Complex dynamic substrate control: dual-tone hydrogel photoresists allow double-dissociation of topography and modulus

Backbone vs. side-chain: two light-degradable polyurethanes based on 6-nitropiperonal

Two novel polyurethanes, which are based on 6-nitropiperonal and differ in the implementation of the light-cleavable unit, were synthesized to develop a drug delivery system that only releases cargo upon application of a certain trigger.

Mechanically robust photodegradable gelatin hydrogels for 3D cell culture and in situ mechanical modification

Highly conjugated, hydrophobically modified gelatin hydrogels were synthesized, polymerized and degraded with orthogonal wavelengths of light.

Dynamic covalent bond-based hydrogels with superior compressive strength, exceptional slice-resistance and self-healing properties

A novel dynamic-covalent bond-based single network hydrogel was developed, of which the failure compressive stress and strain as well as the failure tensile stress and strain could exceed 27.3 MPa and 98.4% as well as 0.23 MPa and 282.3%, respectively. In addition, the gel shows remarkable slice-resistance and self-healing properties.

Shape-Changing Photodegradable Hydrogels for Dynamic 3D Cell Culture

Inspired by natural examples of swelling-actuated self-folding, we utilize photodegradable hydrogels as dynamically tunable, shape-changing scaffolds for culturing cells. Poly(ethylene glycol) diacrylate-based thin films incorporating ortho-nitrobenzyl (o-NB) moieties are transformed from flat 2D sheets to folded 3D structures by exposure to 365 nm UV light. As the UV light is attenuated through the thickness of the gel, a cross-link density gradient is formed. This gradient gives rise to differential swelling and a bending moment, resulting in gel folding. By tuning the UV light dose and the molar ratio of photodegradable to nondegradable species, both the initial degree of folding and the relaxation of tubular structures can be accurately controlled. These self-folding photodegradable gels were further functionalized with a cell-adhesive RGD peptide for both seeding and encapsulation of C2C12 mouse myoblasts. Light-induced folding of RGD functionalized hydrogels from flat sheets to tubular structures was demonstrated 1 or 3 days after C2C12 seeding. The C2C12s remained adhered on the inner walls of folded tubes for up to 6 days after folding. The minimum measured diameter of a tubular structure containing C2C12s was 1 mm, which is similar to the size of muscle fascicles. Furthermore, the viability of encapsulated C2C12s was not adversely affected by the UV light-induced folding. This is the first account of a self-folding material system that allows 2D-3D shape change in the presence of both seeded and encapsulated cells at a user-directed time point of choice.

Direct Gradient Photolithography of Photodegradable Hydrogels with Patterned Stiffness Control with Submicrometer Resolution

Cell response to matrix mechanics is well-known; however, the ability to spatially pattern matrix stiffness to a high degree of control has been difficult to attain. This study describes the use of maskless photolithography as a flexible process for direct, noncontact gradient patterning of photodegradable hydrogels with custom graphics. Any input gray scale image can be used to directly chart hydrogel cross-link density as a function of spatial position. Hydrogels can be patterned with submicron resolution, with length scales within a single substrate spanning several orders of magnitude. A quantitative relationship between input grayscale image pixel intensity and output gel stiffness is validated, allowing for direct gradient patterning. Such physical gradient hydrogel constructs are rapidly produced in a highly controlled fashion with measured stiffness ranges and length scales that are physiologically relevant. Mesenchymal stem cells cultured on these physical gradients matrices congregate and align orthogonal to the gradient direction along iso-degraded lines. This approach results in a robust and high-throughput platform to answer key questions about cell response in heterogeneous physical environments.

Density gradients at hydrogel interfaces for enhanced cell penetration

Interfacial crosslinking density gradients represent a simple strategy to overcome the challenge of the limited penetration of cells seeded on the surface of hydrogels. The strategy here-presented can be used both when cells need to be seeded after hydrogel processing and to enable cell migration through hydrogel elements additively manufactured.