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PARTICLE
SIZE and Shape

The drug delivery of nano transdermal products are
affected by particle size, shape which
further determine physical steadiness and cellular uptake of nano drugs
(Escobar Chavez et al 2012). Nanoformulations can be delivered concurrently
using different means/routes owing to their particle size and physicochemical
properties (Borali 2010). Skin anatomical features only allows free
distribution of the particles <5-7 nm size using  transcellular route (Bouwstra and Ponec 2006, Johnson et al 1997), ?36 nm using intercellulat route  (Cevc 2004, tang et al. 2001) and > 3-10
µm through transfollicular route. Particles having smaller size are preferred
since they provide larger surface area and have higher drug incorporation capacity.
Attama et al (2007) reported that solid lipid nanodispersions 
(SLN) having low particle size are more stable and well tolerated in vivo and
incorporate high drug concentration in active formulations (Attama
AA, Schicke BC, Paepenmüller T, Müller-Goymann CC (2007) Solid lipid
nanodispersions containing mixed lipid core and a polar heterolipid:
Characterization. Eur. J. Pharm. Biopharm. 67: 48-57). Similar conclusions were made by Maestrelli et al
(2009), who investigated ethosomes prepared by different techniques, and found
that small unilamellar vesicles (SUVs) drug efficacy of benzocaine (BZC)  was higher probably due to its small size
and  higher surface area which allowed
more intimate contact with the epithelium and gave drug more time for therapeutic
action (Maestrelli
F, Capasso G, Gonzalez-Rodriguez ML, et al., (2009) Effect of
preparation technique on the properties and in vivo efficacy of
benzocaine-loaded ethosomes. J Liposome Res 19(4): 253-60).  Desai et al.
(2010) and Baroli (2010) concluded that nanoparticles lipophilic in nature
having high partition coefficient and molecular weight <600 Da are best suited for TDDS. Nanoparticles can form different shapes like spherical, ellipsoidal, triangular, needle shaped, cubic and prism like. They are not always rigid (e.g. lipid particles) and deformable and their shape and orientation greatly influence their aggregation, the choice of penetration route and diffusion coefficient (Baroli 2010). Using newer methods nanoparticles of preferred size and shape for TDDS can be engineered. ZETA POTENTIAL Zeta potential is the number of charges a particle carries. It is important to determine the particle size distribution and zeta potential of nanoformulations because it determines the dispersion stability of the non-aqueous suspension Attama AA, Schicke BC, Paepenmüller T, Müller-Goymann CC (2007) Solid lipid nanodispersions containing mixed lipid core and a polar heterolipid: Characterization. Eur. J. Pharm. Biopharm. 67: 48-57. SIZE DISTRIBUTION The size distribution of particles formed by different systems are mostly affected by preparation methods and conditions like temperature, dispersing medium, stirring rate and viscosity of the organic and aqueous phases Pinto Reis C, Nuefeld RJ, Ribeiro AJ, et al., (2006) Nanoencapsulation 1. Methods for preparation of drug-loaded polymeric nanoparticles. Nanomedicine. 2: 8-21, Maestrelli F, Capasso G, Gonzalez-Rodriguez ML, et al., (2009) Effect of preparation technique on the properties and in vivo efficacy of benzocaine-loaded ethosomes. J Liposome Res 19(4): 253-60.

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