Hi Xuan,

Look these papers, inside them you should find your response. Indeed, the two possibilities are applied, but I think that  a transition part bending from deep layer to superficial layer is the technique most developed (or more adapted) in this case.  

Best regards.

http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4126138/

http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3445147/

http://www.ncbi.nlm.nih.gov/pubmed/18767972