Methods of measuring cell viability in tissue engineered products

1. A method of measuring the fraction of viable cells in a tissue-engineered product maintained in a cell culture conditioned medium comprising:

(a) taking, as a sample portion, a first percentage of the tissue engineered product containing cells and a proportional second percentage of the cell culture conditioned medium;

(b) detecting a cell death-stable enzyme activity (Y) in a portion of a cell culture conditioned medium not containing cells of the tissue-engineered product from the sample portion taken in step (a);

(c) disrupting the membrane integrity of the cells in the sample portion of the tissue engineered product taken in step (a);

(d) detecting a cell death-stable enzyme activity (X) in the cells and conditioned medium of the sample portion of the tissue-engineered product taken in step (a); and

(e) (i) when the ratio of the first percentage to the second percentage is 1:1, calculating the fraction of viable cells by comparing the level of cell death-stable enzyme activity detected in steps (b) and (d) according to the formula:

X

-

cY

X

+

Y

wherein

c

=

1

-

f

f

 and f is the fraction of the total sample conditioned medium present in the portion of the cell culture conditioned medium not containing cells of the cell population; or

(ii) when the ratio of the first percentage to the second percentage deviates from 1:1, calculating the fraction of viable cells by comparing the level of cell death-stable enzyme activity detected in steps (b) and (d) according to the formula:

X

-

cY

X

+

Y

+

2

⁢

⁢

Y

⁡

(

α

-

1

)

wherein

c

=

1

-

f

f

 and f is the fraction of the total sample conditioned medium present in portion of the cell culture conditioned medium not containing cells of the cell population; and wherein a is the ratio of the percentage of the total cells to the percentage of the total conditioned medium present in the sample,

wherein the tissue-engineered product comprises a three-dimensional scaffold or matrix and cells are present in the scaffold or matrix.

2. The method of claim 1 , wherein the membrane integrity of the tissue engineered product is disrupted by shearing, sonication, low barometric pressure, high temperature, low temperature, chemical or enzymatic lysis, or membrane decoupling agents.

3. The method of claim 2 , wherein the membrane integrity of the tissue engineered product is disrupted by the addition of an amphiphile.

4. The method of claim 3 , wherein the amphiphile is saponin.

5. The method of claim 1 , comprising:

(a) taking a portion of the tissue engineered product containing cells and a proportional amount of the cell culture conditioned medium;

(b) dividing the portion taken in step a) to obtain a portion of the cell culture conditioned medium not containing cells of the tissue engineered product;

(c) adding saponin, and bis-(Ala-Ala-Phe)-Rhodamine-110 to the portions of steps a) and b); and

(d) detecting fluorescences corresponding to cleaved bis-(Ala-Ala-Phe)-Rhodamine-110 in the portions of steps a) and b),

wherein the cells are human chondrocytes, maintained in a matrix at a density of between 1.5×10 4 and 6×10 6 cells/cm 2 .

6. The method of claim 1 , wherein the cell death-stable enzyme activity is measured by the steps comprising:

(a) contacting a sample with a substrate of the cell death-stable enzyme activity wherein the substrate in conjugated to a detectable leaving group; and

(b) detection of the leaving group,

wherein the amount of leaving group detected is proportional to the level of cell death-stable enzyme activity.

7. The method of claim 6 , further comprising the step of adding an agent which modulates the signal of the detectable leaving group.

8. The method of claim 6 , wherein the substrate is bis-(Ala-Ala-Phe)-Rhodamine-110.