Design, fabrication and characterization of thin film piezoelectric devices for bulk acoustic wave acoustophoresis of micrometer-sized particles.

Many mammalian tissues have a specific cellular arrangement that enables their unique function. For example, parallel alignment of myofibers enables uniaxial muscle contraction. To engineer structured tissues ex vivo, it is critical to recapitulate this cellular arrangement. Conventional 3D encapsulation often fails to recapitulate this complexity, motivating the need for advanced patterning approaches. In this work, an acoustofluidic device to continuously pattern mammalian cells within hydrogel fibers is engineered. Contactless acoustofluidic forces are used to control the spacing between parallel lines of cells. To enable continuous extrusion of cell-laden hydrogel fibers, a low friction Teflon tube is integrated into the device. A photopolymerizable hydrogel allows triggering gelation externally with light once the cells are under the influence of the acoustic field, setting the patterned cells within the hydrogel fiber. Using this device, the muscle progenitor cells (myoblasts) within the hydrogel are patterned in parallel lines to mimic the structure of skeletal muscle. The increased formation of myotubes and spontaneous twitching of the myotubes in patterned samples are observed. This approach combining continuous fabrication with the tunability of acoustofluidics can create complex 3D tissues to engineer skeletal muscles as well as tendons, ligaments, vascular networks, or combinations thereof in the future.

Recent advances in additive manufacturing (AM) technologies provide tools to fabricate biological structures with complex three-dimensional (3D) organization. Deposition-based approaches have been exploited to manufacture multimaterial constructs. Stimulus-triggered approaches have been used to fabricate scaffolds with high resolution. Both features are useful to produce biomaterials that mimic the hierarchical organization of human tissues. Recently, multitechnology biofabrication approaches have been introduced that integrate benefits from different AM techniques to enable more complex materials design. However, few methods allow for tunable properties at both micro-and macro-scale in materials that are conducive for cell growth. To improve the organization of biofabricated constructs, we integrated direct ink writing (DIW) with digital light processing (DLP) to form multimaterial constructs with improved spatial control over final scaffold mechanics. Polymer-nanoparticle hydrogels were combined with methacryloyl gelatin (GelMA) to engineer dual inks that were compatible with both DIW and DLP. The shear-thinning and self-healing properties of the dual inks enabled extrusion-based 3D printing. The inclusion of GelMA provided a handle for spatiotemporal control of cross-linking with DLP. Exploiting this technique, complex multimaterial constructs were printed with defined mechanical reinforcement. In addition, the multitechnology approach was used to print live cells for biofabrication applications. Overall, the combination of DIW and DLP is a simple and efficient strategy to fabricate hierarchical biomaterials with user-defined control over material properties at both micro-and macro-scale.

Hydrogel-based three-dimensional (3D) cellular models are attractive for bioengineering and pharmaceutical development as they can more closely resemble the cellular function of native tissue outside of the body. In general, these models are composed of tissue specific cells embedded within a support material, such as a

Complex 3D in vitro models are emerging as a key technology to support research areas in personalised medicine. Methods to manipulate and control the position of microtissues are needed to efficiently assemble many 3D in vitro models.