CA2187512C - Process for producing a graduated coating of calcium phosphate phases and metallic oxide phases on metal implants - Google Patents
Process for producing a graduated coating of calcium phosphate phases and metallic oxide phases on metal implants Download PDFInfo
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- CA2187512C CA2187512C CA002187512A CA2187512A CA2187512C CA 2187512 C CA2187512 C CA 2187512C CA 002187512 A CA002187512 A CA 002187512A CA 2187512 A CA2187512 A CA 2187512A CA 2187512 C CA2187512 C CA 2187512C
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- A—HUMAN NECESSITIES
- A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
- A61L—METHODS OR APPARATUS FOR STERILISING MATERIALS OR OBJECTS IN GENERAL; DISINFECTION, STERILISATION OR DEODORISATION OF AIR; CHEMICAL ASPECTS OF BANDAGES, DRESSINGS, ABSORBENT PADS OR SURGICAL ARTICLES; MATERIALS FOR BANDAGES, DRESSINGS, ABSORBENT PADS OR SURGICAL ARTICLES
- A61L27/00—Materials for grafts or prostheses or for coating grafts or prostheses
- A61L27/28—Materials for coating prostheses
- A61L27/30—Inorganic materials
- A61L27/32—Phosphorus-containing materials, e.g. apatite
-
- C—CHEMISTRY; METALLURGY
- C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
- C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
- C25D9/00—Electrolytic coating other than with metals
- C25D9/04—Electrolytic coating other than with metals with inorganic materials
-
- A—HUMAN NECESSITIES
- A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
- A61F—FILTERS IMPLANTABLE INTO BLOOD VESSELS; PROSTHESES; DEVICES PROVIDING PATENCY TO, OR PREVENTING COLLAPSING OF, TUBULAR STRUCTURES OF THE BODY, e.g. STENTS; ORTHOPAEDIC, NURSING OR CONTRACEPTIVE DEVICES; FOMENTATION; TREATMENT OR PROTECTION OF EYES OR EARS; BANDAGES, DRESSINGS OR ABSORBENT PADS; FIRST-AID KITS
- A61F2310/00—Prostheses classified in A61F2/28 or A61F2/30 - A61F2/44 being constructed from or coated with a particular material
- A61F2310/00389—The prosthesis being coated or covered with a particular material
- A61F2310/00592—Coating or prosthesis-covering structure made of ceramics or of ceramic-like compounds
- A61F2310/00796—Coating or prosthesis-covering structure made of a phosphorus-containing compound, e.g. hydroxy(l)apatite
Abstract
The invention concerns a process for producing a gradient coating of calcium phosphate phases and metal oxide phases on metallic implants, in particular made of titanium or titanium alloys, for use as dental, jaw or joint implants. A solution containing calcium ions and phos-phate ions is used as an electrolyte the pH value of which is slightly acidic to approximately neutral. The substrate electrodes are alternately polarized to be cathodic or anodic. The depos-ited layer forms a gradient coating, which is strongly adherent, has a fine structure and is dis-tinguished for its high degree of biocompatibility.
Description
Proce.ss for producing a graduated coating of calcium phosphate phases and metallic oxide phases on metal implants The invention refers to a process for producing a gradient coating containing calcium phos-phate phases and metal oxide phases on metallic implants, especially on titanium or titanium alloys, for use as dental, maxillofacial or joint implants.
It is well known that the time of ingrowth of a metallic implant until full mechanical loadability is achieved can be reduced if the metallic implants have been coated with calcium phosphate phases, especially with hydroxyapatite, a calcium phosphate phase similar to bone.
The connection between the metal implant and calcium phosphate can be realized in different ways. According to EP-A 0006544, spherical calcium phosphate particles are molded in a model together with the implant material. In US-PS 4.145.764 a process is described in which ceramic particles are thermically sprayed onto an implant. However, these techniques are very energy intensive, expensive and time consuming. Further, from EP 0232791 and processes are known, in which a resorbable calcium phosphate ceramic is deposited on tita-nium by means of anodic oxidation under spark discharge in an aqueous electrolyte solution.
