The study of plasma neutral lipid sorption by cyclically flexed biomedical elastomers
Description
The sorption of lipid by polymeric biomaterials has been shown in numerous cases to adversely affect their function and properties. Imbibement of anionic lipids by blood contacting polyurethane elastomers has been suggested to initiate the onset of observed mineralization on smooth-surfaced, blood contacting biomaterials, particularly in regions of high strain. An in vitro study has been designed to determine whether the subjection of biomedical elastomers to either cyclic or static strain while simultaneously immersed in a lipid containing media enhances plasma lipid uptake relative to static controls. In addition to adult bovine serum, materials were exposed to a microemulsion consisting of the lipid composition, solution concentration, and size ($$ static strain $>$ static control. Lipid uptake after 14 days of testing was in the order PEUU $>$ PDMS $>$ PEU $>$ PAFP. Subjecting the PEUU samples to flexation testing in the VLDL-analog microemulsion also had a deleterious effect on the mechanical properties of the material with observed reduction in the toughness and initial modulus of the material. Analysis of the calcifiability of the cyclically flexed, lipid imbibed surfaces was performed by cyclic strain of these samples while immersed in a tris-buffered metastable calcium solution. Assay of sorbed calcium on the lipid imbibed surface versus controls revealed higher calcium precipitation in lipid exposed samples versus controls in all the test elastomers with the exception of the PEUU sample. Scanning electron microscopy of the cyclically flexed serum-exposed PEUU surfaces revealed the presence of a significant degree of surface degradation. It is proposed that such degradation is responsible for the high degree of lipid sorption and calcium imbibement in these materials when under cyclic flexation. These studies illustrate a simple method for assessing lipid and calcium sorption of novel biomaterials as well as monitoring their resistance to degradation in a physiological media