Natural polymer hydrogel improves material properties

A unique, reusable and self-healing natural polymer hydrogel (chitosan/polymethylacrylic acid-CMA) was proposed by Chinese researchers in the latest paper published in gels.

Study: Highly flexible, self-healing and recyclable natural polymer hydrogels. Image Credit: Gilmanshin/Shutterstock.com

Advantages and disadvantages of hydrogels

Hydrogels are nanoscale polymers that are swollen by water and have excellent hydrophilic three-dimensional (3D) networking due to mechanical or chemical cross-connections.

Hydrogels have distinct characteristics due to their unique structure. They possess high inherent softness, natural hydrophilic nature, distinct swelling behavior as well as sensitivity to physiological environment.

Hydrogel-based functional materials have stimulated research interest and have been widely used in sorption polymers, controlled drug delivery, synthetic biology, and wearable elastic electrical devices over the past decades.

Even though hydrogels have obvious beneficial results, they are discarded due to permanent degradation (eg, mechanical breakages, dryness, or when part of the hydrogel is missing).

Due to the lack of meaningful recycling techniques, neglected materials contribute significantly to waste and environmental problems. As a result, a new reusable hydrogel with higher efficiency should be produced.

.  (A) Preparation of CMA hydrogels.  (B) FTIR spectra of CS, MA and CMA-3 hydrogels.  (C) XRD model of the CMA-3 hydrogel.  (D) SEM image of the CMA-3 hydrogel.

Figure 1. (A) Preparation of CMA hydrogels. (B) FTIR spectra of CS, MA and CMA-3 hydrogels. (VS) XRD model of the CMA-3 hydrogel. (D) SEM image of the CMA-3 hydrogel.© H. Miao., et al. (2022)

Self-Healing Hydrogels

Various functional hydrogels have been developed in recent years to address reusability issues.

The self-healing hydrogel is considered an excellent choice for treating mechanical stress. When touched by two-way and continuous contact, the self-healing hydrogel can effectively repair its structural system and restore its functionality.

The researchers created a hydrogel that could combine into a single piece in 2 minutes and restore 87% of its mechanical strength after 40 minutes at 25 degrees Celsius.

Industrial use of hydrogels

Since the discovery of the first artificial hydrogels in 1954 by Wichterle and Lim, hydrogel techniques have been applied to agricultural production, drug carriers, medical products, synthetic biology, diagnostic tests, wound dressings, isolation of biological molecules or cells and barrier components to monitor and control genetic contractures and biosensors.

Mechanical properties of CMA hydrogels: (A) Tensile strain curve at 10 mm min-1.  (B) Compressive stress curve at 5 mm min-1.  (C) Stretch-release cycles.  Photographs of CMA-3 hydrogel showing excellent stretching and bending flexibility (D, E).

Figure 2. Mechanical properties of CMA hydrogels: (A) Tensile strain curve at 10 mm min−1. (B) Deformation curve in compression at 5 mm min−1. (VS) Stretch-release cycles. Photographs of CMA-3 hydrogel exhibiting excellent stretching and bending flexibility (D,E). © H. Miao., et al. (2022)

Various technologies for the production of hydrogels

While hydrogels are typically made using hydrophilic monomers, hydrophobic monomers are sometimes used to modify characteristics for certain uses.

In general, hydrogels can be made from synthetic and natural polymers. In its most basic form, a hydrogel is just a hydrophilic polymer matrix that has been bridged in some way producing a flexible structure.

Accordingly, any approach that can be used to make a cross-linked polymer can also be used to build a hydrogel.

To make hydrogels, radical copolymerization/crosslinking polymerizations are often used.

Other technologies such as bulk polymerization, solution polymerization (often called crosslinking) and suspension polymerization are used for their synthesis.

search results

CMA hydrogels were fabricated using free radical polymerization using bidirectional hydrogen bonding with 3D lattice architectures associated with the natural lattice structure of chitosan (CS) and functional monomer-methacrylic acid (MA) .

Mechanical characteristics are an important performance metric to consider when evaluating hydrogel materials. The stress increased from 26 kPa to 125 kPa when the MA content increased from 1.0 g to 3.0 g, the tensile strain increased from 1357% to 3012%, and the Young’s modulus increased from 20. 3kPa to 42.9kPa.

Under 50% compressive stress, the compressive stress increased from 32 kPa to 176 kPa when the MA concentration increased from 1.0 g to 3.0 g.

It also showed considerable flexibility without snapping. Even when under human weight stress, the hydrogel was able to maintain its consistency without splitting and quickly return to its previous state when the load was removed.

Two CMA-3 hydrogel discs were fabricated and stained to directly illustrate this self-healing ability. The stained hydrogel discs were split in half.

Then the red and orange halves were brought together at room temperature. After 1 minute, the two hydrogel halves had effectively self-healed into one.

In short, the synthesized hydrogel demonstrated excellent mechanical, self-healing, and failure-recovery properties. Based on these advantages, the CMA hydrogel could be beneficial in a variety of applications.

(A) Photographs of the CMA-3 hydrogel powder self-healing capabilities.  (B) Photographs of CMA-3 hydrogel exhibiting excellent stretch flexibility.  (C) Photographs of CMA-3 hydrogel repairing partially missing hydrogel.

Picture 3. (A) Photographs of the CMA-3 hydrogel powder self-healing abilities. (B) Photographs of CMA-3 hydrogel exhibiting excellent stretch flexibility. (VS) Photographs of CMA-3 hydrogel repairing partially missing hydrogel. © H. Miao., et al. (2022)

Reference

H.Miao., et al. (2022) Highly flexible, self-healing and recyclable natural polymer hydrogels. capsules. 8(2). 89. Available at: https://www.mdpi.com/2310-2861/8/2/89

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