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5.3 MIP Formats and Polymerization Approaches
MIPs are synthetic receptors capable of specifically binding to a predetermined target with higher affinity than other structural analogues. So far, different polymerization strategies have been used to synthesize these materials, giving rise to imprinted
polymers presenting diverse formats and sizes. The natural evolution experienced
by the MIT has allowed the preparation of new smart materials more versatile in
their applications. Free and controlled radical polymerization have been primarily
responsible for this result, the latter being, as discussed above, currently contributing mostly to the development of MIPs with improved binding characteristics, comparable to monoclonal antibodies. Both FRP and CRP strategies have been reported
in the literature as preferred approaches to synthesize MIPs through bulk, precipitation and emulsion polymerization, which leads to different MIP formats such as
monoliths, micro- and NPs, films and membranes. The polymerization approach to
be used depends not only on the characteristics required for the final material, but
also on the nature of the template to be imprinted.
5.3.1 Bulk MIPs
In bulk polymerization, a known target compound, referred as template, is imprinted
as a whole in a polymer matrix. To this end, the monomers, the crosslinker(s) and a
radical initiator are mixed in a small volume of porogen and the polymerization is
started by heating or exposure to UV radiation. The resulting polymer monolith
usually has to be ground and sieved to obtain fine MIP particles, which have irregular shapes and sizes. Consequently, MIPs developed in this way are usually associated with a slow mass transfer kinetics, being far from ideal, since they lead to a
slow analyte diffusion towards binding sites (Vasapollo et al. 2011). In addition,
polymer grinding and sieving processes lead to the waste of a substantial fraction of
particles, which can be estimated between 50% and 75% of the initial powder
(Baggiani 2005). The scarce control of the MIP physical form and the difficulties in
scaling up the MIP production are important drawbacks, so alternative methods to
prepare novel physical formats have been developed (Poma et al. 2010; Wackerlig
and Lieberzeit 2015; Gomez-Caballero et al. 2016).
5.3.2 MIP Beads (Micro- and Nanobeads)
Spherical MIPs can be prepared using different polymerization methods, such as
emulsion, suspension and precipitation polymerization, solid-phase synthesis or
even by means of surface polymerization using preformed beads, namely the coreshell approach (Fig. 5.7).
5 Plastic Receptors Developed by Imprinting Technology as Smart Polymers Imitating…
5.3 MIP Formats and Polymerization Approaches
MIPs are synthetic receptors capable of specifically binding to a predetermined target with higher affinity than other structural analogues. So far, different polymerization strategies have been used to synthesize these materials, giving rise to imprinted
polymers presenting diverse formats and sizes. The natural evolution experienced
by the MIT has allowed the preparation of new smart materials more versatile in
their applications. Free and controlled radical polymerization have been primarily
responsible for this result, the latter being, as discussed above, currently contributing mostly to the development of MIPs with improved binding characteristics, comparable to monoclonal antibodies. Both FRP and CRP strategies have been reported
in the literature as preferred approaches to synthesize MIPs through bulk, precipitation and emulsion polymerization, which leads to different MIP formats such as
monoliths, micro- and NPs, films and membranes. The polymerization approach to
be used depends not only on the characteristics required for the final material, but
also on the nature of the template to be imprinted.
5.3.1 Bulk MIPs
In bulk polymerization, a known target compound, referred as template, is imprinted
as a whole in a polymer matrix. To this end, the monomers, the crosslinker(s) and a
radical initiator are mixed in a small volume of porogen and the polymerization is
started by heating or exposure to UV radiation. The resulting polymer monolith
usually has to be ground and sieved to obtain fine MIP particles, which have irregular shapes and sizes. Consequently, MIPs developed in this way are usually associated with a slow mass transfer kinetics, being far from ideal, since they lead to a
slow analyte diffusion towards binding sites (Vasapollo et al. 2011). In addition,
polymer grinding and sieving processes lead to the waste of a substantial fraction of
particles, which can be estimated between 50% and 75% of the initial powder
(Baggiani 2005). The scarce control of the MIP physical form and the difficulties in
scaling up the MIP production are important drawbacks, so alternative methods to
prepare novel physical formats have been developed (Poma et al. 2010; Wackerlig
and Lieberzeit 2015; Gomez-Caballero et al. 2016).
5.3.2 MIP Beads (Micro- and Nanobeads)
Spherical MIPs can be prepared using different polymerization methods, such as
emulsion, suspension and precipitation polymerization, solid-phase synthesis or
even by means of surface polymerization using preformed beads, namely the coreshell approach (Fig. 5.7).
5 Plastic Receptors Developed by Imprinting Technology as Smart Polymers Imitating…