A METHOD FOR PREPARING A NON-FIBROUS POROUS MATERIAL

Abstract: A method for preparing a non-fibrous porous material essentially consisting of one or more hydrophilic polymers and/or pharmaceutical medicaments comprising forming an aqueous solution, sol or gel comprising one or more hydrophilic polymers and/or pharmaceutical medicaments, freezing the solution, sol or gel and extracting the frozen water selectively using a hydrophilic organic solvent being miscible with water at a temperature below 5 DEG C at which temperature the solvent is not able to dissolve the frozen solutes, leaving the non-fibrous material in a solid, porous form.

Description: TITLE A method for preparing a non-fibrous porous material FIELD OF THE INVENTION The present invention relates to a method for preparing a non-fibrous porous ma¬ terial essentially consisting of one or more hydrophilic polymers and/or pharma¬ ceutical water-soluble medicaments BACKGROUND OF THE INVENTION Non-fibrous porous materials essentially consisting of one or more hydrophilic polymers and/or pharmaceutical water-soluble medicaments and methods for preparing such materials is disclosed in WO 95/05204 and in JP 01-011 141 One method for preparing such products using a hydrous solution of a hydro¬ philic polymer such as casein, gelatine, collagen, albumin, fibroin, cellulose, starch, agar, sodium carboxyl methyl cellulose, methyl cellulose, polyvinyl alco- hoi, polyacrylic acid, or polyacrylamide is disclosed in JP 01-011 141 According to JP 01-011141 , surfactant of non-ionic, cationic, anionic or amphoteric type is added to the hydrous solution and then freeze-drying is carried out The polymer is dispersed in water to a concentration of 0 05 to 50%, and the surfactant is used in amounts of from 0 5-100% Another method or preparing such products using a hydrous solution of a hydro¬ philic polymer such as a synthetic hydrophilic polymer, a polysaccharide or a bio¬ logical hydrophilic polymer is disclosed in WO 95/05204 According to WO 95/05204 one or more pharmaceutical medicaments and/or hydrophilic polymers are dissolved in water to provide a solution or a sol, a freeze plate is pre- nucleated by passive condensation or by evaporating or atomising water or the aqueous solution of the pharmaceutical medicaments and/or hydrophilic poly¬ mers and/or salts, the solution of one or more pharmaceutical medicaments and/or hydrophilic polymers is provided on the pre-nucleated freeze plate, the temperature of which is to be kept below the freezing point of the atomised water or solution the solution is frozen to provide an ice sheet comprising the pre- nucleated frozen material, the sheet is freeze dried, and the resulting sheet is op¬ tionally cut into pieces of suitable sizes Freeze drying is a time-consuming process and is therefor often being a bottle- neck in a production line, it has high requirements of capital and is a highly energy-consuming process Thus, there is an incentive to try to circumvent freeze drying if possible EP 343 456 discloses dehydrating of macromolecular substances by freezing a hydrated gel or sol which is then immersed and thawed in a hydrophilic solvent generally at a temperature above +5°C Such process is not suitable for dehy¬ drating frozen solutions of macromolecular substances being easy to redissolve in water and would not permit the obtaining of a controlled porous structure It has now surprisingly been found that it is possible to avoid the freeze drying when removing water from frozen solutions of various solutes, especially from frozen solutions of non-fibrous porous materials essentially consisting of one or more hydrophilic polymers and/or pharmaceutical medicaments and to preserve a controlled microporous structure BRIEF DESCRIPTION OF THE DRAWINGS The invention is illustrated disclosed more in detail with reference to the drawings in which Fig 1 shows a photograph of four sheets made by freezing an aqueous solution comprising a sodium alginate and extracting the frozen water selectively using ethanol at -10°C, -5°C and +5°C and by freeze drying, respectively, Fig 2 shows a SEM photograph of the surface of sheet No IS -10°C of Fig 1 extracted at -10°C , Fig 3 shows a SEM photograph of the surface of sheet No IS -10°C of Fig 1 ex¬ tracted at -10°C in a greater magnification, Fig 4 shows a SEM photograph of the surface of sheet No IS -5°C of Fig 1 ex¬ tracted at -5°C, Fig 5 shows a SEM photograph of the surface of sheet No IS -5°C of Fig 1 ex¬ tracted at -5°C in a greater magnification, Fig 6 shows a SEM photograph of the surface of sheet No IS +5°C of Fig 1 ex¬ tracted at +5°C Fig 7 shows a SEM photograph of the surface of sheet No IS +5°C of Fιg 1 ex¬ tracted at +5°C in a greater magnification, Fig 8 shows a SEM photograph of the surface of sheet No IS FD of Fig 1 dehy- drated by freeze drying, Fig 9 shows a SEM photograph of the surface of sheet No IS FD of Fig 