User blog comment:Xilinoc/Ch. 554 - Desperate Lights/@comment-5698464-20131023182528/@comment-5398287-20131028011409

Well, Aizen DID get hit the first time, but he adjusted afterward because plot. If you're referring to how the wound on his shoulder wasn't there afterward, he had the Hogyoku implanted in him, and that healed all of the wounds he sustained in all of his battles fairly quickly.