In Vitro Calcification Evaluation of Polycarbonate Urethane-Impact of Production Processes

Abstract

Background: Heart valve diseases remain a leading cause of death in industrialized nations. Polycarbonate urethane (PCU) is a promising material for heart valve prostheses due to its biocompatibility and low calcification tendency. However, the impact of processing methods on calcification remains unclear.

Methods: PCU patches were fabricated via hot pressing or solution casting. Both groups (n = 3 each), along with bovine pericardium patches as positive controls (n = 3), were incubated for 10 weeks in a custom in vitro calcification fluid. Calcification, cytocompatibility, and material properties were assessed using light and electron microscopy, infrared spectroscopy, and gel permeation chromatography (GPC).

Results: Calcification was observed in hot-pressed PCU and control patches but not in solution-cast PCU. Both PCU types showed comparable cytocompatibility. Spectroscopy and GPC revealed chemical and structural changes in hot-pressed PCU, likely promoting calcification.

Conclusion: Hot pressing alters the chemical structure of PCU and increases its calcification propensity without affecting cytocompatibility. These findings highlight the importance of process control and in vitro screening during heart valve material development.

Keywords: biomaterials; electron microscopy; hot pressing; patch testing; prosthetic heart valve materials; surface analysis.

FIGURE 1

Exemplary structure of a polyurethane carbonate. Highlighted in green are the urethane groups while the carbonate group is highlighted in blue. The residuals R ₁ und R ₂ can be equal but don't have to be. R ₃ is the residual group of the employed isocyanate during synthesis. R ₁–R ₃ can be varied depending on the application of the final product. [Color figure can be viewed at wileyonlinelibrary.com]

FIGURE 2

Overview of the employed patches before testing. Top row, the PCU‐patches made from solution. Middle row, the patches made by hot‐pressing. Bottom row, the pericardium patches used as control. [Color figure can be viewed at wileyonlinelibrary.com]

FIGURE 3

Comparison of the patches' back sides after the test. Patches 1, 4, 5, and 6 show calcifications. Only Patch 2 does not show calcification inside the region of interest. [Color figure can be viewed at wileyonlinelibrary.com]

FIGURE 4

Calcification of the pericardium patches. Pericardium Patch 2 is shown with calcification in 10× (top left). The calcification is referenced via arrows in the close‐up images in 50× magnification. [Color figure can be viewed at wileyonlinelibrary.com]

FIGURE 5

Overview of the residual material at 50× magnification. Top row patch material from solution before testing (left) and after testing (right). Bottom row hot‐pressed patch material before testing (left) and after testing (right).

FIGURE 6

Calcification on Patch 4 after 10 weeks of testing—Light microscopy (20×) linked to the SEM image (100×). [Color figure can be viewed at wileyonlinelibrary.com]

FIGURE 7

Mean transmission spectra of the residual material from the hot‐pressed patches and the ones made from solution. [Color figure can be viewed at wileyonlinelibrary.com]

FIGURE 8

Microscopy results of live/dead staining after 3 days of cytocompatibility testing of solution‐casted and hot‐pressed PCU patches as well as untreated cells (positive control) and Triton X‐100–treated lysed cells (negative control) (100× magnification). [Color figure can be viewed at wileyonlinelibrary.com]