Agriculture Reference
In-Depth Information
ketoconazole, miconazole, econazole, and oxiconazole is difficult since they are
very water insoluble (Gupta and Cooper
2008
). However, these lipophilic com-
pounds can be efficiently encapsulated into SLNs. The combined small particle size
and occlusive effect of SLNs can extend drug residence time on the epidermis and
enhance drug penetration through the skin (Jain et al.
2010
; Wavikar and Vavia
2013
). These properties could be also useful to facilitate antimicrobial penetration
through plant cuticles.
SLNs can be an interesting model for delivery of antimicrobials in food prod-
ucts, since food-grade lipids can be used in the formulation. SLNs for controlled
release of nisin were prepared by HPH using Imwitor 90 as lipid base and
poloxamer 188 and sodium deoxycholate as surfactant and cosurfactant, respec-
tively. Platelet-shaped nanostructures with a mean diameter size of 119 nm were
obtained, and the controlled release of nisin with effective antimicrobial activity
was observed for up to 20 days (Prombutara et al.
2012
).
6.3.5 Nanofibers
Nanofibers can be produced from diverse polymers specifically treated to form
filaments with a diameter in the nanometer scale. Materials like polyurethane, poly
(lactic acid), poly(lactic-
co
-glycolic acid), polyvinyl alcohol, silk fibroin, gelatin,
and chitosan acetate are among the widely used polymeric substances used to
develop nanofibers (Huang et al.
2003
).
Several methods are used for production of ultrafine fibers, but the
electrospinning method is the most effective and simple to produce nanofibers in
quantity. In this method, an electrode is positioned in the polymer solution and the
other is connected to a manifold, which is generally a metal tube or plate (static or
rotating). The charge forms a Taylor cone at the tip of the needle and causes the
acceleration of the polymer solution, the solvent evaporates and forms the nanofiber
(Huang et al.
2003
; Pham et al.
2006
). The coaxial electrospinning is used to
produce nanofibers with a core-shell structure. This method can be used to produce
mixed nanofibers formed by a core of polyethylene oxide and a shell of chitosan
(Pakravan et al.
2012
) or other polymer combinations. Nanoemulsion nanofibers
are formed from an emulsion prepared with an aqueous phase containing the
hydrophilic polymer in an organic phase containing the polymer that makes the
shell. An example of nanoemulsion nanofiber is the preparation of polyethylene
oxide (core) in copolymer PEG-PLA (shell).
The quality and characteristics of the nanofiber depend on various factors such
as the temperature, viscosity, surface tension of the solution, and electric field
strength (Deitzel et al.
2001
). Thicker fibers are often obtained with increasing
polymer concentration. Under specific conditions, nanofibers with mean diameters
of 20, 50, and 300 nm are obtained with polyvinylpyrrolidone concentrations of
4, 8, and 10 %, respectively. Also, the morphology of nanofibers can be altered
according to the polymer concentration. Morphological differences of poly(lactic
