Masayuki Yamato, Satoshi Tsuneda and Teruo Okano would like to retract this protocol after concerns were raised by the community about some of the figures. Specifically, concerns were raised that the fourth graph in Figure 5a and the first graph in Figure 5b look very similar, and some of the error bars look unevenly positioned. Masayuki Yamato, Satoshi Tsuneda and Teruo Okano have been unable to locate some of the raw data to verify these figures and are no longer confident in the paper's results. Given that these results are key to demonstrating the reliability and reproducibility of the protocol, these authors wish to retract the protocol, and they sincerely apologize for the adverse consequences that may have resulted from its publication. Haruko Obokata could not be reached by the journal for comment on the retraction.