As I know, PRISMA is a checklist dedicated to appropriately address all required items in the systematic review / meta-analysis. It is a form of guideline if you follow it, your work can be assessed very high. However, if you plan to perform risk of bias evaluation of studies you want to include into review, you should find appropriate scale. Look at the Cochrane Handbook, there are a couple of tools you can used.
In Vitro Studies are not included in the Evidence based Pyramid.. So even each report that you included were done with a high methodological design, they don't bellow at the hierarchy of the actual evidence.