HARDENABLE CERAMIC HYDRAULIC CEMENT

Abstract: The hardenable ceramic hydraulic cement comprises a drug to be delivered to the human or animal body upon degradation or dissolution of the hardened cement. The cement comprises the following reactive components to be mixed: component A: calcium and/or sodium salts of inorganic and/or organic acids; and component B: an aqueous solution of sodium or calcium silicate. The main advantage of the cement according to the invention is the relatively short dissolving time of the hardened implanted cement compared to prior art cements which allows for faster delivery of drugs.

Description: Hardenable ceramic hydraulic cement This invention concerns a cement in accordance with the pre-characterising portion of Claim 1. In particular it relates to fast degrading or fast dissolving hydraulic cements which are implantable in the human or animal body and are capable of delivering drugs upon degradation or dissolution of the hardened cement. Ceramic cements which harden in si tu can be used for various applications. Such cements may be applied to reinforce porotic bones, to enhance fixation of fractures of porotic bones, to fill bone defects or to release bone growth factors. Recently, resorbable cements consisting of β-tricalcium- phosphate, monocalciurn phosphate and so-called carbonized cements containing calcium carbonate became known which set at the body temperature. These known cements have the disadvantage of long resorption or dissolution times. While this property is indispensable when cements are used to enhance bone fracture fixation, it is undesirable when cements are applied as carriers for fast local delivery of drugs. The invention as claimed aims at solving both of the above described problems. The present invention provides a cement as defined in Claim 1. The main advantage of the invention is the relatively short dissolving time of the hardened implanted cement compared to the above mentioned prior art cements which allows for faster delivery of drugs, in particular of osteogenic drugs. In a preferred embodiment of the invention a further component C which is an organic carboxylic acid is used. The organic carboxylic acid may be chosen from the group of ascorbic acid, citric acid or tartaric acid and has the function of neutralizing the alkaline components (sodium or calcium silicate) of the cement. Further advantages are the better compatibility with the environment and the faculty to complex calcium ions from the body fluids more easily and to deposit in the bone defect treated with the cement . The use of ascorbic acid further contributes to the formation of collagen in the bone defect treated with the cement. Component A may preferably comprise calcium and/or sodium salts of carbonic acid, phosphoric acid or glycerophosphoric acid which are highly biocompatible, in particular if selected from the group of hydroxyapatite (HA) , tricalcium phosphate (TCP) , calcium carbonate, calcium hydrogen phosphate, disodium hydrogen phosphate or calcium glycerophosphate . In a preferred embodiment water is incorporated in component B prior to mixing in order to obtain a shorter mixing time. In a further preferred embodiment concentration of the aqueous solution of sodium or calcium silicate of component B is in the range of 0,01 to 10,00 % which makes it more easy to prepare the cement and contributes in controlling the acidity thereof. In a further preferred embodiment drugs are added to the cement chosen from the group of: osteogenic drugs, tissue growth factors (TGF-beta) , osteocalcine, calcium binding proteins (GLA) , bone morphogenetic protein (BMP), antimicrobial drugs or vitamins. The concentration is specific for the particular application and drug used. The various features of novelty which characterize the invention are pointed out with particularity in the claims annexed to and forming part of this disclosure. For the better understanding of the invention, its operating advantages and specific objects attained by its use, reference should be had to the examples and descriptive matter in which are illustrated and described preferred embodiments of the invention. Example 1 5 parts by weight of calcium glycerophosphate and 1,5 parts by weight of 0,001-% aqueous solution of sodium silicate were mixed together and place in a plastic cylindrical mold. The mixture set within 60 to 90 minutes, and disintegrated when placed in water within 7 hours. Example 2 3 parts by weight of hydroxyapatite (HA) and 1 part by weight of ascorbic acid were mixed with 2 parts by weight of water and 0,1 parts by weight of sodium silicate. The mixture set within 10 to 20 minutes, and disintegrated when placed in water within 40 hours. Example 3 3 parts by weight of tricalcium phosphate (TCP) and 1 part by weight of ascorbic acid were mixed with 2 parts by weight of water and 0,1 parts by weight of sodium silicate. The mixture set within 10 to 20 minutes, and disintegrated when placed in water within 30 hours. Example 4 3 parts by weight of hydroxyapatite (HA) and 1 part by weight of ascorbic acid were mixed with 1 part by weight of water and 0.1 part by weight of calcium silicate. The mixture set within 15 minutes, and disintegrated when placed in water within 50 hours. Example 5 3 parts by weight of tricalcium phosphate (TCP) and 1 part by weight of ascorbic acid were mixed with 1 part by weight of water and 0,1 part by weight of calcium silicate. The mixture set within 15 minutes, and disintegrated when placed in water within 12 hours. Example 6 2 parts by weight of hydroxyapatite (HA) were mixed with 1 part by weight of an aqueous solution sodium silicate (glass water) and 0,2 part by weight of ascorbic acid. The paste was mixed for 5 minutes and the paste obtained was allowed to set for 5 hours. When placed in water or saline solution it dissolved within 12 hours. Example 7 2 parts by weight of tricalcium phosphate (TCP) were mixed with 1 part by weight of an aqueous solution of sodium silicate (glass water) and 0,2 part by weight of ascorbic acid. The paste was mixed for 5 minutes and the paste obtained was allowed to set for 5 hours. When placed in water or saline solution it dissolved within 12 hours. Example 8 2 parts by weight of hydroxyapatite (HA) were mixed with 1 part by weight of ascorbic acid and 0,1 part by weight of an aqueous solution of sodium silicate (glass water) . The paste obtained set within 15 minutes and dissolved when placed in water within 40 days. Increasing the amount of ascorbic acid in the cement mixture decreases time required for the cement setting and extends the dissolution time in water. Example 9 2 parts by weight of tricalcium phosphate (TCP) were mixed with 0,5 parts by weight of ascorbic acid and 0,1 part by weight of an aqueous solution of sodium silicate (glass water) . The paste obtained set within 15 minutes and dissolved when placed in water within 40 days. Increasing the amount of ascorbic acid in the cement mixture decreases time required for the cement setting and extends the dissolution time in water. Example 10 2 parts by weight of calcium carbonate were mixed with 1 part by weight of an aqueous solution of sodium silicate (glass water) and 1 part by weight of ascorbic acid. The cement set within 20 minutes and dissolved in water within 40 days. Example 11 2 parts by weight of calcium carbonate were mixed with 1 part by weight of an aqueous solution of sodium silicate (glass water) and 0,5 parts by weight of ascorbic acid. The cement set within 20 minutes and dissolved in water within 30 days. Example 12 3 parts by weight of tricalcium phosphate (TCP) were mixed with 3 parts by weight of calcium glycerol phosphate and 0,5 part of ascorbic acid, 0,01 parts by weight of an aqueous solution of sodium silicate (glass water) and 1 part of water. The paste obtained set within 30 minutes. Disintegration time in water was from 10 days. Example 13 4 parts by weight of calcium glycerophosphate, 0,01 part by weight of an aqueous solution of sodium silicate (glass water) and 0,05 part by weight 1 wt-% aqueous solution of ascorbic acid were mixed together with 1 part by weight of deionised water. The resulting paste set within 1 hour. the paste disintegration. Example 14 In this example the cement composition is stored in three separate containers X, Y and Z. Container X contained 10 parts by weight of calcium carbonate. Container Y contained 2 parts by weight of ascorbic acid. Container Z contained sodium silicate dissolved in water (glass water of the density in the range of 1,3 to 1,4 g/ml) . For initiating the hardening process the liquid in container Z was put into contact with the powder of container X and subsequently the liquid in container Y was added. The resulting paste was mixed either by hand with a spatula or mechanically in mixing bowl . Physical properties of the hardened cements according to the examples The hardened cements showed a tensile strength in the range of 0,6 to 5,0 MPa; most of them in the range of 1 to 3 MPa . Depending on the chemical composition, the hardened cement mixtures according to the invention dissolve when placed in water within 10 hours to 4 months. The short dissolution times from 10 hours to 30 days are preferably when cements are used for local delivery of osteogenic drugs, e.g. growth factors. Salts used for preparation of cements should be of non-toxic nature. Acidity (pH-value) of the cements can be adjusted by changing the composition. Glass water contains either sodium compounds in a form as expressed in Na 2 0 between 6 to 10 % or silica compounds as expressed in Si0 from 10 to 50 %. While the foregoing description and drawings represent the preferred embodiments of the present invention, it will be obvious for those skilled in the art that various changes and modifications may be made therein without departing from the true spirit and scope of the present invention.

