Hydrogels

By: Batool Murtaza

Abstract

Hydrogels have been around for almost half a century, and one of the oldest recordings of crosslinked hydroxyethyl methacrylate (HEMA) hydrogels dates back to the 1950s. Hydrogels continue to intrigue material scientists and biological researchers today, and significant progress has been made in terms of formulations and applications. Hydrogels are a type of material that consists of a self-supporting, water-swollen three-dimensional (3D) viscoelastic network that allows molecules and cells to diffuse and adhere. Hydrogels, on the other hand, have recently received a lot of attention for their usage in a wide range of biological applications, including cell therapies, wound healing, cartilage/bone regeneration, and medication sustained release. This is due to their biocompatibility and physical qualities that are similar to those of natural tissue. Based on ancient and new papers in this subject, this study attempts to provide an overview of the historic and modern design concepts of hydrogels and their various uses. (Yahia, n.d.)

Introduction

Due to chemical or physical cross-linking of individual polymer chains, a hydrogel is a three- dimensional (3D) network of hydrophilic polymers that can swell in water and hold a high amount of water while keeping their structure. Wichterle and Lm (1960) were the first to describe hydrogels. For a material to be classified as a hydrogel, it must contain at least 10% water by weight (or volume). Because of their high water content, hydrogels have a similar degree of flexibility to genuine tissue. The presence of hydrophilic groups such as -NH2, -COOH, -OH, -CONH2, -CONH -, and - SO3H contribute to the network's hydrophilicity. (Bahram, 2016)

Hydrogel product sensitive to environmental conditions

Hydrogels are three-dimensional cross-linked hydrophilic polymer networks that may swell and de- swell reversibly in water while retaining a high volume of liquid. Hydrogels can be engineered to shrink or expand in response to changes in external environmental conditions.

They may undergo significant volume transitions in response to a number of physical and chemical stimuli, including temperature, electric or magnetic fields, light, pressure, and sound, as well as pH, solvent composition, ionic strength, and molecular species.

The degree of swelling or de-swelling in reaction to changes in the hydrogel's external environment can be so extreme that the event is known as volume collapse or phase transition [Shin et al., 2010]. Synthetic hydrogels have been the subject of intensive research over the past four decades, and they are still a hot topic in academia today.

Applications of hydrogels

Electrophoresis, bioseparations, proteomic, chromatography, tissue engineering, and other applications all use hydrogels. They're well-known as absorbents in disposable diapers, water purification filters, and chromatography and electrophoresis separation materials in foods and medications. They're also useful for regulating drug release and concentrating dilute macromolecule solutions [Wellner et al., 1998].

•  Domestic uses: High-tech devices with out-of-sight objectives aren't required for life-changing inventions. Sometimes the simplest solution can lead to more advancement than the most expensive and cutting-edge technology. This is also true with hydrogels. This family of materials offers a wide range of household applications that take advantage of its capacity to load, retain, and release fluids to greatly improve daily life.

• Perfume delivery: During the 1990s, the number of patents describing volatile species delivery devices began to rise. Procter&Gamble appears to have released the most significant patented inventions in the industry, converting perfumes into cyclodextrin complexes [Scott L (2015), Trinh T, Gardlik JM (1990), Subkowski T, Bollschweiler C, Wittenberg J, Siegel W, Pelzer R (2013)].

The overall goal was to create devices that could progressively release fragrances into the environment over time, replacing traditional salt-based (sodium dodecylbenzenesulphonate) tablets with new, more practical, and, dare we say, finer house care solutions. The involvement of hydrogels in the process is centred on their swelling capabilities, which can be used in materials “wherein the release of a perfume scent is initiated by the dynamic swelling force of the polymer when the polymer is wetted” [Trinh T, 1990]. The osmotic diffusion of the specie from the swollen hydrogel to new water in the surroundings allows these devices to discharge volatile particles.

•  Bacterial culture: Hydrogels can house a large number of microorganisms in their matrix for water purification, biomolecule manufacturing, or basic bacterial cultivation on their own.

Indeed, in biotechnological applications, agar is known as the gold standard substrate for bacterial culture [Sokker et al., 2011]. It provides an ideal environment for the culture of bacteria and microorganisms on a solid substrate since it is indigestible to a large number of bacteria and microorganisms [Heginbothom et al., 1990]. Different types of agar have been investigated, each with the potential to be used by different microorganisms. The most frequent agars include brucella agar, columbi agar, schaedler agar, and trypicasesoy agar. None of these gels outperforms the others in terms of results; instead, due to their various advantages and disadvantages, they are all suited for distinct applications [Smith A(2012), Cover TL (2012)].

 

References

1.     Yahia, L. (n.d.). History and Applications of Hydrogels | Insight Medical Publishing. Retrieved September 23, 2021, from https://www.jbiomeds.com/biomedical-sciences/history-and- applications-of-hydrogels.php?aid=7218

2.      Bahram, M. (2016, August 24). An Introduction to Hydrogels and Some Recent Applications. IntechOpen. https://www.intechopen.com/chapters/51535

3.      Shin, J., Braun, P. V., & Lee, W. (2010). Fast response photonic crystal pH sensor based on templated photo-polymerized hydrogel inverse opal. Sensors and Actuators B: Chemical,150(1), 183–190. https://doi.org/10.1016/j.snb.2010.07.018

4.      Wellner, N., Kačuráková, M., Malovıková, A., Wilson, R. H., & Belton, P. S. (1998). FT-IR study of pectate and pectinate gels formed by divalent cations. Carbohydrate Research, 308(1–2), 123–131. https://doi.org/10.1016/s0008-6215(98)00065-2

5.      Chalker-Scott L (2015)The Myth of Polyacrylamide Hydrogels

6.      Trinh T, Gardlik JM (1990) European Patent EP 0392608 A2. Solid consumer product compositions containing small particle cyclodextrin complexes

7.      Subkowski T, Bollschweiler C, Wittenberg J, Siegel W, Pelzer R (2013) International Patent WO 1999004830 A1. Low molecular weight modulators of the cold-menthol receptor trpm8 and use thereof.

8.      Heginbothom, M., Fitzgerald, T. C., & Wade, W. G. (1990). Comparison of solid media for cultivation of anaerobes. Journal of Clinical Pathology, 43(3), 253–256. https://doi.org/10.1136/jcp.43.3.253

9.      Smith A(2012) History of the Agar Plate. Laboratory News

10.  Cover TL (2012) Perspectives on methodology for in vitro culture of Helicobacter pylori.Methods MolBiol 921: 11-15.