Biomedical Engineering Reference
In-Depth Information
For instance, in the case of PEM capsules, diffusion is a method for loading molecules
within the capsule's interior and investigating their permeability using fluorescent dex-
trans (Tong et al. 2005). The diffusion of small model molecules, such as dyes, in planar
LbL films is often investigated. Kharlampieva and Sukhisvili (2004) found for hydrogen-
bonded multilayers that dye loading capacity was largely affected by the nature of the
polyelectrolyte on top of the film (of opposite charge to that of the dye). An extraction of
the dye through the film by polymers in solution contributed significantly to dye release
in the case of electrostatically assembled films. Control of entrapment and the diffusion
of silver (Ag) ions have attracted great interest due to the antibacterial properties of these
ions (see Section 8.3.5).
Thick films that are hydrated and/or porous are particularly suitable for being used as
reservoirs for active compounds. Using PLL/HA film as a matrix, Vodouhê et al. (2006)
observed, using CLSM, that paclitaxel Green 488 molecules diffused throughout the whole
(PLL/HA)
60
film section and that the fluorescence was homogeneously distributed over
the whole thickness of the film (12 μm). A similar strategy was employed by Schneider
et al. (2007c), who loaded cross-linked PLL/HA films with the anti-inflammatory drug
sodium diclofenac and with paclitaxel. The amount of drug loaded could be adjusted by
varying the film's thickness (Schneider et al. 2007a). Paclitaxel-loaded films were efficient
in killing cells, as less than 10% of the cells were still alive after 3 days of culture (Fig-
ure 8.9) (Schneider et al. 2007c). Control of film porosity at the micrometer and nanometer
scales is an important step toward controlling diffusion. Berg et al. (2006) showed that it
is possible to adjust the amount of ketoprofen and cytochalasin D released from films by
varying the number of layers in the porous regions of films, and the release rate depended
on film pore size.
Larger molecules, such as proteins, can diffuse within or at the surface of films, depend-
ing on the film's structural properties. Thus, albumin was found to diffuse in and on PSS/
PAH films (Szyk et al. 2001). Recently, the diffusion of staphylococcal nuclease (SNase) was
investigated by neutron reflectometry (Jackler et al. 2005). It was shown that the SNase is
***
Control
Taxol
(a)
(b)
100
*
300
80
200
60
***
***
40
100
**
**
***
20
0
0
24 h
48 h
72 h
24 h
48 h
72 h
FIGURE 8.9
Acid phosphatase (AP) activity for HT29 cells cultured on cross-linked (PLL/HA)
12
films loaded or not with
paclitaxel, after different time periods of 24, 48, and 72 h in culture. Error bars represent standard deviation.
Two different representations are shown: (a) value of 100% has been arbitrarily attributed to CL films at 24 h
(**
p
< 0.01; ***
p
< 0.001 versus control at 24 h for control films or versus paclitaxel at 24 h for paclitaxel loaded
films). (b) Value of 100% has been arbitrarily set at 100% for CL films at each time period (*
p
< 0.05; **
p
< 0.01;
***
p
< 0.001 versus controls, which are CL films at time 24, 48, and 72 h, respectively. (Reproduced with permis-
sion from Schneider et al.,
Biomacromolecules
, 8, 139-145, 2007c. Copyright ACS 2007.)
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