This study presents the development of advanced agarose-based semi-interpenetrating polymer networks (semi-IPN) incorporating cross-linked functional methacrylic copolymers to overcome the limited mechanical performance and structural stability of conventional agarose matrices. A library of thirty-one copolymers was synthesized by reversible addition−fragmentation chain-transfer polymerization (RAFT), atom transfer radical polymerization (ATRP), iron-mediated ATRP, photoinduced electron-transfer RAFT (PET-RAFT), or activators regenerated by electron transfer ATRP (ARGET-ATRP) using 2-hydroxyethyl methacrylate (HEMA), oligo(ethylene glycol) methacrylate (OEGMA), and 2–(N,N–dimethylamino)ethyl methacrylate (DMAEMA) as primary monomers, and furfuryl methacrylate (FMA) or vinyl methacrylate (VMA) as cross-linkable co-monomers. Polymerization outcomes depended strongly on monomer composition and synthetic route: RAFT was particularly effective for OEGMA-rich systems, ATRP for DMAEMA-containing copolymers, and PET-RAFT for VMA-based materials. Four selected copolymers were subsequently cross-linked through Diels–Alder (DA), thiol–ene, or combined covalent–ionic strategies, yielding stable hydrogels with tunable responsiveness. Three copolymer systems were successfully integrated into agarose matrices, resulting in different semi-IPN with substantially enhanced mechanical reinforcement, with improvements of 150- to 1330-fold relative to controls. The OEGMA-based, DA-cross-linked system exhibited the strongest overall reinforcement, while its DMAEMA counterpart (covalent and ionically cross-linked) showed the most pronounced relative enhancement over its corresponding agarose-free hydrogel. Scanning electron micrographs revealed homogeneous, well-defined, interconnected microporous structures, and thermorheological tests confirmed temperature-responsive behavior in the DA-based systems. Overall, this work establishes a versatile synthetic strategy for constructing degradable, mechanically robust, and biomedically relevant agarose-based semi-IPN with potential in tissue engineering, wound healing, and drug delivery.
4D-printing of shape-memory polymers using extrusion-based technologies attracts widespread interest, although reversible shape-memory effects (SMEs) in additively manufactured architectures remain poorly explored. Here, a polymeric system is presented that is processable by Fused Particle Fabrication (FPF), enabling the production of structures exhibiting multi-responsive two-way stress-free SME. The system consists of blends of photo-crosslinkable poly[(ε-caprolactone)-b-(butylene succinate)-b-(ε-caprolactone)]dimethacrylate (PCL-PBS-PCL) triblock copolymers with different chain lengths. Thermo-responsive shape-memory behavior originates from the reversible melting and crystallization of active PCL crystallites under the internal stress imposed by the crystalline PBS domains acting as the structural skeleton. Photo-responsivity is introduced by incorporating near-infrared-sensitive plasmonic titanium nitride nanoparticles. Shape-memory performances are tuned by varying the blend composition and were initially investigated in bulk crosslinked films. The reversible stress-free elongation depends on the balance between PCL and PBS crystallinity, and reaches values up to 23 % and 11 % in formulations without and with nanoparticles, respectively. 3D-printed architectures show SME regardless of raster angle or layer number, although actuation is lower than in bulk films because of non-optimal room-temperature photo-crosslinking conditions required to ensure shape fidelity. These findings demonstrate the feasibility of producing multi-responsive stress-free reversible shape-memory architectures via FPF, opening new avenues for shape-memory actuators in soft robotics.
