Quadruple shape memory hydrogels were prepared by one-pot in situ copolymerization using acrylamide, acrylic acid, agar, and poly(vinyl alcohol). The hydrogels have multiple reversible shape memory based on the coordination bonds of poly(acrylic acid) with Fe³⁺, borate bonds based on poly(vinyl alcohol), and hydrogen bonds of agar and poly(vinyl alcohol). The hydrogel demonstrated tunable mechanical properties when the hydrogels immersed in different solutions for various lengths of time. After immersion in the ferric chloride solution, tensile stress and elastic moduli of the hydrogels were enhanced with increasing soaking time. After immersion in the borax solution, tensile stress first increased and then decreased with increasing soaking time. Due to the reversible effect of the borate bond, the hydrogel achieved ultra-fast self-healing. The hydrogel after immersion in borax solution could begin healing in 24 h and healed at 44 h. The tensile stress and tensile strain of the self-healing hydrogel increased when soaking time increased from 48 to 96 h, and tensile stress at healing times of 96 h was nearly as the same as that of the original hydrogel when compared with it. The combination of tunable mechanical properties, efficient recoverability and self-healing abilities coupled with facile preparation endowed the developed hydrogel a high potential for use in biomedical applications.

中文翻译：

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基于配位，硼酸酯键和温度的可自我修复的四重形状记忆水凝胶，具有可调节的机械性能

使用丙烯酰胺，丙烯酸，琼脂和聚乙烯醇通过一锅法原位共聚制备四重形状记忆水凝胶。基于聚丙烯酸与Fe ³⁺的配位键，水凝胶具有多种可逆的形状记忆，基于聚乙烯醇的硼酸酯键以及琼脂和聚乙烯醇的氢键。当水凝胶浸入不同溶液中不同的时间长度时，水凝胶显示出可调节的机械性能。浸入氯化铁溶液后，水凝胶的拉伸应力和弹性模量随浸泡时间的增加而增强。浸入硼砂溶液后，拉伸应力首先随着浸泡时间的增加而增加，然后降低。由于硼酸酯键的可逆作用，水凝胶实现了超快速的自愈。浸入硼砂溶液中的水凝胶可在24小时内开始愈合，并在44小时后愈合。当浸泡时间从48小时增加到96小时时，自愈水凝胶的拉伸应力和拉伸应变增加，与之相比，愈合时间为96 h时的拉伸应力几乎与原始水凝胶相同。可调的机械性能，有效的可恢复性和自愈能力与便捷的制备相结合，使这种开发的水凝胶在生物医学应用中具有很高的潜力。