1 dehy¬ drated by freeze drying in a greater magnification and Fig 10 shows a graphical representation of a DSC scan for determining the melt¬ ing point of a frozen sheet BRIEF DESCRIPTION OF THE INVENTION The present invention relates, in its broadest aspect, to a method for removing frozen water from a frozen solution, sol or gel of various solutes or solubihsed components, especially from frozen solutions of non-fibrous porous materials es¬ sentially consisting of one or more hydrophilic polymers and/or pharmaceutical medicaments by extraction with a solvent being able to "dissolve" frozen water under conditions leaving the solutes or solubihsed components in an essentially unchanged solid state In principle, the method is applicable for all materials be¬ ing soluble or which may be solubilised in water, but not being soluble in another solvent or solution being liquid at the relevant temperatures for removing the wa- ter from the frozen aqueous solution DETAILED DESCRIPTION OF THE INVENTION In one aspect, the invention relates to a method for preparing a non-fibrous po¬ rous material essentially consisting of one or more hydrophilic polymers and/or pharmaceutical medicaments comprising forming an aqueous solution, sol or gel comprising one or more hydrophilic polymers and/or pharmaceutical medicaments, freezing the solution and extracting the frozen water selectively using a hydrophilic organic solvent being miscible with water at a temperature below 5°C at which temperature the solvent is not being able to dissolve the sol¬ utes, leaving the non-fibrous porous material in a solid, porous form The freezing of the solution, sol or gel may be carried out at a temperature of from -100 to -5°C Preferably, the freezing is carried out at a temperature from -75 to -15°C, more preferred at a temperature from -30 to -20°C The hydrophilic organic solvent being miscible with water but not being able to dissolve the solutes is preferably a lower molecular weight straight or branched or cyclic aliphatic mono or divalent alcohol such as methanol ethanol, propanol or cyclohexanol or ethylene glycol or propylene glycol or an aromatic mono or dialcohol such as benzyl alcohol or phenol or a hydroxyl phenol or a ketone such as acetone or ethyl methyl ketone In one embodiment of the invention one or more hydrophilic polymers and/or pharmaceutical medicaments is/are dissolved in water to provide a solution or sol, a freeze plate is pre-nucleated, the solution of one or more pharmaceutical medicaments and/or hydrophilic polymers is provided on the pre-nucleated freeze plate, the temperature of which is to be kept below the freezing point of the water or solution, the solution is frozen to provide an ice plate comprising the pre-nucleated frozen material and the water is extracted selectively using a hy¬ drophilic organic solvent being miscible with water at a temperature below 5°C at which temperature the solvent is not able to dissolve the solutes, leaving the non-fibrous porous material in a solid, porous form The freeze plate may, according to the invention, e g be pre-nucleated by pas- sive condensation or by evaporating or atomising water or the aqueous solution of the pharmaceutical medicaments and/or hydrophilic polymers and/or salts The aqueous solution to be frozen comprises preferably one or more hydrophilic polymers selected from polyvinyl pyrrohdone (PVP), polyvinyl alcohol (PVA) polyacrylic acids, polyacrylic amide acids, polyethylene oxides, polypropylene ox¬ ides or copolymers thereof, copolymers of polymethyl vinyl ether and maleic an- hydride, collagen, gelatine, and polysaccharides such as chitin/chitosan, starches, alginates, pectm/pectat, gallan, carregenans, glycomannan, Guar gum, and lo¬ cust bean gum, cellulose derivatives, e g sodium carboxymethyl cellulose, hy¬ droxyethyl cellulose, or hydroxypropyl cellulose, proteogiycanes/glycosamino glycanes, e g hyalur onic acid, or chondroitin sulfphate It is preferred that the solution to be frozen comprises one or more polysaccha¬ rides which may give rise to the formation of a non-fibrous material in the ice sheet after the water has started freezing as a pure phase The polysaccharιde(s) is/are preferably alginate in the form of a sodium alginate or a mixture of sodium and calcium alginates In one embodiment of the invention both an exchange of ions and extraction of frozen water is carried out as a combined step This ensures that the ion ex¬ change rendering the frozen solution insoluble in water takes place simultane¬ ously with the extraction The extraction may be carried out at any temperature at which the solvent is not able to dissolve the frozen solutes, leaving the solutes in a solid, porous form The extraction generally carried out at a temperature below the freezing point of pure water, and below the initial melting point of the frozen solutes more pre¬ ferred at a temperature of -5°C or