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with low degree of substitution, would enable good solubility in low hazardous or-
ganic solvents, such as ethyl acetate. Moreover, propyl-starches may allow a better
quality control since degree of substitution can be determined after acidic degradation
to the respective glucose derivatives by 1H-NMR spectroscopy. Two propyl-starch
derivatives and one un-modifi ed starch polymer were used as basic constituents for the
preparation of nanoparticles, representing two different degrees of substitutions (Ds)
1.05 (PS-1) and 1.45 (PS-1.45), respectively. Nanoparticles were formulated by emul-
sifi cation-diffusion technique. This method has several advantages such as high yields
generally obtained, high batch to batch reproducibility and easy scaling up. Moreover,
it is possible to control the size and polydispersity of nanoparticles by the control of
the oil/water phase ratio. Once nanoparticles were formed, a thorough physicochemi-
cal characterization was carried out. Afterwards, the capacity of these nanoparticles as
drug delivery systems was explored by the encapsulation and release of three different
model drugs, fl ufenamic acid (FFA), testosterone (Test), and caffeine (Caff). Finally,
considering the nanoparticles characterization results, it was possible to establish the
use of these nanoparticles as TDDS. Hence, the potential application of these nanopar-
ticles as TDDS was analyzed by studying their infl uence on the permeability of human
heat-separated epidermis (HSE).
Enzyme-catalyzed regioselective modification of starch nanoparticles
Starch is an abundant, inexpensive, naturally occurring polysaccharide. It is biocom-
patible, biodegradable, and nontoxic, so it can be used as biocompatible implant ma-
terials and drug carriers. Literature reports describe the use of chemically modified
forms of starch for sustained drug delivery systems. For example, epichlorohydrin
cross-linked high amylose starch was used as a matrix for the controlled release of
contramid. A complex of amylose, butan-1-ol, and an aqueous dispersion of ethylcel-
lulose was used to coat pellets containing salicylic acid to treat colon disorders. Starch
has also been used as a carrier for phenethylamines, acetylsalicylic acid, and estrone.
Hydrogels composed of starch/cellulose acetate blends were reported as possible bone
cements. While starch-based biomaterials appear promising, scientific challenges re-
main to be solved. For example, it would be advantageous if starch esters used as
matrices for drug delivery could be prepared so that they are modified at selected po-
sitions of the glucose residues (i.e., at only the primary or secondary positions). This
is difficult due to the presence of three hydroxyl groups per glucose residue each in
different chemical environments. Furthermore, to solubilize starch for homogeneous
modification, polar aprotic solvents such as dimethyl sulfoxide are needed. For ex-
ample, to modify the primary (6-O) hydroxyl sites of amylose, starch was heteroge-
neously persilylated, the persilylated derivative in carbon tetrachloride was acylated
with an anhydride, and then the silyl protecting groups were removed. Previous work
has investigated the use of enzymes to regioselectively modify polysaccharides under
mild conditions. Hydroxyethylcellulose (HEC) particles were suspended in dimethyl-
acetamide and acylated with vinyl stearate using
Candida antartica
Lipase B (CALB)
as catalyst. After 48 h, a product with degree of substitution (DS) 0.1 was formed.
Lipase-catalyzed modification of HEC in film or powder form by reaction with CL
gave low-DS HEC-
g
-PCL copolymers [94-101].
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