Well-defined synthetic copolymers with pendent aldehydes form biocompatible strain-stiffening hydrogels and enable competitive ligand displacement

Abstract

Dynamic hydrogels are attractive platforms for tissue engineering and regenerative medicine, but there are limited polymer platforms amenable to the formation of these dynamic materials. Most architectures reported are based either on telechelic synthetic polymers or side-chain modified natural polymers; synthetic versions of side-chain modified polymers are noticeably absent. Dynamic hydrogels are key tools for their ability to mimic key extracellular (ECM) mechanical properties like strain stiffening and stress relaxation, while enabling enhanced processing characteristics like injectability, 3D printing, and self-healing. Currently, the limited chemical design space is hindering progress. To facilitate access to new classes of dynamic hydrogels, we report the straightforward synthesis of a water-soluble copolymer with a tunable fraction of pendent aldehyde groups (12–64%) using controlled radical polymerization, and their formation into hydrogel biomaterials with dynamic crosslinks. We found the polymer synthesis to be well-controlled with the determined reactivity ratios consistent with blocky gradient microarchitecture. Subsequently, we observed fast gelation kinetics with imine-type crosslinking. We were able to vary hydrogel stiffness from ≈ 2–20 kPa and tune the onset of strain-stiffening towards a biologically relevant regime (critical stress ≈ 10 Pa). Moreover, we used fluorescence resonance energy transfer (FRET) to demonstrate ligand displacement along the copolymer backbone via competitive binding and highlighted the cytocompatibility of our system using human dermal fibroblasts. The combination of highly tunable composition, stiffness, and strain-stiffening, in conjunction with temporal control over ligand exchange/presentation, positions these cytocompatible copolymers as a powerful synthetic platform for the rational design of next generation synthetic biomaterials.

Structure-reactivity relationships in a small library of imine-type dynamic covalent materials: Determination of rate and equilibrium constants enables model prediction and validation of a unique mechanical softening in dynamic hydrogels

“…For details regarding their preparation, see our previous publication. 19,38 All other materials were used as received unless otherwise specified. For the preparation of phosphate-buffered D2O, deuterium oxide (Sigma, 99.9 atom% D, D2O), potassium dideuterium phosphate (Sigma, 98 atom% D, KD2PO4), potassium phosphate tribasic (Sigma, ≥ 98%, K3PO4), and…”

“…1), as a model compound, oxidized alginate (2), as representative of the oxidized natural polysaccharides commonly used as biomaterials, and a synthetic aldehyde polymer (3), as a synthetic and well-defined system for comparison. 38 (Right) Series of amine nucleophiles (4-9) chosen for this study. Starting from propylamine, we can make a series of incremental single-point changes (highlighted in red) to the reactive group to highlight how even a single atomic change can have significant changes on the rate and equilibrium constants (vide infra).…”

“…License: CC BY-NC 4.0 a well-defined copolymer with pendant aldehyde groups. 38 This copolymer is referred to as pSM-co-OMAm and its structure (3) is given in Figure 2.…”

“…(Left) Three aliphatic aldehydes chosen for this study. Isobutyraldehyde (1), as a model compound, oxidized alginate (2), as representative of the oxidized natural polysaccharides commonly used as biomaterials, and a synthetic aldehyde polymer (3), as a synthetic and well-defined system for comparison 38. (Right) Series of amine nucleophiles (4-9) chosen for this study.…”