Rational synthesis of novel biocompatible thermoresponsive block copolymer worm gels

• Published in: Soft matter 2021-06, Vol.17 (22), p.562-5612
• Main Authors: Beattie, Deborah L, Mykhaylyk, Oleksandr O, Ryan, Anthony J, Armes, Steven P
• Format: Article
• Language: English
• Subjects: Ambient temperature; Biocompatibility; Biomedical materials; Block copolymers; Chain transfer; Chemical synthesis; Cooling; Gels; Hydrogels; Hydrophobicity; Hydroxypropyl methacrylate; Macromolecules; Morphology; NMR; Nuclear magnetic resonance; Phosphorylcholine; Polymerization; Rheological properties; Rheology; Scaling laws; Worms; X-ray scattering
• ISSN: 1744-683X; 1744-6848
• DOI: 10.1039/d1sm00460c

It is well known that reversible addition-fragmentation chain transfer (RAFT) aqueous dispersion polymerization of 2-hydroxypropyl methacrylate (HPMA) enables the rational design of diblock copolymer worm gels. Moreover, such hydrogels can undergo degelation on cooling below ambient temperature as a result of a worm-to-sphere transition. However, only a subset of such block copolymer worms exhibit thermoresponsive behavior. For example, PMPC 26 -PHPMA 280 worm gels prepared using a poly(2-(methacryloyloxy)ethyl phosphorylcholine) (PMPC 26 ) precursor do not undergo degelation on cooling to 6 °C (see S. Sugihara et al. , J. Am. Chem. Soc. , 2011, 133 , 15707-15713). Informed by our recent studies (N. J. Warren et al. , Macromolecules , 2018, 51 , 8357-8371), we decided to reduce the mean degrees of polymerization of both the PMPC steric stabilizer block and the structure-directing PHPMA block when targeting a pure worm morphology. This rational approach reduces the hydrophobic character of the PHPMA block and hence introduces the desired thermoresponsive character, as evidenced by the worm-to-sphere transition (and concomitant degelation) that occurs on cooling a PMPC 15 -PHPMA 150 worm gel from 40 °C to 6 °C. Moreover, worms are reconstituted on returning to 40 °C and the original gel modulus is restored. This augurs well for potential biomedical applications, which will be examined in due course. Finally, small-angle X-ray scattering studies indicated a scaling law exponent of 0.67 ( 2/3) for the relationship between the worm core cross-sectional diameter and the PHPMA DP for a series of PHPMA-based worms prepared using a range of steric stabilizer blocks, which is consistent with the strong segregation regime for such systems. Judicious control over the mean degree of polymerization of each block in a amphiphilic diblock copolymer ensures that the corresponding worm gel exhibits thermoreversible (de)gelation behavior, as judged by TEM, SAXS and rheology studies.