below most preferred a temperature of -10°C or below The degree of ion exchange may optionally be increased by performing a sepa¬ rate further step in which the sheet is wetted with a solution comprising the de¬ sired ions in the same manner as disclosed in WO 95/05204 The initial melting temperature of the frozen solutes is considered the tempera¬ ture at which the slope of a plot the heat capacity of the frozen material versus the temperature as measured by DSC When extracting water from a frozen aqueous sol or solution of sodium alginate it is preferred to carry out the extraction using ethanol comprising calcium chloride in order to exchange the sodium ions with calcium ions in order to transform the alginate into a form not being soluble in ethanol compπsing minor amounts of water The extraction is preferably carried out at a temperature below the initial melting temperature T, of the non-fibrous porous material in order to preserve the struc¬ ture of the solute, e g when preparing non-fibrous porous materials as disclosed In accordance with another aspect of the invention the solution to be fi ozeπ may essentially be based on pharmaceutical medicaments or a mixture of the hydro- phihc polymers mentioned above and pharmaceutical medicaments Suitable pharmaceutical medicaments are for example growth hormones or polypeptide growth factors such as TGF, FGF, PDGF, EGF, IGF-1 IGF-2 and the like In accordance with one aspect of the invention the solution to be frozen com¬ prises a cytochine such as growth hormone or a polypeptide growth factor giving rise to the incorporation of such active substances in a form being apt to local ap¬ plication in a wound in which the medicament may exercise its effect on the wound Cytokines such as growth hormone or polypeptide growth factor may ac¬ tivate local receptors and enhance the wound healing process Furthermore, the material produced in accordance with the invention may com- prise minor amounts of other medicaments such as bactenostatic or bacteπcide compounds, e g iodine, lodopovidone complexes, chloramine chlorhexidine sil¬ ver salts, zinc or salts thereof, metronidazol sulpha drugs and penicillins tissue- healing enhancing agents e g RGD tripeptides and the like, enzymes for cleans¬ ing of wounds, e g pepsin trypsin and the like, cytotoxic agents and proliferation inhibitors for use in for example surgical insertion of the product in cancer tissue and/or other therapeutic agents which optionally may be used for topical application The material produced in accordance with the invention shows the same charac¬ teristics and may be used for the same purposes as the materials disclosed in WO 95/05204, e g in wound treatment products In still another aspect, the invention relates to a method for removing water from an aqueous solution of a solute wherein the solution is frozen and the water is re¬ moved by extraction with a solvent being miscible with water but not being able to dissolve the solutes at the conditions of the extraction In one embodiment this method comprises dissolving one or more hydrophilic polymers and/or pharmaceutical medicaments in water to provide a solution or sol, pre-nucleatmg a freeze plate providing the solution of one or more pharma¬ ceutical medicaments and/or hydrophilic polymers on the pre-nucleated freeze plate, the temperature of which is to be kept below the freezing point of the atom¬ ised water or solution, freezing the solution to provide an ice sheet comprising the pre-nucleated frozen material and extracting the water selectively using a sol- vent being miscible with water but not being able to dissolve the solutes, leaving the solutes in a solid, porous form The pre-nucleation may be effected by passive condensation or by evaporating or atomising water or the aqueous solution of the pharmaceutical medicaments and/or hydrophilic polymers and/or salts, The invention also relates to a non-fibrous porous material whenever prepared by a method of the invention ln the present context growth hormone is intended to designate any growth hor¬ mone which is applicable in the non-fibrous porous material produced in accor¬ dance with the invention such as human, bovine ovine, porcine, equine salmon or tuna growth hormone or analogues or derivatives thereof such as shortened or extended growth hormones such as methionyl growth hormone A growth hor¬ mone is preferably human growth hormone MATERIALS AND METHODS 96% vol ethanol from Danisco Distillers (D D S F) Copenhagen Denmark CaCI 2 »2H 2 0 (3881 ) from Sigma Sorbalg® PH125 sodium alginate from Danisco Ingredients, Brabrand Denmark HDPE net H514 from Smith & Nephew, London, UK EXPERIMENTAL PART EXAMPLE 1 Ice sheets was produced by the following method A base solution waε prepared by dissolving 2 50 g of Sorbalg® PH125 sodium alginate in 97 5 g of distilled H 2 0 After storage at 6-8°C for 10-14 hours the base solution was frozen to an