I think nanoparticles don't diffuse, but rather they can disperse in the gels.

Hi, according to me Nanoparticles can surely diffuse through swollen hydrophilic gels. This can be achieved by optimised selection of the gel composition as well as the nanoparticle composition. We need to formulate such nanoparticles which retain their features till the desired targeting is achieved and do not degrade during their diffusion through the hydrophilic gel. It will also depend on where you actually want to deliver the nanoparticle and the route of administration. Whereas natural gel components like Agar, Xanthan gum may not give you the desirable drug release profile and even if they give , you will find reproducibility issues, hydrogels may give the desired release with reproducibility. Please find a reference for the same.

Nanoparticles diffusion is possible, moreover, this is an important technique to study the gels properties (check references with nanorheology or microrheology + gel keywords). However, targeted diffusion in a selected direction might be an issue, unless external stimulus is applied (say, electric field + charged nanoparticles).

Here you can find several references about hydrogels and their interactions with other molecules: http://www.sciencedirect.com/science?_ob=ArticleListURL&_method=list&_ArticleListID=-326831252&_sort=r&_st=13&view=c&_acct=C000068853&_version=1&_urlVersion=0&_userid=5915660&md5=7bc654e433cf356175e5941b707d35ae&searchtype=a

I did myself study the diffusion of drug/cyclodextrin complex into crosslinked hydrogels. Check the results in: http://www.sciencedirect.com/science/article/pii/S0144861710000147

It may be of interest for you to consider swollen macroporous cryogels. Nanoparticles and even larger particles like microbial cells can go inside the macropores quite easily, typically by convection with a stream of aqueous solution. Once being inside the particles may diffuse as well.

There were many publications on cryogels, some references are here:

J.Chromatogr. B 807 (2004)129 , Biotechnol. Prog. 21 (2005) 644