PROCESS FOR PRODUCING AN ANTIBACTERIAL COATING COMPOSITION FOR IMPLANTS

Abstract

A process for producing an antibacterial coating composition for implants. The process includes the steps i) reaction of a monomer A which is based on (meth)acrylic acid and contains at least one epoxide with a polyguanidine by reaction of an amino group of the polyguanidine with the epoxide to give a (meth)acrylic acid-polyguanidine macromolecule and ii) polymerization of the (meth)acrylic acid-polyguanidine macromolecule with a monomer B which contains at least one polymerizable double bond and at least one phosphonate group by free-radical polymerization of the (meth)acrylic acid unit and the double bond.

Claims

1. A process for producing an antibacterial coating composition for implants, which comprises the steps: reaction of a monomer A which is based on (meth)acrylic acid and contains at least one epoxide with a polyguanidine by reaction of an amino group of the polyguanidine with the epoxide to give a (meth)acrylic acid-polyguanidine macro-molecule and polymerization of the (meth)acrylic acid-polyguanidine macromolecule with a monomer B which contains at least one polymerizable double bond and at least one phosphonate group by free-radical polymerization of the (meth)acrylic acid unit and the double bond.

2. The process according to claim 1, wherein the monomer A is 2,3-epoxypropyl methacrylate.

3. The process according to claim 1, wherein the monomer B is diethyl (4-vinylbenzyl)phosphonate, 2-(dimethoxyphosphoryl)ethyl methacrylate or 2-(dimethoxyphosphoryl)methyl methacrylate.

4. The process according to claim 1, wherein the polyguanidine is poly-2-(2-ethoxy)ethoxyethylguanidine hydrochloride.

5. The process according to claim 1, wherein the polyguanidine is prepared by reaction of guanidine hydrochloride with 1,2-bis(2-aminoethoxy)ethane and has at least one of the following formulae: ##STR00002## where n is an integer in the range from 1 to 10, preferably from 3 to 6, and is in particular 5.

6. The process according to claim 4, wherein the molecular weight of the polyguanidine is from 800 to 1300 g/mol.

7. The process according to claim 1, wherein the proportion of the monomer B based on the antibacterial coating composition is about 67 mol %.

8. The antibacterial implant coating composition produced by a process according to claim 1.

9. The process for coating an implant with an antibacterial coating, which comprises the steps: reaction of a monomer A which is based on (meth)acrylic acid and contains at least one epoxide with a polyguanidine by reaction of an amino group of the polyguanidine with the epoxide to give a (meth)acrylic acid-polyguanidine macromolecule, polymerization of the (meth)acrylic acid-polyguanidine macromolecule with a monomer B which contains at least one polymerizable double bond and at least one phosphonate group by free-radical polymerization of the (meth)acrylic acid unit and the double bond to produce a coating composition, dissolution of the coating composition in a solvent, provision and degreasing of an implant, application of the solution of the coating composition to the implant and binding of the coating composition to the implant under the action of temperatures in the range from 50 to 200 C.

10. The process according to claim 9, characterized by a washing step and a subsequent drying step after binding of the coating composition.

11. The process according to claim 9, wherein the application of the solution of the coating composition is carried out by spin coating or a dipping or spraying process.

12. The process according to claim 9, wherein the concentration of the coating composition in the solvent is from 2 to 20 mg/ml, in particular from 8 to 12 mg/ml.

13. The antibacterially coated implant produced by a process according to claim 9, wherein the implant consists of titanium, zirconium, tantalum, stainless steel or zirconium oxide and the average layer thickness of the antibacterial coating is from 5 to 50 nm and in particular from 15 to 25 nm.

Description

[0025] Further details, advantages and features of the present invention can be derived from the following description of working examples with the aid of the drawing. The drawing shows:

[0026] FIG. 1 a reaction scheme for producing an antimicrobial coating composition according to a first embodiment of the invention,

[0027] FIG. 2 a reaction scheme for producing an antimicrobial coating composition according to a second embodiment of the invention,

[0028] FIG. 3 an overview of possible structures of PEDBEG,

[0029] FIG. 4 a schematic depiction of micrographs after colonization by Staphylococcus aureus, and

[0030] FIG. 5 a graph showing the cell count of adhering gingiva fibroblasts after 24 hours and 72 hours.

[0031] The present invention will be explained in detail with the aid of working examples. Here, only the aspects of the invention which are essential to the invention are presented, all other aspects will be left out in the interests of clarity.

[0032] In detail, FIG. 1 shows a reaction scheme for producing an antimicrobial coating composition for the example of copolymer PEDBEG-GMA-co-DMMEP. Reaction step A is the synthesis of PEDBEG by polycondensation of guanidine hydrochloride and 2,2-(ethylenedioxy)bis(ethylamine), where n is preferably 5. For this purpose, 50 mmol (7.41 g) of 2,2-(ethylenedioxy)bis(ethylamine) and 525 mmol (5 g) of guanidine hydrochloride are placed in a 50 ml three-neck flask provided with mechanical stirrer. The reaction mixture is heated to 170 C. over a period of 30 minutes and then stirred at this temperature under a nitrogen atmosphere for 300 minutes. The ammonia liberated during the reaction is passed through an aqueous hydrochloric acid solution and thus neutralized. After the reaction, ammonia still present in the reaction mixture is removed by stirring for 40 minutes at 170 C. under reduced pressure. The product is a yellowish viscous solution which becomes solid on cooling.

