The incorporation of functional groups includes methods such as oxidation (e.g., peroxide oxidation or ozone oxidation), amination, nitration, halogenation (e.g., fluorination), and the like. This subcategory has the disadvantage that the effect gained by the surface treatment (i.e., wettability) is unstable and degenerates over time, leading to a short shelf life of the treated surface and storage instability. Lack of stability of the treated surface is a severe problem, in particular for biopolymers used for (in vivo) medical applications as it may result in undesired features such as alteration of the substrate properties and/or an altered degradation profile and thus possible unpredictable results and/or undesired side effects. On the other hand, the grafting of functional monomers or polymers onto the surfaces is a more stable/permanent alternative (see Section 8.3.3).
Common techniques used to incorporate functional groups to the surface of a biopolymer include flame treatment, radiation, corona treatment, and plasma, which can increase the surface energy of a biopolymer. Flame treatment is a rather obsolete surface treatment technique.