Biomedical Engineering Reference
In-Depth Information
protein stamps indicated that styrene monomer was a good candidate as the functional
monomer with tetraethylene glycol dimethacrylate to form poly(styrene-
co
-tetraethylene
glycol dimethacrylate) lysozyme-imprinted polymers. The poly(styrene-
co
-polyethylene
glycol 400 dimethacrylate) RNase A-imprinted polymers also showed good potential to
achieve higher rebinding ability with RNase A. On the other hand, for myoglobin, the highest
affinity functional monomer is methyl methacrylate.
Although generally neglected, the removal of target molecules from molecular imprinted
polymers is a key factor in the rebinding capability of the receptor. The removal of template
proteins is complicated by the fact that the high molecular weight of proteins makes it
difficult for them to navigate the highly cross-linked matrix. The system of polyacrylamide
incorporated with methacrylic acid and 2-(dimethylamino)ethyl methacrylate was studied for
the possibility of imprinting of lysozyme [89]. The results showed that approximately 27%
(w/w) of the lysozyme template was not able to be extracted from the molecularly imprinted
acrylamide polymers. It was found that the amount of template could be extracted was lower
with molecular imprinted polymers at higher concentration of cross-linking agent and
functional monomer. It may be due to the fact that a more compact gel was formed at a higher
preparation concentration. Therefore, it is getting more difficult for the diffusion and removal
of templates. For the first time, Hawkins et al. [90] explored in detail a variety of template
removal methods, including the use of sodium dodecylsulphate:acetic acid and trypsin digest,
for removing template bovine haemoglobin from a polyacrylamide imprinted hydrogel. The
optimum ratio of sodium dodecylsulphate:acetic acid was found to be a 10% (w/v):10% (v/v)
for the most effective template removal. This resulted in >90% (imprinting efficiency) of re-
loaded template molecule being selectively bound within the MIP. At 15%:15% of sodium
dodecylsulphate:acetic acid, although there was even more initial template removal,
subsequent re-binding studies showed a decrease in imprinting efficiency (67.9%). Trypsin
solutions were also used as a method of template removal. Up to 87.4% of template was
reproducibly removed initially; however, the imprinting efficiency was only 20.4%. In
another example [91], horseradish peroxidase imprinted polymers was treated either with
alkaline, neutral, or acidic solutions in order to select the most effective washing procedure. It
is found that no template release was observed for alkaline washing, while washing with acid
in the presence of a neutral detergent gave a logarithmic decrease of the template contents in
the polymer. After five to six cycles, there was only minute amounts (<10%) of the template
protein remained in the molecular imprinted polymer. Further experiments indicated that the
quantity of template remaining trapped in the polymer, after the proteolytic enzyme trypsin
treatment for 18 hours, did not differ significantly from the results obtained simply by acidic
washing. It was pointed out that the stabilizing function of the support and spatial orientation
of the polymer chains and template functional groups are the major factors affecting the
imprint formation and template recognition.
Recently, the utilization of molecular modeling procedures to the field of molecular
imprinting to understand more deeply the fundamental molecular mechanisms has attracted
much attention [6, 92, 93]. Given the current state-of-the-art in rationally designing molecular
imprinted polymers, such simulations may enable selecting combinations of template,
functional monomers, cross-linkers, and solvents providing the most stable complex in the
pre-polymerization solution, which will then be selected for molecular dynamics simulations
investigating the interaction and conformation of the pre-polymerization complex. Enoki et
al. studied the effects of frustration on molecular imprinting involving copolymerization of
