Department of Chemistry, Istanbul Technical University, 34469Maslak, IstanbulTurkey.
ACS Appl Bio Mater. 2023 Feb 20;6(2):703-711. doi: 10.1021/acsabm.2c00939. Epub 2023 Jan 26.
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/m), 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.
能够对外界刺激进行动态编程的智能材料的增材制造被称为 4D 打印。在可 4D 打印的材料中，水凝胶由于其分级结构、与天然人体组织的相似性以及卓越的生物活性，在各种生物医学领域中得到了广泛的研究。然而，传统的智能水凝胶存在机械性能差、响应速度慢以及响应形状不稳定等问题。在此，我们提出了一种基于聚丙烯酸的 4D 打印水凝胶，其同时具有形状记忆和自修复性能。通过无溶剂共聚亲水性丙烯酸（AAc）和疏水性十六烷丙烯酸酯（C16A）单体，在 TPO 光引发剂存在下，使用基于立体光刻的商业树脂打印机打印水凝胶，然后在水中溶胀。打印的水凝胶在人体温度以下和以上经历可逆的强-弱凝胶转变，这归因于疏水性 C16A 域的熔融和结晶。通过调节单体的摩尔比，可以在接近体温的条件下神奇地触发水凝胶的形状记忆和自修复性能。此外，打印的水凝胶表现出高杨氏模量（高达约 215 MPa）和高韧性（高达约 7 MJ/m），并且其机械性能可以通过降低 C16A 的摩尔分数或变形速度从脆性调节到韧性。总的来说，开发的 4D 可打印水凝胶在各种生物医学应用中具有巨大的潜力。