However, the so produced coating does not consist of hydroxyapatite or fluorapatite but of oxides and strongly resorbable calcium phosphate phases.
With a complete resorption of the calcium phosphate phases also the bioactive character of the implant is lost.
DE 43 03 575 C 1 describes a process for producing apatite coatings on metal implants by in-ducing a plasma-chemical reaction by means of alternating current in aqueous solutions. An electrolyte solution is used made from the salts of alkali or alkaline earth metals, in which hy-droxyapatite and/or fluorapatite is dispersed with a defined grain size and concentration. The plasma-chemical process leads to coatings which consist of pure hydroxyapatite or fluorapatite with an extent of up to 95 %.
Disadvantages of this process are, especially, the large thickness of the coating (up to 250 m) as well as the coarse grain size of the coating (up to 100 m). Furthermore, the bonding strength between the coatings and implants is not optimal.
It is well known that the time of ingrowth of a metallic implant until full mechanical loadability is achieved can be reduced if the metallic implants have been coated with calcium phosphate phases, especially with hydroxyapatite, a calcium phosphate phase similar to bone.
The connection between the metal implant and calcium phosphate can be realized in different ways. According to EP-A 0006544, spherical calcium phosphate particles are molded in a model together with the implant material. In US-PS 4.145.764 a process is described in which ceramic particles are thermically sprayed onto an implant. However, these techniques are very energy intensive, expensive and time consuming. Further, from EP 0232791 and processes are known, in which a resorbable calcium phosphate ceramic is deposited on tita-nium by means of anodic oxidation under spark discharge in an aqueous electrolyte solution.
However, the so produced coating does not consist of hydroxyapatite or fluorapatite but of oxides and strongly resorbable calcium phosphate phases.
With a complete resorption of the calcium phosphate phases also the bioactive character of the implant is lost.
DE 43 03 575 C 1 describes a process for producing apatite coatings on metal implants by in-ducing a plasma-chemical reaction by means of alternating current in aqueous solutions. An electrolyte solution is used made from the salts of alkali or alkaline earth metals, in which hy-droxyapatite and/or fluorapatite is dispersed with a defined grain size and concentration. The plasma-chemical process leads to coatings which consist of pure hydroxyapatite or fluorapatite with an extent of up to 95 %.
Disadvantages of this process are, especially, the large thickness of the coating (up to 250 m) as well as the coarse grain size of the coating (up to 100 m). Furthermore, the bonding strength between the coatings and implants is not optimal.
WO 92/13984 describes a process of the deposition of bioactive coatings on conductive sub-strates. An electrolyte cell contains an inert anode and an electrolyte consisting of an aqueous solution of ions of the ceramic, having a pH value of less than 8. The activated conductive sub-strate is dipped into the electrolyte solution and the potential between the anode and the con-ductive substrate is chosen such that a ceramic layer is deposited on the conductive substrate based on the pH rise at the boundary between electrolyte and conductive substrate.
A disadvantage of this solution is that'the deposition of the layer proceeds only on the surface of the substrate. This means, on the one hand, that there is no mechanically loadable connec-tion. On the other hand, the coating can be completely resorbed biologically.
Furthermore, the coating always consists of three components, a- and 0-tricalcium phosphate and components of the chemical formula Ca5(PO4)3_x(C03)x(OH),+x with X = 0.2 or less. This means that the coating is always a mixture of these components not approximating the composition of bone.
The object of the invention is the coating of metallic implants, preferably of titanium implants or implants made of titanium alloys, with a gradient layer made of calcium phosphate phases and metal oxide phases. Thus, in addition to the effect of accelerated ingrowth a permanent improvement of the interaction between the implant surface and the biological system will be achieved. Moreover, the composition of the calcium phosphate phases is controllable via the process parameters so that, optionally, hydroxyapatite, octacalcium phosphate or brushite as well as defined combinations of these phases can be produced.
