Thermoreversible and Injectable ABC Polypeptoid Hydrogels: Controlling the Hydrogel Properties through Molecular Design

Abstract

A series of ABC triblock copolypeptoids [i.e., poly(N-allyl glycine)-b-poly(N-methyl glycine)-b-poly(N-decyl glycine) (AMD)] with well-defined structure and varying composition have been synthesized by sequential primary amine-initiated ring-opening polymerization of the corresponding N-substituted N-carboxyanhydride monomers (Al-NCA, Me-NCA, and De-NCA). The ABC block copolypeptoids undergo sol-to-gel transitions with increasing temperature in water and biological media at low concentrations (2.5–10 wt %). The sol–gel transition is rapid and fully reversible with a narrow transition window, evidenced by the rheological measurements. The gelation temperature (Tgel) and mechanical stiffness of the hydrogels are highly tunable: Tgel in the 26.2–60.0 °C range, the storage modulus (G′) and Young’s modulus (E) in the 0.2–780 Pa and 0.5–2346 Pa range, respectively, at the physiological temperature (37 °C) can be readily accessed by controlling the block copolypeptoid composition and the polymer solution concentration. The hydrogel is injectable through a 24 gauge syringe needle and maintains their shape upon in contact with surfaces or water baths that are kept above the sol–gel transition temperature. The hydrogels exhibit minimal cytotoxicity toward human adipose derived stem cells (hASCs), evidenced from both alamarBlue and PicoGreen assays. Furthermore, quantitative PCR analysis revealed significant up-regulation of the Col2a1 gene and down-regulation of ANGPT1 gene, suggesting that the hydrogel exhibit biological activity in inducing chondrogenesis of hASCs. It was also demonstrated that the hydrogel can be used to quantitatively encapsulate water-soluble enzymes (e.g., horseradish peroxidase) by manipulating the sol–gel transition. The enzymatic activity of HRP remain unperturbed after encapsulation at 37 °C for up to 7 d, suggesting that the hydrogel does not adversely affect the enzyme structure and thereby the enzymatic activity. These results suggest that the polypeptoid hydrogel a promising synthetic platform for tissue engineering or protein storage applications.

Micellization and gelatinization in aqueous media of pH- and thermo-responsive amphiphilic ABC (PMMA82-b-PDMAEMA150-b-PNIPAM65) triblock copolymer synthesized by consecutive RAFT polymerization

“…Besides high critical gelation concentration, these hydrogels oen exhibit broad or slow sol-gel transitions. 32,33 Comparing to ABA model, ABC triblock copolymers, which the C block is hydrophobic and the B and A blocks are water-soluble below the sol-gel transition temperature, are more efficient to realize the sol-gel transition. 18,19 Because the three blocks are mutually immiscible, they can form diverse nanostructures in aqueous solution in response to the change of the environment.…”

Polypeptoid polymers: Synthesis, characterization, and properties

“…[101] Adapted with permission from the Wiley-VCH , and C, all ABC triblock copolypeptoids. [87] Adapted with permission from American Chemical Society [87] Adapted with permission from American Chemical Society…”

“…For example, investigation of polypeptoid-based drug delivery carriers, [90,96,97] gene delivery carriers, [78] and 3D culture/tissue engineering scaffolds has started to emerge. [87] Demonstration of their unique properties and capabilities that are unrivaled by other nonpolypeptoid-based systems will be critical in moving polypeptoids to the forefront of biomaterials applications. …”

Recent advances in crystallization and self‐assembly of polypeptoid polymers

“…Taking advantage of the nature of living polymerization, multiple block copolymers of polypeptoid can be prepared by sequence ROP of NNCA. Zhang and coworkers synthesized ABC triblock copolypeptoids, that is, poly( N ‐allyl glycine)‐ block ‐poly( N ‐methyl glycine)‐ block ‐poly( N ‐decyl glycine), and studied their hydrogel properties, as well as the potential application in tissue engineering materials . All the block copolymers own a relatively narrow dispersity (<1.10).…”