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KMID : 0366919960080010082
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Sungkyun Pharmceutical Journal
1996 Volume.8 No. 1 p.82 ~ p.92
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Water uptake in to polyanhydride devices
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Park, Eun-Seok
Maniar, Manoj/Shah, Jaymin
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Abstract
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Polyanhydrides are known as surface eroding biodegradable polymers since they are hydrophobic, which is believed to prevent penetration of water into the bulk and hence only the labile bonds on the surface are hydrolyzed. We wanted to test the hypothesis that polyanhydrides, specifically poly(fatty acid dimer-sebacic acid; FAD-SA) undergo pure surface erosion. If P(FAD-SA) does indeed undergo pure surface erosion, very little water should be present in the device since the polymer is hydrophobic and hydrolyzed on contact with water. An understanding of water uptake is also necessary to predict the stability and release of the incorporated drug. The specific aims of this study were to establish the rate of water uptake into P(FAD-SA) devices of cylinder and disk shapes at various pH conditions, and to study the effect of loaded model drug compounds (having different molecular size, aqueous solubility and dissolution rate) on water uptake. The model compounds included: mannitol, inulin and stearic acid, loaded at 10%(w/w) in disk-shaped devices. Water uptake was estimated from the amount of tritiated water found in the devices after they were soaked and gently mixed with buffers (pH 1-9) containing tritiated water (1μCi/ml) at various time intervals. The results showed that water uptake by the devide is a function of pH (pH 9＞pH 7.4≫pH 1-5). Significantly higher amount of water was taken up at pH 7.4 and 9.0 (8-9% (v/v) for cylindrical devices, 15-25% (v/v) for disk-shaped device in 2 weeks), compared to less than 5% (v/v) uptake between pH 1 and 5. Disk-shaped devices showed a faster uptake rate compared to cylinder-shaped devices due to their higher surface area to volume ratio. The loaded compounds had no significant effect on either the water uptake profile or water uptake kinetics at all pH values examined. From the large amount of water (up to 20% (v/v)) found in the devices at pH 7.4 and pH 9.0, it appears that P(FAD-SA) does not undergo pure surface erosion. The photomicrographs of the devices at various stages of water uptake showed channels on the rough surface indicative of bulk erosion rather than pure surface erosion.
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