Treatment of bioprosthetic tissues to mitigate post implantation calcification

Abstract

Bioprosthetic tissues are treated by immersing or otherwise contacting fixed, unfixed or partially fixed tissue with a glutaraldehyde solution that has previously been heat-treated or pH adjusted prior to its contact with the tissue. The prior heat treating or pH adjustment of the glutaraldehyde solution causes its free aldehyde concentration to decrease by about 25% or more, preferably by as much as 50%, and allows a “stabilized” glutaraldehyde solution to be obtained at the desired concentration and pH for an optimal fixation of the tissue at high or low temperature. This treatment results in a decrease in the tissue's propensity to calcify after being implanted within the body of a human or animal patient. The heat-treated or pH adjusted glutaraldehyde solution may, in some cases, also be used as a terminal sterilization solution such that the calcification-decreasing treatment with the previously treated glutaraldehyde and a terminal sterilization may be carried out simultaneously and/or in a single container.

1 . A method for mitigating post-implantation calcification of a bioprosthetic implant material, said method comprising the steps of: 
 providing a solution selected from the group consisting of a glutaraldehyde solution and a physiologic solution;    adjusting the pH of the solution to a pH in the range of about 5.0 to 7.0;    contacting a quantity of biological tissue that contains connective tissue protein with the pH-adjusted solution; and    heating the solution and the tissue to a heat treating temperature in the range of about 30° C. to 70° C. for a period of time.    
     
     
         2 . The method of  claim 1 , wherein the heat treating temperature is in the range of about 40° C. to 60° C.  
     
     
         3 . The method of  claim 1 , wherein the heat treating temperature is about 50° C.±5° C.  
     
     
         4 . The method of  claim 1 , wherein the period of time is between about one hour and six months.  
     
     
         5 . The method of  claim 1 , wherein the period of time is between about one day and two months.  
     
     
         6 . The method of  claim 1 , wherein the period of time is between about 5 days to 10 days.  
     
     
         7 . The method of  claim 1 , wherein the period of time is about 7 days.  
     
     
         8 . The method of  claim 1 , wherein the pH of the solution is adjusted to about 6.0.  
     
     
         9 . The method of  claim 1 , wherein the pH of the solution is adjusted by heating the solution to a pre-heat temperature for a pre-heat period.  
     
     
         10 . The method of  claim 9 , wherein the pre-heat temperature is between 60-80° C.  
     
     
         11 . The method of  claim 10 , wherein the pre-heat temperature is about 70° C.±5° C.  
     
     
         12 . The method of  claim 1 , wherein the pH of the solution is adjusted without heating the solution.  
     
     
         13 . The method of  claim 12 , wherein the pH of the solution is adjusted to about 6.0.  
     
     
         14 . The method of  claim 13  wherein the heat treating temperature is about 50° C.±5 20  C.  
     
     
         15 . The method of  claim 13  wherein the period of time is between about 5 days to 10 days.  
     
     
         16 . The method of  claim 1 , wherein the solution is aqueous glutaraldehyde buffered to a starting pH, wherein the step of adjusting comprises lowering the pH.  
     
     
         17 . The method of  claim 16 , wherein the starting pH is between about 7.2 to 7.8.  
     
     
         18 . A method for mitigating post-implantation calcification of a bioprosthetic heart valve, said method comprising the steps of: 
 harvesting desired biological tissue from a human cadaver or animal donor, and preparing the tissue by trimming to size and washing with a suitable washing solution;    exposing the tissue to a fixation process to form cross-linkages in the tissue to obtain fixed tissue;    providing a solution selected from the group consisting of a glutaraldehyde solution and a physiologic solution and adjusting the pH of the solution to between about 5.0 and 7.0;    immersing the fixed tissue in the solution;    heating the solution and the fixed tissue to a heat treating temperature in the range of about 30° C. to 70° C. for a period of time; and    assembling the heat treated and fixed tissue with non-biological components to form a bioprosthetic heart valve.    
     
     
         19 . The method of  claim 18 , wherein the heat treating temperature is in the range of about 40° C. to 60° C.  
     
     
         20 . The method of  claim 19 , wherein the heat treating temperature is about 50° C.±5° C.  
     
     
         21 . The method of  claim 18 , wherein the period of time is between about one day and two months.  
     
     
         22 . The method of  claim 18 , wherein the period of time is between about 5 days to 10 days.  
     
     
         23 . The method of  claim 18 , wherein the period of time is about 7 days.  
     
     
         24 . The method of  claim 18 , wherein the pH of the solution is adjusted to about 6.0.  
     
     
         25 . The method of  claim 18 , further including, after the tissue has been fixed and heat treated, and prior to assembly into a heart valve, subjecting the fixed tissue to a first bioburden reduction process including: 
 contacting the fixed tissue with a mixture containing: 
 i) a crosslinking agent,  
 ii) a denaturing agent and  
 iii) a surfactant.  
   
     
     
         26 . The method of  claim 25 , further including, after assembling the heart valve, subjecting the fixed tissue to a second bioburden reduction process including: 
 contacting the fixed tissue with a mixture containing: 
 i) a crosslinking agent,  
 ii) a denaturing agent and  
 iii) a surfactant.  
   
     
     
         27 . The method of  claim 26 , wherein the second bioburden reduction process is done at a temperature of about 37° C. for a period of time longer than the first bioburden reduction process.  
     
     
         28 . The method of  claim 27 , further including storing the heart valve in a solution of glutaraldehyde.  
     
     
         29 . The method of  claim 18 , wherein the solution is aqueous glutaraldehyde buffered to a starting pH, wherein the step of adjusting comprises lowering the pH.  
     
     
         30 . The method of  claim 29 , wherein the starting pH is between about 7.2 to 7.8.