Filtration directly into a cassette through a lens paper while processing biopsies is the safest and fastest method. An option for filtration is to use the core of a disposable diaper as an underlying background.
I use a square or rectangular pad that is cut from a baby diaper and placed on the bottom of an empty standard glass slides box. A cassette with a moistened lens paper is placed on the wet diaper fragment. The cassette lid rests on the border of the box, freeing my hands to operate. The excess water is then discarded. One pad is effective for four or five filtrations.
Here is a short remainder of a disposable baby diaper design in regard to filtration. The acquisition layer of a diaper works like blotting paper, while the core of a diaper includes granular super-absorbent hydrophilic polymer (sodium polyacrylate with sodium carboxylate groups). In contact with water the sodium detaches leaving only carboxyl ions. Being negatively charged, these ions repel one another so that the polymer unwinds and absorbs water. Water becomes slightly gelled when passed through the acquisition layer unraveling the polymer net. The polymer transforms in numerous swollen granules like white caviar. The wet polymer core works as a pump soaking water from the filtration surface. The diaper fragments become engorged slowly.
The brand of the diaper does not matter substantially. Ironically, the cheapest brands, like Happies, work the best. The speed of filtration is sometimes limited by the permeability of the lens paper (bone marrow aspirates, for example, filtrate slowly).
If a manufacturer were to pick up production of a diaper- like filtration pad for surgical pathology, it would be a good idea to seam 2 cm from the core to leave space for the polymer to expand. Since diaper rash is not an issue, it might be expedient to experiment with the osmotic gradient and capillarity of the acquisition layer in order to hasten the filtration process. Neither urine, nor fixative solutions are clear water. The salts diminish the osmotic gradient that makes the polymer core less absorbent. The porous acquisition layer like of a Ketlax sanitary napkin looks as preferable.
Placed in the cassette, the material like Kimberly-Clark surgical mask’s internal layer can increase the speed of filtration due to better permeability than the lens paper. (See FILTRATION IN SURGICAL PATHOLOGY in the link Grossing Techniques). The combination of a diaper pad with permeable material in the cassette can make filtration efficient and fast. The ball for developing of a kit for filtration in the cassette is in the manufacturers court.
The employment of a diaper- like material for filtration in surgical pathology may be a methodological step ahead. This new method might make filtration of biopsy specimen a standard procedure in the vast majority of biopsies. The main advantage is the complete submission of the specimen.