Bioprinting has exciting prospects for printing three-dimensional (3-D) tissue 
constructs by delivering living cells with appropriate matrix materials. 
However, progress in this field is currently extremely slow due to limited 
choices of bioink for cell encapsulation and cytocompatible gelation mechanisms. 
Here we report the development of clinically relevant sized tissue analogs by 
3-D bioprinting, delivering human nasal inferior turbinate tissue-derived 
mesenchymal progenitor cells encapsulated in silk fibroin-gelatin (SF-G) bioink. 
Gelation in this bioink was induced via in situ cytocompatible gelation 
mechanisms, namely enzymatic crosslinking by mushroom tyrosinase and physical 
crosslinking via sonication. Mechanistically, tyrosinases oxidize the accessible 
tyrosine residues of silk and/or gelatin into reactive o-quinone moieties that 
can either condense with each other or undergo nonenzymatic reactions with 
available amines of both silk and gelatin. Sonication alters the hydrophobic 
interaction and accelerates self-assembly of silk fibroin macromolecules to form 
β-sheet crystals, which physically crosslink the hydrogel. However, sonication 
has no effect on the conformation of gelatin. The effect of optimized rheology, 
secondary conformations of silk-gelatin bioink, temporally controllable gelation 
strategies and printing parameters were assessed to achieve maximum cell 
viability and multilineage differentiation of the encapsulated human nasal 
inferior turbinate tissue-derived mesenchymal progenitor cells. This strategy 
offers a unique path forward in the direction of direct printing of spatially 
customized anatomical architecture in a patient-specific manner.