According to the invention, there is provided a process for producing a gradient coating of calcium phosphate phases and metal oxide phases on a metal implant, comprising: providing a metal implant; providing an electrolyte solution containing calcium phosphate ions, and having a pH of between 4.0 and 7.5; providing a counter electrode in the electrolyte solution; placing the implant in the electrolyte solution; applying an electrical potential between the counter electrode and the implant, so that the implant initially acts as a substrate cathode; periodically reversing the polarity of the electrical potential a plurality of times, so that the implant alternates between cathodic polarization and anodic polarization, to deposit a gradient coating of calcium phosphate phases and metal oxide phases on the implant.
2a Preferably, the ratio of the concentration of the calcium and phosphate ions is chosen such that it is equal to their concentration ratio.in hydroxyapatite. In a preferred implementation of the invention the electrolyte is produced from an aqueous solution of CaCl2 and NHaH2POa with a ratio of concentration of calcium and phosphate ions equal to that of hydroxyapatite. The pH
value is preferably adjusted between 4 and 7.5 by means of a diluted 1VH4OH
solution. The use of other readily soluble calcium salts and phosphates (for example, alkali phosphates) is also possible. Beyond that the conditions of the electrolysis mainly determine the formation of par-ticular calcium phosphate phases and their mixtures, respectively. It is also possible to choose different concentration ratios of calcium and phosphate ions.
In an arrangement consisting of a substrate electrode, reference electrode and counter elec-trode the substrate electrode formed by the implant is polarized varying the polarization from cathodic to anodic and vice versa. l'referably, the substrate electrode is polarized cathodically in the first step. In repeating steps anodic and cathodic polarizations are added, preferably fin-ishing the deposition with a cathodic polarization of the substrate electrode.
It: is advantageous to raise the time periods of the cathodic and anodic polarizations during the repeating steps and/or to carry out the anodic polarizations with a potential becoming more and more anodic. Cathodic and anodic polarizations of the substrate electrode are executed aiternately with a total cathodic polarization time of between I and 60 min and a total anodic polarization time of between 1 and 60 min.
The cathodic polarization can be realized potentiostatically or galvanostatically and the anodic polarization can be realized potentiostatically, potentiodynamically or galvanostatically until the desired target potential is reached. The target potential is in the region of 2 to 150 VSCE.
The choice of the target potential determines the thickness of the titanium oxide layer to be built up and, hence, the thickness of' the gradient region of the coating.
The current density of the cathodic galvanostatic polarization is preferably chosen to be 0.1 to mA/cmZ.
The three-electrode arrangement for the execution of the process according to the invention, is made of a saturated calomel electrode as the reference electrode, a platinum sheet as the counter electrode, and the metallic implant as the substrate electrode. A
thermostatically con-trolled cell is used as the electrolyte cell. The electrochemical reaction is carried out preferably at a temperature of 60 C.
W'ith the help of the process described by the invention, the desired calcium phosphate phase or the defined mixture of calcium phosphate phases can be built up from the used electrolyte solution as a gradient structure with ttie metal oxide of the implant material. The coating de-posited on the metal implant induces a good growing of the bone towards the implant sup-porting the incorporation of the implant into the biological system. Under the influence of sub-stances of the body the coating is normally resorbed. To give the bone an orientation through-out the whole lifetime, calcium phosphate particles are not only fixed to the implant, but also i.nserted in it. This is possible because of the step-by-step process of the cathodic and anodic polarization of the substrate electrode. The desired calcium phosphate phase or mixture of phases is deposited on this substrate electrode from the electrolyte during the cathodic polari-zation. During the anodic polarization the oxide layer of the implant metal begins to grow over t:he deposited calcium phosphate particles, which results in their incorporation into the oxide layer of the metal. Repeating these steps increases the thickness of the layer. It is advantageous for the growth of the layer to raise the time periods of the steps and to carry out the second step with a potential becoming more and more anodic. To obtain a surface layer of calcium phosphate phases, finishing the process of making the gradient layer with a cathodic polariza-tion is advantageous.
