Complex sentence: There are currently 3 biomaterial and tissue engineering approaches for the treatment of MI, but these are in an even earlier stage of medical research, so many questions and issues must be addressed before they can be applied to patients.
Split into simpler sentences: There are currently 3 biomaterial and tissue engineering approaches for the treatment of MI, but these are in an even earlier stage of medical research. Many questions and issues must be addressed before they can be applied to patients.