The development of bone tissue-engineered scaffolds requires materials that combine adequate mechanical strength, biocompatibility, and interconnected porosity, while maintaining stability under physiological conditions. However, highly porous polymer-based scaffolds often exhibit reduced mechanical stability in hydrated environments due to water-induced plasticisation. In this study, highly porous polymer-based scaffolds were functionalised using electrostatic Layer-by-Layer (LbL) assembly to enable controlled modification of surface and bulk properties. Multilayer nanocomposite coatings comprising poly-l-lysine, poly-L-glutamic acid, poly(diallyldimethylammonium chloride), and montmorillonite were deposited using LbL assembly. To improve mechanical stability under physiological conditions, the LbL-coated scaffolds were chemically crosslinked using a 1 wt% aqueous tannic acid (TA) solution as a naturally derived green crosslinker. Physicochemical characterisation was conducted using scanning electron microscopy (SEM), Fourier-transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD), energy-dispersive X-ray (EDX) analysis, and contact angle measurements. SEM analysis confirmed the formation of a uniform and dense multilayer coating following TA crosslinking. Under hydrated conditions (phosphate-buffered saline, PBS, 37 °C), TA-crosslinked scaffolds retained 75% of their dry-state elastic modulus, demonstrating improved mechanical stability. Contact angle measurements showed an increase in surface hydrophilicity, with values decreasing from 138.8 ± 2.85° for uncoated polyurethane to 70.3 ± 3.10° after crosslinking. Biodegradation studies under enzymatic and dynamic conditions showed controlled mass loss (10.5% over 8 weeks), consistent with enhanced structural stability. In vitro evaluation using MC3T3-E1 pre-osteoblasts confirmed no cytotoxic effects, with cell attachment on crosslinked scaffolds reaching 97.3% ± 2.2% after 24 h. The crosslinked scaffolds supported cell proliferation and maintained favourable cell morphology over 14 days. These results indicate that TA-crosslinked LbL-coated polyurethane scaffolds provide improved mechanical stability, surface properties, and cytocompatibility, supporting their potential use in bone tissue engineering applications.