This study presents the synthesis and characterization of hexadecyl-modified SiO₂ (HD-SiO₂) nanoparticles and their application in the fabrication of a multilayered elastomer hybrid sheet to enhance water resistance in implantable biomedical devices. The surface modification of SiO₂ nanoparticles was confirmed via FT-IR and TGA analyses, showing the successful grafting of hydrophobic hexadecyl groups. FE-SEM and DLS analyses revealed spherical HD-SiO₂ nanoparticles with an average size of 360 nm. A multilayered elastomer hybrid sheet, consisting of a PDMS-based circuit-protecting body, a water resistance layer of HD-SiO₂, a planarization layer, and a biocompatible layer of polydopamine, was fabricated and characterized. The water resistance layer exhibited superhydrophobic properties, with a water contact angle of 154.7° and a 27% reduction in water vapor transmission rate (WVTR) compared to the circuit-protecting body alone. The device packaged with both the circuit-protecting body and water resistance layer demonstrated a tenfold increase in operational lifespan in water medium compared to the device without the water resistance layer. Cytotoxicity and cell proliferation tests on human dermal fibroblast cells (HDFn) confirmed the biocompatibility of the multilayered sheet, with no significant cytotoxicity observed over 48 h.

Despite their potential as reinforcing agents for poly(lactic acid) (PLA), cellulose nanocrystals (CNCs) tend to self-aggregate, limiting both optical transparency and mechanical reinforcement. In this study, incorporating poly(L-lactic acid)-grafted CNCs (LCNCs) into PLA simultaneously enhanced both optical transparency and mechanical reinforcement compared to neat CNCs. Three types of LCNCs—LCNC1 (apparent molar substitution, MS_app = 3.36), LCNC2 (MS_app = 25.6), and LCNC3 (MS_app = 56.9)—were synthesized. Fourier transform infrared (FT-IR) and ¹H nuclear magnetic resonance (¹H NMR) spectra revealed poly(L-lactic acid) (PLLA) grafting onto the CNC surface, and the MS_app values were estimated from the ¹H NMR peak integrals. X-ray diffraction patterns (XRD) showed that the native crystalline structure of the CNCs was preserved even after surface modification. LCNC3 (MS_app = 56.9) exhibited a smaller hydrodynamic size in an organic solvent, consistent with reduced aggregation, whereas LCNC1 (MS_app = 3.36) remained severely aggregated like neat CNCs. The PLA/LCNC3 nanocomposite retained transparency comparable to neat PLA and achieved the highest tensile strength among the nanocomposites considered here. These results indicate that a higher MS_app, reflecting greater PLLA graft development on CNCs, is associated with improved dispersion, optical transparency, and mechanical reinforcement in PLA nanocomposites.