23.3.4 Photosensitive or Temperature Sensitive
Photo-irradiation is a type of responsiveness that could be triggered externally.
Photo-irradiation could also be used to heat up target tissues with the assistance of
photosensitizer. Compared to physiological stimuli, physical stimuli are capable of
being applied in a local region and turned on/turned off by remote control on
demand. Azobenzene is one of the most frequently used photo-switches. By applying photo-irradiation in UV or visible wavelength, azobenzene could be switched
between cis- and trans-configurations. The transition in configuration may lead to
cargo release. Small-molecule photosensitizers, such as porphyrin, or some nanoparticles, such as gold nanorods, could be used to heat up target tissues.
23.3.5 Guest Responsiveness
For self-assembly systems based on host-guest interaction, in addition to the common stimuli types as mentioned above, guests could also be used to trigger responsiveness. Guest displacement has been used to monitor biological process with
fluorescent indicator. The same design principle has been applied to drug delivery,
in which encapsulated drug is displaced by guest introduced into the system. While
externally introduced guest displacement only works for in vitro study, DDSs have
been successfully designed to release cargo in vivo by responding to biomarker, such
as ATP.
23.4 Drug Delivery Applications
To achieve efficacy of therapeutic agents, it is often necessary to develop DDSs to
solubilize, stabilize, or targeted deliver pharmaceutical drugs. Small-molecule drugs,
including antitumor drugs, antimicrobial drugs, and regenerative drugs, are involved
in drug delivery. In recent years, nucleic acid, proteins, and other biomacromolecule
drugs have emerged as another type of highly important pharmaceutics for drug
delivery.
Depending on types of target tissues, drug delivery routes are composed of
subcutaneous administration, intravenous injection, transdermal delivery, and so
on. Multiple biological barriers need to be overcome. Take intravenous administration as an example, first, DDSs have to withstand blood circulation and avoid quick
clearance. Next, enhanced accumulation of pharmaceutical drugs in target tissues is
desired. Subsequently, DDSs are designed to be efficiently internalized by cells and
quickly release drug to achieve required efficacy. As for some types of drug delivery,
there are additional biological barriers to overcome. For example, to deliver pharmaceutical drugs into brain, blood-brain barrier (BBB) has to be penetrated.
DDSs are divided into several categories, including organic/polymeric nanoparticles, inorganic nanoparticles, and hydrogel biomaterials. Organic and polymeric
nanoparticles are either self-assembled or cross-linked, which could encapsulate
23 Stimuli-Responsive Self-Assembly Based on Macrocyclic Hosts and Biomedical. . .
613
Photo-irradiation is a type of responsiveness that could be triggered externally.
Photo-irradiation could also be used to heat up target tissues with the assistance of
photosensitizer. Compared to physiological stimuli, physical stimuli are capable of
being applied in a local region and turned on/turned off by remote control on
demand. Azobenzene is one of the most frequently used photo-switches. By applying photo-irradiation in UV or visible wavelength, azobenzene could be switched
between cis- and trans-configurations. The transition in configuration may lead to
cargo release. Small-molecule photosensitizers, such as porphyrin, or some nanoparticles, such as gold nanorods, could be used to heat up target tissues.
23.3.5 Guest Responsiveness
For self-assembly systems based on host-guest interaction, in addition to the common stimuli types as mentioned above, guests could also be used to trigger responsiveness. Guest displacement has been used to monitor biological process with
fluorescent indicator. The same design principle has been applied to drug delivery,
in which encapsulated drug is displaced by guest introduced into the system. While
externally introduced guest displacement only works for in vitro study, DDSs have
been successfully designed to release cargo in vivo by responding to biomarker, such
as ATP.
23.4 Drug Delivery Applications
To achieve efficacy of therapeutic agents, it is often necessary to develop DDSs to
solubilize, stabilize, or targeted deliver pharmaceutical drugs. Small-molecule drugs,
including antitumor drugs, antimicrobial drugs, and regenerative drugs, are involved
in drug delivery. In recent years, nucleic acid, proteins, and other biomacromolecule
drugs have emerged as another type of highly important pharmaceutics for drug
delivery.
Depending on types of target tissues, drug delivery routes are composed of
subcutaneous administration, intravenous injection, transdermal delivery, and so
on. Multiple biological barriers need to be overcome. Take intravenous administration as an example, first, DDSs have to withstand blood circulation and avoid quick
clearance. Next, enhanced accumulation of pharmaceutical drugs in target tissues is
desired. Subsequently, DDSs are designed to be efficiently internalized by cells and
quickly release drug to achieve required efficacy. As for some types of drug delivery,
there are additional biological barriers to overcome. For example, to deliver pharmaceutical drugs into brain, blood-brain barrier (BBB) has to be penetrated.
DDSs are divided into several categories, including organic/polymeric nanoparticles, inorganic nanoparticles, and hydrogel biomaterials. Organic and polymeric
nanoparticles are either self-assembled or cross-linked, which could encapsulate
23 Stimuli-Responsive Self-Assembly Based on Macrocyclic Hosts and Biomedical. . .
613