(Bio)degradation in response to external stimuli (stimuli-responsive degradation, SRD) is a desired property in constructing novel nanostructured materials. For polymer-based multifunctional drug delivery applications, the degradation enables fast and controlled release of encapsulated therapeutic drugs from delivery vehicles in targeted cells. It also ensures the clearance of the empty device after drugs are delivered to the body. This review summarizes recent development of various strategies to the design and synthesis of self-assembled micellar aggregates based on novel amphiphilic block copolymers having different numbers of stimuli-responsive cleavable elements at various locations. These cleavable linkages including disulfide, acid-labile, and photo-cleavable linkages are incorporated into micelles, and then are cleaved in response to cellular triggers such as reductive reaction, light, and low acid. The well-designed SRD micelles have been explored as controlled/enhanced delivery vehicles of drugs and genes. For future design and development of effective stimuli-responsive degradable micelles toward tumor-targeting delivery applications in vivo, a high degree of control over degradation for tunable release of encapsulated anticancer drugs as well as bioconjugation for active tumor-targeting is required.

Polylactide (PLA) and its copolymers are one type of hydrophobic aliphatic polyester based on hydroxyalkanoic acids. They possess exceptional qualities: biocompatibility; FDA approval for clinical use; biodegradability by enzyme and hydrolysis under physiological conditions; low immunogenicity; and good mechanical properties. These critical properties have facilitated their value as sutures, implants for bone fixation, drug delivery vehicles, and tissue engineering scaffolds in pharmaceutical and biomedical applications. However, the hydrophobicity of PLA and its copolymers remains concerns for further biological and biomedical applications. One promising approach is to design and synthesize well-controlled PLA-based amphiphilic block copolymers (ABPs); typical hydrophilic copolymers include poly(meth)acrylates, poly(ethylene glycol), polypeptides, polysaccharides, and polyurethanes. This review summarizes recent advances in the synthesis and self-assembly of PLA-containing ABPs and their bio-related applications including drug delivery and imaging platforms of self-assembled nanoparticles, and tissue engineering of crosslinked hydrogels.

Colloidal CdX (X = Se, S, and Te) and their core/shell quantum dots (QDs) have narrow and size-dependent emission spectra, multicolor excitation with large extinction coefficients, and excellent photostability against photobleaching. Because of these unique photoluminescence properties of QDs over conventional fluorescent organic dyes and fluorescent proteins, QDs are useful for various applications such as biological labeling, biosensing and detection, light emitting diodes (LED), and solar cells (photovoltaics). Toward successful biological applications, control of the surface chemistry of QDs is required, enabling the preparation of QDs with water-solubility (or colloidal stability), biocompatibility, nonspecific adsorption to cells, efficient fluorescence, and active targeting. This highlight describes recent strategies developed for the modification of the surface of CdX-based QDs for biological applications.

Degradation of amphiphilic block copolymer (ABP) micelles in response to external stimuli (stimuli-responsive degradation) is a desired property in the design of controlled delivery vehicles. Here, a versatile methodology that combines facile carbodiimide coupling polycondensation with controlled radical polymerization to synthesize thiol-responsive degradable ABP micelles is described. These smart micelles consist of a hydrophobic degradable polyester block with disulfide linkages labeled repeatedly along the main chain; more importantly, in response to thiols they exhibit rapid and controlled degradation, thereby leading to enhanced release of encapsulated model drugs. Moreover, the proposed method allows for a facile bioconjugation of hydrophilic coronas using cell-targeting biomolecules during polymerization.