Biomer extracted

In Vivo Studies. Segments of bovine-implanted Biomer LVAD bladders were obtained from researchers at the Thermo Electron Corporation. Segments that possessed observed calcifications were also obtained. In addition, a control bladder sample, steam sterilized at 121.1°C for 3 h, was obtained. Samples were vacuum dried at 50°C for 24 h, followed by a 24-h CHC13 solvent extraction. Extract solutions were reduced to 1 mL prior to gas chromatographic (GC) analysis. 

Solvent Extraction Studies. Techniques necessary to detect lipid species extracted from in vitro and in vivo exposed Biomer were developed. Extractions with a nonpolar swelling solvent (e.g., CHC13) employing a soxhlet apparatus were performed to extract preferentially lipophilic biological components from Biomer or previously isolated neointimal samples. Experimentation demonstrated the high solubility in chloroform of polymer-derived monomeric and oligomeric components. A separation of lipids from these components was therefore required. 

The effectiveness of solvent extraction was evaluated by a lipid-doped polymer study. Selected lipids were dispersed in Biomer. Then, two sample films, one containing 1 mg, the other 10 mg of palmitic acid, cholesterol, and tripalmitin were cast from two consecutive castings each of 10% Biomer in dimethylacetamide (DMAC). Lipid concentrations of the 1-mg- and 10-mg-doped samples were calculated to be 0.1% and 1%, respectively. Following casting, a soxhlet extraction and quantitative analysis of extracted lipids were performed. The final extracted concentrations were compared with initial solution concentrations, resulting in an extraction efficiency ratio for each type of component. 

Figure 4. Chromatograph of CHCl3 extract of steam-sterilized Biomer bladder. Column conditions 1% Dexsil 300 100°-350°C at 8°C/min and carrier—30 mL/min helium.

In Vivo Analytical Results. Indications of the presence of lipids at or within the polymer surface of bovine-implanted Biomer LVAD bladders and calcified neointimal areas were observed in GC solvent-extraction analyses. In addition, concentrations of polymer-derived species extracted from the Biomer bladder were detected. Although analytical techniques were effective in selectively separating lipids from extracted polymer components,... 

Figure 5. Weight of lipids CHCl3 extracted from Biomer in vitro. Key A, palmitic acid , linoleic acid and , cholesterol.

Figure 6. Reproduction of chromatographs from in vitro CHCl3 extractions (top) Biomer 3 days in vitro and (bottom) Biomer 1 year in vitro. Column conditions 1% Dexsil 300 100°-350°C at 15°Clmin and carrier—30 mL/min helium. Key 1, palmitic acid 2, linoleic acid 3, cholesterol 4, cholesterol acetate 5, cholesterol palmitate and 6, tripalmitin.

As previously mentioned, in vitro studies demonstrated a selectivity of Biomer for free LCFA s extraction of in vivo samples would not be expected to extract identifiable concentrations of these species because of their susceptibility to calcium complexation. 

Polymer-derived monomeric and oligomeric species are readily extractable from Biomer LVAD bladders. Lipid sorption definitely occurs in vitro on/in various elastomers presently being used or considered for LVAD or AHD applications. Apparently, lipid sorption does occur in vivo, and may be involved in surface calcification observed on both smooth and textured... 

Table 3. Effect of Heterogeneous Halogenation (20 min) on Extraction of Biomer Pro-stheses in Ethanol... 

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