heat, or light. In the past decade, the SMPs and SHPs fields have undergone
explosive development. Many innovative SMPs and SHPs, such as multishape,
multiresponsive, and multifunctional SMPs and SHPs, have emerged [5–7]. In the
case of many types of SMPs and SHPs, cyclodextrins (CDs)-based supramolecular
forces has been increasingly utilized as driving forces to achieve shape memory or
self-healing functions on account of its distinct features as compared to other
supramolecular interactions. The most important advantages of using CDs-based
interactions as driving forces are that (1) CDs are cyclic oligosaccharides made from
starch, which show extremely low toxicity and are widely available. Therefore,
CDs-based materials show great potential in biomedical applications; (2) CDs are
capable of including a variety of compounds ranging from small molecules and ions
to polymers in their cavities with high selectivity to form inclusion complexes (ICs).
Thus, a number of SMPs and SHPs could be developed; (3) the inclusion complexation between CDs and many guests is sensitive to diversified stimuli. Therefore,
CDs-based interactions are good candidates for developing novel stimulus-sensitive
or stimulus-multisensitive SMPs and SHPs.
This chapter outlines recent progress in SMPs and SHPs based on CDs-guest
interactions, provides insights into the materials design, and points out future
opportunities.
22.2 SMPs Based on CDs-Guest Interactions
22.2.1 General Aspect
In principle, SMPs should possess at least two different kinds of segments: netpoints
for stabilizing the whole material and determining the permanent shape and reversible segments for switching on/off the molecular mobility so as to freeze/release the
temporary shape. The netpoints can be chemical cross-links, physical cross-links
(e.g., molecular entanglement), or crystallites with a high melting point. The
switching segments are generally segments that show reversible melting transitions
or glass transitions at low temperature [8–10].
From an energy perspective, the shape memory effect of polymeric materials is an
entropic phenomenon. In a typical one-way dual-shape memory process, the initial
SMPs sample is rigid and hard to deform. The molecular chains in this initial shape
are at a higher entropy (lower energy) state. Upon applying stimuli, the sample
becomes soft because the mobility of some molecular chains is activated; as a result,
the sample is easy to deform to a temporary shape when an external force is applied.
This deformation leads to an entropic change (energy state raises). When depressing
the mobility of chains by stimuli, the deformation imposed to the sample can be
maintained even after removal of the external force. At the same time, the entropic
energy in the system is stored. Once the mobility of chains is again activated, the
entropic energy is released, driving the system back to its higher entropy (lower
energy) state. Thus, the sample recovers to its original shape [11].
588
S. Zhang et al.
explosive development. Many innovative SMPs and SHPs, such as multishape,
multiresponsive, and multifunctional SMPs and SHPs, have emerged [5–7]. In the
case of many types of SMPs and SHPs, cyclodextrins (CDs)-based supramolecular
forces has been increasingly utilized as driving forces to achieve shape memory or
self-healing functions on account of its distinct features as compared to other
supramolecular interactions. The most important advantages of using CDs-based
interactions as driving forces are that (1) CDs are cyclic oligosaccharides made from
starch, which show extremely low toxicity and are widely available. Therefore,
CDs-based materials show great potential in biomedical applications; (2) CDs are
capable of including a variety of compounds ranging from small molecules and ions
to polymers in their cavities with high selectivity to form inclusion complexes (ICs).
Thus, a number of SMPs and SHPs could be developed; (3) the inclusion complexation between CDs and many guests is sensitive to diversified stimuli. Therefore,
CDs-based interactions are good candidates for developing novel stimulus-sensitive
or stimulus-multisensitive SMPs and SHPs.
This chapter outlines recent progress in SMPs and SHPs based on CDs-guest
interactions, provides insights into the materials design, and points out future
opportunities.
22.2 SMPs Based on CDs-Guest Interactions
22.2.1 General Aspect
In principle, SMPs should possess at least two different kinds of segments: netpoints
for stabilizing the whole material and determining the permanent shape and reversible segments for switching on/off the molecular mobility so as to freeze/release the
temporary shape. The netpoints can be chemical cross-links, physical cross-links
(e.g., molecular entanglement), or crystallites with a high melting point. The
switching segments are generally segments that show reversible melting transitions
or glass transitions at low temperature [8–10].
From an energy perspective, the shape memory effect of polymeric materials is an
entropic phenomenon. In a typical one-way dual-shape memory process, the initial
SMPs sample is rigid and hard to deform. The molecular chains in this initial shape
are at a higher entropy (lower energy) state. Upon applying stimuli, the sample
becomes soft because the mobility of some molecular chains is activated; as a result,
the sample is easy to deform to a temporary shape when an external force is applied.
This deformation leads to an entropic change (energy state raises). When depressing
the mobility of chains by stimuli, the deformation imposed to the sample can be
maintained even after removal of the external force. At the same time, the entropic
energy in the system is stored. Once the mobility of chains is again activated, the
entropic energy is released, driving the system back to its higher entropy (lower
energy) state. Thus, the sample recovers to its original shape [11].
588
S. Zhang et al.