The advantages of the deposited layers according to the invention are an improved transmis-sion of forces and a permanent improvement of the biocompatibility by means of the incorpo-ration of calcium phosphate phases in the implant surtace. The possibility of the adjustment of the composition of the layer to the composition of the inorganic bone substance a quick in-growth into the bone is supported.
The invention is explained in more detail by means of the following examples:
F?xample I
A disc made of 99.7% pure titaniutn having a diameter of 13 mm and a thickness of 2 mm is ground, cleaned in alcohol, rinsed in deionized water and dried with a fan. As the electrolyte solution a calcium phosphate solution is used, produced as follows: 10 mi stock solution of CaCl2 = 2H20 and NH4H2PO4, in concentrations of 33 mM and 20 mM, respectively, are di-luted and mixed, resulting in 200 ml of 1.67 mM calcium and 1 .0 mM phosphate.
Previously, the pH value is adjusted using diluted NH4OH solution to 6.4 The solution is heated to 60 C
and poured into a double jacket cell. A three-electrode arrangement is set up.
A saturated calomel electrode is used as a reference electrode. A platinum sheet is the counter electrode.
~I'he titanium disc forms the working electrode. After this the potentiostat is contacted. The formation of the hydroxyapatite layer is realized through an alternating polarization:
min cathodic polarization of the titanium sample, galvanostatically, with I =
1 mA (ls' step);
10 min anodic polarization, potentiostatically, with U== 5 VSc~E (2 d step);
min cathodic polarization according to step I(3"d step);
10 min anodic polarization with U= 10 VSCE (4'h step);
finishing with 35 min of cathodic polarization according to the lY' step (5'~' step).
The sample is removed from the electrolyte, rinsed with deionized water and dried with a fan.
The deposited layer looks whitish yellow, is uniformly developed and has a good interface bonding. Investigations carried out with a scanning electron microscope revealed a closed coating, consisting of agglomerates of very fine needles having a length of about 500 nm. The analysis of the composition by means of energy dispersive X-ray analysis showed a Ca/P ratio oPthe phase in the coating equal to that of commercial hydroxyapatite. X-ray diffraction analy-sis verified the phase to be hydroxyapatite.
The wedge-shaped preparation shows a gradient structure of the coating. Under the scanning electron microscope no sharp transition between substrate and coating is observed.
Example 2 An electrolyte identical to that of example I is used. The titanium disc is prepared according to example 1. The electrochemical setting is equal to example 1. After a galvanostatic, cathodic polarization (I = 0.3 mA, 10 min) (1 g' step), the 2 d step is carried out starting with the poten-tial set up by the process of the galvanostatic, cathodic polarization, as an anodic polarization at a polarization rate of 5 mV/s until a level of 5 VscF; is reached. After having reached this potential a cathodic polarization with 0.3 mA is carried out in step 3.
Starting with the poten-tial set up by the process of the galvanostatic, cathodic polarization, the 40' step is an anodic polarization with a polarization rate of 5 mV/s until a level of 10 VSCE is reached. The process is finished with a cathodic polarization of 3 5 min according to the 1 st step (5'" step).
T'he coating on the substrate electrode consists of octacalcium phosphate.
Electron micro-scopical investigations show crystals with shapes from needles to bands with dimensions up to m. X-ray diffractornetric and raman spectroscopic analyses done for comparison, show that the coating is made of octacalcium phosphate.
The wedge-shaped preparation shows a gradient transition in the phase boundary. Under the scanning electron microscope no sharp transition between substrate and coating is observed.
Example 3 A titanium disc is prepared according to example i. 200 ml of calciumphosphate solution are used as an electrolyte solution with the following composition realized by weighing in the salts:
40 mM CaClz and 25 mM 1VH.,HZP04. The pH value is adjusted to 4.4.
