In an example of the method, a functionalized coating layer is applied in depressions of a patterned flow cell substrate. The depressions are separated by interstitial regions. A primer is grafted to the functionalized coating layer to form a grafted functionalized coating layer in the depressions. A hydrogel is applied on at least the grafted functionalized coating layer.

In an example of the method, a functionalized coating layer is applied in depressions of a patterned flow cell substrate. The depressions are separated by interstitial regions. A primer is grafted to the functionalized coating layer to form a grafted functionalized coating layer in the depressions. A hydrogel is applied on at least the grafted functionalized coating layer.

In an example of the method, a functionalized coating layer is applied in depressions of a patterned flow cell substrate. The depressions are separated by interstitial regions. A primer is grafted to the functionalized coating layer to form a grafted functionalized coating layer in the depressions. A hydrogel is applied on at least the grafted functionalized coating layer.

In an example of the method, a functionalized coating layer is applied in depressions of a patterned flow cell substrate. The depressions are separated by interstitial regions. A primer is grafted to the functionalized coating layer to form a grafted functionalized coating layer in the depressions. A hydrogel is applied on at least the grafted functionalized coating layer.