Claims: Claims 1. Hardenable ceramic hydraulic cement comprising a drug to be delivered to the human or animal body upon degradation or dissolution of the hardened cement, characterized in that it comprises the following reactive components to be mixed: component A: calcium and/or sodium salts of inorganic and/or organic acids; and component B: an aqueous solution of sodium or calcium silicate. 2. Cement according to claim 1, characterized by a further component C which is an organic carboxylic acid. 3. Cement according to claim 2, characterized in that the organic carboxylic acid is chosen from the group of ascorbic acid, citric acid or tartaric acid. 4. Cement according to one of the claims 1 to 3 , characterized by a further component D which is pure water. 5. Cement according to one of the claims 1 to 4 , characterized in that component A comprises calcium and/or sodium salts of carbonic acid, phosphoric acid or glycerophosphoric acid. 6. Cement according to one of the claims 1 to 4, characterized in that component A is selected from the group of hydroxyapatite (HA) , tricalcium phosphate (TCP) , calcium carbonate, calcium hydrogen phosphate, disodium hydrogen phosphate, calcium glycerophosphate . 7. Cement according to one of the claims 1 to 6, characterized in that water is incorporated in component B prior to mixing. 8. Cement according to one of the claims 1 to 7, characterized in that the concentration of the aqueous solution of sodium or calcium silicate of component B is in the range of 0,01 % to 10,00 %. 9. Cement according to one of the claims 1 to 8 , characterized in that component A contains a therapeutically active drug. 10. Cement according to one of the claims 4 to 9, characterized in that component D contains a therapeutically active drug. 11. Cement according to claim 9 or 10, characterized in that the drugs are chosen from the group of: osteogenic drugs, tissue growth factors (TGF-beta) , osteocalcine, calcium binding proteins (GLA) , bone morphogenetic protein (BMP) , antimicrobial drugs or vitamins .

Inventors: GOGOLEWSKI SYLWESTER, GOGOLEWSKI, SYLWESTER
Applicants: GOGOLEWSKI SYLWESTER, SYNTHES AG, SYNTHES USA, GOGOLEWSKI, SYLWESTER, SYNTHES (U.S.A.), SYNTHES AG CHUR
Application year: 1998
Main classification: A61L25
IPC codes: A61L24, A61L27