The electrochemical arrangement is equal to example I
After the first potentiostatic cathodic polarization with UscF =-1300 mV, 10 min (step 1), the electrode is anodically polarized under galvanostatic conditions in a second step, 1 mA, 10 min. After 15 min of cathodic polarization according to step I(3rd step), the galvanostatic anodic polarization is done in a 4"' step for 10 min with 2 mA. The process is finished with a cathodic polarization of 35 nun according to step 1(5'h step).
The coating on the substrate electrode consists of crystals having the shape of small plates and dimensions up to 30 m.
Energy dispersive X-ray analysis gives a Ca/P ratio of the phase in the coating equal to that of commercial brushite. X-ray diffract.ion revealing the crystal structure confirms that the phase is hydroxyapatite.
The wedge-shaped preparation shows a gradient transition in the phase boundary. Under the scanning electron microscope no sharp transition between substrate and coating is observed.
Example 4 An electrolyte identical to the one of example 1 is used. The titanium disc is produced accord-ing to example 1 and, additionally, polished until a mirror-like surface is obtained, and is oxi-datively etched in 50 ml of a solution consisting of 0.5 M. NaOH and 0.1 M
H202 for 4 min at a temperature of 65 C. Under the electron microscope, the etched surface shows a varying cor-i-osion of the titanium crystallites and a structure in the nanometer range.
Deposition of the coating takes place in the same way as in example 1. Electron microscopic analysis shows the needle-like crystals as in example 1 with the Ca/P ratio of hydroxyapatite.
Altogether, the coating has a higher roughness. The coating shows a better ititerface bonding to the substrate than in example 1. The wedge-shaped cut shows, in addition to the graduated transition, an interlocking between substrate and coating.
A disadvantage of this solution is that'the deposition of the layer proceeds only on the surface of the substrate. This means, on the one hand, that there is no mechanically loadable connec-tion. On the other hand, the coating can be completely resorbed biologically.
Furthermore, the coating always consists of three components, a- and 0-tricalcium phosphate and components of the chemical formula Ca5(PO4)3_x(C03)x(OH),+x with X = 0.2 or less. This means that the coating is always a mixture of these components not approximating the composition of bone.
The object of the invention is the coating of metallic implants, preferably of titanium implants or implants made of titanium alloys, with a gradient layer made of calcium phosphate phases and metal oxide phases. Thus, in addition to the effect of accelerated ingrowth a permanent improvement of the interaction between the implant surface and the biological system will be achieved. Moreover, the composition of the calcium phosphate phases is controllable via the process parameters so that, optionally, hydroxyapatite, octacalcium phosphate or brushite as well as defined combinations of these phases can be produced.
According to the invention, there is provided a process for producing a gradient coating of calcium phosphate phases and metal oxide phases on a metal implant, comprising: providing a metal implant; providing an electrolyte solution containing calcium phosphate ions, and having a pH of between 4.0 and 7.5; providing a counter electrode in the electrolyte solution; placing the implant in the electrolyte solution; applying an electrical potential between the counter electrode and the implant, so that the implant initially acts as a substrate cathode; periodically reversing the polarity of the electrical potential a plurality of times, so that the implant alternates between cathodic polarization and anodic polarization, to deposit a gradient coating of calcium phosphate phases and metal oxide phases on the implant.
2a Preferably, the ratio of the concentration of the calcium and phosphate ions is chosen such that it is equal to their concentration ratio.in hydroxyapatite. In a preferred implementation of the invention the electrolyte is produced from an aqueous solution of CaCl2 and NHaH2POa with a ratio of concentration of calcium and phosphate ions equal to that of hydroxyapatite. The pH
value is preferably adjusted between 4 and 7.5 by means of a diluted 1VH4OH
solution. The use of other readily soluble calcium salts and phosphates (for example, alkali phosphates) is also possible. Beyond that the conditions of the electrolysis mainly determine the formation of par-ticular calcium phosphate phases and their mixtures, respectively. It is also possible to choose different concentration ratios of calcium and phosphate ions.
In an arrangement consisting of a substrate electrode, reference electrode and counter elec-trode the substrate electrode formed by the implant is polarized varying the polarization from cathodic to anodic and vice versa. l'referably, the substrate electrode is polarized cathodically in the first step. In repeating steps anodic and cathodic polarizations are added, preferably fin-ishing the deposition with a cathodic polarization of the substrate electrode.
