Improved Biocompatibility of Intra-Arterial Poly-L-Lactic Acid Stent by Tantalum Ion Implantation. Confocal laser scanning microscopy (upper figure) shows larger numbers of adhered endothelial cells on images tantalum-implanted poly-Llactic acid (PLLA) surfaces (upper row) than bare surface (lower row). The tantalum-implanted poly-Llactic acid (PLLA) surfaces shows higher surface coverage of endothelial cells (lower figure).