Biomedical Engineering Reference
In-Depth Information
functional ligands (that interact with the imprint molecule) and backbone monomers. It was
shown that post-crosslinking in the presence of the target molecule minimizes frustration and
thus allowed the imprinted copolymer gel to approach its free energy minimum and that the
affinity toward the target molecule increased exponentially with increasing concentrations of
post-crosslinking agent. Using mean-field theory, Srebnik et al. [94] investigated the induced
porosity of polymer networks obtained through various imprinting approaches, concentrating
on the induced porous structure of the final imprinted gel under various preparation
conditions. It was found that cross-linking induced microphase separation, and when
accompanied by polycondensation, the pore size distribution was affected in an unexpected
manner. The model also predicted the extent of microphase separation of the chemically
different monomers as a function of the chemical constitution, the degree of cross-linking,
and the size of the leaving group. A few years later, Srebnik further introduced a measure of
imprinting efficiency (a measure of the degree of complexation) and researched the effect of
size and functionality of the imprinting agent on the imprinting efficiency using a lattice
model, concentrating on the effect of solvent-template-monomer interactions on the
equilibrium population of monomer-template complexes. The extent of template
complexation at equilibrium is governed by the change in Gibbs free energy of formation for
each mode of template-monomer interactions, generally resulting in a population of sites with
various affinities for the imprinted molecule. Neglecting template-template association, it was
found that stronger template-monomer interactions resulted in higher functional complexes
and thus higher imprinting efficiencies. However, the efficiency strongly depended on the
preparation conditions.
In addition, using molecular dynamics simulations through a topological analysis of the
imprinted network configuration before and after removal of the templates, the imprinting
quality of cross-linked polymer networks was investigated [95]. Low qualities of the
imprinted polymers were attributed to the aggregation of the templates in the pre-
polymerization solution, aggregation of the imprinting-induced sites with small pores inherent
to the polymer, and deformation of the binding sites due to relaxation of the gel after removal
of the templates. The formation of distinct individual cavities that retained the size and shape
of the template was enhanced by high degrees of cross-linking and low template
concentrations. Henthorm et al. [96] developed an all-atom kinetic gelation simulation
technique to study the recognitive polymeric network formation which incorporates both
intramolecular as well as intermolecular interactions and the subsequent effects they have on
the end network structure.
6. Conclusion
Molecular imprinting is a valuable technique for the preparation of synthetic materials for
the selective recognition of biologically relevant molecules such as amino acids, peptides, and
proteins. The key factors for the advancement in molecular imprinted polymer research for
biomacromolecular targets lie in the preparation of molecular imprinted polymers providing
high affinity to the macromolecular template molecule without disrupting the bioreactivit or
biofunctionality of the target analyte. However, despite the recent advancements made in the
synthesis and characterization of molecular imprinted polymers, there is still an enormous
amount of work that needs to be conducted in the field. The exact recognition mechanism,
