Polymer hydrogels exhibit actuation properties that result in reversible shape transformations and have promising applications in soft robotics, drug delivery systems, sensors, and microfluidic devices. Actuation occurs due to differential hydrogel swelling and is generally achieved by modulating hydrogel composition. Here a different approach to hydrogel actuation that originates solely from its structural anisotropy is reported. For 3D-printed single-layer hydrogels formed by cellulose nanocrystals (CNCs) and gelatin methacryloyl it is shown that shear-induced orientation of CNCs results in anisotropic mechanical and swelling properties of the hydrogel. Upon swelling in water, planar hydrogels acquire multiple complex 3D shapes that are achieved by i) varying CNC orientation with respect to the shape on the hydrogel sheet and ii) patterning the hydrogel with the regions of shearmediated and random CNC orientation. This study shows the capability to generate multiple shapes from the same hydrogel actuator based on the degree of its structural anisotropy. In addition, it introduces a biocompatible nanocolloidal ink with shear-thinning and self-healing properties for additive manufacturing of hydrogel actuators.

Growth of three-dimensional cancer spheroids (CSs) in man-made hydrogels mimicking natural extracellular matrix is an important and challenging task. Herein, we report on a supramolecular temperature-responsive hydrogel designed for the growth and subsequent release of CSs. A filamentous hydrogel was formed at 37 °C from an aqueous suspension of cellulose nanocrystals surface-functionalized with temperature-responsive polymer molecules. The encapsulation of cells in the hydrogel enabled effective growth of CSs with dimensions determined by the concentration of cellulose nanocrystals in the hydrogel. On demand release of CSs without loss of cell viability and spheroid integrity was achieved upon hydrogel cooling. The tumorigenic properties of the released CSs were examined by encapsulating and re-growing them in fibrin hydrogel. The results in this work can be used in fundamental cancer research and in cancer drug screening.

Interactions between tumor cells and the extracellular matrix (ECM) are an important factor contributing to therapy failure in cancer patients. Current in vitro breast cancer spheroid models examining the role of mechanical properties on spheroid response to chemotherapy are limited by the use of two-dimensional cell culture, as well as simultaneous variation in hydrogel matrix stiffness and other properties, e.g., hydrogel composition, pore size, and cell adhesion ligand density. In addition, currently used hydrogel matrices do not replicate the filamentous ECM architecture in a breast tumor microenvironment. Here, we report a collagen-alginate hydrogel with a filamentous architecture and a 20-fold variation in stiffness, achieved independently of other properties, used for the evaluation of estrogen receptor-positive breast cancer spheroid response to doxorubicin. The variation in hydrogel mechanical properties was achieved by altering the degree of cross-linking of alginate molecules. We show that soft hydrogels promote the growth of larger MCF-7 tumor spheroids with a lower fraction of proliferating cells and enhance spheroid resistance to doxorubicin. Notably, the stiffness-dependent chemotherapeutic response of the spheroids was temporally mediated: it became apparent at sufficiently long cell culture times, when the matrix stiffness has influenced the spheroid growth. These findings highlight the significance of decoupling matrix stiffness from other characteristics in studies of chemotherapeutic resistance of tumor spheroids and in development of drug screening platforms.

Organotypic micrometre-size 3D aggregates of skin cells (multicellular spheroids) have emerged as a promising in vitro model that can be utilized as an alternative of animal models to test active...

requires rapid prototyping, iteration, and optimization of MF devices, the cost and the time of their fabrication are important considerations for the outcome of this work. [16] In addition, MF devices with complex designs are often required for achieving sufficient mixing of the ingredients or for generating spatially heterogeneous (patterned) materials. Another requirement is the device stability and integrity during its operation: it should withstand pressure, wear, and exposure to solvents and reagents without feature distortion, cracking, or delamination, particularly important when many-hour MF device operation is expected.Over the past decades, MF devices have been fabricated in silicon, glass, metals, and polymers. [17][18][19] Currently, soft lithography is the main fabrication method of MF devices in polydimethylsiloxane (PDMS). This method offers high fidelity and resolution down to the sub-micrometer size range, however PDMS swells in many organic solvents, absorbs amino-containing reagents, delaminates under high pressures, and has high gas permeability. [19][20][21][22] Injection molding and hot embossing microfabrication offer the capability of high-volume device production from chemically resistant polymers, [23] however high cost of molds or stamps and the challenge in the fabrication of devices with complex designs limit the applications of these techniques. Fabrication in silicon provides high thermal conductivity of MF devices, however this method is expensive and labor-and time-consuming. Similarly, fabrication of MF devices in glass is cost-intensive and utilizes hazardous agents such as hydrofluoric acid. [17] Recently, 3D printing has offered a cost-, time-, and laborefficient method for one-step fabrication of 3D objects with complex designs. [19,[24][25][26] This method provides the capability to fabricate MF devices with features that are impossible or challenging to implement by other fabrication techniques, as well as the ability of rapid device prototyping. [27] Prior to the fabrication, the desired device design is implemented in a CAD file, which is then transferred to the printer. The device is then printed in a layer-by-layer fashion. [26] Microfluidic mixers, [28,29] microreactors, [30] and droplet generators [31] have been fabricated in poly(propylene), [30] poly(lactic acid), [32] photocurable resins, [25,28,29] and glass. [33] The utilization of 3D-printed MF devices for materials synthesis and assembly is still in its infancy. [19,26] To the best of our knowledge, 3D-printed MF reactors have been used only the solution-based synthesis of gold and Prussian blue nanoparticles (NPs), [30,34] and their use for extrusion and spraying Microfluidics (MFs) has emerged as a valuable and in some cases, unique platform for the synthesis and assembly of inorganic and polymeric materials. 3D printing enables time-, labor-, and cost-efficient prototyping of MF devices, their durability during operation, and the ability to implement complex designs, however the applications of 3D-printed M...