Vitreous molecular diffusion

Molecular diffusion and solubility of hydrogen isotopes in vitreous silica. 

Molecular gases, diffusion through vitreous silica, 22 422... 

In addition to the corneal route, topically applied ocular drugs may be absorbed via a noncorneal absorption route that involves drug transport across the bulbar conjunctiva and underlying sclera into the uveal tract and vitreous humor.65 The intercellular spaces of the conjunctival epithelium are wider than those of the corneal epithelium. As a result, the conjunctiva has higher permeability than the cornea to agents such as mannitol, inulin, and FITC-dextran.86 The penetration of peptides, however, is limited by enzymatic degradation.87 The limit of molecular size for conjunctival penetration is between 20,000 and 40,000 Da. Vitreous can act as an aqueous and unstirred diffusion barrier to drug permeation.64... 

The vitreous constitutes approximately 80% of the ocular mass. It may be considered an unstirred fluid with free diffusion for small molecules. Some molecular species can diffuse between the posterior chamber and the vitreous. However, very high-molecular-weight substances, such as hyaluronate, are held in place by the zonules and lens capsule and diffuse out of the vitreous only after intracapsular lens extraction. From this discussion, it is apparent that the vitreous can serve both as a major reservoir for drugs and as a temporary storage depot for metabolites. For low-molecular-weight substances, a free path of diffusion exists from the ciliary body through the posterior aqueous humor. 

D. A. Litton and S. H. Garofalini,/. Non-Cryst. Solids, 217,250 (1997). Vitreous Silica Bulk and Surface Self-Diffusion Analysis by Molecular Dynamics. 

Litton DA, Garofahni SH (1997) Vitreous sihca bulk and surface self-diffusion analysis by molecular dynamics. J Non-Cryst Sol 217 250-263... 

The relatively open structure of vitreous silica provides space for the incorporation and diffusion of molecular species. The data in the literature are not very consistent Table 3.4-18 should serve as an orientation. 

Table 3.4-18 Solubility and diffusion of molecular gases in vitreous silica (Lithosil )...

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