43
the drug could then be released after judging the intensity of the signal. The polymer
gel can usually be used as carries for drug delivery, because the gel could respond
to a specific signal, such as chemicals, electric field, pH, temperature, among others.
Santini et al. (1999) synthesized from poly(N,N-diethyl acrylamide) norfloxacinloaded thermo-sensitive SMGs for drug release above its LCST, due to the contraction of the network. This type of material could thus be designed to respond to a
specific stimulus to treat some disease. With this in mind, Freiberg and Zhu (2004)
prepared a dual sensitive hydrogel (pH and temperature) for controlled release of
papain (enzyme). This hydrogel would restrict the release of the enzyme by diffusion at pH = 1.4 and temperatures lower than 37 °C, while the enzyme would be
released at pH = 7.4 and 37 °C, due to the swelling of the gel.
As for the intelligent control system, the controlled drug release could be given
according to the intensity of the signal or the external stimulus. An electric field
sensitive polyelectrolyte could for example serve as a vehicle for an electric field
sensitive drug delivery system. In this same line, Cao and Jana (2007). synthesized
from 2-acrylamido-2-methylpropanesulfonic acid and N-butyl methacrylate chlortetracycline-loaded electric field-responsive hydrogels for the controlled release of
this antibiotic. In this sense, SMGs have great potential in the field of emerging
technologies, such as artificial muscles, chemical valves and smart materials.
3.4.2 Shape Memory PU (SMPUs)
In particular, SMPUs have attracted the attention of many researchers, due to their
biodegradability, easy processing, good mechanical properties, light weight and low
cost, which makes them potential candidates for the manufacture of synthetic medical materials, as well as aerospace textiles (Cao and Jana 2007; Lendlein 2002; Ni
et al. 2007a).
3.4.2.1 Thermo-Responsive SMPUs
PUs is a thermoplastic polymer made up of two types of polymeric materials with
different T g values, which can be used as SMPs (Chen et al. 2014; Gu et al. 2015;
Wang et al. 2013a; Yang et al. 2014). Microseparation of phases in the internal structure of SMPUs, due to thermodynamic incompatibility, can be thermally tuned. In
this context, the PU segments with the lowest T g value are referred to as the soft
segment, and play an important role in the strain of the material, while the hard segments are those with the highest T g value, and are associated with the restrictions on
the movements of the amorphous polymer chains. Therefore, upon reaching the T g
of the soft segments, the immobile hard segments act as crystallization sites, thus
generating the shape memory phenomenon, as long as the temperature does not
exceed the T g of the hard segments. In this sense, higher Mws and hard segment
contents, the shape memory phenomenon is positively affected (Ahmad et al. 2011;
Chen et al. 2009a, 2010a, b; Hu et al. 2005a; Merline et al. 2008; Ping et al. 2005;
3 Smart and Shape Memory Polymers
the drug could then be released after judging the intensity of the signal. The polymer
gel can usually be used as carries for drug delivery, because the gel could respond
to a specific signal, such as chemicals, electric field, pH, temperature, among others.
Santini et al. (1999) synthesized from poly(N,N-diethyl acrylamide) norfloxacinloaded thermo-sensitive SMGs for drug release above its LCST, due to the contraction of the network. This type of material could thus be designed to respond to a
specific stimulus to treat some disease. With this in mind, Freiberg and Zhu (2004)
prepared a dual sensitive hydrogel (pH and temperature) for controlled release of
papain (enzyme). This hydrogel would restrict the release of the enzyme by diffusion at pH = 1.4 and temperatures lower than 37 °C, while the enzyme would be
released at pH = 7.4 and 37 °C, due to the swelling of the gel.
As for the intelligent control system, the controlled drug release could be given
according to the intensity of the signal or the external stimulus. An electric field
sensitive polyelectrolyte could for example serve as a vehicle for an electric field
sensitive drug delivery system. In this same line, Cao and Jana (2007). synthesized
from 2-acrylamido-2-methylpropanesulfonic acid and N-butyl methacrylate chlortetracycline-loaded electric field-responsive hydrogels for the controlled release of
this antibiotic. In this sense, SMGs have great potential in the field of emerging
technologies, such as artificial muscles, chemical valves and smart materials.
3.4.2 Shape Memory PU (SMPUs)
In particular, SMPUs have attracted the attention of many researchers, due to their
biodegradability, easy processing, good mechanical properties, light weight and low
cost, which makes them potential candidates for the manufacture of synthetic medical materials, as well as aerospace textiles (Cao and Jana 2007; Lendlein 2002; Ni
et al. 2007a).
3.4.2.1 Thermo-Responsive SMPUs
PUs is a thermoplastic polymer made up of two types of polymeric materials with
different T g values, which can be used as SMPs (Chen et al. 2014; Gu et al. 2015;
Wang et al. 2013a; Yang et al. 2014). Microseparation of phases in the internal structure of SMPUs, due to thermodynamic incompatibility, can be thermally tuned. In
this context, the PU segments with the lowest T g value are referred to as the soft
segment, and play an important role in the strain of the material, while the hard segments are those with the highest T g value, and are associated with the restrictions on
the movements of the amorphous polymer chains. Therefore, upon reaching the T g
of the soft segments, the immobile hard segments act as crystallization sites, thus
generating the shape memory phenomenon, as long as the temperature does not
exceed the T g of the hard segments. In this sense, higher Mws and hard segment
contents, the shape memory phenomenon is positively affected (Ahmad et al. 2011;
Chen et al. 2009a, 2010a, b; Hu et al. 2005a; Merline et al. 2008; Ping et al. 2005;
3 Smart and Shape Memory Polymers