Spectral Trajectory Analysis of Drug Release from Bioprinted Alginate-Based Hydrogels

The release of molecular probes from soft hydrogel matrices involves coupled transport and structural relaxation processes that are difficult to capture using predefined kinetic models. Here we investigate the release dynamics of indocyanine green from bioprinted alginate-based hydrogels, including alginate-gelatin and calcium-cross-linked alginate-poly-(vinyl alcohol) matrices, using a data-driven spectroscopic approach. Time-resolved UV-vis absorption spectra collected in the surrounding aqueous phase are analyzed by singular value decomposition to construct reduced-dimensional trajectories in spectral space. The spectral evolution exhibits a rapid initial increase followed by progressive saturation, indicating a transition from transient release to a quasi-stationary regime. Singular value analysis reveals an effectively low-dimensional dynamics, with two dominant modes capturing the essential temporal behavior across both systems. The resulting trajectories provide characteristic time scales and a compact, model-independent representation of release pathways directly from spectroscopic observables.