where, r1 and r0 are the entrance radius
and exit radius of the needle, respectively; P is the pressure exerted
and θ is the angle between the needle and the deposition surface. In
addition, τy, n, and K are the yield stress, flow index,
and viscosity index, respectively. Note that n and K are related to
temperature and θ is related to the length of the needle. As previously
analysed by extruding-based bioprinting for pressure
drop
within nozzle diameter Ds and nozzle length L[39],
the flow rate can be determined by the following equation: