We need to see Splinter and Mikey interact more because as of now it kind of seems like Splinter doesn't like Mikey to much. Splinter becomes easily annoyed with him and didn't seem to worried when Mikey was brought back to the lair unconscious, all he did was feel Mikey's forehead wonder where Leo was and head back to his room. Mikey's also the only turtle who Splinter hasn't had a one-on-one conversation with.