Multilayered "SMART" hydrogel systems for on-site drug delivery applications

In recent practices, multi-stimuli responsive polymers that respond to diverse physiological or externally applied stimuli are proven to have great utility as regenerative biomaterials. These biocompatible intelligent materials are designed to "detect" the surrounding physiological environments and release encapsulated therapeutic cargos into particular sites on-demand delivery basis. Multi-layered "smart" hydrogels with the arrangement of various functional layers have been the materials of choice for drug delivery. The first part of the review highlights the formation mechanism of multi-layered structures using different methods. In addition, their morphology, orientation, and formulation aspects were also presented. Moreover, recent studies and potential applications are also highlighted. We have also discussed the 3D bioprinting-electrospinning approach for designing smart hydrogels as a new perspective for expanding their applications in controlled drug delivery and tissue engineering.