4D Printing of Body Temperature-Responsive Hydrogels Based on Poly(acrylic acid) with Shape-Memory and Self-Healing Abilities

Abstract

Additive manufacturing of smart materials that can be dynamically programmed with external stimuli is known as 4D printing. Among the 4D printable materials, hydrogels are the most extensively studied materials in various biomedical areas because of their hierarchical structure, similarity to native human tissues, and supreme bioactivity. However, conventional smart hydrogels suffer from poor mechanical properties, slow actuation speed, and instability of actuated shape. Herein, we present 4D-printed hydrogels based on poly(acrylic acid) that can concurrently possess shape-memory and self-healing properties. The printing of the hydrogels is achieved by solvent-free copolymerization of the hydrophilic acrylic acid (AAc) and hydrophobic hexadecyl acrylate (C16A) monomers in the presence of TPO photoinitiator using a stereolithography-based commercial resin printer followed by swelling in water. The printed hydrogels undergo a reversible strong-to-weak gel transition below and above human body temperature due to the melting and crystallization of the hydrophobic C16A domains. In this way, the shape-memory and self-healing properties of the hydrogels can be magically actuated near the body temperature by adjusting the molar ratio of the monomers. Furthermore, the printed hydrogels display a high Young’s modulus (up to ∼215 MPa) and high toughness (up to ∼7 MJ/m3), and their mechanical properties can be tuned from brittle to ductile by reducing the molar fraction of C16A, or the deformation speed. Overall, the developed 4D printable hydrogels have great potential for various biomedical applications.

Preshaped 4D Photocurable Ultratough Organogel Microcoils for Personalized Endovascular Embolization

“…This toughness change guarantees the shape memory behavior described in previous sections. The tensile modulus of B368‐organogel is 511.63 MPa at 20 °C, from the color bar shown in Figure 3A, this value is 10 4 −10 6 times tougher than natural hydrogels, 10 2 −10 3 times tougher than silicone rubber materials, and more than two times of another body‐temperature‐triggered 4D printed hydrogel, [ 41 ] whose tensile modulus is reported to be 216 ± 8 MPa at the maximum. Its ultratoughness ensures the 4D microcoil capability to be twisted and programmed into different complicated shapes without breaking.…”

“…F) Demonstration of shape memory effect of 4D organogel microcoils with B368 crosslinker at 38 °C, the shape-changing procedure from straight line to 3D Omega-shaped microcoil could be completed within seconds. than two times of another body-temperature-triggered 4D printed hydrogel, [41] whose tensile modulus is reported to be 216 ± 8 MPa at the maximum. Its ultratoughness ensures the 4D microcoil capability to be twisted and programmed into different complicated shapes without breaking.…”

Application of Shape Memory and Self-Healable Polymers/Composites in the Biomedical Field: A Review

“…The hand was then submerged at 43 °C to examine the shape memory. The outcome demonstrated simultaneous recovery from folding and stretching, and the printed hand regained its original shape in less than 1 min of recovery (Figure c,d) . This showed the enormous potential of C16A and PAAc copolymerized hydrogels in a wide range of fields, especially where dynamic adaptation is necessary, such as soft robotics, aerospace, and biomedical applications.…”

Designing Lignin-Based Biomaterials as Carriers of Bioactive Molecules

“…Since its invention in 1981, many types of AM techniques, such as stereolithography (SLA), digital light processing (DLP), direct ink writing (DIW), fused deposition modeling (FDM), selective laser sintering, and selective laser melting, have been established to print broad ranges of materials, ranging from polymers to metals and ceramics [140,141]. In addition, many innovative AM techniques, such as 4D/5D/6D printing [142][143][144], melt electrowriting (MEW) [145], and cryoprinting [146], are continuously emerging to advance this technology to new heights. Currently, it has become one of the fastest developing technologies that is expected to ultimately replace many traditional manufacturing industries [147,148].…”