After soft tissues, bone, drug delivery and packaging, PLA aims at blood

• The family of lactic acid-based aliphatic polyesters is much larger than generally believed.
• Outstanding interrelated macromolecular structures, morphologies and degradation characteristics.
• Stereocopolymers more versatile than homopolymers to fulfil requirements of specific biomedical applications.
• Bioresorbable stents made of semi-crystalline PLAs are now implanted in humans.
• Albumin may be more efficient than pegylation to minimize protein adsorption on PLA surfaces.

Natural polymeric materials have been used for thousands of years by humans, including in medicine. However, such materials lacked reproducibility and presented risks of immunogenicity in the case of therapeutic applications. Polyesters derived from lactic acid enantiomers have been extensively investigated in medicine to make various devices like bone plates and screws, pins, staples, etc., or to serve as matrices of implants, micro- and nanoparticles in pharmacology, and more recently to replace biostable plastics in some of their environmental applications. Prior to extend this large spectrum to blood and stenting, structural and degradation particularities that make lactic acid-based polymers suitable for blood and stenting are recalled. The clues to select a stereocopolymer instead of the homopoly(l-lactic acid) to make a bioresorbable stent are discussed in comparison with stenting requirements. Occasionally, the contact of a stent with blood generates the formation of thrombi. The first event is always protein deposition with possible activation of the coagulation cascade and of defence proteins of the complement. In a recent work, the adhesion of model proteins (albumin, fibrinogen and γ-globulins) at physiological concentration was investigated using Optical Waveguide Lightmode Spectroscopy (OWLS). Under the selected model conditions, it was shown that pegylation minimized albumin deposition but did not exclude proteins totally. In contrast, albumin deposited first on any surface, including a pegylated one, precluded any further deposition of the other proteins. This unexpected finding may be of great interest to improve the hemocompatibility of surfaces in contact with blood like those of stent struts.

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