Colloquium- mechanical properties of skin

Question 1

Mechanical properties of human skin

Aim of study

Answer 1

To determine the type of mechanical properties of human skin- elastic, viscous or
viscoelastic
* To estimate the elastic modulus E (Young’s modulus) of human skin

Question 2

Write the formula for quantitative description of deformation of viscoelastic material. Explain
the meaning of the parameters involved (7)

Answer 2

Stress =Youngs modulus x Strain + viscosity*difference in strain/diff in time

Question 3

Mechaical properties of the skin

Describe shortly the experimental work and measurements performed in this practice (8)

Answer 3

Aspiration of the skin- use vaccum pump connected by pipes? Theres a 1 way+3 way turn clock, micrometer, manometer

Negative pressure is applied to the skin of the forehand with the aspiration device
* The magnitude of the pressure difference is recorded and controlled with a
manometer
* With the micrometer the length of the part of the skin aspirated in the deformation
device is determined, which serves as a measure of strain

Question 4

Which law is used for the calculation of the young’s modulus E? (5)

Answer 4

Hookes law

STRESS= MODULUS OF ELASTICITYxSTRAIN

Question 5

Describe the model system and conditions for the occurrence of
diffusion potential (7)

• draw diagram

Answer 5

Membrane is fully permeable for all ions
* In the system a concentration gradient exists (ions from high conc. Move to lower conc.)
* The ions have different mobilities (u->u+)

Question 6

Below is given the definition expression for the coefficient of iontophoretic permeability of
the skin(k). Explain the meaning of the parameters involved in the formula (7)

k=m/Ixtxs

Answer 6

K= coefficient of iontophoretic permeability
* M=mass of the drug transferred into the skin
* I=Electric current
* T=time
* S=area of skin through which drug is delivered

Question 7

Write the equation for the volume flux (Jv) transportation by filtration. Explain the
parameters involved (7)

The Lp is baso pouseilles law

Answer 7

Lp=filtration coefficeint
* Trip=change in pressure
* n=number of pores per 1m2 membrane area
* R= pore radius
* L= membrane thickness
* Viscosity of the medium

Jv=Lp V p Lp= pir^4/8viscol

Question 8

Plot as a graph the dependence of the zeta sedimentation ratio (ZSR) on the concentration of aggregating agents (5)

Answer 8

look on answer sheet

curve and line

Question 9

From the graph above draw conclusions about the effect of concentration and molecular
mass of the polymers on the RBC aggregation (5)

Answer 9

Higher ZSR shows higher RBC aggregation, here higher concentration of agents gives
a higher ZSR and a larger mass of the polymer gives a higher ZSR at lower
concentration levels

• Higher molecular mass of the aggregating agent gives a faster rate of RBC aggregation
• As the concentration of the aggregating agent increases, the value of ZSR also
  increases

Question 10

Calculate the following parameter (4)

question 10 of test 1

Answer 10

P= 1x10-7