Ultrathin Film Hydrogels with Controlled Swelling and Viscoelastic Properties Deposited by Nanosecond Pulsed Plasma Induced-Polymerization

Development of ultrathin film (utf) hydrogels for cutting-edge biomedical applications (i.e. artificial skins) is receiving increasing attention. Nonetheless, achieving accurate control on the structure and thickness of utf-hydrogels becomes extremely complex when assessed through conventional techniques. In this work, an atmospheric-pressure plasma-assisted deposition technique is reported, showing great thickness accuracy and versatility, to design utf-hydrogels with customized properties. For the first time, specific and independent control on the generation and nature of cross-links by only changing the plasma exposure frequency (fPE) during the synthesis process are reported. Thus, utf-hydrogels are successfully prepared with tuned swelling ratios and viscoelastic properties (ranging from 150 to 20 kPa). Moreover, a thickness accuracy of 9 nm is reported, permitting the accurate synthesis of utf-hydrogels below 150 nm. Exhaustive structural and topographical analyses allow elucidating the effects of the fPE on the cross-link generation mechanism, discarding any undesired effect on the thickness accuracy. To support the structural results obtained, quartz-crystal microbalance with dissipation (QCM-D) coupled with spectroscopic ellipsometry are put in the spotlight as an efficient and viable alternative for the characterization of the resulting properties of ultrathin film soft materials, including the presence of a hydrated layer at the interface. Plasma-deposited thin film hydrogels with customized swelling and mechanical properties are characterized by means of coupled spectroscopic ellipsometry and quartz-crystal microbalance with dissipation techniques. The presence of a hydrated layer at the interface is measured.image