Collagen is the primary component of the extracellular matrix in the human body for its function of structure holding, cell attaching and signal transmission inside the extracellular matrix. But the resolution of 3D printing object is still a challenge.
Lee et al. presented a method to 3D-bioprint collagen using freeform reversible embedding of suspended hydrogels (FRESH) to engineer components of the human heart at various scales, from capillaries to the full organ, which can receive the precisely structure and materials component control of part of human heart (up to 20 ㎛).
Link: https://science.sciencemag.org/content/365/6452/482