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R. Herrero-Vanrell, A.C. Rincón, I.T. Molina-Martínez, J. Reguera, M. Alonso, M.F. Refojo, J.C. Rodriguez-Cabello; Poly (VPAVG) as Potential Vehicle for Intraocular Drug Delivery Systems . Invest. Ophthalmol. Vis. Sci. 2003;44(13):4441.
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Purpose:Poly (Val-Pro-Al-Val-Gly)(VPAVG) is a sinthetic bioelastic polymer. This polymer is highly biocompatible since the immune system cannot differentiate them from the natural elastin. Poly (VPAVG) is soluble in water and it presents a characteristic molecular transition. Above the transition temperature(Tt)the polymer contracts to expel excess of water forming aggregates. On this way poly (VPAVG) can be loaded with drugs by first swelling and then contracting. The properties mentioned previously suggest the use of poly (VPAVG) as vehicle for the preparation of intraocular drug delivery systems. In this work poly(VPAVG)microparticles loaded with dexamethasone Phosphate (DMP)were prepared. Methods: Particles were formed by polymer aggregation from an aqueous solution. The polymer was first dissolved by cooling (4°C) and then heating (37°C) over the Tt. Different amounts of polymer were dissolved in an aqueous solution of DMP to obtain poly (VPAVG)concentrations of 20mg/ml and 30mg/ml. The effect of the initial DMP concentrations(4mg/ml; 2mg/ml and 1mg/ml) on the encapsulation rate of the drug was evaluated. Experiments were carried out by duplicate. Results: Microparticles formed resulted in a mean size of 1,91µm ±1,26µm. The percentage of the incorporated drug into the particles depends on the initial concentration of DMP in the aqueous solution. Encapsulation rates ranged between 2,82% and 23,08%) referred to the initial amount of drug.The best results were obtained for the microparticles formed from a DMP (1mg/ml) solution and a polymer concentration of 20mg/mg with an encapsulation rate value of 23,08% ±4,75% referred to the initial amount of drug. Conclusions: Poly (VPAVG) shows interesting properties as vehicle for the preparation of intraocular drug delivery systems such as microspheres.The encapsulation rate depends on the initial drug concentration in the aqueous polymer solution.
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