Mermaid diagram line break
It appears you can use <br> instead:
mermaid("graph TB A[GE Solution]-->C{ } B[GA Solution]-->C{ } C{ }-->D[Stir 10 mins at 500 r/min] D[Stir 10 mins at 500 r/min]-->E[Homogenisation at 10000 r/min] E[Homogenisation at 10000 r/min]-->F(Stir 10 min 450 r/min <br> Complex coacervation) ")