It: is advantageous to raise the time periods of the cathodic and anodic polarizations during the repeating steps and/or to carry out the anodic polarizations with a potential becoming more and more anodic. Cathodic and anodic polarizations of the substrate electrode are executed aiternately with a total cathodic polarization time of between I and 60 min and a total anodic polarization time of between 1 and 60 min.
The cathodic polarization can be realized potentiostatically or galvanostatically and the anodic polarization can be realized potentiostatically, potentiodynamically or galvanostatically until the desired target potential is reached. The target potential is in the region of 2 to 150 VSCE.
The choice of the target potential determines the thickness of the titanium oxide layer to be built up and, hence, the thickness of' the gradient region of the coating.
The current density of the cathodic galvanostatic polarization is preferably chosen to be 0.1 to mA/cmZ.
The three-electrode arrangement for the execution of the process according to the invention, is made of a saturated calomel electrode as the reference electrode, a platinum sheet as the counter electrode, and the metallic implant as the substrate electrode. A
thermostatically con-trolled cell is used as the electrolyte cell. The electrochemical reaction is carried out preferably at a temperature of 60 C.
W'ith the help of the process described by the invention, the desired calcium phosphate phase or the defined mixture of calcium phosphate phases can be built up from the used electrolyte solution as a gradient structure with ttie metal oxide of the implant material. The coating de-posited on the metal implant induces a good growing of the bone towards the implant sup-porting the incorporation of the implant into the biological system. Under the influence of sub-stances of the body the coating is normally resorbed. To give the bone an orientation through-out the whole lifetime, calcium phosphate particles are not only fixed to the implant, but also i.nserted in it. This is possible because of the step-by-step process of the cathodic and anodic polarization of the substrate electrode. The desired calcium phosphate phase or mixture of phases is deposited on this substrate electrode from the electrolyte during the cathodic polari-zation. During the anodic polarization the oxide layer of the implant metal begins to grow over t:he deposited calcium phosphate particles, which results in their incorporation into the oxide layer of the metal. Repeating these steps increases the thickness of the layer. It is advantageous for the growth of the layer to raise the time periods of the steps and to carry out the second step with a potential becoming more and more anodic. To obtain a surface layer of calcium phosphate phases, finishing the process of making the gradient layer with a cathodic polariza-tion is advantageous.
The advantages of the deposited layers according to the invention are an improved transmis-sion of forces and a permanent improvement of the biocompatibility by means of the incorpo-ration of calcium phosphate phases in the implant surtace. The possibility of the adjustment of the composition of the layer to the composition of the inorganic bone substance a quick in-growth into the bone is supported.
The invention is explained in more detail by means of the following examples:
F?xample I
A disc made of 99.7% pure titaniutn having a diameter of 13 mm and a thickness of 2 mm is ground, cleaned in alcohol, rinsed in deionized water and dried with a fan. As the electrolyte solution a calcium phosphate solution is used, produced as follows: 10 mi stock solution of CaCl2 = 2H20 and NH4H2PO4, in concentrations of 33 mM and 20 mM, respectively, are di-luted and mixed, resulting in 200 ml of 1.67 mM calcium and 1 .0 mM phosphate.
Previously, the pH value is adjusted using diluted NH4OH solution to 6.4 The solution is heated to 60 C
and poured into a double jacket cell. A three-electrode arrangement is set up.
A saturated calomel electrode is used as a reference electrode. A platinum sheet is the counter electrode.
~I'he titanium disc forms the working electrode. After this the potentiostat is contacted. The formation of the hydroxyapatite layer is realized through an alternating polarization:
min cathodic polarization of the titanium sample, galvanostatically, with I =
1 mA (ls' step);
10 min anodic polarization, potentiostatically, with U== 5 VSc~E (2 d step);
min cathodic polarization according to step I(3"d step);
10 min anodic polarization with U= 10 VSCE (4'h step);
finishing with 35 min of cathodic polarization according to the lY' step (5'~' step).
