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GATE 2020 BM – Question 48

Biomaterials and Tissue Engineering · Biocompatibility and Implant Characteristics · 2 marks · Multiple choice

A degradable surgical suture loses 40% of its original tensile strength after 10 days and 50% after 20 days. Assuming exponential decay, what closest time gives strength 20% of the original?

  1. 35 days
  2. 45 days
  3. 60 days
  4. 70 days

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Correct answer: (D) 70 days

Explanation

Fit S(t)=Ae⁻ᵏᵗ to the two measured fractions S(10)=.6S₀ and S(20)=.5S₀. Their ratio gives k=ln(1.2)/10≈.018232/day, and the fitted intercept is A=.72S₀. Setting .72e⁻ᵏᵗ=.2 gives t≈70.25 days, D. The supplied percentages cannot both follow an exact single exponential constrained to S(0)=S₀; the official answer uses the two-point exponential fit with a free intercept.

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