A Channeled Chitosan-Based Polyelectrolyte Scaffold Platform for Localized Osteogenic Cue Delivery and Spatial Control of Mineralization in Centimeter-Scale Constructs

Abstract

Large bone defects remain difficult to regenerate due to limited nutrient diffusion and delayed vascularization, which restrict cell survival and tissue formation in volumetric constructs. Accordingly, there remains a need for natural-polymer-rich materials (>50% natural content) that can support architected, centimeter-scale scaffolds while integrating molecular-delivery and mineralization functions for volumetric bone engineering. Here, we investigated a hybrid polyelectrolyte complex (PEC) composed of chitosan and polystyrene sulfonate (CS/PSS) for the development of porous, channeled centimeter-scale scaffolds for bone regeneration. CS:PSS ratios spanning 1:0.5 to 1:2 were systematically evaluated to establish composition–structure–property relationships governing scaffold formation, architecture, mechanical behavior, and biofunctionality. The near-stoichiometric 1:1 formulation was identified as the most balanced composition, combining elastic recovery, mechanical robustness, interconnected porosity, cytocompatibility, self-mineralization, and charge-mediated drug delivery. Sacrificial templating was then used to fabricate volumetric CS/PSS porous scaffolds (>1 cm3) with defined microchannel networks (200–300 μm) that maintained structural integrity under dynamic cell seeding and culture while supporting volumetric tissue ingrowth. Leveraging intrinsic electrostatic interactions within the CS/PSS network, charged molecules, including the osteogenic cue β-glycerophosphate (β-GP), were loaded into the scaffold to achieve sustained release governed by hindered diffusion. Notably, scaffold-incorporated β-GP promoted osteogenic-associated behavior, collagen deposition, and mineral formation comparable to β-GP supplementation in the culture medium, despite an approximately 10-fold lower cumulative dose. Microcomputed tomography and histological analyses further showed that scaffold-mediated β-GP localization improved mineral uniformity throughout the scaffold volume relative to media supplementation. Collectively, these findings establish CS/PSS as a hybrid polyelectrolyte complex platform for integrating structural stability, localized molecular delivery, and architected bone scaffold design, while highlighting strong/weak polyelectrolyte coupling as a promising strategy for translating natural-polymer-rich systems into robust centimeter-scale scaffolds.