Concentration-dependent bacterial cellulose patches: a strategy for modulating the drug release beyond the modifications of the native cellulose hydrogel

Considering the increasing interest in the need-specific drug release profiles in transdermal patches, the understanding of the complex relationship between the release kinetics and factors like the drug loading and matrix environment really becomes important. In light of this fact, the current study investigates the concentration-dependent loading and its effect on the release profile in a patch based on the bacterial cellulose (BC) hydrogel matrix. We have succeeded in achieving sustained release and burst release behavior by varying the concentration of the diclofenac sodium (DFC) loading media from low concentrations of 100, and 200 μg/ml to higher concentrations of 500 and 5000 μg/ml. Interestingly, the fraction of drug release in high DFC matrices exceeded 90% at the end of 3 h, whereas the release in low DFC matrices saturates between 50 and 70%. This becomes even more interesting due to the two observations across each sample, irrespective of the concentration of the DFC loading solution: (i) the fraction of loaded DFC in each mg of freeze-dried bacterial cellulose (FDBC) matrix from the loading media is almost the same, (ii) the amount of residual DFC per mg of FDBC matrix after the saturation of release is almost the same. We found that higher loading concentrations more likely lead to the DFC clusters that are physically trapped and give a higher fraction of release with an initial burst release. Conversely, at lower loading concentrations, chemically attached DFC plays a significant role and gives a comparatively slower release profile with a lesser fraction of DFC from the matrix. This study addresses the drug-matrix interactions through the interplay of matrix sites and the amount of drug in BC-based patches for tuning the release profile as per the need. This study also shows that the irreversible binding, notably in lower concentrations, must be considered in the fabrication of a drug delivery system from BC and another similar type of matrices that is being tremendously researched for its biocompatibility and as a delivery vehicle.