Delivery of Cas9, sgRNA, and associated complexes into cells can occur via viral and non-viral systems. Electroporation of DNA, RNA, or ribonucleocomplexes is a common technique, though it can result in harmful effects on the target cells.[43] Chemical transfection techniques utilizing lipids and peptides have also been used to introduce sgRNAs in complex with Cas9 into cells.[44][45] Types of cells that are more difficult to transfect (e.g. stem cells, neurons, and hematopoietic cells) require more efficient delivery systems, such as those based on lentivirus (LVs), adenovirus (AdV), and adeno-associated virus (AAV).[46][47][48]