2.1.8.2. Absorbency Under Load (AUL) - BADA

1.7.1.3. Crosslinking by UV-Irradiation Method
In addition to ionizing radiation, ultraviolet (UV) radiation can also be used due to obtain free
radicals (see section 1.7.2.1). UV radiation, however, is more limited in that the depth of
penetration into a sample. Also it has significantly less energy compare to γ-irradiation. The UV-
induced crosslinking reaction of macromolecules arise only a thin layer on the surface. This
property, though, may be practical if it is desirable to crosslink only the surface layer of polymer
[19] . The UV- irradiation of proteins at 254 nm creates radicals in the form of unpaired electrons
located principally on the nuclei of the aromatic residues such as tyrosine and phenylalanine.
Bonding between these two radicals establishes crosslinking. As a result, proteins can be
crosslinked by exposure to UV light [26] .
1.7.2. Chemical Crosslinking of Proteins
Chemical crosslinking of water–soluble polymers are obtained by the addition of bifunctional or
multifunctional reactants results in chemical hydrogels. The active side chains of polymers,
particularly their nucleophilic nature could be employed in crosslinkage formation by using
bifunctional crosslinkers [29] . The crosslinking reagent includes reactive groups at both ends and
links two molecules by covalent bonding. If the macromolecules have functional parts only at their
end groups, then bifunctional crosslinking agents easily attach macro molecules to result in block
copolymers. If macromolecules have functional groups in the length of the backbone, hydrogel can
be creat by bi-functional reagents.
The proficiency of crosslinking reaction by bi- and multifunctional reactants depends on specific
groups that it should be functionalized. Hence, the selection of crosslinking reagents is so
important to successful crosslinking [16] .
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