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

Ultrasonication is used to initiate cross-linking and polymerization during hydrogel production. Ultrasonic dispersion is used to distribute nanoparticles in hydrogels.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.

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Ultrasonic cavitation promotes the cross-linking and polymerization during hydrogel synthesis. Ultrasonic dispersion facilitates the uniform distribution of nanomaterials for hybrid hydrogel fabrication.

Ultrasonicator UIP1000hdT with glass reactor for hydrogel synthesis

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.

Ultrasonic Dispersion of Nano-Silica

Ultrasonic Dispersion of

  • nanoparticles, e.g. TiO2
  • carbon nanotubes (CNTs)
  • cellulose nanocrystals (CNCs)
  • cellulose nanofibrils
  • gums, e.g. xanthan, sage seed gum
  • proteins
Ultrasonic nano-dispersion with the ultrasonicator UP400ST

Hydrogel formation via ultrasonically-assisted gelation using the ultrasonicator UP100H

Hydrogel formation via ultrasonically-assisted gelation using the ultrasonicator UP100H

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Ultrasonication is compatible with all kinds of polymers and biopolymers and allows to reinforce hybrid hydrogels with nano-structured materials such as nanoparticles, nanocrystals or nanofibres. Reinforcing hydrogels with various nanomaterials allows to modify and control physicochemical and rheo-mechanical properties of nanocomposite hydrogels, since the microstructures are the key factor for the obtained material properties.

Ultrasonication is applied to produce high-performance hydrogels containing nano-materials

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.

Why Hielscher Ultrasonics?

  • high efficiency
  • state-of-the-art technology
  • reliability & robustness
  • batch & inline
  • for any volume
  • intelligent software
  • smart features (e.g., data protocolling)
  • CIP (clean-in-place)

Ask us today for additional technical information, pricing and a noncommittal quotation. Our long-time experienced staff is glad to consult you!
The table below gives you an indication of the approximate processing capacity of our ultrasonicators:

Batch Volume Flow Rate Recommended Devices
1 to 500mL 10 to 200mL/min UP100H
10 to 2000mL 20 to 400mL/min UP200Ht, UP400St
0.1 to 20L 0.2 to 4L/min UIP2000hdT
10 to 100L 2 to 10L/min UIP4000hdT
n.a. 10 to 100L/min UIP16000
n.a. larger cluster of UIP16000

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Ultrasonic high-shear homogenizers are used in lab, bench-top, pilot and industrial processing.

Hielscher Ultrasonics manufactures high-performance ultrasonic homogenizers for mixing applications, dispersion, emulsification and extraction on lab, pilot and industrial scale.

Literature / References

Facts Worth Knowing

What are Hydrogels used for?

Hydrogels are used in many industries such as in pharma for drug delivery (e.g. time-released, oral, intravenous, topical or rectal drug delivery), medicine (e.g. as scaffolds in tissue engineering, breast implants, biomechanical material, wound dressings), cosmetic products, care products (e.g. contact lenses, diapers, sanitary napkins), agriculture (e.g. for pesticide formulations, granules for holding soil moisture in arid areas), material research as functional polymers (e.g. water gel explosives, encapsulation of quantum dots, thermodynamic electricity generation), coal dewatering, artificial snow, food additives, and other products (e.g., glue).

Classification of Hydrogels

When the classification of hydrogels is made depending on their physical structure can be classified as follows:

  • amorphous (non-crystalline)
  • semicrystalline: A complex mixture of amorphous and crystalline phases
  • crystalline

When focused on polymeric composition, hydrogels can be also classified into the following three categories:

  • homopolymeric hydrogels
  • copolymeric hydrogels
  • multipolymeric hydrogels / IPN hydrogels

Based on type of crosslinking, hydrogels are classified into:

  • chemically crosslinked networks: permanent junctions
  • physically crosslinked networks: transient junctions

Physical appearance leads to classification into:

  • matrix
  • film
  • microsphere

Classification based on network electrical charge:

  • nonionic (neutral)
  • ionic (including anionic or cationic)
  • amphoteric electrolyte (ampholytic)
  • zwitterionic (polybetaines)

Hielscher Ultrasonics supplies high-performance ultrasonic homogenizers from lab to industrial size.

High performance ultrasonics! Hielscher’s product range covers the full spectrum from the compact lab ultrasonicator over bench-top units to full-industrial ultrasonic systems.