In situ formed aldehyde-modified hyaluronic acid hydrogel with polyelectrolyte complexes of aldehyde-modified chondroitin sulfate and gelatin: An approach for minocycline delivery.

Polysaccharides like hyaluronan (HA) and chondroitin sulfate (CS) are native of the brain's extracellular matrix crucial for myelination and brain maturation. Despite extensive research on HA and CS as drug delivery systems (DDS), their high water solubility limits their application as drug carriers. This study introduces an injectable DDS using aldehyde-modified hyaluronic acid (HAOX) hydrogel containing polyelectrolyte complexes (PEC) formed with calcium, gelatin, and either CS or aldehyde-modified CS (CSOX) to deliver minocycline for Multiple Sclerosis therapy. PECs with CSOX enable covalent crosslinking to HAOX, creating immobilized PECs (HAOX_PECOX), while those with CS remain unbound (HAOX_PECS). The in situ forming DDS can be administered via a 20 G needle, with rapid gelation preventing premature leakage. The system integrates into an implanted device for minocycline release through either Fickian or anomalous diffusion, depending on PEC immobilization. HAOX_PECOX reduced burst release by 88 %, with a duration of 127 h for 50 % release. The DDS exhibited an elastic modulus of 3800 Pa and a low swelling ratio (0-1 %), enabling precise control of minocycline release kinetics. Released minocycline reduced IL-6 secretion in the Whole Blood Monocytes Activation Test, suggesting that DDS formation may not alter the biological activity of the loaded drug.