Fiber-reinforced hydrogels are a class of soft composites that are seeing increased use in tissue engineering, regenerative medicine, and bio-printing. These hydrogels exhibit mechanical and biological properties that are similar to those found in living tissues. While advancements are being made on the biological feasibility of fiber-reinforced hydrogels, there are limits to the geometries realized using electrospinning techniques. To this end, the objective of this paper is to develop a freeform fabrication process that addresses two key limitations of existing fiber-reinforced hydrogel manufacturing processes, viz., their inability to manufacture (i) tall structures in the tens of millimeters height range; and (ii) structures with external overhangs. The freeform fabrication process involves the use of a direct-write far-field electrospinning print-head that enables the printing of specific electrospun fiber layers based on the cross-sectional geometry of the part. These fiber layers are then stacked to create a three-dimensional fiber pre-form. Finally, the fiber pre-form is submerged in specific hydrogel and cross-linking solutions to realize the fiber-reinforced hydrogel part of interest. In order to create an external overhang, a sacrificial support material is incorporated using hydrophobic fiber pre-forms to resist the infiltration of the hydrogel solution during the submersion step. The process has been successfully demonstrated both for thin parts with contours, and vasculature-mimicking tubular structures. Mechanical testing of the ∼1.6 wt. % fiber-reinforced hydrogels shows an order of magnitude improvement in the tensile properties when compared to published results for pure hydrogel.

纤维增强水凝胶是一类柔软的复合材料，在组织工程，再生医学和生物打印中的使用日益广泛。这些水凝胶的机械和生物学特性与活组织中的相似。尽管在纤维增强水凝胶的生物学可行性上取得了进步，但是使用电纺丝技术实现的几何形状存在局限性。为此，本文的目的是开发一种自由形式的制造工艺，以解决现有纤维增强水凝胶制造工艺的两个主要局限性，即它们无法制造（i）在数十毫米高度范围内的高层结构；（ii）具有外部悬挑的结构。自由形式的制造过程涉及使用直接写入远场静电纺丝打印头，该打印头能够根据零件的横截面几何形状来印刷特定的电纺纤维层。然后将这些纤维层堆叠以产生三维纤维预制件。最后，将纤维预成型件浸入特定的水凝胶和交联溶液中，以实现感兴趣的纤维增强水凝胶部分。为了产生外部悬垂，使用疏水性纤维预成型件并入牺牲性支撑材料以在浸没步骤中抵抗水凝胶溶液的渗透。该工艺已成功地证明了具有轮廓的薄型零件和模仿脉管系统的管状结构。约1.6 wt。