Hydrogels chemical cross-links

Hydrogels are three-dimensional, hydrophilic, polymeric networks that can take up large amounts of water or other biological fluids. The networks consist of homopolymers or copolymers having physical or chemical cross-links that make them insoluble, which are responsible for the integrity of the network. 

Pharmaceutical grade poly(ethylene glycols) are poly(ethylene oxides) with terminal hydroxyl groups and have been approved by the E.D.A. and listed in both the United States Pharmacopoeia and Martindale under Macrogols for use as ointment and suppository bases (4J. Poly(ethylene glycol) can be chemically cross-linked retaining the hydrophilic nature of the PEO backbone in an infinite hydrogel network which will imbibe water and swell but not... 

Fig. 1 Representative methods of hydrogel formation. (A) Chemically cross-linked hydrogels are prepared from monomers, oligomers, or polymers in the presence of cross-linking agents. The chemical cross-linking proceeds via radical polymerization or polycondensation reaction. (B) Physically cross-linked hydrogels can be formed by ionic interactions, hydrophobic interaction, or hydrogen bonding.

Fig. 7. Equilibrium water uptakes of chemically cross-linked polyampholyte hydrogel as a function of pH, compositions in mole fractions MAA/DMAEMA/ HEMA/EGDMA. Formulation A 10/10/79.5/0.5 (open squares). Formulation B 30/30/39.5/0.5 (open circles). Formulation C 49.75/49.75/0/0.5 (fitted circles)...

Hydrogels are physically or chemically cross-linked polymer networks swollen with large amounts of water. Due to their crosslinked nature, these gels do not dissolve in aqueous media but contain an enormous amount of solvated water molecules within the entangled polymer chain matrix. Hydrogel properties are reviewed elsewhere in this book. This chapter is dedicated to a unique hydrogel family that responds to... 

A nanogel is a nanosized hydrogel made of physically or chemically cross-linked polymers that are water-soluble. A nanogel that is composed of responsive polymers may change volume depending on the external environment [23]. 

Trabbic-Carlson, K., Setton, L. A., and Chdkoti, A. Swelling and mechanical behaviors of chemically cross-linked hydrogels of elastin-like polypeptides. Biomacromolecules 4, 572-580 (2003). 

The term nanogel or microgel usually defines aqueous dispersions of hydrogel particles or colloidal networks formed by physically or chemically cross-linked polymer chains of nano-or microscale size. 

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