about 4 mm thick ice sheet by the freezing method described in WO 95/05204 A horizontal steel freeze plate was maintained at - 20°C while it was pre-nucleated by spraying droplets of distilled H 2 0 onto the freeze plate When the droplets were frozen - in a layer of about 500 μm - the base solution was poured over the white frost layer and allowed to freeze by a unilateral cooling from the freeze plate at -20°C The ice sheets were stored at -20°C until dehydration Three solvents were prepared for the Ice Extraction ( dehydration) procedure in which the morphology of the sodium alginate in the ice sheets was retained The extraction was carried as follows 1 100 grams of the ice sheet was immersed in 300 grams of solvent 1 in a Petn dish at -10°C and frozen in a Gram TFB 245 freezer The Petn dish was agitated manually every 15 minutes for at least two hours 2 After the ice was dissolved, the wet sheet was removed from solvent 1 Ex¬ cessive solvent was allowed to drain off before the wet sheet was immersed in 300 grams of solvent 2 in a Petn dish at ambient temperature The Petn dish was placed on a shaking table for at least one hour 3 The procedure under 2 above was repeated using solvent 3 4 Before drying 70-75% of the solvent was removed using a suction filter 5 The residual solvent was removed by drying at 60°C for about thirty minutes EXAMPLE 2 A laminate of materials was produced using the same materials and dehydration process as stated as in Example 1 A 2 mm thick layer of the base solution was casted over the white frost On top of this layer, a HDPE net H514 (Smith & Nephew) was placed before the last 2 mm of base solution was casted over the plate The last casting should take place before the freezing front reaches the surface of the first casted layer EXAMPLE 3 Frozen balls of alginate Sodium alginate solution is added dropwise to liquid isobutane at -60 C C (m p -145, b p -10°C) and frozen in the form of balls Isobutane on the frozen balls is 5 evaporated at -10°C Thereafter, the balls are dehydrated by extraction of ice in the same manner as disclosed in Example 1 leaving porous balls of alginate EXAMPLE 4 The experiment of Example 3 is repeated only using liquid nitrogen for the freez¬ ing instead of liquid butane n EXAMPLE 5 Frozen threads or filaments of alginate The experiment of Example 3 was changed in that the sodium alginate solution is added by pouring carefully or passing through a die into the liquid isobutane -60°C (m p -145, b p -10°C) and frozen in the form of threads Thereafter, the 15 threads or filaments are dehydrated by extraction of ice in the same manner as disclosed in Example 1 leaving porous threads of alginate EXAMPLE 6 The experiment of Example 5 is repeated only using liquid nitrogen for the freez¬ ing instead of liquid butane ?n EXAMPLE 7 Four ice sheets were produced by the following method A base solution was prepared by dissolving of 40 0 g of Sorbalg® PH125 in 1960 g of distilled H 2 0 The solution was then stored at 6-8°C for 10-14 hours After storage the solution ice sheets were produced in the same manner as described in Example 2 In 25 this example the freezing plate temperature was -25°C and the final dimension of the ice sheets were 18x34x0 4 cm Tree solvents was prepared for the ice extraction ( dehydration ) Solvent 1 Solvent 2 Solvent 3 Ethanol 96% v/v 70 0 % wt 99 0 %wt 100%wt Dist H 2 0 28 0 %wt CaCI 2 -2H,0 2 0 % wt 1 0 %wt Extraction was carried out at tree different temperatures and as control a sample was freeze-dπed as described in WO95/05204 Process temperatures at the ion exchange process Sample No 1 (IS -10) 2 (IS -5) 3 (IS +5) 4 (IS FD) Dehydration Ice extraction Ice extraction Ice extraction Freeze drying process Solvent 1 -10°C -5°C +5°C ambient Solvent 2 3 ambient ambient ambient ambient 1 An ice sheet was immersed for 2 hours solvent 1 in an agitated cryo bath ( Heto CB 10) kept at the temperature stated Solvent 1 was in excess (5-10 kg) ensuring essentially constant concentration during the extraction process 2 After the ice was dissolved, the wet sheet was drained washed and dried as described in Example 1 steps 2-5 3 The control was dehydrated by freeze drying at a pressure of 1 mbar for 20 hours at a shelve temperature of 40°C After freeze-drying the dehydrated sheet was washed with the three solvents as described above Analysis of morphology of the samples The shape of the four different samples after dehydration is shown i Fig 1 The sheet dehydrated by Ice extraction at -10°C shows the same dimensional stability of the sheet dehydrated by freeze drying whereas the sheet subjected to ice ex¬ traction at -5°C shows distinct shrinkage and the sheet extracted at +5°C shows excessive shrinkage This is confirmed by the scanning electron micrographs is shown in Figs 2-9 Figs 2 and 3 and Figs 8 and 9 show that the resulting sheets obtained by ice extraction at -10°C and freeze drying, respectively