Biomedical Engineering Reference
In-Depth Information
Tabl e 3
Effect of supercritical CO
2
processing (323 K and 20 MPa) on the
morphology of the samples
Relative variation (%)
a
CBC film
CBC foam
AGA foam
C
169:9
C
4:1
C
23:6
Total intrusion volume (mL/g)
C
266:3
C
33:5
C
102:4
Totalporearea(m²/g)
Average pore diameter (
m)
26:3
22:0
38:9
Apparent (skeletal) density (g/mL)
10:6
C
19:3
C
0:6
Porosity (%)
C
39:6
C
1:6
C
1:5
a
Relative
variation
(%)
D
(after
processing-before
processing)/before
proce-
ssing
100
7
Fluid Handling Properties of Prepared Polymeric Samples
The ability to control the loss of moisture from a wound is commonly determined
by the moisture vapor permeability of the dressing or dressing system. As already
mentioned, excessive exudate can cause maceration of the periwound skin, which
in turn can lead to infection, and therefore the wound dressing material should be
highly absorbent to prevent fluid from spreading over the surrounding healthy tissue
and simultaneously permeable to water vapor and thus permitting the passage of a
significant quantity of the aqueous component of exudate from the wound to the
environment by evaporation. The fluid handling capacity (FHC) of a material is
given by the following equation:
FHC
D
Absorbency
C
Moisture Vapor Loss
(1)
where the absorbency and the moisture vapor loss represent the mass of water vapor
absorbed and permeated by the dressing material. These parameters were measured
for the CBC and AGA membranes following standard procedures and as described
in the literature [
45
]. The absorbency of the membranes was measured at 305 K with
the membranes exposed to a 95% relative humidity (RH) atmosphere. The moisture
vapor loss was determined according to a modified ASTM standard (inverted-cup,
E96-90, Procedure D) by monitoring the amount/mass of evaporated water through
the test-sample membrane and by measuring the weight loss from a water-filled
homemademodifiedPayneCupat305Kfilledwith5gofde-ionizedanddistilled
water and the test-sample membrane was fixed onto its opening, with an exposed
central circular aperture of 3.14
10
4
m
2
exposed to a relative humidity (RH)
of approximately 20% at 305 K. By way of illustration, Fig.
5
compares the fluid
handling capacity of CBC and AGA membranes with some commercial materials
over 24, 48 and 96 h. The results show that different materials present different
rates of hydration with time. Some products reach full absorbency after 24 h, others
are still absorbing after 96 h. These differences clearly have potentially important
clinical implications for the use of the products concerned. The studied materials
reach equilibrium absorbency after 12 h with values equal to 50%, 45% and 30%
for CBC film, CBC foam and AGA foam, respectively. The values obtained for the
