A NEW DYNAMIC MODEL OF RELEASE FOR NOT CORRODED DRUG SYSTEM──REVISION AND USE OF FICK'S FIRST LAW

Based on the facts that the diffusion coefficient in original Fick's first law is not a strict constant but changes with concentration and that the original Fick's first law is only suitable for the stable diffusion with constant concentration gradient but many experiments have shown that the concentration gradient is a function of time. The authors suggest that the diffusion coefficient and the concentration gradient should be revised, respectively, as a concentration function and a time function. That is,D=D₀Cⁿn>0d(dC/d_x)/dt=α dC/d_xSo, the Fick's first law is revised asdW/dt=-D₀CⁿAC_{0e^αtIn the formula, dW/dt represents the rate of diffusion, D0 is the intrinsic diffusion coefficient that is a constant only concerning the temperature and the character of the substance diffused. A is the area of diffusion surface, α is the constant concerning the change of concentration gradient, C⁰ and C is, respectively, the concentration on the diffusion surface at time t0 and any time t. Based on this, the dynamic model of release on the preparations notcorroded is derived:dW/dt=-k0e}^αtWnHere,k₀ is the release constant concerning D₀, temparature, C₀ and A.The model gave better results than other models in common use for simulating the release dynamic process and the physical meanings of the model parameters are explicit.