Bowtell R, Sharp J C, Peters A, Mansfield P, Rajabi-Siahboomi A R, Davies M C, Melia C D
Department of Physics, University of Nottingham, University Park, UK.
Magn Reson Imaging. 1994;12(2):361-4. doi: 10.1016/0730-725x(94)91556-3.
NMR microscopy has been used to monitor the formation of the gel layer in hydrating hydrophilic polymer tablets. Such tablets are used in the controlled delivery of drugs, where it has been found that the rate and extent of the swelling of the outer gel layer critically influences the kinetics of drug release. Tablets were hydrated in distilled water at 37 degrees C and then imaged at discrete time intervals using a 500 MHz microscope. The growth of the gel layer was clearly observed in time sequences of radial and axial sections. Axial images showed some interesting dimensional changes, with the gel at the flat surface of the tablet developing a concave shape. This is probably a reflection of the occurrence of uni-axial stress relaxation as hydration proceeds. Diffusion- and T2-weighted images provided evidence that the water in the gel layer is more strongly bound close to the dry core of the tablet than at the more fully hydrated outer surface. In images of tablets containing diclofenac, disruption of the gel layer was shown to occur primarily from the flat surfaces of the tablet, whilst the distribution of particles could be seen in tablets doped with insoluble calcium phosphate.
核磁共振显微镜已被用于监测水合亲水性聚合物片剂中凝胶层的形成。此类片剂用于药物的控释，研究发现，外部凝胶层的溶胀速率和程度对药物释放动力学有至关重要的影响。将片剂在37摄氏度的蒸馏水中水合，然后使用500兆赫显微镜在离散的时间间隔进行成像。在径向和轴向截面的时间序列中可以清楚地观察到凝胶层的生长。轴向图像显示了一些有趣的尺寸变化，片剂平面上的凝胶呈现出凹形。这可能反映了随着水合作用的进行单轴应力松弛的发生。扩散加权图像和T2加权图像提供了证据，表明凝胶层中的水在靠近片剂干芯处的结合比在水合更充分的外表面处更强。在含有双氯芬酸的片剂图像中，凝胶层的破坏主要发生在片剂的平面上，而在掺杂有不溶性磷酸钙的片剂中可以看到颗粒的分布。
