Bioresponsive Polymers for Nanomedicine—Expectations and Reality!

Abstract

Bioresponsive polymers in nanomedicine have been widely perceived to selectively activate the therapeutic function of nanomedicine at diseased or pathological sites, while sparing their healthy counterparts. This idea can be described as an advanced version of Paul Ehrlich’s magic bullet concept. From that perspective, the inherent anomalies or malfunction of the pathological sites are generally targeted to allow the selective activation or sensory function of nanomedicine. Nonetheless, while the primary goals and expectations in developing bioresponsive polymers are to elicit exclusive selectivity of therapeutic action at diseased sites, this remains difficult to achieve in practice. Numerous research efforts have been undertaken, and are ongoing, to tackle this fine-tuning. This review provides a brief introduction to key stimuli with biological relevance commonly featured in the design of bioresponsive polymers, which serves as a platform for critical discussion, and identifies the gap between expectations and current reality.

Nanophotosensitizers Composed of Phenyl Boronic Acid Pinacol Ester-Conjugated Chitosan Oligosaccharide via Thioketal Linker for Reactive Oxygen Species-Sensitive Delivery of Chlorin e6 against Oral Cancer Cells

“…As illustrated in Figure 12 , the degradation of the thioketal group and PBAP moiety is known to be affected by the presence of ROS [ 61 , 62 , 63 ]. Lee et al also reported that phenyl boronic acid can be degraded in the presence of ROS, such as H 2 O 2 , and, after that, acid release by H 2 O 2 catalyzes the hydrolysis of the polymer backbone [ 61 ].…”

“…Gao and Xiong also showed that the thioketal group can be degraded by reactive oxygens and then degraded into thiol groups [ 62 ]. PBAP moieties and thioketal linkers in the polymer backbone resulted in hydrophobic–hydrophilic changes and degradation by ROS-sensitive behavior [ 63 ]. These changes accelerated the release rate of bioactive agents and anticancer drugs and then emphasized their anticancer activities.…”

Non‐activated Esters as Reactive Handles in Direct Post‐Polymerization Modification

“…[191,192] The more sterically hindered PMA requires mild heating (60 °C), [193,194] while PMMA requires extensive heating (120 °C) for several days. [195] The obtained hydrazide products have been used in a variety of applications, including polymer-drug conjugates, [191,192,[196][197][198] injectable stimuli-responsive hydrogels, [199,200] gene delivery, [201] self-healing materials, [202,203] and sensors. [204]…”