Filter for the exchange of heat and moisture for application in the medical field and procedure for the production thereof

Process for preparing a material useful for the production of Heat and Moisture Exchange (HME) filters, which comprises the following steps:

• a) preparing an acidic aqueous solution of chitosan in a concentration from 1 to 2.5% by weight;
• b) preparing an aqueous solution of a gelatin of animal origin in a concentration from 2.5 to 5% by weight, operating at a temperature between 40 and 50° C.;
• c) mixing the two solutions from steps a) and b) in such quantities as to obtain a mixture having a weight ratio of gelatin:chitosan from 80:20 to 50:50, gently stirring the mixture to avoid the formation of a foam until obtaining a homogeneous solution, and subsequently diluting the homogeneous solution to obtain a polymer solution having a total polymer concentration of from 2 to 4% by weight;
• d) pouring the polymer solution prepared in step c) into a container with the bottom made of a material having thermal conductivity greater than or equal to 15 W/(m·K) and side walls made of a material having thermal conductivity less than or equal to 1 W/(m·K);
• e) freeze-drying, inside said container, the polymer solution obtained in step c) according to the following phases:
• freezing the polymer solution to a temperature of from −20 to −60° C. by placing the bottom of the container in contact with a refrigerating system;
• primary drying by heating with a rate between 2 and 8° C./h up to a temperature between −5 and −10° C., operating at a pressure between 0.001 mbar and atmospheric pressure and;
• secondary drying by heating with a rate between 1 and 5° C./h up to a temperature between 15 and 20° C., operating at a pressure between 0.001 mbar and atmospheric pressure;
• and
• f) a crosslinking treatment consisting of a step of subjecting the freeze-dried product obtained in step e) to a thermal dehydration.