Design and Characterization of a Synthetically Accessible, Photodegradable Hydrogel for User-Directed Formation of Neural Networks

Abstract

Hydrogels with photocleavable units incorporated into the cross-links have provided researchers with the ability to control mechanical properties temporally and study the role of matrix signaling on stem cell function and fate. With a growing interest in dynamically tunable cell culture systems, methods to synthesize photolabile hydrogels from simple precursors would facilitate broader accessibility. Here, a step-growth photodegradable poly(ethylene glycol) (PEG) hydrogel system cross-linked through a strain promoted alkyne-azide cycloaddition (SPAAC) reaction and degraded through the cleavage of a nitrobenzyl ether moiety integrated into the cross-links is developed from commercially available precursors in three straightforward synthetic steps with high yields (>95%). The network evolution and degradation properties are characterized in response to one-and two-photon irradiation. The PEG hydrogel is employed to encapsulate embryonic stem cell-derived motor neurons (ESMNs), and in situ degradation is exploited to gain three-dimensional control over the extension of motor axons using two-photon infrared light. Finally, ESMNs and their in vivo synaptic partners, myotubes, are coencapsulated, and the formation of user-directed neural networks is demonstrated.

Photodegradable Gelatin-Based Hydrogels Prepared by Bioorthogonal Click Chemistry for Cell Encapsulation and Release

“…5,6 Several hydrogels prepared from poly(ethylene glycol) (PEG) or polysaccharides with robust mechanical strength have been used in cell encapsulation and have demonstrated very high cell viability. [7][8][9][10][11][12] However, cells cannot bind to these networks unless additional cellular recognition signals, such as integrin binding peptide sequences e.g. Arg-Gly-Asp (RGD), are incorporated within the structure.…”

“…Arg-Gly-Asp (RGD), are incorporated within the structure. 7,9,11 Alternatively gelatin, which contains the RGD sequence in its structure, can be used to prepare hydrogel networks providing cell support.…”

“…1 To address this problem, light-induced degradation chemistry has been utilized for spatial and temporal degradation of hydrogel structures. 7,11,18,[29][30][31][32][33][34][35][36][37][38][39][40][41] This approach often utilizes a photolabile o-nitrobenzyl (NB) moiety which becomes reactive upon irradiation with ultraviolet (UV) light and induces the cleavage of the adjacent group.…”

Spatially and temporally controlled hydrogels for tissue engineering

“…With modifications to prepolymer structures and crosslinking reactions for primary network formation, this platform could be used towards fabrication of cell culture matrix with gradient degradation, patterned surface erosion, as well as 3D interconnected local erosion, which could serve as excellent in vitro models to isolate individual factors to study cell-material interactions and cell behaviors [281–285]. For example, McKinnon et al reported a photodegradable step-growth PEG hydrogels based on the SPAAC reaction [285].…”

Photoactivation of Butyric Acid from 6‐Aminobenzocoumarin Cages

“…upon irradiation, [4] ii) photoactive polymers for encapsulation of guest molecules and as drug delivery systems, [5,6] iii) photoactive nanoparticle carriers for therapeutic agent release, iv) targeted cancer therapies, in nanomedicine and diagnostics, [7][8][9][10] v) photoactive hydrogels with tunable mechanical properties as scaffolds for cell culture and tissue regeneration, [11,12] vi) light controlled antibacterial agents for selecting specific bacterial strains from microbial mixtures for healthcare and microbiology research, [13] vii) agents enabling photocontrolled synthesis of aptamer-drug conjugates for selective tissue recognition in targeted cancer therapy, [14] viii) photolabile linkers for solid phase synthesis of peptides and heterocycles, [15,16] and ix) agents to enable the uncaging of bioactive molecules such as antibiotics, oligonucleotides and neurotransmitters from photolabile precursors.…”