WO2018158684 – Filter for the exchange of heat and moisture for application in the medical field and procedure for the production thereof

RIF.: 102017000022625 Inventors: Sandri Monica, Sprio Simone, Tampieri Anna Owner: Consiglio Nazionale delle Ricerche Priority Data: 28/02/2017 Description The present invention refers to a filter, made entirely with natural and biodegradable materials, for the protection of the respiratory tract of patients in the medical-surgical field; the invention also refers to the process for making the filter. Claims: 1. Process for preparing a material useful for the production of 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 thus obtained in such quantities as to obtain a weight ratio gelatin:chitosan from 80:20 to 50:50, preferably 70:30, gently stirring the resulting solution to avoid the formation of a foam until obtaining a homogeneous solution, and subsequently diluting the mixture to obtain a total polymer concentration of from 2 to 4%, preferably 2%, by weight; c’) optionally, adding a chemical crosslinker to the solution obtained in step c); d) pouring the solution prepared in step c) or 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); d’) in case step c’) has been carried out, keeping said contain closed until obtaining a hydrogel; e) freeze-drying, inside said container, the solution obtained in step c) or the hydrogel obtained in step d’) according to the following phases: – freezing the hydrogel to a temperature of from -20 to -60 °C, preferably -40 °C, carried out by placing the bottom of the container in contact with a refrigerating system; – primary drying by heating with a speed 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; – secondary drying by heating with a speed 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; f) in case steps c’) and d’) have not been carried out, subjecting the freeze-dried product obtained in step e) to a crosslinking treatment by thermal dehydration. 2. Process according to claim 1, wherein the crosslinking agent employed in step c’) is selected from 1,4-butanediol diglycidyl ether (BDDGE), glutaraldehyde, tannic acid and genipin, in amounts from 0.5% to 4%, preferably 1%, compared to the sum of the weights of chitosan and gelatin. 3. Process according to any one of the preceding claims, wherein the container in which the hydrogel is formed has the bottom made with steel, copper or silicon, and the walls made with a plastic, Teflon or glass. 4. Process according to claim 1 in which step f) is carried out with a heat treatment which consists in subjecting the freeze-dried material to a temperature from 140 to 160 °C, preferably 160 °C, at a pressure between 0.001 mbar and the atmospheric pressure and for a duration between 24 and 48h. 5. Process according to any one of the preceding claims in which, prior to the introduction of the solution in the container in which the hydrogel is formed, in the same container is introduced a paramagnetic core comprising a hydroxyapatite in which an amount of between 2 and 40 atomic% of calcium is replaced by iron present in both of its oxidation states (II) and (III), produced by a process which comprises the following steps: g) preparing an aqueous solution containing a precursor of calcium, at least one soluble salt of iron (II) and at least one soluble salt of iron (III); h) preparing an aqueous solution containing a water soluble compound of phosphorus, preferably phosphoric acid; i) preparing an aqueous solution containing a precursor of one or more hydrophilic polymers; j) slowly adding the phosphorus compound solution to the solution containing the precursor of calcium and the iron salts, obtaining a suspension; k) optionally, immediately adding the solution obtained in step i) to the suspension obtained in step j); l) if step k) has been carried out, allowing the system to react at a temperature between ambient T and 70 °C for a time between 1 and 5 hours; k’) in case steps k) and l) have not been carried out, allowing the system obtained in step j) to react at a temperature between ambient T and 70 °C for a time between 1 and 24 hours; and l’) if step k’) has been carried out, mixing the suspension obtained with the aqueous solution obtained in step i); m) subjecting to a freeze-drying treatment the product obtained in step 1) or in step 1’); n) immersing the freeze-dried product in a CaCl2 solution at a concentration between 0.5 and 1.5 M for a period of time between 15 and 45 minutes, at the end of which washing the device by immersion in distilled water; o) again subjecting to freeze-drying treatment the material. 6. Process according to claim 5, wherein sodium alginate is used as hydrophilic polymer. 7. Process according to any one of claims 5 or 6 in which the reactants are employed in amounts such that the weight ratio between the magnetic core and the surrounding polymeric material is between 40:60 and 80:20. 8. Process according to any one of the preceding claims in which, at the end of the process, between 3 and 5 mm of the upper face and of the lower face of the obtained product are mechanically removed. 9. HME filter obtained according to the process of any one of claims 1, 2, 3, 4 and 8, having a porosity between 80 and 98% and pores of diameter between 100 and 350 μm and in which the pores have the shape of channels open at their ends and essentially parallel to each other. 10. HME filter obtained according to any one of claims 5 to 8, comprising: – a central core formed by a porous matrix made with one or more hydrophilic polymers, containing particles of modified hydroxyapatite, in which a quantity between 2 and 40 atomic% of calcium is replaced by iron present in both of its oxidation states (II) and (III); and – a shell surrounding the core formed by chitosan and a natural gelatin, having a porosity between 80 and 98% and pores of diameter between 100 and 350 μm, and in which the pores have the shape of channels open at their ends and essentially parallel to each other. Contacts: Monica Sandri