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[9] [11] [12] [13] The crosslinking mechanism of the hydrophilic macromolecules are driven by covalent bonding, resulting in a physical- or chemical-type hydrogel. Physical hydrogels contain reversible matrices of hydrogen and non-covalent bonds, while chemical hydrogels are composed of irreversible matrices that are molecularly held together ...
A nanogel is a polymer-based, crosslinked hydrogel particle on the sub-micron scale. [1] [2] [3] These complex networks of polymers present a unique opportunity in the field of drug delivery at the intersection of nanoparticles and hydrogel synthesis.
Crosslinking is the process of joining two or more polymer chains. Both chemical and physical crosslinking exists. In addition, both natural polymers such as proteins or synthetic polymers with a high affinity for water may be used as starting materials when selecting a hydrogel. [1]
A hydrogel generated through the use of physical crosslinks is sometimes called a 'reversible' hydrogel. [13] Chemical crosslinks consist of covalent bonds between polymer strands. Hydrogels generated in this manner are sometimes called 'permanent' hydrogels.
Similar to physical solidification, some chemical crosslinking methods have been developed to produce hydrogel fibers. And the key for the achievement of hydrogel production through the chemical crosslinking method is the effective separation between the formed network and the tube wall.
Specifically, hydrogels can be designed to release drugs or other agents in response to physical characteristics of the environment like temperature and pH. [12] The responsiveness of hydrogels is a result of their molecular structure and polymer networks. [12] Hydrogel nanoparticles have a promising future in the drug delivery field.
In polymer chemistry "cross-linking" usually refers to the use of cross-links to promote a change in the polymers' physical properties. When "crosslinking" is used in the biological field, it refers to the use of a probe to link proteins together to check for protein–protein interactions, as well as other creative cross-linking methodologies.
Cross-linking can be introduced using N,N-methylenebisacrylamide. Some crosslinked materials are swellable but not soluble, i.e., they are hydrogels. Partial hydrolysis occurs at elevated temperatures in aqueous media, converting some amide substituents to carboxylates. This hydrolysis thus makes the polymer particularly hydrophilic.