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.
- nanoparticles, e.g. TiO2
- carbon nanotubes (CNTs)
- cellulose nanocrystals (CNCs)
- cellulose nanofibrils
- gums, e.g. xanthan, sage seed gum
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.
- 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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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
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:
Classification based on network electrical charge:
- nonionic (neutral)
- ionic (including anionic or cationic)
- amphoteric electrolyte (ampholytic)
- zwitterionic (polybetaines)
Literature / References
- Mohammadinezhada, Alireza; Marandi, Gholam Bagheri; Farsadrooh, Majid; Javadian, Hamedreza (2018): Synthesis of poly(acrylamide-co-itaconic acid)/MWCNTs superabsorbent hydrogel nanocomposite by ultrasound-assisted technique: Swelling behavior and Pb (II) adsorption capacity. Ultrasonics Sonochemistry Vol. 49, 2018. 1-12.
- Cass, Peter; Knower, Warren; Pereeia, Eliana; Holmes, Natalie P.; Hughes Tim (2010): Preparation of hydrogels via ultrasonic polymerization. Ultrasonics Sonochemistry Volume 17, Issue 2, February 2010. 326-332.
- Willfahrt, A., Steiner, E., Hoetzel, J., Crispin, X. (2019): Printable acid-modified corn starch as non-toxic, disposable hydrogel-polymer electrolyte in supercapacitors. Applied Physics A, 125(7), 474.
- Butylina, Svetlana; Geng, Shiyu; Laatikainen, Katri; Oksman, Kristiina (2020): Cellulose Nanocomposite Hydrogels: From Formulation to Material Properties. Frontiers in Chemistry, Vol. 8, 655, 2020.
- Rutgeerts, Laurens A. J.; Soultan, Al Halifa; Subramani, Ramesh; Toprakhisar, Burak; Ramon, Herman; Paderes, Monissa C.; De Borggraeve, Wim M.; Patterson, Jennifer (2019): Robust scalable synthesis of a bis-urea derivative forming thixotropic and cytocompatible supramolecular hydrogels. Chemical Communications Issue 51, 2019.
- Oleyaei, Seyed Amir; Razavi, Seyed Mohammad Ali; Mikkonen, Kirsi S. (2018): Physicochemical and rheo-mechanical properties of titanium dioxide reinforced sage seed gum nanohybrid hydrogel. International Journal of Biological Macromolecules Vol. 118, Part A, 2018. 661-670.