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Stimuli‐sensitive synthetic polypeptides are unique biodegradable and biocompatible synthetic polymers with structures mimicking natural proteins. These polymers exhibit reversible secondary conformation transitions and/or hydrophilic–hydrophobic transitions in response to changes in environmental conditions such as pH and temperature. The stimuli‐triggered conformation and/or phase transitions lead to unique self‐assembly behaviors, making these materials interesting for controlled drug and gene delivery applications. Therefore, stimuli‐sensitive synthetic polypeptide‐based materials have been extensively investigatid in recent years. Various polypeptide‐based materials, including micelles, vesicles, nanogels, and hydrogels, have been developed and tested for drug‐ and gene‐delivery applications. In addition, the presence of reactive side groups in some polypeptides facilitates the incorporation of various functional moieties to the polypeptides. This Review focuses on recent advances in stimuli‐sensitive polypeptide‐based materials that have been designed and evaluated for drug and gene delivery applications. In addition, recent developments in the preparation of stimuli‐sensitive functionalized polypeptides are discussed.

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Polylactide (PLA) is a biodegradable, aliphatic polyester derived from lactic acid. It has similar mechanical properties to polyethylene terephthalate, but has a significantly lower maximum continuous use temperature. PLA products can be recycled after use either by remelting and processing the material a second time or by hydrolyzing to lactic acid, the basic chemical. In this review, the technologies for polymerization of the lactic acid and the comparison of physical, thermal and mechanical properties, biodegradability, and biocompatibility of the PLA and copolymers with other similar polymers are described.

Synthetic glycopolypeptides have attracted much interest for application in biomedical field as they are structural mimics to the natural glycopeptides or glycoproteins. However, the synthesis methods toward glycopolypeptides are still few or less efficient. Herein, we present a facile route to preparation of glycopolypeptides with highly effective "glycosylation" by click postpolymerization modification. First, an alkyne-substituted N-carboxyanhydride (NCA) monomer was synthesized and subsequently polymerized to afford the polypeptide with "clickable" alkyne pendants. The alkyne-functionalized polypeptide was then "glycosylated" by click reaction of different sugar azides to the alkyne pendants with high efficiency. All the obtained glycopolypeptides were soluble and preferred α-helix conformation in water. Primary studies on the obtained glycopolypeptides binding with Con A lectin were assessed by turbidimetric assay. The more quantitive studies of the interactions between lectin proteins and the synthetic glycopolypeptides, and the application of these materials as the multivalent ligands are in progress.

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A monoethylaluminum Schiff base complex (2) with formula LAlEt (L = N,N'-(2,2-dimethylpropylene)bis(3,5-di-tert-butylsalicylideneimine) was synthesized and employed for the stereoselective ring-opening polymerization of rac-lactide (rac-LA). The complex 2 was characterized by nuclear magnetic resonance, crystal structure, and elemental analysis. It contains a five-coordinate aluminum atom with distorted trigonal bipyramidal geometry in the solid state. In the presence of 2-propanol, 2 showed high stereoselectivity for the polymerization of rac-LA. The polymerization yielded crystalline poly(rac-LA) with a high melting temperature (193-201 degrees C). NMR, differential scanning calorimetry, and wide-angle X-ray diffraction indicated that the poly(rac-LA) was highly isotactic, and a stereocomplex was formed between poly-l- and poly-d-lactide block sequences. By the analysis of electrospray-ionization mass spectrometry and (1)H NMR, the polymer was demonstrated to be endcapped in both terminals with an isopropyl ester and a hydroxy group, respectively. The polymerization was of first order in rac-LA concentration. The relationship between the rac-LA conversion and molecular weights of the polymer was linear so that the polymerization could be well controlled.