Moldable Double-Network Hydrogel Adhesives for Self-Healing
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Solution Overview
Problem
Conventional hydrogels suffer from poor stretchability and repairability, failing to meet the needs of applications requiring soft materials that are easy to deform, self-heal, and relax stress.
Innovation Solution
A double network hydrogel system is developed, comprising a dynamically crosslinked poly(vinyl alcohol) network with boric acid crosslinks and a chitosan network tethered via hydrogen bonding, which allows for extreme stretchability, spontaneous self-healing, and fast stress relaxation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If conventional hydrogels are used, then they provide basic adhesive properties, but they exhibit poor stretchability and repairability
Solution Approach 1:
The patent creates a composite hydrogel system combining two distinct polymer networks: poly(vinyl alcohol) crosslinked with boric acid and chitosan networks. This composite structure allows the material to simultaneously achieve extreme stretchability through the dynamic boronic ester bonds and self-healing capability through the hydrogen bonding between chitosan chains, directly resolving the contradiction between stretchability and repairability
Solution Approach 2:
The patent introduces dynamic reversible bonds (boronic ester bonds) that can break and reform under stress, enabling the hydrogel to dynamically adapt its structure. This dynamic character allows the material to stretch extensively when needed while maintaining the ability to self-heal by reforming bonds, thus resolving the contradiction between stretchability and repairability
2Stability of the object's composition
If conventional hydrogels are used, then they maintain structural stability, but they fail to relax stress rapidly
Solution Approach 1:
The dynamic boronic ester bonds in the poly(vinyl alcohol) network can reversibly break and reform, allowing the hydrogel to rapidly relax stress while maintaining overall structural integrity. This dynamic bond exchange enables fast stress relaxation without compromising structural stability, resolving the contradiction between these two properties
3Reliability
If conventional hydrogels are used, then they provide basic adhesion, but they lack self-healing capability
Solution Approach 1:
The patent employs a composite network structure where chitosan chains form hydrogen bonds that enable self-healing. The addition of chitosan, while increasing structural complexity, provides the specific hydrogen bonding capability needed for self-healing, thus resolving the contradiction between self-healing capability and structural complexity by introducing a functional component that directly enables the desired property
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The hydrogel exhibits up to 310 times elongation, instant self-healing, and rapid stress relaxation, making it suitable for applications in cell engineering, soft robotics, and wearable electronics.
Implementation Method 1
a first network that comprises at least two hydroxyl-bearing chains of a first polymer, the at least two hydroxyl-bearing polymer chains being crosslinked by crosslinks that comprise one or more boronic ester bonds
Implementation Method 2
a second network that comprises at least two hydroxyl-bearing chains of a second polymer, and the second polymer optionally hydrogen bonding to the first polymer
Data Source
AI summary
Cell engineering, soft robotics and wearable electronics often desire soft materials that are easy to deform, self-heal, and relax stress. Hydrogel, a type of hydrophilic networks, which can be made responsive to environmental stimuli, are often used in the aforementioned applications. However, conventional hydrogels often suffer from poor stretchability and repairability. Here, we report hydrogels consisting of boronic ester dynamic covalent bonds in a double network of poly(vinyl alcohol) together with chitosan, demonstrating extreme stretchability (up to 310 times of the original length), instant self-healing (within 5 sec), reusability as well as inherent adhesion. Their instant stress relaxation as a result of low activation energy of the boronic ester bond exchange (less than 20 KJ/mol) contributes to the extreme stretchability and self-healing behaviors. The hydrophilic environment readily incorporates various additives and provide opportunities in conductive soft materials, bio-signaling, and soft artificial joint.