NMR imaging of the diffusion of water at 310 K into poly[(2‐hydroxyethyl methacrylate)‐co‐(tetrahydrofurfuryl methacrylate)] containing vitamin B₁₂ or aspirin

Abstract

The ingress of water into copolymers of 2-hydroxyethyl methacrylate (HEMA) and tetrahydrofurfuryl methacrylate (THFMA) loaded with either one of two model drugs, ie vitamin B 12 or aspirin, was studied at 310 K using three-dimensional nuclear magnetic resonance (3D NMR) imaging. The poly(HEMA) was loaded with 5 wt% of the drugs. From the imaging profiles it was observed that incorporation of vitamin B 12 into the polymers rich in HEMA resulted in crack formation at the interface between the rubbery region and the glassy core on sorption of water, although these cracks were 'healed' behind the diffusion front. However, for the copolymers with low HEMA contents and for those containing aspirin, no evidence for similar crack formation was found. For the copolymers loaded with 5 wt% of aspirin or vitamin B 12 the values of the water diffusion coefficients, determined by curve-fitting the relative water concentration profiles from magnetic resonance imaging (MRI) measurements, were found to be smaller than those obtained from a mass uptake study.

NMR Imaging of the Diffusion of Water at 37 °C into Poly(2-hydroxyethyl methacrylate) Containing Aspirin or Vitamin B12

“…Thus, the observations suggest that the deviations of the experimental data from the predictions for Fickian diffusion in Figure B have their origins in the formation of cracks in the matrix but that the extent of crack formation is less than that found for PHEMA in the absence of any drugs and PHEMA−B 12 systems. This proposal is consistent with the previously demonstrated plasticizing effect of the aspirin on the PHEMA matrix, which would be expected to reduce the tendency for cracking to occur and to enhance the crack repair processes. However, plasticization of the matrix may not be the only reason for the absence of crack formation, and for example, the presence of the drug during polymerization may also play a role.…”

“…The dashed line in Figure B shows the profile generated using eq 1 for Fickian diffusion with a diffusion coefficient of 1.3 × 10 -11 m 2 s -1 , which is consistent with the value obtained from a gravimetric sorption analysis, 1.4 ± 0.1 × 10 -11 m 2 s -1 . The dashed line demonstrates the poor fit of the predicted curve to the experimental profile near the edges.…”

“…The dashed curve in Figure B has been generated for a sorption time of 6.1 h using eq 1 and a value of the diffusion coefficient of 1.3 × 10 -11 m 2 s -1 , which is similar to that obtained from an analysis of the mass uptake data at 37 °C, 1.4 × 10 -11 m 2 s -1 . The curve clearly shows that the underlying water concentration profiles can be predicted well using this value of the diffusion coefficient, thereby confirming that the water diffusion process in the PHEMA−vitamin B 12 systems is Fickian.…”

“…The polymer cylinders were rigid and glassy and showed no evidence for the presence of any water-soluble polymer, even though the presence of the aspirin and vitamin B 12 may influence the polymerization processes and reduce the average kinetic chain lengths through chain transfer reactions. A water mass uptake study 15 on the cylinders showed that they behaved very similarly to PHEMA cylinders prepared in the absence of any drugs.…”

“…To complement the previous studies on PHEMA in the absence of added drugs 9 and a more recent study on PHEMA when model drugs are present, 15 a MRI study of the water diffusion front during sorption of water into two PHEMAdrug systems has been undertaken. The two drugs chosen for study were vitamin B 12 and aspirin, which are soluble in water and which vary significantly in molecular size, having molecular masses of 1355 and 180 g mol -1 , respectively.…”