Mercox-methylmethacrylic acid mixture penetrates into cells. A scanning and transmission electron microscopic study

During preparation of vascular casts using mixtures of Mercox and methylmethacrylic acid for scanning electron microscopy, occasionally irregular structures were observed adhering to otherwise well prepared corrosion casts. These artifacts were further analyzed in sections of cast preparations. The bizarre-shaped structures varied in size and were often tightly connected to vascular casts; they withstood KOH maceration and cleaning with formic acid. The persistence of biological material, connective tissue fibers and cells or cellular fragments, became obvious in ultrathin sections. Transmission electron microscopy also showed inhomogeneity of the polymerized casting medium (Mercox-methylmethacrylate mixture; v/v: 4:1). An unidentified compound of this resin was found to penetrate into endothelial cells, blood cells, and even neighboring structures. In this way, biological material was infiltrated by a component of the resin, withstood maceration, and remained as mummified structure. This phenomenon was not generalized. Supposedly, phase separation occurring in a certain stage of resin polymerization provides an unidentified less hydrophobic component that is capable to infiltrate and mummify cells. In addition, polymerization leads to increased temperature which facilitates diffusion and reduces surface tension between this compound and the aqueous phase. The significance of higher temperature for tissue mummification becomes evident as pulmonary tissue most frequently revealed such artifacts. Alveolar air content serves as an isolating medium that reduces heat conduction from the polymerizing resin.