Structural characterization of chitosan/nanoclay nanocomposites as emergent engineered nanohybrid biomaterials

Chitosan-nanoclay nanocomposites (CNNCs) are attractive aqueous platforms for biorelevant manufacturing, yet the impact of clay morphology under identical preparation and testing conditions remains insufficiently resolved. In the present work, low-molecular-weight chitosan (CS) was combined with three nanoclays, bentonite (BEN, layered), halloysite (HAL, tubular) and sepiolite (SEP, fibrous), to prepare hybrid suspensions at pH 4.5 spanning defined CS/nanoclay ratios. BEN and SEP series were formulated from 15/85 to 75/25 (CS/nanoclay, w/w); HAL series ranged from 5/95 to 55/45. After 48 h aging and intermittent sonication, rheology was measured: all hybrids exhibited pronounced shear-thinning. For each clay type, the apparent viscosity increased steadily with higher chitosan content. This trend suggests that the flow behavior is mainly governed by the polymer, as protonated chitosan chains adsorb onto silicate surfaces and form bridges between particles, creating transient networks. Sepiolite-based hybrids showed the highest viscosities and the strongest shear-thinning, consistent with a network, fiber-driven architecture. Halloysite formulations displayed high viscosities with indications of a yield-like response, whereas bentonite afforded intermediate viscosities and smooth flow. The results indicate that nanoclay morphology plays a key role in determining network formation efficiency, enabling controlled modulation of rheological properties under fixed processing conditions. Complementary FTIR/XRPD and X-ray micro-computed tomography supported hybrid formation and uniform three-dimensional dispersion of the nanoclays. Collectively, these results provide clear design rules for programming CNNC rheology under mild, aqueous conditions, offering practical guidance for casting, molding and printing of bioactive formulations that require high shear injectability and structural integrity at rest. The materials palette provides a tunable basis for bioactive formulations and future device-oriented investigations.