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  1. Blending sacrificial, cell-laden microgels with structural, UV-crosslinkable microgels produces a family of modular bioinks with tunable void fractions that influence cellular morphology while maintaining a depth-independent cell distribution.

     
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    Free, publicly-accessible full text available November 21, 2024
  2. Abstract

    Microextrusion‐based 3D bioprinting into support baths has emerged as a promising technique to pattern soft biomaterials into complex, macroscopic structures. It is hypothesized that interactions between inks and support baths, which are often composed of granular microgels, can be modulated to control the microscopic structure within these macroscopic‐printed constructs. Using printed collagen bioinks crosslinked either through physical self‐assembly or bioorthogonal covalent chemistry, it is demonstrated that microscopic porosity is introduced into collagen inks printed into microgel support baths but not bulk gel support baths. The overall porosity is governed by the ratio between the ink's shear viscosity and the microgel support bath's zero‐shear viscosity. By adjusting the flow rate during extrusion, the ink's shear viscosity is modulated, thus controlling the extent of microscopic porosity independent of the ink composition. For covalently crosslinked collagen, printing into support baths comprised of gelatin microgels (15‐50 µm) results in large pores (≈40 µm) that allow human corneal mesenchymal stromal cells (MSCs) to readily spread, while control samples of cast collagen or collagen printed in non‐granular support baths do not allow cell spreading. Taken together, these data demonstrate a new method to impart controlled microscale porosity into 3D printed hydrogels using granular microgel support baths.

     
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  3. Abstract

    3D bioprinting has enabled the fabrication of tissue‐mimetic constructs with freeform designs that include living cells. In the development of new bioprinting techniques, the controlled use of diffusion has become an emerging strategy to tailor the properties and geometry of printed constructs. Specifically, the diffusion of molecules with specialized functions, including crosslinkers, catalysts, growth factors, or viscosity‐modulating agents, across the interface of printed constructs will directly affect material properties such as microstructure, stiffness, and biochemistry, all of which can impact cell phenotype. For example, diffusion‐induced gelation is employed to generate constructs with multiple materials, dynamic mechanical properties, and perfusable geometries. In general, these diffusion‐based bioprinting strategies can be categorized into those based on inward diffusion (i.e., into the printed ink from the surrounding air, solution, or support bath), outward diffusion (i.e., from the printed ink into the surroundings), or diffusion within the printed construct (i.e., from one zone to another). This review provides an overview of recent advances in diffusion‐based bioprinting strategies, discusses emerging methods to characterize and predict diffusion in bioprinting, and highlights promising next steps in applying diffusion‐based strategies to overcome current limitations in biofabrication.

     
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  4. Abstract

    While the human body has many different examples of perfusable structures with complex geometries, biofabrication methods to replicate this complexity are still lacking. Specifically, the fabrication of self‐supporting, branched networks with multiple channel diameters is particularly challenging. Herein, the Gelation of Uniform Interfacial Diffusant in Embedded 3D Printing (GUIDE‐3DP) approach for constructing perfusable networks of interconnected channels with precise control over branching geometries and vessel sizes is presented. To achieve user‐specified channel dimensions, this technique leverages the predictable diffusion of cross‐linking reaction‐initiators released from sacrificial inks printed within a hydrogel precursor. The versatility of GUIDE‐3DP to be adapted for use with diverse physicochemical cross‐linking mechanisms is demonstrated by designing seven printable material systems. Importantly, GUIDE‐3DP allows for the independent tunability of both the inner and outer diameters of the printed channels and the ability to fabricate seamless junctions at branch points. This 3D bioprinting platform is uniquely suited for fabricating lumenized structures with complex shapes characteristic of multiple hollow vessels throughout the body. As an exemplary application, the fabrication of vasculature‐like networks lined with endothelial cells is demonstrated. GUIDE‐3DP represents an important advance toward the fabrication of self‐supporting, physiologically relevant networks with intricate and perfusable geometries.

     
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