A tissue cassette assembly includes a housing having a recess formed therein, and a compressible reservoir disposed partially or wholly inside of, or otherwise attached in fluid communication with, the housing recess, the compressible reservoir containing a tissue embedding material. The tissue cassette further includes a port disposed in the housing, the port in fluid communication with the compressible reservoir at one end and terminating in a sample cavity at another end. During operation, the compressible reservoir is compressed or squeezed to release the tissue embedding material into the sample cavity containing the biological sample.