Rheological analysis of a novel phenylboronic acid-closomer gel

This study aims to characterize the rheological behavior of a novel phenylboronic acid (PBA)-based closomer nanoconjugate (Closogel) with potential application in pharmaceutical formulation. PBA was used as a cross-linking agent and model (antiviral) drug. The PBA loaded Closogel chemical structure was analyzed by boron (¹¹B) NMR and Fourier transform infrared (FTIR) spectroscopy. The Closogel and control hydroxyethyl cellulose (HEC) gel were analyzed under oscillatory and continuous shear rheometry followed by mathematical modeling to characterize the gel flow behavior. The chemical analysis confirmed the existence of characteristic borate esters peaks and Boron chemical shifts within Closogel spectra. Due to its more flexible molecular structure, undiluted Closogel exhibited lower, yield stress, viscosity and relaxation time (30 Pa &163 Pa.s & 0.21 s vs 45 Pa &301 Pa.s & 0.39 s for HEC). Both Closogel and HEC gels exhibited a thixotropic behavior. The plastic undiluted and pseudoplastic 2.5 % w/v aqueous Closogels were more viscous than elastic (tan (δ) > 1) in the linear viscoelastic range. The Herschel-Bulkley model showed a significant fitting to all experimental data (R² > 0.95). The 0.25 % w/v aqueous Closogel nearly exhibited a Newtonian behavior with a flow index of 0.93. These data suggest that PBA loaded Closomer-based gels have similar rheological behavior, with lower complex modulus than that of HEC gels, and they can be a promising platform used for delivery of topical antiviral or other bioactive agents.