Covalently Adaptable Elastin‐Like Protein–Hyaluronic Acid (ELP–HA) Hybrid Hydrogels with Secondary Thermoresponsive Crosslinking for Injectable Stem Cell Delivery

Abstract

Shear-thinning, self-healing hydrogels are promising vehicles for therapeutic cargo delivery due to their ability to be injected using minimally invasive surgical procedures. An injectable hydrogel using a novel combination of dynamic covalent crosslinking with thermoresponsive engineered proteins is presented. Ex situ at room temperature, rapid gelation occurs through dynamic covalent hydrazone bonds by simply mixing two components: hydrazine-modified elastin-like protein (ELP) and aldehyde-modified hyaluronic acid. This hydrogel provides significant mechanical protection to encapsulated human mesenchymal stem cells during syringe needle injection and rapidly recovers after injection to retain the cells homogeneously within a 3D environment. In situ, the ELP undergoes a thermal phase transition, as confirmed by coherent anti-Stokes Raman scattering microscopy observation of dense ELP thermal aggregates. The formation of the secondary network reinforces the hydrogel and results in a tenfold slower erosion rate compared to a control hydrogel without secondary thermal crosslinking. This improved structural integrity enables cell culture for three weeks postinjection, and encapsulated cells maintain their ability to differentiate into multiple lineages, including chondrogenic, adipogenic, and osteogenic cell types. Together, these data demonstrate the promising potential of ELP-HA hydrogels for injectable stem cell transplantation and tissue regeneration. for generously sharing the uronic acid assay protocol. The authors acknowledge Brad Krajina for assistance in characterization of polymer molecular weight.

Three‐dimensional extrusion bioprinting of single‐ and double‐network hydrogels containing dynamic covalent crosslinks

“…Moreover, increasing the shear rate led to decreased material viscosity, demonstrating shear‐thinning [Fig. (A)] and corroborating previous reports that demonstrated the shear‐thinning ability of hydrogels assembled through hydrazone bonds . Recognizing the ability for these hydrogels to undergo shear‐thinning, we demonstrated qualitatively that the hydrogels could be ejected from a 27G × 1/2 in.…”

“…The hydrazone bond is a unique dynamic covalent bond that is formed between an electron‐dense, nucleophilic hydrazide (R‐NHNH 2 ) and an electron‐deficient, electrophilic aldehyde (R‐CHO). Hydrazone crosslinked hydrogels and imine variants of the hydrazone bond have previously been explored for their injectable, shear‐thinning and self‐healing properties . They have further been shown to protect cells during extrusion through a needle, adding to the advantages of using this system for 3D printing .…”

Cytocompatible, Injectable, and Electroconductive Soft Adhesives with Hybrid Covalent/Noncovalent Dynamic Network

“…[24] Fourier transform infrared spectroscopy (FTIR) was used to confirm the reaction, with a newly formed peak at 1733 cm −1 corresponding to the stretching vibration of the CO bond in HA-ALD ( Figure S3, Supporting Information). [24] Fourier transform infrared spectroscopy (FTIR) was used to confirm the reaction, with a newly formed peak at 1733 cm −1 corresponding to the stretching vibration of the CO bond in HA-ALD ( Figure S3, Supporting Information).…”

Methods To Assess Shear-Thinning Hydrogels for Application As Injectable Biomaterials

“…27−31 Dynamic covalent cross-links have also been explored for injection, where their dynamic nature confers shear-thinning during injection and then slow self-healing after injection. 32,33 …”