Microfluidics has become an important tool to engineer microenvironments with high precision, comprising devices and methods for controlling and manipulating fluids at the submillimeter scale. A specific branch of microfluidics comprises open fluidic systems, which is mainly characterized by displaying a higher air/liquid interface when compared with traditional closed-channel setups. The use of open channel systems has enabled the design of singular architectures in devices that are simple to fabricate and to clean. Enhanced functionality and accessibility for liquid handling are additional advantages inputted to technologies based on open fluidics. While benchmarked against closed fluidics approaches, the use of directly accessible channels decreases the risk of clogging and bubble-driven flow perturbation. In this review, we discuss the advantages of open fluidics systems when compared to their closed fluidics counterparts. Platforms are analyzed in two separated groups based on different confinement principles: wall-based physical confinement and wettability-contrast confinement. The physical confinement group comprises both open and traditional microfluidics; examples based on open channels with rectangular and triangular cross-section, suspended microfluidics, and the use of narrow edge of a solid surface for fluid confinement are addressed. The second group covers (super)hydrophilic/(super) hydrophobic patterned surfaces, and examples based on polymer-, textile-and paper-based microfluidic devices are explored. The technologies described in this review are critically discussed concerning devices' performance and versatility, manufacturing techniques and fluid transport/manipulation methods. A gather-up of recent biomedical applications of open fluidics devices is also presented.

The therapeutic effectiveness and biological relevance of technologies based on adherent cells depend on platforms that enable long-term culture in controlled environments. Liquid-core capsules have been suggested as semipermeable moieties with spatial homogeneity due to the high mobility of all components in their core. The lack of cell-adhesive sites in liquid-core structures often hampers their use as platforms for stem cell-based technologies for long-term survival and cell-directed self-organization. Here, the one-step fast formation of robust polymeric capsules formed by interfacial complexation of oppositely charged polyelectrolytes in an all-aqueous environment, compatible with the simultaneous encapsulation of mesenchymal stem/stromal cells (MSCs) and microcarriers, is described. The adhesion of umbilical cord MSCs to polymeric microcarriers enables their aggregation and culture for more than 21 days in capsules prepared either manually by dropwise addition, or by scalable electrohydrodynamic atomization, generating robust and stable capsules. Cell aggregation and secretion overtime can be tailored by providing cells with static or dynamic (bioreactor) environments.

Compartmentalized structures obtained in all‐aqueous settings have shown promising properties as cell encapsulation devices, as well as reactors for trans‐membrane chemical reactions. While most approaches focus on the preparation of spherical devices, advances on the production of complex architectures have been enabled by the interfacial stability conferred by emulsion systems, namely mild aqueous two‐phase systems (ATPS), or non‐equilibrated analogues. However, the application of non‐spherical structures has mostly been reported while keeping the fabricated materials at a stable interface, limiting the free‐standing character, mobility and transposition of the obtained structures to different setups. Here, the fabrication of self‐standing, malleable and perfusable tubular systems through all‐aqueous interfacial assembly is shown, culminating in the preparation of independent objects with stability and homogeneity after disruption of the polymer‐based aqueous separating system. Those hollow structures can be fabricated with a variety of widths, and rapidly printed as long structures at flow rates of 15 mm s−1. The materials are used as compartments for cell culture, showcasing high cytocompatibility, and can be tailored to promote cell adhesion. Such structures may find application in fields that benefit from freeform tubular structures, including the biomedical field with, for example, cell encapsulation, and benchtop preparation of microfluidic devices.

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