD remains unaffected.
- Peptide backbone stability is not significantly influenced by NaCl concentration.
- KRSR's sensitivity to ionic strength is attributed to its electrostatic properties.

## Abstract

Bioactive peptide coatings modulate cell–implant interactions on TiO2 surfaces; however, most molecular-level studies of peptide adsorption are performed under low or fixed ionic conditions. Physiological environments exhibit non-negligible and variable electrolyte concentrations, so understanding ionic strength effects is crucial for designing effective peptide-functionalized titanium implants. An amorphous TiO2 surface was generated from a crystalline rutile precursor and simulated in explicit water using classical molecular dynamics at nine NaCl concentrations. For each condition, seven independent simulations with different initial peptide placements/orientations were performed. Peptide backbone RMSD, minimum peptide–surface distance, and adsorption time ratio were analysed as functions of NaCl concentration. For both peptides, backbone RMSD remained stable and showed no statistically significant correlation with NaCl concentration. KRSR exhibited a significant increase in minimum distance with increasing NaCl concentration and a significant decrease in adsorption time ratio, indicating reduced persistence of close surface contact at higher salt levels. In contrast, RGD showed no significant dependence of either minimum distance or adsorption time ratio within the tested range. Within the limits of the applied force-field MD framework and the investigated NaCl range, KRSR adsorption on TiO2 is more sensitive to ionic strength than RGD, consistent with the stronger electrostatic contribution for the net-positively charged KRSR motif.