Effect of Sulfated Polysaccharides and Laponite in Composite Porous Scaffolds on Osteogenesis

The design of biomaterial scaffolds for bone tissue engineering requires a balance between bioactivity, porosity, mechanical stability, and osteoinductivity. Kappa- (KC) and iota-carrageenan (IC) have been explored for scaffold fabrication due to their biocompatibility and structural similarity to glycosaminoglycans. However, there are limited reports on how their distinct sulfation degree affects the osteogenic differentiation of cells cultured on them. While laponite has been reported as an osteoinductive nanoclay, its combined effect with different carrageenan types and its concentration-dependent effect on scaffold functionality remain unexplored. Therefore, we developed composite scaffolds comprising poly(vinyl alcohol) (PVA) and gelatin (GEL), reinforced with kappa- or iota-carrageenan (KC, IC) and functionalized with two different concentrations of laponite (LAP), 0.5 and 1% w/v, to monitor composition-structure-function relationships. The scaffolds were fabricated via lyophilization and dual crosslinking, and characterized for their physicochemical, structural, mechanical, and biological properties. The incorporation of both carrageenans into scaffolds, maintained high swelling ratios of 600% after 24 h, and increased porosity without altering their apparent density (0.09-0.11 g/cm³), whereas LAP preserved interconnectivity, densified pore walls, raised their compressive modulus at >220 kPa, and improved stability (>60% mass retained after 40 days). In vitro validation using MC3T3-E1 pre-osteoblastic cells demonstrated robust cytocompatibility, with the LAP-containing scaffolds significantly promoting cell adhesion, proliferation, and osteogenic differentiation, evidenced by elevated alkaline phosphatase activity, calcium production and collagen secretion. Direct comparison between KC and IC scaffolds confirmed that differences in sulfate substitution modulated scaffold stiffness, swelling, and degradation, while variation in LAP concentration affected the biological response, with the 0.5 wt% concentration favoring early cell proliferation, whereas the 1 wt% significantly promoted the osteogenic differentiation. This compositional strategy demonstrates how tuning the interplay between carrageenan and laponite can balance scaffold hydration, mechanical and biological properties, thereby guiding the design of scaffolds for bone repair.