Advantageous Hydrogel Production via Ultrasonication

Sonication is a highly efficacious, reliable and simple technique for the preparation of high-performance hydrogels. These hydrogels offer excellent material properties such as absorption capacities, viscoelasticity, mechanical strength, compression modulus, and self-healing functionalities.

Ultrasonic Polymerization and Dispersion for Hydrogel Production

Hydrogels are hydrophilic, three-dimensional polymeric networks that are able to absorb large quantities of water or fluids. Hydrogels exhibit an extraordinary swelling capacity. Common building blocks of hydrgels include polyvinyl alcohol, polyethylene glycol, sodium polyacrylate, acrylate polymers, carbomers, polysaccharides or polypeptides with a high number of hydrophilic groups, and natural proteins such as collagen, gelatine and fibrin.
So-called hybrid hydrogels consist of various chemically, functionally, and morphologically distinct materials, such as proteins, peptides, or nano- / microstructures.
Ultrasonic dispersion is widely used as an highly efficient and reliable technique to homogenize nano-materials such as carbon nanotubes (CNTs, MWCNTs, SWCNTs), cellulose nano-crystals, chitin nanofibres, titanium dioxide, silver nanoparticles, proteins and other micron- or nanostructures into the polymeric matrix of hydrogels. This makes sonication a main tool to produce high-performance hydrogels with extraordinary qualities.

What Research Shows – Ultrasonic Hydrogel Preparation

First, ultrasonication promotes polymerization and cross-linking reactions during hydrogel formation.
Secondly, ultrasonication has been proven as reliable and effective dispersion technique for the production of hydrogels and nanocomposite hydrogels.

Ultrasonic Cross-Linking and Polymerization of Hydrogels

Ultrasonication assists the formation of polymeric networks during hydrogel synthesis via free radical generation. Intense ultrasound waves generate acoustic cavitation which cause high-shear forces, molecular shearing and free radical formation.

Cass et al. (2010) prepared several “acrylic hydrogels were prepared via ultrasonic polymerization of water soluble monomers and macromonomers. Ultrasound was used to create initiating radicals in viscous aqueous monomer soluions using the additives glycerol, sorbitol or glucose in an open system at 37°C. The water soluble additives were essential for the hydrogel production, glycerol being the most effective. Hydrogels were prepared from the monomers 2-hydroxyethyl methacrylate, poly(ethylene glycol) dimethacrylate, dextran methacrylate, acrylic acid/ethylene glycol dimethacrylate and acrylamide/bis-acrylamide.” [Cass et al. 2010] Ultrasound application using a probe ultrasonicator was found to be an effective method for the polymerization of water soluble vinyl monomers and the subsequent preparation of hydrogels. The ultrasonically initiated polymerization occurs rapidly in the absence of a chemical initiator.

Read more about ultrasonic synthesis of nanocomposite hydrogels and nanogels!

SEM of poly(acrylamide-co-itaconic acid hydrogel containing MWCNTs. The MWCNTs were ultrasonically dispersed using the ultrasonicator UP200S.
study and picture: Mohammadinezhada et al., 2018

Fabrication of Poly(acrylamide-co-itaconic acid) – MWCNT Hydrogel using Sonication

Mohammadinezhada et al. (2018) successfully produced a superabsorbent hydrogel composite containing poly(acrylamide-co-itaconic acid) and multi-walled carbon nanotubes (MWCNTs). Ultrasonication was performed with the Hielscher ultrasonic device UP200S.The stability of the hydrogel increased with increasing MWCNTs ratios, which might be attributed to the hydrophobic nature of the MWCNTs as well as the increase of the crosslinker density. The water retention capacity (WRC) of the P(AAm-co-IA) hydrogel was also increased in the presence of the MWCNT (10 wt%). In this study, the effects of ultrasonication were rated superior in regards to the uniform distribution of the carbon nanotubes on the polymer surface. The MWCNTs were intact without any interruption in the polymeric structure. Additionally, the strength of the obtained nanocomposite and its water retention capacity and the absorption of other soluble materials like Pb (II) were increased. Sonication broke the initiator and dispersed the MWCNTs as an excellent filler in the polymer chains under increasing temperature.
The researchers conclude that these “reaction conditions cannot be achieved through conventional methods, and the homogeneity and good-dispersion of particles into the host cannot be achieved. In addition, sonication process separate nanoparticles into single particle, while stirring cannot do this. Another mechanism for the size reduction is the effect of powerful acoustic waves on the secondary bonds like hydrogen bonding which this irradiation breaks the H-bonding of particles, and subsequently, dissociates the aggregated particles and increase the number of free adsorptive groups like -OH and accessibility. Thus, this important happening makes sonication process as a superior method over the others like magnetic stirring applied in the literatures.” [Mohammadinezhada et al., 2018]

High Performance Ultrasonicators for Hydrogel Synthesis

Hielscher Ultrasonics manufactures high-performance ultrasonic equipment for the synthesis of hydrogels. From small and mid-size R&D and pilot ultrasonicators to industrial systems for commercial hydrogel manufacturing in continuous mode, Hielscher Ultrasonics has your process requirements covered.
Industrial-grade ultrasonicators can deliver very high amplitudes, which allow for reliable cross-linking and polymerization reactions and the uniform dispersion of nano particles. Amplitudes of up to 200µm can be easily continuously run in 24/7/365 operation. For even higher amplitudes, customized ultrasonic sonotrodes are available.

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The table below gives you an indication of the approximate processing capacity of our ultrasonicators: