Improving Hydrophobicity of Collagen with Silica Nanoparticles: Probing a Noncovalent Approach.

Collagen-based materials have a wide range of applications in wound care, tendon repair, cartilage repair, etc. Improving certain properties such as hydrophobicity can diversify the application areas. In this work, we investigated the noncovalent interactions of suitably functionalized silica nanoparticles with collagen for the possibility of improving hydrophobicity. Functionalization on silica nanoparticles was achieved via Cu(I)-catalyzed azide-alkyne cycloaddition (CuAAC) or "click" reaction using surface grafting methods. Furthermore, we synthesized two different silica nanoparticles (SiNPs) functionalized with the fluorine-containing substrate or only with an aryl moiety (silica--4EMB and silica--ETFMB) for comparison. The functionalized SiNPs immobilized along with the model system trans-4-hydroxy-l-proline (HPA) (usually present in abundant quantities in collagen) have been probed using nuclear magnetic resonance (NMR) spin relaxation to appreciate the influence of SiNPs on HPA. Furthermore, we effectively utilized a saturated transfer difference (STD) NMR experiment to measure the interaction parameters between judiciously functionalized silica nanoparticles and substrates of interest. In essence, such a detailed study on noncovalent interactions employing an arsenal of experimental approaches facilitated the immobilization of suitably functionalized silica nanoparticles to collagen and leather (where collagen is a major constituent), leading to improvements in hydrophobicity.