and PEG [18]. The partial α-CD-PCL not only showed good shape memory
properties with the recovery ratio exceeding 90% but also good degradability in
the presence of lipase. It was demonstrated that the formation of inclusion segments
significantly accelerated the degradation of materials. In the case of γ-CD-PEG
network, the PEG chains were cross-linked by interlocking γ-CDs rather than
covalent bond or traditional physical attractive interaction. In this material, the
PEG/γ-CD inclusion cross-links, and the PEG crystallites accounted for the fixing
and reversible cross-links, respectively. By adjusting the mass content of inclusion
segments, the shape fixed at 100% and the shape recovery at >95% were observed.
In addition, Zhang and co-workers designed a thermally responsive SMP utilizing
H-bonding between α-CDs [19]. This responsive SMP was prepared by block
copolymerization of acrylamide-(AM) and dimethyhexadecyl [2-(dimethylamino)
ethyl-methacrylate] ammonium bromide (C 16 DMAEMA) in the presence of α-CD.
The crystalline domains, induced by the H-bonding between α-CDs threaded on the
hydrophobic side of the polymer chains, could reversibly melt and crystallize in
response to temperature. As a result, the material showed excellent shape memory
properties.
Manufacturing SMPs using CDs-polymer interactions is a very simple way to
endow shape memory function to classical polymers. However, to date, this kind
of shape memory material has only been triggered by temperature.
22.2.3 SMPs Based on CDs-Guest Group Interactions
It has been demonstrated that the ICs between CDs and various small molecular
guests can be modulated by diversified stimuli. In the past decade, introducing CDs
and guest moieties into polymer chains has become a very effective method for
building intelligent responsive materials [20, 21]. Our group first used the CDs-guest
interactions to design athermal-responsive shape memory materials [22]. As shown
in Fig. 2, a pH-sensitive shape memory material was prepared by cross-linking the
β-CD-modified alginate (Alg) and diethylenetriamine (DETA)-modified Alg. In a
basic medium (pH 11.5), the DETA groups showed a hydrophobic feature and
formed IC with β-CD. In a neutral medium, the DETA became hydrophilic due to
the ionization of the amine and resulted in dissociation of the β-CD-DETA IC. This
pH-dependent reversible formation/dissociation of β-CD-DETA IC switched off/on
the molecular mobility so as to freeze/release the temporary shape, and the crosslinked Alg chains served as fixing netpoints for stabilizing the permanent shape. It
was shown that this material can be processed into a temporary shape as needed at
pH 11.5 and recover to its initial shape at pH 7.0. Both the recovery and fixity ratios
were around 95%. Furthermore, this material showed good degradability and biocompatibility; thus, it had a high potential for medical applications.
The interactions between CD and guests may also be sensitive to other stimuli,
such as light and redox. Therefore, using host-guest interactions as molecular
switches, we can design a variety of new SMPs with novel triggers other
than thermal stimulus. For example, in our later study, a redox-induced SMP was
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S. Zhang et al.
properties with the recovery ratio exceeding 90% but also good degradability in
the presence of lipase. It was demonstrated that the formation of inclusion segments
significantly accelerated the degradation of materials. In the case of γ-CD-PEG
network, the PEG chains were cross-linked by interlocking γ-CDs rather than
covalent bond or traditional physical attractive interaction. In this material, the
PEG/γ-CD inclusion cross-links, and the PEG crystallites accounted for the fixing
and reversible cross-links, respectively. By adjusting the mass content of inclusion
segments, the shape fixed at 100% and the shape recovery at >95% were observed.
In addition, Zhang and co-workers designed a thermally responsive SMP utilizing
H-bonding between α-CDs [19]. This responsive SMP was prepared by block
copolymerization of acrylamide-(AM) and dimethyhexadecyl [2-(dimethylamino)
ethyl-methacrylate] ammonium bromide (C 16 DMAEMA) in the presence of α-CD.
The crystalline domains, induced by the H-bonding between α-CDs threaded on the
hydrophobic side of the polymer chains, could reversibly melt and crystallize in
response to temperature. As a result, the material showed excellent shape memory
properties.
Manufacturing SMPs using CDs-polymer interactions is a very simple way to
endow shape memory function to classical polymers. However, to date, this kind
of shape memory material has only been triggered by temperature.
22.2.3 SMPs Based on CDs-Guest Group Interactions
It has been demonstrated that the ICs between CDs and various small molecular
guests can be modulated by diversified stimuli. In the past decade, introducing CDs
and guest moieties into polymer chains has become a very effective method for
building intelligent responsive materials [20, 21]. Our group first used the CDs-guest
interactions to design athermal-responsive shape memory materials [22]. As shown
in Fig. 2, a pH-sensitive shape memory material was prepared by cross-linking the
β-CD-modified alginate (Alg) and diethylenetriamine (DETA)-modified Alg. In a
basic medium (pH 11.5), the DETA groups showed a hydrophobic feature and
formed IC with β-CD. In a neutral medium, the DETA became hydrophilic due to
the ionization of the amine and resulted in dissociation of the β-CD-DETA IC. This
pH-dependent reversible formation/dissociation of β-CD-DETA IC switched off/on
the molecular mobility so as to freeze/release the temporary shape, and the crosslinked Alg chains served as fixing netpoints for stabilizing the permanent shape. It
was shown that this material can be processed into a temporary shape as needed at
pH 11.5 and recover to its initial shape at pH 7.0. Both the recovery and fixity ratios
were around 95%. Furthermore, this material showed good degradability and biocompatibility; thus, it had a high potential for medical applications.
The interactions between CD and guests may also be sensitive to other stimuli,
such as light and redox. Therefore, using host-guest interactions as molecular
switches, we can design a variety of new SMPs with novel triggers other
than thermal stimulus. For example, in our later study, a redox-induced SMP was
590
S. Zhang et al.