Biomedical Engineering Reference
In-Depth Information
most abundant of the flavonoid molecules, is widely distributed in the plant kingdom
being found in many usually consumed foods, including apple, onion, tea, berries,
and brassica vegetables, as well as many seeds, nuts, flowers, barks, and leaves. It is
also found in medicinal botanicals, including Ginkgo biloba , Hypericum perforatum
(St. John's Wort), Sambucus canadensis (elder), and many others, and is often a
component of the medicinal activity of the plant [ 79 ]. Among other properties,
quercetin is recognized as an intra-arterial pressure reducer preventing cardiovas-
cular disease [ 80 ] also presenting strong antioxidant [ 81 - 84 ], antiinflammatory [ 85 ]
and antiviral activities [ 86 ]. Despite its wide spectrum of potential pharmacological
properties, the use of quercetin in the pharmaceutical field is quite limited and
few human quercetin absorption studies exist due to its low aqueous solubility
and to its easy degradation in aqueous intestinal fluids [ 87 ]. It appears that only
a small percentage of about 2% of quercetin is absorbed after an oral dose [ 88 ].
In order to make the administration effective, high oral doses of about 400-500 mg
three times per day is typically used in clinical practice. In order to overcome this
issue, quercetin chalcone, a water soluble derivative, is usually administrated and it
might be used in smaller doses; typically 250 mg three times per day [ 89 ]. Topical
and transdermal administration may provide an efficient alternative for quercetin
delivery in order to enrich the endogeneous cutaneous protection system, which
would represent a successful strategy for diminishing ultraviolet radiation oxidative
damages as well as any involved inflammation processes of the skin [ 90 ].
The transdermal delivery of relatively high molecular weight compounds is
usually enhanced by the simultaneous administration of skin permeation enhancers
like terpenes of which L-menthol is a successful reported example [ 91 ]. These
compounds reduce the diffusional penetration barrier by inducing a temporary and
reversible increase on its permeability by disrupting the hydrogen-bonding network
and increasing the hydration levels of the lipid system, probably by forming new
aqueous channels [ 91 - 93 ]. Thymol is a monoterpenic phenol usually found in thyme
oil with chemical structure similar to L-menthol that can in principle be used as
permeation enhancer. Besides, it presents strong antioxidant, anaesthetic, antiseptic
and antiinflammatory activities [ 94 , 95 ] being also an anti-bacterial and/or anti-
microbial agent showing a broad-spectrum of biological activities against bacteria,
yeasts and fungi [ 96 , 97 ]. These properties strengthen the potential applicability of
this substance as an active compound for impregnated wound dressing materials.
5
Materials and Processes
The molecular structures of employed bioactive substances and polymeric bio-
materials are represented in Fig. 2 . N-carboxybutylchitosan (CBC) and agarose
(AGA) solutions were prepared according to the procedure already described
in the literature and references therein [ 45 ]. Films of CBC and foams of CBC
and AGA were prepared by the solvent casting method and by freeze-drying,
respectively. The average thickness of all obtained sample materials was 95
˙
5
m
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