Methods of depositing discrete hydroxyapatite regions on medical implants

Abstract

A method for electrochemically depositing discrete regions of calcium phosphate onto a medical implant. The method includes providing an implant including at least one area having a metallic surface. At least a portion of the metallic surface is contacted with an electrolyte solution comprising calcium ions and phosphate ions. The metallic surface is used as a cathode, and an electrical potential is applied between the cathode and the electrolyte solution. The electrical potential is applied with a constant current density of from about 10 to about 50 mA/cm 2 for a period of time of from about 1 to about 20 minutes. A plurality of discrete regions of needle-shaped hydroxyapatite crystals are electrochemically deposited onto the metallic surface.

1 . A method for electrochemically depositing a discrete region of a calcium phosphate onto a medical implant comprising at least one area having an electroconductive surface, the method comprising:
 a. contacting at least a portion of the electroconductive surface of the implant with an electrolyte solution comprising calcium ions and phosphate ions; and   b. applying an electrical potential between the electroconductive surface and the electrolyte solution, thereby forming a plurality of discrete regions of a calcium phosphate onto the electroconductive surface, wherein the calcium phosphate comprises a needle-shaped morphology.   
     
     
         2 . The method of  claim 1 , wherein the applying an electrical potential comprises applying a constant current density of from about 10 to about 50 mA/cm 2  for a period of time of from about 1 to about 20 minutes, wherein the calcium phosphate phase comprises hydroxyapatite. 
     
     
         3 . The method of  claim 2 , wherein the applying an electrical potential comprises applying a constant current density of about 40 mA/cm 2  for a period of time of from about 2 to about 5 minutes. 
     
     
         4 . The method of  claim 1 , wherein the electrolyte solution comprises calcium chloride and ammonium dihydrogen phosphate in an amount that corresponds to a calcium:phosphate ion ratio of about 1.7:1. 
     
     
         5 . The method of  claim 4 , wherein the concentration of calcium ions in the electrolyte solution is about 1.7 mM. 
     
     
         6 . The method of  claim 1 , wherein the electrolyte solution is maintained at a pH of from about 3 to about 7 using hydrochloric acid or ammonium hydroxide. 
     
     
         7 . The method of  claim 1 , wherein the contacting comprises placing the implant in a bath containing the electrolyte solution and rotating the implant during application of the electrical potential. 
     
     
         8 . The method of  claim 1 , wherein the electrolyte solution has a pH of about 5.1, a concentration of calcium ions of about 1.7 mM, and a concentration of phosphate ions of about 1.0 mM, and wherein the applying an electrical potential comprises applying a constant current density of about 40 mA/cm 2  is provided for about 2 minutes at ambient temperature. 
     
     
         9 . The method of  claim 1 , wherein the electrolyte solution has a pH of about 6, a concentration of calcium ions of about 0.2 mM, and a concentration of phosphate ions of about 0.1 mM, and wherein the applying an electrical potential comprises applying a constant current density of about 30 mA/cm 2  for about 10 minutes at ambient temperature. 
     
     
         10 . The method of  claim 1 , wherein the electroconductive surface of the implant comprises a material from the group consisting of titanium, a titanium alloy, titanium nitrate, a CoCrMo alloy, stainless steel, an electroconductive polymer, and mixtures thereof. 
     
     
         11 . The method of  claim 1 , wherein the electroconductive surface of the implant comprises nano-scale texturing. 
     
     
         12 . A method for electrochemically depositing a discrete region of a calcium phosphate onto a medical implant comprising at least one area having a metallic surface, the method comprising:
 a. contacting at least a portion of the metallic surface of the implant with an electrolyte solution comprising calcium ions and phosphate ions; and   b. applying an electrical potential between the metallic surface as a cathode and the electrolyte solution having a constant current density of from about 10 to about 50 mA/cm 2  for a period of time of from about 1 to about 20 minutes, thereby depositing a plurality of discrete regions of needle-shaped hydroxyapatite crystals onto the metallic surface.   
     
     
         13 . The method of  claim 12 , further comprising allowing partial dissolution of the hydroxyapatite to occur concurrent with the depositing. 
     
     
         14 . The method of  claim 13 , wherein the electrolyte solution is maintained at a pH of from about 5 to about 7. 
     
     
         15 . The method of  claim 12 , wherein the applying the electrical potential comprises applying the electrical potential for at least two discrete intervals of time. 
     
     
         16 . A process for making a plurality of medical implants having discrete regions of a calcium phosphate, comprising:
 a. preparing an electrolyte solution comprising calcium ions and phosphate ions having a concentration ratio of calcium:phosphate of about 1.7:1;   b. placing a plurality of implants into the electrolyte solution, wherein each implant comprises at least one area having an electroconductive surface; and   c. applying a constant electrical potential between the electroconductive surfaces as cathodes and the electrolyte solution, wherein the electrical potential has a constant current density of from about 10 to about 50 mA/cm 2  and is applied for a period of time of from about 1 to about 20 minutes, thereby depositing a plurality of discrete regions of needle-shaped hydroxyapatite crystals onto the electroconductive surfaces.   
     
     
         17 . The process of  claim 16 , wherein the electrolyte solution is in an inner bath container that is disposed within an outer bath container, and the outer bath container contains circulating water maintained at a temperature of about 37° C. 
     
     
         18 . The process of  claim 16 , further comprising removing the plurality of implants from the electrolyte solution after the depositing, rinsing the implants, and anodizing the implants. 
     
     
         19 . The process of  claim 16 , wherein the electrolyte solution comprises deionized water, calcium chloride dihydrate, and ammonium dihydrogen phosphate. 
     
     
         20 . The process of  claim 16 , further comprising cleaning the plurality of implants using an ultrasonic wash prior to placing the plurality of implants in the electrolyte solution.