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Jang T-S, et al.

resin (Emax 904 Gel-SC) for the reinforcement. Composite reinforcement amount inside the hydrogel matrix. They
digital models of hydrogel matrix and fiber reinforcement showed extremely wide range of fiber volume fraction
were constructed using computer-aided designs and the from 0 to 100% inside alginate hydrogel matrix, and the
printing path was also precisely generated by the software. bone between the hydrogel and fiber is stronger than
For evaluating mechanical properties of fiber reinforced pure hydrogel so that under the applied stress, matrix
composite hydrogel, a dog-bone shaped tensile strength and fibers were equally deformed without any interfacial
specimen with uniaxial oriented continuous epoxy fiber slipping between them. The reinforced fibers experience
[95]
was successfully fabricated as shown in (Figure 7C). a greater stress than the hydrogel matrix . So far, these
The printed composite hydrogels showed a combination studies have only demonstrated the feasibility of 3D
of properties in between pure hydrogel and epoxy resin, printing for fiber-reinforced composite hydrogel, but the
and its elastic modulus, failure strength, failure strain further development of composite 3D printing techniques
properties were gradually increased by increasing the is crucial before they can be applied to various tissue
relative volume of epoxy fibers. A noticeable finding engineering applications such as biofabrication of skin,
in this study is that there is no limitation of fiber muscle, tendons, and cartilage in the near future.

Figure 7. (A) Schematic images of cellulose short fiber alignment during the 3D printing (reproduced with permission from [92].
Copyright 2016, Macmillan Ltd). (B) Overview of 3D printing process of PLA nanofiber-alginate hydrogel composite, and its internal
structure (reproduced with permission from [93]. Copyright 2016, ACS Publications). (C) Schematic image of the fabrication of hydrogel
composite tensile specimen, and its photographs with different Emax volume fractions (reproduced with permission from [95]. Copyright
2014, ACS Publications).

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