Structure–Mechanical Relationships in Alginate–Chitosan Polymer Composites

Alginate–chitosan composites are widely used bio-based materials due to their biocompatibility, biodegradability, and relatively simple processing methods. By combining the complementary properties of alginate and chitosan, these systems offer adjustable mechanical characteristics suitable for applications such as tissue engineering, wound healing, drug delivery, and sustainable packaging. However, although many studies report improved mechanical properties, the link between structural design and mechanical behavior is often discussed within specific applications rather than examined in a broader context. This review focuses on how polymer ratio, charge balance, crosslinking strategy, reinforcement approach, and processing conditions influence the mechanical properties of alginate–chitosan composites. Instead of considering these factors separately, the available studies are discussed in terms of how the internal structure of the composite affects stiffness, strength, deformability, and stability. This review brings together findings from various fields to highlight shared structure–mechanical relationships and to provide guidance for designing alginate–chitosan composites with specific mechanical properties.