3D printing of biological tissues has been of increasing interest to the biomaterials community in part because of its potential to produce spatially heterogeneous constructs. Such technology is particularly promising for orthopedic applications, which require the generation of complex geometries to match patient anatomy and complex microstructures to produce spatial heterogeneity and anisotropy. Prior research has demonstrated the capacity to create precisely shaped 3D printed constructs using biocompatible alginate hydrogels. However, alginate is extremely compliant and brittle, and high-density collagen hydrogels could be a preferable option for load-bearing applications. This research focused on developing and evaluating a method of printing soft tissue implants with high-density collagen hydrogels using a commercially available 3D printer, modified for tissue-engineering purposes. The tissue constructs, seeded with primary meniscal fibrochondrocytes, were evaluated using measures of geometric fidelity, cell viability, mechanical properties, and fiber microstructure. The constructs were found to be mechanically stable and were able to support and maintain cell growth. Furthermore, heterogeneous 3D-printed constructs were generated, consisting of discrete domains with distinct mechanical properties.

An auxetic conductive cardiac patch (AuxCP) for the treatment of myocardial infarction (MI) is introduced. The auxetic design gives the patch a negative Poisson’s ratio, providing it with the ability to conform to the demanding mechanics of the heart. The conductivity allows the patch to interface with electroresponsive tissues such as the heart. Excimer laser microablation is used to micropattern a re-entrant honeycomb (bow-tie) design into a chitosan-polyaniline composite. It is shown that the bow-tie design can produce patches with a wide range in mechanical strength and anisotropy, which can be tuned to match native heart tissue. Further, the auxetic patches are conductive and cytocompatible with murine neonatal cardiomyocytes in vitro. Ex vivo studies demonstrate that the auxetic patches have no detrimental effect on the electrophysiology of both healthy and MI rat hearts and conform better to native heart movements than unpatterned patches of the same material. Finally, the AuxCP applied in a rat MI model results in no detrimental effect on cardiac function and negligible fibrotic response after two weeks in vivo. This approach represents a versatile and robust platform for cardiac biomaterial design and could therefore lead to a promising treatment for MI.

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