The sample is removed from the electrolyte, rinsed with deionized water and dried with a fan.
The deposited layer looks whitish yellow, is uniformly developed and has a good interface bonding. Investigations carried out with a scanning electron microscope revealed a closed coating, consisting of agglomerates of very fine needles having a length of about 500 nm. The analysis of the composition by means of energy dispersive X-ray analysis showed a Ca/P ratio oPthe phase in the coating equal to that of commercial hydroxyapatite. X-ray diffraction analy-sis verified the phase to be hydroxyapatite.
The wedge-shaped preparation shows a gradient structure of the coating. Under the scanning electron microscope no sharp transition between substrate and coating is observed.
Example 2 An electrolyte identical to that of example I is used. The titanium disc is prepared according to example 1. The electrochemical setting is equal to example 1. After a galvanostatic, cathodic polarization (I = 0.3 mA, 10 min) (1 g' step), the 2 d step is carried out starting with the poten-tial set up by the process of the galvanostatic, cathodic polarization, as an anodic polarization at a polarization rate of 5 mV/s until a level of 5 VscF; is reached. After having reached this potential a cathodic polarization with 0.3 mA is carried out in step 3.
Starting with the poten-tial set up by the process of the galvanostatic, cathodic polarization, the 40' step is an anodic polarization with a polarization rate of 5 mV/s until a level of 10 VSCE is reached. The process is finished with a cathodic polarization of 3 5 min according to the 1 st step (5'" step).
T'he coating on the substrate electrode consists of octacalcium phosphate.
Electron micro-scopical investigations show crystals with shapes from needles to bands with dimensions up to m. X-ray diffractornetric and raman spectroscopic analyses done for comparison, show that the coating is made of octacalcium phosphate.
The wedge-shaped preparation shows a gradient transition in the phase boundary. Under the scanning electron microscope no sharp transition between substrate and coating is observed.
Example 3 A titanium disc is prepared according to example i. 200 ml of calciumphosphate solution are used as an electrolyte solution with the following composition realized by weighing in the salts:
40 mM CaClz and 25 mM 1VH.,HZP04. The pH value is adjusted to 4.4.
The electrochemical arrangement is equal to example I
After the first potentiostatic cathodic polarization with UscF =-1300 mV, 10 min (step 1), the electrode is anodically polarized under galvanostatic conditions in a second step, 1 mA, 10 min. After 15 min of cathodic polarization according to step I(3rd step), the galvanostatic anodic polarization is done in a 4"' step for 10 min with 2 mA. The process is finished with a cathodic polarization of 35 nun according to step 1(5'h step).
The coating on the substrate electrode consists of crystals having the shape of small plates and dimensions up to 30 m.
Energy dispersive X-ray analysis gives a Ca/P ratio of the phase in the coating equal to that of commercial brushite. X-ray diffract.ion revealing the crystal structure confirms that the phase is hydroxyapatite.
The wedge-shaped preparation shows a gradient transition in the phase boundary. Under the scanning electron microscope no sharp transition between substrate and coating is observed.
Example 4 An electrolyte identical to the one of example 1 is used. The titanium disc is produced accord-ing to example 1 and, additionally, polished until a mirror-like surface is obtained, and is oxi-datively etched in 50 ml of a solution consisting of 0.5 M. NaOH and 0.1 M
H202 for 4 min at a temperature of 65 C. Under the electron microscope, the etched surface shows a varying cor-i-osion of the titanium crystallites and a structure in the nanometer range.
Deposition of the coating takes place in the same way as in example 1. Electron microscopic analysis shows the needle-like crystals as in example 1 with the Ca/P ratio of hydroxyapatite.
Altogether, the coating has a higher roughness. The coating shows a better ititerface bonding to the substrate than in example 1. The wedge-shaped cut shows, in addition to the graduated transition, an interlocking between substrate and coating.
