Synthetic dynamic hydrogels promote degradation-independent in vitro organogenesis.

Epithelial organoids are most efficiently grown from mouse-tumour-derived, reconstituted extracellular matrix hydrogels, whose poorly defined composition, batch-to-batch variability and immunogenicity limit clinical applications. Efforts to replace such ill-defined matrices for organoid culture have largely focused on non-adaptable hydrogels composed of covalently crosslinked hydrophilic macromolecules. However, the excessive forces caused by tissue expansion in such elastic gels severely restrict organoid growth and morphogenesis. Chemical or enzymatic degradation schemes can partially alleviate this problem, but due to their irreversibility, long-term applicability is limited. Here we report a family of synthetic hydrogels that promote extensive organoid morphogenesis through dynamic rearrangements mediated by reversible hydrogen bonding. These tunable matrices are stress relaxing and thus promote efficient crypt budding in intestinal stem-cell epithelia through increased symmetry breaking and Paneth cell formation dependent on yes-associated protein 1. As such, these well-defined gels provide promising versatile matrices for fostering elaborate in vitro morphogenesis.

Synthetic 3D PEG-Anisogel Tailored with Fibronectin Fragments Induce Aligned Nerve Extension.

An enzymatically cross-linked polyethylene glycol (PEG)-based hydrogel was engineered to promote and align nerve cells in a three-dimensional manner. To render the injectable, otherwise bioinert, PEG-based material supportive for cell growth, its mechanical and biochemical properties were optimized. A recombinant fibronectin fragment (FNIII9*-10/12-14) was coupled to the PEG backbone during gelation to provide cell adhesive and growth factor binding domains in close vicinity. Compared to full-length fibronectin, FNIII9*-10/12-14 supports nerve growth at similar concentrations. In a 3D environment, only the ultrasoft 1 w/v% PEG hydrogels with a storage modulus of ∼10 Pa promoted neuronal growth. This gel was used to establish the first fully synthetic, injectable Anisogel by the addition of magnetically aligned microelements, such as rod-shaped microgels or short fibers. The Anisogel led to linear neurite extension and represents a large step in the direction of clinical translation with the opportunity to treat acute spinal cord injuries.

Bioinspired Hydrogels for 3D Organoid Culture.

Organoids have stepped into the limelight as unique in vitro systems for modeling organ development, function and disease. This review provides a perspective on how chemically defined, bio-inspired hydrogels could be used for replacing ill-defined matrices derived from the native extracellular matrix (ECM) that are used for generating organoids in 3D stem cell culture. In particular, we propose the use of self-healing and light-responsive matrices that should afford control over the inherently stochastic self-organization process that currently underlies organoid morphogenesis. Such designer ECMs could accelerate the translation of organoid technology from the laboratory into various real-life applications.