[0033] Reaction step B is the coupling reaction of the PEDBEG oligomers obtained in reaction step A with 2,3-epoxypropyl methacrylate (glycidyl methacrylateGMA) (monomer A) to give a (meth)acrylic acid-polyguanidine macromolecule. Only one structure of a PEDBEG oligomer is shown by way of example. As regards further structures, reference is made for completeness to FIG. 3. 5 mmol of PEDBEG (5 g) together with 20 ml of methanol are placed in a 50 ml two-neck flask and 150 mg of GMA (1.2 mmol) are then added. The solution is refluxed for 40 hours. It is worked up by taking off the solvent under reduced pressure.

[0034] In reaction step C, the copolymerization of PEDBEG-GMA with 2-(dimethoxyphosphoryl)ethyl methacrylate (DMMEP) (monomer B) is carried out as a free-radical copolymerization in methanol using AIBN as free-radical initiator. For this purpose, a one molar solution of the monomer B in methanol is prepared. In addition, an initiator solution containing 164 mg of AIBN in 10 ml of methanol is made up. The batches have a volume of 5 ml and are produced in a 1:1 ratio of phosphonate to PEDBEG-GMA with 0.5 ml of initiator solution in each case. The screw-cap reagent bottles are flushed with nitrogen for two minutes to remove oxygen and then firmly closed. The copolymerization is carried out at 60 C. for 14 hours and stopped by dipping into ice water. The work-up is carried out by precipitation of the polymers in cold diethyl ether, filtration with suction on POR2 frits and drying under reduced pressure for three days at room temperature. In the PEDBEG-GMA-co-DMMEP obtained, x is approximately 23 mol % and y is approximately 67 mol %.

[0035] The resulting coating composition, viz. the copolymer PEDBEG-GMA-co-DMMEP, displays a high readiness to bind to conventional implant surfaces such as titanium, stainless steel, zirconium, tantalum and zirconium oxide.

[0036] To bind the coating composition to an implant surface, PEDBEG-GMA-co-DMMEP was applied as a solution having a concentration of 10 g/l in methanol to degreased samples of implant surfaces (e.g. titanium grade 5), stored at 120 C. for 16 hours to bind the coating composition and then washed twice with the solvent methanol in an ultrasonic bath for in each case 20 minutes.

[0037] The antimicrobial implant produced in this way displayed excellent antimicrobial properties and was very cell-compatible.

[0038] FIG. 2 shows the reaction steps B and C of FIG. 1 for a copolymerization of PEDBEG-GMA with diethyl (4-vinylbenzyl)phosphonate (VBP). The chemical reaction is carried out in a manner analogous to the description for FIG. 1.

[0039] The coating composition obtained according to FIG. 2, viz. the copolymer PEDBEG-GMA-co-VBP, in which x is approximately 23 mol % and y is approximately 67 mol %, displays a high readiness to bind to conventional implant surfaces such as titanium, stainless steel, zirconium, tantalum and zirconium oxide. To bind the coating composition to an implant surface, PEDBEG-GMA-co-VBP was applied as a solution having a concentration of 10 g/l in methanol to degreased samples of implant surfaces (e.g. titanium grade 5), stored at 120 C. for 16 hours to bind the coating composition and then washed twice with the solvent methanol in an ultrasonic bath for in each case 20 minutes.

[0040] FIG. 3 gives an overview of possible oligomeric structures of PEDBEG, where n is preferably 5.

[0041] FIG. 4 is a schematic depiction of micrographs after colonization with Staphylococcus aureus. For this purpose, bacteria (Staphylococcus aureus) were sown on the surface of implant samples A, B and C and cultivated for 24 hours. The adhering bacteria were subsequently stained with a fluorescent dye and made visible. Implant sample A was titanium (grade 5) without antimicrobial coating, implant sample B was titanium (grade 5) coated with VBP-GMA+PEDBEG and implant sample C was coated with coating composition produced according to the reaction scheme in FIG. 1 (PEDBEG-GMA-co-DMMEP 67% mol % of DMMEP).

[0042] As regards implant sample B, it may be said that the coating was produced by firstly polymerizing VBP with GMA, binding the copolymer to the titanium and only then carrying out a further reaction with PEDBEG.

[0043] In FIG. 4, a reduction in the number of germs on the PEDBEG-GMA-co-DMMEP coating can clearly be seen, while strong germ growth was observed on the coating of implant sample B and on implant sample A.

[0044] Furthermore, the cell compatibility of implant samples was examined. The results are shown in the graph in FIG. 5. For this purpose, implant samples D, E and F were produced as follows: implant sample D: titanium (grade 5), implant sample E (comparative example): titanium (grade 5) coated with GMA-co-VBP+PEDBEG and implant sample F (example according to the invention): titanium (grade 5) coated with PEDBEG-GMA-co-DMMEP and colonized with human gingiva fibroblasts (HGFib). Here, both adhesion and proliferation of the cells on the surfaces were assessed. The results for adhesion were examined after 24 hours and the results of proliferation were examined after 72 hours.

[0045] As regards implant sample E, it may be said that the coating was produced by firstly polymerizing VBP with GMA, binding the copolymer to the titanium and only then carrying out a further reaction with PEDBEG.

[0046] The adhesion of HGFib to the implant sample E is at the same level as in the case of bare titanium (D). A slightly better value is obtained for proliferation. The adhesion of HGFib on the implant sample F is at a level similar to the case of bare titanium (D). Even a slightly better value is obtained for proliferation. The coating composition PEDBEG-GMA-co-DMMEP according to the invention thus does not not have an adverse effect on HGFib cells in the adhesion test. The coating composition according to the invention displayed excellent biocompatibility.

[0047] To supplement the disclosure of the above written description of the invention, reference is explicitly made to the pictorial illustration of the invention in FIGS. 1 to 5.