Claims (9)
1. A process for producing a gradient coating of calcium phosphate phases and metal oxide phases on a metal implant, comprising:
providing a metal implant;
providing an electrolyte solution containing calcium phosphate ions, and having a pH
of between 4.0 and 7.5;
providing a counter electrode in the electrolyte solution;
placing the implant in the electrolyte solution;
applying an electrical potential between the counter electrode and the implant, so that the implant initially acts as a substrate cathode;
periodically reversing the polarity of the electrical potential a plurality of times, so that the implant alternates between cathodic polarization and anodic polarization, to deposit a gradient coating of calcium phosphate phases and metal oxide phases on the implant.
providing a metal implant;
providing an electrolyte solution containing calcium phosphate ions, and having a pH
of between 4.0 and 7.5;
providing a counter electrode in the electrolyte solution;
placing the implant in the electrolyte solution;
applying an electrical potential between the counter electrode and the implant, so that the implant initially acts as a substrate cathode;
periodically reversing the polarity of the electrical potential a plurality of times, so that the implant alternates between cathodic polarization and anodic polarization, to deposit a gradient coating of calcium phosphate phases and metal oxide phases on the implant.
2. A process according to claim 1, wherein the ratio of calcium to phosphate ions in the electrolyte is equal to that of hydroxyapatite.
3. A process according to claim 1, wherein the deposition is halted after a cathodic polarization step.
4. A process according to claim 1, wherein the time period of polarization is raised for at least one step after the initial polarization.
5. A process according to claim 1, wherein the anodic polarization is carried out with increasingly positive potential.
6. A process according to claim 1, wherein the cathodic polarization is carried out potentiostatically or galvanostatically and the anodic polarization is carried out potentiodynamically or galvanostatically until a target potential of between 2 and 150 V SCE is reached.
7. A process according to claim 1, wherein the total time of anodic polarization is between 1 and 60 minutes, and the total time of cathodic polarization is between 1 and 60 minutes.
8. A process according to claim 1, wherein the cathodic polarization is galvanostatic, and is carried out at a current density of between 0.1 and 5 mA/cm2.
9. A process according to claim 1, wherein each period of polarization lasts at least 10 minutes.
Applications Claiming Priority (3)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| DE19504386A DE19504386C2 (en) | 1995-02-10 | 1995-02-10 | Process for the production of a graded coating from calcium phosphate phases and metal oxide phases on metallic implants |
| DE19504386.3 | 1995-02-10 | ||
| PCT/DE1996/000197 WO1996024391A1 (en) | 1995-02-10 | 1996-02-06 | Process for producing a graduated coating of calcium phosphate phases and metallic oxide phases on metal implants |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| CA2187512A1 CA2187512A1 (en) | 1996-08-15 |
| CA2187512C true CA2187512C (en) | 2007-05-29 |
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| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002187512A Expired - Fee Related CA2187512C (en) | 1995-02-10 | 1996-02-06 | Process for producing a graduated coating of calcium phosphate phases and metallic oxide phases on metal implants |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA2187512C (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN102492974A (en) * | 2011-12-30 | 2012-06-13 | 浙江大学 | Method for preparing degradable magnesium-doped amorphous calcium phosphate coating on surface of titanium implant |
Families Citing this family (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CA2574115A1 (en) * | 2004-07-21 | 2006-01-26 | The University Of British Columbia | Method of electrolytically depositing a pharmaceutical coating onto a conductive osteal implant |
| CN102014975A (en) | 2008-02-29 | 2011-04-13 | 史密夫和内修有限公司 | Gradient coating for biomedical applications |
-
1996
- 1996-02-06 CA CA002187512A patent/CA2187512C/en not_active Expired - Fee Related
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN102492974A (en) * | 2011-12-30 | 2012-06-13 | 浙江大学 | Method for preparing degradable magnesium-doped amorphous calcium phosphate coating on surface of titanium implant |
Also Published As
| Publication number | Publication date |
|---|---|
| CA2187512A1 (en) | 1996-08-15 |
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