Described are medical devices which are or can be used to form tubular medical devices, and related methods. Preferred devices include tubular grafts of biomaterial having lumen walls which present no seam edge that traverses the entire length of the lumen, illustratively including devices having lumen walls which have a discontinuous seam presenting multiple seam edges. Such a device may include a tubular structure formed by inserting a plurality of extensions of a biomaterial sheet through a plurality of corresponding apertures of the sheet.