Brown seaweed is a naturally occurring composite that integrates alginate and cellulose within a hierarchical, hydrated architecture analogous to engineered hydrogel systems. This study hypothesizes that leveraging the native structure–function relationships of brown seaweed enables the development of functional hydrogel biomaterials while minimizing synthetic and chemical processing. Strategies are investigated to exploit the intrinsic biological structure and composition of brown seaweed blades across multiple formats, including native and purified blade structures, as well as fibrillated blades reassembled into hydrogels and foam structures via 3D printing and freeze-drying. The resulting biomaterials are characterized in terms of structure, hydrogel stability, and liquid absorption capacity in different media. The effects of purification are compared with those of native materials. In addition, porosity, mechanical, rheological, and cytocompatibility properties of the fibrillated and reassembled structures are evaluated. By preserving the natural architecture and avoiding extensive fractionation, this approach demonstrates the potential to create resource-efficient biomaterials with high liquid absorption (∼3600%), high porosity (∼93%), and shape-memory behavior after compression. Cytocompatibility reaches ∼73% viability at 50% extract but decreases to ∼59% at full concentration, indicating a concentration-dependent biological response, underscoring the need to balance minimal processing with biological performance for biomedical applications.