SME
Biomaterials · Problem type
Extract cytotoxicity (viability)
Use this for “An extract reads 0.62 against a control of 0.85 and a blank of 0.05. Is it cytotoxic?”
Diagram
71.2% of 0.8 is 0.57.
This is an example. Type your own values to start a new problem.
ΔAₛ
=
Aₛ
−
Ab
ΔAc
=
Ac
−
Ab
V
%
=
100
×
ΔAₛ
ΔAc
Aₛ, Ac and Ab are the sample’s, the control’s and the blank’s absorbances; the bar is the sample above the blank out of the control above it.
Formulas
ΔAₛ = Aₛ − Ab
0.57 = 0.62 − 0.05
ΔAc = Ac − Ab
0.8 = 0.85 − 0.05
V
=
100
×
ΔAₛ
ΔAc
71.25
=
100
×
0.57
0.8
Assumptions
•
The dye’s color tracks living cells: the absorbance above the blank grows in step with the living cells.
•
The control is cells grown with no extract, so its reading above the blank stands for 100% viable.
•
ISO 10993-5 calls an extract cytotoxic when viability falls under 70% of the control.
Step-by-step
WE KNOW
Aₛ = 0.62, Ac = 0.85, Ab = 0.05
FIND
sample above blank (ΔAₛ), control above blank (ΔAc), viability (V)
Step 1 · Find sample above blank (ΔAₛ)
Use ΔAₛ = Aₛ − Ab
Take the blank off the sample: what is left is the color its living cells made.
ΔAₛ = 0.62 − 0.05
ΔAₛ = 0.57
Step 2 · Find control above blank (ΔAc)
Use ΔAc = Ac − Ab
Take the blank off the control: this is the color of fully viable cells.
ΔAc = 0.85 − 0.05
ΔAc = 0.8
Step 3 · Find viability (V)
Use V = 100 × ΔAₛ ÷ ΔAc
Viability is the sample’s net color as a percent of the control’s.
V
=
100
×
0.57
0.8
V
=
57
0.8
V
=
71.25%
→
V
≥
70%:
the
extract
passes;
it
is
not
cytotoxic.
Check
Put the numbers back in. Both sides should match.
0.57 = 0.62 − 0.05 ✓
0.8 = 0.85 − 0.05 ✓
71.25
=
100
×
0.57
0.8
✓
Topic check
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