Link:  Pharm/Biotech Resources

Title:  Method for preparing a calcium phosphate pasty material for injection

United States Patent:  6,923,989

Issued:  August 2, 2005

Inventors:  Lacout; Jean-Louis (Toulouse, FR); Freche; Michèle (Fonsegrives-Quint, FR); Goncalves; Stephane (Toulouse, FR); Rodriguez; Fernand (Aureville, FR)

Assignee:  Ceravic (Vic en Bigorre, FR)

Appl. No.:  220052

Filed:  February 27, 2001

PCT Filed:  February 27, 2001

PCT NO:  PCT/FR01/00563

371 Date:  August 27, 2002

102(e) Date:  August 27, 2002

PCT PUB.NO.:  WO01/64260

PCT PUB. Date:  September 7, 2001

A method for preparing a calcium phosphate pasty material for injection which after, setting, is designed to form an apatite material consists in: producing from water and calcium phosphates pasty mixture capable of developing, hardening and forming a hydroxyapatite. The method is characterised in that it consists in adding to the calcic phosphates or to the pasty mixture before it is injected a methicone having relative to the mixture more than 0.30 wt. % and less than 10 wt. %. The resulting material can be injected, that is it can be transported in pasty form into a conduit under moderate pressure levels. The material sets on the site of implantation and hardens to form an apatite biomaterial in a manner similar to known methicone-free calcium phosphate mixtures.

The invention relates to a process for the preparation of an injectable pasty material from a mixture of water and calcium phosphates which is capable of developing, hardening and forming a hydroxyapatite, the latter constituting a biomaterial useful particularly in orthopedics or dentistry. The expression "injectable" pasty material is understood as meaning that the pasty material is capable of traveling through a tube appropriate to the intended application under a pressure which is non-destructive towards said material and is compatible with this application and the equipment used. The term "biomaterial" is understood in the present description as meaning the solid material obtained after hardening, this material having biocompatibility properties and being intended to replace or treat an organ or a function in humans or animals.

Calcium phosphate hydroxyapatites are well-known materials which are increasingly used in the fields of surgery and dentistry because of their biocompatibility and bone conduction properties. They can be used in dentistry for periodontal filling, the restoration of bone ridges, the filling of cysts or alveoli after dental extraction, etc., and in bone surgery for the filling of bone defects, interstitial filling between prosthesis and cortical bone, injection into bodies of vertebra, the treatment of osteoporosis, etc. The biomaterial introduced in this way may optionally contain active substances which, after hardening in situ, are slowly diffused.

These apatite biomaterials are obtained in particular by the hardening of a pasty mixture prepared by combining a mixture of calcium phosphates with water; in the applications mentioned above, the pasty mixture sets and hardens in situ at the site of application. At the present time, pasty mixtures of this type are either introduced into open sites, where they are applied by hand or with a spatula, or pushed over very short distances under high pressure into directly accessible sites. Because of their viscosity characteristics, these pasty mixtures are actually incapable of traveling under moderate pressure over distances greater than a few centimeters.

This non-injectable character limits the field of application of these materials to interventions at directly accessible sites, which do not represent the general case or entail traumatizing and complicated open surgery.

The aim of the present invention is to provide a process for the preparation of a novel injectable pasty calcium phosphate material, i.e. a material which, before it develops, can be transported under moderate pressures over considerable distances (a few tens of centimeters), said material having similar setting and hardening times to those of the existing calcium phosphate materials and producing, after hardening, an apatite biomaterial whose mechanical characteristics are comparable or superior to those of the apatite biomaterials obtained from the existing mixtures.

The process for the preparation of the injectable pasty material to which the invention relates is of the type in which water and calcium phosphates are used to produce a pasty mixture capable of developing, hardening and forming a hydroxyapatite. According to the present invention, this process comprises adding, to the calcium phosphates or the pasty mixture prior to injection, a methicone in a proportion by weight greater than 0.3% and less than 10%, and advantageously of between approximately 0.5% and 1.4%, based on the mixture. It should be remembered that methicone is a polysiloxane (belonging to the silicone family) which has a CH₃ group on at least one of the silicon bonds of its unit.

It has been shown experimentally that the pasty material obtained in this way is injectable and can be transported in the form of a paste through tubes of the catheter type, particularly flexible tubes, under moderate pressures (relative pressures below 1 bar) which are compatible with the conditions of surgical or dental intervention and the equipment used. This pasty material sets even in a moist environment and hardens in a similar manner to the mixture not containing methicone; however, in the absence of methicone, the mixture is impossible to inject, as is known to those skilled in the art. Furthermore, tests have made it possible to observe that the addition of methicone is capable of bringing about a significant improvement in the mechanical characteristics of the biomaterial obtained after hardening.

It should be emphasized that, in general, silicones are well-known lubricants which are used especially for coating walls so as to enable a solid or a liquid to slide along them more easily. By contrast, the methicone in the present case is intimately mixed with the pasty material and its wall-lubricating properties do not explain the injectability property which is obtained for the paste without degradation of the mechanical characteristics of the material after hardening, said characteristics even being improved. As will be seen in the Examples, wall lubrication slightly improves the ability of the paste to move over a few centimeters, but does not allow transport over a few tens of centimeters under moderate pressures (especially relative pressures below 1 bar). The injectability property obtained is difficult to explain at present: it probably involves a sliding effect between the particles, platelets and needles which form and develop during setting, this interparticulate sliding being conditioned by interfacial modifications due to the methicone; it should be pointed out, however, that the improvement in the mechanical properties obtained for the biomaterial after hardening suggests that the methicone also has a physicochemical action on the development of the material and its crystallization to apatite.

Preferably, as is known per se, the pasty mixture of calcium phosphates produced has an atomic ratio Ca/P of between 1.5 and 1.67. The biomaterial which is obtained after injection and hardening consists of a pure phase of hydroxyapatite whose chemical composition is very similar to that of the mineral part of the bone. Outside this range of atomic ratios, the biomaterial obtained is multiphase (which may be sought in certain applications).

Additives, particularly known additives for increasing the uniformity of setting of the paste (good homogeneity, absence of lumps), can be incorporated into the pasty calcium phosphate material according to the invention. For example, a water-soluble glycerophosphate, especially sodium, potassium or calcium glycerophosphate, can be added to the mixture so that the percentage by weight of this compound is less than 10%, based on the final mixture. This compound helps to improve the uniformity of setting and slightly reduces the setting rate. It should be noted that the methicone already plays a part in greatly improving the uniformity of setting of the paste and its homogeneity, so the amount of glycerophosphates can be less than that envisaged for similar mixtures not containing methicone. It should be emphasized that, in this type of cold reaction, the glycerophosphate is not decomposed and does not participate as a chemical reagent in the apatite formation reaction; the atomic ratios Ca/P are therefore given throughout the text without taking glycerophosphate into account.

The methicone used preferably has a viscosity of between approximately 20 centistokes and 500 centistokes, corresponding to a density of between approximately 0.90 and 0.98 (ratio of the density to that of water). It is advantageous to use a dimethicone containing two CH₃ groups on the silicon of its unit, particularly a cyclic dimethicone.

The conditions of implementation of the process of the invention can advantageously be those defined in French patent application no. 2 776 282. In one preferred mode of carrying out the process, the pasty mixture is particularly produced in the cold from a pulverulent cement of tricalcium phosphate and tetracalcium phosphate and an aqueous solution containing calcium and phosphate, the pulverulent cement and the aqueous solution being mixed at room temperature (i.e. between about 15° C. and 30° C.); the mode of implementation is preferably as follows: