**Please respond with explanations** Chem Engr Drop-on-demand (DoD) technology i
ID: 1023629 • Letter: #
Question
**Please respond with explanations** Chem Engr
Drop-on-demand (DoD) technology is an emerging form of drug delivery in which a reservoir
is lled with a solution of an active pharmaceutical ingredient (API) dissolved in a volatile
liquid, and a device sprays nanometer-scale drops of the solution onto an edible substrate,
such as a small strip the size of a stick of chewing gum. The liquid evaporates very rapidly,
causing the API to crystallize on the substrate. The exact dose required by a patient canbe administered based on the known concentration of the API in the reservoir and the volume of solution deposited on the substrate, enabling greater dosage accuracy than can be provided by administering fractions of tablets.
(a) A DoD device is charged with a 1.20 molar solution of ibuprofen (the API) in n-hexane.
The molecular weight of ibuprofen is 206.3 g/mol. If a prescribed dosage is 5.0 mg
ibuprofen/kg patient weight, how many milliliters of solution should be sprayed for a
245-pound man and a 65-pound child? How many drops are in each dose, assuming
that each drop is a sphere with a radius of 1 nm?
(b) The DoD device is to be automated, so that the operator enters a patient's body
weight into a computer that determines the required solution volume and causes that
volume to be sprayed on the substrate. Derive a formula for the volume, Vdose (mL),
in terms of the following variables:
Ms (mol API/L) = molarity of reservoir solution
SGs = speci c gravity of reservoir solution
MWAPI (g/mol) = molecular weight of API
D (mg AOI/kg body weight) = prescribed dosage
WP (lbf ) = patient's weight
Check your formula by verifying your solution to Part (a).
(c) Calculate the surface-to-volume ratio of a sphere of radius r. Then calculate the total
drop surface area of 1 mL (= 1 cm3) of the solution if it were sprayed as drops of
(i) radius 1 nm and (ii) 1 mm. Speculate on the likely reason for spraying nanoscale
drops instead of much larger drops.
Explanation / Answer
a.
1.20 molar solution of ibuprofen means there are 1.20 moles of ibuprofen in 1 lit sol of n-hexane.
so there are 206.3 g/mol * 1.20 mol/litre = 247.56 g in 1000 ml of n hexane
so there is 0.24756 g/ml solution
for 245 pound man{111.13 kg} dosage = 5*10^-3 *111.13 g = 0.55565 g /x ml = 0.24756
x = 0.55565/0.24756 = 2.24450 ml
no of drops * volume of one drop = 2.24450 ml
no of drops = 2.24450 *3/4*10^-27 *10^3 = 1.683375 *10^24 drops
for 65 pound man{29.835 kg} dosage = 5*10^-3 *29.835 g = 0.149175 g/x ml = 0.24756
x = 0.149175/0.24756 = 0.6025 ml
no of drops * volume of one drop = 0.6025 ml
no of drops = 0.6025 *3/4*10^-27 *10^3 = 4.51875 *10^23 drops
b.
v dose = {prescribed dosage * patient's weight}/ { molarity of reservoir solution * molecular weight of API /1000}
= {prescribed dosage * patient's weight}/ { specific gravity*density of the volatile liquid /1000}
c.
surface to volume ratio of sphere of radius r = 3/r
surafce area of 1 ml of solution = 3/10^-9 *10^-6 = 3000 m2
surface area of 1 ml of solution = 3/10^-3 * 10^-6 = 0.003 m2
nanoscale drops offer a large surface area than similar masses of larger-scale materials. As surface area per mass of a material increases, a greater amount of the material can come into contact with surrounding materials, thus affecting reactivity.
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