Acellular dermal allografts and method of preparation
A method for preparing a sterilized human acellular dermal allograft where the dermal allograft is sterilized by irradiation and has a greatly reduced bio-burden and enzymatic and antigenic activity. This product line of allografts can be easily used by surgeons in soft tissue replacement or repair and has an extended shelf life, of up to at least about three years.
1. A method of preparing an irradiation sterilized acellular dermal allograft that can be stored for periods of at least about 3 years before use in grafting procedures, the method comprising:
processing skin tissue comprising the following steps in the order of:
(i) removing the cells of the skin tissue by exposing said skin tissue to a cell removal solution to remove cells and provide a first processed skin tissue, said cell removal solution comprising at least two detergents: (1) deoxycholate at a concentration about 1% to 10% (v:v); and (2) a polyethylene glycol p-tert-octylphenyl ether, sodium dodecyl sulfate, or polysorbate at a concentration about 0.5% to 5% (v:v);
(ii) deteriorating the epidermis by exposing the first processed skin tissue to a separate epidermis removal solution comprising at least one detergent at a concentration about 0.2 to 2.8% (v:v) to deteriorate the epidermis of the first processed skin tissue and form a second processed skin tissue;
wherein the cell removal and epidermis removal solutions do not contain enzymes;
(iii) removing the epidermis of the second processed skin tissue after exposure to the epidermis removal solution to produce a dermal allograft;
(iv) exposing the dermal allograft to a gamma irradiation protection solution;
(v) preparing the dermal allograft for irradiation by performing at least one step from among: drying the dermal allograft by lyophilization, freezing the dermal allograft, or placing the dermal allograft in saline; and
(vi) exposing the prepared dermal allograft to irradiation;
whereby the skin tissue can then be stored until use for periods of up to at least about 3 years.
2. The method of claim 1 , wherein the gamma irradiation protection solution comprises at least two sugars and one sugar is trehalose.
3. The method of claim 1 , which further comprises placing the dermal allograft in a container after exposing the dermal allograft to the gamma irradiation protection solution, wherein the container is a bag made of polyethylene and/or polyester laminated with spunbond high density polyethylene fibers.
4. The method of claim 1 , wherein the skin tissue is placed in a stabilization media prior to exposure to processing with the cell removal solution.
5. The method of claim 4 , wherein the stabilization media is a cell growth media which contains an antibiotic.
6. The method of claim 1 , wherein the step of preparing the allograft for the irradiation step is by lyophilization of the allograft.
7. The method of claim 1 , wherein the step of preparing the allograft for the irradiation step is by freezing of the allograft.
8. The method of claim 1 , wherein the step of preparing the allograft for irradiation comprises placing the allograft in saline inside a container.
9. The method of claim 1 , wherein after the step of preparing the allograft for irradiation, the allograft may be stored for up to about one year before irradiation.
10. The method of claim 1 , wherein the irradiation is gamma irradiation.
11. The method of claim 1 , wherein the irradiation is from Cobalt 60 or Cesium 137 .
12. The method of claim 11 , wherein the irradiation is from Cobalt 60 .
13. The method of claim 11 , wherein the irradiation delivers an absorbed radiation dose of 5-35 kGy.
14. The method of claim 13 , wherein the absorbed radiation dose is about 10-23 kGy.
15. The method of claim 13 , wherein the absorbed radiation dose is about 17-23 kGy.
16. The method of claim 1 , comprising a further step, before the processing step, storage of the skin tissue in glycerol at −20° C. to 10° C. for up to about 5 years.
17. The method of claim 16 , wherein prior to storage in glycerol, the graft is treated by exposure to at least two increasing concentration of glycerol, the lowest concentration being about 25% (v:v) and the highest about 100% (v:v).
18. The method of claim 17 , wherein the exposure to increasing concentration of glycerol, comprises exposure to 50%, 75% and 100% glycerol (v:v).
19. The method of claim 1 , wherein the cell removal solution of step (i) further comprises a phosphate buffered saline solution containing a chelating agent.
20. The method of claim 1 , wherein the epidermis removal solution of step (ii) further comprises a water-based solution that includes electrolytes and a chelating agent.
21. The method of claim 1 , wherein the two detergents in the cell removal solution are at a combined concentration of at least 5.5%.