289
Another technique used to determine the cyclodextrin content in the polymers is
CHN elemental analysis. This method is especially useful and simple for polymers
cross-linked with diisocyanates, since the nitrogen content is directly proportional
to the amount of cross-linker in the polymer (Lee et al. 2002). Nevertheless, it must
be used with great care in the case of cyclodextrin-epichlorohydrin polymers due to
the similar elemental composition of both constituents (Romo et al. 2006).
Other Novel Cyclodextrin Polymers
The reticulated cyclodextrins, also known as nanosponges, have evolved into more
complex structures in the last 10–20 years. Four generations of nanosponges can be
defined, according to the classification by Trotta’s group (Caldera et al. 2017). First
of all, a reticulation reaction using a simple molecule such as epichlorohydrin gave
us the first generation of “nanosponges.” Besides those ether linkages, ester, carbonate, and urethane are the main connectors investigated in the literature. The decoration of those primary nanosponges using a cross-linker plus a special functional
group produced the second generation. If this extra space arm or the added functions
react to external stimuli (such as temperature or pH), allowing the nanosponges to
change their shape, swelling behavior, or sorption/release capabilities, then the new
“smart material” synthesized is said to belong to the third generation. Finally, a
fourth generation of nanosponges is feasible by creating molecular imprinting polymers using a template, in order to improve the selectivity of the matrix toward such
molecules (Caldera et al. 2017).
From a historical point of view, the last three classes can be considered as those
of the present days, although some of these new attractive features of novel cyclodextrin nanosponges have been known for a couple of decades. Thus, molecular
imprinted polymers using cyclodextrin moieties were already produced in the late
1990s (Piletsky et al. 1998). Stimuli-responsive polymers based on cyclodextrins
were prepared in 1995 using the ubiquitous N-isopropylacrylamide monomer
(Nozaki et al. 1995). Interpenetrated networks containing cyclodextrins also
appeared at that time (Sreenivasan 1997). Fenyvesi et al. (1996) encapsulated several cationic disinfectant agents, in chemically modified (carboxymethylated) nanosponges, based on cyclodextrin linked to polyvinyl alcohol, to be used in the
prolonged treatment of wounds.
Nanogels combine the advantages of hydrogels and nanoparticles into a single
carrier that can be tailored for specific therapeutic molecules, such as low molecular
weight drugs, peptides, or proteins, and target them to specific tissues or cells
(Moya-Ortega et al. 2012). Liu et al. (2004) prepared cyclodextrin microgels,
including one interpenetrated network, by inverse-emulsion polymerization. About
10 years ago, nanoparticles with differing charge densities were synthesized by a
one-step condensation polymerization of β-cyclodextrin, choline chloride, and epichlorohydrin by Gil et al. (2009). The top-down approach can break bigger networks into the nanoscale size by using ultrasounds (Swaminathan et al. 2010). The
water-in-oil emulsion method has been thoroughly employed in the last decade to
6 Cyclodextrin-Based Polymers for Food and Pharmaceutical Applications…
Another technique used to determine the cyclodextrin content in the polymers is
CHN elemental analysis. This method is especially useful and simple for polymers
cross-linked with diisocyanates, since the nitrogen content is directly proportional
to the amount of cross-linker in the polymer (Lee et al. 2002). Nevertheless, it must
be used with great care in the case of cyclodextrin-epichlorohydrin polymers due to
the similar elemental composition of both constituents (Romo et al. 2006).
Other Novel Cyclodextrin Polymers
The reticulated cyclodextrins, also known as nanosponges, have evolved into more
complex structures in the last 10–20 years. Four generations of nanosponges can be
defined, according to the classification by Trotta’s group (Caldera et al. 2017). First
of all, a reticulation reaction using a simple molecule such as epichlorohydrin gave
us the first generation of “nanosponges.” Besides those ether linkages, ester, carbonate, and urethane are the main connectors investigated in the literature. The decoration of those primary nanosponges using a cross-linker plus a special functional
group produced the second generation. If this extra space arm or the added functions
react to external stimuli (such as temperature or pH), allowing the nanosponges to
change their shape, swelling behavior, or sorption/release capabilities, then the new
“smart material” synthesized is said to belong to the third generation. Finally, a
fourth generation of nanosponges is feasible by creating molecular imprinting polymers using a template, in order to improve the selectivity of the matrix toward such
molecules (Caldera et al. 2017).
From a historical point of view, the last three classes can be considered as those
of the present days, although some of these new attractive features of novel cyclodextrin nanosponges have been known for a couple of decades. Thus, molecular
imprinted polymers using cyclodextrin moieties were already produced in the late
1990s (Piletsky et al. 1998). Stimuli-responsive polymers based on cyclodextrins
were prepared in 1995 using the ubiquitous N-isopropylacrylamide monomer
(Nozaki et al. 1995). Interpenetrated networks containing cyclodextrins also
appeared at that time (Sreenivasan 1997). Fenyvesi et al. (1996) encapsulated several cationic disinfectant agents, in chemically modified (carboxymethylated) nanosponges, based on cyclodextrin linked to polyvinyl alcohol, to be used in the
prolonged treatment of wounds.
Nanogels combine the advantages of hydrogels and nanoparticles into a single
carrier that can be tailored for specific therapeutic molecules, such as low molecular
weight drugs, peptides, or proteins, and target them to specific tissues or cells
(Moya-Ortega et al. 2012). Liu et al. (2004) prepared cyclodextrin microgels,
including one interpenetrated network, by inverse-emulsion polymerization. About
10 years ago, nanoparticles with differing charge densities were synthesized by a
one-step condensation polymerization of β-cyclodextrin, choline chloride, and epichlorohydrin by Gil et al. (2009). The top-down approach can break bigger networks into the nanoscale size by using ultrasounds (Swaminathan et al. 2010). The
water-in-oil emulsion method has been thoroughly employed in the last decade to
6 Cyclodextrin-Based Polymers for Food and Pharmaceutical Applications…