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Abstract:
Fiber-based approaches hold great promise for tendon tissue engineering enabling the possibility of manufacturing aligned hydrogel filaments that can guide collagen fiber orientation, thereby providing a biomimetic micro-environment for cell attachment, orientation, migration, and proliferation. In this study, a 3D system composed of cell-laden, highly aligned hydrogel yarns is designed and obtained via wet spinning in order to reproduce the morphology and structure of tendon fascicles. A bioink composed of alginate and gelatin methacryloyl (GelMA) is optimized for spinning and loaded with human bone morrow mesenchymal stem cells (hBM-MSCs). The produced scaffolds are subjected to mechanical stretching to recapitulate the strains occurring in native tendon tissue. Stem cell differentiation is promoted by addition of bone morphogenetic protein 12 (BMP-12) in the culture medium. The aligned orientation of the fibers combined with mechanical stimulation results in highly preferential longitudinal cell orientation and demonstrates enhanced collagen type I and III expression. Additionally, the combination of biochemical and mechanical stimulations promotes the expression of specific tenogenic markers, signatures of efficient cell differentiation towards tendon. The obtained results suggest that the proposed 3D cell-laden aligned system can be used for engineering of scaffolds for tendon regeneration.

Keywords:
hydrogel fibers, static mechanical stretching, stem cell alignment, tenogenic differentiation, wet spinning

Abstract:
Injection of cell‐laden scaffolds in the form of mesoscopic particles directly to the site of treatment is one of the most promising approaches to tissue regeneration. Here, a novel and highly efficient method is presented for preparation of porous microbeads of tailorable dimensions (in the range ≈300–1500 mm) and with a uniform and fully interconnected internal porous texture. The method starts with generation of a monodisperse oil‐in‐water emulsion inside a flow‐focusing microfluidic device. This emulsion is later broken‐up, with the use of electric field, into mesoscopic double droplets, that in turn serve as a template for the porous microbeads. By tuning the amplitude and frequency of the electric pulses, the template droplets and the resulting porous bead scaffolds are precisely produced. Furthermore, a model of pulsed electrodripping is proposed that predicts the size of the template droplets as a function of the applied voltage. To prove the potential of the porous microbeads as cell carries, they are tested with human mesenchymal stem cells and hepatic cells, with their viability and degree of microbead colonization being monitored. Finally, the presented porous microbeads are benchmarked against conventional microparticles with nonhomogenous internal texture, revealing their superior performance.

Abstract:
We report automated generation of arbitrary sequences of multiple microdroplets with online and individual control over the number of cores and volumes of all the constituents (cores and shells) of each of the multiple droplets. We show that a given sequence of volumes of the cores always folds to the same final three-dimensional architecture. The method presents the first proof-of-concept for the ability to design the three-dimensional structure of multiple droplets. We discuss the potential use of the technique in the formulation of predetermined distribution of drug release capsules and for automated generation of functional chemical microdroplet networks.

Keywords:
multiple droplets, microfluidics

Abstract:
Microfluidic droplet-on-demand systems allow the controllable construction of multiple droplets of previously unattainable morphologies. Guided by the diagrams of the possible topologies of double droplets we investigate in detail the vistas to control the morphology of Janus droplets. We also explore and control new morphologies of multiple Janus droplets, i.e., arbitrarily long chains of alternating immiscible segments. Theoretical calculations together with the control offered by the use of automation allow the design of both the topology and the geometry (e.g. curvatures of the interfaces) of the multiple droplets. The ability to rationally design convex–convex, convex–concave and concave–convex segments may be useful in material science, while the ability to tune the distances between the interfaces in the chains of droplets may have applications in designing artificial biochemical signalling networks.

Keywords:
multiple droplets, microfluidics

Abstract:
We report a microfluidic technique for high-throughput generation of droplets of nanolitre volume in parallel channels with online control of the volumes, volume fraction and distribution of droplet volumes with the use of two external valves.

Keywords:
microfluidics, droplet generation, droplets