LR White Resin

LR White

Resin with initiator (BPO) packaged separately. Accelerator 18185 can be used for cold-cure (room temperature). Heat cure is 24 hours between 50°C and 65°C. Gelatin capsules are recommended for temperatures below 60°C. Tightly closed BEEM® Capsules and PTFE Molds with ACLAR® as cover (Cat. No. 10506 or 10508) work well at 65°C. Widely used because of excellent immunolabeling results. LR White is a polar, monomer polyhydroxylated aromatic acrylic resin (see PTFE Molds).

Sections from LR White appear "bumpy" in contrast to Epon resin sections. It is possible that Epon links covalently to tissue proteins while LR White links more weakly. "LR White appears to act in a manner similar to ice in a freeze-fractured specimen."17 A. Yamamoto and Y. Tashiro, using AFM, found a strong relief surface on LR White sections, 3-4nm on average. Depressions ranged from 6 to 30nm. Protrusions could be seen on the complimentary surface. Epon sections show relatively smooth surfaces.18 Micrographs appear similar to freeze-etched images but scaled to nm instead of µm. Viscosity ~= 8cP

Landmark Paper, Freeze-Fracture
Steere RL: Electron microscopy of structural detail in frozen biological specimens. J Biophys Biochem Cytol, 3, pp 45-60, 1957

Newman GR: Use and abuse of LR White. J. Histochem, 19, 118, 1987.
Newman GR: LR White embedding medium for colloidal gold methods. In: Colloidal Gold: Principles, Methods, and Applications, V. 2, (Hayat MA, ed)