are equivalent with respect to morphology and form stability The structure found is in accordance with the structure disclosed in WO 95/05204 with respect lo freeze drying Figs 4 and 5 show that there is a beginning collapsing of the structure when extracting ice at -5°C, and Figs 6 and 7 show that en extensive breakdown of the structure occurs at +5°C Determination of initial melting point Analysis of the initial melting point (T,) of the frozen polysaccharide solution was carried out by a DSC scan at rc/minute from -15 to +2°C using N 2 gas as con¬ trol The result appears from Fig 10 The graph shows an offset melting point at -3 9°C which has to be corrected by -1 5±0 2°C giving an initial melting point of T = -5 4±0 2°C The result of the DSC scan is in accordance with analysis of the morphology of the samples show that if the temperature in the ice extraction bath is kept below T, of the frozen base solution, then extraction of ice using a hydrophilic organic solvent may substitute freeze drying At temperatures above T , ice extraction re- suits in extensive breakdown of the structure, probably due to partial dissolution of the frozen base solution

Claims: CLAIMS 1 A method for preparing a non-fibrous porous material essentially consisting of one or more hydrophilic polymers and/or pharmaceutical medicaments compris¬ ing forming an aqueous solution, sol or gel comprising one or more hydrophilic polymers and/or pharmaceutical medicaments, freezing the solution and extract¬ ing the frozen water selectively using a hydrophilic organic solvent being miscible with water at a temperature below 5°C at which temperature the solvent is not able to dissolve the frozen solutes, leaving the non-fibrous porous material in a solid, porous form 2 A method as claimed in claim 1 comprising dissolving one or more hydrophilic polymers and/or pharmaceutical medicaments in water to provide a solution, sol or gel pre-nucleatmg a freeze plate, providing the solution of one or more phar¬ maceutical medicaments and/or hydrophilic polymers on the pre-nucleated freeze plate, the temperature of which is to be kept below the freezing point of the water or solution, freezing the solution to provide an ice sheet comprising the pre-nucleated frozen material and extracting the water selectively using a hydrophilic organic solvent being miscible with water at a temperature below 5°C at which temperature the solvent is not able to dissolve the frozen solutes, leaving the solutes in a solid, porous form 3 A method as claimed in claim 2 wherein the aqueous solution to be frozen comprises one or more hydrophilic polymers selected from polyvinyl pyrro done (PVP), polyvinyl alcohol (PVA), polyacrylic acids, polyacrylic amide acids, poly¬ ethylene oxides, polypropylene oxides or copolymers thereof, copolymers of po¬ lymethyl vinyl ether and maleic anhydride, collagen, gelatine, and polysaccharides such as chitin/chitosan, starches, alginates, pectin/pectat, gal- Ian, carregenans, glycomannan, Guar gum, and locust bean gum, cellulose de¬ rivatives, e g sodium carboxymethyl cellulose, hydroxyethyl cellulose or hydroxypropyl cellulose, proteoglycanes/glycosamino glycanes, e g hyaluronic acid, or chondroitin sulfphate 4 A method as claimed in claim 3 wherein the solution to be frozen comprises one or more polysaccharides 5 A method as claimed in claim 4 wherein the polysacchaπde(s) is alginate in the form of a sodium alginate or a mixture of sodium and calcium alginates 6 A method as claimed in one of claims 1 - 5 wherein the solution to be frozen comprises a growth hormone or a polypeptide growth factor 7 A method for removing water from an aqueous solution of a solute wherein the water is frozen and removed by extraction with a solvent being miscible with water but not being able to dissolve the solutes at the conditions for extraction 8 A method as claimed in claim 7 comprising dissolving one or more hydro¬ philic polymers and/or pharmaceutical medicaments in water to provide a solu¬ tion, sol or gel, prenucleating a freeze plate, providing the solution of one or more pharmaceutical medicaments and/or hydrophilic polymers on the prenucle- ated freeze plate, the temperature of which is to be kept below the freezing point ot the atomised water or solution, freezing the solution to provide an ice sheet comprising the pre-nucleated frozen material and extracting the water selectively using a solvent being miscible with water but not being able to dis¬ solve the solutes, leaving the solutes in a solid, porous form 9 A non-fibrous porous material whenever prepared by the method of any of claims 1 - 8

Inventors: NIELSEN PETER SYLVEST, SCHOENFELDT LARS, NIELSEN, PETER, SYLVEST, SCHOENFELDT, LARS
Applicants: COLOPLAST AS, NIELSEN PETER SYLVEST, SCHOENFELDT LARS, COLOPLAST A/S, NIELSEN, PETER, SYLVEST, SCHOENFELDT, LARS
Application year: 1996
Main classification: C08J9
IPC codes: C08J9